Fight Aging! Newsletter, August 28th 2017

Researchers have reported a causal link between senescent cells - the cells associated with aging and age-related disease - and bone loss in mice. Targeting these cells led to an increase in bone mass and strength. "While we know from previous work that the accumulation of senescent cells causes tissue dysfunction, the role of cell senescence in osteoporosis up to this point has been unclear. The novelty of this work for the bone field lies in the fact that, rather than targeting a bone-specific pathway, as is the case for all current treatments for osteoporosis, we targeted a fundamental aging process that has the potential to improve not only bone mass, but also alleviate other age-related conditions as a group."

In the study, researchers used multiple approaches to target senescent cells in mice with established bone loss between 20 and 22 months of age. That's the equivalent of over age 70 in humans. Approaches included using: (a) a genetic model where senescent cells can be killed off; (b) a pharmacological approach, where senolytic drugs eliminate senescent cells; and (c) a Janus kinase inhibitor - a drug that blocks the activity of Janus kinase enzymes - to eliminate the toxic products produced by senescent cells. "The effects of all three approaches on aging bone were strikingly similar. They all enhanced bone mass and strength by reducing bone resorption but maintaining or increasing bone formation, which is fundamentally different from all current osteoporosis drugs."

The benefits on bone found in elderly mice were not evident in younger mice. That, coupled with the finding that the senolytic drugs were effective when given only intermittently, supports the link between senescent cells and age-related bone loss. Researchers administered a senolytic drug combination (dasatinib and quercetin) once per month to eliminate senescent cells. "Even though this senolytic drug combination was only present in the mice for a couple of hours, it eliminated senescent cells and had a long-lasting effect. This is another piece of the mounting evidence that senolytic drugs are targeting basic aging processes and could have widespread application in treating multiple chronic diseases."

Aging is associated with increased cellular senescence, which is hypothesized to drive the eventual development of multiple comorbidities. Here we investigate a role for senescent cells in age-related bone loss through multiple approaches. In particular, we used either genetic (i.e., the INK-ATTAC 'suicide' transgene encoding an inducible caspase 8 expressed specifically in senescent cells) or pharmacological (i.e., 'senolytic' compounds) means to eliminate senescent cells. We also inhibited the production of the proinflammatory secretome of senescent cells using a JAK inhibitor (JAKi).

In aged (20- to 22-month-old) mice with established bone loss, activation of the INK-ATTAC caspase 8 in senescent cells or treatment with senolytics or the JAKi for 2-4 months resulted in higher bone mass and strength and better bone microarchitecture than in vehicle-treated mice. The beneficial effects of targeting senescent cells were due to lower bone resorption with either maintained or higher bone formation as compared to control mice. In vitro studies demonstrated that senescent-cell conditioned medium impaired osteoblast mineralization and enhanced osteoclast-progenitor survival, leading to increased osteoclastogenesis.

Collectively, these data establish a causal role for senescent cells in bone loss with aging, and demonstrate that targeting these cells has both anti-resorptive and anabolic effects on bone. Given that eliminating senescent cells and/or inhibiting their proinflammatory secretome also improves cardiovascular function, enhances insulin sensitivity, and reduces frailty, targeting this fundamental mechanism to prevent age-related bone loss suggests a novel treatment strategy not only for osteoporosis, but also for multiple age-related comorbidities.

TC: What did you study at MIT?

LD: I majored in physics actually, but I continued to work in a couple of labs, including [one overseen by] Lenny Guarente [a biologist known for his research on life span extension]. It was a lot of fun. I thought I'd be a scientist, but a grad student familiar with the Thiel fellowship told me I should apply and I did. It's funny, one of the directors of the [Thiel] program told me recently that he thought I'd fail, even though he was very supportive. After we closed the first fund, he was like, "I never thought that would work out."

TC: Why?

LD: In part because not long ago, if you talked with most VCs about aging, they didn't think there was anything there. I think aging is such a young science, they hadn't heard about it. Meanwhile, I care a lot about it, and though we don't know if it'll work or not, it's not unlike [biotech companies trying to tackle] cancer in that way, and if you believe in cancer companies, you should also care about aging companies.

TC: How much did you raise for that first fund?

LD: A grand total of 4 million, and I was very proud of this. To be honest, I'd assumed 100,000 was enough to build a fund until I arrived in San Francisco and realized it was really enough to live on for two years. When I started fundraising, I was 17 - too young to legally sign contracts. I'd never managed money before. But I could talk to people about the science and got them on board with that. In the end, we had great anchor investors come together, and we invested in five companies that kind of proved out the strategy.

TC: One of your portfolio companies is Unity Biotechnology, a company that's trying to reverse aging through therapeutics. Didn't it just raise a giant Series B round this week?

LD: It did. All of the companies in that portfolio have [at least] raised series A rounds of 30 million or more to get to that proof of concept.

TC: Given the amounts involved, is the plan to form special purpose vehicles, or SPVs, around your break-out winners?

LD: We like to help LPs follow on, so we look to do that in whatever way makes sense for both parties. With Unity, we put in money as early as possible because Ned Davis, who runs the company, is amazing and we thought its aging thesis would succeed.

TC: Do you think your work will be harder, given that investors seem to be paying much more attention to aging suddenly?

LD: No. With our first fund, we spent up to six months with each deal, tracking the company before it was even raising. It's something LPs really value from us; they know when they invest in something that they don't need to re-do the diligence, that we've already looked at a bunch of stuff and we know this is the best possible investment in [a particular vertical]. Earlier, our biggest challenge was getting other investors on board and convincing them that aging has become a place to play. Now that's a non-issue, which is great. Our job is to help the companies get other investors on board, so it's wonderful to see excitement in the space begin to build.

Antoxerene has the look of a sizable expansion of the work at Ichor Therapeutics. Could you give an overview of the initiative?

Antoxerene is a pharmaceutical company that develops small molecule drugs for pathways of aging. Many protein-protein interactions are known to contribute to the onset and progression of age-associated disease. One such example is p53. p53 is a master cell regulator that should force apoptosis in cells that become cancerous or senescent. Cancer is obviously a major disease of aging. Senescent cells are non-dividing pro-inflammatory cells that exacerbate or may even cause many diseases of aging. A common feature of both cancerous cells and senescent cells is the ability to inhibit p53. Many cancers achieve this by overexpressing a protein called MDM2, which binds p53. Similarly in senescent cells, a protein called FOXO4 is overexpressed which binds p53. In both cases, p53 is prevented from performing its function and cells that should be eliminated from the body are allowed to persist. One of our goals is to identify small molecules that can disrupt these interactions and reactivate p53. These leads can then be developed as highly targeted drugs to treat cancers and diseases of cellular senescence.

What is it about the underlying protein production technology that makes now a great time to be undertaking this drug discovery work?

Antoxerene is following a traditional small molecule drug discovery path, but we have advanced the state of the art. The typical workflow for drugging a pathway is to manufacture large quantities of the proteins of interest (for example, p53 and FOXO4), then test a library of compounds to identify "hits" that stop the proteins from binding. However, protein manufacturing is often non-trivial, and large quantities of protein are required for a high throughput screen. Complicated proteins like p53 cannot be made using inexpensive microbial systems like E. coli because these bugs lack essential machinery found in mammalian cells. Expression within mammalian systems is possible, but cannot be scaled cost effectively. Because of this, the state of the art for drug discovery is to use small fragments of the proteins of interest, rather than full-length protein. Of course, this is analogous to evaluating a used car by looking at a hubcap. It may or may not accurately depict the state of the entire car.

Under a co-development deal with Finger Lakes Bio, Antoxerene has used proprietary RecombiPure expression technology to manufacture full-length, properly folded, bioactive proteins at scale in E. coli. While everyone else is looking at hubcaps, we see the entire car.

One of your Antoxerene development projects, BuckyProtector, is an antioxidant. Antioxidants have a decidedly mixed history when it comes to therapeutic application and aging. What is new and different here?

BuckyProtector is a combination moon-shot / community service project. Back in 2012, Baati et al described a profound decrease in all-cause mortality in rats that were fed a fullerene formulation. No group has replicated those findings, but a number of people have begun consuming this product from various online vendors. In our hands, we find tremendous variance in the formulation from vendor to vendor, and none of the vendors we contacted were able to provide quality assurance data that support label claims of contents and purity. Preliminary studies suggest that some of these formulations may be highly toxic. We have brought proper manufacturing and quality control in house and are working to definitively answer whether development of a fullerene therapeutic is worthy of a serious translational effort. We hope to have more to report on this front in the coming months.

I see that FOXO4-p53 is on the list of targeted mechanisms. Is Ichor getting into the senescent cell clearance field in a significant way? What do you think of the prospects for this area of development?

Our interest in the senescent cell clearance field will largely depend on what we find during our initial screens. However, we are open to the idea of having a significant focus in the space. The field is heating up, and we have specific expertise in drugging p53 pathway interactions that make us uniquely suited to take on a discovery initiative around FOXO4-p53. This seems like an area where we can make a large impact in a cost effective and timely manner.

The last few years have seemed very positive from the point of view of progress towards the treatment of aging, in terms of gaining support and building working technology. What are your predictions for the next five to ten years?

This is difficult to predict because it is unclear to me what impact the tech sector will have on the life sciences, and drug development in general. What I have observed over the past 3-5 years is a growing interest among software and tech entrepreneurs and investors in the life sciences, and the aging space in general. Some companies, such as BioAge Labs and Insilico Medicine, are looking to apply modern computational approaches to drug discovery, with a focus on aging. Others, such as Unity Biotechnology or Oisin Biotechnologies, are pursuing more traditional translational research initiatives, but with substantial financial support from tech investors. We even see a number of software and tech entrepreneurs entering the life sciences, such as with Immusoft.

It is uncertain what levels of success these companies will achieve, but I am optimistic. To the best of my understanding these are well thought out initiatives being led by strong teams. However, there is a tendency for some people from the software and tech sectors to think biology is a coding problem that can be solved by throwing money at it, and seem to gravitate towards personalized health, synthetic biology, biohacking, and similar initiatives. This is great for driving interest in aging research or developing a profitable consumer product, but when lofty expectations are met with the harsh reality of bench science, particularly in drug development, there is a high risk that ambitions will be stifled.

The Ellison Medical Foundation was an early example of this. Up to 40 million per year was spent on aging research starting in 1998. With relatively little to show for it, the program was concluded in 2013. It is not sufficient to throw money at research problems, particularly when drug discovery is the goal. And this is a trap high net worth individuals seem to repeatedly fall into. The basic science, medicinal chemistry, toxicology, formulation work, regulatory pathway, clinical trials, IP strategy, and business strategy all rely upon incredibly divergent skill sets. It is rare to find a team that possesses all of them. New investors in particular should be grilling entrepreneurs on the details of these points, not getting caught up in the hype of cool technology (though the latter is certainly the more fun part).

All that said, collectively I believe the future for the treatment of aging is bright. Aging research is becoming a mainstream discipline as the research questions are becoming clearer. "How do we cure aging?" doesn't fly. Better questions lead to better answers. "What level of therapeutic efficacy will be achieved for disease X with a targeted FOXO4-p53 drug that selectively eliminates senescent cells?" We hope to find out.

How can our community help Ichor to succeed in this latest venture?

By writing. Ichor has a great opportunity to begin leveraging NY government programs for funding, tax incentives, and exposure. If pursued properly, these can do an enormous amount to leverage investor funding and promote public interest in aging research. There are not a lot of players in the Syracuse area where we operate, and we are getting noticed. Letters from the community will help. It does not matter where you live. Type or write two copies of a letter made out to Senator John DeFrancisco and Rob Simpson and physically mail it to Senator John DeFrancisco's Syracuse office or Rob Simpson's Syracuse office respectively.

Tell them that you read about the exciting new research Ichor Therapeutics is doing in Syracuse. Tell them that their Grants for Growth program provided essential seed funding for getting both of Ichor's initiatives (Lysoclear and Antoxerene) off the ground, and raise millions in follow-on funding. Tell them that you are excited to see people in government taking an active role in promoting medical research on age-related disease, particularly start-ups. Tell them that you wish your government would do the same. Tell them that you hope they continue to support companies like Ichor in the Syracuse region. It is important that these letters be "mainstream" friendly. Ichor is not curing aging. We are developing first in class drugs for age-associated disease. It doesn't have to be long or fancy, but in a small city like Syracuse, your letters will be noticed. They will matter. They will drive decisions.

Parkinson's disease (PD) is diagnosed on the basis of what are called "motor symptoms" of the disease. This group of symptoms is caused by the progressive loss of dopamine-generating neurons in an area of the brain called the substantia nigra pars compacta (SNc). But there's another group of PD symptoms, termed the "non-motor symptoms" (NMS) of PD, that gets far less attention, even though NMS begin to manifest earlier in the disease, are harder to treat with current therapies, and include some of the most crippling features of living with the later stages of PD.

Whereas PD motor symptoms are driven by loss of dopamine-producing neurons, many of the nonmotor symptoms are instead linked to the accumulation of Lewy bodies and other malformed clumps and fibrils of the protein alpha-synuclein (AS) inside and between neurons. The various forms of aggregated AS first appear in neurons in the periphery of the body (that is, outside of the brain and spinal cord), and then invade the brain, starting from the base of the skull and slowly spreading their way forward across the brain over the course of the disease.

Because most NMS are not driven primarily by loss of dopamine signaling, dopamine-boosting treatments are completely ineffective in controlling most of them. Yet there's now hope: a race amongst several biotech companies to develop rejuvenation biotechnologies to clear AS aggregates out of the aging and early PD brain. These companies are taking what, in SENS terminology, is the amyloSENS approach, developing and testing antibodies that recognize and bind to malformed AS, allowing them to interdict the toxic proteins as they spread from one neuron to the next, and possibly also capturing some of the aggregates inside existing neurons and facilitating their degradation. By sweeping away AS aggregates before they get a chance to spread, AS immunotherapies have the potential to hold the nonmotor symptoms of PD at bay, slowing the overall progress of the disease, and - when combined with mature cell therapy - eventually preventing the disease altogether, and potentially even reversing it.

When we last reported news from Prothena Corp PLC, the founder had recently presented the results of studies using their AS-targeting antibodies at SENS Research Foundation's Rejuvenation Biotechnology 2014 conference. Scientists at Prothena had confirmed that several of their candidate antibodies were able to clear AS pathology out of the brains and spinal cords of mouse models of PD and related disorders, substantially shielding them against the PD-like motor and cognitive impairments suffered by their untreated cousins. They also revealed some very early information specific to PRX002, the humanized version of the most promising antibody tested in the mouse studies, which was then slated to enter into early-stage human trials.

Now we can report on the first published results of those trials, and on early information coming out of an additional trial that has not yet been formally published. For their first basic safety and pharmacokinetics trial, Prothena scientists recruited 40 healthy people without PD to receive either placebo injections or or one of 5 doses of PRX002, ranging from 1 to 30 mg/kg. An hour after dosing, the lowest dose of the antibody led to a reduction of AS in the circulation of more than 30%, with the highest doses reducing it by up to 96%; 24 hours later, levels remained similarly suppressed in the higher-dose groups.

We learned more about the potential of PRX002 from a sneak peak at the interim results from an ongoing Phase 1b clinical trial of of PRX002 in PD patients. This was a larger (80 subjects) trial that for the first time involved volunteers suffering PD - most with the early stages of the disease. The effects of the first dose of PRX002 on serum AS in PD patients were similar to what was seen in young, healthy people in the first trial: up to a 97% decline in the ratio of free to total AS at the highest dose, with the ratio remaining strongly suppressed for at least four hours. But now for the first time, they could see the longer-term effects of each dose. A month after receiving their first dose, just before taking their second shot, subjects' free-to-bound AS ratios had only partially returned to where they had been before receiving their first dose. No serious adverse reactions to PRX002 were observed in trial participants. There was no improvement in symptoms or other signs of disease progression, but no firm conclusion can be drawn from this due to the short duration of the trial period.

Biotech pioneer Biogen has been rather quiet about their work on their AS-targeting antibody BIIB054 - unlike their widely-heralded Aducanumab, another amyloSENS-style immunotherapy, which has generated enormous excitement for what seems to be the clearest-cut effect on both beta-amyloid and problems with cognitive function in people with Alzheimer's disease. They initiated their Phase 1 BIIB054 trial in 2015, and reported promising early results of its use in an animal model of Parkinson's back in the summer of 2016, but have never published the results, issued press releases, or held conference calls to share their findings with the wider public. But all the while, BIIB054 has been jumping one hurdle after another, and the company is powering ahead.

BIIB054 initially emerged as a strong candidate anti-AS imunotherapy. In further testing, BIIB054 selectively bound aggregated AS in tissue samples from people with PD and with Dementia with Lewy Bodies (DLB - a related disease of AS-driven neurological aging), while leaving native AS alone. The company's scientists also report that when they then injected preformed AS fibrils into the brains of mice, BIIB054 slowed the self-templating spread of AS pathology across the brain, and held much of the ensuing motor dysfunction at bay. Based on these results, Biogen advanced BIIB054 into a Phase 1 clinical trial in 2015. 48 healthy people without PD, aged 40-65, were given a single dose of BIIB054 at one of six doses across a very wide range, and followed up for the next 16 weeks using multiple clinical and laboratory assessments, as well as MRI and electrocardiogram data. The results reported so far are similar to the PRX002 results as far as they go, but are clearly at an earlier stage.

Overall this is an exciting moment. Multiple amyloSENS rejuvenation biotechnologies have now emerged from the rejuvenation biotechnology ecosystem, targeting the removal of aggregated alpha-synuclein from the brain and being tested in early-to-mid-stage human clinical trials. Each uses a different approach to targeting these malformed proteins, and is supported by data in animal models - and the early human evidence looks favorable, if very preliminary. And there are more in the pipeline, including candidate AS immunotherapies from Proclara, NeuroPore, and BioArctic Neuroscience. All this suggests that multiple developments are converging toward groundbreaking progress in this area.

Here at the SENS Research Foundation, I have been working with derivatives of drugs which have been shown to solubilize cholesterol and/or harmful derivatives of cholesterol such as oxysterols. Cholesterol and its harmful derivatives are taken up by cells as they attempt to process these molecules for the body. As macrophage lysosomes become more and more saturated with debris from cholesterol molecules, the cells become useless and form foam cells when they can no longer process the excess cholesterol. These malfunctioning foam cells accumulate in the arterial walls, becoming part of the problem instead of the solution and contributing to the plaques which cause atherosclerosis, or hardening of the arteries. In order to develop a safer, more effective treatment for atherosclerosis, a rational drug design venture is underway at SENS. Various tests have been and will be conducted with novel drugs for the purpose of removing cholesterol and its derivatives from atherosclerotic plaques. For my project, experiments have been designed to assess the effectiveness and safety of these drugs for the purpose of reducing atherosclerotic plaques in human arteries.

Historically, the pharmaceutical industry's mode of operation is to rely on blockbuster drugs by conducting expensive clinical trials followed by marketing in developed economies if the trials are successful. Unfortunately, this tactic isn't working very well. My research project will attempt to use machine learning methods to improve this dismal statistic. How? Machine learning is a tool that helps us understand how several quantities are related to one another purely on the basis of the data provided. It challenges preconceived notions about factors that influence an output. And, in the field of drug development, this is what is needed given the abysmal attrition rate and burgeoning costs. The algorithms that I will employ will highlight the factors that influence the probability that a drug will clear clinical trials. I plan on predicting the launch or failure of new molecular entities using a model that takes a holistic approach with regards to which variables affect drug success.

Growing up, I hardly thought of aging as a disease as opposed to a natural result of life. However, as I focused on muscle atrophy during a summer internship, I soon saw the larger scope of the problem. After this experience, I sought to better understand tissue growth, wanting to branch out beyond atrophy. Though Alzheimer's Disease (AD) is a dementia characterized by deficits in memory, spatial skills, and language, over half of AD patients also display psychotic symptoms. The shared psychiatric symptoms between schizophrenia and AD suggest common molecular pathophysiology. Furthermore, previous research has shown that the two diseases bear similarities in neural pathology and biochemical dysfunction. Thus, it would be of interest to study the novel use of antipsychotics, particularly clozapine, to investigate AD psychosis. As a SRF Summer Scholar, I will be working to explore the relationship between AD, clozapine, and CRMP2.

Prior to joining the SRF Summer Scholars Program, I was heavily involved in a research project aimed at understanding the biology of low-grade gliomas. My project this summer aims to create the best model for lung-to-brain cancer metastasis. Secondary brain metastases are a devastating condition, bearing a dismal prognosis. A large number of brain metastases originate from lung carcinomas, specifically non-small cell lung adenocarcinomas. Due to its complicated biology and tendency to metastasize, it remains one of the deadliest tumors in the field and has posed a great challenge in finding a cure. A promising step toward finding a cure has been the discovery of TRAIL (Tumor Necrosis Factor-Related Apoptosis Inducing Ligand). TRAIL produce anti-tumor effects by causing tumor cells to essentially "suicide," and its specificity for tumor cells but not healthy cells makes it a great therapeutic approach. My project will focus on selecting a good model to recapitulate the biology of metastatic lung adenocarcinoma and gather the preclinical data for a modified TRAIL as a therapy.

This summer, I will explore stem cell treatment for Parkinson's disease (PD). I will be assessing the genotypes of induced pluripotent stem cell (iPSC) lines from 10 patients with PD to evaluate their genomic integrity. Single nucleotide polymorphisms (SNPs) are common sites of genetic variation between humans. By determining the precise nucleotide at common sites of variation, we begin to get a picture of the genome, and the more SNP sites we examine, the more the resolution of the genomic picture increases. I will load patient skin cell and iPSC DNA onto a microarray chip that can detect the nucleotide identity at 4.3 million SNPs across the genome and use bioinformatics software to identify variations. The results will indicate which of the stem cell lines from each patient are safe to use for transplanting neurons. Using SNP microarrays to assess genomic integrity represents a high throughput quality control testing that can be used to safely create functional neurons from the cells of patients that require no immunosuppression after transplantation.

This summer, my project is to design and test different constructs that can potentially improve the allotopic expression of ATP6 to mitochondria in mutant cell lines. Mitochondria are double-membrane bound organelles that provide energy in the form of ATP to power the biochemical reactions of a cell. Unlike other organelles, however, mitochondria have their own DNA separate from the nucleus, and 13 out of those 37 genes encode for oxidative phosphorylation complex proteins. Due to possible leakage of the high-energy electrons of the respiratory chain, which results in the formation of reactive oxygen species, the oxidative stress mitochondrial-DNA (mtDNA) is subjected to can lead to mutations, aging, and cell death. For instance, the mutations of ATP6 have been implicated in different human diseases that affect neural development, vision, and motor movement.

Allotopic expression has been proposed as a gene therapy approach that can potentially treat mitochondrial-DNA diseases. This method aims to express a wild-type copy of an affected mitochondrial gene in the nucleus of a cell, target it to the mitochondria, and allow functional replacement of the defective protein. Stable allotopic co-expression of ATP8 and ATP6 is able to rescue a cell line that is null for the ATP8 protein and has significantly lowered ATP6 protein levels. However, improving the exogenous amount of ATP6 that can be expressed or targeted to the mitochondria may be necessary in order to achieve complete restoration. Therefore, my project will investigate whether appending an additional gene sequence, the soluble tag, can help stabilize ATP6 and prevent unfolding before it is inserted into mitochondria.

Through the SRF Summer Scholars Program, I will be studying the TOR pathway in intestinal stem cells of fruit flies to understand the effect of metabolism on stem cell function. The TOR pathway is involved in cell growth by regulating protein synthesis and metabolism, autophagy, transcription and ribosome biogenesis. The TOR pathway seems to be critical for both the proliferation and differentiation of stem cells and is regulated by many different mechanisms. It has been shown that nutrients can regulate TOR, but the exact molecular mechanism involved in regulating TOR is unknown. Thus, the goal of this project is to better understand the molecular mechanisms that are responsible for TOR activation in intestinal stem cells in response to injury.

Autophagy is the process by which cells degrade old and damaged organelles and proteins, allowing the cells to prevent damage inflicted by these impaired components. In humans, autophagy helps to prevent the aging of cells, but levels of autophagy tend to diminish as we age. When autophagy levels are lower, muscle disorders and heart issues can occur. My goal this summer is to discover the effect of spermidine, a natural polyamine which has been shown to increase mouse lifespan, on liver tissue and to understand whether spermidine acts in the same way as another autophagy-inducing chemical, rapamycin. The main two protein complexes I will be focusing on are mTORC1 (mechanistic target of rapamycin) and mTORC2, which are protein complexes that regulate autophagy and cell regulation as well as cell metabolism. While the drug rapamycin has been shown to reduce autophagy by lowering levels of mTORC1 and therefore elevating autophagy, it is unclear if spermidine acts through the same pathway, despite producing the same effect. By testing mTOR levels, I will be able to discover whether spermidine acts using the same pathway as rapamycin.

This summer, I will be working with the SRF Mitochondrial Team. Mitochondria generate the cellular energy consumed by mammalian cells through the process of oxidative phosphorylation. Like the nucleus, mitochondria possess their own DNA, termed mtDNA, which encode for 13 proteins critical to cellular respiration. Unfortunately, mitochondria do not have an efficient system for repairing damaged DNA, leading to mutation rates 10 times greater than that detected in nuclear DNA. Scientists believe evolutionary forces have driven mitochondrial genes from the mitochondria into the nucleus, where they are protected from the highly-reactive oxygen molecules produced by oxidative phosphorylation. The SRF Mitochondrial team hopes to mimic this evolutionary process by providing cells with a modified "backup" copy of the remaining mitochondrial genes at a safe harbor within the nucleus. The procedure of expressing genes in the nucleus originating from the mitochondria is called allotopic expression. Prior to this project, allotopic expression studies on mitochondrial genes had been performed via traditional transfection / virus induction procedures which integrate the new DNA randomly into the host genome. The goal of this study is to express the mitochondrial genes from an identified safe-harbor site in the nucleus in order to minimally disrupt the host genome and ensure the gene functions predictably.

I am concentrating my efforts on determining the regenerative process of the heart, focusing on the epicardium. Certain animal species, such as zebrafish, can fully repair cardiac tissue that is lost by injury. In adult zebrafish, activation of the epicardium is observed during the immediate response to tissue damage. This summer, I will be investigating the regulatory sequences that are differentially accessible in the regenerating adult epicardium based on ATAC-seq data. This ATAC-seq data shows which chromatin regions on a specific gene are open and accessible and which regions may possibly act as regenerative enhancers on the epicardium. By selecting certain open chromatin regions at different stages of the regenerative process and by performing perturbation experiments in zebrafish, we aim to further elucidate epicardial contributions during cardiac regeneration. By more thoroughly understanding the molecular events that drive cardiac regeneration, we may be able to provide a new perspective and mechanism for clinical intervention after myocardial infarction.

My project this summer will explore neuronal circuit connectivity of hiPSCs (cells reprogrammed to become embryonic-like stem cells that can differentiate into various cell types) derived from Alzheimer's Disease (AD) neurons. We are going to investigate how Alzheimer's disease affects neural circuitry and the complexity of communication between affected neurons. Firstly, we will obtain a line of AD stem cells and differentiate them into neurons. AD neurons will be cultured and investigated in a multielectrode array (MEA) plate. This relatively new technology allows measurement of individual neuron depolarization. Using data obtained from MEAs, we can analyze the complexity and duration of communication between neurons. Compared to data collected from an unaffected line of neurons, changes in duration and frequency of bursts (synchronized firing of neurons) can inform us about the complexity of information transferred between neurons.

My projects will use Drosophila melanogaster, better known as fruit flies, as a model system. In my first project I will investigate the role of a member of the sirtuin family in regulating protein homeostasis (proteostasis) in intestinal stem cells (ISCs). My second project will assess whether altering proteostasis in ISCs influences the proteostasis of cell types found in different tissues. For the cell to remain healthy there must be a fine balance between synthesis/degradation and refolding of misfolded or elimination of damaged proteins. The most common mechanisms a cell can employ to degrade damaged proteins are via proteasome or autophagosome. Unfortunately, aging causes a decline in proteostasis; protein aggregates are more likely to form in certain cells of older organisms. I am interested in understating how adult somatic stem cells (SCs) maintain proteostasis, and I will use Drosophila intestinal SCs (ISCs) as a model system to study proteostasis in adult somatic SCs.

Although aortic valvular sclerosis and aortic stenosis (AS) have long been thought of as two independent entities, they are now considered to be different stages of the same process. This disease manifests initially as valve thickening caused by lipocalcified deposits, leading to progressive reduction of the valve orifice which, over time, causes hemodynamically significant stenosis. Its incidence increases exponentially with age and hence was long considered a simple passive age-related degenerative process with calcium buildup. However, several studies have shown that, in addition to age, calcific aortic valve disease (CAVD) is related to the presence of cardiovascular risk factors such as male sex, arterial hypertension, diabetes mellitus, dyslipidemia, and smoking, sharing many similarities with the process that regulates atherosclerosis.

There is therefore a direct relationship between the presence of valvular calcium deposits and the development of coronary disease and cardiovascular events, to the point that some authors even consider aortic calcification a possible marker of atherosclerosis and subclinical coronary artery disease. In 1986, it was suggested that the presence of aortic alcification was a form of atherosclerosis and numerous authors have since demonstrated this fact. In the Cardiovascular Health Study, the presence of aortic sclerosis in patients without previous coronary disease increased the risk of myocardial infarction and cardiovascular mortality 1.4 and 1.5 times, respectively.

In the initial stage of the disease, there is a thickening of the valves with formation of calcium nodules that begins on the aortic valve side. These valves remain flexible for a long time, so that their opening mechanism is not affected. With the passage of time, the areas of thickening converge in large calcified masses that end up protruding into the exit tract of the aortic valve, conferring greater stiffness to the valves and significantly decreasing the valvular area, thus interfering with its normal functioning. From the microscopic point of view, there are many similarities with the lesions observed in the earliest stages of atherosclerosis. These lesions, initially interspersed with areas of normal tissue, will eventually coalesce and are characterized by disruption of the basement membrane, with areas of inflammation and cellular infiltration, deposit of atherogenic lipoproteins, and participation of the active mediators of calcification.

Lipid deposit plays an important initiator role in the cascade of cellular signaling leading to valvular calcification. The lipoproteins involved in the process include low-density lipoproteins (LDLs) and lipoprotein A. These are atherosclerosis molecules that undergo oxidation with the release of free radicals which are highly cytotoxic and also capable of stimulating inflammatory activity and mineralization. LDLs are phagocytized by macrophages, converting them into foam cells, the fundamental substrate of the atherosclerotic plaque. With progressive lipid uptake, these macrophages begin an irreversible transformation process that ends with apoptosis. Apoptosis also causes the release of factors that promote atherogenesis and progression to the complicated plaque stage, characterized by the presence of necrotic areas.

Unlike atherosclerotic plaque where the nucleus is composed of lipids associated with foam cells and areas of necrosis, in calcified valves the lipids are deposited mainly in the subendothelial zone and to a lesser extent in the deeper areas. Lipid-laden macrophages are evenly distributed in areas where there are high lipid concentrations and no areas of necrosis. In atherosclerotic plaques, the toxic accumulation of oxidized LDL causes cell death leading to plaque fracture. This is the major event that precipitates the appearance of clinically relevant symptoms. However, this mechanism has not been demonstrated in the case of CAVD, where the onset of symptoms is conditioned by the progression of calcification and increased valve rigidity.

In the more advanced phases of the disease there is remodeling of the extracellular matrix and calcification. Alteration of the matrix is promoted by the release of inflammatory cytokines. Aortic calcification is a very complex active process involving the production of proteins that promote tissue calcification. In fact, extracellular matrix proteins normally found in bone, such as osteocalcin, osteopontin, and osteonectin, can also be found in calcified valves. This presence reveals pathological calcification and bone formation at the valve level. In short, this process involves different mechanisms of bone mineralization and resorption.

In conclusion, CAVD is highly prevalent. Long understood as a passive process, it is now known to be complex and one which involves pathophysiological mechanisms similar to those of atherosclerosis. Understanding these mechanisms could help to establish new therapeutic targets that might allow us to halt or at least slow down the progression of the disease.

The intervertebral disc (IVD) is located between the vertebral bodies and is responsible for distributing forces experienced by the spinal column. It is composed of nucleus pulposus (NP) surrounded by annulus fibrosus (AF). The NP is compression resistant and rich in type II collagen and proteoglycans. The AF is comprised of multiple lamellae of angle-ply and aligned bundles of collagen fibrils, which confer the stability for spinal motion by resisting tensile forces. Adding to the complexity of the AF structure, the extracellular matrix (ECM) composition of the AF varies from the inner zone adjacent to the NP, where it is rich in proteoglycans and both type II and I collagen, to the outer zone, which is rich in type I collagen.

Replacement of the damaged disc with an in vitro formed IVD that has the functionality of a healthy disc is a reparative approach that is currently being investigated. However, recapitulating the unique architecture of the disc has been a limitation to developing this approach for clinical use. Previous studies showed that NP tissues with compressive strength can be formed scaffold free and integrated to the top surface of a porous bone substitute material such as calcium polyphosphate (CPP). The bone substitute will help anchor the implanted tissue as bone ingrowth will fix it into the bone.

AF tissue has been generated using biodegradable electrospun-aligned nanofibrous polycarbonate urethane (PU). This scaffold has the tensile strength of a native AF lamella and fiber diameters similar to the native collagen fibrils, allowing seeded AF cells to accumulate collagen aligned parallel to the scaffold. However, the successful integration of in vitro generated NP and AF tissues is crucial for it to be mechanically functional in vivo and for the longevity of the engineered IVD replacement as the NP and AF function together to resist reduction in disc height and extraneous deformation. Defective integration between in vitro engineered AF and NP tissues would resemble a fissure within a disc and thus could result in the failure of disc replacement.

Thus, the goal of engineering of an IVD replacement should be focused toward generation of a disc that can serve as a functional motion segment that recapitulates the complex architecture of the disc, exhibits the capability to withstand complex forces in vivo, and shows integration between the different tissue types in the engineered disc and with the host tissues that will be maintained postimplantation. In this study, we report the development of a two-step process to form an in vitro integrated IVD model composed of preformed multilamellated AF tissue utilizing nanofibrous aligned PU scaffolds and NP tissues formed on a bone substitute material. This tissue was characterized histologically, by immunohistochemical staining, and biomechanically. To assess integration and adherence to the bone substitute in vivo, short-term evaluation of this construct in a bovine model was performed.

This study shows that it is possible to form a model of the IVD in vitro by combining preformed AF and NP tissues. These tissues integrate and have mechanical stability. This is the first report, to the best of our knowledge, describing integration of in vitro formed AF and NP tissues and evaluation of the interfacial shear strength. The mechanism that led to this integration is unknown. A previous study that examined bioengineered cartilage-cartilage integration suggested that the matrix between the two tissues intermingle as studies showed thin collagen fibers that were produced by the bioengineered cartilage admixed with the mature collagen fibers of the native cartilage across the interface with the host tissue. The presence of both type I and II collagens at the AF-NP interface suggests that this may be occurring in this situation as well.

Interestingly, it has been proposed that the integration of distinct tissue types requires an intervening region that serves as a gradual and continuous transition in ECM properties and/or mechanical properties. In summary, this study demonstrates that it is possible to generate a model of an IVD by combining the individual tissue components and forming various interfaces with sufficient mechanical strength to be handled. The construct was present 1 month after implantation and the AF tissue was intact. Further studies are required to optimize implant fixation and scale up the disc size to evaluate its suitability as a disc replacement in an animal model.

This book considers the multidisciplinary aspects of longevity promotion, from the advocacy, historical, philosophical and scientific perspectives. The first part on longevity advocacy includes examples of pro-longevity campaigns, outreach materials, frequent debates and policy suggestions and frameworks that may assist in the promotion of research and development for healthy longevity. The second part on longevity history includes analyses of the definition of life-extensionism as a social and intellectual movement, the dialectics of reductionism vs. holism and the significance of the concept of constancy in the history of life extension research, an historical overview of evolutionary theories of aging, and a tribute to one of the founding figures of modern longevity science.

The third part on longevity philosophy surveys the aspirations and supportive arguments for increasing healthy longevity in the philosophical and religious traditions of ancient Greece, India, the Middle East, in particular in Islam and Judaism, and the Christian tradition. Finally, the fourth part on longevity science includes brief discussions of some of the scientific issues in life extension research, in particular regarding some potential interventions to ameliorate degenerative aging, some methodological issues with diagnosing and treating degenerative aging as a medical condition, the application of information theory for aging and longevity research, some potential physical means for life extension, and some resources for further consideration.

These discussions are in no way exhaustive, but are intended to simulate additional interest, consultation and study of longevity science and its social and cultural implications. It is hoped that this book will contribute to broadening, diversifying and strengthening the academic and public deliberation on the prospects of healthy life extension for the entire population. The setting and careful consideration of a goal may be seen as a first step toward its accomplishment.

In the lifetime of an adult mouse or human heart, new cardiomyocytes (CMs) are generated albeit at very low rates of ~1%. On the other hand, adult zebrafish and neonatal mouse hearts can fully regenerate upon surgical resection or infarct injury. Like the zebrafish and neonatal mouse, new CMs in the adult mouse appear to arise by mitosis of pre-existing CMs, but a sufficient level of endogenous mitosis is lacking to allow for adequate regeneration and repair during disease progression. Loss of the full capacity to regenerate occurs soon after the seventh postnatal day when CMs in the neonatal mouse heart exit the cell cycle.

This highlights two key questions for the field of cardiac regeneration: (a) what holds back adult CMs from dividing and (b) can any adult CM be induced to divide? Indeed lineage tracing studies in regenerating hearts of zebrafish and neonatal mice, show that proliferation potency is achieved by cell cycle re-entry of pre-existing CMs. Consistent with this, Hippo/Yap pathway components, the transcription factor Meis1, and a series of microRNAs have been separately implicated in the regulation of CM proliferation. While the majority of CMs in adult mouse hearts permanently exit the cell cycle, a rare subset existing in relatively hypoxic microenvironment of the myocardium, retain proliferative neonatal CM features, and have smaller size, mono-nucleation and lower oxidative DNA damage. Although this specialized subset of CM may explain the ~1% endogenous proliferation capacity in the adult myocardium, it remains unexplored whether heterogeneity of the stress-response gene expression changes among the larger majority of cell cycle-arrested CMs would uncover a sub-population that could be motivated to re-enter the cell cycle.

We therefore undertook nuclear RNA sequencing of healthy and failing hearts, and uncovered the heterogeneity of CM transcriptomic stress-response. We noted distinct sub-populations of CMs and uncovered gene regulatory networks specific for each sub-population, displaying specific sub-group upregulation of cell cycle, and de-differentiation genes. Using co-expression analysis, gene networks were constructed that pointed to key long intergenic non-coding RNAs (lincRNA). Our results altogether suggest that sub-populations of adult CMs exist, and possess a unique endogenous potential for cardiac repair by the targeting of key regulator lincRNA. Further work is warranted to investigate their direct effects on cardiac regeneration.

A class of chemicals made by intestinal bacteria, known as indoles, help worms, flies and mice maintain mobility and resilience for more of their lifespans, scientists have discovered. Healthspan is a term used to describe the length of time a human or animal, while aging, can stay active and resist stress. In this research, the focus is on whether the animals live healthier, but not necessarily longer. "This is a direct avenue to a drug that could make people live better for longer. We need a better understanding of healthspan. With medical advances, people are living longer; but you might not really want to live longer if it means spending those extra years frail and infirm." The burden imposed by diseases of aging on the healthcare system is expected to skyrocket in coming decades.

Interest in the health effects of the microbes that live in our bodies has exploded in recent years. In humans and mice, some studies have shown that the spectra of bacteria in our bodies become narrower with age. Indole, produced by many types of bacteria through breakdown of the amino acid tryptophan, can smell noxious or flowery depending on the concentration. Indole and its chemical relatives can be found in plants, especially vegetables such as broccoli and kale. One such relative is also known as auxin, a growth hormone for plants needed for light-seeking and root development.

The roundworm C. elegans is one of the premier organisms in which to study aging. Studies in C. elegans led to discovery of a set of genes that control how long the worms can live. Several of the genes are components of the insulin signaling pathway, and they influence lifespan in flies and mice as well. Worms normally eat bacteria. So researchers fed them E. coli bacteria that produce indoles, and compared them with worms fed E. coli that cannot produce indoles. As they age, older worms spend less time moving around, can't swallow as well and are more sensitive to stressors. Although indoles didn't change the maximal lifespan, they markedly increased the amount of time worms were mobile after the age of 15 days, and it increased their swallowing strength and resistance to heat stress, even in young animals. In addition, worms usually stop reproduction at the age of 5 days, but dietary indole more than doubled their reproductive span, allowing them to remain fertile up to 12 days.

Indole had similar effects on mobility and resistance to heat in Drosophila fruit flies, and with mice, a comparable pattern was evident. Researchers treated mice with antibiotics to eliminate the existing flora, and then re-colonized them with either normal E. coli, or, as a control, with bacteria that cannot produce indole. In very old mice (28 months), indoles helped animals maintain their weight, mobility and activity levels. In younger mice, indoles extended survival after exposure to lethal radiation. Indoles may be keeping the intestinal barrier intact and/or limiting systemic inflammatory effects. Researchers are now investigating how indoles exert their effects in aging animals, how dysregulation of indoles produced by the microbiota contribute to frailty, and how indoles can be used to reverse these effects.

Mesenchymal stem cells (MSCs) have been found to broadly distribute throughout the body and have the potential to differentiate into lineages of mesenchymal tissues such as bone, fat, and cartilage cells. Recently, MSCs have become a promising tool for cell-based therapy in tissue engineering and regenerative medicine. There is considerable evidence that MSC senescence is considered as a contributing factor to aging and aging-related diseases and replicative senescence impairs the regenerative potential of MSCs. To better understand and monitor cell senescence in MSCs, it is necessary to have a reliable biomarker for identification of these cells.

Unique phenotypic alterations of senescent MSCs have been reported including enlarged morphology, arrested proliferative capability, increased β-galactosidase activity, telomere shortening, accumulation of DNA damage, alteration of chromatin organization, reduced expression of surface antigen markers, up-regulation of cell cycle inhibitors (P16INK4A and P21WAF1), and senescence-associated secretory phenotype (SASP). Since surface and external factors can be detected without intracellular delivery of a probe and without harming the cells, they can serve as ideal biomarkers to identify senescent cells. Senescent MSCs release a specific secretome, including matrix metalloproteinases (MMP2, TIMP2), cytokines (IL-6), insulin like growth factors binding proteins (IGFBP4, IGFBP7), and monocyte chemoattractant protein-1 (MCP-1). The role of these factors has been investigated in the identification of MSC senescence.

As a key component of the cell secretome, microvesicles (MVs) are shed from cell surface by their parental cells into the extracellular environment. Recent reports indicate that these small vesicles can mirror the molecular and functional characteristics of their parental cells and participate in important biological processes, such as the surface-membrane trafficking and the horizontal transfer of proteins and RNAs among neighboring cells. A growing body of evidences has shown that MVs shed by MSCs (MSC-MVs) express MSC-related markers, which act as key effectors of MSCs. Many biological functions have been attributed to MSC-MVs, such as tissue repair, hematopoietic support, immunomodulatory regulation, and inhibition of tumor growth. Recently, it has been reported that old rat MSC-MVs have unique miRNAs and significantly inhibited TGF-β1-mediated epithelial-mesenchymal transition; however, no information is available on whether MSC-MVs could represent characteristics of their parental cells in senescence.

In the present study, we investigated the changes in MSC-MVs when their parental MSCs experienced senescence, including MSC-MV size distribution, concentration, surface antigens, osteogenesis-related functions and miRNA content, to characterize these senescent MSC-MVs and evaluate their ability to resemble their parental senescent MSCs. Our findings provide evidence that MSC-MVs are a key factor in the senescence-associated secretory phenotype of MSCs and demonstrate that their integrated characteristics can dynamically reflect the senescence state of MSCs representing a potential biomarker for monitoring MSC senescence.

A research team has found that a protein called Piezo1 in the lining of blood vessels is able to detect a change in blood flow during exercise. They have described the protein as an 'exercise sensor'. During physical activity - as the heart pumps more blood around the body - the Piezo1 protein in the endothelium or lining of the arteries taking blood from the heart to the stomach and intestines senses the increased pressure on the wall of the blood vessels. In response, it slightly alters the electrical balance in the endothelium and this results in the blood vessels constricting. In a clever act of plumbing, that narrowing of the blood vessels reduces blood flow to the stomach and intestines, allowing more blood to reach the brain and muscles actively engaged in exercise.

The scientists say this is ground-breaking research because it identifies for the first time a key biomolecular mechanism by which exercise is sensed. They believe the health benefit of exercise maybe linked with the fact that blood flow is being controlled to the intestinal area. "If we can understand how these systems work, then we may be able to develop techniques that can help tackle some of the biggest diseases afflicting modern societies. We know that exercise can protect against heart disease, stroke and many other conditions. This study has identified a physiological system that senses when the mammalian body is exercising."

The researchers also investigated the effect of an experimental compound called Yoda1 on the action of the Piezo1 protein. They found that it mimicked the action of increasing blood flow on the walls of the endothelium which is experienced during physical activity, raising the possibility that a drug could be developed which enhances the health benefits of exercise. "One of our ideas is that Piezo1 has a special role in controlling blood flow to the intestines and this is really an important part of the body when we start to think about something called the metabolic syndrome which is associated with cardiovascular disease and type 2 diabetes. By modifying this protein in the intestines then perhaps we could overcome some of the problems of diabetes and perhaps this Yoda1 compound could target the Piezo1 in the intestinal area to have a functional effect. It may be that by understanding the working of the Yoda1 experimental molecule on the Piezo1 protein, we can move a step closer to having a drug that can help control some major chronic conditions."

Age-related decreases in vascular health are a common finding in the literature and represent one of many potential mechanisms that contribute to declines in the integrity of the aged brain. Identifying clinical markers of vascular health that serve as surrogate signs of brain health is paramount for early intervention and prevention efforts. Ideal markers of vascular health would be non-invasive, able to detect early changes in vascular function, easily administered in clinical settings, and related to neuroimaging techniques that are sensitive to age-related vascular decline.

Neuroimaging indicators of white matter (WM) health, including fractional anisotropy (FA) and WM hyperintensities (WMHs), are sensitive biomarkers of age-related vascular decline. WMHs are associated with increased pulse-wave velocity, a measure of conduit artery stiffness, and FA is significantly decreased in vascular disease. In addition, changes in FA appear to precede the manifestation of irreversible WM lesions, and are predictive of future cerebrovascular incidents. Despite this evidence, less is known about the relationship between these neuroimaging predictors and early detectors of cardiovascular disease, such as endothelial function.

The vascular endothelium is a single cell layer lining all blood vessels. It plays a critical role in regulating vascular tone by mediating the relationship between luminal blood flow and arterial smooth muscle. When compromised, the endothelium contributes to the pathogenesis of vascular disease. Advancing age is associated with endothelial dysfunction, and endothelial dysfunction is associated with Alzheimer's disease and vascular dementia. Moreover, blood markers of chronic endothelial dysfunction are associated with rarefaction of WM. Collectively, these findings suggest that endothelial function may play a critical role in combating age-related declines in brain health.

Endothelial function can be measured non-invasively through the use of digital pulse amplitude technology, which allows for the assessment of vascular function at the fingertip. This measure of peripheral arterial tone (PAT) is correlated with changes in vascular tone using flow-mediated dilation techniques. Little is known about the relationship between endothelial function and WM health. Endothelial cells mediate vessel caliber, and age-related endothelial dysfunction may induce vasoconstriction and chronic hypoperfusion of WM. Ischemia can then lead to myelin degeneration and selective oligodendrocyte death. Recent findings support this mechanism by demonstrating a relationship between microvessel caliber and normal appearing WM.

The Trail Making Test (TMT) is a reliable and valid assessment of executive function that is related to WM health and overall brain health. In the present study, we used a non-invasive measure of PAT to test the hypothesis that endothelial function is associated with WM health and executive function. We then expanded on these findings by exploring the potential relationships between a measure of executive function, the TMT, and both WM health and reactive hyperemia. Our results demonstrate that a peripheral measure of endothelial function, reactive hyperemia index (RHI), is positively correlated with WM microstructure in the corpus callosum in older adults, but is not related to WMH volume. The results from tractography analyses suggest that portions of the corpus callosum most strongly correlated with WM microstructure were those involved in higher-level cognitive processes. These findings motivate future longitudinal studies aimed to determine if increasing endothelial function, through lifestyle modification, attenuates age-related declines in WM microstructure and executive function.

Infection with human papilloma virus (HPV) is the primary cause of cervical cancer and a subset of head and neck cancers worldwide. A new paper describes a fascinating mechanism that links these two conditions - viral infection and cancer. The link, basically, is a family of enzymes called APOBEC3. These APOBEC3 enzymes are an essential piece of the immune system's response to viral infection, attacking viral DNA to cause disabling mutations. Unfortunately, the action of family member APOBEC3A can spill over from its attack against viruses to induce DNA mutations and damage in the host genome as well. In other words, this facet of the immune system designed to scramble viral DNA can scramble human DNA as well, sometimes in ways that cause cancer.

"We know that the majority of cancers are caused by genetic mutations. And we know some of the mechanisms that cause these mutations, for example UV radiation can cause mutations that lead to skin cancer and smoking can cause mutations that lead to lung cancer. But there are many more cancers in which we don't know the source of the mutations. The APOBEC3 family can explain how some of these mutations are created. In fact, APOBEC3A can be activated in many ways - not just with HPV infection - and its action may drive a percentage of oncogenic mutations across many cancer types."

Data from the Cancer Genome Atlas showed signatures of APOBEC3-mediated mutations in the PIK3CA gene of about 40 percent of HPV-positive head and neck cancers, but only about 10 percent of HPV-negative head and neck cancers. Adding to this storyline of APOBEC3A-mediated oncogenesis was the fact that expression of APOBEC3A was much higher in HPV-positive cancers. Interestingly, this system that so heavily risks damaging host DNA doesn't work so well against its intended target - APOBEC3A does not successfully eliminate the HPV virus, which remains as a chronic infection. "We have another paper from 2015 showing that HPV has revised their genome against this APOBEC3 enzyme, altering and reducing the target sequences in their own DNA. If APOBEC3 fails to recognize its target sequence, it does not interrupt the DNA. In this, we can see the complex race of evolution - the host evolves the APOBEC3 system to target viruses, but then the viruses evolve their DNA to evade APOBEC3. We are not at any endpoint of evolution - what we may be seeing is the our body's attempt to use this APOBEC3 system to help it evolve more quickly in response to the virus."

Central nervous system (CNS) damage, a hallmark of many CNS disorders, is causatively associated with severe neurological deficits in motor, sensory, cognitive, and other functions. Because damaged CNS can spontaneously regenerate after injury, these neurological deficits partially recover over time. One such regenerative process in the mammalian CNS, remyelination, is initiated by proliferation of oligodendrocyte precursor cells (OPCs), which are distributed widely throughout the mammalian CNS. OPC proliferation and subsequent remyelination processes (e.g., migration, differentiation into mature oligodendrocytes) ensure the restoration of saltatory conduction, provision of trophic support for axons, and promotion of functional recovery; therefore, the mechanism of remyelination has attracted considerable attention in regard to its potential applications in regenerative medicine aimed at treating CNS demyelinating diseases.

Disruption of vascular barriers occurs in several types of disease, including multiple sclerosis, cerebral ischemia, brain tumors, and other neurological diseases. Disrupted vascular barriers can lead to hemorrhage, brain hypoperfusion, and transmigration of inflammatory cells into the CNS; consequently, vascular barrier disruption may exacerbate pathological processes. However, OPC proliferation increases in proximity to demyelinating lesions, which are often characterized by vascular barrier disruption. In addition, some of the cells in the CNS express peripheral-hormone receptors, such as the insulin and mineralocorticoid receptors, which regulate neurogenesis in the adult CNS. Although the role of vascular barrier disruption in CNS regeneration has not yet been clarified, we hypothesized that vascular barrier disruption mediated by CNS injury induces the leakage of circulating factors into the CNS, resulting in remyelination.

In this study, we found that circulating FGF21 promotes OPC proliferation. OPC proliferation was elevated in the spinal cords of mice with toxin-induced demyelination, and this proliferation was inhibited by silencing of FGF21 expression in the pancreas. OPCs expressed β-klotho, an essential coreceptor for FGF21, and inhibition of β-klotho expression in OPCs prevented the increase in OPC proliferation and subsequent remyelination. The results of this study reveal an unexpected role of FGF21, which has been previously characterized as a metabolic regulator. In reviewing previous findings regarding FGF21 function in the CNS, we noted that FGF21 can cross the blood-brain barrier, but the FGF21 level in the cerebrospinal fluid of healthy patients is approximately 40% of that in the plasma. Thus, CNS entry of peripheral FGF21 is limited in normal adult subjects.

We should note that FGF21-mediated OPC proliferation is only one of the mechanisms of remyelination. In terms of molecular mechanism, we just focused on the direct action of FGF21 on OPC proliferation; however, FGF also regulates expression of VEGF receptor 2. Because VEGF signaling is related to brain homeostasis, including OPC migration, a process that involves remyelination, an indirect effect of FGF21 on OPCs may also contribute to oligodendrocyte development and remyelination. Meanwhile, FGF21-associated drugs for treating diabetes have recently been developed by pharmaceutical companies, and some of these compounds have reached the stage of clinical trials. We believe that these FGF21-associated drugs may exert FGF21-mediated remyelination effect and provide clinical benefits in patients with CNS demyelination.