Rsearchers have now succeeded in describing the unexpected diversity of thymic epithelial cells at the transcriptional level. Algorithms developed for the precise description of differences in the gene activity of individual cells made it possible to identify potential precursor cells. As a result, for the first time it became possible to study the development of thymic epithelium at different ages in equisite molecular detail. This kind of analysis is of particular interest to immunologists because the thymus is subject to significant changes during life. Rapid organ growth and massive T-cell production are characteristic of the early developmental stages. In contrast, there is a gradual loss of functional thymic epithelial cells in old age and, therefore, decreased T-cell production. These age-related changes are associated with a reduced immune function.

The researchers identified two bipotent progenitor populations of the thymic epithelium in their analysis. An "early" progenitor population takes over the primary role in the thymus formation during embryonic development. While in the juvenile organism, a subsequent "postnatal" progenitor population significantly determines the continued thymus formation in adulthood.

T cell development in the thymus is essential for cellular immunity and depends on the organotypic thymic epithelial microenvironment. In comparison with other organs, the size and cellular composition of the thymus are unusually dynamic, as exemplified by rapid growth and high T cell output during early stages of development, followed by a gradual loss of functional thymic epithelial cells (TECs) and diminished naive T cell production with age. Here we combine scRNA-seq and a new CRISPR-Cas9-based cellular barcoding system in mice to determine qualitative and quantitative changes in the thymic epithelium over time. This dual approach enabled us to identify two principal progenitor populations: an early bipotent progenitor type biased towards cortical epithelium and a postnatal bipotent progenitor population biased towards medullary epithelium.

We further demonstrate that continuous autocrine provision of Fgf7 leads to sustained expansion of thymic microenvironments without transgenicexhausting the epithelial progenitor pools, suggesting a strategy to modulate the extent of thymopoietic activity. Mice treated with pharmacological doses of the Fgfr2b ligand KGF, the human homologue of Fgf7, exhibit an increase in the number of TECs. However, it is not known whether Fgf stimulation targets progenitors, mature TECs, or both. To examine this question, we generated several mouse models for continuous autocrine provision of an Fgfr2b ligand in the thymus. We established that, under physiological conditions, the extent of Fgf signalling in TECs is determined by limiting levels of ligands, rather than the receptor; notably, we found that pharmacological supplementation of the Fgfr2b ligand Fgf7 could be mimicked in vivo by ectopic expression of Fgf7 in the TECs of transgenic mice. Continuous autocrine provision of Fgf7 within the epithelial compartment in this transgenic model increased the number of TECs and thymocytes and resulted in a massive and sustained increase in thymus size.

Several studies on the genetics of longevity have been reviewed in this paper. The results show that, despite the efforts made by the international scientific community and the use of high-throughput genotyping methodologies, satisfactory results have not been obtained. The most significant associations have been obtained with the two genes, APOE and FOXO3A, which had already been identified for some time with simple case-control studies. From the evolutionary point of view, longevity depends on the residual maintenance functions after the end of the reproduction period. Aging depends on stochastic events and the aging phenotype is the result of the accumulation of cellular damage that cannot be repaired by the cellular maintenance systems that are running out. Therefore, longevity depends on the possibility of survival after the end of the reproductive period and the genes that lead to longevity are "survival genes" rather than "longevity genes".

Several studies of formal genetics strongly suggest the role of genes in achieving longevity. The comparison between the survival of the siblings of centenarians and that of their brothers-in-law, who likely shared the same lifestyle for most of their lives, showed that "the survival advantage" of siblings of long-lived subjects was not fully shared from their brothers-in-law. This suggested that beyond the family environment, there are genetic factors that influence survival and, consequently, longevity. This was not true comparing the survival of sisters with that of sisters-in-law. Interestingly, in this study, the survival curve of the sisters of long-lived subjects did not differ from the one of sisters-in-law, suggesting that the genetic component explains longevity in men more than in women. The genetic component of lifespan in humans has also been analyzed by comparing the age of death of monozygotic and dizygotic twins. This has allowed to estimate that about 25% of the variation in human longevity can be due to genetic factors and indicated that this component is higher at older ages and is more important in males than in females.

It is thought that for the first eight decades of life, a correct lifestyle is a stronger determinant of health and life span than genetics. Genetics then appears to play a progressively important role in keeping individuals healthy and live as they age into their eighties and beyond. For centenarians, it reaches up to 33% for women and 48% for men. However, in general, the effect sizes were not large, suggesting that many genes of small effect play a role, as indeed in all multifactorial traits; however, it needs to be considered that there is a dynamic interplay between genetic and environmental variations in the development of individual differences in health, and hence, longevity. Therefore, it is not surprising that GWAS-replicated associations of common variants with longevity have been few since they pool different populations losing the "ecological" dimension of longevity.

Overall, the findings discussed in this paper strongly suggest that longevity genetics are closely associated with protection against age-related diseases, particularly cardiovascular diseases (CVDs). The association with longevity is not surprising because CVDs are the leading cause of death globally, with an estimated 17.9 million deaths annually.

Researchers studied the production of blood cells from the bone marrow, analysing 10 individuals ranging in age from new-borns to the elderly. They sequenced the whole genomes of 3,579 blood stem cells, identifying all the somatic mutations contained in each cell. The team used this to reconstruct 'family trees' of each person's blood stem cells, showing, for the first time, an unbiased view of the relationships among blood cells and how these relationships change across the human lifespan.

The researchers found that these 'family trees' changed dramatically after the age of 70 years. The production of blood cells in adults aged under 65 came from 20,000 to 200,000 stem cells, each of which contributed in roughly equal amounts. In contrast, blood production in individuals aged over 70 was very unequal. A reduced set of expanded stem cell clones - as few as 10 to 20 - contributed as much as half of all blood production in every elderly individual studied. These highly active stem cells had progressively expanded in numbers across that person's life, caused by a rare subset of somatic mutations known as 'driver mutations'.

These findings led the team to propose a model in which age-associated changes in blood production come from somatic mutations causing 'selfish' stem cells to dominate the bone marrow in the elderly. This model, with the steady introduction of driver mutations that cause the growth of functionally altered clones over decades, explains the dramatic and inevitable shift to reduced diversity of blood cell populations after the age of 70. Which clones become dominant varies from person to person, and so the model also explains the variation seen in disease risk and other characteristics in older adults.

Age-related change in human haematopoiesis causes reduced regenerative capacity, cytopenias, immune dysfunction, and increased risk of blood cancer, but the reason for such abrupt functional decline after 70 years of age remains unclear. Here we sequenced 3,579 genomes from single cell-derived colonies of haematopoietic cells across 10 human subjects from 0 to 81 years of age. Haematopoietic stem cells or multipotent progenitors (HSC/MPPs) accumulated a mean of 17 mutations per year after birth and lost 30 base pairs per year of telomere length. Haematopoiesis in adults less than 65 years of age was massively polyclonal, with high clonal diversity and a stable population of 20,000-200,000 HSC/MPPs contributing evenly to blood production. By contrast, haematopoiesis in individuals aged over 75 showed profoundly decreased clonal diversity. In each of the older subjects, 30-60% of haematopoiesis was accounted for by 12-18 independent clones, each contributing 1-34% of blood production.

Simulations of haematopoiesis, with constant stem cell population size and constant acquisition of driver mutations conferring moderate fitness benefits, entirely explained the abrupt change in clonal structure in the elderly. Rapidly decreasing clonal diversity is a universal feature of haematopoiesis in aged humans, underpinned by pervasive positive selection acting on many more genes than currently identified.

The treatments of Alzheimer's disease (AD) fall into two main categories: symptomatic and disease-modifying. The purpose of symptomatic treatments is cognitive improvement or control of neuropsychiatric symptoms, without having an impact on the biological causes leading to neuronal death. By contrast, disease-modifying treatments are designed to induce neuroprotection through changing the neuropathology of AD, often acting on a variety of intermediate mechanisms. Unfortunately, most therapeutic agents developed in the last 15 years have failed.

Despite being such an important disease, the number of drugs in development for AD is much lower than in other diseases with a higher therapeutic arsenal. This reflects the fact that AD's biology is poorly understood, and the availability of biomarkers is a very limited. Moreover, the duration of clinical trials for assessing AD treatments is very long, which increases the risk of failure.

In any case, we may wonder why the treatments in development are failing or are not effective. Based on numerous trials of failed drugs in patients with AD, a plausible explanation could be that amyloid-β (Aβ) therapies are being administered too late, when the disease is completely developed and the effectiveness of the treatments is dramatically reduced. Therefore, an earlier (pre-symptomatic) diagnosis should be made, including a rethinking of the AD diagnostic criteria, which should be based primarily on biomarkers. Following this line of thought, drugs in phase III clinical development are being tested primarily in subjects during the early stages of the disease (mild cognitive impairment), in the preclinical phase of AD or even in asymptomatic subjects at high risk of developing AD.

An additional explanation could be that the initial hypotheses proposed for β-amyloid and tau as the main responsible neurotoxins for AD, are not able to entirely explain the pathophysiology of the disease. Hence, β-amyloid plaques and neurofibrillary tangles would have a secondary role in AD's origin. Indeed, if we review the clinical trials developed during the last 5 years, we find a progressive emphasis on non-amyloid targets, including candidate treatments for inflammation, synapse and neuronal protection, vascular factors, neurogenesis, and epigenetic interventions. There has also been an increase in the study of "reused drugs", that is to say, drugs that are used to treat other pathologies but are also thought to be useful for AD treatment. Two clear examples of these are escitalopram and metformin. In any case, the complexity of AD's etiopathogenesis demands multiple therapeutic strategies that can be proposed according to the molecular and physiological processes involved.

Undoubtedly, the trends in therapeutic strategies for AD will involve an increase in the diversity of non-amyloid or tau targets, including inflammation, insulin resistance, synapse and neuronal protection, cardiovascular factors, neurogenesis and epigenetic interventions. Indeed, some authors consider that AD should no longer be considered a brain disease, since its development is also attributed to peripheral factors as, for instance, intestinal dysbiosis.

The SASP contributes to the secretion of inflammatory cell cytokines and chemokines that induce local and systemic inflammatory responses, immune system activation, tissue damage and fibrosis, and cell apoptosis and dysfunction. Moreover, the SASP can also induce the enlargement of local and systemic senescence to neighbouring cells via paracrine or endocrine mechanisms. Furthermore, a variety of molecules involved in the SASP can serve as promoters and biomarkers of cardiovascular diseases including atherosclerosis.

Recent clinical trials have clearly demonstrated a causal relationship between inflammation and human atherosclerosis. Atherosclerosis is considered a chronic inflammatory disease, and atherosclerotic plaques present with cell senescence. Cell senescence and atherosclerosis have multiple common aetiological stimuli, but senescent cells are not just simple bystanders. Senescent cells from atherosclerotic plaques lack proliferation, overexpress P16INK4A, P53, P21, and increase the activity of senescence-associated beta-galactosidase (SAβG). They can also establish the SASP, which can cause increased secretion of various inflammatory cell cytokines, chemokines and matrix-degrading proteases. Notably, there is evidence that the SASP, as a source of chronic inflammation and some plaque instability factors, is involved in the pathogenesis and development of atherosclerosis.

The SASP from senescent cells exerts many pro-atherogenic effects, which may involve vascular remodelling, plaque formation and rupture. There is evidence that plaque-rich arteries contain various typical SASP components, including matrix metalloproteinases and multiple inflammatory factors. However, these phenomena are not present in normal adjacent blood vessels. Senescent cells in blood vessels with the SASP release various inflammatory cytokines (interleukin-6 and interleukin-8) and growth factors (such as VEGF, PDGF, chemokines and matrix metalloproteinases). Studies have shown that some of these are known cardiovascular risk factors. Additionally, a study reported that p16 positive cells are the main driver of the aged heart phenotype that causes a reduced lifespan in mice, so removing senescent cells with p16 promoter activity can inhibit the occurrence and development of atherosclerotic plaques and improve the stability of plaques

Therefore, the prevention of accelerated cellular senescence and the SASP represents an important therapeutic opportunity, and understanding the mechanisms responsible for this change is essential for the promotion of prevention and therapy of atherosclerosis and other age-associated diseases.

Recent studies suggested that noncoding RNAs are involved in healthy aging and/or age-related diseases. It remains, however, largely unknown whether circular RNAs (circRNAs), a class of endogenous noncoding RNA with a covalently closed continuous loop predominantly generated from back-splicedback-spliced exons, and acting as 'microRNA sponges' or 'scaffolding' for RNA-binding protein, in human longevity. Increasing evidence has revealed the crucial roles of circRNAs in multiple biological processes and even in human diseases. For instance, several circRNAs were related with age-related diseases, including neurodegenerative diseases, cardiovascular diseases, type 2 diabetes, and, even, cancers. Nevertheless, their roles in the process of human lifespan extension are largely unexplored.

In this study, we investigated the circRNAs expression pattern of longevous families, from a Chinese cohort of longevity. Based on weighted circRNA co-expression network analysis, we found that longevous elders (98.3 ± 3.4 years) specifically gained eight but lost seven conserved circRNA-circRNA co-expression modules compared with normal elder controls (spouses of offspring of long-lived individuals, age = 59.3 ± 5.8 years). Both the gained and lost module-related genes were enriched in infectious disease-related pathways. This suggests that these elders might have a history of infection, which could be related to life in the early and middle twentieth century when medical health care was poorer and contagious diseases were prevalent. It seems that these circRNAs may be associated with previous responses to infectious diseases.

Given that these modules, as predicted by mRNA-circRNA co-expression analysis, were closely related to processes involved in lifespan extension, the gain and loss of these circRNA-circRNA co-expression modules in very long-lived individuals are unlikely to be a random process but rather contribute to healthy human aging and may represent a new target for the regulation of healthy human aging.

Elevated blood pressure (BP) has been linked to impaired cognition and dementia in older adults. However, few studies have accounted for long-term cumulative BP exposure. The aim of this study was to test whether long-term cumulative BP was independently associated with subsequent cognitive decline, incident dementia, and all-cause mortality among cognitively healthy adults. This study used data from the HRS (Health and Retirement Study) and ELSA (English Longitudinal Study of Ageing). A total of 7,566 and 9,294 participants from ELSA and the HRS were included, with a median age of 62.0 years.

The median follow-up duration was 8.0 years. Elevated cumulative systolic BP and pulse pressure were independently associated with accelerated cognitive decline, elevated dementia risk, and all-cause mortality. In conclusion, long-term cumulative BP was associated with subsequent cognitive decline, dementia risk, and all-cause mortality in cognitively healthy adults aged ≥50 years. Efforts are required to control long-term systolic BP and pulse pressure and to maintain adequate diastolic BP.

Researchers compared the gene expression patterns of 26 mammalian species with diverse maximum lifespans, from two years (shrews) to 41 years (naked mole rats). They identified thousands of genes related to a species' maximum lifespan that were either positively or negatively correlated with longevity. They found that long-lived species tend to have low expression of genes involved in energy metabolism and inflammation; and high expression of genes involved in DNA repair, RNA transport, and organization of cellular skeleton (or microtubules).

Previous researchhas shown that features such as more efficient DNA repair and a weaker inflammatory response are characteristic of mammals with long lifespans. The opposite was true for short-lived species, which tended to have high expression of genes involved in energy metabolism and inflammation and low expression of genes involved in DNA repair, RNA transport, and microtubule organization.

When the researchers analyzed the mechanisms that regulate expression of these genes, they found two major systems at play. The negative lifespan genes - those involved in energy metabolism and inflammation - are controlled by circadian networks. That is, their expression is limited to a particular time of day, which may help limit the overall expression of the genes in long-lived species. On the other hand, positive lifespan genes - those involved in DNA repair, RNA transport, and microtubules - are controlled by what is called the pluripotency network. The pluripotency network is involved in reprogramming somatic cells into embryonic cells, which can more readily rejuvenate and regenerate, by repackaging DNA that becomes disorganized as we age.

Previous studies have shown that the polyamine spermidine increased the maximum life span in C. elegans and the median life span in mice. Since spermidine increases autophagy, we asked if treatment with chloroquine, an inhibitor of autophagy, would shorten the lifespan of mice. Recently, chloroquine has intensively been discussed as a treatment option for COVID-19 patients. To rule out unfavorable long-term effects on longevity, we examined the effect of chronic treatment with chloroquine given in the drinking water on the lifespan and organ pathology of male middle-aged NMRI mice. We report that, surprisingly, daily treatment with chloroquine extended the median life span by 11.4% and the maximum life span of the middle-aged male NMRI mice by 11.8%.

Subsequent experiments show that the chloroquine-induced lifespan elevation is associated with dose-dependent increase in LC3B-II, a marker of autophagosomes, in the liver and heart that was confirmed by transmission electron microscopy. This supports the hypothesis that long-term treatment led to an accumulation of autophagosomes due to impaired autophagosome fusion with lysosomes. Quite intriguingly, chloroquine treatment was also associated with a decrease in glycogenolysis in the liver suggesting a compensatory mechanism to provide energy to the cell. Accumulation of autophagosomes was paralleled by an inhibition of proteasome-dependent proteolysis in the liver and the heart as well as with decreased serum levels of insulin growth factor binding protein-3 (IGFBP3), a protein associated with longevity. We propose that inhibition of proteasome activity in conjunction with an increased number of autophagosomes and decreased levels of IGFBP3 might play a central role in lifespan extension by chloroquine in male NMRI mice.

The implication of the heterogeneous spectrum of pro- and anti-inflammatory macrophages (Macs) has been an important area of investigation over the last decade. The polarization of Macs alters their functional phenotype in response to their surrounding microenvironment. Macs are the major immune cells implicated in the pathogenesis of atherosclerosis. A hallmark pathology of atherosclerosis is the accumulation of pro-inflammatory M1-like macrophages in coronary arteries induced by pro-atherogenic stimuli; these M1-like pro-inflammatory macrophages are incapable of digesting lipids, thus resulting in foam cell formation in the atherosclerotic plaques.

Recent findings suggest that the progression and stability of atherosclerotic plaques are dependent on the quantity of infiltrated Macs, the polarization state of the Macs, and the ratios of different types of Mac populations. The polarization of Macs is defined by signature markers on the cell surface, as well as by factors in intracellular and intranuclear compartments. At the same time, pro- and anti-inflammatory polarized Macs also exhibit different gene expression patterns, with differential cellular characteristics in oxidative phosphorylation and glycolysis. Macs are reflective of different metabolic states and various types of diseases.

In this review, we discuss the major differences between M1-like Macs and M2-like Macs, their associated metabolic pathways, and their roles in atherosclerosis. Mechanisms that minimize Mac inflammation, increase lipid degradation, and prevent foam cell formation, are likely to decrease atherosclerosis progression. Future works are needed to further elucidate the mechanisms of actions by which different factors induce inflammatory or anti-inflammatory Macs in the context of foam cell formation. A better understanding of Mac infiltration, differentiation, polarization, and phagocytosis would be extremely beneficial for the prevention and treatment of atherosclerosis.

Osteoarthritis (OA) is a musculoskeletal disease characterized by cartilage degeneration and stiffness, with chronic pain in the affected joint. It has been proposed that OA progression is associated with the development of low-grade inflammation (LGI) in the joint. In support of this principle, LGI is now recognized as the major contributor to the pathogenesis of obesity, aging, and metabolic syndromes, which have been documented as among the most significant risk factors for developing OA. These discoveries have led to a new definition of the disease, and OA has recently been recognized as a low-grade inflammatory disease of the joint.

Damage-associated molecular patterns (DAMPs), or alarmin molecules, the major cellular components that facilitate the interplay between cells in the cartilage and synovium, activate various molecular pathways involved in the initiation and maintenance of LGI in the joint, which, in turn, drives OA progression. A better understanding of the pathological mechanisms initiated by LGI in the joint represents a decisive step toward discovering therapeutic strategies for the treatment of OA. Recent findings and discoveries regarding the involvement of LGI mediated by DAMPs in OA pathogenesis are discussed. Modulating communication between cells in the joint to decrease inflammation represents an attractive approach for the treatment of OA.

Study findings argue that neuronal damage characteristic of Alzheimer's disease takes root inside cells and well before these thread-like amyloid plaques fully form and clump together in the brain. The study traced the root dysfunction observed in mice bred to develop Alzheimer's disease to the brain cells' lysosomes. These are small sacs inside every cell, filled with acidic enzymes involved in the routine breakdown, removal, and recycling of metabolic waste from everyday cell reactions, as well as from disease. Lysosomes are also key, researchers note, to breaking down and disposing of a cell's own parts when the cell naturally dies.

As part of the study, researchers tracked decreasing acid activity inside intact mouse cell lysosomes as the cells became injured in the disease. Imaging tests developed to track cellular waste removal showed that certain brain cell lysosomes became enlarged as they fused with so-called autophagic vacuoles filled with waste that had failed to be broken down. These autophagic vacuoles also contained earlier forms of amyloid beta. In neurons most heavily damaged and destined for early death as a result, the vacuoles pooled together in "flower-like" patterns, bulging out from the cells' outer membranes and massing around each cell's center, or nucleus. Accumulations of amyloid beta formed filaments inside the cell, another hallmark of Alzheimer's disease. Indeed, researchers observed almost-fully formed plaques inside some damaged neurons.

"Previously, the working hypothesis mostly attributed the damage observed in Alzheimer's disease to what came after amyloid buildup outside of brain cells, not before and from within neurons. This new evidence changes our fundamental understanding of how Alzheimer's disease progresses; it also explains why so many experimental therapies designed to remove amyloid plaques have failed to stop disease progression, because the brain cells are already crippled before the plaques fully form outside the cell."

For patients with cancer, prevalent type 2 diabetes at the date of cancer diagnosis is associated with increased cancer-specific and all-cause mortality. Yet, despite potential health implications, there is limited knowledge on whether cancer is also a risk factor for type 2 diabetes. We investigated the incidence of type 2 diabetes following a cancer diagnosis and evaluated the influence of new-onset type 2 diabetes in patients with cancer on overall survival.

We included 51,353 incident cancer case subjects diagnosed from 2004 to 2015 living in the Greater Copenhagen area without type 2 diabetes. We sampled all 112 million tests from 1.3 million individuals, performed by the Copenhagen General Practitioners' Laboratory, contained in the Copenhagen Primary Care Laboratory Database (CopLab) (2015-57-0121) from 2000 to 2015, data for which were merged with data on incident cancer from the Danish Cancer Registry. The median follow-up time was 2.34 years for all case subjects and 4.41 years for cancer-free control subjects.

We found an increased hazard of new-onset type 2 diabetes for all cancers (hazard ratio [HR] 1.09). The hazard of new-onset type 2 diabetes for different cancer types in comparisons with control subjects was particularly strong for pancreatic cancer (HR 5.00), cancer of the brain and other parts of the nervous system (HR 1.54), and cancer of the corpus uteri (HR 1.41). Patients diagnosed with lung (HR 1.38) and urinary tract (HR 1.32) cancers also had a significantly increased hazard of type 2 diabetes.

Our results align with a smaller study of 15,130 incident cancer survivors where investigators observed an overall 35% increase in the hazard of diabetes following a cancer diagnosis. We included more than three times the number of incident cancer cases and observed similar effects; thus, our findings bolster the evidence for associations that was previously less strongly supported. The underlying mechanisms still remain to be defined but could include common risk factors, tumor-secreted factors, or effects of treatment.

Arterial stiffness (AS) is one of the earliest detectable signs of structural and functional alterations of the vessel wall and an independent predictor of cardiovascular events and death. The emerging field of metabolomics can be utilized to detect a wide spectrum of intermediates and products of metabolism in body fluids that can be involved in the pathogenesis of AS. Research over the past decade has reinforced this idea by linking AS to circulating acylcarnitines, glycerophospholipids, sphingolipids, and amino acids, among other metabolite species.

Some of these metabolites influence AS through traditional cardiovascular risk factors (e.g., high blood pressure, high blood cholesterol, diabetes, smoking), while others seem to act independently through both known and unknown pathophysiological mechanisms. We propose the term 'arteriometabolomics' to indicate the research that applies metabolomics methods to study AS. The 'arteriometabolomics' approach has the potential to allow more personalized cardiovascular risk stratification, disease monitoring, and treatment selection. One of its major goals is to uncover the causal metabolic pathways of AS. Such pathways could represent valuable treatment targets in vascular ageing.

Since sirtuins were found to extend the lifespan of Saccharomyces cerevisiae and Caenorhabditis elegans, the mechanism of sirtuin lifespan extension and whether it can extend the lifespan of other species has been actively studied. With increasing research in the last 5 years, sirtuins are increasingly recognized as being critical for regulating mitophagy and maintaining mitochondrial homeostasis. Taken together, the sirtuin family can activate or inhibit mitophagy through multiple pathways, for instance deacetylation of PGC-1α and FOXO1/FOXO3 and reduction of reactive oxygen species, thereby affecting aging and age-related diseases. By targeting these pathways, it may be possible to delay aging.

A consensus has now emerged from many studies of sirtuin activators that sirtuins mediated aspects of caloric restriction. Sirtuin activators can modulate aging and age-related diseases by activating a variety of sirtuin-induced biological functions, and have demonstrated significant aging delay and disease mitigation in experimental models. Excitingly, some sirtuin activators are already in clinical trials. For example, resveratrol acts in neurological diseases, SRT2104 in inflammation, and nicotinamide riboside in the cardiovascular system. Furthermore, decreased NAD+ levels during aging reduce sirtuin activity, which may contribute to the aging process.

However, there are still many unresolved issues. First, while there is substantial evidence implicating sirtuins in delayed aging and suppression of the aging phenotype through activation of mitophagy, there are few experiments directly demonstrating this pathway. Secondly, the effects of different sirtuin family members on mitophagy and the mechanisms of sirtuin-induced mitophagy in aging remain poorly understood. Sirtuin family members are redundant in regulating lifespan and whether other enzyme activities (excluding acetylation activity) are involved in the aging process. Thirdly, sirtuin in different tissues seems to have different effects. The specificity of sirtuin-induced mitophagy for different aging tissues and age-related diseases also merits further investigation. Fourthly, cancer cells often use mitophagy to maintain their metabolic reprogramming and growth. This is a negative effect of sirtuin-mediated mitophagy. This raises the question that whether activation of mitophagy promotes the growth of cancer cells. Fifthly, it is still unclear about the pharmacokinetics and pharmacodynamics of sirtuin activator NAD+ precursors and the mechanism of their transport through cell membranes into the blood and cells. Hopefully, these questions will be addressed in the future and provide a clearer direction for delaying human aging.