Unlike dietary restriction, rapamycin fails to extend lifespan and reduce transcription stress in progeroid DNA repair-deficient mice

Does diet influence aging? Evidence from animal studies

Nutrition profoundly influences the risk for many age-related diseases. Whether nutrition influences human aging biology directly is less clear. Studies in different animal species indicate that reducing food intake ("caloric restriction" [CR]) can increase lifespan and delay the onset of diseases and the biological hallmarks of aging. Obesity has been described as "accelerated aging" and therefore the lifespan and health benefits generated by CR in both aging and obesity may occur via similar mechanisms. Beyond calorie intake, studies based on nutritional geometry have shown that protein intake and the interaction between dietary protein and carbohydrates influence age-related health and lifespan. Studies where animals are calorically restricted by providing free access to diluted diets have had less impact on lifespan than those studies where animals are given a reduced aliquot of food each day and are fasting between meals. This has drawn attention to the role of fasting in health and aging, and exploration of the health effects of various fasting regimes. Although definitive human clinical trials of nutrition and aging would need to be unfeasibly long and unrealistically controlled, there is good evidence from animal experiments that some nutritional interventions based on CR, manipulating dietary macronutrients, and fasting can influence aging biology and lifespan.

Different Purkinje cell pathologies cause specific patterns of progressive gait ataxia in mice

Gait ataxia is one of the most common and impactful consequences of cerebellar dysfunction. Purkinje cells, the sole output neurons of the cerebellar cortex, are often involved in the underlying pathology, but their specific functions during locomotor control in health and disease remain obfuscated. We aimed to describe the effect of gradual adult-onset Purkinje cell degeneration on gaiting patterns in mice, and to determine whether two different mechanisms that both lead to Purkinje cell degeneration cause different patterns in the development of gait ataxia. Using the ErasmusLadder together with a newly developed limb detection algorithm and machine learning-based classification, we subjected mice to a challenging locomotor task with detailed analysis of single limb parameters, intralimb coordination and whole-body movement. We tested two Purkinje cell-specific mouse models, one involving stochastic cell death due to impaired DNA repair mechanisms (Pcp2-Ercc1-/-), the other carrying the mutation that causes spinocerebellar ataxia type 1 (Pcp2-ATXN1[82Q]). Both mouse models showed progressive gaiting deficits, but the sequence with which gaiting parameters deteriorated was different between mouse lines. Our longitudinal approach revealed that gradual loss of Purkinje cell function can lead to a complex pattern of loss of function over time, and that this pattern depends on the specifics of the pathological mechanisms involved. We hypothesize that this variability will also be present in disease progression in patients, and that our findings will facilitate the study of therapeutic interventions in mice, as subtle changes in locomotor abilities can be quantified by our methods.

Initiation phase cellular reprogramming ameliorates DNA damage in the ERCC1 mouse model of premature aging

Unlike aged somatic cells, which exhibit a decline in molecular fidelity and eventually reach a state of replicative senescence, pluripotent stem cells can indefinitely replenish themselves while retaining full homeostatic capacity. The conferment of beneficial-pluripotency related traits via in vivo partial cellular reprogramming in vivo partial reprogramming significantly extends lifespan and restores aging phenotypes in mouse models. Although the phases of cellular reprogramming are well characterized, details of the rejuvenation processes are poorly defined. To understand whether cellular reprogramming can ameliorate DNA damage, we created a reprogrammable accelerated aging mouse model with an ERCC1 mutation. Importantly, using enhanced partial reprogramming by combining small molecules with the Yamanaka factors, we observed potent reversion of DNA damage, significant upregulation of multiple DNA damage repair processes, and restoration of the epigenetic clock. In addition, we present evidence that pharmacological inhibition of ALK5 and ALK2 receptors in the TGFb pathway are able to phenocopy some benefits including epigenetic clock restoration suggesting a role in the mechanism of rejuvenation by partial reprogramming.

Lifestyle effects on aging and CVD: A spotlight on the nutrient-sensing network

Aging is widespread worldwide and a significant risk factor for cardiovascular disease (CVD). Mechanisms underlying aging have attracted considerable attention in recent years. Remarkably, aging and CVD overlap in numerous ways, with deregulated nutrient sensing as a common mechanism and lifestyle as a communal modifier. Interestingly, lifestyle triggers or suppresses multiple nutrient-related signaling pathways. In this review, we first present the composition of the nutrient-sensing network (NSN) and its metabolic impact on aging and CVD. Secondly, we review how risk factors closely associated with CVD, including adverse life states such as sedentary behavior, sleep disorders, high-fat diet, and psychosocial stress, contribute to aging and CVD, with a focus on the bridging role of the NSN. Finally, we focus on the positive effects of beneficial dietary interventions, specifically dietary restriction and the Mediterranean diet, on the regulation of nutrient metabolism and the delayed effects of aging and CVD that depend on the balance of the NSN. In summary, we expound on the interaction between lifestyle, NSN, aging, and CVD.

The central role of DNA damage in immunosenescence

Ageing is the biggest risk factor for the development of multiple chronic diseases as well as increased infection susceptibility and severity of diseases such as influenza and COVID-19. This increased disease risk is linked to changes in immune function during ageing termed immunosenescence. Age-related loss of immune function, particularly in adaptive responses against pathogens and immunosurveillance against cancer, is accompanied by a paradoxical gain of function of some aspects of immunity such as elevated inflammation and increased incidence of autoimmunity. Of the many factors that contribute to immunosenescence, DNA damage is emerging as a key candidate. In this review, we discuss the evidence supporting the hypothesis that DNA damage may be a central driver of immunosenescence through senescence of both immune cells and cells of non-haematopoietic lineages. We explore why DNA damage accumulates during ageing in a major cell type, T cells, and how this may drive age-related immune dysfunction. We further propose that existing immunosenescence interventions may act, at least in part, by mitigating DNA damage and restoring DNA repair processes (which we term "genoprotection"). As such, we propose additional treatments on the basis of their evidence for genoprotection, and further suggest that this approach may provide a viable therapeutic strategy for improving immunity in older people.

Targeting the biology of aging with mTOR inhibitors

Inhibition of the protein kinase mechanistic target of rapamycin (mTOR) with the Food and Drug Administration (FDA)-approved therapeutic rapamycin promotes health and longevity in diverse model organisms. More recently, specific inhibition of mTORC1 to treat aging-related conditions has become the goal of basic and translational scientists, clinicians and biotechnology companies. Here, we review the effects of rapamycin on the longevity and survival of both wild-type mice and mouse models of human diseases. We discuss recent clinical trials that have explored whether existing mTOR inhibitors can safely prevent, delay or treat multiple diseases of aging. Finally, we discuss how new molecules may provide routes to the safer and more selective inhibition of mTOR complex 1 (mTORC1) in the decade ahead. We conclude by discussing what work remains to be done and the questions that will need to be addressed to make mTOR inhibitors part of the standard of care for diseases of aging.

Gene expression changes in cerebellum induced by dietary restriction

Background

Dietary restriction (DR) is a well-established universal anti-aging intervention, and is neuroprotective in multiple models of nervous system disease, including models with cerebellar pathology. The beneficial effects of DR are associated with a rearrangement of gene expression that modulate metabolic and cytoprotective pathways. However, the effect of DR on the cerebellar transcriptome remained to be fully defined.

Results

Here we analyzed the effect of a classical 30% DR protocol on the transcriptome of cerebellar cortex of young-adult male mice using RNAseq. We found that about 5% of expressed genes were differentially expressed in DR cerebellum, the far majority of whom showing subtle expression changes. A large proportion of down-regulated genes are implicated in signaling pathways, in particular pathways associated with neuronal signaling. DR up regulated pathways in large part were associated with cytoprotection and DNA repair. Analysis of the expression of cell-specific gene sets, indicated a strong enrichment of DR down genes in Purkinje cells, while genes specifically associated with granule cells did not show such a preferential down-regulation.

Conclusion

Our data show that DR may have a clear effect on the cerebellar transcriptome inducing a mild shift from physiology towards maintenance and repair, and having cell-type specific effects.

Hypoxia extends lifespan and neurological function in a mouse model of aging

There is widespread interest in identifying interventions that extend healthy lifespan. Chronic continuous hypoxia delays the onset of replicative senescence in cultured cells and extends lifespan in yeast, nematodes, and fruit flies. Here, we asked whether chronic continuous hypoxia is beneficial in mammalian aging. We utilized the Ercc1 Δ/- mouse model of accelerated aging given that these mice are born developmentally normal but exhibit anatomic, physiological, and biochemical features of aging across multiple organs. Importantly, they exhibit a shortened lifespan that is extended by dietary restriction, the most potent aging intervention across many organisms. We report that chronic continuous 11% oxygen commenced at 4 weeks of age extends lifespan by 50% and delays the onset of neurological debility in Ercc1 Δ/- mice. Chronic continuous hypoxia did not impact food intake and did not significantly affect markers of DNA damage or senescence, suggesting that hypoxia did not simply alleviate the proximal effects of the Ercc1 mutation, but rather acted downstream via unknown mechanisms. To the best of our knowledge, this is the first study to demonstrate that "oxygen restriction" can extend lifespan in a mammalian model of aging.

Metabolism, homeostasis, and aging

We propose a two-mode (pursuit/maintenance) model of metabolism defined by usable resource availability. Pursuit, consisting of anabolism and catabolism, dominates when usable resources are plentiful and leads to the generation of metabolic waste. In turn, maintenance of a system is activated by elevated metabolic waste during resource depletion. Interaction with the environment results in pendulum-like swings between these metabolic states in thriveless attempts to maintain the least deleterious organismal state - ephemeral homeostasis. Imperfectness of biological processes during these attempts supports the accumulation of the deleteriome, driving organismal aging. We discuss how metabolic adjustment by the environment and resource stabilization may modulate healthspan and lifespan.

Purkinje-cell-specific DNA repair-deficient mice reveal that dietary restriction protects neurons by cell-intrinsic preservation of genomic health

Dietary restriction (DR) is a universal anti-aging intervention, which reduces age-related nervous system pathologies and neurological decline. The degree to which the neuroprotective effect of DR operates by attenuating cell intrinsic degradative processes rather than influencing non-cell autonomous factors such as glial and vascular health or systemic inflammatory status is incompletely understood. Following up on our finding that DR has a remarkably large beneficial effect on nervous system pathology in whole-body DNA repair-deficient progeroid mice, we show here that DR also exerts strong neuroprotection in mouse models in which a single neuronal cell type, i.e., cerebellar Purkinje cells, experience genotoxic stress and consequent premature aging-like dysfunction. Purkinje cell specific hypomorphic and knock-out ERCC1 mice on DR retained 40 and 25% more neurons, respectively, with equal protection against P53 activation, and alike results from whole-body ERCC1-deficient mice. Our findings show that DR strongly reduces Purkinje cell death in our Purkinje cell-specific accelerated aging mouse model, indicating that DR protects Purkinje cells from intrinsic DNA-damage-driven neurodegeneration.

Loss of epigenetic information as a cause of mammalian aging

All living things experience an increase in entropy, manifested as a loss of genetic and epigenetic information. In yeast, epigenetic information is lost over time due to the relocalization of chromatin-modifying proteins to DNA breaks, causing cells to lose their identity, a hallmark of yeast aging. Using a system called "ICE" (inducible changes to the epigenome), we find that the act of faithful DNA repair advances aging at physiological, cognitive, and molecular levels, including erosion of the epigenetic landscape, cellular exdifferentiation, senescence, and advancement of the DNA methylation clock, which can be reversed by OSK-mediated rejuvenation. These data are consistent with the information theory of aging, which states that a loss of epigenetic information is a reversible cause of aging.

Rapamycin not dietary restriction improves resilience against pathogens: a meta-analysis

Dietary restriction (DR) and rapamycin both increase lifespan across a number of taxa. Despite this positive effect on lifespan and other aspects of health, reductions in some physiological functions have been reported for DR, and rapamycin has been used as an immunosuppressant. Perhaps surprisingly, both interventions have been suggested to improve immune function and delay immunosenescence. The immune system is complex and consists of many components. Therefore, arguably, the most holistic measurement of immune function is survival from an acute pathogenic infection. We reanalysed published post-infection short-term survival data of mice (n = 1223 from 23 studies comprising 46 effect sizes involving DR (n = 17) and rapamycin treatment (n = 29) and analysed these results using meta-analysis. Rapamycin treatment significantly increased post infection survival rate (lnHR =  - 0.72; CI =  - 1.17, -0.28; p = 0.0015). In contrast, DR reduced post-infection survival (lnHR = 0.80; CI = 0.08, 1.52; p = 0.03). Importantly, the overall effect size of rapamycin treatment was significantly lower (p < 0.001) than the estimate from DR studies, suggesting opposite effects on immune function. Our results show that immunomodulation caused by rapamycin treatment is beneficial to the survival from acute infection. For DR, our results are based on a smaller number of studies, but do warrant caution as they indicate possible immune costs of DR. Our quantitative synthesis suggests that the geroprotective effects of rapamycin extend to the immune system and warrants further clinical trials of rapamycin to boost immunity in humans.

The use of progeroid DNA repair-deficient mice for assessing anti-aging compounds, illustrating the benefits of nicotinamide riboside

Despite efficient repair, DNA damage inevitably accumulates with time affecting proper cell function and viability, thereby driving systemic aging. Interventions that either prevent DNA damage or enhance DNA repair are thus likely to extend health- and lifespan across species. However, effective genome-protecting compounds are largely lacking. Here, we use Ercc1 ^Δ/- and Xpg ^-/- DNA repair-deficient mutants as two bona fide accelerated aging mouse models to test propitious anti-aging pharmaceutical interventions. Ercc1 ^Δ/- and Xpg ^-/- mice show shortened lifespan with accelerated aging across numerous organs and tissues. Previously, we demonstrated that a well-established anti-aging intervention, dietary restriction, reduced DNA damage, and dramatically improved healthspan, strongly extended lifespan, and delayed all aging pathology investigated. Here, we further utilize the short lifespan and early onset of signs of neurological degeneration in Ercc1 ^Δ/- and Xpg ^-/- mice to test compounds that influence nutrient sensing (metformin, acarbose, resveratrol), inflammation (aspirin, ibuprofen), mitochondrial processes (idebenone, sodium nitrate, dichloroacetate), glucose homeostasis (trehalose, GlcNAc) and nicotinamide adenine dinucleotide (NAD⁺) metabolism. While some of the compounds have shown anti-aging features in WT animals, most of them failed to significantly alter lifespan or features of neurodegeneration of our mice. The two NAD⁺ precursors; nicotinamide riboside (NR) and nicotinic acid (NA), did however induce benefits, consistent with the role of NAD⁺ in facilitating DNA damage repair. Together, our results illustrate the applicability of short-lived repair mutants for systematic screening of anti-aging interventions capable of reducing DNA damage accumulation.

Soluble guanylate cyclase activator BAY 54-6544 improves vasomotor function and survival in an accelerated ageing mouse model

DNA damage is a causative factor in ageing of the vasculature and other organs. One of the most important vascular ageing features is reduced nitric oxide (NO)soluble guanylate cyclase (sGC)-cyclic guanosine monophosphate (cGMP) signaling. We hypothesized that the restoration of NO-sGC-cGMP signaling with an sGC activator (BAY 54-6544) may have beneficial effects on vascular ageing and premature death in DNA repair-defective mice undergoing accelerated ageing. Eight weeks of treatment with a non-pressor dosage of BAY 54-6544 restored the decreased in vivo microvascular cutaneous perfusion in progeroid Ercc1^∆/- mice to the level of wild-type mice. In addition, BAY 54-6544 increased survival of Ercc1^∆/- mice. In isolated Ercc1^∆/- aorta, the decreased endothelium-independent vasodilation was restored after chronic BAY 54-6544 treatment. Senescence markers p16 and p21, and markers of inflammation, including Ccl2, Il6 in aorta and liver, and circulating IL-6 and TNF-α were increased in Ercc1^∆/- , which was lowered by the treatment. Expression of antioxidant genes, including Cyb5r3 and Nqo1, was favorably changed by chronic BAY 54-6544 treatment. In summary, BAY 54-6544 treatment improved the vascular function and survival rates in mice with accelerated ageing, which may have implication in prolonging health span in progeria and normal ageing.

Meeting Report: Aging Research and Drug Discovery

Aging is the single largest risk factor for most chronic diseases, and thus possesses large socioeconomic interest to continuously aging societies. Consequently, the field of aging research is expanding alongside a growing focus from the industry and investors in aging research. This year’s 8th Annual Aging Research and Drug Discovery (ARDD) meeting was organized as a hybrid meeting from August 30th to September 3rd 2021 with more than 130 attendees participating on-site at the Ceremonial Hall at University of Copenhagen, Denmark, and 1800 engaging online. The conference comprised of presentations from 75 speakers focusing on new research in topics including mechanisms of aging and how these can be modulated as well as the use of AI and new standards of practices within aging research. This year, a longevity workshop was included to build stronger connections with the clinical community.

Common Pathogenetic Mechanisms Underlying Aging and Tumor and Means of Interventions

Recently, there has been an increase in the incidence of malignant tumors among the older population. Moreover, there is an association between aging and cancer. During the process of senescence, the human body suffers from a series of imbalances, which have been shown to further accelerate aging, trigger tumorigenesis, and facilitate cancer progression. Therefore, exploring the junctions of aging and cancer and searching for novel methods to restore the junctions is of great importance to intervene against aging-related cancers. In this review, we have identified the underlying pathogenetic mechanisms of aging-related cancers by comparing alterations in the human body caused by aging and the factors that trigger cancers. We found that the common mechanisms of aging and cancer include cellular senescence, alterations in proteostasis, microbiota disorders (decreased probiotics and increased pernicious bacteria), persistent chronic inflammation, extensive immunosenescence, inordinate energy metabolism, altered material metabolism, endocrine disorders, altered genetic expression, and epigenetic modification. Furthermore, we have proposed that aging and cancer have common means of intervention, including novel uses of common medicine (metformin, resveratrol, and rapamycin), dietary restriction, and artificial microbiota intervention or selectively replenishing scarce metabolites. In addition, we have summarized the research progress of each intervention and revealed their bidirectional effects on cancer progression to compare their reliability and feasibility. Therefore, the study findings provide vital information for advanced research studies on age-related cancers. However, there is a need for further optimization of the described methods and more suitable methods for complicated clinical practices. In conclusion, targeting aging may have potential therapeutic effects on aging-related cancers.

Evaluating the beneficial effects of dietary restrictions: A framework for precision nutrigeroscience

Dietary restriction (DR) has long been viewed as the most robust nongenetic means to extend lifespan and healthspan. Many aging-associated mechanisms are nutrient responsive, but despite the ubiquitous functions of these pathways, the benefits of DR often vary among individuals and even among tissues within an individual, challenging the aging research field. Furthermore, it is often assumed that lifespan interventions like DR will also extend healthspan, which is thus often ignored in aging studies. In this review, we provide an overview of DR as an intervention and discuss the mechanisms by which it affects lifespan and various healthspan measures. We also review studies that demonstrate exceptions to the standing paradigm of DR being beneficial, thus raising new questions that future studies must address. We detail critical factors for the proposed field of precision nutrigeroscience, which would utilize individualized treatments and predict outcomes using biomarkers based on genotype, sex, tissue, and age.

Compromised DNA Repair Promotes the Accumulation of Regulatory T Cells With an Aging-Related Phenotype and Responsiveness

Decline of immune function during aging has in part been ascribed to the accumulation of regulatory T cells (Tregs) and decreased T-cell responses with age. Aside from changes to T cells that occur over a lifetime, the impact of intracellular aging processes such as compromised DNA repair on T cells remains incompletely defined. Here we aimed to define the impact of compromised DNA repair on T-cell phenotype and responsiveness by studying T cells from mice with a deficiency in their DNA excision-repair gene Ercc1. These Ercc1 mutant (Ercc1^−/Δ7) mice show accumulation of nuclear DNA damage resulting in accelerated aging. Similarly to wild-type aged mice, Ercc1^−/Δ7 mice accumulated Tregs with reduced CD25 and increased PD-1 expression among their naive T cells. Ercc1-deficiency limited the capacity of Tregs, helper T cells, and cytotoxic T cells to proliferate and upregulate CD25 in response to T-cell receptor- and IL-2-mediated stimulation. The recent demonstration that the mammalian target of rapamycin (mTOR) may impair DNA repair lead us to hypothesize that changes induced in the T-cell population by compromised DNA repair may be slowed down or reversed by blocking mTOR with rapamycin. In vivo dietary treatment of Ercc1^−/Δ7 mice with rapamycin did not reduce Treg levels, but highly increased the proportion of CD25⁺ and PD-1⁺ memory Tregs instead. Our study elucidates that compromised DNA repair promotes the accumulation of Tregs with an aging-related phenotype and causes reduced T-cell responsiveness, which may be independent of mTOR activation.

DNA- and telomere-damage does not limit lifespan: evidence from rapamycin

Failure of rapamycin to extend lifespan in DNA repair mutant and telomerase-knockout mice, while extending lifespan in normal mice, indicates that neither DNA damage nor telomere shortening limits normal lifespan or causes normal aging.