Delayed and accelerated aging share common longevity assurance mechanisms

Dietary Restriction Mitigates Vascular Aging, Modulates the cGAS-STING Pathway and Reverses Macrophage-Like VSMC Phenotypes in Progeroid DNA-Repair-Deficient Ercc1Δ /- Mice

Aging is a major risk factor for cardiovascular diseases, and the accumulation of DNA damage significantly contributes to the aging process. This study aimed to identify the underlying molecular mechanisms of vascular aging in DNA-repair-deficient progeroid Ercc1Δ/- mice and to explore the therapeutic effect of dietary restriction (DR). RNA sequencing analysis revealed that DR reversed gene expression of vascular aging processes, including extracellular matrix remodeling, in the Ercc1Δ/- aorta. Notably, this analysis indicated the presence of macrophage-like vascular smooth muscle cells (VSMCs) and suggested cGAS-STING pathway activation. The presence of macrophage-like VSMCs and increased STING1 expression were confirmed in Ercc1Δ/- aortic tissue and were both reduced by DR. In vitro, cisplatin-induced DNA damage activated the cGAS-STING pathway in Ercc1Δ/- VSMCs but not in wildtype VSMCs. These findings identify the involvement of the cGAS-STING pathway in DNA damage-driven vascular aging and underscore the therapeutic benefits of DR for vascular aging. Furthermore, upstream regulator analysis revealed compounds that may replicate the beneficial effects of DR, providing promising leads for further investigation.

Short-term fasting before living kidney donation has an immune-modulatory effect

Background

Short-Term Fasting (STF) is an intervention reducing the intake of calories, without causing undernutrition or micronutrient-related malnutrition. It aims to systemically improve resilience against acute stress. Several (pre-)clinical studies have suggested protective effects of STF, marking the systemic effects STF can induce in respect to surgery and ischemia-reperfusion injury. In addition, STF also affects the number of circulating immune cells. We aim to determine the effect of STF on the abundance and phenotype of different immune cell populations.

Methods

Thirty participants were randomly selected from the FAST clinical trial, including living kidney donors, randomized to an STF-diet or control arm. In an observational cohort sub-study we prospectively included 30 patients who donated blood samples repeatedly during study runtime. Using flow cytometry analyses, immune cell phenotyping was performed on peripheral blood mononuclear cells. Three panels were designed to investigate the presence and activation status of peripheral T cells, B cells, dendritic cells (DCs) and myeloid cells.

Results

Eight participants were excluded due to sample constraints. Baseline characteristics showed no significant differences, except for fasting duration. Weight changes were minimal and non-significant across different time intervals, with slight trends toward long-term weight loss pre-surgery. Glucose, insulin, and β-hydroxybutyrate levels differed significantly between groups, reflecting adherence to the fasting diet. Flow cytometry and RNA sequencing analysis revealed no baseline differences between groups, with high variability within each group. STF changes the levels and phenotype of immune cells, reducing the abundance and activation of T cells, including regulatory T cells, increased presence of (naïve) B cells, and elevation of type 1 conventional DCs (cDC1s). In addition, a decrease in central memory T cells was observed.

Discussion

In this study, we observed significant changes due to fasting in B cells, T cells, and DCs, specifically toward less specialized lymphocytes, suggesting an arrest in B and T cell development. Further research should focus on the clinical implications of changes in immune cells and significance of these observed immunological changes.

Conclusion

STF results in reduced numbers and activation status of T cells and Tregs, increased presence of (naïve) B cells, and elevation of cDC1s.

Improved health by combining dietary restriction and promoting muscle growth in DNA repair-deficient progeroid mice

BACKGROUND

Ageing is a complex multifactorial process, impacting all organs and tissues, with DNA damage accumulation serving as a common underlying cause. To decelerate ageing, various strategies have been applied to model organisms and evaluated for health and lifespan benefits. Dietary restriction (DR, also known as caloric restriction) is a well-established long-term intervention recognized for its universal anti-ageing effects. DR temporarily suppresses growth, and when applied to progeroid DNA repair-deficient mice doubles lifespan with systemic health benefits. Counterintuitively, attenuation of myostatin/activin signalling by soluble activin receptor (sActRIIB), boosts the growth of muscle and, in these animals, prevents muscle wasting, improves kidney functioning, and compresses morbidity.

METHODS

Here, we investigated a combined approach, applying an anabolic regime (sActRIIB) at the same time as DR to Ercc1Δ/- progeroid mice. Following both single treatments and combined, we monitored global effects on body weight, lifespan and behaviour, and local effects on muscle and tissue weight, muscle morphology and function, and ultrastructural and transcriptomic changes in muscle and kidney.

RESULTS

Lifespan was mostly influenced by DR (extended from approximately 20 to 40 weeks; P < 0.001), with sActRIIB clearly increasing muscle mass (35-65%) and tetanic force (P < 0.001). The combined regime yielded a stable uniform body weight, but increased compared with DR alone, synergistically improved motor coordination and further delayed the onset and development of balance problems. sActRIIB significantly increased muscle fibre size (P < 0.05) in mice subjected to DR and lowered all signs of muscle damage. Ercc1Δ/- mice showed abnormal neuromuscular junctions. Single interventions by sActRIIB treatment or DR only partially rescued this phenotype, while in the double intervention group, the regularly shaped junctional foldings were maintained. In kidney of Ercc1Δ/- mice, we observed a mild but significant foot process effacement, which was restored by either intervention. Transcriptome analysis also pointed towards reduced levels of DNA damage in muscle and kidney by DR, but not sActRIIB, while these levels retained lower in the double intervention.

CONCLUSIONS

In muscle, we found synergistic effects of combining sActRIIB with DR, but not in kidney, with an overall better health in the double intervention group. Crucially, the benefits of each single intervention are not lost when administered in combination, but rather strengthened, even when sActRIIB was applied late in life, opening opportunities for translation to human.

Transcription stress at telomeres leads to cytosolic DNA release and paracrine senescence

Transcription stress has been linked to DNA damage -driven aging, yet the underlying mechanism remains unclear. Here, we demonstrate that Tcea1-/- cells, which harbor a TFIIS defect in transcription elongation, exhibit RNAPII stalling at oxidative DNA damage sites, impaired transcription, accumulation of R-loops, telomere uncapping, chromatin bridges, and genome instability, ultimately resulting in cellular senescence. We found that R-loops at telomeres causally contribute to the release of telomeric DNA fragments in the cytoplasm of Tcea1-/- cells and primary cells derived from naturally aged animals triggering a viral-like immune response. TFIIS-defective cells release extracellular vesicles laden with telomeric DNA fragments that target neighboring cells, which consequently undergo cellular senescence. Thus, transcription stress elicits paracrine signals leading to cellular senescence, promoting aging.

Age-Related Alterations in Immune Function and Inflammation: Focus on Ischemic Stroke

The aging of the global population poses significant scientific challenges. Moreover, the biological process of aging is the most significant risk factor for most chronic illnesses; therefore, understanding the molecular and cellular mechanisms underlying these aging-related challenges is crucial for extending the healthy lifespan of older individuals. Preventing brain aging remains a priority public health goal, and integrative and comprehensive aging analyses have revealed that immunosenescence is a potential cause of age-related brain damage and disease (e.g., stroke). Importantly, the neuroinflammatory and immune systems present two-way contact and thus can affect each other. Emerging evidence supports the numerous effects of immunosenescence- and inflammation-mediated immunity in neurologically injured brains. In this study, we briefly outline how aging alters the pathophysiology and transcriptional amplitude in patients who experienced stroke and then discuss how the immune system and its cellular components and molecular mechanisms are affected by age after stroke. Finally, we highlight emerging interventions with the potential to slow down or reduce aging and prevent stroke onset.

Musculoskeletal crosstalk in chronic obstructive pulmonary disease and comorbidities: Emerging roles and therapeutic potentials

Chronic Obstructive Pulmonary Disease (COPD) is a multifaceted respiratory disorder characterized by progressive airflow limitation and systemic implications. It has become increasingly apparent that COPD exerts its influence far beyond the respiratory system, extending its impact to various organ systems. Among these, the musculoskeletal system emerges as a central player in both the pathogenesis and management of COPD and its associated comorbidities. Muscle dysfunction and osteoporosis are prevalent musculoskeletal disorders in COPD patients, leading to a substantial decline in exercise capacity and overall health. These manifestations are influenced by systemic inflammation, oxidative stress, and hormonal imbalances, all hallmarks of COPD. Recent research has uncovered an intricate interplay between COPD and musculoskeletal comorbidities, suggesting that muscle and bone tissues may cross-communicate through the release of signalling molecules, known as "myokines" and "osteokines". We explored this dynamic relationship, with a particular focus on the role of the immune system in mediating the cross-communication between muscle and bone in COPD. Moreover, we delved into existing and emerging therapeutic strategies for managing musculoskeletal disorders in COPD. It underscores the development of personalized treatment approaches that target both the respiratory and musculoskeletal aspects of COPD, offering the promise of improved well-being and quality of life for individuals grappling with this complex condition. This comprehensive review underscores the significance of recognizing the profound impact of COPD on the musculoskeletal system and its comorbidities. By unravelling the intricate connections between these systems and exploring innovative treatment avenues, we can aspire to enhance the overall care and outcomes for COPD patients, ultimately offering hope for improved health and well-being.

Ercc1 DNA repair deficiency results in vascular aging characterized by VSMC phenotype switching, ECM remodeling, and an increased stress response

Cardiovascular diseases are the number one cause of death globally. The most important determinant of cardiovascular health is a person's age. Aging results in structural changes and functional decline of the cardiovascular system. DNA damage is an important contributor to the aging process, and mice with a DNA repair defect caused by Ercc1 deficiency display hypertension, vascular stiffening, and loss of vasomotor control. To determine the underlying cause, we compared important hallmarks of vascular aging in aortas of both Ercc1Δ/- and age-matched wildtype mice. Additionally, we investigated vascular aging in 104 week old wildtype mice. Ercc1Δ/- aortas displayed arterial thickening, a loss of cells, and a discontinuous endothelial layer. Aortas of 24 week old Ercc1Δ/- mice showed phenotypical switching of vascular smooth muscle cells (VSMCs), characterized by a decrease in contractile markers and a decrease in synthetic markers at the RNA level. As well as an increase in osteogenic markers, microcalcification, and an increase in markers for damage induced stress response. This suggests that Ercc1Δ/- VSMCs undergo a stress-induced contractile-to-osteogenic phenotype switch. Ercc1Δ/- aortas showed increased MMP activity, elastin fragmentation, and proteoglycan deposition, characteristic of vascular aging and indicative of age-related extracellular matrix remodeling. The 104 week old WT mice showed loss of cells, VSMC dedifferentiation, and senescence. In conclusion, Ercc1Δ/- aortas rapidly display many characteristics of vascular aging, and thus the Ercc1Δ/- mouse is an excellent model to evaluate drugs that prevent vascular aging in a short time span at the functional, histological, and cellular level.

Changes in the amount of nucleotide sugars in aged mouse tissues

Aging affects tissue glycan profiles, which may alter cellular functions and increase the risk of age-related diseases. Glycans are biosynthesized by glycosyltransferases using the corresponding nucleotide sugar, and the availability of nucleotide sugars affects glycosylation efficiency. However, the effects of aging on nucleotide sugar profiles and contents are yet to be elucidated. Therefore, this study aimed to investigate the effects of aging on nucleotide sugars using a new LC-MS/MS method. Specifically, the new method was used to determine the nucleotide sugar contents of various tissues (brain, liver, heart, skeletal muscle, kidney, lung, and colon) of male C57BL/6NCr mice (7- or 26-month-old). Characteristic age-associated nucleotide sugar changes were observed in each tissue sample. Particularly, there was a significant decrease in UDP-glucuronic acid content in the kidney of aged mice and a decrease in the contents of several nucleotide sugars, including UDP-N-acetylgalactosamine, in the brain of aged mice. Additionally, there were variations in nucleotide sugar profiles among the tissues examined regardless of the age. The kidneys had the highest concentration of UDP-glucuronic acid among the seven tissues. In contrast, the skeletal muscle had the lowest concentration of total nucleotide sugars among the tissues; however, CMP-N-acetylneuraminic acid and CDP-ribitol were relatively enriched. Conclusively, these findings may contribute to the understanding of the roles of glycans in tissue aging.

p53 regulates diverse tissue-specific outcomes to endogenous DNA damage in mice

DNA repair deficiency can lead to segmental phenotypes in humans and mice, in which certain tissues lose homeostasis while others remain seemingly unaffected. This may be due to different tissues facing varying levels of damage or having different reliance on specific DNA repair pathways. However, we find that the cellular response to DNA damage determines different tissue-specific outcomes. Here, we use a mouse model of the human XPF-ERCC1 progeroid syndrome (XFE) caused by loss of DNA repair. We find that p53, a central regulator of the cellular response to DNA damage, regulates tissue dysfunction in Ercc1-/- mice in different ways. We show that ablation of p53 rescues the loss of hematopoietic stem cells, and has no effect on kidney, germ cell or brain dysfunction, but exacerbates liver pathology and polyploidisation. Mechanistically, we find that p53 ablation led to the loss of cell-cycle regulation in the liver, with reduced p21 expression. Eventually, p16/Cdkn2a expression is induced, serving as a fail-safe brake to proliferation in the absence of the p53-p21 axis. Taken together, our data show that distinct and tissue-specific functions of p53, in response to DNA damage, play a crucial role in regulating tissue-specific phenotypes.

Aging under endocrine hormone regulation

Aging is a biological process in which the environment interacts with the body to cause a progressive decline in effective physiological function. Aging in the human body can lead to a dysfunction of the vital organ systems, resulting in the onset of age-related diseases, such as neurodegenerative and cardiovascular diseases, which can seriously affect an individual's quality of life. The endocrine system acts on specific targets through hormones and related major functional factors in its pathways, which play biological roles in coordinating cellular interactions, metabolism, growth, and aging. Aging is the result of a combination of many pathological, physiological, and psychological processes, among which the endocrine system can achieve a bidirectional effect on the aging process by regulating the hormone levels in the body. In this paper, we explored the mechanisms of growth hormone, thyroid hormone, and estrogen in the aging process to provide a reference for the exploration of endocrine mechanisms related to aging.

Mitochondrial complex III deficiency drives c-MYC overexpression and illicit cell cycle entry leading to senescence and segmental progeria

Accumulating evidence suggests mitochondria as key modulators of normal and premature aging, yet whether primary oxidative phosphorylation (OXPHOS) deficiency can cause progeroid disease remains unclear. Here, we show that mice with severe isolated respiratory complex III (CIII) deficiency display nuclear DNA damage, cell cycle arrest, aberrant mitoses, and cellular senescence in the affected organs such as liver and kidney, and a systemic phenotype resembling juvenile-onset progeroid syndromes. Mechanistically, CIII deficiency triggers presymptomatic cancer-like c-MYC upregulation followed by excessive anabolic metabolism and illicit cell proliferation against lack of energy and biosynthetic precursors. Transgenic alternative oxidase dampens mitochondrial integrated stress response and the c-MYC induction, suppresses the illicit proliferation, and prevents juvenile lethality despite that canonical OXPHOS-linked functions remain uncorrected. Inhibition of c-MYC with the dominant-negative Omomyc protein relieves the DNA damage in CIII-deficient hepatocytes in vivo. Our results connect primary OXPHOS deficiency to genomic instability and progeroid pathogenesis and suggest that targeting c-MYC and aberrant cell proliferation may be therapeutic in mitochondrial diseases.

Influence of the Mediterranean Diet on Healthy Aging

The life expectancy of the global population has increased. Aging is a natural physiological process that poses major challenges in an increasingly long-lived and frail population. Several molecular mechanisms are involved in aging. Likewise, the gut microbiota, which is influenced by environmental factors such as diet, plays a crucial role in the modulation of these mechanisms. The Mediterranean diet, as well as the components present in it, offer some proof of this. Achieving healthy aging should be focused on the promotion of healthy lifestyle habits that reduce the development of pathologies that are associated with aging, in order to increase the quality of life of the aging population. In this review we analyze the influence of the Mediterranean diet on the molecular pathways and the microbiota associated with more favorable aging patterns, as well as its possible role as an anti-aging treatment.

Mechanisms Underlying Brain Aging Under Normal and Pathological Conditions

Aging is a major risk factor for many human diseases, including cognitive impairment, which affects a large population of the elderly. In the past few decades, our understanding of the molecular and cellular mechanisms underlying the changes associated with aging and age-related diseases has expanded greatly, shedding light on the potential role of these changes in cognitive impairment. In this article, we review recent advances in understanding of the mechanisms underlying brain aging under normal and pathological conditions, compare their similarities and differences, discuss the causative and adaptive mechanisms of brain aging, and finally attempt to find some rules to guide us on how to promote healthy aging and prevent age-related diseases.

Genome-wide RNA polymerase stalling shapes the transcriptome during aging

Gene expression profiling has identified numerous processes altered in aging, but how these changes arise is largely unknown. Here we combined nascent RNA sequencing and RNA polymerase II chromatin immunoprecipitation followed by sequencing to elucidate the underlying mechanisms triggering gene expression changes in wild-type aged mice. We found that in 2-year-old liver, 40% of elongating RNA polymerases are stalled, lowering productive transcription and skewing transcriptional output in a gene-length-dependent fashion. We demonstrate that this transcriptional stress is caused by endogenous DNA damage and explains the majority of gene expression changes in aging in most mainly postmitotic organs, specifically affecting aging hallmark pathways such as nutrient sensing, autophagy, proteostasis, energy metabolism, immune function and cellular stress resilience. Age-related transcriptional stress is evolutionary conserved from nematodes to humans. Thus, accumulation of stochastic endogenous DNA damage during aging deteriorates basal transcription, which establishes the age-related transcriptome and causes dysfunction of key aging hallmark pathways, disclosing how DNA damage functionally underlies major aspects of normal aging.

Metabolome profiling in the study of aging processes

Aging of a living organism is closely related to systemic metabolic changes. But due to the multilevel and network nature of metabolic pathways, it is difficult to understand these connections. Today, this problem is solved using one of the main approaches of metabolomics — untargeted metabolome profiling. The purpose of this publication is to systematize the results of metabolomic studies based on such profiling, both in animal models and in humans.

Metabolome Profiling in Aging Studies

Organism aging is closely related to systemic metabolic changes. However, due to the multilevel and network nature of metabolic pathways, it is difficult to understand these connections. Today, scientists are trying to solve this problem using one of the main approaches of metabolomics-untargeted metabolome profiling. The purpose of this publication is to review metabolomic studies based on such profiling, both in animal models and in humans. This review describes metabolites that vary significantly across age groups and include carbohydrates, amino acids, carnitines, biogenic amines, and lipids. Metabolic pathways associated with the aging process are also shown, including those associated with amino acid, lipid, and energy metabolism. The presented data reveal the mechanisms of aging and can be used as a basis for monitoring biological age and predicting age-related diseases in the early stages of their development.

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.

The damage-independent evolution of ageing by selective destruction

Ageing is widely believed to reflect the accumulation of molecular damage due to energetic costs of maintenance, as proposed in disposable soma theory (DST). Here we use agent-based modelling to describe an alternative theory by which ageing could undergo positive selection independent of energetic costs. We suggest that the selective advantage of aberrant cells with fast growth might necessitate a mechanism of counterselection we name selective destruction that specifically removes the faster cells from tissues, preventing the morbidity and mortality risks they pose. The resulting survival advantage of slower mutants could switch the direction of selection, allowing them to outcompete both fast mutants and wildtype cells, causing them to spread and induce ageing in the form of a metabolic slowdown. Selective destruction could therefore provide a proximal cause of ageing that is both consistent with the gene expression hallmarks of ageing, and independent of accumulating damage. Furthermore, negligible senescence would acquire a new meaning of increased basal mortality.

DNA damage, inflammation and aging: Insights from mice

Persistent DNA lesions build up with aging triggering inflammation, the body’s first line of immune defense strategy against foreign pathogens and irritants. Once established, DNA damage-driven inflammation takes on a momentum of its own, due to the amplification and feedback loops of the immune system leading to cellular malfunction, tissue degenerative changes and metabolic complications. Here, we discuss the use of murine models with inborn defects in genome maintenance and the DNA damage response for understanding how irreparable DNA lesions are functionally linked to innate immune signaling highlighting their relevance for developing novel therapeutic strategies against the premature onset of aging-associated diseases.

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.

Horizons in Human Aging Neuroscience: From Normal Neural Aging to Mental (Fr)Agility

While aging is an important risk factor for neurodegenerative disorders such as Alzheimer's disease and Parkinson's disease, age-related cognitive decline can also manifest without apparent neurodegenerative changes. In this review, we discuss molecular, cellular, and network changes that occur during normal aging in the absence of neurodegenerative disease. Emerging findings reveal that these changes include metabolic alterations, oxidative stress, DNA damage, inflammation, calcium dyshomeostasis, and several other hallmarks of age-related neural changes that do not act on their own, but are often interconnected and together may underlie age-related alterations in brain plasticity and cognitive function. Importantly, age-related cognitive decline may not be reduced to a single neurobiological cause, but should instead be considered in terms of a densely connected system that underlies age-related cognitive alterations. We speculate that a decline in one hallmark of neural aging may trigger a decline in other, otherwise thus far stable subsystems, thereby triggering a cascade that may at some point also incur a decline of cognitive functions and mental well-being. Beyond studying the effects of these factors in isolation, considerable insight may be gained by studying the larger picture that entails a representative collection of such factors and their interactions, ranging from molecules to neural networks. Finally, we discuss some potential interventions that may help to prevent these alterations, thereby reducing cognitive decline and mental fragility, and enhancing mental well-being, and healthy aging.

Distinct and additive effects of calorie restriction and rapamycin in aging skeletal muscle

Preserving skeletal muscle function is essential to maintain life quality at high age. Calorie restriction (CR) potently extends health and lifespan, but is largely unachievable in humans, making “CR mimetics” of great interest. CR targets nutrient-sensing pathways centering on mTORC1. The mTORC1 inhibitor, rapamycin, is considered a potential CR mimetic and is proven to counteract age-related muscle loss. Therefore, we tested whether rapamycin acts via similar mechanisms as CR to slow muscle aging. Here we show that long-term CR and rapamycin unexpectedly display distinct gene expression profiles in geriatric mouse skeletal muscle, despite both benefiting aging muscles. Furthermore, CR improves muscle integrity in mice with nutrient-insensitive, sustained muscle mTORC1 activity and rapamycin provides additive benefits to CR in naturally aging mouse muscles. We conclude that rapamycin and CR exert distinct, compounding effects in aging skeletal muscle, thus opening the possibility of parallel interventions to counteract muscle aging.

The anti-aging intervention calorie restriction (CR) is thought to act via the nutrient-sensing multiprotein complex mTORC1. Here the authors show that the mTORC1-inhibitor rapamycin and CR use largely distinct mechanisms to slow mouse muscle aging.

Fasting Intervention for Children With Unilateral Renal Tumors to Reduce Toxicity

Childhood renal tumors account for around 6% of all childhood cancers and 90% of these cases are Wilms tumor. In Europe, the SIOP-RTSG approach is considered standard of care and has resulted in five-year survival rates of over 90%. Efforts to decrease toxicity are now being pursued. Short-term fasting (STF), a short but strong reduction in calorie-intake, is associated with improved fitness, enhanced coping with acute physical stress and a lower risk of age-associated diseases. STF temporarily reduces growth to boost resilience, maintenance, and defense-mechanisms, by which toxic side-effects of (oxidative) damage and inflammation are largely prevented. Renal surgery for Wilms tumor carries a risk of acute kidney injury (AKI) and pediatric patients that had an episode of AKI are at increased risk for developing chronic renal disease. STF could mitigate surgery-induced stress and could further improve outcomes. We aim to investigate the effect of STF on renal function recovery after renal tumor surgery by conducting a single-center, prospective, randomized, non-blinded, intervention study. Children diagnosed with a unilateral renal tumor and opting for curative treatment are eligible for inclusion. The main study objective is to investigate the potential decrease in occurrence of AKI due to STF. Secondary objectives include renal function recovery, child's wellbeing, physical functioning, and feasibility of and adherence to STF in children with cancer.

Endothelial and systemic upregulation of miR-34a-5p fine-tunes senescence in progeria

Endothelial defects significantly contribute to cardiovascular pathology in the premature aging disease Hutchinson-Gilford progeria syndrome (HGPS). Using an endothelium-specific progeria mouse model, we identify a novel, endothelium-specific microRNA (miR) signature linked to the p53-senescence pathway and a senescence-associated secretory phenotype (SASP). Progerin-expressing endothelial cells exert profound cell-non-autonomous effects initiating senescence in non-endothelial cell populations and causing immune cell infiltrates around blood vessels. Comparative miR expression analyses revealed unique upregulation of senescence-associated miR34a-5p in endothelial cells with strong accumulation at atheroprone aortic arch regions but also, in whole cardiac- and lung tissues as well as in the circulation of progeria mice. Mechanistically, miR34a-5p knockdown reduced not only p53 levels but also late-stage senescence regulator p16 with no effect on p21 levels, while p53 knockdown reduced miR34a-5p and partially rescued p21-mediated cell cycle inhibition with a moderate effect on SASP. These data demonstrate that miR34a-5p reinforces two separate senescence regulating branches in progerin-expressing endothelial cells, the p53- and p16-associated pathways, which synergistically maintain a senescence phenotype that contributes to cardiovascular pathology. Thus, the key function of circulatory miR34a-5p in endothelial dysfunction-linked cardiovascular pathology offers novel routes for diagnosis, prognosis and treatment for cardiovascular aging in HGPS and potentially geriatric patients.

Fasting before living-kidney donation: effect on donor well-being and postoperative recovery: study protocol of a multicenter randomized controlled trial

BACKGROUND

One of the main effectors on the quality of life of living-kidney donors is postoperative fatigue. Caloric restriction (CR) and short-term fasting (STF) are associated with improved fitness and increased resistance to acute stress. CR/STF increases the expression of cytoprotective genes, increases immunomodulation via increased anti-inflammatory cytokine production, and decreases the expression of pro-inflammatory markers. As such, nutritional preconditioning by CR or STF represents a non-invasive and cost-effective method that could mitigate the effects of acute surgery-induced stress and postoperative fatigue. To investigate whether preoperative STF contributes to a reduction in fatigue after living-kidney donation, a randomized clinical trial is indicated.

METHODS

We aim to determine whether 2.5 days of fasting reduces postoperative fatigue score in subjects undergoing living-kidney donation. In this randomized study, the intervention group will follow a preoperative fasting regime for 2.5 days with a low-dose laxative, while the control group will receive standard care. The main study endpoint is postoperative fatigue, 4 weeks after living-kidney donation. Secondary endpoints include the effect of preoperative fasting on postoperative hospital admission time, the feasibility of STF, and the postoperative recovery of donor and recipient kidney function. This study will provide us with knowledge of the feasibility of STF and confirm its effect on postoperative recovery.

DISCUSSION

Our study will provide clinically relevant information on the merits of caloric restriction for living-kidney donors and recipients. We expect to reduce the postoperative fatigue in living-kidney donors and improve the postoperative recovery of living-kidney recipients. It will provide evidence on the clinical merits and potential caveats of preoperative dietary interventions.

TRIAL REGISTRATION

Netherlands Trial Register NL9262 . EudraCT 2020-005445-16 . MEC Erasmus MC MEC-2020-0778. CCMO NL74623.078.21.

The Gut Microbiome, Metformin, and Aging

Metformin has been extensively used for the treatment of type 2 diabetes, and it may also promote healthy aging. Despite its widespread use and versatility, metformin's mechanisms of action remain elusive. The gut typically harbors thousands of bacterial species, and as the concentration of metformin is much higher in the gut as compared to plasma, it is plausible that microbiome-drug-host interactions may influence the functions of metformin. Detrimental perturbations in the aging gut microbiome lead to the activation of the innate immune response concomitant with chronic low-grade inflammation. With the effectiveness of metformin in diabetes and antiaging varying among individuals, there is reason to believe that the gut microbiome plays a role in the efficacy of metformin. Metformin has been implicated in the promotion and maintenance of a healthy gut microbiome and reduces many age-related degenerative pathologies. Mechanistic understanding of metformin in the promotion of a healthy gut microbiome and aging will require a systems-level approach. Expected final online publication date for the Annual Review of Pharmacology and Toxicology, Volume 62 is January 2022. Please see http://www.annualreviews.org/page/journal/pubdates for revised estimates.

PTEN regulates adipose progenitor cell growth, differentiation, and replicative aging

The tumor suppressor phosphatase and tensin homolog (PTEN) negatively regulates the insulin signaling pathway. Germline PTEN pathogenic variants cause PTEN hamartoma tumor syndrome (PHTS), associated with lipoma development in children. Adipose progenitor cells (APCs) lose their capacity to differentiate into adipocytes during continuous culture, whereas APCs from lipomas of patients with PHTS retain their adipogenic potential over a prolonged period. It remains unclear which mechanisms trigger this aberrant adipose tissue growth. To investigate the role of PTEN in adipose tissue development, we performed functional assays and RNA-Seq of control and PTEN knockdown APCs. Reduction of PTEN levels using siRNA or CRISPR led to enhanced proliferation and differentiation of APCs. Forkhead box protein O1 (FOXO1) transcriptional activity is known to be regulated by insulin signaling, and FOXO1 was downregulated at the mRNA level while its inactivation through phosphorylation increased. FOXO1 phosphorylation initiates the expression of the lipogenesis-activating transcription factor sterol regulatory element-binding protein 1 (SREBP1). SREBP1 levels were higher after PTEN knockdown and may account for the observed enhanced adipogenesis. To validate this, we overexpressed constitutively active FOXO1 in PTEN CRISPR cells and found reduced adipogenesis, accompanied by SREBP1 downregulation. We observed that PTEN CRISPR cells showed less senescence compared with controls and the senescence marker CDKN1A (p21) was downregulated in PTEN knockdown cells. Cellular senescence was the most significantly enriched pathway found in RNA-Seq of PTEN knockdown versus control cells. These results provide evidence that PTEN is involved in the regulation of APC proliferation, differentiation, and senescence, thereby contributing to aberrant adipose tissue growth in patients with PHTS.

The splicing factor XAB2 interacts with ERCC1-XPF and XPG for R-loop processing

RNA splicing, transcription and the DNA damage response are intriguingly linked in mammals but the underlying mechanisms remain poorly understood. Using an in vivo biotinylation tagging approach in mice, we show that the splicing factor XAB2 interacts with the core spliceosome and that it binds to spliceosomal U4 and U6 snRNAs and pre-mRNAs in developing livers. XAB2 depletion leads to aberrant intron retention, R-loop formation and DNA damage in cells. Studies in illudin S-treated cells and Csb^m/m developing livers reveal that transcription-blocking DNA lesions trigger the release of XAB2 from all RNA targets tested. Immunoprecipitation studies reveal that XAB2 interacts with ERCC1-XPF and XPG endonucleases outside nucleotide excision repair and that the trimeric protein complex binds RNA:DNA hybrids under conditions that favor the formation of R-loops. Thus, XAB2 functionally links the spliceosomal response to DNA damage with R-loop processing with important ramifications for transcription-coupled DNA repair disorders.

XPA-binding protein (XAB)-2 is the human homologue of the yeast pre-mRNA splicing factor Syf1. Here the authors use an in vivo biotinylation tagging approach to show XAB2’s role in DNA repair, RNA splicing and transcription during mammalian development.

Relationship between inflammatory biomarkers and testosterone levels in male master athletes and non-athletes

BACKGROUND

Aging is often associated with low-grade systemic inflammation and reduced anabolic hormone levels. To investigate whether lifelong exercise training can decrease the age-related low-grade inflammation and anabolic hormone levels, we examined hormonal and inflammatory parameters among highly-trained male masters athletes and age-matched non-athletes.

METHODS

From 70 elite power and endurance master athletes - EMA (51.3 ± 8.0 yr), 32 young controls - YC (23.7 ± 3.9 yr) and 24 untrained age-matched controls - MAC (47.2 ± 8.0 yr) venous blood was drawn to measure inflammatory parameters (interleukin-6 [IL-6], tumor necrosis factor-α [TNF-α] and interleukin-10 [IL-10]) and circulating hormones (luteinizing hormone [LH], total testosterone, estradiol, sex hormone-binding globulin [SHBG] and free androgen index [FAI]).

RESULTS

EMA showed a better anti-inflammatory status than MAC (higher IL-10 and IL-10/IL-6 ratio and lower IL-6), but a lower anti-inflammatory status than YC (higher TNF-α) (p < 0.05). The MAC group had lower testosterone levels compared to the YC and EMA group (p < 0.05), and lower estradiol levels and testosterone/LH ratio compared to YC (p < 0.05). In the control groups (MAC and YC), testosterone correlated negatively with age and proinflammatory parameters, and positively with anti-inflammatory parameters.

CONCLUSION

Elite master athletics elevated levels of anti-inflammatory cytokines above that seen in non-athlete peers and mitigated the age-related reduction in testosterone levels.

The central role of DNA damage in the ageing process

Ageing is a complex, multifaceted process leading to widespread functional decline that affects every organ and tissue, but it remains unknown whether ageing has a unifying causal mechanism or is grounded in multiple sources. Phenotypically, the ageing process is associated with a wide variety of features at the molecular, cellular and physiological level-for example, genomic and epigenomic alterations, loss of proteostasis, declining overall cellular and subcellular function and deregulation of signalling systems. However, the relative importance, mechanistic interrelationships and hierarchical order of these features of ageing have not been clarified. Here we synthesize accumulating evidence that DNA damage affects most, if not all, aspects of the ageing phenotype, making it a potentially unifying cause of ageing. Targeting DNA damage and its mechanistic links with the ageing phenotype will provide a logical rationale for developing unified interventions to counteract age-related dysfunction and disease.

Increased insulin sensitivity and diminished pancreatic beta-cell function in DNA repair deficient Ercc1d/- mice

BACKGROUND

Type 2 diabetes (T2DM) is an age-associated disease characterized by hyperglycemia due to insulin resistance and decreased beta-cell function. DNA damage accumulation has been associated with T2DM, but whether DNA damage plays a role in the pathogenesis of the disease is unclear. Here, we used mice deficient for the DNA excision-repair gene Ercc1 to study the impact of persistent endogenous DNA damage accumulation on energy metabolism, glucose homeostasis and beta-cell function.

METHODS

ERCC1-XPF is an endonuclease required for multiple DNA repair pathways and reduced expression of ERCC1-XPF causes accelerated accumulation of unrepaired endogenous DNA damage and accelerated aging in humans and mice. In this study, energy metabolism, glucose metabolism, beta-cell function and insulin sensitivity were studied in Ercc1^d/- mice, which model a human progeroid syndrome.

RESULTS

Ercc1^d/- mice displayed suppression of the somatotropic axis and altered energy metabolism. Insulin sensitivity was increased, whereas, plasma insulin levels were decreased in Ercc1^d/- mice. Fasting induced hypoglycemia in Ercc1^d/- mice, which was the result of increased glucose disposal. Ercc1^d/- mice exhibit a significantly reduced beta-cell area, even compared to control mice of similar weight. Glucose-stimulated insulin secretion in vivo was decreased in Ercc1^d/- mice. Islets isolated from Ercc1^d/- mice showed increased DNA damage markers, decreased glucose-stimulated insulin secretion and increased susceptibility to apoptosis.

CONCLUSION

Spontaneous DNA damage accumulation triggers an adaptive response resulting in improved insulin sensitivity. Loss of DNA repair, however, does negatively impacts beta-cell survival and function in Ercc1^d/- mice.

Transcriptomic profiling of long- and short-lived mutant mice implicates mitochondrial metabolism in ageing and shows signatures of normal ageing in progeroid mice

Genetically modified mouse models of ageing are the living proof that lifespan and healthspan can be lengthened or shortened, and provide a powerful context in which to unravel the molecular mechanisms at work. In this study, we analysed and compared gene expression data from 10 long-lived and 8 short-lived mouse models of ageing. Transcriptome-wide correlation analysis revealed that mutations with equivalent effects on lifespan induce more similar transcriptomic changes, especially if they target the same pathway. Using functional enrichment analysis, we identified 58 gene sets with consistent changes in long- and short-lived mice, 55 of which were up-regulated in long-lived mice and down-regulated in short-lived mice. Half of these sets represented genes involved in energy and lipid metabolism, among which Ppargc1a, Mif, Aldh5a1 and Idh1 were frequently observed. Based on the gene sets with consistent changes, and also the whole transcriptome, the gene expression changes during normal ageing resembled the transcriptome of short-lived models, suggesting that accelerated ageing models reproduce partially the molecular changes of ageing. Finally, we identified new genetic interventions that may ameliorate ageing, by comparing the transcriptomes of 51 mouse mutants not previously associated with ageing to expression signatures of long- and short-lived mice and ageing-related changes.

Nutritional Preconditioning in Cancer Treatment in Relation to DNA Damage and Aging

Dietary restriction (DR) is the most successful nutritional intervention for extending lifespan and preserving health in numerous species. Reducing food intake triggers a protective response that shifts energy resources from growth to maintenance and resilience mechanisms. This so-called survival response has been shown to particularly increase life- and health span and decrease DNA damage in DNA repair-deficient mice exhibiting accelerated aging. Accumulation of DNA damage is the main cause of aging, but also of cancer. Moreover, radiotherapies and most chemotherapies are based on damaging DNA, consistent with their ability to induce toxicity and accelerate aging. Since fasting and DR decrease DNA damage and its effects, nutritional preconditioning holds promise for improving (cancer) therapy and preventing short- and long-term side effects of anticancer treatments. This review provides an overview of the link between aging and cancer, highlights important preclinical studies applying such nutritional preconditioning, and summarizes the first clinical trials implementing nutritional preconditioning in cancer treatment.

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

Dietary restriction (DR) and rapamycin extend healthspan and life span across multiple species. We have recently shown that DR in progeroid DNA repair‐deficient mice dramatically extended healthspan and trippled life span. Here, we show that rapamycin, while significantly lowering mTOR signaling, failed to improve life span nor healthspan of DNA repair‐deficient Ercc1^∆/− mice, contrary to DR tested in parallel. Rapamycin interventions focusing on dosage, gender, and timing all were unable to alter life span. Even genetically modifying mTOR signaling failed to increase life span of DNA repair‐deficient mice. The absence of effects by rapamycin on P53 in brain and transcription stress in liver is in sharp contrast with results obtained by DR, and appoints reducing DNA damage and transcription stress as an important mode of action of DR, lacking by rapamycin. Together, this indicates that mTOR inhibition does not mediate the beneficial effects of DR in progeroid mice, revealing that DR and rapamycin strongly differ in their modes of action.

Principles of the Molecular and Cellular Mechanisms of Aging

Aging can be defined as a state of progressive functional decline accompanied by an increase in mortality. Time-dependent accumulation of cellular damage, namely lesions and mutations in the DNA and misfolded proteins, impair organellar and cellular function. Ensuing cell fate alterations lead to the accumulation of dysfunctional cells and hamper homeostatic processes, thus limiting regenerative potential; trigger low-grade inflammation; and alter intercellular and intertissue communication. The accumulation of molecular damage together with modifications in the epigenetic landscape, dysregulation of gene expression, and altered endocrine communication, drive the aging process and establish age as the main risk factor for age-associated diseases and multimorbidity.

DNA Damage and the Aging Epigenome

In mammals, genome instability and aging are intimately linked as illustrated by the growing list of patients with progeroid and animal models with inborn DNA repair defects. Until recently, DNA damage was thought to drive aging by compromising transcription or DNA replication, thereby leading to age-related cellular malfunction and somatic mutations triggering cancer. However, recent evidence suggests that DNA lesions also elicit widespread epigenetic alterations that threaten cell homeostasis as a function of age. In this review, we discuss the functional links of persistent DNA damage with the epigenome in the context of aging and age-related diseases.

The Aging Stress Response and Its Implication for AMD Pathogenesis

Aging induces several stress response pathways to counterbalance detrimental changes associated with this process. These pathways include nutrient signaling, proteostasis, mitochondrial quality control and DNA damage response. At the cellular level, these pathways are controlled by evolutionarily conserved signaling molecules, such as 5’AMP-activated protein kinase (AMPK), mechanistic target of rapamycin (mTOR), insulin/insulin-like growth factor 1 (IGF-1) and sirtuins, including SIRT1. Peroxisome proliferation-activated receptor coactivator 1 alpha (PGC-1α), encoded by the PPARGC1A gene, playing an important role in antioxidant defense and mitochondrial biogenesis, may interact with these molecules influencing lifespan and general fitness. Perturbation in the aging stress response may lead to aging-related disorders, including age-related macular degeneration (AMD), the main reason for vision loss in the elderly. This is supported by studies showing an important role of disturbances in mitochondrial metabolism, DDR and autophagy in AMD pathogenesis. In addition, disturbed expression of PGC-1α was shown to associate with AMD. Therefore, the aging stress response may be critical for AMD pathogenesis, and further studies are needed to precisely determine mechanisms underlying its role in AMD. These studies can include research on retinal cells produced from pluripotent stem cells obtained from AMD donors with the mutations, either native or engineered, in the critical genes for the aging stress response, including AMPK, IGF1, MTOR, SIRT1 and PPARGC1A.

The Gene-Regulatory Footprint of Aging Highlights Conserved Central Regulators

Many genes and pathways have been linked to aging, yet our understanding of underlying molecular mechanisms is still lacking. Here, we measure changes in the transcriptome, histone modifications, and DNA methylome in three metabolic tissues of adult and aged mice. Transcriptome and methylome changes dominate the liver aging footprint, whereas heart and muscle globally increase chromatin accessibility, especially in aging pathways. In mouse and human data from multiple tissues and regulatory layers, age-related transcription factor expression changes and binding site enrichment converge on putative aging modulators, including ZIC1, CXXC1, HMGA1, MECP2, SREBF1, SREBF2, ETS2, ZBTB7A, and ZNF518B. Using Mendelian randomization, we establish possible epidemiological links between expression of some of these transcription factors or their targets, including CXXC1, ZNF518B, and BBC3, and longevity. We conclude that conserved modulators are at the core of the molecular footprint of aging, and variation in tissue-specific expression of some may affect human longevity.

DNA Damage Response and Metabolic Reprogramming in Health and Disease

Nuclear DNA damage contributes to cellular malfunction and the premature onset of age-related diseases, including cancer. Until recently, the canonical DNA damage response (DDR) was thought to represent a collection of nuclear processes that detect, signal and repair damaged DNA. However, recent evidence suggests that beyond nuclear events, the DDR rewires an intricate network of metabolic circuits, fine-tunes protein synthesis, trafficking, and secretion as well as balances growth with defense strategies in response to genotoxic insults. In this review, we discuss how the active DDR signaling mobilizes extranuclear and systemic responses to promote cellular homeostasis and organismal survival in health and disease.

Healthspan pathway maps in C. elegans and humans highlight transcription, proliferation/biosynthesis and lipids

The molecular basis of aging and of aging-associated diseases is being unraveled at an increasing pace. An extended healthspan, and not merely an extension of lifespan, has become the aim of medical practice. Here, we define health based on the absence of diseases and dysfunctions. Based on an extensive review of the literature, in particular for humans and C. elegans, we compile a list of features of health and of the genes associated with them. These genes may or may not be associated with survival/lifespan. In turn, survival/lifespan genes that are not known to be directly associated with health are not considered. Clusters of these genes based on molecular interaction data give rise to maps of healthspan pathways for humans and for C. elegans. Overlaying healthspan-related gene expression data onto the healthspan pathway maps, we observe the downregulation of (pro-inflammatory) Notch signaling in humans and of proliferation in C. elegans. We identify transcription, proliferation/biosynthesis and lipids as a common theme on the annotation level, and proliferation-related kinases on the gene/protein level. Our literature-based data corpus, including visualization, should be seen as a pilot investigation of the molecular underpinnings of health in two different species. Web address: http://pathways.h2020awe.eu.

Peptide Hormone Regulation of DNA Damage Responses

DNA damage response (DDR) and DNA repair pathways determine neoplastic cell transformation and therapeutic responses, as well as the aging process. Altered DDR functioning results in accumulation of unrepaired DNA damage, increased frequency of tumorigenic mutations, and premature aging. Recent evidence suggests that polypeptide hormones play a role in modulating DDR and DNA damage repair, while DNA damage accumulation may also affect hormonal status. We review the available reports elucidating involvement of insulin-like growth factor 1 (IGF1), growth hormone (GH), α-melanocyte stimulating hormone (αMSH), and gonadotropin-releasing hormone (GnRH)/gonadotropins in DDR and DNA repair as well as the current understanding of pathways enabling these actions. We discuss effects of DNA damage pathway mutations, including Fanconi anemia, on endocrine function and consider mechanisms underlying these phenotypes. (Endocrine Reviews 41: 1 - 19, 2020).

The aging transcriptome: read between the lines

The increasing sophistication of gene expression technologies has given rise to the idea that aging could be understood by analyzing transcriptomes. Mapping trajectories of gene expression changes in aging organisms, across different tissues and brain regions has provided insights on how biological functions change with age. However, recent publications suggest that transcriptional regulation itself deteriorates with age. Loss of transcriptional regulation will lead to non-regulated gene expression changes, but current analysis strategies were not designed to disentangle mixtures of regulated and non-regulated changes. Disentangling transcriptional data to distinguish adaptive, regulatory changes, from those that are the consequence of the age-associated deterioration is likely to create an analytical challenge but promises to unlock yet poorly understood aspects of many age-associated transcriptomes.

Tissue-infiltrating macrophages mediate an exosome-based metabolic reprogramming upon DNA damage

DNA damage and metabolic disorders are intimately linked with premature disease onset but the underlying mechanisms remain poorly understood. Here, we show that persistent DNA damage accumulation in tissue-infiltrating macrophages carrying an ERCC1-XPF DNA repair defect (Er1^F/−) triggers Golgi dispersal, dilation of endoplasmic reticulum, autophagy and exosome biogenesis leading to the secretion of extracellular vesicles (EVs) in vivo and ex vivo. Macrophage-derived EVs accumulate in Er1^F/− animal sera and are secreted in macrophage media after DNA damage. The Er1^F/− EV cargo is taken up by recipient cells leading to an increase in insulin-independent glucose transporter levels, enhanced cellular glucose uptake, higher cellular oxygen consumption rate and greater tolerance to glucose challenge in mice. We find that high glucose in EV-targeted cells triggers pro-inflammatory stimuli via mTOR activation. This, in turn, establishes chronic inflammation and tissue pathology in mice with important ramifications for DNA repair-deficient, progeroid syndromes and aging.

DNA damage is associated with metabolic disorders, but the mechanism in unclear. Here, the authors show that persistent DNA damage induced by lack of the endonuclease XPF-ERCC1 triggers extracellular vesicle biogenesis in tissue infiltrating macrophages, and that vesicle uptake stimulates glucose uptake in recipient cells, leading to increased inflammation.

The Klotho proteins in health and disease

The Klotho proteins, αKlotho and βKlotho, are essential components of endocrine fibroblast growth factor (FGF) receptor complexes, as they are required for the high-affinity binding of FGF19, FGF21 and FGF23 to their cognate FGF receptors (FGFRs). Collectively, these proteins form a unique endocrine system that governs multiple metabolic processes in mammals. FGF19 is a satiety hormone that is secreted from the intestine on ingestion of food and binds the βKlotho-FGFR4 complex in hepatocytes to promote metabolic responses to feeding. By contrast, under fasting conditions, the liver secretes the starvation hormone FGF21, which induces metabolic responses to fasting and stress responses through the activation of the hypothalamus-pituitary-adrenal axis and the sympathetic nervous system following binding to the βKlotho-FGFR1c complex in adipocytes and the suprachiasmatic nucleus, respectively. Finally, FGF23 is secreted by osteocytes in response to phosphate intake and binds to αKlotho-FGFR complexes, which are expressed most abundantly in renal tubules, to regulate mineral metabolism. Growing evidence suggests that the FGF-Klotho endocrine system also has a crucial role in the pathophysiology of ageing-related disorders, including diabetes, cancer, arteriosclerosis and chronic kidney disease. Therefore, targeting the FGF-Klotho endocrine axes might have therapeutic benefit in multiple systems; investigation of the crystal structures of FGF-Klotho-FGFR complexes is paving the way for the development of drugs that can regulate these axes.

Murine single-cell RNA-seq reveals cell-identity- and tissue-specific trajectories of aging

Aging is a pleiotropic process affecting many aspects of mammalian physiology. Mammals are composed of distinct cell type identities and tissue environments, but the influence of these cell identities and environments on the trajectory of aging in individual cells remains unclear. Here, we performed single-cell RNA-seq on >50,000 individual cells across three tissues in young and old mice to allow for direct comparison of aging phenotypes across cell types. We found transcriptional features of aging common across many cell types, as well as features of aging unique to each type. Leveraging matrix factorization and optimal transport methods, we found that both cell identities and tissue environments exert influence on the trajectory and magnitude of aging, with cell identity influence predominating. These results suggest that aging manifests with unique directionality and magnitude across the diverse cell identities in mammals.

DNA damage responses in ageing

Ageing appears to be a nearly universal feature of life, ranging from unicellular microorganisms to humans. Longevity depends on the maintenance of cellular functionality, and an organism's ability to respond to stress has been linked to functional maintenance and longevity. Stress response pathways might indeed become therapeutic targets of therapies aimed at extending the healthy lifespan. Various progeroid syndromes have been linked to genome instability, indicating an important causal role of DNA damage accumulation in the ageing process and the development of age-related pathologies. Recently, non-cell-autonomous mechanisms including the systemic consequences of cellular senescence have been implicated in regulating organismal ageing. We discuss here the role of cellular and systemic mechanisms of ageing and their role in ageing-associated diseases.

DNA damage and transcription stress cause ATP-mediated redesign of metabolism and potentiation of anti-oxidant buffering

Accumulation of DNA lesions causing transcription stress is associated with natural and accelerated aging and culminates with profound metabolic alterations. Our understanding of the mechanisms governing metabolic redesign upon genomic instability, however, is highly rudimentary. Using Ercc1-defective mice and Xpg knock-out mice, we demonstrate that combined defects in transcription-coupled DNA repair (TCR) and in nucleotide excision repair (NER) directly affect bioenergetics due to declined transcription, leading to increased ATP levels. This in turn inhibits glycolysis allosterically and favors glucose rerouting through the pentose phosphate shunt, eventually enhancing production of NADPH-reducing equivalents. In NER/TCR-defective mutants, augmented NADPH is not counterbalanced by increased production of pro-oxidants and thus pentose phosphate potentiation culminates in an over-reduced redox state. Skin fibroblasts from the TCR disease Cockayne syndrome confirm results in animal models. Overall, these findings unravel a mechanism connecting DNA damage and transcriptional stress to metabolic redesign and protective antioxidant defenses.

ERCC1 is involved in a number of DNA repair pathways including nucleotide excision repair. Here the authors showed that reduced transcription in Ercc1-deficient mouse livers and cells increases ATP levels, suppressing glycolysis and rerouting glucose into the pentose phosphate shunt that generates reductive stress.

Genetic Pathways of Aging and Their Relevance in the Dog as a Natural Model of Human Aging

Aging research has experienced a burst of scientific efforts in the last decades as the growing ratio of elderly people has begun to pose an increased burden on the healthcare and pension systems of developed countries. Although many breakthroughs have been reported in understanding the cellular mechanisms of aging, the intrinsic and extrinsic factors that contribute to senescence on higher biological levels are still barely understood. The dog, Canis familiaris, has already served as a valuable model of human physiology and disease. The possible role the dog could play in aging research is still an open question, although utilization of dogs may hold great promises as they naturally develop age-related cognitive decline, with behavioral and histological characteristics very similar to those of humans. In this regard, family dogs may possess unmatched potentials as models for investigations on the complex interactions between environmental, behavioral, and genetic factors that determine the course of aging. In this review, we summarize the known genetic pathways in aging and their relevance in dogs, putting emphasis on the yet barely described nature of certain aging pathways in canines. Reasons for highlighting the dog as a future aging and gerontology model are also discussed, ranging from its unique evolutionary path shared with humans, its social skills, and the fact that family dogs live together with their owners, and are being exposed to the same environmental effects.

Mouse Models to Disentangle the Hallmarks of Human Aging

Model organisms have provided fundamental evidence that aging can be delayed and longevity extended. These findings gave rise to a new era in aging research aimed at elucidating the pathways and networks controlling this complex biological process. The identification of 9 hallmarks of aging has established a framework to evaluate the relative contribution of each hallmark and the interconnections among them. In this review, we revisit these hallmarks with the information obtained exclusively through the generation of genetically modified mouse models that have a significant impact on the aging process. We discuss within each hallmark those interventions that accelerate aging or that have been successful at increasing lifespan, with the final goal of identifying the most promising antiaging avenues based on the current knowledge provided by in vivo models.