Longevity Papers

The adaptive starvation response allows us to survive periods of starvation - a characteristic of the environment in which humans evolved. We are now in an evolutionary transition from a global environment which was characterized by periods of famine to a world where obesity and caloric excess have become a new reality, but the mechanisms of fasting physiology remain relevant. First, many parts of the world are still plagued by famine with insufficient food resources and therefore the adaptive mechanisms required for survival during periods of decreased caloric intake are not simply relevant to our evolutionary past. Second, the obesity epidemic provides strong rationale for understanding the biology of fasting, as the same efficiencies that have evolved to allow us to survive periods of starvation also likely drive a genetic predisposition to obesity, and therefore some of the adaptive mechanisms may be maladaptive in the setting of food excess. A third compelling reason to explore the biology of fasting is that in model organisms, caloric restriction without overt starvation, is an intervention that prolongs lifespan. The purpose of this review is to provide an overview of the biology of fasting. We will highlight potential mechanisms of benefit from fasting as well as examine data from model organisms and humans that indicate potential health risks to fasting, particularly related to bone fragility. Finally, we will review clinical studies to date that have investigated the effects of fasting on metabolic outcomes and suggest signals of benefit.

Improving gut health by altering the activity of intestinal stem cells is thought to have the potential to reverse aging. The aged Drosophila midgut undergoes hyperplasia and barrier dysfunction. However, it is still unclear how to limit hyperplasia to extend lifespan. Here, we show that early midgut injury prevents the abrupt onset of aging hyperplasia and extends lifespan in flies. Daily transcriptome profiling and lineage tracing analysis show that the abrupt onset of aging hyperplasia is due to the collective turnover of developmentally generated "old" enterocytes (ECs). Early injury introduces new ECs into the old EC population, forming the epithelial age mosaic. Age mosaic avoids collective EC turnover and facilitates septate junction formation, thereby improving the epithelial barrier and extending lifespan. Furthermore, we found that intermittent time-restricted feeding benefits health by creating an EC age mosaic. Our findings suggest that age mosaic may become a therapeutic approach to reverse aging.

Thin endometrium (TE) is generally recognized as a contributing factor to reduced pregnancy rates and adverse perinatal outcomes, yet the pathogenesis of the disease remains elusive. We conducted an analysis and validation of the single-cell RNA sequencing (scRNA-seq) data pertaining to TE and demonstrated that insulin-like growth factor binding protein 2 (IGFBP2) expression is down-regulated, resulting in the senescence of endometrial epithelial cells. In both human primary endometrial epithelial cells and the Ishikawa cell line (a well-established endometrial-derived epithelial cell), the introduction of recombinant human IGFBP2 protein effectively alleviates hydrogen peroxide (H2O2)-induced cellular senescence. Notably, it demonstrates superior performance compared to the well-known anti-aging agent Dasatinib in specific aspects. Specifically, transfecting IGFBP2 protein siRNAs promotes cyclin dependent kinase inhibitor 1A (P21) accumulation through the phosphatidylinositol 3-kinase (PI3K)/AKT serine/threonine kinase (AKT) signaling pathway by regulating phosphatase and tensin homolog deleted on chromosome ten (PTEN) activity. Furthermore, administering IGFBP2 protein or Dasatinib to TE mouse models, which was established by endometrial curettage combined with H2O2 instillation, restored endometrial thickness by inhibiting senescence. Our findings demonstrate that down-regulation of IGFBP2 protein plays a pivotal role in mediating the senescence of endometrial epithelial cells in TE. This offers novel insights into elucidating the pathogenesis of TE and identifying potential new therapeutic targets.

Middle age represents a critical period of accelerated brain changes and provides a window for early detection and intervention in age-related neurological decline. Hearing loss is a key early marker of such decline and is linked to numerous comorbidities in older adults. Yet, ~10% of middle-aged individuals who report hearing difficulties show normal audiograms. Cochlear neural degeneration (CND) could contribute to these hidden hearing deficits, though its role remains unclear due to a lack of objective diagnostics and uncertainty regarding its perceptual outcomes. Here, we employed a cross-species design to examine neural and behavioral signatures of CND. We measured envelope following responses (EFRs) - neural ensemble responses to sound originating from the peripheral auditory pathway - in young and middle-aged adults with normal audiograms and compared these responses to young and middle-aged Mongolian gerbils, where CND was histologically confirmed. We observed near-identical changes in EFRs across species that were associated with CND. Behavioral assessments revealed age-related speech-in-noise deficits under challenging conditions, while pupil-indexed listening effort increased with age even when behavioral performance was matched. Together, these results demonstrate that CND contributes to speech perception difficulties and elevated listening effort in midlife, which may ultimately lead to listening fatigue and social withdrawal.

Aging increases the vulnerability of kidneys to injury and impairs their regenerative capacity. SIRT3 expression declines with aging and is associated with multiple age-related pathologies. The expression profile and functional role of SIRT3 in renal aging remain unclear. Here, SIRT3 expression in aging kidneys is assessed and analyzed for its promoter methylation patterns using methylation-specific PCR (MSP). It is found that aging exacerbates UUO-induced renal fibrosis, associated with downregulated SIRT3 expression. Mechanistically, age-related SIRT3 downregulation is mediated by hypermethylation of its promoter region. SIRT3 knockout exacerbated renal fibrosis in young mice subjected to UUO, whereas SIRT3 overexpression attenuated fibrosis in aged UUO mice. Integration of RNA-seq and immunoprecipitation-mass spectrometry (IP-MS) analyses revealed that SIRT3 deficiency leads to hyperacetylation of GSK3β at lysine 15 (K15). This K15 hyperacetylation inhibited GSK3β activity, consequently stabilizing its substrate β-catenin. Furthermore, self-assembled PEG-PCL-PEG micelles are designed and synthesized to encapsulate hydrophobic honokiol (HKL). These micelles significantly enhanced the aqueous solubility and oral bioavailability of free HKL, maintained stable blood concentrations, and ultimately improved its anti-fibrotic efficacy. These findings propose novel therapeutic strategies for managing renal fibrosis in the aging population and provide a foundation for developing new drugs and combination therapies.

One of the most promising interventional targets for brain health is cerebral perfusion, but its link to white matter (WM) aging remains unclear. Motivated by existing literature demonstrating links between declining cortical perfusion and the development of WM hyperintensities, we posit that regional WM hypoperfusion precedes deteriorating WM integrity. Using the Human Connectome Project Aging (HCP-A) data set, we examine tract-wise associations between WM microstructural integrity (i.e. fractional anisotropy, mean diffusivity, axial diffusivity, and radial diffusivity) and perfusion (i.e. cerebral blood flow and arterial transit time) in ten major bilateral WM tracts. Results show that tracts displaying the largest CBF decline in aging do not necessarily display the largest ATT decline, and vice versa. Moreover, significant WM perfusion-microstructure canonical correlations were found in all tracts, but the drivers of these correlations vary by both tract and sex, with female subjects demonstrating more tracts with large microstructural variations contributing to the correlations. Importantly, age-effects on arterial transit time peak at a younger age than those of all other parameters investigated, preceding age-related microstructural differences and CBF in several tracts. This study contributes compelling evidence to the vascular hypothesis of WM degeneration and highlights the utility of blood-flow timing as an early marker of aging.

The DNA-dependent protease SPRTN maintains genome stability by degrading toxic DNA-protein crosslinks (DPCs). To understand how SPRTN's promiscuous protease activity is confined to cleavage of crosslinked proteins, we reconstitute the repair of DPCs including their modification with SUMO and ubiquitin chains in vitro. We discover that DPC ubiquitylation strongly activates SPRTN independently of SPRTN's known ubiquitin-binding domains. Using protein structure prediction, MD simulations and NMR spectroscopy we reveal that ubiquitin binds to SPRTN's protease domain, promoting an open, active conformation. Replacing key interfacial residues prevents allosteric activation of SPRTN by ubiquitin, leading to genomic instability and cell cycle defects in cells expressing truncated SPRTN variants that cause premature aging and liver cancer in Ruijs-Aalfs syndrome patients. Collectively, our results reveal a ubiquitin-dependent regulatory mechanism that ensures SPRTN activity is deployed precisely when and where it is needed.

Cognitive ageing is marked by progressive decline in episodic memory and dopaminergic function, yet the extent to which individual differences in dopaminergic system integrity influence memory under motivational contexts remains unclear. In this study, we investigated how baseline D2/D3 receptor availability (BPND0) in key dopaminergic pathways relates to reward-modulated memory performance in healthy older adults. Thirty-three healthy seniors (aged 64-85) underwent two session concurrent MR-PET imaging with [18F]fallypride involving scene categorisation task with high- and low-motivational contexts. We quantified BPND0 across nine dopaminergic regions of interest and examined their relationships with recognition memory performance at short (~15m) and long (~24h) delays. Baseline D2/D3 receptor availability showed high test-retest reliability and regionally distinct profiles, suggesting it reflects a stable neurochemical characteristic in healthy ageing, and principal axis factor analysis revealed two partially independent dopaminergic subsystems (dorsal striatal vs mesolimbic) based on interindividual patterns in receptor densities. Region-specific associations further linked D2/D3 receptor availability to distinct memory outcomes. Higher caudate D2/D3 receptor availability was associated with a liberal response bias (increased hits and false alarms both), whereas higher putamen D2/D3 predicted more durable long-term memory retention. Greater thalamic D2/D3 receptor availability correlated with fewer short-term false memories, while greater D2/D3 receptor availability in the amygdala was associated with better recognition at longer delays. In contrast, higher midbrain (substantia nigra and ventral tegmental area) D2/D3 availability which was linked to poorer reward-related memory performance. These findings suggest several complementary dopaminergic circuits supporting episodic memory. Our results highlight dopaminergic neuromodulation as a key factor in cognitive ageing and a potential target for interventions to bolster memory in late life.

Obesity and aging are major risk factors for diseases such as Type 2 diabetes mellitus, dementia, and osteoporosis. High-fat diet (HFD) consumption is one of the most important factors contributing to obesity. To elucidate and provide resources on how long-term HFD to aging (LHA) affects the bone marrow and solid organs, we established an LHA mice model and demonstrated that LHA caused a shift from osteogenesis to adipogenesis in the bone marrow microenvironment. Single-cell transcriptomics of bone marrow cells highlighted LHA-driven perturbations in immune cell populations with distinct metabolic adaptations to LHA. We demonstrated that bone marrow macrophages of the LHA group upregulated Chil3 and Fabp4, which are associated with inflammatory response and regulation of adipocytes. Moreover, we identified the Ptn-Sdc3 axis and Cxcl12-Cxcr4 axis between bone marrow macrophages and brain epithelial cells as possible candidates for crosstalk between bone marrow and brain in LHA mice. Our findings indicated the bone marrow microenvironment as a central hub of LHA-induced pathology, where adipogenic reprogramming and myeloid cell dysfunction collectively drive skeletal and systematic inflammation. This resource highlights therapeutic opportunities targeting bone marrow to mitigate obesity-accelerated aging.

Whether and how ovarian hormone fluctuations mediate the skeletal muscle response to ageing in females remains to be elucidated. We examined a tightly controlled, cross-sectional cohort of 96 females between 18-80 years of age to map the functional and molecular trajectory of muscle ageing and determine its relationship with female sex hormones. Across every decade, we quantified body composition using dual-energy x-ray absorptiometry, muscle morphology using peripheral quantitative computed tomography and voluntary and evoked muscle strength. Circulating sex hormone concentrations were measured with gas chromatography mass spectrometry and immunoassays. Morphology and gene expression of vastus lateralis muscle samples were assessed with immunohistochemical staining and RNA sequencing, respectively. After adjusting for the relevant variables, age was negatively associated with muscle mass, strength, and muscle fibre size, and positively associated with hybrid type I/II fibre prevalence and fibrosis. We found 37 unique patterns of gene expression across individual decades of age. Immune signalling, cellular adhesion, and extracellular matrix organisation pathways were the most upregulated with age, while mitochondrial function pathways were the most downregulated. Independently of age, circulating oestradiol and progesterone, but not testosterone, concentrations were positively associated with lean mass and negatively associated with hybrid muscle fibres across the lifespan. Oestrogen receptor binding sites were significantly enriched in upregulated genes in pre- versus post-menopausal muscle, suggesting a reduction in the translation of oestrogen target genes after menopause. The effects of sex hormone fluctuations across the female lifespan should therefore be considered in the development of therapies to mitigate age-related muscle wasting.

As the innermost lining of blood vessels, endothelial cells (ECs) regulate blood flow, maintain vascular tone, and limit inflammation for vessel health. EC-derived nitric oxide (NO), synthesized by endothelial nitric oxide synthase (eNOS), is a vasodilator essential for improving blood flow and vascular homeostasis. The RhoA/ROCK pathway regulates eNOS levels, where overactivation decreases eNOS expression and downstream NO production. As such, RhoA/ROCK hyperactivity and increased pMLC have been identified as major contributors to age-associated vasoconstriction and hypertension. Intriguingly, recent studies identify Sun1, a key component of the linker of nucleoskeleton and cytoskeleton (LINC) complex, as a major regulator of RhoA/ROCK activity. Moreover, endothelial aging deteriorates nuclear pore complexes (NPCs) (i.e. nucleoporin [Nup93]) and impairs nucleocytoplasmic transport, thereby insinuating a role for nuclear envelope components in vessel homeostasis. Here, we show that targeted loss of endothelial Nup93 in adult mice significantly reduces eNOS expression and NO bioavailability for consequent defects in NO-dependent vasodilatory responses. In vitro knockdown of Nup93 in primary human ECs also decreases both eNOS expression and NO production. Mechanistically, we find that loss of Nup93 significantly reduces endothelial Sun1 levels for a concomitant increase in RhoA activity. Indeed, restoring Sun1 protein levels in Nup93-deficient ECs mitigates RhoA activity to rescue both eNOS expression and NO production. Taken together, we demonstrate endothelial Nup93, through Sun1 stabilization, as a novel regulator of eNOS-NO signaling and vessel reactivity, contributing to the growing importance of nuclear membrane components in EC and vascular biology.

Large-scale bone defects require complex surgical procedures to repair, but full restoration of the bone is not guaranteed due to the significant tissue loss involved. In contrast, fractures can frequently be treated with conservative techniques. Particularly, ribs have a remarkable ability to spontaneously regenerate large-scale bone defects. However, we show here that skeletal maturity and age are associated with a decrease in the regenerative potential of human ribs. To investigate skeletal maturity and age-related cellular and transcriptional changes during large-scale bone regeneration, we used a mouse model that mimics the regenerative clinical features of human ribs. Unlike immature mice, mature mice lose the ability to regenerate after rib resection, and instead of bone, the resected rib space is repaired with abundant fibronectin cells. In addition, bone repair in mature mice presents reduced immune cell infiltration, which coincides with decreased levels of circulatory pro-inflammatory factors. To address the role of cell-cell communication and test whether skeletal maturity and age-related changes in immune cells and circulatory factors influence bone regeneration, we used immunodeficient mouse strains and performed heterochronic parabiosis. In immature mice, defective immune cell function altered callus composition rather than inhibiting bone regeneration. Remarkably, under parabiosis, a systemic pro-regenerative response is triggered exclusively in resected immature mice and is capable of partially rescuing bone regeneration in mature mice otherwise unable to regenerate spontaneously. Collectively, these findings suggest that therapeutic strategies focused on identifying pro-regenerative immune factors are promising for supporting the regeneration of large bone defects.