No abstract

Aging results in an elevated burden of senescent cells, senescence‐associated secretory phenotype (SASP), and tissue infiltration of immune cells contributing to chronic low‐grade inflammation and a host of age‐related diseases. Recent evidence suggests that the clearance of senescent cells alleviates chronic inflammation and its associated dysfunction and diseases. However, the effect of this intervention on metabolic function in old age remains poorly understood. Here, we demonstrate that dasatinib and quercetin (D&Q) have senolytic effects, reducing age‐related increase in senescence‐associated β‐galactosidase, expression of p16 and p21 gene and P16 protein in perigonadal white adipose tissue (pgWAT; all p ≤ 0.04). This treatment also suppressed age‐related increase in the expression of a subset of pro‐inflammatory SASP genes ( mcp1, tnf‐α, il‐1α, il‐1β, il‐6, cxcl2, and cxcl10 ), crown‐like structures, abundance of T cells and macrophages in pgWAT (all p ≤ 0.04). In the liver and skeletal muscle, we did not find a robust effect of D&Q on senescence and inflammatory SASP markers. Although we did not observe an age‐related difference in glucose tolerance, D&Q treatment improved fasting blood glucose ( p = 0.001) and glucose tolerance ( p = 0.007) in old mice that was concomitant with lower hepatic gluconeogenesis. Additionally, D&Q improved insulin‐stimulated suppression of plasma NEFAs ( p = 0.01), reduced fed and fasted plasma triglycerides (both p ≤ 0.04), and improved systemic lipid tolerance ( p = 0.006). Collectively, results from this study suggest that D&Q attenuates adipose tissue inflammation and improves systemic metabolic function in old age. These findings have implications for the development of therapeutic agents to combat metabolic dysfunction and diseases in old age.

Advancing age leads to an accumulation of senescent endothelial cells (ECs) within arteries. Senescent cells have undergone permanent cell cycle arrest, are pro‐oxidative and pro‐inflammatory, and therefore represent a likely cause of age‐related EC dysfunction. Yet, the molecular mechanisms and physiological consequences of EC senescence remain incompletely understood. Telomeres are repeat DNA sequences that cap chromosomes. Telomeres shorten with each cell division and are highly susceptible to oxidative damage. When telomeres become critically short or damaged, they become uncapped, which activates the DNA damage response and leads to cellular senescence. Here, we tested the hypothesis that aging results in EC telomere uncapping that induces senescence, leading to physiological hallmarks of aging. To assess whether aging results in EC telomere uncapping, we compared ECs from young (~3 mo) and old (~27 mo) mice. Aging resulted in ~4‐fold greater EC telomere uncapping (p<0.001, Figure 1A). To determine if EC telomere uncapping induces senescence, we deleted the telomere capping protein, TRF2, in ECs of young (~3.5mo) mice (TRF2‐ecKO). Compared to wildtype (WT) littermate controls, TRF2‐ecKO mice had a ~78% reduction in TRF2 gene expression (p<0.0001). TRF2 deletion reduced EC division by ~47% (p<0.0001, Figure 1B), indicative of senescence. To examine the physiological consequences of EC senescence, we examined hallmarks of vascular aging including perfused microvascular density and endothelium‐dependent dilation (EDD). TRF2‐ecKO mice had an ~18% reduction in perfused mesenteric microvessels between 5‐25 µM (p<0.001, Figure 1C). Likewise, TRF2‐ecKO displayed ~26% reduction in mesenteric artery EDD compared to WT mice (p<0.05, Figure 1D). Furthermore, TRF2‐ecKO arterial EDD was ameliorated by the superoxide scavenger, TEMPOL (p>0.05, Figure 1D). Endothelium‐independent dilation to the exogenous nitric oxide donor sodium nitroprusside was not different between WT and TRF2‑ecKO mice (p>0.05). These data suggest EC telomere uncapping leads to senescence that reduces perfused microvascular density, and to elevated oxidative stress that suppresses EDD, similar to advanced age. To assess metabolic and muscle function, we performed an intraperitoneal glucose tolerance test (GTT, 2g/kg body mass) and a forelimb grip strength test. TRF2‐ecKO mice had ~21% greater area under the curve during GTT compared to WT mice (p<0.05, Figure 2A) as well as a ~14% reduction in grip strength (p<0.05, Figure2B). Taken together, these data provide evidence that aging results in EC telomere uncapping that induces senescence and age‐related physiological dysfunction.

No abstract

Atherogenic remodeling often occurs at arterial locations with disturbed blood flow (i.e., low or oscillatory) and both aging and western diet (WD) increase the likelihood for pro-atherogenic remodeling. However, it is unknown if old age and/or a WD modify the pro-atherogenic response to disturbed blood flow. We induced disturbed blood flow by partial carotid ligation (PCL) of the left carotid artery in young and old, normal chow (NC) or WD fed male B6D2F1 mice. Three weeks post-PCL, ligated carotid arteries had greater intima media thickness, neointima formation, and macrophage content compared with un-ligated arteries. WD led to greater remodeling and macrophage content in the ligated artery compared with NC mice, but these outcomes were similar between young and old mice. In contrast, nitrotyrosine content, a marker of oxidative stress, did not differ between WD and NC fed mice, but was greater in old compared with young mice in both ligated and un-ligated carotid arteries. In primary vascular smooth muscle cells, aging reduced proliferation, whereas conditioned media from fatty acid treated endothelial cells increased proliferation. Taken together, these findings suggest that the remodeling and pro-inflammatory response to disturbed blood flow is increased by WD, but is not increased by aging.