Jurk, Diana

Abstract Although cellular senescence is increasingly recognized as driving multiple age-related co-morbidities through the senescence-associated secretory phenotype (SASP), in vivo senescent cell identification, particularly in bulk or single cell RNA-sequencing (scRNA-seq) data remains challenging. Here, we generated a novel gene set (SenMayo) and first validated its enrichment in bone biopsies from two aged human cohorts. SenMayo also identified senescent cells in aged murine brain tissue, demonstrating applicability across tissues and species. For direct validation, we demonstrated significant reductions in SenMayo in bone following genetic clearance of senescent cells in mice, with similar findings in adipose tissue from humans in a pilot study of pharmacological senescent cell clearance. In direct comparisons, SenMayo outperformed all six existing senescence/SASP gene sets in identifying senescent cells across tissues and in demonstrating responses to senescent cell clearance. We next used SenMayo to identify senescent hematopoietic or mesenchymal cells at the single cell level from publicly available human and murine bone marrow/bone scRNA-seq data and identified monocytic and osteolineage cells, respectively, as showing the highest levels of senescence/SASP genes. Using pseudotime and cellular communication patterns, we found senescent hematopoietic and mesenchymal cells communicated with other cells through common pathways, including the Macrophage Migration Inhibitory Factor (MIF) pathway, which has been implicated not only in inflammation but also in immune evasion, an important property of senescent cells. Thus, SenMayo identifies senescent cells across tissues and species with high fidelity. Moreover, using this senescence panel, we were able to characterize senescent cells at the single cell level and identify key intercellular signaling pathways associated with these cells, which may be particularly useful for evolving efforts to map senescent cells (e.g., SenNet). In addition, SenMayo represents a potentially clinically applicable panel for monitoring senescent cell burden with aging and other conditions as well as in studies of senolytic drugs.

Angiotensin II receptor blockers (telmisartan) prevent rodents from diet-induced obesity and improve their metabolic status. Hyperglycemia and obesity are associated with reduced cerebral blood flow and neurovascular uncoupling which may lead to behavioral deficits. We wanted to know whether a treatment with telmisartan prevents these changes in obesity. We put young mice on high-fat diet and simultaneously treated them with telmisartan. At the end of treatment, we performed laser speckle imaging and magnetic resonance imaging to assess the effect on neurovascular coupling and cerebral blood flow. Different behavioral tests were used to investigate cognitive function. Mice developed diet-induced obesity and after 16, not 8 weeks of high-fat diet, however, the response to whisker pad stimulation was about 30% lower in obese compared to lean mice. Simultaneous telmisartan treatment increased the response again by 10% compared to obese mice. Moreover, telmisartan treatment normalized high-fat diet-induced reduction of cerebral blood flow and prevented a diet-induced anxiety-like behavior. In addition to that, telmisartan affects cellular senescence and string vessel formation in obesity. We conclude, that telmisartan protects against neurovascular unit impairments in a diet-induced obesity setting and may play a role in preventing obesity related cognitive deficits in Alzheimer’s disease.

Abstract Cellular senescence is characterized by an irreversible cell cycle arrest and a pro‐inflammatory senescence‐associated secretory phenotype (SASP), which is a major contributor to aging and age‐related diseases. Clearance of senescent cells has been shown to improve brain function in mouse models of neurodegenerative diseases. However, it is still unknown whether senescent cell clearance alleviates cognitive dysfunction during the aging process. To investigate this, we first conducted single‐nuclei and single‐cell RNA‐seq in the hippocampus from young and aged mice. We observed an age‐dependent increase in p16 Ink4a senescent cells, which was more pronounced in microglia and oligodendrocyte progenitor cells and characterized by a SASP. We then aged INK ‐ ATTAC mice, in which p16 Ink4a ‐positive senescent cells can be genetically eliminated upon treatment with the drug AP20187 and treated them either with AP20187 or with the senolytic cocktail Dasatinib and Quercetin. We observed that both strategies resulted in a decrease in p16 Ink4a exclusively in the microglial population, resulting in reduced microglial activation and reduced expression of SASP factors. Importantly, both approaches significantly improved cognitive function in aged mice. Our data provide proof‐of‐concept for senolytic interventions' being a potential therapeutic avenue for alleviating age‐associated cognitive impairment.

Abstract Age-related chronic inflammation promotes cellular senescence, chronic disease, cancer, and reduced lifespan. In this study, we wanted to explore the effects of a moderate exercise regimen on inflammatory liver disease and tumorigenesis. We used an established model of spontaneous inflammaging, steatosis, and cancer (nfkb1−/− mouse) to demonstrate whether 3 mo of moderate aerobic exercise was sufficient to suppress liver disease and cancer development. Interventional exercise when applied at a relatively late disease stage was effective at reducing tissue inflammation (liver, lung, and stomach), oxidative damage, and cellular senescence, and it reversed hepatic steatosis and prevented tumor development. Underlying these benefits were transcriptional changes in enzymes driving the conversion of tryptophan to NAD+, this leading to increased hepatic NAD+ and elevated activity of the NAD+-dependent deacetylase sirtuin. Increased SIRT activity was correlated with enhanced deacetylation of key transcriptional regulators of inflammation and metabolism, NF-κB (p65), and PGC-1α. We propose that moderate exercise can effectively reprogram pre-established inflammatory and metabolic pathologies in aging with the benefit of prevention of disease.

Senescence is the consequence of a signaling mechanism activated in stressed cells to prevent proliferation of cells with damage. Senescent cells (Sncs) often develop a senescence-associated secretory phenotype to prompt immune clearance, which drives chronic sterile inflammation and plays a causal role in aging and age-related diseases. Sncs accumulate with age and at anatomical sites of disease. Thus, they are regarded as a logical therapeutic target. Senotherapeutics are a new class of drugs that selectively kill Sncs (senolytics) or suppress their disease-causing phenotypes (senomorphics/senostatics). Since 2015, several senolytics went from identification to clinical trial. Preclinical data indicate that senolytics alleviate disease in numerous organs, improve physical function and resilience, and suppress all causes of mortality, even if administered to the aged. Here, we review the evidence that Sncs drive aging and disease, the approaches to identify and optimize senotherapeutics, and the current status of preclinical and clinical testing of senolytics.

AbstractChronic inflammation is a common feature of many age‐related conditions including neurodegenerative diseases such as Alzheimer's disease. Cellular senescence is a state of irreversible cell‐cycle arrest, thought to contribute to neurodegenerative diseases partially via induction of a chronic pro‐inflammatory phenotype. In this study, we used a mouse model of genetically enhanced NF‐κB activity (nfκb1−/−), characterized by low‐grade chronic inflammation and premature aging, to investigate the impact of inflammaging on cognitive decline. We found that during aging, nfkb1−/− mice show an early onset of memory loss, combined with enhanced neuroinflammation and increased frequency of senescent cells in the hippocampus and cerebellum. Electrophysiological measurements in the hippocampus of nfkb1−/− mice in vitro revealed deficits in gamma frequency oscillations, which could explain the decline in memory capacity. Importantly, treatment with the nonsteroidal anti‐inflammatory drug (NASID) ibuprofen reduced neuroinflammation and senescent cell burden resulting in significant improvements in cognitive function and gamma frequency oscillations. These data support the hypothesis that chronic inflammation is a causal factor in the cognitive decline observed during aging.

AbstractOne of the hallmarks of aging is the progressive accumulation of senescent cells in organisms, which has been proposed to be a contributing factor to age‐dependent organ dysfunction. We recently reported that Bruton's tyrosine kinase (BTK) is an upstream component of the p53 responses to DNA damage. BTK binds to and phosphorylates p53 and MDM2, which results in increased p53 activity. Consistent with this, blocking BTK impairs p53‐induced senescence. This suggests that sustained BTK inhibition could have an effect on organismal aging by reducing the presence of senescent cells in tissues. Here, we show that ibrutinib, a clinically approved covalent inhibitor of BTK, prolonged the maximum lifespan of a Zmpste24−/− progeroid mice, which also showed a reduction in general age‐related fitness loss. Importantly, we found that certain brain functions were preserved, as seen by reduced anxiety‐like behaviour and better long‐term spatial memory. This was concomitant to a decrease in the expression of specific markers of senescence in the brain, which confirms a lower accumulation of senescent cells after BTK inhibition. Our data show that blocking BTK has a modest increase in lifespan in Zmpste24−/− mice and protects them from a decline in brain performance. This suggests that specific inhibitors could be used in humans to treat progeroid syndromes and prevent the age‐related degeneration of organs such as the brain.

Abstract Adipose tissue inflammation and dysfunction are associated with obesity‐related insulin resistance and diabetes, but mechanisms underlying this relationship are unclear. Although senescent cells accumulate in adipose tissue of obese humans and rodents, a direct pathogenic role for these cells in the development of diabetes remains to be demonstrated. Here, we show that reducing senescent cell burden in obese mice, either by activating drug‐inducible “suicide” genes driven by the p16 Ink4a promoter or by treatment with senolytic agents, alleviates metabolic and adipose tissue dysfunction. These senolytic interventions improved glucose tolerance, enhanced insulin sensitivity, lowered circulating inflammatory mediators, and promoted adipogenesis in obese mice. Elimination of senescent cells also prevented the migration of transplanted monocytes into intra‐abdominal adipose tissue and reduced the number of macrophages in this tissue. In addition, microalbuminuria, renal podocyte function, and cardiac diastolic function improved with senolytic therapy. Our results implicate cellular senescence as a causal factor in obesity‐related inflammation and metabolic derangements and show that emerging senolytic agents hold promise for treating obesity‐related metabolic dysfunction and its complications.

AbstractIncreased activation of the major pro‐inflammatory NF‐κB pathway leads to numerous age‐related diseases, including chronic liver disease (CLD). Rapamycin, an inhibitor of mTOR, extends lifespan and healthspan, potentially via suppression of inflammaging, a process which is partially dependent on NF‐κB signalling. However, it is unknown if rapamycin has beneficial effects in the context of compromised NF‐κB signalling, such as that which occurs in several age‐related chronic diseases. In this study, we investigated whether rapamycin could ameliorate age‐associated phenotypes in a mouse model of genetically enhanced NF‐κB activity (nfκb1−/−) characterized by low‐grade chronic inflammation, accelerated aging and CLD. We found that, despite showing no beneficial effects in lifespan and inflammaging, rapamycin reduced frailty and improved long‐term memory, neuromuscular coordination and tissue architecture. Importantly, markers of cellular senescence, a known driver of age‐related pathology, were alleviated in rapamycin‐fed animals. Our results indicate that, in conditions of genetically enhanced NF‐κB, rapamycin delays aging phenotypes and improves healthspan uncoupled from its role as a suppressor of inflammation.