Tripathi, Utkarsh

ABSTRACT The senescent cell (SC) fate is linked to aging, multiple disorders and diseases, and physical dysfunction. Senolytics, agents that selectively eliminate 30%–70% of SCs, act by transiently disabling the senescent cell antiapoptotic pathways (SCAPs), which defend those SCs that are proapoptotic and pro‐inflammatory from their own senescence‐associated secretory phenotype (SASP). Consistent with this, a JAK/STAT inhibitor, Ruxolitinib, which attenuates the pro‐inflammatory SASP of senescent human preadipocytes, caused them to become “senolytic‐resistant”. Administering senolytics to obese mice selectively decreased the abundance of the subset of SCs that is pro‐inflammatory. In cell cultures, the 30%–70% of human senescent preadipocytes or human umbilical vein endothelial cells (HUVECs) that are senolytic‐resistant (to Dasatinib or Quercetin, respectively) had increased p16 INK4a , p21 CIP1 , senescence‐associated β‐galactosidase (SAβgal), γH2AX, and proliferative arrest similarly to the total SC population (comprising senolytic‐sensitive plus‐resistant SCs). However, the SASP of senolytic‐resistant SCs entailed less pro‐inflammatory/apoptotic factor production, induced less inflammation in non‐senescent cells, and was equivalent or richer in growth/fibrotic factors. Senolytic‐resistant SCs released less mitochondrial DNA (mtDNA) and more highly expressed the anti‐inflammatory immune evasion signal, glycoprotein non‐melanoma‐B (GPNMB). Transplanting senolytic‐resistant SCs intraperitoneally into younger mice caused less physical dysfunction than transplanting the total SC population. Because Ruxolitinib attenuates SC release of proapoptotic SASP factors, while pathogen‐associated molecular pattern factors (PAMPs) can amplify the release of these factors rapidly (acting as “senosensitizers”), senolytic‐resistant and senolytic‐sensitive SCs appear to be interconvertible.

ABSTRACT Objective Aging alters mesenchymal stromal cell (MSC) function, leading to dysregulated adipogenesis across tissues through biased lineage commitment. Fat redistribution from adipose depots to skeletal muscle and bone marrow is common in aging, but the underlying mechanisms remain unclear. This study investigates how MSC senescence modulates adipogenesis. Methods Primary MSCs were isolated from mouse skeletal muscle (FAPs), adipose tissue (APCs), and bone marrow (BMSCs). Single‐cell RNA sequencing was performed to compare transcriptional profiles among these populations. In vitro adipogenic differentiation and DNA damage–induced senescence assays were conducted, and the effects of autologous conditioned media from senescent MSCs on adipogenesis were assessed. Results Transcriptional analyses revealed that FAPs and APCs share greater similarity with each other than with BMSCs. All MSC types exhibited adipogenic potential and developed a robust senescence‐associated secretory phenotype (SASP) upon senescence induction. Conditioned media from senescent MSCs enhanced adipogenesis in BMSCs but inhibited adipogenesis in FAPs and APCs, revealing tissue‐specific paracrine effects. Conclusions MSC senescence reprograms adipogenic bias in a tissue‐dependent, non–cell autonomous manner, contributing to age‐related fat redistribution among adipose tissue, skeletal muscle, and bone marrow. Understanding these mechanisms may provide new therapeutic approaches for improving tissue composition and function in the context of aging.

Abstract Multiple changes occur in hormonal regulation with aging and across various endocrine organs. These changes are associated with multiple age-related disorders and diseases. A better understanding of responsible underling biological mechanisms could help in the management of multiple endocrine disorders over and above hormone replacement therapy (HRT). Cellular senescence is involved in multiple biological aging processes and pathologies common in elderly individuals. Cellular senescence, which occurs in many older individuals but also across the lifespan in association with tissue damage, acute and chronic diseases, certain drugs, and genetic syndromes, may contribute to such endocrine disorders as osteoporosis, metabolic syndrome, and type 2 diabetes mellitus. Drugs that selectively induce senescent cell removal, “senolytics,”, and drugs that attenuate the tissue-destructive secretory state of certain senescent cells, “senomorphics,” appear to delay the onset of or alleviate multiple diseases, including but not limited to endocrine disorders such as diabetes, complications of obesity, age-related osteoporosis, and cancers as well as atherosclerosis, chronic kidney disease, neurodegenerative disorders, and many others. More than 30 clinical trials of senolytic and senomorphic agents have already been completed, are underway, or are planned for a variety of indications. Targeting senescent cells is a novel strategy that is distinct from conventional therapies such as HRT, and thus might address unmet medical needs and can potentially amplify effects of established endocrine drug regimens, perhaps allowing for dose decreases and reducing side effects.

Aging is the leading predictor of acquired cardiovascular disease (CVD), and emerging evidence suggests cellular senescence plays a causal role in development of clinically-significant CVD. While we previously reported that senescent cell elimination delays or prevents progression of several aging phenotypes in aging mice, the responsible types of senescent cells contributing to cardiovascular dysfunction in vivo are not yet elucidated. To test the hypothesis that senescent endothelial cells are a major contributor to cardiovascular dysfunction, we developed Tie2-Cre; p16 Ink4a - LOX-ATTAC mice, which allows for specific elimination of p16 Ink4a+ senescent endothelial cells upon administration of AP20187 (which only affects cells carrying the conditionally-expressed ATTAC construct). Using a mouse model of diabetic vascular disease (40% fat diet for 12 weeks , HFD), we found that biweekly selective removal of senescent endothelial cells alleviated HFD-induced endothelial dysfunction in aorta (assessed ex vivo using isolated organ baths). Additionally, ejection fraction (assessed using in vivo echocardiography) was preserved in AP20187-treated mice (driving ATTAC-dependent removal of senescent endothelial cells) compared to their vehicle-treated controls (76.6%±4.2, 63.2%±4.2). In addition to improvement in cardiovascular function, metabolic parameters (HbA1c and fasting glucose levels) were improved by senescent endothelial cell elimination. Collectively, these data suggest that elimination of p16 Ink4a+ senescent endothelial cells may be a viable therapeutic strategy for alleviation of metabolic disease-induced cardiovascular dysfunction.

Abstract Decreased α-Klotho, a geroprotective factor, and increased senescent cell burden are both associated with early onset of physical disability, cognitive impairment, and premature all-cause mortality. It has been demonstrated that eliminating senescent cells can enhance physical function, cognition, and survival in mice, as does overexpressing α-Klotho. Mice with low α-Klotho exhibit accelerated senescent cell accumulation, recombinant α-Klotho decreases senescent cell burden and restores lifespan in these mice, and senescent epidermal cells are reduced in mice overexpressing α-Klotho. Here, we tested the hypothesis that senescent cells cause decreased α-Klotho and hence that reducing senescent cells can increase α-Klotho. Senescent cell conditioned medium (CM) reduced α-Klotho in cultured non-senescent human umbilical vein endothelial cells (HUVECs), renal tubular endothelial cells, and astrocytes. These effects of senescent CM were partially attenuated by neutralizing antibodies against the senescence-associated secretory phenotype (SASP) factors, activin A and IL-1α. Transplanting senescent cells into younger mice caused decreased urine and brain α-Klotho. Genetically reducing highly p16Ink4a-expressing cells in old INK-ATTAC mice or administering the senolytics, Dasatinib plus Quercetin (D+Q) or Fisetin (F), to young mice transplanted with senescent cells, young diet-induced obese (DIO) mice, or naturally-aged mice increased urine, kidney, and/or brain α-Klotho. Treating patients with idiopathic pulmonary fibrosis (IPF), a cellular senescence-related disease, with D+Q led to increased urinary α-Klotho. Thus, targeting senescent cells causes increases in the geroprotective factor α-Klotho, potentially amplifying the beneficial effects of senolytic drugs.

Senescent cells exacerbate COVID-19 Cellular senescence is a state elicited in response to stress signals and is associated with a damaging secretory phenotype. The number of senescent cells increases with advanced age and this in turn drives age-related diseases. Camell et al. show that senescent cells have an amplified inflammatory response to severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) (see the Perspective by Cox and Lord). This response is communicated to nonsenescent cells, suppressing viral defense mechanisms and increasing the expression of viral entry proteins. In old mice infected with a SARS-CoV-2–related virus, treatment with senolytics to reduce the senolytic cell burden reduced mortality and increased antiviral antibodies. Science , abe4832, this issue p. eabe4832 ; see also abi4474, p. 281