White, Thomas A.

ABSTRACTCellular senescence is a biological mechanism of aging and age‐related diseases. The aim of this study was to examine whether senescence biomarkers are associated with frailty and physical function trajectories in patients undergoing kidney transplantation (KT). We also discussed the relationship between senescence biomarkers and KT function. In this multicenter study, we prospectively assessed plasma levels of senescence biomarkers, frailty as measured by the Physical Frailty Phenotype, and physical function as measured by the Short Physical Performance Battery prior to KT. Frailty, physical function, and KT function were also measured 1 year after KT. Variable associations were assessed using Cox and relaxed least absolute shrinkage and selection operation regression. The cohort consisted of 197 participants (mean age 53 ± 13 years, 61.4% male, and 80.2% White race). Higher pre‐KT levels of macrophage‐derived chemokine (MDC/CCL22) and growth differentiation factor‐15 (GDF‐15) were independently associated with less improvement in frailty and/or physical function during the first year after KT. Higher pre‐KT levels tumor necrosis factor receptor superfamily member 6 (FAS) and MMP‐9 levels were independently associated with lower KT function one year after KT. Pre‐KT cellular senescence may contribute to frailty, physical function, and kidney function trajectories during the first year after KT.

Abstract Obesity accelerates the onset and progression of age-related conditions. In preclinical models, obesity drives cellular senescence, a cell fate that compromises tissue health and function, in part through a robust and diverse secretome. In humans, components of the secretome have been used as senescence biomarkers that are predictive of age-related disease, disability, and mortality. Here, using biospecimens and clinical data from two large and independent cohorts of older adults, we tested the hypothesis that the circulating concentrations of senescence biomarkers are influenced by body mass index. After adjusting for age, sex, and race, we observed significant increases in activin A, Fas, MDC, PAI1, PARC, TNFR1, and VEGFA, and a significant decrease in RAGE, from normal weight, to overweight, to obesity body mass index categories by linear regression in both cohorts (all p < .05). These results highlight the influence of body mass index on circulating concentrations of senescence biomarkers.

ABSTRACT His domain protein tyrosine phosphatase (HD-PTP; also known as PTPN23) facilitates function of the endosomal sorting complexes required for transport (ESCRTs) during multivesicular body (MVB) formation. To uncover its role in physiological homeostasis, embryonic lethality caused by a complete lack of HD-PTP was bypassed through generation of hypomorphic mice expressing reduced protein, resulting in animals that are viable into adulthood. These mice exhibited marked lipodystrophy and decreased receptor-mediated signaling within white adipose tissue (WAT), involving multiple prominent pathways including RAS/MAPK, phosphoinositide 3-kinase (PI3K)/AKT and receptor tyrosine kinases (RTKs), such as EGFR. EGFR signaling was dissected in vitro to assess the nature of defective signaling, revealing decreased trans-autophosphorylation and downstream effector activation, despite normal EGF binding. This corresponds to decreased plasma membrane cholesterol and increased lysosomal cholesterol, likely resulting from defective endosomal maturation necessary for cholesterol trafficking and homeostasis. The ESCRT components Vps4 and Hrs have previously been implicated in cholesterol homeostasis; thus, these findings expand knowledge on which ESCRT subunits are involved in cholesterol homeostasis and highlight a non-canonical role for HD-PTP in signal regulation and adipose tissue homeostasis.

Background: Tissue factor pathway inhibitor (TFPI) is a key regulator of the tissue factor/factor VIIa complex. Systemic genetic disruption of TFPI exon 4 results in intrauterine lethality in mice. As such, the ability to study the biologic and tissue specific effects of TFPI deficiency has been limited. To define the tissue specific roles of TFPI we utilized a Cre-lox strategy and generated mice with flanking loxP sites surrounding exon 4 (encodes for the K1 domain). Homozygous floxed mice (TFPI Flox ) were crossed with the Tie2 Cre + or LysM Cre + mice and subsequently inbred to create homozygously floxed mice expressing Cre (TFPI Tie2 or TFPI LysM ). Methods and Results: The presence and efficiency of the deleted mRNA product was determined by RT-PCR. TFPI Tie2 and TFPI LysM mice were phenotypically similar to TFPI Flox littermates including weight, blood counts, and prothrombin and activated partial thromboplastin times. TFPI Tie2 mice have complete deletion in endothelial cells, blood cells and bone marrow cells. TFPI LysM mice show partial deletion in blood cells and complete deletion in macrophages. TFPI Tie2 mice had a 60% reduction (P < 0.0001) in circulating TFPI activity compared to TFPI Flox littermate controls. TFPI LysM mice did not have a significant reduction in circulating TFPI activity levels compared to their TFPI Flox counterparts. Neither TFPI Tie2 nor TFPI LysM mice had significant changes in hemostasis compared to TFPI Flox mice as determined by a tail bleeding assay. In an ADP-induced model of thromboembolism there were no significant changes in mortality between the TFPI Tie2 or TFPI LysM and their TFPI Flox littermates. In a ferric chloride model of arterial thrombosis, TFPI Tie2 mice had a significant reduction (P < 0.05) in time to occlusion while TFPI LysM mice did not differ compared to TFPI Flox mice. Conclusions: Deletion of TFPI from cells expressing Tie2 or LysM is consistent with normal development and hemostasis. TFPI Tie2 mice have decreased circulating levels of TFPI and an enhanced thrombotic response to ferric chloride. These data support an important regulatory role for EC TFPI in arterial thrombosis.

Abstract Aging, a major risk factor for delirium, is associated with accumulation of senescent cells in many tissues of the body. Senescent cells produce a host of proinflammatory and tissue remodeling factors collectively termed the senescence-associated secretory phenotype (SASP), which are secreted into circulation. The relationship between increased senescent cell burden and risk of delirium is not known. This study aimed to determine whether changes in circulating SASP proteins are associated with increased risk of postoperative delirium in cognitively intact older adults. Participants were recruited among patients scheduled for surgical or transcatheter aortic valve replacement, and blood was obtained at the presurgical visit. SASP factors were measured using commercially available multiplex magnetic bead immunoassays based on Luminex xMAP multianalyte profiling platform and analyzed on a MAGPIX system. Activin A concentration was determined by a Quantikine ELISA kit. Delirium cases were identified by manual chart abstraction, utilizing the problem list, ICD-10 codes, clinical notes, and nursing flowsheets. Eight of 62 (12.9%) of patients within the cohort developed postoperative delirium. Length of stay was significantly longer for patients who developed delirium (10.6 days) versus patients without delirium (6 days). Concentrations of SASP factors Activin A and PAPP-A were significantly higher in plasma of patients with delirium vs. those who did not develop delirium. IL-1 alpha concentration was significantly lower in patients with delirium vs without delirium. Other SASP factors measured were not statistically different between groups. More study is needed to determine whether these changes are directly related to increased senescent cell burden.

AbstractSenescent cells compromise tissue structure and function in older organisms. We recently identified senescent fibroadipogenic progenitors (FAPs) with activated chemokine signaling pathways in the skeletal muscle of old mice, and hypothesized these cells may contribute to the age‐associated accumulation of immune cells in skeletal muscle. In this study, through cell–cell communication analysis of skeletal muscle single‐cell RNA‐sequencing data, we identified unique interactions between senescent FAPs and macrophages, including those mediated by Ccl2 and Spp1. Using mouse primary FAPs in vitro, we verified increased expression of Ccl2 and Spp1 and secretion of their respective proteins in the context of both irradiation‐ and etoposide‐induced senescence. Compared to non‐senescent FAPs, the medium of senescent FAPs markedly increased the recruitment of macrophages in an in vitro migration assay, an effect that was mitigated by preincubation with antibodies to either CCL2 or osteopontin (encoded by Spp1). Further studies demonstrated that the secretome of senescent FAPs promotes polarization of macrophages toward an M2 subtype. These data suggest the unique secretome of senescent FAPs may compromise skeletal muscle homeostasis by recruiting and directing the behavior of macrophages.

Cachexia is a debilitating skeletal muscle wasting condition for which we currently lack effective treatments. In the context of cancer, certain chemotherapeutics cause DNA damage and cellular senescence. Senescent cells exhibit chronic activation of the transcription factor NF-κB, a known mediator of the proinflammatory senescence-associated secretory phenotype (SASP) and skeletal muscle atrophy. Thus, targeting NF-κB represents a logical therapeutic strategy to alleviate unintended consequences of genotoxic drugs. Herein, we show that treatment with the IKK/NF-κB inhibitor SR12343 during a course of chemotherapy reduces markers of cellular senescence and the SASP in liver, skeletal muscle, and circulation and, correspondingly, attenuates features of skeletal muscle pathology. Lastly, we demonstrate that SR12343 mitigates chemotherapy-induced reductions in body weight, lean mass, fat mass, and muscle strength. These findings support senescent cells as a promising druggable target to counteract the SASP and skeletal muscle wasting in the context of chemotherapy.

Abstract Calorie restriction (CR) with adequate nutrient intake is a potential geroprotective intervention. To advance this concept in humans, we tested the hypothesis that moderate CR in healthy young‐to‐middle‐aged individuals would reduce circulating biomarkers of cellular senescence, a fundamental mechanism of aging and aging‐related conditions. Using plasma specimens from the Comprehensive Assessment of Long‐term Effects of Reducing Intake of Energy (CALERIE™) phase 2 study, we found that CR significantly reduced the concentrations of several senescence biomarkers at 12 and 24 months compared to an ad libitum diet. Using machine learning, changes in biomarker concentrations emerged as important predictors of the change in HOMA‐IR and insulin sensitivity index at 12 and 24 months, and the change in resting metabolic rate residual at 12 months. Finally, using adipose tissue RNA‐sequencing data from a subset of participants, we observed a significant reduction in a senescence‐focused gene set in response to CR at both 12 and 24 months compared to baseline. Our results advance the understanding of the effects of CR in humans and further support a link between cellular senescence and metabolic health.

Abstract Studies in mice and cross-sectional studies in humans support the premise that cellular senescence is a contributing mechanism to age-associated deficits in physical function. We tested the hypotheses that circulating proteins secreted by senescent cells are (i) associated with the incidence of major mobility disability (MMD), the development of persistent mobility disability (PMMD), and decrements in physical functioning in older adults, and (ii) influenced by physical activity (PA). Using samples and data obtained longitudinally from the Lifestyle Interventions in Elders Study clinical trial, we measured a panel of 27 proteins secreted by senescent cells. Among 1 377 women and men randomized to either a structured PA intervention or a healthy aging (HA) intervention, we observed significant associations between several senescence biomarkers, most distinctly vascular endothelial growth factor A (VEGFA), tumor necrosis factor receptor 1 (TNFR1), and matrix metallopeptidase 7 (MMP7), and the onset of both MMD and PMMD. Moreover, VEGFA, GDF15, osteopontin, and other senescence biomarkers were associated with reductions in short physical performance battery scores. The change in senescence biomarkers did not differ between PA and HA participants. In the whole cohort, higher levels of PA were associated with significantly greater reductions in 10 senescence-related proteins at 12 and/or 24 months. These data reinforce cellular senescence as a contributing mechanism of age-associated functional decline and the potential for PA to attenuate this hallmark of aging. Clinical Trials Registration Number: NCT01072500

AbstractA robust and heterogenous secretory phenotype is a core feature of most senescent cells. In addition to mediators of age‐related pathology, components of the senescence associated secretory phenotype (SASP) have been studied as biomarkers of senescent cell burden and, in turn, biological age. Therefore, we hypothesized that circulating concentrations of candidate senescence biomarkers, including chemokines, cytokines, matrix remodeling proteins, and growth factors, could predict mortality in older adults. We assessed associations between plasma levels of 28 SASP proteins and risk of mortality over a median follow‐up of 6.3 years in 1923 patients 65 years of age or older with zero or one chronic condition at baseline. Overall, the five senescence biomarkers most strongly associated with an increased risk of death were GDF15, RAGE, VEGFA, PARC, and MMP2, after adjusting for age, sex, race, and the presence of one chronic condition. The combination of biomarkers and clinical and demographic covariates exhibited a significantly higher c‐statistic for risk of death (0.79, 95% confidence interval (CI): 0.76–0.82) than the covariates alone (0.70, CI: 0.67–0.74) (p < 0.001). Collectively, these findings lend further support to biomarkers of cellular senescence as informative predictors of clinically important health outcomes in older adults, including death.