Citations

ABSTRACT Estrogen deficiency is a seminal mechanism in the pathogenesis of osteoporosis. Mounting evidence, however, establishes that cellular senescence, a fundamental mechanism that drives multiple age-related diseases, also causes osteoporosis. Recently, we systematically identified an accumulation of senescent cells, characterized by increased p16Ink4a and p21Cip1 levels and development of a senescence-associated secretory phenotype (SASP), in mouse bone/marrow and human bone with aging. We then demonstrated that elimination of senescent cells prevented age-related bone loss using multiple approaches, eg, treating old mice expressing a “suicide” transgene, INK-ATTAC, with AP20187 to induce apoptosis of p16Ink4a-senescent cells or periodically treating old wild-type mice with “senolytics,” ie, drugs that eliminate senescent cells. Here, we investigate a possible role for estrogen in the regulation of cellular senescence using multiple approaches. First, sex steroid deficiency 2 months after ovariectomy (OVX, n = 15) or orchidectomy (ORCH, n = 15) versus sham surgery (SHAM, n = 15/sex) in young adult (4-month-old) wild-type mice did not alter senescence biomarkers or induce a SASP in bone. Next, in elderly postmenopausal women, 3 weeks of estrogen therapy (n = 10; 74 ± 5 years) compared with no treatment (n = 10; 78 ± 5 years) did not alter senescence biomarkers or the SASP in human bone biopsies. Finally, young adult (4-month-old) female INK-ATTAC mice were randomized (n = 17/group) to SHAM+Vehicle, OVX+Vehicle, or OVX+AP20187 for 2 months. As anticipated, OVX+Vehicle caused significant trabecular/cortical bone loss compared with SHAM+Vehicle. However, treatment with AP20187, which eliminates senescent cells in INK-ATTAC mice, did not rescue the OVX-induced bone loss or alter senescence biomarkers. Collectively, our data establish independent roles of estrogen deficiency and cellular senescence in the pathogenesis of osteoporosis, which has important implications for testing novel senolytics for skeletal efficacy, as these drugs will need to be evaluated in preclinical models of aging as opposed to the current FDA model of prevention of OVX-induced bone loss. © 2019 American Society for Bone and Mineral Research.

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.

Abstract Aging leads to increased cellular senescence and is associated with decreased potency of tissue‐specific stem/progenitor cells. Here, we have done an extensive analysis of cardiac progenitor cells (CPCs) isolated from human subjects with cardiovascular disease, aged 32–86 years. In aged subjects (>70 years old), over half of CPCs are senescent (p16 INK4A , SA‐β‐gal, DNA damage γH2AX, telomere length, senescence‐associated secretory phenotype [SASP]), unable to replicate, differentiate, regenerate or restore cardiac function following transplantation into the infarcted heart. SASP factors secreted by senescent CPCs renders otherwise healthy CPCs to senescence. Elimination of senescent CPCs using senolytics abrogates the SASP and its debilitative effect in vitro. Global elimination of senescent cells in aged mice (INK‐ATTAC or wild‐type mice treated with D + Q senolytics) in vivo activates resident CPCs and increased the number of small Ki67‐, EdU‐positive cardiomyocytes. Therapeutic approaches that eliminate senescent cells may alleviate cardiac deterioration with aging and restore the regenerative capacity of the heart.

Abstract Aim Critical illness myopathy ( CIM ) is a consequence of modern critical care, leading to skeletal muscle atrophy/paralysis with negative consequences for mortality/morbidity and health care costs. Glucocorticoids ( GC s) have been proposed to trigger CIM . Here, we compare outcomes of two GC s, the commonly used prednisolone and the newly developed dissociative vamorolone in response to the intensive care unit ( ICU ) condition for 5 days, ie, sedation, immobilization, and mechanical ventilation. Methods Rats were divided into a 0‐day sham‐operated control group, and three groups exposed to 5 days ICU condition during treatment with prednisolone ( PRED ) or vamorolone ( VAM ) or none of these GC s ( ICU ‐group). Survival, body and muscle weights, cytokine concentrations, regulation of muscle contraction in single fast‐ and slow‐twitch muscle fibres, myofibrillar protein expression and protein degradation pathways were studied. Results Critical illness myopathy geno‐ and pheno‐types were confirmed in the ICU group. However, VAM and PRED groups showed reduced atrophy/weakness than the ICU group, and muscle specific differences with more severe negative effects on fast‐twitch muscle fibres in the PRED than the other groups. Conclusion These results show that vamorolone provides a GC intervention superior to typical GC s in improving CIM outcomes. Further, the findings do not support the notion that moderate‐dose GC treatment represents a factor triggering CIM .

There is no therapy that promotes maturation and functionality of a dialysis arteriovenous fistula (AVF). The search for such therapies largely relies on evaluation of vascular responses and putative therapies in experimental AVFs. We studied an AVF in mice with chronic kidney disease (CKD). We demonstrate numerous stressors in the vein of the AVF-CKD group, including pathological shear, mitogenic, inflammatory, and hypoxia-reoxygenation stress. Because stress promotes premature senescence, we examined whether senescence is induced in the vein of the AVF-CKD model. We demonstrate a senescence phenotype in the AVF-CKD model, as indicated by increased expression of p16Ink4a, p21Cip1, and p53 and expected changes for certain senescence-associated microRNAs. RNA-sequencing analysis demonstrated differential expression of ~10,000 genes, including upregulation of proinflammatory and proliferative genes, in the vein of the AVF-CKD group. The vein in the AVF-CKD group exhibited telomere erosion and increased senescence-associated β-galactosidase activity and staining. Senescence was induced in the artery of the AVF-CKD group and in the vein of the AVF without CKD. Finally, given the rapidly rising clinical interest in senolytics, we provide proof of concept of senolytics as a therapeutic approach by demonstrating that senolytics decrease p16Ink4a expression in the AVF-CKD model. This study introduces a novel concept underlying the basis for maturational and functional failure in human dialysis AVFs and identifies a new target for senolytic therapy.

The improvement in survival of childhood cancer observed across the past 50 years has resulted in a growing acknowledgment that simply extending the lifespan of survivors is not enough. It is incumbent on both the cancer research and the clinical care communities to also improve the health span of survivors. It is well established that aging adult survivors of childhood cancer are at increased risk of chronic health conditions, relative to the general population. However, as the first generation of survivors age into their 50s and 60s, it has become increasingly evident that this population is also at risk of early onset of physiologic aging. Geriatric measures have uncovered evidence of reduced strength and speed and increased fatigue, all components of frailty, among survivors with a median age of 33 years, which is similar to adults older than 65 years of age in the general population. Furthermore, frailty in survivors independently increased the risk of morbidity and mortality. Although there has been a paucity of research investigating the underlying biologic mechanisms for advanced physiologic age in survivors, results from geriatric populations suggest five biologically plausible mechanisms that may be potentiated by exposure to cancer therapies: increased cellular senescence, reduced telomere length, epigenetic modifications, somatic mutations, and mitochondrial DNA infidelity. There is now a critical need for research to elucidate the biologic mechanisms of premature aging in survivors of childhood cancer. This research could pave the way for new frontiers in the prevention of these life-changing outcomes.

AbstractAimMuscle wasting is one of the factors most strongly predicting mortality and morbidity in critically ill intensive care unit (ICU). This muscle wasting affects both limb and respiratory muscles, but the understanding of underlying mechanisms and muscle‐specific differences remains incomplete. This study aimed at investigating the temporal expression and phosphorylation of the Janus kinase/signal transducer and activator of transcription (JAK/STAT) pathway in muscle wasting associated with the ICU condition to characterize the JAK/STAT proteins and the related changes leading or responding to their activation during exposure to the ICU condition.MethodsA novel experimental ICU model allowing long‐term exposure to the ICU condition, immobilization and mechanical ventilation, was used in this study. Rats were pharmacologically paralysed by post‐synaptic neuromuscular blockade and mechanically ventilated for durations varying between 6 hours and 14 days to study muscle‐specific differences in the temporal activation of the JAK/STAT pathway in plantaris, intercostal and diaphragm muscles.ResultsThe JAK2/STAT3 pathway was significantly activated irrespective of muscle, but muscle‐specific differences were observed in the temporal activation pattern between plantaris, intercostal and diaphragm muscles.ConclusionThe JAK2/STAT3 pathway was differentially activated in plantaris, intercostal and diaphragm muscles in response to the ICU condition. Thus, JAK2/STAT3 inhibitors may provide an attractive pharmacological intervention strategy in immobilized ICU patients, but further experimental studies are required in the study of muscle‐specific effects on muscle mass and function in response to both short‐ and long‐term exposure to the ICU condition prior to the translation into clinical research and practice.