Kirkland, James L.

Abstract Aging causes functional decline of multiple organs and increases the risk of age-related pathologies. In advanced lives, accumulation of senescent cells, which develop the senescence-associated secretory phenotype (SASP), promotes chronic inflammation and causes diverse conditions. Here we report the frontline outcome of screening a natural product library with human primary stromal cells as an experimental model. Multiple candidate compounds were assayed, and grape seed extract (GSE) was selected for further investigation due to its leading capacity in targeting senescent cells. We found procyanidin C1 (PCC1), a polyphenolic component, plays a critical role in mediating the antiaging effects of GSE. PCC1 blocks the SASP expression when used at low concentrations. Importantly, it selectively kills senescent cells upon application at higher concentrations, mainly by enhancing production of reactive oxygen species (ROS) and disturbing mitochondrial membrane potential, processes accompanied by upregulation of Bcl-2 family pro-apoptotic factors Puma and Noxa in senescent cells. PCC1 depletes senescent cells in treatment-damaged tumor microenvironment (TME) and enhances therapeutic efficacy when combined with chemotherapy in preclinical assays. Intermittent administration of PCC1 to both senescent cell-implanted mice and naturally aged animals alleviated physical dysfunction and prolonged post-treatment survival, thus providing substantial benefits in late life stage. Together, our study identifies PCC1 as a distinct natural senolytic agent, which may be exploited to delay aging and control age-related pathologies in future medicine.

Mesenchymal stem/stromal cells (MSCs) facilitate repair in experimental diabetic kidney disease (DKD). However, the hyperglycemic and uremic milieu may diminish regenerative capacity of patient-derived therapy. We hypothesized that DKD reduces human MSC paracrine function. Adipose-derived MSC from 38 participants with DKD and 16 control subjects were assessed for cell surface markers, trilineage differentiation, RNA sequencing (RNA-seq), in vitro function (coculture or conditioned medium experiments with T cells and human kidney cells [HK-2]), secretome profile, and cellular senescence abundance. The direction of association between MSC function and patient characteristics were also tested. RNA-seq analysis identified 353 differentially expressed genes and downregulation of several immunomodulatory genes/pathways in DKD-MSC versus Control-MSC. DKD-MSC phenotype, differentiation, and tube formation capacity were preserved, but migration was reduced. DKD-MSC with and without interferon-γ priming inhibited T-cell proliferation greater than Control-MSC. DKD-MSC medium contained higher levels of anti-inflammatory cytokines (indoleamine 2,3-deoxygenase 1 and prostaglandin-E2) and prorepair factors (hepatocyte growth factor and stromal cell–derived factor 1) but lower IL-6 versus control-MSC medium. DKD-MSC medium protected high glucose plus transforming growth factor-β–exposed HK-2 cells by reducing apoptotic, fibrotic, and inflammatory marker expression. Few DKD-MSC functions were affected by patient characteristics, including age, sex, BMI, hemoglobin A1c, kidney function, and urine albumin excretion. However, senescence-associated β-galactosidase activity was lower in DKD-MSC from participants on metformin therapy. Therefore, while DKD altered the transcriptome and migratory function of culture-expanded MSCs, DKD-MSC functionality, trophic factor secretion, and immunomodulatory activities contributing to repair remained intact. These observations support testing of patient-derived MSC therapy and may inform preconditioning regimens in DKD clinical trials.

Abstract Cellular senescence is an essential tumor suppressive mechanism that prevents the propagation of oncogenically activated, genetically unstable, and/or damaged cells. Induction of tumor cell senescence is also one of the underlying mechanisms by which cancer therapies exert antitumor activity. However, an increasing body of evidence from preclinical studies demonstrates that radiation and chemotherapy cause accumulation of senescent cells (SnCs) both in tumor and normal tissue. SnCs in tumors can, paradoxically, promote tumor relapse, metastasis, and resistance to therapy, in part, through expression of the senescence-associated secretory phenotype. In addition, SnCs in normal tissue can contribute to certain radiation- and chemotherapy-induced side effects. Because of its multiple roles, cellular senescence could serve as an important target in the fight against cancer. This commentary provides a summary of the discussion at the National Cancer Institute Workshop on Radiation, Senescence, and Cancer (August 10-11, 2020, National Cancer Institute, Bethesda, MD) regarding the current status of senescence research, heterogeneity of therapy-induced senescence, current status of senotherapeutics and molecular biomarkers, a concept of “one-two punch” cancer therapy (consisting of therapeutics to induce tumor cell senescence followed by selective clearance of SnCs), and its integration with personalized adaptive tumor therapy. It also identifies key knowledge gaps and outlines future directions in this emerging field to improve treatment outcomes for cancer patients.

Key points Critical illness myopathy (CIM) is a frequently observed negative consequence of modern critical care. Chronic Janus kinase (JAK)/signal transducer and activator of transcription activation impairs muscle size and function and is prominent following mechanical ventilation. We identify pSTAT‐3 activation in tibialis anterior of CIM patients, before examining the potential benefits of JAK1/2 inhibition in an experimental model of CIM, where muscle mass and function are impaired. CIM activates complement cascade and increased monocyte infiltration in the soleus muscle, which was ameliorated by JAK1/2 inhibition, leading to reduced muscle degeneration and improved muscle force. Here, we demonstrate that JAK1/2 inhibition augments CIM muscle function through regulation of the complement cascade. AbstractCritical illness myopathy (CIM) is frequently observed in response to modern critical care with negative consequences for patient quality of life, morbidity, mortality and healthcare costs. Janus kinase (JAK)/signal transducer and activator of transcription (STAT) activation is observed in limb muscles following controlled mechanical ventilation. Chronic JAK/STAT activation promotes loss of muscle mass and function. Thus, we hypothesized that JAK1/2 inhibition would improve muscle outcomes for CIM. Following 12 days of intensive care unit conditions, pSTAT‐3 levels increased in tibialis anterior muscle of CIM patients (P = 0.0489). The potential of JAK1/2 inhibition was assessed in an experimental model of CIM, where soleus muscle size and force are impaired. JAK1/2 inhibition restores soleus force (P < 0.0001). CIM activated muscle complement cascade, which was ameliorated by JAK1/2 inhibition (P < 0.05, respectively). Soleus macrophage number corresponded with complement activity, leading to reduced muscle degeneration and augmented muscle function (P < 0.05). Thus, JAK/STAT inhibition improves soleus function by modulating the complement cascade and muscle monocyte infiltration. Collectively, we demonstrate that JAK/STAT inhibition augments muscle function in CIM.

Abstract Therapeutics that target cellular senescence, including novel “senolytic” compounds, hold significant promise for treating or preventing obesity-induced metabolic dysfunction, type 2 diabetes, and the multiple complications of diabetes and obesity. Senolytics selectively clear senescent cells, which accumulate with aging and obesity and represent a fundamental mechanism of aging that contributes to metabolic dysfunction and diabetes pathogenesis. In addition to improving metabolic function, targeting senescent cells holds promise as a preventive strategy to reduce the incidence and severity of diabetes complications. The intermittent administration schedule used for senolytic therapy may confer benefits in terms of improving adherence and limiting adverse effects. It is necessary to design effective clinical trials that will safely translate discoveries from preclinical models into human studies that may pave the way for a novel therapeutic class for treating obesity, diabetes, and their complications. In this review, we outline what is known regarding the role of cellular senescence in the pathogenesis of type 2 diabetes and its complications, present evidence from preclinical models that targeting cellular senescence is beneficial, review senolytic drugs, and outline the features of clinical trials investigating the role of targeting senescent cells for diabetes.

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 Cellular senescence contributes to age-related disorders including physical dysfunction, disabilities, and mortality caused by tissue inflammation and damage. Senescent cells accumulate in multiple tissues with aging and at etiological sites of multiple chronic disorders. The senolytic drug combination, Dasatinib plus Quercetin (D+Q), is known to reduce senescent cell abundance in aged mice. However, the effects of long-term D+Q treatment on intestinal senescent cell and inflammatory burden and microbiome composition in aged mice remain unknown. Here, we examine the effect of D+Q on senescence (p16Ink4a and p21Cip1) and inflammation (Cxcl1, Il1β, Il6, Mcp1, and Tnfα) markers in small (ileum) and large (caecum and colon) intestine in aged mice (n = 10) compared to age-matched placebo-treated mice (n = 10). Additionally, we examine microbial composition along the intestinal tract in these mice. D+Q-treated mice show significantly lower senescent cell (p16 and p21 expression) and inflammatory (Cxcl1, Il1β, Il6, Mcp1, and Tnfα expression) burden in small and large intestine compared with control mice. Further, we find specific microbial signatures in ileal, cecal, colonic, and fecal regions that are distinctly modulated by D+Q, with modulation being most prominent in small intestine. Further analyses reveal specific correlation of senescence and inflammation markers with specific microbial signatures. Together, these data demonstrate that the senolytic treatment reduces intestinal senescence and inflammation while altering specific microbiota signatures and suggest that the optimized senolytic regimens might improve health via reducing intestinal senescence, inflammation, and microbial dysbiosis in older subjects.

Abstract Aging is the leading risk factor for many chronic diseases. Through traditional approaches to drug development and treatment focus on treating one disease at a time, the geroscience hypothesis posits that by targeting fundamental aging processes one could alleviate multiple age-related diseases. Now several geroscience-guided interventions are at the point of entering human clinical trials. To accelerate testing of this important hypothesis, an interdisciplinary Translational Geroscience Network (TGN; R33 AG061456) has recently been established. The TGN is a new national resource of aging research centers committed to working together toward complementary, small-scale, proof-of-concept “use case” clinical studies. One such pilot will be highlighted: a translational trial of senolytics, or drugs targeting the biological aging process cellular senescence in patients with idiopathic pulmonary fibrosis. The promise of geroscience provides another reason “why age matters”: by studying the basic biology of aging, we may open novel therapeutic opportunities for challenging age-related diseases.

Abstract Senescent cells (SC) accumulate with aging and at causal sites of multiple chronic disorders and diseases, including those accounting for the bulk of morbidity, mortality, and health expenditures. SC do not replicate. Some SC release factors that cause tissue dysfunction, the senescence-associated secretory phenotype (SASP). Transplanting small numbers of SC into younger mice to above a critical threshold leads to frailty, early onset of multiple age-related diseases, and premature death. A report in 2004 showing caloric restriction causes both healthspan extension and delayed SC accumulation prompted us to begin efforts to discover senolytic drugs, agents that selectively eliminate SC. We used a hypothesis-driven, mechanism-based strategy to discover senolytics, reasoning that senescent cell anti-apoptotic pathways (SCAPs) exist that defend SC against their own SASP, allowing them to survive, despite killing neighboring cells. Senolytics cause SC apoptosis by transiently disabling these SCAPs. Because SC take weeks to re-accumulate, senolytics can be administered intermittently – a “hit-and-run” approach. Senolytics delay, prevent, or alleviate frailty and cardiovascular, neuropsychiatric, liver, kidney, musculoskeletal, lung, eye, hematological, metabolic, and skin disorders as well as complications of organ transplantation, radiation, and cancer treatment in pre-clinical models. As anticipated for agents targeting the fundamental aging mechanisms that are “root cause” contributors to multiple disorders, potential uses of senolytics are protean, potentially alleviating over 40 conditions in preclinical studies, opening a new route for treating age-related dysfunction and diseases. We review the discovery of senolytics and potential strategies for translation into the clinic. Early trials indicate effectiveness of senolytics in humans.

Abstract Aging is the biggest risk factor for the most serious chronic diseases and disabilities. Cellular senescence, a state in which cells stop dividing but release factors that damage other cells, may contribute to both age-related and chronic diseases. Removal of senescent cells from aged mice has been shown to delay aging and age–related disabilities. Our goal was to determine the ability of potential senolytic agents to remove senescent cells in a primate model. Several agents and combinations were tested including Fisetin, Navitoclax, combined Dasatinib and Quercetin, and combined Dasatinib and Fisetin. Here we describe the Dasatinib and Fisetin trial. Dasatinib is an FDA approved oral anticancer drug that has been used to treat chronic myelogenous leukemia in humans. Fisetin is a flavonoid that can be found in many plants, particularly strawberries, and acts as a coloring agent. After baseline measurements, six older (mean age=21 years) female rhesus monkeys (Macaca mulatta) were given a combined oral dose of Dasatinib (5 mg/kg) and Fisetin (100 mg/kg) on two consecutive days. Animals were additionally assessed at 1- and 7-weeks following dosing. At 7 weeks post dosing, there were fewer (p&lt;0.05) p16+ cells in the epidermis compared to baseline. Similarly, there was a reduction (p&lt;0.05) in p21+ cells in the epidermis at 1- and 7-weeks post dosing compared to baseline. There were no negative outcomes associated with treatment. This study provides preliminary evidence for the senolytic potential of combined Dasatinib and Fisetin treatment and indicates that pharmacological mitigation of age-related changes is possible.