Kirkland, James L.

ABSTRACT Cellular senescence is a stress response mechanism marked by irreversible growth arrest, upregulation of antiapoptotic pathways, loss of cellular function, and remodelling of the cellular secretory profile. In both humans and mice, pancreatic β-cells undergo senescence with age and insulin resistance. Targeted removal of senescent cells in mouse models of diabetes improves glucose homeostasis, demonstrating the role β-cell senescence in diabetes progression. In contrast, β-cell senescence also promotes immune surveillance, promoting β-cell survival and function. Thus, a better understanding of senescent cells’ phenotypic and functional heterogeneity is needed to develop effective therapeutic strategies. Herein, we show that subpopulations of senescent β-cells in mice and humans, which were identified through the expression of Cdkn1a (encoding p21 Cip1 ) and Cdkn2a (encoding p16 Ink4a ) by single-cell RNA sequencing (scRNA-seq), flow cytometry, spatial transcriptomics, and spatial proteomics, exhibit distinct transcriptional and functional identities. The predominant senescent β-cell subpopulation expressed Cdkn1a and was characterized by a lack of glucose responsiveness, high basal insulin secretion, and transcription of canonical SASP factors. The SASP of Cdkn1a -expressing β-cells had non-cell autonomous effects on neighbouring cells. A subset of four SASP factors from Cdkn1a + cells was sufficient to induce secondary senescence and β-cell dysfunction in vitro . JAK inhibitors (JAK1/2 and JAK1/3) counteracted secondary senescence induction and restored β-cell function in high-fat diet-fed mice and human islets from donors with or without type 2 diabetes. GRAPHICAL ABSTRACT

Marfan Syndrome (MFS) is often associated with progressive aortic root dilation, ultimately leading to aortic aneurysm and dissection. While recent work showed increased transforming growth factor beta (TGF-β) signaling contributes to aneurysm formation in aorta, efficacious therapeutic targets remain elusive. Consistent with prior reports of progeroid phenotypes in a subset of Marfan patients we previously demonstrated increased cellular senescence in a MFS mouse model. Here, we sought to determine whether administration of senolytic drugs reduces cellular senescent markers, TGF-β signaling, and aortic root dilation in aged MFS mice by assessing aortic root dimensions by echocardiography and gene expression levels by quantitative real time PCR at 15 months of age following treatment with vehicle (VEH) or the senolytic compound Fisetin for one month. As expected, aortic sinus dimensions were increased dramatically in fibrillin-1 mutant mice compared to wild-type controls and were associated with increased expression of TGF-β1, the senescence marker CDKN2A, the matrix remodeling enzyme MMP2, and the osteogenic and proliferative gene RUNX2. Consistent with previous data from our group, Fisetin treatment dramatically reduced CDKN2A expression in marfanoid mice compared to VEH, which was associated with reductions in TGF-β1, MMP2, and RUNX2. Phenotypically, we observed modest reductions in aortic sinus dimensions compared to VEH, but no substantive change in ascending aortic dilatation. Collectively, these data suggest that senescent cells are significant contributors to molecular changes occurring in MFS and clearance of senescent cells with Fisetin slows the progression aortic root-dilation in fibrillin-1 mutant mice.

Key Points Activin A is implicated in profibrotic and prosenescent kidney injury and correlates with kidney injury markers in animals and humans. Follistatin, through activin A antagonism, reduces senescence burden, macrophage infiltration, and proinflammatory pathway activation in murine diabetic kidney disease. Follistatin and other antagonists of activin A signaling pathways may be promising, novel therapeutics for diabetic kidney disease. Background Circulating activin A, an inflammatory mediator implicated in profibrotic kidney injury and cellular senescence-induced adipose tissue dysfunction, is increased in human diabetic kidney disease (DKD) and directly correlates with kidney dysfunction. We tested the hypothesis that activin A increases kidney injury, senescent cell abundance, and macrophage infiltration in DKD and antagonism through follistatin (FS) therapy diminishes these effects. Methods An accelerated nephropathy type 2 diabetes (db/db) mouse model was generated by implantation of angiotensin II-loaded osmotic minipumps resulting in increased albuminuria and glomerular and tubular injury. Kidney repair effects of FS (5 µ g intraperitoneal; two doses) were assessed through markers of kidney injury, fibrosis, inflammation, cellular senescence, and macrophage infiltration. In vitro studies examined antiactivin effects of FS on high glucose-exposed human monocytes, renal fibroblasts, and renal tubule epithelial cells. Results Activin A antagonism with FS reduced senescence (p19), proinflammatory (including senescence-associated secretory phenotype), and profibrotic markers including activin A. FS improved kidney morphology, restored podocyte markers (nephrin and Wilms tumor-1), and reduced kidney injury biomarkers, albuminuria and kidney fibrosis. FS decreased kidney macrophage and leukocyte infiltration and absent in melanoma 2 inflammasome activation. FS seemed to suppress inflammation through the toll-like receptor-4/NF kappa-light-chain-enhancer of activated B cells pathway in vivo further supported in human macrophages in vitro . In addition, FS reduced hyperglycemia-induced renal fibroblast activation and renal tubule epithelial cell senescence in vitro . Conclusions Activin A is a mediator of kidney injury through macrophage-associated inflammation in murine DKD. FS acts through senomorphic activities which inhibit profibrotic, proinflammatory, and prosenescence signaling by activin A. Hence, antiactivin targeting may aid in the development of a promising, novel therapeutic for DKD.

Abstract Bisphosphonates (BPs) have been the major class of medicines used to treat disorders of excessive bone loss for over five decades. Recently it has been recognized that BPs may also have additional significant beneficial extra-skeletal effects. These include a reduction of all-cause mortality and of conditions commonly linked to ageing, such as cancer and cardiovascular disease. Here we show that bisphosphonates co-localize with lysosomal and endosomal organelles in non-skeletal cells and stimulate cell growth at low doses. In vivo spatial transcriptomic analysis revealed differentially expressed senescence markers in multiple organs of aged BP-treated mice, and a shift in cellular composition toward those of young counterparts. Similarly, a 5000-plex plasma proteome analysis from osteopenic patients before and after BP-treatment showed significant alterations in ∼400 proteins including GTPase regulators and markers of senescence, autophagy, apoptosis, and inflammatory responses. Furthermore, treatment with BPs protected against the onset of senescence in vitro . Proteome-wide target deconvolution using 2D thermal profiling revealed novel BP-binding targets (PHB2, ASAH1), and combined with RNA- and ATAC-seq of BP-treated cells and patient data, suggests downstream regulation of the MEF2A transcription factor within the heart. Collectively, these results indicate how BPs may beneficially modify the human plasma proteome, and directly impact multiple non-skeletal cell types through previously unidentified proteins, thereby influencing a range of pathways related to senescence and ageing.

Abstract Aging‐related bone loss significantly impacts the growing elderly population globally, leading to debilitating conditions such as osteoporosis. Senescent osteocytes play a crucial role in the aging process of bone. This longitudinal study examines the impact of continuous local and paracrine exposure to senescence‐associated secretory phenotype (SASP) factors on biophysical and biomolecular markers in osteocytes. Significant cytoskeletal stiffening in irradiated (IR) osteocytes are found, accompanied by expansion of F‐actin areas and a decline in dendritic integrity. These changes, correlating with alterations in pro‐inflammatory cytokine levels and osteocyte‐specific gene expression, support the reliability of biophysical markers for identifying senescent osteocytes. Notably, local accumulation of SASP factors have a more pronounced impact on osteocyte biophysical properties than paracrine effects, suggesting that the interplay between local and paracrine exposure can substantially influence cellular aging. This study underscores the importance of osteocyte mechanical and morphological properties as biophysical markers of senescence, highlighting their time dependence and differential effects of local and paracrine SASP exposure. Collectively, the investigation into biophysical senescence markers offers unique and reliable functional hallmarks for the non‐invasive identification of senescent osteocytes, providing insights that can inform therapeutic strategies to mitigate aging‐related bone loss.

Background We tested whether biologic age, as estimated by deficits, functional impairments, or Age‐Gap or their combination, provide improved estimation of cause‐specific death as compared with chronological age. Methods Cardiovascular and noncardiovascular deficits, functional impairments, and Age‐Gap were prospectively collected in 535 patients aged ≥55 years undergoing percutaneous coronary interventions between August 1, 2014, and March 31, 2018. Age‐Gap was calculated as the difference between chronological age and age estimated by artificial intelligence ECG using a convolutional neural network. The full biological age model included deficits, functional impairments, and Age‐Gap >2 SD. A multivariable reduced model with the least number of variables was also created to provide a comparable C index to the full model. Results The average chronological age was 72.1±9.5 years, and there were 68% of men. During a median follow‐up of 2.61 years, 124 (23%) patients died. There was a modest correlation between Age‐Gap and biological age ( r =0.28 [95% CI, 0.20–0.35]; P <0.001). When modeled with chronologic age as a covariate, Age‐Gap predicted all‐cause (hazard ratio [HR], 1.07 [95% CI, 1.04–1.10]; P <0.001) and cardiovascular (HR, 1.07 [95% CI, 1.04–1.11]; P <0.001) mortality. As compared with chronological age, the full biological age model noted significant improvement in the prediction of long‐term overall (95% CI, 0.65–0.78), cardiovascular (95% CI, 0.69–0.77), and noncardiovascular (95% CI, 0.55–0.86) mortality. In the reduced models, most prognostic information for noncardiovascular mortality (C index: 0.79) was obtained by subjective difficulty in performing tasks, whereas the deficit‐based estimation predicted cardiovascular mortality (C index: 0.72). Conclusions Estimated biological age from deficits and functional impairments was superior to chronological age in predicting long‐term cause‐specific mortality following percutaneous coronary interventions.

Modulating immune function is a critical strategy in cancer and atherosclerosis treatments. For cancer, boosting or maintaining the immune system is crucial to prevent tumor growth. However, in vascular disease, mitigating immune responses can decrease inflammation and slow atherosclerosis progression. Anti-inflammatory therapy, therefore, presents a unique dilemma for cancer survivors: while it may decrease cardiovascular risk, it might also promote cancer growth and metastasis by suppressing the immune response. Senescence presents a potentially targetable solution to this challenge; senescence increases the risk of both cancer therapy resistance and vascular disease. Exercise, notably, shows promise in delaying this premature senescence, potentially improving cancer outcomes and lowering vascular disease risk post-treatment. This review focuses on the long-term impact of cancer therapies on vascular health. We underscore the importance of modulating senescence to balance cancer treatment’s effectiveness and its vascular impact, and we emphasize investigating the role of exercise-mediated suppression of senescence in improving cancer survivorship.

Multiple myeloma (MM) is an incurable plasma cell (PC) malignancy. Despite therapeutic advances that have vastly improved survival, all patients are expected to relapse. Current standard of care includes autologous stem cell transplant (ASCT) with high-dose melphalan (HDM) administered as a conditioning agent. Cytotoxic chemotherapies such as melphalan have been shown to drive therapy-induced senescence (TIS) in several tissues. We hypothesize that HDM activates TIS pathways in surviving MM cells and that this may correlate with patient outcomes post-ASCT. We developed an in vitro HDM model using 5TGM1 mouse MM cells treated with vehicle (Veh) or HDM (10µM, IC90) for 6h, followed by co-culture with primary mouse bone marrow stromal cells. Image analysis was performed to quantify proliferation by cumulative population doublings (CPDs) over 10 days, after which 5TGM1 cells were evaluated for cell size, telomere-associated DNA damage foci (TAFs), sensitivity to senolysis, and senescence gene expression (scRNA-seq and RT-qPCR). The effect of HDM on CPDs and cell size was also evaluated in human MM cell lines RPMI-8226 and H929. scRNA-seq was used to analyze CD138+ PCs from MM patients at various timepoints post-ASCT. Longitudinal MM patient iliac crest biopsies (diagnosis, post-ASCT; N=20) were stained for CD138+ PCs; PC burden was quantified by AI-assisted histology. Lastly, we established an in vivo model of induction therapy (bortezomib) followed by HDM/SCT in Vk*MYC mouse MM engrafted C57BL/6 mice. Tumor burden was tracked by serum protein electrophoresis for M-spike using submandibular bleeds. Bone marrow was then flushed from long bones and analyzed by flow cytometry and immunofluorescence. HDM-5TGM1 showed decreased CPDs (HDM 0.32±0.31, Veh 6.72±0.69, p&lt;0.0001, N=3), increased size (median pixel size: HDM 413.2±99.98, Veh 207±8.88, p&lt;0.05, N=3), and increased TAF+ cells (Percent TAF+ cells: HDM 34.77%±10.74%, Veh 11.41%±1.58%, p&lt;0.05, N=3) consistent with known TIS features. Preliminary assessment (N=1) of human MM cell lines showed similar growth arrest (RPMI-8226 CPDs: HDM 0.058±0.101, Veh 4.185±0.358; H929 CPDs: HDM 0±0, Veh 4.61±0.243) and size increase (RPMI-8226 mean pixel size: HDM 804.1±6.048, Veh 526.9±2.115; H929 mean pixel size: HDM 371.2±26.95, Veh 130.3±41.43), suggesting a translatable mechanism. HDM-5TGM1 cells were more sensitive to senolysis by dasatinib+quercetin (viability: HDM 54.9%±0.09%, Veh 76.0%±0.05%, N=2). scRNA-seq analysis showed that HDM-5TGM1 were enriched for gene sets related to senescence pathways, including the published set SenMayo (FDR&lt;0.25). HDM-5TGM1 cells also exhibited myeloid gene expression consistent with previous publications on MM dormancy. RT-qPCR confirmed significant increases in HDM-5TGM1 (p&lt;0.001, N=3) in senescence markers (Cdkn1a, Cdkn1c, Glb1), senescent cell anti-apoptosis pathway genes (SCAPs, Bcl2l1), senescence associated secretory phenotype (SASP) genes (Ccl5, Icam1, Mmp13), and myeloid markers (Axl, Fcer1g, Mpeg1). scRNA-seq of patient CD138+ PCs confirmed a myeloid-like cluster that gained prominence in relapsed patients with resistant disease. CD138+ PCs were detected in patient bone biopsies post-ASCT. Interestingly, patients who relapsed (≤3 years, N=9) had a greater percent reduction in PC burden from diagnosis to post-ASCT when compared to patients that did not relapse (N=11) in that time (p=0.02). Further, CD138+ PC burden post-ASCT positively correlated with time in remission in relapsed patients (R=0.697, p=0.03). Bortezomib reduced serum M-spike in Vk*MYC-engrafted mice (p=0.0003); M-spike was further reduced by HDM/SCT compared to Veh-treated mice (p=0.0007). Flow cytometry confirmed a decrease in Vk*MYC cells after HDM/SCT (p=0.0043), and the percentage of Vk*MYC cells with greater size and complexity was increased compared to Veh-treated mice (p=0.0043), consistent with our in vitro data. Vk*MYC cells from HDM-treated mice also trended for more TAF+ cells (&gt;3 TAFs) compared to Veh-treated mice (p=0.0714). Our findings suggest that HDM can induce a TIS and myeloid signature in surviving MM cells. Greater MM burden post-ASCT appears to be associated with longer durable response, again suggesting that these cells may be in growth arrest consistent with TIS. Finally, senolytics may be a novel approach to eliminate surviving MM cells and prevent relapse.

Abstract Senescent osteocytes are key contributors to age‐related bone loss and fragility; however, the impact of mechanobiological changes in these cells remains poorly understood. This study provides a novel analysis of these changes in primary osteocytes following irradiation‐induced senescence. By integrating subcellular mechanical measurements with gene expression analyses, we identified significant, time‐dependent alterations in the mechanical properties of senescent bone cells. Increases in classical markers such as SA‐β‐Gal activity and p16 Ink4a expression levels confirmed the senescence status post‐irradiation. Our key findings include a time‐dependent increase in cytoskeletal Young's modulus and altered viscoelastic properties of the plasma membrane, affecting the contractility of primary osteocytes. Additionally, we observed a significant increase in Sclerostin ( Sost ) expression 21 days post‐irradiation. These biophysical changes may impair osteocyte mechanosensation and mechanotransduction, contributing to bone fragility. This is the first study to time‐map senescence‐associated mechanical changes in the osteocyte cytoskeleton. Our findings highlight the potential of biophysical markers as indicators of cellular senescence, providing more specificity than traditional, variable biomolecular markers. We believe these results may support biomechanical stimulation as a potential therapeutic strategy to rejuvenate aging osteocytes and enhance bone health.

Key Points The rat arteriovenous fistula (AVF) model exhibits marked upregulation of p16 Ink4a and p21 Cip1 and multiple markers of senescence. Fisetin, an established vasoprotective senolytic agent, when administered for 3 weeks, increases AVF blood flow and AVF outward remodeling. Heme is shown to be a novel prosenescence metabolite, and when chronically administered, it decreases AVF blood flow. Background Maturational failure of dialysis arteriovenous fistulas (AVFs) not uncommonly occurs and is of considerable and timely importance. Our prior studies demonstrate that senescence, a phenotypic process that promotes vascular and other diseases, occurs in the murine AVF. In this study, we examined whether senescence also occurs in the rat AVF model and the effect of compounds that inhibit or accelerate senescence. Methods The rat AVF was created in the femoral vessels by an end vein-side artery anastomosis. In the AVF, we assessed the expression of critical drivers of senescence, specifically, the cell cycle inhibitors p16 Ink4a and p21 Cip1 , and such indices of a senescence phenotype as senescence-associated β -galactosidase (SA- β -gal) activity, SA- β -gal staining, and a senescence-associated secretory phenotype. We examined the effects of compounds that retard or accelerate senescence on AVF blood flow. Results The AVF evinced upregulation of p16 Ink4a and p21 Cip1 when assessed 3 days after AVF creation. The AVF also demonstrated increased SA- β -gal activity in the artery and vein; staining for SA- β -gal in the AVF artery, anastomosis, and vein; and a prominent senescence-associated secretory phenotype. Fisetin, an established senolytic that is protective in other models of vascular injury, when administered for 3 weeks, increased AVF blood flow and outward remodeling. Hemin, when administered for 3 weeks, decreased AVF blood flow. We demonstrate that hemin is a novel inducer of a senescence phenotype in endothelial cells, as reflected by several senescence indices. However, when administered relatively acutely (for 5 days), hemin increased AVF blood flow by heme oxygenase–dependent mechanisms because the latter was entirely prevented by a competitive inhibitor of heme oxygenase activity. Conclusions The rat AVF exhibits senescence within 3 days of its creation. Chronic administration of a senolytic compound (fisetin) increases AVF blood flow, whereas chronic administration of a prosenescence compound (hemin) decreases AVF blood flow.