Khosla, Sundeep

Abstract Cellular senescence has been implicated in the pathophysiology of radiotherapy-associated bone loss. Based on our previous work, clearance of senescent cells using genetic and pharmacological tools alleviates the anomalies associated with radiation-associated bone deterioration. The pro-inflammatory senescence associated secretome referred to as senescence associated secretory phenotype (SASP), is a hallmark of cellular senescence. The modulation of SASP by senomorphic drugs, potentially can suppress the pro-inflammatory secretome of senescent cells, irrespective of the underlying senescence mechanism. In this study we tested a senomorphic drug, ruxolitinib, a Janus kinase inhibitor (JAKi), during acute and chronic radiotherapy related effects on the bone. Our clinical data indicate an early increase in several pro-inflammatory SASP proteins following radiotherapy of spinal metastasis in prostate cancer patients. Longitudinal assessment of SASP-related genes confirmed this acute elevation in several SASP markers in systemic circulation following irradiation of male mouse femurs. In studies done in male mice, following three preclinical radiotherapy regimens of 30Gy (5 x 6Gy), 60Gy (5 x 12Gy) and a single dose of 24Gy, suppression of SASP by JAKi was efficacious in suppressing radiation-induced bone damage. In comparison and as shown before, the senolytic combination of D+Q was also able to alleviate radiation-associated bone loss. Early and intermittent suppression of SASP using JAK inhibitors in male mice alleviated chronic bone deterioration, diminished telomere dysfunction, lowered senescence and SASP marker expression and reduced bone-marrow adiposity. Overall, our study shows that early targeting of SASP proteins could be a potential therapeutic to prevent radiotherapy-related chronic bone loss and risk of fractures.

Abstract In 2024, the National Academies of Sciences, Engineering, and Medicine (NASEM) published a report entitled Advancing Research on Chronic Conditions in Women. A major purpose of this report was to summarize the current state of research into a series of 21 chronic conditions that affect women differently or that are more common in women. The American Society for Bone and Mineral Research (ASBMR) established a working group to evaluate the NASEM report’s implications for women’s musculoskeletal (MSK) health. This perspective summarizes key research gaps identified in the NASEM report, including the lack of sex-specific data, underrepresentation of women in clinical studies, and minimal integration of MSK health with other chronic conditions. The NASEM report underscores the need for more comprehensive study designs that consider hormonal, genetic, and social determinants of health across the lifespan. In addition to osteoporosis, in this perspective, the ASBMR working group highlights emerging but poorly understood evidence of detrimental effects on musculoskeletal biology in non-MSK, chronic diseases that were identified in the NASEM report to disproportionately affect women. To advance the field, we advocate for better diagnostics, increased investment, and stronger representation of women in research studies. Addressing these gaps is critical for improving prevention, care, and outcomes for chronic conditions that uniquely or disproportionately affect women.

SUMMARY Neurodegenerative diseases are often accompanied by systemic comorbidities, including changes in bone health, but the molecular relationship between neurodegeneration, skeletal decline, and cellular senescence remains poorly understood. In this study, we investigated sex-specific changes in circulating bone- and senescence-related proteins across the spectrum of Alzheimer’s disease(AD), Lewbody dementia(LB) and Parkinson’s disease(PD). Plasma proteomic profiling was performed on samples from 408 participants deeply phenotyped for neurodegenerative diseases, followed by differential protein and pathway analyses. This study reveals sex-dependent alterations in bone and senescence-related circulating proteins in AD-related, PD and LB-related neurodegenerative diseases, providing insights into the complex relationship between neurodegeneration and bone health. Several candidate proteins were also associated with established plasma neurodegeneration biomarkers, particularly pTau181. Pathway analyses revealed shared mitochondrial and metabolic dysfunction across neurodegenerative diseases, with disease-specific features including vesicle trafficking disruption in AD and inflammatory-senescence pathways in LB, plus sex-divergent patterns in inflammatory signaling and bone-related pathways.

Abstract Context Patients with mild autonomous cortisol secretion (MACS) have higher rates of vertebral fractures compared to patients with non-functioning adrenal nodules, yet bone density is not always reduced. Objective To characterize the effect of MACS on bone density, metabolism, and microstructure as measured by high-resolution peripheral quantitative computed tomography (HR-pQCT). Design Cross-sectional study, 2019-2022 Setting Tertiary referral center Participants Seventy-five patients with MACS and 75 age-, sex-, and gonadal status–matched referent subjects. Measurements Bone turnover markers, dual-energy x-ray absorptiometry (DXA) scan, and HR-pQCT. Outcomes Areal and volumetric bone mineral density (aBMD, vBMD), trabecular bone score (TBS), microstructural parameters including trabecular bone volume to total volume (BV/TV) ratio. Results While no differences in aBMD were observed at any skeletal site, patients with MACS had decreased TBS (1.389 vs 1.475, P < .001) and lower osteocalcin concentration (17.1 vs 19.5 ng/mL, P = .030) than referent subjects. On HR-pQCT at the tibia, patients with MACS had reduced trabecular BV/TV (0.220 vs 0.233, P = .015) compared to referent subjects. On multivariable analysis, MACS was associated with lower TBS (odds ratio [OR] per SD decrease 2.87 [1.65-5.00]), lower trabecular BV/TV at the radius (OR per SD decrease 2.58 [1.33-5.00]), and lower trabecular BV/TV at the tibia (OR per SD decrease 4.06 [2.10-7.86]). Conclusion Patients with MACS have microstructural deterioration that may not be evident on routine DXA aBMD testing.

Abstract Cellular senescence has been implicated in the pathophysiology of radiotherapy-related bone loss. Based on our previous work, clearance of senescent cells using genetic and pharmacological tools alleviates the anomalies associated with radiation-associated bone deterioration. The pro-inflammatory senescence associated secretome referred to as senescence associated secretory phenotype (SASP), is a hallmark of cellular senescence. The modulation of SASP by senomorphic drugs, potentially can suppress the pro-inflammatory secretome of senescent cells, irrespective of the underlying senescence mechanism. In this study we tested a senomorphic drug, ruxolitinib, a Janus kinase inhibitor (JAKi), during acute and chronic radiotherapy related effects on the bone. Our clinical data indicate an early increase in several pro-inflammatory SASP proteins following radiotherapy of spinal metastasis in prostate cancer patients. Longitudinal assessment of SASP-related genes confirmed this acute elevation in several SASP markers in systemic circulation following irradiation of mouse femurs. In a proof-of-concept study, following two preclinical radiotherapy regimens of cumulative doses of 30Gy (5 x 6Gy) and 60Gy (5 x 12Gy), a senomorphic approach of JAKi treatment was more effective in alleviating radiation-related bone loss compared to the senolytic cocktail of D+Q. Early and intermittent suppression of SASP using JAK inhibitors alleviated chronic bone deterioration, diminished telomere dysfunction, lowered senescence and SASP marker expression, reduced bone-marrow adiposity, and mitigated radiation related lymphatic impairment. Overall, our study shows that early targeting of SASP proteins could be a potential therapeutic to prevent radiotherapy-related chronic bone loss and risk of fractures. Lay Summary Radiotherapy as part of cancer treatment is correlated with an acute increase in senescent cells. Here we show that the pro-inflammatory senescence associated secretory phenotype (SASP) becomes much more prominent soon after radiotherapy in both patients and mice. Suppression of the SASP using a Janus kinase inhibitor, ruxolitinib, reduced the overall senescent cell burden, improved bone architecture by promoting bone formation, reduced bone marrow adiposity, and mitigated radiation-induced lymphatic impairment. Overall, these findings suggest that early inhibition of the SASP may help mitigate several bone anomalies and prevent long-term bone loss and fractures after radiotherapy. Graphical Abstract

Cellular senescence is a heterogeneous phenotype characterized primarily in mesenchymal cells, but the extent to which immune cells differ in their senescence phenotype, or “senotype,” is unclear. Here, we applied single-cell approaches alongside both global and cell-specific genetic senolytic mouse models to evaluate the senotype of immune cells in the bone marrow of aging mice. We found that myeloid-lineage cells exhibited the highest expression of p16 and senescence-associated secretory phenotype markers among all immune cell types. In contrast with clearance of p16 + senescent mesenchymal cells, targeted clearance of p16 + myeloid cells in aged mice had only minor effects on age-related bone loss in male mice, with no effects in females. In more detailed analyses, p16 + myeloid cells were only acutely cleared, being repopulated back to basal levels within a short time. This led to a lack of long-lasting reduction in senescent cell burden, unlike when targeting bone mesenchymal cells. In vitro, myeloid-lineage cells differed markedly from mesenchymal cells in the development of a senescent phenotype. Collectively, our findings indicate that aged bone marrow myeloid cells do not achieve the fully developed senescent phenotype originally described in mesenchymal cells, justifying further characterization of senotypes of immune cells across tissues.

Abstract Cellular senescence is a key mechanism of skeletal aging in both physiological and accelerated conditions, such as radiotherapy. This study aimed to identify common differentially regulated microRNAs (miRs) across these contexts. We performed miR sequencing on three models: femurs from young (5-month-old) versus old (24-month-old) mice; focally radiated versus non-radiated femurs; and osteocytes from young versus old mice. Osteocytes were included in the comparison, as they have the longest lifespan in the mineralized bone matrix and they form 90-95% of all mesenchymal bone cell types. Among the three groups, miR-135a-5p and miR-671-5p were the common (i.e., shared) miRs that were downregulated, and miR-183-5p, a miR that regulates the WNT pathway, was the only shared upregulated miR, while miR-155-5p, a miR that regulates the Senescence-Associated Secretory Phenotype (SASP), was elevated in two conditions. The WNT-pathway has been positively associated with bone health and Sclerostin, a WNT-pathway inhibitor produced and secreted by osteocytes, has been implicated in accelerated skeletal deterioration following radiation. Thus, we used a neutralizing antibody to Sclerostin (Scl-Ab), to assess genes related to the WNT pathway and senescence, which are regulated by miR-183-5p and miR-155-5p, respectively. We further performed miR sequencing in radiated bones from mice treated with Scl-Ab and identified miR-133a-3p, a key miR that inhibits bone metabolism and function, which is upregulated in accelerated skeletal aging (i.e., focal radiation) downregulated by Scl-Ab. Overall, our study identifies potential regulatory gene pathways that modulate skeletal aging in the presence and absence of a WNT activator, Scl-Ab.

ABSTRACT Alzheimer's disease (AD), a leading cause of dementia in the elderly, is traditionally characterized by neurodegeneration driven by amyloid‐beta plaques and tau tangles. However, emerging evidence reveals that AD's impact extends beyond the brain, significantly affecting skeletal health. This review integrates clinical and transgenic mouse model data to elucidate the mechanistic interplay between AD pathology and bone metabolism. AD patients exhibit increased risk for hip fractures and low bone mineral density (BMD), independent of cognitive impairment severity. We found altered calcium and alkaline phosphate levels in the blood of patients with mild cognitive impairment and AD, as assessed from the Alzheimer's Disease Neuroimaging Initiative data. Convergent risk factors—age, sex, APOE4 genotype, smoking, and vitamin D deficiency—contribute to both neurodegeneration and bone fragility. Key molecular pathways, such as Wnt/β‐catenin signaling and TREM2‐mediated osteoclast regulation, underscore shared mechanisms driving disease pathology in both systems. Mouse models of AD consistently demonstrate disrupted bone remodeling, impaired osteoblast function, and heightened osteoclast activity. Therapeutic strategies targeting overlapping pathways, including lithium, anti‐FSH antibodies, and NF‐κB inhibitors, show promise in mitigating both cognitive decline and bone loss. Collectively, these insights advocate for a more integrated view of AD that includes skeletal comorbidities, potentially guiding the development of dual‐purpose interventions.

Aging plays a major role in the development of numerous chronic diseases, one of which is a marked decline in skeletal health. Beyond diminishing bone mass and strength, mammals of advanced age experience a decline in skeletal mechanotransduction—that is, the ability of the skeleton to respond adaptively to mechanical perturbation. One possibility for the loss of mechanotransduction in bone with aging is an age-associated increase in the population density of senescent cells—those cells that have undergone irreversible cell cycle arrest, resistance to apoptosis, and production of a modified secretome (the SASP) that has damaging effects to nearby healthy (non-senescent) cells. We investigated whether the presence of senescent cells might drive some of the diminished mechanical response observed in aged bone, by testing the hypothesis that the clearance of senescent cells via intermittent senolytic treatment promotes mechanical responsiveness in an aged skeleton. C57BL/6 mice aged 6 months and 22 months were treated weekly with the senolytic cocktail Dasatinib and Quercetin (D + Q) for 1 month, then subjected to low level in vivo mechanical loading of the ulna for 1 week. The 6-month-old mice exhibited a doubling of load-induced ulnar periosteal bone formation when treated with D + Q, compared to vehicle-treated mice, but the periosteal response to loading was not significantly altered by D + Q in the aged (22-month) mice. We further probed the efficacy of D + Q in mechanotransduction by switching to an endocortical model—the axial tibia loading system. Here, the 22-month-old mice had nearly double the load-induced endocortical bone formation compared to vehicle-treated mice. We further assayed the cortical bone gene expression profile in loaded and control tibias from treatment-naïve 6-month and 22-month mice, to determine whether there is significant overlap between mechanically induced signaling genes and SASP genes. We found significant load-induced changes among several SASP genes, suggesting that inhibition of the SASP (i.e., senomorphics) might interfere with mechanical signaling from otherwise healthy cells. In summary, clearance of senescent cells via intermittent D + Q treatment is effective at improving endocortical mechanical responsiveness in the aged skeleton, which is commonly diminished throughout the course of aging.

Abstract With the goal of preventing more hip fractures, a next generation of the VirtuOst Biomechanical Computed Tomography (BCT) test was developed that integrates measurements from a clinical CT scan related to fall risk, impact force, and femoral strength, the three main determinants of hip fracture. Here, we introduce the test and validate it against BMD and FRAX. Our source population from a large healthcare system comprised of 341364 patients (≥65 yr) with an abdominal-pelvic CT during care. Using data from 3035 patients (1790 with hip fracture), we developed a “BCT Risk Score” (range: 0-100) having input risk factors of age, femoral strength, ratio of trabecular/cortical BMD, muscle area, intramuscular fat, FN volume, hip width, and posterior fat thickness. In a geographically distinct set of 2124 patients (1293 with hip fracture), we then compared the BCT Risk Score against a DXA-equivalent hip BMD T-score (lowest hip value, measured from the CT scan by VirtuOst) and FRAX hip fracture risk (with BMD but without parental fracture history) for predicting a first incident hip fracture within 5 yr. For the women, the c-statistic for predicting fracture was higher for BCT (0.89, 95% CI: 0.87-0.90) than for BMD (0.81, 0.79-0.84) or FRAX (0.85, 0.83-0.87). Using binary thresholds to identify high-risk patients, sensitivity for BCT (Risk Score ≥ 75) was higher than for BMD (T-score ≤ −2.5) and FRAX (hip risk ≥ 3.0%): 81.4% vs 47.8% vs 75.9%, respectively; positive predictive values confirmed comparable high-risk status (BCT 13.6% vs BMD 15.3% vs FRAX 12.7%). Similar trends were observed for the men, 2-yr outcomes, and identifying very-high-risk patients. We conclude that, compared to both BMD and FRAX, the integrative BCT test better predicted hip fracture and its high sensitivity should improve fracture prevention.