BACKGROUND:Postmenopausal female individuals are disproportionately affected by knee osteoarthritis (KOA), experiencing earlier onset and more severe pathology compared to their male counterparts. Despite this clinical disparity, the molecular mechanisms underlying female-specific vulnerability remain poorly defined. OBJECTIVE:To evaluate the mechanistic role of relaxin-2 in postmenopausal KOA. DESIGN:This was a translational research study that evaluated relaxin-2 using an in vitro postmenopausal human KOA chondrocyte culture model and in silico network medicine simulation. SETTING:Research laboratory. SPECIMENS:KOA chondrocytes isolated from a 67-year-old postmenopausal female human donor. INTERVENTIONS:Female KOA chondrocytes were treated with varying relaxin-2 concentrations (control: 0 pg/mL, low: 0.496 pg/mL, medium: 49.6 pg/mL, and high: 4960 pg/mL; n = 5-7/group), with doses based on previously reported physiologic serum levels for pre- and postmenopausal female individuals. MAIN OUTCOME MEASURE(S):Effects were evaluated by immunofluorescence analysis of chondrogenicity markers (type II collagen [Col2], aggrecan [ACAN]), fibrotic markers (type I collagen [Col1], type III collagen [Col3]), extracellular matrix degradation markers (matrix metalloproteinase-13 [MMP-13], A Disintegrin And Metalloproteinase with Thrombospondin Motifs 4 [ADAMTS4]), and mitochondrial integrity and function markers (translocase of the outer mitochondrial membrane 20 [TOMM20], Succinate Dehydrogenase Subunit A [SDHA], Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha [PGC-1α]). RESULTS:Relaxin-2 increased Col2 at low and medium concentrations (p < .05), with the Col2/Col1 ratio highest at the low dose relaxin-2. MMP-13 expression was greatest for the medium compared to the control (p = .73), low (p = .002), and high relaxin-2 concentrations (p = .005), whereas ACAN and ADAMTS4 showed no differences across concentrations (p > .05). In silico analysis revealed that postmenopausal female individuals exhibit a fibrotic transcriptomic signature and that mitochondrial function is regulated by relaxin-2 in fibrotic chondrocytes. Computational analyses were validated experimentally, with TOMM20 and SDHA elevated at all relaxin-2 concentrations (p < .05), whereas PGC-1α was reduced at high concentration (p < .05). CONCLUSIONS:These findings demonstrate that relaxin-2 reprograms fibrotic osteoarthritic chondrocytes toward a healthier, less fibrotic state by restoring mitochondrial function.

In December 2025, the Division of Aging Biology, National Institute on Aging (NIA) at the National Institutes of Health (NIH), in collaboration with staff from other NIA divisions, NIH institutes and the Veterans Health Administration, convened a workshop to explore the mechanistic bases and health effects of sex differences across tissues and ages. Novel research discoveries, technologies and visions to advance sex-differences research were discussed.

Resistance exercise can stimulate new bone formation and result in changes to circulating markers of bone metabolism, but the relationship between the bone metabolic response to resistance exercise and bone morphological phenotypes is unknown. This study compared circulating bone biomarker responses to acute ballistic resistance exercise between groups characterized by bone phenotypes. Fuzzy c-means clustering (n = 287, 47% women) of tibial HR-pQCT parameters and micro finite element analysis (both 4% and 30% sites) determined bone phenotypes. Biomarkers of bone formation (PINP, ALP), resorption (βCTx, TRAP5b), mechanical sensing (sclerostin), and systemic anabolism (IGF-I) were assessed by ELISA before and after an acute ballistic lower body resistance exercise test (AET). DXA assessed body composition. Linear mixed-effects modeling analyzed biomarker responses between clusters, controlling for sex, age, and total lean mass with participants as random intercepts. Clustering revealed two phenotypes (C1 n = 150, 78% women; C2 n = 137, 14% women, p < 0.001), with C2 having wider, denser, and stronger bones with more trabeculae. C2 had higher lean mass (mean difference = 9.1 kg, p < 0.001) than C1. Interaction effects showed IGF-I increased in C2 (p = 0.019) versus no change in C1 (p = 0.999), and TRAP5b decreased to a greater extent in C2 (p < 0.001) compared to C1 (p = 0.029) post-AET. Time effects showed ALP (p = 0.001) and βCTx (p < 0.001) decreased while sclerostin increased (p < 0.001) post-AET overall. Individuals with wider, denser bones exhibit post-exercise biomarker responses potentially conducive to osteogenic adaptation, although the effects on bone structure remain unclear. Unsupervised machine learning derived bone phenotypes provides a novel approach to investigate bone health.

As Nature Aging celebrates its fifth anniversary, the journal asks some of the researchers who contributed to the journal early on to reflect on the past and the future of aging and age-related disease research, the impact of the field on human health now and in the future, and what challenges need to be addressed to ensure sustained progress.

OBJECTIVES:While sexual dimorphism of knee osteoarthritis (KOA) is well established, sex-specific clinical manifestations-particularly involving periarticular tissues undetectable by radiography-remain underexplored. This study aimed to define female-specific alterations in joint integrity, periarticular muscle quality, symptom presentation, and the transcriptomic landscape of periarticular muscles, with the goal of uncovering the mechanistic contributions of each to KOA pathophysiology. METHODS:Forty-nine participants (32 females, 17 males; Kellgren-Lawrence grade 1-2) underwent clinical assessment, including (1) quantitative ultrasound assessment of the vastus medialis and rectus femoris muscles; (2) magnetic resonance imaging to assess joint integrity; and (3) patient-reported outcomes. Principal component analysis followed by receiver operating characteristic curve analysis was conducted to identify discriminative sex-specific imaging and symptom features. Correlation-based network analysis examined sex-specific interdependencies among clinical variables. Publicly available transcriptomic datasets were analyzed to identify molecular drivers underlying female-specific muscle quality changes. RESULTS:Despite similar radiographic severity and symptom presentation across the sexes, female individuals exhibited greater cartilage degeneration and higher fatty infiltration in the vastus medialis and rectus femoris. These features were central to sex separation in the principal component analysis, with both features identified as network hubs in female individuals, indicating interconnected muscle-joint degeneration. Transcriptomic analysis revealed enrichment of adipogenic reprogramming in female individuals, suggesting aberrant intramuscular fat programming. DISCUSSION:Our findings uncover a distinct female-specific musculoskeletal phenotype in early-stage KOA, characterized by muscle degeneration and cartilage deterioration undetectable by radiography. These female-specific clinical manifestations may be due, at least partly, to aberrant adipogenic programming in muscle. These findings provide mechanistic and clinical insight into sexual dimorphism in KOA.

The decline in mobility with aging is a major health concern, associated with a high risk for disability. Despite the widespread prevalence of gait slowing in elderly adults, this issue has not been adequately addressed. The central nervous system and skeletal muscle system are key regulators of gait speed. However, direct molecular communication along the brain-muscle axis and the role of these interactions in mobility resilience remain poorly studied. Recently, extracellular vesicles (EV), membrane bound vesicles secreted by cells, have emerged as a key player in long distance inter-cellular communication. Nevertheless, the potential of EVs as biological predictor of mobility resilience in older adults has not been yet studied. In the present study, we used serum samples from 23 participants with gait speed >1.0 m/sec (mobility-resilient group) and 22 participants with gait <1.0 m/sec (mobility non-resilient group) from the Health, Aging and Body Composition (Health ABC) study. First, total circulating serum EVs were isolated and characterized for small noncoding RNAs using un-biased small noncoding RNA sequencing. Given the central role of mitochondria in muscle energy metabolism and their emerging link to age-related physical decline, next, muscle-derived EVs (MDE) were isolated and characterized for specific mitochondrial markers (TOM20, mtCox2, PDH, and VDAC) by flow cytometry, the expression of a panel of 13 miRNAs related to mitochondrial function by RT-PCR, and PPAR-γ expression by ELISA. The results showed differential enrichment of various miRNAs, circRNAs, and mitochondrial proteins in total EVs and/or MDE between mobility-resilient and non-resilient groups, highlighting their potential as non-invasive biomarkers for mobility outcomes. Overall, the findings from the present study suggest a role for serum EVs in mediating molecular communication related to functional aging phenotypes and underscores the potential of EV biomarkers in modulating mobility and promoting healthy aging.

Resistance exercise augments circulating extracellular vesicle (EV) and metabolite signalling in manners that assist musculoskeletal and systemic adaptations. Women are often underrepresented in exercise research and recent attention has focused on whether hormonal fluctuations during the menstrual cycle and use of hormonal contraception (HC) impact exercise performance and adaptation. We investigated if menstrual phase (follicular and luteal) or HC usage (oral contraceptive pill and hormonal intrauterine device) impact the EV and metabolite response to exercise. Overall, we observed an exercise-induced response across all four groups for EV microRNAs and circulating metabolites. Women in the follicular phase had baseline differences in the most abundant miRNAs and exercise-relevant miRNAs and had the greatest miRNA response to exercise compared to other groups. Relevant metabolites were observed in EVs, but the overall response to exercise was minimally influenced by group among annotated metabolites. Multi-omic analysis showed potential presence of molecular signatures based on circulating hormone concentrations, but trends were not differentiated enough to suggest clear phenotypic differences. Overall, our data highlights unique miRNA profiles at baseline in follicular phase women but does not support the notion that circulating EV and metabolite responses to exercise are heavily influenced by menstrual cycle phase or HC use.Trial Registration: ClinicalTrials.gov identifier: NCT06972862

Regenerative rehabilitation combines rehabilitation science with regenerative medicine approaches to achieve synergistic and more effective outcomes. Within the field of regenerative medicine, there has been a growing number of cell and gene therapies (CGTs) that are either approved for clinical use or actively undergoing clinical trials. Many of these therapies-especially those targeting neurological and musculoskeletal disorders-use functional outcomes as primary or secondary endpoints, prompting discussion about how physical medicine and rehabilitation (PM&R) physicians can support the integration of CGTs into clinical care. In this perspective article, we explain why physicians specializing in PM&R could take a leading role in advancing the clinical translation of CGTs. Currently, CGTs are not confined to a single medical specialty, presenting a timely opportunity for PM&R-working collaboratively with neurology, hematology, and other disciplines-to assume greater leadership and influence the development and implementation of these transformative treatments. To our knowledge, this is the first publication within PM&R literature to emphasize the importance of our specialty serving as a leader and driving force in the adoption of these therapies.

Maintenance of organismal function requires tightly regulated biomolecular communication. However, with aging, communication deteriorates, thereby disrupting effective information flow. Using information theory applied to skeletal muscle single-cell RNA-seq data from young, middle-aged, and aged animals, we quantified the loss of communication efficiency over time. We considered communication channels between transcription factors (TFs; "input message") and corresponding target genes (TGs; "output message"). Mutual information (MI), defined as the information effectively transmitted between TFs and TGs, declined with age. This decline was attributed to escalating biological noise and loss of precision with which TFs regulate TGs (ie, channel capacity). When we ranked TF:TG pairs by MI, pairs associated with fatty acid oxidation displayed the greatest loss of communication with aging, whereas the system preserved communication between pairs related to RNA synthesis. These data suggest ineffective communication with aging against a backdrop of resource reallocation to support essential cellular functions.

Aging is characterized by a gradual decline of cellular and physiological functions over time and an increased risk of different diseases. RNA therapeutics constitute an emerging approach to target the molecular mechanisms of aging and age-related diseases via rational design and have several advantages over traditional drug therapies, including high specificity, low toxicity and the potential for rapid development and production. Here, we discuss the latest developments in RNA therapeutics designed to promote healthy aging, including RNA activation, messenger RNA therapy, RNA interference, antisense oligonucleotides, aptamers and CRISPR–Cas-mediated RNA editing. We also review the latest preclinical and clinical studies of RNA technology for treating age-related diseases, including neurodegenerative, cardiovascular and musculoskeletal diseases. Finally, we discuss the challenges of RNA technology aimed at supporting healthy aging. We anticipate that the fusion of RNA therapeutics and aging biology will have an important effect on the development of new medicines and maximization of their efficacy. Chen and colleagues explore how RNA therapeutics targeting mechanisms of aging can be used to treat age-related diseases and promote healthy aging. They discuss current preclinical and clinical progress, along with key challenges and future directions.

IMPORTANCE:Clinical practice guidelines (CPGs) play a critical role in shaping medical care and healthcare policies, yet there is growing concern about the lack of diversity in CPG authorship. This systematic review and meta-analysis aim to assess gender, race, and ethnicity representation among authors of CPGs across different medical specialties. OBJECTIVE:To evaluate the representation of women and individuals from minoritized racial and ethnic groups among authors and contributors of CPGs. DATA SOURCES:A comprehensive literature search was conducted in databases including Ovid MEDLINE, Embase.com, Web of Science, Cochrane CENTRAL, and ClinicalTrials.gov from inception to September 2023. Studies focusing on CPG authorship disparities by gender, race, and ethnicity were selected for review. STUDY SELECTION:Eligible studies included those that reported data on gender, racial, and ethnic composition among CPG authors. Out of 2,436 articles screened, 20 studies met the inclusion criteria for full-text review and meta-analysis. DATA EXTRACTION AND SYNTHESIS:Data extraction was performed independently by two reviewers, with disagreements resolved through consensus, in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines. A meta-analysis was then conducted using a random-effects model. MAIN OUTCOMES AND MEASURES:The primary outcome was the proportion of women and individuals from minoritized racial and ethnic groups among CPG authors. The meta-analysis estimated pooled proportions of women's authorship across the different medical specialties. RESULTS:The 20 included studies covered a total of 36,783 author positions. Women's authorship varied widely across specialties, with an overall pooled proportion of 25.7% (95% Confidence Interval (CI): 21.8%-30.1%). Racial and ethnic data were available in only a few studies, with significant gaps in reporting. The findings indicate persistent gender disparities in CPG authorship, particularly in specialties such as cardiology and gastroenterology. CONCLUSIONS:This analysis demonstrated that substantial disparities in gender, race, and ethnicity remain in CPGs' authorship. More inclusive representation is essential to ensure diverse perspectives in shaping healthcare guidelines.

Diverse organisms exploit the geomagnetic field (GMF) for migration. Migrating birds employ an intrinsically quantum mechanical mechanism for detecting the geomagnetic field: absorption of a blue photon generates a radical pair whose two electrons precess at different rates in the magnetic field, thereby sensitizing cells to the direction of the GMF. In this work, using an in vitro injury model, we discovered a quantum-based mechanism of cellular migration. Specifically, we show that migrating cells detect the GMF via an optically activated, electron spin-based mechanism. Cell injury provokes acute emission of blue photons, and these photons sensitize muscle progenitor cells to the magnetic field. We show that the magnetosensitivity of muscle progenitor cells is (a) activated by blue light, but not by green or red light, and (b) disrupted by the application of an oscillatory field at the frequency corresponding to the energy of the electron-spin/magnetic field interaction. A comprehensive analysis of protein expression reveals that the ability of blue photons to promote cell motility is mediated by activation of calmodulin calcium sensors. Collectively, these data suggest that cells possess a light-dependent magnetic compass driven by electron spin dynamics.

Menopause drives fibrotic remodeling and consequent tissue dysfunction across multiple organs, yet the tissue-conserved versus tissue-specific mechanisms underlying this phenomenon remain poorly defined. Here, we employed a network inference framework to uncover how menopause triggers coordinated shifts in intercellular signaling cascades that promote fibrosis. We leveraged publicly archived single-cell RNA-sequencing data from the liver, lung, pancreas, and skeletal muscle of ovariectomized and control mice. Given the central role of immune cells in orchestrating inflammation and fibrosis, we focused our analysis on immune cell populations. Using canonical markers of immune cells, we annotated major cell types and reconstructed cell-cell interaction networks to map transcriptional responses to hormonal shifts. Network analysis revealed pervasive reshaping of intercellular signaling common to all tissues evaluated in the setting of menopause. Within this immune-centered framework, we found that estrogen-responsive macrophages consistently function as major signaling hubs across all tissues evaluated, exhibiting extensive interactions with myofibroblasts-key drivers of extracellular matrix production and fibrotic remodeling. Notably, these shared signaling patterns were not detectable using conventional differential gene expression analysis, which revealed minimal overlap in gene-level responses in macrophages across tissues. In addition to conserved patterns, we identified tissue-specific interaction networks that reflect unique immune adaptations to hormonal loss. As an example, natural killer cells acted as a signaling hub in muscle-specific patterns, suggesting their direct contribution to menopausal skeletal muscle adaptation. Tissue-specific patterning was also evident in the liver, lung, and pancreas, where other immune cell types, such as CD8 + T cells and endothelial cells, functioned as prominent signaling hubs, indicating diverse remodeling of the immune microenvironment. The network approach introduced here represents a systems-level framework for mapping multicellular network rewiring following hormonal depletion and highlights conserved immune-stromal modules as potential therapeutic targets to prevent menopause-associated dysfunction.

ABSTRACT:Post-traumatic osteoarthritis (PTOA) is a form of osteoarthritis that arises secondary to trauma or an injury. The knee is most commonly affected, and risk for PTOA increases substantially following anterior cruciate ligament (ACL) injury. Blood-based biomarkers have been analyzed following ACL injury to predict PTOA progression and severity. The purpose of this review is to synthesize the literature on blood biomarkers related to inflammation and cartilage turnover in association with the development of PTOA following an ACL injury. Of the eight identified studies, the majority, 75%, were cohort based (n = 6). The collective findings suggest potential value in blood biomarkers for evaluating the systemic changes after ACL injury. However, current evidence for the clinical utility of these markers to identify individuals after ACL injury who will develop PTOA is inconclusive. Further work is needed to advance these findings and clarify differences by sex, race, and ethnicity.

Despite the growing burden of knee osteoarthritis on aging populations, our mechanistic understanding of this disease remains lacking. Though knee osteoarthritis is a whole joint disease, the impact of intra-articular structures such as the infrapatellar fat pad (IFP) on cartilage health is unclear. This study investigated the effect of age on paracrine communication between the IFP and chondrocytes. To isolate the effects of the IFP secretome on chondrocytes, aged chondrocytes from male and female mice were incubated with conditioned media from sex-matched young IFPs, aged IFPs, or control media. Extracellular matrix protein expression increased in both male and female chondrocytes exposed to young, but not aged, conditioned media relative to control media. The effect of the young IFP was not concomitant with changes in extracellular matrix degradation proteins, ADAMTS4 or MMP13. To identify factors mediating the effects of the IFP on chondrocytes that are altered with aging, we performed mass spectrometry of young and aged conditioned media and transcriptomics of aged chondrocytes treated with young or aged conditioned media. We then integrated the 2 datasets using network analyses. From the conditioned media, 2 secreted proteins, Mfge8 and Apoa4, were significantly changed with aging. In silico perturbation of the corresponding receptors of these IFP-secreted factors identified multiple enriched pathways in chondrocytes, including negative regulation of nitric oxide synthase activity. Overall, the data suggest that young IFPs release paracrine factors that promote extracellular matrix production in chondrocytes, potentially via regulation of nitric oxide levels, but that this effect is diminished with aging.

Female individuals who are post-menopausal present with higher incidence of knee osteoarthritis (KOA) than male counterparts; however, the mechanisms underlying this disparity are unknown. The most commonly used preclinical models lack human-relevant menopausal phenotypes, which may contribute to our incomplete understanding of sex-specific differences in KOA pathogenesis. Here we chemically induced menopause in middle-aged (14–16 months) C57/BL6N female mice. When we mapped the trajectory of KOA over time, we found that menopause aggravated cartilage degeneration relative to non-menopause controls. Network medicine analyses revealed that loss of 17β-estradiol and progesterone with menopause enhanced susceptibility to senescence and extracellular matrix disassembly. In vivo, restoration of 17β-estradiol and progesterone in menopausal mice protected against cartilage degeneration compared to untreated menopausal controls. Accordingly, post-menopausal human chondrocytes displayed decreased markers of senescence and increased markers of chondrogenicity when cultured with 17β-estradiol and progesterone. These findings implicate menopause-associated senescence and extracellular matrix disassembly in the sex-specific pathogenesis of KOA. Knee osteoarthritis has a sex-specific phenotype with post-menopausal persons experiencing the highest incidence. Here the authors investigate the underlying mechanisms in a mouse model of menopause and find that the loss of 17β-estradiol and progesterone enhanced susceptibility to senescence, extracellular matrix disassembly and cartilage degradation.

Objective The aim of the study was to demonstrate the utility of network medicine for enhancing regenerative rehabilitation approaches. Design We employed a scientometric approach to illustrate the scientific evolution of regenerative rehabilitation and network medicine over the past 20 yrs. We then present two exemplars of a novel application of network medicine, first to optimize the development of a multimodal rehabilitation program for osteoarthritis and, second, to demonstrate the potential utility of a regenerative rehabilitation protocol for neurological applications. Results The scientometric analysis revealed thematic clusters guiding the fields of regenerative rehabilitation, while also revealing a notable gap in the integration of advanced computational biology tools, such as network medicine. To address this gap, we applied a network medicine paradigm as a proof-of-principle in rehabilitation, demonstrating its ability to predict previously known combinational benefits of a multimodal rehabilitation protocol for osteoarthritis and potential of a regenerative rehabilitation protocol to enhance outcomes after stroke. Conclusions The trajectory of progress in regenerative rehabilitation has been defined by embracing new technologies and approaches. We propose that network medicine is a new frontier for the field. Toward the design of efficient and optimized clinical protocols, we anticipate that the network medicine paradigm may have broad applications in the field of rehabilitation, even beyond the examples presented here.

Injuries to skeletal muscle are among the most common injuries in civilian and military populations, accounting for nearly 60% of extremity injuries. The standard of care for severe extremity injury has been focused upon limb salvage procedures and the utilization of tissue grafts or orthotics in conjunction with rehabilitation to avoid amputation. Nonetheless, many patients have persistent strength and functional deficits that permanently impact their quality of life. Preclinical and clinical studies have shown that partial restoration of functional skeletal muscle tissue following injury can be achieved by the implantation of a biologic scaffold composed of extracellular matrix (ECM). These favorable outcomes are mediated, at least in part, through local immunomodulation. The mechanisms underlying this immunomodulatory effect, however, are poorly understood. The present study investigates a potential mechanistic driver of the immunomodulatory effects; specifically, the effect of selected ECM components upon inflammation resolution and repair. Results show that the host response to skeletal muscle injury is profoundly altered and functional recovery decreased in il33−/− mice compared to age- and sex-matched wildtype counterparts by 14 days post-injury. Results also show that IL-33, contained within matrix-bound nanovesicles (MBV), supports skeletal muscle regeneration by regulating local macrophage activation toward a pro-remodeling phenotype via canonical and non-canonical pathways to improve functional recovery from injury compared to untreated il33−/− counterparts. Taken together, these data suggest that MBV and their associated IL-33 cargo represent a novel homeostatic signaling mechanism that contributes to skeletal muscle repair.