Stem cell senescence as a regenerative bottleneck in age-related skeletal degeneration: Mechanistic crosstalk and translational strategies.

Skeletal degeneration is a major cause of pain, disability, fragility fracture, and loss of independence in aging populations. Although osteoporosis, osteoarthritis, and intervertebral disc degeneration are usually managed as anatomically separate disorders, they share a common regenerative failure: endogenous stem and progenitor cells lose renewal capacity, acquire inflammatory secretory programs, and become less able to rebuild damaged matrix. This narrative review synthesizes evidence on senescence in bone marrow mesenchymal stem/stromal cells, skeletal stem cells, hematopoietic stem cells, cartilage progenitor cells, synovial mesenchymal stromal cells, and disc-derived progenitor populations. Priority is given to primary mechanistic, omics, translational, and early clinical studies that connect senescence markers with functional impairment or intervention response. We discuss telomere-associated DNA damage, mitochondrial and oxidative stress, nutrient- and mechanosensing pathways, epigenetic remodeling, dysregulated autophagy and mitophagy, and the senescence-associated secretory phenotype as interlocking mechanisms that reshape skeletal niches. Disease-specific sections then examine how senescent progenitor compartments drive osteoporosis, osteoarthritis, and intervertebral disc degeneration through impaired osteogenesis or chondrogenesis, matrix catabolism, inflammatory vesicle signaling, and maladaptive mechanical feedback. Finally, we compare senolytics, senomorphics, metabolic and mitochondrial regulators, cell rejuvenation, extracellular vesicle engineering, biomaterials, and gene-based delivery platforms from a regenerative medicine perspective. Stem/progenitor cell senescence should be treated not simply as a biomarker of aging, but as a compartment-specific therapeutic bottleneck. Translation will require rigorous cell identity, multi-parameter senescence assays, disease-stage stratification, and therapies that restore regenerative competence without suppressing physiological repair.