ESCRT Protein CHMP5 Drives Bone Overgrowth Through Cellular Senescence
Deleting CHMP5 in bone cells triggers endolysosomal dysfunction, mitochondrial ROS, and cell senescence — causing abnormal bone growth reversible by senolytic drugs.
Summary
Researchers discovered that CHMP5, an ESCRT-III protein, normally restrains bone formation in osteogenic cells. When CHMP5 is genetically deleted in mice, endolysosomal function breaks down due to reduced VPS4A protein levels. This dysfunction impairs mitochondria, elevates reactive oxygen species (ROS), and drives skeletal cell senescence. Senescent cells then promote abnormal bone overgrowth through both direct (cell-autonomous) and indirect (paracrine) mechanisms, causing joint stiffness, skeletal deformity, and muscle loss. Critically, treating mice with senolytic drugs — which selectively eliminate senescent cells — significantly alleviated these musculoskeletal abnormalities, pointing to a potential therapeutic strategy for lysosomal storage diseases affecting the skeleton.
Detailed Summary
Lysosomal storage diseases and other endolysosomal pathway disorders frequently cause debilitating musculoskeletal complications, including bone deformity, joint stiffness, and muscle atrophy. Yet the cellular mechanisms linking endolysosomal dysfunction to skeletal pathology have remained poorly understood. This study identifies CHMP5, a component of the ESCRT-III membrane-remodeling complex, as a critical regulator of bone formation and skeletal cell health in mice.
Using conditional knockout strategies, researchers deleted Chmp5 specifically in Ctsk-expressing periskeletal progenitors and Dmp1-expressing osteocytes/mature osteoblasts. Both models developed progressive, age-dependent bone overgrowth, cortical bone expansion, joint stiffness, reduced bone quality (lower stiffness and fracture stress despite greater mass), skeletal muscle atrophy, and impaired motor function. Lineage-tracing experiments confirmed that Ctsk+ progenitors are the primary cell population expanding into aberrant periskeletal bone in knockout animals.
Mechanistically, Chmp5 deletion caused endolysosomal dysfunction characterized by reduced VPS4A protein levels — an ATPase essential for ESCRT-III disassembly and MVB formation. Conversely, CHMP5 overexpression was sufficient to restore VPS4A levels, establishing a direct regulatory link. Endolysosomal dysfunction subsequently disrupted mitochondrial morphology and function, elevated mitochondrial reactive oxygen species (mitoROS), and triggered canonical markers of cellular senescence: increased p21, p16, SA-β-galactosidase activity, and a senescence-associated secretory phenotype (SASP). Both cell-autonomous differentiation defects and paracrine SASP signals from senescent skeletal cells contributed to the aberrant osteogenic activity observed in vitro and in vivo.
Crucially, administration of senolytic drugs (dasatinib plus quercetin, or navitoclax) to Chmp5 conditional knockout mice selectively cleared senescent skeletal cells and substantially reduced musculoskeletal abnormalities, validating cell senescence as a druggable mechanism in this context. These findings establish a linear pathway: CHMP5 loss → VPS4A reduction → endolysosomal dysfunction → mitochondrial ROS elevation → skeletal cell senescence → abnormal bone formation.
The work has broad implications for lysosomal storage diseases, which share endolysosomal dysfunction as a common pathological feature and for which skeletal complications remain largely refractory to current therapies including enzyme replacement and hematopoietic stem cell transplantation. Identifying senolytic intervention as an effective strategy in a genetic mouse model offers a translatable therapeutic concept for this under-addressed disease dimension.
Key Findings
- Chmp5 deletion in osteogenic cells causes progressive periskeletal bone overgrowth, joint stiffness, and muscle atrophy in mice.
- CHMP5 loss reduces VPS4A protein, impairing endolysosomal function and disrupting mitochondrial integrity.
- Elevated mitochondrial ROS following endolysosomal dysfunction drives skeletal cell senescence (p21, p16, SA-β-gal, SASP).
- Senescent skeletal cells promote aberrant bone formation via both cell-autonomous and paracrine mechanisms.
- Senolytic drugs (dasatinib + quercetin; navitoclax) clear senescent cells and alleviate musculoskeletal pathology in knockout mice.
Methodology
The study used tissue-specific Cre-lox conditional knockout mice (Ctsk-Cre and Dmp1-Cre drivers) to delete Chmp5 in osteogenic lineage cells, combined with lineage tracing, micro-CT, histology, mechanical testing, and in vitro osteogenic assays. Senolytic interventions (dasatinib + quercetin and navitoclax) were administered to evaluate therapeutic efficacy in vivo.
Study Limitations
The study is conducted entirely in mice, and translation to human lysosomal storage diseases requires validation in patient-derived cells and clinical models. The specific contribution of different osteogenic cell subpopulations (progenitors vs. mature osteoblasts/osteocytes) to the observed phenotype needs further dissection, and long-term safety of senolytic treatment in growing skeletal tissue was not fully addressed.
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