The Essence of Degenerative Joint Disease Is Organelle Collapse, Not Wear; Changing the Treatment Paradigm through Mitochondrial Quality Control
Background
For a long time, academia and clinical fields have treated degenerative musculoskeletal diseases such as osteoarthritis (OA), intervertebral disc degeneration (IVDD), and osteoporosis (OP) as simple mechanical wear or physical damage due to aging. The classical explanatory model—that articular cartilage wears away or spinal discs are damaged because they cannot withstand pressure—only led to symptom-relief therapies centered on anti-inflammatory painkillers, failing to develop fundamental treatments that stop or reverse disease progression. While physical load acts as a major trigger, existing explanatory frameworks have struggled to account for why disease onset patterns and rates of exacerbation vary significantly among patients even under identical mechanical environments.
A turning point has arrived as focus shifts to the breakdown of molecular homeostasis occurring within degenerative musculoskeletal tissues. Researchers tracking how chondrocytes, nucleus pulposus cells, and osteocytes lose function and die amidst chronic metabolic deficiency and inflammatory microenvironments have focused on mitochondria, the cell's energy factory and survival control tower. The perception is taking root that physical wear is merely a surface-level result, and that the underlying cause of tissue degeneration is the collapse of the organelle-level quality control system.
Key Findings
The mitochondrial quality control (MQC) network in cells consists of a precise combination of dynamic fusion and fission, mitophagy (the selective removal of damaged organelles), and biogenesis (the creation of new organelles). This analysis clearly identified the molecular logic that all three types of degenerative musculoskeletal diseases share a malfunction of the aging-inflammation-metabolism axis stemming from MQC collapse.
When the MQC system collapses, mitochondrial DNA (mtDNA) fragments leak out of the mitochondria into the cytoplasm. These released fragments act as damage-associated molecular patterns (DAMPs), stimulating the cGAS-STING innate immune pathway. Consequently, an intense immune-inflammatory response is triggered within the organization. The accumulation of intermediate metabolites due to disruption of metabolic pathways induces histone lactylation, which remodels the epigenome and converts acute stress responses into chronic metabolic memory.
Based on multi-omics data and cell-free mtDNA-based liquid biopsy analysis, the researchers proposed a prototype pathway for classifying osteoarthritis patients into three subtypes: bioenergetic deficiency, immuno-inflammatory activation, and senescent cell accumulation. Each subtype is characterized by distinct primary molecular manifestations of mitochondrial dysfunction.
Treatment strategies are also shifting from conventional symptom management to 'organelle medicine,' which aims to repair or replace the organelles themselves. Major alternatives emerging include cardiolipin stabilizers that protect lipids in the inner mitochondrial membrane, proteolysis-targeting chimera (PROTAC) technology, mitochondrial base editing, and mitochondrial transplantation technology that directly inject functional organelles. In terms of clinical evidence, the metabolic regulator metformin is undergoing follow-up verification after confirming cartilage protection effects in a randomized controlled trial for knee osteoarthritis. NAD+ precursors have entered early clinical stages, and the peptide-based cardiolipin stabilizer SS-31 (elamipretide) has received accelerated approval only for the rare mitochondrial disease Barth syndrome, while remaining in the preclinical stage for musculoskeletal diseases.
Significance and Outlook
The approach that identifies the collapse of organelle networks as the root cause of degenerative musculoskeletal diseases, previously attributed to mechanical wear in tissues, fundamentally changes the framework for understanding these diseases. By unifying osteoarthritis, intervertebral disc degeneration, and osteoporosis not as separate destructive diseases but as abnormalities in a shared mitochondrial metabolic and immune axis, this approach opens the possibility for developing pan-musculoskeletal targeted therapies. If molecular subtype diagnosis using liquid biopsy is introduced, a precision medicine system will emerge in which patients with the same knee osteoarthritis are prescribed different treatments, such as anti-inflammatory agents versus energy metabolism promoters.
Clear barriers to actual clinical application also remain. Articular cartilage and intervertebral discs are avascular tissues with minimal blood vessel distribution, making it extremely difficult to deliver therapeutic agents intact into the mitochondria. Because disease heterogeneity among patients is very high, the proposed three molecular subtype classifications must undergo verification in independent clinical cohorts within osteoarthritis, and further proof is essential to determine if they can be extended to spinal disc or osteoporosis patient groups. In the future, the key to commercialization is expected to be the fusion of AI-based decision-making systems capable of interpreting large-scale patient data, along with the construction of biomimetic models to overcome delivery limitations.
Degenerative musculoskeletal disorders, including osteoarthritis (OA), intervertebral disc degeneration (IVDD), and osteoporosis (OP), are increasingly viewed as disorders of mitochondrial quality control (MQC) rather than passive mechanical wear. The MQC network, comprising mitochondrial dynamics, mitophagy-biogenesis coupling, and inter-organelle communication, organizes the aging-inflammation-metabolism axis. Its collapse releases mtDNA fragments that act as damage-associated molecular patterns (DAMPs) activating innate immunity via cGAS-STING, and metabolic intermediates that remodel the epigenome through histone lactylation, potentially locking acute stress into a "metabolic memory", although the mtDNA-methylation component remains hypothesis-level. Multi-omics and cell-free mtDNA liquid biopsy underpin a proposed subtyping into bioenergetic failure, immuno-inflammatory activation, and senescent cell accumulation, still a within-OA hypothesis pending independent and cross-disease validation. Therapy is shifting from symptom management toward organelle medicine, including cardiolipin stabilizers, PROTAC-mediated protein degradation, mitochondrial base editing, and engineered mitochondrial transplantation. Metformin has randomized trial evidence in knee OA pending confirmation, NAD+ precursors are in early clinical testing, and SS-31 holds accelerated approval only for Barth syndrome; other strategies remain preclinical. Delivery barriers and disease heterogeneity require precision stratification, biomimetic models, and AI-driven decision-making. This review delineates the shared molecular logic of the three diseases and proposes a prototype subtyping-to-treatment roadmap pending validation.
This research presents a new milestone in the development of Disease-Modifying Osteoarthritis Drugs (DMOAD) for chronic joint diseases. In scenarios of direct intra-articular injection, the administration of customized MQC regulators formulated as nanoparticles based on patient molecular characteristics identified via liquid biopsy, rather than simple hyaluronic acid or steroids, could become a reality. For example, a treatment paradigm will be established that directly blocks chondrocyte death and delays joint surgery by several years through the localized delivery of vehicles combined with cGAS-STING inhibitors for patients with active inflammation, or cardiolipin stabilizers or engineered exogenous mitochondrial agents for patients with energy deficiency.