The local-mechanical and systemic-metabolic dialogue: A new dawn in osteoarthritis treatment
Osteoarthritis (OA), long perceived as a passive, wear-and-tear degeneration of articular cartilage, is now unequivocally recognized as a complex and active disease of the entire joint. It affects over half a billion people, yet it remains notoriously lacking disease-modifying pharmacological therapies, with standard of care focusing on symptom management and ultimately joint replacement in the end-stage disease. The convergence of emerging technologies, bone biology, and clinical medicine is driving a new OA research paradigm, focused on identifying cartilage stem/progenitor cells and repurposing existing drugs. Two seminal studies published in 2025, one in Cell by Zhu et al.4 and another in Science by Yang et al.,5 have risen to this challenge. They highlight two complementary pathways in OA pathogenesis and repair: joint mechanosensitive progenitor cells and a systemic gut-derived metabolic axis, together establishing a new research paradigm and unveiling novel therapeutic targets.
Zhu and colleagues identified a previously elusive joint progenitor cell population crucial for cartilage maintenance and regeneration. The study begins with the elegant use of Procr-CreERT2; tdTomato mice for precise genetic lineage tracing. The authors have critically discovered that in the postnatal knee joint, protein C receptor-positive (Procr+) cells represent a distinct subset of Prg4-expressing superficial cells, and Procr+ cells are not evenly distributed. They are mainly found in the tibial articular cartilage superficial areas and the meniscus and are less abundant in the femur. The initial indicator of their functionality is this spatial particularity; the tibial plateau is the most exposed to mechanical forces, and it is proposed that these cells are mechano-responsive. These cells reach a peak number during puberty and decrease with age.
The authors then elegantly demonstrated a causal relationship between mechanical forces and Procr+ cell activity. Subjecting mice to forced running (a model of increased load) not only significantly expanded the pool of Procr+ cells in the tibia but also induced their increase in the femur. Conversely, tail suspension (a model of mechanical unloading) significantly reduced their numbers (Figure 1A). This was not simply a passive response; applying cyclic tensile strain to sorted Procr+ cells in vitro revealed that expression of Procr itself, as well as known mechanosensitive genes. Piezo1 and Klf2 were upregulated in a strain-dependent manner. This establishes Procr not only as a marker but also as a mechanosensitive component of these progenitor cells.
