Intra-Articular Sprouting Of Nociceptors Accompanies Progressive Osteoarthritis: Comparative Evidence In Four Murine Models
ObjectiveKnee joints are densely innervated by nociceptors. Sprouting of nociceptors has been reported in late-stage osteoarthritis (OA), both in human knees and in rodent models. Here, we sought to describe progressive nociceptor remodeling in four mouse models of knee OA, capturing early and late-stage disease. MethodsSham surgery, destabilization of the medial meniscus (DMM), partial meniscectomy (PMX), or non-invasive anterior cruciate ligament rupture (ACLR) was performed in the right knee of 10-12-week old male C57BL/6 NaV1.8-tdTomato mice. Mice were euthanized (1) 4, 8 or 16 weeks after DMM or sham surgery; (2) 4 or 12 weeks after PMX or sham; (3) 1 or 4 weeks after ACLR injury or sham. Additionally, a cohort of naive male wildtype mice was evaluated at 6 and 24 months. Twenty-m thick mid-joint cryosections were assessed qualitatively and quantitatively for NaV1.8+ and PGP9.5+ innervation. Cartilage damage (using a modified OARSI score), synovitis, and osteophytes were assessed blindly. ResultsProgressive OA developed in the medial compartment after DMM, PMX, and ACLR. Synovitis and associated neo-innervation by nociceptors peaked in early-stage OA. In the subchondral bone, channels containing sprouting nociceptors appeared early, and progressed with worsening joint damage. Two-year old mice developed primary OA in both the medial and the lateral compartment, accompanied with neuroplasticity in the synovium and the subchondral bone. All 4 models had an increased nerve signal in osteophytes. ConclusionAnatomical neuroplasticity of nociceptors was observed in association with joint damage in 4 distinct mouse models, suggesting that it is intrinsic to OA pathology.