Background/Purpose: Nociceptors abundantly innervate the knee joint. In experimental osteoarthritis (OA), nociceptors sprout in the medial synovium and in subchondral bone channels. We aimed to determine the effect of selective ablation of knee-innervating nociceptors in murine OA.

Methods: Adeno-associated virus AAV.PHP.S carrying diphtheria toxin A (dtA) (AAV-dtA) or control AAV (AAV-Ctrl) was injected intra-articularly (i.a.) into the knee cavity of 7-week old male NaV1.8-Cre mice. Destabilization of the medial meniscus (DMM) or sham surgery were performed 3 weeks later. Pain-related behaviors (weight bearing and knee hyperalgesia) were assessed up to 16 weeks after surgery. Knee joints were collected for histology, microCT, innervation analysis, and protein antibody array. Lumbar dorsal root ganglia (DRG) were collected for immunofluorescence staining or qPCR analysis.

Results: Injection of AAV-dtA effectively ablated joint nociceptors. This had no effect on knee hyperalgesia but attenuated weight bearing deficits (Fig. 1A-B), with decreased Ccl2 in DRG (Fig. 1C). AAV-dtA administration suppressed nociceptor sprouting in subchondral bone channels (Fig. 1D), but not in the medial synovium (Fig. 1E). Marked cartilage damage observed in AAV-Ctrl injected joints was attenuated in AAV-dtA injected mice (Fig. 2A), while synovitis, osteophytes, and microCT of the subchondral bone were similar in both groups. Knee joint lysates showed lower levels of calcitonin gene-related peptide (CGRP) 4 and 8 weeks after DMM in AAV-dtA injected mice (Fig. 2B), as well as decreased pro-inflammatory factors 8 weeks after DMM and increased levels of cartilage-anabolic markers 16 weeks after DMM (Fig. 2C). CGRP+ neurons were also decreased in ipsilateral lumbar DRGs, along with reduced NaV1.8+ neurons after ablation.

Conclusion: Knee-innervating nociceptor ablation before DMM attenuated weight bearing asymmetry, subchondral bone nerve sprouting, and cartilage degeneration. Cartilage anabolic factors were increased in the joints, while CGRP levels were decreased. The neurogenic contribution to OA may result from the neuropeptides released from nerve endings in early stages of OA.

Fig. 1. Pain behavioral tests and knee joint innervation analysis in DMM mice with IA NaV1.8+ neuron ablation. (A) Weight bearing tests. (B) Knee hyperalgesia tests. (C) Expression of pro-algesic Ccl2 mRNA in ipsilateral L3-L5 DRG. (D, E) Nerve sprouting in subchondral bone (D) and medial synovium (E) was analyzed with IF staining of a pan-neuronal marker TUBB3.

Fig. 2. Knee joint histopathological analysis and joint lysate protein analysis of DMM mice with intra-articular NaV1.8+ neuron ablation. (A) Representative images of medial compartments of mouse knee sections stained with toluidine blue. Cartilage degeneration and osteophyte formation were evaluated using a modified OARSI scoring system. (B) ELISA assay of CGRP protein in DMM knee joint lysates. (C) Antibody arrays of DMM knee joint lysates (Quantibody® Mouse Cytokine Antibody Array, RayBiotech).

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/targeted-ablation-of-knee-innervating-nociceptors-attenuates-pain-and-cartilage-degeneration-in-experimental-osteoarthritis/