Background/Purpose: Osteoarthritis (OA) is a painful disease of the synovial joint and is the most common form of arthritis with a large global burden. A subset of individuals with knee OA complain of neuropathic type pain with symptomology of burning, paresthesia, and spontaneous pain in the affected joint. Since nociceptive and neuropathic pain components may require different treatment strategies, it is imperative to understand mechanisms underlying each symptomology. However, it is unknown how changes in the joint may be driving neuropathic like symptoms. Thus, we set out to compare transcriptomic data of synovial joint samples between individuals with and without neuropathic type pain undergoing joint replacement for knee OA.

Methods: A total of 35 individuals (10 males, 25 females) were enrolled who were diagnosed with knee OA by an orthopedic surgeon and undergoing total knee arthroplasty surgery. All individuals completed the painDETECT questionnaire prior to surgery to determine level of neuropathic pain symptomology. Synovial joint samples from the surgical knee were collected and frozen in pulverized dry ice. A painDETECT cutoff score of ≤12 was used to group individuals into low or moderate/high probability of neuropathic pain. RNA was extracted from tissues and bulk RNA sequencing was performed to compare transcriptomic differences between individuals with low (n=25, 8 males, 17 females) and moderate/high painDETECT scores (n=10, 2 males, 8 females). To determine differentially expressed genes (DEGs), the R package DESeq was used to compare differences between low and moderate/high painDETECT score, with sex run as a covariate (DEG: log2fc >0.585, adjusted p-value < 0.1). To make predictions surrounding synovial joint to nociceptor signaling, a ligand receptor interactome was used to intersect upregulated DEG’s encoding for ligands with their known receptors on human nociceptive neurons.

Results: A total of 121 DEGs were identified with 115 upregulated and 6 downregulated. Gene pathway assessment of the upregulated genes revealed enrichment of genes responsible for neutrophil degranulation and extracellular matrix organization. The ligand receptor interactome revealed potential interactions between 5 ligands and 24 receptors on human nociceptive neurons. This included interactions with neurotrophic factors such as L1CAM, CBLN4, and NRXN3. These neurotrophic factors bind to several receptors on neurons which have been shown to drive increased nerve growth including DCC, EGFR, and NEO1.

Conclusion: We found a set of upregulated genes specific to individuals with knee OA who complain of neuropathic like pain. These genes revealed potential enhancement of neutrophil degranulation and increased neurite growth in individuals with neuropathic symptoms. Future work will look to validate these targets using cultured human dorsal root ganglion neurons.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/synovial-joint-transcriptomic-differences-in-individuals-with-knee-osteoarthritis-and-neuropathic-pain-symptomology/