Expression of transient receptor potential vanilloid 1 (TRPV1) in synovial fibroblasts from patients with osteoarthritis and rheumatoid arthritis

The transient receptor potential vanilloid 1 (TRPV1) is a nonselective cation channel, which is mainly expressed by nociceptive neurons in dorsal root and trigeminal ganglia. However, there is increasing evidence that TRPV1 expression is not limited to primary afferent neurons but that the receptor is expressed in various cell types throughout the body. Here, we demonstrate the expression of TRPV1 in synovial fibroblasts (SF) from patients with symptomatic osteoarthritis (OA) and rheumatoid arthritis (RA). In addition, the mRNA expression of TRPV1 was shown in PBMCs from healthy controls and from OA patients. The presence of TRPV1 was confirmed at the protein level. Stimulation of cultured OA- and RA-SF with the TRPV1 agonist capsaicin led to increased expression of IL-6 mRNA as well as of IL-6 protein in the cell culture supernatants. IL-6 protein expression could be antagonized with capsazepine. Thus, we hypothesize that TRPV1 may play a role in non-neuronal mechanisms that might modulate nociception in symptomatic OA and RA patients.