Transient Receptor Potential Ankyrin 1 (TRPA1) Mediates Lipopolysaccharide (LPS)-Induced Inflammatory Responses in Primary Human Osteoarthritic Fibroblast-Like Synoviocytes.

Transient receptor potential ankyrin 1 (TRPA1) is a membrane-associated cation channel, widely expressed in neuronal and non-neuronal cells. Recently, emerging evidences suggested the crucial role of TRPA1 in the disease progression of osteoarthritis (OA). Therefore, we aimed to investigate whether TRPA1 mediate lipopolysaccharide (LPS)-induced inflammatory responses in primary human OA fibroblast-like synoviocytes (OA-FLS). The expression of TRPA1 in LPS-treated OA-FLS was assessed by polymerase chain reaction (PCR) and western blot (WB), and the functionality of TRPA1 channel by Ca2+ influx measurements. Meanwhile, production of interleukin (IL)-1ß, tumor necrosis factor (TNF)-α, IL-6, matrix metalloproteinase (MMP)-1, and MMP-3 in LPS-treated cells was measured by immunoassay. Histological observation after inhibition of TRPA1 was also performed in rats with LPS-induced inflammatory arthritis. After being induced by LPS, the gene and protein expression of TRPA1 was increased in the time-dependent or dose-dependent manner. Meanwhile, Ca2+ influx mediated by TRPA1 in human OA-FLS was also enhanced. In addition, pharmacological inhibition and gene silencing of TRPA1 downregulated the production of IL-1ß, TNF-α, IL-6, MMP-1, and MMP-3 in LPS-treated FLS. Finally, synovial inflammation and cartilage degeneration were also reduced by the TRPA1 antagonist. We found the LPS caused the increased functional expression of TRPA1, the activation of which involved in LPS-reduced inflammatory responses in primary human OA-FLS, and the inhibition of TRPA1 produces protective effect in LPS-induced arthritis.

Mechanism of TRPA1 and TRPV4 Participating in Mechanical Hyperalgesia of Rat Experimental Knee Osteoarthritis.

OBJECTIVES: This study aims to observe both transient receptor potential ankyrin 1 (TRPA1) and transient receptor potential vanilloid 4 (TRPV4) expressions in synovial tissues of rats with mechanical hyperalgesia induced by experimental knee osteoarthritis (KOA). PATIENTS AND METHODS: Forty-five four-month-old Sprague Dawley male rats, weight ranging from 440 g to 470 g, were randomly allocated into three groups, namely KOA group, KOA-antagonist group, and normal group. Mechanical withdrawal thresholds of five rats from each group were detected one week before modeling, and two, four, six, and eight weeks after modeling, respectively. Synovial and cartilage tissues from diseased knee were collected after sacrificing the rats eight weeks after modeling so to observe pathological morphology at cartilage tissues and to determine protein and gene expressions of TRPA1 and TRPV4 at synovial tissues. RESULTS: Rats with KOA showed obvious mechanical hyperalgesia from two weeks after modeling to the latest follow-up, eight weeks after modeling. The abnormally low level of mechanical withdrawal thresholds can be increased by TRPA1 and TRPV4 ion channel blockers. CONCLUSION: Up-regulating expressions of TRPA1 and TRPV4 participate in the occurrence mechanism of mechanical hyperalgesia induced by KOA.