Macrophage regulator of G-protein signaling 12 contributes to inflammatory pain hypersensitivity

Pain is a predominant symptom in rheumatoid arthritis (RA) patients that results from joint inflammation and is augmented by central sensitization. Regulator of G-protein signaling 12 (RGS12) is the largest protein in the RGS protein family and plays a key role in the development of inflammation. This study investigated the regulation of RGS12 in inflammatory pain and explored the underlying mechanisms and potential RA pain targets.

Macrophage-specific RGS12-deficient (LysM-Cre⁺;RGS12^fl/fl) mice were generated by mating RGS12^fl/fl mice with LysM-Cre⁺ transgenic mice. Collagen antibody-induced arthritis (CAIA) models were induced in LysM-Cre⁺;RGS12^fl/fl mice by the administration of a cocktail of five monoclonal antibodies and LPS. Mouse nociception was examined using the von Frey and heat plate tests. Primary macrophages and RAW264.7 cells were used to analyze the regulatory function and mechanism of RGS12 in vitro. The expression and function of RGS12 and COX2 (cyclooxygenase 2) were determined by real-time PCR, ELISA, and luciferase assays.

Ablation of RGS12 in macrophages decreased pain-related phenotypes, such as paw swelling, the clinical score, and the inflammatory score, in the CAIA model. LysM-Cre⁺;RGS12^fl/fl mice displayed increased resistance to thermal and mechanical stimulation from day 3 to day 9 during CAIA, indicating the inhibition of inflammatory pain. Overexpression of COX2 and PGE2 in macrophages enhanced RGS12 expression, and PGE2 regulated RGS12 expression through the G-protein-coupled receptors EP2 and EP4. Furthermore, RGS12 or the RGS12 PTB domain strengthened the transcriptional regulation of COX2 by NF-κB, whereas inhibiting NF-κB suppressed RGS12-mediated regulation of COX2 in macrophages.

Our results demonstrate that the deletion of RGS12 in macrophages attenuates inflammatory pain, which is likely due to impaired regulation of the COX2/PGE2 signaling pathway.