Calcitonin gene-related peptide: An intra-articular therapeutic target for TMJ disorders

Objectives: The goal of this project was to evaluate the role of calcitonin gene-related peptide (CGRP) in the development of arthritis. Methods: Herein, we employed somatic mosaic analysis in two different joints by FIV(CGRP) intra-articular inoculation in the knees or temporomandibular joints (TMJ) of young adult male C57/BL6 mice. FIV(CGRP) is a feline immunodeficiency virus over-expressing full-length CGRP. Joint pathology and function were evaluated at the histopathological and behavioral levels. In addition, CGRP signaling was inhibited by intra-articular inoculation using FIV(CGRP_8-37), such that the inhibitory peptide CGRP(8-37) was overexpressed 4 weeks after induction of joint inflammation in the TMJ of IL-1β^XAT transgenic mouse model. The mice were evaluated for behavior and killed for evaluation of knee and TMJ pathology. Results: Overexpression of CGRP in the joints of wild-type mice induced the development of joint anomalies, including meniscal hypertrophy and articular pathology, associated with nocifensive behavior. Intriguingly, overexpression of the CGRP(8-37) inhibitory peptide in the knee and TMJ of IL-1β^XAT transgenic mice with joint inflammation resulted in partial amelioration of the attendant joint pathology. Conclusions: The results of this study suggest that CGRP is sufficient and necessary for the development of joint pathology and may serve as an intra-articular therapeutic target using gene therapy or monoclonal antibody-based therapies.