Yuan, Gongsheng, Yang, Shu-ting, Yang, Shuying
University of Pennsylvania School of Dental Medicine, Department of Basic and Translational Sciences
Osteoarthritis (OA) is the most common joint disorder which affects more than 500 million people worldwide. Regulator of G-protein signaling 12 (RGS12) is a multifunctional protein that plays a key role in regulating inflammation and bone remodeling. This study aims to investigate the role of RGS12 in OA and explore underlying mechanisms.Methods
Macrophage lineage RGS12 deficient (cKO) mice were generated by mating RGS12fl/fl mice with LysM-Cre+ transgenic mice. Osteoarthritis was created by transection of anterior cruciate ligaments on the right knee joints of 8-week-old female RGS12 cKO and LysM-Cre+ control mice. BMMs from 8-week-old WT and RGS12 cKO mice were analyzed to compare the protein profiles by performing the liquid chromatography-mass spectrometry (LC-MS) proteomic analysis. The phenotype of osteoarthritis was evaluated by histology analysis and OARCI score. Primary macrophages and RAW264.7 cells were used to analyze the function and mechanism of RGS12 in vitro. Macrophage function and activity were determined by the overexpression of RGS12 (RGS12 OE) and knockdown of RGS12. The biological mechanism was analyzed by immunofluorescence (IF), real-time PCR, western blot, and immunoprecipitation (IP).Results
We found that RGS12 deficiency in macrophages inhibits OA, cartilage damage, and the release of proinflammatory cytokines in vivo study. Mechanically, we found that RGS12 in macrophages promotes the association between ubiquitin and IκB during inflammation. RGS12 promotes the degradation of IκB by enhancing the ubiquitination which is inhibited by MG132 (proteasome inhibitor). Moreover, the increased ubiquitination further inhibits the expression of MTAP, which indirectly activates the phosphorylation of IκB. The degradation of IκB leads to nuclear translocation of NF-κB, which further promotes the gene expression of cytokines such as IL1β, IL6, and TNFα during inflammation. Importantly, RGS12 deficiency prevents ubiquitination and inflammation in surgically induced OA.Conclusion
We conclude that the lack of RGS12 in macrophages interferes with the ubiquitination and degradation of IκB, thereby, prevents inflammation and cartilage damage.