Glucocorticoids promote joint microenvironment alteration of GABBR1 expression associated with mitigating rheumatoid arthritis.

ABSTRACT

GABBR1 receptors have been implicated in the progression of rheumatoid arthritis (RA), and p38 MAP kinase (MAPK) was shown to be downregulated by GABA and result in unchecked production of pro-inflammatory cytokine. GABBR1 is a member of GABA receptors, and it is known to be upregulated and plays a vital role in RA. Glucocorticoids are efficient therapeutics in rheumatoid arthritis (RA) and are known to regulate GABA actions; therefore, we intended to investigate the potential of glucocorticoids in RA concerning the potential pathway GABBR1/MAPK. Joint specimens were obtained from collagen-induced arthritis mouse model. A double-blind semi-quantitative analysis of vascularity, cell infiltration, as well as lining thickness by help of a 4-point scale setting was used to assess joint inflammation. Expression of GABBR1 and p38 was evaluated immunohistochemically. In vitro peripheral blood (PB), synovial fluid (SF), and mononuclear cells (MCs) were acquired from RA mice. Western blotting was used for detecting expression of GABBR1 and p38 proteins. The presence of high levels of GABBR1 and p38 was prevalent in RA joints relative to healthy joints and related to the inflammation level. Glucocorticoid treatment alters GABBR1 along with p38 protein expression in joints while reducing joint inflammation. Ex vivo and in vitro assays revealed glucocorticoids have a direct impact on p38, such as the decreased GABBR1 expression level after dexamethasone incubation with SFMC. GABBR1 together with p38 expression in RA joints depends on local inflammation and can be targeted by glucocorticoids.