Background/Purpose Helper T lymphocyte-17 (Th17) has recognized to be an important factor in rheumatoid arthritis (RA) pathogenesis. The natural ligand of glucocorticoid-induced tumor necrosis factor receptor (GITRL) could exacerbate autoimmune arthritis via the enhancement of Th17 cells expansion. It has reported that GITRL/GITR could trigger phosphorylation of p38 mitogen-activated protein kinase in T cell. The purpose of this study is to investigate the role of p38 signaling during the enhancement of Th17 expansion and exacerbation of autoimmune arthritis by GITRL stimulation.

Methods We used mouse GITRL (mGITRL) protein as a co-stimulatory factor for Th17 differentiation in presence or absence of p38 inhibitor and detected ability of Th17 differentiation. Activated naïve CD4⁺T cells were pretreated with or without p38 inhibitor before stimulated with mGITRL and phosphorylation of p38 and STAT3 were examined by western blot. And we injected mGITRL protein into collagen induced arthritis (CIA) mice alone or combine with the p38 inhibitor, and observed development of arthritis. 

Results In previous study, we have certificated a function of GITRL in exacerbating autoimmune arthritis via the enhancement of Th17 cells expansion. In this study, naïve CD4⁺T cells could differentiate into higher frequency of Th17 cells under the mGITRL co-stimulated and be attenuated in a concentration dependent manner by p38 inhibitor treatment. Also, the relative expression of RORγt and IL-17 mRNA was impaired with p38 inhibitor in a concentration dependent manner. Phosphorylation of p38 was reinforced in activated naïve CD4⁺T cells after stimulated with GITRL protein. STAT3 has two important phosphorylation sites, tyrosine705 (Tyr705) and serine727 (Ser727). An enhancement of STAT3Ser727 phosphorylation by mGITRL stimulate was observed and been attenuated in activated naïve CD4⁺T cells with p38 inhibitor pretreated. CIA models were established for investigate the function of p38 in the process of arthritis. Compared with the group treated by mGITRL protein (mGITRL-CIA group), the group injected with mGITRL and p38 inhibitor (mGITRL-SB203580-CIA group) had a later onset of symptoms and reached the peak score gently. There were more serious inflammatory changes in the mGITRL-CIA group. Th17 cells and the level of IL-17 in serum of the mGITRL-group increased significantly compared with the mGITRL-SB203580-CIA group. 

Conclusion Our results suggested that the enhancement of Th17 cells differentiation with mGITRL stimulation was influenced by p38-STAT3 singnaling pathway activation; the exacerbation of CIA development in mice by mGITRL can be released with p38 inhibitor treatment and correlate with the attenuation of Th17 cells. This phenomenon may provide a new insight in the study of RA pathopoiesis and clinical treatment.

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ACR Meeting Abstracts - https://acrabstracts.org/abstract/ligand-of-glucocorticoid-induced-tumor-necrosis-factor-receptor-enhances-th17-cells-response-in-collagen-induced-arthritis-via-p38-mapk-and-stat3-pathway/