GPR65 promotes intestinal mucosal Th1 and Th17 cell differentiation and gut inflammation through downregulating NUAK2

Abstract

G protein‐coupled receptor 65 (GPR65), a susceptibility gene for inflammatory bowel diseases (IBD), has been identified to promote Th17 cell pathogenicity and induce T cell apoptosis. However, the potential role of GPR65 in modulating CD4+ T cell immune responses in the pathogenesis of IBD stills not entirely understood. Here, we displayed that GPR65 expression was increased in inflamed intestinal mucosa of IBD patients and positively associated with disease activity. It was expressed in CD4+ T cells and robustly upregulated through the TNF‐α‐caspase 3/8 signalling pathway. Ectopic expression of GPR65 significantly promoted the differentiation of peripheral blood (PB) CD4+ T cells from IBD patients and HC to Th1 and Th17 cells in vitro. Importantly, conditional knockout of Gpr65 in CD4+ T cells ameliorated trinitrobenzene sulfonic acid (TNBS)‐induced acute murine colitis and a chronic colitis in Rag1–/– mice reconstituted with CD45RBhighCD4+ T cells in vivo, characterised by attenuated Th1 and Th17 cell immune response in colon mucosa and decreased infiltration of CD4+ T cells, neutrophils and macrophages. RNA‐seq analysis of Gpr65ΔCD4 and Gpr65flx/flxCD4+ T cells revealed that NUAK family kinase 2 (Nuak2) acts as a functional target of Gpr65 to restrict Th1 and Th17 cell immune response. Mechanistically, GPR65 deficiency promoted NUAK2 expression via the cAMP‐PKA‐C‐Raf‐ERK1/2‐LKB1‐mediated signalling pathway. Consistently, silencing of Nuak2 facilitated the differentiation of Gpr65ΔCD4 and Gpr65flx/flxCD4+ T cells into Th1 and Th17 cells. Therefore, our data point out that GPR65 promotes Th1 and Th17 cell immune response and intestinal mucosal inflammation by suppressing NUAK2 expression, and that targeting GPR65 and NUAK2 in CD4+ T cells may represent a novel therapeutic approach for IBD.

GPR65, a novel regulator of helper T‐cell polarization in inflammatory bowel disease

“…The elevated GPR65 + CD4 + cell findings in active IBD patients and pre‐clinical study outcomes reported by Lin et al. 5 support that GPR65 in CD4 + T cells acts as a positive regulator of IBD.…”

“…Lin and co‐authors 5 overexpressed GPR65 in cultured human CD4 + T cells to show that GPR65 prompts CD4 + T cells to polarize into T H 1 and T H 17 cells. Experimentally inducing colitis in conditional GPR65‐CD4 + T‐cell knockout mice resulted in a milder colitis phenotype compared to control mice.…”

“… 6 , 7 While previous reports relied on global GPR65 knockout mice, Lin et al. 5 employed a conditional knockout model and other approaches to show that GPR65 in CD4 + T cells prompts T H 1 and T H 17 cell polarization and exacerbates experimental IBD.…”

“…Investigations have reported that toll‐like receptor and MHC class II pathways can support one another due to similar processing of ligands/antigens within endosomal cellular compartments. 9 Considering GPR65 actions maintain lysosomal pH and function in macrophages 6 and promote T H 1 and T H 17 cell polarization, 5 GPR65 could be a significant player in innate‐adaptive immune cell crosstalk during IBD.…”

“…Work by Lin et al. 5 lays a foundation for future investigations defining GPR65's role in immune cell crosstalk, and underscores the need for research advancing knowledge about GPR65's role in gut microbiota–host interactions contributing to IBD. Because pH is a determinant for GPR65 function and IBD responses, it would be interesting to consider how shifts in the gut microbiota modulate the onset and progression of IBD.…”