The Role And Mechanism Of GPR34 In Type 3 Innate Lymphoid Cell Activation And Tissue Repair

Effective repair after tissue injury is important for survival of all living organisms and abnormal tissue repair leads to development of epithelial injury-associated diseases,such as inflammatory bowel disease(IBD)and dermatitis.Previous studies have shown that type 3 innate lymphoid cells(ILC3s)can be activated rapidly after tissue injury and produce cytokines such as interleukin 22(IL-22)to promote tissue repair.Therefore,analyzing the mechanisms of ILC3 activation during tissue injury may provide a new therapeutic target for treatment of above diseases.G protein-coupled receptor(GPCR)family members are drug targets for human diseases.As a member of GPCR family,G protein-coupled receptor 34(GPR34)has been reported to sense lysophosphatidylserine(LysoPS),but the biological function is not clear.Our results show that,during tissue injury,GPR34 functions as a new danger-associated molecular pattern(DAMP)-sensing receptor recognizing LysoPS released by damaged tissues to trigger ILC3 activation and tissue repair.The main findings include:1.Gpr34-/-mice exhibit impaired tissue repair after colon injury.During dextran sodium sulfate(DSS)-induced colon injury,Gpr34-/-mice showed impaired tissue repair compared with Gpr34+/+ mice,indicating that GPR34 promoted tissue repair of damaged colon.2.Gpr34-/-mice show compromised ILC3 activation in damaged colon.During DSS-induced colon injury,the poorer tissue repair in Gpr34-/-mice than in Gpr34+/+mice was due to less IL-22 production of Gpr34-/-ILC3s and independent of Th22 cells,intestinal microenvironment,IL-23 signaling pathway and intestinal microbiota.3.LysoPS-GPR34 axis promotes ILC3 activation.In vitro,LysoPS induced ILC3s to produce IL-22 via GPR34.In addition,other receptors of LysoPS,such as GPR174 and P2RY10,were not involved in ILC3 activation and tissue repair of damaged colon.4.The PI3K-AKT and RAS-ERK signaling pathways act downstream of GPR34 to promote ILC3 activation.In vitro,inhibition of PI3K-AKT and RAS-ERK signaling pathways caused impaired ILC3 activation and IL-22 production,but inhibition of PLC or activation of AC signaling pathways had no effects on IL-22 secretion.5.ILC3-intrinsic expression of Gpr34 facilitates tissue repair of damaged colon.During DSS-induced colon injury,Gpr34fl/fl Rorccre mice and Gpr34-/-Rag1-/-mice exhibited impaired tissue repair compared with littermate control mice,suggesting that ILC3-intrinsic expression of Gpr34 mediated tissue repair of damaged colon.6.GPR34 promotes tissue repair of injured skin.During full-thickness resection-induced skin injury,Gpr34-/-mice and Gpr34fl/fl Rorccre mice showed impaired skin repair compared with littermate control mice,and rmIL-22 supplementation rescued the delayed wound healing of Gpr34fl/flRorccre mice,demonstrating that GPR34 also mediated tissue repair of injured skin.In a conclusion,our findings demonstrate that ILC3s can directly sense LysoPS released by damaged tissues via intrinsic GPR34 and produce reparative cytokine IL-22 to promote tissue repair.More importantly,our study shows that GPR34 is a new DAMP-sensing receptor and has potential to be the therapeutic target for treatment of IBD,dermatitis and other diseases.