Molecular Mechanism Research Of Acid And Mechanical Dual-sensing Receptor G Protein Coupled Receptor 68 In The Repair Of Cartilage Defect

Cartilage defect is a common joint disease in the clinic.At present,there is no method to completely repair cartilage defect.Articular cartilage is a mechanosensitive organization,and moderate force stimulation can protect the joints.It has been reported that the cell membrane receptor Gpr68 is not only a p H sensing receptor,but also a mechanical sensing receptor.In order to determine whether Gpr68 can promote cartilage repair and use it as a target to treat articular cartilage defect,we conducted the following research.In this study,we developed a cartilage injury model.Compared with wild type mice(Gpr68+/+),the repair of cartilage injury in Gpr68 knockout mice(Gpr68-/-)was significantly slowed,and the expression of cartilage matrix synthesis markers such as type II collagen(Col2a1),aggrecan(Acan)and superficial zone protein(Prg4)was reduced.In addition,the deletion of Gpr68 increased the pain induced by cartilage injury.The results of in vitro cell experiments showed that the differentiation of articular chondrocyte precursor cells without Gpr68 was inhibited and the hypertrophy process was promoted.In contrast,we treated the articular chondrocyte precursor cells with an agonist of Gpr68 named Ogerin and found that chondrocyte differentiation was significantly enhanced.In addition,Micro-CT showed that Ogerin can significantly increase subchondral bone regeneration and promote cartilage repair in the C57BL/6 cartilage defect mouse model;Histological staining showed that Ogerin significantly improved the microscopic score of cartilage repair,and the accumulation of cartilage synthesis markers Col2a1 and Prg4 was significantly increased.Finally,we initially explored the mechanism of Gpr68 in the repair of cartilage defect,and found that activating Gpr68 can inhibit the infiltration of inflammatory cells,recruit bone marrow mesenchymal stem cells(BMSCs)to differentiate into chondrocytes,and activate the phosphorylation of Creb in chondrocytes to upregulate the expressions of Prg4 and Col2a1,which ultimately promotes cartilage repair.At the same time,we found that Ogerin can promote the migration of human bone marrow mesenchymal stem cells and maintain the phenotype of human chondrocytes in vitro.These results indicate that the acid and mechanical dual-sensing receptor Gpr68 can not only alleviate pain induced by cartilage defect,but also play an important role in cartilage protection and regeneration by regulating anti-inflammatory functions,recruiting BMSCs and improving extracellular matrix components.It can be used as a drug target for relieving pain induced by cartilage defect and promoting cartilage repair.The agonist of Gpr68 named Ogerin can improve the repair ability of damaged cartilage and effectively alleviate the pain induced by cartilage defect.Ogerin has the potential to be developed into a drug for cartilage defect.