Study On The Regulation Of Immunosuppressive Properties Of Adipose-derived Mesenchymal Stem Cells And The Associated Mechanisms

Mesenchymal stem cells?MSCs?are widely used in the field of tissue engineering and regenerative medicine.Traditionally,MSCs were considered to play a therapeutic role in the tissue repair through differentiating into functional cells instead of partially damaged cells.With the advancement in understanding of their biological properties,MSCs have found to have immunosuppressive properties.They can secrete a variety of immunosuppressive factors,mediating the conversion of macrophages into anti-inflammatory response phenotype,thereby improving the microenvironment of the injured tissue and promoting tissue regeneration and repair.Adipose-derived mesenchymal stem cells?ASCs?have the advantages of large reserves in the body,easy access,and strong proliferative ability.Thus,they gradually show great potential in tissue engineering applications.This thesis attempts to use two different strategies to regulate the immunosuppressive properties of ASCs and to explore the underlying associated mechanisms,which may provide a new idea and theoretical basis for further study and clinical application of ASCs in tissue regeneration.The surface of biomaterials can not only provide cells with structural support for migration and growth,but also provide specific physical and chemical stimuli to regulate the cell phenotype and improve the local microenvironment.Fiber orientation as one of the key physical properties of fibrous biomaterials,plays an important regulatory role in regulating cellular behaviors.Therefore,this thesis first studied the influence of electrospun fibers orientation on the immunosuppressive properties of ASCs and its molecular mechanism.The results showed that fibers with the same orientation?Aligned fibers?promoted the expression of multiple immunomodulatory factors?such as PGE₂,TSG-6 etc?in ASCs compared to randomly oriented fibers.Conditioned media contained these factors further induce polarization of dTHP-1 cells toward an anti-inflammatory phenotype?M2type?macrophages.Further studies revealed that the FAK-ERK1/2and YAP/TAZ signaling pathways mediate the regulation of immunosuppressive properties of ASCs by aligned fibers.miRNA-146a is the first microRNA?miRNA?found to have a regulatory role in the immune system and plays a crucial role in regulating the differentiation and fuction of innate and adaptive immune cells.miRNA sponges is a kind of mi RNA antisense sequence which specifically"adsorbs"target mi RNA family,thereby reducing the content of mature miRNA.Therefore,in this thesis,a specific miRNA sponges was designed and constructed to target miR-146a.miR-146a sponges was transferred into ASCs to down-regulate miR-146a expression.We found that the downregulation of miR-146a promoted ASCs to express a variety of immunomodulatory factors?such as TSG-6,IDO,etc.?and chemokines?such as MCP-1?.Conditioned media contained these factors further promoted the migration of dTHP-1 cells and induce their polarization toward an anti-inflammatory phenotype?M2type?macrophages.In addition,the down-regulation of mi R-146a also enhanced the osteogenic differentiation of ASCs by stimulating the expression of major osteogenic genes?such as ALP,Runx2,etc.?,including the synthesis of alkaline phosphatase and the deposition of calcium nodules.