Study On The Effect And Mechanism Of PDGFR?⁺ Cells In Fibrotic Scar Formation After Spinal Cord Injury

Background: After spinal cord injury(SCI),fibroblasts gradually proliferate,migrate,and deposit extracellular matrix,corralling the macrophages at the injured core to form a fibrotic scar structure.Inhibition of fibrotic scar formation can promote axon regeneration and function recovery,but the molecular mechanism of fibrotic scar formation is still unclear,and fibrotic scar lacks specific intervention targets.It has been reported that platelet-derived growth factor receptor beta(PDGFR?),as a marker of fibroblasts after SCI,can only be activated by platelet-derived growth factor(PDGF)B or PDGFD.Therefore,this study aimed to investigate the effect of the PDGF/PDGFR?pathway in fibrotic scar formation after SCI.Methods: A spinal cord compression injury C57BL/6 mouse model was used.in situ injection of exogenous PDGFB or PDGFD in the spinal cord was used to specifically activate the PDGFR? pathway in the uninjured spinal cord,while intrathecal injection of SU16 f was used to specifically block the PDGFR? pathway in the uninjured or injured spinal cord.Immunofluorescence staining was performed to explore the distributions and cell sources of PDGFB and PDGFD,and to evaluate astrocytic scar,fibrotic scar,inflammatory cells,lesion and axon regeneration after SCI.Basso Mouse Scale(BMS)and footprint analysis were performed to evaluate locomotor function recovery after SCI.Results: We found that the expression of PDGFD and PDGFB increased successively after SCI,and PDGFB was mainly secreted by astrocytes and distributed outside the injured core,while PDGFD was mainly secreted by macrophages/microglia and fibroblasts and distributed inside the injured core.In addition,in situ injection of exogenous PDGFB or PDGFD can lead to the formation of fibrotic scar in the uninjured spinal cord,while this profibrotic effect could be specifically blocked by the PDGFR?inhibitor SU16 f.After treating mice after SCI with SU16 f,we found that SU16 f can reduce fibrotic scar,interrupt the contiguous boundary of scar and reduce inflammation and lesion,which ultimately promoted axon regeneration and locomotor function recovery after SCI.Conclusions: The PDGF/PDGFR? pathway can directly induce fibrotic scar formation after SCI,and specific blocking of this pathway would contribute to axon regeneration and function recovery after SCI.The PDGF/PDGFR? pathway is expected to be a specific molecular therapeutic target for SCI.Background: After spinal cord injury(SCI),pericytes/fibroblasts migrate to the injured site and deposit extracellular matrix(ECM)to form fibrotic scar,thereby hindering axon regeneration and function recovery.The mechanism of fibrotic scar formation is still unclear,and related studies have shown that macrophages may be involved in recruiting pericytes/fibroblasts to injured site,and macrophages exhibit M1 or M2 polarization and play different functions in various disease states.Therefore,this study aimed to investigate the effect of macrophage polarization on pericytes/fibroblasts migration and ECM secretion after SCI.Methods: The spinal cord compression injury C57BL/6 mouse was used for in vivo studies,and RAW 264.7 and MBVP cells were used for in vitro studies.Immunofluorescence staining was used to observe the spatiotemporal distribution relationship between macrophages and pericytes/fibroblasts and the polarization of macrophages after SCI.Scratch assay and Transwell assay were used to evaluate cell migration ability.Western Blot and immunocytochemistry staining were used to detect the expression level of ECM.Results: This study found that platelet-derived growth factor receptor(PDGFR)?+ pericytes/fibroblasts and macrophages synchronously aggregated to the injured site from 3 to 14 days after SCI,and finally PDGFR?+ pericytes/fibroblasts corralled macrophages to form fibrotic scar.At 3 and 7 days after SCI,macrophages were predominantly M2 phenotype,and at 14 days after SCI,macrophages were predominantly M1 phenotype.In addition,conditioned medium of M2 macrophages can induce PDGFR?+ pericytes to migrate and secrete ECM laminin in vitro.Conclusion: After SCI,macrophages are closely related to the spatiotemporal distribution of PDGFR?+ pericytes/fibroblasts,and macrophages are mainly M2 phenotype in the early stage of SCI,and then change to M1 phenotype.In addition,M2 macrophages can promote PDGFR?+ pericytes migration and secrete ECM.This study is expected to provide a basis for M2 macrophages regulating fibrotic scar formation after SCI.