The Role Of PKM2 In Glioma Proliferation Invasion And Immunosuppression Under Metabolic Competition Microenvironment

Background: Malignant glioma(MG)is the most common primary malignant tumor in the central nervous system,which has the characteristics of abnormal proliferation,extensive infiltration,high heterogeneity as well as radiotherapy and chemotherapy resistance.Glioblastoma(GBM)is the most typical malignant glioma.There is growing evidence that cancer is a metabolic disorder with specific metabolic remodeling.At present,the existing treatment methods have not significantly prolonged the overall survival of GBM in the past 20 years,immunotherapy has brought hope.Aerobic glycolysis is a significant feature of the metabolic changes in GBM,and also needed for the rapid response of immune cells.Metabolic competition between tumor cells and immune cells in tumor microenvironment provides a clue to seek treatment targets.Pyruvate kinase M2(Pyruvate Kinase M2,PKM2)plays a key role in aerobic glycolysis and is a key rate-limiting enzyme in the final of the cellular glycolysis pathway.This study investigated the distribution and expression of PKM2 in gliomas and its role in the proliferation and invasion of tumor cells.Did inhibiting the PKM2 of tumor cells effect tumor growth and model animal survival? Whether the immunosuppressive state in tumor microenvironment can be changed? This study mainly focused on PKM2.Methods: By means of bioinformatics analysis,the expression of PKM2 in normal human tissues and different tumors were compared and analyzed with MERAV,Oncomine,Murat Brain and Sun Brain.The differences of the expression of PKM2 in control brain tissue and glioblastoma were analyzed emphatically.The TCGA and CGGA databases were further used to analyze PKM2 and related pathways in different histological types and pathological grades,summarized their characteristics,and also summarized the expression in immune-related cells.Cell fluorescence,immunohistochemical staining,Western blot and other experiments were performed to detect the expression of PKM2 in different grade of glioma tumor resection specimens and glioma cell lines.The model of intracranial implanting of C67BL/6 mouse with GL261 cells and the subcutaneous model of mouse GL261 cells were made to show the effects of inhibiting PKM2 on tumor growth inhibition and animal biological behavior and survival,and the changes of Tumor associated macrophage M2 in tumor specimens.Results: Compared to normal tissue cells,PKM2 is highly expressed in tumor cells and immune cells that rapid proliferation.PKM2 was expressed at all grades of gliomas,and the expression increased with the elevated grade.Inhibiting the expression of PKM2 can be able to inhibit the proliferation of cells,but it enhanced the invasion ability of tumor cells,and the possible mechanism is to enhance oxidative phosphorylation and initiate the expression of downstream skeleton protein.In vivo inhibition tests showed that tumor growth was inhibited,and the survival of mice was prolonged.The decrease of Tumor associated macrophage M2 was found in tumor specimens,which could relieve partial immunosuppressive effect due to the decrease of lactic acid.Conclusions: PKM2 is the key rate-limiting enzyme of aerobic glycolysis,which is highly expressed in malignant glioma,increased with the elevated grade.Abnormal expression of PKM2 resulted in the progression of tumor,knockdown the expression of PKM2 inhibited cell proliferation,but promoted cell invasion.Animal model experiments suggested that inhibiting PKM2 suppress the growth of tumor and prolong the survival of mouse.After inhibiting PKM2,M2 subtype tumor-related macrophages and expression of PD-L1 decreased in tumor tissue,and the immunosuppressive state in microenvironment could be changed.and the complex mechanism involved needed further study.