Studies On Gut Microbiome And Palmitic Acid Mediating Macrophage M2 Polarization To Promote The Progression Of Glioblastoma

Background and objectiveGlioblastoma(GBM)is the most common intracranial malignant tumors,originating from glial cells.Its 5-year mortality rate is only below that of pancreatic and lung tumor among systemic tumors.The clinical treatments of GBM include maximal surgical resection,postoperative radiotherapy and chemotherapy.Although the application of Temozolomide,a new chemotherapy drug has improved the prognosis of GBM,the median survival time is only 12 to 15 months.Despite many advances in clinical and basic experimental researches,the prognosis of GBM has not improved significantly.This is related to the unknown etiology of GBM,highly invasive characteristics and molecular heterogeneity,which limit the effectiveness of treatments.More and more molecular biomarkers discovered,only few of these could be convertible.There is an urgent clinical need to develop non-invasive and more effective markers of GBM.Recent studies have found that gut microbiome and metabolites play an important role in many central nervous disorders and extra-intestinal malignancies.GBM is a malignant disease of the central nervous system.Whether the gut microbiome plays an important role in GBM?In this study,we described the alterations of the gut micirobiome and metabolites in GBM patients and investigated the clinical significance in the diagnosis and prognosis of GBM.At the same time,the relationship between the gut microbiome,metabolites and GBM was further investigated in GBM mice model.In vitro or vivo experiments,the mechanism of gut microbiome and metabolites regulating M2 macrophage polarization in GBM microenvironment was conducted.MethodsWe recruited 24 patients with primary glioblastoma who underwent surgery in Nanfang Hospital of Southern Medical University,and 28 healthy individuals as control group.We collected fecal samples from patients before operation and healthy individuals.We used 16S rRNA sequencing was used to analyze the compositions of the gut microbiome in GBM.Specific gut microbiome signature of GBM was found.Intestinal metabolites were compared between GBM group and control group by LC-MS non-target metabolomics.A GBM diagnostic model was constructed to evaluate the significance of gut micirobiome in distinguishing and predicting prognosis of GBM.We verifed the correlation between gut microbiome,metabolites and GBM in the GBM mice models through microbiological analysis,fecal and serum metabolome analysis.The effect of intestinal flora disturbance on macrophages in GBM tumor microenvironment was analyzed by flow flow analysis.In addition,in vitro and in vivo cell biology experiments,we studied the effect of palmitic acid on macrophage M2 polarization and its possible mechanismResultsWe systematically described the alterations of the gut microbiome and metabolites in GMB patients.We found 15 specifc differential microbiotas,which were closely related to differential metabolites.We used 4 species and 6 metabolites to construct a diagnostic model,which had a high potential to identify GBM(AUC=0.94).The microbiota could predict the prognosis of GBM effectively.The disturbance of gut microbiome and metabolites promoted the progression of GBM and influenced macrophage polarization in GBM models.Metabolomics analysis showed that the changes of gut microbiome and metabolites mainly affected fatty acid metabolism and amino acid metabolism.Abnormal increased level of palmitic acid was found in both human and mouse.Spearman correlation analysis showed that palmitic acid was positively correlated with macrophage M2 polarization(rho=0.6,p<0.05).In vitro and vivo results indicated that palmitic acid might mediated macrophage M2 phenotype expression and the release of anti-inflammatory factors by CD36/PI3K/AKT pathway.ConclusionOur results of this study suggest that glioblastoma has specific gut microbiome and metabolites signatures,which can effectively identify GBM and predict prognosis.The metabolites caused by microbial disturbance regulate the polarization of M2 macrophages and promote the progression of GBM.These results are expected to be potential markers for GBM diagnosis and prognosis evaluation,and provide new targets for GBM intervention.