Autophagy inhibition reduces irradiation-induced subcortical white matter injury not by reducing inflammation, but by increasing mitochondrial fusion and inhibiting mitochondrial fission

Abstract

Background Radiotherapy is an effective tool in the treatment of malignant brain tumors, but irradiation-induced late-onset toxicity remains a major problem. The purpose of this study was to investigate if genetic inhibition of autophagy has impact on subcortical white matter development in the juvenile mouse brain after irradiation. Methods Ten-day-old selective Atg7 knockout (KO) mice and wild-type (WT) littermates were subjected to a single 6 Gy dose of whole-brain irradiation and evaluated at 5 days after irradiation. Results Neural Atg7 deficiency partially prevented myelin disruption compared to the WT mice after irradiation, as indicated by myelin basic protein staining. Irradiation induced oligodendrocyte progenitor cell loss in the subcortical white matter, and Atg7 deficiency partly prevented this. There was no significant change between the KO and WT mice in the number of microglia and astrocytes in the subcortical white matter after irradiation. Transcriptome analysis showed there were numbers of differentially expressed genes (DEGs) in both Atg7 KO and WT group after irradiation, but GSEA analysis showed that the GO mitochondrial gene expression pathway was significantly enriched in the remaining DEGs between the KO and WT group after irradiation. Compared with WT mice, expression of the mitochondrial fusion protein OPA1 and phosphorylation of the mitochondrial fission protein DRP1 were dramatically decreased in KO mice under physiological conditions. The protein levels of phosphorylated DRP1 and OPA1 showed no differences in WT mice between the non-irradiated group and the irradiated group but had remarkably increased level in the KO mice after irradiation. Conclusions These results indicate that inhibition of autophagy reduces irradiation-induced subcortical white matter injury not by reducing inflammation, but by increasing mitochondrial fusion and inhibiting mitochondrial fission.