Widespread Mitochondrial DNA Methylation Drift Contributes to Postoperative Delirium in Young and Old Mice

Abstract Background: Mitochondrial dysfunction is linked to the etiopathogenesis of postoperative delirium (POD), which severely affects the prognosis of elderly patients undergoing surgery. The methylation of mitochondrial DNA (mtDNA), a new and incompletely described phenomenon that regulates the structure and function of mitochondria, is associated with aging. However, the relationship between mtDNA methylation and POD has not been established. Methods: 5-methylcytosine (5-mC) at 5 CpG sites of the displacement loop (D-loop) and at 60 CpG sites of coding gene loci in the mitochondrial genome after surgery of the hippocampus, prefrontal cortex, amygdala, and anterior cingulate cortex in 6- and 18-month-old mice were detected using bisulfite pyrosequencing. Mitochondrial structure, mitochondrial gene expression and mtDNA copy number were also examined using Electron microscopy and real time PCR to find the association with mtDNA methylationResults: The mtDNA methylation drift manifested as a decrease in the methylation levels at the D-loop and an increase or decrease in the methylation levels at several coding gene loci, ultimately resulting in reduced mtDNA copy numbers, altered mitochondrial gene expression, and damaged mitochondrial structures in the hippocampus and prefrontal cortex after surgery. The activation of Silent information regulator-1 (SIRT1) ameliorated anesthesia- and surgery-induced mitochondrial dysfunction and delirium-like behaviors by regulating mtDNA methyltransferase-mediated mtDNA methylation. Conclusions: These data support the existence of epigenetic mtDNA regulation in POD; however, further studies are required to explore the specific mechanisms.