The Expression of Interleukin-1β Is Regulated by DNA Methylation in Microglia of Hippocampus to Participate Postoperative Cognitive Dysfunction in Aged Mice

Abstract BackgroundPostoperative cognitive dysfunction (POCD) is one of the common postoperative complications in the elderly. The main clinical manifestation is memory impairment, which can cause permanent damage and even dementia in severe cases. However, the pathogenesis of POCD is still unknown. Age and neuroinflammation are known to be closely related to its occurrence, while DNA methylation is very important for transcriptional silencing and neuroinflammation. Consequently, this study intended to establish a mouse model of POCD to explore the role of DNA methylation in regulating the expression of interleukin-1β which participated POCD in aged mice.MethodsPOCD model was established by exploratory laparotomy and evaluated by new object experiment and Y maze test. In addition, ELISA, RT-PCR, Western blotting, immunofluorescence, microglia isolation and flow cytometry methods were used to detect the inflammatory state of dorsal hippocampal after surgery. Moreover, MSP, MeDIP and IL-1β promoter DNA methylation sequencing were used to explore the regulation of DNA methylation on IL-1β in this model. Finally, Golgi staining and Western blotting were used to further explore the role of IL-1β in POCD and its possible mechanisms. ResultsCognitive impairment was observed in aged but not adult mice at 1 day after surgery. There was a significant correlation between the level of IL-1β in dorsal hippocampus and the performance of cognitive function. The microglia in the dorsal hippocampus was activated and the IL-1β promoter DNA methylation was decreased in the aged mice. The increased expression of IL-1β impaired synaptic plasticity and hippocampus-dependent memory formation. Intracerebroventricular administration of IL-1β receptor antagonist could prevent the cognitive impairment of aged mice after surgery, reverse the decrease of dendritic spine density and synapse-associated protein expression induced by surgery.ConclusionDNA methylation regulation may be an important mechanism for greater susceptibility to POCD in aged mice by regulating the expression of IL-1β. IL-1β inhibiting prevented surgery-induced cognitive decline and synaptic plasticity dysfunction. The research also provided a new target for the clinical prevention of the occurrence of POCD in the elderly.