Hippocampal HDAC6 promotes POCD by regulating NLRP3-induced microglia pyroptosis via HSP90/HSP70 in aged mice

Background: Postoperative Cognitive Dysfunction (POCD) has attracted increased attention, but its precise mechanism remains to be explored. This study aimed to figure out whether HDAC6 could regulate NLRP3-induced Pyroptosis by modulating the functions of HSP70 and HSP90 in microglia to participate in postoperative cognitive dysfunction in aged mice.

Methods: Animal models of postoperative cognitive dysfunction in aged mice were established by splenectomy under sevoflurane anesthesia. Morris water maze was used to examine the cognitive function and motor ability. Sixteen-months-old C57BL/6 male mice were randomly divided into six groups: control group (C group), sham surgery group (SA group), splenectomy group (S group), splenectomy + HDAC6 Inhibitor ACY-1215 group (ACY group), splenectomy + HDAC6 Inhibitor ACY-1215 + HSP70 Inhibitor Apoptozole group (AP group), splenectomy + solvent control group (SC group). The serum and hippocampus of mice were taken after mice were executed. The protein levels of HDAC6, HSP90, HSP70, NLRP3, GSDMD-N, cleaved-Caspase-1 (P20), IL-1β were detected by western blotting. Serum IL-1β, IL-6 and S100β were measured using ELISA assay, and cell localization of HDAC6 was detected by immunofluorescence. In vitro experiments, BV2 cells were used to validate whether this mechanism worked in microglia. The protein levels of HDAC6, HSP90, HSP70, NLRP3, GSDMD-N, P20, IL-1β were detected by western blotting and the content of IL-1β in the supernatant was measured using ELISA assay. The degree of acetylation of HSP90, the interaction of HSP70, HSP90 and NLRP3 were analyzed by coimmunoprecipitation assay.

Results: Splenectomy under sevoflurane anesthesia in aged mice could prolong the escape latency, reduce the number of crossing platforms, increase the expression of HDAC6 and activate the NLRP3 inflammasome to induce Pyroptosis in hippocampus microglia. Using ACY-1215 could reduce the activation of NLRP3 inflammasome, the Pyroptosis of microglia and the degree of spatial memory impairment. Apoptozole could inhibit the binding of HSP70 to NLRP3, reduce the degradation of NLRP3 and reverse the protective effect of HDAC6 inhibitors. The results acquired in vitro experiments closely resembled those in vivo, LPS stimulation led to the Pyroptosis of BV2 microglia cells and the release of IL-1β due to the activation of the NLRP3 inflammasome, ACY-1215 showed the anti-inflammatory effect and Apoptozole exerted the opposite effect.

Conclusions: Our findings suggest that hippocampal HDAC6 promotes POCD by regulating NLRP3-induced microglia Pyroptosis via HSP90/HSP70 in aged mice.