Hyperglycemia induces microglial pyroptosis by increasing oxygen extraction rate: Implication in neurological impairment during ischemic stroke.

ABSTRACT

Elevated levels of blood glucose in patients with ischemic stroke are associated with a worse prognosis. The present study aimed to explore whether hyperglycemia promotes microglial pyroptosis by increasing the oxygen extraction rate in an acute ischemic stroke model. C57BL/6 mice that underwent middle cerebral artery occlusion were used for assessment of blood glucose level and neurological function. The cerebral oxygen extraction ratio (CERO2), oxygen consumption rate (OCR) and partial pressure of brain tissue oxygen (PbtO2) were measured. To investigate the significance of the NOD­like receptor protein 3 (NLRP3) inflammasome, NLRP3­/­ mice were used, and the expression levels of NLRP3, caspase­1, full­length gasdermin D (GSDMD­FL), GSDMD­N domain (GSDMD­N), IL­1ß and IL­18 were evaluated. In addition, Z­YVAD­FMK, a caspase­1 inhibitor, was used to treat microglia to determine whether activation of the NLRP3 inflammasome was required for the enhancing effect of hyperglycemia on pyroptosis. It was revealed that hyperglycemia accelerated cerebral injury in the acute ischemic stroke model, as evidenced by decreased latency to fall and the percentage of foot fault. Hyperglycemia aggravated hypoxia by increasing the oxygen extraction rate, as evidenced by increased CERO2 and OCR, and decreased PbtO2 in response to high glucose treatment. Furthermore, hyperglycemia­induced microglial pyroptosis was confirmed by detection of increased levels of caspase­1, GSDMD­N, IL­1ß and IL­18 and a decreased level of GSDMD­FL. However, the knockout of NLRP3 attenuated these effects. Pharmacological inhibition of caspase­1 also reduced the expression levels of GSDMD­N, IL­1ß and IL­18 in microglial cells. These results suggested that hyperglycemia stimulated NLRP3 inflammasome activation by increasing the oxygen extraction rate, thus leading to the aggravation of pyroptosis following ischemic stroke.