Binding of RAGE (AAs 362-367) and RIPK1 induces cognitive deficit in chronic hyperglycemia-derived neuroinflammation

Abstract

Background Chronic hyperglycemia-induced inflammation of the hippocampus is an important cause of cognitive deficit in diabetic patients. The receptor for advanced glycation end products (RAGE), which is widely expressed in the hippocampus of the brain, and is a crucial factor of inflammation and cognitive deficits. However, the precise role of RAGE in neuroinflammation is not fully elucidated. In the present study, we aimed to reveal the underlying mechanism by which RAGE regulates neuroinflammation in the pathogenesis of diabetes-induced cognitive impairment. Methods We employed db/db mice as type 2 diabetic mouse models for investigating whether receptor-interacting serine/threonine protein kinase 1 (RIPK1), which expressed in microglia in the hippocampal region, is a key protein that interacts with RAGE. GST pull-down assay and AutoDock Vina were performed to specify the key structural domain in RAGE that binds to RIPK1. Sophisticated molecular technologies including western blot (WB), co-immunoprecipitation (Co-IP) and immunofuorescence (IF) were applied to detect levels of key protein molecules. Furthermore, cognitive deficit of mice was assessed with Morris water maze (MWM), new object recognition (NOR) and fear conditioning tests. Results RAGE binds directly to RIPK1 via its amino acid sequences (AAs) 362–367, thereby upregulating the phosphorylation level of RIPK1, which is accompanied by the activation of NLRP3 inflammasome in microglia and ultimately leads to cognitive impairment in db/db mice. RAGE AAs 362–367 was mutated to reverse neuroinflammation and improve cognitive function in the hippocampus, suggesting that RAGE AAs 362–367 is a key structural domain that binds directly to PIPK1, while implying that hyperglycemia-induced inflammation in hippocampus is dependent on direct binding of RAGE and RIPK1. Conclusions These findings indicate that direct interaction of RAGE and RIPK1 via AAs 362–367 is an important mechanism for enhanced neuroinflammation in the hyperglycemic environment and is a key node in the development of cognitive deficit in diabetes.