Hyperglycemia-Driven Insulin Signaling Defects Promote Parkinson's Disease-like Pathology in Mice

This study aims to determine the effect of chronic hyperglycemia, induced by a high-fat diet and STZ-induced diabetes, on the development of Parkinson's disease-like characteristics. Understanding this relationship is crucial in pharmacology, neurology, and diabetes, as it could potentially lead to developing new therapeutic strategies for Parkinson's disease. Our study employed a comprehensive approach to investigate the effect of hyperglycemia on Parkinson's disease-like characteristics. Hyperglycemia was induced by a high-fat diet for 6- and 9-week duration with a single intraperitoneal STZ (100 mg/kg) injection at week 5 in C57/BL6 mice. Rotenone (10 mg/kg p.o.) was administered to C57/BL6 mice for 6 and 9 weeks. Time-dependent behavioral studies (wire-hang tests, pole tests, Y-maze tests, and round beam walk tests) were carried out to monitor pathology progression and deficits. Molecular protein levels (GLP1, PI3K, AKT, GSK-3β, NF-κB, and α-syn), oxidative stress (GSH and MDA) parameters, and histopathological alterations (H&E and Nissl staining) were determined after 6 weeks as well as 9 weeks. After 9 weeks of study, molecular protein expression (p-AKT and p-α-syn) was determined. Hyperglycemia induced by HFD and STZ induced significant motor impairment in mice, correlated with the rotenone group. Insulin receptor signaling (GLP1/PI3K/AKT) was found to be disrupted in the HFD+STZ group and also in rotenone-treated mice, which further enhanced phosphorylation of α-syn, suggesting its role in α-syn accumulation. Histopathological alterations indicating neuroinflammation and neurodegeneration were quite evident in the HFD+STZ and rotenone groups. Exposure to hyperglycemia induced by HFD+STZ administration exhibits PD-like characteristics after 9 weeks of duration, which was correlative with rotenone-induced PD-like symptoms.