Pathophysiology Associated with Diabetes-induced Tauopathy and Development of Alzheimer's Disease

Alzheimer's disease (AD) is the most common type of dementia that affects the elderly around the world. Chronic type 2 diabetes (T2DM) has been proven to be closely related to neurodegeneration, especially AD. T2DM is characterized by the cell's failure to take up insulin as well as chronic hyperglycemia. In the central nervous system, insulin plays vital regulatory roles, while in chronic hyperglycemia, it leads to the formation and accumulation of advanced glycation end products (AGEs). Inflammation plays a crucial role in development of insulin resistance in AD and T2DM. The microtubule-related protein tau is involved in the pathogenesis of several neurological diseases known as tauopathies, and is found to be abnormally hyperphosphorylated in AD and accumulated in neurons. Chronic neuroinflammation causes the breakdown of the blood-brain barrier (BBB) observed in tauopathies. The development of pro-inflammatory signaling molecules, such as cytokines, chemokines from glial cells, neurons and endothelial cells, decides the structural integrity of BBB and immune cell migration into the brain. This review highlights the use of antidiabetic compounds as promising therapeutics for AD, and also describes several new pathological molecular mechanisms associated with diabetes that increase AD pathogenesis.