Figure 1.

Role of insulin in the healthy brain and impairments in brain insulin resistance (BIR) identified in Alzheimer’s disease. Insulin in the brain predominantly originates from the pancreas, yet small amounts of insulin synthesis within the brain and choroid plexus have recently been discovered. Brain insulin is degraded by the insulin degrading enzyme (IDE) to regulate signaling. Under healthy conditions, brain insulin helps regulate mood, glucose metabolism, cognition, food intake, and brain perfusion. In Alzheimer’s disease, when BIR is present, there are decreased levels of brain insulin, decreased levels of IDE leading to increases in amyloid β plaques, increased mood disorders, worsened cognition, impaired glucose metabolism, and decreases in insulin receptor (INSR) activation. Parts of the figure were drawn by using pictures from Servier Medical Art.