title: Deficient brain insulin signalling pathway in Alzheimer's disease and diabetes.
abstract: Brain glucose metabolism is impaired in Alzheimer's disease (AD), the most common form of dementia. Type 2 diabetes mellitus (T2DM) is reported to increase the risk for dementia, including AD, but the underlying mechanism is not understood. Here, we investigated the brain insulin-PI3K-AKT signalling pathway in the autopsied frontal cortices from nine AD, 10 T2DM, eight T2DM-AD and seven control cases. We found decreases in the levels and activities of several components of the insulin-PI3K-AKT signalling pathway in AD and T2DM cases. The deficiency of insulin-PI3K-AKT signalling was more severe in individuals with both T2DM and AD (T2DM-AD). This decrease in insulin-PI3K-AKT signalling could lead to activation of glycogen synthase kinase-3β, the major tau kinase. The levels and the activation of the insulin-PI3K-AKT signalling components correlated negatively with the level of tau phosphorylation and positively with protein O-GlcNAcylation, suggesting that impaired insulin-PI3K-AKT signalling might contribute to neurodegeneration in AD through down-regulation of O-GlcNAcylation and the consequent promotion of abnormal tau hyperphosphorylation and neurodegeneration. The decrease in brain insulin-PI3K-AKT signalling also correlated with the activation of calpain I in the brain, suggesting that the decrease might be caused by calpain over-activation. Our findings provide novel insight into the molecular mechanism by which type 2 diabetes mellitus increases the risk for developing cognitive impairment and dementia in Alzheimer's disease.
authors: Department of Neurochemistry, New York State Institute for Basic Research in Developmental Disabilities, Staten Island, NY 10314, USA.
authors: Ying
authors: Y
authors: Liu
authors: Fei
authors: F
authors: Liu
authors: Inge
authors: I
authors: Grundke-Iqbal
authors: Khalid
authors: K
authors: Iqbal
authors: Cheng-Xin
authors: CX
authors: Gong
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