High-fat diet increases tau expression in the brain of T2DM and AD mice independently of peripheral metabolic status.

Alzheimer's disease and type 2 diabetes mellitus are risk factors for each other. To investigate the effects of both genetic and high-fat-induced diabetic phenotype on the expression and exon 10 splicing of tau, we used the Alzheimer's disease mouse model (APdE9) cross-bred with the type 2 diabetes mouse model over-expressing insulin-like growth factor 2 in the pancreas. High-fat diet, regardless of the genotype, significantly induced the expression of four repeat tau mRNA and protein in the temporal cortex of female mice. The mRNA levels of three repeat tau were also significantly increased by high-fat diet in the temporal cortex, although three repeat tau expression was considerably lower as compared to four repeat tau. Moreover, high-fat diet significantly increased the mRNA ratio of four repeat tau vs. three repeat tau in the temporal cortex of these mice. All of these effects were independent of the peripheral hyperglycemia, hyperinsulinemia and insulin resistance. Increased four repeat tau and three repeat tau levels significantly associated with impaired memory and reduced rearing in the female mice. High-fat diet did not affect neuroinflammation, Akt/GSK3β signaling pathway or the expression of tau exon 10 splicing enhancers in the temporal cortex. Our study suggests that the high-fat diet independently of type 2 diabetes or Alzheimer's disease background induces the expression and exon 10 inclusion of tau in the brain of female mice.