Brain insulin resistance and Alzheimer’s molecular changes induced by Western diet

Abstract

AbstractBackgroundWestern diet (WD) is a type of nourishment based on ultra‐processed foods, rich in simple sugars and saturated fats. Long‐term consumption of WD may lead to disruption of insulin signaling and development of insulin resistance. It is supposed that insulin resistance is a probable risk factors for Alzheimer’s disease (AD). The aim of this study was to verify this hypothesis in wild type mice by checking the WD effect on initiation and propagation of main neuropathological AD features such as amyloid‐β (Aβ) plaques and neurofibrillary tangles, which start from the entorhinal cortex in the temporal area, and progresses to the hippocampus, resulting in the loss of memory and cognition.MethodMales of wild type C57BL/6J mice were fed WD diet or standard diet (SD; CTR). Mice experimental groups (WD and CTR) were divided into age subgroups 4‐, 8‐, 12‐ and 16‐month‐old. In the first step, the WD‐diet dependent insulin signaling was analyzed, and the levels of the insulin pathway components: p‐IRS‐1(Ser616), p‐Akt(473), p‐GSK‐3β(Ser9) in the entorhinal cortex and hippocampus were assessed. To analyze further whether WD‐derived impairments in insulin signaling may induce neuropathological AD features, p‐Tau(Thr231) and APP/Aβ were analyzed by immunoblotting and immunofluorescence of mouse brain tissue sections from entorhinal cortex and the hippocampus.ResultEntorhinal cortex proved to be more sensitive to WD‐dependent insulin impairments than the hippocampus: immunoblotting analysis of mouse entorhinal cortex brain lysates revealed an increase in p‐IRS‐1(Ser616) levels, indicating the development of insulin resistance under WD diet. Moreover, a change in the localization of p‐Tau(Thr231) in cellular compartments from fibers to nerve cell bodies indicated a progressive tauopathy. In addition, we also observed an age‐dependent decrease in APP protein levels correlating with the appearance of Aβ peptides in the cytoplasm of neurons under the WD diet.ConclusionObtained results suggest that the WD diet, by inducing abnormalities in insulin signaling in the brain, promotes the development of AD, and may be consider as a significant modifiable risk factor for AD, additional to the genetic risk factors.