In
Alzheimer's disease (AD), brain
insulin and
insulin-like growth factor (IGF) resistance and deficiency begin early, and worsen with severity of disease. The factors mediating progression of brain
insulin/IGF resistance in AD are not well understood. We hypothesize that AD progression is mediated via negative cross-talk that promotes toxic
ceramide generation and endoplasmic reticulum (ER) stress. The rationale is that
insulin resistance dysregulates lipid metabolism and promotes
ceramide accumulation, and thereby increases
inflammation and stress. Consequences include disruption of cytoskeletal function and AβPP-Aβ secretion. The present study correlates AD stage with activation of pro-
ceramide genes,
ceramide levels, and molecular indices of ER stress in postmortem human brain tissue. The results demonstrated that in AD, brain
insulin/IGF resistance was associated with constitutive activation of multiple pro-
ceramide genes, increased
ceramide levels, and increased expression of pro-ER stress pathway genes and
proteins. Expression of several pro-
ceramide and pro-apoptotic ER stress pathway molecules increased with AD severity and brain
insulin/IGF resistance. In contrast, ER stress molecules that help maintain homeostasis with respect to unfolded protein responses were mainly upregulated in the intermediate rather than late stage of AD. These findings support our hypothesis that in AD, a triangulated mal-signaling network initiated by brain
insulin/IGF resistance is propagated by the dysregulation of
ceramide and ER stress homeostasis, which themselves promote
insulin resistance. Therefore, once established, this reverberating loop must be targeted using multi-pronged approaches to disrupt the AD neurodegeneration cascade.