Modeling Sporadic Alzheimer's Disease: The Insulin Resistant Brain State Generates Multiple Long-Term Morphobiological Abnormalities Including Hyperphosphorylated Tau Protein and Amyloid-β

Nosologically, Alzheimer's disease (AD) is not a single disorder. Missense gene mutations involved in increased formation of the amyloid-beta protein precursor derivatives amyloid-beta (A beta)(1-40) and A beta(1-42/43) lead to autosomal dominant familial AD, found in the minority of AD cases. However, millions of subjects suffer from sporadic AD (sAD) of late onset, for which no convincing evidence suggests A beta as the primary disease-generating compound. Environmental factors operating during pregnancy and postnatally may affect susceptibility genes and stress factors (e. g., cortisol), consequently affecting brain development both structurally and functionally, causing diseases that only manifest late in life. With aging, a desynchronization of biological systems may result, increasing further brain entropy/declining criticality. In sAD, this desynchronization may involve stress components, cortisol and noradrenaline, reactive oxygen species, and membrane damage as major candidates causing an insulin resistant brain state with decreased glucose/energy metabolism. This further leads to a derangement of ATP-dependent cellular and molecular work, of the cell function in general, as well as derangements in the endoplasmic reticulum/Golgi apparatus, axon, synapses, and membranes, in particular. A self-propagating process is thus generated, including the increased formation of hyperphosphorylated tau-protein and A beta as abnormal terminal events in sAD rather than causing the disorder, as elaborated in the review.