APP and Alzheimer disease: The major lesions in AD, leading to synaptic loss and consequential neuronal death, are composed of neurofibrillary tangles (the highly stable polymers of intracellular protein aggregates composed of hyperphosphorylated microtubule-associated tau) and senile plaque (extracellular deposits of insoluble fibrillary amyloid-β (Aβ) peptide, a proteolytic product of amyloid-β precursor protein (APP)) [3,4].