Alteration of scaffold: Possible role of MACF1 in Alzheimer's disease pathogenesis

Alzheimer's disease (AD) is a progressive neurodegenerative disease, with the sign of sensory or motor function loss, memory decline, and dementia. Histopathological study shows AD neuron has irregular cytoskeleton and aberrant synapse. Amyloid-beta (A beta) is believed as the trigger of AD, however, the detailed pathogenesis is not fully elucidated. Microtubule-actin crosslinking factor 1 (MACF1) is a unique giant molecule which can bind to all three types of cytoskeleton fibers, different linkers/adaptors, as well as various functional proteins. MACF1 is a critical scaffold for orchestrating the complex 3D structure, and is essential for correct synaptic function. MACF1's binding ability to microtubule depends on Glycogen synthase kinase 3 Bate (GSK3 beta) mediated phosphorylation. While GSK3 beta can be regulated by the binding of A beta and the receptor Paired immunoglobulin-like receptor B (PirB), possibly via Protein phosphatase 2A (PP2A). So based on literature search and logic analysis, we propose a hypothesis: A beta binds to its receptor PirB, and triggers cytosol PP2A, which might activate GSK3 beta. GSK3 beta might further phosphorylates microtubule-binding domain (MTBD) of MACF1, causes the separation of microtubule and MACF1. Thus MACF1 might lose the control of the whole cytoskeleton system, synapse might change and AD might develop. That is A beta-PirB-PP2A-GSK3 beta-MACF1 axis might give rise to AD. We hope our hypothesis might provide new clue and evidence to AD pathogenesis.