Dysregulation of mTOR by tau in Alzheimer's disease

Abstract

Tau was discovered in the mid 1970's as a microtubule‐associated protein that stimulates tubulin polymerization, and subsequently was shown to be expressed primarily in neurons, where it is most concentrated in axons. Interest in tau rose by the late 1980's, when it was shown to be the principal subunit of the neurofibrillary tangles (NFTs) that accumulate in Alzheimer's disease (AD) brain, and achieved new heights by the late 1990's, when numerous tau mutations were found to be highly penetrant for AD‐related disorders that also are associated with NFTs and came to be known as non‐Alzheimer's tauopathies. The role of tau in neurodegeneration is far more complex than whatever effects on neurons may be caused by NFTs, however, and here we review our work on dysregulation of mTOR by tau in AD. mTOR is a protein kinase and master regulator of myriad aspects of cellular behavior. We have defined a complex signaling network whereby aberrant tau phosphorylation provoked by amyloid‐β oligomers (AβOs), the building blocks of the amyloid plaques that form in AD brain, cause post‐mitotic neurons to re‐enter the cell cycle, but to die eventually instead of dividing, which may account for most neuron death in AD. Remarkably, we found that this same neuronal signaling network also poisons a fundamental cell biological process that we discovered, nutrient‐induced mitochondrial activation, or NiMA. Tau‐dependent cell cycle re‐entry and NiMA inhibition occur in cultured neurons within a few hours of exposure to AβOs, and thus may represent seminal processes in AD pathogenesis.

Disrupted mitochondrial response to nutrients is a presymptomatic event in the cortex of the APPSAAknock-in mouse model of Alzheimer’s disease

“…Among them, disruption of synaptic functioning and neurodegeneration have been recognized for a long time, leading to the concept that AD is a "synaptic disease" [54]. The fact that disruption of NiMA was detected in the cortex of APP SAA/+ mice months before cognitive decline [18] leads us to propose that chronic metabolic disruption caused by an AβO-induced, tau-dependent mechanism represents a very early event in human AD [55].…”