The Tau-mitochondria connection and its impact on cellular energy metabolism in Alzheimer's disease

Alzheimer's disease (AD) is a complex multifactorial neurodegenerative disease process resulting in progressive cognitive deterioration and synaptic dysfunction. The primary research approach in AD has traditionally focused on amyloid- pathology however an increasingly evidence suggests that tau protein is a key mediator of neuronal damage via a direct action on mitochondrial bioenergetics. In this chapter we look at the nature of the tau-mitochondrial interface, and propose a paradigm of tau-induced energy failure in AD. Physiologically tau provides stability to the microtubules and is involved in transport mechanisms within cells. In AD, tau is excessively post-translationally modified hyperphosphorylated and truncated tau species form toxic oligomers that incorrectly translocate to mitochondria, interacting pathologically with critical proteins such as voltage-dependent anion channel 1 (VDAC1) and adenine nucleotide translocase (ANT), impeding the mitochondrial ATP/ADP exchange and reducing oxidative phosphorylation efficiency. Tau also further damages mitochondria by excessive fission, inhibition of axonal transport and Inhibition of mitophagy by interrupting PINK1-Parkin signaling. In turn, the build-up of dysfunctional mitochondria leads to ROS production, mtDNA damage and calcium imbalance creating a vicious cycle toward oxidative stress and tau pathology. At the cellular level they cause an energy depletion of the synapse and at the systems level cause glucose hypometabolism and activation of neuroinflammation. The chapter additionally discusses novel therapeutic approaches that target both tau and mitochondrial abnormalities, namely antisense oligonucleotides (ASO), mitochondria targeted compounds and mitophagy modifiers, stressing that it would be more effective to utilize a cocktail of these inhibitors. As a whole, in the context of decreased bioenergetics, the tau-mitochondria axis is an important factor to consider in the successful treatment of AD.