Cell Death Regulation by Pro-Apoptotic BOK in Tauopathies

PROJECT SUMMARY Alzheimer's disease (AD), and other neurodegenerative tauopathies, are defined by their pathologic accumulation of overexpressed, hyperphosphorylated, and oligomerized tau. Tau tangles result in proteotoxic stress through the endoplasmic reticulum (ER), cell death, and ultimately neurodegeneration. Understanding the

molecular mechanisms that lead from tau aggregation to neuron loss is key to identify novel therapeutic targets. We have elucidated how the BCL-2 family member BOK induces apoptosis in response to ER stress stimuli. Specifically, we have found that BOK, which is predominantly bound to the inositol-3-phosphate (IP3R) calcium

transporter in the ER, regulates the unfolded protein response (UPR) as well as the transfer of calcium from the ER to the mitochondria. Critically, BOK plays an important role in the formation of mitochondrial-ER contact sites (MERCs), also known as mitochondrial ER-associated membranes (MAMs). MAMs are central signaling hubs

for the cell, mediating processes like calcium transfer, the UPR, mitochondrial shape and metabolic homeostasis. Neurodegenerative diseases have been associated with the abnormal quantity, formation and function of MAMs. In preliminary work we find that BOK regulates metabolic survival and cell death pathways in neurons. Our goal

is to determine how the control of metabolic pathways through MAMs by BOK regulates neuronal cell death due to tau. Aim 1 will examine how BOK regulates tau-induced neuronal cell death through its regulation of ER to mitochondrial calcium transfer. Aim 2 will determine how BOK impacts autophagy through MAMs and its

consequences for tauopathy. Aim 3 will define the ability of BOK to control lipid metabolism in tau-bearing neurons. Each of these aims focuses on metabolic pathways that signal through MAMs, that are known to be important for AD, and for which we have preliminary data implicating a role for BOK. This project will benefit from

a multidisciplinary approach that includes neuronal genetic reprogramming, cutting-edge intravital microscopy, and advanced lipidomics. We will employ 2Phatal, two-photon chemical apoptotic targeted ablation, a novel technique we developed to induce and measure cell death in live mammalian brains without neighboring injury.

These novel tools will enable us to address our conceptually innovative hypothesis that tauopathy-induced neuronal cell death is regulated by BOK's control of metabolic pathways that signal through MAMs. Discernment of the signaling networks that control the balance between metabolic homeostasis and cell death during tau-

induced neurodegeneration is expected to provide targets for therapeutic development.