Molecular Genetic Analysis of TORC1 and TORC2 Signaling in Neuronal Maintenance

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Project Summary Age-related neurodegenerative diseases such as Parkinson's disease (PD) impose tremendous socioeconomic burdens due to the lack of disease-modifying treatment options. Mitochondrial dysfunction is intimately linked to neurodegenerative diseases. How mitochondrial abnormalities arise and how they relate to other features of neurodegenerative diseases such as proteostasis failure, Ca2+ dyshomeostasis, and neuroinflammation are poorly understood. Dynamic control of the structure, function, and distribution of mitochondria is also essential for normal neuronal function, a requirement necessitated by the highly polarized shape and unique physiology of neurons. Despite intensive efforts, many fundamental questions remain regarding the mechanisms linking mitochondrial regulation to neuronal maintenance. Pten-induced kinase 1(PINK1) and Parkin (encoding an E3 ubiquitin ligase), two genes associated with familial PD, have defined a genetic pathway important for mitochondrial and neuronal maintenance in flies and mammals. Identification of this pathway offers a much-needed entry point to understand the regulation of mitochondrial function in response to neuronal activity and metabolic needs, and to decipher the mechanistic link between mitochondrial dysfunction and other pathological hallmarks of disease. Our genetic studies revealed that PINK1/Parkin directs an interconnected mitochondrial quality control (MQC) process important for the maintenance of dopaminergic (DA) neurons. The multifaceted MQC process encompasses translational control of respiratory chain complex (RCC) biogenesis, mitochondrial fission/fusion dynamics, transport, and removal of defective mitochondria by autophagy (mitophagy). In the past funding period we have shown that the conserved target of rapamycin complexes (TORC1 and TORC2) act as important mediators of PINK1-directed MQC. One exciting finding from our investigation is that the PINK1/mTORC2 pathway exerts translational control of nuclear encoded RCC (nRCC) mRNAs. The goal of this proposal is to move away from the status quo of mitophagy-centric focus of PINK1-directed MQC by focusing on the newly discovered translational control function of PINK1/mTORC2 signaling. We will use a unique combination of molecular genetic, genomic, cell biological, and biochemical tools, and move between in vivo fly models and in vitro induced DA neuron (iDN) models. Our central hypothesis is that PINK1/mTORC2 signaling regulates DA neuron function and survival through ribosome-associated co-translational quality control (RQC) of select nuclear-encoded mitochondrial mRNAs, thus mechanistically linking mitochondrial function to protein homeostasis. We propose to elucidate how the RQC pathway mediates the effects of PINK1/mTORC2 on mitochondrial regulation and DA neuron maintenance (Aim 1), and dissect the molecular mechanism of RQC regulation by PINK1/mTORC2 signaling in both Drosophila models and patient-derived iDN models (Aim 2). These studies will significantly advance our understanding of how PINK1/mTORC2 signaling regulates DA neuron homeostasis, shed light on the poorly understood phenomenon of neuronal vulnerability to RQC failure, and potentially lead to novel and rational therapy for PD and other neurological disease conditions.