Molecular Mechanisms of Tubulin Polymerization Promoting Protein in Mitochondrial Function and Neuronal Survival

ABSTRACT Parkinson’s disease (PD), Alzheimer’s disease and related dementias (AD/ADRD) are debilitating progressive neurodegenerative diseases. These diseases have no effective treatments currently and are among the greatest unmet challenges in healthcare today affecting millions of people globally with enormous economic and societal burdens. These disorders are characterized by neurodegeneration among other pathologies. A highly conserved, yet less understood family of human genes, Tubulin Polymerization Promoting Proteins (TPPP), has long been implicated in PD and ADRD such as Lewy Body Dementia. However, the pathogenic mechanisms involving TPPP remain unknown. We recently developed a novel fly (Drosophila) model relevant to PD by utilizing a mutation in the single Drosophila homolog of human TPPP, named Ringer. Ringer mutants recapitulate many of the characteristics observed in human PD patients including severe locomotor disabilities, progressive neurodegeneration (including dopaminergic neuron loss) and mitochondrial structural damage and dysfunction. We have made novel observations that Ringer and human TPPP are both present in mitochondrial preparations from Drosophila and postmortem human brain tissues, respectively. Co-immunoprecipitations from fly brain mitochondrial preparations followed by mass spectrometry-based proteomics analyses revealed that Ringer interacts with the electron transport chain (ETC) Complex I (CI) subunits and members of the SLC25A family of mitochondrial carrier proteins, thus highlighting a novel and unique role of Ringer in mitochondria. Our overarching hypothesis is that Ringer interacts with CI subunits and SLC25A solute carriers to stabilize the ETC complexes and maintain mitochondrial bioenergetics that is crucial for neuronal survival. The overall objective of this proposal is to delineate the mechanisms of Ringer function in mitochondria and extend our studies to postmortem human brains to determine the functional conservation of TPPP and the relevance of human TPPP to PD and related disorders. Using enzymatic assays, respirometry, LC-MS, biochemical, behavioral, pharmacological, cell biological and genetic methodologies, our specific aims will: (1) Determine the consequences of Ringer loss on mitochondrial bioenergetics, (2) Identify the molecular mechanisms by which Ringer promotes ETC function and neuronal survival, and (3) Determine the cellular and sub-cellular localization of human TPPP and any alterations in TPPP in PD brain tissues. Our proposed studies will for the first time uncover a novel Ringer/TPPP function in maintaining mitochondrial health which is essential to prevent neuronal cell death. We expect that our completed studies will provide unprecedented insights into potential pathogenic mechanisms of human TPPP in PD and related disorders, and may contribute towards uncovering therapeutic targets in the future.