Author ORCID Identifier
Date of Graduation
Cell and Regulatory Biology
Doctor of Philosophy (PhD)
Edgar T. Walters
Neurodegenerative diseases, despite constituting a major and growing cause of mortality globally, have few effective treatments. In order to develop novel therapeutics to combat neurodegeneration, a better understanding of the molecular mechanisms underlying these diseases is needed. Neurons rely on Ca2+ to mediate many of their unique functions, and aberrant Ca2+ signaling has been broadly implicated in neurodegeneration. The goal of this dissertation is to delineate specific examples of Ca2+ dyshomeostasis that I have uncovered in Drosophila models of neurodegeneration.
I first define the role a neurodegeneration-associated mutation plays in perturbing presynaptic [Ca2+], which is an important determinant of proper morphological development of the Drosophila neuromuscular junction (NMJ). While previous reports have shown how low [Ca2+] contributes to morphological defects in synaptic boutons by destabilizing microtubules, this project elaborates on this story by demonstrating that high [Ca2+] can also cause a similar phenotype. Deviations in typical presynaptic [Ca2+] that result in improper NMJ morphology are mediated by a pair of counteracting Ca2+-sensitive enzymes, a phosphatase and a kinase, which act on the same microtubule-stabilizing substrate.
I next describe how depolarization of the plasma membrane potentiates Phospholipase Cβ (PLCβ) activity, which led to greater inositol trisphosphate receptor (IP3R)-mediated Ca2+ release. Depolarization-induced augmentation of PLCβ-IP3R signaling increased mitochondrial [Ca2+] and ATP production, suggesting that activity of this mechanism constitutes a homeostatic response that compensates for the intensive bioenergetic needs of the neuron. Furthermore, in Drosophila models of neurodegeneration that decouple depolarization from this putative homeostatic response, misappropriation of this signaling axis induced increased endolysosomal Ca2+ loading, and a reduction in longevity. Interventions that decreased PLCβ-IP3R signaling or attenuated endolysosomal Ca2+ overload prevented shortening of lifespan in flies expressing neurodegenerative transgenes.
This dissertation endeavors to expand the body of knowledge describing mechanisms of Ca2+ dyshomeostasis that are relevant to neurodegeneration. I hope that, in the future, what is outlined here will contribute to the development of therapeutics needed to combat neurodegenerative diseases.
neurodegeneration, calcium signaling, endoplasmic reticulum calcium channels, lysosomes, excitability, neuronal bioenergetics, longevity, Drosophila neurobiology, neuromuscular junction