Thesis Defence: The Investigation of the Role of PLCgamma1 in the TrkA Dependent Degenerative Pathway within Dorsal Root Ganglion Sensory Neurons

Xueying (Michelle) Lu, supervised by Dr. Phil A. Barker and Dr. Julien Gibon, will defend their thesis titled “The Investigation of the Role of PLCgamma1 in the TrkA Dependent Degenerative Pathway within Dorsal Root Ganglion Sensory Neurons” in partial fulfillment of the requirements for the degree of Master of Science in Biochemistry and Molecular Biology.

An abstract for Xueying (Michelle) Lu’s thesis is included below.

Defences are open to all members of the campus community as well as the general public. Please email philip.barker@ubc.ca to receive the Zoom link for this defence.

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ABSTRACT

Developmental axon remodelling is an essential process that ensures the proper development and functioning of the nervous system. Dysregulation of this process is associated with neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease, and amyotrophic lateral sclerosis. Tropomyosin receptor kinase A (TrkA) has shown characteristics of a dependence receptor for NGF. However, how TrkA initiates degeneration and the downstream players remain unclear. This thesis aim to determine if PLCγ1 acts downstream of TrkA-dependent axonal degeneration in dorsal root ganglion (DRG) sensory neurons. It is hypothesized that in the absence of NGF, TrkA induced axon degeneration by activating PLCγ1 through inducing cytotoxic Ca2+ mobilization in
the axons. The first chapter of this thesis investigates the role of PLCγ1 in the axonal degeneration of nerve growth factor (NGF) dependent DRG through drug and in the second chapter, a genetic approach is utilized. First, a drug inhibitor, U73122, is employed to inhibit PLC activities. Unexpectedly, U73122 is proven to be an unsuitable inhibitor of PLCγ1 in DRGs. Our results reveal that U73122 induced changes in axon morphology, increases in Ca2+ mobilization, disruption of mitochondria outer membrane potential (MOMP), and a significant increase in PLCγ1 phosphorylation in DRGs. Next, a PLCγ1 Cre-Lox mouse model is used to study DRG degeneration in the absence of PLCγ1. Our results determined that PLCγ1 fl/fl DRGs show similar levels of NGFdependent growth and degeneration as wild-type DRGs, but in the absence of PLCγ1, DRGs show significantly reduced axonal-induced Ca2+ mobilization after NGF deprivation. In Chapter 3, TrkAY785F knock-in DRGs were generated and characterized. Phosphorylation of TrkA at Y785 allows PLCγ1 to interact, become phosphorylated, and activated. They were shown to possess normal NGF-dependent growth and degeneration. Moreover, they were shown to have defective TrkA Y785 phosphorylation and show reduced Ca2+ mobilization following NGF deprivation compared to wild-type DRGs. Together these results suggest PLCγ1 may play an important role in TrkA dependent degenerative pathway in DRG sensory neurons. A better understanding of this degenerative pathway could advance therapeutic drug development in the treatment of neurodegenerative disorders by targeting specific components of TrkA-PLC degenerative pathway.