Open Collections

Lu, Xueying

University of British Columbia

Developmental axon remodeling 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 aims 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, thereby inducing cytotoxicity. 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 NGF-dependent 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 5, 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.

Text

2024-08-26

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/89025

Biochemistry and Molecular Biology

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/