Date Available

4-25-2024

Year of Publication

2022

Degree Name

Master of Science in Medical Sciences (MSMS)

Document Type

Master's Thesis

College

Medicine

Department/School/Program

Medical Sciences

First Advisor

Dr. D. Allan Butterfield

Abstract

More than 10 million people are living with Parkinson’s disease (PD), one million of which are people in the United States. PD is the second most common age-related neurodegenerative disorder, after Alzheimer’s disease, and is characterized by the accumulation of a-synuclein aggregates and the degeneration of dopaminergic neurons. The loss of endogenous dopamine in PD brain accounts for the motor decline presented clinically in PD patients. Etiological factors of PD include oxidative damage and inflammation, although the detailed mechanisms remain unknown. Risk factors for PD include gender, age, environmental factors, and gene mutations.

The current thesis research employed phosphatase and tensin homolog (PTEN)-induced kinase 1 (PINK1) knockout (KO) rats because mutations in PINK1 lead to familial PD. In normal brain, PINK1 serves to recruit Parkin, an E3 ubiquitin protein ligase, to the outer mitochondrial membrane of depolarized mitochondria to induce mitophagy, a mitochondrial quality control mechanism in which damaged mitochondria are degraded. In brain lacking PINK1, mitochondrial homeostasis cannot be maintained, resulting in mitochondrial dysfunction, oxidative damage, and neuronal cell death.

The PINK1 KO rat brain was studied in conjunction with the mammalian target of rapamycin (mTOR) cell signaling pathway due to the capability of mTOR to regulate autophagy, glucose metabolism, mitochondrial function, and neuronal development and function. A disturbance in mTOR signaling in the brain, thus disturbances to such pathways, have shown to be implicated in cancer, diabetes, and neurodegeneration.

This thesis project studied the expression and phosphorylation (resulting in the activation or inhibition dependent upon the phosphorylation site of the protein in question) of the key enzymes in the mTOR pathway of a PINK1 KO rat brain model of familial PD as a function of age. The proteins studied include phosphoinositide 3-kinase (PI3K), protein kinase B (Akt), mammalian target of rapamycin complex I (mTORC1), ribosomal protein S6 kinase (P70S6K), and insulin receptor substrate 1 (IRS-1). The control group (male and female wild type (WT) rat brain at 2 months of age) and the male and female PINK1 KO rat brain at 4 months, 6 months, and 8 months of age were analyzed with the ProteinSimple JessTM instrument, which employs capillary electrophoresis for automated Western blotting. Three rats per group (WT 2-month, KO 4-month, KO 6-month, KO 8-month) were ran in duplicates for each protein (non-phosphorylated and phosphorylated form) with the JessTM instrument. The expression and phosphorylation levels of PI3K, Akt, mTOR, P70S6K, and IRS-1 in the male and female PINK1 KO rat brain were studied to gain further insight into autophagic function and insulin resistance in the rat brain lacking PINK1 to advance understanding of familial PD caused by the loss-of-function mutation in PINK1.

Digital Object Identifier (DOI)

https://doi.org/10.13023.107

Funding Information

This work was supported in part by National Institutes of Health grants to Prof. Butterfield: R21 NSO94891 09/01/2015-8/31/2019

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