Degree Type

Dissertation

Date of Award

2019

Degree Name

Doctor of Philosophy

Department

Animal Science

Major

Molecular, Cellular and Developmental Biology

First Advisor

Joshua Selsby

Abstract

Duchenne muscular dystrophy (DMD) is a fatal muscle wasting disease caused by the absence of functional dystrophin protein. Dystrophin-deficiency results in numerous cellular dysfunctions and increased muscle injury leading to progressive muscle weakness and ultimately death due to cardiomyopathy or respiratory insufficiency. Overexpression of the transcriptional coactivator, PGC-1α, has been shown to provide therapeutic benefits for dystrophic muscle. In a preliminary experiment, quercetin, a nutraceutical that can drive PGC-1α through SIRT1, protected dystrophin-deficient skeletal muscle following 6 months of treatment. Therapies for DMD must demonstrate long-term efficacy, therefore in the first research chapter we evaluated the effect of 12 months of quercetin treatment on dystrophin-deficient skeletal muscle. To improve the lasting efficacy of quercetin, in the second and third research chapters we fed dystrophic mice quercetin in combination with several agents intended to potentiate or augment the effects of quercetin. We found that these quercetin-based cocktails failed to protect muscle from injury or preserve respiratory or muscle function. Collectively, these studies suggest that quercetin and these quercetin-based cocktails do not attenuate disease pathology long-term.

Stemming from our biochemical experiments from the first research chapter, we began to investigate the role of autophagy in dystrophic muscle. During autophagy a membrane is formed around protein aggregates or dysfunctional organelles, which then fuses with a lysosome for degradation. To better understand autophagy in the context of DMD and identify new therapeutic targets, in the fourth research chapter we evaluated autophagy at 7 weeks and 17 months of age in healthy and dystrophic mice. We discovered that autophagy was impaired in dystrophic muscle. Additionally, we discovered that lysosome abundance was decreased with advanced disease and Transcription Factor EB (TFEB), a transcription factor that drives lysosome biogenesis, was partially excluded from dystrophic myonuclei. In the fifth research chapter we used an adeno-associated virus (AAV) vector to drive PGC-1α expression, which is known to increase TFEB protein abundance in healthy tissue. The data suggest that PGC-1α overexpression increased TFEB nuclear localization and subsequently lysosome abundance and autophagosome degradation.

Copyright Owner

Hannah Spaulding

Language

en

File Format

application/pdf

File Size

200 pages

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