Date of Award

2019

Embargo Period

8-2-2024

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Cell and Molecular Pharmacology

College

College of Graduate Studies

First Advisor

Marcelo R. Vargas

Second Advisor

Craig C. Beeson

Third Advisor

Joseph B. Blumer

Fourth Advisor

John J. Lemasters

Fifth Advisor

Kenneth D. Tew

Abstract

Amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease is caused by the progressive degeneration of motor neurons in the spinal cord, brain stem, and motor cortex. Motor neuron death leads to muscle weakness and paralysis causing death in one to five years from the time of symptoms onset. Most ALS cases are sporadic (sALS) and exposure to yet unidentified environmental factors might be responsible for sALS. About 5-10% of the cases are inherited (familial ALS, fALS) and the first ALS-linked gene identified was superoxide dismutase 1 (SOD1). SOD1 mutations account for up to 20% of FALS and 1-2% of apparently SALS. Rodent models over-expressing ALS-linked mutant SOD1 develop an ALS-like phenotype. The study of these models has significantly contributed to our understanding of the human pathology. The molecular mechanism underlying the toxic gain-of-function of mutant hSOD1s remains uncertain, however several lines of evidence suggest that toxicity to motor neurons requires damage to non-neuronal cells. In line with this observation, primary astrocytes isolated from mutant hSOD1 over-expressing mice induce motor neuron death in co-culture. Mitochondrial alterations and increased oxidative stress have been documented in both sporadic and familial ALS, as well as in ALS-animal models. Sirtuins are nicotinamide adenine dinucleotide (NAD+)-dependent enzymes that have emerged as key modulators of mitochondrial function and oxidative stress resistance. Recent studies have demonstrated that endogenous sirtuin activity is limited by the availability of NAD+. The hypothesis tested in this thesis is that increased NAD+ availability in ALS-astrocytes may revert their toxicity towards co-cultured motor neurons through a sirtuin-dependent mechanism. Since strategies aimed at reverting the neurotoxicity of ALS astrocytes have been shown to extend the survival of SOD1-linked ALS mouse models, we also investigated the effect of modulating NAD+ availability in ALS animal models. We observed that increasing total and mitochondrial NAD+ content in ALS astrocytes increases oxidative stress resistance and reverts their toxicity toward co-cultured motor neurons. In addition, an NAD+ precursor-supplemented diet reduces inflammation, appears to provide metabolic flexibility, and increases survival in hSOD1G93A mice. Taken together, our results suggest that different strategies aimed at enhancing NAD+ content in astrocytes have therapeutic potential to prevent astrocyte-mediated motor neuron death in ALS.

Rights

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