ORCID

http://orcid.org/0000-0003-1222-0775

Date of Award

Winter 12-15-2021

Author's School

Graduate School of Arts and Sciences

Author's Department

Biology & Biomedical Sciences (Molecular Cell Biology)

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

Dyslipidemia and lipotoxicity are pathologic signatures of the metabolic syndrome and type 2 diabetes. Excess lipid causes cell dysfunction and induces cell death through pleiotropic mechanisms that link to oxidative stress. However, pathways that regulate the response to metabolic stress are not fully understood. To identify novel genes involved in metabolic stress, our group performed an unbiased forward genetic screen for lipotoxicity resistance. My studies focused on characterizing one of the mutant cell lines isolated from this screen, in which promoter trap mutagenesis disrupted one allele of the small nucleolar RNA hosting gene 3 (Snhg3).

I demonstrate that diminished expression of U17 snoRNAs from Snhg3 causes resistance to lipid-induced cell death and general oxidative stress in cultured cells. Protection from metabolic stress in U17 snoRNA-deficient cells is associated with broad reprogramming of oxidative metabolism, characterized by increased catabolism of glucose, fatty acids, and amino acids. This metabolic rewiring contributes to increased antioxidant capacity and altered redox balance, and is dependent on upregulated signaling through the mammalian target of rapamycin (mTOR) axis, a consequence of alterations in U17 snoRNA-mediated rRNA processing.

I extended my analyses by showing that knockdown of U17 snoRNAs in the liver recapitulates many phenotypic aspects of Snhg3 mutant cells, including increased antioxidant capacity, altered rRNA processing, and augmented mTOR signaling. Using the methionine- and choline-deficient diet (MCD) murine model of hepatic lipotoxicity, I show that depletion of U17 snoRNAs suppresses hepatic steatosis, oxidative stress, and inflammatory cell infiltration. Hepatic stellate cell activation, as measured by expression of pro-fibrotic mRNA transcripts, was also blunted by U17 snoRNA knockdown. To examine the role of U17 snoRNAs in the metabolic syndrome, I used high-fat diet (HFD) feeding to induce obesity and insulin resistance in C57BL6/J mice. In this model, U17 snoRNA depletion improved glucose tolerance and insulin-mediated glucose disposal without affecting weight gain. These findings suggest that genetic changes resulting in decreased expression or function of U17 snoRNAs could contribute to phenotypic variability in diet-induced metabolic dysfunction including fatty liver disease and insulin resistance.

Language

English (en)

Chair and Committee

Jean Schaffer

Committee Members

Brian Finck

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