Date of Award

1-1-2016

Embargo Period

11-2-2020

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Molecular and Cellular Biology and Pathobiology

College

College of Graduate Studies

First Advisor

Donald R. Menick

Second Advisor

Amy D. Bradshaw

Third Advisor

Craig E. Crosson

Fourth Advisor

Jeffrey A. Jones

Fifth Advisor

Michael R. Zile

Abstract

This dissertation aims to develop a better understanding on how epigenetics regulate microRNAs during pathological cardiac remodeling and fibrosis. Histone modifications by acetylation and/or methylation, DNA methylation and miRNAs are epigenetic mechanisms that play an essential role during development and differentiation. In the light of recent studies, there is strong evidence linking epigenetics to the pathogenesis of a variety of diseases, including cancer, fibrotic diseases and heart failure. MicroRNAs have emerged as major players in the progression of heart failure yet the transcription of microRNAs in heart failure is poorly understood. An important aspect of epigenetic regulation is cross-talk between epigenetic mechanisms; DNA methylation, histone modifications and chromatin remodeling are linked to microRNA-mediated mechanisms in cancer cells. What remains unclear is how this cross-talk affects the expression of microRNAs in cardiac hypertrophy and heart failure. We hypothesize that (1) histone deacetylases (HDACs) which regulate histone acetylation, (2) DNA methyltransferases (DNMTs) which regulate DNA methylation, and (3) lysine demethylase (LSD1) which regulates histone methylation, regulate certain microRNAs that mediate cardiac remodeling and fibrosis. In murine pressure overload (PO) and ischemia-reperfusion induced cardiac remodeling models, we show increased HDAC activity and recruitment of HDAC2 to miR-133a promoter during PO stress along with an increase in DNMT1 abundance. Using selective inhibitors targeting HDACs (SAHA), DNMTs (azacitidine) and LSD1 (C1 and GSK), we show that the pathological expression of several miRNAs can be modulated, cardiac function improved and fibrosis dampened. Additionally we show that pri-miR-133a1 and mature miR-133a expressions follow a similar pattern, suggesting that in mouse tissue miR-133a is transcriptionally regulated. In human cardiac fibroblasts obtained from patients suffering dilated cardiomyopathy (DCM), we show that miR-133a expression is downregulated in DCM cells as compared to normal cells and that HDAC inhibition increased miR-133a significantly. We also show that expression of pri-miR- 133a1 is upregulated when mature miR-133a is downregulation, suggesting that in human DCM fibroblasts miR-133a is not regulated at the transcriptional level. Taken together these results emphasized that miRNAs are subject to many layers of epigenetic regulation during PO-induced remodeling, making them potential therapeutic candidates in heart failure given the availability of specific, non-toxic inhibitors.

Rights

All rights reserved. Copyright is held by the author.

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