All ETDs from UAB

Advisory Committee Chair

Rajasekaran Namakkal-Soorappan

Advisory Committee Members

Trent E Tipple

Michael R Crowley

Selvarangan Ponnazhagan

Document Type

Dissertation

Date of Award

2019

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Excessive accumulation of reactive oxygen and nitrogen species (ROS/RNS) promotes cardiac pathophysiology. Although extreme oxidative burden is cytotoxic, ROS/RNS are continually generated within multiple domains of cardiac myocytes, and these species play fundamental roles in signal transduction through reversible thiol oxidation. Nuclear factor, erythroid 2 Like 2 (Nfe2l2/NRF2) is activated by ROS/RNS and binds cis regulatory antioxidant response elements (AREs) to induce the expression of a host of thiol oxidoreductases which regulate signaling events at the post-translational, transcriptional and epigenetic levels. Although oxidative stress has been linked to cardiac disease, adaptive processes in the heart require reduction-oxidation (redox) reactions as a loss of physiological ROS/RNS through hyperactive NRF2 signaling results in reductive stress. Gain-of-function mutations in Nfe2l2 were recently identified in human patients; however, experimental models to study NRF2-mediated reductive stress are lacking and a comprehensive understanding of the genes regulated by NRF2 in the heart remains elusive. Accordingly, this dissertation utilized next-generation mRNA and microRNA (miRNA) sequencing on myocardial tissue from NRF2 knockout and transgenic mouse models to deduce the complete transcriptomic landscape governed by NRF2. For the first time, the current thesis identifies transcriptional signatures for reductive stress in hearts expressing constitutively active NRF21. Furthermore, these data solidify NRF2 as a necessary regulator of miRNA expression in the heart, an organ well-known to require stable miRNA activity. In addition to the essential role for NRF2 on cardiac miRNA induction, a distinct subset of ARE-harboring and NRF2-dose-dependent miRNAs (i.e. reductomiRs) were found to underlie the progression of reductive stress. NRF2-driven reductomiRs closely resembled previously reported miRNA signatures of cardiac hypertrophy, and computational analysis implicated reductomiRs as putative regulators of myocardial gene expression. MiR-671 was highlighted as the most sensitive reductomiR whose post-transcriptional regulatory activity modulates the dynamics of glutathione, a tripeptide thiol largely accounting for the reductive capacity of the NRF2 pathway. Taken together, this dissertation elucidates the genomic loci regulated by NRF2 in the heart and indicates a pivotal link between NRF2 transcriptional activity and miRNA dysregulation during myocardial reductive stress

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