Nox4 and Epigenetics in chronically enhanced cardiac protein O-GlcNAcylation

PROJECT SUMMARY
Global diabetes prevalence is nearing 10%, and despite advancements in treatments, compared to non-diabetic,
individuals with diabetes have 2-fold higher rates of heart failure, as well as increased mortality due to
cardiovascular disease. Specifically, diabetic cardiomyopathy (DCM) is a diagnosis based on cardiac
insufficiency attributable only to diabetes, and characterized by the triad of cardiac hypertrophy, fibrosis, and
apoptosis. We believe these are consequences of and contributors to epigenetic changes that regulate
expression of genes responsible for the pathological state. Epigenetic changes are stable, yet reversible
modifications to chromatin and genetic material (e.g., histones, DNA). It is an established regulator of gene
expression associated with diabetes and heart failure—with the field studying the intersection of these topics still
relatively young. Additionally, our prior work found that glucose can signal through a specific post-translational
protein modification, O-linked -N-acetyl-glucosamine (O-GlcNAc), and building upon current literature, our lab
has shown using our novel mouse model that chronically enhanced O-GlcNAc is sufficient to cause pathology
associated with diabetic hearts. My work focuses on identifying and studying molecular pathways regulated by
DNA methylation changes during chronic O-GlcNAc which lead to pathology. Upon RNA-sequencing, my prior
analysis identified significantly increased NADPH Oxidase 4 (Nox4) with chronically increased cardiac protein
O-GlcNAc. Similarly, methylation-sequencing of DNA from cardiac tissue of diabetic mice revealed hypo-
methylation (an epigenetic mark associated with increased gene expression) at the Nox4 promoter associated
CPG island. Nox4 is a significant producer of reactive oxygen species (ROS), and its activity is governed by
levels of expression. The field of Nox4 in the context of chronic diabetic hearts is relatively young, and little is
known about its regulatory mechanisms. With these opportunities and encouraging preliminary data, I seek to
build upon the rigors of past research to contribute novel knowledge and develop resources to study Nox4’s
regulation and role in chronic diabetic hearts. I hypothesize that with chronically enhanced protein O-GlcNAc (a
key facet of diabetic hearts), cardiac Nox4 is induced via DNA hypomethylation, and its upregulation is necessary
to promote cardiac dysfunction and pathology. The proposal will test the following two aims: (1) Determine the
mechanism of O-GlcNAcylation initiated DNA methylation changes leading to cardiac Nox4 upregulation. (2)
Establish that Nox4 depletion can prevent cardiac remodeling seen during chronically enhanced cardiac protein
O-GlcNAc. In summary, this proposal will determine a new regulatory mechanism for Nox4 and provide
foundational research for the development of precision therapeutics to treat underlying pathological mechanisms
driving disease in diabetic hearts. This proposal will also provide the foundation for my career as a physician-
scientist with the scientific reasoning, research, and translational skills in cardiovascular research/medicine.

Grant Number: 5F30HL172687-02
NIH Institute/Center: NIH
Principal Investigator: Samuel Chang