Targeting O-GlcNAcylation as a treatment for diabetes-induced cardiomyopathy

Background:
Diabetic cardiomyopathy is a common complication of diabetes. It is characterised by left ventricular (LV) diastolic dysfunction (impaired cardiac muscle relaxation), increased LV reactive oxygen species (ROS) generation, cardiac fibrosis, cardiomyocyte hypertrophy, increased cardiomyocyte apoptosis and is often accompanied by later onset of LV systolic dysfunction (impaired cardiac muscle contractile function). When left untreated, diabetic cardiomyopathy can lead to heart failure and death, so there is an urgent need for an effective treatment.

Our laboratory is interested in the hexosamine biosynthesis pathway (HBP), an alternate, minor fate for glucose metabolism (as opposed to the more predominant glycolysis and the pentose phosphate pathway), as a potential target for treating diabetic cardiomyopathy. It is estimated that very small amounts of glucose normally shuttles through the HBP, leading to the production of another type of sugar molecule, called GlcNAc. This sugar can attach to proteins, via a post-translational modification (PTM) of proteins known as O-GlcNAcylation, hence altering their function. What makes this PTM unique is the fact that is only regulated by two distinct, opposing enzymes. O-GlcNAC transferase, OGT, facilitates the addition of GlcNAc onto proteins to make them O-GlcNAc modified. Coversely, O-GlcNAc-ase, or OGA, removes the GlcNAc molecule to restore protein function. In diabetes, there is an increased flux through the HBP, leading to an increase in global O-GlcNAcylation, which in the heart has been associated with the development of diabetic cardiomyopathy.

We have developed a gene therapy containing the human isoform of the OGA enzyme, which specifically targets the heart to remove the O-GlcNAc molecule in order to reduce global cardiac O-GlcNAcylation in diabetic heart. We propose that the increase in cardiac OGA will limit diabetes-induced cardiac remodelling and improve cardiac function.

Project aim:
The aim of this project is to investigate whether targeting the hexosamine biosynthesis pathway in the hearts of diabetic mice may be used as a potential treatment for diabetic cardiomyopathy.

Techniques:
This project will involve extraction of RNA and protein from heart samples from these non-diabetic and diabetic mice. This will be followed by RTPCR and western blotting to investigate whether OGA gene therapy counteracts the detrimental impact of diabetes on the heart, by examining changes in expression of the specific genes and proteins responsible for the structural and functional impairments implicated in diabetic cardiomyopathy. The student will also use histological techniques to visualize impact of diabetes on cardiac morphology (including fibrosis, ROS dysregulation and inflammation) in the absence and presence of gene therapy. Changes in various components of the hexosamine biosynthesis pathway will also be examined.