Novel gene therapy for the treatment of diabetes-induced heart failure

Abstract

People with diabetes are at risk of developing myocardial abnormalities known as diabetic cardiomyopathy. This is characterised by diabetes-induced left-ventricular (LV) impairment, which develops independent of hypertension, coronary artery or valvular heart disease, leading to an increased risk of heart failure. To date, there is still no effective or specific treatment for diabetic cardiomyopathy. Hence, the overall aim of my thesis was to investigate the therapeutic potential of targeting two distinct novel pathways, the phosphoinositide 3-kinase (PI3K)p110α axis and the hexosamine biosynthesis pathway (HBP)/O-GlcNAcylation, in the setting of diabetic cardiomyopathy.

PI3K(p110α) is a lipid kinase that regulates several physiological functions, including membrane trafficking, adhesion, actin rearrangement, cell growth, and survival. Recent findings from our laboratory and others have highlighted that PI3K(p110α) is cardioprotective in a range of different cardiac pathologies. In Chapter 3, I investigated whether cardiac-directed PI3K(p110α) gene therapy ameliorates diabetic cardiomyopathy in a mouse model of type-1 diabetes (T1D) in vivo. I revealed that administration of recombinant adeno-associated virus-6 constitutively-active PI3K(p110α) (rAAV6-caPI3K) attenuated diabetic cardiomyopathy, even when administered after the initial manifestation of LV diastolic dysfunction. I then proceeded to investigate the cardioprotective effects of rAAV6-caPI3K in the more clinically-prevalent type-2 diabetes (T2D) setting. In Chapter 4, I elucidated that restoration of cardiac PI3K(p110α) activity, through the administration of rAAV6-caPI3K gene therapy, attenuates T2D-induced cardiomyopathy, together with limiting ROS generation.

In comparison to the cardioprotective nature of PI3K(p110α), the HBP and subsequent protein O-GlcNAcylation have been implicated in the development of diabetic cardiomyopathy. The generation of β-N-acetylglucosamine (O-GlcNAc) from HBP is a substrate for the post-translational protein modification (PTM) called O-GlcNAcylation. Two specific enzymes regulate the addition and removal of O-GlcNAc modification; O-GlcNAc transferase (OGT) catalyses the addition of GlcNAc to proteins and O-GlcNAc-ase (OGA) facilitates its removal. In Chapter 5, I aimed to elucidate the effect of cardiac manipulation of O-GlcNAcylation in the setting of diabetes-induced cardiac dysfunction in vivo. I demonstrated here that a cardiac-selective increase in OGT (via rAAV6-OGT gene delivery), the enzyme responsible for O-GlcNAcylation, is sufficient to drive cardiac dysfunction and remodelling, resembling that seen in diabetic cardiomyopathy. In contrast, increasing cardiac OGA (via rAAV6-OGA gene delivery), the enzyme responsible for the removal of the O-GlcNAc moiety, attenuates several characteristics of diabetic cardiomyopathy, likely at least in part through the improvement of mitochondrial function. Finally, in Chapter 6 I investigated the impact of O-GlcNAcylation on the PI3K(p110α), pathway and the effect of PI3K(p110α) gene therapy on HBP signalling. I elucidated that PI3K(p110α) can negatively regulate consequences of the HBP and O-GlcNAcylation as part of its cardioprotective actions in diabetic cardiomyopathy, while HBP/O-GlcNAcylation inhibits PI3K(p110α)-mediated signalling, likely contributing to the ability for this pathway to exert cardiac impairments.

In conclusion, data from this thesis reveal that gene therapies targeting PI3K(p110α) and HBP/O-GlcNAcylation are viable therapeutic targets for diabetic cardiomyopathy. These results hence provide a basis for pursuing gene therapy for the treatment of diabetes-induced heart failure.