Fine-tuning the cardiac O-GlcNAcylation regulatory enzymes governs the functional and structural phenotype of the diabetic heart

Abstract

Aims The glucose-driven enzymatic modification of myocardial proteins by the sugar moiety, β-N-acetylglucosamine (O-GlcNAc), is increased in pre-clinical models of diabetes, implicating protein O-GlcNAc modification in diabetes-induced heart failure. Our aim was to specifically examine cardiac manipulation of the two regulatory enzymes of this process on the cardiac phenotype, in the presence and absence of diabetes, utilising cardiac-targeted recombinant-adeno-associated viral-vector-6 (rAAV6)-mediated gene delivery. Methods and Results In human myocardium, total protein O-GlcNAc modification was elevated in diabetic relative to non-diabetic patients, and correlated with left ventricular (LV) dysfunction. The impact of rAAV6-delivered O-GlcNAc transferase (rAAV6-OGT, facilitating protein O-GlcNAcylation), O-GlcNAcase (rAAV6-OGA, facilitating de-O-GlcNAcylation) and empty vector (null) were determined in non-diabetic and diabetic mice. In non-diabetic mice, rAAV6-OGT was sufficient to impair LV diastolic function and induce maladaptive cardiac remodelling, including cardiac fibrosis and increased Myh-7 and Nppa pro-hypertrophic gene expression, recapitulating characteristics of diabetic cardiomyopathy. In contrast, rAAV6-OGA (but not rAAV6-OGT) rescued LV diastolic function and adverse cardiac remodelling in diabetic mice. Molecular insights implicated impaired cardiac PI3K(p110α)-Akt signalling as a potential contributing mechanism to the detrimental consequences of rAAV6-OGT in vivo. In contrast, rAAV6-OGA preserved PI3K(p110α)-Akt signalling in diabetic mouse myocardium in vivo and prevented high glucose-induced impairments in mitochondrial respiration in human cardiomyocytes in vitro. Conclusion Maladaptive protein O-GlcNAc modification is evident in human diabetic myocardium, and is a critical regulator of the diabetic heart phenotype. Selective targeting of cardiac protein O-GlcNAcylation to restore physiological O-GlcNAc balance may represent a novel therapeutic approach for diabetes-induced heart failure. Translational perspective There remains a lack of effective clinical management of diabetes-induced cardiac dysfunction, even via conventional intensive glucose-lowering approaches. Here we reveal that the modification of myocardial proteins by O-GlcNAc, a glucose-driven process, is not only increased in human diabetic myocardium, but correlates with reduced cardiac function in affected patients. Moreover, manipulation of the two regulatory enzymes of this process exert opposing influences on the heart, whereby increasing O-GlcNAc transferase (OGT) is sufficient to replicate the cardiac phenotype of diabetes (in the absence of this disease), while increasing O-GlcNAc-ase (OGA) rescues diabetes-induced impairments in both cardiac dysfunction and remodelling. Cardiac O-GlcNAcylation thus represents a novel therapeutic target for diabetes-induced heart failure.

CaMKII Inhibition is a Novel Therapeutic Strategy to Prevent Diabetic Cardiomyopathy

“…In DM, glucose may be favoured to be metabolised through alternative pathways such as the HBP due to impairments in insulin signaling, leading to elevated concentrations of UDP-GlcNAc in diabetic mice (Clark et al, 2003). This increase in UDP-GlcNAc production causes an elevation in O-GlcNAc modifications on proteins, as has been observed in left ventricular and right atrial appendage samples from diabetic patients (Prakoso et al, 2021).…”

Protein O‐GlcNAcylation in the heart

“…The diabetic heart is characterized by increased left ventricular stiffness due to the accumulation of collagen and AGEs 115,116 . Recently, Prakoso et al 50 demonstrated that overexpression of OGT in non‐diabetic mice was sufficient to impair left ventricular diastolic function and increase cardiac interstitial and perivascular collagen deposition, replicating the cardiac phenotype of diabetes. Increased deposition of interstitial extracellular matrix which results in fibrosis in the diabetic heart has been associated with an increase in fibroblast proliferation 117‐119 .…”

Bone Morphogenetic Protein 7 Gene Delivery Improves Cardiac Structure and Function in a Murine Model of Diabetic Cardiomyopathy

“…The BMP7 construct, previously utilised in skeletal muscle (Winbanks et al, 2013), was cloned into an rAAV6 expression plasmid consisting of a cytomegalovirus (CMV) promoter/ enhancer packaged into pseudotype-6 capsids (rAAV6), as previously described (Gregorevic et al, 2004;Winbanks et al, 2013;Prakoso et al, 2017;Prakoso et al, 2020;Prakoso et al, 2021a). The purified vector preparations were titered with a customised sequence-specific quantitative PCR-based reaction.…”