Post-natal activity of cardiac O-GlcNAcase is regulated to maintain physiological levels of O-GlcNAc

Abstract

During post-natal development, the organism is subjected to 2 metabolic transitions. The weaning transition is particularly interesting as it is associated with a change in glucose metabolism. O-GlcNAcylation is an ubiquitous post-translational modification, described as a nutrient sensor. The GlcNAc moiety is added and removed by O-GlcNAc transferase (OGT) and O-GlcNAcase (OGA), respectively. Interestingly, cardiac O-GlcNAc levels decrease throughout post-natal development but its regulatory mechanism and impact on proteins have never been studied under this condition. Study the regulatory mechanism involved in O-GlcNAc regulation and its potential impact on proteins implied in cardiac metabolism. Hearts from 28 day-olds (D28) Wistar rats fed with a standard or low-carbohydrate (low-CHO) diet (D28F: 50% fat, 30% protein, 3% carbohydrates) during the weaning period (D12 to D28) were studied. O-GlcNAc levels and regulatory enzymes expression were evaluated by western blot. The OGA activity was evaluated with a spectrophotometric assay. The impact of selected protein expression in response to O-GlcNAc levels variations (Thiamet-G, OGA inhibitor) was evaluated on cell culture (HEK and COS). No change was reported on O-GlcNAc levels between the diets (D28: 1.00 ± 0.06; D28F: 0.99 ± 0.08). Cardiac OGA expression was 5 times lower in D28F however OGA activity remained stable (D28: 1.00 ± 0.03; D28F: 0.83 ± 0.16 AU). Protein expression, acetyl-CoA transferase 1 (ACAT1) and acetyl-CoA synthetase 1 (ACSS1), was reduced both in HEK and COS cells in responses to O-GlcNAc stimulation with Thiamet-G. While OGA expression is lower with the low-CHO diet, OGA activity and O-GlcNAc levels remain stable. This indicates a strong regulatory mechanism to control O-GlcNAc levels throughout post-natal development. This regulatory mechanism could help to modulate the expression of key metabolic enzymes such as ACAT1 or ACSS1.