Regulation of mitochondrial morphology and function by O-GlcNAcylation in neonatal cardiac myocytes

Abstract

Mitochondria are crucial organelles in cell life serving as a source of energy production and as regulators of Ca(2+) homeostasis, apoptosis, and development. Mitochondria frequently change their shape by fusion and fission, and recent research on these morphological dynamics of mitochondria has highlighted their role in normal cell physiology and disease. In this study, we investigated the effect of high glucose on mitochondrial dynamics in neonatal cardiac myocytes (NCMs). High-glucose treatment of NCMs significantly decreased the level of optical atrophy 1 (OPA1) (mitochondrial fusion-related protein) protein expression. NCMs exhibit two different kinds of mitochondrial structure: round shape around the nuclear area and elongated tubular structures in the pseudopod area. High-glucose-treated NCMs exhibited augmented mitochondrial fragmentation in the pseudopod area. This effect was significantly decreased by OPA1 overexpression. High-glucose exposure also led to increased O-GlcNAcylation of OPA1 in NCMs. GlcNAcase (GCA) overexpression in high-glucose-treated NCMs decreased OPA1 protein O-GlcNAcylation and significantly increased mitochondrial elongation. In addition to the morphological change caused by high glucose, we observed that high glucose decreased mitochondrial membrane potential and complex IV activity and that OPA1 overexpression increased both levels to the control level. These data suggest that decreased OPA1 protein level and increased O-GlcNAcylation of OPA1 protein by high glucose lead to mitochondrial dysfunction by increasing mitochondrial fragmentation, decreasing mitochondrial membrane potential, and attenuating the activity of mitochondrial complex IV, and that overexpression of OPA1 and GCA in cardiac myocytes may help improve the cardiac dysfunction in diabetes.

Mitochondrial O-GlcNAc Transferase (mOGT) Regulates Mitochondrial Structure, Function, and Survival in HeLa Cells

“…Indeed, exposure of cardiac myocytes to high glucose increases mitochondrial protein O-GlcNAcylation; impairs the activity of complex I, III, and IV; and lowers cellular ATP and mitochondrial calcium content (21). High glucose also increases mitochondrial fragmentation and decreases mitochondrial membrane potential (48). Furthermore, a recent study revealed that the levels of OGT and OGA are dramatically altered in mitochondria from diabetic mice hearts with significant mislocalization of OGT in the mitochondrial matrix and reduced interaction of OGT with complex IV (22).…”

OPA1 in Cardiovascular Health and Disease

“…The overexpression of OPA1 may be a therapeutic strategy for preventing the mitochondrial fission and dysfunction which occurs in the diabetic heart, thereby preventing the cardiac dysfunction observed in diabetic cardiomyopathy. In this regard, the over-expression of OPA1 has been shown to improve mitochondrial morphology in coronary endothelial cells isolated from a diabetic heart supporting the notion that OPA1 may be a potential therapeutic target to improve cardiac dysfunction in diabetes (33,64).…”

“…Makino et al (33) have shown in neonatal cardiomyocytes that in the presence of high glucose, O-GlcNAcylation of OPA1 suppressed OPA1 activity resulting in mitochondrial fission. The potential implications of this for the diabetic heart are discussed in a later section.…”

“…A number of potential mechanisms have been proposed: (1) In neonatal cardiomyocytes it has been shown that in the presence of high glucose, OGlcNAcylation of OPA1 occurs, the consequence of which was suppression of OPA1 activity resulting in mitochondrial fission and dysfunction (33). Overexpression of GlcNAcase decreased OPA1 protein O-GlcNAcylation and significantly increased mitochondrial elongation (33).…”

“…A number of potential mechanisms have been proposed: (1) In neonatal cardiomyocytes it has been shown that in the presence of high glucose, OGlcNAcylation of OPA1 occurs, the consequence of which was suppression of OPA1 activity resulting in mitochondrial fission and dysfunction (33). Overexpression of GlcNAcase decreased OPA1 protein O-GlcNAcylation and significantly increased mitochondrial elongation (33). Moreover, OPA1 overexpression was able to prevent the changes in mitochondrial morphology induced by the hyperglycemia; (2) In the diabetic heart, OPA1 has been shown to be hyper-acetylated, reducing its activity and resulting in mitochondrial fragmentation (34).…”