Diabetes-associated dysregulation of O -GlcNAcylation in rat cardiac mitochondria

Abstract

Elevated mitochondrial O-GlcNAcylation caused by hyperglycemia, as occurs in diabetes, significantly contributes to mitochondrial dysfunction and to diabetic cardiomyopathy. However, little is known about the enzymology of mitochondrial O-GlcNAcylation. Herein, we investigated the enzymes responsible for cycling O-GlcNAc on mitochondrial proteins and studied the mitochondrial transport of UDP-GlcNAc. Analyses of purified rat heart mitochondria from normal and streptozocin-treated diabetic rats show increased mitochondrial O-GlcNAc transferase (OGT) and a concomitant decrease in the mito-specific O-GlcNAcase (OGA). Strikingly, OGT is mislocalized in cardiac mitochondria from diabetic rats. Interaction of OGT and complex IV observed in normal rat heart mitochondria is visibly reduced in diabetic samples, where OGT is mislocalized to the matrix. Live cell OGA activity assays establish the presence of O-GlcNAcase within the mitochondria. Furthermore, we establish that the inner mitochondrial membrane transporter, pyrimidine nucleotide carrier, transports UDP-GlcNAc from the cytosol to the inside of the mitochondria. Knockdown of this transporter substantially lowers mitochondrial O-GlcNAcylation. Inhibition of OGT or OGA activity within neonatal rat cardiomyocytes significantly affects energy production, mitochondrial membrane potential, and mitochondrial oxygen consumption. These data suggest that cardiac mitochondria not only have robust O-GlcNAc cycling, but also that dysregulation of O-GlcNAcylation likely plays a key role in mitochondrial dysfunction associated with diabetes.

O-GlcNAcase deficiency suppresses skeletal myogenesis and insulin sensitivity in mice through the modulation of mitochondrial homeostasis

“…The values are the means ± SEM; n = 4; *p < 0.05; **p < 0.01. siOga, Oga siRNA mitochondrial O-GlcNAcylation was dramatically reduced because of increased mitochondrial OGA levels. This finding is supported by the recent discovery of OGA mitochondrial localisation [25]. In addition to the mitochondrial density affected by OGA deficiency, we also showed that mitochondrial protein O-GlcNAcylation was altered in response to OGA knockdown during myogenesis and in fully differentiated myotubes, and was accompanied by impaired mitochondrial function, including significantly lowered ATP content, increased ROS content and protein and lipid oxidation.…”

“…2c). In response to a recent report of localised OGA in mitochondria [25], we analysed the mitochondria and found that mitochondrial OGA levels sharply increased during myogenesis and were accompanied by decreased mitochondrial O-GlcNAcylation (Fig. 2d).…”

“…Impaired mitochondrial O-GlcNAcylation has been associated with mitochondrial dysfunction in neurons [40] and cardiomyocytes [25,41]. Thus, we hypothesised that elevated mitochondrial O-GlcNAcylation may contribute to mitochondrial dysfunction in diabetic skeletal muscle.…”

“…Following the observation of OGT localisation to the mitochondria by Love et al [24], the presence of OGA was recently reported in cardiac mitochondria in rats [25]. Despite a recently identified association between OGA-mediated O-GlcNAcylation and diabetes progression [25,26], there have been no reports of the effects of OGA activity on mitochondrial regulation. In the current study in mice, we report that OGA deficiency promotes peroxisome proliferator-activated receptor γ coactivator 1α (PGC-1α) degradation by increasing its O-GlcNAcylation, leading to suppressed mitochondrial biogenesis and myogenesis.…”

“…Impaired content or activity of enzymes related to mitochondrial function has been reported in STZ-or HFD-induced diabetic animal models [20][21][22][23]. Following the observation of OGT localisation to the mitochondria by Love et al [24], the presence of OGA was recently reported in cardiac mitochondria in rats [25]. Despite a recently identified association between OGA-mediated O-GlcNAcylation and diabetes progression [25,26], there have been no reports of the effects of OGA activity on mitochondrial regulation.…”