Blocked O-GlcNAc cycling alters mitochondrial morphology, function, and mass

Abstract

O-GlcNAcylation is a prevalent form of glycosylation that regulates proteins within the cytosol, nucleus, and mitochondria. The O-GlcNAc modification can affect protein cellular localization, function, and signaling interactions. The specific impact of O-GlcNAcylation on mitochondrial morphology and function has been elusive. In this manuscript, the role of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and the activity of electron transport chain (ETC) complexes were evaluated. In a cellular environment with hyper O-GlcNAcylation due to the deletion of O-GlcNAcase (OGA), mitochondria showed a dramatic reduction in size and a corresponding increase in number and total mitochondrial mass. Because of the increased mitochondrial content, OGA knockout cells exhibited comparable coupled mitochondrial Oxphos and ATP levels when compared to WT cells. However, we observed reduced protein levels for complex I and II when comparing normalized mitochondrial content and reduced linked activity for complexes I and III when examining individual ETC complex activities. In assessing mitochondrial fission, we observed increased amounts of O-GlcNAcylated dynamin-related protein 1 (Drp1) in cells genetically null for OGA and in glioblastoma cells. Individual regions of Drp1 were evaluated for O-GlcNAc modifications, and we found that this post-translational modification (PTM) was not limited to the previously characterized residues in the variable domain (VD). Additional modification sites are predicted in the GTPase domain, which may influence enzyme activity. Collectively, these results highlight the impact of O-GlcNAcylation on mitochondrial dynamics and ETC function and mimic the changes that may occur during glucose toxicity from hyperglycemia.

Disruption of O-GlcNAcylation Homeostasis Induced Ovarian Granulosa Cell Injury in Bovine

“…Overexpression of OGT or OGA caused significant decreases in cellular respiration and glycolysis as well as a reduction in several TCA cycle proteins, which implies that mitochondrial function is sensitive to O-GlcNAc cycling [52]. In the current study, we identified a marked decrease in MMP and ATP production in response to changes in O-GlcNAc homeostasis, which is in agreement with those of a recent study conducted on murine embryonic fibroblasts [53]. Furthermore, we observed that pharmacological inhibition of OGA led to a decrease in MDH activity, but the variation of SDH activity was intriguingly increased by alterations in O-GlcNAc cycling.…”

Short O-GlcNAcase Is Targeted to the Mitochondria and Regulates Mitochondrial Reactive Oxygen Species Level

“…Various studies have shown that perturbations of O-GlcNAc cycling that increase or decrease O-GlcNAcylation can affect mitochondria homoeostasis, respiration, and ROS production [ 7 , 11 , 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ]. However, only few studies directly evaluated the specific effect of modulating the expression of mOGT on ROS production.…”

“…Increases in O-GlcNAcylation of mitochondrial proteins have been observed upon high-glucose conditions [ 8 , 9 ], and recent work pointed to perturbation in the localization of mOGT in cardiomyocytes mitochondria from diabetic mice [ 10 ]. Several lines of evidence indicate that alteration of O-GlcNAc cycle disrupts mitochondrial homoeostasis [ 7 , 11 , 12 , 13 , 14 , 15 , 16 ], including alteration in reactive oxygen species production [ 14 , 16 , 17 , 18 , 19 , 20 ].…”

The strange case of Drp1 in autophagy: Jekyll and Hyde?

“…[7,8] Additionally, a series of post-translational modifications (PTM) of Drp1 has been reported such as phosphorylation, ubiquitination, SUMOylation, glycosylation, acetylation, and nitrosylation (Figure 1A), which modulate Drp1 translocation to the mitochondrial membrane. [9][10][11][12][13][14][15][16] Therefore, these PTM directly linked the metabolic status of the cell and the mitochondrial network structure.…”