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

Area of Science:

• Biochemistry
• Cell Biology
• Metabolic Regulation

Background:

• O-GlcNAcylation is a key post-translational modification regulating protein function in various cellular compartments.
• Its specific role in mitochondrial morphology and function remains largely uncharacterized.
• Mitochondrial dynamics and oxidative phosphorylation (Oxphos) are critical for cellular energy production.

Purpose of the Study:

• To investigate the impact of O-GlcNAcylation on mitochondrial fission, oxidative phosphorylation (Oxphos), and electron transport chain (ETC) complex activity.
• To elucidate the role of O-GlcNAcase (OGA) deletion in altering mitochondrial O-GlcNAcylation.
• To examine the effect of O-GlcNAcylation on dynamin-related protein 1 (Drp1) modification and its implications for mitochondrial fission.

Main Methods:

• Utilized OGA knockout (KO) cells to induce hyper O-GlcNAcylation.
• Assessed mitochondrial morphology, size, number, and total mass.
• Quantified Oxphos, ATP levels, and individual ETC complex activities.
• Analyzed protein levels of ETC complexes.
• Investigated O-GlcNAcylation of dynamin-related protein 1 (Drp1) in OGA KO and glioblastoma cells.

Main Results:

• OGA deletion led to smaller, more numerous mitochondria with increased total mass.
• Despite increased mitochondrial content, coupled Oxphos and ATP levels were comparable to wild-type (WT) cells.
• Normalized mitochondrial content revealed reduced protein levels for ETC complexes I and II.
• Individual ETC complex activity assays showed reduced activity for complexes I and III.
• Increased O-GlcNAcylated Drp1 was observed, with modifications potentially extending beyond known sites to the GTPase domain.

Conclusions:

• O-GlcNAcylation significantly impacts mitochondrial dynamics, promoting fission and altering mitochondrial mass.
• Hyper O-GlcNAcylation dysregulates electron transport chain complex function and protein levels.
• These findings highlight O-GlcNAcylation's role in mitochondrial health and suggest a link to metabolic disorders like hyperglycemia-induced glucose toxicity.