Cardiolipin-deficient cells depend on anaplerotic pathways to ameliorate defective TCA cycle function

Area of Science:

• Cell Biology
• Biochemistry
• Metabolic Engineering

Background:

• Cardiolipin (CL) is crucial for mitochondrial function.
• CL deficiency in yeast (crd1Δ mutant) leads to reduced acetyl-CoA and impaired TCA cycle enzyme activity.
• This suggests a defect in cellular energy metabolism.

Purpose of the Study:

• Investigate the metabolic adaptations in CL-deficient yeast.
• Determine the essentiality of signaling and anaplerotic pathways in crd1Δ mutant cells.
• Elucidate the role of acetyl-CoA import and beta-oxidation in compensating for TCA cycle defects.

Main Methods:

• Genetic analysis of synthetic lethality between crd1Δ and other metabolic mutants.
• Measurement of metabolite levels (e.g., glutamate, succinate, citrate).
• Gene expression analysis of glyoxylate cycle genes.
• Assessment of growth phenotypes with nutrient supplementation (e.g., oleate) and gene deletions (e.g., carnitine-acetylcarnitine translocase).

Main Results:

• The crd1Δ mutant exhibits synthetic lethality with mutations in the TCA cycle, RTG pathway, glyoxylate cycle, and pyruvate carboxylase 1.
• Glutamate levels decreased, causing glutamate auxotrophy.
• Glyoxylate cycle genes were upregulated, increasing succinate and citrate levels.
• Mitochondrial import of acetyl-CoA and functional beta-oxidation were essential for crd1Δ viability.
• Oleate supplementation rescued growth defects.

Conclusions:

• TCA cycle dysfunction due to cardiolipin absence triggers the activation of anaplerotic pathways.
• These pathways are vital for replenishing acetyl-CoA and TCA cycle intermediates.
• Findings provide insights into Barth syndrome, a disorder linked to cardiolipin metabolism.