Polyunsaturated fatty acid sequestration protects against mitochondrial dysfunction-induced ferroptosis

Abstract

Impaired energy production is a hallmark of mitochondrial oxidative phosphorylation (OXPHOS) defects. However, secondary metabolic disturbances also represent an important trigger for pathologies originating from OXPHOS aberrations. Here we show that cells with OXPHOS deficiencies accumulate triacylglycerols enriched in polyunsaturated fatty acids (PUFAs), which are stored in lipid droplets. Sequestration of PUFAs is a critical component of a broader stress response, which also includes downregulation of cellular desaturases and upregulation of glutathione peroxidase 4 (GPX4). We demonstrate that this mechanism represents a physiologically relevant protective strategy, manifesting in cells under hypoxia and in immortalised fibroblasts derived from patients with primary mitochondrial complex IV deficiency. As a proof of principle, we observe elevated PUFA-enriched triacylglycerols in the plasma of patients with Myoclonic Epilepsy with Ragged Red Fibres (MERRF). Our findings reveal a novel protective mechanism against ferroptosis, which preserves membrane integrity when mitochondrial respiration is compromised. OXPHOS-deficient cells activate a coordinated multilayered polyunsaturated fatty acid (PUFA) stress response, which preserves membrane integrity against lipid peroxidation-driven ferroptosis. It is conserved across distinct OXPHOS complex deficiencies, is recapitulated under hypoxia, and is detectable in patients with mitochondrial disease. OXPHOS-deficient cells trigger a PUFA stress response that includes sequestration of PUFAs to triacylglycerols (TGs), downregulation of fatty acid desaturases, and upregulation of glutathione peroxidase 4. PUFA trafficking to TGs stored in lipid droplets protects the cells against lipid peroxidation and ferroptosis. OXPHOS-deficient cells synthesise fatty acids de novo from glutamine-derived acetyl-CoA when reductive carboxylation is permissible. PUFA stress response is activated in patients with mitochondrial deficiencies and during hypoxia. OXPHOS-deficient cells trigger a PUFA stress response that includes sequestration of PUFAs to triacylglycerols (TGs), downregulation of fatty acid desaturases, and upregulation of glutathione peroxidase 4. PUFA trafficking to TGs stored in lipid droplets protects the cells against lipid peroxidation and ferroptosis. OXPHOS-deficient cells synthesise fatty acids de novo from glutamine-derived acetyl-CoA when reductive carboxylation is permissible. PUFA stress response is activated in patients with mitochondrial deficiencies and during hypoxia. OXPHOS-deficient cells activate a coordinated multilayered polyunsaturated fatty acid (PUFA) stress response, which preserves membrane integrity against lipid peroxidation-driven ferroptosis. It is conserved across distinct OXPHOS complex deficiencies, is recapitulated under hypoxia, and is detectable in patients with mitochondrial disease.