CLD1 Reverses the Ubiquinone Insufficiency of Mutant cat5/coq7 in a Saccharomyces cerevisiae Model System.

Ubiquinone (Qn) functions as a mobile electron carrier in mitochondria. In humans, Q biosynthetic pathway mutations lead to Q10 deficiency, a life threatening disorder. We have used a Saccharomyces cerevisiae model of Q6 deficiency to screen for new modulators of ubiquinone biosynthesis. We generated several hypomorphic alleles of coq7/cat5 (clk-1 in Caenorhabditis elegans) encoding the penultimate enzyme in Q biosynthesis which converts 5-demethoxy Q6 (DMQ6) to 5-demethyl Q6, and screened for genes that, when overexpressed, suppressed their inability to grow on non-fermentable ethanol-implying recovery of lost mitochondrial function. Through this approach we identified Cardiolipin-specific Deacylase 1 (CLD1), a gene encoding a phospholipase A2 required for cardiolipin acyl remodeling. Interestingly, not all coq7 mutants were suppressed by Cld1p overexpression, and molecular modeling of the mutant Coq7p proteins that were suppressed showed they all contained disruptions in a hydrophobic α-helix that is predicted to mediate membrane-binding. CLD1 overexpression in the suppressible coq7 mutants restored the ratio of DMQ6 to Q6 toward wild type levels, suggesting recovery of lost Coq7p function. Identification of a spontaneous Cld1p loss-of-function mutation illustrated that Cld1p activity was required for coq7 suppression. This observation was further supported by HPLC-ESI-MS/MS profiling of monolysocardiolipin, the product of Cld1p. In summary, our results present a novel example of a lipid remodeling enzyme reversing a mitochondrial ubiquinone insufficiency by facilitating recovery of hypomorphic enzymatic function.

Mitochondrial metabolites extend lifespan.

Disruption of mitochondrial respiration in the nematode Caenorhabditis elegans can extend lifespan. We previously showed that long-lived respiratory mutants generate elevated amounts of α-ketoacids. These compounds are structurally related to α-ketoglutarate, suggesting they may be biologically relevant. Here, we show that provision of several such metabolites to wild-type worms is sufficient to extend their life. At least one mode of action is through stabilization of hypoxia-inducible factor-1 (HIF-1). We also find that an α-ketoglutarate mimetic, 2,4-pyridinedicarboxylic acid (2,4-PDA), is alone sufficient to increase the lifespan of wild-type worms and this effect is blocked by removal of HIF-1. HIF-1 is constitutively active in isp-1(qm150) Mit mutants, and accordingly, 2,4-PDA does not further increase their lifespan. Incubation of mouse 3T3-L1 fibroblasts with life-prolonging α-ketoacids also results in HIF-1α stabilization. We propose that metabolites that build up following mitochondrial respiratory dysfunction form a novel mode of cell signaling that acts to regulate lifespan.