Ubiquinone Is Necessary for Caenorhabditis elegansDevelopment at Mitochondrial and Non-mitochondrial Sites

Abstract

Ubiquinone (UQ) is a lipid co-factor that is involved in numerous enzymatic processes and is present in most cellular membranes. In particular, UQ is a crucial electron carrier in the mitochondrial respiratory chain. Recently, it was shown that clk-1 mutants of the nematode worm Caenorhabditis elegans do not synthesize UQ 9 but instead accumulate demethoxyubiquinone (DMQ 9 ), a biosynthetic precursor of UQ 9 (the subscript refers to the length of the isoprenoid side chain). DMQ 9 is capable of carrying out the function of UQ 9 in the respiratory chain, as demonstrated by the functional competence of mitochondria isolated from clk-1 mutants, and the ability of DMQ 9 to act as a co-factor for respiratory enzymes in vitro. However, despite the presence of functional mitochondria, clk-1 mutant worms fail to complete development when feeding on bacteria that do not produce UQ 8 . Here we show that clk-1 mutants cannot grow on bacteria producing only DMQ 8 and that worm coq-3 mutants, which produce neither UQ 9 nor DMQ 9 , arrest development even on bacteria producing UQ 8 . These results indicate that UQ is required for nematode development at mitochondrial and non-mitochondrial sites and that DMQ cannot functionally replace UQ at those non-mitochondrial sites. Ubiquinone (UQ)1 is a prenylated benzoquinone that is an essential co-factor in the mitochondrial respiratory chain, where its function is best characterized. UQ is also found in many other locations in the cell, such as the lysosome and Golgi membranes, as well as in nuclear and plasma membranes (1). The exact role of UQ at these extramitochondrial sites is being actively explored (e.g. Refs. 2 and 3).The gene clk-1 of the nematode Caenorhabditis elegans affects many physiological rates, including embryonic and postembryonic development, rhythmic behaviors, reproduction, and life span (4). clk-1 encodes a 187-amino acid protein that is localized in mitochondria (5) and that is homologous to the yeast protein Coq7p, which has been shown to be required for UQ biosynthesis (6). clk-1 has also been shown to be necessary for UQ biosynthesis in worms (7,8) and in the mouse (9). Indeed, UQ 9 is entirely absent from mitochondria purified from worm and mouse clk-1 mutants (8, 9) (the subscript refers to the length of the isoprenoid side chain). Instead, these mitochondria accumulate demethoxyubiquinone (DMQ 9 ), which is an intermediate in the synthesis of UQ 9 (8, 9). Consistently, recent evidence suggests that clk-1 encodes a DMQ hydroxylase (10), which converts DMQ to ubiquinol. In Escherichia coli, DMQ 8 is able to sustain respiration in isolated membranes although at a lower rate than Q 8 (11). Similarly, DMQ 9 is capable of sustaining electron transport in eukaryotic mitochondria, as the function of purified mitochondria (5), and mitochondrial enzymes (8), from clk-1 worm mutants appears to be almost intact compared with the wild type. In addition, synthetic DMQ 2 has been shown to function in vitro as a co-factor for electron transport from worm complex I and, ...

Coenzyme Q protects Caenorhabditis elegans GABA neurons from calcium-dependent degeneration

“…We observed that homozygous coq-1 animals develop to at least the third larval stage with a few adult escapers. This finding is likely to mean that the coq-1(ok749) mutation results in a maternal effect lethal phenotype in which the first generation of viable offspring progress through larval development with maternally provided CoQ (23). Homozygous coq-1 mutants appear Unc as L3 larvae.…”

Molecular Mechanism of Maternal Rescue in the clk-1 Mutants of Caenorhabditis elegans

“…This phenotype is likely the most direct consequence of the Q 9 biosynthesis defect of clk-1 mutants, as the wild-type and other long-lived mutant strains have normal growth and reproduction on a Q-deficient food source (10). Thus, the ability to complete growth and produce progeny on Q-deficient E. coli reflects the endogenous Q status of the animal (10,23). Consequently, we assayed the ability of clk-1 maternally rescued animals to complete growth and produce a full brood on a Q 8 -deficient food source.…”

“…Reproductive Development When Raised on Q-deficient Bacteria-clk-1 mutants raised on E. coli strains defective in Q 8 biosynthesis arrest development or become sterile, depending on the time of transfer onto the Q-deficient food source (4,10). This phenotype is likely the most direct consequence of the Q 9 biosynthesis defect of clk-1 mutants, as the wild-type and other long-lived mutant strains have normal growth and reproduction on a Q-deficient food source (10).…”

“…Despite the presence of DMQ, clk-1 mutants require Q from their bacterial food source to proceed through development and become fertile adults (4,10). Indeed, when clk-1 mutants are transferred onto a Q 8 -deficient E. coli strain before the early larval stages, they arrest development at the second larval stage, and when the animals are transferred onto Q 8 -deficient bacteria later in development, they become sterile adults.…”

The mitochondrial unfolded protein response activator ATFS-1 protects cells from inhibition of the mevalonate pathway

“…However, several lines of evidence argue against CoQ depletion accounting for the effects of statins on mitochondria: (i) supplying CoQ to C. elegans conferred no protection from the toxic effects of statins (CoQ 10 was tested at 50 μg/mL and concentrations of CoQ 9 ranging from 10 to 80 μg/mL were tested, all without effect); (ii) the atfs-1(et15) mutant is not resistant to rotenone, antimycin A, or sodium azide, which are inhibitors of the mitochondrial respiratory chain (25,26) (Fig. S7 B-D); and (iii) it is well known that CoQ is dietarily available to C. elegans that are fed Escherichia coli as in our experiments (27,28) and that very little endogenous CoQ is sufficient for a wild-type phenotype even in the absence of dietary CoQ (29).…”