A Regulated Response to Impaired Respiration Slows Behavioral Rates and Increases Lifespan in Caenorhabditis elegans

When mitochondrial respiration or ubiquinone production is inhibited in Caenorhabditis elegans, behavioral rates are slowed and lifespan is extended. Here, we show that these perturbations increase the expression of cell-protective and metabolic genes and the abundance of mitochondrial DNA. This response is similar to the response triggered by inhibiting respiration in yeast and mammalian cells, termed the “retrograde response”. As in yeast, genes switched on in C. elegans mitochondrial mutants extend lifespan, suggesting an underlying evolutionary conservation of mechanism. Inhibition of fstr-1, a potential signaling gene that is up-regulated in clk-1 (ubiquinone-defective) mutants, and its close homolog fstr-2 prevents the expression of many retrograde-response genes and accelerates clk-1 behavioral and aging rates. Thus, clk-1 mutants live in “slow motion” because of a fstr-1/2–dependent pathway that responds to ubiquinone. Loss of fstr-1/2 does not suppress the phenotypes of all long-lived mitochondrial mutants. Thus, although different mitochondrial perturbations activate similar transcriptional and physiological responses, they do so in different ways

Primary Coenzyme Q Deficiency in Pdss2 Mutant Mice Causes Isolated Renal Disease

Coenzyme Q (CoQ) is an essential electron carrier in the respiratory chain whose deficiency has been implicated in a wide variety of human mitochondrial disease manifestations. Its multi-step biosynthesis involves production of polyisoprenoid diphosphate in a reaction that requires the enzymes be encoded by PDSS1 and PDSS2. Homozygous mutations in either of these genes, in humans, lead to severe neuromuscular disease, with nephrotic syndrome seen in PDSS2 deficiency. We now show that a presumed autoimmune kidney disease in mice with the missense Pdss2kd/kd genotype can be attributed to a mitochondrial CoQ biosynthetic defect. Levels of CoQ9 and CoQ10 in kidney homogenates from B6.Pdss2kd/kd mutants were significantly lower than those in B6 control mice. Disease manifestations originate specifically in glomerular podocytes, as renal disease is seen in Podocin/cre,Pdss2loxP/loxP knockout mice but not in conditional knockouts targeted to renal tubular epithelium, monocytes, or hepatocytes. Liver-conditional B6.Alb/cre,Pdss2loxP/loxP knockout mice have no overt disease despite demonstration that their livers have undetectable CoQ9 levels, impaired respiratory capacity, and significantly altered intermediary metabolism as evidenced by transcriptional profiling and amino acid quantitation. These data suggest that disease manifestations of CoQ deficiency relate to tissue-specific respiratory capacity thresholds, with glomerular podocytes displaying the greatest sensitivity to Pdss2 impairment

A regulated response to impaired respiration slows behavioral rates and increases lifespan in Caenorhabditis elegans.

When mitochondrial respiration or ubiquinone production is inhibited in Caenorhabditis elegans, behavioral rates are slowed and lifespan is extended. Here, we show that these perturbations increase the expression of cell-protective and metabolic genes and the abundance of mitochondrial DNA. This response is similar to the response triggered by inhibiting respiration in yeast and mammalian cells, termed the "retrograde response". As in yeast, genes switched on in C. elegans mitochondrial mutants extend lifespan, suggesting an underlying evolutionary conservation of mechanism. Inhibition of fstr-1, a potential signaling gene that is up-regulated in clk-1 (ubiquinone-defective) mutants, and its close homolog fstr-2 prevents the expression of many retrograde-response genes and accelerates clk-1 behavioral and aging rates. Thus, clk-1 mutants live in "slow motion" because of a fstr-1/2-dependent pathway that responds to ubiquinone. Loss of fstr-1/2 does not suppress the phenotypes of all long-lived mitochondrial mutants. Thus, although different mitochondrial perturbations activate similar transcriptional and physiological responses, they do so in different ways

Primary coenzyme Q deficiency in Pdss2 mutant mice causes isolated renal disease.

Coenzyme Q (CoQ) is an essential electron carrier in the respiratory chain whose deficiency has been implicated in a wide variety of human mitochondrial disease manifestations. Its multi-step biosynthesis involves production of polyisoprenoid diphosphate in a reaction that requires the enzymes be encoded by PDSS1 and PDSS2. Homozygous mutations in either of these genes, in humans, lead to severe neuromuscular disease, with nephrotic syndrome seen in PDSS2 deficiency. We now show that a presumed autoimmune kidney disease in mice with the missense Pdss2(kd/kd) genotype can be attributed to a mitochondrial CoQ biosynthetic defect. Levels of CoQ9 and CoQ10 in kidney homogenates from B6.Pdss2(kd/kd) mutants were significantly lower than those in B6 control mice. Disease manifestations originate specifically in glomerular podocytes, as renal disease is seen in Podocin/cre,Pdss2(loxP/loxP) knockout mice but not in conditional knockouts targeted to renal tubular epithelium, monocytes, or hepatocytes. Liver-conditional B6.Alb/cre,Pdss2(loxP/loxP) knockout mice have no overt disease despite demonstration that their livers have undetectable CoQ9 levels, impaired respiratory capacity, and significantly altered intermediary metabolism as evidenced by transcriptional profiling and amino acid quantitation. These data suggest that disease manifestations of CoQ deficiency relate to tissue-specific respiratory capacity thresholds, with glomerular podocytes displaying the greatest sensitivity to Pdss2 impairment

Plasma cholesterol levels in mice with conditional knockout and control genotypes

<p>All mice were at least 120 days old; data express mean +/− SEM; N is shownin parentheses. For B6.<i>Podocin/cre,Pdss2^loxP/loxP vs.</i> B6. <i>Pdss2^loxP/loxP</i>, t = 3.50 and p = 0.004; for B6.<i>Podocin/cre,Pdss2^loxP/loxP vs.</i> B6.<i>Alb/crePdss2^loxP/loxP</i>, t = 2.09 and p = 0.058; for B6.<i>Alb/cre,Pdss2^loxP/loxP vs.</i> B6. <i>Pdss2^loxP/loxP</i>, t = 3.34 and p = 0.006.</p

Glomerular Electron Micrographs From <i>Pdss2</i> Mutant and Control Mice.

<p>Electron micrographs from mutant and control mouse kidney glomeruli; original magnifications all 10,000x; scale bar = 2 microns. <i>A</i>, B6, 362 days old; arrows show podocyte foot processes. <i>B,</i> B6.<i>Pdss2^kd/kd</i>, 267 days old; arrows show regions of foot process effacement. <i>C</i>, B6.<i>Pdss2^loxP/loxP</i> mouse, 248 days old; arrows show foot processes. <i>D</i>, B6.<i>Podocin/cre,Pdss2^loxP/loxP</i> 290 days old; arrows show regions of foot process effacement.</p

<i>Pdss2</i> Mutants Have Altered Amino Acid Profiles in Liver.

<p><i>Pdss2</i> mutants have altered amino acid profiles in liver. Quantitative liver amino acid analysis detects significant differences in B6.<i>Pdss2^kd/kd</i> missense mutants compared with B6 controls (Panels A and B), as well as in B6.<i>Alb/cre,Pdss2^loxP/loxP</i> mutants compared with B6.<i>Pdss2^loxP/loxP</i> controls (Panels C and D). To better demonstrate differences in all amino acids, results for three amino acids in highest abundance are shown separately (Panels B and D) with a greater scale compared to that used for the remainder of the amino acids present in relatively lower abundance (Panels A and C). Values represent mean +/− SEM. Statistical analyses comparing mutants and controls were performed by Student's t-test, where * indicates p<0.05 and ** indicates p<0.01.</p