Reliance on Cox10 and oxidative metabolism for antigen-specific NK cell expansion.

Natural killer (NK) cell effector functions are dependent on metabolic regulation of cellular function; however, less is known about in vivo metabolic pathways required for NK cell antiviral function. Mice with an inducible NK-specific deletion of Cox10, which encodes a component of electron transport chain complex IV, were generated to investigate the role of oxidative phosphorylation in NK cells during murine cytomegalovirus (MCMV) infection. Ncr1-Cox10Δ/Δ mice had normal numbers of NK cells but impaired expansion of antigen-specific Ly49H+ NK cells and impaired NK cell memory formation. Proliferation in vitro and homeostatic expansion were intact, indicating a specific metabolic requirement for antigen-driven proliferation. Cox10-deficient NK cells upregulated glycolysis, associated with increased AMP-activated protein kinase (AMPK) and mammalian target of rapamycin (mTOR) activation, although this was insufficient to protect the host. These data demonstrate that oxidative metabolism is required for NK cell antiviral responses in vivo.

Impaired mitophagy links mitochondrial disease to epithelial stress in methylmalonyl-CoA mutase deficiency.

Deregulation of mitochondrial network in terminally differentiated cells contributes to a broad spectrum of disorders. Methylmalonic acidemia (MMA) is one of the most common inherited metabolic disorders, due to deficiency of the mitochondrial methylmalonyl-coenzyme A mutase (MMUT). How MMUT deficiency triggers cell damage remains unknown, preventing the development of disease-modifying therapies. Here we combine genetic and pharmacological approaches to demonstrate that MMUT deficiency induces metabolic and mitochondrial alterations that are exacerbated by anomalies in PINK1/Parkin-mediated mitophagy, causing the accumulation of dysfunctional mitochondria that trigger epithelial stress and ultimately cell damage. Using drug-disease network perturbation modelling, we predict targetable pathways, whose modulation repairs mitochondrial dysfunctions in patient-derived cells and alleviate phenotype changes in mmut-deficient zebrafish. These results suggest a link between primary MMUT deficiency, diseased mitochondria, mitophagy dysfunction and epithelial stress, and provide potential therapeutic perspectives for MMA.

Inhibiting PGGT1B Disrupts Function of RHOA, Resulting in T-cell Expression of Integrin α4ß7 and Development of Colitis in Mice.

BACKGROUND & AIMS: It is not clear how regulation of T-cell function is altered during development of inflammatory bowel diseases (IBD). We studied the mechanisms by which geranylgeranyltransferase-mediated prenylation controls T-cell localization to the intestine and chronic inflammation. METHODS: We generated mice with T-cell-specific disruption of the geranylgeranyltransferase type I, beta subunit gene (Pggt1b), called Pggt1bΔCD4 mice, or the ras homolog family member A gene (Rhoa), called RhoaΔCD4 mice. We also studied mice with knockout of CDC42 or RAC1 and wild-type mice (controls). Intestinal tissues were analyzed by histology, multiphoton and confocal microscopy, and real-time polymerase chain reaction. Activation of CDC42, RAC1, and RHOA were measured with G-LISA, cell fractionation, and immunoblots. T cells and lamina propria mononuclear cells from mice were analyzed by flow cytometry or transferred to Rag1-/- mice. Mice were given injections of antibodies against integrin alpha4beta7 or gavaged with the RORC antagonist GSK805. We obtained peripheral blood and intestinal tissue samples from patients with and without IBD and analyzed them by flow cytometry. RESULTS: Pggt1bΔCD4 mice developed spontaneous colitis, characterized by thickening of the intestinal wall, edema, fibrosis, accumulation of T cells in the colon, and increased expression of inflammatory cytokines. Compared with control CD4+ T cells, PGGT1B-deficient CD4+ T cells expressed significantly higher levels of integrin alpha4beta7, which regulates their localization to the intestine. Inflammation induced by transfer of PGGT1B-deficient CD4+ T cells to Rag1-/- mice was blocked by injection of an antibody against integrin alpha4beta7. Lamina propria of Pggt1bΔCD4 mice had increased numbers of CD4+ T cells that expressed RORC and higher levels of cytokines produced by T-helper 17 cells (granulocyte-macrophage colony-stimulating factor, interleukin [IL]17A, IL17F, IL22, and tumor necrosis factor [TNF]). The RORC inverse agonist GSK805, but not antibodies against IL17A or IL17F, prevented colitis in Pggt1bΔCD4 mice. PGGT1B-deficient CD4+ T cells had decreased activation of RHOA. RhoAΔCD4 mice had a similar phenotype to Pggt1bΔCD4 mice, including development of colitis, increased numbers of CD4+ T cells in colon, increased expression of integrin alpha4beta7 by CD4+ T cells, and increased levels of IL17A and other inflammatory cytokines in lamina propria. T cells isolated from intestinal tissues from patients with IBD had significantly lower levels of PGGT1B than tissues from individuals without IBD. CONCLUSION: Loss of PGGT1B from T cells in mice impairs RHOA function, increasing CD4+ T-cell expression of integrin alpha4beta7 and localization to colon, resulting in increased expression of inflammatory cytokines and colitis. T cells isolated from gut tissues from patients with IBD have lower levels of PGGT1B than tissues from patients without IBD.

Systemic or Forebrain Neuron-Specific Deficiency of Geranylgeranyltransferase-1 Impairs Synaptic Plasticity and Reduces Dendritic Spine Density.

Isoprenoids and prenylated proteins regulate a variety of cellular functions, including neurite growth and synaptic plasticity. Importantly, they are implicated in the pathogenesis of several diseases, including Alzheimer's disease (AD). Recently, we have shown that two protein prenyltransferases, farnesyltransferase (FT) and geranylgeranyltransferase-1 (GGT), have differential effects in a mouse model of AD. Haplodeficiency of either FT or GGT attenuates amyloid-ß deposition and neuroinflammation but only reduction in FT rescues cognitive function. The current study aimed to elucidate the potential mechanisms that may account for the lack of cognitive benefit in GGT-haplodeficient mice, despite attenuated neuropathology. The results showed that the magnitude of long-term potentiation (LTP) was markedly suppressed in hippocampal slices from GGT-haplodeficient mice. Consistent with the synaptic dysfunction, there was a significant decrease in cortical spine density and cognitive function in GGT-haplodeficient mice. To further study the neuron-specific effects of GGT deficiency, we generated conditional forebrain neuron-specific GGT-knockout (GGTf/fCre+) mice using a Cre/LoxP system under the CAMKIIα promoter. We found that both the magnitude of hippocampal LTP and the dendritic spine density of cortical neurons were decreased in GGTf/fCre+ mice compared with GGTf/fCre- mice. Immunoblot analyses of cerebral lysate showed a significant reduction in cell membrane-associated (geranylgeranylated) Rac1 and RhoA but not (farnesylated) H-Ras, in GGTf/fCre+ mice, suggesting that insufficient geranylgeranylation of the Rho family of small GTPases may underlie the detrimental effects of GGT deficiency. These findings reinforce the critical role of GGT in maintaining spine structure and synaptic/cognitive function in development and in the mature brain.

A Personalized Model of COQ2 Nephropathy Rescued by the Wild-Type COQ2 Allele or Dietary Coenzyme Q10 Supplementation.

Clinical studies have identified patients with nephrotic syndrome caused by mutations in genes involved in the biosynthesis of coenzyme Q10 (CoQ10), a lipid component of the mitochondrial electron transport chain and an important antioxidant. However, the cellular mechanisms through which these mutations induce podocyte injury remain obscure. Here, we exploited the striking similarities between Drosophila nephrocytes and human podocytes to develop a Drosophila model of these renal diseases, and performed a systematic in vivo analysis assessing the role of CoQ10 pathway genes in renal function. Nephrocyte-specific silencing of Coq2, Coq6, and Coq8, which are genes involved in the CoQ10 pathway that have been associated with genetic nephrotic syndrome in humans, induced dramatic adverse changes in these cells. In particular, silencing of Coq2 led to an abnormal localization of slit diaphragms, collapse of lacunar channels, and more dysmorphic mitochondria. In addition, Coq2-deficient nephrocytes showed elevated levels of autophagy and mitophagy, increased levels of reactive oxygen species, and increased sensitivity to oxidative stress. Dietary supplementation with CoQ10 at least partially rescued these defects. Furthermore, expressing the wild-type human COQ2 gene specifically in nephrocytes rescued the defective protein uptake, but expressing the mutant allele derived from a patient with COQ2 nephropathy did not. We conclude that transgenic Drosophila lines carrying mutations in the CoQ10 pathway genes are clinically relevant models with which to explore the pathogenesis of podocyte injury and could serve as a new platform to test novel therapeutic approaches.

Coenzyme Q deficiency causes impairment of the sulfide oxidation pathway.

Coenzyme Q (CoQ) is an electron acceptor for sulfide-quinone reductase (SQR), the first enzyme of the hydrogen sulfide oxidation pathway. Here, we show that lack of CoQ in human skin fibroblasts causes impairment of hydrogen sulfide oxidation, proportional to the residual levels of CoQ. Biochemical and molecular abnormalities are rescued by CoQ supplementation in vitro and recapitulated by pharmacological inhibition of CoQ biosynthesis in skin fibroblasts and ADCK3 depletion in HeLa cells. Kidneys of Pdss2kd/kd mice, which only have ~15% residual CoQ concentrations and are clinically affected, showed (i) reduced protein levels of SQR and downstream enzymes, (ii) accumulation of hydrogen sulfides, and (iii) glutathione depletion. These abnormalities were not present in brain, which maintains ~30% residual CoQ and is clinically unaffected. In Pdss2kd/kd mice, we also observed low levels of plasma and urine thiosulfate and increased blood C4-C6 acylcarnitines. We propose that impairment of the sulfide oxidation pathway induced by decreased levels of CoQ causes accumulation of sulfides and consequent inhibition of short-chain acyl-CoA dehydrogenase and glutathione depletion, which contributes to increased oxidative stress and kidney failure.

Primary coenzyme Q10 deficiency presenting as fatal neonatal multiorgan failure.

Coenzyme Q10 deficiency is a clinically and genetically heterogeneous disorder, with manifestations that may range from fatal neonatal multisystem failure, to adult-onset encephalopathy. We report a patient who presented at birth with severe lactic acidosis, proteinuria, dicarboxylic aciduria, and hepatic insufficiency. She also had dilation of left ventricle on echocardiography. Her neurological condition rapidly worsened and despite aggressive care she died at 23 h of life. Muscle histology displayed lipid accumulation. Electron microscopy showed markedly swollen mitochondria with fragmented cristae. Respiratory-chain enzymatic assays showed a reduction of combined activities of complex I+III and II+III with normal activities of isolated complexes. The defect was confirmed in fibroblasts, where it could be rescued by supplementing the culture medium with 10 µM coenzyme Q10. Coenzyme Q10 levels were reduced (28% of controls) in these cells. We performed exome sequencing and focused the analysis on genes involved in coenzyme Q10 biosynthesis. The patient harbored a homozygous c.545T>G, p.(Met182Arg) alteration in COQ2, which was validated by functional complementation in yeast. In this case the biochemical and morphological features were essential to direct the genetic diagnosis. The parents had another pregnancy after the biochemical diagnosis was established, but before the identification of the genetic defect. Because of the potentially high recurrence risk, and given the importance of early CoQ10 supplementation, we decided to treat with CoQ10 the newborn child pending the results of the biochemical assays. Clinicians should consider a similar management in siblings of patients with CoQ10 deficiency without a genetic diagnosis.

A novel mutation in COQ2 leading to fatal infantile multisystem disease.

Coenzyme Q10 (ubiquinone or CoQ10) serves as a redox carrier in the mitochondrial oxidative phosphorylation system. The reduced form of this lipid-soluble antioxidant (ubiquinol) is involved in other metabolic processes as well, such as preventing reactive oxygen species (ROS) induced damage from the mitochondrial membrane. Primary coenzyme Q10 deficiency is a rare, autosomal recessive disorder, often presenting with neurological and/or muscle involvement. Until now, five patients from four families have been described with primary coenzyme Q10 deficiency due to mutations in COQ2 encoding para-hydroxybenzoate polyprenyl transferase. Interestingly, four of these patients showed a distinctive renal involvement (focal segmental glomerular sclerosis, crescentic glomerulonephritis, nephrotic syndrome), which is only very rarely seen in correlation with mitochondrial disorders. The fifth patient deceases due to infantile multi organ failure, also with renal involvement. Here we report a novel homozygous mutation in COQ2 (c.905C>T, p.Ala302Val) in a dizygotic twin from consanguineous Turkish parents. The children were born prematurely and died at the age of five and six months, respectively, after an undulating disease course involving apneas, seizures, feeding problems and generalized edema, alternating with relative stable periods without the need of artificial ventilation. There was no evidence for renal involvement. We would like to raise awareness for this potentially treatable disorder which could be under diagnosed in patients with fatal neonatal or infantile multi-organ disease.

Tissue-specific oxidative stress and loss of mitochondria in CoQ-deficient Pdss2 mutant mice.

Primary human CoQ(10) deficiencies are clinically heterogeneous diseases caused by mutations in PDSS2 and other genes required for CoQ(10) biosynthesis. Our in vitro studies of PDSS2 mutant fibroblasts, with <20% CoQ(10) of control cells, revealed reduced activity of CoQ(10)-dependent complex II+III and ATP synthesis, without amplification of reactive oxygen species (ROS), markers of oxidative damage, or antioxidant defenses. In contrast, COQ2 and ADCK3 mutant fibroblasts, with 30-50% CoQ(10) of controls, showed milder bioenergetic defects but significantly increased ROS and oxidation of lipids and proteins. We hypothesized that absence of oxidative stress markers and cell death in PDSS2 mutant fibroblasts were due to the extreme severity of CoQ(10) deficiency. Here, we have investigated in vivo effects of Pdss2 deficiency in affected and unaffected organs of CBA/Pdss2(kd/kd) mice at presymptomatic, phenotypic-onset, and end-stages of the disease. Although Pdss2 mutant mice manifest widespread CoQ(9) deficiency and mitochondrial respiratory chain abnormalities, only affected organs show increased ROS production, oxidative stress, mitochondrial DNA depletion, and reduced citrate synthase activity, an index of mitochondrial mass. Our data indicate that kidney-specific loss of mitochondria triggered by oxidative stress may be the cause of renal failure in Pdss2(kd/kd) mice.

RETRACTED: Bezafibrate improves mitochondrial function in the CNS of a mouse model of mitochondrial encephalopathy.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy). This retraction was suggested by the University of Cologne Investigation committee and seconded by the authors who the journal was able to contact (Wenz, T., Dillon, L., Diaz, F., Hida, A., and Moraes, C.T.). Following an investigation of the last author, Dr. Tina Wenz, by the University of Cologne, Germany, the university determined that data presented in this article have been inappropriately manipulated https://www.portal.uni-koeln.de/9015.html?&tx_news_pi1%5Bnews%5D=4335&tx_news_pi1%5Bcontroller%5D=News&tx_news_pi1%5Baction%5D=detail&cHash=1deb8399d7f796d65ca9f6ae4764a1ce. Specifically, western blot images in Figure 5F (tubulin in cortex), 2F (COXI in hippocampus) and 3B (Sod2 in hippocampus) were re-used from an earlier article published elsewhere [Increased muscle PGC-1alpha expression protects from sarcopenia and metabolic disease during aging" Wenz T, Rossi SG, Rotundo RL, Spiegelman BM, and Moraes CT. Proc Natl Acad Sci U S A. 2009;106:20405-10, doi: 10.1073/pnas.0911570106] representing different experimental findings. Therefore, whether or not the main conclusions are still valid, the authors request retraction of this publication because the scientific integrity of the study was compromised. The authors sincerely apologize to the scientific community.

A defect in the mitochondrial complex III, but not complex IV, triggers early ROS-dependent damage in defined brain regions.

We have created two neuron-specific mouse models of mitochondrial electron transport chain deficiencies involving defects in complex III (CIII) or complex IV (CIV). These conditional knockouts (cKOs) were created by ablation of the genes coding for the Rieske iron-sulfur protein (RISP) and COX10, respectively. RISP is one of the catalytic subunits of CIII and COX10 is an assembly factor indispensable for the maturation of Cox1, one of the catalytic subunits of CIV. Although the rates of gene deletion, protein loss and complex dysfunction were similar, the RISP cKO survived 3.5 months of age, whereas the COX10 cKO survived for 10-12 months. The RISP cKO had a sudden death, with minimal behavioral changes. In contrast, the COX10 cKO showed a distinctive behavioral phenotype with onset at 4 months of age followed by a slower but progressive neurodegeneration. Curiously, the piriform and somatosensory cortices were more vulnerable to the CIII defect whereas cingulate cortex and to a less extent piriform cortex were affected preferentially by the CIV defect. In addition, the CIII model showed severe and early reactive oxygen species damage, a feature not observed until very late in the pathology of the CIV model. These findings illustrate how specific respiratory chain defects have distinct molecular mechanisms, leading to distinct pathologies, akin to the clinical heterogeneity observed in patients with mitochondrial diseases.

Glycolytic oligodendrocytes maintain myelin and long-term axonal integrity.

Oligodendrocytes, the myelin-forming glial cells of the central nervous system, maintain long-term axonal integrity. However, the underlying support mechanisms are not understood. Here we identify a metabolic component of axon-glia interactions by generating conditional Cox10 (protoheme IX farnesyltransferase) mutant mice, in which oligodendrocytes and Schwann cells fail to assemble stable mitochondrial cytochrome c oxidase (COX, also known as mitochondrial complex IV). In the peripheral nervous system, Cox10 conditional mutants exhibit severe neuropathy with dysmyelination, abnormal Remak bundles, muscle atrophy and paralysis. Notably, perturbing mitochondrial respiration did not cause glial cell death. In the adult central nervous system, we found no signs of demyelination, axonal degeneration or secondary inflammation. Unlike cultured oligodendrocytes, which are sensitive to COX inhibitors, post-myelination oligodendrocytes survive well in the absence of COX activity. More importantly, by in vivo magnetic resonance spectroscopy, brain lactate concentrations in mutants were increased compared with controls, but were detectable only in mice exposed to volatile anaesthetics. This indicates that aerobic glycolysis products derived from oligodendrocytes are rapidly metabolized within white matter tracts. Because myelinated axons can use lactate when energy-deprived, our findings suggest a model in which axon-glia metabolic coupling serves a physiological function.

Severe hepatocellular disease in mice lacking one or both CaaX prenyltransferases.

Protein farnesyltransferase (FTase) and protein geranylgeranyltransferase-I (GGTase-I) add 15- or 20-carbon lipids, respectively, to proteins that terminate with a CaaX motif. These posttranslational modifications of proteins with lipids promote protein interactions with membrane surfaces in cells, but the in vivo importance of the CaaX prenyltransferases and the protein lipidation reactions they catalyze remain incompletely defined. One study concluded that a deficiency of FTase was inconsequential in adult mice and led to little or no tissue pathology. To assess the physiologic importance of the CaaX prenyltransferases, we used conditional knockout alleles and an albumin-Cre transgene to produce mice lacking FTase, GGTase-I, or both enzymes in hepatocytes. The hepatocyte-specific FTase knockout mice survived but exhibited hepatocellular disease and elevated transaminases. Mice lacking GGTase-I not only had elevated transaminases but also had dilated bile cannaliculi, hyperbilirubinemia, hepatosplenomegaly, and reduced survival. Of note, GGTase-I-deficient hepatocytes had a rounded shape and markedly reduced numbers of actin stress fibers. Hepatocyte-specific FTase/GGTase-I double-knockout mice closely resembled mice lacking GGTase-I alone, but the disease was slightly more severe. Our studies refute the notion that FTase is dispensable and demonstrate that GGTase-I is crucial for the vitality of hepatocytes.

Nogo-B receptor is necessary for cellular dolichol biosynthesis and protein N-glycosylation.

Dolichol monophosphate (Dol-P) functions as an obligate glycosyl carrier lipid in protein glycosylation reactions. Dol-P is synthesized by the successive condensation of isopentenyl diphosphate (IPP), with farnesyl diphosphate catalysed by a cis-isoprenyltransferase (cis-IPTase) activity. Despite the recognition of cis-IPTase activity 40 years ago and the molecular cloning of the human cDNA encoding the mammalian enzyme, the molecular machinery responsible for regulating this activity remains incompletely understood. Here, we identify Nogo-B receptor (NgBR) as an essential component of the Dol-P biosynthetic machinery. Loss of NgBR results in a robust deficit in cis-IPTase activity and Dol-P production, leading to diminished levels of dolichol-linked oligosaccharides and a broad reduction in protein N-glycosylation. NgBR interacts with the previously identified cis-IPTase hCIT, enhances hCIT protein stability, and promotes Dol-P production. Identification of NgBR as a component of the cis-IPTase machinery yields insights into the regulation of dolichol biosynthesis.

Respiratory-chain deficiency presenting as diffuse mesangial sclerosis with NPHS3 mutation.

Renal manifestations of mitochondrial cytopathies have been described, but nephrotic syndrome with respiratory-chain disorders have been described extremely rarely. We report a 9-month-old boy with a mitochondrial cytopathy preceded by a 2-month history of steroid-resistant nephrotic syndrome. Percutaneous renal biopsy revealed diffuse mesangial sclerosis, and mutational analysis was compatible with PLCE1 mutation. However, electron microscopic findings of renal tissue, sensorineural hearing loss, and other ocular and neurologic findings led us to suspect mitochondrial cytopathy. Muscle tissue analysis showed a deficiency of the respiratory chain complex IV. The clinical presentation of our patient is not typical for primary cytochrome oxidase (COX) deficiency but showed similarities with patients carrying AR mutations in COX10. This was the first case in the literature with both PLCE1 mutation and COX deficiency. We could not identify pathogenic mutations in the COX10 gene, suggesting that PLCE1 deficiency could be the cause of the secondary deficiency of COX. Another, more likely, possibility is that the mitochondriopathy phenotype is caused by another mutation homozygous by descent in a yet unidentified recessive gene.

The perplexing case of the geranylgeranyl transferase-deficient mouse.

Proteins that end with a CAAX sequence are targeted to cellular membranes by a series of posttranslational modifications that include prenylation, proteolysis, and carboxyl methylation. Two prenyltransferases modify CAAX proteins: farnesyltransferase and geranylgeranyltransferase type I (GGTase-I). Rho family GTPases that control the actin cytoskeleton and are therefore critical to inflammatory cell function are substrates for GGTase-I. In this issue of the JCI, Khan et al. examined mice in which GGTase-I was conditionally deleted in macrophages. Rather than obtunded cells, the authors found activated Rho proteins in fully functional macrophages that hypersecreted inflammatory cytokines and induced an erosive, inflammatory arthritis. This surprising result calls into question the role of protein geranylgeranylation in inflammatory cell signaling.

Geranylgeranyltransferase type I (GGTase-I) deficiency hyperactivates macrophages and induces erosive arthritis in mice.

RHO family proteins are important for the function of inflammatory cells. They are modified with a 20-carbon geranylgeranyl lipid in a process catalyzed by protein geranylgeranyltransferase type I (GGTase-I). Geranylgeranylation is viewed as essential for the membrane targeting and activity of RHO proteins. Consequently, inhibiting GGTase-I to interfere with RHO protein activity has been proposed as a strategy to treat inflammatory disorders. However, here we show that mice lacking GGTase-I in macrophages develop severe joint inflammation resembling erosive rheumatoid arthritis. The disease was initiated by the GGTase-I-deficient macrophages and was transplantable and reversible in bone marrow transplantation experiments. The cells accumulated high levels of active GTP-bound RAC1, CDC42, and RHOA, and RAC1 remained associated with the plasma membrane. Moreover, GGTase-I deficiency activated p38 and NF-κB and increased the production of proinflammatory cytokines. The results challenge the view that geranylgeranylation is essential for the activity and localization of RHO family proteins and suggest that reduced geranylgeranylation in macrophages can initiate erosive arthritis.

Endurance exercise is protective for mice with mitochondrial myopathy.

Defects in the mitochondrial ATP-generating system are one of the most commonly inherited neurological disorders, but they remain without treatment. We have recently shown that modulation of the peroxisome proliferator-activated receptor-gamma coactivator-1alpha (PGC-1alpha) level in skeletal muscle of a mitochondrial myopathy mouse model offers a therapeutic approach. Here we analyzed if endurance exercise, which is known to be associated with an increased PGC-1alpha level in muscle, offers the same beneficial effect. We subjected male and female mice that develop a severe mitochondrial myopathy due to a cytochrome-c oxidase deficiency at 3 mo of age to endurance exercise training and monitored phenotypical and metabolic changes. Sedentary myopathy and wild-type mice were used as controls. Exercise increased PGC-1alpha in muscle, resulting in increased mitochondrial biogenesis, and successfully stimulated residual respiratory capacity in muscle tissue. As a consequence, ATP levels were increased in exercised mice compared with sedentary myopathy animals, which resulted in a delayed onset of the myopathy and a prolonged lifespan of the exercised mice. As an added benefit, endurance exercise induced antioxidant enzymes. The overall protective effect of endurance exercise delayed the onset of the mitochondrial myopathy and increased life expectancy in the mouse model. Thus stimulating residual oxidative phosphorylation function in the affected muscle by inducing mitochondrial biogenesis through endurance exercise might offer a valuable therapeutic intervention for mitochondrial myopathy patients.

Expression of the alternative oxidase complements cytochrome c oxidase deficiency in human cells.

Cytochrome c oxidase (COX) deficiency is associated with a wide spectrum of clinical conditions, ranging from early onset devastating encephalomyopathy and cardiomyopathy, to neurological diseases in adulthood and in the elderly. No method of compensating successfully for COX deficiency has been reported so far. In vitro, COX-deficient human cells require additional glucose, pyruvate and uridine for normal growth and are specifically sensitive to oxidative stress. Here, we have tested whether the expression of a mitochondrially targeted, cyanide-resistant, alternative oxidase (AOX) from Ciona intestinalis could alleviate the metabolic abnormalities of COX-deficient human cells either from a patient harbouring a COX15 pathological mutation or rendered deficient by silencing the COX10 gene using shRNA. We demonstrate that the expression of the AOX, well-tolerated by the cells, compensates for both the growth defect and the pronounced oxidant-sensitivity of COX-deficient human cells.

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.