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Myocardial infarction (MI) is one of the leading causes of high mortality worldwide. Long non-coding RNA myocardial infarction associated transcript (MIAT) and mitochondrial coupling factor 6 (CF6) aggravate MI. This study aimed to elucidate whether miR-203 interacted with MIAT and CF6 in MI. Results revealed that MIAT and CF6 expressions were upregulated and that miR-203 was downregulated in mouse myocardial tissues after MI, as well as in hypoxic mouse cardiomyocytes. The overexpression of MIAT in mouse cardiomyocytes raised CF6 expression, whereas the knockdown of MIAT had the opposite effect. Mechanistically, the luciferase reporter and RNA pull-down assays corroborated the binding between miR-203 and CF6 3'UTR and between miR-203 and MIAT. The simultaneous overexpression of miR-203 and MIAT restored the reduction of CF6 caused by miR-203 overexpression alone, and the overexpression of miR-203 diminished the percentage of infarct area and the apoptosis of cardiomyocytes in vivo. Our findings corroborate that overexpressing miR-203 alleviates MI via interacting with MIAT and CF6.

Diet-induced metabolic acidosis is associated with the impairment of bone metabolism and an increased risk of a number of chronic noncommunicable diseases, such as type 2 diabetes mellitus and hypertension. The serum bicarbonate level is an independent predictor of chronic kidney disease progression. We investigated whether proton accelerates aging by analyzing both coupling factor 6-overexpressing transgenic (TG) and high salt-fed mice which display sustained intracellular acidosis, due to enhanced proton import through ecto-F 1 F o complex and/or reduced proton export through Na + -K + ATPase inhibition. Both types of mice displayed shortened lifespan and early senescence-associated phenotypes such as signs of hair greying and alopecia, weight loss, and/or reduced organ mass. In chronic intracellular acidosis mice, autophagy was impaired by regression of Atg7, an increase in nuclear acetylated LC3 II, and acetylation of Atg7. The increase in histone 3 trimethylation at lysine 4 (H3K4me3) and H4K20me3 and the decrease in H3K9me3 and H3K27me3 were observed in the heart and kidney obtained from both TG and high salt-fed mice. The decrease in lamin A/C, emerin, and heterochromatin protein 1α without changes in barrier-to-autointegration factor and high-mobility group box 1 was confirmed in TG and high salt-fed mice. Suppression of nuclear histone deacetylase 3-emerin system is attributable to epigenetic regression of Atg7 and H4K5 acetylation. These findings will shed light on novel aging and impaired autophagy mechanism, and provide implications in a target for antiaging therapy., (© 2018 Wiley Periodicals, Inc.)

Diet-induced metabolic acidosis is associated with the impairment of bone metabolism and an increased risk of a number of chronic noncommunicable diseases, such as type 2 diabetes mellitus and hypertension. Low serum bicarbonate is associated with high mortality in healthy older individuals. Recently, we demonstrated that both coupling factor 6 (CF6)-overexpressing transgenic (TG) and high salt-fed mice which had sustained intracellular acidosis, due to enhanced proton import through ecto-F 1 F o complex and/or reduced proton export through Na + -K + ATPase inhibition, displayed shortened lifespan and early senescence-associated phenotypes such as signs of hair greying and alopecia, weight loss, and/or reduced organ mass. In this study, we searched causative genes of proton-induced aging in CF6-overexpressing TG and high salt-fed mice. We discovered NM_026333 as a novel anti-aging gene which was downregulated in the heart and kidney in both types of mice. NM_026333 protein consists of 269 amino acids with transmembrane region (90-193aa). Induction of NM_026333 or recombinant protein rescued TG cells and CF6-treated human cells from aging hallmarks of impaired autophagy, genomic instability, and epigenetic alteration. NM_026333 protein directly bound plasma membrane Na + -Ca 2+ exchanger 1 (NCX1) to suppress its reverse mode, and cancelled proton-induced epigenetic regression of Atg7 that was caused by H3K4 and H4K20 tri-methylation via suppression of demethylase and H4K5 acetylation via suppression of nuclear HDAC3-HDAC4-emerin system. NM_026333 also attenuated proton-induced impaired formation of autolysosome, an increase in nuclear acetylated LC3 II, and acetylation of Atg7. These effects reappeared by NCX1 inhibitor. Furthermore, NCX1 inhibitor extended lifespan compared with vehicle-treatment in TG mice. This study will shed light on novel aging mechanism and provide implications in a target for anti-aging therapy., (Copyright © 2018 Elsevier Ltd. All rights reserved.)

Coupling factor 6 (CF6) forces a counter-clockwise rotation of plasma membrane F 1 F o complex, resulting in proton import and accelerated aging. Inhibitory factor peptide 1 (IF1) suppresses a unidirectional counter-clockwise rotation of F 1 F o complex without affecting ATP synthesis. We tested the hypothesis that IF1 may attenuate CF6-induced aging signaling in CF6-overexpressing transgenic (TG) cells. In IF1-GFP overexpressing wild type (WT) cells, the diffuse peripheral staining of tubular mitochondria was observed with a dense widely distributed network around the nucleus. In TG cells, however, the only peri-nuclear network of fragmented mitochondria was observed at 24 h, but it was developed to a widely distributed mitochondrial network of tubular mitochondria at 72 h. TG cells displayed aging hallmarks of telomere attrition, epigenetic alterations, defective proteostasis, and genomic instability with a decrease in emerin and lamin and loss of heterochromatin. IF1 induction rescued TG cells from telomere attrition, expression of genomic instability with the increase in emerin and lamin, and that of epigenetic alterations with recovery of heterochromatin. In defective proteostasis, IF1 induction restored a potent peri-nuclear staining of autolysosomes compared with the baseline weak staining. The decrease in Atg7 was restored, whereas the increase in P62 was abolished. We conclude that genetic disruption of proton signals by IF1 induction suppressed CF6-induced expression of aging hallmarks such as telomere attrition, epigenetic alterations, defective proteostasis, and genomic instability. Given the widespread biological actions of CF6, the physiological and pathological actions of IF1 may be complex., (© 2018 Wiley Periodicals, Inc.)

The incidence and development of colorectal cancer (CRC) is a process with multiple gene interactions. We have previously demonstrated that ATP synthase-coupling factor 6, mitochondrial (ATP5J) is associated with CRC migration and 5-fluorouracil resistance; nevertheless, the exact molecular mechanism remains unclear. The following study uses microarray and bioinformatics methods to identify candidate genes and long non-coding RNAs (lncRNAs) in CRC cells (two pairs) with upregulated and downregulated ATP5J. Briefly, a total of 2,190 differentially expressed mRNAs (DEmRNAs) were sorted. Reverse transcription-quantitative polymerase chain reaction (RT-qPCR) was performed for 4 DEmRNAs to validate the results of microarray analysis. Functional annotation and pathway enrichment were analyzed for DEmRNAs using the Database for Annotation, Visualization and Integrated Discovery. Significantly enriched pathways included the regulation of gene expression and cell growth. The protein‑protein interaction network was constructed, and AKT serine/threonine kinase 2 (AKT2) was considered as one of the hub genes. For further analysis, 51 DEmRNAs and 30 DElncRNAs were selected that were positively or negatively associated with the expression of ATP5J in the two cell pairs. X-inactive specific transcript (XIST), premature ovarian failure 1B (POF1B) and calmin (CLMN) were identified in the DEmRNA-DElncRNA co-expression network. The expression of AKT2 and XIST in CRC cells was confirmed by RT-qPCR. To sum up, the candidate genes and lncRNAs, as well as potential signaling pathways, which were identified using integrated bioinformatics analysis, could improve the understanding of molecular events involved in the function of ATP5J in CRC.

To investigate the effect of excessive fluoride on the mitochondrial function of cardiomyocytes, 20 healthy male mice were randomly divided into 2 groups of 10, as follows: control group (animals were provided with distilled water) and fluoride group (animals were provided with 150 mg/L F - drinking water). Ultrastructure and pathological morphological changes of myocardial tissue were observed under the transmission electron and light microscopes, respectively. The content of hydrolysis ATP enzyme was observed by ATP enzyme staining. The expression levels of ATP5J and ATP5H were measured by Western blot and quantitative real-time PCR. The morphology and ultrastructure of cardiomyocytes mitochondrial were seriously damaged by fluoride, including the following: concentration of cardiomyocytes and inflammatory infiltration, vague myofilaments, and mitochondrial ridge. The damage of mitochondrial structure was accompanied by the significant decrease in the content of ATP enzyme for ATP hydrolysis in the fluoride group. ATP5J and ATP5H expressions were significantly increased in the fluoride group. Thus, fluoride induced the mitochondrial dysfunction in cardiomyocytes by damaging the structure of mitochondrial and interfering with the synthesis of ATP. The proactive ATP5J and ATP5H expression levels were a good response to the mitochondrial dysfunction in cardiomyocytes.

The present study aimed to elucidate the role of marine collagen peptides (MCPs) in protection of carotid artery vascular endothelial cells (CAVECs) in type 2 diabetes mellitus (T2DM), and the mechanism underlying this process. In an in vivo experiment, diabetic Wistar rats were divided randomly into four groups (n=10/group): Diabetes control, and three diabetes groups administered low, medium and high doses of MCPs (2.25, 4.5 and 9.0 g/kg body weight/day, respectively). Another 10 healthy rats served as the control. In an in vitro experiment, human umbilical‑vein endothelial cells (HUVECs) were incubated in normal and high concentrations of glucose with or without MCPs (3.0, 15.0 and 30.0 mg/ml, respectively) for 24, 48 or 72 h. Blood vessel/endothelial construction, inflammatory exudation and associated molecular biomarkers in CAVECs were detected and analyzed. The results of the present study demonstrated that in rats, MCP treatment for 4 weeks significantly lowered blood glucose and attenuated endothelial thinning and inflammatory exudation in carotid‑artery vascular endothelial cells. In vitro, the high‑glucose intervention significantly increased cell apoptosis in HUVECs, and medium and high doses of MCPs (4.5 and 9.0 g/kg body weight/day, respectively) partially ameliorated this high glucose‑mediated apoptosis and decreased levels of apoptosis biomarkers. In conclusion, a moderate oral MCP dose (≥4.5 g/kg body weight/day) may be a novel therapeutic tool to protect against early cardiovascular complications associated with T2DM by inhibiting apoptosis and reducing the expression of coupling factor 6 and microparticles.

Familial apparently balanced translocations (ABTs) segregating with discordant phenotypes are extremely challenging for interpretation and counseling due to the scarcity of publications and lack of routine techniques for quick investigation. Recently, next generation sequencing has emerged as an efficacious methodology for precise detection of translocation breakpoints. However, studies so far have mainly focused on de novo translocations. The present study focuses specifically on familial cases in order to shed some light to this diagnostic dilemma. Whole-genome mate-pair sequencing (WG-MPS) was applied to map the breakpoints in nine two-way ABT carriers from four families. Translocation breakpoints and patient-specific structural variants were validated by Sanger sequencing and quantitative Real Time PCR, respectively. Identical sequencing patterns and breakpoints were identified in affected and non-affected members carrying the same translocations. PTCD1, ATP5J2-PTCD1, CADPS2, and STPG1 were disrupted by the translocations in three families, rendering them initially as possible disease candidate genes. However, subsequent mutation screening and structural variant analysis did not reveal any pathogenic mutations or unique variants in the affected individuals that could explain the phenotypic differences between carriers of the same translocations. In conclusion, we suggest that NGS-based methods, such as WG-MPS, can be successfully used for detailed mapping of translocation breakpoints, which can also be used in routine clinical investigation of ABT cases. Unlike de novo translocations, no associations were determined here between familial two-way ABTs and the phenotype of the affected members, in which the presence of cryptic imbalances and complex chromosomal rearrangements has been excluded. Future whole-exome or whole-genome sequencing will potentially reveal unidentified mutations in the patients underlying the discordant phenotypes within each family. In addition, larger studies are needed to determine the exact percentage for phenotypic risk in families with ABTs., Competing Interests: The authors have declared that no competing interests exist.

Background: Pulmonary arterial hypertension (PAH) is a progressive and life-threatening disease associated with high morbidity and mortality rates. However, the exact regulatory mechanism of PAH is unknown. Although coupling factor 6 (CF6) is known to function as a repressor, its role in PAH has not been explored. Here, we investigated the involvement of endogenous CF6 in the development of PAH., Methods: PAH was induced with monocrotaline (MCT), as demonstrated by significant increases in pulmonary artery pressure and vessel wall thickness. The adeno-associated virus (AAV) carrying CF6 short hairpin RNA (shRNA) or control vector (2×10(10) gp) was intratracheally transfected into the lungs of rats 2 weeks before or after MCT injection., Results: A 2-6-fold increase in CF6 was observed in the lungs and circulation of the MCT-injected rats as confirmed by qRT-PCR and ELISA. Immunohistochemistry analysis revealed a small quantity of CF6 localized to endothelial cells (ECs) under physiological conditions spread to surrounding tissues in a paracrine manner in PAH lungs. Notably, CF6 shRNA effectively inhibited CF6 expression, abolished lung macrophage infiltration, reversed endothelial dysfunction and vascular remodeling, and ameliorated the severity of pulmonary hypertension and right ventricular dysfunction at 4 weeks both as a pretreatment and rescue intervention. In addition, the circulating and lung levels of 6-keto-PGF1a, a stable metabolite of prostacyclin, were reversed by CF6 inhibition, suggesting that the effect of CF6 inhibition may partly be mediated through prostacyclin., Conclusions: CF6 contributes to the pathogenesis of PAH, probably in association with downregulation of prostacyclin. The blockage of CF6 might be applied as a novel therapeutic approach for PAH and PA remodeling.

Coupling factor 6 (CF6) forces a counter-clockwise rotation of plasma membrane F1 Fo complex unlike a proton-mediated clockwise rotation in the mitochondria, resulting in ATP hydrolysis, proton import, and apoptosis. Inhibitory peptide 1 (IF1) inhibits a unidirectional counter-clockwise rotation of F1 Fo complex without affecting ATP synthesis by a clockwise rotation. We tested the hypothesis that IF1 may antagonize the biological action of CF6 in human embryonic kidney 293 cells. We generated mature and immature IF1 expression vectors and those labeled with GFP at the C-terminus. In the immature IF1-GFP overexpressing cells, the mitochondrial network of IF1-GFP was newly found at the plasma membrane after peripheral translocation, whereas in mature IF1-GFP transfected cells, a less punctuate rather homogenous pattern was found in the cytoplasm. IF1 protein was detected in the exosome fraction of culture media, and it was enhanced by mature or immature IF1 transfection. Extracellular ATP hydrolysis was enhanced by CF6, whereas immature or mature IF1 transfection suppressed ATP hydrolysis in response to CF6. Intracellular pH was decreased by CF6 but was unchanged after immature IF1 transfection. CF6-induced increase in apoptotic cells was blocked by immature or mature IF1, being accompanied by protein kinase B (PKB) phosphorylation. IF1 antagonizes the pro-apoptotic action of CF6 by relief of intracellular acidification and resultant phosphorylation of PKB. Given the widespread biological actions of CF6, the physiological and pathological functions of IF1 may be expected to be complex. J. Cell. Biochem. 117: 1680-1687, 2016. © 2015 Wiley Periodicals, Inc., (© 2015 Wiley Periodicals, Inc.)

Glioblastoma (GBM) is the most common primary malignant brain tumor. Microvascular proliferation is one of the characteristic pathologic features of GBM. Mitochondrial dysfunction plays an important role in the pathogenesis of GBM. In this study, microvascular proliferation from GBM and normal brain blood vessels were laser microdissected and total RNA was isolated from these microvasculatures. The difference of mRNA expression profiles among GBM microvasculature, normal brain blood vessels and GBM tumor cells was evaluated by mitochondria and metabolism PCR gene arrays. It was found that the mRNA levels of ATP5A1 and ATP5B in GBM tumor cells as well as microvascular proliferation were significantly higher compared with normal brain blood vessels. Immunohistochemical stains with anti-ATP5A1 antibody or anti-ATP5B antibody were performed on tissue microarray, which demonstrated strongly positive expression of ATP5A1 and ATP5B in GBM tumor cells and GBM microvascular proliferation while normal blood vessels were negative. By analyzing The Cancer Genome Atlas data sets for GBM and other cancers, genomic DNA alterations (mutation, amplification or deletion) were less likely the reason for the high expression of ATP5A1 and ATP5B in GBM. Our miRNA microarray data showed that miRNAs that target ATP5A1 or ATP5B were down-regulated, which might be the most likely reason for the high expression of ATP5A1 and ATP5B in GBM tumor cells and microvascular proliferation. These findings help us better understand the pathogenesis of GBM, and agents against ATP5A1 and/or ATP5B might effectively kill both tumor cells and microvascular proliferation in GBM. MiRNAs, such as Let-7f, miR-16, miR-23, miR-100 and miR-101, that target ATP5A1 or ATP5B, might be potential therapeutic agents for GBM.

Glycosylation with O-linked β-N-acetylglucosamine (O-GlcNAc) is one of the protein glycosylations affecting various intracellular events. However, the role of O-GlcNAcylation in neurodegenerative diseases such as Alzheimer's disease (AD) is poorly understood. Mitochondrial adenosine 5'-triphosphate (ATP) synthase is a multiprotein complex that synthesizes ATP from ADP and Pi. Here, we found that ATP synthase subunit α (ATP5A) was O-GlcNAcylated at Thr432 and ATP5A O-GlcNAcylation was decreased in the brains of AD patients and transgenic mouse model, as well as Aβ-treated cells. Indeed, Aβ bound to ATP synthase directly and reduced the O-GlcNAcylation of ATP5A by inhibition of direct interaction between ATP5A and mitochondrial O-GlcNAc transferase, resulting in decreased ATP production and ATPase activity. Furthermore, treatment of O-GlcNAcase inhibitor rescued the Aβ-induced impairment in ATP production and ATPase activity. These results indicate that Aβ-mediated reduction of ATP synthase activity in AD pathology results from direct binding between Aβ and ATP synthase and inhibition of O-GlcNAcylation of Thr432 residue on ATP5A., (© The Author 2015. Published by Oxford University Press. All rights reserved. For Permissions, please email: journals.permissions@oup.com.)

Background: Our recent study has demonstrated that inhibition of calpain by transgenic overexpression of calpastatin reduces myocardial proinflammatory response and dysfunction in endotoxemia. However, the underlying mechanisms remain to be determined. In this study, we used cardiomyocyte-specific capn4 knockout mice to investigate whether and how calpain disrupts ATP synthase and induces mitochondrial superoxide generation during endotoxemia., Methods and Results: Cardiomyocyte-specific capn4 knockout mice and their wild-type littermates were injected with lipopolysaccharides. Four hours later, calpain-1 protein and activity were increased in mitochondria of endotoxemic mouse hearts. Mitochondrial calpain-1 colocalized with and cleaved ATP synthase-α (ATP5A1), leading to ATP synthase disruption and a concomitant increase in mitochondrial reactive oxygen species generation during lipopolysaccharide stimulation. Deletion of capn4 or upregulation of ATP5A1 increased ATP synthase activity, prevented mitochondrial reactive oxygen species generation, and reduced proinflammatory response and myocardial dysfunction in endotoxemic mice. In cultured cardiomyocytes, lipopolysaccharide induced mitochondrial superoxide generation that was prevented by overexpression of mitochondria-targeted calpastatin or ATP5A1. Upregulation of calpain-1 specifically in mitochondria sufficiently induced superoxide generation and proinflammatory response, both of which were attenuated by ATP5A1 overexpression or mitochondria-targeted superoxide dismutase mimetics., Conclusions: Cardiomyocyte-specific capn4 knockout protects the heart against lipopolysaccharide-induced injury in endotoxemic mice. Lipopolysaccharides induce calpain-1 accumulation in mitochondria. Mitochondrial calpain-1 disrupts ATP synthase, leading to mitochondrial reactive oxygen species generation, which promotes proinflammatory response and myocardial dysfunction during endotoxemia. These findings uncover a novel mechanism by which calpain mediates myocardial dysfunction in sepsis., (© 2015 American Heart Association, Inc.)

Background/aims: Nephrotoxicity is a frequent and major limitation in cisplatin (CDDP)-based chemotherapy. 5-Aminolevulinic acid (ALA) is widely distributed in animal cells, and it is a precursor of tetrapyrole compounds such as heme that is fundamentally important in aerobic energy metabolism. The aim of this study is to evaluate the protective role of ALA in CDDP-induced acute kidney injury (AKI)., Method: We used CDDP-induced AKI rat model and cultured renal tubular cells (NRK-52E). We divided four groups of rats: control, CDDP only, CDDP + ALA(post);(ALA 10 mg/kg + Fe in drinking water) after CDDP, CDDP + ALA(pre & post)., Result: CDDP increased Cr up to 6.5 mg/dl, BUN up to 230 mg/dl, and ALA significantly reduced these changes. ALA ameliorates CDDP-induced morphological renal damages, and reduced tubular apoptosis evaluated by TUNEL staining and cleaved caspase 3. Protein and mRNA levels of ATP5α, complex(COX) IV, UCP2, PGC-1α in renal tissue were significantly decreased by CDDP, and ALA ameliorates reduction of these enzymes. In contrast, Heme Oxigenase (HO)-1 level is induced by CDDP treatment, and ALA treatment further up-regulates HO-1 levels. In NRK-52E cells, the CDDP-induced reduction of protein and mRNA levels of mitochondrial enzymes was significantly recovered by ALA + Fe. CDDP-induced apoptosis were ameliorated by ALA + Fe treatment. Furthermore, we evaluated the size of transplantated bladder carcinoma to the rat skin, and ALA did not change the anti cancer effects of CDDP., Conclusion: These data suggested that the protective role of ALA in cisplatin-induced AKI is via protection of mitochondrial viability and prevents tubular apoptosis. Also there are no significant effects of ALA on anticancer efficiency of CDDP in rats. Thus, ALA has the potential to prevent CDDP nephrotoxicity without compromising its anticancer efficacy.

Recently we found that ATP5J was over-expressed in tissue samples from patients with colorectal cancer. However, the clinical significance and function of the over-expression of ATP5J in these patients remains unclear. We investigated these issues in the current study. Our results indicated that expression of ATP5J was significantly higher in colorectal cancer tissue than in adjacent tissue, and it was also significantly higher in metastatic lymph nodes than in primary cancer tissue (P<0.05). A correlation between ATP5J expression and tumor differentiation was detected, but no correlation with gender, age, T stage, lymph node metastasis, or survival status was observed. Down-regulation of ATP5J expression attenuated the ability of cell migration and increased the sensitivity to 5-fluorouracil (5-Fu) in cells of the DLD1 cell line. Inversely, up-regulation of ATP5J expression enhanced cell migration and decreased 5-Fu sensitivity, suggesting that the function of ATP5J in colorectal cancer might involve cell migration and 5-Fu sensitivity.

Whole exome sequencing is a powerful tool to detect novel pathogenic mutations in patients with suspected mitochondrial disease. However, the interpretation of novel genetic variants is not always straightforward. Here, we present two siblings with a severe neonatal encephalopathy caused by complex V deficiency. The aim of this study was to uncover the underlying genetic defect using the combination of enzymatic testing and whole exome sequence analysis, and to provide evidence for causality by functional follow-up. Measurement of the oxygen consumption rate and enzyme analysis in fibroblasts were performed. Immunoblotting techniques were applied to study complex V assembly. The coding regions of the genome were analysed. Three-dimensional modelling was applied. Exome sequencing of the two siblings with complex V deficiency revealed a heterozygous mutation in the ATP5A1 gene, coding for complex V subunit α. The father carried the variant heterozygously. At the messenger RNA level, only the mutated allele was expressed in the patients, whereas the father expressed both the wild-type and the mutant allele. Gene expression data indicate that the maternal allele is not expressed, which is supported by the observation that the ATP5A1 expression levels in the patients and their mother are reduced to ∼50%. Complementation with wild-type ATP5A1 restored complex V in the patient fibroblasts, confirming pathogenicity of the defect. At the protein level, the mutation results in a disturbed interaction of the α-subunit with the β-subunit of complex V, which interferes with the stability of the complex. This study demonstrates the important value of functional studies in the diagnostic work-up of mitochondrial patients, in order to guide genetic variant prioritization, and to validate gene defects.

Background: Regular exercise improves systolic cardiac dysfunction through Akt cascade-mediated physiological hypertrophy in congestive heart failure. Tissue acidosis impairs Akt cascade, and coupling factor 6 induces tissue acidosis via activation of ecto-F(1)F(o) complex. We tested the hypothesis that coupling factor 6 attenuates physiological cardiac hypertrophy induced by exercise and its benefit in mice., Methods and Results: Adult wild-type mice (n = 20) and coupling factor 6-overexpressing transgenic mice (n = 20) were divided into two groups with or without 4-week exercise consisting of 90-min swimming twice daily. Left ventricular posterior wall and interventricular septum thicknesses were increased by 0.12 ± 0.1 and 0.16 ± 0.1 mm, respectively, after 4-week swimming in wild-type mice (both P < 0.01), but unchanged in transgenic mice. Fractional shortening was increased from 37 ± 1 to 41 ± 1% after 4-week swimming in wild-type mice (P < 0.05), whereas it was unchanged in transgenic. The insulin-like growth factor 1 (IGF-1) receptor protein and its phosphorylated form in the heart were both increased by 1.83 ± 0.23 and 1.83 ± 0.09 times, respectively, after 4-week swimming in wild-type mice (both P < 0.05), but were unchanged in transgenic. Downstream phosphoinsulin receptor substrate 1, phosphoinositide 3-kinase, and phospho-Akt were increased by 2.22 ± 0.22, 1.78 ± 0.31, and 2.24 ± 0.49 times, respectively, in wild-type mice (all P < 0.05), but were unchanged in transgenic. Restoration of phospho-Akt by IGF-1 injection recovered left ventricular hypertrophy and systolic function after 4-week swimming in transgenic., Conclusion: Overexpression of coupling factor 6 attenuates exercise-induced physiological cardiac hypertrophy by downregulating Akt signaling, thereby cancelling its benefit for cardiac function in mice. Reduction in coupling factor 6 level seems to be useful for drawing the exercising effects on cardiac function.

Point mutations at m.8993T>C and m.8993T>G of the mtDNA ATPase 6 gene cause the neurogenic weakness, ataxia and retinitis pigmentosa (NARP) syndrome, a mitochondrial disorder characterized by retinal, central and peripheral neurodegeneration. We performed detailed neurological, neuropsychological and ophthalmological phenotyping of a mother and four daughters with NARP syndrome from the mtDNA m.8993T>C ATPase 6 mutation, including 3-T brain MRI, spectral domain optical coherence tomography (SD-OCT), adaptive optics scanning laser ophthalmoscopy (AOSLO), electromyography and nerve conduction studies (EMG-NCS) and formal neuropsychological testing. The degree of mutant heteroplasmy for the m.8993T>C mutation was evaluated by real-time allele refractory mutation system quantitative PCR of mtDNA from hair bulbs (ectoderm) and blood leukocytes (mesoderm). There were marked phenotypic differences between family members, even between individuals with the greatest degrees of ectodermal and mesodermal heteroplasmy. 3-T MRI revealed cerebellar atrophy and cystic and cavitary T2 hyperintensities in the basal ganglia. SD-OCT demonstrated similarly heterogeneous areas of neuronal and axonal loss in inner and outer retinal layers. AOSLO showed increased cone spacing due to photoreceptor loss. EMG-NCS revealed varying degrees of length-dependent sensorimotor axonal polyneuropathy. On formal neuropsychological testing, there were varying deficits in processing speed, visual-spatial functioning and verbal fluency and high rates of severe depression. Many of these cognitive deficits likely localize to cerebellar and/or basal ganglia dysfunction. High-resolution retinal and brain imaging in NARP syndrome revealed analogous patterns of tissue injury characterized by heterogeneous areas of neuronal loss.

Objective: Reactive oxygen species are involved in the pathogenesis of congestive heart failure. We recently showed that coupling factor 6, a component of adenosine trisphosphate (ATP) synthase, induces hypertension by intracellular acidosis, which is related to reactive oxygen species generation. We investigated the effect of high-salt diet on the cardiac performance and reactive oxygen species generation in coupling factor 6-overexpressing transgenic mice., Methods and Results: Baseline echocardiographic findings, reactive oxygen species generation, protein expression of sarcoplasmic/endoplasmic reticulum of Ca-ATPase 2 and phospholamban, and ATP content in the heart were similar between 7-week-old transgenic and wild-type mice. When the mice were fed with 8% salt diet for 20-24 weeks, fractional shortening of the left ventricle was decreased in transgenic mice compared with wild-type mice and was recovered by intraperitoneal administration of anticoupling factor 6 antibody. Nicotinamide adenine dinucleotide phosphate oxidase activity in the heart was increased in transgenic mice after the high-salt diet concomitantly with c-Src activation. The level of 8-iso-prostaglandin F2α was increased in transgenic heart compared with wild-type heart. The protein expression of sarcoplasmic/endoplasmic reticulum of Ca-ATPase 2 was decreased and that of phospholamban was increased in transgenic heart. In cDNA microarray analysis, the genes related to ATP synthesis and glycolysis were decreased in transgenic heart, concomitantly with the decrease in ATP content and the increase in β-myosin heavy chain., Conclusion: These suggest that coupling factor 6 induces the development of systolic dysfunction and upregulation of nicotinamide adenine dinucleotide phosphate oxidase in the heart under the high-salt diet.

Ectopic expression of coupling factor B in animal cells resulted in altered mitochondrial morphology. Cells expressing factor B fused to green fluorescent protein (GFP) contained fragmented, balloon-shaped or thinned, filamentous mitochondria, terminating at one end with balloon-like structures. Ultrastructural analysis using transmission electron microscopy revealed changes in the organization of mitochondrial cristae in cells expressing factor B-GFP fusion protein.

The recent surge in mitochondrial research has been driven by the identification of mitochondria-associated diseases and the role of mitochondria in apoptosis and aging. Mitochondrial DNA (mtDNA) has been proposed to be involved in carcinogenesis because of its high susceptibility to mutations and limited repair mechanisms in comparison to nuclear DNA. As mtDNA lacks introns, it has been suggested that most mutations will occur in coding sequences. The subsequent accumulation of mutations may lead to tumor formation. By virtue of their clonal nature, high copy number and high frequent mutations may provide a powerful molecular biomarker for the detection of cancer. It has been suggested that the extent of mtDNA mutations might be useful in the prognosis of cancer outcome and/or the response to certain therapies. In this review article, we aim to provide a brief summary of our current understanding of mitochondrial genetics and biology, review the mtDNA alterations reported in breast cancer, and offer some perspectives as to the emergence of mtDNA mutations, including their functional consequences in cancer development, diagnostic criteria, and therapeutic implications.

Background: Both the putative modifier gene ATP5a1 and the tumour suppressor gene TP53 are involved in the regulation of apoptosis and may be involved in the development of colorectal cancers., Aims: To investigate the relationship between these genes in 16 colorectal cancer cell lines., Methods: Each gene was screened for mutation using high resolution melting analysis and sequencing. Expression of ATP5a1 mRNA was tested by quantitative PCR., Results: Sequence changes in ATP5a1 were found in 9/16 (56%) cell lines and consisted of mainly novel single nucleotide polymorphisms (SNPs) found in the 5' UTR, introns 4/5/9 and exon 7. TP53 mutations were also found in 9/16 (56%) cell lines; these were consistent with previous reports. High levels of ATP5a1 expression were seen in cell lines with TP53 mutation compared with those with wild type TP53 (p = 0.02). Furthermore, an A-->G change at the -18 position in intron 4 of ATP5a1 was significantly associated with increased gene expression (p = 0.0391). Comparison with genotype showed that cell lines with chromosomal instability (CIN) had significantly higher levels of ATP5a1 expression than those with microsatellite instability (MSI) (p = 0.02)., Conclusion: Higher levels of ATP5a1 expression are associated with certain SNPs and with TP53 mutation. High expression also occurs in CIN and may facilitate tumour development along this pathway. Conversely, low levels of ATP5a1 expression may facilitate development of tumours with MSI.

Since the early studies on the resolution and reconstitution of the oxidative phosphorylation system from animal mitochondria, coupling factor B was recognized as an essential component of the machinery responsible for energy-driven ATP synthesis. At the phenomenological level, factor B was agreed to lie at the interface of energy transfer between the respiratory chain and the ATP synthase complex. However, biochemical characterization of the factor B polypeptide has proved difficult. It was not until 1990 that the N-terminal amino acid sequence of bovine mitochondrial factor B was reported, which followed, a decade later, by the report describing the amino acid sequence of full-length human factor B and its functional characterization. The present review summarizes the recent advances in structure-functional studies of factor B, including its recently determined crystal structure at 0.96 A resolution. Ectopic expression of human factor B in cultured animal cells has unexpectedly revealed its role in shaping mitochondrial morphology. The supramolecular assembly of ATP synthase as dimer ribbons at highly curved apices of the mitochondrial cristae was recently suggested to optimize ATP synthesis under proton-limited conditions. We propose that the binding of the ATP synthase dimers with factor B tetramers could be a means to enhance the efficiency of the terminal step of oxidative phosphorylation in animal mitochondria.

Aims: Coupling factor 6 (CF6) induces hypertension by attenuating the endothelial generation of prostacyclin. However, intracellular signalling of CF6 in the resistance arteriole vascular smooth muscle cells (VSMCs) that are directly related to vasoconstriction has not been determined. Here we investigated the direct effect of exogenous CF6 on Ca2+ signalling in cultured VSMCs and the in vivo role of endogenous CF6 in the genesis of hypertension using CF6 transgenic (TG) mice., Methods and Results: CF6 induced a monophasic increase in the intracellular free Ca2+ concentration ([Ca2+]i) through nifedipine-sensitive Ca2+ channels in A7r5 cells, a cell line of VSMCs, and enhanced the angiotensin II-induced spike phase of [Ca2+]i to a greater degree in VSMCs derived from spontaneously hypertensive rats (SHRs). In the mesenteric arterioles obtained from CF6-TG mice that manifested hypertension, angiotensin II-induced vasoconstriction was enhanced, compared with wild-type mice, and its enhancement was abolished by an anti-CF6 antibody. Pre-treatment with PP1, a tyrosine kinase c-Src inhibitor, blocked CF6-induced increase in Ca2+ signalling in VSMCs and vasoconstriction in TG mice. The receptor of CF6 was F1 motor of adenosine triphosphate (ATP) synthase with a higher affinity in SHRs. CF6 decreased intracellular pH via activation of ATPase activity and led to c-Src activation to a greater degree in SHR-derived VSMCs., Conclusion: CF6 causes hypertension by directly enhancing Ca2+ signalling in VSMCs and vasoconstriction in the mesenteric arteriolar network via c-Src activation.

Background: Impaired oxidative capacity of skeletal muscle mitochondria contribute to insulin resistance and type 2 diabetes (T2D). Furthermore, mRNA expression of genes involved in oxidative phosphorylation, including ATP5O, is reduced in skeletal muscle from T2D patients. Our aims were to investigate mechanisms regulating ATP5O expression in skeletal muscle and association with glucose metabolism, and the relationship between ATP5O single nucleotide polymorphisms (SNPs) and risk of T2D., Methodology/principal Findings: ATP5O mRNA expression was analyzed in skeletal muscle from young (n = 86) and elderly (n = 68) non-diabetic twins before and after a hyperinsulinemic euglycemic clamp. 11 SNPs from the ATP5O locus were genotyped in the twins and a T2D case-control cohort (n = 1466). DNA methylation of the ATP5O promoter was analyzed in twins (n = 22) using bisulfite sequencing. The mRNA level of ATP5O in skeletal muscle was reduced in elderly compared with young twins, both during basal and insulin-stimulated conditions (p<0.0005). The degree of DNA methylation around the transcription start of ATP5O was <1% in both young and elderly twins and not associated with mRNA expression (p = 0.32). The mRNA level of ATP5O in skeletal muscle was positively related to insulin-stimulated glucose uptake (regression coefficient = 6.6; p = 0.02). Furthermore, two SNPs were associated with both ATP5O mRNA expression (rs12482697: T/T versus T/G; p = 0.02 and rs11088262: A/A versus A/G; p = 0.004) and glucose uptake (rs11088262: A/A versus A/G; p = 0.002 and rs12482697: T/T versus T/G; p = 0.005) in the young twins. However, we could not detect any genetic association with T2D., Conclusions/significance: Genetic variation and age are associated with skeletal muscle ATP5O mRNA expression and glucose disposal rate, suggesting that combinations of genetic and non-genetic factors may cause the reduced expression of ATP5O in T2D muscle. These findings propose a role for ATP5O, in cooperation with other OXPHOS genes, in the regulation of in vivo glucose metabolism.

Coupling factor B (FB) is a mitochondrial inner membrane polypeptide that facilitates the energy-driven catalysis of ATP synthesis in animal mitochondria by blocking a proton leak across the membrane. Here, we report the crystal structure of the bovine mitochondrial FB mutant with Gly-3-Glu substitution determined at a resolution of 0.96 A and that of the WT polypeptide at a resolution of 2.9 A. The structure reveals an oblong, oval-shaped molecule with a unique globular N-terminal domain that is proposed to be the membrane anchor domain and the capping region to the C-terminal leucine-rich repeats domain. A short N-terminal alpha-helix, which extends away from the molecule's body, is suggestive of functioning as an anchor for FB to the matrix side of the mitochondrial inner membrane. Identification of a bound Mg(2+) ion reveals that FB is a metalloprotein. We also report the cocrystal structures of FB bound with phenylarsine oxide and Cd(2+), two known inhibitors of the FB coupling activity.

Treatment of the recombinant bovine factor B with trypsin yielded a fragment (amino acid residues 62-175) devoid of coupling activity. Removal of the N-terminal Trp2-Gly3-Trp4 peptide resulted in a significant loss of coupling activity in the FB(DeltaW)(2)(-W)(4) deletion mutant. Sucrose density gradient centrifugation demonstrated co-sedimentation of recombinant factor B with the ADP/ATP carrier, which is present in preparations of H(+)-translocating F(0)F(1)-ATPase, but not in preparations of complex V. The N-terminally truncated factor B mutant FB(DeltaW)(2)(-W)(4) did not co-sediment with the ADP/ATP carrier. Recombinant factor B co-sedimented with partially purified membrane sector F(0), extracted from F(1)-stripped bovine submitochondrial particles with n-dodecyl-beta-d-maltoside. Factor B inhibited the passive proton conductance catalyzed by F(0) reconstituted into asolectin liposomes. A factor B mutant, bearing a photoreactive unnatural amino acid pbenzoyl-l-phenylalanine (pBpa) substituted for Trp2, cross-linked with F(0) subunits e and g as well as the ADP/ATP carrier. These results suggest that the N-terminal domain and, in particular, the proximal N-terminal amino acids are important for the coupling activity and protein-protein interactions of bovine factor B.

As a novel vasoactive peptide, plasma coupling factor 6 (CF6) was shown to be elevated in patients with diabetes mellitus, yet the mechanism involved is unknown. We studied CF6 protein release and its potential mechanism in human umbilical vein endothelial cells (HUVECs) incubated with high glucose levels. High glucose level enhanced CF6 expression and peptide secretion in HUVECs in a time- and concentration-dependent manner, which was independent of increased osmolarity. PKC or p38 MAPK inhibition significantly suppressed high glucose-mediated CF6 release in HUVECs, and the inhibition rate was -45% and -30%, respectively. Also, high glucose-induced CF6 production was antagonized by insulin treatment. Hence, high glucose increases the expression and secretion of CF6 in endothelial cells and appears to be mediated by PKC and p38 MAPK activity.

We showed that humanin (HN), an endogenous peptide against Alzheimer disease-related insults, was expressed in muscles of patients with chronic progressive external ophthalmoplegia (CPEO), a major mitochondrial disease. Because HN was recently found to block proapoptotic Bax function and exert its versatile cytoprotective effects in association with an increase in ATP levels, HN expression may thus reflect a physiological response against degenerative changes in the muscles of patients with CPEO. We found HN expression in all four patients examined, each of whom had different mitochondrial DNA mutations including two different single DNA deletions, multiple deletions, and no major mutations detected. We also found that HN expression was not linked to focal cytochrome c deficiency, strongly associated with the subtype of CPEO with single deletions. These results suggest that HN expression is more closely related to degenerative changes in all types of CPEO. Notably, HN was also expressed in non-degenerative muscle fibers of patients with CPEO or Leigh syndrome, who had the 8993T>G mutation in the mitochondrial ATPase 6 gene known to be associated with impaired ATP synthesis. Collectively, our findings suggest that HN may be specifically expressed in response to defects in energy production in muscles with mitochondrial abnormalities.

Objective: We previously showed that mitochondrial coupling factor 6 (CF6), an endogenous inhibitor of prostacyclin synthesis and a vasoconstrictor, is present on the surface of human umbilical vein endothelial cells (HUVEC) and is released outside of the cells by shear stress. We investigated the intracellular signaling mechanism for shear-induced release of CF6 in HUVEC and the effects of troglitazone and 15-deoxy-delta(12,14)-prostaglandin J2 (15d-PGJ2), both peroxisome proliferator-activated receptor (PPAR)-gamma ligands, on it., Methods and Results: The release and gene expression of CF6 in HUVEC were enhanced by shear stress at 25 dyn/cm2, measured by radioimmunoassay and real-time RT-PCR, respectively. The intracellular content of CF6 was decreased after exposure to shear stress at 25 dyn/cm2. Transfection experiments with deletional and mutational CF6 promoter constructs, and with dominant negative mutant IkappaB kinase alpha (K44M) demonstrated that shear-induced CF6 transcription was dependent on nuclear factor-kappa B (NF-kappaB) activation. Pretreatment with troglitazone or 15d-PGJ2 inhibited the shear-induced release and gene expression of CF6, whereas fenofibric acid, a PPAR-alpha ligand, had no influence on them. Western blot and immunostaining showed that troglitazone and 15d-PGJ2 inhibited the shear-induced, reactive oxygen species (ROS)-mediated activation of NF-kappaB at the level of IkappaB protein., Conclusions: The shear-induced gene expression and release of CF6 in HUVEC are mediated by the ROS-related activation of NF-kappaB signaling pathway. Troglitazone and 15d-PGJ2 inhibit them at the IkappaB protein level.

Objective: We recently showed that mitochondrial coupling factor 6 (CF6) is present as a pressor substance and a prostacyclin inhibitor in systemic circulation. However, the regulation mechanism for circulating CF6 is unknown. We investigated the role of tumor necrosis factor-alpha (TNF-alpha) in the generation and release of CF6., Methods and Results: We used two kinds of cells, human umbilical vein endothelial cells (HUVEC) and ECV-304. The concentration of CF6 in the medium increased with time in both ECV-304 and HUVEC. Treatment of ECV-304 and HUVEC with TNF-alpha enhanced the release of CF6 in a dose-dependent manner concomitantly with the decrease in CF6 content in the mitochondria at 24 h. The released CF6 was characterized to be an active full-length peptide by Western blot. The ratio of CF6 to GAPDH mRNA, measured by real-time polymerase chain reaction, was 1.7 fold increased at 1 h after exposure to TNF-alpha in ECV-304 and HUVEC. This enhanced gene expression and release was blocked or suppressed by 70% by stable transfection of dominant negative mutant I kappa B kinase alpha whose efficacy was confirmed by blockade of translocation of NF-kappa B p65 protein and of degradation of I kappa B alpha protein. Flow cytometry analysis revealed that the cell surface-associated CF6 was significantly increased at 24 h after TNF-alpha in a dose-dependent manner., Conclusions: TNF-alpha stimulates the gene expression of CF6 via activation of NF-kappa B signaling pathway, and promotes the release of CF6 from ECV-304 and HUVEC.

Background: We showed that mitochondrial coupling factor 6 (CF6), an endogenous inhibitor of prostacyclin synthesis, is present in the systemic circulation as a pressor substance in rats. We investigated the possibility of vascular endothelial cells as a source of circulating CF6., Methods and Results: We used 2 cultured endothelial cell lines, human umbilical vein endothelial cells (HUVECs) and ECV 304 cells (transformed HUVECs), for this study. Immunofluorescence microscopy of both ECV 304 and HUVECs confirmed the surface-associated immunoreactivity of anti-CF6 antibody on the plasma membrane. The concentration of CF6 in the medium increased gradually with time in both ECV 304 and HUVECs in static conditions. Exposure of ECV 304 and HUVECs to a fluid shear stress enhanced the release of CF6: In ECV 304, the concentration of CF6 in the medium (ng. well(-1). 6 hours(-1)) was 2.1+/-0.8 at baseline, 4.3+/-0.8 after shear at 15 dynes/cm(2), and 57.7+/-8.4 after shear at 25 dynes/cm(2). CF6 contents in the cell homogenate and mitochondria were both significantly increased after exposure of ECV 304 to 6-hour shear at 15 dynes/cm(2), whereas they were unchanged after shear stress at 25 dynes/cm(2). The ratio of CF6 to GAPDH mRNA was enhanced significantly, by 1.8+/-0.2-fold, after 6-hour shear stress at 25 dynes/cm(2). Flow cytometry analysis revealed that the surface-associated CF6 was significantly increased in a 3-hour static condition after the previous exposure of the cells to shear stress for 3 hours., Conclusions: Vascular endothelial cells are a source of CF6, and shear stress regulates the release of the surface-associated CF6.

We demonstrated recently that coupling factor 6, an essential component of the energy-transducing stalk of mitochondrial ATP synthase, suppresses the synthesis of prostacyclin in vascular endothelial cells. Here, we tested the hypothesis that coupling factor 6 is present on the cell surface and is involved in the regulation of systemic circulation. This peptide is present on the surface of CRL-2222 vascular endothelial cells and is released by these cells into the medium. In vivo, the peptide circulates in the vascular system of the rat, and its gene expression and plasma concentration are higher in spontaneously hypertensive rats (SHRs) than in normotensive controls. Elevation of blood pressure with norepinephrine did not affect the plasma concentration of coupling factor 6. Intravenous injection of recombinant peptide increased blood pressure, apparently by suppressing prostacyclin synthesis, whereas a specific Ab to coupling factor 6 decreased systemic blood pressure concomitantly with an increase in plasma prostacyclin. Interestingly, the antibody's hypotensive effect could be abolished by treating with the cyclooxygenase inhibitor indomethacin. These findings indicate that mitochondrial coupling factor 6 functions as a potent endogenous vasoconstrictor in the fashion of a circulating hormone and may suggest a new mechanism for hypertension.

A T --> G mutation at position 8993 in human mitochondrial DNA is associated with the syndrome neuropathy, ataxia, and retinitis pigmentosa and with a maternally inherited form of Leigh's syndrome. The mutation substitutes an arginine for a leucine at amino acid position 156 in ATPase 6, a component of the F0 portion of the mitochondrial ATP synthase complex. Fibroblasts harboring high levels of the T8993G mutation have decreased ATP synthesis activity, but do not display any growth defect under standard culture conditions. Combining the notions that cells with respiratory chain defects grow poorly in medium containing galactose as the major carbon source, and that resistance to oligomycin, a mitochondrial inhibitor, is associated with mutations in the ATPase 6 gene in the same transmembrane domain where the T8993G amino acid substitution is located, we created selective culture conditions using galactose and oligomycin that elicited a pathological phenotype in T8993G cells and that allowed for the rapid selection of wild-type over T8993G mutant cells. We then generated cytoplasmic hybrid clones containing heteroplasmic levels of the T8993G mutation, and showed that selection in galactose-oligomycin caused a significant increase in the fraction of wild-type molecules (from 16 to 28%) in these cells.

A cDNA clone encoding the precursor to the rat mitochondrial protein coupling factor 6 (F6) has been isolated and sequenced. The deduced amino acid sequence of the rat precursor protein shows 78% and 74% identity with the human and bovine F6 pre-proteins, respectively.

Escherichia coli strain KF148(SD-) defective in translation of the uncC gene for the epsilon subunit of H(+)-ATPase could not support growth by oxidative phosphorylation due to lack of F1 binding to Fo (M. Kuki, T. Noumi, M. Maeda, A. Amemura, and M. Futai, 1988, J. Biol. Chem. 263, 17, 437-17, 442). Mutant uncC genes for epsilon subunits lacking different lengths from the amino terminus were constructed and introduced into strain KF148(SD-). F1 with an epsilon subunit lacking the 15 amino-terminal residues could bind to F0 in a functionally competent manner, indicating that these amino acid residues are not absolutely necessary for formation of a functional enzyme. However, mutant F1 in which the epsilon subunit lacked 16 amino-terminal residues showed defective coupling between ATP hydrolysis (synthesis) and H(+)-translocation, although the mutant F1 showed partial binding to Fo. These findings suggest that the epsilon subunit is essential for binding of F1 to F0 and for normal H(+)-translocation. Previously, Kuki et al. (cited above) reported that 60 residues were not necessary for a functional enzyme. However, the mutant with an epsilon subunit lacking 15 residues from the amino terminus and 4 residues from the carboxyl terminus was defective in oxidative phosphorylation, suggesting that both terminal regions affect the conformation of the region essential for a functional enzyme.

Large scale deletions of mitochondrial DNA (mtDNA) or altered inter-genomic regulation in skeletal muscle have been demonstrated in patients with mitochondrial encephalomyopathies due to Cytochrome C oxidase (COx) deficiency. We have analyzed by Southern blotting and Polymerase Chain Reaction (PCR) the mtDNA in primary muscle cultures (myoblast-myotube stages and at clonal densities) and in fibrogenic subclones obtained from 9 patients with partial COx deficiency who had in their muscle biopsy a subpopulation of mtDNA showing deletions of variable size (between 2.1 and 6.5 Kb). Only in the cultures from one patient, southern analysis revealed in myoblasts and myotubes a mtDNA almost identical to that found in the original muscle biopsy and persistence of deletion in muscle cells grown at clonal densities. The deletion was detectable in fibrogenic lineage only by PCR amplification. The deleted mtDNA molecules were detectable in myogenic or fibrogenic cultures from other patients only by PCR amplification. The different amounts of deleted mtDNA in the various tissues could be due either to an unequal distribution of the altered mtDNA during embryogenesis with amplification of deleted molecules in myogenic lineage or could result from negative selection against the altered mtDNA in rapidly proliferating cells, such as fibroblasts.

Coupling factor 6 (F6) is a component of mitochondrial ATP synthase which is required for the interactions of the catalytic and proton-translocating segments. A human fetal muscle cDNA clone encoding this protein was isolated by screening a lambda gt10 library with oligodeoxyribonucleotide probes. The 497-bp F6 cDNA included a 96-bp segment that delineated a presequence of 32 amino acids (aa) in the precursor protein, and 140 bp of 3'-untranslated sequence. The remainder of the cDNA sequence coded for a mature human F6 protein of 76 aa. The deduced primary aa sequence showed 81% homology to that of bovine F6, differing in 14 aa. Almost all of these aa substitutions were conservative and comparison of the hydropathy profiles revealed a similar pattern.

Site-directed mutagenesis was used to generate three mutations in the uncB gene encoding the a-subunit of the F0 portion of the F0F1-ATPase of Escherichia coli. These mutations directed the substitution of Arg-210 by Gln, or of His-245 by Leu, or of both Lys-167 and Lys-169 by Gln. The mutations were incorporated into plasmids carrying all the structural genes encoding the F0F1-ATPase complex and these plasmids were used to transform strain AN727 (uncB402). Strains carrying either the Arg-210 or His-245 substitutions were unable to grow on succinate as sole carbon source and had uncoupled growth yields. The substitution of Lys-167 and Lys-169 by Gln resulted in a strain with growth characteristics indistinguishable from a normal strain. The properties of the membranes from the Arg-210 or His-245 mutants were essentially identical, both being proton impermeable and both having ATPase activities resistant to the inhibitor DCCD. Furthermore, in both mutants, the F1-ATPase activities were inhibited by about 50% when bound to the membranes. The membrane activities of the mutant with the double lysine change were the same as for a normal strain. The results are discussed in relation to a previously proposed model for the F0 (Cox, G.B., Fimmel, A.L., Gibson, F. and Hatch, L. (1986) Biochim. Biophys. Acta 849, 62-69).

Extramitochondrial pools of mitochondrial precursor polypeptides can be detected in yeast spheroplasts which had been pulse-labeled for 3 min in the absence of inhibitors or for 10 min in the presence of an uncoupler of oxidative phosphorylation. In either case, these precursors can be post-translationally converted to the mature forms during a subsequent chase. Post-translational maturation of the precursor to F1-ATPase beta-subunit is accompanied by uptake of the polypeptide into mitochondria. Pools of precursor polypeptides are also found in pulse-labeled intact yeast cells, the pool sizes depending on the metabolic status of the cells. For example, if the rate of protein synthesis is lowered by cycloheximide, the precursor pool size decreases. This indicates that living yeast cells can, and apparently do, import polypeptides into mitochondria post-translationally.