Cytochrome c oxidase (COX) deficiency is a frequent biochemical abnormality in mitochondrial diso... more Cytochrome c oxidase (COX) deficiency is a frequent biochemical abnormality in mitochondrial disorders, but a large fraction of cases remains genetically undetermined. Whole-exome sequencing led to the identification of APOPT1 mutations in two Italian sisters and in a third Turkish individual presenting severe COX deficiency. All three subjects presented a distinctive brain MRI pattern characterized by cavitating leukodystrophy, predominantly in the posterior region of the cerebral hemispheres. We then found APOPT1 mutations in three additional unrelated children, selected on the basis of these particular MRI features. All identified mutations predicted the synthesis of severely damaged protein variants. The clinical features of the six subjects varied widely from acute neurometabolic decompensation in late infancy to subtle neurological signs, which appeared in adolescence; all presented a chronic, long-surviving clinical course. We showed that APOPT1 is targeted to and localized w...
Disorders of the mitochondrial energy metabolism are clinically and genetically heterogeneous. An... more Disorders of the mitochondrial energy metabolism are clinically and genetically heterogeneous. An increasingly recognized subgroup is caused by defective mitochondrial iron-sulfur (Fe-S) cluster biosynthesis, with defects in 13 genes being linked to human disease to date. Mutations in three of them, NFU1, BOLA3, and IBA57, affect the assembly of mitochondrial [4Fe-4S] proteins leading to an impairment of diverse mitochondrial metabolic pathways and ATP production. Patients with defects in these three genes present with lactic acidosis, hyperglycinemia, and reduced activities of respiratory chain complexes I and II, the four lipoic acid-dependent 2-oxoacid dehydrogenases and the glycine cleavage system (GCS). To date, five different NFU1 pathogenic variants have been reported in 15 patients from 12 families. We report on seven new patients from five families carrying compound heterozygous or homozygous pathogenic NFU1 mutations identified by candidate gene screening and exome sequenc...
TTC19 deficiency is a progressive neurodegenerative disease associated with isolated mitochondria... more TTC19 deficiency is a progressive neurodegenerative disease associated with isolated mitochondrial respiratory chain (MRC) complex III deficiency and loss-of-function mutations in the TT19 gene in the few patients reported so far. We performed exome sequencing and selective mutational analysis of TTC19, respectively, in patients from three unrelated families presenting with initially unspecific clinical signs of muscular hypotonia and global developmental delay followed by regression, ataxia, loss of speech, and rapid neurological deterioration. One patient showed severe lactic acidosis at the neonatal age and during intercurrent illness. We identified homozygous mutations in all three index cases, in two families novel missense mutations (c.544 T > C/p.Leu185Pro; c.917 T > C/p.Leu324Pro). The younger sister of the severely affected patient 3 showed only mild delay of motor skills and muscular hypotonia so far but is also homozygous for the same mutation. Notably, one patient ...
Restless legs syndrome (RLS) is a sensorimotor disorder with an age-dependent prevalence of up to... more Restless legs syndrome (RLS) is a sensorimotor disorder with an age-dependent prevalence of up to 10% in the general population above 65 years of age. Affected individuals suffer from uncomfortable sensations and an urge to move in the lower limbs that occurs mainly in resting situations during the evening or at night. Moving the legs or walking leads to an improvement of symptoms. Concomitantly, patients report sleep disturbances with consequences such as reduced daytime functioning. We conducted a genome-wide association study (GWA) for RLS in 922 cases and 1,526 controls (using 301,406 SNPs) followed by a replication of 76 candidate SNPs in 3,935 cases and 5,754 controls, all of European ancestry. Herein, we identified six RLS susceptibility loci of genome-wide significance, two of them novel: an intergenic region on chromosome 2p14 (rs6747972, P = 9.03 × 10(-11), OR = 1.23) and a locus on 16q12.1 (rs3104767, P = 9.4 × 10(-19), OR = 1.35) in a linkage disequilibrium block of 140 ...
Defining the mitochondrial proteome is a prerequisite for fully understanding the organelles func... more Defining the mitochondrial proteome is a prerequisite for fully understanding the organelles function as well as mechanisms underlying mitochondrial pathology. The core functions of mitochondria include oxidative phosphorylation, amino acid metabolism, fatty acid oxidation, and ion homeostasis. In addition to these well-known functions, many crucial properties in cell signaling, cell differentiation and cell death are only now being elucidated, and with them the proteins involved. With the wealth of information arriving from single protein studies and sophisticated genome-wide approaches, MitoP2 was designed and is maintained to consolidate knowledge on mitochondrial proteins in one comprehensive database, thus making all pertinent data readily accessible (http://www.mitop2.de). Although the identification of the human mitochondrial proteome is ultimately the prime objective, integration of other species includes Saccharomyces cerevisiae, mouse, Arabidopsis thaliana, and Neurospora ...
Methods in molecular biology (Clifton, N.J.), 2007
The impact of mitochondria on several fundamental cellular processes is reflected in their involv... more The impact of mitochondria on several fundamental cellular processes is reflected in their involvement in the pathophysiology of common diseases such as Parkinson's disease, diabetes, and obesity and a wide range of monogenic disorders primarily associated with energy impairment or metabolic diseases. The importance of mitochondria is also reflected by the steep increase of proteins, which has been localized to this organelle. In yeast, more than 500 of the expected 700-800 mitochondrial proteins are already annotated. In the mammalian species, the expected numbers are estimated to be in the range of 1500-2000 proteins, and the currently annotated entries reach almost 700. In addition to the studies dealing with single proteins, there are many high-throughput approaches that improve the description of the mitochondrial proteome. They include computational predictions of signaling sequences, proteome mapping, mutant screening, expression profiling, protein-protein interaction, an...
Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was ... more Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was proposed that it is required to mediate the interaction of the mitochondrial outer membrane with the actin cytoskeleton. We report the cloning and characterization of MMM1 of the filamentous fungus Neurospora crassa, an organism that uses microtubules for mitochondrial transport. Mutation of the mmm-1 gene leads to a temperature-sensitive slow growth phenotype and female sterility. Mutant cells harbor abnormal giant mitochondria at all stages of the asexual life cycle, whereas actin filament-depolymerizing drugs have no effect on mitochondrial morphology. The MMM1 protein has a single transmembrane domain near the N terminus and exposes a large C-terminal domain to the cytosol. The protein can be imported into the outer membrane in a receptor-dependent manner. Our findings suggest that MMM1 is a factor of general importance for mitochondrial morphology independent of the cytoskeletal sys...
Genome-wide association studies (GWAS) have uncovered numerous genetic variants (SNPs) that are a... more Genome-wide association studies (GWAS) have uncovered numerous genetic variants (SNPs) that are associated with blood pressure (BP). Genetic variants may lead to BP changes by acting on intermediate molecular phenotypes such as coded protein sequence or gene expression, which in turn affect BP variability. Therefore, characterizing genes whose expression is associated with BP may reveal cellular processes involved in BP regulation and uncover how transcripts mediate genetic and environmental effects on BP variability. A meta-analysis of results from six studies of global gene expression profiles of BP and hypertension in whole blood was performed in 7017 individuals who were not receiving antihypertensive drug treatment. We identified 34 genes that were differentially expressed in relation to BP (Bonferroni-corrected p<0.05). Among these genes, FOS and PTGS2 have been previously reported to be involved in BP-related processes; the others are novel. The top BP signature genes in a...
The study was focused on leukoencephalopathies of unknown cause in order to define a novel, homog... more The study was focused on leukoencephalopathies of unknown cause in order to define a novel, homogeneous phenotype suggestive of a common genetic defect, based on clinical and MRI findings, and to identify the causal genetic defect shared by patients with this phenotype. Independent next-generation exome-sequencing studies were performed in 2 unrelated patients with a leukoencephalopathy. MRI findings in these patients were compared with available MRIs in a database of unclassified leukoencephalopathies; 11 patients with similar MRI abnormalities were selected. Clinical and MRI findings were investigated. Next-generation sequencing revealed compound heterozygous mutations in AARS2 encoding mitochondrial alanyl-tRNA synthetase in both patients. Functional studies in yeast confirmed the pathogenicity of the mutations in one patient. Sanger sequencing revealed AARS2 mutations in 4 of the 11 selected patients. The 6 patients with AARS2 mutations had childhood- to adulthood-onset signs of...
The proinflammatory cytokine interleukin (IL)-1β is implicated in the development of insulin resi... more The proinflammatory cytokine interleukin (IL)-1β is implicated in the development of insulin resistance and β-cell dysfunction, whereas higher circulating levels of IL-1 receptor antagonist (IL-1RA), an endogenous inhibitor of IL-1β, has been suggested to improve glycemia and β-cell function in patients with type 2 diabetes. To elucidate the protective role of IL-1RA, this study aimed to identify genetic determinants of circulating IL-1RA concentration and to investigate their associations with immunological and metabolic variables related to cardiometabolic risk. In the analysis of seven discovery and four replication cohort studies, two single nucleotide polymorphisms (SNPs) were independently associated with circulating IL-1RA concentration (rs4251961 at the IL1RN locus [n = 13,955, P = 2.76 × 10(-21)] and rs6759676, closest gene locus IL1F10 [n = 13,994, P = 1.73 × 10(-17)]). The proportion of the variance in IL-1RA explained by both SNPs combined was 2.0%. IL-1RA-raising allele...
Acyl-CoA dehydrogenase 9 (ACAD9) is an assembly factor for mitochondrial respiratory chain Comple... more Acyl-CoA dehydrogenase 9 (ACAD9) is an assembly factor for mitochondrial respiratory chain Complex I (CI), and ACAD9 mutations are recognized as a frequent cause of CI deficiency. ACAD9 also retains enzyme ACAD activity for long-chain fatty acids in vitro but the biological relevance of this function remains controversial partly because of the tissue-specificity of ACAD9 expression: high in liver and neurons and minimal in skin fibroblasts. In this study, we hypothesized that this enzymatic ACAD activity is required for full fatty acid oxidation capacity in cells expressing high levels of ACAD9, and that loss of this function is important in determining phenotype in ACAD9 deficient patients. First, we confirmed that HEK293 cells express ACAD9 abundantly. Then, we showed that ACAD9 knockout in HEK293 cells affected long-chain fatty acid oxidation along with Cl, both of which were rescued by wild-type ACAD9. Further, we evaluated whether the loss of ACAD9 enzymatic fatty acid oxidatio...
Cytochrome c oxidase (COX) deficiency is a frequent biochemical abnormality in mitochondrial diso... more Cytochrome c oxidase (COX) deficiency is a frequent biochemical abnormality in mitochondrial disorders, but a large fraction of cases remains genetically undetermined. Whole-exome sequencing led to the identification of APOPT1 mutations in two Italian sisters and in a third Turkish individual presenting severe COX deficiency. All three subjects presented a distinctive brain MRI pattern characterized by cavitating leukodystrophy, predominantly in the posterior region of the cerebral hemispheres. We then found APOPT1 mutations in three additional unrelated children, selected on the basis of these particular MRI features. All identified mutations predicted the synthesis of severely damaged protein variants. The clinical features of the six subjects varied widely from acute neurometabolic decompensation in late infancy to subtle neurological signs, which appeared in adolescence; all presented a chronic, long-surviving clinical course. We showed that APOPT1 is targeted to and localized w...
Disorders of the mitochondrial energy metabolism are clinically and genetically heterogeneous. An... more Disorders of the mitochondrial energy metabolism are clinically and genetically heterogeneous. An increasingly recognized subgroup is caused by defective mitochondrial iron-sulfur (Fe-S) cluster biosynthesis, with defects in 13 genes being linked to human disease to date. Mutations in three of them, NFU1, BOLA3, and IBA57, affect the assembly of mitochondrial [4Fe-4S] proteins leading to an impairment of diverse mitochondrial metabolic pathways and ATP production. Patients with defects in these three genes present with lactic acidosis, hyperglycinemia, and reduced activities of respiratory chain complexes I and II, the four lipoic acid-dependent 2-oxoacid dehydrogenases and the glycine cleavage system (GCS). To date, five different NFU1 pathogenic variants have been reported in 15 patients from 12 families. We report on seven new patients from five families carrying compound heterozygous or homozygous pathogenic NFU1 mutations identified by candidate gene screening and exome sequenc...
TTC19 deficiency is a progressive neurodegenerative disease associated with isolated mitochondria... more TTC19 deficiency is a progressive neurodegenerative disease associated with isolated mitochondrial respiratory chain (MRC) complex III deficiency and loss-of-function mutations in the TT19 gene in the few patients reported so far. We performed exome sequencing and selective mutational analysis of TTC19, respectively, in patients from three unrelated families presenting with initially unspecific clinical signs of muscular hypotonia and global developmental delay followed by regression, ataxia, loss of speech, and rapid neurological deterioration. One patient showed severe lactic acidosis at the neonatal age and during intercurrent illness. We identified homozygous mutations in all three index cases, in two families novel missense mutations (c.544 T > C/p.Leu185Pro; c.917 T > C/p.Leu324Pro). The younger sister of the severely affected patient 3 showed only mild delay of motor skills and muscular hypotonia so far but is also homozygous for the same mutation. Notably, one patient ...
Restless legs syndrome (RLS) is a sensorimotor disorder with an age-dependent prevalence of up to... more Restless legs syndrome (RLS) is a sensorimotor disorder with an age-dependent prevalence of up to 10% in the general population above 65 years of age. Affected individuals suffer from uncomfortable sensations and an urge to move in the lower limbs that occurs mainly in resting situations during the evening or at night. Moving the legs or walking leads to an improvement of symptoms. Concomitantly, patients report sleep disturbances with consequences such as reduced daytime functioning. We conducted a genome-wide association study (GWA) for RLS in 922 cases and 1,526 controls (using 301,406 SNPs) followed by a replication of 76 candidate SNPs in 3,935 cases and 5,754 controls, all of European ancestry. Herein, we identified six RLS susceptibility loci of genome-wide significance, two of them novel: an intergenic region on chromosome 2p14 (rs6747972, P = 9.03 × 10(-11), OR = 1.23) and a locus on 16q12.1 (rs3104767, P = 9.4 × 10(-19), OR = 1.35) in a linkage disequilibrium block of 140 ...
Defining the mitochondrial proteome is a prerequisite for fully understanding the organelles func... more Defining the mitochondrial proteome is a prerequisite for fully understanding the organelles function as well as mechanisms underlying mitochondrial pathology. The core functions of mitochondria include oxidative phosphorylation, amino acid metabolism, fatty acid oxidation, and ion homeostasis. In addition to these well-known functions, many crucial properties in cell signaling, cell differentiation and cell death are only now being elucidated, and with them the proteins involved. With the wealth of information arriving from single protein studies and sophisticated genome-wide approaches, MitoP2 was designed and is maintained to consolidate knowledge on mitochondrial proteins in one comprehensive database, thus making all pertinent data readily accessible (http://www.mitop2.de). Although the identification of the human mitochondrial proteome is ultimately the prime objective, integration of other species includes Saccharomyces cerevisiae, mouse, Arabidopsis thaliana, and Neurospora ...
Methods in molecular biology (Clifton, N.J.), 2007
The impact of mitochondria on several fundamental cellular processes is reflected in their involv... more The impact of mitochondria on several fundamental cellular processes is reflected in their involvement in the pathophysiology of common diseases such as Parkinson's disease, diabetes, and obesity and a wide range of monogenic disorders primarily associated with energy impairment or metabolic diseases. The importance of mitochondria is also reflected by the steep increase of proteins, which has been localized to this organelle. In yeast, more than 500 of the expected 700-800 mitochondrial proteins are already annotated. In the mammalian species, the expected numbers are estimated to be in the range of 1500-2000 proteins, and the currently annotated entries reach almost 700. In addition to the studies dealing with single proteins, there are many high-throughput approaches that improve the description of the mitochondrial proteome. They include computational predictions of signaling sequences, proteome mapping, mutant screening, expression profiling, protein-protein interaction, an...
Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was ... more Mmm1p is a protein required for maintenance of mitochondrial morphology in budding yeast. It was proposed that it is required to mediate the interaction of the mitochondrial outer membrane with the actin cytoskeleton. We report the cloning and characterization of MMM1 of the filamentous fungus Neurospora crassa, an organism that uses microtubules for mitochondrial transport. Mutation of the mmm-1 gene leads to a temperature-sensitive slow growth phenotype and female sterility. Mutant cells harbor abnormal giant mitochondria at all stages of the asexual life cycle, whereas actin filament-depolymerizing drugs have no effect on mitochondrial morphology. The MMM1 protein has a single transmembrane domain near the N terminus and exposes a large C-terminal domain to the cytosol. The protein can be imported into the outer membrane in a receptor-dependent manner. Our findings suggest that MMM1 is a factor of general importance for mitochondrial morphology independent of the cytoskeletal sys...
Genome-wide association studies (GWAS) have uncovered numerous genetic variants (SNPs) that are a... more Genome-wide association studies (GWAS) have uncovered numerous genetic variants (SNPs) that are associated with blood pressure (BP). Genetic variants may lead to BP changes by acting on intermediate molecular phenotypes such as coded protein sequence or gene expression, which in turn affect BP variability. Therefore, characterizing genes whose expression is associated with BP may reveal cellular processes involved in BP regulation and uncover how transcripts mediate genetic and environmental effects on BP variability. A meta-analysis of results from six studies of global gene expression profiles of BP and hypertension in whole blood was performed in 7017 individuals who were not receiving antihypertensive drug treatment. We identified 34 genes that were differentially expressed in relation to BP (Bonferroni-corrected p<0.05). Among these genes, FOS and PTGS2 have been previously reported to be involved in BP-related processes; the others are novel. The top BP signature genes in a...
The study was focused on leukoencephalopathies of unknown cause in order to define a novel, homog... more The study was focused on leukoencephalopathies of unknown cause in order to define a novel, homogeneous phenotype suggestive of a common genetic defect, based on clinical and MRI findings, and to identify the causal genetic defect shared by patients with this phenotype. Independent next-generation exome-sequencing studies were performed in 2 unrelated patients with a leukoencephalopathy. MRI findings in these patients were compared with available MRIs in a database of unclassified leukoencephalopathies; 11 patients with similar MRI abnormalities were selected. Clinical and MRI findings were investigated. Next-generation sequencing revealed compound heterozygous mutations in AARS2 encoding mitochondrial alanyl-tRNA synthetase in both patients. Functional studies in yeast confirmed the pathogenicity of the mutations in one patient. Sanger sequencing revealed AARS2 mutations in 4 of the 11 selected patients. The 6 patients with AARS2 mutations had childhood- to adulthood-onset signs of...
The proinflammatory cytokine interleukin (IL)-1β is implicated in the development of insulin resi... more The proinflammatory cytokine interleukin (IL)-1β is implicated in the development of insulin resistance and β-cell dysfunction, whereas higher circulating levels of IL-1 receptor antagonist (IL-1RA), an endogenous inhibitor of IL-1β, has been suggested to improve glycemia and β-cell function in patients with type 2 diabetes. To elucidate the protective role of IL-1RA, this study aimed to identify genetic determinants of circulating IL-1RA concentration and to investigate their associations with immunological and metabolic variables related to cardiometabolic risk. In the analysis of seven discovery and four replication cohort studies, two single nucleotide polymorphisms (SNPs) were independently associated with circulating IL-1RA concentration (rs4251961 at the IL1RN locus [n = 13,955, P = 2.76 × 10(-21)] and rs6759676, closest gene locus IL1F10 [n = 13,994, P = 1.73 × 10(-17)]). The proportion of the variance in IL-1RA explained by both SNPs combined was 2.0%. IL-1RA-raising allele...
Acyl-CoA dehydrogenase 9 (ACAD9) is an assembly factor for mitochondrial respiratory chain Comple... more Acyl-CoA dehydrogenase 9 (ACAD9) is an assembly factor for mitochondrial respiratory chain Complex I (CI), and ACAD9 mutations are recognized as a frequent cause of CI deficiency. ACAD9 also retains enzyme ACAD activity for long-chain fatty acids in vitro but the biological relevance of this function remains controversial partly because of the tissue-specificity of ACAD9 expression: high in liver and neurons and minimal in skin fibroblasts. In this study, we hypothesized that this enzymatic ACAD activity is required for full fatty acid oxidation capacity in cells expressing high levels of ACAD9, and that loss of this function is important in determining phenotype in ACAD9 deficient patients. First, we confirmed that HEK293 cells express ACAD9 abundantly. Then, we showed that ACAD9 knockout in HEK293 cells affected long-chain fatty acid oxidation along with Cl, both of which were rescued by wild-type ACAD9. Further, we evaluated whether the loss of ACAD9 enzymatic fatty acid oxidatio...
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