RESUMO
Acyl-CoA dehydrogenase 9 (ACAD9) is a recently identified member of the acyl-CoA dehydrogenase family. It closely resembles very long-chain acyl-CoA dehydrogenase (VLCAD), involved in mitochondrial beta oxidation of long-chain fatty acids. Contrary to its previously proposed involvement in fatty acid oxidation, we describe a role for ACAD9 in oxidative phosphorylation. ACAD9 binds complex I assembly factors NDUFAF1 and Ecsit and is specifically required for the assembly of complex I. Furthermore, ACAD9 mutations result in complex I deficiency and not in disturbed long-chain fatty acid oxidation. This strongly contrasts with its evolutionary ancestor VLCAD, which we show is not required for complex I assembly and clearly plays a role in fatty acid oxidation. Our results demonstrate that two closely related metabolic enzymes have diverged at the root of the vertebrate lineage to function in two separate mitochondrial metabolic pathways and have clinical implications for the diagnosis of complex I deficiency.
Assuntos
Acil-CoA Desidrogenases/metabolismo , Complexo I de Transporte de Elétrons/biossíntese , Fosforilação Oxidativa , Acil-CoA Desidrogenase de Cadeia Longa/química , Acil-CoA Desidrogenase de Cadeia Longa/classificação , Acil-CoA Desidrogenase de Cadeia Longa/genética , Acil-CoA Desidrogenase de Cadeia Longa/metabolismo , Acil-CoA Desidrogenases/química , Acil-CoA Desidrogenases/classificação , Acil-CoA Desidrogenases/genética , Proteínas Adaptadoras de Transdução de Sinal/genética , Proteínas Adaptadoras de Transdução de Sinal/metabolismo , Sequência de Aminoácidos , Animais , Células Cultivadas , Ácidos Graxos/metabolismo , Feminino , Fibroblastos/citologia , Fibroblastos/fisiologia , Humanos , Lactente , Masculino , Mitocôndrias/metabolismo , Modelos Moleculares , Dados de Sequência Molecular , Mutação , NADH Desidrogenase/genética , NADH Desidrogenase/metabolismo , Oxirredução , Filogenia , Gravidez , Estrutura Terciária de Proteína , Interferência de RNA , Análise de Sequência , Análise de Sequência de DNARESUMO
Mitochondrial mutations have previously been reported anecdotally in families with maternally inherited, nonsyndromic hearing impairment. To ascertain the contribution of mitochondrial mutations to postlingual but early-onset, nonsyndromic hearing impairment, we screened patients collected from within two different populations (southern Italy and UK) for previously reported mtDNA mutations associated with hearing disorders. Primer extension (SNP analysis) was used to screen for specific mutations, revealing cases of heteroplasmy and its extent. The most frequently implicated tRNA genes, Leu(UUR) and Ser(UCN), were also sequenced in all Italian patients. All tRNA genes were sequenced in those UK patients showing the clearest likelihood of maternal inheritance. Causative mtDNA mutations were found in approximately 5% of patients in both populations, representing almost 10% of cases that were clearly familial. Age of onset, where known, was generally before adulthood, and hearing loss was typically progressive. Haplogroup analysis revealed a possible excess of haplogroup cluster HV in the patients, compared with population controls, but of borderline statistical significance. In contrast, we did not find any of the previously reported mtDNA mutations, nor a significant deviation from haplogroup cluster frequencies typical of the control population, in patients with late adult-onset hearing loss (age-related hearing impairment) from the UK or Finland.
