Subcomplex Iλ Specifically Controls Integrated Mitochondrial Functions in Caenorhabditis elegans

Complex I dysfunction is a common, heterogeneous cause of human mitochondrial disease having poorly understood pathogenesis. The extensive conservation of complex I composition between humans and Caenorhabditis elegans permits analysis of individual subunit contribution to mitochondrial functions at both the whole animal and mitochondrial levels. We provide the first experimentally-verified compilation of complex I composition in C. elegans, demonstrating 84% conservation with human complex I. Individual subunit contribution to mitochondrial respiratory capacity, holocomplex I assembly, and animal anesthetic behavior was studied in C. elegans by RNA interference-generated knockdown of nuclear genes encoding 28 complex I structural subunits and 2 assembly factors. Not all complex I subunits directly impact respiratory capacity. Subcomplex Iλ subunits along the electron transfer pathway specifically control whole animal anesthetic sensitivity and complex II upregulation, proportionate to their relative impairment of complex I-dependent oxidative capacity. Translational analysis of complex I dysfunction facilitates mechanistic understanding of individual gene contribution to mitochondrial disease. We demonstrate that functional consequences of complex I deficiency vary with the particular subunit that is defective

Gene Expression in a Drosophila Model of Mitochondrial Disease

Background A point mutation in the Drosophila gene technical knockout (tko), encoding mitoribosomal protein S12, was previously shown to cause a phenotype of respiratory chain deficiency, developmental delay, and neurological abnormalities similar to those presented in many human mitochondrial disorders, as well as defective courtship behavior. Methodology/Principal Findings Here, we describe a transcriptome-wide analysis of gene expression in tko25t mutant flies that revealed systematic and compensatory changes in the expression of genes connected with metabolism, including up-regulation of lactate dehydrogenase and of many genes involved in the catabolism of fats and proteins, and various anaplerotic pathways. Gut-specific enzymes involved in the primary mobilization of dietary fats and proteins, as well as a number of transport functions, were also strongly up-regulated, consistent with the idea that oxidative phosphorylation OXPHOS dysfunction is perceived physiologically as a starvation for particular biomolecules. In addition, many stress-response genes were induced. Other changes may reflect a signature of developmental delay, notably a down-regulation of genes connected with reproduction, including gametogenesis, as well as courtship behavior in males; logically this represents a programmed response to a mitochondrially generated starvation signal. The underlying signalling pathway, if conserved, could influence many physiological processes in response to nutritional stress, although any such pathway involved remains unidentified. Conclusions/Significance These studies indicate that general and organ-specific metabolism is transformed in response to mitochondrial dysfunction, including digestive and absorptive functions, and give important clues as to how novel therapeutic strategies for mitochondrial disorders might be developed.Public Library of Scienc

A Patient with Complex I Deficiency Caused by a Novel ACAD9 Mutation Not Responding to Riboflavin Treatment

Contains fulltext : 127628.pdf (publisher's version ) (Open Access)Here we report a patient with a new pathogenic mutation in ACAD9. Shortly after birth she presented with respiratory insufficiency and a high lactate level. At age 7 weeks, she was diagnosed with severe hypertrophic cardiomyopathy and she suffered from muscle weakness and hypotonia. Her condition deteriorated during intercurrent illnesses and she died at 6 months of age in cardiogenic shock. Analysis of respiratory chain activities in muscle and fibroblasts revealed an isolated complex I deficiency. A genome-wide screen for homozygosity revealed several homozygous regions. Four candidate genes were found and sequencing revealed a homozygous missense mutation in ACAD9. The mutation results in an Ala220Val amino acid substitution located near the catalytic core of ACAD9. SDS and BN-PAGE analysis showed severely decreased ACAD9 and complex I protein levels, and lentiviral complementation of patient fibroblasts partially rescued the complex I deficiency. Riboflavin supplementation did not ameliorate the complex I deficiency in patient fibroblasts. More than a dozen ACAD9 patients with complex I deficiency have been identified in the last 3 years, indicating that ACAD9 is important for complex I assembly, and that ACAD9 mutations are a relatively frequent cause of complex I deficiency

A new mitochondrial DNA mutation in ND3 gene causing severe Leigh syndrome with early lethality

We describe a new mitochondrial DNA mutation in a male infant who presented clinical and magnetic resonance imaging features of Leigh syndrome and died at the age of 9 mo. The patient's development was reportedly normal in the first months of life. At the age of 5 mo, he presented severe generalized hypotonia, nystagmus, and absent eye contact. Laboratory examination showed increased lactate and pyruvate in both serum and cerebrospinal fluid. Brain magnetic resonance imaging revealed multiple necrotic lesions in the basal ganglia, brain stem, and thalamus. Muscle histopathology was unremarkable, whereas respiratory chain enzyme analysis revealed a severe complex I deficiency. The patient died after an acidotic coma at age 9 mo. Sequence analysis of the entire mtDNA disclosed a new T10158C mutation with variable tissue heteroplasm (muscle: 83%; blood: 48%). The mutation was undetectable in the blood of his unaffected mother. The transition changes a serine residue into a proline, in a highly conserved region of the NADH dehydrogenase subunit 3 (ND3). This is the first description of a mitochondrial ND3 gene in Leigh syndrome with early lethality

Human CIA30 is involved in the early assembly of mitochondrial complex I and mutations in its gene cause disease

In humans, complex I of the respiratory chain is composed of seven mitochondrial DNA (mtDNA)-encoded and 38 nuclear-encoded subunits that assemble together in a process that is poorly defined. To date, only two complex I assembly factors have been identified and how each functions is not clear. Here, we show that the human complex I assembly factor CIA30 (complex I intermediate associated protein) associates with newly translated mtDNA-encoded complex I subunits at early stages in their assembly before dissociating at a later stage. Using antibodies we identified a CIA30-deficient patient who presented with cardioencephalomyopathy and reduced levels and activity of complex I. Genetic analysis revealed the patient had mutations in both alleles of the NDUFAF1 gene that encodes CIA30. Complex I assembly in patient cells was defective at early stages with subunits being degraded. Complementing the deficiency in patient fibroblasts with normal CIA30 using a novel lentiviral system restored steady-state complex I levels. Our results indicate that CIA30 is a crucial component in the early assembly of complex I and mutations in its gene can cause mitochondrial disease