cytochrome-c-t and Ataxia

To describe the clinical features, muscle pathological characteristics, and molecular studies of a patient with a mutation in the gene encoding the accessory subunit (p55) of polymerase gamma (POLG2) and a mutation in the OPA1 gene.. Clinical examination and morphological, biochemical, and molecular analyses.. Tertiary care university hospitals and molecular genetics and scientific computing laboratory.. A 42-year-old man experienced hearing loss, progressive external ophthalmoplegia (PEO), loss of central vision, macrocytic anemia, and hypogonadism. His family history was negative for neurological disease, and his serum lactate level was normal.. A muscle biopsy specimen showed scattered intensely succinate dehydrogenase-positive and cytochrome-c oxidase-negative fibers. Southern blot of muscle mitochondrial DNA showed multiple deletions. The results of screening for mutations in the nuclear genes associated with PEO and multiple mitochondrial DNA deletions, including those in POLG (polymerase gamma gene), ANT1 (gene encoding adenine nucleotide translocator 1), and PEO1, were negative, but sequencing of POLG2 revealed a G1247C mutation in exon 7, resulting in the substitution of a highly conserved glycine with an alanine at codon 416 (G416A). Because biochemical analysis of the mutant protein showed no alteration in chromatographic properties and normal ability to protect the catalytic subunit from N-ethylmaleimide, we also sequenced the OPA1 gene and identified a novel heterozygous mutation (Y582C).. Although we initially focused on the mutation in POLG2, the mutation in OPA1 is more likely to explain the late-onset PEO and multisystem disorder in this patient.

Topics: Adult; Anemia, Macrocytic; Ataxia; Biopsy; Blotting, Southern; Cytochromes c; DNA Polymerase gamma; DNA-Directed DNA Polymerase; DNA, Mitochondrial; Dynamins; GTP Phosphohydrolases; Hearing Loss; Humans; Hypogonadism; Immunohistochemistry; Lactic Acid; Male; Models, Molecular; Muscle Fibers, Skeletal; Muscle, Skeletal; Mutation, Missense; Oncogene Protein p55(v-myc); Ophthalmoplegia; Reverse Transcriptase Polymerase Chain Reaction; Succinate Dehydrogenase; Vision Disorders

Apoptosis can be mediated by mechanisms other than the traditional caspase-mediated cleavage cascade. There is growing recognition that alternative proteolytic enzymes such as the lysosomal cathepsin proteases can initiate or propagate proapoptotic signals, but it is currently unclear how cathepsins achieve these actions. Recent in vitro evidence suggests that cathepsins cleave the proapoptotic Bcl-2 family member Bid, thereby activating it and allowing it to induce the mitochondrial release of cytochrome c and subsequent apoptosis. We have tested this hypothesis in vivo by breeding mice that lack cathepsin inhibition (cystatin B-deficient mice) to Bid-deficient mice, to determine whether the apoptosis caused by cathepsins is dependent on Bid signaling. We found that cathepsins are still able to promote apoptosis even in the absence of Bid, indicating that these proteases mediate apoptosis via a different pathway, or that some other molecule can functionally substitute for Bid in this system.

Topics: Age Factors; Animals; Apoptosis; Ataxia; BH3 Interacting Domain Death Agonist Protein; Blotting, Western; Carrier Proteins; Cathepsins; Cell Death; Cerebellum; Cystatin B; Cystatins; Cytochromes c; Disease Models, Animal; Electroencephalography; Genotype; In Situ Nick-End Labeling; Lysosomes; Mice; Mice, Knockout; Mitochondria; Myoclonic Epilepsies, Progressive; Phenotype; Proto-Oncogene Proteins c-bcl-2; Signal Transduction