bims-resufa Biomed News
on Respiratory supercomplex factors
Issue of 2019‒12‒22
three papers selected by
Vera Strogolova
Strong Microbials, Inc

  1. Cell Rep. 2019 Dec 17. pii: S2211-1247(19)31537-2. [Epub ahead of print]29(12): 3825-3834.e4
    Murgia M, Tan J, Geyer PE, Doll S, Mann M, Klopstock T.
      The mosaic distribution of cytochrome c oxidase+ (COX+) and COX- muscle fibers in mitochondrial disorders allows the sampling of fibers with compensated and decompensated mitochondrial function from the same individual. We apply laser capture microdissection to excise individual COX+ and COX- fibers from the biopsies of mitochondrial myopathy patients. Using mass spectrometry-based proteomics, we quantify >4,000 proteins per patient. While COX+ fibers show a higher expression of respiratory chain components, COX- fibers display protean adaptive responses, including upregulation of mitochondrial ribosomes, translation proteins, and chaperones. Upregulated proteins include C1QBP, required for mitoribosome formation and protein synthesis, and STOML2, which organizes cardiolipin-enriched microdomains and the assembly of respiratory supercomplexes. Factoring in fast/slow fiber type, COX- slow fibers show a compensatory upregulation of beta-oxidation, the AAA+ protease AFG3L1, and the OPA1-dependent cristae remodeling program. These findings reveal compensatory mechanisms in muscle fibers struggling with energy shortage and metabolic stress.
    Keywords:  COX; CPEO; chronic progressive external ophthalmoplegia; cytochrome c oxidase; laser microdissection; mass spectrometry; mitochondrial myopathy; proteomics; single muscle fibers
  2. Mitochondrion. 2019 Dec 17. pii: S1567-7249(19)30001-7. [Epub ahead of print]
    Erickson RP, Aras S, Purandare N, Hüttemann M, Liu J, Dragotto J, Fiorenza MT, Grossman LI.
      It has long been known that there is decreased mitochondrial function in several tissues of Niemann-Pick C1 model mice and cultured cells. These defects contribute to the accumulation of Reactive Oxygen Species (ROS) and tissue damage. It is also well established that there is increased unesterified cholesterol, stored in late endosomes/lysosomes, in many tissues in mutant humans, mouse models, and mutant cultured cells. Using a mouse model with an NPC1 point mutation that is more typical of the most common form of the disease, and highly purified liver mitochondria, we find markedly decreased mitochondrial membrane cholesterol. This is compared to previous reports of increased mitochondrial membrane cholesterol. We also find that, although in wild-type or heterozygous mitochondria cytochrome c oxidase (COX) activity decreases with age as expected, surprisingly, COX activity in homozygous mutant mice improves with age. COX activity is less than half of wild-type amounts in young mutant mice but later reaches wild-type levels while total liver cholesterol is decreasing. Mutant mice also contain a decreased number of mitochondria that are morphologically abnormal. We suggest that the decreased mitochondrial membrane cholesterol is causative for the mitochondrial energy defects. In addition, we find that the mitochondrial stress regulator protein MNRR1 can stimulate NPC1 synthesis and is deficient in mutant mouse livers. Furthermore, the age curve of MNRR1 deficiency paralleled levels of total cholesterol. The role of such altered mitochondria in initiating the abnormal autophagy and neuroinflammation found in NPC1 mouse models is discussed.
    Keywords:  Niemann-Pick C1; cytochrome c oxidase; liver; mitochondria; mitophagy; unesterified cholesterol
  3. Biol Open. 2019 Dec 18. pii: bio.047936. [Epub ahead of print]
    Hara T, Shibata Y, Amagai R, Okado-Matsumoto A.
      The in-gel activity assay (IGA) is a powerful technique that uses enzymatic activity and compares intensities of detected bands in mitochondrial respiratory chain supercomplexes, and it is applicable to eukaryotic organisms. However, no IGA has been established for complex III because of the difficulty of access by ubiquinol, a substrate for complex III. Herein, we demonstrate that cytochrome c (Cyt c) showed peroxidase activity on IGA as a component of complexes III and IV. We used pre-incubation with sodium dodecyl sulfate (SDS) before IGA to loosen complexes in the gel after high-resolution clear native polyacrylamide gel electrophoresis (hrCN-PAGE), a refinement of blue native PAGE. The signals of IGA based on peroxidase activity were obtained using enhanced chemiluminescence solution. Then, the gel was directly used in western blotting or hrCN/SDS 2-dimensional PAGE. Our findings indicate that IGA for Cyt c reflected the indirect activity of complexes III and IV.
    Keywords:  Cytochrome c; High-resolution clear native polyacrylamide gel electrophoresis; In-gel activity assay; Mitochondrial respiratory chain complexes