bims-cytox1 2022-12-04 papers

Issue of 2022‒12‒04
three papers selected by
Gavin McStay
Liverpool John Moores University

Brain Pathol. 2022 Nov 30. e13134

Leigh syndrome is the main clinical characteristic of PTCD3 deficiency.

Gerard Muñoz-Pujol, Juan D Ortigoza-Escobar, Abraham J Paredes-Fuentes, Cristina Jou, Olatz Ugarteburu, Laura Gort, Delia Yubero, Angels García-Cazorla, Mar O'Callaghan, Jaume Campistol, Jordi Muchart, Vicente A Yépez, Mirjana Gusic, Julien Gagneur, Holger Prokisch, Rafael Artuch, Antonia Ribes, Roser Urreizti, Frederic Tort.

Mitochondrial translation defects are a continuously growing group of disorders showing a large variety of clinical symptoms including a wide range of neurological abnormalities. To date, mutations in PTCD3, encoding a component of the mitochondrial ribosome, have only been reported in a single individual with clinical evidence of Leigh syndrome. Here, we describe three additional PTCD3 individuals from two unrelated families, broadening the genetic and phenotypic spectrum of this disorder, and provide definitive evidence that PTCD3 deficiency is associated with Leigh syndrome. The patients presented in the first months of life with psychomotor delay, respiratory insufficiency and feeding difficulties. The neurologic phenotype included dystonia, optic atrophy, nystagmus and tonic-clonic seizures. Brain MRI showed optic nerve atrophy and thalamic changes, consistent with Leigh syndrome. WES and RNA-seq identified compound heterozygous variants in PTCD3 in both families: c.[1453-1G>C];[1918C>G] and c.[710del];[902C>T]. The functional consequences of the identified variants were determined by a comprehensive characterization of the mitochondrial function. PTCD3 protein levels were significantly reduced in patient fibroblasts and, consistent with a mitochondrial translation defect, a severe reduction in the steady state levels of complexes I and IV subunits was detected. Accordingly, the activity of these complexes was also low, and high-resolution respirometry showed a significant decrease in the mitochondrial respiratory capacity. Functional complementation studies demonstrated the pathogenic effect of the identified variants since the expression of wild-type PTCD3 in immortalized fibroblasts restored the steady-state levels of complexes I and IV subunits as well as the mitochondrial respiratory capacity. Additionally, minigene assays demonstrated that three of the identified variants were pathogenic by altering PTCD3 mRNA processing. The fourth variant was a frameshift leading to a truncated protein. In summary, we provide evidence of PTCD3 involvement in human disease confirming that PTCD3 deficiency is definitively associated with Leigh syndrome.

Keywords: Leigh syndrome; PTCD3; mitochondria; mitochondrial disorder; mitochondrial translation

DOI: https://doi.org/10.1111/bpa.13134

Trends Endocrinol Metab. 2022 Nov 23. pii: S1043-2760(22)00199-0. [Epub ahead of print]

Mitochondrial copper in human genetic disorders.

Natalie M Garza, Abhinav B Swaminathan, Krishna P Maremanda, Mohammad Zulkifli, Vishal M Gohil.

Copper is an essential micronutrient that serves as a cofactor for enzymes involved in diverse physiological processes, including mitochondrial energy generation. Copper enters cells through a dedicated copper transporter and is distributed to intracellular cuproenzymes by copper chaperones. Mitochondria are critical copper-utilizing organelles that harbor an essential cuproenzyme cytochrome c oxidase, which powers energy production. Mutations in copper transporters and chaperones that perturb mitochondrial copper homeostasis result in fatal genetic disorders. Recent studies have uncovered the therapeutic potential of elesclomol, a copper ionophore, for the treatment of copper deficiency disorders such as Menkes disease. Here we review the role of copper in mitochondrial energy metabolism in the context of human diseases and highlight the recent developments in copper therapeutics.

Keywords: Menkes disease; Wilson disease; copper; elesclomol; mitochondria; mitochondrial disease

DOI: https://doi.org/10.1016/j.tem.2022.11.001

Front Mol Biosci. 2022 ;9 1037941

The mitochondrial Cu+ transporter PiC2 (SLC25A3) is a target of MTF1 and contributes to the development of skeletal muscle in vitro.

Cat McCann, Michael Quinteros, Ifeoluwa Adelugba, Marcos N Morgada, Aida R Castelblanco, Emily J Davis, Antonio Lanzirotti, Sarah J Hainer, Alejandro J Vila, Juan G Navea, Teresita Padilla-Benavides.

The loading of copper (Cu) into cytochrome c oxidase (COX) in mitochondria is essential for energy production in cells. Extensive studies have been performed to characterize mitochondrial cuproenzymes that contribute to the metallation of COX, such as Sco1, Sco2, and Cox17. However, limited information is available on the upstream mechanism of Cu transport and delivery to mitochondria, especially through Cu-impermeable membranes, in mammalian cells. The mitochondrial phosphate transporter SLC25A3, also known as PiC2, binds Cu+ and transports the ion through these membranes in eukaryotic cells, ultimately aiding in the metallation of COX. We used the well-established differentiation model of primary myoblasts derived from mouse satellite cells, wherein Cu availability is necessary for growth and maturation, and showed that PiC2 is a target of MTF1, and its expression is both induced during myogenesis and favored by Cu supplementation. PiC2 deletion using CRISPR/Cas9 showed that the transporter is required for proliferation and differentiation of primary myoblasts, as both processes are delayed upon PiC2 knock-out. The effects of PiC2 deletion were rescued by the addition of Cu to the growth medium, implying the deleterious effects of PiC2 knockout in myoblasts may be in part due to a failure to deliver sufficient Cu to the mitochondria, which can be compensated by other mitochondrial cuproproteins. Co-localization and co-immunoprecipitation of PiC2 and COX also suggest that PiC2 may participate upstream in the copper delivery chain into COX, as verified by in vitro Cu+-transfer experiments. These data indicate an important role for PiC2 in both the delivery of Cu to the mitochondria and COX, favoring the differentiation of primary myoblasts.

Keywords: MTF1; PiC2; SLC25A3; copper transport; cytochrome c oxidase; mitochondria

DOI: https://doi.org/10.3389/fmolb.2022.1037941