bims-cytox1 2021-06-27 papers

Issue of 2021–06–27
five papers selected by
Gavin McStay, Staffordshire University

Invest Ophthalmol Vis Sci. 2021 Jun 01. 62(7): 22

Leber's Hereditary Optic Neuropathy Arising From the Synergy Between ND1 3635G>A Mutation and Mitochondrial YARS2 Mutations.

Xiaofen Jin, Juanjuan Zhang, Qiuzi Yi, Feilong Meng, Jialing Yu, Yanchun Ji, Jun Q Mo, Yi Tong, Pingping Jiang, Min-Xin Guan.

Purpose: To investigate the mechanism underlying the synergic interaction between Leber's hereditary optic neuropathy (LHON)-associated ND1 and mitochondrial tyrosyl-tRNA synthetase (YARS2) mutations.
Methods: Molecular dynamics simulation and differential scanning fluorimetry were used to evaluate the structure and stability of proteins. The impact of ND1 3635G>A and YARS2 p.G191V mutations on the oxidative phosphorylation machinery was evaluated using blue native gel electrophoresis and enzymatic activities assays. Assessment of reactive oxygen species (ROS) production in cell lines was performed by flow cytometry with MitoSOX Red reagent. Analysis of effect of mutations on autophagy was undertaken via flow cytometry for autophagic flux.
Results: Members of one Chinese family bearing both the YARS2 p.191Gly>Val and m.3635G>A mutations exhibited much higher penetrance of optic neuropathy than those pedigrees carrying only the m.3635G>A mutation. The m.3635G>A (p.Ser110Asn) mutation altered the ND1 structure and function, whereas the p.191Gly>Val mutation affected the stability of YARS2. Lymphoblastoid cell lines harboring both m.3635G>A and p.191Gly>Val mutations revealed more reductions in the levels of mitochondrion-encoding ND1 and CO2 than cells bearing only the m.3635G>A mutation. Strikingly, both m.3635G>A and p.191Gly>Val mutations exhibited decreases in the nucleus-encoding subunits of complex I and IV. These deficiencies manifested greater defects in the stability and activities of complex I and complex IV and overproduction of ROS and promoted greater autophagy in cell lines harboring both m.3635G>A and p.191Gly>Val mutations compared with cells bearing only the m.3635G>A mutation.
Conclusions: Our findings provide new insights into the pathophysiology of LHON arising from the synergy between ND1 3635G>A mutation and mitochondrial YARS2 mutations.

DOI: https://doi.org/10.1167/iovs.62.7.22

Hum Mol Genet. 2021 Jun 24. pii: ddab156. [Epub ahead of print]

Mitochondrial DNA disorders: From pathogenic variants to preventing transmission.

Tiago M Bernardino Gomes, Yi Shiau Ng, Sarah J Pickett, Doug M Turnbull, Amy E Vincent.

Mitochondrial DNA (mtDNA) disorders are recognised as one of the most common causes of inherited metabolic disorders. The mitochondrial genome occurs in multiple copies resulting in both homoplasmic and heteroplasmic pathogenic mtDNA variants. A biochemical defect arises when the pathogenic variant level reaches a threshold, which differs between variants. Moreover, variants can segregate, clonally expand, or be lost from cellular populations resulting in a dynamic and tissue-specific mosaic pattern of oxidative deficiency. MtDNA is maternally inherited but transmission patterns of heteroplasmic pathogenic variants are complex. During oogenesis, a mitochondrial bottleneck results in offspring with widely differing variant levels to their mother, whilst highly deleterious variants, such as deletions, are not transmitted. Complemented by a complex interplay between mitochondrial and nuclear genomes, these peculiar genetics produce marked phenotypic variation, posing challenges to the diagnosis and clinical management of patients. Novel therapeutic compounds and several genetic therapies are currently under investigation, but proven disease-modifying therapies remain elusive. Women who carry pathogenic mtDNA variants require bespoke genetic counselling to determine their reproductive options. Recent advances in in vitro fertilisation techniques, have greatly improved reproductive choices, but are not without their challenges. Since the first pathogenic mtDNA variants were identified over thirty years ago, there has been remarkable progress in our understanding of these diseases. However, many questions remain unanswered and future studies are required to investigate the mechanisms of disease progression and to identify new disease-specific therapeutic targets.

DOI: https://doi.org/10.1093/hmg/ddab156

Lancet Neurol. 2021 Jul;pii: S1474-4422(21)00098-3. [Epub ahead of print]20(7): 573-584

Mitochondrial disease in adults: recent advances and future promise.

Yi Shiau Ng, Laurence A Bindoff, Gráinne S Gorman, Thomas Klopstock, Cornelia Kornblum, Michelangelo Mancuso, Robert McFarland, Carolyn M Sue, Anu Suomalainen, Robert W Taylor, David R Thorburn, Doug M Turnbull.

Mitochondrial diseases are some of the most common inherited neurometabolic disorders, and major progress has been made in our understanding, diagnosis, and treatment of these conditions in the past 5 years. Development of national mitochondrial disease cohorts and international collaborations has changed our knowledge of the spectrum of clinical phenotypes and natural history of mitochondrial diseases. Advances in high-throughput sequencing technologies have altered the diagnostic algorithm for mitochondrial diseases by increasingly using a genetics-first approach, with more than 350 disease-causing genes identified to date. While the current management strategy for mitochondrial disease focuses on surveillance for multisystem involvement and effective symptomatic treatment, new endeavours are underway to find better treatments, including repurposing current drugs, use of novel small molecules, and gene therapies. Developments made in reproductive technology offer women the opportunity to prevent transmission of DNA-related mitochondrial disease to their children.

DOI: https://doi.org/10.1016/S1474-4422(21)00098-3

Dtsch Arztebl Int. 2021 Oct 01. pii: arztebl.m2021.0251. [Epub ahead of print]

Mitochondrial Disorders.

Thomas Klopstock, Claudia Priglinger, Ali Yilmaz, Cornelia Kornblum, Felix Distelmaier, Holger Prokisch.

BACKGROUND: Mitochondrial disorders are among the most common heritable diseases, with an overall lifetime risk of approximately one in 1500. Nonetheless, their diagnosis is often missed because of their extreme phenotypic and genotypic heterogeneity.
METHODS: This review is based on publications retrieved by a selective literature search on the clinical features, genetics, pathogenesis, diagnosis, and treatment of mitochondrial diseases.
RESULTS: Pathogenic defects of energy metabolism have been described to date in over 400 genes. Only a small number of these genes lie in the mitochondrial DNA; the corresponding diseases are either maternally inherited or of sporadic distribution. The remaining diseaseassociated genes are coded in nuclear DNA and cause diseases that are inherited according to Mendelian rules, mostly autosomal recessive. The most severely involved organs are generally those with the highest energy requirements, including the brain, the sensory epithelia, and the extraocular, cardiac, and skeletal musculature. Typical manifestations include epileptic seizures, stroke-like episodes, hearing loss, retinopathy, external ophthalmoparesis, exercise intolerance, and diabetes mellitus. More than two manifestations of these types should arouse suspicion of a disease of energy metabolism. The severity of mitochondrial disorders ranges from very severe disease, already evident in childhood, to relatively mild disease arising in late adulthood. The diagnosis is usually confirmed with molecular-genetic methods. Symptomatic treatment can improve patients' quality of life. The only disease-modifying treatment that has been approved to date is idebenone for the treatment of Leber hereditary optic neuropathy. Intravitreal gene therapy has also been developed for the treatment of this disease; its approval by the European Medicines Agency is pending.
CONCLUSION: Patients with mitochondrial diseases have highly varied manifestations and can thus present to physicians in practically any branch of medicine. A correct diagnosis is the prerequisite for genetic counseling and for the initiation of personalized treatment.

DOI: https://doi.org/10.3238/arztebl.m2021.0251

Dis Model Mech. 2021 Jun 01. pii: dmm048912. [Epub ahead of print]14(6):

Mitochondrial function in development and disease.

Marlies P Rossmann, Sonia M Dubois, Suneet Agarwal, Leonard I Zon.

Mitochondria are organelles with vital functions in almost all eukaryotic cells. Often described as the cellular 'powerhouses' due to their essential role in aerobic oxidative phosphorylation, mitochondria perform many other essential functions beyond energy production. As signaling organelles, mitochondria communicate with the nucleus and other organelles to help maintain cellular homeostasis, allow cellular adaptation to diverse stresses, and help steer cell fate decisions during development. Mitochondria have taken center stage in the research of normal and pathological processes, including normal tissue homeostasis and metabolism, neurodegeneration, immunity and infectious diseases. The central role that mitochondria assume within cells is evidenced by the broad impact of mitochondrial diseases, caused by defects in either mitochondrial or nuclear genes encoding for mitochondrial proteins, on different organ systems. In this Review, we will provide the reader with a foundation of the mitochondrial 'hardware', the mitochondrion itself, with its specific dynamics, quality control mechanisms and cross-organelle communication, including its roles as a driver of an innate immune response, all with a focus on development, disease and aging. We will further discuss how mitochondrial DNA is inherited, how its mutation affects cell and organismal fitness, and current therapeutic approaches for mitochondrial diseases in both model organisms and humans.

Keywords: Mitochondrial diseases; Mitochondrial fusion and fission; Mitochondrial unfolded protein response; Mitophagy; mtDNA heteroplasmy and inheritance; mtDNA-mediated innate immune response

DOI: https://doi.org/10.1242/dmm.048912