bims-mitran 2022-01-09 papers

Issue of 2022–01–09
three papers selected by
Andreas Kohler, Stockholm University

BMC Biol. 2022 Jan 07. 20(1): 12

mtIF3 is locally translated in axons and regulates mitochondrial translation for axonal growth.

Soyeon Lee, Dongkeun Park, Chunghun Lim, Jae-Ick Kim, Kyung-Tai Min.

BACKGROUND: The establishment and maintenance of functional neural connections relies on appropriate distribution and localization of mitochondria in neurites, as these organelles provide essential energy and metabolites. In particular, mitochondria are transported to axons and support local energy production to maintain energy-demanding neuronal processes including axon branching, growth, and regeneration. Additionally, local protein synthesis is required for structural and functional changes in axons, with nuclear-encoded mitochondrial mRNAs having been found localized in axons. However, it remains unclear whether these mRNAs are locally translated and whether the potential translated mitochondrial proteins are involved in the regulation of mitochondrial functions in axons. Here, we aim to further understand the purpose of such compartmentalization by focusing on the role of mitochondrial initiation factor 3 (mtIF3), whose nuclear-encoded transcripts have been shown to be present in axonal growth cones.
RESULTS: We demonstrate that brain-derived neurotrophic factor (BDNF) induces local translation of mtIF3 mRNA in axonal growth cones. Subsequently, mtIF3 protein is translocated into axonal mitochondria and promotes mitochondrial translation as assessed by our newly developed bimolecular fluorescence complementation sensor for the assembly of mitochondrial ribosomes. We further show that BDNF-induced axonal growth requires mtIF3-dependent mitochondrial translation in distal axons.
CONCLUSION: We describe a previously unknown function of mitochondrial initiation factor 3 (mtIF3) in axonal protein synthesis and development. These findings provide insight into the way neurons adaptively control mitochondrial physiology and axonal development via local mtIF3 translation.

Keywords: Axon development; Bimolecular fluorescence complementation; Local translation; Mitochondria; Mitochondrial translation

DOI: https://doi.org/10.1186/s12915-021-01215-w

Mol Neurobiol. 2022 Jan 03.

Reduced mtDNA Copy Number in the Prefrontal Cortex of C9ORF72 Patients.

Maria Isabel Alvarez-Mora, Petar Podlesniy, Teresa Riazuelo, Laura Molina-Porcel, Ellen Gelpi, Laia Rodriguez-Revenga.

Hexanucleotide repeat expansion in C9ORF72 gene is the most common genetic cause of amyotrophic lateral sclerosis and frontotemporal dementia (C9ALS/FTD). Loss of C9ORF72 protein function and a toxic gain-of-function directly by the RNA or RAN translation have been proposed as triggering pathological mechanisms, along with the accumulation of TDP-43 protein. In addition, mitochondrial defects have been described to be a major driver of disease initiation. Mitochondrial DNA copy number has been proposed as a useful biomarker of mitochondrial dysfunction. The aim of our study was to determine the presence of mtDNA copy number alterations in C9ALS/FTD patients. Therefore, we assessed mtDNA copy number in postmortem prefrontal cortex from 18 C9ORF72 brain donors and 9 controls using digital droplet PCR. A statistically significant decrease of 50% was obtained when comparing C9ORF72 samples and controls. This decrease was independent of age and sex. The reduction of mtDNA copy number was found to be higher in patients' samples presenting abundant TDP-43 protein inclusions. A growing number of studies demonstrated the influence of mtDNA copy number reduction on neurodegeneration. Our results provide new insights into the role of mitochondrial dysfunction in the pathogenesis of C9ALS/FTD.

Keywords: C9ALS/FTD; C9ORF72; Neurodegeneration; ddPCR; mtDNA copy number

DOI: https://doi.org/10.1007/s12035-021-02673-7

Hum Hered. 2022 Jan 06.

Screening for Mitochondrial tRNA Mutations in 318 Patients with Dilated Cardiomyopathy.

Yujuan Qi, Zhenhua Wu, Yaobang Bai, Yan Jiao, Peijun Li.

OBJECTIVES: Dilated cardiomyopathy (DCM) is a complex cardiovascular disease with unknown etiology. Although nuclear genes play active roles in DCM, mitochondrial dysfunction was believed to be involved in the pathogenesis of DCM. The objective of this study is to analysis the association between mitochondrial tRNA (mt-tRNA) mutations and DCM.
MATERIAL AND METHODS: We performed a mutational analysis of mt-tRNA genes in a cohort of 318 patients with DCM and 200 age- and gender-matched control subjects. To further assess their pathogenicity, phylogenetic analysis and mitochondrial functions including mtDNA copy number, ATP and ROS were analyzed.
RESULTS: 7 possible pathogenic mutations: MT-TL1 3302A>G, MT-TI 4295A>G, MT-TM 4435A>G, MT-TA 5655T>C, MT-TH 12201T>C, MT-TE 14692A>G and MT-TT 15927G>A were identified in DCM group but absent in controls. These mutations occurred at extremely conserved nucleotides of corresponding tRNAs, and led to the failure in tRNAs metabolism. Moreover, a significant reduction in ATP and mtDNA copy number, whereas a markedly increased in ROS level were observed in polymononuclear leukocytes (PMNs) derived from the DCM patients carrying these mt-tRNA mutations, suggesting that these mutations may cause mitochondrial dysfunction that was responsible for DCM.
CONCLUSIONS: Our data indicated that mt-tRNA mutations may be the molecular basis for DCM, which shaded novel insight into the pathophysiology of DCM that was manifestated by mitochondrial dysfunction.

DOI: https://doi.org/10.1159/000521615