bims-midmar 2022-02-27 papers

Issue of 2022‒02‒27
four papers selected by
Flavia Söllner
Ludwig-Maximilians University

Biomedicines. 2022 Feb 18. pii: 490. [Epub ahead of print]10(2):

The Mitochondrial Genome in Aging and Disease and the Future of Mitochondrial Therapeutics.

Sanjana Saravanan, Caitlin J Lewis, Bhavna Dixit, Matthew S O'Connor, Alexandra Stolzing, Amutha Boominathan.

Mitochondria are intracellular organelles that utilize nutrients to generate energy in the form of ATP by oxidative phosphorylation. Mitochondrial DNA (mtDNA) in humans is a 16,569 base pair double-stranded circular DNA that encodes for 13 vital proteins of the electron transport chain. Our understanding of the mitochondrial genome's transcription, translation, and maintenance is still emerging, and human pathologies caused by mtDNA dysfunction are widely observed. Additionally, a correlation between declining mitochondrial DNA quality and copy number with organelle dysfunction in aging is well-documented in the literature. Despite tremendous advancements in nuclear gene-editing technologies and their value in translational avenues, our ability to edit mitochondrial DNA is still limited. In this review, we discuss the current therapeutic landscape in addressing the various pathologies that result from mtDNA mutations. We further evaluate existing gene therapy efforts, particularly allotopic expression and its potential to become an indispensable tool for restoring mitochondrial health in disease and aging.

Keywords: allotopic expression; gene therapy; mitochondria; mitochondrial diseases; mtDNA; mtDNA editing; mtDNA mutations

DOI: https://doi.org/10.3390/biomedicines10020490

Nucleic Acids Res. 2022 Feb 22. pii: gkac103. [Epub ahead of print]

Mechanisms of mitochondrial promoter recognition in humans and other mammalian species.

Angelica Zamudio-Ochoa, Yaroslav I Morozov, Azadeh Sarfallah, Michael Anikin, Dmitry Temiakov.

Recognition of mammalian mitochondrial promoters requires the concerted action of mitochondrial RNA polymerase (mtRNAP) and transcription initiation factors TFAM and TFB2M. In this work, we found that transcript slippage results in heterogeneity of the human mitochondrial transcripts in vivo and in vitro. This allowed us to correctly interpret the RNAseq data, identify the bona fide transcription start sites (TSS), and assign mitochondrial promoters for > 50% of mammalian species and some other vertebrates. The divergent structure of the mammalian promoters reveals previously unappreciated aspects of mtDNA evolution. The correct assignment of TSS also enabled us to establish the precise register of the DNA in the initiation complex and permitted investigation of the sequence-specific protein-DNA interactions. We determined the molecular basis of promoter recognition by mtRNAP and TFB2M, which cooperatively recognize bases near TSS in a species-specific manner. Our findings reveal a role of mitochondrial transcription machinery in mitonuclear coevolution and speciation.

DOI: https://doi.org/10.1093/nar/gkac103

J Clin Lab Anal. 2022 Feb 26. e24298

Maternally transmitted nonsyndromic hearing impairment may be associated with mitochondrial tRNAAla 5601C>T and tRNALeu(CUN) 12311T>C mutations.

Xuejiao Yu, Sheng Li, Yu Ding.

BACKGROUND: Sequence alternations in mitochondrial genomes, especially in genes encoding mitochondrial tRNA (mt-tRNA), were the important contributors to nonsyndromic hearing loss (NSHL); however, the molecular mechanisms remained largely undetermined.METHODS: A maternally transmitted Chinese pedigree with NSHL underwent clinical, genetic, and biochemical assessment. PCR and direct sequence analyses were performed to detect mitochondrial DNA (mtDNA), GJB2, and SLC26A4 gene mutations from matrilineal relatives of this family. Mitochondrial functions including mitochondrial membrane potential (MMP), ATP, and ROS were evaluated in polymononuclear leukocytes (PMNs) derived from three deaf patients and three controls from this pedigree.
RESULTS: Four of nine matrilineal relatives developed hearing loss at the variable age of onset. Two putative pathogenic mutations, m.5601C>T in tRNAAla and m.12311T>C in tRNALeu(CUN) , were identified via PCR-Sanger sequencing, as well as 34 variants that belonged to mtDNA haplogroup G2b2. Intriguingly, m.5601C>T mutation resided at very conserved nucleotide in the TψC loop of tRNAAla (position 59), while the T-to-C substitution at position 12311 located at position 48 in the variable stem of tRNALeu(CUN) and was believed to alter the aminoacylation and the steady-state level of tRNA. Biochemical analysis revealed the impairment of mitochondrial functions including the significant reductions of ATP and MMP, whereas markedly increased ROS levels were found in PMNs derived from NSHL patients with m.5601C>T and m.12311T>C mutations. However, we did not detect any mutations in GJB2 and SLC26A4 genes.
CONCLUSION: Our data indicated that mt-tRNAAla m.5601C>T and tRNALeu(CUN) 12311T>C mutations were associated with NSHL.

Keywords: NSHL; m.12311T>C; m.5601C>T; mitochondrial dysfunctions; mt-tRNA mutations

DOI: https://doi.org/10.1002/jcla.24298

Genome Res. 2022 Feb 22.

Low-input RNase footprinting for simultaneous quantification of cytosolic and mitochondrial translation.

Qianru Li, Haiwang Yang, Emily K Stroup, Hongbin Wang, Zhe Ji.

We describe a low-input RNase footprinting approach for the rapid quantification of ribosome-protected fragments with as few as 1000 cultured cells. The assay uses a simplified procedure to selectively capture ribosome footprints based on optimized RNase digestion. It simultaneously maps cytosolic and mitochondrial translation with single-nucleotide resolution. We applied it to reveal selective functions of the elongation factor TUFM in mitochondrial translation, as well as synchronized repression of cytosolic translation after TUFM perturbation. We show the assay is applicable to small amounts of primary tissue samples with low protein synthesis rates, including snap-frozen tissues and immune cells from an individual's blood draw. We showed its feasibility to characterize the personalized immuno-translatome. Our analyses revealed that thousands of genes show lower translation efficiency in monocytes compared with lymphocytes, and identified thousands of translated noncanonical open reading frames (ORFs). Altogether, our RNase footprinting approach opens an avenue to assay transcriptome-wide translation using low-input samples from a wide range of physiological conditions.

DOI: https://doi.org/10.1101/gr.276139.121