bims-mitran 2024-10-20 papers

Issue of 2024–10–20
five papers selected by
Andreas Kohler, Umeå University

Nature. 2024 Oct 16.

Quantifying constraint in the human mitochondrial genome.

Nicole J Lake, Kaiyue Ma, Wei Liu, Stephanie L Battle, Kristen M Laricchia, Grace Tiao, Daniela Puiu, Kenneth K Ng, Justin Cohen, Alison G Compton, Shannon Cowie, John Christodoulou, David R Thorburn, Hongyu Zhao, Dan E Arking, Shamil R Sunyaev, Monkol Lek.

Mitochondrial DNA (mtDNA) has an important yet often overlooked role in health and disease. Constraint models quantify the removal of deleterious variation from the population by selection and represent powerful tools for identifying genetic variation that underlies human phenotypes1-4. However, nuclear constraint models are not applicable to mtDNA, owing to its distinct features. Here we describe the development of a mitochondrial genome constraint model and its application to the Genome Aggregation Database (gnomAD), a large-scale population dataset that reports mtDNA variation across 56,434 human participants5. Specifically, we analyse constraint by comparing the observed variation in gnomAD to that expected under neutrality, which was calculated using a mtDNA mutational model and observed maximum heteroplasmy-level data. Our results highlight strong depletion of expected variation, which suggests that many deleterious mtDNA variants remain undetected. To aid their discovery, we compute constraint metrics for every mitochondrial protein, tRNA and rRNA gene, which revealed a range of intolerance to variation. We further characterize the most constrained regions within genes through regional constraint and identify the most constrained sites within the entire mitochondrial genome through local constraint, which showed enrichment of pathogenic variation. Constraint also clustered in three-dimensional structures, which provided insight into functionally important domains and their disease relevance. Notably, we identify constraint at often overlooked sites, including in rRNA and noncoding regions. Last, we demonstrate that these metrics can improve the discovery of deleterious variation that underlies rare and common phenotypes.

DOI: https://doi.org/10.1038/s41586-024-08048-x

Anal Chem. 2024 Oct 16.

Visualization of Mitochondrial DNA G-Quadruplexes with Isaindigotone Derived Near-Infrared Fluorogenic Probe.

Yuan Zhang, Yidan Cheng, Xianjun Liu, Hao Tang, Fenglin Wang, Li-Juan Tang, Jian-Hui Jiang.

Mitochondrial DNA G-quadruplexes (mtDNA G4s) play potential regulatory roles in mitochondrial functions. Fluorescent probes for imaging mtDNA G4s may provide useful information to unveil their regulating dynamics and functions. However, the existing probes for mtDNA G4s still exhibit short absorption and emission wavelengths and limited sensitivity. Here, we develop a new isaindigotone-derived near-infrared (NIR) fluorogenic probe for imaging mtDNA G4s in live cells and in vivo. Different fluorescent probes are engineered by conjugating the isaindigotone scaffold with varying electron-donating groups. It is shown that the probe ISAP using dimethylaminophenyl as the electron-donating group exhibits near-infrared absorption/emission and a high fluorescence activation fold in response to G4s. Molecular docking simulations reveal that ISAP binds to c-Myc G4 via multiple π-π stacking and hydrogen-bond interaction. Cellular studies show that ISAP exhibits an excellent mitochondrial targeting ability and allows specific imaging of mtDNA G4s. We further employed ISAP to image the dynamics of mtDNA G4s under glycolysis and oxidative stresses in live cells. Its capability to mtDNA G4s in vivo is showcased using a tumor-bearing mice model. This probe may serve as a useful tool to image mtDNA G4s and interrogate their biological roles in living systems.

DOI: https://doi.org/10.1021/acs.analchem.4c03722

EMBO J. 2024 Oct 18.

The mitochondrial long non-coding RNA lncMtloop regulates mitochondrial transcription and suppresses Alzheimer's disease.

Wandi Xiong, Kaiyu Xu, Jacquelyne Ka-Li Sun, Siling Liu, Baizhen Zhao, Jie Shi, Karl Herrup, Hei-Man Chow, Lin Lu, Jiali Li.

Maintaining mitochondrial homeostasis is crucial for cell survival and organismal health, as evidenced by the links between mitochondrial dysfunction and various diseases, including Alzheimer's disease (AD). Here, we report that lncMtDloop, a non-coding RNA of unknown function encoded within the D-loop region of the mitochondrial genome, maintains mitochondrial RNA levels and function with age. lncMtDloop expression is decreased in the brains of both human AD patients and 3xTg AD mouse models. Furthermore, lncMtDloop binds to mitochondrial transcription factor A (TFAM), facilitates TFAM recruitment to mtDNA promoters, and increases mitochondrial transcription. To allow lncMtDloop transport into mitochondria via the PNPASE-dependent trafficking pathway, we fused the 3'UTR localization sequence of mitochondrial ribosomal protein S12 (MRPS12) to its terminal end, generating a specified stem-loop structure. Introducing this allotropic lncMtDloop into AD model mice significantly improved mitochondrial function and morphology, and ameliorated AD-like pathology and behavioral deficits of AD model mice. Taken together, these data provide insights into lncMtDloop as a regulator of mitochondrial transcription and its contribution to Alzheimer's pathogenesis.

Keywords: lncMtDloop ; Alzheimer’s Disease; Mitochondrial Homeostasis; TFAM; mtDNA

DOI: https://doi.org/10.1038/s44318-024-00270-7

Aging Cell. 2024 Sep;23(9): e14242

Single-cell mitochondrial sequencing reveals low-frequency mitochondrial mutations in naturally aging mice.

Fuyan Liu, Xiaolin Sun, Cai Wei, Liu Ji, Yali Song, Chenlu Yang, Yue Wang, Xin Liu, Daqing Wang, Jingmin Kang.

Mitochondria play a crucial role in numerous biological processes; however, limited methods and research have focused on revealing mitochondrial heterogeneity at the single-cell level. In this study, we optimized the DNBelab C4 single-cell ATAC (assay for transposase-accessible chromatin) sequencing workflow for single-cell mitochondrial sequencing (C4_mtscATAC-seq). We validated the effectiveness of our C4_mtscATAC-seq protocol by sequencing the HEK-293T cell line with two biological replicates, successfully capturing both mitochondrial content (~68% of total sequencing data) and open chromatin status simultaneously. Subsequently, we applied C4_mtscATAC-seq to investigate two mouse tissues, spleen and bone marrow, obtained from two mice aged 2 months and two mice aged 23 months. Our findings revealed higher mitochondrial DNA (mtDNA) content in young tissues compared to more variable mitochondrial content in aged tissues, consistent with higher activity scores of nuclear genes associated with mitochondrial replication and transcription in young tissues. We detected a total of 22, 15, and 21 mtDNA mutations in the young spleen, aged spleen, and bone marrow, respectively, with most variant allele frequencies (VAF) below 1%. Moreover, we observed a higher number of mtDNA mutations with higher VAF in aged tissues compared to young tissues. Importantly, we identified three mtDNA variations (m.9821A>T, m.15219T>C, and m.15984C>T) with the highest VAF in both aged spleen and aged bone marrow. By comparing cells with and without these mtDNA variations, we analyzed differential open chromatin status to identify potential genes associated with these mtDNA variations, including transcription factors such as KLF15 and NRF1. Our study presents an alternative single-cell mitochondrial sequencing method and provides crude insights into age-related single-cell mitochondrial variations.

Keywords: ATAC; aging; mitochondrial DNA (mtDNA); mitochondrial mutation; single cell sequencing

DOI: https://doi.org/10.1111/acel.14242

Nat Commun. 2024 Oct 18. 15(1): 9008

Post-transcriptional methylation of mitochondrial-tRNA differentially contributes to mitochondrial pathology.

Sunita Maharjan, Howard Gamper, Yuka Yamaki, Thomas Christian, Robert Y Henley, Nan-Sheng Li, Takeo Suzuki, Tsutomu Suzuki, Joseph A Piccirilli, Meni Wanunu, Erin Seifert, Douglas C Wallace, Ya-Ming Hou.

Human mitochondrial tRNAs (mt-tRNAs), critical for mitochondrial biogenesis, are frequently associated with pathogenic mutations. These mt-tRNAs have unusual sequence motifs and require post-transcriptional modifications to stabilize their fragile structures. However, whether a modification that stabilizes a wild-type (WT) mt-tRNA would also stabilize its pathogenic variants is unknown. Here we show that the N1-methylation of guanosine at position 9 (m1G9) of mt-Leu(UAA), while stabilizing the WT tRNA, has a destabilizing effect on variants associated with MELAS (mitochondrial myopathy, encephalopathy, lactic acidosis, and stroke-like episodes). This differential effect is further demonstrated, as removal of the m1G9 methylation, while damaging to the WT tRNA, is beneficial to the major pathogenic variant, improving the structure and activity of the variant. These results have therapeutic implications, suggesting that the N1-methylation of mt-tRNAs at position 9 is a determinant of pathogenicity and that controlling the methylation level is an important modulator of mt-tRNA-associated diseases.

DOI: https://doi.org/10.1038/s41467-024-53318-x