Regulation of nuclear transcription by mitochondrial RNA in endothelial cells

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    This work is fundamental in providing compelling evidence of mitochondria-encoded RNAs playing a role in controlling nuclear gene expression. How mitochondria and the nucleus communicates is an important but yet not well-appreciated area of biology. Using the iMARI (in situ mapping of RNA-Genome Interactions) technology developed by this team, the authors found that mitochondria-encoded RNAs play an unexpected role in regulating nuclear gene expressions in endothelial cells and intriguingly, depletion or overexpression of a specific mt-caRNA altered stress-induced transcription of nuclear genes encoding for innate inflammation and endothelial activation. Overall, these findings are interesting and supported by experimental confirmation, bulk-RNA-seq, and snRNA and scRNA-seq data and will be of interest to the field studying RNA regulation, gene expression and cell biology.

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Abstract

Chromatin-associated RNAs (caRNAs) form a relatively poorly recognized layer of the epigenome. The caRNAs reported to date are transcribed from the nuclear genome. Here, leveraging a recently developed assay for detection of caRNAs and their genomic association, we report that mitochondrial RNAs (mtRNAs) are attached to the nuclear genome and constitute a subset of caRNA, thus termed mt-caRNA. In four human cell types analyzed, mt-caRNAs preferentially attach to promoter regions. In human endothelial cells (ECs), the level of mt-caRNA–promoter attachment changes in response to environmental stress that mimics diabetes. Suppression of a non-coding mt-caRNA in ECs attenuates stress-induced nascent RNA transcription from the nuclear genome, including that of critical genes regulating cell adhesion, and abolishes stress-induced monocyte adhesion, a hallmark of dysfunctional ECs. Finally, we report increased nuclear localization of multiple mtRNAs in the ECs of human diabetic donors, suggesting many mtRNA translocate to the nucleus in a cell stress and disease-dependent manner. These data nominate mt-caRNAs as messenger molecules responsible for mitochondrial–nuclear communication and connect the immediate product of mitochondrial transcription with the transcriptional regulation of the nuclear genome.

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  1. eLife assessment

    This work is fundamental in providing compelling evidence of mitochondria-encoded RNAs playing a role in controlling nuclear gene expression. How mitochondria and the nucleus communicates is an important but yet not well-appreciated area of biology. Using the iMARI (in situ mapping of RNA-Genome Interactions) technology developed by this team, the authors found that mitochondria-encoded RNAs play an unexpected role in regulating nuclear gene expressions in endothelial cells and intriguingly, depletion or overexpression of a specific mt-caRNA altered stress-induced transcription of nuclear genes encoding for innate inflammation and endothelial activation. Overall, these findings are interesting and supported by experimental confirmation, bulk-RNA-seq, and snRNA and scRNA-seq data and will be of interest to the field studying RNA regulation, gene expression and cell biology.

  2. Reviewer #1 (Public Review):

    Recently, chromatin-associated RNAs (caRNAs) were found to be involved in transcriptional regulation through multiple mechanisms, playing important roles in disease and development. Mitochondria has its own genome known as mtDNA, which codes crucial genes involved in oxidative phosphorylation. Additionally, mtDNA produces non-coding RNAs (ncRNAs), including small and long noncoding RNAs, the functions of which are still being explored. The communication between mitochondria and the nucleus is essential for coordinating gene expression and cellular function. Recent studies have identified the presence of mitochondrial RNAs (mtRNAs) in the nucleus, such as SncmtRNA, which can influence stress-induced transcription of genes related to cell adhesion.

    In this manuscript, using the iMARI (in situ mapping of RNA-Genome Interactions) technology developed by the authors, they found that mitochondria-encoded lncRNA plays a role in regulating nuclear gene expressions. They then performed experimental confirmation, bulk-RNA-seq, snRNA, and scRNA-seq to demonstrate and verify the function of SncmtRNA in regulating nuclear gene expression in endothelial cells. This discovery is ground-breaking and the manuscript provides convincing evidence that mitochondrial RNAs can enter the cellular nucleus to regulate gene expression.

  3. Reviewer #2 (Public Review):

    The communication between mitochondria and the nucleus is crucial for maintaining cellular homeostasis and coordinating various cellular processes. The work by Sriram and colleagues discovers a potentially novel messenger molecule between mitochondrial-nuclear crosstalk through the widespread association of mitochondrial RNAs with nuclear chromatin. They termed this as mt-caRNAs that establishes a direct connection between mtRNA and the epigenome. These mt-caRNAs were found to preferentially attach to promoter regions, which led them to investigate how mt-caRNAs may regulate nuclear-encoded transcripts. Using an endothelial cell model, depletion/ overexpression of a specific mt-caRNA altered stress-induced transcription of nuclear genes encoding for innate inflammation and endothelial activation. Overall, these findings are interesting and warrant further investigation of the role of mt-caRNA-mediated nuclear transcription in controlling cellular processes.