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The MicroRNAs target mitochondrial dynamics and metabolism to regulate mitochondrial-mediated antiviral innate immunity

ABSTRACT: MicroRNAs (miRNAs) are short non-coding RNAs act as a suppressor of multiple genes and it is known that miRNAs link to numerous biological functions. Mitochondria act as a platform for innate immune response against RNA viruses via a mitochondrial outer membrane protein, MAVS. Here we report miR-302b and miR-372 involve in mitochondrial-mediated antiviral response. These miRNAs were upregulated by viral infection and influenced not only the production of type I interferon and inflammatory cytokines, but also mitochondrial function. Furthermore, we revealed that these phenotypes were induced by changing several mitochondrial genes expression. miR-302b induced mitochondrial fragmentation by changing gene expression related to mitochondrial dynamics to regulate Drp1 activity. Indeed, downregulation of SLC25A12 by miR-302b suppressed antiviral responses via inhibiting the MAVS activation directly. We first propose that miR-302b and miR-372 act as negative regulator of antiviral response by affecting mitochondrial function to inhibit excessive innate immune response.

ORGANISM(S): Homo sapiens

PROVIDER: GSE129615 | GEO | 2019/11/22

REPOSITORIES: GEO

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Project description:MicroRNAs (miRNAs) are small non-coding RNAs that associate with Argonaute 2 protein to regulate gene expression at the post-transcriptional level in the cytoplasm. However, recent studies have reported that some miRNAs localize to and function in other cellular compartments. Mitochondria harbour their own genetic system that may be a potential site for miRNA-mediated post-transcriptional regulation. We aimed at investigating whether nuclear-encoded miRNAs can localize to and function in human mitochondria. To enable identification of mitochondrial-enriched miRNAs, we profiled the mitochondrial and cytosolic RNA fractions from the same HeLa cells by miRNA microarray analysis. Mitochondria were purified using a combination of cell fractionation and immunoisolation, and assessed for the lack of protein and RNA contaminants. We found 57 miRNAs differentially expressed in HeLa mitochondria and cytosol. Of these 57, a signature of 13 nuclear-encoded miRNAs was reproducibly enriched in mitochondrial RNA and validated by RT-PCR for hsa-miR-494, hsa-miR-1275 and hsa-miR-1974. This study provides the first comprehensive view of the localization of RNA interference components to the mitochondria. Our data outline the molecular bases for a novel layer of crosstalk between nucleus and mitochondria through a specific subset of human miRNAs that we termed ‘mitomiRs’. To assess whether nuclear-encoded miRNA are detectable in human mitochondria, we performed the following four steps approach. First, cultured HeLa cells were allowed to reach 80-100% confluence and subjected to fractionation in order to isolate the cytosolic fraction. From the same HeLa cells, mitochondria were isolated by immunomagnetic Anti-TOM22 MicroBeads from the Mitochondria Isolation Kit (Miltenyi Biotec). In total, six mitochondria preparations were perfromed, three of these were additionally treated with RNase A. Second, total RNA was extracted from the mitochondrial and cytosolic fractions. Third, mitochondrial and cytosolic RNA were respectively profiled by microRNA microarray analysis. Last, data were analyzed and normalized.Three independent assays were performed.

Project description:Viruses often induce a complex rewiring of cellular physiology to maximize their propagation. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) expresses high amounts of the viral antagonistic protein Orf9b. Increased amounts and mutated versions of Orf9b were found to correlate with improved transmission of more evolved virus forms such as the Alpha and Omicron variants. Orf9b binds to the mitochondrial surface receptor Tom70 which stiffens its highly flexible structure. Tom70 plays a critical role in the antiviral response since it serves as recruiting factor for the mitochondrial antiviral signaling (MAVS) protein. However, the predominant and MAVS-independent role of Tom70 is that of a receptor component of the mitochondrial import system. Whether Orf9b also interferes with this predominant function of Tom70 is unknown. In this study, we expressed Orf9b in human HEK293 cells and observed the Orf9b-mediated depletion of mitochondrial proteins, particularly in respiring cells. The spectrum of depleted mitochondrial proteins was comparable to that of cells in which Tom70 was depleted, consistent with an Orf9b-mediated impairment of Tom70-dependent protein import. To exclude that the observed depletion was caused by the antiviral response triggered by Orf9b expression, we generated a yeast system in which the yeast Tom70 was replaced by a humanized version of Tom70. Upon expression of Orf9b in these cells, we again observed a general but moderate reduction of mitochondrial proteins. Similar to the situation in human cells, a number of mitochondrial proteins were particular sensitive to Orf9b expression, suggesting a rather specific modulation of the mitochondrial import system. In vitro import experiments with semi-intact cells confirmed this Orf9b-mediated impairment of the mitochondrial protein import. Thus, the SARS-CoV-2 virus seems to modulate the mitochondrial proteome by a direct effect of Orf9b on mitochondrial Tom70-dependent protein import.

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The MicroRNAs target mitochondrial dynamics and metabolism to regulate mitochondrial-mediated antiviral innate immunity

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