Pre-microRNA and Mature microRNA in Human Mitochondria

Abstract

BackgroundBecause of the central functions of the mitochondria in providing metabolic energy and initiating apoptosis on one hand and the role that microRNA (miRNA) play in gene expression, we hypothesized that some miRNA could be present in the mitochondria for post-transcriptomic regulation by RNA interference. We intend to identify miRNA localized in the mitochondria isolated from human skeletal primary muscular cells.Methodology/Principal FindingsTo investigate the potential origin of mitochondrial miRNA, we in-silico searched for microRNA candidates in the mtDNA. Twenty five human pre-miRNA and 33 miRNA aligments (E-value<0.1) were found in the reference mitochondrial sequence and some of the best candidates were chosen for a co-localization test. In situ hybridization of pre-mir-302a, pre-let-7b and mir-365, using specific labelled locked nucleic acids and confocal microscopy, demonstrated that these miRNA were localized in mitochondria of human myoblasts. Total RNA was extracted from enriched mitochondria isolated by an immunomagnetic method from a culture of human myotubes. The detection of 742 human miRNA (miRBase) were monitored by RT-qPCR at three increasing mtRNA inputs. Forty six miRNA were significantly expressed (2nd derivative method Cp>35) for the smallest RNA input concentration and 204 miRNA for the maximum RNA input concentration. In silico analysis predicted 80 putative miRNA target sites in the mitochondrial genome (E-value<0.05).Conclusions/SignificanceThe present study experimentally demonstrated for the first time the presence of pre-miRNA and miRNA in the human mitochondria isolated from skeletal muscular cells. A set of miRNA were significantly detected in mitochondria fraction. The origin of these pre-miRNA and miRNA should be further investigate to determine if they are imported from the cytosol and/or if they are partially processed in the mitochondria.

MicroRNAs in myocardial ischemia: identifying new targets and tools for treating heart disease. New frontiers for miR-medicine

“…Indeed, theycan regulate pre-mRNA processing in the nucleus, act as chaperones to modify structure, or modulate mRNA-protein interactions [13]. while miRNAs generally function in the cytoplasm, they can be imported in the nucleus [14], in the mitochondrium [15], and even be secreted from the cell [16] or transferred from one cell to another [17,18]. Nevertheless, the relevance of subcellular localization for miRNA regulation is still a matter of study [19].…”

“…Mef2 promotes the expression of mitochondrial proteins that, in turn, induce mtTfa [40]. Intriguingly, the presence of several myomiRs translocated from the cytosol to mitochondria has been demonstrated in human skeletal muscle cells [15]. Among these, miR-133 was predicted to target the mitochondrial NADH dehydrogenase subunit 1 and was implicated in mitochondrial mRNA silencing [15] The comprehension of the role and regulation of miRNAs during cardiac development, as well as in pathological conditions in the adult, constitutes the basis for new targeted therapies for cardiac disease.…”

MicroRNAs: The Mega Regulators in Eukaryotic Genomes

“…The human genome may encode over 1000 miRNAs [7]. In humans the miRNAs have been reported in mitochondria as well [8]. …”

Mitochondrial dysfunction in breast cancer

“…In addition, it is important to note that the expression pattern of mitomiRs may be tissue specific. In their study, Barrey et al 56 identified mitomiRs that are enriched in myoblasts, while another study reported cardiac-specific mitomiRs. 57 Therefore, it is possible that some mitomiRs may be expressed specifically in the breast.…”

“…Barrey et al 56 have identified 243 miRNA in the mitochondrial RNA fraction. Intriguingly, three miRNAs, miR-146a, miR-103, and miR-16, were found in the IMS.…”