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      Role of MicroRNAs in Fibrosis

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          Abstract

          Fibrosis is the leading cause of organ dysfunction in diseases such as systemic sclerosis, liver cirrhosis, cardiac fibrosis, progressive kidney disease, and idiopathic pulmonary fibrosis. The hallmark of fibrosis is tissue remodeling with excess deposition of extracellular matrix components, predominantly collagens. Different cell types, cytokines, growth factors, and enzymes interact in complex pathogenic networks with myofibroblasts playing a pivotal role. MicroRNAs are small non-coding RNAs acting as negative regulators of gene expression at the post-transcriptional level. MicroRNAs have been associated with many basic cellular processes as well as with a wide spectrum of diseases, most notably cancer. This review provides a comprehensive overview of microRNAs regulating profibrotic pathways and extracellular matrix synthesis. The potential of miRNA for targeted therapeutic approaches in fibrotic disorders is also discussed.

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          Most cited references68

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          A coding-independent function of gene and pseudogene mRNAs regulates tumour biology

          The canonical role of messenger RNA (mRNA) is to deliver protein-coding information to sites of protein synthesis. However, given that microRNAs bind to RNAs, we hypothesized that RNAs possess a biological role in cancer cells that relies upon their ability to compete for microRNA binding and is independent of their protein-coding function. As a paradigm for the protein-coding-independent role of RNAs, we describe the functional relationship between the mRNAs produced by the PTEN tumour suppressor gene and its pseudogene (PTENP1) and the critical consequences of this interaction. We find that PTENP1 is biologically active as determined by its ability to regulate cellular levels of PTEN, and that it can exert a growth-suppressive role. We also show that PTENP1 locus is selectively lost in human cancer. We extend our analysis to other cancer-related genes that possess pseudogenes, such as oncogenic KRAS. Further, we demonstrate that the transcripts of protein coding genes such as PTEN are also biologically active. Together, these findings attribute a novel biological role to expressed pseudogenes, as they can regulate coding gene expression, and reveal a non-coding function for mRNAs.
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            Switching from repression to activation: microRNAs can up-regulate translation.

            AU-rich elements (AREs) and microRNA target sites are conserved sequences in messenger RNA (mRNA) 3' untranslated regions (3'UTRs) that control gene expression posttranscriptionally. Upon cell cycle arrest, the ARE in tumor necrosis factor-alpha (TNFalpha) mRNA is transformed into a translation activation signal, recruiting Argonaute (AGO) and fragile X mental retardation-related protein 1 (FXR1), factors associated with micro-ribonucleoproteins (microRNPs). We show that human microRNA miR369-3 directs association of these proteins with the AREs to activate translation. Furthermore, we document that two well-studied microRNAs-Let-7 and the synthetic microRNA miRcxcr4-likewise induce translation up-regulation of target mRNAs on cell cycle arrest, yet they repress translation in proliferating cells. Thus, activation is a common function of microRNPs on cell cycle arrest. We propose that translation regulation by microRNPs oscillates between repression and activation during the cell cycle.
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              Dysregulation of microRNAs after myocardial infarction reveals a role of miR-29 in cardiac fibrosis.

              Acute myocardial infarction (MI) due to coronary artery occlusion is accompanied by a pathological remodeling response that includes hypertrophic cardiac growth and fibrosis, which impair cardiac contractility. Previously, we showed that cardiac hypertrophy and heart failure are accompanied by characteristic changes in the expression of a collection of specific microRNAs (miRNAs), which act as negative regulators of gene expression. Here, we show that MI in mice and humans also results in the dysregulation of specific miRNAs, which are similar to but distinct from those involved in hypertrophy and heart failure. Among the MI-regulated miRNAs are members of the miR-29 family, which are down-regulated in the region of the heart adjacent to the infarct. The miR-29 family targets a cadre of mRNAs that encode proteins involved in fibrosis, including multiple collagens, fibrillins, and elastin. Thus, down-regulation of miR-29 would be predicted to derepress the expression of these mRNAs and enhance the fibrotic response. Indeed, down-regulation of miR-29 with anti-miRs in vitro and in vivo induces the expression of collagens, whereas over-expression of miR-29 in fibroblasts reduces collagen expression. We conclude that miR-29 acts as a regulator of cardiac fibrosis and represents a potential therapeutic target for tissue fibrosis in general.
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                Author and article information

                Journal
                Open Rheumatol J
                Open Rheumatol J
                TORJ
                The Open Rheumatology Journal
                Bentham Open
                1874-3129
                15 June 2012
                2012
                : 6
                : 130-139
                Affiliations
                [1 ]Center of Experimental Rheumatology, ZIHP, University Hospital Zurich, Gloriastrasse 25, CH-8091 Zurich, Switzerland
                [2 ]Department of Clinical Medicine, Cardiovascular and Immunologic Sciences, University of Naples “Federico II”, via Pansini 5, 80131 I-Naples, Italy
                Author notes
                [* ]Address correspondence to this author at the University Hospital Zurich, Gloriastrasse 25, 8091 Zurich, Switzerland; Tel: +41-44-255-2977; Fax: +41-44-255-4170; E-mail: oliver.distler@ 123456usz.ch
                Article
                TORJ-6-130
                10.2174/1874312901206010130
                3396185
                22802911
                3b170215-bfba-4828-85a4-5416340c0bec
                © Vettori et al.; Licensee Bentham Open.

                This is an open access article licensed under the terms of the Creative Commons Attribution Non-Commercial License ( http://creativecommons.org/licenses/by-nc/3.0/) which permits unrestricted, non-commercial use, distribution and reproduction in any medium, provided the work is properly cited.

                History
                : 3 March 2012
                : 27 March 2012
                : 4 April 2012
                Categories
                Article
                Suppl 1

                Rheumatology
                microrna (mirna)-mediated gene regulation regulation,transforming growth factor-beta (tgf-β),signaling pathways,connective tissue growth factor (ctgf),extracellular matrix (ecm),fibrosis,fibroblasts,epithelial-to-mesenchymal transition (emt),antagomirs.

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