Abstract-MicroRNAs (miRNAs) are a recently discovered class of endogenous, small, noncoding RNAs that regulate about 30% of the encoding genes of the human genome. However, the role of miRNAs in vascular disease is currently completely unknown. Using microarray analysis, we demonstrated for the first time that miRNAs are aberrantly expressed in the vascular walls after balloon injury. The aberrantly expressed miRNAs were further confirmed by Northern blot and quantitative real-time polymerase chain reaction. Modulating an aberrantly overexpressed miRNA, miR-21, via antisense-mediated depletion (knock-down) had a significant negative effect on neointimal lesion formation. In vitro, the expression level of miR-21 in dedifferentiated vascular smooth muscle cells was significantly higher than that in fresh isolated differentiated cells. Depletion of miR-21 resulted in decreased cell proliferation and increased cell apoptosis in a dose-dependent manner. MiR-21-mediated cellular effects were further confirmed in vivo in balloon-injured rat carotid arteries. Western blot analysis demonstrated that PTEN and Bcl-2 were involved in miR-21-mediated cellular effects. The results suggest that miRNAs are novel regulatory RNAs for neointimal lesion formation. MiRNAs may be a new therapeutic target for proliferative vascular diseases such as atherosclerosis, postangioplasty restenosis, transplantation arteriopathy, and stroke. (Circ Res. 2007;100:1579-1588.)Key Words: microRNAs Ⅲ vascular smooth muscle cells Ⅲ proliferation Ⅲ apoptosis Ⅲ neointimal formation M icroRNAs (miRNAs) are endogenous, noncoding, single-stranded RNAs of Ϸ22 nucleotides and constitute a novel class of gene regulators. [1][2][3] Although the first miRNA, lin-4, was discovered in 1993, 4,5 their presence in vertebrates was confirmed only in 2001. 6 MiRNAs are initially transcribed by RNA polymerase II (Pol II) in the nucleus to form large pri-miRNA transcripts. 7 The primiRNAs are processed by the RNase III enzymes, Drosha and Dicer, to generate 18-to 24-nucleotide mature miRNAs. The mature miRNAs negatively regulate gene expression in 1 of 2 ways that depend on the degree of complementarity between the miRNA and its target. MiRNAs that bind to 3ЈUTR of mRNA with imperfect complementarity block protein translation. In contrast, miRNAs that bind to mRNA with perfect complementarity induce targeted mRNA cleavage. Currently, more than 400 miRNAs have been cloned and sequenced in human, and the estimated number of miRNA genes is as high as 1000 in the human genome. 8,9 As a group, miRNAs are estimated to regulate 30% genes of the human genome. 10 Analogous to the first RNA revolution in the 1980s with Cech discovering the enzymatic activity of RNA, 11 this recent discovery of RNAi and miRNA may represent the second RNA revolution. 12 Small interfering RNAs (siRNAs) are another class of small noncoding RNAs that have similar mechanism for gene expression regulation. However, they are different from each other. 5,13 The chief difference lies in their origins....

Abstract-Phenotypic modulation of vascular smooth muscle cells (VSMCs) plays a critical role in the pathogenesis of a variety of proliferative vascular diseases. Recently, we have found that microRNA (miRNA) miR-145 is the most abundant miRNA in normal vascular walls and in freshly isolated VSMCs; however, the role of miR-145 in VSMC phenotypic modulation and vascular diseases is currently unknown. Here we find that miR-145 is selectively expressed in VSMCs of the vascular wall and its expression is significantly downregulated in the vascular walls with neointimal lesion formation and in cultured dedifferentiated VSMCs.

-MicroRNAs (miRNAs) comprise a novel class of endogenous, small, noncoding RNAs that negatively regulate gene expression. Functionally, an individual miRNA is as important as a transcription factor because it is able to regulate the expression of its multiple target genes. Recently, miR-221 and miR-222 have been found to play a critical role in cancer cell proliferation. However, their roles in vascular smooth muscle cell (VSMC) biology are currently unknown.In the present study, the time course changes and cellular distribution of miR-221 and miR-222 expression were identified in rat carotid arteries after angioplasty, in which their expression was upregulated and localized in VSMCs in the injured vascular walls. In cultured VSMCs, miR-221 and miR-222 expression was increased by growth stimulators. Knockdown of miR-221 and miR-222 resulted in decreased VSMC proliferation in vitro. Using both gain-of-function and loss-of-function approaches, we found that p27(Kip1) and p57(Kip2) were 2 target genes that were involved in miR-221-and miR-222-mediated effect on VSMC growth. Finally, knockdown of miR-221 and miR-222 in rat carotid arteries suppressed VSMC proliferation in vivo and neointimal lesion formation after angioplasty. The results indicate that miR-221 and miR-222 are novel regulators for VSMC proliferation and neointimal hyperplasia. These findings may also represent promising therapeutic targets in proliferative vascular diseases. Key Words: microRNAs Ⅲ vascular smooth muscle cells Ⅲ gene regulation Ⅲ proliferation Ⅲ vascular disease R ecently, the most significant breakthrough regarding gene expression regulation has been the discovery of microRNAs (miRNAs). 1 miRNAs comprise a novel class of endogenous, small, noncoding RNAs that negatively regulate gene expression via degradation or translational inhibition of their target mRNAs. [1][2][3][4][5] More importantly, one miRNA is able to regulate the expression of multiple genes because it can bind to its mRNA targets as either an imperfect or perfect complementarity. Thus, one miRNA is as functionally important as a transcription factor. 6 More than 700 miRNAs have been identified and sequenced in humans, 7 and the estimated number of miRNA genes is as high as 1000 in the human genome. 8 As a group, miRNAs may directly regulate at least 30% of the genes in the human genome. 9 It is not surprising that miRNAs are involved in the regulation of almost all major cellular functions, such as cell differentiation, proliferation/growth, mobility, and apoptosis. 1 For that reason, miRNAs could be the pivotal regulators in normal development and physiology and disease development, including cancer and cardiovascular disease. 10 -13 The biological function of an individual miRNA is cell specific. One miRNA may have different cellular effects on different cells. For example, miR-21 has an antiapoptotic effect on glioblastoma cells but increases Hela cell apoptosis. 14,15 Recent studies have revealed that miR-221 and miR-222 are upregulated in cancer cells....

Several recent reports have suggested that microRNAs (miRNAs) might play critical roles in acute myocardial infarction (AMI). However, the miRNA expression signature in the early phase of AMI has not been identified. In this study, the miRNA expression signature was investigated in rat hearts 6 h after AMI. Compared with the expression signature in the noninfarcted areas, 38 miRNAs were differentially expressed in infarcted areas and 33 miRNAs were aberrantly expressed in the border areas. Remarkably, miR-21 expression was significantly down-regulated in infarcted areas, but was up-regulated in border areas. The down-regulation of miR-21 in the infarcted areas was inhibited by ischemic preconditioning, a known cardiac protective method. Overexpression of miR-21 via adenovirus expressing miR-21 (Ad-miR-21) decreased myocardial infarct size by 29% at 24 h and decreased the dimension of left ventricles at 2 weeks after AMI. Using both gain-of-function and loss-offunction approaches in cultured cardiac myocytes, we identified that miR-21 had a protective effect on ischemia-induced cell apoptosis that was associated with its target gene programmed cell death 4 and activator protein 1 pathway. The protective effect of miR-21 against ischemia-induced cardiac myocyte damage was further confirmed in vivo by decreased cell apoptosis in the border and infarcted areas of the infarcted rat hearts after treatment with Ad-miR-21. The results suggest that miRNAs such as miR-21 may play critical roles in the early phase of AMI. MicroRNAs (miRNAs)3 are endogenous, noncoding, singlestranded RNAs of ϳ22 nucleotides and constitute a novel class of gene regulators (1-3). Analogous to the first RNA revolution in the 1980s, when Zaug and Cech (4) discovered the enzymatic activity of RNA, the more recent discoveries of RNA interference and miRNA may represent the second RNA revolution (5).Although the first miRNA, lin-4, was discovered in 1993 (6, 7), their presence in vertebrates was confirmed only in 2001 (8). miRNAs are initially transcribed in the nucleus by RNA polymerase II or III to form large pri-miRNA transcripts (9). These pri-miRNAs are then processed by the RNase III enzymes, Drosha, Pasha, and Dicer, to generate 18-to 24-nucleotide mature miRNAs. In addition to this miRNA biogenesis pathway, some miRNA precursors are able to bypass Drosha processing to produce miRNAs via Dicer, possibly representing an alternative pathway for miRNA biogenesis (10, 11). The mature miRNAs bind to the 3Ј-untranslated region of their mRNA targets and negatively regulate gene expression via degradation or translational inhibition.Currently, about 600 miRNAs have been cloned and sequenced in humans, and the estimated number of miRNA genes is as high as 1,000 in the human genome (12, 13). Functionally, an individual miRNA is as important as a transcription factor because it is able to regulate the expression of its multiple target genes. As a group, miRNAs are estimated to regulate over 30% of the genes in a cell (14). It is thus not surprising th...

MicroRNAs (miRNAs) are a recently discovered class of endogenous, small, noncoding RNAs that regulate gene expression. Although miRNAs are highly expressed in the heart, their roles in heart diseases are currently unclear. Using microarray analysis designed to detect the majority of mammalian miRNAs identified thus far, we demonstrated that miRNAs are aberrantly expressed in hypertrophic mouse hearts. The time course of the aberrant miRNA expression was further identified in mouse hearts at 7, 14, and 21 days after aortic banding. Nineteen of the most significantly dysregulated miRNAs were further confirmed by Northern blot and/or real-time polymerase chain reaction, in which miR-21 was striking because of its more than fourfold increase when compared with the sham surgical group. Similar aberrant expression of the most up-regulated miRNA, miR-21, was also found in cultured neonatal hypertrophic cardiomyocytes stimulated by angiotensin II or phenylephrine. Modulating miR-21 expression via antisense-mediated depletion (knockdown) had a significant negative effect on cardiomyocyte hypertrophy. The results suggest that miRNAs are involved in cardiac hypertrophy formation. miRNAs might be a new therapeutic target for cardiovascular diseases involving cardiac hypertrophy such as hypertension, ischemic heart disease, valvular diseases, and endocrine disorders. (Am J