We recommend that more evidence should be gathered from clinical studies and trials to clarify our diagnostic criteria and management strategies.

Deep Impact? On 15 February 2013, the Russian district of Chelyabinsk, with a population of more than 1 million, suffered the impact and atmospheric explosion of a 20-meter-wide asteroid—the largest impact on Earth by an asteroid since 1908. Popova et al. (p. 1069 , published online 7 November; see the Perspective by Chapman ) provide a comprehensive description of this event and of the body that caused it, including detailed information on the asteroid orbit and atmospheric trajectory, damage assessment, and meteorite recovery and characterization.

Background-Recently, elevation of circulating muscle-specific microRNA (miRNA) levels has been reported in patients with acute myocardial infarction. However, it is still unclear from which part of the myocardium or under what conditions miRNAs are released into circulating blood. The purpose of this study was to identify the source of elevated levels of circulating miRNAs and their function in cardiovascular diseases. Methods and Results-Serum levels of miRNA (miR)-1 and miR-133a were increased significantly in patients not only with acute myocardial infarction but also with unstable angina pectoris and Takotsubo cardiomyopathy without elevation of serum creatine phosphokinase or cardiac troponin. MicroRNA microarray analysis of the heart from a mouse model of myocardial infarction indicated that the levels of miR-1, miR-133a, miR-208a, and miR-499 were significantly reduced in the infarcted myocardium. In situ hybridization of miR-133a also showed that miR-133a levels were very low in the infarcted and peri-infarcted myocardium. It has been shown that circulating miRNAs are localized inside exosomes, which are released after Ca 2ϩ stimulation. We stimulated H9c2 cardiomyoblasts with A23187 and measured miR-133a levels in the exosome fraction of the culture medium. A23187 induced a dose-dependent release of miR-133a, and significant elevation was observed only at concentrations where dead cells were detected. We also found that miR-133a-containing exosomes reduced the luciferase activity of 293FT cells transfected with an miR-133a sensor vector. Conclusions-These results suggest that elevated levels of circulating miR-133a in patients with cardiovascular diseases originate mainly from the injured myocardium. Circulating miR-133a can be used as a marker for cardiomyocyte death, and it may have functions in cardiovascular diseases. (Circ Cardiovasc Genet. 2011;4:446-454.)Key Words: circulating microRNA Ⅲ myocardial infarction Ⅲ cell death Ⅲ calcium ionophore M icroRNAs (miRNAs) are endogenous, single-stranded, Ϸ22-nucleotide noncoding RNAs. MicroRNAs are generally regarded as negative regulators of gene expression through inhibition of translation and/or promotion of mRNA degradation by base-pairing to complementary sequences within the 3Ј untranslated region (3ЈUTR) of protein-coding mRNA transcripts. 1 The first miRNA assigned to a specific function was lin-4, which targets lin-14 during temporal pattern formation in Caenorhabditis elegans. 2 Since then, a variety of miRNAs have been discovered. More than 500 miRNAs have been cloned and sequenced in humans, and the estimated number of miRNA genes may be as high as 1000 in the human genome. 3 Each miRNA regulates dozens to hundreds of distinct target genes; thus miRNAs are estimated to regulate the expression of more than one-third of human protein-coding genes. 4 Clinical Perspective on p 454The implications of miRNAs in the pathological process of the cardiovascular system have been recognized recently, and research on miRNAs in relation to cardiovascular dise...

Sterol regulatory element-binding protein 2 (SREBP-2) transcription factor has been identified as a key protein in cholesterol metabolism through the transactivation of the LDL receptor and cholesterol biosynthesis genes. Here, we generated mice lacking microRNA (miR)-33, encoded by an intron of the Srebp2, and showed that miR-33 repressed the expression of ATP-binding cassette transporter A1 (ABCA1) protein, a key regulator of HDL synthesis by mediating cholesterol efflux from cells to apolipoprotein A (apoA)-I. In fact, peritoneal macrophages derived from miR-33-deficient mice showed a marked increase in ABCA1 levels and higher apoA-I-dependent cholesterol efflux than those from WT mice. ABCA1 protein levels in liver were also higher in miR-33-deficient mice than in WT mice. Moreover, miR-33-deficient mice had significantly higher serum HDL cholesterol levels than WT mice. These data establish a critical role for miR-33 in the regulation of ABCA1 expression and HDL biogenesis in vivo.A TP-binding cassette transporter A1 (ABCA1), a 254-kDa cytoplasmic membrane protein, is a pivotal regulator of lipid efflux from cells to apolipoproteins (1). ABCA1 mediates the ratecontrolling step in HDL particle formation and plays an important role in reverse cholesterol transfer (2, 3). Mutations in the ABCA1 gene cause Tangier disease, which is characterized by the near absence of plasma HDL cholesterol associated with storage of cholesterol esters in reticuloendothelial tissues (4-7). Abca1 mRNA and protein are very unstable, with a half life of 1-2 h in murine macrophages (8), which indicates that new transcription and translation are major factors in ensuring constant and inducible ABCA1 expression.Sterol regulatory element-binding proteins (SREBPs), including SREBP-1a, -1c, and -2, modulate the transcription of a number of genes involved in the synthesis and receptor-mediated uptake of cholesterol and fatty acids (9-11). In sterol-depleted cells, SREBPs are cleaved by proteases in the Golgi, releasing the N-termini, which translocate into the nucleus and bind to SREs in the enhancers of multiple genes encoding enzymes and proteins involved in cholesterol biosynthesis and lipid uptake (11-13). Results to date support the notion that SREBP-1 primarily activates the fatty acid triglyceride and phospholipid pathways, whereas SREBP-2 is the prominent isoform for cholesterol synthesis and uptake (9,10,12).MicroRNAs (miRs) are small, non-protein-coding RNAs that base pair with specific mRNAs and inhibit translation or promote mRNA degradation. Recent reports have indicated that miR-33 controls cholesterol homeostasis based on knockdown experiments using antisense technology (14-16). Antisense inhibition of miRNA function has been an important tool for elucidating miRNA biology. However, to determine the potential developmental function of specific miRNAs and to perform longer-term studies, it is necessary to generate mice lacking each miRNA. We generated miR-33-deficient mice, which were born at the expected Mendelian ratio, a...