Long noncoding RNA-microRNA-mRNA: a novel tripartite axis in the regulation of cardiac hypertrophy.

A large fraction of mammalian genomes is transcribed into noncoding RNAs. 1 Despite the prevalence in the genome, up until recently, noncoding RNAs were regarded as junk RNAs that do not code for protein and, thereby, have no biological purpose. However, over the past decade, it has become increasingly evident that noncoding RNAs can and do serve important regulatory functions in pathophysiological processes. 1 Short noncoding RNAs called microRNAs, typically 20 to 24 nucleotides in length, have been widely reported to post-transcriptionally regulate gene expression by binding to partially complementary sequences in target mRNAs or promoting mRNA degradation and translational repression. 2 Another class of noncoding RNAs, typically >200 nucleotides in length, called long noncoding RNAs (lncRNAs) have been recently discovered to regulate gene expression not only at the post-transcriptional level, but also at transcriptional and epigenetic levels. 3 Notably, lncRNAs have also been reported to function as microRNA sponges, altering microRNA expression levels by binding to and sequestering microRNAs. In the present study, Wang et al 6 present evidence that a lncRNA modulates the ability of a microRNA to target an mRNA, which plays a role in the development of cardiac hypertrophy. To identify microRNAs whose expression is altered by hypertrophic stimulation, the authors 6 performed microRNA microarray analysis and quantitative reverse transcription– polymerase chain reaction (qRT-PCR) on neonatal mouse cardiomyocytes treated with or without angiotensin II (Ang-II). In particular, microRNA-489 (miR-489) was found to be most downregulated microRNA in response to Ang-II treatment. The authors used several methods to study the role of miR-489 in cardiac hypertrophy. First, they infected cardio-myocytes with adenoviruses encoding miR-489 to overex-press miR-489 and subsequently treated the cardiomyocytes with Ang-II. Second, they transfected cardiomyocytes with miR-489 antagomirs (anta-489) to knockdown the expression of miR-489, followed by treatment of the cardiomyo-cytes with Ang-II. Third, they generated transgenic C57BL/6 mice overexpressing miR-489 in a cardiac-specific manner (miR-489 Tg mice) and induced a prohypertrophic condition in these mice by implanting osmotic Ang-II–containing mini-pumps. The authors assessed cardiac hypertrophy by measuring cell surface area, determining protein/DNA ratio, and using qRT-PCR to measure mRNA levels of the hypertrophic markers, atrial natriuretic factor (ANF), brain natriuretic pep-tide (BNP), and β-myosin heavy chain (β-MHC). To determine the target gene of miR-489, the authors performed luciferase 3′ untranslated region (3′UTR) reporter assays in human embryonic kidney 293 (HEK293) cells to screen the several genes associated with cardiac hypertrophy and identified myeloid …