Transcribed Ultraconserved Regions, Uc.323, Ameliorates Cardiac Hypertrophy by Regulating the Transcription of CPT1b (Carnitine Palmitoyl transferase 1b)

Transcribed ultraconserved regions (T-UCRs) are a novel class of long noncoding RNAs transcribed from UCRs, which exhibit 100% DNA sequence conservation among humans, mice, and rats. However, whether T-UCRs regulate cardiac hypertrophy remains unclear. We aimed to explore the effects of T-UCRs on cardiac hypertrophy. First, we performed long noncoding RNA microarray analysis on hearts of mice subjected to sham surgery or aortic banding and found that the T-UCR uc.323 was decreased significantly in mice with aortic banding-induced cardiac hypertrophy. In vitro loss- and gain-of-function experiments demonstrated that uc.323 protected cardiomyocytes against hypertrophy induced by phenylephrine. Additionally, we discovered that mammalian target of rapamycin 1 contributed to phenylephrine-induced uc.323 downregulation and uc.323-mediated cardiomyocyte hypertrophy. We further mapped the possible target genes of uc.323 through global microarray mRNA expression analysis after uc.323 knockdown and found that uc.323 regulated the expression of cardiac hypertrophy-related genes such as CPT1b (Carnitine Palmitoyl transferase 1b). Then, chromatin immunoprecipitation proved that EZH2 (enhancer of zeste homolog 2) bound to the promoter of CPT1b via H3K27me3 (trimethylation of lysine 27 of histone H3) to induce CPT1b downregulation. And overexpression of CPT1b could block uc.323-mediated cardiomyocyte hypertrophy. Finally, we found that uc.323 deficiency induced cardiac hypertrophy. Our results reveal that uc.323 is a conserved T-UCR that inhibits cardiac hypertrophy, potentially by regulating the transcription of CPT1b via interaction with EZH2.