MicroRNA-30b-5p is involved in the regulation of cardiac hypertrophy by targeting CaMKIIδ.

BACKGROUND: MicroRNAs (miRNAs) participate in the regulation of cardiac hypertrophy. However, it remains largely unknown as to how miRNAs are integrated into the hypertrophic program. Ca/calmodulin-dependent protein kinase II (CaMKII) is a hypertrophic signaling marker. It is not yet clear which miRNAs can regulate CaMKIIδ. PURPOSE: In this study, we identified which miRNAs could regulate CaMKIIδ and how to regulate CaMKIIδ. METHODS: Through computational and expression analyses, miR-30b-5p was identified as a candidate regulator of CaMKIIδ. Quantitative expression analysis of hypertrophic models demonstrated significant down-regulation of miR-30b-5p compared with control groups. Luciferase reporter assay showed that miR-30b-5p could significantly inhibit the expression of CaMKIIδ. Moreover, through gain-of-function and loss-of-function approaches, we found miR-30b-5p could negatively regulate the expression of CaMKIIδ and miR-30b-5p was a regulator of cardiac hypertrophy. CONCLUSION: Our study demonstrates that the expression of miR-30b-5p is down-regulated in cardiac hypertrophy, and restoration of its function inhibits the expression of CaMKIIδ, suggesting that miR-30b-5p may act as a hypertrophic suppressor.

Tetrodotoxin attenuates isoproterenol-induced hypertrophy in H9c2 rat cardiac myocytes.

Cardiac hypertrophy is often associated with an increased sympathetic drive, and both in vitro and in vivo studies have demonstrated the development of cardiomyocyte hypertrophy in response to either α- or ß- adrenergic stimulation. The present study was carried out to determine whether the reversible sodium channel blocker tetrodotoxin (TTX) exerts a direct anti-hypertrophic effect on isoproterenol (ISO)-induced cell hypertrophy and find the underlying mechanism that regulate [Na(+)]( i ). The experiments were performed on cultured H9c2 cells exposed to ISO (10 µM) alone or combined with TTX (1 µM) for 48 h. Our results showed that ISO significantly increased cell surface area by 30 % and atrial natriuretic peptide gene expression by nearly twofold (p < 0.05 for both). These effects were associated with a significant reduction in the gene expression of Na(+)/K(+)-ATPase isoforms α2 and α3, whereas the α1 isoform was unaffected. Conversely, ISO increased Na(+)-H(+) exchanger 1 (NHE-1) gene expression by approximately 40 % and significantly increased [Na(+)]( i ) level by 50 % (p < 0.05 for both). ISO was also found to significantly increase aquaporin 4 gene expression by nearly ninefold (p < 0.05). All these effects were prevented when identical experiments were carried out in the presence of TTX, but the expression of NHE-1. The expression of sodium channel protein type 5 subunit alpha was unaffected by either ISO or TTX. When taken together, these studies show that TTX attenuates the hypertrophic effect of ISO and suggest a possible approach to limiting ISO-induced hypertrophy in clinical treatment.