Thioredoxin (Trx)1 inhibits pathological cardiac hypertrophy. MicroRNAs (miRNAs) are small noncoding RNAs that downregulate posttranscriptional expression of target molecules.

We investigated the role of miRNAs in mediating the antihypertrophic effect of Trx1 on angiotensin II (Ang II)–induced cardiac hypertrophy.

Microarray analyses of mature rodent microRNAs and quantitative RT-PCR/Northern blot analyses showed that Trx1 upregulates members of the let-7 family, including miR-98, in the heart and the cardiomyocytes therein. Adenovirus-mediated expression of miR-98 in cardiomyocytes reduced cell size both at baseline and in response to Ang II. Knockdown of miR-98, and of other members of the let-7 family, augmented Ang II–induced cardiac hypertrophy, and attenuated Trx1-mediated inhibition of Ang II–induced cardiac hypertrophy, suggesting that endogenous miR-98/let-7 mediates the antihypertrophic effect of Trx1. Cyclin D2 is one of the predicted targets of miR-98. Ang II significantly upregulated cyclin D2, which in turn plays an essential role in mediating Ang II–induced cardiac hypertrophy, whereas overexpression of Trx1 inhibited Ang II–induced upregulation of cyclin D2. miR-98 decreased both expression of cyclin D2 and the activity of a cyclin D2 3′UTR luciferase reporter, suggesting that both Trx1 and miR-98 negatively regulate cyclin D2. Overexpression of cyclin D2 attenuated the suppression of Ang II–induced cardiac hypertrophy by miR-98, suggesting that the antihypertrophic actions of miR-98 are mediated in part by downregulation of cyclin D2.

These results suggest that Trx1 upregulates expression of the let-7 family, including miR-98, which in turn inhibits cardiac hypertrophy, in part through downregulation of cyclin D2.