MiR-132 Regulates Rem Expression in Cardiomyocytes During Long-Term β-Adrenoceptor Agonism

Aims: To characterize the effects of long-term β-adrenergic receptor stimulation on Rem protein and mRNA expression in rat heart and possible involvement of miR-132. Methods: Adult rats were treated with isoproterenol (ISO, 150 µg.kg.h -1 ) for 2 d and Rem, miR-132, and α 1c (the principal subunit of Cav1.2 channels) were measured at protein and mRNA levels with western blot and quantitative reverse transcriptase polymerase chain reaction (qRTPCR) experiments, respectively. Ca 2+ currents and intracellular Ca 2+ signals were evaluated in isolated cardiomyocytes. Results: Systemic administration of ISO led to decreases in Rem protein and mRNA levels (down to 49%). Furthermore, levels of the microRNAs (miRs) miR-132 and miR-214 were upregulated 5- and 9-fold, respectively. Transfection of miR-132, but not miR-214, into HEK293 cells reduced the expression of a luciferase reporter gene controlled by a conserved 3´-untranslated region (UTR) of Rem by half. Chronic ISO administration also led to a 25% decrease in the amplitude of peak L-type Ca 2+ currents, a 40% decrease in α 1c subunit protein abundance at the membrane level, and a 60% decrease in expression of α 1c channel subunit mRNA. Conclusions: These results suggest that Rem expression is down-regulated posttranscriptionally by miR-132 in response to long-term activation of β-adrenergic signaling, but this down-regulation does not produce a larger Ca 2+ influx through Cav1.2 channels.