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 α1c (the principal subunit of Cav1.2 channels) were measured at protein and mRNA levels with western blot and quantitative reverse transcriptase polymerase chain reaction (qRT-PCR) 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 α1c subunit protein abundance at the membrane level, and a 60% decrease in expression of α1c 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.