Purpose: Changes to the cellular expression of numerous microRNAs (miRs) have been implicated in disease development. MiR-1 expression is down-regulated in human heart failure (HF) and our in vivo rat HF model, we aimed to further understand its significance in HF. We previously showed that miR-1 expression was restored by in vitro adenovirus-mediated restoration of SERCA2a in adult rat HF cardiomyocytes, in response to diastolic calcium changes.
Methods: Adult rats that underwent surgical ligation of the left anterior descending coronary artery to induce myocardial infarction (>30%) were maintained 16-20 weeks until HF developed. Cardiomyocytes were isolated for in vitro transfection by lipofection with miR-1 constructs followed by 48 hours culture. We examined cardiomyocyte calcium handling, contractile function, and gene expression analysis by quantitative RT-PCR.
Results: The contractile beta-adrenoceptor (βAR) response to isoprenaline was depressed in cardiomyocytes from HF rats, but was restored in HF cardiomyocytes by increasing miR-1 expression (Figure 1) with a mature miR-1 construct. Selective pharmacological inhibition revealed that SERCA2a function was unchanged, and that it was an elevated β2AR response that had improved cell shortening in the HF cardiomyocytes to levels comparable to healthy. β2AR expression was unchanged after pre miR-1 treatment, implying it is the functional signalling of the receptor that is influenced by miR-1.
Conclusion: Restoration of miR-1 reverses HF-induced βAR desensitisation. We suggest that the SERCA2a down-regulation and consequent increase of diastolic calcium may signal through miR-1 reduction to produce βAR signalling alterations in HF.