Abstract 254: MicroRNA Regulation of G Protein-Coupled Receptor Kinase 2 After Cardiac Injury

Abstract

The development and progression of heart failure (HF) involves many processes that occur after cardiac stress and/or injury. Compensatory neuro-hormonal activation and chronic stimulation of the sympathetic nervous system (SNS) is accompanied by the pathological increase in G protein-coupled receptor kinase (GRK) 2 expression. Data indicates that elevated GRK2 activity participates in the progression of HF after cardiac injury such as a myocardial infarction (MI) and this includes chronic β 1 -adrenergic receptor (β 1 AR) desensitization. The molecular transcriptional or translational mechanism of GRK2 upregulation in the heart is largely unknown. MicroRNAs (miRNAs) have been discovered as critical regulatory molecules in the heart as their expression profiles become dysregulated after cardiac injury. Further, miRNAs can play key roles in orchestrating many phenotypic changes observed in HF. Previous studies have shown that components of the βAR pathway, including the β 1 AR, are targeted by miRNAs whose levels are aberrant during cardiac injury. This study was started to determine if GRK2 may also be targeted by a miRNA that goes down after injury, participating in the up-regulation of this pathological kinase. MiRNA profiles of 2 week post-MI C57BL/6 mice were examined through miRNA microarray analysis. MiRNAs that were down-regulated after MI and had seed sequence complementarity to GRK2’s 3’UTR were selected as candidates for further testing. MiR-378a-5p (miR-378a) was chosen as a suitable candidate and transfection of a miR-378a mimic into neonatal rat ventricular myocytes was able to significantly reduce GRK2 protein levels compared to a negative control, while mRNA levels seem to be unaffected. This suggests miR-378a may work primarily through translational inhibition rather than transcriptional inhibition. Using a 3’UTR reporter system, we found that miR-378a was able to directly bind to the 3’UTR of GRK2 and inhibit reporter activity. These data support the hypothesis that GRK2 is regulated by a miRNA in the heart and provides a possible mechanism for GRK2 post-transcriptional regulation . In vivo studies are currently in progress to determine if miR-378a may be a novel therapeutic strategy to decrease GRK2 levels in the failing heart.