Abstract 318: MicroRNA Regulation of G Protein-Coupled Receptor Kinase 2 After Cardiac Injury

Abstract

The increase in myocardial expression and activity of G Protein-Coupled Receptor (GPCR) Kinase 2 (GRK2) during the development and progression of heart failure (HF) has been documented to be pathological. Upregulation of GRK2 that is involved with deactivating agonist-activated β-adrenergic receptors (βARs) results in weakened contractile responsiveness through decreases in βAR density, coupling, and sensitivity. Non-GPCR activity of GRK2 has also been shown to be involved in cardiac dysfunction. Studies with knockout or blockade of GRK2 are able to significantly reduce and/or prevent HF phenotypes. Conversely, models with over-expressed GRK2 produce increased injury and accelerated HF development. Being such an important kinase in cardiac disease, regulation of GRK2 expression and activity is critical. Of interest, there is not much known about how GRK2 is regulated (mRNA or protein) in the heart and mechanisms for its up-regulation after cardiac injury are not well understood. There is evidence of GRK2 being regulated by microRNAs (miRNAs) in endothelial and blood cells. We believe cardiac GRK2 may also be regulated in a similar miRNA-mediated fashion. MiRNA profiles become dysregulated with the onset of stress/injury and contribute to orchestrating many classical HF phenotypes, including βAR aberrations. We hypothesize that the expression of a GRK2-regulating miRNA is altered in HF, which contributes to changes in GRK2 regulation resulting in its pathological increase. MiRNA microarray analysis was done on 2-week post-myocardial infarction (MI) murine hearts to examine miRNA profiles compared to sham-operated. Cardiac miRNA species were examined for their expression levels, seed sequence, and TargetScan prediction and alignment to mouse and human GRK2 3’UTR. Candidate miRNAs underwent 3’UTR analysis against GRK2 3’UTR and transfection into AC16 cardiac cells. Two miRNAs were identified to significantly reduce GRK2 protein and/or RNA levels as well directly bind to the 3’UTR of GRK2. Further studies will be done to elucidate the mechanism these miRNAs are able to regulate GRK2 levels. Results from these studies can be applied towards GRK2 inhibition via miRNA-based therapeutics.