βARKct gene-therapy improves β2-adrenergic receptor-dependent neoangiogenesis following hindlimb ischemia

Following hindlimb ischemia (HI) increased catecholamine levels within the ischemic muscle can cause dysregulation of β2-adrenergic receptor (β2AR) signaling leading to reduced revascularization. Indeed, in vivo β2AR overexpression, via gene therapy, enhances angiogenesis in a rat model of HI. G protein-coupled receptor kinase 2 (GRK2) is a key regulator of βAR signaling, and βARKct, a peptide inhibitor of GRK2, has been shown to prevent βAR down-regulation and to protect cardiac myocytes and stem cells from ischemic injury, through restoration of β2AR protective signaling (i.e. Akt/eNOS). Herein, we tested potential therapeutic effects of adenoviral-mediated βARKct gene transfer in an experimental model of HI and its effects on βAR signaling and on endothelial cell (EC) function in vitro. Accordingly, in this study, we surgically induced HI in rats by femoral artery resection (FAR). Fifteen days of ischemia resulted in significant βAR down-regulation that was paralleled by an about 2-fold increase in GRK2 levels in the ischemic muscle. Importantly, in vivo gene transfer of the βARKct in the hindlimb of rats at the time of FAR resulted in a marked improvement of hindlimb perfusion, with increased capillary and βAR density in the ischemic muscle, compared to control groups. The effect of βARKct expression was also assessed, in vitro in cultured ECs. Interestingly, in ECs expressing the βARKct, fenoterol, a β2AR-agonist, induced enhanced β2AR pro-angiogenic signaling and increased EC function. In conclusion, our results suggest that βARKct gene-therapy and subsequent GRK2 inhibition promotes angiogenesis in a model of HI by preventing ischemia-induced β2AR downregulation.