The functional role of beta-arrestins in beta-adrenergic receptor (beta-AR) desensitization and recycling in physiological contexts remains largely elusive. Here, we demonstrate that deficiency of beta-arrestin2 in mice (beta-arrestin2 KO) causes defects in cardiac contractile response to stimulation of both beta-AR subtypes. The reduced beta-AR responsiveness is not associated with alterations in the expression of Gs or Gi proteins or the receptor density or its ligand binding properties, but is accompanied by a marked increase in phosphorylation of both bAR subtypes. Furthermore, the increased phosphorylation of b2AR is associated with markedly reduced binding of the receptor to PP2A, indicating that b-arrestins is necessary for the physical interaction between b2AR and PP2, thus for the receptor resensitization. Indeed, inhbition of b2AR phosphorylation by BARK1 via adenoviral gene transfer of a BARK1 peptide inhibitor, BARK-ct, is able to rescue the function of both b1AR and b2AR in myocytes from b-arrestin2 knockout mice. This unexpected finding is in sharp contrast to the established paradigm that beta-arrestin2 promotes beta-AR desensitization, and argues against the hypothesis that reduction or deficiency of beta-arrestin2 should enhance beta-AR signaling efficiency. Importantly, adenoviral gene transfer of beta-arrstin2 is able to fully restore beta-AR mediated contractile response in cardiomyocytes from beta-arrestin2 KO mice, indicating that the defect of beta-AR contractile response is attributable to the deficiency of beta-arrestin2 rather that the gene knockout associated nonspecific adaptive changes. These results also suggest that beta-arrestin2 plays an essential role in beta-AR resensitiztion, but not in the receptor desensitization. This conclusion is corroborated by the fact that in the failing hearts from spontaneous hypertensive rats (SHR), the abundance of beta-arrestin2 is markedly decreased before the onset of heart failure, and that the downregulation of beta-arrestin2 is accompanied by overtly attenuated cardiac contractile response to either beta-AR subtype stimulation. These findings have revealed a previously unrecognized crucial role of beta-arrestin2 in catecholamine-mediated contractile support and a potential causal relation between downregulation of beta-arresin2 and the development of heart failure. Thus, our study might reveals novel causal factors and potential therapeutic targets of heart failure.
| Zhu, Weizhong; Petrashevskaya, Natalia; Ren, Shuxun et al. (2012) Gi-biased ?2AR signaling links GRK2 upregulation to heart failure. Circ Res 110:265-74 |
