B-Arrestin2 Is Required for BAR Resensitization But Not its Desensitization

在生理环境下，β -抑制素在β -肾上腺素能受体（β -ar）脱敏和再循环中的功能作用仍然难以捉摸。在这里，我们证明了小鼠β -arrestin2的缺乏（β -arrestin2 KO）导致对两种β -ar亚型刺激的心脏收缩反应缺陷。降低的β - ar反应性与Gs或Gi蛋白表达、受体密度或其配体结合特性的改变无关，但伴随着两种bAR亚型磷酸化的显著增加。此外，b2AR磷酸化的增加与受体与PP2A结合的显著减少有关，这表明b-阻滞蛋白对于b2AR和PP2之间的物理相互作用是必要的，因此对于受体的再敏化是必要的。事实上，BARK1通过腺病毒转移BARK1肽抑制剂BARK-ct抑制b2AR磷酸化，能够在b-arrestin2敲除小鼠的肌细胞中恢复b1AR和b2AR的功能。这一意想不到的发现与β -arrestin2促进β -ar脱敏的既定范式形成鲜明对比，并反驳了β -arrestin2的减少或缺乏应该提高β -ar信号传导效率的假设。重要的是，β -arrestin2的腺病毒基因转移能够完全恢复β -ar介导的心肌细胞收缩反应，这表明β -ar收缩反应的缺陷是由于β -arrestin2的缺乏，而不是基因敲除相关的非特异性适应性变化。这些结果也表明β -arrestin2在β -ar再敏中起重要作用，但在受体脱敏中不起作用。在自发性高血压大鼠（SHR）的衰竭心脏中，β -arrestin2的丰度在心力衰竭发作前明显下降，并且β -arrestin2的下调伴随着对β -ar亚型刺激的心脏收缩反应明显减弱，这一事实证实了这一结论。这些发现揭示了β -arresin2在儿茶酚胺介导的收缩支持中的关键作用，以及β -arresin2下调与心力衰竭发展之间的潜在因果关系。因此，我们的研究可能会揭示心力衰竭的新病因和潜在的治疗靶点。

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.