Heterodimer of b1-AR and b2-AR Optimizes b-AR Modulation

在各种实验系统中，相似的和不同的G蛋白偶联受体亚家族的成员之间的分子间相互作用已经被证明。在这里，我们展示了心脏中主要的b-肾上腺素能受体(BAR)亚型b1AR和B2AR的异二聚化及其生理相关性。在缺乏天然b1AR和B2AR的完整成年小鼠心肌细胞中，两种bar亚型的共表达导致了受体的异二聚化，这表现为它们的免疫共沉淀、光学分辨率的共定位，并显著增加了亚型选择配体的结合亲和力。结果表明，心肌细胞对异丙肾上腺素(ISO)激动剂刺激的心肌细胞收缩的量效曲线左移约1.5个数量级，细胞cAMP生成对ISO的反应增强，提示BAR亚型的分子间相互作用导致这些受体对激动剂刺激的敏化。相反，b1AR的存在极大地抑制了共存的b2AR的非配体依赖的自发活动。因此，b1AR和B2AR在完整的心肌细胞中的异源二聚化形成了一个具有不同功能和药理学特性的新的条群，导致在沉默配体非依赖性受体激活的同时提高了对激动剂刺激的信号效率，从而优化了b-肾上腺素能对心肌收缩的调节。

Intermolecular interactions between members of both similar and divergent G protein-coupled receptor subfamilies have been shown in various experimental systems. Here, we demonstrate heterodimerization of predominant b-adrenergic receptor (bAR) subtypes expressed in the heart, b1AR and b2AR, and its physiological relevance. In intact adult mouse cardiac myocytes lacking native b1AR and b2AR, co-expression of both bAR subtypes led to receptor heterodimerization, as evidenced by their co-immunoprecipitation, co-localization at optical resolution, and markedly increased binding affinity for subtype-selective ligands. As a result, the dose-response curve of myocyte contraction to bAR agonist stimulation with isoproterenol (ISO) was shifted leftward by ~1.5 orders of magnitude, and the response of cellular cAMP formation to ISO was enhanced concomitantly, indicating that intermolecular interactions of bAR subtypes resulted in sensitization of these receptors in response to agonist stimulation. In contrast, the presence of b1AR greatly suppressed ligand-independent spontaneous activity of co-existing b2ARs. Thus, heterodimerization of b1AR and b2AR in intact cardiac myocytes creates a novel population of bARs with distinct functional and pharmacological properties, resulting in enhanced signaling efficiency in response to agonist stimulation while silencing ligand-independent receptor activation, thereby optimizing b-adrenergic modulation of cardiac contractility.