Gi-biased β2AR signaling links GRK2 upregulation to heart failure

Rationale: Phosphorylation of β ₂-adrenergic receptor (β ₂AR) by a family of serine/threonine kinases known as G protein-coupled receptor kinase (GRK) and protein kinase A (PKA) is a critical determinant of cardiac function. Upregulation of G protein-coupled receptor kinase 2 (GRK2) is a well-established causal factor of heart failure, but the underlying mechanism is poorly understood. Objective: We sought to determine the relative contribution of PKA-and GRK-mediated phosphorylation of β ₂AR to the receptor coupling to G _i signaling that attenuates cardiac reserve and contributes to the pathogenesis of heart failure in response to pressure overload. Methods and Results: Overexpression of GRK2 led to a G _i-dependent decrease of contractile response to βAR stimulation in cultured mouse cardiomyocytes and in vivo. Importantly, cardiac-specific transgenic overexpression of a mutant β ₂AR lacking PKA phosphorylation sites (PKA-TG) but not the wild-type β ₂AR (WT-TG) or a mutant β ₂AR lacking GRK sites (GRK-TG) led to exaggerated cardiac response to pressure overload, as manifested by markedly exacerbated cardiac maladaptive remodeling and failure and early mortality. Furthermore, inhibition of G _i signaling with pertussis toxin restores cardiac function in heart failure associated with increased β ₂AR to G _i coupling induced by removing PKA phosphorylation of the receptor and in GRK2 transgenic mice, indicating that enhanced phosphorylation of β ₂AR by GRK and resultant increase in G _i-biased β ₂AR signaling play an important role in the development of heart failure. Conclusions: Our data show that enhanced β ₂AR phosphorylation by GRK, in addition to PKA, leads the receptor to G _i-biased signaling, which, in turn, contributes to the pathogenesis of heart failure, marking G _i-biased β ₂AR signaling as a primary event linking upregulation of GRK to cardiac maladaptive remodeling, failure and cardiodepression.