Abstract
Background In human heart failure, increased expression of G protein–coupled receptor kinases (GRKs) causes the loss of β-adrenergic receptor (βAR) signaling and function. Mechanical unloading with a left ventricular assist device (LVAD) promotes reverse remodeling, which includes restoration of βAR responsiveness. We tested the hypothesis that LVAD support of the failing human heart alters the expression and activity of GRKs and we sought to determine whether changes in myocardial GRKs could be tracked in lymphocytes. Methods and Results Paired samples of human LV tissue (n = 12) and blood were obtained at the time of LVAD implantation (heart failure) and subsequent cardiac transplantation (LVAD). βAR signaling was quantified by receptor density and adenylyl cyclase activity. Immunoblotting and real-time reverse transcription polymerase chain reaction were used to measure GRK2 and GRK5 protein and mRNA levels. Rhodopsin phosphorylation was used to assess total GRK activity. Consistent with reverse remodeling, βAR density and signaling were restored to nonfailing levels after LVAD support. GRK2 protein levels were significantly reduced 55% after LVAD support and GRK2 mRNA was similarly reduced. In contrast, GRK5 protein and mRNA levels were unchanged. Total myocardial GRK activity was reduced similar to the drop in GRK2 expression. In lymphocytes, GRK2 protein levels were decreased after LVAD support and there was a significant positive correlation between myocardial and lymphocyte GRK2 levels in both heart failure and LVAD samples. Conclusion The changes in myocardial GRK2 expression and activity that are mirrored in lymphocytes provide a possible mechanism for the restoration of βAR signaling and reverse remodeling after mechanical unloading in the failing heart. Moreover, lymphocytes may provide a surrogate marker of myocardial GRK2 in these patients.
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