Abstract Body: Introduction: Inhibition of the G-protein-coupled receptor kinase 2 (GRK2) is a promising experimental treatment approach for heart failure. However, so far, a GRK2 inhibitor for patient use is not available. A major problem is that GRK2 exerts indispensable physiological functions which cannot be inhibited without major side effects, and the knockout of GRK2 is lethal.
Research Question and Aim: The development of successful GRK2 inhibitors could be supported by molecular markers which serve as indicators for cardioprotective GRK2 inhibition. We aimed to identify such markers in vivo, in hearts with GRK2 inhibition compared to hearts with unrestrained GRK2.
Methods: As a GRK2 inhibitor, we applied the GRK2-inhibitory, dominant negative mutant, GRK2K220R. To investigate cardiac effects of GRK2 inhibition, we generated transgenic mice with myocardium-specific expression of GRK2K220R. Male transgenic Tg-GRK2K220R mice aged 8 months were compared to male, age-matched, non-transgenic B6 mice. Cardiac function and cardiac dimensions were measured by echocardiographic imaging. Transcriptome changes were determined by next generation sequencing (NGS), and cardiac proteins were quantified by immunoblot.
Results: Transgenic Tg-GRK2K220R mice with inhibition of cardiac GRK2 were healthy and had a significantly improved left ventricular ejection fraction (LVEF). The LVEF of Tg-GRK2K220R mice was 55.6 ± 1.8 %, whereas the LVEF of non-transgenic B6 mice was 51.0 ± 2.3 % (n=6, mean ± s.d., p = 0.0033, t=3.826, df = 10). Heart dimensions were not changed by GRK2K220R. Transcriptome profiling by NGS found that transcript levels of two heart failure markers, Nppb (natriuretic peptide B) and Adipoq (adiponectin), were significantly lower in Tg-GRK2K220R mice when compared to non-transgenic B6 mice with unrestrained GRK2. As a marker of cardiac oxygen deficiency, cardiac protein levels of SUMO1 were determined, which is induced by hypoxia. Immunoblot detection found that cardiac SUMO1 levels were significantly lower in Tg-GRK2K220R mice compared to those of non-transgenic mice.
Conclusion: Taken together, unbiased NGS transcriptome profiling and immunoblot detection found that GRK2 inhibition by GRK2K220R in mice improved markers of heart failure and hypoxia when compared to healthy non-transgenic, age-matched and sex-matched control mice.