Abstract 1629: Adrenal-Targeted GRK2 Gene Deletion Ameliorates Sympathetic Overstimulation and Improves Function of the Failing Heart
Chronic heart failure (HF) is characterized by sympathetic overactivity reflected by enhanced circulating catecholamines (CAs), which contribute to increased morbidity and mortality. We recently reported that adrenal G-protein coupled receptor kinase-2 (GRK2) is up-regulated in chronic HF, leading to enhanced CA release via desensitization/downregulation of the chromaffin cell a2-adrenergic receptors (a2ARs) that normally inhibit CA secretion. We also showed that adrenal GRK2 inhibition via adenoviral-mediated in vivo gene therapy acutely decreases circulating CAs and improves cardiac inotropic reserve and function ( Lymperopoulos, A. et al., Nat. Med. 13 : 315–323, 2007). In the present study, we hypothesized that adrenal-targeted GRK2 gene deletion might be beneficial in chronic HF by means of normalizing sympathetic activity.
Methods: To specifically delete GRK2 only in the chromaffin cells of the adrenal gland, we utilized the Cre/loxP technology, crossing PNMT-Cre mice, which express Cre recombinase under the gene promoter of phenylethanolamine N-methyl transferase (PNMT), a chromaffin cell-specific enzyme. We crossed these mice with floxGRK2+/+ mice, which have the GRK2 gene flanked by loxP sites, thus targeted for deletion by Cre. At 2 months of age, offspring underwent surgical myocardial infarction (MI) to induce HF, and 4 weeks later, cardiac function, adrenal physiology and CA levels were assessed.
Results: Genetic screening and western blotting in adrenal extracts confirmed a significant (54 ± 10 % vs. control, non-crossed floxGRK2+/+) reduction of adrenal GRK2 protein levels in PNMTCre/floxGRK2 mice. Adrenal weight-to-body weight ratio was also significantly lower at 4 weeks post-MI, indicating prevention of post-MI adrenal hypertrophy. Additionally, plasma circulating CAs were reduced, and, importantly, cardiac ejection fraction of PNMTCre/floxGRK2 mice was markedly higher than that of floxGRK2+/+ mice at 4-weeks post-MI (39.6 ± 1.0%, n = 9, vs. 30.9 ± 1.6%, n = 11, respectively, p = 0.0005). Moreover, contractile function and βAR signaling significantly improved.
Conclusions: Adrenal-targeted GRK2 gene knockout decreases circulating CAs, leading to improved cardiac inotropic/adrenergic reserve in post-MI HF.
This research has received full or partial funding support from the American Heart Association, AHA Great Rivers Affiliate (Delaware, Kentucky, Ohio, Pennsylvania & West Virginia).