Loss of S-nitrosylation of G Protein-Coupled Receptor Kinase 2 Leads to Cardiovascular Dysfunction With Aging

Nitric oxide (NO) and S-nitrosothiol (SNO) have cardiovascular-protective properties and we have shown that one mechanism is through SNO-modification of G protein-coupled receptor (GPCR) kinase 2 (GRK2). S-nitrosylation at Cys340 (C340S) of GRK2 inhibits its activity on GPCRs such as β-adrenergic receptors in the heart and other GRK2 dependent processes. S-nitrosylation is believed to act as a brake on this pathological kinase. We generated global knock-in (KI) mice that express endogenous levels of GRK2, but with C340 mutated to Ser (GRK2-C340S). The C340 site is the primary site of S-nitrosylation and is largely responsible for eNOS-mediated cardioprotection after acute ischemic injury of the heart. In this study we observed that the loss of SNO-mediated inhibition of GRK2 leads to cardiovascular dysfunction during normal aging. GRK2 has been shown to be up-regulated during several cardiovascular (CV) pathologies including hypertension and heart failure, and aging is a major risk factor of CV disease (CVD). GRK2-C340S KI mice compared to their wild-type (WT) controls showed significant pathology as early as 52 weeks of age and was maintained up to 82 weeks. Maladaptive cardiac hypertrophy was present in aged GRK2-C340S mice with significant perivascular myocardial fibrosis. Fibrosis was prevalent in the kidneys as well. These histological changes were accompanied by reduced systolic function and pulse pressure compared to WT mice. Within the vasculature, aged GRK2-C340S aortas had reduced medial thickness and had reduced contraction in response to PE, KCl, or L-NAME. Acetylcholine-induced relaxation responses remained intact. Consistent with enhanced GRK2 activity in vivo in the heart, we found increased circulating levels of serum catecholamines. Many of these phenotypes we observed in GRK2-C340S mice are also observed in human aging and CVD. These phenotypes predispose patients to developing other diseases. As the US population becomes increasingly older, understanding the dynamic between aging and CVD is important in disease management and therapy. The aged GRK2-C340S mouse model represents a model of higher CVD risk and provides insights into consequences of chronic GRK2 global over-activity when the regulation of this kinase by NO is lost.