Neonatal cardiomyocyte hypertrophy induced by endothelin-1 is blocked by estradiol acting on GPER.

Estradiol (E2) prevents cardiac hypertrophy, and these protective actions are mediated by estrogen receptor (ER)α and ERß. The G protein-coupled estrogen receptor (GPER) mediates many estrogenic effects, and its activation in the heart has been observed in ischemia and reperfusion injury or hypertension models; however, the underlying mechanisms need to be fully elucidated. Herein, we investigated whether the protective effect of E2 against cardiomyocyte hypertrophy induced by endothelin-1 (ET-1) is mediated by GPER and the signaling pathways involved. Isolated neonatal female rat cardiomyocytes were treated with ET-1 (100 nmol/l) for 48 h in the presence or absence of E2 (10 nmol/l) or GPER agonist G-1 (10 nmol/l) and GPER antagonist G-15 (10 nmol/l). ET-1 increased the surface area of cardiomyocytes, and this was associated with increased expression of atrial and brain natriuretic peptides. Additionally, ET-1 increased the phosphorylation of extracellular signal-related protein kinases-1/2 (ERK1/2). Notably, E2 or G-1 abolished the hypertrophic actions of ET-1, and that was reversed by G-15. Likewise, E2 reversed the ET-1-mediated increase of ERK1/2 phosphorylation as well as the decrease of phosphorylated Akt and its upstream activator 3-phosphoinositide-dependent protein kinase-1 (PDK1). These effects were inhibited by G-15, indicating that they are GPER dependent. Confirming the participation of GPER, siRNA silencing of GPER inhibited the antihypertrophic effect of E2. In conclusion, E2 plays a key role in antagonizing ET-1-induced hypertrophy in cultured neonatal cardiomyocytes through GPER signaling by a mechanism involving activation of the PDK1 pathway, which would prevent the increase of ERK1/2 activity and consequently the development of hypertrophy.

Noncanonical Roles of G Protein-coupled Receptor Kinases in Cardiovascular Signaling.

G protein-coupled receptor kinases (GRKs) are classically known for their role in regulating the activity of the largest known class of membrane receptors, which influence diverse biological processes in every cell type in the human body. As researchers have tried to uncover how this family of kinases, containing only 7 members, achieves selective and coordinated control of receptors, they have uncovered a growing number of noncanonical activities for these kinases. These activities include phosphorylation of nonreceptor targets and kinase-independent molecular interactions. In particular, GRK2, GRK3, and GRK5 are the predominant members expressed in the heart. Their canonical and noncanonical actions within cardiac and other tissues have significant implications for cardiovascular function in healthy animals and for the development and progression of disease. This review summarizes what is currently known regarding the activity of these kinases, and particularly the role of GRK2 and GRK5 in the molecular alterations that occur during heart failure. This review further highlights areas of GRK regulation that remain poorly understood and how they may represent novel targets for therapeutic development.

Localization of G protein-coupled receptor kinases (GRKs) in the avian retina.

G protein-coupled receptor kinases (GRKs) are enzymes involved in agonist-dependent regulation of G protein-coupled receptors. In the present work, we characterized, by immunohistochemistry, the presence of GRKs 2, 3 and 5 in the chick retina, a tissue whose structure and neurochemistry are well known. These enzymes are expressed in specific cell types and regions of the retina. Immunoreactivity for GRK2 was found over photoreceptor inner segments, cell bodies of horizontal, amacrine and ganglion cells. Labeling for this enzyme was also observed over the two plexiform layers. Immunoreactivity for GRK3 was found in cell bodies of amacrine and ganglion cells. In plexiform layers, specific GRK3 immunoreactivity was observed only at the inner plexiform layer, where three bands of high labeling were detected. In contrast to GRK2 and 3, intense immunoreactivity for GRK5 was observed only over Müller cells. Occasionally, labeled amacrine cell bodies were also observed. These results suggest that GRKs 2, 3 and 5 are expressed and involved in the physiology of specific cells types of the retina. They also suggest that receptor-GRK specificity may be determined by the co-expression of the receptor and the kinase within individual cell populations in this tissue.