Internalized ß2-Adrenergic Receptors Oppose PLC-Dependent Hypertrophic Signaling.

ABSTRACT

BACKGROUND: Chronically elevated neurohumoral drive, and particularly elevated adrenergic tone leading to ß-adrenergic receptor (ß-AR) overstimulation in cardiac myocytes, is a key mechanism involved in the progression of heart failure. ß1-AR (ß1-adrenergic receptor) and ß2-ARs (ß2-adrenergic receptor) are the 2 major subtypes of ß-ARs present in the human heart; however, they elicit different or even opposite effects on cardiac function and hypertrophy. For example, chronic activation of ß1-ARs drives detrimental cardiac remodeling while ß2-AR signaling is protective. The underlying molecular mechanisms for cardiac protection through ß2-ARs remain unclear. METHODS: ß2-AR signaling mechanisms were studied in isolated neonatal rat ventricular myocytes and adult mouse ventricular myocytes using live cell imaging and Western blotting methods. Isolated myocytes and mice were used to examine the roles of ß2-AR signaling mechanisms in the regulation of cardiac hypertrophy. RESULTS: Here, we show that ß2-AR activation protects against hypertrophy through inhibition of phospholipaseCε signaling at the Golgi apparatus. The mechanism for ß2-AR-mediated phospholipase C inhibition requires internalization of ß2-AR, activation of Gi and Gßγ subunit signaling at endosome and ERK (extracellular regulated kinase) activation. This pathway inhibits both angiotensin II and Golgi-ß1-AR-mediated stimulation of phosphoinositide hydrolysis at the Golgi apparatus ultimately resulting in decreased PKD (protein kinase D) and histone deacetylase 5 phosphorylation and protection against cardiac hypertrophy. CONCLUSIONS: This reveals a mechanism for ß2-AR antagonism of the phospholipase Cε pathway that may contribute to the known protective effects of ß2-AR signaling on the development of heart failure.