GRK2-Mediated Desensitization of AdipoR1 in Failing Heart
Background—Phosphorylative desensitization of G-protein coupled receptors (GPCR) contributes significantly to post-myocardial infarction (MI) remodeling and heart failure (HF). Here, we determined whether adiponectin receptors 1 and 2 (AdipoR1/AdipoR2, the 7-transmembrane domain-containing receptors mediating adiponectin functions) are phosphorylatively modified and functionally impaired post-MI.
Methods and Results—Post-MI HF was induced by coronary artery occlusion. Receptor phosphorylation, kinase expression, and APN function were determined via in vivo, ex vivo, and in vitro models. AdipoR1/AdipoR2 are not phosphorylated in the normal heart. However, AdipoR1 was significantly phosphorylated post-MI, peaking at 7 days and remaining significantly phosphorylated thereafter. The extent of post-MI AdipoR1 phosphorylation positively correlated with the expression level of GPCR kinase 2 (GRK2), the predominant GRK isoform upregulated in the failing heart. Cardiac-specific GRK2 knockout virtually abolished post-MI AdipoR1 phosphorylation, whereas virus-mediated GRK2 overexpression significantly phosphorylated AdipoR1 and blocked APN metabolic-regulatory/anti-inflammatory signaling. Mass spectrometry identified Ser7, Thr24, and Thr53 (residues located in the n-terminal intracellular AdipoR1 region) as the GRK2 phosphorylation sites. Ex vivo experiments demonstrated AMPK activation and anti-TNFα effect of APN were significantly inhibited in cardiomyocytes isolated from non-ischemic area 7 days post-MI. In vivo experiments demonstrated that acute APN administration-induced cardiac GLUT4 translocation and eNOS phosphorylation was blunted 7 days post-MI. Continuous APN administration beginning 7 days post-MI failed to protect the heart from adverse remodeling and HF progression. Finally, cardiac-specific GRK2 knockdown restored APN cardioprotective effect.
Conclusions—AdipoR1 is phosphorylatively modified and desensitized by GRK2 in failing cardiomyocytes, contributing to post-MI remodeling and HF progression.
- Received December 31, 2014.
- Revision received February 9, 2015.
- Accepted February 13, 2015.