A peptide of the amino-terminus of GRK2 induces hypertrophy and yet elicits cardioprotection after pressure overload

Abstract

G protein-coupled receptor (GPCR) kinase 2 (GRK2) expression and activity are elevated early on in response to several forms of cardiovascular stress and are a hallmark of heart failure. Interestingly, though, in addition to its well-characterized role in regulating GPCRs, mounting evidence suggests a GRK2 "interactome" that underlies a great diversity in its functional roles. Several such GRK2 interacting partners are important for adaptive and maladaptive myocyte growth; therefore, an understanding of domain-specific interactions with signaling and regulatory molecules could lead to novel targets for heart failure therapy. Herein, we subjected transgenic mice with cardiac restricted expression of a short, amino terminal fragment of GRK2 (βARKnt) to pressure overload and found that unlike their littermate controls or previous GRK2 fragments, they exhibited an increased left ventricular wall thickness and mass prior to cardiac stress that underwent proportional hypertrophic growth to controls after acute pressure overload. Importantly, despite this enlarged heart, βARKnt mice did not undergo the expected transition to heart failure observed in controls. Further, βARKnt expression limited adverse left ventricular remodeling and increased cell survival signaling. Proteomic analysis to identify βARKnt binding partners that may underlie the improved cardiovascular phenotype uncovered a selective functional interaction of both endogenous GRK2 and βARKnt with AKT substrate of 160 kDa (AS160). AS160 has emerged as a key downstream regulator of insulin signaling, integrating physiological and metabolic cues to couple energy demand to membrane recruitment of Glut4. Our preliminary data indicate that in βARKnt mice, cardiomyocyte insulin signaling is improved during stress, with a coordinate increase in spare respiratory activity and ATP production without metabolite switching. Surprisingly, these studies also revealed a significant decrease in gonadal fat weight, equivalent to human abdominal fat, in male βARKnt mice at baseline and following cardiac stress. These data suggest that the enhanced AS160-mediated signaling in the βARKnt mice may ameliorate pathological cardiac remodeling through direct modulation of insulin signaling within cardiomyocytes, and translate these to beneficial effects on systemic metabolism.

A Cardiac Amino-Terminal GRK2 Peptide Inhibits Maladaptive Adipocyte Hypertrophy and Insulin Resistance During Diet-Induced Obesity

“… 5 , 6 Histological analysis of gWAT by hematoxylin and eosin staining revealed an expected increase in adipocyte size in both the NLC and TgβARKnt mice from baseline to 4 and 16 weeks of HFD, but with a visually observable decrease in adipocyte crowning in the βARKnt tissues compared with control ( Figure 3A ). Interestingly, and consistent with our pressure overload study, 23 gWAT weight was significantly reduced in the βARKnt mice at 4 and 16 weeks after HFD compared with control mice ( Figure 3B ). Further, there was a coordinate decrease in average adipocyte size in these mice at 16 weeks compared with NLC ( Figure 3C ), despite no overall difference in cell number between groups ( Figure 3D ).…”

“… 8 This increase in insulin and AS160 signaling led to enhanced cardiomyocyte ATP production and spare respiratory capacity in the presence of both glucose and the fatty acid substrate palmitate. 23 Further, these βARKnt mice exhibited a decrease in gonadal white adipose tissue (gWAT) weight, equivalent to human abdominal fat, both at baseline and 4 weeks after cardiac stress. 23 In the present study, we subjected these cardiac-specific βARKnt transgenic (Tg) male mice to high fat diet (HFD) stress to investigate the linkage between these beneficial cardiac and metabolic effects and determine whether they might prove cardioprotective during metabolic dysfunction.…”

“… 23 Further, these βARKnt mice exhibited a decrease in gonadal white adipose tissue (gWAT) weight, equivalent to human abdominal fat, both at baseline and 4 weeks after cardiac stress. 23 In the present study, we subjected these cardiac-specific βARKnt transgenic (Tg) male mice to high fat diet (HFD) stress to investigate the linkage between these beneficial cardiac and metabolic effects and determine whether they might prove cardioprotective during metabolic dysfunction. Our data indicate beneficial effects on both cardiac remodeling and systemic metabolism after HFD and support the idea that the βARKnt peptide is not only cardioprotective during cardiac stress, but also demonstrates a novel means of cardioprotection and cardiac-mediated regulation of obesity and systemic metabolism during metabolic stress.…”

“…GRK2, also known as βARK1, consists of 3 functional domains: the amino-terminus, central catalytic domain, and carboxyl-terminus. 22 , 23 Overexpression of the catalytic domain negatively affects cardiac function, whereas overexpression of either the carboxyl-terminus (βARKct, a competitive inhibitor of GRK2) or N-terminus (βARKrgs) is cardioprotective. 22 Recent studies have also shown that overexpression of full-length GRK2 in response to cardiac injury down-regulates fatty acid uptake in the heart, whereas overexpression of βARKct enhances fatty acid uptake.…”

“… 15 Our group has recently found that mice overexpressing a short peptide of the amino-terminus, βARKnt, exhibit baseline hypertrophy, a normal adaptive response to transaortic constriction, and yet cardioprotection during chronic pressure overload. 23 Interestingly, these studies uncovered a significant increase in cardiomyocyte insulin and Akt substrate of 160 kDa (AS160) signaling in the βARKnt mice, in contrast to endogenous GRK2, which is known to phosphorylate insulin receptor substrate 1 (IRS-1) and negatively regulate insulin signaling in the heart. 8 This increase in insulin and AS160 signaling led to enhanced cardiomyocyte ATP production and spare respiratory capacity in the presence of both glucose and the fatty acid substrate palmitate.…”