G _βγ -Independent Recruitment of G-Protein Coupled Receptor Kinase 2 Drives Tumor Necrosis Factor α–Induced Cardiac β-Adrenergic Receptor Dysfunction

Abstract

Back ground Pro-inflammatory cytokine tumor necrosis factor α (TNFα) induces β-adrenergic receptor (βAR) desensitization, but mechanisms proximal to the receptor in contributing to cardiac dysfunction are not known. Methods and Results Two different pro-inflammatory transgenic mouse models with cardiac overexpression of Myotrophin (a pro-hypertrophic molecule) or TNFα showed that TNFα alone is sufficient to mediate βAR desensitization as measured by cardiac adenylyl cyclase activity. M-mode echocardiography in these mouse models showed cardiac dysfunction paralleling βAR desensitization independent of sympathetic overdrive. TNFα-mediated βAR desensitization that precedes cardiac dysfunction is associated with selective upregulation of G-protein coupled receptor kinase 2 (GRK2) in both the mouse models. In vitro studies in β2 AR overexpressing HEK 293 cells showed significant βAR desensitization, GRK2 upregulation and recruitment to the βAR complex following TNFα. Interestingly, inhibition of PI3K abolished GRK2-mediated βAR phosphorylation and GRK2 recruitment upon TNFα. Furthermore, TNFα-mediated βAR phosphorylation was not blocked with βAR antagonist propranolol. Additionally, TNFα administration in transgenic mice with cardiac overexpression of Gβγ sequestering peptide βARK-ct could not prevent βAR desensitization or cardiac dysfunction showing that GRK2 recruitment to the βAR is Gβγ independent. siRNA knock down of GRK2 resulted in loss of TNFα-mediated βAR phosphorylation. Consistently, cardiomyocytes from mice with cardiac-specific GRK2 ablation normalized the TNFα-mediated loss in contractility showing that TNFα-induced βAR desensitization is GRK2 dependent. Conclusions TNFα-induced βAR desensitization is mediated by GRK2 and is independent of Gβγ uncovering a hitherto unknown cross-talk between TNFα and βAR function providing the underpinnings of inflammation-mediated cardiac dysfunction.

Cardiac Biomarkers in Youth with Type 2 Diabetes Mellitus: Results from the TODAY Study

“…Laboratory studies have implicated TNF in regulation of myocardial cell function. 11 Two large cohort studies of T2D suggest TNF receptor 1 (R1) and TNF receptor 2 (R2) predict future kidney disease, CVD, and total mortality. 12–14 …”

Trafficking of β-Adrenergic Receptors

“…Vasudevan et al have reported that βAR dysfunction is independent of sympathetic overdrive in conditions of inflammation. 78 The observed βAR dysfunction is associated with selective upregulation of GRK2 in two proinflammatory mouse models of heart failure (Myo-Tg and TNFα-Tg). Studies from TNFR1 or TNFR2 knockout mice show that TNFR2 preferentially recruits GRK2-mediating β 2 AR phosphorylation.…”

“…Therefore, these findings have identified that TNFα-induced agonist-independent βAR internalization is mediated by GRK2, uncovering a cross talk between TNFR2 and βAR function, providing the underpinnings of inflammation-mediated cardiac dysfunction. 78 The neurohormone arginine vasopressin (AVP) is elevated in patients with heart failure, and there is a direct relationship between plasma levels of AVP and disease severity and mortality. Tilley et al have reported that AVP acutely inhibits βAR-mediated cardiac contractility via a GRKdependent and Gq protein-independent mechanism.…”

Proinflammatory Cytokines Mediate GPCR Dysfunction

“…The immediate effects of pro-inflammatory cytokines are identified to be on EC coupling 19, 28–40 , on nitric oxide production by NOS 65–82 , on Sphingomyelinase-dependent signaling 56, 71, 74, 76, 81–95 , and/or on phospholipase A2 (PLA2) and arachidonic acid (AA) activation 85, 96–102 . In contrast, to these immediate effects, delayed effects that play a key role in modulating contractile function include altered βAR signaling and loss of βAR responsiveness to its cognate βAR agonist like isoproterenol 10, 71, 103, 104 .…”

“…Given these observations, it becomes imperative to revisit the role of TNFα in pathogenesis of heart failure in the context of recent advances in understanding molecular mechanisms involved in TNFα signaling. Studies have shown that pro-inflammatory cytokines especially TNFα blunts the responsiveness of G protein coupled receptors (GPCRs) particularly beta-adrenergic receptors (βARs) impairing contractile function of the cardiac myocytes 8–10 . Similarly, studies have also shown that βAR receptor signaling can mediate beneficial cardiac effects through TNFα receptor 2 (TNFR2) in contrast to TNFR1 11 .…”