Background Alterations in cardiac energy metabolism downstream of neurohormonal stimulation play a crucial role in the pathogenesis of heart failure (HF). The chronic adrenergic stimulation that accompanies HF is a signaling abnormality that leads to the up-regulation of G protein-coupled receptor kinase 2 (GRK2), which is pathological in the myocyte during disease progression in part due to uncoupling of the β-adrenergic receptor (βAR) system. In this study we explored the possibility that enhanced GRK2 expression and activity, as seen during HF, can negatively affect cardiac metabolism as part of its pathogenic profile. Methods and Results Positron Emission Tomography (PET) studies revealed that transgenic mice with cardiac-specific overexpression of GRK2 negatively impacted cardiac metabolism by inhibiting glucose uptake and desensitization of insulin signaling, which increases after ischemic injury and precedes HF development. Mechanistically, GRK2 interacts with and directly phosphorylates insulin receptor substrate-1 (IRS1) in cardiomyocytes causing insulin-dependent negative signaling feedback including inhibition of membrane translocation of the glucose transporter, GLUT4. This identifies IRS1 as a novel non-receptor target for GRK2 and represents a new pathological mechanism for this kinase in the failing heart. Importantly, inhibition of GRK2 activity prevents post-ischemic defects in myocardial insulin signaling and improves cardiac metabolism via normalized glucose uptake, which appears to participate in GRK2-targeted prevention of HF. Conclusions Our data provide novel insight into how GRK2 is pathological in the injured heart. Moreover, it appears to be a critical mechanistic link within neurohormonal crosstalk governing cardiac contractile signaling/function through βARs and metabolism through the insulin receptor.

Rationale GRK2 is abundantly expressed in the heart and its expression and activity is increased in injured or stressed myocardium. This up-regulation has been shown to be pathological. GRK2 can promote cell death in ischemic myocytes and its inhibition by a peptide comprised of the last 194 amino acids of GRK2 (known as βARKct) is cardioprotective. Objective The aim of this study was to elucidate the signaling mechanism that accounts for the pro-death signaling seen in the presence of elevated GRK2 and the cardioprotection afforded by the βARKct. Methods and Results Using in vivo mouse models of ischemic injury and also cultured myocytes we found that GRK2 localizes to mitochondria providing novel insight into GRK2-dependent pathophysiological signaling mechanisms. Mitochondrial localization of GRK2 in cardiomyocytes was enhanced after ischemic and oxidative stress, events that induced pro-death signaling. Localization of GRK2 to mitochondria was dependent upon phosphorylation at residue Ser670 within its extreme carboxyl-terminus by extracellular signal-regulated kinases (ERKs), resulting in enhanced GRK2 binding to heat shock protein 90 (Hsp90), which chaperoned GRK2 to mitochondria. Mechanistic studies invivo and invitro showed that ERK regulation of the C-tail of GRK2 was an absolute requirement for stress-induced, mitochondrial-dependent pro-death signaling, and blocking this led to cardioprotection. Elevated mitochondrial GRK2 also caused increased Ca2+-induced opening of the mitochondrial permeability transition pore, a key step in cellular injury. Conclusions We identify GRK2 as a pro-death kinase in the heart acting in a novel manner through mitochondrial localization via ERK regulation.

Recent cases of porcine reproductive and respiratory syndrome virus (PRRSV) infection in United States swine-herds have been associated with high mortality in piglets and severe morbidity in sows. Analysis of the ORF5 gene from such clinical cases revealed a unique restriction fragment polymorphism (RFLP) of 1-7-4. The genome diversity of seventeen of these viruses (81.4% to 99.8% identical; collected 2013-2015) and the pathogenicity of 4 representative viruses were compared to that of SDSU73, a known moderately virulent strain. Recombination analyses revealed genomic breakpoints in structural and nonstructural regions of the genomes with evidence for recombination events between lineages. Pathogenicity varied between the isolates and the patterns were not consistent. IA/2014/NADC34, IA/2013/ISU-1 and IN/2014/ISU-5 caused more severe disease, and IA/2014/ISU-2 did not cause pyrexia and had little effect on pig growth. ORF5 RFLP genotyping was ineffectual in providing insight into isolate pathogenicity and that other parameters of virulence remain to be identified.

BackgroundEnhancing our prognostic capabilities in terms of response to evidence-based therapies in heart failure (HF) may lead to improved patient outcomes and a more cost-eff ective approach to this complex syndrome. Biomarkers appropriately satisfy this role by providing the potential to enhance our diagnostic, therapeutic, and prognostic approach to the complex treatment of HF patients. Th ere have been many research endeavors examining various natriuretic peptides, extracellular and intracellular molecules, neurohormones, and infl ammatory mediators with the hope of providing insight into the pathophysiologic mechanism(s) of left ventricular (LV) systolic dysfunction, the volume-overload state, decompensation, and prognosis.1 Despite these discoveries, we still lack a complete understanding of the complex pathophysiology of HF and response to various therapies.Evidence-based medical therapies, including β-adrenergic receptor (βAR) antagonists (β-blockers), angiotensin-converting enzyme (ACE) inhibitors, and aldosterone receptor antagonists, are the cornerstones of pharmacologic therapy for LV systolic dysfunction and congestive HF. It is unclear as to why LV systolic function improves and sometimes even normalizes in some patients, while others show no improvement in ejection fraction or LV remodeling refl ected in ventricular dimensions.We, and others, have previously studied how these G protein-coupled receptors (GPCRs) are dysregulated in the heart.2,3 Much of this work has focused on GPCR kinases (GRKs), which are responsible for the desensitization of βARs and other receptors in the heart dampening signal transduction throughout the myocyte. G protein-coupled receptor kinase 2 (GRK2) is the most abundant GRK expressed in cardiac myocytes, and it has been known for over a decade that this kinase is elevated in failing myocardium. 4 Importantly, we have shown that human myocardial levels of GRK2 are mirrored by levels found in white blood cells.5 Moreover, levels of blood GRK2 expression were inversely correlated with LV systolic function, and higher levels of expression were seen with more advanced New York Heart Association (NYHA) functional classes of HF. 5Of note, we have previously found that modalities that improve cardiac function and reverse LV remodeling can decrease GRK2 levels in both cardiac tissue and white blood cells.6 This was shown in severe HF patients undergoing implantation of mechanical LV assist devices (LVADs), which are an important therapeutic option for many patients needing additional hemodynamic support either as a bridge to ventricular recovery or cardiac transplantation or as destination therapy. 7 LVAD patients were followed with cardiac and blood samples taken at the time of LVAD implantation and also 2-3 months later during cardiac transplantation, and LV unloading caused a signifi cant downregulation of cardiac GRK2 and improved βAR signaling, which was mirrored in decreased lymphocyte levels of GRK2.6 Th is fi nding supports our hypothesis that blood GRK2 levels may be ...

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