Cardiopulmonary bypass decreases G protein-coupled receptor kinase activity and expression in human peripheral blood mononuclear cells

The Role of G Protein-Coupled Receptor Kinase 6 Regulation in Inflammation and Pain

The G protein-coupled receptor kinase 6 is associated with inflammation and pathological pain. Impairment of GRK6 expression was described in chronic inflammatory diseases such as rheumatoid arthritis and this was shown to be accompanied by an imbalance of downstream signaling pathways. Here, we discuss novel aspects of GRK6 interaction and its impact upon hyperalgesia and inflammatory processes. In this review, we compile important findings concerning GRK6 regulation for a better pathophysiological understanding of the intracellular interaction in the context of inflammation and show clinical implications-for example, the identification of possible therapy goals in the treatment of chronic inflammatory hyperalgesia.

CP-25, a compound derived from paeoniflorin: research advance on its pharmacological actions and mechanisms in the treatment of inflammation and immune diseases

Total glycoside of paeony (TGP) has been widely used to treat inflammation and immune diseases in China. Paeoniflorin (Pae) is the major active component of TGP. Although TGP has few adverse drug reactions, the slow onset and low bioavailability of Pae limit its clinical use. Enhanced efficacy without increased toxicity is pursued in developing new agents for inflammation and immune diseases. As a result, paeoniflorin-6'-O-benzene sulfonate (CP-25) derived from Pae, is developed in our group, and exhibits superior bioavailability and efficacy than Pae. Here we describe the development process and research advance on CP-25. The pharmacokinetic parameters of CP-25 and Pae were compared in vivo and in vitro. CP-25 was also compared with the first-line drugs methotrexate, leflunomide, and hydroxychloroquine in their efficacy and adverse effects in arthritis animal models and experimental Sjögren's syndrome. We summarize the regulatory effects of CP-25 on inflammation and immune-related cells, elucidate the possible mechanisms, and analyze the therapeutic prospects of CP-25 in inflammation and immune diseases, as well as the diseases related to its potential target G-protein-coupled receptor kinases 2 (GRK2). This review suggests that CP-25 is a promising agent in the treatment of inflammation and immune diseases, which requires extensive investigation in the future. Meanwhile, this review provides new ideas about the development of anti-inflammatory immune drugs.

Proinflammatory switch from Gαs to Gαi signaling by Glucagon-like peptide-1 receptor in murine splenic monocyte following burn injury

OBJECTIVE

Glucagon-like peptide-1 (GLP-1)-based therapy via G protein-coupled receptor (GPCR) GLP-1R, to attenuate hyperglycemia in critical care has attracted great attention. However, the exaggerated inflammation by GLP-1R agonist, Exendin-4, in a mouse model of burn injury was quite unexpected. Recent studies found that GPCR might elicit proinflammatory effects by switching from Gαs to Gαi signaling in the immune system. Thus, we aimed to investigate the possible Gαs to Gαi switch in GLP-1R signaling in monocyte following burn injury.

MATERIALS AND METHODS

Splenic monocytes from sham and burn mice 24 h following burn injury were treated with consecutive doses of Exendin-4 alone or in combination with an inhibitor of Gαi signaling (pertussis toxin, PTX), or a blocker of protein kinase A (H89). Cell viability was assessed by CCK-8, and the supernatant was collected for cytokine measurement by ELISA. Intracellular cAMP level, phosphorylated PKA activity, and nuclear NF-κB p65 were determined by ELISA, ERK1/2 activation was analyzed by Western blot. The expression of GLP-1R downstream molecules, Gαs, Gαi and G-protein coupled receptor kinase 2 (GRK2) were examined by immunofluorescence staining and Western blot.

RESULTS

Exendin-4 could inhibit the viability of monocyte from sham rather than burn mice. Unexpectedly, it could also reduce TNF-α secretion from sham monocyte while increase it from burn monocyte. The increased secretion of TNF-α by Exendin-4 from burn monocyte could be reversed by pretreatment of PTX or H89. Accordingly, Exendin-4 could stimulates cAMP production dose dependently from sham instead of burn monocyte. However, the blunt cAMP production from burn monocyte was further suppressed by pretreatment of PTX or H89 after 6-h incubation. Nevertheless, phosphorylated PKA activity was significantly increased by low dose of Exendin-4 in sham monocyte, by contrast, it was enhanced by high dose of Exendin-4 in burn monocyte after 1-h incubation. Following Exendin-4 treatment for 2 h ex vivo, total nuclear NF-κB and phosphorylated NF-κB activity, as well as cytoplasmic pERK1/2 expressions were reduced in sham monocyte, however, only pERK1/2 was increased by Exendin-4 in burn monocytes. Moreover, reduced expressions of GLP-1R, GRK-2 and Gαs in contrast with increased expression of Gαi were identified in burn monocyte relative to sham monocyte.

CONCLUSIONS

This study presents an unexpected proinflammatory switch from Gαs to Gαi signaling in burn monocyte, which promotes ERK1/2 and NF-κB activation and the downstream TNF-α secretion. This phenomenon is most probably responsible for proinflammatory response evoked by Gαs agonist Exendin-4 following burn injury.

Molecular Mechanisms Linking Autonomic Dysfunction and Impaired Cardiac Contractility in Critical Illness

OBJECTIVES

Molecular mechanisms linking autonomic dysfunction with poorer clinical outcomes in critical illness remain unclear. We hypothesized that baroreflex dysfunction alone is sufficient to cause cardiac impairment through neurohormonal activation of (nicotinamide adenine dinucleotide phosphate oxidase dependent) oxidative stress resulting in increased expression of G-protein-coupled receptor kinase 2, a key negative regulator of cardiac function.

DESIGN

Laboratory/clinical investigations.

SETTING

University laboratory/medical centers.

SUBJECTS

Adult rats; wild-type/nicotinamide adenine dinucleotide phosphate oxidase subunit-2-deficient mice; elective surgical patients.

INTERVENTIONS

Cardiac performance was assessed by transthoracic echocardiography following experimental baroreflex dysfunction (sino-aortic denervation) in rats and mice. Immunoblots assessed G-protein-coupled receptor recycling proteins expression in rodent cardiomyocytes and patient mononuclear leukocytes. In surgical patients, heart rate recovery after cardiopulmonary exercise testing, time/frequency measures of parasympathetic variables were related to the presence/absence of baroreflex dysfunction (defined by spontaneous baroreflex sensitivity of <6 ms mm Hg). The associations of baroreflex dysfunction with intraoperative cardiac function and outcomes were assessed.

MEASUREMENTS AND MAIN RESULTS

Experimental baroreflex dysfunction in rats and mice resulted in impaired cardiac contractility and upregulation of G-protein-coupled receptor kinase 2 expression. In mice, genetic deficiency of gp91 nicotinamide adenine dinucleotide phosphate oxidase subunit-2 prevented upregulation of G-protein-coupled receptor kinase 2 expression in conditions of baroreflex dysfunction and preserved cardiac function. Baroreflex dysfunction was present in 81 of 249 patients (32.5%) and was characterized by lower parasympathetic tone and increased G-protein-coupled receptor kinase 2 expression in mononuclear leukocytes. Baroreflex dysfunction in patients was also associated with impaired intraoperative cardiac contractility. Critical illness and mortality were more frequent in surgical patients with baroreflex dysfunction (relative risk, 1.66 [95% CI, 1.16-2.39]; p = 0.006).

CONCLUSIONS

Reduced baroreflex sensitivity is associated with nicotinamide adenine dinucleotide phosphate oxidase subunit-2-mediated upregulation of G-protein-coupled receptor kinase 2 expression in cardiomyocytes and impaired cardiac contractility. Autonomic dysfunction predisposes patients to the development of critical illness and increases mortality.

The GRK2 Overexpression Is a Primary Hallmark of Mitochondrial Lesions during Early Alzheimer Disease

Increasing evidence points to vascular damage as an early contributor to the development of two leading causes of age-associated dementia, namely Alzheimer disease (AD) and AD-like pathology such as stroke. This review focuses on the role of G protein-coupled receptor kinases (GRKs) as they relate to dementia and how the cardio and cerebrovasculature is involved in AD pathogenesis. The exploration of GRKs in AD pathogenesis may help bridge gaps in our understanding of the heart-brain connection in relation to neurovisceral damage and vascular complications of AD. The a priori basis for this inquiry stems from the fact that kinases of this family regulate numerous receptor functions in the brain, myocardium and elsewhere. The aim of this review is to discuss the finding of GRK2 overexpression in the context of early AD pathogenesis. Also, we consider the consequences for this overexpression as a loss of G-protein coupled receptor (GPCR) regulation, as well as suggest a potential role for GPCRs and GRKs in a unifying theory of AD pathogenesis through the cerebrovasculature. Finally, we synthesize this newer information in an attempt to put it into context with GRKs as regulators of cellular function, which makes these proteins potential diagnostic and therapeutic targets for future pharmacological intervention.

Insights into cerebrovascular complications and Alzheimer disease through the selective loss of GRK2 regulation

Alzheimer disease (AD) and stroke are two leading causes of age-associated dementia. Increasing evidence points to vascular damage as an early contributor to the development of AD and AD-like pathology. In this review, we discuss the role of G protein-coupled receptor kinase 2 (GRK2) as it relates to individuals affected by AD and how the cardiovasculature plays a role in AD pathogenesis. The possible involvement of GRKs in AD pathogenesis is an interesting notion, which may help bridge the gap in our understanding of the heart–brain connection in relation to neurovisceral damage and vascular complications in AD, since kinases of this family are known to regulate numerous receptor functions both in the brain, myocardium, and elsewhere. The aim of this review is to discuss our findings of overexpression of GRK2 in the context of the early pathogenesis of AD, because increased levels of GRK2 immunoreactivity were found in vulnerable neurons of AD patients as well as in a two-vessel occlusion (2-VO) mammalian model of ischaemia. Also, we consider the consequences for this overexpression as a loss of G-protein coupled receptor (GPCR) regulation, as well as suggest a potential role for GPCRs and GRKs in a unifying theory of AD pathogenesis, particularly in the context of cerebrovascular disease. We synthesize this newer information and attempt to put it into context with GRKs as regulators of diverse physiological cellular functions that could be appropriate targets for future pharmacological intervention.

Effects of crocin on reperfusion-induced oxidative/nitrative injury to cerebral microvessels after global cerebral ischemia

This paper studied the effects of crocin, a pharmacologically active component of Crocus sativus L., on ischemia/reperfusion (I/R) injury in mice cerebral microvessels. Transient global cerebral ischemia (20 min), followed by 24 h of reperfusion, significantly promoted the generation of nitric oxide (NO) and malondialdehyde (MDA) in cortical microvascular homogenates, as well as markedly reduced the activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-px) and promoted the activity of nitric oxide synthase (NOs). Reperfusion for 24 h led to serous edema with substantial microvilli loss, vacuolation, membrane damage and mitochondrial injuries in cortical microvascular endothelial cells (CMEC). Furthermore, enhanced phosphorylation of extracellular signal-regulated kinase 1/2 (ERK1/2) and decreased expression of matrix metalloproteinase-9 (MMP-9) were detected in cortical microvessels after I (20 min)/R (24 h). Reperfusion for 24 h also induced membrane (functional) G protein-coupled receptor kinase 2 (GRK2) expression, while it reduced cytosol GRK2 expression. Pretreatment with crocin markedly inhibited oxidizing reactions and modulated the ultrastructure of CMEC in mice with 20 min of bilateral common carotid artery occlusion (BCCAO) followed by 24 h of reperfusion in vivo. Furthermore, crocin inhibited GRK2 translocation from the cytosol to the membrane and reduced ERK1/2 phosphorylation and MMP-9 expression in cortical microvessels. We propose that crocin protects the brain against excessive oxidative stress and constitutes a potential therapeutic candidate in transient global cerebral ischemia.

Overexpression of GRK2 in Alzheimer disease and in a chronic hypoperfusion rat model is an early marker of brain mitochondrial lesions

Heterotrimeric guanine nucleotide-binding (G) protein-coupled receptor kinases (GRKs) are cytosolic proteins that are known to contribute to the adaptation of the heptahelical G protein-coupled receptors (GPCRs) and to regulate downstream signals through these receptors. GPCRs mediate the action of messengers that are key modulators of cardiac and vascular cell function, such as growth and differentiation. GRKs are members of a multigene family, which are classified into three subfamilies and are found in cardiac, vascular and cerebral tissues. Increasing evidence strongly supports the hypothesis that vascular damage is an early contributor to the development of Alzheimer disease (AD) and/or other pathology that can mimic human AD. Based on this hypothesis, and since kinases of this family are known to regulate numerous receptor functions both in the brain, myocardium and elsewhere, we explored cellular and subcellular localization by immunoreactivity of G protein-coupled receptor kinase 2 (GRK2), also known as beta-adrenergic receptor kinase-1(betaARK1), in the early pathogenesis of AD and in ischemia reperfusion injury models of brain hypoperfusion. In the present study, we used the two-vessel carotid artery occlusion model, namely the 2-VO system that results in chronic brain hypoperfusion (CBH) and mimics mild cognitive impairment (MCI) and vascular changes in AD pathology. Our findings demonstrate the early overexpression of GRK2 member kinase in the cerebrovasculature, especially endothelial cells (EC) following CBH, as well as in select cells from human AD tissue. We found a significant increase in GRK2 immunoreactivity in the EC of AD patients and after CBH, which preceded any amyloid deposition. Since GRK2 activity is associated with certain compensatory changes in brain cellular compartments and in ischemic cardiac tissue, our findings suggest that chronic hypoperfusion initiates oxidative stress in these conditions and appears to be the main initiating injury stimulus for disruption of brain and cerebrovascular homeostasis and metabolism.

Sodium pump reduction correlates with aortic clamp time in pediatric heart surgery

Myocardial depression after cardiac surgery is modulated by cardiopulmonary bypass (CPB) and the underlying heart disease. The sodium pump is a key component for myocardial function. We hypothesized that the change in sodium pump expression during CPB correlates with intraoperative and postoperative laboratory and clinical parameters in neonates and children with various congenital heart defects. Sodium pump isoforms alpha1 (ATP1A1) and alpha3 (ATP1A3) mRNA expression in right atrial myocardium, excised before and after CPB, was quantified. Groups were assigned according to presence (VO group, n = 8) or absence (NO group, n = 8) of right atrial volume overload. CPB and aortic clamp time correlated with postoperative troponin-I values and ICU stay. ATP1A1 (P = 0.008) and ATP1A3 (P = 0.038) mRNA expression were significantly reduced during CPB. Longer aortic clamp times were associated with lower postoperative ATP1A1 (P = 0.045) and ATP1A3 (P = 0.002) mRNA expression. Low postoperative ATP1A1 (P = 0.043) and ATP1A3 (P = 0.002) expressions were associated with high troponin-I values. These results were restricted to the VO group. No correlation of sodium pump mRNA expression was found with the duration of ICU stay or ventilation. The postoperative troponin-I and clinical parameters correlated with the length of CPB, regardless of volume overload. In contrast, only dilated right atrium seemed to be susceptible to CPB in terms of sodium pump expression, showing a reduction during the operation and a correlation of sodium pump with postoperative troponin-I values.

Lymphocyte levels of GRK2 (betaARK1) mirror changes in the LVAD-supported failing human heart: lower GRK2 associated with improved beta-adrenergic signaling after mechanical unloading

BACKGROUND

In human heart failure, increased expression of G protein-coupled receptor kinases (GRKs) causes the loss of beta-adrenergic receptor (betaAR) signaling and function. Mechanical unloading with a left ventricular assist device (LVAD) promotes reverse remodeling, which includes restoration of betaAR responsiveness. We tested the hypothesis that LVAD support of the failing human heart alters the expression and activity of GRKs and we sought to determine whether changes in myocardial GRKs could be tracked in lymphocytes.

METHODS AND RESULTS

Paired samples of human LV tissue (n = 12) and blood were obtained at the time of LVAD implantation (heart failure) and subsequent cardiac transplantation (LVAD). betaAR signaling was quantified by receptor density and adenylyl cyclase activity. Immunoblotting and real-time reverse transcription polymerase chain reaction were used to measure GRK2 and GRK5 protein and mRNA levels. Rhodopsin phosphorylation was used to assess total GRK activity. Consistent with reverse remodeling, betaAR density and signaling were restored to nonfailing levels after LVAD support. GRK2 protein levels were significantly reduced 55% after LVAD support and GRK2 mRNA was similarly reduced. In contrast, GRK5 protein and mRNA levels were unchanged. Total myocardial GRK activity was reduced similar to the drop in GRK2 expression. In lymphocytes, GRK2 protein levels were decreased after LVAD support and there was a significant positive correlation between myocardial and lymphocyte GRK2 levels in both heart failure and LVAD samples.

CONCLUSION

The changes in myocardial GRK2 expression and activity that are mirrored in lymphocytes provide a possible mechanism for the restoration of betaAR signaling and reverse remodeling after mechanical unloading in the failing heart. Moreover, lymphocytes may provide a surrogate marker of myocardial GRK2 in these patients.

Cardiopulmonary bypass reduces atrial Na+-K+-ATPase expression in children

Cardiopulmonary bypass (CPB) may induce serious side effects, potentially leading to myocardial failure. The Na(+)-K(+)-ATPase is a key component for myocardial function. Due to its developmental regulation, results from adult studies cannot be adopted to the situation in childhood. Right atrial myocardium from patients with left-to-right shunts at atrial level (VO, n=8) and those without (NO, n=8) was excised during heart surgery before and after CPB. Na(+)-K(+)-ATPase isoforms ATP1A1 (p=0.008) and ATP1A3 (p=0.038) decreased during CPB, which decrease was restricted to the VO group. This study highlights the importance of the underlying heart defect for susceptibility to the effects of CPB, showing a reduced Na(+)-K(+)-ATPase mRNA expression only in patients with left-to-right shunts on the atrial level. This seemed to be an early molecular event, as apart from one, none of the patients showed heart failure before or after surgery.

Pathophysiological roles of G-protein-coupled receptor kinases

G-protein-coupled receptor kinases (GRKs) interact with the agonist-activated form of G-protein-coupled receptors (GPCRs) to effect receptor phosphorylation and to initiate profound impairment of receptor signalling, or desensitization. GPCRs form the largest family of cell surface receptors known and defects in GRK function have the potential consequence to affect GPCR-stimulated biological responses in many pathological situations. This review focuses on the physiological role of GRKs revealed by genetically modified animals but also develops the involvement of GRKs in human diseases as, Oguchi disease, heart failure, hypertension or rhumatoid arthritis. Furthermore, the regulation of GRK levels in opiate addiction, cancers, psychiatric diseases, cystic fibrosis and cardiac diseases is discussed. Both transgenic mice and human pathologies have demonstrated the importance of GRKs in the signalling pathways of rhodopsin, beta-adrenergic and dopamine-1 receptors. The modulation of GRK activity in animal models of cardiac diseases can be effective to restore cardiac function in heart failure and opens a novel therapeutic strategy in diseases with GPCR dysregulation.

Hypoxia/ischemia modulates G protein-coupled receptor kinase 2 and beta-arrestin-1 levels in the neonatal rat brain

BACKGROUND AND PURPOSE

Neurotransmitters, neuropeptides, chemokines, and many other molecules signal through G protein-coupled receptors (GPCRs). GPCR kinases (GRKs) and beta-arrestins play a crucial role in regulating the responsiveness of multiple GPCRs. Reduced expression of GRK and beta-arrestins leads to supersensitization of GPCRs and will thereby increase the response to neuropeptides and neurotransmitters. We analyzed GRK and beta-arrestin expression after cerebral hypoxia/ischemia (HI).

MATERIALS AND METHODS

Twelve-day-old rat pups were exposed to 90 minutes of hypoxia (fraction of inspired oxygen [FiO2] 0.08) after ligation of the right carotid artery, a procedure that induces unilateral damage in the right hemisphere. At 6, 12, 24, and 48 hours after HI, the left (hypoxic) and right (hypoxic/ischemic) hemispheres were analyzed for GRK and beta-arrestin protein and mRNA expression by Western blotting and real-time polymerase chain reaction, respectively. In addition, we analyzed GRK2 expression in the hippocampus by immunohistochemistry.

RESULTS

HI downregulated GRK2 protein expression in both hemispheres at 24 to 48 hours after HI, and the effect was more pronounced in the ipsilateral hemisphere. HI induced no global change in GRK6 protein expression. However, GRK2 was markedly decreased in the hippocampal region of the ipsilateral hemisphere that will be severely damaged after HI. No changes in global mRNA levels for GRK2 were detected. In contrast, HI increased beta-arrestin-1 protein expression as well as mRNA levels at 6 to 12 hours after HI.

CONCLUSIONS

Neonatal HI-induced brain damage is associated with specific changes in the GPCR desensitization machinery. We hypothesize that these changes result in supersensitization of multiple GPCRs and might therefore contribute to HI-induced brain damage.