Adiponectin protects against angiotensin II or tumor necrosis factor alpha-induced endothelial cell monolayer hyperpermeability: role of cAMP/PKA signaling

Adipose tissue as a therapeutic target for vascular damage in Alzheimer's disease

Adipose tissue has recently been recognized as an important endocrine organ that plays a crucial role in energy metabolism and in the immune response in many metabolic tissues. With this regard, emerging evidence indicates that an important crosstalk exists between the adipose tissue and the brain. However, the contribution of adipose tissue to the development of age-related diseases, including Alzheimer's disease, remains poorly defined. New studies suggest that the adipose tissue modulates brain function through a range of endogenous biologically active factors known as adipokines, which can cross the blood-brain barrier to reach the target areas in the brain or to regulate the function of the blood-brain barrier. In this review, we discuss the effects of several adipokines on the physiology of the blood-brain barrier, their contribution to the development of Alzheimer's disease and their therapeutic potential. LINKED ARTICLES: This article is part of a themed issue From Alzheimer's Disease to Vascular Dementia: Different Roads Leading to Cognitive Decline. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v181.6/issuetoc.

The Influence of Adiponectin on Transport of Low-Density Lipoproteins through Human Endothelial Cell Monolayer In Vitro

The influence of adiponectin, a protein secreted by adipocytes, on the activation of transendothelial LDL transport, the initial event of atherogenesis, was studied. The addition of adiponectin to the cultured endothelial hybridoma EA.hy926 cells did not affect both basal and TNF-stimulated transendothelial transport of LDL. In addition, adiponectin affects neither expression levels of CAV1, SCARB1, and ACVRL1 genes encoding proteins involved in transendothelial LDL transport, nor the MMP secretion by the EA.hy926cells. At the same time, adiponectin suppressed the TNF-stimulated IL-8 production and expression of the adhesion molecule gene ICAM1 in these cells. Thus, adiponectin reduces proinflammatory activation of EA.hy926 cells, which is not accompanied by changes in the transendothelial LDL transport. We speculate that anti-inflammatory action of adiponectin is the base for the influence of this adipokine on atherogenesis.

Targeting Adiponectin Receptor 1 Phosphorylation Against Ischemic Heart Failure

BACKGROUND

Despite significantly reduced acute myocardial infarction (MI) mortality in recent years, ischemic heart failure continues to escalate. Therapeutic interventions effectively reversing pathological remodeling are an urgent unmet medical need. We recently demonstrated that AdipoR1 (APN [adiponectin] receptor 1) phosphorylation by GRK2 (G-protein-coupled receptor kinase 2) contributes to maladaptive remodeling in the ischemic heart. The current study clarified the underlying mechanisms leading to AdipoR1 phosphorylative desensitization and investigated whether blocking AdipoR1 phosphorylation may restore its protective signaling, reversing post-MI remodeling.

METHODS

Specific sites and underlying molecular mechanisms responsible for AdipoR1 phosphorylative desensitization were investigated in vitro (neonatal and adult cardiomyocytes). The effects of AdipoR1 phosphorylation inhibition upon APN post-MI remodeling and heart failure progression were investigated in vivo.

RESULTS

Among 4 previously identified sites sensitive to GRK2 phosphorylation, alanine substitution of Ser²⁰⁵ (AdipoR1^S205A), but not other 3 sites, rescued GRK2-suppressed AdipoR1 functions, restoring APN-induced cell salvage kinase activation and reducing oxidative cell death. The molecular investigation followed by functional determination demonstrated that AdipoR1 phosphorylation promoted clathrin-dependent (not caveolae) endocytosis and lysosomal-mediated (not proteasome) degradation, reducing AdipoR1 protein level and suppressing AdipoR1-mediated cytoprotective action. GRK2-induced AdipoR1 endocytosis and degradation were blocked by AdipoR1^S205A overexpression. Moreover, AdipoR1^S205E (pseudophosphorylation) phenocopied GRK2 effects, promoted AdipoR1 endocytosis and degradation, and inhibited AdipoR1 biological function. Most importantly, AdipoR1 function was preserved during heart failure development in AdipoR1-KO (AdipoR1 knockout) mice reexpressing hAdipoR1^S205A. APN administration in the failing heart reversed post-MI remodeling and improved cardiac function. However, reexpressing hAdipoR1^WT in AdipoR1-KO mice failed to restore APN cardioprotection.

CONCLUSIONS

Ser²⁰⁵ is responsible for AdipoR1 phosphorylative desensitization in the failing heart. Blockade of AdipoR1 phosphorylation followed by pharmacological APN administration is a novel therapy effective in reversing post-MI remodeling and mitigating heart failure progression.

A venous-specific purinergic signaling cascade initiated by Pannexin 1 regulates TNFα-induced increases in endothelial permeability

The endothelial cell barrier regulates the passage of fluid between the bloodstream and underlying tissues, and barrier function impairment exacerbates the severity of inflammatory insults. To understand how inflammation alters vessel permeability, we studied the effects of the proinflammatory cytokine TNFα on transendothelial permeability and electrophysiology in ex vivo murine veins and arteries. We found that TNFα specifically decreased the barrier function of venous endothelium without affecting that of arterial endothelium. On the basis of RNA expression profiling and protein analysis, we found that claudin-11 (CLDN11) was the predominant claudin in venous endothelial cells and that there was little, if any, CLDN11 in arterial endothelial cells. Consistent with a difference in claudin composition, TNFα increased the permselectivity of Cl^- over Na⁺ in venous but not arterial endothelium. The vein-specific effects of TNFα also required the activation of Pannexin 1 (Panx1) channels and the CD39-mediated hydrolysis of ATP to adenosine, which subsequently stimulated A_2A adenosine receptors. Moreover, the increase in vein permeability required the activation of the Ca²⁺ channel TRPV4 downstream of Panx1 activation. Panx1-deficient mice resisted the pathologic effects of sepsis induced by cecal ligation and puncture on life span and lung vascular permeability. These data provide a targetable pathway with the potential to promote vein barrier function and prevent the deleterious effects of vascular leak in response to inflammation.

Soluble RAGE attenuates AngII-induced endothelial hyperpermeability by disrupting HMGB1-mediated crosstalk between AT1R and RAGE

Increased endothelial permeability, one of the earliest signs of endothelial dysfunction, is associated with the development of cardiovascular diseases such as hypertension and atherosclerosis. Recent studies suggest that the receptor for advanced glycation end products (RAGE) regulates endothelial permeability in inflammation. In the present study, we investigated the regulatory mechanism of RAGE in endothelial hyperpermeability induced by angiotensin II (Ang II), a well-known inflammatory mediator, and the potential therapeutic effect of soluble RAGE (sRAGE), a decoy receptor for RAGE ligands. For in vitro studies, Ang II-treated human umbilical vein endothelial cells (HUVECs) were treated with siRNA specific to either RAGE or sRAGE to disrupt RAGE-mediated signaling. Endothelial permeability was estimated using FITC-labeled dextran 40 and a resistance meter. To evaluate intercellular junction disruption, VE-cadherin expression was examined by western blotting and immunocytochemistry. Ang II increased the expression of the Ang II type 1 receptor (AT1R) and RAGE, and this increase was inhibited by sRAGE. sRAGE prevented Ang II-induced VE-cadherin disruption in HUVECs. For in vivo studies, Ang II-infused, atherosclerosis-prone apolipoprotein E knockout mice were utilized. Endothelial permeability was assessed by Evans blue staining of the aorta. Ang II increased endothelial barrier permeability, and this effect was significantly attenuated by sRAGE. Our data demonstrate that blockade of RAGE signaling using sRAGE attenuates Ang II-induced endothelial barrier permeability in vitro and in vivo and indicate the therapeutic potential of sRAGE in controlling vascular permeability under pathological conditions.

A decoy version of a protein involved in regulating the leakiness of blood vessels can help ameliorate vascular problems that lead to high blood pressure and plaque deposition in the arteries. A team from South Korea led by Soyeon Lim from Catholic Kwandong University in Gangneung and Sungha Park from Yonsei University College of Medicine in Seoul induced hyper-permeability in both human vein cells and atherosclerosis-prone mice. They then blocked signaling through a membrane-bound protein called RAGE, a receptor that helps boost vessel permeability by using a soluble version of this same protein. In both the human cells and mouse models, this free-floating RAGE bound and blocked the receptor’s normal activator, leading to suppressed permeability and improved function of the blood vessel lining. This decoy strategy holds therapeutic promise for people prone to cardiovascular disease.

Endothelial permeability, LDL deposition, and cardiovascular risk factors-a review

Early atherosclerosis features functional and structural changes in the endothelial barrier function that affect the traffic of molecules and solutes between the vessel lumen and the vascular wall. Such changes are mechanistically related to the development of atherosclerosis. Proatherogenic stimuli and cardiovascular risk factors, such as dyslipidaemias, diabetes, obesity, and smoking, all increase endothelial permeability sharing a common signalling denominator: an imbalance in the production/disposal of reactive oxygen species (ROS), broadly termed oxidative stress. Mostly as a consequence of the activation of enzymatic systems leading to ROS overproduction, proatherogenic factors lead to a pro-inflammatory status that translates in changes in gene expression and functional rearrangements, including changes in the transendothelial transport of molecules, leading to the deposition of low-density lipoproteins (LDL) and the subsequent infiltration of circulating leucocytes in the intima. In this review, we focus on such early changes in atherogenesis and on the concept that proatherogenic stimuli and risk factors for cardiovascular disease, by altering the endothelial barrier properties, co-ordinately trigger the accumulation of LDL in the intima and ultimately plaque formation.

The Role of Plasma Transfusion in Massive Bleeding: Protecting the Endothelial Glycocalyx?

Massive hemorrhage is a leading cause of death worldwide. During the last decade several retrospective and some prospective clinical studies have suggested a beneficial effect of early plasma-based resuscitation on survival in trauma patients. The underlying mechanisms are unknown but appear to involve the ability of plasma to preserve the endothelial glycocalyx. In this mini-review, we summarize current knowledge on glycocalyx structure and function, and present data describing the impact of hemorrhagic shock and resuscitation fluids on glycocalyx. Animal studies show that hemorrhagic shock leads to glycocalyx shedding, endothelial inflammatory changes, and vascular hyper-permeability. In these animal models, plasma administration preserves glycocalyx integrity and functions better than resuscitation with crystalloids or colloids. In addition, we briefly present data on the possible plasma components responsible for these effects. The endothelial glycocalyx is increasingly recognized as a critical component for the physiological vasculo-endothelial function, which is destroyed in hemorrhagic shock. Interventions for preserving an intact glycocalyx shall improve survival of trauma patients.

Adiponectin controls the apoptosis and the expression of tight junction proteins in brain endothelial cells through AdipoR1 under beta amyloid toxicity

Alzheimer’s disease (AD) is the most common neurodegenerative disease, characterized by excessive beta amyloid (Aβ) deposition in brain, leading to blood–brain barrier (BBB) disruption. The mechanisms of BBB disruption in AD are still unclear, despite considerable research. The adipokine adiponectin is known to regulate various metabolic functions and reduce inflammation. Though adiponectin receptors have been reported in the brain, its role in the central nervous system has not been fully characterized. In the present study, we investigate whether adiponectin contributes to the tight junction integrity and cell death of brain endothelial cells under Aβ-induced toxicity conditions. We measured the expression of adiponectin receptors (AdipoR1 and AdipoR2) and the alteration of tight junction proteins in in vivo 5xFAD mouse brain. Moreover, we examined the production of reactive oxygen species (ROS) and the loss of tight junction proteins such as Claudin 5, ZO-1, and inflammatory signaling in in vitro brain endothelial cells (bEnd.3 cells) under Aβ toxicity. Our results showed that Acrp30 (a globular form of adiponectin) reduces the expression of proinflammatory cytokines and the expression of RAGE as Aβ transporters into brain. Moreover, we found that Acrp 30 attenuated the apoptosis and the tight junction disruption through AdipoR1-mediated NF-κB pathway in Aβ-exposed bEnd.3 cells. Thus, we suggest that adiponectin is an attractive therapeutic target for treating BBB breakdown in AD brain.

Adiponectin Receptor Agonist, AdipoRon, Causes Vasorelaxation Predominantly Via a Direct Smooth Muscle Action

OBJECTIVE

AdipoRon, an adiponectin receptor agonist, was recently proposed for treating insulin resistance and hyperglycemia. As adiponectin is vasoprotective via NO-mediated signaling, it was hypothesized that adipoRon similarly exerts potentially beneficial vasodilator effects. We therefore examined if adipoRon induces vasorelaxation and via what contributing mechanisms.

METHODS

Vascular function was assessed in skeletal muscle arteries from rats and cerebral/coronary arteries from mice using pressure and wire myography.

RESULTS

Using qPCR, mRNA for adiponectin receptors was demonstrated in skeletal muscle, cerebral and coronary arteries. AdipoRon-caused vasorelaxation was not abolished by compound C (10 μM; AMPK inhibitor). Inhibition of endothelium-dependent relaxation with combinations of l-NAME/indomethacin/apamin/TRAM-34 only slightly reduced adipoRon-mediated vasorelaxation in cerebral and coronary arteries. EC-denuded cremaster arteries showed similar relaxant responses to adipoRon as in intact vessels, suggesting adipoRon directly impacts VSMCs. K(+) currents measured in VSMCs isolated from mouse basilar and LAD arteries were not altered by adiopRon. In cremaster arteries, adipoRon induced vasorelaxation without a marked decrease in VSMC [Ca(2+)]i . Adiponectin, itself, caused vasodilation in intact cremaster arteries while failing to cause significant dilation in EC-denuded arteries, consistent with endothelium dependency of adiponectin.

CONCLUSIONS

AdipoRon exerts vasodilation by mechanisms distinct to adiponectin. The dominant mechanism for adipoRon-induced vasorelaxation occurs independently of endothelium-dependent relaxing factors, AMPK activation, K(+) efflux-mediated hyperpolarization and reductions in cytosolic [Ca(2+)]i .

Adiponectin in Fresh Frozen Plasma Contributes to Restoration of Vascular Barrier Function After Hemorrhagic Shock

Hemorrhagic shock is the leading cause of preventable deaths in civilian and military trauma. Use of fresh frozen plasma (FFP) in patients requiring massive transfusion is associated with improved outcomes. FFP contains significant amounts of adiponectin, which is known to have vascular protective function. We hypothesize that FFP improves vascular barrier function largely via adiponectin. Plasma adiponectin levels were measured in 19 severely injured patients in hemorrhagic shock (HS). Compared with normal individuals, plasma adiponectin levels decreased to 49% in HS patients before resuscitation (P < 0.05) and increased to 64% post-resuscitation (but not significant). In a HS mouse model, we demonstrated a similar decrease in plasma adiponectin to 54% but a significant increase to 79% by FFP resuscitation compared with baseline (P < 0.05). HS disrupted lung vascular barrier function, leading to an increase in permeability. FFP resuscitation reversed these HS-induced effects. Immunodepletion of adiponectin from FFP abolished FFP's effects on blocking endothelial hyperpermeability in vitro, and on improving lung vascular barrier function in HS mice. Replenishment with adiponectin rescued FFP's effects. These findings suggest that adiponectin is an important component in FFP resuscitation contributing to the beneficial effects on vascular barrier function after HS.

Monomeric adiponectin modulates nitric oxide release and calcium movements in porcine aortic endothelial cells in normal/high glucose conditions

AIMS

Perivascular adipose tissue can be involved in the process of cardiovascular pathology through the release of adipokines, namely adiponectins. Monomeric adiponectin has been shown to increase coronary blood flow in anesthetized pigs through increased nitric oxide (NO) release and the involvement of adiponectin receptor 1 (AdipoR1). The present study was therefore planned to examine the effects of monomeric adiponectin on NO release and Ca(2+) transients in porcine aortic endothelial cells (PAEs) in normal/high glucose conditions and the related mechanisms.

MAIN METHODS

PAEs were treated with monomeric adiponectin alone or in the presence of intracellular kinases blocker, AdipoR1 and Ca(2+)-ATPase pump inhibitors. The role of Na(+)/Ca(2+) exchanger was examined in experiments performed in zero Na(+) medium. NO release and intracellular Ca(2+) were measured through specific probes.

KEY FINDINGS

In PAE cultured in normal glucose conditions, monomeric adiponectin elevated NO production and [Ca(2+)]c. Similar effects were observed in high glucose conditions, although the response was lower and not transient. The Ca(2+) mobilized by monomeric adiponectin originated from an intracellular pool thapsigargin- and ATP-sensitive and from the extracellular space. Moreover, the effects of monomeric adiponectin were prevented by kinase blockers and AdipoR1 inhibitor. Finally, in normal glucose condition, a role for Na(+)/Ca(2+) exchanger and Ca(2+)-ATPase pump in restoring Ca(2+) was found.

SIGNIFICANCE

Our results add new information about the control of endothelial function elicited by monomeric adiponectin, which would be achieved by modulation of NO release and Ca(2+) transients. A signalling related to Akt, ERK1/2 and p38MAPK downstream AdipoR1 would be involved.

Metabolic hormones, apolipoproteins, adipokines, and cytokines in the alveolar lining fluid of healthy adults: compartmentalization and physiological correlates

Objectives

Our current understanding of hormone regulation in lung parenchyma is quite limited. We aimed to quantify a diverse array of biologically relevant protein mediators in alveolar lining fluid (ALF), compared to serum concentrations, and explore factors associated with protein compartmentalization on either side of the air-blood barrier.

Research Design and Methods

Participants were 24 healthy adult non-smoker volunteers without respiratory symptoms or significant medical conditions, with normal lung exams and office spirometry. Cell-free bronchoalveolar lavage fluid and serum were analyzed for 24 proteins (including enteric and metabolic hormones, apolipoproteins, adipokines, and cytokines) using a highly sensitive multiplex ELISA. Measurements were normalized to ALF concentrations. The ALF:serum concentration ratios were examined in relation to measures of protein size, hydrophobicity, charge, and to participant clinical and spirometric values.

Results

ALF measurements from 24 individuals detected 19 proteins, including adiponectin, adipsin, apoA-I, apoA-II, apoB, apoC-II, apoC-III, apoE, C-reactive protein, ghrelin, glucose-dependent insulinotropic peptide (GIP), glucagon-like peptide-1 (GLP-1), glucagon, insulin, leptin, monocyte chemoattractant protein-1, plasminogen activator inhibitor-1, resistin, and visfatin. C-peptide and serpin E1 were not detected in ALF for any individual, and IL-6, IL-10, and TNF-alpha were not detected in either ALF or serum for any individual. In general, ALF levels were similar or lower in concentration for most proteins compared to serum. However, ghrelin, resistin, insulin, visfatin and GLP-1 had ALF concentrations significantly higher compared to serum. Importantly, elevated ALF:serum ratios of ghrelin, visfatin and resistin correlated with protein net charge and isoelectric point, but not with molecular weight or hydrophobicity.

Conclusions

Biologically relevant enteric and metabolic hormones, apolipoproteins, adipokines, and cytokines can be detected in the ALF of healthy individuals. For the proteins measured, charge may influence trafficking and compartmentalization to the alveolar airspace more than molecular weight or hydrophobicity. These data may have implications for homeostasis and drug delivery to the lung.

Differential effects of leptin and adiponectin in endothelial angiogenesis

Obesity is a major health burden with an increased risk of cardiovascular morbidity and mortality. Endothelial dysfunction is pivotal to the development of cardiovascular disease (CVD). In relation to this, adipose tissue secreted factors termed "adipokines" have been reported to modulate endothelial dysfunction. In this review, we focus on two of the most abundant circulating adipokines, that is, leptin and adiponectin, in the development of endothelial dysfunction. Leptin has been documented to influence a multitude of organ systems, that is, central nervous system (appetite regulation, satiety factor) and cardiovascular system (endothelial dysfunction leading to atherosclerosis). Adiponectin, circulating at a much higher concentration, exists in different molecular weight forms, essentially made up of the collagenous fraction and a globular domain, the latter being investigated minimally for its involvement in proinflammatory processes including activation of NF-κβ and endothelial adhesion molecules. The opposing actions of the two forms of adiponectin in endothelial cells have been recently demonstrated. Additionally, a local and systemic change to multimeric forms of adiponectin has gained importance. Thus detailed investigations on the potential interplay between these adipokines would likely result in better understanding of the missing links connecting CVD, adipokines, and obesity.

METABOLIC EFFECTS OF ADIPONECTINE

The metabolic effects of adiponectine are discussed and its possible role in the development of metabolic syndrome, insulin resistance, diabetes mellitus 2nd type, atherosclerosis; prognostic significance of adiponectine as a marker for ischemic heart disease and future cardiovascular events, therapeutical perspectives of adiponectine use. 

Long-term globular adiponectin administration improves adipose tissue dysmetabolism in high-fat diet-fed Wistar rats

Adiponectin administration to obese or type 2 diabetic patients is still far off, due to its expensive costs and absence of studies demonstrating the effectiveness of its chronic administration. We performed long-term globular adiponectin administration, testing its usefulness in improving adipose tissue metabolism. Adiponectin (98 υg/day) was administered through a subcutaneous minipump with continued release (28 days) to Wistar rats fed a high-fat diet. Adiponectin decreased body weight and adipocyte size, while decreasing circulating leptin levels. More, adiponectin was able to increase IkappaBalpha and PPARgamma levels and to prevent high-fat diet-induced impairment of insulin signalling, especially in epididymal adipose tissue. This resulted in improved glucose profile. High-fat diet caused an impairment of lipolysis in epididymal adipose tissue, which was partially restored by adiponectin treatment. Long-term globular adiponectin administration was able to improve pathways of insulin signalling and lipid storage in adipose tissue of high-fat diet-fed rats, contributing to a better metabolic profile.

Effects of adiponectin on calcium-handling proteins in heart failure with preserved ejection fraction

BACKGROUND

Despite the increasing prevalence of heart failure with preserved ejection fraction (HFpEF) in humans, there remains no therapeutic options for HFpEF. Adiponectin, an adipocyte-derived cytokine, exerts cardioprotective actions, and its deficiency is implicated in the development of hypertension and HF with reduced ejection fraction. Similarly, adiponectin deficiency in HFpEF exacerbates left ventricular hypertrophy, diastolic dysfunction, and HF. However, the therapeutic effects of adiponectin in HFpEF remain unknown. We sought to test the hypothesis that chronic adiponectin overexpression protects against the progression of HF in a murine model of HFpEF.

METHODS AND RESULTS

Adiponectin transgenic and wild-type mice underwent uninephrectomy, a continuous saline or d-aldosterone infusion and given 1.0% sodium chloride drinking water for 4 weeks. Aldosterone-infused wild-type mice developed HFpEF with hypertension, left ventricular hypertrophy, and diastolic dysfunction. Aldosterone infusion increased myocardial oxidative stress and decreased sarcoplasmic reticulum Ca(2+)-ATPase protein expression in HFpEF. Although total phospholamban protein expression was unchanged, there was a decreased expression of protein kinase A-dependent phospholamban phosphorylation at Ser16 and CaMKII (Ca(2+)/calmodulin-dependent protein kinase II)-dependent phospholamban phosphorylation at Thr17. Adiponectin overexpression in aldosterone-infused mice ameliorated left ventricular hypertrophy, diastolic dysfunction, lung congestion, and myocardial oxidative stress without affecting blood pressure and left ventricular EF. This improvement in diastolic dysfunction parameters in aldosterone-infused adiponectin transgenic mice was accompanied by the preserved protein expression of protein kinase A-dependent phosphorylation of phospholamban at Ser16. Adiponectin replacement prevented the progression of aldosterone-induced HFpEF, independent of blood pressure, by improving diastolic dysfunction and by modulating cardiac hypertrophy.

CONCLUSIONS

These findings suggest that adiponectin may have therapeutic effects in patients with HFpEF.

Bariatric surgery relieves type 2 diabetes and modulates inflammatory factors and coronary endothelium eNOS/iNOS expression in db/db mice

Overexpression of endothelial nitric oxide synthetase (eNOS)/inducible nitric oxide synthase (iNOS) and inhibition of inflammatory factors can improve vascular function. We hypothesized that bariatric (gastric bypass) surgery could inhibit inflammatory factors and improve the eNOS/iNOS expression of coronary arterioles in the db/db mice. The animals were randomly allocated to the following groups: sham-operated lean mice, lean mice that underwent surgery, sham-operated db/db mice, and db/db mice that underwent surgery (5, 10, 20, and 30 days post-operation). The plasma levels of adiponectin, ghrelin, and IL-6, as well as the protein expression of eNOS/iNOS in coronary arterioles were measured with Western blot. Bariatric surgery decreased body mass and blood glucose levels in db/db mice. Ghrelin receptor and GHS-R1a expression in the hypothalamus were increased in db/db mice, but surgery attenuated GHS-R1a expression. Bariatric surgery elevated plasma concentration and protein expression of adiponectin and ghrelin, and attenuated plasma concentration and protein expression of IL-6. Coronary protein expression of eNOS and SOD2 was lower in the sham-operated db/db mice, and bariatric surgery increased eNOS and SOD2 expression. Gastric bypass surgery upregulates ghrelin and adiponectin expression, and decreases IL-6 expression, which might induce up-regulation of eNOS and SOD2, and down-regulation of iNOS. These interactions could counteract the endothelium dysfunction in type 2 diabetes mellitus.

Guanine nucleotide exchange factor-H1 signaling is involved in lipopolysaccharide-induced endothelial barrier dysfunction

BACKGROUND

Gram-negative bacterial lipopolysaccharide (LPS) leads to the pathologic increase of vascular leakage under septic conditions. However, the mechanisms behind LPS-induced vascular hyperpermeability remain incompletely understood. In this study, we tested hypothesis that guanine nucleotide exchange factor-H1 (GEF-H1) signaling might be a key pathway involved in endothelial cells (ECs) barrier dysfunction.

METHODS

The roles of GEF-H1 signaling pathway in LPS-induced ECs barrier dysfunction were accessed by Evans blue dye-labeled albumin (EB-albumin) leak across the human umbilical vein EC (HUVEC) monolayers and Western blot assays. Furthermore, the effect of GEF-H1 signaling on LPS-induced alteration of cytoskeletal proteins and disruption of cell-cell junctions were analyzed by immunofluorescent analysis and Western blot assays, respectively.

RESULTS

We found that LPS could rapidly activated GEF-H1/RhoA/Rho-associated protein kinase (ROCK) signaling pathway in ECs. The LPS-mediated increase in EB-albumin flux across human HUVECs monolayers could be prevented by GEF-H1 depletion or ROCK inactivation. ECs permeability is controlled by actin filaments and cell-cell contact protein complexes. Actin stress fiber formation and/or cell-cell contact proteins loss cause vascular barrier disruption. Here, GEF-H1 knockdown or ROCK inactivation both not only significantly inhibited LPS-induced actin stress fiber formation, phosphorylation of myosin light chain, and myosin-associated phosphatase type 1, but also suppressed LPS-induced loss of occludin, claudin-1, and vascular endothelial (VE)-cadherin in ECs, which suggested that LPS-induced stress fiber formation and cell-cell junctions disruption were closely associated with GEF-H1/RhoA/ROCK signaling activation.

CONCLUSION

Our findings indicate that GEF-H1/RhoA/ROCK pathway in ECs plays an important role in LPS-mediated alteration of cell morphology and disruption of cell-cell junctions, consequently regulate LPS-induced vascular permeability dysfunction.

Activation of systemic, but not local, renin-angiotensin system is associated with upregulation of TNF-α during prolonged fasting in northern elephant seal pups

Northern elephant seal pups naturally endure a 2-3 month post-weaning fast that is associated with activation of systemic renin-angiotensin system (RAS), a decrease in plasma adiponectin (Acrp30), and insulin resistance (IR)-like conditions. Angiotensin II (Ang II) and tumor necrosis factor-alpha (TNF-α) are potential causal factors of IR, while Acrp30 may improve insulin signaling. However, the effects of fasting-induced activation of RAS on IR-like conditions in seals are not well described. To assess the effects of prolonged food deprivation on systemic and local RAS, and their potential contribution to TNF-α as they relate to an IR condition, the mRNA expressions of adipose and muscle RAS components and immuno-relevant molecules were measured along with plasma RAS components. Mean plasma renin activity and Ang II concentrations increased by 89 and 1658%, respectively, while plasma angiotensinogen (AGT) decreased by 49% over the fast, indicative of systemic RAS activation. Prolonged fasting was associated with decreases in adipose and muscle AGT mRNA expressions of 69 and 68%, respectively, corresponding with decreases in tissue protein content, suggesting suppression of local AGT production. Muscle TNF-α mRNA and protein increased by 239 and 314%, whereas those of adipose Acrp30 decreased by 32 and 98%, respectively. Collectively, this study suggests that prolonged fasting activates a systemic RAS, which contributes to an increase in muscle TNF-α and suppression of adipose Acrp30. This targeted and tissue-specific regulation of TNF-α and Acrp30 is likely coordinated to synergistically contribute to the development of an IR-like condition, independent of local RAS activity. These data enhance our understanding of the adaptive mechanisms evolved by elephant seals to tolerate potentially detrimental conditions.

The barrier within: endothelial transport of hormones

Hormones are involved in a plethora of processes including development and growth, metabolism, mood, and immune responses. These essential functions are dependent on the ability of the hormone to access its target tissue. In the case of endocrine hormones that are transported through the blood, this often means that the endothelium must be crossed. Many studies have shown that the concentrations of hormones and nutrients in blood can be very different from those surrounding the cells on the tissue side of the blood vessel endothelium, suggesting that transport across this barrier can be rate limiting for hormone action. This transport can be regulated by altering the surface area of the blood vessel available for diffusion through to the underlying tissue or by the permeability of the endothelium. Many hormones are known to directly or indirectly affect the endothelial barrier, thus affecting their own distribution to their target tissues. Dysfunction of the endothelial barrier is found in many diseases, particularly those associated with the metabolic syndrome. The interrelatedness of hormones may help to explain why the cluster of diseases in the metabolic syndrome occur together so frequently and suggests that treating the endothelium may ameliorate defects in more than one disease. Here, we review the structure and function of the endothelium, its contribution to the function of hormones, and its involvement in disease.

Adipokines and the cardiovascular system: mechanisms mediating health and disease

This review focuses on the role of adipokines in the maintenance of a healthy cardiovascular system, and the mechanisms by which these factors mediate the development of cardiovascular disease in obesity. Adipocytes are the major cell type comprising the adipose tissue. These cells secrete numerous factors, termed adipokines, into the blood, including adiponectin, leptin, resistin, chemerin, omentin, vaspin, and visfatin. Adipose tissue is a highly vascularised endocrine organ, and different adipose depots have distinct adipokine secretion profiles, which are altered with obesity. The ability of many adipokines to stimulate angiogenesis is crucial for adipose tissue expansion; however, excessive blood vessel growth is deleterious. As well, some adipokines induce inflammation, which promotes cardiovascular disease progression. We discuss how these 7 aforementioned adipokines act upon the various cardiovascular cell types (endothelial progenitor cells, endothelial cells, vascular smooth muscle cells, pericytes, cardiomyocytes, and cardiac fibroblasts), the direct effects of these actions, and their overall impact on the cardiovascular system. These were chosen, as these adipokines are secreted predominantly from adipocytes and have known effects on cardiovascular cells.

Adiponectin diminishes organ-specific microvascular endothelial cell activation associated with sepsis

Experimental sepsis was induced in male C57BL/6j, adiponectin-deficient mice (ADPNKO), and wild-type littermates by i.p. injection of 16 mg/kg lipopolysaccharide or cecal ligation and puncture. Blood and tissue samples were harvested 24 h after model induction. Circulating adiponectin is reduced in mice with endotoxemic challenge and after cecal ligation and puncture compared with healthy control mice. Quantitative reverse transcriptase-polymerase chain reaction for adiponectin reveals a pattern of response that is both model- and organ-specific. When challenged with sepsis, adiponectin deficiency results in increased expression of endothelial adhesion and coagulation molecules in the lung, liver, and kidney as quantified by reverse transcriptase-polymerase chain reaction, increased macrophage and neutrophil infiltration by immunohistochemistry, and vascular leakage in the liver and kidney. Adiponectin-deficient mice have reduced survival following cecal ligation and puncture and increased blood levels of interleukin 6, soluble vascular endothelial growth factor receptor 1, and soluble endothelial adhesion molecules E-selectin and intercellular adhesion molecule 1. Finally, ADPNKO promoted end-organ injury in the liver and kidney, whereas the lungs were not affected. These data suggest a protective role of adiponectin in diminishing microvascular organ-specific endothelial cell activation during sepsis.

Regulation and roles of urocortins in the vascular system

Urocortins (Ucns) are members of the corticotropin-releasing factor (CRF) family of peptides. Ucns would have potent effects on the cardiovascular system via the CRF receptor type 2 (CRF(2) receptor). Regulation and roles of each Ucn have been determined in the vascular system. Ucns have more potent vasodilatory effects than CRF. Human umbilical vein endothelial cells (HUVECs) express Ucns1-3 mRNAs, and the receptor, CRF(2a) receptor mRNA. Ucns1-3 mRNA levels are differentially regulated in HUVECs. Differential regulation of Ucns may suggest differential roles of those in HUVECs. Ucn1 and Ucn2 have strong effects on interleukin (IL)-6 gene expression and secretion in rat aortic smooth muscle A7r5 cells. The increase that we observed in IL-6 levels following Ucn treatment of A7r5 cells suggests that smooth muscle cells may be a source of IL-6 secretion under physiological stress conditions. Ucns are important and unique modulators of vascular smooth muscle cells and act directly or indirectly as autocrine and paracrine factors in the vascular system.

Angiotensin II increases the permeability and PV-1 expression of endothelial cells

Angiotensin II (ANG II), the major effector molecule of the renin-angiotensin system (RAS), is a powerful vasoactive mediator associated with hypertension and renal failure. In this study the permeability changes and its morphological attributes in endothelial cells of human umbilical vein (HUVECs) were studied considering the potential regulatory role of ANG II. The effects of ANG II were compared with those of vascular endothelial growth factor (VEGF). Permeability was determined by 40 kDa FITC-Dextran and electrical impedance measurements. Plasmalemmal vesicle-1 (PV-1) mRNA levels were measured by PCR. Endothelial cell surface was studied by atomic force microscopy (AFM), and caveolae were visualized by transmission electron microscopy (TEM) in HUVEC monolayers. ANG II (10(-7) M), similarly to VEGF (100 ng/ml), increased the endothelial permeability parallel with an increase in the number of cell surface openings and caveolae. AT1 and VEGF-R2 receptor blockers (candesartan and ZM-323881, respectively) blunted these effects. ANG II and VEGF increased the expression of PV-1, which could be blocked by candesartan or ZM-323881 pretreatments and by the p38 mitogem-activated protein (MAP) kinase inhibitor SB-203580. Additionally, SB-203580 blocked the increase in endothelial permeability and the number of surface openings and caveolae. In conclusion, we have demonstrated that ANG II plays a role in regulation of permeability and formation of cell surface openings through AT1 receptor and PV-1 protein synthesis in a p38 MAP kinase-dependent manner in endothelial cells. The surface openings that increase in parallel with permeability may represent transcellular channels, caveolae, or both. These morphological and permeability changes may be involved in (patho-) physiological effects of ANG II.

Systemic adiponectin malfunction as a risk factor for cardiovascular disease

Adiponectin (Ad) is an abundant protein hormone regulatory of numerous metabolic processes. The 30 kDa protein originates from adipose tissue, with full-length and globular domain circulatory forms. A collagenous domain within Ad leads to spontaneous self-assemblage into various oligomeric isoforms, including trimers, hexamers, and high-molecular-weight multimers. Two membrane-spanning receptors for Ad have been identified, with differing concentration distribution in various body tissues. The major intracellular pathway activated by Ad includes phosphorylation of AMP-activated protein kinase, which is responsible for many of Ad's metabolic regulatory, anti-inflammatory, vascular protective, and anti-ischemic properties. Additionally, several AMP-activated protein kinase-independent mechanisms responsible for Ad's anti-inflammatory and anti-ischemic (resulting in cardioprotective) effects have also been discovered. Since its 1995 discovery, Ad has garnered considerable attention for its role in diabetic and cardiovascular pathology. Clinical observations have demonstrated the association of hypoadiponectinemia in patients with obesity, cardiovascular disease, and insulin resistance. In this review, we elaborate currently known information about Ad malfunction and deficiency pertaining to cardiovascular disease risk (including atherosclerosis, endothelial dysfunction, and cardiac injury), as well as review evidence supporting Ad resistance as a novel risk factor for cardiovascular injury, providing insight about the future of Ad research and the protein's potential therapeutic benefits.

The role of adiponectin in human vascular physiology

Adiponectin (ApN) is an adipose tissue-derived hormone which is involved in a wide variety of physiological processes including energy metabolism, inflammation, and vascular physiology via actions on a broad spectrum of target organs including liver, skeletal muscle, and vascular endothelium. Besides possessing insulin sensitizing and anti-inflammatory properties ApN also exerts a pivotal role in vascular protection through activation of multiple intracellular signaling cascades. Enhancement of nitric oxide generation and attenuation of reactive oxygen species production in endothelial cells along with reduced vascular smooth muscle cell proliferation and migration constitute some of ApN's vasoprotective actions. Additionally, recent data indicate that ApN has direct myocardio-protective effects. Decreased plasma ApN levels are implicated in the pathogenesis of the metabolic syndrome and atherosclerosis and may serve as a diagnostic and prognostic biomarker as well as a rational pharmaco-therapeutic target to treat these disorders. This review article summarizes recent work on the cardiovascular actions of ApN.

Adiponectin is related with carotid artery intima-media thickness and brachial flow-mediated dilatation in young adults--the Cardiovascular Risk in Young Finns Study

AIMS

Adiponectin may be involved in the pathogenesis of atherosclerosis. We investigated the relation of adiponectin on early functional and structural markers of subclinical atherosclerosis in a large population-based cohort of young men and women.

METHODS AND RESULTS

We measured serum adiponectin using radioimmunoassay in 2,147 young adults (ages 24-39 years) participating in the Cardiovascular Risk in Young Finns Study. The subjects had ultrasound data on carotid intima-media thickness (IMT), carotid artery elasticity (n = 2,139) and brachial flow-mediated dilatation (FMD) (n = 1,996). In univariate analysis, adiponectin was inversely associated with IMT (r = -0.16, P < 0.0001) and directly with FMD (r = 0.12, P < 0.0001) and carotid elasticity (r = 0.20, P < 0.0001). The associations for IMT and FMD remained significant in multivariable models adjusted for age, sex, obesity indices, serum lipids, blood pressure, leptin, glucose, and C-reactive protein: IMT (β = -0.018 ± 0.005, P = 0.0002) and FMD (β = 0.72 ± 0.25, P = 0.004). The relation between adiponectin and carotid elasticity attenuated to non-significant after adjusting for waist circumference and systolic blood pressure.

CONCLUSION

In young healthy adults, low serum adiponectin concentration is independently related with increased carotid IMT and attenuated brachial FMD, supporting the role of adiponectin in the pathogenesis of early atherosclerosis.

Rimonabant inhibits TNF-α-induced endothelial IL-6 secretion via CB1 receptor and cAMP-dependent protein kinase pathway

AIM

To investigate whether rimonabant, a cannabinoid receptor antagonist, had inhibitory effects on inflammatory reactions in human umbilical vein endothelial cells (HUVEC).

METHODS

TNF-α-induced IL-6 production was measured by ELISA and effects on related signaling pathways were investigated by immunoblot analysis. Cellular cAMP level was measured using kinase-coupled luciferase reaction.

RESULTS

Rimonabant at 1 and 10 μmol/L significantly inhibited TNF-α-induced IL-6 production when added 15, 30 and 60 minutes before TNF-α treatment. Rimonabant also inhibited TNF-α-induced phosphorylation of IκB kinase (IKK) α/β and IκB-α degradation. ACEA, a cannabinoid receptor subtype 1 (CB1) agonist, added before rimonabant abolished the former effects of rimonabant. H-89, an inhibitor of cAMP-dependent protein kinase (PKA), abolished the inhibitory effects of rimonabant on TNF-α induced IL-6 production. Rimonabant also increased the phosphorylation of PKA regulatory subunit II (PKA-RII), implying the essential role of PKA activation in the inhibitory effects of rimonabant. Treatment with the phosphatidylinositol 3-kinase (PI3K) inhibitor, wortmannin did not abolish the inhibitory effects of rimonabant on TNF-α induced IL-6 production.

CONCLUSION

Rimonabant had anti-inflammatory effects on endothelial cells and inhibited TNF-α-induced IKKα/β phosphorylation, IκB-α degradation and IL-6 production in HUVEC. This effect was related to CB1 antagonism and PKA activation.

Epigallocatechin gallate inhibits angiotensin II-induced endothelial barrier dysfunction via inhibition of the p38 MAPK/HSP27 pathway

AIM

To investigate the effect of epigallocatechin gallate (EGCG) on angiotensin II (Ang II)-induced stress fiber formation and hyperpermeability in endothelial cells.

METHODS

Human umbilical vein endothelial cells (HUVECs) were treated with Ang II in the absence or presence of EGCG or mitogen-activated protein kinases (MAPKs) inhibitors. The resulting stress fibers were stained with rhodamine-phalloidin and examined using confocal microscopy. The permeability of the endothelium was tested with fluorescein-isothiocyanate labeled bovine serum albumin (FITC-BSA), and the phosphorylation levels of several proteins were determined using Western blot analysis.

RESULTS

Ang II (1-100 nmol/L) treatment markedly provoked stress fiber formation and hyperpermeability in HUVECs in a time- and dose-dependent manner. These effects were abolished by pretreatment with the p38 MAPK inhibitor SB203580 10 μmol/L, indicating that the Ang II-induced endothelial barrier dysfunction was via activation of the p38 MAPK/HSP27 pathway. Furthermore, treatment with EGCG (5-25) μmol/L inhibited Ang II-induced activation of the p38 MAPK/HSP27 pathway, thereby reducing endothelial stress fiber formation and hyperpermeability.

CONCLUSION

Our data demonstrate that EGCG inhibits Ang II-induced endothelial stress fiber formation and hyperpermeability via inactivation of p38 MAPK/HSP27 pathway, and suggest that EGCG may protect against endothelial barrier dysfunction and injury.

Microvascular responses to cardiovascular risk factors

Hypertension, hypercholesterolemia, diabetes, and obesity are among a growing list of conditions that have been designated as major risk factors for cardiovascular disease (CVD). While CVD risk factors are well known to enhance the development of atherosclerotic lesions in large arteries, there is also evidence that the structure and function of microscopic blood vessels can be profoundly altered by these conditions. The diverse responses of the microvasculature to CVD risk factors include oxidative stress, enhanced leukocyte- and platelet-endothelial cell adhesion, impaired endothelial barrier function, altered capillary proliferation, enhanced thrombosis, and vasomotor dysfunction. Emerging evidence indicates that a low-grade systemic inflammatory response that results from risk factor-induced cell activation and cell-cell interactions may underlie the phenotypic changes induced by risk factor exposure. A consequence of the altered microvascular phenotype and systemic inflammatory response is an enhanced vulnerability of tissues to the deleterious effects of secondary oxidative and inflammatory stresses, such as ischemia and reperfusion. Future efforts to develop therapies that prevent the harmful effects of risk factor-induced inflammation should focus on the microcirculation.

T-cadherin modulates endothelial barrier function

T-cadherin is an atypical member of the cadherin family, which lacks the transmembrane and intracellular domains and is attached to the plasma membrane via a glycosylphosphatidylinositol anchor. Unlike canonical cadherins, it is believed to function primarily as a signaling molecule. T-cadherin is highly expressed in endothelium. Using transendothelial electrical resistance measurements and siRNA-mediated depletion of T-cadherin in human umbilical vein endothelial cells, we examined its involvement in regulation of endothelial barrier. We found that in resting confluent monolayers adjusted either to 1% or 10% serum, T-cadherin depletion modestly, but consistently reduced transendothelial resistance. This was accompanied by increased phosphorylation of Akt and LIM kinase, reduced phosphorylation of p38 MAP kinase, but no difference in tubulin acetylation and in phosphorylation of an actin filament severing protein cofilin and myosin light chain kinase. Serum stimulation elicited a biphasic increase in resistance with peaks at 0.5 and 4-5 h, which was suppressed by a PI3 kinase/Akt inhibitor wortmannin and a p38 inhibitor SB 239063. T-cadherin depletion increased transendothelial resistance between the two peaks and reduced the amplitude of the second peak. T-cadherin depletion abrogated serum-induced Akt phosphorylation at Thr308 and reduced phosphorylation at Ser473, reduced phosphorylation of cofilin, and accelerated tubulin deacetylation. Adiponectin slightly improved transendothelial resistance irrespectively of T-cadherin depletion. T-cadherin depletion also resulted in a reduced sensitivity and delayed responses to thrombin. These data implicate T-cadherin in regulation of endothelial barrier function, and suggest a complex signaling network that links T-cadherin and regulation of barrier function.

Antiatherosclerotic and anti-insulin resistance effects of adiponectin: basic and clinical studies

Adiponectin is a protein secreted by adipose cells that may couple regulation of insulin sensitivity with energy metabolism and serve to link obesity with insulin resistance. Obesity-related disorders characterized by insulin resistance including the metabolic syndrome, diabetes, atherosclerosis, hypertension, and coronary artery disease are associated with both decreased adiponectin levels and endothelial dysfunction. Recent studies demonstrate that adiponectin has insulin-sensitizing effects as well as antiatherogenic properties. Lifestyle modifications and some drug therapies to treat atherosclerosis, hypertension, diabetes, and coronary heart disease have important effects in increasing adiponectin levels, decreasing insulin resistance, and improving endothelial dysfunction. In this review, we discuss insights into the relationships between adiponectin levels, insulin resistance, and endothelial dysfunction that are derived from various therapeutic interventions. The effects of lifestyle modifications and cardiovascular drugs on adiponectin levels and insulin resistance suggest plausible mechanisms that may be important for understanding and treating atherosclerosis and coronary heart disease.

Microtubule stabilization opposes the (TNF-alpha)-induced loss in the barrier integrity of corneal endothelium

Microtubule disassembly breaks down the barrier integrity in a number of epithelial and endothelial monolayers. This study has investigated effects of TNF-alpha, which is implicated in corneal allograft rejection, on microtubules and barrier integrity in cultured bovine corneal endothelial cells. Exposure to TNF-alpha led to disassembly of the microtubules, and also caused disruption of the perijunctional actomyosin ring (PAMR). As a measure of barrier integrity, trans-endothelial electrical resistance (TER) was determined based on electrical cell-substrate impedance sensing in realtime. Exposure to TNF-alpha caused a slow decline in TER for > 20 h, and a similar exposure to cells grown on porous culture inserts led to a significant increase in permeability to FITC dextran. These changes, indicating a loss of barrier integrity, were also reflected by dislocation of ZO-1 at the cell border and disassembly of cadherins. These effects of TNF-alpha were inhibited upon stabilization of microtubules by pre-treatment with paclitaxel or epothilone B. Microtubule stabilization may be a useful strategy to overcome (TNF-alpha)-induced loss of the barrier integrity of corneal endothelium during inflammation associated with transplant rejection and uveitis.

Role of TRPC1 and NF-kappaB in mediating angiotensin II-induced Ca2+ entry and endothelial hyperpermeability

Endothelial dysfunction is associated with cardiovascular diseases. The Ca(2+) influx occurring via activation of plasmalemma Ca(2+) channels was shown to be critical in signaling the increase in endothelial permeability in response to a variety of permeability-increasing mediators. It has been reported that angiotensin II (AngII) could induce Ca(2+) signaling in some cells, and transient receptor potential canonical 1 (TRPC1) had an important role in this process. The objective of this study was to examine the mechanism of AngII-induced Ca(2+) entry and vascular endothelial hyperpermeability. Human umbilical vein endothelial cells (HUVECs) exposed to AngII exhibited dose-dependent increase in [Ca(2+)]i and endothelial permeability. Quantitative real-time RT-PCR and Western blotting showed that the level of TRPC1 expression had increased significantly at 12h and at 24h after treatment of HUEVCs with AngII. The expression of p65 was suppressed using an RNAi strategy. The results showed that the NF-kappaB signaling pathway and type-1 receptor of AngII was involved in AngII-induced TRPC1 upregulation. Moreover, knockdown of TRPC1 and NF-kappaB expression attenuates AngII-induced [Ca(2+)]i and endothelial permeability. NF-kappaB and TRPC1 have critical roles in AngII-induced Ca(2+) entry and endothelial permeability.

The role of the renin-angiotensin-aldosterone system in cardiovascular progenitor cell function

Intervention in the RAAS (renin-angiotensin-aldosterone system) is one of the leading pharmacotherapeutic strategies, among others, used for the treatment of cardiovascular disease to improve the prognosis after myocardial infarction and to reduce hypertension. Recently, regenerative progenitor cell therapy has emerged as a possible alternative for pharmacotherapy in patients after myocardial infarction or ischaemic events elsewhere, e.g. in the limbs. Angiogenic cell therapy to restore the vascular bed in ischaemic tissues is currently being tested in a multitude of clinical studies. This has prompted researchers to investigate the effect of modulation of the RAAS on progenitor cells. Furthermore, the relationship between hypertension and endothelial progenitor cell function is being studied. Pharmacotherapy by means of angiotensin II type 1 receptor antagonists or angiotensin-converting enzyme inhibitors has varying effects on progenitor cell levels and function. These controversial effects may be explained by involvement of multiple mediators, e.g. angiotensin II and angiotensin-(1-7), that have differential effects on mesenchymal stem cells, haematopoietic progenitor cells and endothelial progenitor cells. Importantly, angiotensin II can either stimulate endothelial progenitor cells by improvement of vascular endothelial growth factor signalling, or invoke excessive production of reactive oxygen species causing premature senescence of these cells. On the other hand, angiotensin-(1-7) stimulates haematopoietic cells and possibly also endothelial progenitor cells. Furthermore, aldosterone, bradykinin and Ac-SDKP (N-acetyl-Ser-Asp-Lys-Pro) may also affect progenitor cell populations. Alternatively, the variability in effects of angiotensin II type 1 receptor and angiotensin-converting enzyme inhibition on cardiovascular progenitor cells might reflect differences between the various models or diseases with respect to circulating and local tissue RAAS activation. In the present review we discuss what is currently known with respect to the role of the RAAS in the regulation of cardiovascular progenitor cells.

Adiponectin inhibits insulin-like growth factor-1-induced cell migration by the suppression of extracellular signal-regulated kinase 1/2 activation, but not Akt in vascular smooth muscle cells

Adiponectin, an adipocyte-derived hormone, has been proposed to show antiatherogenic properties through the inhibitory effects against various growth factors. Insulin-like growth factor-1 (IGF-1) is one of the potent mitogens, which has been considered to play important roles in both atherogenesis and plaque stabilization in accordance to the phase of atherosclerosis. The aim of this study is to elucidate the adiponectin effects on IGF-1-induced cell migration and its intracellular signaling pathways in vascular smooth muscle cells (VSMCs). In this study, we assessed cell migration and several kinase activities in cultured rat aortic smooth muscle cells (RASMCs). Adiponectin pretreatment suppressed IGF-1-induced cell migration and extracellular signal-regulated kinase (ERK)1/2 activation, which is one of the major mediators for IGF-1-induced cell migration. In RASMCs, adiponectin and 5-aminoimidazole-4-carboxamide riboside (AICAR), a 5'-AMP-activated protein kinase (AMPK) activator, stimulated AMPK activation. AMPK activation by AICAR inhibited IGF-1-induced ERK1/2 activation and cell migration in RASMCs. On the other hand, phosphorylation of Akt and Bad, proapoptotic molecules of the Bcl-2 family, which were increased by IGF-1 stimulation, was not diminished by the pretreatment with adiponectin. It was shown that adiponectin inhibited IGF-1-induced VSMC migration through suppression of ERK1/2 activation, which might be implicated in AMPK activation. Furthermore, adiponectin selectively inhibited ERK1/2 pathway, not Akt-Bad pathway, stimulated by IGF-1. From these findings, it was implied that adiponectin suppressed IGF-1-induced VSMC migration and its signaling selectivity.

Protective vascular and myocardial effects of adiponectin

Adiponectin is an abundant plasma protein secreted from adipocytes that elicits protective effects in the vasculature and myocardium. In obesity and insulin-resistant states, adiponectin levels are reduced and loss of its protective effects might contribute to the excess cardiovascular risk observed in these conditions. Adiponectin ameliorates the progression of macrovascular disease in rodent models, consistent with its correlation with improved vascular outcomes in epidemiological studies. The mechanisms of adiponectin signaling are multiple and vary among its cellular sites of action. In endothelial cells, adiponectin enhances production of nitric oxide, suppresses production of reactive oxygen species, and protects cells from inflammation that results from exposure to high glucose levels or tumor necrosis factor, through activation of AMP-activated protein kinase and cyclic AMP-dependent protein kinase (also known as protein kinase A) signaling cascades. In the myocardium, adiponectin-mediated protection from ischemia-reperfusion injury is linked to cyclo-oxygenase-2-mediated suppression of tumor necrosis factor signaling, inhibition of apoptosis by AMP-activated protein kinase, and inhibition of excess peroxynitrite-induced oxidative and nitrative stress. In this Review, we provide an update of studies of the signaling effects of adiponectin in endothelial cells and cardiomyocytes.

Adenovirus-mediated gene transfer of adiponectin reduces the severity of collagen-induced arthritis in mice

Adiponectin (APN) is a hormone released by adipose tissue with anti-inflammatory properties. The purpose of this study was to examine the therapeutic effects of systemic delivery of APN in murine arthritis model. Collagen-induced arthritis (CIA) was induced in male DBA1/J mice, and adenoviral vectors encoding human APN (Ad-APN) or beta-galactosidase (Ad-beta-gal) as control were injected either before or during arthritis progression. Systemic APN delivery at both time points significantly decreased clinical disease activity scores of CIA. In addition, APN treatment before arthritis progression significantly decreased histological scores of inflammation and cartilage damage, bone erosion, and mRNA levels of pro-inflammatory cytokines in the joints, without altering serum anti-collagen antibodies levels. Immunohistochemical staining showed significant inhibition of complement C1q and C3 deposition in the joints of Ad-APN infected CIA mice. These results provide novel evidence that systemic APN delivery prevents inflammation and joint destruction in murine arthritis model.

Angiotensin receptor blockers in the treatment of NASH/NAFLD: could they be a first-class option?

Nonalcoholic fatty liver disease (NAFLD) is a condition pathogenically linked to metabolic syndrome (MS) by insulin resistance (IR), and characterized by hepatic steatosis in the absence of significant alcohol use, hepatotoxicity, and/or other known liver diseases.The principles of NAFLD therapy target IR: the key point of MS. As the renin-angiotensin system (RAS) plays a central role in IR, and subsequently in NAFLD and nonalcoholic steatohepatitis (NASH), an attempt to block the deleterious effects of RAS overexpression seems a logical target. While many potential therapies tested in NASH target only the consequences of this condition, or try to "get rid" of excessive fat, angiotensin receptor blockers (ARBs) could act as an elegant tool for adequate correction of the various imbalances that act in harmony in NASH/NAFLD. Indeed, by inhibiting RAS we can improve the intracellular insulin signaling pathway, better control adipose tissue proliferation and adipokine production, and produce more balanced local and systemic levels of various cytokines. At the same time, by controlling the local RAS in the liver we might be able to prevent at least fibrosis and also slow down the vicious cycle that links steatosis to necroinflammation. By targeting the pancreatic effects of angiotensin we should be able to preserve an adequate insulin secretion and acquire a better metabolic balance.In our opinion there are two major advantages of ARBs that make them a possible therapeutic option for treating NASH and MS: their specific antihypertensive effect, and their impact on liver fibrosis. In light of this, and based on the current evidence (including existent human studies), we can speculate that some ARBs like telmisartan, candesartan, and losartan can be beneficial in treating NASH/NAFLD and its consequences, and further larger controlled clinical trials will bring consistent data into this field.