Endothelial cell activation in inflammation: lessons from mutant mouse models

Extent and features of liver steatosis in vitro pave the way to endothelial dysfunction without physical cell-to-cell contact

BACKGROUND AND AIMS

Several chronic multifactorial diseases originate from energy unbalance between food intake and body energy expenditure, including non-alcoholic fatty liver disease (NAFLD), diabetes, and cardiovascular disorders. Vascular endothelium plays a central role in body homeostasis, and NAFLD is often associated with endothelial dysfunction (ED), the first step in atherosclerosis. Both sugars and fatty acids (FAs) are fuel sources for energy production, but their excess leads to liver steatosis which may trigger ED through a network of mechanisms which need to be clarified. Here, we investigated the crosstalk pathways between in vitro cultured steatotic hepatocytes (FaO) and endothelial cells (HECV) being mediated by soluble factors.

METHODS AND RESULTS

We employed the conditioned medium approach to test how different extent and features of hepatic steatosis distinctively affect endothelium leading to ED. The steatogenic media collected from steatotic hepatocytes were characterized by high triglyceride content and led to lipid accumulation and fat-dependent dysfunction in HECV cells. We found a parallelism between (i) extent of hepatocyte steatosis and level of lipid accumulation in HECV cells; (ii) type of hepatocyte steatosis (with macro- or microvesicular LDs) and extent of oxidative stress, lipid peroxidation, nitric oxide release and expression of ED markers in HECV cells.

CONCLUSIONS

The present findings seem to suggest that, in addition to triglycerides, other soluble mediators should be released by steatotic hepatocytes and may influence lipid accumulation and function of HECV cells. Further studies need to depict the exact profile of soluble factors involved in steatotic hepatocyte-endothelium crosstalk.

Jedi-1 deficiency increases sensory neuron excitability through a non-cell autonomous mechanism

The dorsal root ganglia (DRG) house the primary afferent neurons responsible for somatosensation, including pain. We previously identified Jedi-1 (PEAR1/MEGF12) as a phagocytic receptor expressed by satellite glia in the DRG involved in clearing apoptotic neurons during development. Here, we further investigated the function of this receptor in vivo using Jedi-1 null mice. In addition to satellite glia, we found Jedi-1 expression in perineurial glia and endothelial cells, but not in sensory neurons. We did not detect any morphological or functional changes in the glial cells or vasculature of Jedi-1 knockout mice. Surprisingly, we did observe changes in DRG neuron activity. In neurons from Jedi-1 knockout (KO) mice, there was an increase in the fraction of capsaicin-sensitive cells relative to wild type (WT) controls. Patch-clamp electrophysiology revealed an increase in excitability, with a shift from phasic to tonic action potential firing patterns in KO neurons. We also found alterations in the properties of voltage-gated sodium channel currents in Jedi-1 null neurons. These results provide new insight into the expression pattern of Jedi-1 in the peripheral nervous system and indicate that loss of Jedi-1 alters DRG neuron activity indirectly through an intercellular interaction between non-neuronal cells and sensory neurons.

Pathophysiology of an hypoxic–ischemic insult during the perinatal period

Hypoxia-ischemia is a leading cause of morbidity and mortality in the perinatal period with an incidence of 1/4000 live births. Biochemical events such as energy failure, membrane depolarization, brain edema, an increase of neurotransmitter release and inhibition of uptake, an increase of intracellular Ca(2+), production of oxygen-free radicals, lipid peroxidation, and a decrease of blood flow are triggered by hypoxia-ischemia and may lead to brain dysfunction and neuronal death. These abnormalities can result in mental impairments, seizures, and permanent motor deficits, such as cerebral palsy. The physical and emotional strain that is placed on the children affected and their families is enormous. The care that these individuals need is not only confined to childhood, but rather extends throughout their entire life span, so it is very important to understand the pathophysiology that follows a hypoxic-ischemic insult. This review will highlight many of the mechanisms that lead to neuronal death and include the emerging area of white matter injury as well as the role of inflammation and will provide a summary of therapeutic strategies. Hypothermia and oxygen will also be discussed as treatments that currently lack a specific target in the hypoxic/ischemic cascade.

Agmatine promotes the migration of murine brain endothelial cells via multiple signaling pathways

AIMS

The combination of adhesion and migration of endothelial cells (ECs) is an integral process for evolution, organization, repair and vessel formation in living organisms. Agmatine, a polycationic amine existing in brain, has been investigated to exert neuroprotective effects. Up to date, there are no studies reporting that agmatine modulates murine brain endothelial (bEnd.3) cells migration. In the present study, we intend to investigate the role of agmatine in bEnd.3 cells migration and the molecular mechanism mediating this action.

MAIN METHODS

The effect of agmatine on the bEnd.3 cells migration was examined by migration assay, and the mechanism involved for this effect was investigated by western blot analysis and NO contents measurements.

KEY FINDINGS

Agmatine treatment (50, 100 and 200 μM) significantly accelerated bEnd.3 cells migration in a concentration-dependent manner. Western blotting revealed that agmatine treatment significantly induced vascular endothelial growth factor (VEGF), VEGF receptor 2 (Flk-1/KDR or VEGFR2), phosphatidylinositol 3-kinase (PI3K), Akt/protein kinase B (also known as PKB, PI3K downstream effector protein), endothelial nitric oxide synthase (eNOS) nitric oxide (NO; product by eNOS) and intercellular adhesion molecule 1 (ICAM-1) expressions during bEnd.3 cells migration. The expression of ICAM-1 and migration of bEnd.3 cells, induced by agmatine, were significantly attenuated by treatment of wortmannin, a specific PI3K inhibitor.

SIGNIFICANCE

Taken together, we provide the first evidence that activation of VEGF/VEGFR2 and the consequential PI3K/Akt/eNOS/NO/ICAM-1 signaling pathways are serial events, through which the treatment of agmatine could lead to bEnd.3 cells migration.

FXR protects lung from lipopolysaccharide-induced acute injury

Acute lung injury and its more severe form, acute respiratory distress syndrome, are characterized by an acute inflammatory response in the airspaces and lung parenchyma. The nuclear receptor farnesoid X receptor (FXR) is expressed in pulmonary artery endothelial cells. Here, we report a protective role of FXR in a lipopolysaccharide-induced mouse model of acute lung injury. Upon intratracheal injection of lipopolysaccharide, FXR-/- mice showed higher lung endothelial permeability, released more bronchoalveolar lavage cells to the alveoli, and developed acute pneumonia. Cell adhesion molecules were expressed at higher levels in FXR-/- mice as compared with control mice. Furthermore, lung regeneration was much slower in FXR-/- mice. In vitro experiments showed that FXR activation blocked TNFα-induced expression of P-selectin but stimulated proliferation of lung microvascular endothelial cells through up-regulation of Foxm1b. In addition, expression of a constitutively active FXR repressed the expression of proinflammatory genes and improved lung permeability and lung regeneration in FXR-/- mice. This study demonstrates a critical role of FXR in suppressing the inflammatory response in lung and promoting lung repair after injury.

REVIEW paper: pathophysiology of myocardial reperfusion injury: the role of genetically engineered mouse models

Coronary heart disease is the leading cause of death worldwide, affecting millions of men and women each year. Following an acute myocardial infarction, early and successful reperfusion therapy with thrombolytic therapy or primary percutaneous coronary intervention plays an important role in minimizing tissue injury associated with cessation of blood flow. The process of restoring blood flow to the ischemic myocardium, however, can induce additional injury. This phenomenon, termed myocardial ischemia-reperfusion (MI-R) injury, can paradoxically reduce the beneficial effects of myocardial reperfusion. MI-R injury is characterized by the formation of oxygen radicals upon reintroduction of molecular oxygen to the ischemic tissue, resulting in widespread lipid and protein oxidative modifications, mitochondrial injury, and cell death. In addition, studies have shown that MI-R is characterized by an inappropriate immune response in the microcirculation, resulting in leukocyte-endothelial cell interactions mediated by the upregulation of both leukocyte and endothelial cell adhesion molecules. Furthermore, MI-R ameliorates the production of certain cardioprotective factors such as nitric oxide. Advances in the generation of genetically modified mouse models enable researchers to identify the functional importance of genes involved in these processes.

Stromal cell-derived factor-1/CXCL12 stimulates chemorepulsion of NOD/LtJ T-cell adhesion to islet microvascular endothelium

OBJECTIVE

Diabetogenic T-cell recruitment into pancreatic islets facilitates beta-cell destruction during autoimmune diabetes, yet specific mechanisms governing this process are poorly understood. The chemokine stromal cell-derived factor-1 (SDF-1) controls T-cell recruitment, and genetic polymorphisms of SDF-1 are associated with early development of type 1 diabetes.

RESEARCH DESIGN AND METHODS

Here, we examined the role of SDF-1 regulation of diabetogenic T-cell adhesion to islet microvascular endothelium. Islet microvascular endothelial cell monolayers were activated with tumor necrosis factor-alpha (TNF-alpha), subsequently coated with varying concentrations of SDF-1 (1-100 ng/ml), and assayed for T-cell/endothelial cell interactions under physiological flow conditions.

RESULTS

TNF-alpha significantly increased NOD/LtJ T-cell adhesion, which was completely blocked by SDF-1 in a dose-dependent manner, revealing a novel chemorepulsive effect. Conversely, SDF-1 enhanced C57BL/6J T-cell adhesion to TNF-alpha-activated islet endothelium, demonstrating that SDF-1 augments normal T-cell adhesion. SDF-1 chemorepulsion of NOD/LtJ T-cell adhesion was completely reversed by blocking G(i)alpha-protein-coupled receptor activity with pertussis toxin. CXCR4 protein expression was significantly decreased in NOD/LtJ T-cells, and inhibition of CXCR4 activity significantly reversed SDF-1 chemorepulsive effects. Interestingly, SDF-1 treatment significantly abolished T-cell resistance to shear-mediated detachment without altering adhesion molecule expression, thus demonstrating decreased integrin affinity and avidity.

CONCLUSIONS

In this study, we have identified a previously unknown novel function of SDF-1 in negatively regulating NOD/LtJ diabetogenic T-cell adhesion, which may be important in regulating diabetogenic T-cell recruitment into islets.

Hepatocyte growth factor suppresses acute renal inflammation by inhibition of endothelial E-selectin

Vascular endothelial activation, marked by de novo expression of E-selectin, is an early and essential event in the process of leukocyte extravasation and inflammation. Evidence suggests that hepatocyte growth factor (HGF) ameliorates inflammation in animal models of renal disease, implying that HGF might inhibit specific components of the inflammatory response. This study examined the effect of HGF on endothelial E-selectin expression in acute inflammation induced by tumor necrosis factor (TNF)-α. In vitro, HGF suppressed TNF-α-induced cell surface expression of E-selectin in human umbilical vein endothelial cells (HUVEC) and inhibited E-selectin mediated monocytic adhesion to endothelial monolayers. HGF activated phosphatidylinositol 3-kinase (PI3K)–Akt that in turn inhibited its downstream transducer glycogen synthase kinase (GSK)3. Blockade of the PI3K–Akt pathway with specific inhibitors abrogated HGF induced inhibitory phosphorylation of GSK3 and suppression of E-selectin. In addition, selective inhibition of GSK3 activity by lithium suppressed TNF-α-induced E-selectin expression and monocytic adhesion, reminiscent of the action of HGF. Moreover, ectopic expression of an uninhibitable mutant GSK3β, in which the regulatory serine-9 is replaced by alanine, abolished HGF's suppressive effect on endothelial E-selectin. In vivo, administration of exogenous HGF reduced endothelial expression of E-selectin induced by bolus injection of TNF-α. This was associated with less sequestration of circulating fluorescence-labeled macrophages in the kidney. These findings suggest that HGF ameliorates acute renal inflammation in part by downregulating E-selectin mediated macrophage adhesion to the inflamed endothelium.

Anti-inflammatory effect of hepatocyte growth factor in chronic kidney disease: targeting the inflamed vascular endothelium

Recent studies show that hepatocyte growth factor (HGF) has potent anti-inflammatory effects in multiple animal models of disease in various organ systems, including the kidney, suggesting that HGF may suppress a common proinflammatory process. The aim of this study was to examine the molecular mechanism of HGF's anti-inflammatory actions in a model of chronic kidney disease. Beginning 2 wk after subtotal nephrectomy, rats received a continuous infusion of recombinant HGF, neutralization of endogenous HGF by daily injection of an anti-HGF antibody, or preimmune IgG for an additional 2 wk. The effects on inflammation and injury were examined. HGF administration ameliorated whereas neutralizing endogenous HGF worsened renal inflammation in remnant kidneys. This was accompanied by parallel alterations in endothelial activation and inflammation, marked respectively by de novo E-selectin expression in renal vascular endothelium and leukocyte adhesion to endothelium. In vitro, HGF abrogated monocyte adhesion to TNF-alpha-activated endothelial monolayers and suppressed endothelial expression of E-selectin, which depended on NF-kappaB signaling. In addition, HGF suppressed NF-kappaB reporter gene activity that was induced by TNF-alpha and counteracted TNF-alpha-elicited NF-kappaB interaction with kappaB elements at the E-selectin gene level. Dissection of the NF-kappaB signaling cascade revealed that suppression of NF-kappaB depended on HGF's inhibitory action on NF-kappaB and IkappaB phosphorylation and IkappaB degradation. In vivo, continuous infusion of exogenous HGF markedly diminished sequestration of circulating fluorescence-labeled macrophages in the remnant kidney, mimicking the action of an E-selectin blocking antibody. These findings suggest that HGF has potent and direct anti-inflammatory effects on the basis of suppression of NF-kappaB activation and downstream endothelial inflammation.

VEGF-A stimulation of leukocyte adhesion to colonic microvascular endothelium: implications for inflammatory bowel disease

Inflammatory bowel disease (IBD) is a chronic inflammatory disorder characterized by increased leukocyte recruitment and subsequent tissue damage. An increase in the density of the microvasculature of the colon during IBD has been suggested, leading to the concept that angiogenesis may play a pathological role in IBD. Increased tissue and serum levels of the angiogenic cytokine VEGF-A have been reported in cases of active IBD. In this study, we examined the hypothesis that VEGF-A exerts a proinflammatory effect on colon microvascular endothelium that contributes to colonic inflammation. Leukocyte adhesion to VEGF-A-stimulated colon microvascular endothelial cells was examined using a parallel-plate hydrodynamic flow chamber. ICAM-1 adhesion molecule expression on colonic microvascular endothelium also was determined in response to VEGF-A stimulation, along with characterization of leukocyte adhesion molecule expression. High-dose VEGF-A (50 ng/ml) stimulation increased neutrophil and T cell adhesion to and decreased rolling velocities on activated endothelium, whereas low-dose VEGF-A (10 ng/ml) was without effect. Colonic endothelium constitutively expressed ICAM-1, which was significantly increased by treatment with 50 ng/ml VEGF-A or 10 ng/ml TNF-alpha but not 10 ng/ml VEGF-A. T cells expressed CD18 and CD11a with no expression of CD11b, whereas neutrophils expressed CD18, CD11a, and CD11b. Finally, VEGF-A-dependent leukocyte adhesion was found to occur in a CD18-dependent manner. These results demonstrate that VEGF-A levels found in IBD exert a proinflammatory effect similar to other inflammatory agents and suggest that this cytokine may serve as an intermediary between angiogenic stimulation and cell-mediated immune responses.

Regulation of dextran sodium sulfate induced colitis by leukocyte beta 2 integrins

Inflammatory bowel diseases (IBD) are chronic inflammatory disorders whose etiology remains unknown. Reports have shown that infiltration of leukocytes into intestinal tissue is a pathognomonic hallmark for this disease. Leukocyte beta(2) integrins are heterodimeric adhesion membrane proteins that are exclusively expressed on leukocytes and participate in immune cell adhesion and activation. In this study, we examined the pathophysiological role of the beta(2) integrins CD18, CD11a, and CD11b in the pathogenesis of dextran sodium sulfte (DSS)-induced experimental colitis. Disease activity was measured by daily assessment of clinical parameters including stool consistency, weight loss, occult blood, and gross rectal bleeding. Histopathological changes including severity of inflammation, surface epithelial/crypt damage, and depth of injury were also determined. The CD18 null and CD11a null mice had significantly lower disease activity and cumulative histopathological scores compared to wild-type mice. Interestingly, CD11b null mice did not show protection against DSS colitis and displayed increased disease activity compared to wild-type mice. Examination of specific leukocyte populations in the distal colon from various mice revealed significant attenuation of neutrophil and macrophage infiltrates in CD18, CD11a, and CD11b null mice. Surprisingly, the CD11b null mice showed a significant increase in plasma cell infiltration in response to DSS suggesting that this molecule may influence plasma cell function during colitis. This study demonstrates that genetic loss of CD18 or CD11a is protective during experimental colitis and that CD11b may serve a regulatory role during development of disease.

Revealing anti-inflammatory mechanisms of soy isoflavones by flow: modulation of leukocyte-endothelial cell interactions

The antiatherogenic effects of soy isoflavone consumption have been demonstrated in a variety of studies. However, the mechanisms involved remain poorly defined. Adhesion of monocytes to vascular endothelial cells is a key step within the inflammatory cascade that leads to atherogenesis. Many factors, including the physical forces associated with blood flow, regulate this process. Using an in vitro flow assay, we report that genistein, a principal component of most isoflavone preparations, inhibits monocyte adhesion to cytokine (TNF-alpha)-stimulated human vascular endothelial cells at physiologically relevant concentrations (0-1 microM). This effect is absolutely dependent on flow and is not observed under static conditions. Furthermore, this inhibition was dependent on activation of endothelial peroxisomal proliferator-activated receptor-gamma. No significant role for other reported properties of genistein, including antioxidant effects, inhibition of tyrosine kinases, or activation of estrogen receptors, was observed. Furthermore, the antiadhesive effects of genistein did not occur via modulation of the adhesion molecules E-selectin, ICAM-1, VCAM-1, or platelet-endothelial cell adhesion molecule-1. These data reveal a novel anti-inflammatory mechanism for isoflavones and identify the physical forces associated with blood flow and a critical mediator of this function.

Alpha L-integrin I domain cyclic peptide antagonist selectively inhibits T cell adhesion to pancreatic islet microvascular endothelium

Insulitis is a hallmark feature of autoimmune diabetes that ultimately results in islet beta-cell destruction. We examined integrin requirements and specific inhibition of integrin structure in T cell and monocyte adhesion to pancreatic islet endothelium. Examination of cell surface integrin expression on WEHI 7.1 T cells revealed prominent expression of beta-, beta(1)-, alpha(L)-integrins, and low expression of alpha(M)-integrins; whereas WEHI 274.1 monocytes showed significant staining for beta(2)-, beta(1)-, alpha(M)-molecules and no expression of alpha(L)-molecules. Unstimulated islet endothelium showed constitutive levels of ICAM-1 counter-ligand expression with minimal VCAM-1 expression; however, TNF-alpha stimulation increased cell surface density of both molecules. TNF-alpha increased T cell and monocyte rolling and adhesion under hydrodynamic flow conditions. Administration of a cyclic peptide competitor for the alpha(L)-integrin I domain binding sites (cyclo1,12-PenITDGEATDSGC) blocked T cell adhesion without inhibiting monocyte adhesion. Examination of T cell rolling revealed that cLAB.L treatment increased the average rolling velocity on activated endothelium and significantly decreased the fraction of T cells rolling at < or =50 microm/s, suggesting that cLAB.L treatment interferes with signal activation events required for the conversion of T cell rolling to firm adhesion. These data demonstrate for the first time that cyclic peptide antagonists against alpha(L)-integrin I domain attenuate T cell recruitment to islet endothelium.

Intercellular adhesion molecule-1 (ICAM-1) regulates endothelial cell motility through a nitric oxide-dependent pathway

Coordinated regulation of endothelial cell migration is an integral process during angiogenesis. However, molecular mechanisms regulating endothelial cell migration remain largely unknown. Increased expression of cell adhesion molecules has been implicated during angiogenesis, yet the precise role of these molecules is unclear. Here, we examined the hypothesis that intercellular adhesion molecule-1 (ICAM-1) is important for endothelial cell migration. Total cell displacement and directional migration were significantly attenuated in ICAM-1-deficient endothelium. Closer examination of ICAM-1-deficient cells revealed decreased Akt Thr(308) and endothelial nitric-oxide synthase Ser(1177) phosphorylation and NO bioavailability, increased actin stress fiber formation, and a lack of distinct cell polarity compared with wild-type endothelium. Supplementation of ICAM-1 mutant cells with the NO donor DETA NONOate (0.1 microM) corrected the migration defect, diminished stress fiber formation, and enhanced pseudopod and uropod formation. These data demonstrate that ICAM-1 facilitates the development of cell polarity and modulates endothelial cell migration through a pathway regulating endothelial nitric-oxide synthase activation and organization of the actin cytoskeleton.