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Aggrecan cleavage by a disintegrin and metalloproteinase with a thrombospondin type 1 motif, member 5 (ADAMTS-5) is crucial for the breakdown of cartilage matrix during osteoarthritis (1,2,) a degenerative joint disease that leads to the progressive destruction of articular structures. The mechanisms of ADAMTS-5 activation and their links to the pathogenesis of osteoarthritis remain poorly understood, but syndecans have been shown to be involved in the activation of ADAMTS-4 (ref. 3). Here we show that syndecan-4 is specifically induced in type X collagen-producing chondrocytes both in human osteoarthritis and in murine models of the disease. The loss of syndecan-4 in genetically modified mice and intra-articular injections of syndecan-4-specific antibodies into wild-type mice protect from proteoglycan loss and thereby prevent osteoarthritic cartilage damage in a surgically induced model of osteoarthritis. The occurrence of less severe osteoarthritis-like cartilage destruction in both syndecan-4-deficient mice and syndecan-4-specific antibody-treated wild-type mice results from a marked decrease in ADAMTS-5 activity. Syndecan-4 controls the activation of ADAMTS-5 through direct interaction with the protease and through regulating mitogen-activated protein kinase (MAPK)-dependent synthesis of matrix metalloproteinase-3 (MMP-3). Our data suggest that strategies aimed at the inhibition of syndecan-4 will be of great value for the treatment of cartilage damage in osteoarthritis., Human osteoarthritis is a common and often debilitating disorder of the joints that in Western populations affects about 15% of all individuals above 60 years of age (4). One main [...]

Background: Cardiac surgery with cardiopulmonary bypass (CPB) is commonly associated with acute kidney injury, and microvascular endothelial inflammation is a potential underlying mechanism. We hypothesized that pro-inflammatory components of plasma from patients who underwent coronary artery bypass graft surgery with CPB induce endothelial adhesion molecule expression when incorporating altered shear stress in the in vitro model. Methods: The clinical characteristics and markers of systemic inflammation and kidney injury were analyzed pre and postoperatively in 29 patients undergoing coronary artery bypass grafting with CPB. The effects of tumor necrosis factor (TNF)-α and patient plasma on the expression of endothelial inflammation and adhesion markers were analyzed in vitro. Results: Plasma TNF-α was elevated 6 h postoperation (median: 7.3 pg/ml (range: 2.5–94.8 pg/ml)). Neutrophil gelatinase-associated lipocalin in plasma peaked 6 h (99.8 ng/ml (52.6–359.1 ng/ml)) and in urine 24 h postoperation (1.6 ng/mg (0.2–6.4 ng/mg)). Urinary kidney injury molecule-1 concentration peaked 24 h postoperation (0.5 ng/mg (0.2–1.2 ng/mg). In vitro, the expression of E-selectin was induced by 20 pg/ml TNF-α. In addition, the expression of interleukin-8, intercellular adhesion molecule-1, and vascular cell adhesion molecule-1 was induced by 100 pg/ml TNF-α. Compared to healthy control plasma exposure, postoperative plasma did not increase the expression of markers of endothelial inflammation and adhesion under shear stress in vitro. Conclusion: Patients undergoing CPB surgery showed mild systemic inflammation and kidney injury. However, the plasma components did not stimulate endothelial inflammation and adhesion molecule expression in vitro. [ABSTRACT FROM AUTHOR]

Background: Patients undergoing vascular surgery are prone to perioperative organ injury because of both higher prevalence of cardiovascular risk factors and the extent of surgery. Early detection of organ failure is essential to facilitate appropriate medical care. Midregional pro-adrenomedullin (MR-proADM) has been investigated in acute medical care settings to guide clinical decision-making regarding patient pathways and to identify patients prone to imminent cardiovascular or inflammatory complications. In this study, we evaluated the impact of perioperative MR-proADM levels as an early marker of perioperative cardiovascular and inflammatory stress reactions and kidney injury. Methods: The study was conducted as a monocentric, prospective, noninterventional trial at Hannover Medical School, Germany. A total of 454 consecutive patients who underwent open vascular surgery were followed from the day prior to until 30 days after surgery. The composite primary end point was defined as the occurrence of major adverse cardiac events (MACEs), acute kidney injury (AKI), or systemic inflammatory response syndrome (SIRS). Measurements were correlated with both medical history and postoperative MACE, AKI, or SIRS using univariate and multivariate regression analysis. Results: One hundred thirty-nine (31%) of the patients reached the primary end point within the study interval. Midregional pro-adrenomedullin change was associated with the combined primary end point and with the intensity of surgical trauma. Midregional pro-adrenomedullin change was increased in patients reaching the secondary end points, SIRS (optimal cutoff: 0.2 nmol/L) and AKI (optimal cutoff: 0.7 nmol/L), but not in patients with MACEs. Conclusion: Increased levels of MR-proADM within the perioperative setting (1) were linked to the invasiveness of surgery and (2) identified patients with ongoing loss of renal function. Increased MR-proADM levels may therefore identify a subgroup of patients prone to excessive cardiovascular stress but did not directly correlate with adverse cardiac events. Consistently low levels of MR-proADM may identify a subgroup of patients with acceptable low risk to guide discharge from high-density care units. [ABSTRACT FROM AUTHOR]

The iron-sulfur cluster containing protein mitoNEET is known to modulate the oxidative capacity of cardiac mitochondria but its function during myocardial reperfusion injury after transient ischemia is unknown. The purpose of this study was to analyze the impact of mitoNEET on oxidative stress induced cell death and its relation to the glutathione-redox system in cardiomyocytes in an in vitro model of hypoxia and reoxygenation (H/R). Our results show that siRNA knockdown (KD) of mitoNEET caused an 1.9-fold increase in H/R induced apoptosis compared to H/R control while overexpression of mitoNEET caused a 53% decrease in apoptosis. Necrosis was not affected. Apoptosis of both, mitoNEET-KD and control cells was diminished to comparable levels by using the antioxidants Tiron and glutathione compound glutathione reduced ethyl ester (GSH-MEE), indicating that mitoNEET-dependent apoptosis is mediated by oxidative stress. The interplay between mitoNEET and glutathione redox system was assessed by treating cardiomyocytes with 2-acetylamino-3-[4-(2-acetylamino-2-carboxyethylsulfanylthio-carbonylamino) phenylthiocarbamoylsulfanyl] propionic acid (2-AAPA), known to effectively inhibit glutathione reductase (GSR) and to decrease the GSH/GSSG ratio. Surprisingly, inhibition of GSR-activity to 20% by 2-AAPA decreased apoptosis of control and mitoNEET-KD cells to 23% and 25% respectively, while at the same time mitoNEET-protein was increased 4-fold. This effect on mitoNEET-protein was not accessible by mitoNEET-KD but was reversed by GSH-MEE. In conclusion we show that mitoNEET protects cardiomyocytes from oxidative stress-induced apoptosis during H/R. Inhibition of GSH-recycling, GSR-activity by 2-AAPA increased mitoNEET-protein, accompanied by reduced apoptosis. Addition of GSH reversed these effects suggesting that mitoNEET can in part compensate for imbalances in the antioxidative glutathione-system and therefore could serve as a potential therapeutic approach for the oxidatively stressed myocardium. [ABSTRACT FROM AUTHOR]

Antibody-mediated rejection (AMR) is a key limiting factor for long-term graft survival in solid organ transplantation. Human leukocyte antigen (HLA) class I (HLA I) antibodies (Abs) play a major role in the pathogenesis of AMR via their interactions with HLA molecules on vascular endothelial cells (ECs). The antioxidant enzyme heme oxygenase (HO)-1 has anti-inflammatory functions in the endothelium. As complement-independent effects of HLA I Abs can activate ECs, it was the goal of the current study to investigate the role of HO-1 on activation of human ECs by HLA I Abs. In cell cultures of various primary human macro- and microvascular ECs treatment with monoclonal pan- and allele-specific HLA I Abs up-regulated the expression of inducible proinflammatory adhesion molecules and chemokines (vascular cell adhesion molecule-1 [VCAM-1], intercellular cell adhesion molecule-1 [ICAM-1], interleukin-8 [IL-8] and monocyte chemotactic protein 1 [MCP-1]). Pharmacological induction of HO-1 with cobalt-protoporphyrin IX reduced, whereas inhibition of HO-1 with either zinc-protoporphyrin IX or siRNA-mediated knockdown increased HLA I Ab-dependent up-regulation of VCAM-1. Treatment with two carbon monoxide (CO)-releasing molecules, which liberate the gaseous HO product CO, blocked HLA I Ab-dependent EC activation. Finally, in an in vitro adhesion assay exposure of ECs to HLA I Abs led to increased monocyte binding, which was counteracted by up-regulation of HO-1. In conclusion, HLA I Ab-dependent EC activation is modulated by endothelial HO-1 and targeted induction of this enzyme may be a novel therapeutic approach for the treatment of AMR in solid organ transplantation. [ABSTRACT FROM AUTHOR]

Objective: Atherosclerosis, a chronic inflammatory disease, arises from metabolic disorders and is driven by inappropriate recruitment and proliferation of monocytes / macrophages and vascular smooth-muscle-cells. The receptor for the urokinase-type plasminogen activator (uPAR, Plaur) regulates the proteolytic activation of plasminogen. It is also a coactivator of integrins and facilitates leukocyte-endothelial interactions and vascular smooth-muscle-cell migration. The role of uPAR in atherogenesis remains elusive. Methods and Results: We generated C57Bl6/J low-density lipoprotein receptor (LDL) and uPAR double knockout (uPAR-/-/LDLR-/-) mice to test the role of uPAR in two distinct atherosclerosis models. In LDLR-/- mice, hepatic overexpression following hydrodynamic transfection of soluble uPAR that competes with endogenous membrane-bound uPAR was performed as an interventional strategy. Aortic root atherosclerotic lesions induced by feeding a high-fat diet were smaller and comprised less macrophages and vascular smooth-muscle-cells in double knockout mice and animals overexpressing soluble uPAR when compared to controls. In contrast, lesion size, lipid-, macrophage-, and vascular smooth muscle cell content of guide-wire-induced intima lesions in the carotid artery were not affected by uPAR deficiency. Adhesion of uPAR-/--macrophages to TNFα-stimulated endothelial cells was decreased in vitro accompanied by reduced VCAM-1 expression on primary endothelial cells. Hepatic overexpression of soluble full-length murine uPAR in LDLR-/- mice led to a reduction of diet-induced atherosclerotic lesion formation and monocyte recruitment into plaques. Ex vivo incubation with soluble uPAR protein also inhibited adhesion of macrophages to TNFα-stimulated endothelial cells in vitro. Conclusion: uPAR-deficiency as well as competitive soluble uPAR reduced diet-promoted but not guide-wire induced atherosclerotic lesions in mice by preventing monocyte recruitment and vascular smooth-muscle-cell infiltration. Soluble uPAR may represent a therapeutic tool for the modulation of hyperlipidemia-associated atherosclerotic lesion formation. [ABSTRACT FROM AUTHOR]

Objective: Precise perioperative risk stratification is important in vascular surgery patients who are at high risk for major adverse cardiovascular events (MACE) peri- and postoperatively. In clinical practice, the patient’s perioperative risk is predicted by various indicators, e.g. revised cardiac index (RCRI) or modifications thereof. Patients suffering from chronic kidney disease (CKD) are stratified into a higher risk category. We hypothesized that Copeptin as a novel biomarker for hemodynamic stress could help to improve the prediction of perioperative cardiovascular events in patients undergoing vascular surgery including patients with chronic kidney disease. Methods: 477 consecutive patients undergoing abdominal aortic, peripheral arterial or carotid surgery from June 2007 to October 2012 were prospectively enrolled. Primary endpoint was 30-day postoperative major adverse cardiovascular events (MACE). Results: 41 patients reached the primary endpoint, including 63.4% aortic, 26.8% carotid, and 9.8% peripheral surgeries. Linear regression analysis showed that RCRI (P< .001), pre- (P< .001), postoperative Copeptin (P< .001) and Copeptin level change (P= .001) were associated with perioperative MACE, but CKD remained independently associated with MACE and Copeptin levels. Multivariate regression showed that increased Copeptin levels added risk predictive information to the RCRI (P= .003). Especially in the intermediate RCRI categories was Copeptin significantly associated with the occurrence of MACE. (P< .05 Kruskal Wallis test). Subdivision of the study cohort into CKD stages revealed that preoperative Copeptin was significantly associated with CKD stages (P< .0001) and preoperative Copeptin measurements could not predict MACE in patients with more severe CKD stages. Conclusion: Preoperative Copeptin loses its risk predictive potential for perioperative MACE in patients with chronic kidney disease undergoing vascular surgery. [ABSTRACT FROM AUTHOR]

Platelet dysfunction can cause clinically relevant bleeding. Treatment with DDAVP is advocated for this condition. DDAVP increases von Willebrand factor (VWF) on endothelial cells (ECs) and in plasma. VWF could facilitate platelet deposition on subendothelial collagen. VWF also facilitates platelet/EC interactions. Therefore DDAVP could precipitate thromboembolic events. We used a flow chamber model to study in vitro and ex vivo if DDAVP alters recruitment of platelets to EC and collagen. Resting or TRAP-activated platelets and EC were treated individually or simultaneously with 0.4 ng/ml DDAVP. Fluorophor-labeled platelets (106/ml) were resuspended in reconstituted blood and superfused across EC and collagen in an in vitro flow chamber model at arterial shear (320 s−1). Adhesion of platelets to the respective surface was recorded fluorescence microscopically and platelet covered area was assessed. TRAP significantly induced adhesiveness of platelets for collagen and EC. DDAVP pretreatment of platelets did not affect adhesiveness of resting or TRAP-activated platelets for collagen or EC. Adhesiveness of resting but not TRAP-activated platelets was induced on DDAVP-treated EC. DDAVP-conditioned EC supernatant contained vWF and significantly increased platelet deposition on collagen. Platelets from patients with clinically suspected platelet dysfunction undergoing aortic valve replacement exhibited decreased platelet deposition on collagen surfaces. In summary, our data confirm that DDAVP can induce release of platelet adhesion promoting factors from EC, which is most likely vWF. DDAVP has no direct effect on platelets. Blood samples from DDAVP-treated patients do not exhibit significantly augmented platelet deposition on collagen ex vivo. This influence of released promoting factors might cause an increase of undesirable interactions of platelets with EC. [ABSTRACT FROM AUTHOR]

Background: In the present study, the influence of bacterial infection, lipopolysacharides (LPS) and hydroxyethyl starch (HES) on platelet function in a parallel plate flow chamber were measured. Experiments were performed with non-activated and protease-activating-receptor (PAR) 4 agonist activated platelets. Comparative measurements were in vivo capillary bleeding time, platelet function analyzer and impedance aggregometry. Results: PAR 4 agonist did not increase platelet adhesion of platelets from dogs with bacterial inflammation in the flow chamber in contrast to platelets of healthy dogs. Except from impedance aggregometry with lower sensitivity and specificity, PFA did not detect platelet dysfunctions in dogs with infection. In vitro addition of LPS or HES significantly reduced platelet covered area after PAR-activation. Conclusions: The flow chamber detects platelet dysfunctions in dogs with inflammatory diseases. In vitro addition of LPS highlights the inhibiting effect of bacterial wall components on platelet function. Platelet dysfunction induced by infection could possibly also be diagnosed after treatment of sepsis with colloids has commenced. The flow chamber could be a useful tool to detect sepsis associated platelet dysfunction given that larger prospective trials confirm these findings from a proof of concept study. [ABSTRACT FROM AUTHOR]

HDL, through sphingosine-1-phosphate (S1P), exerts direct cardioprotective effects on ischemic myocardium. It remains unclear whether other HDL-associated sphingophospholipids have similar effects. We therefore examined if HDL-associated sphingosylphosphorylcholine (SPC) reduces infarct size in a mouse model of transient myocardial ischemia/reperfusion. Intravenously administered SPC dose-dependently reduced infarct size after 30 minutes of myocardial ischemia and 24 hours reperfusion compared to controls. Infarct size was also reduced by postischemic, therapeutical administration of SPC. Immunohistochemistry revealed reduced polymorphonuclear neutrophil recruitment to the infarcted area after SPC treatment, and apoptosis was attenuated as measured by TUNEL. In vitro, SPC inhibited leukocyte adhesion to TNFα-activated endothelial cells and protected rat neonatal cardiomyocytes from apoptosis. S1P3 was identified as the lysophospholipid receptor mediating the cardioprotection by SPC, since its effect was completely absent in S1P3-deficient mice. We conclude that HDL-associated SPC directly protects against myocardial reperfusion injury in vivo via the S1P3 receptor. [ABSTRACT FROM AUTHOR]

Norepinephrine (NE) is mostly used to treat severe hypotension. However, NE has potentially adverse vasoconstrictive effects on regional vascular beds of kidney, liver, and gut, with a potential for ensuing organ dysfunction. NE therefore is considered as a last reserve in otherwise refractory hypotension. During sepsis, a loss of catecholamine responsiveness occurs that is often interpreted as down-regulation of catecholamine receptors. Therefore, the doses of NE needed to maintain or restore blood pressure may be extremely high. Surprisingly, no adverse vasoconstriction with subsequent hypoperfusion occurs during sepsis, despite the high doses of NE administered. Instead, NE rather causes an increase in blood flow and oxygen delivery. [Copyright &y& Elsevier]

Objectives: We evaluated the role of intracoronary, intrapulmonary and macrophage-mediated delivery of C. pneumoniae (Cp) on coronary lesion formation. Methods: Pigs were allocated to one of three coronary protocols (intracoronary, macrophage or control groups) or to a fourth—a pulmonary group. In the intracoronary group Cp was injected into the wall of the left anterior descending (LAD) and right coronary arteries (RCA) and vehicle into the circumflex (CX). In the macrophage group autologous macrophages preincubated with Cp or not were injected into the LAD and CX wall, respectively. Animals in the control group received vehicle in LAD and CX. In the pulmonary group aerosolised Cp was given intrabronchially, after a single injection of vehicle into the LAD wall. Delivery into the coronary artery wall was performed with a balloon catheter with low-profile injector ports. Results: Seroconversion occurred in the following proportions: 5/6 (intracoronary group), 4/5 (macrophage group), 0/6 (control group), and 1/6 (intrapulmonary group). Significantly higher maximal intimal thickness (MIT) was observed in LADs of intracoronary and pulmonary groups when compared to corresponding CXs. The presence of Cp antigen was associated with higher MIT (r=0.73; P<0.0001). Injection of macrophages into the coronary artery wall did not induce proliferation. Arteries without coronary interventions were morphologically normal. Conclusions: Intracoronary and intrapulmonary but not macrophage-mediated Cp inoculation were associated with moderate intimal proliferation in the absence of a lipid-rich diet. Pre-existing coronary lesions seem a prerequisite for Cp-induced proliferation. [Copyright &y& Elsevier]

Objective: To assess the effect of hypercholesterolemia on neointima formation and vascular remodelling after porcine coronary angioplasty. Methods: Left anterior descending coronary angioplasty was carried out in five control and 16 age-matched hypercholesterolemic miniature pigs. Vascular remodelling was measured by intravascular ultrasound. Neointima size and composition were assessed by quantitative image analysis. Coronary smooth muscle cells (SMC) from control and diet pigs were collected 1 h after angioplasty for in vitro study of the effect of hypercholesterolemic serum on SMC migration and of macrophage-induced matrix degradation on SMC adhesion. Results: Twenty-eight days after angioplasty, lumen increase was 0.08±1.7 mm2 in diet and 2.7±2.7 mm2 (P=0.016) in control pigs. Lumen increase correlated with vascular remodelling (IELpost/IELpre; R2=0.59; P<0.001) and with the circumferential gain relative to the neointima (R2=0.32; P<0.01) but not with neointimal area that was similar in control and diet pigs. Circumferential gain correlated with VSMC deposition at the site of the injury (R2=0.28; P<0.01) that correlated with organized collagen (R2=0.34; P<0.01). The VSMC and collagen content of neointima in diet pigs was lower whereas the macrophage content was higher. Hypercholesterolemic serum and oxidised LDL reduced migration of VSMC from diet pigs. Macrophage-induced degradation of VSMC extracellular matrix reduced VSMC adhesion (P=0.015). Conclusion: Hypercholesterolemia impairs vascular remodelling of balloon-treated coronary arteries. It decreases VSMC and collagen accumulation at the site of injury. Our in vitro data suggest that this decrease can be due to macrophage-induced matrix degradation and reduced VSMC adhesion and to impaired VSMC migration. Oxidised LDL mimics the inhibitory effect of hypercholesterolemic serum. [Copyright &y& Elsevier]

Hypoxia stimulates angiogenesis through the binding of hypoxia-inducible factors to the hypoxia-response element in the vascular endothelial growth factor (Vegf) promotor. Here, we report that deletion of the hypoxia-response element in the Vegf promotor reduced hypoxic Vegf expression in the spinal cord and caused adult-onset progressive motor neuron degeneration, reminiscent of amyotrophic lateral sclerosis. The neurodegeneration seemed to be due to reduced neural vascular perfusion. In addition, Vegf165 promoted survival of motor neurons during hypoxia through binding to Vegf receptor 2 and neuropilin 1. Acute ischemia is known to cause nonselective neuronal death. Our results indicate that chronic vascular insufficiency and, possibly, insufficient Vegf-dependent neuroprotection lead to the select degeneration of motor neurons. [ABSTRACT FROM AUTHOR]

Focuses on impaired myocardial angiogenesis and ischemic cardiomyopathy in mice lacking the vascular endothelial growth factor isoforms VEGF. Generation of VEGF in mice; Impaired cardiac performance; Impaired myocardial angiogenesis.

Fibulin-6, an essential component of extracellular matrix determines the architecture of cellular junctions in tissues undergoing strain. Increased expression and deposition of fibulin-6 facilitates fibroblast migration in response to TGF-β, following myocardial infarction in mouse heart. The underlying mechanism still remains elusive. In conjunction with our previous study, we have now demonstrated that in fibulin-6 knockdown (KD) fibroblasts, not only TGF-β dependent migration, but also stress fiber formation, cellular networking and subsequently fibroblast wound contraction is almost abrogated. SMAD dependent TGF-β pathway shows ~75% decreased translocation of R-SMAD and co-SMAD into the nucleus upon fibulin-6 KD. Consequently, SMAD dependent pro-fibrotic gene expression is considerably down regulated to basal levels both in mRNA and protein. Also, investigating the non-SMAD pathways we observed a constitutive increase in pERK-levels in fibulin-6 KD fibroblast compared to control, but no change was seen in pAKT. Immunoprecipitation studies revealed 60% reduced interaction of TGF-β receptor II and I (TGFRII and I) accompanied by diminished phosphorylation of TGFRI at serin165 in fibulin-6 KD cells. In conclusion, fibulin-6 plays an important role in regulating TGF-β mediated responses, by modulating TGF-β receptor dimerization and activation to further trigger downstream pathways. [ABSTRACT FROM AUTHOR]

Abstract: Syndecan-4 is an ubiquitous, plasma membrane-spanning heparan sulfate proteoglycan involved in proliferation, differentiation, adhesion and migration of cells in vitro. Syndecan-4 knockout (KO) mice show no obvious defects but respond abnormally to experimental stress conditions. In the adult, syndecan-4 is the most abundant syndecan of renal tissue. We therefore investigated the consequences of syndecan-4 deficiency during progression of kidney disease using unilaterally nephrectomized mice, a model of glomerular hyperfiltration and renal hypertrophy. 60 days after unilateral nephrectomy (UNX), mesangial expansion, enhanced matrix production (collagens I and IV, fibronectin) and focal segmental glomerulosclerosis, resembling early stages of diabetic nephropathy, was apparent in male but not female syndecan-4 KO mice. No defect was detected in wild type UNX males. Syndecan-2 mRNA and protein were not detectable in renal glomeruli of wild type mice, but were induced specifically in the glomeruli of the syndecan-4 deficient kidneys after unilateral nephrectomy. Due to the structural similarities of syndecans-2 and -4 we hypothesize that de novo-production of syndecan-2 in kidneys after unilateral nephrectomy reflects a compensatory response. However, this response is counterproductive since syndecan-2 supports the pro-sclerotic activity of TGF-β1 which is increased in parallel with syndecan-2 synthesis. By contrast, signaling through syndecan-4 negatively controls the production of pro-sclerotic TGF-β1. [Copyright &y& Elsevier]

Focuses on impaired myocardial angiogenesis and ischemic cardiomyopathy in mice lacking the vascular endothelial growth factor isoforms VEGF. Generation of VEGF in mice; Impaired cardiac performance; Impaired myocardial angiogenesis.

Aim Antibody-mediated rejection (AMR) is a key limiting factor for long-term graft survival in heart and kidney transplantation. Activation of endothelial cells (ECs) via complement-independent effects of human leukocyte antigen class I (HLA I) antibodies (Abs) plays a major role in the pathogenesis of AMR. As the antioxidant enzyme heme oxygenase (HO)-1 is known to have cell type-specific anti-inflammatory effects in the endothelium, we investigated its role on HLA I Ab-dependent activation of human ECs. Methods Regulation of inducible proinflammatory endothelial adhesion molecules and chemokines (VCAM-1, ICAM-1, IL-8 and MCP-1) by monoclonal pan- and allele-specific HLA I Abs was determined in cell cultures of primary human umbilical venous, aortic macrovascular and microvascular ECs. HO-1 was modulated by pharmacological regulators and siRNA-mediated knockdown. Adherence of THP-1 monocytes to ECs was determined by leukocyte adhesion assay. Results Exposure of human macro- and microvascular EC cultures to HLA I Abs caused endothelial activation, as indicated by up-regulation of VCAM-1, ICAM-1, MCP-1 and IL-8. This up-regulation was mediated via the phosphatidylinositol-3 kinase (PI3K)/Akt and NF- κ B pathways. Pharmacological induction of HO-1 with cobalt-protoporphyrin IX reduced, whereas inhibition of HO-1 with either zinc-protoporphyrin IX or siRNA-mediated knockdown increased HLA I Ab-dependent EC activation. Binding of THP-1 monocytes was enhanced in HLA I Ab-stimulated ECs. This effect was counteracted by HO 1 up-regulation. Conclusion HLA I Ab-dependent EC activation is modulated by specific HO-1 up-regulation. Thus, targeted regulation of endothelial HO-1 may be a novel therapeutic approach for the treatment of AMR in kidney and heart transplantation. S. Immenschuh: Grant/Research Support; Company/Organization; Else Kröner-Fresenius Stiftung EKFS 2012 _ A309. [ABSTRACT FROM AUTHOR]