Down-regulation of neprilysin (EC3.4.24.11) expression in vascular endothelial cells by laminar shear stress involves NADPH oxidase-dependent ROS production

Enzymological Characterization of 64Cu-Labeled Neprilysin Substrates and Their Application for Modulating the Renal Clearance of Targeted Radiopharmaceuticals

The applicability of radioligands for targeted endoradionuclide therapy is limited due to radiation-induced toxicity to healthy tissues, in particular to the kidneys as primary organs of elimination. The targeting of enzymes of the renal brush border membrane by cleavable linkers that permit the formation of fast eliminating radionuclide-carrying cleavage fragments gains increasing interest. Herein, we synthesized a small library of ⁶⁴Cu-labeled cleavable linkers and quantified their substrate potentials toward neprilysin (NEP), a highly abundant peptidase at the renal brush border membrane. This allowed for the derivation of structure-activity relationships, and selected cleavable linkers were attached to the somatostatin receptor subtype 2 ligand [Tyr³]octreotate. Radiopharmacological characterization revealed that a substrate-based targeting of NEP in the kidneys with small peptides entails their premature cleavage in the blood circulation by soluble and endothelium-derived NEP. However, for a kidney-specific targeting of NEP, the additional targeting of albumin in the blood is highlighted.

LCZ696 ameliorates lipopolysaccharide-induced endothelial injury

Lipopolysaccharide (LPS)-induced endothelial dysfunction plays an important role in the pathogenesis of cardiovascular diseases. LCZ696, the dual-acting angiotensin receptor blocker, and neprilysin inhibitor has been used for the treatment of heart failure with reduced ejection fraction. Recent work suggests that LCZ696 therapy might have an anti-inflammatory effect in cardiovascular tissue. In the current study, we show that LCZ696 attenuates LPS-induced oxidative stress by reducing the production of intracellular reactive oxygen species (ROS) and the measurements of malonyl dialdehyde (MDA) level in human umbilical vascular endothelial cells (HUVECs). LCZ696 inhibits LPS-induced expressions and secretions of the pro-inflammatory cytokines, interleukin-6 (IL-6), interleukin-1α (IL-1α), and tumor necrosis factor β (TNF-β) as well as the chemokines, monocyte chemotactic protein 1 (MCP-1), and chemokine (C-X-C motif) ligand 1 protein (CXCL1). Additionally, we found that LCZ696 reduces LPS-induced expressions of vascular cell adhesion molecule 1 (VCAM-1) and P-selectin and the attachment of U937 monocytes to HUVECs. Mechanistically, LCZ696 prevents LPS-induced activation of the TLR4/Myd88 pathway and nuclear translocation of nuclear factor kappa-B (NF-κB) p65 factor. Based on these findings, we conclude that LCZ696 is capable of ameliorating LPS-induced endothelial dysfunction via anti-inflammatory properties.

Maternal Overweight Downregulates MME (Neprilysin) in Feto-Placental Endothelial Cells and in Cord Blood

Maternal overweight in pregnancy alters the metabolic environment and generates chronic low-grade inflammation. This affects fetal development and programs the offspring’s health for developing cardiovascular and metabolic disease later in life. MME (membrane-metalloendopeptidase, neprilysin) cleaves various peptides regulating vascular tone. Endothelial cells express membrane-bound and soluble MME. In adults, the metabolic environment of overweight and obesity upregulates endothelial and circulating MME. We here hypothesized that maternal overweight increases MME in the feto-placental endothelium. We used primary feto-placental endothelial cells (fpEC) isolated from placentas after normal vs. overweight pregnancies and determined MME mRNA, protein, and release. Additionally, soluble cord blood MME was analyzed. The effect of oxygen and tumor necrosis factor α (TNFα) on MME protein in fpEC was investigated in vitro. Maternal overweight reduced MME mRNA (−39.9%, p < 0.05), protein (−42.5%, p = 0.02), and MME release from fpEC (−64.7%, p = 0.02). Both cellular and released MME protein negatively correlated with maternal pre-pregnancy BMI. Similarly, cord blood MME was negatively associated with pre-pregnancy BMI (r = −0.42, p = 0.02). However, hypoxia and TNFα, potential negative regulators of MME expression, did not affect MME protein. Reduction of MME protein in fpEC and in cord blood may alter the balance of vasoactive peptides. Our study highlights the fetal susceptibility to maternal metabolism and inflammatory state.

SAA1 increases NOX4/ROS production to promote LPS-induced inflammation in vascular smooth muscle cells through activating p38MAPK/NF-κB pathway

Background

To investigate the effects of serum amyloid A1 (SAA1) on lipopolysaccharide (LPS) -induced inflammation in vascular smooth muscle cells (VSMCs). SAA1 expression was detected in LPS induced VSMCs at different concentrations for different time by using Western blotting. After pre-incubation with recombinant SAA1 protein, VSMCs were treated with 1 μg/ml LPS for 24 h. The VSMCs were then divided into Control, SAA1 siRNA, Nox4 siRNA, LPS, LPS + SAA1 siRNA, LPS + Nox4 siRNA and LPS + SAA1 siRNA + Nox4 groups. MTT was performed to observe the toxicity of VSMCs. Lucigenin-enhanced chemiluminescence method was used to detect superoxide anion (O₂⁻) production and NADPH oxidase activity. Quantitative real-time polymerase chain reaction (qRT-PCR) was used to determine expressions of inflammatory factors. Western blotting was used to determine expressions of NOX-4 and p38MAPK/NF-κB pathway related proteins.

Results

LPS promoted SAA1 protein expression in a concentration−/time-dependent manner. Recombinant SAA1 protein could increase NOX4/ROS production and promote the release of inflammatory factors (IL-1β, IL-6, IL-8, IL-17, TNF-α and MCP-1) in LPS (1 μg/ml) - induced VSMCs. Besides, both SAA1 siRNA and NOX-4 siRNA could not only enhance the O₂⁻ production and NADPH oxidase activity, but also up-regulate the protein expression of NOX4, the release of inflammatory factors, and the levels of p-p38 and p-NF-κB p65 in LPS-induced VSMCs. However, no significant differences in each index were observed between LPS group and LPS + SAA1 siRNA + Nox4 group.

Conclusion

SAA1-mediated NOX4/ROS pathway could activate p38MAPK/NF-κB pathway, thereby contributing to the release of inflammatory factors in LPS-induced VSMCs.

HIV-1 Transactivator Protein Induces ZO-1 and Neprilysin Dysfunction in Brain Endothelial Cells via the Ras Signaling Pathway

Amyloid beta (Aβ) deposition is increased in human immunodeficiency virus-1- (HIV-1-) infected brain, but the mechanisms are not fully understood. The aim of the present study was to evaluate the role of Ras signaling in HIV-1 transactivator protein- (Tat-) induced Aβ accumulation in human cerebral microvascular endothelial cells (HBEC-5i). Cell viability assay showed that 1 μg/mL Tat and 20 μmol/L of the Ras inhibitor farnesylthiosalicylic acid (FTS) had no significant effect on HBEC-5i cell viability after 24 h exposure. Exposure to Tat decreased protein and mRNA levels of zonula occludens- (ZO-) 1 and Aβ-degrading enzyme neprilysin (NEP) in HBEC-5i cells as determined by western blotting and quantitative real-time polymerase chain reaction. Exposure to Tat also increased transendothelial transfer of Aβ and intracellular reactive oxygen species (ROS) levels; however, these effects were attenuated by FTS. Collectively, these results suggest that the Ras signaling pathway is involved in HIV-1 Tat-induced changes in ZO-1 and NEP, as well as Aβ deposition in HBEC-5i cells. FTS partially protects blood-brain barrier (BBB) integrity and inhibits Aβ accumulation.

Synergistic Impact of Nicotine and Shear Stress Induces Cytoskeleton Collapse and Apoptosis in Endothelial Cells

Nicotine is the major component in cigarette smoke and has been recognized as a risk factor for various cardiovascular diseases such as atherosclerosis. However, the definite pathogenesis of nicotine-mediated endothelial dysfunction remains unclear because hemodynamic factor in most of prior in vitro studies was excluded. To understand how nicotine affects endothelium in the dynamic environment, human umbilical vein endothelial cells were treated by different laminar shear stresses (LSS; 0, 6, 8, and 12 dynes cm(-2)) with and without 10(-4) M nicotine for 12 h in a parallel plate flow system, following detections of cellular morphology and apoptotic level. Our results showed that cells sheared by 12 dynes cm(-2) LSS with nicotine excessively elongated and aligned with the flow direction, and exhibited significant apoptosis as compared to the groups with nicotine or LSS alone. We reasoned that the irregular morphological rearrangement and elevated apoptosis were resulted from the interruption of mechanostasis due to cytoskeletal collapse. Furthermore, all the impaired responses can be rescued by treatment with free radical scavenger ascorbic acid (10(-4) M), indicating oxidative stress was likely mediated with the impairments. In summary, our findings demonstrated an essential role of LSS in nicotine-mediated endothelial injury occurring in the physiological environment.

Regulation of thrombomodulin expression and release in human aortic endothelial cells by cyclic strain

Background and Objectives

Thrombomodulin (TM), an integral membrane glycoprotein expressed on the lumenal surface of vascular endothelial cells, promotes anti-coagulant and anti-inflammatory properties. Release of functional TM from the endothelium surface into plasma has also been reported. Much is still unknown however about how endothelial TM is regulated by physiologic hemodynamic forces (and particularly cyclic strain) intrinsic to endothelial-mediated vascular homeostasis.

Methods

This study employed human aortic endothelial cells (HAECs) to investigate the effects of equibiaxial cyclic strain (7.5%, 60 cycles/min, 24 hrs), and to a lesser extent, laminar shear stress (10 dynes/cm², 24 hrs), on TM expression and release. Time-, dose- and frequency-dependency studies were performed.

Results

Our initial studies demonstrated that cyclic strain strongly downregulated TM expression in a p38- and receptor tyrosine kinase-dependent manner. This was in contrast to the upregulatory effect of shear stress. Moreover, both forces significantly upregulated TM release over a 48 hr period. With continuing focus on the cyclic strain-induced TM release, we noted both dose (0–7.5%) and frequency (0.5–2.0 Hz) dependency, with no attenuation of strain-induced TM release observed following inhibition of MAP kinases (p38, ERK-1/2), receptor tyrosine kinase, or eNOS. The concerted impact of cyclic strain and inflammatory mediators on TM release from HAECs was also investigated. In this respect, both TNFα (100 ng/ml) and ox-LDL (10–50 µg/ml) appeared to potentiate strain-induced TM release. Finally, inhibition of neither MMPs (GM6001) nor rhomboids (3,4-dichloroisocoumarin) had any effect on strain-induced TM release. However, significantly elevated levels (2.1 fold) of TM were observed in isolated microparticle fractions following 7.5% strain for 24 hrs.

Conclusions

A preliminary in vitro investigation into the effects of cyclic strain on TM in HAECs is presented. Physiologic cyclic strain was observed to downregulate TM expression, whilst upregulating in a time-, dose- and frequency-dependent manner the release of TM.

Downregulation of blood-brain barrier phenotype by proinflammatory cytokines involves NADPH oxidase-dependent ROS generation: consequences for interendothelial adherens and tight junctions

Background and Objectives

Blood-brain barrier (BBB) dysfunction is an integral feature of neurological disorders and involves the action of multiple proinflammatory cytokines on the microvascular endothelial cells lining cerebral capillaries. There is still however, considerable ambiguity throughout the scientific literature regarding the mechanistic role(s) of cytokines in this context, thereby warranting a comprehensive in vitro investigation into how different cytokines may cause dysregulation of adherens and tight junctions leading to BBB permeabilization.

Methods

The present study employs human brain microvascular endothelial cells (HBMvECs) to compare/contrast the effects of TNF-α and IL-6 on BBB characteristics ranging from the expression of interendothelial junction proteins (VE-cadherin, occludin and claudin-5) to endothelial monolayer permeability. The contribution of cytokine-induced NADPH oxidase activation to altered barrier phenotype was also investigated.

Results

In response to treatment with either TNF-α or IL-6 (0–100 ng/ml, 0–24 hrs), our studies consistently demonstrated significant dose- and time-dependent decreases in the expression of all interendothelial junction proteins examined, in parallel with dose- and time-dependent increases in ROS generation and HBMvEC permeability. Increased expression and co-association of gp91 and p47, pivotal NADPH oxidase subunits, was also observed in response to either cytokine. Finally, cytokine-dependent effects on junctional protein expression, ROS generation and endothelial permeability could all be attenuated to a comparable extent using a range of antioxidant strategies, which included ROS depleting agents (superoxide dismutase, catalase, N-acetylcysteine, apocynin) and targeted NADPH oxidase blockade (gp91 and p47 siRNA, NSC23766).

Conclusion

A timely and wide-ranging investigation comparing the permeabilizing actions of TNF-α and IL-6 in HBMvECs is presented, in which we demonstrate how either cytokine can similarly downregulate the expression of interendothelial adherens and tight junction proteins leading to elevation of paracellular permeability. The cytokine-dependent activation of NADPH oxidase leading to ROS generation was also confirmed to be responsible in-part for these events.

Neprilysin regulates pulmonary artery smooth muscle cell phenotype through a platelet-derived growth factor receptor-dependent mechanism

Reduced neprilysin (NEP), a cell surface metallopeptidase, which cleaves and inactivates proinflammatory and vasoactive peptides, predisposes the lung vasculature to exaggerated remodeling in response to hypoxia. We hypothesize that loss of NEP in pulmonary artery smooth muscle cells results in increased migration and proliferation. Pulmonary artery smooth muscle cells isolated from NEP(-/-) mice exhibited enhanced migration and proliferation in response to serum and platelet-derived growth factor, which was attenuated by NEP replacement. Inhibition of NEP by overexpression of a peptidase dead mutant or knockdown by small interfering RNA in NEP(+/+) cells increased migration and proliferation. Loss of NEP led to an increase in Src kinase activity and phosphorylation of PTEN, resulting in activation of the platelet-derived growth factor receptor (PDGFR). Knockdown of Src kinase with small interfering RNA or inhibition with PP2, a src kinase inhibitor, decreased PDGFR(Y751) phosphorylation and attenuated migration and proliferation in NEP(-/-) smooth muscle cells. NEP substrates, endothelin 1 or fibroblast growth factor 2, increased activation of Src and PDGFR in NEP(+/+) cells, which was decreased by an endothelin A receptor antagonist, neutralizing antibody to fibroblast growth factor 2 and Src inhibitor. Similar to the observations in pulmonary artery smooth muscle cells, levels of phosphorylated PDGFR, Src, and PTEN were elevated in NEP(-/-) lungs. Endothelin A receptor antagonist also attenuated the enhanced responses in NEP(-/-) pulmonary artery smooth muscle cells and lungs. Taken together our results suggest a novel mechanism for the regulation of PDGFR signaling by NEP substrates involving Src and PTEN. Strategies that increase lung NEP activity/expression or target key downstream effectors, like Src, PTEN, or PDGFR, may be of therapeutic benefit in pulmonary vascular disease.

Stabilization of brain microvascular endothelial barrier function by shear stress involves VE-cadherin signaling leading to modulation of pTyr-occludin levels

Blood-brain barrier (BBB) regulation involves the coordinated interaction of intercellular adherens and tight junctions in response to stimuli. One such stimulus, shear stress, has been shown to upregulate brain microvascular endothelial cell (BMvEC) barrier function, although our knowledge of the signaling mechanisms involved is limited. In this article, we examined the hypothesis that VE-cadherin can transmit shear signals to tight junction occludin with consequences for pTyr-occludin and barrier function. In initial studies, chronic shear enhanced membrane localization of ZO-1 and claudin-5, decreased pTyr-occludin (in part via a dephostatin-sensitive mechanism), and reduced BMvEC permeability, with flow reduction in pre-sheared BMvECs having converse effects. In further studies, VE-cadherin inhibition (VE-cad ΔEXD) blocked shear-induced Rac1 activation, pTyr-occludin reduction, and barrier upregulation, consistent with an upstream role for VE-cadherin in transmitting shear signals to tight junctions through Rac1. As VE-cadherin is known to mediate Rac1 activation via Tiam1 recruitment, we subsequently confirmed that Tiam1 inhibition (Tiam1-C580) could elicit effects similar to VE-cad ΔEXD. Finally, the observed attenuation of shear-induced changes in pTyr-occludin level and barrier phenotype following Rac1 inhibition (NSC23766, T17N) establishes a downstream role for Rac1 in this pathway. In summary, we describe for the first time in BMvECs a role for VE-cadherin in the transmission of physiological shear signals to tight junction occludin through engagement of Tiam1/Rac1 leading to barrier stabilization. A downstream role is also strongly indicated for a protein tyrosine phosphatase in pTyr-occludin modulation. Importantly, these findings suggest an important route of inter-junctional signaling cross-talk during BBB response to flow.