Complement C1q is hydroxylated by collagen prolyl 4 hydroxylase and is sensitive to off-target inhibition by prolyl hydroxylase domain inhibitors that stabilize hypoxia-inducible factor

Complement C1q is part of the C1 macromolecular complex that mediates the classical complement activation pathway: a major arm of innate immune defense. C1q is composed of A, B, and C chains that require post-translational prolyl 4-hydroxylation of their N-terminal collagen-like domain to enable the formation of the functional triple helical multimers. The prolyl 4-hydroxylase(s) that hydroxylate C1q have not previously been identified. Recognized prolyl 4-hydroxylases include collagen prolyl-4-hydroxylases (CP4H) and the more recently described prolyl hydroxylase domain (PHD) enzymes that act as oxygen sensors regulating hypoxia-inducible factor (HIF). We show that several small-molecule prolyl hydroxylase inhibitors that activate HIF also potently suppress C1q secretion by human macrophages. However, reducing oxygenation to a level that activates HIF does not compromise C1q hydroxylation. In vitro studies showed that a C1q A chain peptide is not a substrate for PHD2 but is a substrate for CP4H1. Circulating levels of C1q did not differ between wild-type mice or mice with genetic deficits in PHD enzymes, but were reduced by prolyl hydroxylase inhibitors. Thus, C1q is hydroxylated by CP4H, but not the structurally related PHD hydroxylases. Hence, reduction of C1q levels may be an important off-target side effect of small molecule PHD inhibitors developed as treatments for renal anemia.

Differential regulation of blood flow-induced neovascularization and mural cell recruitment by vascular endothelial growth factor and angiopoietin signalling

KEY POINTS

Combining nitric oxide (NO)-mediated increased blood flow with angiopoietin-1-Tie2 receptor signalling induces arteriolargenesis - the formation of arterioles from capillaries - in a model of physiological angiogenesis. This NO-Tie-mediated arteriolargenesis requires endogenous vascular endothelial growth factor (VEGF) signalling. Inhibition of VEGF signalling increases pericyte coverage in microvessels. Together these findings indicate that generation of functional neovasculature requires close titration of NO-Tie2 signalling and localized VEGF induction, suggesting that the use of exogenous VEGF expression as a therapeutic for neovascularization may not be successful.

ABSTRACT

Signalling through vascular endothelial growth factor (VEGF) receptors and the tyrosine kinase with IgG and EGF domains-2 (Tie2) receptor by angiopoietins is required in combination with blood flow for the formation of a functional vascular network. We tested the hypothesis that VEGF and angiopoietin-1 (Ang1) contribute differentially to neovascularization induced by nitric oxide (NO)-mediated vasodilatation, by comparing the phenotype of new microvessels in the mesentery during induction of vascular remodelling by over-expression of endothelial nitric oxide synthase in the fat pad of the adult rat mesentery during inhibition of angiopoietin signalling with soluble Tie2 (sTie2) and VEGF signalling with soluble Fms-like tyrosine kinase receptor-1 (sFlt1). We found that NO-mediated angiogenesis was blocked by inhibition of VEGF with sFlt1 (from 881 ± 98% increase in functional vessel area to 279 ± 72%) and by inhibition of angiopoietin with sTie2 (to 337 ± 67%). Exogenous angiopoietin-1 was required to induce arteriolargenesis (8.6 ± 1.3% of vessels with recruitment of vascular smooth muscle cells; VSMCs) in the presence of enhanced flow. sTie2 and sFlt1 both inhibited VSMC recruitment (both 0%), and VEGF inhibition increased pericyte recruitment to newly formed vessels (from 27 ± 2 to 54 ± 3% pericyte ensheathment). We demonstrate that a fine balance of VEGF and angiopoietin signalling is required for the formation of a functional vascular network. Endogenous VEGF signalling prevents excess neovessel pericyte coverage, and is required for VSMC recruitment during increased nitric oxide-mediated vasodilatation and angiopoietin signalling (NO-Tie-mediated arteriogenesis). Therapeutic vascular remodelling paradigms may therefore require treatments that modulate blood flow to utilize endogenous VEGF, in combination with exogenous Ang1, for effective neovascularization.

Hypoxia-induced invadopodia formation: a role for β-PIX

During tumour progression, oxygen tension in the microenvironment surrounding tumour cells is reduced, resulting in hypoxia. It is well established that cancer cells resist the negative effects of hypoxia by inducing angiogenesis predominantly via the activity of transcription factor hypoxia-inducible factor-1 (HIF-1). However, more recently HIF-1α has also been linked to increased invasive potential, although the molecular mechanisms remain to be defined. Invasive cancer cells are thought to employ membrane protrusions, termed invadopodia, to achieve matrix degradation. While many invadopodia components have been identified, signalling pathways that link extracellular stimuli to invadopodia formation remain largely unknown. Indeed, the relationship between invadopodia formation and HIF-1α has not been explored. We now report that HIF-1α is a driver of invadopodia formation. Furthermore, we have identified an important, direct and novel link between the Rho family activator β-PIX, HIF-1α and invadopodia formation. Indeed, we find that β-PIX expression is essential for invadopodia formation. In conclusion, we identify a new HIF-1α mechanistic pathway and suggest that β-PIX is a novel downstream signalling mediator during invadopodia formation.

Prolonged mechanical stretch is associated with upregulation of hypoxia-inducible factors and reduced contraction in rat inferior vena cava

BACKGROUND

Decreased venous tone and vein wall dilation may contribute to varicose vein formation. We have shown that prolonged vein wall stretch is associated with upregulation of matrix metalloproteases (MMPs) and decreased contraction. Because hypoxia-inducible factors (HIFs) expression also increases with mechanical stretch, this study tested whether upregulation of HIFs is an intermediary mechanism linking prolonged vein wall stretch to the changes in MMP expression and venous contraction.

METHODS

Segments of rat inferior vena cava (IVC) were suspended in tissue bath under 0.5-g basal tension for 1 hour, and a control contraction to phenylephrine (PHE, 10(-5)M) and KCl (96 mM) was elicited. The veins were then exposed to prolonged 18 hours of tension at 0.5 g, 2 g, 2 g plus HIF inhibitor U0126 (10(-5)M), 17-[2-(dimethylamino)ethyl] amino-17-desmethoxygeldanamycin (17-DMAG, 10(-5)M), or echinomycin (10(-6)M), or 2 g plus dimethyloxallyl glycine (DMOG; 10(-4)M), a prolyl-hydroxylase inhibitor that stabilizes HIF. The fold-change in PHE and KCl contraction was compared with the control contraction at 0.5-g tension for 1 hour. Vein tissue homogenates were analyzed for HIF-1α, HIF-2α, MMP-2, and MMP-9 messenger RNA (mRNA) and protein amount using real-time reverse transcription polymerase chain reaction and Western blots.

RESULTS

Compared with control IVC contraction at 0.5-g tension for 1 hour, the PHE and KCl contraction after prolonged 0.5-g tension was 2.0 ± 0.35 and 1.1 ± 0.06, respectively. Vein contraction to PHE and KCl after prolonged 2-g tension was significantly reduced (0.87 ± 0.13 and 0.72 ± 0.05, respectively). PHE-induced contraction was restored in IVC exposed to prolonged 2-g tension plus the HIF inhibitor U0126 (1.38 ± 0.15) or echinomycin (1.99 ± 0.40). U0126 and echinomycin also restored KCl-induced contraction in IVC exposed to prolonged 2-g tension (1.14 ± 0.05 and 1.11 ± 0.15, respectively). Treatment with DMOG further reduced PHE- and KCl-induced contraction in veins subjected to prolonged 2-g tension (0.47 ± 0.06 and 0.57 ± 0.01, respectively). HIF-1α and HIF-2α mRNA were overexpressed in IVC exposed to prolonged 2-g tension, and the overexpression was reversed by U0126. The overexpression of HIF-1α and HIF-2α in stretched IVC was associated with increased MMP-2 and MMP-9 mRNA. The protein amount of HIF-1α, HIF-2α, MMP-2, and MMP-9 was also increased in IVC exposed to prolonged 2-g wall tension.

CONCLUSIONS

Prolonged increases in vein wall tension are associated with overexpression of HIF-1α and HIF-2α, increased MMP-2 and MMP-9 expression, and reduced venous contraction in rat IVC. Together with our report that MMP-2 and MMP-9 inhibit IVC contraction, the data suggest that increased vein wall tension induces HIF overexpression and causes an increase in MMP expression and reduction of venous contraction, leading to progressive venous dilation and varicose vein formation.

What have we learnt from targeted anti-TNF therapy?

Anti-tumour necrosis factor (anti-TNF) therapy of patients with rheumatoid arthritis dates back to 1992, when the first proof-of-principle trials were performed in London by Maini and Feldmann. Considerable studies of the mechanism of action were performed, and insights into the way in which anti-TNF therapy delivers its benefit were obtained. In this brief review, certain aspects of knowledge acquired and the many gaps will be reviewed. Focus will be on the TNF-dependent cytokine cascade and what it means, and potential new approaches to treatment. Finally, an entertaining challenge: might many or even all unmet clinical needs be dealt with through cytokine analysis?

Circulating endothelial progenitor cells as a link between synovial vascularity and cardiovascular mortality in rheumatoid arthritis

Cardiovascular disease refers to the class of diseases that involve the heart and/or blood vessels (arteries and veins). Most Western countries face high and ever-increasing rates of cardiovascular disease. Each year, more Americans are killed by heart disease than by cancer. Diseases of the heart alone cause 30% of all deaths, with other diseases of the cardiovascular system causing substantial further deaths and disability. Indeed, cardiovascular disease is the major cause of death and disability in the USA and most European countries. The development of the vascular systems requires an intricate interplay of molecules such as vascular endothelial growth factor and endothelial progenitor cells. A defective vascular repair/regeneration is thought to be responsible for propagation of atherosclerosis, a key feature of cardiovascular disease. This is partly attributed to a reduction in the circulating endothelial progenitor cells in peripheral blood. Patients with rheumatoid arthritis (RA) have a higher than average incidence of cardiovascular disease in comparison with the general population, with an increased risk of stroke and myocardial infarction, and an increased risk of fatality following myocardial infarction. This review focuses on the current evidence linking the role played by endothelial progenitor cells to the development of cardiovascular disease and why this might relate to the increased risk observed in RA patients.

Adenovirus-Mediated VEGF Gene Therapy Enhances Venous Thrombus Recanalization and Resolution

Objective— Rapid thrombus recanalization reduces the incidence of post–thrombotic complications. This study aimed to discover whether adenovirus-mediated transfection of the vascular endothelial growth factor gene (ad.VEGF) enhanced thrombus recanalization and resolution.

Methods and Results— In rats, thrombi were directly injected with either ad.VEGF (n=40) or ad.GFP (n=37). Thrombi in SCID mice (n=12) were injected with human macrophages transfected with ad.VEGF or ad.GFP. Thrombi were analyzed at 1 to 14 days. GFP was found mainly in the vein wall and adventitia by 3 days, but was predominantly found in cells within the body of thrombus by day 7. VEGF levels peaked at 4 days (376±299 pg/mg protein). Ad.VEGF treatment reduced thrombus size by >50% (47.7±5.1 mm 2 to 22.0±4.0 mm 2 , P =0.0003) and increased recanalization by >3-fold (3.9±0.69% to 13.6±4.1%, P =0.024) compared with controls. Ad.VEGF treatment increased macrophage recruitment into the thrombus by more than 50% ( P =0.002). Ad.VEGF-transfected macrophages reduced thrombus size by 30% compared with controls (12.3±0.89 mm 2 to 8.7±1.4 mm 2 , P =0.04) and enhanced vein lumen recanalization (3.39±0.34% to 5.07±0.57%, P =0.02).

Conclusion— Treatment with ad.VEGF enhanced thrombus recanalization and resolution, probably as a consequence of an increase in macrophage recruitment.

Angiogenesis as a therapeutic target in arthritis: learning the lessons of the colorectal cancer experience

The idea of a therapeutic modality aimed at 'starving' a tissue of blood vessels, and consequentially of oxygen and nutrients, was born from the concept that blood vessel formation (angiogenesis) is central to the progression and maintenance of diseases which involve tissue expansion/invasion. In the first instance, solid malignancies were the target for anti-angiogenic treatments, with colorectal cancer being the first disease for which an angiogenesis inhibitor--anti-vascular endothelial growth factor antibody bevacizumab--was approved in 2004. Our understanding of the pathogenesis of rheumatoid arthritis (RA) has lead to many parallels being drawn between this chronic inflammatory disease and solid tumours, in that both involve tissue expansion, invasion, expression of cytokines and growth factors and areas of hypoxia/hypoperfusion. As a result, angiogenesis blockade has been touted as a possible treatment for RA. The lessons learnt during the progression of eventually successful therapies such as bevacizumab should undoubtedly guide us in the future development of comparable treatments for RA.

Cytokine inhibitors in rheumatoid arthritis and other autoimmune diseases

The clinical success of TNFalpha blocking biologics in a growing number of immune-mediated pathologies, including rheumatoid arthritis, Crohn's disease, ankylosing spondylitis and psoriasis, confirms the importance of TNFalpha in driving chronic inflammation and represents an important step forward in the treatment of these conditions. TNFalpha blockade, however, is a treatment, rather than a cure, and is not effective in all patients or in all autoimmune diseases and further research is needed to get closer to a cure. Recently, the identification of a novel, IL-17 producing, T helper cell subset, that plays a dominant pathogenic role in animal models of autoimmunity, is a major advance on existing knowledge, although the role of these cells in human disease remains to be established. Cytokines driving angiogenesis are also important in disease chronicity and thus might be valid therapeutic targets.

Angiogenesis as a Therapeutic Target in Arthritis: Lessons from Oncology

Rheumatoid arthritis (RA) is a chronic disabling autoimmune inflammatory disease of unknown aetiology with a prevalence of about 1% in most parts of the world. As a result of the debilitating nature of the disease, sufferers struggle with the simple activities of daily living and frequently fail to remain in full time employment. Furthermore, the mortality associated with the disease is equivalent to that seen in triple vessel coronary artery disease. Over the 10-15 years, advances in understanding the mechanisms of RA pathogenesis based on studies of human cells and animal models of arthritis have led to the identification of new targets for therapeutic intervention. Despite these advances, a significant proportion of patients continue to exhibit disease which is refractory to such therapy. As an alternative to anti-cytokine therapy, formation of new blood vessels ('angiogenesis') represents a potentially attractive target for therapy in RA. Angiogenesis has been a putative target in cancer since it was first linked to tumour growth and metastases in the 1970s. A number of significant advances have been made in the development of anti-cancer therapy using such an approach. This review focuses on the potential for targeting angiogenesis in RA, building upon the experience of angiogenesis inhibition in the oncological setting. Through this we hope to emphasise the potential value of anti-angiogenic therapy in RA and identify future directions for optimising treatment of this disabling disease.

Targeting rheumatoid tenosynovial angiogenesis with cytokine inhibitors

Proliferation and invasion of the tenosynovial lining of tendons in patients with rheumatoid arthritis can result in tendon damage and rupture, leading to decreased hand function. Angiogenesis is an important process in rheumatoid joint disease; however, the role of angiogenesis in tendon disease is unknown. Our aim was to determine whether rheumatoid tenosynovial lining could produce angiogenic proteins, and if inhibition of tumor necrosis factor-alpha and interleukin-1 could decrease vascular endothelial growth factor production. Samples of encapsulating and invasive tenosynovial lining taken from the same hand and wrist synovial lining were harvested from 58 patients with rheumatoid arthritis having wrist surgery. Ex vivo samples were studied to quantify vascularity, angiogenic protein production under normoxic and hypoxic conditions, and the effect of inhibiting tumor necrosis factor-alpha and interleukin-1 on vascular endothelial growth factor production. Rheumatoid tenosynovial lining was more vascular than rheumatoid joint synovial lining and produced high levels of angiogenic factors such as vascular endothelial growth factor, interleukin-1beta, fibroblast growth factor-2, and angiopoietin-2. Hypoxia induced an increase in production of vascular endothelial growth factor by ex vivo tenosynovial lining cells. Inhibition of the cytokines interleukin-1 and tumor necrosis factor-alpha effectively reduced vascular endothelial growth factor production by tenosynovial samples.

LEVEL OF EVIDENCE

Therapeutic study. Level II (Prospective comparative study). See the Guidelines for Authors for a complete description of levels of evidence.

Cyclooxygenase-2 induction and prostacyclin release by protease-activated receptors in endothelial cells require cooperation between mitogen-activated protein kinase and NF-kappaB pathways

The functional significance of protease-activated receptors (PARs) in endothelial cells is largely undefined, and the intracellular consequences of their activation are poorly understood. Here, we show that the serine protease thrombin, a PAR-1-selective peptide (TFLLRN), and SLIGKV (PAR-2-selective peptide) induce cyclooxygenase-2 (COX-2) protein and mRNA expression in human endothelial cells without modifying COX-1 expression. COX-2 induction was accompanied by sustained production of 6-keto-PGF1alpha, the stable hydrolysis product of prostacyclin, and this was inhibited by indomethacin and the COX-2-selective inhibitor NS398. PAR-1 and PAR-2 stimulation rapidly activated both ERK1/2 and p38MAPK, and pharmacological blockade of MEK with either PD98059 or U0126 or of p38MAPK by SB203580 or SB202190 strongly inhibited thrombin- and SLIGKV-induced COX-2 expression and 6-keto-PGF1alpha formation. Thrombin and peptide agonists of PAR-1 and PAR-2 increased luciferase activity in human umbilical vein endothelial cells infected with an NF-kappaB-dependent luciferase reporter adenovirus, and this, as well as PAR-induced 6-keto-PGF1alpha synthesis, was inhibited by co-infection with adenovirus encoding wild-type or mutated (Y42F) IkappaBalpha. Thrombin- and SLIGKV-induced COX-2 expression and 6-keto-PGF1alpha generation were markedly attenuated by the NF-kappaB inhibitor PG490 and partially inhibited by the proteasome pathway inhibitor MG-132. Activation of PAR-1 or PAR-2 promoted nuclear translocation and phosphorylation of p65-NF-kappaB, and thrombin-induced but not PAR-2-induced p65-NF-kappaB phosphorylation was reduced by inhibition of MEK or p38MAPK. Activation of PAR-4 by AYPGKF increased phosphorylation of ERK1/2 and p38MAPK without modifying NF-kappaB activation or COX-2 induction. Our data show that PAR-1 and PAR-2, but not PAR-4, are coupled with COX-2 expression and sustained endothelial production of vasculoprotective prostacyclin by mechanisms that depend on ERK1/2, p38MAPK, and IkappaBalpha-dependent NF-kappaB activation.

Rac1 and RhoA as regulators of endothelial phenotype and barrier function in hypoxia-induced neonatal pulmonary hypertension

Hypoxia is a common cause of persistent pulmonary hypertension in the newborn (PPHN), a condition associated with endothelial dysfunction and abnormal pulmonary vascular remodeling. The GTPase RhoA has been implicated in the pathogenesis of PPHN, but its contribution to endothelial remodeling and function is not known. We studied pulmonary artery endothelial cells (PAECs) taken from piglets with chronic hypoxia-induced pulmonary hypertension and from healthy animals and analyzed the roles of Rho GTPases in the regulation of the endothelial phenotype and function under basal normoxic conditions, acute hypoxia, and reoxygenation. The activities of RhoA, Rac1, and Cdc42 were correlated with changes in the endothelial cytoskeleton, adherens junctions, permeability, ROS production, VEGF levels, and activities of transcription factors hypoxia-inducible factor (HIF)-1alpha and NF-kappaB. Adenoviral gene transfer was used to express dominant-negative GTPases, kinase-dead p21-activated kinase (PAK)-1, and constitutively activated Rac1 in cells. PAECs from pulmonary hypertensive piglets had a stable abnormal phenotype with a sustained reduction in Rac1 activity and an increase in RhoA activity, which correlated with an increase in actin stress fiber formation, increased permeability, and a decrease in VEGF and ROS production. Cells from pulmonary hypertensive animals were still able to respond to acute hypoxia. They also showed high activities of HIF-1alpha and NF-kappaB, likely to result from changes in the activities of Rho GTPases. Activation of Rac1 and its effector PAK-1 as well as inhibition of RhoA restored the abnormal phenotype and permeability of hypertensive PAECs to normal.

Vascular endothelial growth factor signalling in endothelial cell survival: a role for NFkappaB

Angiogenesis is the development of blood capillaries from pre-existing vessels. Vascular endothelial growth factor (VEGF) is a key regulator of vessel growth and regression, and acts as an endothelial survival factor by protecting endothelial cells from apoptosis. Many genes involved in cell proliferation and apoptosis are regulated by the nuclear factor kappa B (NFkappaB) transcription factor family. This study aimed to address the hypothesis that VEGF-mediated survival effects on endothelium involve NFkappaB. Using an NFkappaB-luciferase reporter adenovirus, we observed activation of NFkappaB following VEGF treatment of human umbilical vein endothelial cells. This was confirmed using electrophoretic mobility shift assay and found to involve nuclear translocation of NFkappaB sub-unit p65. However, NFkappaB activation occurred without degradation of inhibitory IkappaB proteins (IkappaBalpha, IkappaBbeta, and IkappaBepsilon). Instead, tyrosine phosphorylation of IkappaBalpha was observed following VEGF treatment, suggesting NFkappaB activation was mediated by degradation-independent dissociation of IkappaBalpha from NFkappaB. Adenovirus-mediated over-expression of either native IkappaBalpha, or of IkappaBalpha in which tyrosine residue 42 was mutated to phenylalanine, inhibited induction of NFkappaB-dependent luciferase activity in response to VEGF. Furthermore, VEGF-induced upregulation of mRNA for the anti-apoptotic protein Bcl-2 and cell survival following serum withdrawal was reduced following IkappaBalpha over-expression. This study highlights that different molecular mechanisms of NFkappaB activation may be involved downstream of stimuli which activate the endothelial lining of blood vessels.

Immunotherapy of rheumatoid arthritis: past, present and future

Rheumatoid arthritis (RA) is a chronic autoimmune disease, characterized by inflammation of the synovial lining of joints, and the destruction of cartilage and bone. Seminal studies demonstrating that pro-inflammatory cytokines, such as tumor necrosis factor-alpha (TNFalpha), are expressed in RA, has resulted in the approval of anti-TNFalpha biological therapies for its treatment. Although groundbreaking in themselves, these studies have also paved the way for further research to determine whether the targeting of other cytokines and immune pathways might aid in development of the next generation of drugs for the treatment of RA.

Canonical pathway of nuclear factor kappa B activation selectively regulates proinflammatory and prothrombotic responses in human atherosclerosis

Nuclear factor kappa B (NF-kappa B) activation has been observed in human atherosclerotic plaques and is enhanced in unstable coronary plaques, but whether such activation has a protective or pathophysiological role remains to be determined. We addressed this question by developing a short-term culture system of cells isolated from human atherosclerotic tissue, allowing efficient gene transfer to directly investigate signaling pathways in human atherosclerosis. We found that NF-kappa B is activated in these cells and that this activity involves p65, p50, and c-Rel but not p52 or RelB. This NF-kappa B activation can be blocked by overexpression of I kappa B alpha or dominant-negative I kappa B kinase (IKK)-2 but not dominant-negative IKK-1 or NF-kappa B-inducing kinase, resulting in selective inhibition of inflammatory cytokines (tumor necrosis factor alpha, IL-6, and IL-8), tissue factor, and matrix metalloproteinases without affecting the antiinflammatory cytokine IL-10 or tissue inhibitor of matrix metalloproteinases. Our results demonstrate that the canonical pathway of NF-kappa B activation that involves p65, p50, c-Rel, and IKK-2 is activated in human atherosclerosis and results in selective up-regulation of major proinflammatory and prothrombotic mediators of the disease.

T-cell-mediated signalling in immune, inflammatory and angiogenic processes: the cascade of events leading to inflammatory diseases

In the last decade, the understanding of the molecular mechanisms of regulation of the inflammatory process in chronic inflammatory diseases has moved remarkably forward. Recent evidence in various fields has consistently indicated that T-cells play a key role in initiating and perpetuating inflammation, not only via the production of soluble mediators but also via cell/cell contact interactions with a variety of cell types through membrane receptors and their ligands. Signalling through CD40 and CD40 ligand is a versatile pathway that is potently involved in all these processes. In this article, we review how T-cells become activated by dendritic cells or inflammatory cytokines, and how these T-cells activate, in turn, monocytes/macrophages, endothelial cells, smooth muscle cells and fibroblasts to produce pro-inflammatory cytokines (tumour necrosis factor alpha, interleukin-6), chemokines (interleukin-8, monocyte chemotactic protein-1), tissue factor, the main initiator of the coagulation cascade in vivo, and finally matrix metalloproteinases, responsible for tissue destruction. Moreover, we discuss how CD40 ligand at inflammatory sites stimulates fibroblasts and tissue monocyte/macrophage production of VEGF, leading to angiogenesis, which promotes and maintains the chronic inflammatory process. This cascade of events is discussed in the context of disease initiation/progression, with particular reference to atherosclerosis and rheumatoid arthritis, and to potential novel therapeutic targets for their treatment.

Nuclear factor kappaB: a potential therapeutic target in atherosclerosis and thrombosis

Cardiovascular diseases are the leading cause of morbidity and mortality in Western countries. Atherosclerosis, the background for many cardiovascular diseases, is characterized by the accumulation of lipid and fibrotic entities in large arteries and bears many similarities with chronic inflammatory diseases such as rheumatoid arthritis. Common features include extravasation of blood-derived leukocytes, as well as production of cytokines, chemokines and matrix-degrading enzymes. There are also many shared signaling pathways, including activation of the nuclear factor kappaB (NFkappaB) cascade. In the context of atherosclerosis, there are a range of candidate stimuli which can activate NFkappaB, including traditional risk factors, infectious agents, cytokines and cell-cell contact. Many inflammatory genes relevant to the pathogenesis of atherosclerosis are regulated by NFkappaB, the activated form of which is present in atherosclerotic plaques. Thus, it is essential to understand the role of this important signaling cascade in atherosclerosis, in a quest for more specific therapeutic targets.

Anti-TNFalpha therapy of rheumatoid arthritis: what can we learn about chronic disease?

The importance of tumour necrosis factor (TNF)alpha in rheumatoid arthritis (RA) was initially proposed on the basis of analysis of cytokine gene regulation at the local site of the disease, the synovium. This was then verified in animal models and established in an extensive series of clinical trials, culminating in now 250000 treated patients with either of two approved TNF inhibitors, antibody or fusion protein. The degree and magnitude of clinical benefit has enabled analyses of the mechanism by which anti-TNF benefits, and hence insights into important steps in the disease process. It was found that essentially all aspects of RA were ameliorated, and important mechanisms of benefit involved diminution of multiple pro-inflammatory cytokines, adhesion molecules and chemokines, leading to reduced cell trafficking, reduced angiogenesis and most importantly halting of joint destruction. What of the problems? Safety is better than prior drugs, but there is a small increase in severe infections, smaller than might have been anticipated. Cost is the major drawback limiting greater use. In view of the central pathological processes down-regulated, and their role in many diseases, the early clinical success of anti-TNF in RA led to subsequent successful trials and registration in Crohn's disease and juvenile rheumatoid arthritis, and successful trials in ankylosing spondylitis, psoriasis and psoriatic arthritis. The era of anti-cytokine therapeutics is just dawning.

The therapeutic potential of TNF-alpha blockade in rheumatoid arthritis

Rheumatoid arthritis is a chronic autoimmune disease characterised by inflammation of the synovial lining of joints and destruction of cartilage and bone. Many pro-inflammatory cytokines, chemokines and growth factors are expressed in diseased joints, and recognition of the key role of TNF-alpha led to the development of highly effective new therapies. TNF-alpha inhibitors, such as monoclonal anti-TNF-alpha antibody infliximab (Remicade), have demonstrated efficacy in clinical trials. It is now clear that TNF-alpha blockade, in addition to reducing joint inflammation and leukocyte infiltration, also results in decreased formation of new blood vessels in the synovium. Such mechanism of action studies are now paving the way for the development of the next generation of drugs for treatment of rheumatoid arthritis.

Heterogeneous requirement of IkappaB kinase 2 for inflammatory cytokine and matrix metalloproteinase production in rheumatoid arthritis: implications for therapy

OBJECTIVE

To investigate the potential role of IkappaB kinase 1 (IKK-1) and IKK-2 in the regulation of nuclear factor kappaB (NF-kappaB) activation and the expression of tumor necrosis factor alpha (TNFalpha), as well as interleukin-1beta (IL-1beta), IL-6, IL-8, vascular endothelial growth factor (VEGF), and matrix metalloproteinases (MMPs), in rheumatoid arthritis (RA).

METHODS

Recombinant adenoviruses expressing beta-galactosidase, dominant-negative IKK-1 and IKK-2, or IkappaBalpha were used to infect ex vivo RA synovial membrane cultures and synovial fibroblasts obtained from patients with RA undergoing joint replacement surgery, or human dermal fibroblasts, human umbilical vein endothelial cells (HUVECs), and monocyte-derived macrophages from healthy volunteers. Then, their effect on the spontaneous or stimulus-induced release of inflammatory cytokines, VEGF, and MMPs from RA synovial membrane cells was examined.

RESULTS

IKK-2 was not required for lipopolysaccharide (LPS)-induced NF-kappaB activation or TNFalpha, IL-6, or IL-8 production in macrophages, but was essential for this process in response to CD40 ligand, TNFalpha, and IL-1. In synovial fibroblasts, dermal fibroblasts, and HUVECs, IKK-2 was also required for LPS-induced NF-kappaB activation and IL-6 or IL-8 production. In RA synovial membrane cells, IKK-2 inhibition had no effect on spontaneous TNFalpha production but significantly reduced IL-1beta, IL-6, IL-8, VEGF, and MMPs 1, 2, 3, and 13.

CONCLUSION

Our study demonstrates that IKK-2 is not essential for TNFalpha production in RA. However, because IKK-2 regulates the expression of other inflammatory cytokines (IL-1beta, IL-6, and IL-8), VEGF, and MMPs 1, 2, 3, and 13, which are involved in the inflammatory, angiogenic, and destructive processes in the RA joint, it may still be a good therapeutic target.

VEGF expression in human macrophages is NF-kappaB-dependent: studies using adenoviruses expressing the endogenous NF-kappaB inhibitor IkappaBalpha and a kinase-defective form of the IkappaB kinase 2

Vascular endothelial growth factor (VEGF) is the most endothelial cell-specific angiogenic factor characterised to date, and it is produced by a variety of cell types. In macrophages, VEGF has been shown to be upregulated by the inflammatory mediator lipopolysaccharide (LPS) and by engagement of CD40 by CD40 ligand (CD40L). Because LPS and CD40L activate nuclear factor-kappaB (NF-kappaB) in monocytes, we investigated in this study whether VEGF production in macrophages, when stimulated with either LPS or CD40L, is NF-kappaB-dependent. We used adenoviral constructs over-expressing either IkappaBalpha (AdvIkappaBalpha), the endogenous inhibitor of NF-kappaB, or a kinase-defective mutant of IKK-2 (AdvIKK-2dn), an upstream activator of IkappaBalpha, to infect normal human monocyte-derived macrophages. We observed that LPS-induced production of VEGF in human macrophages was almost completely inhibited (>90%) following adenoviral transfer of IkappaBalpha. In addition, we observed significant inhibition of the CD40L-induced VEGF production in macrophages following infection with AdvIkappaBalpha. Expression of IKK-2dn in macrophages decreased VEGF production in response to LPS or CD40L by approximately 50%, suggesting that in addition to IKK-2, other kinases might be involved in NF-kappaB activation. These results show for the first time that VEGF production in human macrophages is NF-kappaB dependent. NF-kappaB regulates many of the genes involved in immune and inflammatory responses, and our study adds the angiogenic cytokine VEGF to the list of NF-kappaB-dependent cytokines.

Is NF-kappaB a useful therapeutic target in rheumatoid arthritis?

There is increasing evidence that NF-kappaB is a major, if not the major transcription factor regulating inflammation and immunity. While this implies that blocking NF-kappaB might be therapeutically beneficial, it raises clear questions regarding the balance between efficacy and safety. In this brief review we discuss the effects of NF-kappaB blockade in rheumatoid arthritis, inflammation and immunity, and consider possible therapeutic targets within the NF-kappaB family.

VEGF release is associated with reduced oxygen tensions in experimental inflammatory arthritis

OBJECTIVE

The contribution of local VEGF production and subsequent angiogenesis within the synovial membrane to the propagation of arthritis is unclear. The relationship between synovial oxygenation and blood flow in the development of arthritic disease is unknown. We have therefore measured oxygen levels and perfusion rates in the synovial space in a murine model of arthritis.

METHODS

Arthritis was induced in DBA/1 mice by immunisation with type II collagen. Oxygen and perfusion levels were measured polarographically using silver needle microelectrodes within the knee joints prior to and 10 days after the onset of arthritis. In addition, synovial cells were isolated from knee joints of naive, pre-arthritic and arthritic mice.

RESULTS

Onset of arthritis was associated with a marked reduction in synovial oxygen tensions (pO2). The perfusion rates in naive and arthritic animals were not significantly different: in naive mice, the rate was 0.58 +/- 0.11 ml/min/g and in arthritic joints, 0.64 +/- 0.17 ml/min/g. Furthermore, synovial cells isolated from the knee joints of naive animals did not express mRNA for VEGF, but significant levels were detected in cells from non-arthritic mice immunised with collagen. The onset of arthritis was associated with expression of VEGF mRNA and protein, and correlated negatively with pO2 levels.

CONCLUSION

These data demonstrate that decreases in intra-articular pO2 occur in established arthritic conditions and may be the stimulus for local VEGF production. However, perfusion was not increased in arthritic animals and vascular density was unaltered, suggesting that the neovascularisation associated with inflammatory arthritis, is insufficient to restore oxygen homeostasis in the joint.

T cell-mediated signaling to vascular endothelium: induction of cytokines, chemokines, and tissue factor

Adhesion of leukocytes to the vascular endothelium is an early event in inflammation. Since cell-cell signaling may be an important stimulus for endothelial activation, we focused in this study on the role of contact-mediated activation by T lymphocytes of endothelial cells (EC). T lymphocytes were cultured with anti-CD3 monoclonal antibody or in the presence of a combination of TNF-alpha, interleukin (IL)-6, and IL-2, prior to fixation and coculture with human umbilical vein EC. Fixed, activated (anti-CD3- or cytokine-stimulated), but not unstimulated T cells, induced release of monocyte chemotactic protein-1, IL-8, and IL-6 by EC in a contact-dependent manner. Moreover, expression of tissue-factor antigen and activity was also significantly increased. Addition of anti-CD40 ligand antibody abolished T cell-induced activation of EC. Our data suggest that contact-mediated activation of EC by T cells, involving ligand:counter ligand interactions such as CD40:CD40 ligand, may represent a novel pathogenic mechanism of progression in inflammatory diseases such as atherosclerosis or rheumatoid arthritis.

Inhibition of retinal neovascularisation by gene transfer of soluble VEGF receptor sFlt-1

Retinal angiogenesis is a central feature of the leading causes of blindness. Current treatments for these conditions are of limited efficacy and cause significant adverse effects. In this study, we evaluated the angiostatic effect of gene transfer of the soluble VEGF receptor sFlt-1 in a mouse model of ischaemia-induced retinal neovascularisation using adenovirus and adeno-associated virus (AAV) vectors. We induced proliferative retinopathy in mice by exposure to 75% oxygen from postnatal day 7 (p7) to p12 and injected intravitreally recombinant viral vectors expressing the reporter green fluorescent protein (GFP) or vectors expressing the VEGF inhibitor sFlt-1. Efficient adenovirus-mediated GFP expression was evident in cells of the corneal endothelium and iris pigment epithelium. AAV-mediated GFP expression was evident in ganglion cells and cells of the inner nuclear layer of the retina. Vector-mediated sFlt-1 expression was confirmed by ELISA of pooled homogenised whole eyes. Injection of either vector expressing sFlt-1 resulted in a reduction in the number of neovascular endothelial cells by 56% and 52% for adenovirus and AAV vectors, respectively (P < 0.05). Local gene transfer of sFlt-1 consistently inhibits experimental retinal neovascularisation by approximately 50% and offers a powerful novel approach to the clinical management of retinal neovascular disorders.

[Cellular mechanisms of regulation of the inflammatory response in atherosclerosis: the role of cell contact-mediated signaling]

The regulatory mechanisms of the inflammatory process in the atherosclerotic plaque are still not clearly understood. Stimulated T cells may have a key role in enhancing and perpetuating inflammation at the atherosclerotic site. They activate endothelial cells, macrophages and smooth muscle cells in the atherosclerotic plaque, not only via the production of soluble mediators, but also through cell-cell contact-mediated interactions (via membrane receptors and their ligands). Cell/cell contact between stimulated T lymphocytes and monocytes/macrophages and endothelial cells induces the production of pro-inflammatory cytokines (tumor necrosis factor-alpha, interleukin-6) and chemokines (interleukin-8, monocyte chemotactic factor-1). Thus, these interactions could play a relevant role in the disregulation of the inflammatory process in the atherosclerotic plaque, representing a novel mechanism of progression and complication of the atherosclerotic disease. Understanding the key ligands and receptors involved may permit the definition of new therapeutic targets.

Future prospects for anti-cytokine treatment

The era of anti-cytokine treatment in rheumatology has just begun. The first generation therapeutic agents, biological agents that block tumour necrosis factor alpha such as monoclonal antibodies or receptor Ig fusion proteins are safe and effective, and so this has generated much interest in how to increase the benefit or deliver it more cost effectively. This article provides a personal view of the coming trends in anti-cytokine treatment. Which of these will be realised in the future will be of interest.

Treatment with soluble VEGF receptor reduces disease severity in murine collagen-induced arthritis

Maintenance of the invasive pannus in rheumatoid arthritis is an integral part of disease progression. The synovial vasculature plays an important role in the delivery of nutrients, oxygen, and inflammatory cells to the synovium. Vascular endothelial growth factor (VEGF), an endothelial mitogen expressed by cells within the synovial membrane, is thought to contribute to the formation of synovial blood vessels. Our objective in this study was to measure the kinetics of VEGF production in a murine model of collagen-induced arthritis and to determine whether VEGF blockade reduces disease progression. Synovial cells isolated from the knee joints of naive or sham-immunized mice, or from mice immunized with collagen but without arthritis, released little or no detectable VEGF. Onset of arthritis was associated with expression of VEGF mRNA and protein. The levels of VEGF secreted by synovial cells isolated from the joints of mice with severe arthritis were significantly higher than from mice with mild disease. To block VEGF activity, animals were treated after arthritis onset with a soluble form of the Flt-1 VEGF receptor (sFlt), which was polyethylene glycol (PEG)-linked to increase its in vivo half-life. Treatment of arthritic mice with sFlt-PEG significantly reduced both clinical score and paw swelling, compared with untreated or control-treated (heat-denatured sFlt-PEG) animals. There was also significantly less joint inflammation and reduced bone and cartilage destruction in sFlt-PEG-treated animals, as assessed by histology. Our data demonstrate that, in collagen-induced arthritis, expression of the potent angiogenic cytokine VEGF correlates with disease severity. Furthermore, specific blockade of VEGF activity results in attenuation of arthritis in both macroscopic and microscopic parameters. These observations indicate that blood vessel formation is integral to the development of arthritis and that blockade of VEGF activity might be of therapeutic benefit in rheumatoid arthritis.