Lymphocyte transendothelial migration toward smooth muscle cells in interleukin-1 beta-stimulated co-cultures is related to fibronectin interactions with alpha 4 beta 1 and alpha 5 beta 1 integrins

Loss of adenomatous poliposis coli-α3 integrin interaction promotes endothelial apoptosis in mice and humans

RATIONALE

Pulmonary hypertension (PH) is characterized by progressive elevation in pulmonary pressure and loss of small pulmonary arteries. As bone morphogenetic proteins promote pulmonary angiogenesis by recruiting the Wnt/β-catenin pathway, we proposed that β-catenin activation could reduce loss and induce regeneration of small pulmonary arteries (PAs) and attenuate PH.

OBJECTIVE

This study aims to establish the role of β-catenin in protecting the pulmonary endothelium and stimulating compensatory angiogenesis after injury.

METHODS AND RESULTS

To assess the impact of β-catenin activation on chronic hypoxia-induced PH, we used the adenomatous polyposis coli (Apc(Min/+)) mouse, where reduced APC causes constitutive β-catenin elevation. Surprisingly, hypoxic Apc(Min/+) mice displayed greater PH and small PA loss compared with control C57Bl6J littermates. PA endothelial cells isolated from Apc(Min/+) demonstrated reduced survival and angiogenic responses along with a profound reduction in adhesion to laminin. The mechanism involved failure of APC to interact with the cytoplasmic domain of the α3 integrin, to stabilize focal adhesions and activate integrin-linked kinase-1 and phospho Akt. We found that PA endothelial cells from lungs of patients with idiopathic PH have reduced APC expression, decreased adhesion to laminin, and impaired vascular tube formation. These defects were corrected in the cultured cells by transfection of APC.

CONCLUSIONS

We show that APC is integral to PA endothelial cells adhesion and survival and is reduced in PA endothelial cells from PH patient lungs. The data suggest that decreased APC may be a cause of increased risk or severity of PH in genetically susceptible individuals.

Adhesive functions of both chains of VLA-integrins are not fully conserved across the human-porcine species barrier: implications for xenotransplantation

BACKGROUND

A possible solution to the shortage of organs for transplantation would be the use of swine as source animals. As current immunosuppressive protocols cannot prevent rejection of these organs, super-selective immunosuppression or the induction of donor-specific central tolerance represent two promising approaches. Central tolerance induction involves bone marrow transplantation, and depends on intrathymic deletion of donor reactive host cells by donor antigen-presenting cells. In super-selective immunosuppression, the aim would be to block specific adhesive interactions on one species side only, leaving the other species side unaffected. As both processes depend on the interaction of adhesion molecules with their ligands, we investigated whether the beta1-integrins, which play roles in hematopoiesis as well as in rejection, can successfully interact across the swine-to-human species barrier.

METHODS

We employed static cell-to-extracellular protein and cell-to-cell adhesion assays, using different cell types and monoclonal antibody as well as peptide-fragments to analyze conservation of cross-species adhesive interactions.

RESULTS

We found that porcine and human cells interact differently with their cross-species ligands than their own and that the adhesive function of the beta1-chain does not seem to be fully conserved across the species barrier.

CONCLUSIONS

Integrin functions are not fully conserved across the pig-to-human species barrier. While the development of multi-transgenic pigs, whose integrins interact with human ligands in a more ''human-like'' manner may be necessary to facilitate tolerance induction, these facts give rise to new possibilities concerning super-selective immunosuppression.

Tick saliva is a potent inhibitor of endothelial cell proliferation and angiogenesis

We report for the first time that saliva of the hard tick and Lyme disease vector, Ixodes scapularis, is a potent inhibitor of angiogenesis. Saliva (< or = 1:500 dilutions) or salivary gland (0.1-0.5 pairs/assay) dose-dependently inhibits microvascular endothelial cell (MVEC) proliferation. Inhibition was also detected with the saliva of the cattle tick Boophilus microplus but not with the salivary gland of Anopheles gambiae, An. stephensi, Lutzomyia longipalpis, Phlebotomus papatasi, Aedes aegypti, Culex quinquefasciatus, and Cimex lectularius. Inhibition of MVEC proliferation by I. Scapularis saliva was accompanied by a change in cell shape (shrinkage of the cytoplasm with loss of cell-cell interactions) and apoptosis which was estimated by expression of phosphatidylserine using the Apopercentage dye, and by a typical pattern of chromatin margination, condensation, and fragmentation as revealed by nuclear staining with Hoechst 33258. The effect of saliva appears to be mediated by endothelial cell alpha5beta1 integrin, because monoclonal antibodies against this but not alphavbeta3, alphavbeta5, alpha9beta1, or alpha2beta1 integrins remarkably block its effect. In addition, SDS/PAGE shows that saliva specifically degrades purified alpha5beta1 but not alphavbeta5 or alphavbeta3 integrins. Incubation of saliva with EDTA and 1,10-phenanthroline, but not phenylmethylsulfonyl fluoride (PMSF), inhibits saliva-dependent degradation of purified alpha5beta1 integrin, suggesting that a metalloprotease is responsible for the activity. Finally, saliva at < or = 1:1,000 dilutions blocks sprouting formation from chick embryo aorta implanted in Matrigel, an in vitro model of angiogenesis. These findings introduce the concept that tick saliva is a negative modulator of angiogenesis-dependent wound healing and tissue repair, therefore allowing ticks to feed for days. Inhibition of angiogenesis was hitherto an unidentified biologic property of the saliva of any blood-sucking arthropod studied so far. Its presence in tick saliva may be regarded as an additional source of angiogenesis inhibitors with potential applications for the study of both vector and vascular biology.

Design, synthesis, and analysis of a polyethelene glycol-modified (PEGylated) small molecule inhibitor of integrin {alpha}4{beta}1 with improved pharmaceutical properties

Integrin alpha4beta1 plays an important role in inflammatory processes by regulating the migration of leukocytes into inflamed tissues. Previously, we identified BIO5192 [2(S)-{[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino}-4-[4-methyl-2(S)-(methyl-{2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl}-amino)-pentanoylamino]-butyric acid], a highly selective and potent (K(D) of 9 pM) small molecule inhibitor of alpha4beta1. Although BIO5192 is efficacious in various animal models of inflammatory disease, high doses and daily treatment of the compound are needed to achieve a therapeutic effect because of its relatively short serum half-life. To address this issue, polyethylene glycol modification (PEGylation) was used as an approach to improve systemic exposure. BIO5192 was PEGylated by a targeted approach in which derivatizable amino groups were incorporated into the molecule. Two sites were identified that could be modified, and from these, five PEGylated compounds were synthesized and characterized. One compound, 2a-PEG (K(D) of 19 pM), was selected for in vivo studies. The pharmacokinetic and pharmacodynamic properties of 2a-PEG were dramatically improved relative to the unmodified compound. The PEGylated compound was efficacious in a rat model of experimental autoimmune encephalomyelitis at a 30-fold lower molar dose than the parent compound and required only a once-a-week dosing regimen compared with a daily treatment for BIO5192. Compound 2a-PEG was highly selective for alpha4beta1. These studies demonstrate the feasibility of PEGylation of alpha4beta1-targeted small molecules with retention of activity in vitro and in vivo. 2a-PEG, and related compounds, will be valuable reagents for assessing alpha4beta1 biology and may provide a new therapeutic approach to treatment of human inflammatory diseases.

An assessment of the mechanistic differences between two integrin alpha 4 beta 1 inhibitors, the monoclonal antibody TA-2 and the small molecule BIO5192, in rat experimental autoimmune encephalomyelitis

Integrin alpha 4 beta 1 plays an important role in inflammatory processes by regulating the migration of lymphocytes into inflamed tissues. Here we evaluated the biochemical, pharmacological, and pharmacodynamic properties and efficacy in experimental autoimmune encephalomyelitis (EAE), a model of multiple sclerosis, of two types of alpha 4 beta 1 inhibitors, the anti-rat alpha 4 monoclonal antibody TA-2 and the small molecule inhibitor BIO5192 [2(S)-[[1-(3,5-dichloro-benzenesulfonyl)-pyrrolidine-2(S)-carbonyl]-amino]-4-[4-methyl-2(S)-(methyl-[2-[4-(3-o-tolyl-ureido)-phenyl]-acetyl]-amino)-pentanoylamino]-butyric acid]. TA-2 has been extensively studied in rats and provides a benchmark for assessing function. BIO5192 is a highly selective and potent (KD of <10 pM) inhibitor of alpha 4 beta 1. Dosing regimens were identified for both inhibitors, which provided full receptor occupancy during the duration of the study. Both inhibitors induced leukocytosis, an effect that was used as a pharmacodynamic marker of activity, and both were efficacious in the EAE model. Treatment with TA-2 caused a decrease in alpha 4 integrin expression on the cell surface, which resulted from internalization of alpha 4 integrin/TA-2 complexes. In contrast, BIO5192 did not modulate cell surface alpha 4 beta 1. Our results with BIO5192 indicate that alpha 4 beta 7 does not play a role in this model and that blockade of alpha 4 beta 1/ligand interactions without down-modulation is sufficient for efficacy in rat EAE. BIO5192 is highly selective and binds with high affinity to alpha 4 beta 1 from four of four species tested. These studies demonstrate that BIO5192, a novel, potent, and selective inhibitor of alpha 4 beta 1 integrin, will be a valuable reagent for assessing alpha 4 beta 1 biology and may provide a new therapeutic for treatment of human inflammatory diseases.

Porcine mononuclear cells adhere to human fibronectin independently of very late antigen-5: implications for donor-specific tolerance induction in xenotransplantation

To combat the shortage of donor organs, transplantation across species barriers has been proposed. Induction of tolerance would overcome the substantial immunologic barriers to xenotransplantation and would avoid the chronic use of immunosuppressive agents. Successful transplantation of hematopoietic cells induces robust specific tolerance to donor antigens in allogeneic and xenogeneic models. The beta1 integrin class of adhesion molecules and their interactions with extracellular matrix components are thought to be integral to the engraftment and maturation of hematopoietic stem cells. We therefore examined the efficacy of porcine very late antigen-5 (VLA-5) and VLA-4 interactions with the human extracellular matrix (ECM) protein, fibronectin. Peripheral blood mononuclear cells (PBMCs) from humans and miniature swine were flourochrome labeled and adhesion to plates coated with whole human fibronectin (whFN) or its 120 KDa fragment containing the VLA-5 binding region was determined. Flow cytometry and immuno- precipitation were used to identify a monoclonal antibody that cross-reacted on porcine VLA-5. Human and pig PBMC adhesion to human fibronectin (hFN) or 120 kDa fragment-coated plates was assessed following incubation with control ab, anti-VLA-4, anti-VLA-5, or soluble fibronectin. Using rabbit complement, cells expressing VLA-5 were purged from PBMC preparations before performing the adhesion assay. Porcine and human PBMC both adhered to hFN in a divalent cation-dependent and activation-dependent manner. Adhesion to hFN of human but not pig PBMC was blocked by anti-VLA-5 monoclonal antibody SAM-1, although this mAb immunoprecipitated a heterodimeric cell surface molecule (155/135 kDa) resembling VLA-5 from pig PBMC. Complement-mediated depletion of VLA-5-expressing cells ablated specific binding of human but not porcine cells to hFN and its 120 kDa fragment. Addition of soluble fibronectin was capable of blocking adhesion of PBMC of both species to hFN. Anti-VLA-4 reduced the binding of PBMC from both species to hFN to a similar extent. Human and pig cells can specifically adhere to hFN and its 120 kDa fragment, suggesting that this critical cell-ECM interaction is preserved across species. While human cells exclusively use VLA-5 for binding to the 120 kDa fragment, porcine cells could not be shown to adhere to whFN or its 120 kDa fragment via VLA-5. However, porcine VLA-4 is capable of mediating adhesion to human FN. We conclude that disparities in the adhesive interactions of beta1 integrins may be a barrier to the use of porcine hematopoietic stem cell transplantation as a means of inducing donor-specific tolerance in the pig to human species combination.

Pathobiology of pulmonary hypertension: Impact on clinical management

Our previous studies showed how analysis of pulmonary vascular changes on lung biopsy tissue and on angiography added to the hemodynamic assessment of pulmonary vascular resistance in predicting the success of a surgical repair. Both the potential for heightened vasoreactivity in the early postoperative period and for reversibility of pulmonary vascular disease at later follow-up were correlated with qualitative and quantitative evaluation of arterial changes. The ability of continuous intravenous prostacylin to arrest progression and even induce regression of structurally advanced pulmonary vascular disease in some cases has led to rethinking how pathological material can be useful in clinical decision making. The presence of occlusive changes and particularly plexiform lesions was thought to represent irreversible disease, but the observation that ongoing cellular proliferation and connective tissue synthesis occurs even in advanced lesions thought to represent end stage 'burnt-out' lesions, led to re-evaluation of the potential of biologically reversing the disease process. Our laboratory has used clinical material, cultured cells, and studies in experimental animals to gain new insights into some of the mechanisms which lead to the progression of vascular changes, and has used this information in strategies aimed at arresting progression and, more recently, inducing regression of pulmonary hypertension and associated vascular lesions. Specifically, we have focused on the increased activity of an endogenous vascular elastase (EVE) and expression of the glycoproteins tenascin and fibronectin in the pathobiology of pulmonary hypertension. This report will first review our studies in children with congenital heart defects, assessment of reversibility of pulmonary hypertension, and then discuss more recent work addressing cellular and molecular mechanisms aimed at developing newer therapeutic strategies. Copyright 2000 by W.B. Saunders Company

Tumor necrosis factor-alpha induces fibronectin synthesis in coronary artery smooth muscle cells by a nitric oxide-dependent posttranscriptional mechanism

Postcardiac transplant coronary arteriopathy is associated with tumor necrosis factor-alpha (TNF-alpha) induction of fibronectin-dependent smooth muscle cell (SMC) migration into the subendothelium, resulting in occlusive neointimal formation. Because expression of inducible nitric oxide synthase (iNOS) is elevated in neointimal formation after transplantation and upregulated in vascular SMCs by TNF-alpha, we investigated whether TNF-alpha induction of fibronectin synthesis in coronary artery (CA) SMCs is mediated by nitric oxide (NO). TNF-alpha caused a dose-dependent increase in reactive oxygen and nitrogen intermediates in CA SMCs (P<0.05). This correlated with increased NO production (P<0.05) and fibronectin synthesis (P<0.05). TNF-alpha induction of fibronectin synthesis was abrogated by the NOS inhibitor N(G)-monomethyl-L-arginine (L-NMMA) (P<0.05) or the flavonoid-containing enzyme inhibitor diphenyleneiodonium (DPI) (P<0.05) and reproduced with the NO donor S-nitroso-N-acetyl-penicillamine (SNAP) (P<0.05). Northern blotting showed no effect of TNF-alpha on steady-state fibronectin mRNA levels. TNF-alpha increased expression of light chain 3 (LC-3), a protein shown previously to facilitate fibronectin mRNA translation through its interaction with an adenosine-uracil rich element (ARE) in the 3'-untranslated region of fibronectin mRNA. RNA gel mobility shift and UV cross-linking assays using CA SMC lysates revealed protein binding complexes with radiolabeled oligonucleotide containing the ARE, similar to those generated with recombinant LC-3. One of these complexes increased after TNF-alpha treatment, an effect inhibited with L-NMMA or DPI. These data demonstrate a novel paradigm whereby cytokines regulate mRNA translation of extracellular matrix proteins through NO-dependent modulation of RNA binding protein interaction with mRNA.

Expression of interleukin-1beta, interleukin-1 receptor, and interleukin-1 receptor antagonist mRNA in rat carotid artery after balloon angioplasty

Interleukin-1beta (IL-1beta) is a pleiotropic cytokine capable of inducing smooth muscle activation and leukocyte recruitment in restenosis and atherosclerosis. Our present study investigated the expression of IL-1beta, IL-1 receptor antagonist (IL-1ra), and IL-1 receptor (IL-1RI and IL-1RII) mRNA in carotid artery after balloon angioplasty using semiquantitative reverse transcription/polymerase chain reaction (RT/PCR) and Northern analysis. Time course studies revealed that IL-1beta mRNA was rapidly induced at 6 h (30-fold increase over control, P < 0.001) post balloon injury and diminished to basal levels at 24 h. The increased expression of IL-1ra mRNA was delayed, reaching a peak at 24 h (400-fold increase, P < 0.001) and sustained up to 14 days. The expression of IL-1RII mRNA was remarkably similar to that of IL-1beta, whereas the IL-1RI (the signaling receptor) mRNA expression was delayed (significantly induced at day 1; 14.2-fold increase, P < 0.01) post balloon injury. Immunohistochemical studies revealed a strong induction of IL-1beta in the area with actively proliferating and migrating smooth muscle cells (i.e., in the inner medial layer at day 1 and in neointima at day 14 after balloon injury). The differential but concomitant expression of IL-1beta, IL-1ra, IL-1RI, and IL-1RII mRNAs after balloon angioplasty suggests that each of these IL-1 system components may play a distinct role in neointima formation.

alpha5beta1 integrin expression and luminal edge fibronectin matrix assembly by smooth muscle cells after arterial injury

Fibronectin is secreted from the cell as a soluble protein that must then polymerize to regulate cell function. To elucidate the process of fibronectin matrix assembly in vascular disease, we immunostained sections of balloon-injured rat carotid artery for the fibronectin-binding alpha5beta1 integrin. Whereas alpha5beta1 integrin was not evident in the normal carotid artery, its expression was induced after a vascular injury. By 14 days, the alpha5beta1 integrin was localized exclusively to the less differentiated smooth muscle cells (SMCs) at the luminal surface of the neointima. Platelet-derived growth factor-BB, dominant in neointimal formation, selectively increased the expression of the alpha5beta1 integrin by human SMCs in culture. To track the assembly of fibronectin fibers, fluorescence-labeled soluble fibronectin protomers were added to cultured SMCs and to fresh segments of normal and balloon-injured rat carotid arteries. Fibronectin fiber formation in cultured SMCs could be detected within 10 minutes, and was blocked by an RGD peptide, an anti-beta1 integrin antibody, and an anti-alpha5beta1 integrin antibody, but not by an anti-beta3 integrin antibody. En face confocal microscopy of arterial segments revealed that soluble fibronectin had polymerized on the alpha5beta1 integrin-expressing SMCs of the luminal surface of the injured arterial neointima, but not on the alpha5beta1 integrin-negative neointimal SMCs below this or on the endothelial cells of uninjured arteries. Furthermore, in situ fibronectin assembly by the neointimal SMCs was inhibited by an RGD peptide and by an anti-beta1 integrin antibody. These studies indicate that a subpopulation of SMCs in the repairing artery wall orchestrates integrin-mediated fibronectin assembly.

EVE and beyond, retro and prospective insights

Our work has focused on the discovery that an endogenous vascular elastase (EVE) plays a pivotal role in the vascular changes associated with the development and progression of pulmonary hypertension. Recent studies have identified serum factors that stimulate transcription of this enzyme and have elucidated a signal transduction process involving activation of the mitogen-activated protein kinase pathway and nuclear expression of the transcription factor AML1. Proteases release and activate growth factors that are bound to the extracellular matrix and also induce, in a beta(3)-integrin-dependent manner, the transcription of the gene for the matrix glycoprotein tenascin. Tenascin alters smooth muscle cell shape and facilitates the proliferative response to growth factors by clustering and activating growth factor receptors. In addition, breakdown products of elastin, elastin peptides, can upregulate the production of fibronectin, a glycoprotein that is critical to smooth muscle cell migration. The mechanisms regulating enhanced fibronectin production have recently been successfully targeted to prevent the development of intimal lesions.

Filamin binds to the cytoplasmic domain of the beta1-integrin. Identification of amino acids responsible for this interaction

Integrins play an important role in regulating cell adhesion, motility, and activation. In an effort to identify intracellular proteins expressed by activated T cells that interact with the cytoplasmic domain of beta1-integrin (CD29), we used the beta1-integrin cytoplasmic domain as bait in the yeast two-hybrid system. Here we report that the cytoplasmic domain of beta1-integrin specifically interacts with the cytoskeletal protein filamin. This interaction required all but the most carboxyl-terminal three residues of the cytoplasmic domain of beta1, and the carboxyl-terminal 477 residues of filamin containing the terminal 4. 5 approximately 96-residue tandem repeats of filamin. To verify this interaction in vivo, we showed that filamin specifically coprecipitated with beta1 in mammalian cells. We also showed that recombinant filamin chimeric proteins were able to bind to the beta1 cytoplasmic domain in vitro. We observed that a subset of single point mutations in the cytoplasmic domain of beta1, which had been previously reported to impair its function, disrupt the interaction between beta1 and filamin. Taken together, these findings suggest that the interaction between beta1 and filamin, which in turn can bind actin, provides a mechanism for the interaction of this cell surface receptor with cytoskeletal proteins and that this interaction plays a role in normal receptor function.

Elastase and the pathobiology of unexplained pulmonary hypertension

Our laboratory has focused on the increased activity of an endogenous vascular elastase in the pathobiology of pulmonary hypertension and on the mechanisms by which it is upregulated and by which it orchestrates abnormal remodeling of the vessel wall, specifically the induction of growth factors, the induction of the glycoprotein tenascin, which amplifies the proliferative response, and fibronectin, which is critical to the process of smooth muscle migration in the context of neointimal formation. We explore strategies by which targetting these processes might arrest progression or induce regression of pulmonary vascular disease associated with unexplained pulmonary hypertension.

L-selectin crosslinking induces integrin-dependent adhesion: evidence for a signaling pathway involving PTK but not PKC

L-selectin mediates the initial contact of leukocytes with the endothelium prior to extravasation. Here we demonstrate that L-selectin engagement can induce rapid and avid integrin-dependent T cell adhesion to recombinant immobilized cell adhesion molecules (CAMs) including ICAM-1, ICAM-3, and VCAM-1, as well as to the extracellular matrix protein fibronectin (FN). L-selectin-induced adhesion to these integrin ligands shares characteristics with CD3 mAb- or phorbol ester-induced adhesion in requiring metabolic energy, tyrosine kinase and ligand-stimulated Ca2+ channel activity. However, L-selectin-induced adhesion is distinct from that induced by phorbol ester or CD3 crosslinking in being relatively independent of protein kinase C (PKC) activity and actin polymerization. Consistent with the higher levels of L-selectin expression on CD45RA+ (naive) cells, L-selectin crosslinking induces a greater proportion of naive relative to memory cell binding to CAMs and FN. In contrast, exposure to phorbol ester or CD3 crosslinking is more effective in inducing CD45RO+ (memory) cell adhesion. Thus, in addition to its role in leukocyte capture and rolling on the endothelium, L-selectin may contribute to beta 1 and beta 2 integrin-dependent binding and arrest.

Elafin, a serine elastase inhibitor, attenuates post-cardiac transplant coronary arteriopathy and reduces myocardial necrosis in rabbits afer heterotopic cardiac transplantation

We have related experimentally induced post-cardiac transplant coronary arteriopathy to increased elastolytic activity, IL-1beta, fibronectin-mediated inflammatory and smooth muscle cell (SMC) migration, and SMC proliferation. Since our in vitro studies show that a serine elastase releases SMC mitogens and facilitates IL-lbeta induction of fibronectin, we hypothesized that administration in vivo of the specific serine elastase inhibitor, elafin, would decrease the post-cardiac transplant coronary arteriopathy. Cholesterol-fed rabbits underwent a heterotopic cardiac transplant without immunosuppression and received elafin (1.79 mg/kg per d continuous infusion after a 9 mg bolus, n = 6) or vehicle (n = 6). 1 wk later, hearts were harvested for morphometric, immunohistochemical, and biochemical analyses. A > 70% decrease in the total number of coronary arteries with intimal thickening in elafin-treated compared to control donor hearts (P < 0.002) was associated with reduced vascular elastolytic activity judged by fewer breaks in the internal elastic lamina (P < 0.03), less accumulation of immunoreactive fibronectin (P < 0.02), and reduced cell proliferation quantified by proliferating cell nuclear antigen (P < 0.0001). Despite myocardial lymphocytic infiltration, wet weight of elafin-treated donor hearts was reduced by 50% compared to untreated controls (P < 0.002) and associated with relative preservation of myocyte integrity, instead of extensive myocardial necrosis (P < 0.004). This protective effect correlated with decreased myocardial elastolytic activity (P < 0.0001) and inflammatory cell proliferation (P < 0.0001) and with an elafin-inhibitable elastase in lymphocytes. Serine elastase activity thus appears an important therapeutic target for post-cardiac transplant coronary arteriopathy and myocardial necrosis induced by rejection.

Elastase and cell matrix interactions in the pathobiology of vascular disease

Ultrastructural observations in lung tissue implicated an endogenous vascular elastase (EVE), in the pathobiology of pulmonary vascular disease. In experimental rats, increased activity of a 20 kDa serine proteinase related to adipsin precedes the development of sustained pulmonary hypertension and vascular abnormalities. A further increase in activity is related to malignant progression of the disease. A cause and effect relationship was suggested by studies in which elastase inhibitors successfully prevented or retarded progression of pulmonary hypertension. In vitro studies have shown that both serum and endothelial factors induce EVE via tyrosine kinase intracellular signalling. Induction of EVE can release basic fibroblast growth factor from the extracellular matrix in an active form stimulating smooth muscle cell proliferation. Elastase activity was also observed in the process of smooth muscle cell migration and neointimal formation in coronary arteries following experimental cardiac transplantation. An immune/inflammatory response is observed with increased production of cytokines, tumor necrosis factor-alpha and interleukin (IL)-1 beta, reciprocally up-regulating production of fibronectin, a glycoprotein which mediated smooth muscle cell migration. The action of IL-1 beta in inducing fibronectin is facilitated by the production of elastin peptides generated by increased activity of an elastase in the coronary arteries. Our studies suggest that ligation of the elastin binding protein by elastin peptides unmasks IL-1 receptors. Fibronectin also stimulates transendothelial migration of lymphocytes which perpetuates the inflammatory response leading to neointimal formation in this model. Masking integrins on T cells with a decoy synthetic CS-1 (fibronectin) peptide largely prevented transendothelial migration and coronary neointimal formation following cardiac transplant.