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PubMed1993

Regulation of fibronectin and laminin synthesis by retinal capillary endothelial cells and pericytes in vitro.

Retinal capillaries are composed of endothelial cells resting on a basement membrane, in which are embedded pericytes. In diabetes mellitus, the basement membrane becomes thickened, and there is a loss of pericytes. The relative contributions of endothelial cells and pericytes to the synthesis of extracellular matrix proteins which are components of the basement membrane are not well-characterized. To determine how a selective loss of pericytes might affect the composition of retinal capillary basement membranes, we used primary cultures of bovine retinal capillary endothelial cells and pericytes to determine the forms and quantify the amounts of laminin and fibronectin synthesized and secreted by these cell types as well as to determine how high glucose concentrations alter these parameters. Results of ELISAs showed that pericyte cell/matrix layers contained nearly ten times more fibronectin than endothelial cells (288 +/- 24 vs. 34 +/- 5 ng micrograms-1 DNA, P < 0.001), but the amounts of laminin were similar. D-glucose (40 mM) tripled the amount of fibronectin incorporated into the endothelial cell/matrix layer (102 +/- 4 vs. 34 +/- 5 ng micrograms-1 DNA, P < 0.05), but had a lesser effect on pericytes. The non-metabolizable analogue L-glucose, also increased the amount of fibronectin incorporated in both pericyte and endothelial cell/matrix layers. The effects of D- and L-glucose on fibronectin secreted into the medium by both cell types were similar to the effects on incorporation of fibronectin into cell/matrix layers. Glucose had no effect on laminin synthesis. [35S]methionine radiolabeling and immunoprecipitation showed that pericytes and endothelial cells synthesize different forms of fibronectin. Both pericytes and endothelial cells synthesized an A and two B chains of laminin which were of similar apparent size, but the two cell types post-translationally modified the subunits differently. We conclude that pericytes and endothelial cells may contribute different forms and amounts of fibronectin and laminin to the retinal capillary basement membrane, so the preferential loss of pericytes in diabetes could result in basement membrane abnormalities which might lead to endothelial cell dysfunction.

Animals↗

PubMed1991

The role of fibronectin and laminin in development and migration of the avian Wolffian duct with reference to somitogenesis.

It has been suggested that matrix molecules like fibronectin and laminin influence the differentiation and migration of embryonic cells. We investigated the role of these two glycoproteins in somitogenesis as well as in the differentiation and migration of the avian Wolffian (pronephric and mesonephric) duct. At first, we described essential steps in the development of these two organ anlagen by light microscopy, SEM and TEM. To localize fibronectin and laminin more exactly in the actual stages, we used the indirect immunoperoxidase reaction at the light microscopic level and the peroxidase-antiperoxidase technique at the ultrastructural level. Fibronectin was found at the surface of the unsegmented paraxial mesoderm, increasing in the cranial direction, and in the basal laminae of somites and Wolffian duct. The mesenchymal tip of the duct contains a moderate amount of fibronectin. In the two investigated organ anlagen, laminin was found mainly in the basal laminae. The role of fibronectin and laminin was investigated further by using synthetic peptides that mimic the main cell binding domain of either fibronectin or laminin, and that competitively inhibit their cell surface receptors. Thus, the pentapeptides GRGDS, YIGSR, and for control, SHLVE were micro-injected under the ectoderm of 2-day-old embryos. After treatment with GRDS, the Wolffian duct and the segmental plate are more compact. The rounded cells exhibit only short processes and narrow intercellular spaces. At the side of injection the duct shows a delay in migration. After treatment with YIGSR the Wolffian duct migrated laterally over the somatopleure. The basal laminae seem to be incomplete. SHLVE had no effect. Our results suggest that fibronectin is a prerequisite for the migration of the Wolffian duct, and that laminin probably plays a role in guiding the duct. The epithelialization during somitogenesis and differentiation of the duct is a more complex process involving also fibronectin and laminin.

Animals↗

PubMed1985

Distribution of fibronectin during the morphogenesis of the truncus.

The distribution of fibronectin during morphogenesis of the truncus has been studied in chick embryo hearts between days 4 and 10 of incubation. Fibronectin appears as a natural marker for some truncal cells and permits the visualization of the different processes of cell rearrangement which result in truncal morphogenesis. The mesenchymal cells involved in formation of the aorto-pulmonary septum and in formation of the arterial tunica media are intensely fluorescent for fibronectin. These cells present fibrillar deposits of fibronectin associated with their surfaces. Very little staining for fibronectin is observed in association with the anlage of the semilunar valves. Prospective adventitial cells are negative for fibronectin. The close association between the fluorescence and the surface of the cells involved in formation of the aorto-pulmonary septum and the arterial tunica media suggests that fibronectin may be implicated in the formation of both structures. The intensity and amount of the fluorescence staining decreases as morphogenesis of the truncus is completed. The decrease in fibronectin staining is suggested to be related to changes in cell phenotypic expression.

Animals↗

PubMed1988

Localization of fibronectin in human middle ear cholesteatoma.

Fibronectin was localized in human cholesteatoma tissues by immunohistochemical methods. The avidin-biotin-peroxidase complex staining method was used with specific fibronectin antibody. Fibronectin appeared to be localized in the matrix of the cholesteatoma studied, particularly on the surface of the cell membranes and the nuclei of the basal cells and in connective tissue. Fibronectin was not seen in the granular layer or in the keratin area. Fibronectin was found on the surface of granulation tissue, mononuclear cells, fibroblasts and endothelial cells of blood vessels. These findings were confirmed by the immunofluorescent staining method. Our previous study showed that fibronectin induced a migration of keratinocytes, macrophages and fibroblasts demonstrated by the Boyden's chamber chemotaxis assay. Macrophages and fibroblasts were shown to produce collagenase, a bone resorption factor, in cholesteatomatous tissue. The present study showed the presence of fibronectin in the matrix of cholesteatoma and granulation tissue, suggesting that fibronectin might play an important role in the clinical development and invasive behavior of cholesteatoma.

Cholesteatoma↗

PubMed1995

Fibronectin and integrins in invasion and metastasis.

The adhesive glycoprotein fibronectin and integrin receptors appear to play important roles in the progression of metastatic disease. Fibronectin is a multifunctional extracellular glycoprotein that has at lest two independent cell adhesion regions with different receptor specificities. The cell adhesive region in the central portion of fibronectin is comprised of at least two minimal amino acid sequences--an Arg-Gly-Asp (RGD) sequence and a Pro-His-Ser-Arg-Asn (PHSRN) sequence--which function in synergy. Another cell adhesive region is located near the carboxy-terminus in the alternatively spliced IIICS module. The critical minimal sequences for this region Leu-Asp-Val (LDV) and Arg-Glu-Asp-Val (REDV) which function in an additive rather than synergistic fashion. Integrins are heterodimeric, transmembrane cell adhesion receptors for fibronectin and other extracellular matrix molecules. Several different integrins bind to fibronectin. The alpha 5 beta 1 fibronectin-specific integrin binds to the central RGD/PHSRN site. The alpha 4 beta 1 integrin binds to the IIICS site. Fibronectin-integrin interactions are important in tumor cell migration, invasion, and metastasis. In addition to promoting cell adhesion to the extracellular matrix, these proteins may also function in chemotaxis and control of proliferation. Peptide and antibody inhibitors of fibronectin and integrin functions have been shown to be effective inhibitors of metastasis, and are potentially important reagents for the study and control of cancer.

Amino Acid Sequence↗

PubMed1985

Loss of surface fibronectin after infection of cultured cells by HSV-1 and 2.

Fibronectin is lost from the surface of HSV infected cells during cell rounding. In order to investigate also the fate of fibronectin during the process of HSV-induced cell-fusion, BHK, Vero as well as primary or secondary rabbit kidney cells were infected with HSV-1 strains producing cell-fusion. By immunofluorescence and immunoelectron microscopy a considerable loss of fibronectin after HSV infection could be demonstrated leaving only irregular clumps of fibronectin containing virus particles on the cell surface. Decrease and disarrangement of fibronectin was similar during cell rounding and cell fusion. Loss of Fibronectin was closely connected with the two types of the cytopathic effect (CPE) and could not be prevented by protease inhibitors. The immediate-early protein 175K is essential for induction of CPE and loss of fibronectin. The damage to the cell membrane during HSV infection shows certain analogous mechanisms with events induced by Cytochalasin B and might be explained by the loss of hypothetical fibronectin receptors.

Actin Cytoskeleton↗

PubMed1990

Diagnostic relevance of fibronectin in cryoprecipitates.

Fibronectin is a known component of plasma cryoprecipitates. It is seen in cryoglobulins from patients with monoclonal gammopathies and also from rheumatoid arthritis, and patients with systemic lupus erythematosus and other connective tissue diseases. We evaluated the clinical relevance of measures of cryoprecipitable fibronectin from the sera of 88 patients with rheumatic diseases and 27 healthy controls. There were 28 patients with rheumatoid arthritis, 19 with systemic vasculitis, 5 with cutaneous vasculitis, and 36 with a systemic connective tissue disorder. We measured total and cryoprecipitable fibronectin and for comparison immunoglobulins G, A, and M and complement C3 and C4. Cryoprecipitable fibronectin was detected in 33% control sera and 42% patient sera. The mean levels were higher in the sera of patients in all diagnostic groups. The highest levels were seen in rheumatoid patients with systemic disease, systemic vasculitis, and connective tissue diseases. The presence of cryoprecipitable fibronectin was related to the clinical activity of systemic vasculitis; none of the 6 patients with clinically inactive vasculitis had detectable fibronectin in their cryoprecipitates; but it was seen in 7 to 13 cases with active vasculitis. There were only weak relationships between cryoprecipitable fibronectin and immunoglobulin and complement levels in cryoprecipitates. We conclude that routinely measuring fibronectin levels in cryoprecipitates is generally of doubtful diagnostic value. However, it appears to be a useful marker of the clinical activity of systemic vasculitis and we recommend its use in the laboratory assessment of vasculitis.

Adult↗

PubMed1996

Characterization and immunocytochemical localization of actin and fibronectin in haemocytes of the mussel Mytilus galloprovincialis.

Cell-extracellular matrix interactions are recognized to be important for human leucocyte functions, including chemotaxis and phagocytosis. These activities depend on a reorganization of the microfilament actin (F-actin) promoted by fibronectin, one of the major components of extracellular matrices. Although invertebrate haemocytes are, in many aspects, similar to the human granulocyte-monocyte-macrophage cell lineage, actin and fibronectin have not been well studied in these cells. Consequently, the characterization and structural organization of actin and fibronectin in mussel (Mytilus galloprovincialis) haemocytes was investigated using Western blotting analysis, indirect immunofluorescence and immunoelectron microscopy. Actin was immunocharacterized by an anti-total actin monoclonal antibody. Fibronectin was immunocharacterized by an autologous polyclonal antiserum directed against the protein of mussel haemolymph. Actin was mainly localized along the peripheral cytoplasm of the haemocyte. The distribution of the F-actin microfilaments was assayed with Rhodamine-labelled phalloidin. F-actin was associated mainly with stress-fibres of spreading haemocytes and with microspikes at the adhesion sites. The labelling by the anti-fibronectin antiserum of the haemocyte rough endoplasmic reticulum vesicles, revealed by immunoelectron microscopy, suggests that these cells are involved in fibronectin biosynthesis. Gold particles were also present along the outer surfaces of the cell plasma membrane and its protrusions. Mussel fibronectin was localized immunohistochemically at the adhesion sites and in the extracellular matrix fibrils. The relationships between fibronectin and the actin cytoskeleton in Mytilus galloprovincialis haemocytes are discussed.

Actins↗

PubMedDate not supplied

Plasma fibronectin, von Willebrand factor antigen, and blood rheology. Association with diabetic microvascular disease.

Plasma fibronectin might play a role in the pathogenesis and progression of diabetic microvascular disease. To test this hypothesis we measured plasma fibronectin, von Willebrand factor antigen, fibrinogen, erythrocyte filtrability, whole-blood viscosity, proteinuria and albuminuria in 25 control subjects and 29 diabetic patients with and without microvascular complications. Plasma fibronectin was significantly higher in the diabetic patients, especially in those with retinopathy and nephropathy. A significant correlation between fibronectin and von Willebrand factor antigen was found in both patients with and without microangiopathy (p less than 0.001). In diabetic patients with and without microvascular complications, several significant correlations were found between increased fibronectin levels and reduced erythrocyte filtrability (p less than 0.001) and between the increase of fibronectin and whole-blood viscosity (p less than 0.001). Furthermore, a significant correlation was found between plasma fibronectin levels, proteinuria (p less than 0.001) and albuminuria (p less than 0.001). The relationship between plasma fibronectin and changes of blood rheology may be important for the occurrence and progression of diabetic microangiopathy.

Aged↗

PubMed1987

Immunohistochemical study of fibronectin, lysozyme, and alpha-fetoprotein (AFP) in human hepatocellular carcinoma.

We have immunohistochemically localized fibronectin, lysozyme and alpha-fetoprotein (AFP) in 21 human hepatocellular carcinoma (HCC) tissues obtained by surgical resection at both light and electron microscopic levels. Three distinct distribution patterns of fibronectin (sinusoidal, periacinar, and pericellular patterns) were observed. The sinusoidal and periacinar patterns were mainly observed in HCC of pseudoglandular or trabecular patterns and of Edmondson's grade I or II, whereas the pericellular pattern was observed in HCC of compact or trabecular patterns and of Edmondson's III grade, suggesting that the pericellular fibronectin was rather associated with undifferentiated HCC. Electron microscopic observation of the pericellular fibronectin showed fibronectin to be present in the dilated intercellular spaces where microvilli were moderately developed. We observed intracytoplasmic staining of fibronectin in 2 of the 21 HCC cases. By immunoelectron microscopy, fibronectin was observed in the endoplasmic reticulum (ER) of some HCC cells. In the 21 HCC cases, lysozyme-positive cancer cells were observed in 10 cases, and AFP in 6 cases. At the ultrastructural level, lysozyme was identified in the ER and the perinuclear spaces of HCC cells, suggesting that lysozyme was synthesized by these cells. Lysozyme-positive cases tended to be more frequently observed in cases with the pericellular pattern of fibronectin rather than those with sinusoidal or periacinar patterns.

Adult↗

PubMed2005

Fibronectin fibril pattern displays the force balance of cell-matrix adhesion.

Formation of fibrillar patterns of fibronectin on polymer substrates with gradated physicochemical surface properties was analysed during early stages of endothelial cell adhesion. Fibronectin was pre-adsorbed onto three maleic anhydride copolymer thin films with distinct differences in the protein adsorption strength as verified by heteroexchange experiments. The evolved micrometer scale fibrillar patterns of fibronectin on the compared polymer surfaces were characterized after 50 min of cellular reorganization by an auto-correlation analysis using fluorescence microscopy data. Statistical analysis revealed a decrease of the typical spacings of the fibronectin fibrils from 2.6 to 1.8 mum with decreasing fibronectin adsorption strength to the substrate. Size and density of focal adhesions correlated with this dependence of the fibronectin fibril pattern. From these data a model was developed relating the fibronectin fibril pattern to the fibronectin-substrate adsorption strength through the cytoskeletal force regulation mechanism of the cell.

Adhesiveness↗

PubMed2000

Enhanced graft healing of high-porosity expanded polytetrafluoroethylene grafts by covalent bonding of fibronectin.

The effect of covalent bonding of fibronectin on the patency and graft healing of high-porosity expanded polytetrafluoroethylene (ePTFE) grafts was evaluated. Bilateral carotid grafting was performed in ten mongrel dogs using high-porosity (60 microm) ePTFE grafts, 4 cm in length and 4 mm in internal diameter, that either had been pretreated by the covalent bonding of fibronectin (fibronectin grafts) or were untreated (control grafts). The grafts were harvested 4 to 6 weeks after surgery and subjected to macroscopic and light-microscopic observations. There was no significant difference in patency between the fibronectin grafts and the control grafts with rates of 80% and 70%, respectively. The thrombus-free area score was significantly greater in the fibronectin grafts than in the control grafts, at 86.9% vs 34.0%. Furthermore, the pseudointima was better replaced by fibrous tissue in the fibronectin grafts than in the control grafts, being lined with a layer of endothelial-like cells. More transmural tissue ingrowth was evident in the fibronectin grafts than in the control grafts. The covalent bonding of fibronectin improves graft healing by stimulating transmural tissue ingrowth in high-porosity ePTFE grafts.

Animals↗

PubMed1980

Plasma fibronectin (opsonic glycoprotein): its synthesis by vascular endothelial cells and role in cardiopulmonary integrity after trauma as related to reticuloendothelial function.

Progressive multiple organ failure in association with septic complications in the surgical, trauma and burn patient is of major clinical importance. Reticuloendothelial system host defense mechanisms are abnormal following severe trauma and burn. Failure in systemic host defense is, in part, mediated by a deficiency in a circulating opsonic alpha 2 surface binding (SB) glycoprotein. This opsonic deficiency and reticuloendothelial host defense failure appears etiologic in the genesis of organ failure with sepsis. Opsonic alpha 2SB glycoprotein is identical to cold-insoluble globulin or plasma fibronectin. Plasma fibronectin is antigenically related to cell surface fibronectin which appears to be synthesized by both fibroblasts and vascular endothelial cells. Although these two proteins are antigenically related, they may or may not be identical with respect to biochemical properties and function. Cell surface fibronectin appears to be an adhesive glycoprotein mediating cell-cell interaction and cell adhesion to a substratum. Plasma fibronectin is a more soluble form which mediates reticuloendothelial or macrophage clearance of particulates such as fibrin microaggregates, collagenous debris, perhaps other bacterial or nonbacterial particulates. Since opsonic glycoprotein is identical to cold-insoluble globulin which can be readily concentrated in plasma cryoprecipitate, it has been shown that cryoprecipitate infusion can reverse opsonic deficiency in the injured patient with sepsis. Reversal of opsonic deficiency by cryoprecipitate infusion results in a marked improvement in cardiopulmonary function which includes a decline in the pulmonary shunt, a decrease in the physiologic dead space, an increase in limb blood flow, an increase in reactive hyperemia of the peripheral circulation and an increase in limb oxygen consumption. This cardiopulmonary response is paralleled by a decline in the septic state and normalization of other hematologic parameters. These studies suggest an important homeostatic role for fibronectins in organ and microvascular integrity, especially in the septic injured patient. Cell surface fibronectin which participates in cell adhesion may, in part, modulate microvascular integrity, vascular permeability and would repair. In contrast, the more soluble plasma fibronectin or opsonic alpha 2SB glycoprotein may mediate reticuloendothelial clearance of blood-borne particulates to prevent pulmonary and peripheral vascular microembolization and organ injury. Thus, reversal of opsonic deficiency may be an effective modality of therapy in the septic injured patient with organ failure.

Animals↗

PubMed1992

The function of elevated plasma fibronectin in preeclampsia.

Total plasma fibronectin is elevated in preeclampsia due to vascular injury release, increased production, or enzymatic degradation resulting in multimers. To examine the etiology of the fibronectin increase in preeclampsia, we quantified plasma fibronectin in nonpregnant women, pregnant women from 28 to 42 weeks' gestation, latent labor, and preeclampsia by both nephelometry and turbidimetry. Western blotting and gel electrophoresis were used to examine the structural integrity of the fibronectin molecule. In addition, functional assays explored the potential for dysfunctional fibronectin. Fibronectin was elevated in pregnant patients compared with nonpregnant patients and exhibited a further significant increase with preeclampsia. The increase was not a result of degradation to multimers but possibly to increased variants. Notably, fibronectin function, as defined by collagen binding, may be impaired during pregnancy and preeclampsia. It appears that the clinical pathophysiology of preeclampsia may be related to dysfunctional fibronectin measured by collagen binding.

Blotting, Western↗

PubMed1995

Fetal fibronectin levels are elevated in maternal plasma and amniotic fluid of patients with severe preeclampsia.

OBJECTIVE: Our purpose was to investigate levels of fetal fibronectin in maternal plasma, amniotic fluid, and umbilical cord plasma from patients with severe preeclampsia. STUDY DESIGN: The study group comprised 20 patients with severe preeclampsia (group A). An antepartum comparison group was composed of 20 healthy patients matched for gestational age (group B). An intrapartum control group consisted of 20 term normotensive patients (group C). Maternal plasma samples were collected before labor (groups A and B), then immediately after delivery, and again at 20 to 24 hours post partum (groups A and C). Amniotic fluid was also collected in early labor, and umbilical cord blood was collected at delivery (groups A and C). Samples were assayed for fetal fibronectin by a specific enzyme-linked immunoassay. RESULTS: Before labor maternal plasma levels of fetal fibronectin were significantly elevated in preeclamptic patients compared with patients in group B (p < 0.0001). Plasma levels of fetal fibronectin were also increased in preeclamptic patients compared with patients in group C at delivery (p < 0.0001) and post partum (p < 0.05). Additionally, amniotic fluid levels of fetal fibronectin in the preeclamptic patients were significantly increased (p < 0.05). In contrast, umbilical cord plasma fetal fibronectin concentrations from the preeclamptic and control patients were similar. CONCLUSIONS: Fetal fibronectin is elevated in the maternal plasma and amniotic fluid, but not umbilical cord plasma, of patients with severe preeclampsia. These findings suggest an increase in production of fetal fibronectin from chorionic trophoblast in patients with preeclampsia or an abnormal interaction between chorionic trophoblast and decidua with resultant increased leakage into the maternal circulation and amniotic fluid.

Adult↗

PubMed1984

Electron spin resonance spin label studies of plasma fibronectin: effect of temperature.

Plasma fibronectin was chemically modified by 4-maleimido-2,2,6,6-tetramethylpiperidinooxyl (maleimide spin label). Only the free sulfhydryl groups of plasma fibronectin were modified by the label under the experimental conditions. The ESR spectrum of spin-labeled fibronectin showed that the sites of labeling were highly immobilized, suggesting that the sulfhydryl groups of the protein are in small, confined environments. The conversion of the strongly immobilized ESR spectrum into a weakly immobilized one was observed when the spin-labeled protein was heated from 30 to 60 degrees C, indicating the thermal unfolding of the protein molecules. The midpoint temperature for the thermal unfolding of plasma fibronectin is about 50 degrees C. The results suggest that plasma fibronectin is stable to about 40 degrees C and starts unfolding above this temperature. The rotational correlation time estimated from the ESR spectrum of spin-labeled fibronectin at 21 degrees C was about 2.0 X 10(-8) s. The rotational correlation time calculated from the Stokes-Einstein equation, assuming a rigid globular configuration for fibronectin with a Stokes radius of 10 nm, was about 7.8 X 10(-7) s. The differences in rotational correlation time by a factor of 39 between experimental and calculated values do not support a globular configuration for plasma fibronectin.

Binding Sites↗

PubMed1988

Acylation of gelatin-agarose and the enhancement by heparin of fibronectin binding.

The enhancement of the binding of plasma fibronectin to collagen or gelatin by heparin was previously thought to be due primarily to interaction of heparin with fibronectin. We observed, however, that the elution of purified human plasma fibronectin from heparin-treated gelatin-agarose required the same high urea concentrations regardless of whether heparin treatment preceded or followed fibronectin adsorption. Acylation of gelatin-agarose with acetic anhydride or succinic anhydride had little effect upon fibronectin binding, yet the heparin enhancement of fibronectin binding was abolished by either acylation reaction. When heparin binding to gelatin-agarose was investigated with dansyl heparin, gelatin-agarose bound substantial quantities of labeled heparin which could be readily dissociated from the matrix with 2 M NaCl. Acetylated gelatin-agarose did not bind detectable amounts of dansyl heparin. We interpret these results as evidence that the stronger binding of fibronectin to gelatin-agarose in the presence of heparin is due to heparin itself binding to gelatin, thus allowing fibronectin to bind simultaneously to both immobilized ligands through appropriate domains of the glycoprotein.

Acylation↗

PubMed1991

Oxidative damage to fibronectin. I. The effects of the neutrophil myeloperoxidase system and HOCl.

Exposure of purified human plasma fibronectin to the myeloperoxidase-H2O2-Cl- system of neutrophils or to reagent HOCl resulted in extensive changes to its primary and tertiary structures. When 1.14 microM fibronectin was exposed to 50-400 microM HOCl or 50-400 microM H2O2 plus myeloperoxidase and Cl-, there was progressive loss of tryptophan fluorescence and cysteines, and an increase in bityrosine fluorescence and carbonyl content. Analysis by SDS-PAGE indicated extensive crosslinking of the fibronectin, the crosslinks being stable under reducing conditions. The coincident increase of bityrosine fluorescence suggests that crosslinking may be largely due to intermolecular bityrosines rather than disulfides. All changes observed with the myeloperoxidase system were inhibited by azide or methionine, and were dependent upon the presence of chloride, indicating that they are mediated by HOCl. The reaction between HOCl and fibronectin resulted in the formation of long-lived chloramines. Exposure to increasing amounts of oxidant resulted in an increase in the susceptibility of fibronectin to proteolytic attack by purified neutrophil elastase. Analysis by SDS-PAGE showed a different fragmentation pattern for oxidant-treated fibronectin compared with the native protein. This suggests that regions of the molecule which were previously resistant to proteolysis were denatured to create susceptible sites for elastase. This demonstration that fibronectin is extensively modified by the myeloperoxidase system has implications for the mechanism of tissue injury by neutrophils in inflammation, since a loss of functional fibronectin would result in cell detachment and a distortion of normal tissue organization.

Azides↗