Release of soluble fibronectin containing an extra type III domain (ED1) during acute pulmonary injury mediated by oxidants or leukocytes in vivo

Glycosylated fibronectin as a first trimester marker for gestational diabetes

Purpose

To evaluate the performance of first trimester maternal serum glycosylated (Sambucus nigra lectin-reactive) fibronectin in prediction of gestational diabetes mellitus (GDM).

Methods

In this case–control study, first trimester maternal serum glycosylated fibronectin and fibronectin were measured in 19 women who consequently developed GDM and in 59 control women with normal pregnancy outcomes. Adiponectin was used as a reference protein to evaluate relation of glycoprotein to SNA-lectin-reactive assay format. Samples were taken during gestational weeks 9⁺⁶–11⁺⁶. Data concerning GDM was obtained from the National Institute for Health and Welfare, which records the pregnancy outcomes of all women in Finland.

Results

There was no difference in maternal serum glycosylated fibronectin concentrations between women with consequent GDM [447.5 μg/mL, interquartile range (IQR) 254.4–540.9 μg/mL] and control women (437.6 μg/mL, IQR 357.1–569.1 μg/mL). Maternal serum fibronectin levels were significantly lower in GDM group (224.2 μg/mL, IQR 156.8–270.6 μg/mL), compared to the control group (264.8 μg/mL, IQR 224.6–330.6 μg/mL, p < 0.01). There was no difference in assay formats for adiponectin.

Conclusion

There was no association between first trimester maternal serum glycosylated (SNA-reactive) fibronectin and GDM.

Cellular fibronectin response to supervised moderate aerobic training in patients with type 2 diabetes

[Purpose] Physical activity is one of the most pivotal targets for the prevention and management of vascular complications, especially endothelial dysfunctions. Cellular fibronectin is an endothelium-derived protein involved in subendothelial matrix assembly. Its plasma levels reflect matrix alterations and vessel wall destruction in patients with type II diabetes. This study investigated the influence of 12 weeks of supervised aerobic training on cellular fibronectin and its relationship with insulin resistance and body weight in type II diabetic subjects. [Subjects and Methods] This study included 50 men with type II diabetes who had a mean age of 48.8 ± 14.6 years and were randomly divided into two groups: an aerobic exercise group (12 weeks, three 50 minutes sessions per week) and control group. To examine changes in cellular fibronectin, glycosylated hemoglobin, insulin resistance, fasting insulin, fasting blood sugar, and lipid profile, 5 ml of blood was taken from the brachial vein of patients before and 48 hours after completion of the exercise period and after 12 hours of fasting at rest. Data analysis was performed using the SPSS-16 software with the independent and paired t-tests. [Results] A significant decrease was observed in body mass index and body fat percentage in the experimental group. Compared with the control group, the aerobic exercise group showed a significant decrease in cellular fibronectin, glycosylated hemoglobin, insulin resistance, fasting insulin, fasting blood sugar, and lipid profile after 12 weeks of aerobic exercise. The change in cellular fibronectin showed positive significant correlation with body mass index, diabetic biomarkers, and physical activity level. [Conclusion] The results showed that supervised aerobic exercise as a stimulus can change the levels of cellular fibronectin as matrix metalloproteinase protein a long with improvement of insulin sensitivity and glycosylated hemoglobin in order to prevent cardiovascular diseases in men with diabetes

Danger-associated molecular patterns (DAMPs) in acute lung injury

Danger-associated molecular patterns (DAMPs) are host-derived molecules that can function to regulate the activation of pathogen recognition receptors (PRRs). These molecules play a critical role in modulating the lung injury response. DAMPs originate from multiple sources, including injured and dying cells, the extracellular matrix, or exist as immunomodulatory proteins within the airspace and interstitium. DAMPs can function as either toll-like receptor (TLR) agonists or antagonists, and can modulate both TLR and nod-like receptor (NLR) signalling cascades. Collectively, this diverse group of molecules may represent important therapeutic targets in the prevention and/or treatment of acute lung injury (ALI) and its more severe form, acute respiratory distress syndrome (ARDS).

Changes in plasma fibronectin isoform levels predict distinct clinical outcomes in critically ill patients

INTRODUCTION

Concentrations of the total pool of fibronectin in plasma (TFN), and the subset of this pool that contains the alternatively spliced EDA segment (A(+)FN), are both affected by disease processes, and the latter pool has gained a reputation as a biomarker for vascular injury. We therefore wished to determine if changes in either FN pool correlate with clinical outcomes in critically ill individuals.

METHODS

We analyzed a database for 57 patients with major trauma (n = 33) or sepsis syndrome (n = 24) in which plasma levels of TFN and A(+)FN had been measured at intervals, along with clinical parameters. Logistic regression analysis was performed to detect associations between predictive variables and three clinical outcomes: 1) the acute respiratory distress syndrome (ARDS), 2) milder acute lung injury designated acute hypoxemic respiratory failure (AHRF), and 3) survival to hospital discharge.

RESULTS

An increase in plasma TFN during the first 24 hours of intensive care unit (ICU) observation was negatively associated with progression to ARDS (odds ratio 0.98 per 1 microgram (μg)/ml increase, 95% CI (0.97, 1.00)) and AHRF (OR 0.97 per 1 μg/ml increase, (0.95, 0.99)), whereas an increase in A(+)FN over the first 24 hours was positively associated with progression to AHRF (OR 1.65 per 1 μg/ml increase, (1.04, 2.62)). Additionally, the ratio of the partial pressure of oxygen in arterial blood (PaO(2)) to the percentage of oxygen in inspired air (FIO(2)) after 24 hours was positively associated with survival (OR 1.01 per 1 unit increase in ratio, (1.00, 1.03)), along with change in A(+)FN (OR 1.30 per 1 μg/ml increase, (0.90, 1.88)).

CONCLUSIONS

Different FN isoforms may constitute predictive covariate markers for distinct clinical outcomes in critically ill patients. The data also suggest that early TFN accumulation in the circulation may confer a clinical benefit to patients at risk for acute lung injury.

Correlations between plasma levels of a fibronectin isoform subpopulation and C-reactive protein in patients with systemic inflammatory disease

Surrogate markers to detect vasculitic processes prior to organ compromise are lacking. To determine if specific populations among the fibronectin (FN) family of alternatively spliced proteins correlate with parameters of vasculitis in at-risk patients, we retrospectively evaluated the association of plasma levels of total FN (TFN) and FN bearing the alternatively spliced EIIIA segment (A(+)FN) with clinical vasculitis status and with levels of two putative vasculitis markers (C-reactive protein (CRP) and von Willebrand factor) in a previously studied cohort of 27 patients with systemic inflammatory disease. We found that the percentage of TFN composed by A(+)FN (%A(+)) and A(+)FN, but not TFN, correlated with plasma levels of CRP, the prototypic inflammation biomarker used to detect vasculitis. These findings suggest that different FNs may confer distinct clinical information, and that their simultaneous measurement merits further investigation in our efforts to identify soluble biomarker systems to detect vasculitis.

Multiple cardiovascular defects caused by the absence of alternatively spliced segments of fibronectin

Alternatively spliced variants of fibronectin (FN) containing exons EIIIA and EIIIB are expressed around newly forming vessels in development and disease but are downregulated in mature vasculature. The sequences and patterns of expression of these splice variants are highly conserved among vertebrates, suggestive of their biological importance; however the functions of EIIIA and EIIIB-containing FNs are unknown. To understand the role(s) of these splice variants, we deleted both EIIIA and EIIIB exons from the FN gene and observed embryonic lethality with incomplete penetrance by embryonic day 10.5. Deletion of both EIIIA and EIIIB exons did not affect synthesis or cell surface deposition of FN, indicating that embryonic lethality was due specifically to the absence of EIIIA and EIIIB exons from FN. EIIIA/EIIIB double-null embryos displayed multiple embryonic cardiovascular defects, including vascular hemorrhage, failure of remodeling embryonic and yolk sac vasculature, defective placental angiogenesis and heart defects. In addition, we observed defects in coverage and association with dorsal aortae of alpha-smooth-muscle-actin-positive cells. Our studies indicate that the presence or absence of EIIIA and EIIIB exons alters the function of FN and demonstrate the requirement for these alternatively spliced exons in cardiovascular development.

Recombinant human Clara cell secretory protein in acute lung injury of the rabbit: effect of route of administration

OBJECTIVE

To test the hypothesis that intratracheal instillation of Clara cell secretory protein (CC 10) to the lung may afford greater protection than intravenous administration from ventilator-induced lung inflammation.

DESIGN

Interventional laboratory study.

SETTING

An academic medical research facility in northeastern United States.

SUBJECTS

Sedated, lavage-injured juvenile rabbits.

INTERVENTIONS

A total of 18 juvenile rabbits were anesthetized, ventilated, injured with saline lavage (Pao2 of <100 mm Hg; respiratory compliance of <0.50 mL.cm H2O.kg and <50% baseline), and randomized to receive intratracheally administered surfactant plus no recombinant human CC 10 (rhCC 10, control), intravenous rhCC 10, or intratracheal rhCC 10.

MEASUREMENT AND MAIN RESULTS

Arterial blood chemistry and pulmonary mechanics were monitored; plasma and urine were collected serially. After 4 hrs of ventilation, lungs were lavaged and harvested. Surfactant function was analyzed from bronchoalveolar lavage samples (surfactometry); rhCC 10, interleukin-8, and lung myeloperoxidase concentrations were measured. Pao2, oxygenation index, ventilatory efficiency index, and respiratory compliance were not different across time or group beyond injury. Surfactometry data identified no differences as a function of group or time. Plasma, bronchoalveolar lavage, and lung interleukin-8 concentrations, lung myeloperoxidase concentrations, and inflammatory cell counts in the alveolar and interstitial spaces of intravenous and intratracheal groups were lower than in the control group (p < .05) but not statistically different from each other. Concentrations of rhCC 10 in lung, bronchoalveolar lavage, and plasma were greater in the intratracheal group than in the intravenous group (p<.05). Urine rhCC 10 concentrations were greater for the intravenous group than for the intratracheal group (p<.05) at 1, 3, and 4 hrs after treatment. No group differences in histomorphometry were noted.

CONCLUSIONS

Both intravenous and intratracheal rhCC 10 delivery, after surfactant therapy, effectively decrease lung inflammation vs. surfactant alone. While supporting the physiologic profile, intratracheal instillation results in greater, maintained lung and plasma rhCC 10 pools compared with intravenous administration. As such, intratracheal instillation of rhCC 10 may afford more prolonged protection against lung inflammation than intravenous administration.

Prediction of preeclampsia: can it be achieved?

In this review, the various biochemical tests that have been proposed for the prediction of preeclampsia are described and evaluated. Placenta hormone markers do not predict future disease. They denounce the early placental changes that are part of the evolving disease and only predict the imminent of preeclamptic syndrome. This explains why tests are better predictors when preeclampsia supervenes shortly, and why screening in the first trimester is unlikely to work as well as in the second trimester. The use of multiple markers in the screening should reflect different aspects of the disease process and could increase the specificity and sensitivity of the screening and work on different etiologic factors. The possible use of second-trimester biochemical screening to predict the risk of preeclampsia remains to be investigated in the high-risk population.

TARGET AUDIENCE

Obstetricians & Gynecologists, Family Physicians

LEARNING OBJECTIVES

After completion of this article, the reader should be able to list the various theories on the etiology of preeclampsia, to relate the various risk factors for the development of preeclampsia, and to describe the various screening tests for preeclampsia.

Deletion of the alternatively spliced fibronectin EIIIA domain in mice reduces atherosclerosis

The alternatively spliced and highly conserved EIIIA domain of fibronectin (FN) is included in most FN of the extracellular matrix in embryos. In adults, both extracellular matrix and plasma FN essentially lack EIIIA. In diverse inflammatory situations however, EIIIA is specifically included by regulated RNA splicing. In atherosclerotic lesions, FN, including the EIIIA domain (EIIIA-FN), is abundant, whereas FN in the flanking vessel wall lacks EIIIA. Lesional EIIIA-FN is localized with endothelial cells and macrophage foam cells. To directly test the function of EIIIA-FN, we generated EIIIA-null (EIIIA–/–) mice that lack the EIIIA exon and crossed them with apolipoprotein E (ApoE)–null (ApoE–/–) mice that develop arterial wall lesions. Compared with ApoE–/– controls, EIIIA–/–ApoE–/– mice had significantly smaller lesions throughout the aortic tree. EIIIA-FN was increased in ApoE–/– plasma, and total plasma cholesterol was reduced in EIIIA–/–ApoE–/– mice, specifically in large lipoprotein particles, suggesting a functional role for plasma EIIIA-FN. To assess a role for macrophage EIIIA-FN in the vessel wall, we conducted in vitro foam cell assays. EIIIA–/–ApoE–/– macrophages accumulated significantly less intracellular lipid than control ApoE–/– cells. These results provide genetic evidence that suggests roles for EIIIA-FN in plasma lipoprotein metabolism and in foam cell formation.

Intraocular and plasma levels of cellular fibronectin in patients with uveitis and diabetes mellitus

AIMS

To determine intraocular and plasma levels of cellular fibronectin (cFN) in patients with uveitis or diabetes mellitus (DM) and to assess the association with disease activity, macular oedema, and vascular leakage on fluorescein angiography. In addition, to examine whether cFN is locally produced in the eye.

METHODS

Intraocular and plasma levels of cFN were determined by ELISA in 39 patients with uveitis (23 active, 16 non-active), in 11 patients with DM (eight with and three without diabetic retinopathy) and in 17 control patients. The influence of diabetic retinopathy, inflammatory activity, vascular leakage, and macular oedema (MO) on intraocular and plasma cFN levels was studied. Local production of cFN was determined by calculating absolute and relative intraocular to plasma ratios. Aqueous and vitreous levels of cFN were compared.

RESULTS

No differences in plasma cFN levels were found between patients with uveitis, DM, or controls. Intraocular cFN levels were significantly raised in patients with uveitis and DM, specifically in those with active disease (active uveitis and active diabetic retinopathy versus controls: p = 0.001 and 0.002 respectively). Further, intraocular cFN levels were significantly elevated in patients with macular oedema or vascular leakage, irrespectively of whether associated with uveitis or DM (p = 0.001 and 0.002). Intraocular cFN levels were consistently higher in the vitreous than the aqueous. Intraocular production of cFN was documented by elevated absolute and relative intraocular to plasma ratios in nine out of 11 patients tested.

CONCLUSIONS

Elevated intraocular cFN levels were found in uveitis and DM, especially in those with active processes, intraocular vascular damage, and MO. These results suggest that locally produced cFN levels reflect intraocular vascular damage.

Plasma levels of fibronectin bearing the alternatively spliced EIIIB segment are increased after major trauma

Using Western-blot analysis and enzyme-linked immunosorbent assay (ELISA) of N-deglycosylated samples, we have observed that plasma levels of fibronectin (FN) bearing the alternatively spliced EIIIB segment (EIIIB(+) FN) increase in patients after admission to the intensive-care unit (ICU) for acute major trauma. Although not increased at the first sampling ("0 hour"), taken within 24 hours of ICU admission, levels measured 24, 48, and 72 hours later were significantly increased compared with levels obtained in healthy controls. Furthermore, average concentrations at these latter time points were significantly increased relative to the 0-hour sampling. EIIIB(+) FN levels then decreased in plasma samples taken 1 month after hospital discharge, such that no significant difference was found between ELISA-measured values at this time and 0 hour or control values. On the basis of comparisons with previous measurements in these samples, it is apparent that after acute major trauma, circulating levels of soluble EIIIB(+) FN exhibit temporal changes that are qualitatively similar to those encountered for FN isoforms bearing the alternatively spliced EIIIA segment (EIIIA(+) FN), yet different from those observed for the total pool of circulating FN. This is the first report of measurement of FN in clinical plasma samples with antibodies specific for the highly conserved EIIIB segment. Like EIIIA(+) forms of FN, EIIIB(+) FNs are recognized as soluble bloodborne markers for vascular tissue injury.

Normalization of vasoactive changes in preeclampsia precedes clinical recovery

OBJECTIVE

The objective of this study is to compare the serum levels of fibronectin, nitric oxide (NO), cyclic guanosine-monophosphate, endothelin-1, and 6-keto-prostaglandin-F 1alpha in women with and without preeclampsia before and after delivery.

METHODS

We studied 20 singleton pregnancies complicated by preeclampsia, and 20 women undergoing elective cesarean delivery were selected as controls. The normalization of circulating concentrations of maternal plasma NO, cyclic guanosine-monophosphate, fibronectin, endothelin-1, thromboxane-B 2 and renin, and urinary 6-keto-prostaglandin-F 1alpha after delivery was evaluated.

RESULTS

Mean systolic and diastolic blood pressure (BP) in the puerperium of preeclamptic women remained high after discharge from hospital, and only circulating fibronectin levels were found to be elevated in affected women at the end of hospital stay 5 days after delivery. Normalization of the imbalance in vasoactive substances and renal impairment in preeclampsia occur more rapidly than the patient's clinical recovery, within 2-3 days postpartum.

CONCLUSIONS

Slow normalization of circulating fibronectin concentrations reflects slow recovery of endothelial damage in preeclampsia, which may play a major role in maintaining high BP in the puerperium. Plasma levels of endothelin-1 declined to normal levels by the third postpartum day and the finding is consistent with the hypothesis that endothelin-1 is not the major vasoconstrictor in the pathophysiology of preeclampsia.

Engagement of α4β7 Integrins by Monoclonal Antibodies or Ligands Enhances Survival of Human Eosinophils In Vitro

Asthma is characterized by an airway inflammatory infiltrate that is rich in eosinophilic leukocytes. Cellular fibronectin and VCAM-1, ligands for α4 integrins, are enriched in the fluid of airways of allergic patients subjected to Ag challenge. We therefore hypothesized that ligands of α4 integrins can promote eosinophil survival independent of cell adhesion. Cellular fibronectin and VCAM-1 increased viability of human peripheral blood eosinophil in a dose- and time-dependant manner whether the ligand was coated on the culture well or added to the medium at the beginning of the assay. Eosinophils cultured with cellular fibronectin were not adherent to the bottom of culture wells after 3 days. Treatment with mAb Fib 30 to β7, but not mAb P4C10 or TS2/16 to β1, increased eosinophil survival. The increased survival of eosinophils incubated with Fib 30 was blocked by Fab fragments of another anti-β7 mAb, Fib 504. Eosinophils incubated with soluble cellular fibronectin or mAb Fib 30 for 6 h demonstrated a higher level of GM-CSF mRNA than eosinophils incubated with medium alone. Addition of neutralizing mAb to GM-CSF during incubation, but not mAbs to IL-3 or IL-5, reduced the enhancement of eosinophil survival by soluble cellular fibronectin or mAb Fib 30 to control levels. Thus, viability of eosinophils incubated with cellular fibronectin or VCAM-1 is due to engagement, probably followed by cross-linking, of α4β7 by soluble ligand (or mAb) that stimulates autocrine production of GM-CSF and promotes eosinophil survival.

Enhancement of fibronectin expression in rat lung by ozone and an inflammatory stimulus

This study investigated the relationship of fibronectin expression and induction of pulmonary inflammation by ozone (O3). Rats were exposed to 0.8 parts/million O3 to induce lung inflammation. A second inflammatory stimulus, rabbit serum, was applied intratracheally to augment O3-induced inflammation. Bronchoalveolar lavage fluid (BALF) and lung tissues were analyzed for fibronectin protein and mRNA expression. Blood plasma was analyzed to investigate the potential of a minimally invasive procedure in predicting lung inflammation and fibronectin levels. Significant increases in the levels of fibronectin protein in the BALF and lung tissue after O3 exposure were further enhanced by pretreatment with normal serum. An increase in fibronectin mRNA following O3 exposure was also enhanced by serum pretreatment, which by itself had no effect on lung fibronectin mRNA expression. Plasma fibronectin levels were comparable in air-PBS and O3-PBS groups but increased in the O3-serum group. The results suggest leakage of fibronectin from blood plasma into the lung following intratracheal application of rabbit serum and upregulation of local synthesis following O3 exposure.

TNF-alpha-induced matrix Fn disruption and decreased endothelial integrity are independent of Fn proteolysis

Exposure of confluent pulmonary arterial endothelial monolayers to tumor necrosis factor (TNF)-alpha causes both a reorganization and/or disruption of fibronectin (Fn) in the extracellular matrix and an increase in transendothelial protein permeability. However, the factors initiating this response to TNF-alpha have not been defined. Because TNF-alpha can induce proteinase expression in endothelial cells, we determined whether proteinases cause both the alteration of the Fn matrix and the permeability increase as is often speculated. Incubation of calf pulmonary arterial endothelial monolayers with TNF-alpha (200 U/ml) for 18 h caused a disruption of the Fn matrix and an increase in transendothelial protein permeability. A reduced colocalization of cell-surface alpha5beta1-Fn integrins with the Fn fibers in focal contacts was also observed. TNF-alpha treatment of endothelial monolayers with matrices prelabeled with 125I-human Fn (hFn) did not cause the release of Fn fragments or alter the content of Fn antigen in the medium as analyzed by SDS-PAGE coupled with autoradiography. Both the content and fragmentation pattern of Fn within the cell layer and the insoluble Fn matrix also appeared unchanged after TNF-alpha exposure as confirmed by Western immunoblot. Fn-substrate zymography revealed that TNF-alpha increased the expression of two proteinases within the conditioned medium in which activity could be blocked by aprotinin but not by EDTA, 1,10-phenanthroline, leupeptin, or pepstatin. However, inhibition of the Fn proteolytic activity of these two serine proteinases did not prevent either the TNF-alpha-induced disruption of the Fn matrix or the increase in permeability. Thus the reorganization and/or disruption of the Fn matrix and the temporally associated increase in endothelial permeability caused by TNF-alpha appear not to be due to proteolytic degradation of Fn within the extracellular matrix. In contrast, decreased alpha5beta1-Fn integrin interaction with Fn fibers in the matrix may be important in the response to TNF-alpha exposure.

Cellular fibronectin concentration in the plasma of patients with malignant and benign diseases: a comparison with CA 19-9 and CEA

EDAcFN enzyme immunoassay (EIA) is a new tumour marker assay measuring the extra domain A-containing isoform of cellular fibronectin (cFN), a component mainly found in extracellular matrices. The concentration cFN was measured in plasma and serum from 468 patients with malignant and benign diseases. The concentrations of cFN were higher in plasma than in serum. Using receiver operating characteristic (ROC) curve analysis, determination from plasma was superior to serum at specificity levels higher than 78% and was chosen for further analysis. The highest frequencies of elevated cFN values were seen in patients with hepato-pancreato-biliary malignancies (50-67%). In pancreatic and bile duct cancers, cFN provided little further information to that obtained by CA 19-9. The greatest advantage over CA 19-9 and CEA was seen in patients with local colorectal cancer and in hepatocellular carcinomas. Four out of nine patients with Dukes' stage B colorectal cancer had an elevated cFn level, but only one had an abnormal CEA level. In hepatocellular carcinomas, cFN was also compared with alpha-fetoprotein. The sensitivity of cFN (72%) was superior to that of AFP (61%), and concomitant use of cFN and AFP raised the sensitivity to 83%. The highest frequencies of elevated values in patients with benign diseases were observed in those with severe liver disease (32%) and biliary (17%) and pancreatic (24%) diseases. A combination of cFN and CA 19-9 showed the highest overall sensitivity of 47%, compared with 31% for cFN and 33% for CA 19-9. The corresponding specificities were 76% for cFN +/- CA 19-9, 85% for cFN and 83% for CA 19-9. The accuracy of a combination of cFN and CA 19-9 or CEA (60% respectively) was higher than that of cFN (55%), CA 19-9 (55%) or CEA (45%) alone. In conclusion, the results of the new cFN test are encouraging and further studies on larger patient materials have been started.

Fibronectin isoform distribution in the mouse. II. Differential distribution of the alternatively spliced EIIIB, EIIIA, and V segments in the adult mouse

The alternatively spliced EIIIB, EIIIA, and V segments of fibronectin (FN) show widespread codistribution in the mouse embryo, suggesting that EIIIB+, EIIIA+, and V+ isoforms serve to facilitate morphogenesis and organogenesis (Peters, JH, and Hynes, RO, 1996, this issue). To gain further clues to functions of these segments, we have used segment-specific anti-FN antibodies to perform immunofluorescence microscopy on tissue sections obtained from mice aged 9 to 15 weeks. Staining for each of the three spliced segments, relative to that for the total FN pool, was reduced in the adult as compared with the embryo. Anti-V antibodies produced patterns which were most similar to those obtained with anti-total FN antibodies, localizing to basement membranes, connective tissues subjacent to epithelia, walls of blood vessels, and cartilage. Anti-EIIIA antibodies produced the next most widespread pattern, which included prominent staining of the walls of blood vessels of all sizes, the lung interstitium, and smooth muscle associated with the gastrointestinal (GI), genitourinary (GU), and respiratory tracts. Although anti-EIIIB antibodies produced the faintest and most restricted pattern of staining, EIIIB+ FN could be detected in the walls of some smaller blood vessels, smooth muscle of the GI, GU, and respiratory tracts, as well as within cartilaginous structures, and eye. There were quantitative and/or qualitative differences in the staining patterns produced by the three segment-specific antibodies in a variety of tissues, including liver, cartilage, synovium, cornea, muscle, peripheral nerve, and lymph node. These findings suggest that each of the spliced segments of the FN molecule may occupy unique physical or functional positions within the extracellular matrix of the adult mouse.

Fibronectin isoform distribution in the mouse. I. The alternatively spliced EIIIB, EIIIA, and V segments show widespread codistribution in the developing mouse embryo

Fibronectins (FNs) are extracellular matrix glycoproteins that are essential for embryonic development. In order to gain clues to possible developmental roles played by the particular isoforms of FN, we used indirect immunofluorescence microscopy to examine and compare the distributions of the alternatively spliced EIIIB, EIIIA, and V segments, as well as the total pool of FNs, in serial sections from mouse embryos. Antibodies to each of these segments produced staining patterns that colocalized during gastrulation (E7.5) and during early morphogenesis of somites and notochord (E9.5). During the period of continuing organogenesis in the latter half of gestation (E10.5 to E16.5), the antibodies generally continued to produce similar staining patterns localized to epithelial basement membranes, stromal connective tissues, blood vessel walls, and muscles. However, as development proceeded, there was a gradual decline in the intensity of staining for the spliced segments relative to the total pool of FN, with a particularly noticeable decline in staining for EIIIB and EIIIA segments in certain glandular organs, including the liver. A specific reduction in expression of these latter two segments was also evident in the uterus and placenta at early timepoints in gestation. However, the most dramatic difference in the expression of the spliced segments occurred in developing hyaline cartilage, which showed a selective reduction in staining for the EIIIA segment that was evident in the axial skeletal precursors by E12.5 and complete throughout the embryo by E15.5. Our findings suggest that the alternatively spliced EIIIB, EIIIA, and V segments are included in the FN that is required for the morphogenesis of "FN dependent" structures, including somites, notochord, and the vasculature. Conversely, these segments would appear to play divergent, and sometimes exclusive, biological roles in specific tissues such as liver, cartilage, and placenta.

Cellular fibronectin and von Willebrand factor concentrations in plasma of rats treated with monocrotaline pyrrole

The monocrotaline pyrrole (MCTP)-treated rat is a useful model for the study of certain chronic pulmonary vascular diseases. A single, i.v. administration of a low dose of MCTP causes pneumotoxicity, pulmonary vascular remodeling, sustained increases in pulmonary arterial pressure, and right ventricular hypertrophy in rats. The pulmonary vascular lesions are characterized by endothelial cell alterations, platelet and fibrin microvascular thrombosis, pulmonary edema, and thickening of the intimal and medial layers of the vessel wall. These lesions suggest that some dysfunction of the hemostatic system occurs in the lungs of rats treated with MCTP. We evaluated the concentrations of two adhesion proteins, cellular fibronectin (cFn) and von Willebrand factor (vWF), in the plasma of rats treated with MCTP. We hypothesized that changes in these factors occur along with markers of pneumotoxicity and ventricular hypertrophy and that such changes might contribute to the genesis of the vascular lesions. Enzyme-linked immunosorbent assays were used to measure cFn and vWF concentrations in the plasma of rats after MCTP treatment. Rats treated with a single i.v. injection of 3.5 mg MCTP/kg body weight had delayed and progressive lung injury characterized at 5 days post-treatment by increases in the lung-to-body weight ratio and in lactate dehydrogenase activity and protein concentration in cell-free bronchoalveolar lavage fluid (BALF). Values for these markers were further increased at 8 days and reached a plateau thereafter. The number of nucleated cells within the BALF was increased at 8 and 14 days. Right ventricular hypertrophy, an indirect marker of pulmonary hypertension, was evident at 14 days. The cFn concentration was increased in plasma in rats at 8 and 14 days after treatment with MCTP. There was no difference between the vWF concentration in plasma of rats treated with MCTP and those treated with vehicle at any time. We conclude that an increase in plasma cFn concentration occurs prior to the onset of right ventricular hypertrophy and that this change is consistent with a role for cFn in the genesis of vascular remodeling and pulmonary hypertension in the MCTP-treated rat. The lung vascular injury and pulmonary hypertension in this model were not reflected in altered vWF concentration in the plasma.

Cellular fibronectin in serum and plasma: a potential new tumour marker?

The concentration of cellular fibronectin (cFN) containing the extra domain A (EDA) was measured in 479 plasma and 300 serum samples from healthy blood donors by a competitive enzyme immunoassay (EIA). Serum and plasma samples contained low concentrations of EDAcFN. The mean concentration of EDAcFN was higher in plasma (2.46 mg l-1) than in serum (0.30 mg l-1). No significant differences between sexes or age groups were found. The EDAcFN concentrations were also measured in 120 patients with various malignancies. The mean values in serum were 4.28 mg l-1, 2.01 mg l-1 and 5.18 mg l-1 in patients with digestive tract malignancies, breast cancer and a group of miscellaneous cancers respectively. In plasma, the corresponding values were 12.26 mg l-1, 4.38 mg l-1 and 11.12 mg l-1 respectively. The serum EDAcFN concentration was higher than the 97.5th percentile level of healthy blood donors in 86% of patients with digestive tract and in 76% with miscellaneous malignancies. In patients with breast cancer 60% had elevated levels of EDAcFN. The corresponding figures for plasma samples in patients with digestive tract and miscellaneous malignancies were 79% and 71% respectively. In patients with breast cancer only 30% had elevated plasma levels of EDAcFN. The mean values in serum and plasma of 20 patients with benign diseases were below the cut-off levels. Consistent with the EIA results, Western blotting revealed increased amounts of EDAcFN in blood samples from cancer patients. Pregnancy did not affect the EDAcFN concentration. The mean values in 20 pregnant women were below the cut-off levels.

Expression of the alternatively spliced EIIIB segment of fibronectin

Previous descriptions of the expression and distribution of the alternatively spliced EIIIB segment of fibronectin (FN) relied upon an antibody which, on subsequent testing, was shown not to recognize this segment directly. This raises concerns regarding the reliability of all such previous descriptions. In order to prepare reagents directly reactive with this segment, we raised polyclonal antibodies to two different bacterial fusion proteins containing intact EIIIB segments, and to a synthetic 36 amino acid peptide from the center of the EIIIB segment. Antibodies raised to each of these three immunogens recognized fusion proteins containing the EIIIB segment, but failed to recognize full length EIIIB+ FNs produced by mammalian cells, suggesting that oligosaccharide linked to Asn1359 within the EIIIB segment, or potentially to other residues in FN, might interfere with antibody recognition of this segment. Consistent with this hypothesis, N-deglycosylation of recombinant full and partial length EIIIB+ FNs permitted their specific recognition by the anti-fusion protein (but not anti-peptide) antibodies. Using anti-fusion protein antibodies coupled with deglycosylation procedures, we provide a series of new results relevant to the functions of the EIIIB segment: 1) Endogenously synthesized EIIIB+ FN is incorporated into the extracellular matrix of cultured fibroblasts, where it appears by immunofluorescence microscopy and radioimmunoprecipitation analyses to have a distribution very similar to both EIIIA+ forms and the total pool of FNs. 2) No reproducible changes can be shown to occur in the extent of synthesis or matrix incorporation of EIIIB+ FNs upon cellular transformation. 3) Low levels of EIIIB+ FN are normally present in blood plasma and consequently also in purified preparations of plasma FN. 4) EIIIB+ FN is present in blood platelets, where it constitutes a minor fraction of total platelet FN, yet is greater than 4-fold enriched relative to plasma FN. 5) EIIIB+ FN is synthesized by first passage cultured endothelial cells, suggesting that the endothelium could constitute a source for this FN isoform in the circulating blood. The antibodies and methods used in this study constitute the first direct assays of EIIIB+ FN protein expression and are applicable to a variety of species.

An improved method for quantification of extra domain A-containing cellular fibronectin (EDAcFN) in different body fluids

A quantitative direct enzyme immunoassay for the extra domain A-containing isoform of cellular fibronectin (EDAcFN) was established for screening of large series of blood samples and various body fluids of different pH and viscosity. The method is based on the monoclonal antibody DH1 recognizing the extra domain A in cellular fibronectin (EDAcFN). Studies on the effect of dilution of plasma and serum samples in this direct assay indicated that the measured concentration of cFN in the samples greatly depend on the ratio of sample dilution. The linearity of the assay was improved with sample dilution and the optimal dilution was 1:5. Stored diluted samples retained their cFN content at +4 degrees C, and -20 degrees C and -70 degrees C for months in contrast to samples stored undiluted. With this direct EIA the detection limit was 0.05 micrograms/ml and the linear portion of the standard curve could be extended above 30 micrograms/ml. Thus, the cFN concentration of blood samples could be measured reliably without inhibition also in samples with very high concentration of cFN. This is particularly important when measuring blood samples from cancer patients, since these samples may contain more than 20 micrograms/ml EDAcFN. The assay was standardized for blood samples but, due to the possibility of sample dilution, it also enabled reliable quantification of EDAcFN in various other body fluids. Undiluted some of the samples with non-neutral pH (urine, bile) or with high viscosity (seminal plasma) interfered with the assay. In addition to blood samples, the EDAcFN concentration was determined in samples of urine, bile, amniotic fluid, cervicovaginal secretions, seminal fluid, cerebrospinal fluid, bronchoalveolar lavage fluid, pleural fluid and saliva. Thereby, this modified method was shown to be applicable to various body fluids.

Isoforms of cellular fibronectin and tenascin in amniotic fluid

Amniotic fluid (AF) obtained from second trimester pregnancies presented extradomain (ED) A, B and an oncofetal (onc-f) domain containing isoforms of cellular fibronectin (cFn) in Western blotting of gelatin-bound polypeptides and directly of AF. Western blotting after sequential immunoprecipitation suggested at least three Fn molecules: one containing EDA and the onc-f domain and another minor component distinctly containing all the domains, and a third one only containing EDA. The immunoblotting results for EDA-cFn and onc-f-cFn were closely similar to that for total Fn, whereas in plasma samples of normal and pregnant women only traces of EDA-cFn and onc-f-cFn, but no EDB-cFn, were found. Western blotting of AF also indicated the presence of three isoforms of tenascin (Tn), M(r) 190,000 and 280,000 polypeptides earlier found in many cells, and a M(r) 200,000 polypeptide, novel for AF and not present in plasma. The results suggest a novel extracellular matrix polypeptide composition for AF.

The value of antithrombin-III and fibronectin in hypertensive disorders of pregnancy

In this study we evaluated fibronectin as a marker of endothelial cell injury and antithrombin III as a marker of chronic activation of intravascular coagulation. The aim of the study was to establish to normal trends of plasma antithrombin III and fibronectin in general obstetric population and to determine the value of both in predicting, distinguishing and understanding the pathophysiology of pregnancy induced hypertension. The all cases consisted of 173 pregnant, 19 of them were chronic hypertensive, 45 were pregnancy induced hypertensive and 119 were normotensive at blood sampling. Out of 119 normotensive cases, 109 cases had no adverse outcome during their pregnancy. These cases were used as a control group and for the normal trends of antithrombin III and fibronectin in general obstetric population. Ten out of 119 cases who developed preeclampsia during follow up, 19 cases with chronic hypertension and 45 cases with pregnancy induced hypertension consisted of the study group. In the cases who developed preeclampsia during follow up, the value of plasma fibronectin level (above 95% confidence limit for that gestational week) to predict preeclampsia had 90% sensitivity and 94.4% specificity. In distinguishing hypertensive disorders of pregnancy (chronic hypertension or pregnancy induced hypertension) fibronectin had 71.1% sensitivity and 100% specificity. Plasma antithrombin III level (of antigenicity) measured by immunodiffusion method had no value in predicting and distinguishing pregnancy induced hypertension.

Competitive enzyme immunoassay for quantification of the cellular form of fibronectin (EDAcFN) in blood samples

A competitive enzyme immunoassay based on the monoclonal antibody DH1 was developed for the quantification of extradomain A (EDA)-containing isoform of cellular fibronectin (cFN). The average EDAcFN concentration in normal plasma was 2.46 micrograms/ml and in serum 0.68 micrograms/ml. Similar results were obtained by gelatin-Sepharose binding and immunoblotting. Studies on the effect of storage of plasma and serum as frozen samples indicated that the amount of EDAcFN decreased rapidly when stored at -20 degrees C. Storage at -70 degrees C resulted in less of a decrease in the concentration of EDAcFN. The method permits the determination of EDAcFN in blood samples from diseases showing increased amounts of the protein at the tissue level.

Expression and alternative splicing of fibronectin mRNA in human diploid endothelial cells during aging in vitro

Different mRNAs for fibronectin arise from the variable processing of a single primary transcript. We used ribonuclease protection assay to investigate the changes occurring in fibronectin expression and the alternative splicing of mRNA precursor during aging in vitro of human diploid endothelial cells. Senescent endothelial cells release more protein and contain 4-5-fold more fibronectin mRNA than young cells. The pattern of alternative splicing of fibronectin mRNA, with the EDA and the CS1 segments largely included (35% and 77%, respectively) and the EDB segment undetectable, correlates well with previous studies at the protein level both in vitro and in vivo. No changes in the splicing pattern of fibronectin mRNA precursor were detected during endothelial cellular senescence. The increased expression of fibronectin in senescent cells may be a result of the activity of interleukin-1 alpha, which is overexpressed in senescent endothelial cells. It could be also important in vivo during aging and in atherosclerotic lesions.

Differential expression of type I collagen and cellular fibronectin isoforms in endothelial cell variants

Endothelial cells in vivo and in vitro are inherently capable of manifesting more than one phenotype. Most endothelial cells in culture, even when maintained at confluent density for an extended period, exhibit only the typical polygonal morphology. Other cultures, albeit few, are characterized by rapid formation of variant "sprout" cells once the cobblestone monolayer is established. In vivo studies have revealed sprout cell formation to be one of the early events in neovascularization. Therefore, elucidation of the factors involved in this process is needed to gain an understanding of the sprouting phenomena. To this end, two morphologically distinct bovine endothelial cell clones derived from a fetal left ventricle were characterized. One culture of cells stably displayed the conventional polygonal phenotype, in contrast to the second culture in which an interconnecting network of sprout cells reproducibly developed beneath the cobblestone monolayer. Analysis of extracellular matrix proteins and RNA transcripts revealed that the sprouting clone showed induction of type I collagen and a shift in fibronectin RNA processing resulting in synthesis of the cellular isoforms. These collagenous and non-collagenous matrix molecules may serve in some manner to affect the processes required during angiogenesis, that is, cell division, cell migration and cell shape change.

Rat hepatocytes in primary culture synthesize and secrete cellular fibronectin

Fibronectins, involved in cell-matrix interactions and cell attachment, are glycoproteins which show a remarkable heterogeneity, due to alternative splicing. The type III-related domains, ED-A and ED-B, are present in cellular fibronectin in a variety of ratios whereas they are absent in circulating plasma fibronectin. Fibronectin synthesis by hepatocytes which are accepted as suppliers of plasma fibronectin was studied in primary cultures during a 6-day culture period. Using site-specific antibodies we demonstrate that rat hepatocytes are also able to synthesize and secrete fibronectin bearing the ED-A domain from Day 3 on after inoculation. By immunocytological characterization of the hepatocyte monolayer with antibodies directed against desmin, laminin, collagen IV, alpha-SM-actin, or ED-1 or factor VIII-related antigen, contaminating mesenchymal hepatic cell-types as a source for cellular fibronectin production could be ruled out. Dexamethasone treatment caused enhanced fibronectin synthesis and cellular fibronectin was already detectable at Day 1 after plating. Elevation of cellular fibronectin synthesis after prolonged culture-terms and by dexamethasone could also be demonstrated on mRNA steady-state level, using ED-A cDNA as a probe in hybridization analysis. Dot blot hybridisation proved a prominent response of cellular fibronectin mRNA level to dexamethasone at Day 1 when dexamethasone treatment resulted in an increased contribution of ED-A-positive fibronectin transcripts to total fibronectin mRNA level.

Epithelial injury, inflammation, and repair in the hamster lung following intratracheal instillation of enzyme-generated oxidants

Oxidant-induced inflammatory and morphologic changes evoked by intratracheally instilled glucose, active glucose oxidase, and lactoperoxidase in hamsters are described. Similar solutions containing heat-denatured (DE) glucose oxidase served as a control treatment. During the 7-week post-treatment period, animals were sacrificed and lavaged, and their lungs were preserved for later study. Although a neutrophil-rich alveolitis was observed initially in both groups, the leukocytic influx and mild morphologic changes in DE-treated animals resolved within 7 days. In contrast, glucose oxidase mixtures caused necrotic alveolar epithelium, fibrin-like exudate, and significantly higher neutrophil and protein levels in bronchoalveolar lavage fluid (BALF) after 1 day. At 4 days, type II cell hyperplasia was extensive and BALF levels of all inflammatory cell types were significantly greater than BALF counts in DE animals. By 7 days, BALF macrophage and lymphocyte levels remained significantly elevated, and epithelial hyperplasia coincided with marked increases in lung hydroxyproline and interstitial cells. BALF parameters suggested that inflammation induced by glucose oxidase resolved within 15 days, yet total hydroxyproline levels remained elevated at 15 days and epithelial lesions were still detectable at 29 days. Oxidant-induced inflammation and epithelial injury were transient and preceded moderate collagen deposition.

Fibronectin fragments containing the RGDS cell-binding domain mediate monocyte migration into the rabbit lung. A potential mechanism for C5 fragment-induced monocyte lung accumulation

Many inflammatory processes are characterized by an early phase of neutrophil migration and a later phase of monocyte migration into the inflammatory site. Mechanisms that govern the transition between phases are the subject of these investigations. Acute lung inflammation induced by C5 fragments in the rabbit leads to an initial neutrophil influx and plasma leakage into the alveolar space, followed by monocyte influx that we have previously shown to be dependent on prior emigration of neutrophils. Neutrophil enzymes are known to cleave intact fibronectin into fragments that are monocyte chemotaxins in vitro. Accordingly, generation of appropriate fibronectin fragments in situ by proteolytic enzymes from infiltrating neutrophils might represent a potential mechanism for attraction of monocytes into the lung. The studies reported herein demonstrate that a 120-kD fragment of fibronectin containing the RGDS fibroblast cell-binding domain induced monocyte migration into the rabbit lung in vivo. Intact fibronectin was inactive. A significant proportion of the monocyte migration was neutrophil independent. Intact fibronectin was present in bronchoalveolar lavage fluid from C5 fragment-treated animals rendered neutropenic, but absent in lavage from normal C5 fragment-treated animals. Fibronectin fragments were present in bronchoalveolar lavage fluid from both C5 fragment-treated and control rabbits. In addition, the amount of fibronectin was significantly increased in lavage of C5 fragment-treated normal but not neutropenic animals. Monoclonal antibodies directed against an epitope of fibronectin containing the RGDS cell-binding domain significantly inhibited the C5 fragment-induced monocyte migration, but not neutrophil migration. These studies suggest that chemotactic fibronectin fragments may in part be responsible for the recruitment of monocytes into areas of acute lung inflammation.

Expression of fibronectin variants in vascular and visceral smooth muscle cells in development

Monoclonal antibodies recognizing extra domain A (ED-A) and extra domain B (ED-B) fibronectin (FN) sequences were used to characterize FN variants expressed in human vascular smooth muscle cells (SMC) during fetal and postnatal development and to compare spectrum of FN variants produced by vascular and visceral SMC. In 8- to 12-week-old fetuses both ED-A-containing FN (A-FN) and ED-B-containing FN (B-FN) were found in all smooth muscles studied--aorta, esophagus, stomach, and jejunum. By 20-25 weeks of gestation relative amounts of both A-FN and B-FN were reduced significantly in the aortic media (fivefold for A-FN and twofold for B-FN), while in visceral SMC only B-FN content was decreased. All the adult visceral smooth muscles examined contained A-FN rather than B-FN. Therefore, the cells from adult aortic media appear to be the only SMC so far known to produce FN that contains neither ED-A nor ED-B. Moreover, the data obtained show that, unlike other cells, medial SMC are embedded in vivo in the extracellular matrix that contains FN lacking both ED-A and ED-B. SMC from the minor intimal thickenings in the human child aorta as well as those from the atherosclerotic plaques produce A-FN rather than B-FN. We conclude that (1) vascular SMC change the spectrum of produced FN variants at least twice--during prenatal development between 12 and 20 weeks of gestation, and during the postnatal period, when they are recruited into the intimal cell population; (2) the production of FN variants in visceral SMC is also developmentally regulated; (3) all visceral SMC unlike the cells from adult aortic media produce A-FN; (4) the presence of ED-A and ED-B sequences in the FN molecule is not necessary for the extracellular matrix assembly in vivo.

Increased plasma levels of ED1+ cellular fibronectin precede the clinical signs of preeclampsia

To evaluate alterations in fibronectin homeostasis in preeclampsia we measured the plasma concentrations of fibronectin bearing an extra type III domain in 33 preeclamptic and 36 control patients at varying gestational ages. This fibronectin variant is concentrated in the endothelium of blood vessels and has been shown to be released at sites of vascular injury. In addition, total circulating fibronectin levels, composed primarily of hepatic-derived fibronectin lacking the extra type III domain, were also determined. Significant elevations in the average circulating concentrations of fibronectin with an extra type III domain (5.5 micrograms/ml [95% confidence interval, 4.7,6.2] versus 3.2 micrograms/ml [95% confidence interval, 2.9,3.5]; p = 0.0001) as well as total fibronectin (387 micrograms/ml [95% confidence interval, 357,417] versus 327 micrograms/ml [95% confidence interval, 305,348]; p = 0.036) were observed in preeclamptic versus control patients. Significant elevations in fibronectin levels with an extra type III domain occurred in the first trimester before clinical evidence of preeclampsia. In addition, multivariate logistic regression demonstrated a 5.4-fold increase in the risk of preeclampsia with each 1 microgram/ml elevation in concentration of fibronectin with an extra type III domain. These findings lend support to the hypothesis that endothelial-vascular injury is a primary event in the genesis of preeclampsia.

Dose-related effects of enzyme-generated oxidants on the biochemistry and morphology of the hamster lung

Reactive oxygen species (ROS) have been closely associated with a number of pathological disorders, including interstitial pulmonary fibrosis. While models of ROS-induced fibrosis offer advantages over chemically-induced fibrosis, the biochemical and morphological features of ROS-induced fibrosis have yet to be extensively documented. In this study, we evaluated the effect of initial ROS dose on lung injury and repair. Male hamsters received a single dose of glucose, glucose oxidase and lactoperoxidase via the intratracheal route. From 3 to 14 days post-treatment, a significant dose-related body weight loss was observed. There was a trend towards greater mortality with increasing dose. After 2 weeks, we noted significant, dose-related increases in lung levels of collagen, lipid peroxidation products, nucleic acids, and protein. Similarly, total lung catalase, lactic dehydrogenase and glutathione reductase activities were also elevated significantly above control values in a dose-related fashion. A concurrent, dose-dependent thickening of alveolar septa in ROS-treated lungs was composed of epithelial hyperplasia, hyperemia, edema and accumulations of interstitial fibers and macrophages. Interstitial and alveolar macrophages in ROS-induced lesions were enlarged and contained numerous primary and secondary lysosomes. These results demonstrate that, in the hamster lung, injury induced by enzyme-generated ROS can initiate dose-dependent fibroproliferative changes which eventuate into interstitial fibrosis.

Expression of extra domain A fibronectin sequence in vascular smooth muscle cells is phenotype dependent

Different fibronectin (FN) variants arise from the single gene transcript alternatively spliced in a tissue-specific manner (Hynes, R. O. 1985. Annu. Rev. Cell Biol. 1:67-90; Owens, R. J., A. R. Kornblihtt, and F. E. Baralle. 1986. Oxf. Surv. Eurcaryotic Genes. 3:141-160). We used mAb IST-9, specific for extra domain A (ED-A) FN sequence, and cDNA probe to ED-A exon to determine whether ED-A is present in FN synthesized by vascular smooth muscle cells (SMCs) and, if so, whether expression of ED-A is SMC phenotype dependent. ED-A-containing FN (A-FN) was not revealed in tunica media of human arteries and normal rat aorta by immunofluorescence and immunoblotting techniques. A cDNA probe to ED-A exon did not hybridize with RNA isolated from human aortic media. A positive reaction with IST-9 was observed in (a) diffuse intimal thickening and atherosclerotic plaque from human arteries; (b) experimentally induced intimal thickening in rat aorta; and (c) cultured vascular SMCs. A-FN mRNA was present in the RNA preparation from human aortic intima as judged by hybridization with cDNA probe to ED-A. On the other hand, an mAb interacting with an epitope common for all FN variants revealed FN in both intima and media of human arteries and in the normal rat aorta. A cDNA probe to a sequence shared by all FN variants hybridized with RNA from both intima and media of human aorta, though the level of expression was higher in intima. The data suggest that ED-A exon is omitted during splicing of the FN mRNA precursor in medial SMCs while the expression of A-FN is characteristic of "modulated" SMCs--those of intimal thickenings, of atherosclerotic lesions, and growing in culture.