Hypertension induces alternatively spliced forms of fibronectin in rat aorta

Aspirin Inhibits Fibronectin Expression and Reverses Fibronectin-Mediated Cell Invasiveness by Activating Akt Signaling in Preeclampsia

Preeclampsia is a severe gestational hypertensive disorder that may lead to maternal multiple organ dysfunction and adverse fetal outcomes. Aspirin provides a protective effect by reducing the risk of preeclampsia; however, its mechanism of action is unclear. Fibronectin (FN) is a key factor in cell motility and is associated with preeclampsia. Here, we demonstrated that cellular FN expression was elevated in the placenta of preeclamptic patients. The functional roles of plasma and cellular FN in trophoblasts were investigated by treating HTR-8/SVneo cells with exogenous recombinant human FN protein (rhFN) and siRNA, respectively. Trophoblast migration and invasion were inhibited by rhFN and facilitated by FN knockdown. Moreover, rhFN activated ERK and Akt signaling in trophoblasts, and FN-suppressed cell motility was rescued by ERK and/or Akt inhibitors. In this study, aspirin suppressed trophoblast cellular FN expression and reversed FN-mediated cell functions, including cell migration, invasion, and ERK/Akt signal changes. Taken together, the results of this study revealed the effects of FN on trophoblast motility and signaling; aspirin inhibits FN expression and reverses FN-mediated trophoblast biology. These results provide a drug mechanism for disease prevention and a target for preeclampsia intervention.

Blockage of Fibronectin 1 Ameliorates Myocardial Ischemia/Reperfusion Injury in Association with Activation of AMP-LKB1-AMPK Signaling Pathway

Myocardial ischemia/reperfusion injury (I/RI) is closely associated with energy substrate metabolism. Fibronectin 1 (Fn1) was markedly elevated in the heart of I/R pigs and ischemic patients, but its role in myocardial I/RI is controversial and the precise mechanism involved remains elusive. Herein, we tested whether blockage of Fn1 with its inhibitor (fibronectin tetrapeptide, RGDS) would alleviate myocardial I/RI. Wild-type (WT) mice were administered with RGDS once 3 h before I/R operation and once at 24 or 48 h postreperfusion, and sacrificed at 24 or 72 h post-I/R, respectively. Cardiac function was evaluated by echocardiography. Myocardial infarction size, apoptosis, fibrosis, and inflammation were examined via histological staining. Uptake of glucose and fatty acids were detected by positron emission tomography (PET) and computer tomography (CT) with [¹⁸F]-2-fluoro-2-deoxy-D-glucose (FDG) and [¹⁸F]-fluoro-6-thia-heptadecanoic acid (FTHA), respectively. Our results showed that administration of RGDS to mice remarkably limited the I/R-induced myocardial infarct size, myocyte apoptosis, inflammation, oxidative stress, and fibrosis and improved cardiac contractile dysfunction. These protective effects were associated with upregulation of the AMP/ATP ratio and the activation of LKB1-AMPK signaling, which subsequently increased AS160-GLUT4-mediated glucose and fatty acid uptake, improved mitochondrial dynamic imbalance, and inactivated TGF-β and NF-κB signals in the I/R heart. In conclusion, the current study identified that blocking Fn1 protects against myocardial I/RI likely through activating the LKB1-AMPK-dependent signals and highlights that inhibition of Fn1 may be a novel therapeutic option for treating ischemic heart diseases.

Vascular Extracellular Matrix Remodeling and Hypertension

Significance: The vascular extracellular matrix (ECM) not only provides mechanical stability but also manipulates vascular cell behaviors, which are crucial for vascular function and homeostasis. ECM remodeling, which alters vascular wall mechanical properties and exposes vascular cells to bioactive molecules, is involved in the development and progression of hypertension. Recent Advances: This brief review summarized the dynamic changes in ECM components and their modification and degradation during hypertension and after antihypertensive treatment. We also discussed how alterations in the ECM amount, assembly, mechanical properties, and degradation fragment generation provide input into the pathological process of hypertension. Critical Issues: Although the relevance between ECM remodeling and hypertension has been recognized, the underlying mechanism by which ECM remodeling initiates the development of hypertension remains unclear. Therefore, the modulation of ECM remodeling on arterial stiffness and hypertension in genetically modified rodent models is summarized in this review. The circulating biomarkers based on ECM metabolism and therapeutic strategies targeting ECM disorders in hypertension are also introduced. Future Directions: Further research will provide more comprehensive understanding of ECM remodeling in hypertension by the application of matridomic and degradomic approaches. The better understanding of mechanisms underlying vascular ECM remodeling may provide novel potential therapeutic strategies for preventing and treating hypertension. Antioxid. Redox Signal. 34, 765-783.

Cellular Fibronectin Containing Extra Domain A Causes Insulin Resistance via Toll-like Receptor 4

We determined the role of cellular fibronectin (CFN) containing the alternatively spliced extra domain A (FN-EDA) in causing insulin resistance (IR) through toll-like receptor 4 (TLR4). Circulating FN-EDA level was evaluated in mouse and rat IR models. Specific anti-FN-EDA antibody and TLR4 inhibitor were used to study its role in IR in mice. CFN protein was injected to evaluate TLR4 dependent effect of FN-EDA in IR. Furthermore, FN-EDA was estimated in blood plasma and correlated with demographic and clinical characteristics in healthy human participants (n = 38). High-fat diet feeding significantly increased circulating FN-EDA in both mouse (P = 0.03) and rat (P = 0.02) IR models. Antibody against FN-EDA protected mice from IR by increasing glucose disposal rate following glucose (P = 0.02) and insulin (P = 0.01) tolerance tests. CFN protein injection caused IR, however, TLR4 inhibitor protected the mice from CFN induced IR. Multivariate regression analysis predicted an independent positive correlation between circulating FN-EDA and fasting plasma glucose (P = 0.003) in healthy human participants. In conclusion, FN-EDA may cause IR through TLR4 by decreasing glucose disposal rate following glucose and insulin load. Targeting FN-EDA thus can be considered as a possible therapeutic strategy to delay prediabetes progression to diabetes.

Fibronectin Containing Extra Domain A Induces Plaque Destabilization in the Innominate Artery of Aged Apolipoprotein E-Deficient Mice

OBJECTIVE

Fibronectin containing extra domain A (Fn-EDA) is an endogenous ligand of TLR4 (toll-like receptor 4) and is abundant in the extracellular matrix of advanced atherosclerotic lesions in human and mice. Irrespective of sex, deletion of Fn-EDA reduces early atherosclerosis in apolipoprotein E-deficient (Apoe^-/-) mice. However, the contribution of Fn-EDA in advanced atherosclerosis remains poorly characterized. We determined the contribution of Fn-EDA in advanced atherosclerotic lesions of aged (1-year-old) Apoe^-/- mice.

APPROACH AND RESULTS

Plaque composition was determined in the innominate artery, a plaque instability site that is known to mimic several histological features of vulnerable human plaques. Female Apoe^-/-, Fn-EDA^-/-Apoe^-/-, TLR4^-/-Apoe^-/-, and Fn-EDA^-/-TLR4^-/-Apoe^-/- mice were fed a high-fat Western diet for 44 weeks. Fn-EDA^-/-Apoe^-/- mice exhibited reduced plaque size characterized by smaller necrotic cores, thick fibrous caps containing abundant vascular smooth muscle cells and collagen, reduced CD68/MMP9 (matrix metalloproteinase 9)-positive content, less accumulation of MMP-cleaved extracellular matrix aggrecan, and decreased vascular smooth muscle cell and macrophage apoptosis (P<0.05 versus Apoe^-/- mice). Together these findings suggest that Fn-EDA induces plaque destabilization. Deletion of TLR4 reduced histological features of plaque instability in Apoe^-/- mice but did not further reduce features of plaque destabilization in Fn-EDA^-/-Apoe^-/- mice, suggesting that TLR4 may contribute to Fn-EDA-induced plaque destabilization. Fn-EDA potentiated TLR4-dependent MMP9 expression in bone marrow-derived macrophages, suggesting that macrophage TLR4 may contribute to Fn-EDA-mediated plaque instability.

CONCLUSIONS

Fn-EDA induces histological features of plaque instability in established lesions of aged Apoe^-/- mice. The abundance of Fn-EDA in advanced atherosclerotic lesions may increase the risk of plaque destabilization.

Toll-like Receptors in the Vascular System: Sensing the Dangers Within

Toll-like receptors (TLRs) are components of the innate immune system that respond to exogenous infectious ligands (pathogen-associated molecular patterns, PAMPs) and endogenous molecules that are released during host tissue injury/death (damage-associated molecular patterns, DAMPs). Interaction of TLRs with their ligands leads to activation of downstream signaling pathways that induce an immune response by producing inflammatory cytokines, type I interferons (IFN), and other inflammatory mediators. TLR activation affects vascular function and remodeling, and these molecular events prime antigen-specific adaptive immune responses. Despite the presence of TLRs in vascular cells, the exact mechanisms whereby TLR signaling affects the function of vascular tissues are largely unknown. Cardiovascular diseases are considered chronic inflammatory conditions, and accumulating data show that TLRs and the innate immune system play a determinant role in the initiation and development of cardiovascular diseases. This evidence unfolds a possibility that targeting TLRs and the innate immune system may be a novel therapeutic goal for these conditions. TLR inhibitors and agonists are already in clinical trials for inflammatory conditions such as asthma, cancer, and autoimmune diseases, but their study in the context of cardiovascular diseases is in its infancy. In this article, we review the current knowledge of TLR signaling in the cardiovascular system with an emphasis on atherosclerosis, hypertension, and cerebrovascular injury. Furthermore, we address the therapeutic potential of TLR as pharmacological targets in cardiovascular disease and consider intriguing research questions for future study.

Genetic Ablation of Extra Domain A of Fibronectin in Hypercholesterolemic Mice Improves Stroke Outcome by Reducing Thrombo-Inflammation

BACKGROUND

The fibronectin-splicing variant containing extra domain A (Fn-EDA) is present in negligible amounts in the plasma of healthy humans but markedly elevated in patients with comorbid conditions, including diabetes mellitus and hypercholesterolemia, which are risk factors for stroke. It remains unknown, however, whether Fn-EDA worsens stroke outcomes in such conditions. We determined the role of Fn-EDA in stroke outcome in a model of hypercholesterolemia, the apolipoprotein E-deficient (Apoe(-/-)) mouse.

METHODS AND RESULTS

In a transient cerebral ischemia/reperfusion injury model, Apoe(-/-) mice expressing fibronectin deficient in EDA (Fn-EDA(-/-)Apoe(-/-) mice) exhibited smaller infarcts and improved neurological outcomes at days 1 and 8 (P<0.05 versus Apoe(-/-) mice). Concomitantly, intracerebral thrombosis [assessed by fibrin(ogen) deposition] and postischemic inflammation (phospho-nuclear factor-κB p65, phospho-IκB kinase α/β, interleukin 1β, and tumor necrosis factor-α) within lesions of Fn-EDA(-/-)Apoe(-/-) mice were markedly decreased (P<0.05 versus Apoe(-/-) mice). In an FeCl3 injury-induced carotid artery thrombosis model, thrombus growth rate and the time to occlusion were prolonged in Fn-EDA(-/-)Apoe(-/-) mice (P<0.05 versus Apoe(-/-) mice). Genetic ablation of TLR4 improved stroke outcome in Apoe(-/-) mice (P<0.05) but had no effect on stroke outcome in Fn-EDA(-/-)Apoe(-/-) mice. Bone marrow transplantation experiments revealed that nonhematopoietic cell-derived Fn-EDA exacerbates stroke through Toll-like receptor-4 expressed on hematopoietic cells. Infusion of a specific inhibitor of Fn-EDA into Apoe(-/-) mouse 15 minutes after reperfusion significantly improved stroke outcome.

CONCLUSIONS

Hypercholesterolemic mice deficient in Fn-EDA exhibit reduced cerebral thrombosis and less inflammatory response after ischemia/reperfusion injury. These findings suggest that targeting Fn-EDA could be an effective therapeutic strategy in stroke associated with hypercholesterolemia.

Fibronectin Splicing Variants Containing Extra Domain A Promote Atherosclerosis in Mice Through Toll-Like Receptor 4

OBJECTIVE

Cellular fibronectin containing extra domain A (EDA(+)-FN) is abundant in the arteries of patients with atherosclerosis. Several in vitro studies suggest that EDA(+)-FN interacts with Toll-like receptor 4 (TLR4). We tested the hypothesis that EDA(+)-FN exacerbates atherosclerosis through TLR4 in a clinically relevant model of atherosclerosis, the apolipoprotein E-deficient (Apoe(-/-)) mouse.

APPROACH AND RESULTS

The extent of atherosclerosis was evaluated in whole aortae and cross sections of the aortic sinus in male and female EDA(-/-)Apoe(-/-) mice (which lack EDA(+)-FN), EDA(fl/fl)Apoe(-/-) mice (which constitutively express EDA(+)-FN), and control Apoe(-/-) mice fed a high-fat Western diet for 14 weeks. Irrespective of sex, EDA(fl/fl)Apoe(-/-) mice exhibited a 2-fold increase in atherosclerotic lesions (aorta and aortic sinus) and macrophage content within plaques, whereas EDA(-/-)Apoe(-/-) mice exhibited reduced atherosclerotic lesions (P<0.05 versus Apoe(-/-), n=10-12 mice/group), although cholesterol and triglyceride levels and circulating leukocytes were similar. Genetic ablation of TLR4 partially reversed atherosclerosis exacerbation in EDA(fl/fl)Apoe(-/-) mice (P<0.05) but had no effect on atherosclerotic lesions in EDA(-/-)Apoe(-/-) mice. Purified cellular FN, which contains EDA, potentiated dose-dependent NFκB-mediated inflammation (increased phospho-NFκB p65/NFκB p65, tumor necrosis factor-α, and interleukin-1β) in bone marrow-derived macrophages from EDA(-/-)Apoe(-/-) mice but not from EDA(-/-)TLR4(-/-)Apoe(-/-) mice. Finally, using immunohistochemistry, we provide evidence for the first time that EDA(+)-FN colocalizes with macrophage TLR4 in murine aortic lesions and human coronary artery atherosclerotic plaques.

CONCLUSIONS

Our findings reveal that TLR4 signaling contributes to EDA(+)-FN-mediated exacerbation of atherosclerosis. We suggest that EDA(+)-FN could be a therapeutic target in atherosclerosis.

Increased stiffness and cell-matrix interactions of abdominal aorta in two experimental nonhypertensive models: long-term chemically sympathectomized and sinoaortic denervated rats

RATIONALE

Sinoaortic denervated (SAD) and chemically sympathectomized (SNX) rats are characterized by a decrease in arterial distensibility without hypertension and would, thus, be relevant for analyzing arterial wall stiffening independently of blood pressure level. The fibronectin network, which plays a pivotal role in cell-matrix interactions, is a major determinant of arterial stiffness. We hypothesized that in SAD and SNX rats, arterial stiffness is increased, due to alterations of cell-matrix anchoring leading to spatial reorganization of the extracellular matrix.

METHODS

The intrinsic elastic properties of the arterial wall were evaluated in vivo by the relationship between incremental elastic modulus determined by echotracking and circumferential wall stress. The changes of cell-extracellular matrix links in the abdominal aorta were evaluated by studying fibronectin, vascular integrin receptors, and ultrastructural features of the aorta by immunochemistry.

RESULTS

In both experimental conditions, wall stiffness increased, associated with different modifications of cell-extracellular matrix adhesion. In SAD rats, increased media cross-sectional area was coupled with an increase of muscle cell attachments to its extracellular matrix via fibronectin and its α5-β1 integrin. In SNX rats, reduced media cross-sectional area was associated with upregulation of αv-β3 integrin and more extensive connections between dense bands and elastic fibers despite the disruption of the elastic lamellae.

CONCLUSION

In aorta of SNX and SAD rats, a similar arterial stiffness is associated to different structural alterations. An increase in αvβ3 or α5β1 integrins together with the already reported increase in the proportion of less distensible (collagen) to more distensible (elastin) components in both models contributes to remodeling and stiffening of the abdominal aorta.

Plasma and cellular fibronectin: distinct and independent functions during tissue repair

Fibronectin (FN) is a ubiquitous extracellular matrix (ECM) glycoprotein that plays vital roles during tissue repair. The plasma form of FN circulates in the blood, and upon tissue injury, is incorporated into fibrin clots to exert effects on platelet function and to mediate hemostasis. Cellular FN is then synthesized and assembled by cells as they migrate into the clot to reconstitute damaged tissue. The assembly of FN into a complex three-dimensional matrix during physiological repair plays a key role not only as a structural scaffold, but also as a regulator of cell function during this stage of tissue repair. FN fibrillogenesis is a complex, stepwise process that is strictly regulated by a multitude of factors. During fibrosis, there is excessive deposition of ECM, of which FN is one of the major components. Aberrant FN-matrix assembly is a major contributing factor to the switch from normal tissue repair to misregulated fibrosis. Understanding the mechanisms involved in FN assembly and how these interplay with cellular, fibrotic and immune responses may reveal targets for the future development of therapies to regulate aberrant tissue-repair processes.

Inflammation modulates fibronectin isoform expression in colonic lamina propria fibroblasts (CLPF)

BACKGROUND

Migration of colonic lamina propria fibroblasts (CLPF) plays an important role during mucosal wound healing as well as fibrosis and fistula formation in Crohn's disease (CD). Recently, we showed that the migratory potential of CD-CLPF was significantly reduced compared to control CLPF. Fistula-derived CD-CLPF migrated less and fibrosis-CLPF more than CLPF from inflamed CD mucosa. These changes in migratory behavior were associated with changes in production of the migration-inducing fibronectin (FN) isoforms ED-A and ED-B. A permanent reduction of the migratory potential of CLPF was mediated by IFN-gamma and tumor necrosis factor (TNF) modulate FN isofom expression in CLPF and thereby might regulate CLPF migration.

MATERIALS AND METHODS

Control CLPF were incubated for 72 h with IFN-gamma, TNF, IFN-gamma plus TNF, or TGF-beta1. Messenger RNA (mRNA) was isolated and expression of FN and isoforms ED-A and ED-B was quantified by real-time polymerase chain reaction. FN, ED-A, and ED-B were investigated by Western blotting. FN receptor integrin alpha5beta1 was analyzed by FACS.

RESULTS

No difference was found for the surface display of integrin alpha5beta1 between stimulated and non-stimulated cells. In TGF-beta1 incubated CLPF mRNA amount of FN and isoforms ED-A and ED-B was slightly increased. IFN-gamma only decreased FN in CLPF, TNF significantly reduced FN-mRNA by 40%, FN ED-A mRNA by 25%, and ED-B mRNA by 50%. The TNF-mediated mRNA downregulation resulted in a decreased protein amount as revealed by Western blotting.

CONCLUSION

Cytokines such as IFN-gamma, TNF, and TGF-beta1 modulate the production of fibronectin isoforms. Our data indicate that inflammation-induced modulation of FN-isoform production is involved in the alterations of migratory potential of CLPF isolated from CD mucosa.

Evidence for a differential expression of fibronectin splice forms ED-A and ED-B in Crohn's disease (CD) mucosa

BACKGROUND AND AIMS

Fibronectin (FN) is an essential factor for the induction of migration of primary colonic lamina propria fibroblasts (CLPF). The FN isoform ED-A is an important inducer of migration. Recently, we have shown that CLPF isolated from inflamed Crohn's disease (CD) mucosa migrated significantly less than control CLPF. We, therefore, investigated changes in FN or integrin expression that could be relevant for CLPF migration.

MATERIALS AND METHODS

mRNA of control-CLPF and CLPF isolated from fibrotic mucosa of CD patients was subtractively hybridized. Expression of FN, ED-A, and ED-B in frozen sections from intestinal mucosa was determined by immunohistochemistry. The mRNA expression of the FN isoforms in control, CD, and fibrosis biopsies was quantified by real-time polymerase chain reaction (PCR). Integrin alpha5beta1 protein and mRNA expression was analyzed by fluorescence activated cell sorting (FACS) and PCR, respectively.

RESULTS

Subtractive hybridization indicated differential regulation of FN isoform expression in CD. The immunohistochemical analysis of FN protein revealed a reduction of FN isoforms in inflamed CD mucosa compared to control mucosa. In CD fistulae, the ED-A and ED-B isoforms were virtually absent. In fibrotic mucosa, both proteins were increased. Real-time PCR showed a decrease of FN and ED-A expression during mucosal inflammation in CD in contrast to UC and a significant increase of FN and isoforms in CD fibrosis. No difference was found for protein and mRNA of integrin alpha5beta1 in control, CD, and fibrosis CLPF by FACS and PCR.

CONCLUSION

Downregulated expression of migration-inducing FN-isoforms in contrast to unchanged FN receptor expression may contribute to the observed alterations of CD CLPF migration.

Levels of extra domain A containing fibronectin in human atherosclerotic plaques are associated with a stable plaque phenotype

BACKGROUND

Extra domain A (EDA), splice-variant of fibronectin, is a Toll-like receptor 4 (Tlr4) ligand. Recently, EDA has been demonstrated to enhance atherogenesis in mice but human data on the role of EDA in atherosclerotic disease are lacking. We hypothesized that EDA is associated with unstable plaque phenotypes and that plasma EDA could serve as biomarker for atherosclerosis.

METHODS

EDA levels were assessed in carotid endarterectomy specimen (206 patients) and related with plaque phenotype. In a second patient cohort, systemic EDA levels in atherosclerotic patients (73 patients) were compared to risk-factor matched controls (68 patients).

RESULTS

EDA plaque levels were associated with characteristics of stable plaques; more smooth muscle cells (P=0.003), more collagen (P=0.071) and less fat (P=0.023). Concomitantly, asymptomatic patients showed higher EDA values in the plaque compared to symptomatic patients (P=0.004). EDA plasma levels did not differ between atherosclerotic patients versus controls (P=0.134).

CONCLUSION

EDA plaque levels are higher in asymptomatic patients and are associated with a stable plaque phenotype. EDA is not a plasma marker for atherosclerotic disease. These results suggest that local presence of endogenous Tlr4 ligand EDA is not associated with in an unstable plaque phenotype in humans.

INHIBITION OF NAD(P)H OXIDASE REDUCES FIBRONECTIN EXPRESSION IN STROKE-PRONE RENOVASCULAR HYPERTENSIVE RAT BRAIN

1. The aim of the present study was to test the hypothesis that in vivo chronic inhibition of NAD(P)H oxidase reduces cerebrovascular fibronectin expression in stroke-prone renovascular hypertensive rats (RHRSP). 2. The RHRSP model was induced by two clips and NAD(P)H oxidase was inhibited with apocynin. The mRNA and protein expression of NAD(P)H oxidase subunit p22(phox) in brains of RHRSP and Sprague-Dawley (control) rats was determined using real-time reverse transcription-polymerase chain reaction, western blot and immunohistochemistry. The expression of fibronectin protein was localized immunohistochemically in cerebral vessels and then quantified by western blot. 3. Cerebrovascular fibronectin levels in RHRSP (n = 6) were significantly higher than control (n = 5) levels 8 weeks after operation (1.29 +/- 0.04 vs 1.15 +/- 0.02, respectively; P = 0.007). The p22(phox) immunopositive reactivity was localized in the cerebral vasculature of control rats and RHRSP. Furthermore, chronic treatment of RHRSP with apocynin, a selective NAD(P)H oxidase inhibitor, in the drinking water for 4 weeks (1.5 mmol/L, 5 weeks after operation) resulted in a significant decrease in the expression of p22(phox) protein (0.85 +/- 0.01 vs 0.93 +/- 0.01 in non-treated RHRSP; n = 5; P = 0.002), with a concomitant reduction of fibronectin levels in the cerebral vasculature (1.31 +/- 0.03 vs 1.56 +/- 0.05 in non-treated RHRSP; n = 5; P = 0.002). No significant differences were detected in the expression of p22(phox) mRNA and protein between RHRSP (4 and 8 weeks after renal artery constriction) and the control group. 4. These findings suggest that the chronic inhibition of NAD(P)H oxidase in vivo by apocynin reduces cerebrovascular fibronectin levels, which may lessen hypertensive cerebrovascular fibrosis.

αV Integrins Are Necessary for Eutrophic Inward Remodeling of Small Arteries in Hypertension

Human essential hypertension is characterized by eutrophic remodeling of small arteries, with little evidence of hypertrophy. Likewise, vessels of young hypertensive TGR(mRen2)27 animals have undergone similar structural alterations. The role of integrins in resistance arteries of TGR(mRen2)27 during the eutrophic-remodeling process was examined as blood pressure rose. Initially, 8 alpha and 3 beta integrins were identified and levels of expression investigated using RT-PCR. As pressure increased and remodeling advanced, integrin expression profiles revealed that only alphaV was significantly raised. In conjunction, we confirmed elevated integrin alphaV protein levels in TGR(mRen2)27 rat arteries and localization to the media using immunofluorescence. beta1 and beta3, but not beta5 integrin subunits were coprecipitated with integrin alphaV and are implicated in the eutrophic remodeling process. Administration of a peptide antagonist of alphaVbeta3 abolished remodeling but enhanced growth, indicating that hypertrophy supervened as a response to hypertension-induced increases in wall stress. We have established that the only upregulated integrin, the alphaV subunit of integrin alphaVbeta3, has a crucial role in the hypertensive remodeling process of TGR(mRen2)27 rat resistance arteries. During hypertensive remodeling, functions of specific alphaVbeta3-extracellular matrix interactions are likely to allow vascular smooth muscle cell-length autoregulation, which includes a migratory process, to maintain a narrowed lumen after a prolonged constricted state.

Prediction of Cerebral Vasospasm in Patients Presenting with Aneurysmal Subarachnoid Hemorrhage: A Review

OBJECTIVE:

Cerebral vasospasm is a devastating medical complication of aneurysmal subarachnoid hemorrhage (SAH). It is associated with high morbidity and mortality rates, even after the aneurysm has been treated. A substantial amount of experimental and clinical research has been conducted in an effort to predict and prevent its occurrence. This research has contributed to significant advances in the understanding of the mechanisms leading to cerebral vasospasm. The ability to accurately and consistently predict the onset of cerebral vasospasm, however, has been challenging. This topic review describes the various methodologies and approaches that have been studied in an effort to predict the occurrence of cerebral vasospasm in patients presenting with SAH.

METHODS:

The English-language literature on the prediction of cerebral vasospasm after aneurysmal SAH was reviewed using the MEDLINE PubMed (1966–present) database.

RESULTS:

The risk factors, diagnostic imaging, bedside monitoring approaches, and pathological markers that have been evaluated to predict the occurrence of cerebral vasospasm after SAH are presented.

CONCLUSION:

To date, a large blood burden is the only consistently demonstrated risk factor for the prediction of cerebral vasospasm after SAH. Because vasospasm is such a multifactorial problem, attempts to predict its occurrence will probably require several different approaches and methodologies, as is done at present. Future improvements in the prevention of cerebral vasospasm from aneurysmal SAH will most likely require advances in our understanding of its pathophysiology and our ability to predict its onset.

Direct test of potential roles of EIIIA and EIIIB alternatively spliced segments of fibronectin in physiological and tumor angiogenesis

Fibronectin splice variants containing the EIIIA and/or EIIIB exons are prominently expressed in the vasculature of a variety of human tumors but not in normal adult tissues. To understand the functions of these splice variants in physiological and tumor angiogenesis, we used EIIIB-null and EIIIA-null strains of mice to examine neovascularization of mouse retinas, pancreatic tumors in Rip-Tag transgenic mice, and transplanted melanomas. Contrary to expectations, physiological and tumor angiogenesis was not significantly affected by the absence of either EIIIA or EIIIB splice variants. Tumor growth was also not affected. In addition, the expression levels of smooth muscle alpha actin, believed to be modulated by EIIIA-containing fibronectins, were not affected either. Our experiments show that despite their tight regulation during angiogenesis, the presence of EIIIA or EIIIB splice variants individually is not essential for neovascularization.

Endothelial cell activation after subarachnoid hemorrhage

OBJECTIVE

Evidence from animal experiments suggests that endothelial cell activation plays a pathogenetic role in the development of cerebral ischemia after subarachnoid hemorrhage (SAH). We measured plasma concentrations of two markers of endothelial cell activation, i.e., ED1-fibronectin (ED1-fn) and von Willebrand factor (vWf), among patients with aneurysmal SAH. We analyzed the relationships of concentrations to initial clinical conditions, treatment modalities, and the occurrence of delayed cerebral ischemia.

METHODS

We collected 123 blood samples from 27 patients with aneurysmal SAH. Aneurysms were treated surgically in 19 cases, were treated endovascularly in 7 cases, and remained untreated in 1 case. Twelve patients developed symptomatic delayed cerebral ischemia.

RESULTS

Initial concentrations of ED1-fn (4.3 +/- 3.7 microg/ml) and vWf (17.8 +/- 8.2 microg/ml) were higher than the reference values (ED1-fn, 1.7 +/- 0.9 microg/ml, P < 0.001; vWf, 11.5 +/- 5.2 microg/ml, P = 0.003). Concentrations were higher among patients in poor clinical condition at admission, compared with patients in good clinical condition (mean difference, ED1-fn, 5.7 microg/ml, P = 0.04; vWf, 10.4 microg/ml, P = 0.02). Levels of both markers increased significantly after surgery (mean increase, ED1-fn, 7.5 microg/ml, P = 0.01; vWf, 13.2 microg/ml, P = 0.05) and after ischemic episodes (mean increase, ED1-fn, 8.3 microg/ml, P = 0.02; vWf, 5.0 microg/ml, P = 0.04).

CONCLUSION

Plasma concentrations of markers of endothelial cell activation were increased early after SAH and were significantly associated with the clinical condition at admission. We also observed a significant increase in concentrations after surgery and after ischemic episodes. Whether endothelial cell activation is a causal or indirectly related factor in the pathogenesis of delayed cerebral ischemia after SAH is still uncertain.

The EIIIA segment of fibronectin is a ligand for integrins alpha 9beta 1 and alpha 4beta 1 providing a novel mechanism for regulating cell adhesion by alternative splicing

Alternative splicing of the fibronectin gene transcript gives rise to forms that include the EIIIA (or ED-A) segment. EIIIA-containing fibronectins are prominently expressed during embryogenesis and wound healing and appear to mediate changes in cell adhesion and gene expression. Nonetheless, integrins that bind the EIIIA segment have not been identified. We previously mapped the epitope for two function-blocking monoclonal antibodies to the C-C' loop region of the EIIIA segment (Liao, Y.-F., Wieder, K. G., Classen, J. M., and Van De Water, L. (1999) J. Biol. Chem. 274, 17876-17884). The sequence of this epitope ((39)PEDGIHELFP(48)) resembles the sequence within tenascin-C to which the integrin alpha(9)beta(1) binds. We now report that either integrin alpha(9)beta(1) or alpha(4)beta(1) can mediate cell adhesion to the EIIIA segment. Moreover, this interaction is blocked both by epitope-mapped EIIIA antibodies as well as by the respective anti-integrins. Deletion mutants of the EIIIA segment that include the C-C' loop and flanking sequence bind cells expressing either alpha(9)beta(1) or alpha(4)beta(1). Adhesion of alpha(4)beta(1)-containing MOLT-3 cells to the EIIIA segment stimulates phosphorylation of p44/42 MAP kinase. Our observation that two integrins bind the EIIIA segment establishes a novel mechanism by which cell adhesion to fibronectin is regulated by alternative splicing.

Expression of fibronectin splice variants in the postischemic rat kidney

Using an in vivo rat model of unilateral renal ischemia, we previously showed that the expression and distribution of fibronectin (FN), a major glycoprotein of plasma and the extracellular matrix, dramatically changes in response to ischemia-reperfusion. In the distal nephron in particular, FN accumulates in tubular lumens, where it may contribute to obstruction. In the present study, we examine whether the tubular FN is the plasma or cellular form, each of which is produced by alternative splicing of a single gene transcript. We demonstrate that FN in tubular lumens does not contain the extra type III A (EIIIA) and/or the extra type III B (EIIIB) region, both of which are unique to cellular FN. It does, however, contain the V95 region, which in the rat is a component of FNs in both plasma and the extracellular matrix. Expression of FN containing EIIIA increases dramatically in the renal interstitium after ischemic injury and continues to be produced at high levels 6 wk later. V95-containing FN also increases in the interstitial space, albeit more slowly and at lower levels than FN containing EIIIA; it also persists 6 wk later. FN containing the EIIIB region is not expressed in the injured kidney. The presence of V95 but not the EIIIA or EIIIB regions of FN in tubular lumens identifies the origin of FN in this location as the plasma; tubular FN is ultimately voided in the urine. The data indicate that both plasma and cellular FNs containing the V95 and/or EIIIA regions may contribute to the pathogenesis of acute renal failure and to the repair of the injured kidney.

Plasma fibronectin levels in ischemic heart disease

Fibronectin is a paradigm adhesive protein which has been implicated in the regulation of several cellular processes and cell-cell interactions. Large amounts of fibronectin have been detected in atherosclerotic plaques, while hypertension in animal models has been shown to rapidly increase fibronectin expression in arterial walls. The aim of the present study was to determine the levels of plasma fibronectin (FN) in 133 patients with ischemic heart disease and in 36 normal controls, and to investigate the possible association with blood pressure. Plasma FN levels in patients with ischemic heart disease were found to be significantly elevated (mean+/-S.D.; 46.5+/-14.2 mg/dl) compared with the control group (38.0+/-14.2 mg/dl) (P=0.002). Plasma FN concentrations were significantly different between the hypertensive group (52.9+/-14.5 mg/dl) and the normal blood pressure group (41.4+/-11.8 mg/dl) among the patients with ischemic heart disease (P<0.001). Plasma FN concentration was positively correlated with total cholesterol, triglyceride, systolic blood pressure and body mass index. In conclusion, the plasma fibronectin level may have pathogenetic implications in association with lipid components and blood pressure in patients with ischemic heart disease.

Identification of two amino acids within the EIIIA (ED-A) segment of fibronectin constituting the epitope for two function-blocking monoclonal antibodies

Alternative splicing of the fibronectin gene transcript gives rise to a group of adhesive glycoproteins showing restricted spatial and temporal expression during embryonic development, tumor growth, and tissue repair. Alternative splicing occurs in three segments termed EIIIB, EIIIA, and V. The EIIIA (or ED-A) segment of fibronectin is expressed prominently but transiently in healing wounds coincident with fibroblast expression of an activation marker, smooth muscle cell alpha-actin. A monoclonal antibody (IST-9) to the EIIIA segment blocks transforming growth factor-beta-mediated smooth muscle cell alpha-actin expression by fibroblasts in culture. A second monoclonal antibody (DH1) blocks chondrocyte condensation in chicken embryos. We find that IST-9 and DH1 react with human, rat, and chicken but not with mouse or frog EIIIA, suggesting that His44 may be important for antibody binding. A series of deletion mutants of rat EIIIA, constructed as glutathione S-transferase fusion proteins, do not react with either IST-9, DH1, or a third monoclonal antibody (3E2). Mutations of pairs of amino acids to alanine have little effect, except for either (Val34Thr35) or (Tyr36Ser37), which are located in a beta strand upstream from His44. For these double mutants, the binding to all three monoclonal antibodies is markedly reduced. By contrast, single mutants at Thr35, Tyr36, or Ser37 retain full activity, suggesting that the epitope for these antibodies is determined in part by conformation. Alanine-scanning mutagenesis of rat EIIIA demonstrates the importance of Ile43 and His44 for binding. Mutation of frog EIIIA (normally Val43Lys44) to rat (Ile43His44) is sufficient to restore fully IST-9 binding and much of the activity of DH1 and 3E2. Our findings demonstrate that the function-blocking antibodies, IST-9 and DH1, bind to the Ile43 and His44 residues in a conformationally dependent fashion, implicating the loop region encompassing both residues as critical for mediating EIIIA function.

Prevention of arterial structural alterations with verapamil and trandolapril and consequences for mechanical properties in spontaneously hypertensive rats

We compared the chronic effects in spontaneously hypertensive rats (SHR) of low doses of an angiotensin converting enzyme inhibitor, trandolapril, a Ca2+ channel antagonist, verapamil, and their combination (trandolapril-verapamil), on arterial mechanical properties, arterial wall hypertrophy and extracellular matrix proteins. Four-week-old SHR were randomly allocated to oral treatment with verapamil (50 mg kg(-1) day(-1)), trandolapril (0.3 mg kg(-1) day(-1)), the combination of verapamil (50 mg kg(-1) day(-1)) plus trandolapril (0.3 mg kg(-1) day(-1)), or placebo for 4 months. A group of Wistar Kyoto (WKY) control rats received placebo for the same period of time. At the end of the treatment, mean blood pressure was lower in verapamil-trandolapril than in trandolapril SHR, but remained higher than in WKY. Verapamil had no effects on blood pressure. Equivalent reduction in aortic wall hypertrophy was obtained in all treated SHR. Trandolapril and verapamil-trandolapril combination produced a significant reduction of aortic collagen density compared with placebo SHR. Carotid total fibronectin, EIIIA fibronectin isoform and alpha5beta1 integrin, were higher in the media of placebo SHR than in WKY. EIIIA fibronectin isoform and alpha5beta1 integrin were reduced in verapamil-SHR compared with placebo-SHR and normalized in trandolapril and verapamil-trandolapril-SHR compared with WKY. SHR-placebo and SHR treated with either verapamil or trandolapril as single-drug treatment showed a 4-fold increase in total fibronectin compared to the WKY. Only SHR treated with verapamil-trandolapril combination had total fibronectin not significantly different from that of WKY. Carotid arterial distensibility increased only in verapamil-trandolapril treated rats. Multivariate analysis showed arterial distensibility to be negatively correlated to mean blood pressure (P < 0.0001) and total fibronectin (P < 0.01). In conclusion, chronic treatment with the verapamil-trandolapril combination significantly improved in vivo arterial distensibility in SHR. The most important effects of the combination on arterial mechanics compared to those of verapamil or trandolapril alone may have been the consequence of its stronger action on arterial pressure, arterial wall hypertrophy and total fibronectin density. However we suggest that, in addition to the structural effects, complete normalization of blood pressure is necessary to obtain normal arterial distensibility.

Mechanism of angiotensin II-mediated regulation of fibronectin gene in rat vascular smooth muscle cells

This study was performed to investigate a mechanism of angiotensin II (Ang II)-mediated activation of the fibronectin (FN) gene in rat vascular smooth muscle cells. Actinomycin D and CV11974 completely inhibited Ang II-mediated increase in FN mRNA levels. Inhibitors of protein kinase C (PKC), protein-tyrosine kinase (PTK), phosphatidylinositol-specific phospholipase C, Ras, phosphatidylinositol 3-kinase, p70 S6 kinase, and Ca2+/calmodulin kinase also decreased Ang II-induced activation of FN mRNA. In contrast, cycloheximide; PD123319; or inhibitors of Gi, protein kinase A, or mitogen-activated protein kinase kinase did not affect the induction. FN promoter contained a putative AP-1 binding site (rFN/AP-1; -463 to -437), and the results of a transient transfection and electrophoretic mobility shift assay showed that Ang II enhanced rFN/AP-1 activity. CV11974 and inhibitors of PKC or PTK suppressed Ang II-mediated increases in rFN/AP-1 activity, although neither PD123319 nor a protein kinase A inhibitor affected the induction. Furthermore, mutation of rFN/AP-1 that disrupted nuclear binding suppressed Ang II-induced transcription in the native FN promoter (-1908 to +136) context. Thus, Ang II activates transcription of the FN gene through the Ang II type 1 receptor in vascular smooth muscle cells, at least in part, via the activation of AP-1 by a signaling mechanism dependent on PKC and PTK.

Fibronectin expression and aortic wall elastic modulus in spontaneously hypertensive rats

Recent studies have shown that large-artery wall remodeling per se does not reduce distensibility in hypertension, indicating qualitative or quantitative changes in arterial components. The aim of the study was to determine in 1-year-old spontaneously hypertensive rats (SHRs) the changes in the elastic properties of large arteries, as assessed by the incremental elastic modulus (E(inc)), and the changes in the extracellular matrix, including fibronectin (FN) and alpha5beta1-integrin. The relationship between E(inc) and circumferential wall stress was calculated from in vivo pulsatile changes in blood pressure and arterial diameter by using a high-resolution echo-tracking system at the site of the abdominal aorta and in vitro medial cross-sectional area. E(inc)-stress curves and FN and integrin alpha5-subunit contents were determined for each animal. Mean stress and E(inc) were higher in SHRs than in Wistar rats. However, in a common range of stress, E(inc)-stress curves for SHRs were superimposable on those for Wistar rats, indicating that wall materials in both strains have equivalent mechanical behavior. Immunohistochemistry indicated that total FN, EIIIA FN isoform, and alpha5-integrin increased in the SHRs aortas without changes in elastin and collagen densities. Total FN was also increased in SHRs as determined by Western blot analysis. No differences in FN and alpha5-subunit mRNAs were detected between SHRs and Wistar rats. These results indicate that the aortic wall material of SHRs and Wistar rats have equivalent mechanical properties, although in SHRs it is subjected to a higher level of stress. By increasing cell-matrix attachment sites, FN may participate in the mechanical adaptation of both cellular and matrix components in SHRs.

The extracellular matrix in balloon arterial injury: a novel target for restenosis prevention

The role of the extracellular matrix (ECM) in the pathobiology of restenosis has not been fully appreciated. Recent discoveries have shown the ECM to be a complex, heterogeneous structure whose components are dynamically altered in response to vascular injury. This report reviews the structure and function of vascular ECM and the importance of the matrix in modulating the vascular response to arterial injury such as balloon angioplasty and atherosclerosis.

Progression of glomerulosclerosis, renal hypertrophy, and an increased expression of fibronectin in the renal cortex associated with aging and salt-induced hypertension in Dahl salt-sensitive rats

Aging and hypertension are known to be closely related with the pathogenesis and development of glomerulosclerosis. In this study, we examined the time course changes in the glomerulus associated with salt-induced hypertension using the inbred Dahl salt-sensitive rats. For this purpose, 5-week-old Dahl salt-sensitive rats (n=36) were fed either 4% NaCl diet (n=18) or 0.3% NaCl diet (n=18) up to 17 weeks of age. The high salt diet caused a dramatic increase in systolic blood pressure and also a dramatic renal hypertrophy as shown by a significant increase in the kidney weight. Histological examination revealed an age-dependent progression of glomerulosclerosis as documented by a quantitative scoring. This age-dependent progression was further accelerated by the co-existence of salt-induced hypertension in the high salt diet group. Northern blot analysis revealed an increase in the steady state mRNA levels of fibronectin, an important component of mesangial matrices, in the renal cortex, but not in the renal medulla, only in salt-loaded Dahl salt-sensitive rats. These findings indicate that salt-induced hypertension accelerates the age-dependent progression of glomerulosclerosis in Dahl salt-sensitive rats, and fibronectin may play a role in the pathogenesis, development, and progression of glomerulosclerosis associated with salt-induced hypertension.

Effect of nitric oxide on DNA replication induced by angiotensin II in rat cardiac fibroblasts

Our previous in vivo studies (Hou et al. J Clin Invest. 1995;96:2469-2477.) demonstrated that chronic inhibition of nitric oxide synthase led to an exaggerated response to relatively low doses of angiotensin II, resulting in a rapid and marked cardiac fibrosis. To examine further the importance of angiotensin II in inducing cardiac fibrosis and the possibility that nitric oxide serves as a modulator of the proliferative effects of angiotensin II, we used cultured rat cardiac fibroblasts to study the interrelationships between these substances. Angiotensin II induced a delayed DNA synthetic response in quiescent cells that occurred 30 hours after exposure to the hormone. The most pronounced effect of angiotensin II on thymidine uptake occurred 36 to 42 hours after the addition to cells. This response was inhibited in a dose-dependent manner by the addition of either S-nitroso-N-acetylpenicillamine or sodium nitroprusside, each a source of nitric oxide. The nitric oxide donor was most effective in reducing thymidine incorporation when added 12 hours after angiotensin II, whereas the metabolite N-acetylpenicillamine had no effect at any time. The inhibitory effect of S-nitroso-N-acetylpenicillamine was mimicked by 8-bromoguanosine 3':5'-cyclic monophosphate but not by 8-bromoadenosine 3':5'-cyclic monophosphate. Nitric oxide donors did not appear to inhibit the induction of c-fos, Egr-1, or other immediate-early genes in response to angiotensin II. The results suggest that nitric oxide affects the cell cycle following the transition into G, and modulates the proliferation of fibroblasts during cardiac fibrosis induced by angiotensin II.

Expression and splicing of the fibronectin gene in healthy and diseased periodontal tissue

Fibronectin is a major component of the extracellular matrix and is considered to have an important role in chronic inflammatory periodontal disease. The fibronectin gene product has been shown to be subject to alternative splicing in 3 regions, each generating different mRNA transcripts associated specifically with normal adult tissue, embryogenesis, tissue regeneration, and wound healing. In the present study, using the reverse-transcribed polymerase chain reaction to examine splicing profiles of the primary transcript, we found that healthy periodontal tissue expressed all alternatively spliced embryonic isoforms, indicative of the extensive and ongoing rebuilding processes which occur in these tissues. In marked contrast, only the exon-skipped transcripts were generated in tissue from chronic inflammatory periodontal disease patients. The loss of the high molecular weight isoforms in lesional tissues may be due to the excess production of inflammatory mediators in this disease, since we observed that high concentrations of the cytokine IL-1beta caused down-regulation of these transcripts in normal periodontal cells in tissue culture. Moreover, we also demonstrated that growth factors likely to be involved in periodontal regeneration and repair, such as PDGF, IGF-1 and TGF-beta, elicited pronounced upregulation of the embryonic isoforms of fibronectin in these cells. Although the functional activities of the antigens corresponding to the alternatively spliced variants of fibronectin are not yet known, our finding that they are selectively expressed suggests that they have highly specific roles in both periodontal breakdown and repair.

Glomerular up-regulation of EIIIA and V120 fibronectin isoforms in proliferative immune complex nephritis

Fibronectin: (FNs) comprise a family of adhesive glycoproteins that are prominent components of mesangial extracellular matrix and accumulate during glomerular injury. By alternative splicing of an unique mRNA precursor, various FN isoforms can be originated. In rat, three regions of the molecule are involved: EIIIA, EIIIB and V. Because specific FN isoforms are expressed in embryogenesis and wound healing, conditions characterized by cell migration and adhesion, we examined the pattern of FN isoforms in the mild and severe phases of a progressive immune complex proliferative nephritis in rats. We constructed specific probes to analyze the splicing pattern of FN pre-mRNAs by ribonuclease protection assays. FN mRNAs containing EIIIA, EIIIB and V regions increased along, the progression of nephritis, though the increment of EIIIB-FN mRNA was modest. However, different regulation of all these isoforms was observed. The percentage of FN mRNA containing the EIIIA exon versus total FN increased with the severity of the disease, while the percentage of FN mRNA containing the EIIIB exon decreased. Relative V-FN mRNA expression versus total FN mRNA increased only in the severe phase. By means of specific antibodies we also studied the presence of EIIIA, EIIIB and V-FN proteins in the kidney. In the normal glomerutus, EIIIA-FN protein was barely detectable in the mesangium, increasing in the mild phase of nephritis. In the severe phase of nephritis, increased EIIIA-FN was localized in the mesangium, in Bowman's capsule and in crescents. By contrast, EIIIB-FN protein in the glomerulus was absent even in the severe phase. V120-FN protein, an isoform that mediates the attachment of leukocytes through the VLA-4 integrin, was present in the mesangium and glomerular capillary loops in control animals, and increased in the severe phase of nephritis, coinciding with a strong leukocyte infiltration. In conclusion, our results show that during immune glomerular injury there were marked changes in the pattern of FN isoforms expression. Since those isoforms, particularly V120 isoform, are important in cell adhesion and migration, their up-regulation may facilitate the recruitment of cells into the injured glomeruli. The blockade of the interaction between V120-FN and infiltrating leukocytes may represent a new approach to the treatment of nephritis.

Temporal alterations in basement membrane components in the pulmonary vasculature of the chronically hypoxic rat: impact of hypoxia and recovery

The hypoxic model of pulmonary hypertension was used to examine temporal alterations in the deposition of the basement membrane (BM) and components of fibronectin, laminin, and Type IV collagen within vascular, airway, and gas exchange compartments of the lung. Because hypoxic pulmonary hypertension is a reversible model of hypertension, changes in fibronectin and laminin synthesis/deposition in the recovering lung were also examined. Long-term hypoxic exposure produced decreases in body weight, increased right ventricular and lung dry weights and elevations in pulmonary arterial pressure. Immunohistochemical analysis revealed consistent and progressive increases in the deposition of fibronectin and laminin, but not type IV collagen, in the subendothelial and medial BMs of large and small pulmonary arteries, but not in airways or lung parenchyma. These changes were observed by day 4 of hypoxia and were most prominent in the conducting vasculature. Northern analysis showed a biphasic pattern of alterations in steady-state levels of BM component mRNA in hypoxic rats with early reductions at days 4 and 7 followed by increases at day 12. Recovery from 12 days of hypoxia resulted in regression of pulmonary hypertension and right ventricular hypertrophy but not increased lung weight. Immunohistochemical analysis of fibronectin, laminin, and type IV collagen levels in the vasculature showed a temporal regression to levels that were not remarkably different from time-matched controls at day 30 of recovery. Northern analysis of lungs from hypoxic-recovery rats revealed increased steady-state levels of mRNA for fibronectin, laminin, and type IV collagen at all time points. These data indicate that long-term hypoxic exposure elicits marked alterations in the synthetic capacity and deposition of the important cell attachment BM glycoproteins fibronectin and laminin. In addition, recovery from hypoxia appears to be characterized by a lack of increased fibronectin and laminin levels in the conducting vasculature, suggesting a marked and rapid reorganization of the vascular BMs on both hypoxic exposure and recovery from hypoxia.

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.

RGD-containing peptides induce endothelium-dependent and independent vasorelaxations of rat aortic rings

Peptides containing the extracellular matrix peptide cell attachment sequence RGD possess potent, endothelium-dependent vasorelaxant properties. In the present study, the ability of RGD-containing peptides to cause vasorelaxation in the presence and absence of a functional endothelium was examined in rat aortic rings along with the ability of RGD-containing peptides to increase cGMP production in these vessels. The active RGD-containing peptide GRGDNP induced rapid relaxation in endothelium-intact, norepinephrine contracted rat aortic rings. When the endothelium was removed, RGD-containing peptides produced a slow relaxation of contracted rings which took approx. 40 min to reach maximum relaxation. Control RGD peptides were without effect either in the presence or absence of a functional endothelium. While acetylcholine and sodium nitroprusside stimulated cGMP production in endothelium-intact and denuded aortic segments, neither the control RGD peptide nor the active GRGDNP increased cGMP in these vessels when compared to controls upon either short (30 s) or long (45 min) incubation times. These data indicate that relaxations of rat aortic rings in response to RGD-containing peptides occur both in the presence and absence of an intact endothelium and that cGMP is likely not the sole mediator of these responses.

Salicylate or aspirin inhibits the induction of the inducible nitric oxide synthase in rat cardiac fibroblasts

To determine if fibroblasts are a source of NO inflammatory myocardial diseases, we have studied the effect of cytokines on the inducible NO synthase (iNOS) in neonatal cardiac fibroblasts and tested whether nonsteroidal anti-inflammatory drugs can diminish the induction of iNOS. In primary cultures, interferon gamma (IFN), interleukin-1 beta (IL-1), or tumor necrosis factor-alpha (TNF) separately did not stimulate nitrite production, whereas IFN combined with IL-1 or TNF synergistically induced iNOS, both at the level of steady state mRNA and nitrite accumulation. Steady state mRNA levels for iNOS were obvious as early as 3 hours after the addition of IFN + TNF and remained elevated for at least 72 hours. Sodium salicylate inhibited cytokine-induced nitrite accumulation in a time- and dose-dependent manner (IC50, 750 mumol/L). The inhibition was reversible and occurred when salicylate was added either before or after cytokine induction. Aspirin (1 mmol/L) also inhibited nitrite production, whereas indomethacin (25 mumol/L) or acetaminophen (100 mumol/L) did not. TNF, either alone or combined with IFN, significantly stimulated prostaglandin E2, which was inhibited by either salicylate (4 mmol/L) or indomethacin (25 mumol/L). Salicylate, when given either before or after IFN + TNF, reduced mRNA levels of iNOS induced by cytokines. Salicylate did not affect iNOS enzymatic activity when added to the cytosolic lysate, although it was able to reduce enzymatic activity to 32% of induced levels when given to intact cells. These studies implicate cardiac fibroblasts as a source of NO in inflammatory cardiac diseases and suggest a possible therapeutic role for salicylate and aspirin in diminishing the steady state levels of iNOS mRNA.

Balloon catheterization induced arterial expression of embryonic fibronectins

Fibronectins (FNs) comprise a family of adhesive extracellular matrix proteins that arise by alternative splicing in three regions: V (IIICS), EIIIA (ED-A), and EIIIB (ED-B). FNs bearing the EIIIA and EIIIB segments are prevalent during embryogenesis, expressed to lesser degrees in normal adult tissues, and may be locally reexpressed at adult tissue injury. RNase mapping shows that normal rat arteries express low levels of FNs that are predominantly EIIIA- and EIIIB-. Following balloon injury, arterial walls produce increased total levels of FN transcripts that preferentially include both the EIIIA and EIIIB segments. However, despite inducing increased total FN mRNA, balloon injury does not alter the relative composition of V120+, V95+, AND V0 spliced forms. In situ hybridization reveals that as early as 4 days after injury medial cells express increased total FN mRNA, and by 7 days substantial neointimal and focal medial synthesis of EIIIA+, EIIIB+, and V120+ FNs occurs; macrophages do not significantly contribute to this observed vascular FN synthesis. Consistent with the mRNA data, immunofluorescence microscopic analysis reveals increased deposition of EIIIB+ and V+ FN protein forms in injured arterial walls, particularly within the neointima. Our results suggest that local synthesis of specific FN isoforms is important to the neointimal formation that ensues after balloon injury.

Differential effects of pressure and flow on DNA and protein synthesis and on fibronectin expression by arteries in a novel organ culture system

Structural adaptation of the blood vessel wall occurs in response to mechanical factors related to blood pressure and flow. To elucidate the relative roles of pressure, flow, and medium composition, we have developed a novel organ culture system in which rabbit thoracic aorta, held at in vivo length, can be perfused and pressurized at independently varied flow and pressure for several days. Histology and histomorphometry, as well as scanning electron microscopy, revealed a well-preserved wall structure. In arteries perfused and pressurized at 80 mm Hg, endothelial injury led to a 2-fold increase in [3H]thymidine incorporation in the media, which peaked at 3 to 5 days and returned to baseline level at 6 to 8 days. In intact endothelialized vessels cultured for 3 days under no-flow conditions, pressure per se had no effect on DNA synthesis. In contrast, in the presence of serum, total protein synthesis, as assessed by [35S]methionine incorporation into the media, was enhanced 6-fold at 150 mm Hg compared with vessels pressurized at 0 or 80 mm Hg. In intact vessels perfused at a constant flow of 40 mL/min for 3 days, DNA synthesis was unchanged regardless of the pressure level when vessels were cultured in the presence of serum but increased 8-fold at both 80 and 150 mm Hg in the absence of serum. Unlike DNA synthesis, total protein synthesis was enhanced 12-fold by flow regardless of the presence or absence of serum. Expression of fibronectin was markedly enhanced at high transmural pressure, and serum potentiated its expression in the arterial wall. This novel organ culture system of perfused and pressurized vessels allowed identification of differential effects of pressure, flow, and serum on DNA and total protein synthesis, including cellular fibronectin expression.

Accumulation of fetal fibronectin mRNAs after balloon denudation of rabbit arteries

BACKGROUND

Fibronectin (FN), a component of the extracellular matrix, influences cellular migration and differentiation. It is a prominent component of the extracellular matrix of normal arteries and is thought to play an important role in the pathogenesis of restenosis after angioplasty. FN exists in multiple forms that arise from a single RNA transcript that can be alternatively spliced. EIIIA- and EIIIB-containing FN mRNAs predominate in the embryo, whereas in the adult, most of the normal tissue FN lacks these domains. Since few data were available concerning pattern of expression of the different alternatively spliced forms of FN mRNA in arteries after endoluminal injury, we analyzed the expression of EIIIA and EIIIB FN isoforms at different times after experimental angioplasty.

METHODS AND RESULTS

The spatial and temporal alterations in FN expression were studied in an in vivo model of endothelial denudation in the rabbit aorta and iliac artery by a combination of immunochemistry and in situ hybridization methods. Alternatively spliced forms of FN EIIIA and EIIIB were detected in the media and the adventitia of both types of vessels 24 to 48 hours after injury. Two weeks after injury, EIIIA and EIIIB mRNAs were found to accumulate within the luminal layers of the neointima. The cellular form of FN protein was not found until 2 weeks after the injury and accumulated in the inner part of the neointima.

CONCLUSIONS

These data demonstrate that FN upregulation is an early and long-lasting process after arterial injury. These results suggest that the induction of the embryonic FN isoforms may be involved in the restenotic process that follows balloon denudation of arteries.

Fibronectin expression during physiological and pathological cardiac growth

Fibronectin (FN) is a dimeric glycoprotein found in the extracellular matrix of most tissues that serves as a bridge between cells and the interstitial collagen meshwork and influences diverse processes including cell growth, adhesion, migration, and wound repair. Multiple FN forms arise by the alternative splicing of a primary transcript originating from a single gene. The spatial and temporal alterations in FN expression in the myocardium has been studied in models of cardiac growth in vivo such as fetal development, and hypertrophy secondary to pressure overload. This review focuses on the differential expression of FN isoforms that are observed in different models of cardiac growth. Using a combination of qualitative and quantitative analyses it is shown that in the rat myocardium: (1) the FN phenotype is developmentally regulated, (2) the re-expression of the fetal FN isoforms is observed in different models of cardiac hypertrophy secondary to a sudden or progressive hypertension and (3) the changes in cardiac FN expression affect mostly the coronary artery smooth muscle cells.

Role of angiotensin II in renal injury of deoxycorticosterone acetate-salt hypertensive rats

To investigate the role of angiotensin II (Ang II) in hypertension-induced tissue injury, we gave TCV-116 (1 mg/kg per day PO), a nonpeptide Ang II type I receptor antagonist, or enalapril (10 mg/kg per day PO) to deoxycorticosterone acetate (DOCA)-salt hypertensive rats for 3 weeks and examined the effects on tissue mRNA levels for transforming growth factor-beta 1 (TGF-beta 1) and extracellular matrix components. Tissue mRNA levels were measured by Northern blot analysis. Renal mRNA levels for TGF-beta 1; types I, III, and IV collagen; and fibronectin in DOCA-salt hypertensive rats were increased by severalfold (P < .01) compared with sham-operated rats. In the aorta of DOCA-salt hypertensive rats, TGF-beta 1 and fibronectin mRNA levels were increased, but types I, III, and IV collagen mRNAs did not increase. In the heart, increased mRNA was found only for fibronectin. Thus, these gene expressions are regulated in a tissue-specific manner. TCV-116 or enalapril did not lower blood pressure in DOCA-salt hypertensive rats. However, the increase in renal mRNAs for TGF-beta 1 and extracellular matrix components in DOCA-salt hypertensive rats was significantly inhibited by treatment with TCV-116 or enalapril, which was associated with a significant decrease in urinary protein and albumin excretions and histological improvement of renal lesions. In contrast, in the aorta and heart these gene expressions were not affected by TCV-116 or enalapril. Thus, local Ang II may contribute to renal injury of DOCA-salt hypertension by stimulating the gene expression of TGF-beta 1 and extracellular matrix components.

Angiotensin II alters aortic fibronectin independently of hypertension

We performed these studies to assess the potential role of hemodynamic forces in mediating the changes in aortic fibronectin mRNA expression that occur in the rat in response to angiotensin II administration. With the use of an acute hypertensive model involving a 3-day infusion with a pressor dose of angiotensin II given by osmotic minipump, a selective increase in fibronectin mRNA expression but not of several other extracellular matrix genes was documented. This change was inhibited by losartan, indicating the importance of angiotensin receptors in the response. Prazosin, hydralazine, or L-arginine added to the drinking water all lowered the angiotensin II-induced increase in blood pressure but did not attenuate the increase in fibronectin mRNA expression. Angiotensin-converting enzyme inhibition using trandolapril did reduce fibronectin mRNA in the angiotensin II-infusion model, despite an inability to reduce blood pressure, whereas when angiotensin I was infused, quinapril lowered both blood pressure and fibronectin expression even at doses that did not completely normalize blood pressure. These studies suggest that angiotensin II induced an increase in aortic fibronectin mRNA that was not dependent solely on blood pressure.

New perspectives in hypertension research. Potentials of vascular biology

The vessel wall was once considered to be a passive conduit responding to the circulating endocrine system. However, the emergence of molecular and vascular biology in hypertension research has redefined our understanding of the role of the vasculature as a vital organ in the pathogenesis of hypertension. It is now recognized that the vasculature can regulate its own tone by a variety of previously unknown autocrine and/or paracrine vasoactive systems. Recent evidence indicates that the process of vascular remodeling in hypertension appears to be mediated by locally generated factors within the vessel wall. This review examines the implications of this new paradigm in hypertension, focusing on five topics that have developed through the emergence of molecular vascular biology: the discovery and characterization of novel biologically active molecules synthesized by the vessel wall, the molecular mechanisms and consequences of vascular remodeling, the developmental biology of the blood vessel and the relation to pathobiology, the use of in vivo gene transfer to test hypotheses in vivo, and novel treatment strategies based on gene therapy of the vessel wall.

Selective induction of an embryonic fibronectin isoform in the rat aorta in vitro

The temporal changes in the expression of fibronectin and other extracellular matrix genes were studied in rat aortic rings incubated in vitro in a serum-free medium. Changes in all forms of fibronectin mRNA increased progressively during the 24-hour incubation period, although an increase in the alternatively spliced form of fibronectin designated EIIIA was most pronounced. Both collagen and elastin mRNA levels decreased markedly during the 24-hour interval, as did alpha-actin mRNA. The increase in the relative amount of the EIIIA isoform after a 24-hour incubation was also shown using ribonuclease protection assays. In situ hybridization showed the distribution of the induced fibronectin mRNA to be within all cell types, including endothelial cells, medial smooth muscle cells, and adventitial fibroblasts. Localization in the media was not uniform and was clearly identified mainly in clusters of cells distributed throughout the media. The early induction of fibronectin mRNA was inhibited by genistein, implicating tyrosine kinase activation as a causative factor in fibronectin expression. The in vitro changes reported may reflect a phenotypic change in vascular cell types that is both similar to and different from the changes reported in vivo under conditions in which vascular injury and repair occur.