Effect of hypertension on fibronectin expression in the rat aorta

Myocardial ischemia-reperfusion injury released cellular fibronectin containing domain A (CFN-EDA): A destructive positive loop amplifying arterial thrombosis formation and exacerbating myocardial reperfusion injury

Previous research has identified intravascular platelet thrombi in regions affected by myocardial ischemia-reperfusion (MI/R) injury and neighbouring areas. However, the occurrence of arterial thrombosis in the context of MI/R injury remains unexplored. This study utilizes intravital microscopy to investigate carotid artery thrombosis during MI/R injury in rats, establishing a connection with the presence of prothrombotic cellular fibronectin containing extra domain A (CFN-EDA) protein. Additionally, the study examines samples from patients with coronary artery disease (CAD) both before and after coronary artery bypass grafting (CABG). Levels of CFN-EDA significantly increase following MI with further elevation observed following reperfusion of the ischemic myocardium. Thrombotic events, such as thrombus formation and growth, show a significant increase, while the time to complete cessation of blood flow in the carotid artery significantly decreases following MI/R injury induced by ferric chloride. The acute infusion of purified CFN-EDA protein accelerates in-vivo thrombotic events in healthy rats and significantly enhances in-vitro adenosine diphosphate and collagen-induced platelet aggregation. Treatment with anti-CFN-EDA antibodies protected the rat against MI/R injury and significantly improved cardiac function as evidenced by increased end-systolic pressure-volume relationship slope and preload recruitable stroke work compared to control. Similarly, in a human study, plasma CFN-EDA levels were notably elevated in CAD patients undergoing CABG. Post-surgery, these levels continued to rise over time, alongside cardiac injury biomarkers such as cardiac troponin and B-type natriuretic peptide. The study highlights that increased CFN-EDA due to CAD or MI initiates a destructive positive feedback loop by amplifying arterial thrombus formation, potentially exacerbating MI/R injury.

Vascular smooth muscle stiffness and its role in aging

Vascular smooth muscle cells (VSMC) are now considered important contributors to the pathophysiological and biophysical mechanisms underlying arterial stiffening in aging. Here, we review mechanisms whereby VSMC stiffening alters vascular function and contributes to the changes in vascular stiffening observed in aging and cardiovascular disease. Vascular stiffening in arterial aging was historically associated with changes in the extracellular matrix; however, new evidence suggests that endothelial and vascular smooth muscle cell stiffness also contribute to overall blood vessel stiffness. Furthermore, VSMC play an integral role in regulating matrix deposition and vessel wall contractility via interaction between the actomyosin contractile unit and adhesion structures that anchor the cell within the extracellular matrix. Aged-induce phenotypic modulation of VSMC from a contractile to a synthetic phenotype is associated with decreased cellular contractility and increased cell stiffness. Aged VSMC also display reduced mechanosensitivity and adaptation to mechanical signals from their microenvironment due to impaired intracellular signaling. Finally, evidence for decreased contractility in arteries from aged animals demonstrate that changes at the cellular level result in decreased functional properties at the tissue level.

Age-Associated Changes in the Vascular Renin-Angiotensin System in Mice

Background. This study evaluated whether the change in the renin-angiotensin system (RAS) is associated with arterial aging in mice. Methods. Histologic changes and expressions of transforming growth factor-β (TGF-β), collagen IV, fibronectin, angiotensin II (Ang II), angiotensin-converting enzyme (ACE), angiotensin-converting enzyme 2 (ACE2), angiotensin II type 1 receptor (AT1R), angiotensin II type 2 receptor (AT2R), prorenin receptor (PRR), Mas receptor (MasR), endothelial nitric oxide synthase (eNOS), NADPH oxidase 2 and oxidase 4 (Nox2 and Nox4), 8-hydroxy-2′-deoxyguanosine (8-OHdG), 3-nitrotyrosine, and superoxide dismutase 1 and dismutase 2 (SOD1 and SOD2) were measured in the thoracic aortas from 2-month-old, 12-month-old, and 24-month-old C57/BL6 mice. Results. Twenty-four-month-old mice showed significantly increased aortic media thickness and expressions of TGF-β, collagen IV, and fibronectin, compared to 2-month-old and 12-month-old mice. The expressions of PRR, ACE, and Ang II, and AT1R-positive area significantly increased, whereas expressions of ACE2 and MasR and AT2R-positive area decreased with age. The expressions of phosphorylated serine¹¹⁷⁷-eNOS, SOD1, and SOD2 decreased, and the 8-OHdG-positive area and the 3-nitrotyrosine-positive area increased with age. The expression of Nox2 significantly increased with age, but that of Nox4 did not change. Conclusions. The enhanced PRR-ACE-Ang II-AT1R axis and reduced ACE2-MasR axis were associated with arterial aging in mice.

"Smooth Muscle Cell Stiffness Syndrome"-Revisiting the Structural Basis of Arterial Stiffness

In recent decades, the pervasiveness of increased arterial stiffness in patients with cardiovascular disease has become increasingly apparent. Though, this phenomenon has been well documented in humans and animal models of disease for well over a century, there has been surprisingly limited development in a deeper mechanistic understanding of arterial stiffness. Much of the historical literature has focused on changes in extracellular matrix proteins—collagen and elastin. However, extracellular matrix changes alone appear insufficient to consistently account for observed changes in vascular stiffness, which we observed in our studies of aortic stiffness in aging monkeys. This led us to examine novel mechanisms operating at the level of the vascular smooth muscle cell (VSMC)—that include increased cell stiffness and adhesion to extracellular matrix—which that may be interrelated with other mechanisms contributing to arterial stiffness. We introduce these observations as a new concept—the Smooth Muscle Cell Stiffness Syndrome (SMCSS)—within the field of arterial stiffness and posit that stiffening of vascular cells impairs vascular function and may contribute stiffening to the vasculature with aging and cardiovascular disease. Importantly, this review article revisits the structural basis of arterial stiffness in light of these novel findings. Such classification of SMCSS and its contextualization into our current understanding of vascular mechanics may be useful in the development of strategic therapeutics to directly target arterial stiffness.

Immunity in arterial hypertension: associations or causalities?

Numerous studies describe associations between markers of inflammation and arterial hypertension (aHT), but does that imply causality? Interventional studies that reduce blood pressure reduced also markers of inflammation, but does immunosuppression improve hypertension? Here, we review the available mechanistic data. Aberrant immunity can trigger endothelial dysfunction but is hardly ever the primary cause of aHT. Innate and adaptive immunity get involved once hypertension has caused vascular wall injury as immunity is a modifier of endothelial dysfunction and vascular wall remodelling. As vascular remodelling progresses, immunity-related mechanisms can become significant cofactors for cardiovascular (CV) disease progression; vice versa, suppressing immunity can improve hypertension and CV outcomes. Innate and adaptive immunity both contribute to vascular wall remodelling. Innate immunity is driven by danger signals that activate Toll-like receptors and other pattern-recognition receptors. Adaptive immunity is based on loss of tolerance against vascular autoantigens and includes autoreactive T-cell immunity as well as non-HLA angiotensin II type 1 receptor-activating autoantibodies. Such processes involve numerous other modulators such as regulatory T cells. Together, immunity is not causal for hypertension but rather an important secondary pathomechanism and a potential therapeutic target in hypertension.

Augmented vascular smooth muscle cell stiffness and adhesion when hypertension is superimposed on aging

Hypertension and aging are both recognized to increase aortic stiffness, but their interactions are not completely understood. Most previous studies have attributed increased aortic stiffness to changes in extracellular matrix proteins that alter the mechanical properties of the vascular wall. Alternatively, we hypothesized that a significant component of increased vascular stiffness in hypertension is due to changes in the mechanical and adhesive properties of vascular smooth muscle cells, and that aging would augment the contribution from vascular smooth muscle cells when compared with the extracellular matrix. Accordingly, we studied aortic stiffness in young (16-week-old) and old (64-week-old) spontaneously hypertensive rats and Wistar-Kyoto wild-type controls. Systolic and pulse pressures were significantly increased in young spontaneously hypertensive rats when compared with young Wistar-Kyoto rats, and these continued to rise in old spontaneously hypertensive rats when compared with age-matched controls. Excised aortic ring segments exhibited significantly greater elastic moduli in both young and old spontaneously hypertensive rats versus Wistar-Kyoto rats. were isolated from the thoracic aorta, and stiffness and adhesion to fibronectin were measured by atomic force microscopy. Hypertension increased both vascular smooth muscle cell stiffness and vascular smooth muscle cell adhesion, and these increases were both augmented with aging. By contrast, hypertension did not affect histological measures of aortic collagen and elastin, which were predominantly changed by aging. These findings support the concept that stiffness and adhesive properties of vascular smooth muscle cells are novel mechanisms contributing to the increased aortic stiffness occurring with hypertension superimposed on aging.

Aging and arterial-cardiac interactions in the elderly

Cardiovascular system changes with aging, and these changes are modified by arteriosclerosis-risk factors, i.e., hypertension and diabetes, as well as arterial-cardiac interactions. Regarding age-related changes in the cardiovascular system, Lakatta et al. reported morphological and functional changes that are specific to the cardiovascular aging and are distinct from arteriosclerotic changes. After then, various studies on the mechanism of aging of the cardiovascular system have been performed from the viewpoint of cellular aging, endothelial or endocardial function, and fibroblast. Aging-related changes in the cardiovascular system include death and dysfunction of cell, and matrix fibrosis, but these can also be induced by various causes other than aging. To elucidate the relationship between aging and remodeling of the cardiovascular system, firstly, it is necessary to clarify the phenomena of cellular aging. Changes also differ between the heart and arteries, and there are time lags between aging and aging-associated morphological and functional changes in the cardiovascular system: some changes appear early (early type) or later (delayed type) and some changes occur at the same speed with aging (linear type). In this report, the latest findings concerning aging-associated functional and morphological changes in the arteries and the heart are reviewed and the studies are summarized. Arteries and the heart change with aging while interacting with each other. These arterial-cardiac interactions are also described.

Elastin in systemic and pulmonary hypertension

Increased elastin production and accumulation is a rapid and sensitive response to elevated vascular wall stress in both systemic and pulmonary hypertension. While initially protecting the vessel wall, these structural changes may in the longer term result in reinforcement of the hypertensive state and contribute to the persistence of the pathology of hypertension. Rapid responses apparently uncorrelated with increased elastin mRNA, at least in the case of systemic vessels, suggest novel mechanisms perhaps including increased efficiency of message translation or matrix accumulation of the protein. Investigations using in vitro organ and cell culture models have indicated a role for phospholipases and protein kinases, including protein kinase C, in stretch-induced elastin synthesis. In addition, tyrosine phosphorylation of membrane/sub-membrane/cytoskeletal sensors, including focal adhesion kinase and members of the lipocortin family, have been shown to be important in this transduction mechanism. Because its turnover is normally very slow, additional vascular elastin accumulated during hypertensive episodes, together with its consequences for the physical properties of the vessel wall, may persist long after blood pressure is restored to normal levels. Thus, recent interest has been drawn to the possibility of achieving regression of accumulated matrix elastin by promoting turnover of this protein through activation of endogenous vascular elastase and collagenase activities.

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.

Angiotensin II modulates frizzled-2 receptor expression in rat vascular smooth muscle cells

Ang II (angiotensin II) has multiple effects on vascular smooth muscle cells through the modulation of different classes of genes. Using the mRNA differential-display method to investigate gene expression in rat aortic smooth muscle cells in culture in response to 3 h of Ang II stimulation, we observed that Ang II down-regulated the expression of a member of the family of transmembrane receptors for Wnt proteins that was identified as Fzd2 [Fzd (frizzled)-2 receptor]. Fzds are a class of highly conserved genes playing a fundamental role in the developmental processes. In vitro, time course experiments demonstrated that Ang II induced a significant increase (P<0.05) in Fzd2 expression after 30 min, whereas it caused a significant decrease (P<0.05) in Fzd2 expression at 3 h. A similar rapid up-regulation after Ang II stimulation for 30 min was evident for TGFβ1 (transforming growth factor β1; P<0.05). To investigate whether Ang II also modulated Fzd2 expression in vivo, exogenous Ang II was administered to Sprague–Dawley rats (200 ng·kg−1 of body weight·min−1; subcutaneously) for 1 and 4 weeks. Control rats received normal saline. After treatment, systolic blood pressure was significantly higher (P<0.01), whereas plasma renin activity was suppressed (P<0.01) in Ang II- compared with the saline-treated rats. Ang II administration for 1 week did not modify Fzd2 expression in aorta of Ang II-treated rats, whereas Ang II administration for 4 weeks increased Fzd2 mRNA expression (P<0.05) in the tunica media of the aorta, resulting in a positive immunostaining for fibronectin at this time point. In conclusion, our data demonstrate that Ang II modulates Fzd2 expression in aortic smooth muscle cells both in vitro and in vivo.

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.

Connective tissue growth factor is a mediator of angiotensin II-induced fibrosis

BACKGROUND

Angiotensin II (Ang II) participates in the development of fibrosis during vascular damage. Connective tissue growth factor (CTGF) is a novel fibrotic mediator. However, the potential link between CTGF and Ang II has not been investigated.

METHODS AND RESULTS

In vivo Ang II effects were studied by systemic infusion into normal rats to evaluate CTGF and extracellular matrix protein (ECM) expression by immunohistochemistry. In aorta of Ang II-infused rats, CTGF staining was markedly increased and ECM overexpression was observed. An AT1 antagonist diminished CTGF and ECM. In growth-arrested vascular smooth muscle cells, Ang II induced CTGF mRNA expression after 1 hour, remained elevated up to 24 hours, and increased CTGF protein production, which was increased up to 72 hours. The AT1 antagonist blocked Ang II-induced CTGF gene and protein expression. Early CTGF upregulation is independent of new protein synthesis. Several intracellular signals elicited by Ang II are involved in CTGF synthesis, including protein kinase C activation, reactive oxygen species, and transforming growth factor-beta endogenous production. Incubation with a CTGF antisense oligonucleotide decreased CTGF and fibronectin upregulation caused by Ang II.

CONCLUSIONS

Our results show that Ang II, via AT1, increases CTGF in vascular cells both in vivo and in vitro. This novel finding suggests that CTGF may be a mediator of the profibrogenic effects of Ang II in vascular diseases.

Increased carotid wall elastic modulus and fibronectin in aldosterone-salt-treated rats: effects of eplerenone

BACKGROUND

Previous studies have demonstrated the development of cardiac fibrosis in aldosterone (Aldo)-salt hypertensive rats. Our aim was to determine the effects of Aldo and the Aldo receptor antagonist eplerenone (Epl) on in vivo mechanical properties of the carotid artery using echo-tracking system.

METHODS AND RESULTS

Aldo was administered (1 microg/h) in uninephrectomized Sprague-Dawley rats (SD) receiving a high-salt diet from 8 to 12 weeks of age. Uninephrectomized control SD rats received a normal salt diet without Aldo. Three groups of Aldo-salt rats were treated with 1, 10, or 30 mg/kg(-1) x d(-1) of Epl by gavage. Elasticity was measured by elastic modulus (Einc)-wall stress curves using medial cross-sectional area (MCSA). The structure of the arterial wall was analyzed by histomorphometry (elastin and collagen), immunohistochemistry (EIIIA fibronectin, Fn), and Northern blot (collagens I and III). Aldo produced increased systolic arterial pressure, pulse pressure, Einc, MCSA, and EIIIA Fn with no change in wall stress or elastin and collagen densities compared with controls without Aldo. No differences in collagen mRNA levels were detected between groups. Epl blunted the increase in pulse pressure in Aldo rats and normalized Einc-wall stress curves, MCSA, and EIIIA Fn. These effects were dose dependent and not accompanied by a reduction in wall stress.

CONCLUSIONS

Aldo is able to increase arterial stiffness associated with Fn accumulation, independently of wall stress. The preventive effects of Epl suggest a direct role for mineralocorticoid receptors in mechanical and structural alterations of large vessels in rat hyperaldosteronism.

Perspectives on mammalian cardiovascular aging: humans to molecules

Age-related changes in cardiovascular function and structure in healthy adult volunteer community dwelling subjects (from 20 to 85 years) is remarkable for changes in pump function [impaired left ventricular (LV) ejection reserve capacity manifest by a reduced ejection fraction and accompanied by diminished cardioacceleration, LV dilation at end diastole and an altered diastolic filling pattern] and increased vascular afterloading. There is also evidence for a reduction in the number of cardiac myocytes with advancing age. Subcellular changes with aging (best understood in rodents) include certain regulatory factors of excitation-contraction-relaxation coupling (i.e. calcium handling), modulation by adrenergic receptor (AR) stimulation, and changes in the generation and sensitivity to the damaging effects of ROS. Coordinated changes in gene expression and/or protein function with aging result in a prolonged action potential (AP), Ca(i) transient, and contraction. L-type Ca(2+) current (I(Ca)) inactivates more slowly, and outwardly-directed K(+) currents are reduced, and likely contribute to AP-prolongation. The rate of Ca(2+) sequestration by the sarcoplasmic reticulum (SR) decreases in the senescent myocardium, in part underlying the prolonged Ca(i) transient. An age-associated reduction in transcription of the SERCA2 gene, coding for the SR Ca(2+) pump, accounts in part for a decrease in the SR pump site density. The contractile response to both beta(1)-AR and beta(2)-AR stimulation diminishes with aging due to decreased adrenergic augmentation of I(Ca), and thus the Ca(i) transient, in senescent vs. young hearts. The age-associated reduction in the postsynaptic response of myocardial cells to beta(1)-AR stimulation appears to be due to multiple changes in molecular and biochemical receptor coupling and post-receptor mechanisms. An increased basal production of ROS is paralleled by increased ROS-sensitivity, markers of chronic ROS damage and mitochondrial functional decline. Overall, these changes lead to a diminished (but not necessarily exhausted) capacity of the heart to adapt to physiological or pathological stress with advancing age.

Vascular remodeling in hypertension: roles of apoptosis, inflammation, and fibrosis

Remodeling of large and small arteries contributes to the development and complications of hypertension. The focus of this review is some of the mechanisms involved in the remodeling of small arteries in hypertension. In hypertension, changes in small artery structure are basically of 2 kinds: (1) inward eutrophic remodeling, in which outer and lumen diameters are decreased, media/lumen ratio is increased, and cross-sectional area of the media is unaltered; and (2) hypertrophic remodeling, in which the media thickens to encroach on the lumen, resulting in increased media cross-sectional area and media/lumen ratio. Growth, apoptosis, inflammation, and fibrosis contribute to vascular remodeling in hypertension. Apoptosis is gene-regulated cell death, with minimal membrane disruption and inflammation, that counters cell proliferation and fine-tunes developmental growth. Apoptosis has been reported in hypertension to be both increased and decreased in different tissues, including blood vessels. Inflammation, which may be low grade, probably plays an important role in triggering fibrosis in cardiovascular disease and hypertension. Vascular fibrosis entails accumulation of collagen, fibronectin, and other extracellular matrix components in the vessel wall and is an important aspect of extracellular matrix remodeling in hypertension. Associated with this, there may be increases in cell-matrix attachment sites (integrins) and changes in their topographical localization that may modulate arterial structure. Imbalance in matrix metalloproteinase/tissue inhibitors of metalloproteinases may contribute to alteration in collagen turnover and extracellular matrix remodeling. Chronic vasoconstriction may lead to embedding of the contracted vessel structure in a remodeled extracellular matrix, contributing to the inward remodeling of the blood vessel as smooth muscle cells are rearranged around a smaller lumen. The resulting remodeling of small arteries may initially be adaptive, but eventually it becomes maladaptive and compromises organ function, contributing to cardiovascular complications of hypertension.

Vascular smooth muscle growth: autocrine growth mechanisms

Vascular smooth muscle cells (VSMC) exhibit several growth responses to agonists that regulate their function including proliferation (hyperplasia with an increase in cell number), hypertrophy (an increase in cell size without change in DNA content), endoreduplication (an increase in DNA content and usually size), and apoptosis. Both autocrine growth mechanisms (in which the individual cell synthesizes and/or secretes a substance that stimulates that same cell type to undergo a growth response) and paracrine growth mechanisms (in which the individual cells responding to the growth factor synthesize and/or secrete a substance that stimulates neighboring cells of another cell type) are important in VSMC growth. In this review I discuss the autocrine and paracrine growth factors important for VSMC growth in culture and in vessels. Four mechanisms by which individual agonists signal are described: direct effects of agonists on their receptors, transactivation of tyrosine kinase-coupled receptors, generation of reactive oxygen species, and induction/secretion of other growth and survival factors. Additional growth effects mediated by changes in cell matrix are discussed. The temporal and spatial coordination of these events are shown to modulate the environment in which other growth factors initiate cell cycle events. Finally, the heterogeneous nature of VSMC developmental origin provides another level of complexity in VSMC growth mechanisms.

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.

Molecular mechanism of fibronectin gene activation by cyclic stretch in vascular smooth muscle cells

Fibronectin plays an important role in vascular remodeling. A functional interaction between mechanical stimuli and locally produced vasoactive agents is suggested to be crucial for vascular remodeling. We examined the effect of mechanical stretch on fibronectin gene expression in vascular smooth muscle cells and the role of vascular angiotensin II in the regulation of the fibronectin gene in response to stretch. Cyclic stretch induced an increase in vascular fibronectin mRNA levels that was inhibited by actinomycin D and CV11974, an angiotensin II type 1 receptor antagonist; cycloheximide and PD123319, an angiotensin II type 2 receptor antagonist, did not affect the induction. In transfection experiments, fibronectin promoter activity was stimulated by stretch and inhibited by CV11974 but not by PD123319. DNA-protein binding experiments revealed that cyclic stretch enhanced nuclear binding to the AP-1 site, which was partially supershifted by antibody to c-Jun. Site-directed mutation of the AP-1 site significantly decreased the cyclic stretch-mediated activation of fibronectin promoter. Furthermore, antisense c-jun oligonucleotides decreased the stretch-induced stimulation of the fibronectin promoter activity and the mRNA expression. These results suggest that cyclic stretch stimulates vascular fibronectin gene expression mainly via the activation of AP-1 through the angiotensin II type 1 receptor.

Age-related changes of gene expression in mouse kidney: fluorescence differential display--PCR analyses

We used a fluorescence differential display--PCR (FDD-PCR) technique to analyze the genes expressed in mouse kidneys collected at nine different developmental stages ranging from 3 days to 15 months after birth. We found ten genes that were age-dependent and differentially-expressed in the kidneys during our experimental period. We confirmed by comparative RT-PCR that of the ten cDNAs, seven showed reproducible age-dependent expression. Four of the nucleotide sequences of these cDNA clones, had high homology with known genes (fibronectin, soluble guanylyl cyclase alpha-1 subunit, cytosolic aldehyde dehydrogenase and mitochondrial DNA), and three with expressed sequence tags of unknown genes. The FDD-PCR method was very useful for detecting new age-related genes expressed differentially in the mouse kidney.

Renin-angiotensin system and fibronectin gene expression in Dahl Iwai salt-sensitive and salt-resistant rats

OBJECTIVE

The tissue renin-angiotensin system and extracellular matrix are involved in the cardiovascular hypertrophy and remodeling induced by hypertension. In this study, we examined the gene expression of the tissue renin-angiotensin system and fibronectin in inbred Dahl Iwai salt-sensitive and salt-resistant rats.

MATERIALS AND METHODS

Eight pairs of 6-week-old male Dahl Iwai salt-sensitive and salt-resistant rats were fed either a low- or high-salt diet (0.3% or 8% NaCl, respectively) for 4 weeks. Activities of the circulating renin-angiotensin system were measured by radioimmunoassay and the gene expression of tissue angiotensinogen, the angiotensin II type 1 receptor (AT1) and fibronectin were analyzed by Northern blot analysis.

RESULTS

Salt loading significantly increased blood pressure and produced cardiovascular hypertrophy and nephrosclerosis in the salt-sensitive rats. Activities of the circulating renin-angiotensin system were lower in salt-sensitive rats than in salt-resistant rats fed the low-salt diet, and salt loading lowered these activities in salt-resistant rats but not in salt-sensitive rats. In salt-resistant rats, salt loading increased renal, cardiac and aortic angiotensinogen, AT1 and fibronectin messenger (m)RNA expression except for aortic fibronectin mRNA expression. In contrast, in the salt-sensitive rats, salt loading stimulated the expression of cardiac fibronectin and aortic angiotensinogen, AT1 and fibronectin mRNAs. Furthermore, the cardiac and aortic fibronectin mRNA levels in salt-sensitive rats were higher than those in salt-resistant rats when both strains were fed the high-salt diet.

CONCLUSIONS

These results demonstrate that the expression of tissue angiotensinogen, AT1 and fibronectin mRNAs is regulated differently in Dahl Iwai salt-sensitive and salt-resistant rats, and indicate that salt-mediated hypertension activates the cardiac fibronectin gene independently of the tissue renin-angiotensin system and stimulates the aortic fibronectin gene with activation of the tissue renin-angiotensin system.

Tissue-localized angiotensin II enhances cardiac and renal disorders in Tsukuba hypertensive mice

OBJECTIVE

To evaluate the relation of tissue-localized angiotensin II (Ang II) concentration with cardiac hypertrophy and glomerulosclerosis in Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes.

DESIGN

Thirty THM aged 12 weeks were distributed equally to a lisinopril dosage group, a hydralazine dosage group, and an untreated group. Ten age-matched C57BL/6 mice were used as normal controls. Administration was performed for 8 weeks from 12 weeks of age. All mice were euthanized at 20 week of age, and the heart-to-body weight ratio, the renal glomerulosclerosis score, tissue Ang II concentration and tissue catecholamine concentration were measured.

RESULTS

In the untreated group, a significant increase in every examination item was found as compared with that in C57BL/6 mice. In the lisinopril group, the observed value of every item was significantly lower than that in the untreated group. In the hydralazine group, tissue Ang II and catecholamine concentrations and the heart-to-body weight ratio were not different from those in the untreated group. Although the glomerulosclerosis score in the hydralazine group was significantly less than that in the untreated group, this was significantly higher than that in the lisinopril group.

CONCLUSION

Tissue Ang II concentration is more important than hypertension in causing cardiac hypertrophy, and both tissue Ang II level and hypertension are important in causing glomerulosclerosis in THM.

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.

Inhibitory effects of a subdepressor dose of L-158,809, an angiotensin II type 1 receptor antagonist, on cardiac hypertrophy and nephropathy via the activated human renin-angiotensin system in double transgenic mice with hypertension

The effects of L-158,809, an angiotensin II type 1 receptor antagonist, on cardiac hypertrophy and nephropathy were examined using Tsukuba hypertensive mice (THM) carrying both human renin and angiotensinogen genes. Nine male THM aged 20 weeks were assigned to each of a no-dosage group and an L-158,809 dosage group, and L-158,809 was administered for 8 weeks. Nine age-matched male C57BL/6 mice were used as normal control animals. At 28 weeks of age, all of the mice were euthanized. Systolic blood pressure, urinary volume, water intake volume, urinary albumin excretion, heart weight and kidney weight to body weight ratios and a glomerulosclerosis index were measured. In the no-dosage group, the values of all of these parameters were larger than those in the control mice. In the L-158,809 group, all of the parameters showed significant improvement, except for blood pressure, which was not significantly different from that in the no-dosage group. These results suggest that the renin-angiotensin system played a crucial role in the cardiac hypertrophy and nephropathy in THM, and that L-158,809 exhibited strong curative effects on cardiac hypertrophy and nephropathy by blocking the angiotensin II type 1 receptor.

Induction of angiotensin converting enzyme and angiotensin II receptors in the atherosclerotic aorta of high-cholesterol fed Cynomolgus monkeys

Antiatherogenic effects of imidapril and involvement of renin angiotensin system were examined in experimental atherosclerosis induced by feeding a high-cholesterol diet to Cynomolgus monkeys. Eighteen male monkeys were divided into three groups and placed under (1) normal diet (normal group), (2) high-cholesterol diet (control group), (3) high-cholesterol diet with imidapril (20 mg/kg body wt/day, orally) treatment (imidapril group). At the end of the experiment, the normal group showed no apparent atherosclerosis in their aorta evaluated by oil red-O staining, while the control group exhibited marked atherosclerotic involvement of the intimal surface of the aorta (58.4 +/- 9.3%, P < 0.01). Imidapril reduced systolic blood pressure and atherosclerotic involvement (24.1 +/- 5.5%, P < 0.05). Total cholesterol content of the descending thoracic aorta was also significantly reduced in the imidapril group. In the atherosclerotic vessels, angiotensin converting enzyme (ACE) activity evaluated by quantitative in vitro autoradiography was significantly increased in the intimal lesion. Further evaluation revealed angiotensin II (Ang II) type I (AT1) receptor density was significantly increased in the medial lesion and type II (AT2) receptor density in the adventitia. When the progression of atherosclerosis was impeded by imidapril treatment, the ACE activity level as well as the AT1 and AT2 receptor density remained at normal. Expression of mRNA for fibronectin, TGF-beta1, types I and III collagen was studied by Northern blot analysis. No significant differences in types I and III collagen mRNA levels were found between the control and imidapril group. On the other hand, mRNA expression for fibronectin and TGF-beta1 were much lower in the imidapril group than in the control group. These results suggest that increased production of Ang II and activated receptors may be involved in atherosclerotic process in this model and also antiatherogenic effect of imidapril may be derived from reduction of local Ang II production as well as its hypotensive action.

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.

Cerebrovascular changes in chronic hypertension. Protective effects of enalapril in rats

BACKGROUND AND PURPOSE

Our recent study demonstrated that in chronic hypertension, hypertrophy of intracerebral arterioles was associated with an increase in the vascular extracellular matrix proteins: fibronectin, laminin, and collagen IV. An additional cerebral finding in chronic hypertension was hypertensive encephalopathy, in which breakdown of the blood-brain barrier (BBB) to serum proteins occurred in multifocal areas of the cortex and basal ganglia. This study was undertaken to determine which of these alterations were attenuated by antihypertensive therapy.

METHODS

Two weeks after the surgery to produce chronic renal hypertension, half the hypertensive rats were treated orally with enalapril (30 mg/kg), an angiotensin-converting enzyme inhibitor, for 5 weeks. Rats were perfusion-fixed, and their brains were removed and processed for morphological studies. The effect of treatment on vascular hypertrophy was assessed by quantitative morphometry and on the vascular extracellular matrix proteins and BBB permeability alterations by immunohistochemistry.

RESULTS

There was increased immunoreactivity for laminin, fibronectin, and collagen IV in pial and intracerebral arterioles of untreated hypertensive rats. Immunoreactivity was greatest in arterioles in areas with breakdown of the BBB to serum proteins. Enalapril treatment for 5 weeks resulted in a significant reduction of the mean systolic blood pressure, which was accompanied by attenuation of vascular hypertrophy and attenuation of changes in the vascular extracellular matrix proteins. In addition, there was reduction in the magnitude of BBB breakdown after treatment.

CONCLUSIONS

Enalapril treatment had a protective effect and attenuated vascular hypertrophy and the increase in vascular extracellular matrix proteins observed in chronic hypertension. In addition, there was reduction in the magnitude of BBB breakdown.

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.

Effects of angiotensin II infusion and inhibition of nitric oxide synthase on the rat aorta

In previous studies, we showed that in vivo infusion of angiotensin II (Ang II) to adult rats induced vascular changes in gene expression, and this effect did not depend solely on blood pressure elevation. To determine whether nitric oxide can influence the effects of Ang II on the vessel wall, we administered to rats Ang II separately or in combination with the arginine analogue N omega-nitro-L-arginine methyl ester, which inhibits nitric oxide synthase chronically when given in vivo. We measured changes in aortic medial thickness, the association of macrophages with the endothelial surface of the aorta, the presence of proliferating cell nuclear antigen in the intima and adventitia as an index of aortic cell cycle changes, and the expression of immunodetectable fibronectin as an index of changes in the extra-cellular matrix. After 18 days of nitric oxide inhibition, the major changes were increased medial thickness and a 3.5-fold increase in the number of adherent macrophages. Rats treated with two different doses of Ang II for 3 days had a fivefold and threefold increase in the number of proliferating cells from the intimal and adventitial regions, respectively. Combined treatment resulted in increased medial thickness, intimal and adventitial cell proliferation, and macrophage adherence. An increased and altered pattern of fibronectin distribution was found in all treatment groups. Losartan administration prevented the effects of Ang II but not of nitric oxide inhibition, whereas administration of L-arginine, prevented both intimal macrophage adherence and increased adventitial proliferation in rats given combined treatment. The data suggest that nitric oxide selectively influences macrophage association with the arterial wall, whereas Ang II and nitric oxide may have opposing effects on arterial cell proliferation.

Suppression of vascular transforming growth factor-beta1 and extracellular matrix gene expressions by cilazapril and nifedipine in hypertensive rats

1. We investigated the protective effects of an angiotensin-converting enzyme inhibitor (ACEI) and a Ca antagonist on vascular injury in hypertension. 2. Thirteen week old stroke-prone spontaneously hypertensive rats (SHRSP) were orally given cilazapril (ACEI 10 mg per kg day) or nifedipine (Ca antagonist 30 mg kg per day) for 12 weeks. After the treatment, the aorta and superior mesenteric artery were excised, and subjected to the extraction of RNA. mRNA levels for the transforming growth factor-beta1 (TGF-beta1) and extracellular matrix components such as fibronectin (FN), collagen type I (CoI), type III (CoIII) and type IV (CoIV) and laminin, were measured by northern blot analysis, using each specific cDNA probe. 3. In the mesenteric artery of SHRSP, TGF-beta1 mRNA levels were increased compared with Wistar-Kyoto (WKY) rats, being accompanied by a significant increase in mRNA levels for FN, CoI, CoIII, CoIV and laminin. In the aorta, only TGF-beta1 and fibronectin mRNAs were increased in SHRSP, but collagen and laminin were not increased. 4. Both cilazapril and nifedipine, to similar extents, suppressed the above mentioned increased gene expressions in both mesenteric artery and aorta, being associated with the improvement of vascular hypertrophy. 5. These results suggest that TGF-beta1 may be responsible for smooth muscle cell hypertrophy and the increased deposition of extracellular matrix in hypertensive blood vessels. Both cilazapril and nifedipine may lessen hypertensive vascular thickening, by suppressing the gene expression of TGF-beta1 and extracellular matrix.

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.

AT1 receptor-mediated stimulation by angiotensin II of rat aortic fibronectin gene expression in vivo

Fibronectin plays an important role in various vascular diseases. A subpressor (200 ng kg-1 min-1) or pressor (1000 ng kg-1 min-1) dose of angiotensin II was continuously infused into rats by osmotic minipump for various times, to investigate the effects on aortic fibronectin gene expression. In rats infused with a subpressor dose of angiotensin II in which blood pressure was normal for 3 days, aortic fibronectin mRNA levels started to increase by 1.4 fold at 12 h and reached the maximal levels (increased by 3.1 fold) at 3 days. Treatment with TCV-116 (3 mg kg-1 day-1), a non-peptide selective AT1 receptor antagonist, completely inhibited the angiotensin II-induced increase in aortic fibronectin mRNA, while hydralazine (10 mg kg-1 day-1) did not block this effect. Similar results were also obtained for a pressor dose of angiotensin II. Thus, angiotensin II directly stimulates aortic fibronectin gene expression in vivo, which is mediated by the AT1 receptor but not by blood pressure.

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.

Hyperplastic growth of aortic smooth muscle cells in renovascular hypertensive rabbits is characterized by the expansion of an immature cell phenotype

Smooth muscle cells (SMCs) of rabbit aorta undergo marked changes in myosin isoform content during development. Analysis of nonmuscle myosin composition at the protein level has permitted the identification of three phases in the SMC differentiation process: fetal, postnatal, and adult. Using monoclonal antibodies specific for smooth muscle and nonmuscle myosins and extra domain A of fibronectin as well as cDNA probes for platelet-derived growth factors (PDGF) and various procollagens, we have evaluated the differentiation pattern of aortic SMCs in two-kidney, one-clip hypertensive rabbits. Morphometric and bromo-deoxyuridine studies indicate that hypertrophy of aortic media along with intimal thickening occurring in hypertensive animals is due to SMC hyperplasia. Western blotting experiments performed on aortic specimens from hypertensive animals with antimyosin antibodies revealed the appearance of a myosin isoform pattern of the "immature" type. Immunofluorescence tests showed that these cells are localized in the thickened intima or distributed in the underlying media (sparsely or in groups). Similarly, the fibronectin variant showing the extra domain A, peculiar to "phenotypically modulated" SMCs, appeared in intimal thickening, and its expression followed the time course of nonmuscle myosin expression. Counting of postnatal-type SMCs in the aortic media revealed that this cell population increases markedly with hypertension (2- up to 15-fold at 4 months) and then declines to near control level in 8-month hypertensive rabbits. Diminution of postnatal-type SMCs at later stages of hypertension was temporally correlated with the slowing down of aortic wall hypertrophy. Average levels of mRNAs, as determined by densitometric analysis in aortas from 1- and 2.5-month hypertensive rabbits, showed an increased expression for PDGF beta receptor (up to twofold), procollagen type I (alpha 1, threefold), procollagen type III (alpha 1, twofold), and fibronectin (up to threefold) compared with controls. Conversely, the steady-state levels of mRNAs for PDGF (A and B chain), PDGF alpha receptor, TGF-beta 1, and procollagen type IV (alpha 1) did not increase significantly. These results provide evidence that in adult renovascular hypertensive rabbits, the hyperplastic growth of aortic SMCs is accompanied by the expansion of an "immature" cell phenotype characteristic of the early stages of development.

Angiotensin II induces fibronectin expression associated with cardiac fibrosis in the rat

Fibronectin expression was studied in the heart of rats given a continuous infusion of angiotensin II (Ang II). Northern blot analysis showed that left ventricular fibronectin steady-state mRNA increased fivefold to eightfold in response to pressor doses of Ang II after 24 hours. Accumulation of immunodetectable fibronectin in the ventricles occurred after the mRNA levels increased. The changes in fibronectin expression were reversible when Ang II treatment was withdrawn. The Ang II-induced increase in fibronectin mRNA accompanied similar increases for collagen type I, collagen type IV, and atrial natriuretic factor steady-state mRNA. Interstitial and perivascular fibrosis was identified in both ventricles of angiotensin-treated rats within 3 days. In situ hybridization identified cells associated with areas of fibrosis as the principal site of fibronectin mRNA accumulation in treated animals. By comparison, normal hearts showed fibronectin expression primarily within ventricular vascular tissue and the atrial endocardium. A dose-dependent reduction of fibronectin expression followed treatment with losartan, indicating an Ang II type 1 receptor-mediated effect. Normalization of blood pressure during Ang II infusion by either hydralazine or prazosin had different effects on the level of fibronectin steady-state mRNA, indicating that blood pressure elevation was not the principal factor responsible for fibronectin induction. Concurrent administration of angiotensin-converting enzyme inhibitors with Ang II attenuated the increased fibronectin expression. Our data indicate that Ang II induces an acute fibrotic response within the heart and suggests that Ang II stimulates fibronectin expression within nonmyocytic cardiac cells by a direct action.

Angiotensin-converting enzyme inhibition partially prevents diabetic organomegaly

The present study was conducted to evaluate whether captopril prevents the organomegaly and accumulation of matrix proteins that normally accompanies the diabetic state. The following groups of rats were studied: normal rats, normal rats treated with captopril (30 mg/kg/d orally), streptozotocin diabetic rats, and diabetic rats treated with captopril. All rats were killed at 10 weeks for histologic and morphometric evaluation of tissues. Compared with the normal rats, the diabetic rats demonstrated significant hepatomegaly, nephromegaly, and cardiomegaly, and the increase in organ size was directly related to increasing levels of protein glycosylation. The development of organomegaly was partially prevented by captopril. We determined by morphometry that the hepatomegaly seen in the diabetic rats was due to an increase in cell size and number, while the nephromegaly seen in the diabetic rats was due to an increase in tubular and glomerular cell size and is associated with glomerular hypertrophy. Captopril prevented the development of hepatic and renal cell hypertrophy and glomerular hypertrophy. These effects of captopril were not associated with detectable changes in body weight or levels of glucose, protein glycosylation, glycosuria, or renal histologic changes secondary to glycosuria. The diabetic rats demonstrated significant glomerular mesangial matrix expansion, and captopril treatment partially prevented that expansion. In conclusion, captopril prevents, in part, the development of organomegaly in diabetic rats, and this effect is due mainly to the prevention of the development of cellular hypertrophy. The present findings are most consistent with a direct effect of captopril on cell metabolism during diabetes mellitus.

Angiotensin II stimulates human fetal mesangial cell proliferation and fibronectin biosynthesis by binding to AT1 receptors

The renin-angiotensin system is activated during vascular development and injury. Furthermore, angiotensin II (Ang II) is a comitogen for fetal mesangial cells in vitro and it may be important in vascular smooth cell growth in disease states. Since fibronectin is an important extracellular matrix protein for vascular development and it too is overexpressed in the mesangium of diseased glomeruli, we explored the interrelationship of fibronectin and Ang II in fetal mesangial cell growth. In human fetal kidney, Ang II type 2 receptors (AT2) were detected in abundance by ex vivo autoradiography. When mesangial cells were isolated from fetal kidney and grown in culture, Ang II type 1 receptors (AT1) were also detected. To explore the mitogenic properties Ang II and fibronectin as well as the effects of Ang II on fibronectin metabolism, studies were performed in vitro, isolated from the potentially confounding variables of hemodynamic influence and circulating growth factors and cytokines. In vitro, mesangial cells expressed a single class of AT1 receptors that were not altered by growth on various substrates. Ang II (10(-7) M) significantly increased thymidine incorporation by confluent human fetal mesangial cells (twofold). When subconfluent, Ang II-stimulated proliferation was greater (fourfold). Ang II significantly increased cell-associated and secreted fibronectin as determined by immunoprecipitation at concentrations that also stimulate mitogenesis. Both of these Ang II-mediated responses were inhibited by the AT1 receptor antagonist DuP-753 (10(-5) M) but not by AT2 receptor antagonist.(ABSTRACT TRUNCATED AT 250 WORDS)

Arterial smooth muscle cell phenotype in stroke-prone spontaneously hypertensive rats

The aim of this study was to determine the phenotype of smooth muscle cells in the arteries of chronically hypertensive animals and to analyze the effects of treatments known to increase the survival of the animal without a clear effect on its hypertensive state. Stroke-prone spontaneously hypertensive rats (SHRSP) kept on a 1% sodium drinking solution were untreated or treated with one of two diuretics, indapamide (3 mg/kg per day) or hydrochlorothiazide (20 mg/kg per day), from 6 to 13 weeks of age. Phenotype was characterized by the immunolabeling of arteries with antibodies raised against a cellular form (EIIIA) of fibronectin, alpha-smooth muscle actin, and nonmuscle myosin. We demonstrated that phenotypes of smooth muscle cells of the SHRSP differ from those found in Wistar-Kyoto rats. The difference in phenotype is specific for the vessel type: ie, an increased expression of nonmuscle myosin in the aorta and of both EIIIA fibronectin and nonmuscle myosin in the coronary arteries. The two diuretics (1) had no effect on blood pressure, (2) prevented or did not prevent the increase in medial thickness, and (3) prevented changes in both smooth muscle cell phenotype and ischemic tissular lesions. Taken together, the results suggest that in SHRSP the changes in the phenotype of smooth muscle cells and the thickness of arteries are unrelated events. We propose that the maintenance of the contractile phenotype of the arterial smooth muscle cells could be an essential parameter involved in the prevention of the deleterious consequences characteristic of a severe hypertensive state.

Coarctation induces alterations in basement membranes in the cardiovascular system

A coarctation hypertensive rat model was used to examine the effects of elevated blood pressure on basement membrane component synthesis by cardiac myocytes and aorta using immunohistochemistry and Northern blot analysis. Carotid arterial pressure increased immediately on coarctation, and left ventricular hypertrophy was maximal within 5 days. In immunohistochemical studies, fibronectin and laminin were increased and the basement membrane chondroitin sulfate proteoglycan decreased in both the subendothelial space and smooth muscle cell basement membranes of the aorta above the clip compared with controls, whereas only fibronectin was elevated in the aorta below the clip. No change in basement membrane staining intensity for the cardiac myocytes was observed. Alterations in steady-state mRNA levels for fibronectin and laminin in the aorta paralleled those observed by immunohistochemical analysis with regard to protein and tissue type affected as well as intensity of the changes. However, changes in mRNA levels (but not protein deposition) for perlecan and type IV collagen were also observed in aortas from hypertensive rats compared with controls. Increases in steady-state mRNA levels for all basement membrane components in the heart and vasculature peaked before maximal cardiac hypertrophy (5 days). These studies indicate that alterations in basement membrane component deposition in the hypertrophied vasculature occur at both transcriptional and translational levels and suggest that the cell attachment glycoproteins fibronectin and laminin may be important factors in the vascular response to elevated transmural pressure.

Cyclic AMP suppresses fibronectin expression in the rabbit aorta in vitro

The effect of cAMP on the in vitro expression of rabbit aortic fibronectin was examined using a previously characterized organ culture system. Elevation of intracellular cAMP in incubated aortic rings by use of forskolin or dibutyryl cAMP (dbcAMP) inhibited the normally observed increase in fibronectin mRNA to levels below that found in unincubated tissue. The effect of dbcAMP on fibronectin mRNA was dose dependent and reversible. dbcAMP did not affect overall protein biosynthesis or the changes in collagen or elastin mRNAs that normally occurred during in vitro incubation, suggesting a selective regulatory effect on fibronectin. The inhibitory effect of dbcAMP on steady-state fibronectin mRNA levels was independent of the dibutyrate moiety, was not a result of cytotoxicity, did not require de novo protein synthesis, and did not appear to occur through a protein kinase A pathway. The data suggested that suppression of fibronectin mRNA levels potentially occurred via an indirect mechanism that may have involved a dbcAMP-induced reduction in intracellular calcium ([Ca2+]i) levels. The resultant decrease in [Ca2+]i may have affected fibronectin expression via a reduction in protein kinase C activity but did not depend on a calmodulin or calmodulin kinase I or II mechanism.