Hemodynamic and endocrine factors are among the most important factors implicated in the physiology and pathophysiology of the vascular wall. Arterial hypertension evokes structural and functional changes of the vascular wall (1, 2). Modifications of the extracellular matrix, including fibronectin (FN) 1 and collagen, have been previously reported in vessel walls of hypertensive animals (3-5). Activation and qualitative changes in the extracellular matrix participate in vascular wall remodeling and in the pathogenesis of atherosclerosis. Vascular remodeling in hypertension may be an adaptive response to increased transmural pressure (6 -9). Mechanical stress seems to play a direct role in vascular remodeling, since mechanical stretch is able to increase protein synthesis by vascular smooth muscle cells (VSMCs) (10). However, neuronal and humoral factors may be critical in hypertension-induced remodeling of vascular wall. Especially, several in vivo studies have reported that hypertension activates the vascular renin-angiotensin system (RAS) including angiotensin-converting enzyme (ACE) (11), and infusion of pressor and subpressor doses of angiotensin II (Ang II) increases aortic FN mRNA in both hypertensive and normotensive animals (12, 13). Ang II evokes diverse physiological response including arterial vasoconstriction to elevate blood pressure in vivo (14) and increases production of collagen with a growth-promoting effect on VSMCs in vitro (15). Pharmacological evidence has defined at least two subtypes of Ang II receptors, Ang II type 1 (AT1) receptor and Ang II type 2 (AT2) receptor. Previous results of molecular cloning have revealed that both receptor subtypes belong to the superfamily of G protein-coupled receptors with seven transmembrane helices (16 -19). According to the recent results of in vitro studies, Ang II initially activates a phosphatidylinositol-specific phospholipase C (PI-PLC) via its binding to AT1 receptor on the surface of VSMCs, leading to the generation of inositol triphosphate and diacylglycerol (20), which are involved in intracellular Ca 2ϩ mobilization (21) and protein kinase C (PKC) activation (22), respectively. In VSMCs, Ang II also induces a rapid increase in expression of the growth-associated nuclear protooncogenes and stimulates tyrosine phosphorylation of multiple substrates (23, 24). These findings, taken together with relatively abundant expression of AT1 receptor in vascular wall and VSMCs, indicate that Ang II plays an important role in vascular remodeling via an AT1 receptor pathway. Thus, investigation of the mechanism of Ang II-induced regulation of extracellular matrix and tissue RAS in VSMCs is essential in elucidating the mechanism of vascular remodeling and the pathogenesis of atherosclerosis.In the present study, we examined the effects of Ang II on gene expression of extracellular matrix components (FN and

Previous investigations have demonstrated certain similarities in the cellular changes occurring in the arterial wall in response to hypertension and aging. We undertook the current studies to examine the expression of platelet-derived growth factor (PDGF) receptors and ligands and transforming growth factor-beta 1 (TGF-beta 1) in aorta and heart of spontaneously hypertensive rats (SHRs), Wistar-Kyoto (WKY) controls, and Wistar rats studied at ages ranging from 5 to 40 weeks. A progressive increase with age in aortic steady-state messenger RNA (mRNA) levels of the receptor for the B chain of PDGF (PDGF-r beta) was present in all three strains but was greatest in the SHR. The aortic expression of PDGF A or B ligands as well as of the PDGF-r alpha-receptor was not significantly influenced by age or blood pressure. In contrast, in the heart of the SHR and WKY rat, there was an age-related decrease in expression of both PDGF receptors and of the PDGF B chain. Hypertension and aging were associated with increases in steady-state mRNA for TGF-beta 1 in aorta, but in the heart, reductions again were observed. These studies indicate that both hypertension and aging increase the in vivo expression of PDGF-r beta and TGF-beta 1 in aortic tissue. Such changes might be functionally significant and provide autocrine or paracrine mechanisms for regulation of cellular growth in the arterial wall in response to these conditions. The findings also provide further support for the concept that hypertension accelerates the arterial changes associated with aging.

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.Extracellular matrix of the vascular wall plays an important role in pathophysiological changes including vascular remodeling and atherosclerosis in response to hypertension. Fibronectin (FN) 1 is an important component of the extracellular matrix and is implicated functionally in the regulation of several cellular processes, including cell adhesion, migration, transformation, and motility and wound healing. FN has been found to modulate the phenotype of vascular smooth muscle cells (VSMCs) and regulate VSMC growth (1). We previously found that angiotensin II (Ang II) enhances transcription of the FN gene through the Ang II type 1 receptor (AT1 receptor) in VSMCs, at least in part via activation of the rat FN promoter AP-1 binding motif (rFN/AP-1) (2). Although rFN/AP-1 may not be involved in the regulation of FN gene expression in cells other than VSMCs (3, 4), this result proposes that rFN/AP-1 is functionally important for the regulation of vascular FN expression in response to various stimuli. Accumulated evidence suggests that hemodynamic forces (including stretch and shear stress) as well as endocrine factors (such as Ang II) are among the most important factors implicated in the physiology and pathophysiology of the vascular wall in vivo. Interactions between extracellular matrix proteins and cellular receptors can transduce signals that lead to changes in shape, motility, and growth of VSMCs. Thus, investigation of mechanical stressmediated regulation of the extracellular matrix and the tissue renin-angiotensin system in VSMCs may be important for the elucidation of a molecular mechanism of vascular remodeli...

Fibronectin expression was shown recently to increase in the rat aorta in response to experimental hypertension. Fibronectin is known to alter the phenotype of vascular smooth muscle and endothelial cells, and relative changes in the expression of different isoforms of fibronectin, generated by alternative splicing and distinguished by the absence or presence of inserts designated as EIIIA, EI1IB, and V, may reflect a change in cell phenotype. In the present study we examined the expression of alternatively spliced forms of aortic fibronectin during deoxycorticosterone-salt hypertension. Aortic RNA was analyzed quantitatively using Northern blot analysis and ribonuclease protection assays. Using Northern blot analysis, deoxycorticosterone-salt treatment for 21 days led to a 4.9-fold increase in EIIT.A fibronectin messenger RNA, while EQIB and V forms increased by 2.6-and 2.5-fold, respectively. As determined by ribonuclease protection assays, the percentage of fibronectin transcripts containing either EIIIA, EIIIB, or V in control aorta was 7.3%, 19%, and 40%, respectively. The percentage of EIIIA transcripts increased 42% over control levels after 21 days of deoxycorticosterone-salt treatment, whereas no proportionate change in the other alternatively spliced forms was found. Thus, all forms increased, but a selective increase in the EIIIA form was induced. Analogous increases in each of the fibronectin isoforms were found in the spontaneously hypertensive rats when compared with age-matched Wistar-Kyoto or Wistar rats, and 40-week-old animals showed increases over 10-week-old animals in all strains, consistent with an age-dependent increase in aortic fibronectin expression. Fibronectin is a matrix-associated glycoprotein that exists in several forms due to alternate splicing of a single gene, the different isoforms distinguished by the presence or absence of exon products, which in the rat are designated as EIIIA, EIIIB, and V.3 Through an interaction with specific cellular receptors known as integrins, fibronectin influences cellular functions that include motility, differentiation, and many of the events associated with wound healing. 4 The role of fibronectin in vascular biology is incompletely understood. Although there are numerous studies where cultured endothelial and smooth muscle cells were used to establish a relation between fibronectin

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.