Culture of renal arteriolar smooth muscle cells. Mitogenic responses to angiotensin II

7-O-methylpunctatin, a Novel Homoisoflavonoid, Inhibits Phenotypic Switch of Human Arteriolar Smooth Muscle Cells

Remodeling of arterioles is a pivotal event in the manifestation of many inflammation-based cardio-vasculopathologies, such as hypertension. During these remodeling events, vascular smooth muscle cells (VSMCs) switch from a contractile to a synthetic phenotype. The latter is characterized by increased proliferation, migration, and invasion. Compounds with anti-inflammatory actions have been successful in attenuating this phenotypic switch. While the vast majority of studies investigating phenotypic modulation were undertaken in VSMCs isolated from large vessels, little is known about the effect of such compounds on phenotypic switch in VSMCs of microvessels (microVSMCs). We have recently characterized a novel homoisoflavonoid that we called 7-O-methylpunctatin (MP). In this study, we show that MP decreased FBS-induced cell proliferation, migration, invasion, and adhesion. MP also attenuated adhesion of THP-1 monocytes to microVSMCs, abolished FBS-induced expression of MMP-2, MMP-9, and NF-κB, as well as reduced activation of ERK1/2 and FAK. Furthermore, MP-treated VSMCs showed an increase in early (myocardin, SM-22α, SM-α) and mid-term (calponin and caldesmon) differentiation markers and a decrease in osteopontin, a protein highly expressed in synthetic VSMCs. MP also reduced transcription of cyclin D1, CDK4 but increased protein levels of p21 and p27. Taken together, these results corroborate an anti-inflammatory action of MP on human microVSMCs. Therefore, by inhibiting the synthetic phenotype of microVSMCs, MP may be a promising modulator for inflammation-induced arteriolar pathophysiology.

Structure Guided Chemical Modifications of Propylthiouracil Reveal Novel Small Molecule Inhibitors of Cytochrome b5 Reductase 3 That Increase Nitric Oxide Bioavailability

NADH cytochrome b5 reductase 3 (CYB5R3) is critical for reductive reactions such as fatty acid elongation, cholesterol biosynthesis, drug metabolism, and methemoglobin reduction. Although the physiological and metabolic importance of CYB5R3 has been established in hepatocytes and erythrocytes, emerging investigations suggest that CYB5R3 is critical for nitric oxide signaling and vascular function. However, advancement toward fully understanding CYB5R3 function has been limited due to a lack of potent small molecule inhibitors. Because of this restriction, we modeled the binding mode of propylthiouracil, a weak inhibitor of CYB5R3 (IC50 = ∼275 μM), and used it as a guide to predict thiouracil-biased inhibitors from the set of commercially available compounds in the ZINC database. Using this approach, we validated two new potent derivatives of propylthiouracil, ZINC05626394 (IC50 = 10.81 μM) and ZINC39395747 (IC50 = 9.14 μM), both of which inhibit CYB5R3 activity in cultured cells. Moreover, we found that ZINC39395747 significantly increased NO bioavailability in renal vascular cells, augmented renal blood flow, and decreased systemic blood pressure in response to vasoconstrictors in spontaneously hypertensive rats. These compounds will serve as a new tool to examine the biological functions of CYB5R3 in physiology and disease and also as a platform for new drug development.

Adenosine A1 receptor-dependent and independent pathways in modulating renal vascular responses to angiotensin II

AIM

Renal afferent arterioles are the effector site for autoregulation of glomerular perfusion and filtration. There is synergistic interaction between angiotensin II (ANG II) and adenosine (Ado) in regulating arteriolar contraction; however, the mechanisms are not clear. In this context, this study investigated the contribution of A1 receptor-dependent and independent signalling mechanisms.

METHODS

Isolated perfused afferent arterioles from transgenic mice (A1 (+/+) and A1 (-/-) ) were used for vascular reactivity studies. Cultured vascular smooth muscle cells (VSMC) were used for phosphorylation studies of signalling proteins that induce arteriolar contraction.

RESULTS

Maximal arteriolar contraction to ANG II was attenuated in A1 (-/-) (22%) compared with A1 (+/+) (40%). Simultaneous incubation with low-dose ado (10(-8)  mol L(-1) ) enhanced ANG II-induced contraction in A1 (+/+) (58%), but also in A1 (-/-) (42%). An ado transporter inhibitor (NBTI) abolished this synergistic effect in A1 (-/-) , but not in wild-type mice. Incubation with Ado + ANG II increased p38 phosphorylation in aortic VSMC from both genotypes, but treatment with NBTI only blocked phosphorylation in A1 (-/-) . Combination of ANG II + Ado also increased MLC phosphorylation in A1 (+/+) but not significantly in A1 (-/-) , and NBTI had no effects. In agreement, Ado + ANG II-induced phosphorylation of p38 and MLC in rat pre-glomerular VSMC was not affected by NBTI. However, during pharmacological inhibition of the A1 receptor simultaneous treatment with NBTI reduced phosphorylation of both p38 and MLC to control levels.

CONCLUSION

Interaction between ANG II and Ado in VSMC normally involves A1 receptor signalling, but this can be compensated by receptor independent actions that phosphorylate p38 MAPK and MLC.

RGS4 inhibits angiotensin II signaling and macrophage localization during renal reperfusion injury independent of vasospasm

Vascular inflammation is a major contributor to the severity of acute kidney injury. In the context of vasospasm-independent reperfusion injury we studied the potential anti-inflammatory role of the Gα-related RGS protein, RGS4. Transgenic RGS4 mice were resistant to 25 minute injury, although post-ischemic renal arteriolar diameter was equal to the wild type early after injury. A 10 minute unilateral injury was performed to study reperfusion without vasospasm. Eighteen hours after injury blood flow was decreased in the inner cortex of wild type mice with preservation of tubular architecture. Angiotensin II levels in the kidneys of wild type and transgenic mice were elevated in a sub-vasoconstrictive range 12 and 18 hours after injury. Angiotensin II stimulated pre-glomerular vascular smooth muscle cells (VSMC) to secrete the macrophage chemoattractant, RANTES; a process decreased by angiotensin II R2 (AT2) inhibition. However, RANTES increased when RGS4 expression was suppressed implicating Gα protein activation in an AT2-RGS4-dependent pathway. RGS4 function, specific to VSMC, was tested in a conditional VSMC-specific RGS4 knockout showing high macrophage density by T2 MRI compared to transgenic and non-transgenic mice after the 10 minute injury. Arteriolar diameter of this knockout was unchanged at successive time points after injury. Thus, RGS4 expression, specific to renal VSMC, inhibits angiotensin II-mediated cytokine signaling and macrophage recruitment during reperfusion, distinct from vasomotor regulation.

ROCK/NF-κB axis-dependent augmentation of angiotensinogen by angiotensin II in primary-cultured preglomerular vascular smooth muscle cells

In angiotensin II (ANG II)-dependent hypertension, the augmented intrarenal ANG II constricts the renal microvasculature and stimulates Rho kinase (ROCK), which modulates vascular contractile responses. Rho may also stimulate angiotensinogen (AGT) expression in preglomerular vascular smooth muscle cells (VSMCs), but this has not been established. Therefore, the aims of this study were to determine the direct interactions between Rho and ANG II in regulating AGT and other renin-angiotensin system (RAS) components and to elucidate the roles of the ROCK/NF-κB axis in the ANG II-induced AGT augmentation in primary cultures of preglomerular VSMCs. We first demonstrated that these preglomerular VSMCs express renin, AGT, angiotensin-converting enzyme, and ANG II type 1 (AT1) receptors. Furthermore, incubation with ANG II (100 pmol/l for 24 h) increased AGT mRNA (1.42 ± 0.03, ratio to control) and protein (1.68 ± 0.05, ratio to control) expression levels, intracellular ANG II levels, and NF-κB activity. In contrast, the ANG II treatment did not alter AT1a and AT1b mRNA levels in the cells. Treatment with H-1152 (ROCK inhibitor, 10 nmol/l) and ROCK1 small interfering (si) RNA suppressed the ANG II-induced AGT augmentation and the upregulation and translocalization of p65 into nuclei. Functional studies showed that ROCK exerted a greater influence on afferent arteriole responses to ANG II in rats subjected to chronic ANG II infusions. These results indicate that ROCK is involved in NF-κB activation and the ROCK/NF-κB axis contributes to ANG II-induced AGT upregulation, leading to intracellular ANG II augmentation.

Gαq G proteins modulate MMP-9 gelatinase during remodeling of the murine femoral artery

BACKGROUND

Vessels heal after injury and G protein-coupled receptors are involved in the vascular smooth muscle cell proliferation required to form intimal hyperplasia. We have previously identified the role of Gαq in vascular smooth muscle cell proliferation in vitro. This study now examines the role of Gαq in the developing intimal hyperplasia in a murine model and the impact of disruption of Gαq signaling on intimal hyperplasia development.

METHODS

We employed a murine femoral wire injury model in which a micro-wire is passed through a branch of the femoral artery and used to denude the common femoral artery. We perfusion-fixed specimens and stained sections with hematoxylin-eosin and Movat's stains such that morphometric analysis could be performed using an Image-Pro system. We also harvested additional specimens of femoral artery and snap-froze them for Western blotting or zymography, to allow for the study of G protein expression and both protease expression and activity. We used contralateral vessels as controls. We immersed additional vessels in pluronic gel containing the chemical Gαq G protein inhibitors GP-2A, siRNA to Gαq or adenovirus containing mutant inactive Gαq.

RESULTS

Gαq expression increased in a time-dependent manner after femoral artery injury. Sham-operated vessels did not produce such a response. Inhibition of Gαq reduced cell proliferation without affecting cell migration. Interruption of Gαq signaling also inhibited the development of intimal hyperplasia. Inhibition of Gαq did not alter peak urinary-type plasminogen activator activity and expression, but did increase early plasminogen activator inhibitor-1 activity and expression. Inhibition of Gαq reduced peak metalloproteinase (MMP)-9 activity at Day 3 but did not influence peak MMP-2 activity at Day 7. Protein expression for MMP-9 was also decreased, but that of MMP-2 was not affected. There were no changes in the expression or the activity of the respective inhibitors for MMP-9 and MMP-2, and tissue inhibitor of metalloproteinases-1 and -2.

CONCLUSIONS

These data demonstrate that femoral wire injury in the mouse is associated with a time-dependent increase in Gαq expression. Inhibition of Gαq alters cell proliferation and is associated with decreased MMP-9 expression and activity.

2'-AMP and 3'-AMP inhibit proliferation of preglomerular vascular smooth muscle cells and glomerular mesangial cells via A2B receptors

Studies show that kidneys produce 2',3'-cAMP, 2',3'-cAMP is exported and metabolized to 2'-AMP and 3'-AMP, 2'-AMP and 3'-AMP are metabolized to adenosine, 2',3'-cAMP inhibits proliferation of preglomerular vascular smooth muscle cells (PGVSMCs) and glomerular mesangial cells (GMCs), and A(2B) (not A(1), A(2A), or A(3)) adenosine receptors mediate part of the antiproliferative effects of 2',3'-cAMP. These findings suggest that extracellular 2',3'-cAMP attenuates proliferation of PGVSMCs and GMCs partly via conversion to corresponding AMPs, which are metabolized to adenosine that activates A(2B) receptors. This hypothesis predicts that extracellular 2'-AMP and 3'-AMP should exert A(2B) receptor-mediated antiproliferative effects. Therefore, we examined the antiproliferative effects (cell counts) of 2'-AMP and 3'-AMP. In PGVSMCs and GMCs, 2'-AMP and 3'-AMP exerted concentration-dependent antiproliferative effects. 3'-AMP was equipotent with and 2'-AMP was 3-fold less potent than 5'-AMP (prototypical adenosine precursor). In PGVSMCs, the effects of 2'-AMP and 3'-AMP were mimicked by adenosine, and 8-[4-[((4-cyanophenyl)carbamoylmethyl)oxy]phenyl]-1,3-di(n-propyl)xanthine (MRS-1754) (A(2B) receptor antagonist) equally blocked the antiproliferative effects of 2'-AMP, 3'-AMP, and adenosine but less effectively blocked the effects of 2',3'-cAMP. Similar results were obtained in GMCs except that MRS-1754 also incompletely blocked the effects of 3'-AMP. We conclude that in PGVSMCs, 2'-AMP and 3'-AMP are antiproliferative, the antiproliferative effects of 2'-AMP and 3'-AMP are mediated nearly entirely by adenosine/A(2B) receptors, and some of the antiproliferative effects of 2',3'-cAMP are independent of adenosine/A(2B) receptors. Similar conclusions apply to GMCs except that 3'-AMP also has actions independent of adenosine/A(2B) receptors. Because A(2B) receptors are renoprotective, 2'-AMP and 3'-AMP may provide renoprotection by generating adenosine that activates A(2B) receptors.

Comparison of inhibitors of superoxide generation in vascular smooth muscle cells

BACKGROUND AND PURPOSE

We compared the dose-dependent reductions in cellular superoxide anion (O(2)(-)) by catalytic agents: superoxide dismutase (SOD), polyethylene glycol (PEG)-SOD and the nitroxide 4-hydroxy-2,2,6,6,-tetramethylpiperidine-1-oxyl (tempol) with uncharacterized antioxidants: 5,10,15,20-tetrakis (4-sulphonatophenyl) porphyrinate iron (III)(Fe-TTPS), (-)-cis-3,3',4',5,7-pentahydroxyflavane (2R,3R)-2-(3,4-dihydroxyphenyl)-3,4-dihydro-1(2H)-benzopyran-3,5,7-triol (-epicatechin), 2-phenyl-1,2-benzisoselenazol-3(2H)-one (ebselen) and N-acetyl-L-cysteine (NAC) with the spin trap nitroblue tetrazolium (NBT) and with the vitamins or their analogues: ascorbate, alpha-tocopherol and 6-hydroxy-2,5,7,8-tetramethylkroman-2-carboxy acid (trolox).

EXPERIMENTAL APPROACH

O(2)(-) was generated in primary cultures of angiotensin II-stimulated preglomerular vascular smooth muscle cells from spontaneously hypertensive rats and detected by lucigenin-enhanced chemiluminescence.

KEY RESULTS

SOD, PEG-SOD, NAC and tempol produced a similar maximum inhibition of O(2)(-) of 80-90%. -Epicatechin, NBT, ebselen and Fe-TTPS were significantly (P < 0.0125) less effective (50-70%), whereas trolox, alpha-tocopherol and ascorbate had little action even over 24 h of incubation (<31%). Effectiveness in disrupted and intact cells was similar for the permeable agents, PEG-SOD and tempol, but was enhanced for SOD. Generation of O(2)(-) was increased by NAC and NBT at low concentrations but reduced at high concentrations.

CONCLUSIONS AND IMPLICATIONS

Maximum effectiveness against cellular production of O(2)(-) requires cell membrane permeability and catalytic action as exemplified by PEG-SOD or tempol. NAC and NBT have biphasic effects on O(2)(-) production. Vitamins C and E or analogues have low efficacy.

Identity of the renin cell is mediated by cAMP and chromatin remodeling: an in vitro model for studying cell recruitment and plasticity

The renin-angiotensin system (RAS) regulates blood pressure and fluid-electrolyte homeostasis. A key step in the RAS cascade is the regulation of renin synthesis and release by the kidney. We and others have shown that a major mechanism to control renin availability is the regulation of the number of cells capable of making renin. The kidney possesses a pool of cells, mainly in its vasculature but also in the glomeruli, capable of switching from smooth muscle to endocrine renin-producing cells when homeostasis is threatened. The molecular mechanisms governing the ability of these cells to turn the renin phenotype on and off have been very difficult to study in vivo. We, therefore, developed an in vitro model in which cells of the renin lineage are labeled with cyan fluorescent protein and cells actively making renin mRNA are labeled with yellow fluorescent protein. The model allowed us to determine that it is possible to culture cells of the renin lineage for numerous passages and that the memory to express the renin gene is maintained in culture and can be reenacted by cAMP and chromatin remodeling (histone H4 acetylation) at the cAMP-responsive element in the renin gene.

Angiotensin-converting enzyme inhibition attenuates myonuclear addition in overloaded slow-twitch skeletal muscle

Because optimal overload-induced skeletal muscle hypertrophy requires ANG II, we aimed to determine the effects of blocking ANG II production [via angiotensin-converting enzyme (ACE) inhibition] on potential mediators of hypertrophy in overloaded skeletal muscle, namely, myonuclear addition and fibroblast content. In a 2 × 2 design, adult (200–225 g) female Sprague-Dawley rats were placed into one of four groups ( n = 8/group): 7-day skeletal muscle overload, sham operation, 7-day skeletal muscle overload with ACE inhibition, or sham operation with ACE inhibition. Functional overloads of the plantaris and soleus muscles were produced via bilateral surgical ablation of the synergistic gastrocnemius muscle, and ACE inhibition was accomplished by the addition of the ACE inhibitor enalapril maleate to the animals' daily drinking water (0.3 mg/ml). Myonuclear addition and extrasarcolemmal nuclear proliferation, as measured by in vivo 5-bromo-2′-deoxyuridine labeling, were significantly ( P ≤ 0.05) increased by overload in both the slow-twitch soleus and fast-twitch plantaris muscles. Furthermore, ACE inhibition attenuated these overload-induced increases in the soleus muscle but not in the plantaris muscle. However, the effect of ACE inhibition on soleus extrasarcolemmal nuclei was not likely due to differences in fibroblast content because overload elicited significant increases in vimentin-positive areas in soleus and plantaris muscles, and these areas were unaffected by ACE inhibition in either muscle. There was no effect of ACE inhibition on any measure in sham-operated muscles. Collectively, these data indicate that ANG II may mediate the satellite cell response to overload in slow-twitch soleus but not in fast-twitch plantaris muscles and that this effect may occur independently of changes in fibroblast content.

Vascular ENaC proteins are required for renal myogenic constriction

The myogenic response is an essential component of renal blood flow autoregulation and is the inherent ability of vascular smooth muscle cells (VSMCs) to contract in response to increases in intraluminal pressure. Although mechanosensitive ion channels are thought to initiate VSMC stretch-induced contraction, their molecular identity is unknown. Recent reports suggest degenerin/epithelial Na(+) channels (DEG/ENaC) may form mechanotransducers in sensory neurons and VSMCs; however, the role of DEG/ENaC proteins in myogenic constriction of mouse renal arteries has not been established. To test the hypothesis that DEG/ENaC proteins are required for myogenic constriction in renal vessels, we first determined expression of ENaC transcripts and proteins in mouse renal VSMCs. Then, we determined pressure- and agonist-induced constriction and changes in vascular smooth muscle cytosolic Ca(2+) and Na(+) in isolated mouse renal interlobar arteries following DEG/ENaC inhibition with amiloride and benzamil. We detect alpha-, beta-, and gammaENaC transcript and protein expression in cultured mouse renal VSMC. In contrast, we detect only beta- and gamma- but not alphaENaC protein in freshly dispersed mrVMSC. Selective DEG/ENaC inhibition, with low doses of amiloride and benzamil, abolishes pressure-induced constriction and increases in cytosolic Ca(2+) and Na(+) without diminishing agonist-induced responses in isolated mouse interlobar arteries. Our findings indicate that DEG/ENaC proteins are required for myogenic constriction in mouse interlobar arteries and are consistent with our hypothesis that DEG/ENaC proteins may be components of mechanosensitive ion channel complexes required for myogenic vasoconstriction.

Enhanced Activation of RhoA by Angiotensin II in SHR Preglomerular Microvascular Smooth Muscle Cells

Angiotensin II causes a greater renal vasoconstriction in spontaneously hypertensive rats (SHR) than in normotensive Wistar Kyoto rats (WKY), and alpha2-adrenoceptor agonists potentiate angiotensin II-induced renal vasoconstriction more in SHR. Because angiotensin II activates RhoA, and RhoA contributes to vasoconstriction, we tested the hypothesis that the ability of angiotensin II to stimulate RhoA in preglomerular vascular smooth muscle cells and the ability of alpha2-adrenoceptor activation to potentiate this response are augmented in cells from SHR. In SHR preglomerular vascular smooth muscle cells, angiotensin II (1 micromol/L) greatly stimulated RhoA activity, and this effect was markedly potentiated by UK 14,304 (1 micromol/L; alpha2-adrenoceptor agonist) (fold increase from vehicle-treated cells: 9.0 +/- 2, 0.8 +/- 0.2, and 13.6 +/- 3.2 in cells treated with angiotensin II, UK 14,304, and angiotensin II + UK 14,304, respectively). In contrast, in WKY cells, angiotensin II only mildly activated RhoA (2.0 +/- 0.50), and this response was not enhanced by UK 14,304. The expression of Galpha12 and Galpha13, G-proteins thought to link G-protein-coupled receptors to RhoA, was not increased in SHR cells. We conclude that angiotensin II-induced activation of RhoA is much more robust in the preglomerular microcirculation of SHR compared with WKY and that this may contribute to the etiology of genetic hypertension.

cAMP phosphodiesterase inhibitors potentiate effects of prostacyclin analogs in hypoxic pulmonary vascular remodeling

We investigated the effects of prostacyclin analogs and isoform-selective phosphodiesterase (PDE) inhibitors, alone and in combination, on pulmonary vascular remodeling in vitro and in vivo. Vascular smooth muscle cells (VSMC) isolated from pulmonary (proximal and distal) and systemic circulations demonstrated subtle variations in expression of PDE isoform mRNA. However, using biochemical assays, we found PDE3 and PDE4 isoforms to be responsible for the majority of cAMP hydrolysis in all VSMC. In growth assays, the prostacyclin analogs cicaprost and iloprost inhibited mitogen-induced proliferation of VSMC in a cAMP-dependent manner. In addition, isoform-selective antagonists of PDEs 1, 3, or 4 inhibited VSMC proliferation, an effect that synergized with the effect of prostacyclin analogs. The inhibitory effects were greater in cells isolated from pulmonary circulation. In an in situ perfused rat lung preparation, administration of prostacyclin analogs or the PDE inhibitors vinpocetine (PDE1), cilostamide (PDE3), or rolipram (PDE4), but not EHNA (PDE2), attenuated acute hypoxic vasoconstriction (HPV). Combinations of agents led to a greater reduction in HPV. Furthermore, during exposure to hypoxia for 13 days, Wistar rats were treated with iloprost, rolipram, cilostamide, or combinations of these agents. Compared with normoxic controls, hypoxic animals developed pulmonary hypertension and distal pulmonary artery muscularization. These parameters were attenuated by iloprost+cilostamide, iloprost+rolipram, and cilostamide+rolipram but were not significantly affected by single agents. Together, these findings provide a greater understanding of the role of cAMP PDEs in VSMC proliferation and provide rationale for combined use of prostacylcin analogs plus PDE3/4 inhibitors in treatment of pulmonary vascular remodeling.

ANG II activates effectors of mTOR via PI3-K signaling in human coronary smooth muscle cells

We have previously shown that the vasoconstrictive peptide angiotensin II (ANG II) is a hypertrophic agent for human coronary artery smooth muscle cells (cSMCs), which suggests that it plays a role in vascular wall thickening. The present study investigated the intracellular signal transduction pathways involved in the growth response of cSMCs to ANG II. The stimulation of protein synthesis by ANG II in cSMCs was blocked by the immunosuppressant rapamycin, which is an inhibitor of the mammalian target of rapamycin (mTOR) signaling pathway that includes the 70-kDa S6 kinase (p70(S6k)) and plays a key role in cell growth. The inhibitory effect of rapamycin was reversed by a molar excess of FK506; this indicates that both agents act through the common 12-kDa immunophilin FK506-binding protein. ANG II caused a rapid and sustained activation of p70(S6k) activity that paralleled its phosphorylation, and both processes were blocked by rapamycin. In addition, both of the phosphatidylinositol 3-kinase inhibitors wortmannin and LY-294002 abolished the ANG II-induced increase in protein synthesis, and wortmannin also blocked p70(S6k) phosphorylation. Furthermore, ANG II triggered dissociation of the translation initiation factor, eukaryotic initiation factor-4E, from its regulatory binding protein 4E-BP1, which was also inhibited by rapamycin and wortmannin. In conclusion, we have shown that ANG II activates components of the rapamycin-sensitive mTOR signaling pathway in human cSMCs and involves activation of phosphatidylinositol 3-kinase, p70(S6k), and eukaryotic initiation factor-4E, which leads to activation of protein synthesis. These signaling mechanisms may mediate the growth-promoting effect of ANG II in human cSMCs.

[Proteomic analysis of proteins involved in the renal phenotype in renovascular hypertension]

Renovascular hypertension is characterised by stenosis of the renal artery and high plasma renin levels due to the recruitment of renin-producing cells along the afferent arterioles. This increase in myoepithelioid cells is mainly a result of the differentiation of existing smooth muscle cells with acquisition of a secretory phenotype. To understand the molecular mechanisms involved in this recruitment, we used the model of renovascular hypertension known as the two-kidney, one-clip model in the Lewis rat. Renal arterioles were isolated using magnetised iron suspension. Differential proteomic analysis was performed using two-dimensional electrophoresis gel followed by mass spectrometry for identification. The most striking protein revealed by proteomics is troponin T, which is down-regulated in the afferent arterioles of the clipped kidney. Confocal microscopy showed that troponin T is specific to the smooth muscle phenotype and absent in the myoepithelioid phenotype.

Isolation and Culture of Arterial Smooth Muscle Cells From Human Placenta

A simple and economical technique was developed to isolate and culture human arterial smooth muscle cells from chorionic plate vessels. Placentas from healthy women were collected at the time of term delivery. Chorionic plate arteries were identified, excised, and cut into small pieces. An explant technique was used to grow cultures of placental arterial smooth muscle (PASM) cells. Small pieces of vessel with lumens down were placed in 100-mm culture plates and grown in Dulbecco modified eagle medium and 10% fetal bovine serum. Cells appeared from explants within 1 week and grew to confluence in approximately 4 weeks. At confluence, PASM cell cultures had a uniform cell morphology that was characterized by elongated cells in parallel rows, typical of smooth muscle cells. Smooth muscle cell phenotype was evaluated by morphology and by immunoblotting and immunofluorescence of smooth muscle myofilament proteins. All PASM cell cultures expressed α-smooth muscle actin, β-tropomyosin, and h-caldesmon. Expression was similar to that of human aortic smooth muscle cells, but not to endothelial cells or fibroblasts. PASM cells stained uniformly for α-smooth muscle actin and lacked staining for a fibroblast-specific antigen. PASM cells were evaluated for their response to inflammatory mediators, tumor necrosis factor-α, and interleukin-1β by measurement of interleukin-8 production. Cells cultured for 18 hours showed a progressive increase in interleukin-8 production with time. Treatment with inflammatory mediators increased interleukin-8 production by 3-fold as compared with media control. This technique provides a simple method to obtain normal human arterial smooth muscle cells for in vitro studies of physiology and pathophysiology.

Role of Gαq in smooth muscle cell proliferation

BACKGROUND

G protein-linked receptors are involved in the processes that lead to intimal hyperplasia. This study examined the role of Galphaq signaling pathways in vascular smooth muscle cell (SMC) proliferation in vitro.

METHODS

Rat pulmonary artery SMCs were cultured in vitro. Standard assays of cellular DNA synthesis, proliferation, phospholipase C-beta (PLCbeta) activation, and extracellular signal-regulated kinase (ERK1/2) phosphorylation were used to study the response to angiotensin II (a specific Galphaq agonist; 0.1-100 micromol/L) in the presence and absence of GP-2A (a competitive Galphaq inhibitor; 10 micromol/L) and the PLCbeta inhibitor U73122 (10micromol/L).

RESULTS

Angiotensin II induced SMC DNA synthesis and cell proliferation. DNA synthesis was inhibited by both Galphaq inhibitor, GP-2A, and PLCbeta inhibitor U73122, in a dose-dependent manner (66% +/- 7% of angiotensin II alone at 10 micromol/L for GP-2A [P <.05] and 63% +/- 6% for U73122). GP-2A completely inhibited angiotensin II-induced Galphaq-mediated PLCbeta phosphorylation. Activation of ERK1/2 by angiotensin II was significantly reduced by GP-2A (P <.05) and by PLCbeta inhibition (P <.05).

CONCLUSION

Inhibition of Galphaq decreases PLCbeta and ERK1/2 phosphorylation, leading to decreased SMC proliferation in vitro. Understanding specific signal transduction pathways will be an integral component of anti-restenosis therapy.Clinical Relevance The universal response of a blood vessel to injury is chronic wound healing, which includes the development of intimal hyperplasia and subsequent remodeling of the vessel wall. This can lead to luminal narrowing in as many as 30% of patients undergoing angioplasty. Neointimal formation is the principal cause of in-stent recurrent stenosis. Intimal hyperplasia is in part produced by smooth muscle cell (SMC) proliferation. Understanding the keys to the proliferation of SMCs will enable therapies to be developed that may inhibit the initial development of intimal hyperplasia. Whereas in the past many studies focused on the multiple mechanical, humoral, and cellular elements that induce SMC proliferation, molecular therapeutics focuses on key choke points within the cell that can be used to inhibit proliferation. One of these key choke points is signal transduction. Galphaq is one of the ubiquitous signal transduction proteins on the membrane of SMCs. Inhibiting G proteins, such as Galphaq, would enable interference with a significant amount of the mechanical, humeral, and cellular elements that produce SMC proliferation, and thus decrease the development of intimal hyperplasia. The present study identifies and begins to map out the role of Galphaq in SMC proliferation and investigates the possible use of a small peptide in its inhibition. Other data suggest that inhibition of other G proteins will also decrease intimal hyperplasia. This is therefore a fertile area for the development of therapeutics to inhibit intimal hyperplasia. The direct relevance to the clinician is that this study identifies a transduction pathway that may be inhibited, and points in the direction of a possible molecular therapeutic target that would be beneficial as an adjunct to angioplasty or as part of a drug-eluding stent regimen.

Calcitonin gene-related peptide partly protects cultured smooth muscle cells from apoptosis induced by an oxidative stress via activation of ERK1/2 MAPK

Oxidative stress induced by a glucose/glucose oxidase (G/GO) generator system dose-dependently decreased the viability of cultured vascular smooth muscle cells (VSMC) as estimated by MTT assay. Cell death was induced in 40% of cells exposed to 0.2 IU/ml of the free radical generating mixture. Annexin-V labeling, Hoechst staining together with DNA laddering demonstrated that apoptosis was responsible for this cell loss. Pretreatment of the cells with 10(-8) M calcitonin gene-related peptide (CGRP) significantly attenuated the damaging effect of the oxidative stress. Indeed, cell viability was estimated to be 80% in CGRP-treated group, instead of 60% in absence of CGRP treatment. This protective effect of CGRP was antagonized by 8-37 CGRP, an antagonist of CGRP-1 receptors, whereas it was not reproduced by amylin, a CGRP analogue. As indicated by the reduction in Hoechst staining and in DNA laddering, CGRP prevented the onset of apoptosis. We also demonstrated that the peptide significantly up-regulated the activation of ERK1/2 and P38 kinases. Inhibitors of the kinases prevented the protective effect of CGRP. We conclude that CGRP antagonizes oxidative stress-induced apoptosis by up-regulating MAP kinase activation and that activation of these kinases was necessary to protection.

Troponin T as a marker of differentiation revealed by proteomic analysis in renal arterioles

Renovascular hypertension is characterized by stenosis of the renal artery and high plasma renin levels. The renal phenotype is characterized by high levels of renin in the hypoperfused kidney due to the recruitment of renin-producing cells along the afferent arterioles. This increase in myoepithelioïd cells is due mainly to the differentiation of existing smooth muscle cells with acquisition of a secretory phenotype. To understand the molecular mechanisms involved in this recruitment, we used the established rat model of renovascular hypertension known as the two-kidney, one-clip model in the Lewis rat. Renal arterioles were isolated using magnetized iron suspension. Differential proteomic analysis was performed using 2-D polyacrylamide gel electrophoresis followed by mass spectrometry. Comparative analysis of soluble proteins extracted from afferent arterioles of clipped and contralateral kidneys showed 14 proteins significantly differentially expressed by at least a factor of 2. These proteins were identified by mass spectrometry. The most striking protein revealed by proteomics is troponin T, which is down-regulated in the afferent arterioles of the clipped kidney. Confocal microscopy showed that troponin T is specific of the smooth muscle phenotype and absent in the myoepithelioïd phenotype. Our data suggest that troponin T is only present in renal smooth muscle cells.

Angiotensin II activates extracellular signal regulated kinases via protein kinase C and epidermal growth factor receptor in breast cancer cells

Angiotensin II (Ang II) induces, through AT1, intracellular Ca(2+) increase in both normal and cancerous breast cells in primary culture (Greco et al., 2002 Cell Calcium 2:1-10). We here show that Ang II stimulated, in a dose-dependent manner, the 24 h-proliferation of breast cancer cells in primary culture, induced translocation of protein kinase C (PKC)-alpha, -beta1/2, and delta (but not -epsilon, -eta, -theta, -zeta, and -iota), and phosphorylated extracellular-regulated kinases 1 and 2 (ERK1/2). The proliferative effects of Ang II were blocked by the AT1 antagonist, losartan. Also epidermal growth factor (EGF) had mitogenic effects on serum-starved breast cancer cells since induced cell proliferation after 24 h and phosphorylation of ERK1/2. The Ang II-induced proliferation of breast cancer cells was reduced by (a) Gö6976, an inhibitor of conventional PKC-alpha and -beta1, (b) AG1478, an inhibitor of the tyrosine kinase of the EGF receptor (EGFR), and (c) downregulation of 1,2-diacylglycerol-sensitive PKCs achieved by phorbol 12-myristate 13-acetate (PMA). A complete inhibition of the Ang II-induced cell proliferation was achieved using the inhibitor of the mitogen activated protein kinase kinase (MAPKK or MEK), PD098059, or using Gö6976 together with AG1478. These results indicate that in human primary cultured breast cancer cells AT1 regulates mitogenic signaling pathways by two simultaneous mechanisms, one involving conventional PKCs and the other EGFR transactivation.

Acute intrarenal infusion of ANG II does not stimulate immediate early gene expression in the kidney

ANG II is capable of stimulating expression of immediate early genes such as egr-1 and c-fos in a variety of cultured cells, including cells of renal origin. To investigate whether ANG II can stimulate early growth response gene expression in vivo, we studied the effects of acute renal artery infusion of low-dose ANG II (2.5 ng small middle dot kg(-1) small middle dot min(-1)) or vehicle on the renal expression of c-fos and egr-1 genes in rats. ANG II infusion for 30 or 240 min decreased renal vascular conductance by approximately 13 and 8%, respectively, compared with the vehicle group. Expression of the early growth response genes c-fos and egr-1 was analyzed using Northern blot hybridization. No significant upregulation of c-fos or egr-1 mRNA levels was detected in rats that received ANG II for either 30 or 240 min, compared with the vehicle groups. We conclude that ANG II, at doses that cause significant physiological effects, does not increase the renal expression of c-fos or egr-1 genes over periods of up to 4 h in vivo.

'Slow pressor' hypertension from low-dose chronic angiotensin II infusion

1. Angiotensin (Ang) II causes growth-related effects on vascular smooth muscle cells in vitro and in vivo. 2. Chronic infusions of AngII systemically, at doses that are initially subpressor, result in slowly progressive increases in arterial pressure ('slow-pressor' hypertension). It has been suggested that the hypertension is due to induced growth in systemic resistance vessel walls by the AngII infusions. 3. We report the results of several studies investigating whether there are also induced structural changes in renal resistance vessels during chronic AngII infusions. We have developed models in Sprague-Dawley rats in which low-dose AngII infusions, either into the renal artery (thus restricting the effects to the kidney) or systemically, result in hypertension. 5. In both models, we have evidence suggesting that chronic AngII infusions have resulted in apparent structurally induced reductions in renal vasculature lumen upstream to the glomerulus. 6. The role of these renal changes in the development of the hypertension remain to be determined.

High glucose induces cell death of cultured human aortic smooth muscle cells through the formation of hydrogen peroxide

Alterations of the vessel structure, which is mainly determined by smooth muscle cells through cell growth and/or cell death mechanisms, are characteristic of diabetes complications. We analysed the influence of high glucose (22 mM) on cultured human aortic smooth muscle cell growth and death, as hyperglycaemia is considered one of the main factors involved in diabetic vasculopathy. Growth curves were performed over 96 h in medium containing 0.5% foetal calf serum. Cell number increased by 2 - 4 fold over the culture period in the presence of 5.5 mM (low) glucose, while a 20% reduction in final cell number was observed with high glucose. Under serum-free conditions, cell number remained constant in low glucose cultures, but a 40% decrease was observed in high glucose cultures, suggesting that high glucose may induce increased cell death rather than reduced proliferation. Reduced final cell number induced by high glucose was also observed after stimulation with 5 or 10% foetal calf serum. The possible participation of oxidative stress was investigated by co-incubating high glucose with different reactive oxygen species scavengers. Only catalase reversed the effect of high glucose. Intracellular H(2)O(2) content, visualized with 2',7'-dichlorofluorescein and quantified by flow cytometry, was increased after high glucose treatment. To investigate the cell death mechanism induced by high glucose, apoptosis and necrosis were quantified. No differences were observed regarding the apoptotic index between low and high glucose cultures, but lactate dehydrogenase activity was increased in high glucose cultures. In conclusion, high glucose promotes necrotic cell death through H(2)O(2) formation, which may participate in the development of diabetic vasculopathy.

Genetic evidence that lethality in angiotensinogen-deficient mice is due to loss of systemic but not renal angiotensinogen

Angiotensinogen (AGT)-deficient mice die shortly after birth presumably due to renal dysfunction caused by the presence of severe vascular and tubular lesions in the kidney. Because AGT is expressed in renal proximal tubule cells, we hypothesized that its loss may be the primary mediator of the lethal phenotype. We generated two models to test this hypothesis by breeding transgenic mice expressing human renin with mice expressing human AGT (hAGT) either systemically or kidney-specifically. We then bred double transgenic mice with AGT+/- mice, intercrossed the compound heterozygotes, and examined the offspring. We previously reported that the presence of the human renin and systemically expressed hAGT transgene complemented the lethality observed in AGT-/- mice. On the contrary, we show herein that the presence of the human renin and kidney-specific hAGT transgene cannot rescue lethality in AGT-/- mice. An analysis of newborns indicated that AGT-/- mice were born in normal numbers, and collection of dead 10-day old pups revealed an enrichment in AGT-/-. Importantly, we demonstrated that angiotensinogen protein and functional angiotensin II was generated in the kidney, and the kidney-specific transgene was temporally expressed during renal development similar to the endogenous AGT gene. These data strongly support the notion that the loss of systemic AGT, but not intrarenal AGT, is responsible for death in the AGT-/- mouse model. Taken together with our previous studies, we conclude that the intrarenal renin-angiotensin system located in the proximal tubule plays an important role in blood pressure regulation and may cause hypertension if overexpressed, but may not be required for continued development of the kidney after birth.

A human tissue-engineered vascular media: a new model for pharmacological studies of contractile responses

Our method for producing tissue-engineered blood vessels based exclusively on the use of human cells, i.e., without artificial scaffolding, has previously been described (1). In this report, a tissue-engineered vascular media (TEVM) was specifically produced for pharmacological studies from cultured human vascular smooth muscle cells (VSMC). The VSMC displayed a differentiated phenotype as demonstrated by the re-expression of VSMC-specific markers and actual tissue contraction in response to physiological stimuli. Because of their physiological shape and mechanical strength, rings of human TEVM could be mounted on force transducers in organ baths to perform standard pharmacological experiments. Concentration-response curves to vasoconstrictor agonists (histamine, bradykinin, ATP, and UTP) were established, with or without selective antagonists, allowing pharmacological characterization of receptors (H1, B2, and P2Y1, and pyrimidinoceptors). Sustained agonist-induced contractions were associated with transient increases in cytosolic Ca2+ concentration, suggesting sensitization of the contractile machinery to Ca2+. ATP caused both Ca2+ entry and Ca2+ release from a ryanodine- and caffeine-sensitive store. Increased cyclic AMP or cyclic GMP levels caused relaxation. This human TEVM displays many of functional characters of the normal vessel from which the cells were originally isolated, including contractile/relaxation responses, cyclic nucleotide sensitivity, and Ca2+ handling mechanisms comparable to those of the normal vessel from which the cells were originally isolated. These results demonstrate the potential of this human model as a versatile new tool for pharmacological research.

Thapsigargin induces apoptosis in cultured human aortic smooth muscle cells

Vascular remodeling is a key feature of many pathologic states, including atherosclerosis, or hypertension. Vascular smooth muscle cells participate in determining the vessel structure by several mechanisms such as cell migration, cell growth, or cell death (necrosis or apoptosis). Here we report that thapsigargin, an inhibitor of endoplasmic reticulum Ca2+ -adenosine triphosphatase (ATPase), is able to induce apoptosis in human vascular smooth muscle cells (HVSMCs). Apoptosis was assessed by three different methods: differential chromatin binding dye staining. cytoplasmic histone-associated DNA fragments detection by enzyme-linked immunosorbent assay (ELISA) and terminal deoxyribonucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). When HVSMCs were treated for 1 h with thapsigargin (100 nM-10 microM), there was a concentration-dependent increase in both parameters 24 h after the thapsigargin pulse. When a time-course experiment was performed, both parameters were significantly enhanced from 3 to 6 h after the exposure to thapsigargin. We conclude that thapsigargin promotes apoptosis in HVSMCs, providing a useful tool for the study of programmed cell death in human vascular smooth muscle.

Culture of vascular smooth muscle cells from small arteries of the rat kidney

BACKGROUND

In contrast to arterioles, small arteries appear to be the preferential site of renal vascular smooth muscle cell (VSMC) proliferation under pathophysiological conditions. To date, techniques have been described to isolate renal arterioles and to culture VSMCs. The aim of the present study was to develop a method of culturing VSMCs from isolated small arteries of the rat kidney and to characterize their growth as compared with that of aortic VSMCs.

METHODS

Renal vascular trees were isolated from kidneys of male Wistar rats by a sieving technique. VSMCs were grown from explants of collagenase-treated renal vascular trees and thoracic aorta. Growth curves and proliferation of renal and aortic VSMCs in response to fetal bovine serum (FBS) were compared by determination of cell number and DNA synthesis, measured as incorporation of 5-bromo-2'-deoxyuridine.

RESULTS

Renal vascular trees consisted mainly of small arteries with a diameter of 80 to 400 microm (interlobar and arcuate arteries). As compared with total kidney or renal cortex, alkaline phosphatase activity was decreased by 81%, and vasopressin (10 micromol/L) was unable to stimulate adenylyl cyclase in renal vascular trees, indicating little tubular contamination. A homogenous population of spindle-shaped cells was cultured from renal vascular trees, which grew in a hill-and-valley pattern and stained positively for smooth muscle alpha-actin, according to the characteristics of VSMC phenotype. Renal VSMCs proliferated more slowly than aortic VSMCs and reached the plateau of growth at about half of the cell density of aortic VSMCs. Furthermore, proliferation of renal VSMCs depended more heavily on FBS concentration, since about threefold higher concentrations of FBS were needed for renal VSMCs to multiply at the same rate and to similarly stimulate DNA synthesis as compared with aortic VSMCs.

CONCLUSIONS

We present a method to culture renal VSMCs from small arteries of the rat kidney, which possess distinct growth characteristics as compared with aortic VSMCs.

Activated STAT1 suppresses proliferation of cultured rat mesangial cells

BACKGROUND

JAK-STAT signaling has been shown to promote development and proliferation in lymphopoietic and hematopoietic lineages. We investigated the effect of activated STAT1 on mesangial cell proliferation.

METHODS

Rat mesangial cells of primary culture (rMCs) were used in the following experiments: (1) Whole cell lysates were immunoblotted against JAK1 and JAK2. (2) Whole cell lysates and nuclear proteins were extracted from rMCs with or without treatment with interferon-gamma, and immunoblotting was performed against both STAT1 and tyrosine (701)-phosphorylated STAT1. (3) rMCs and rMCs electroporated with either wild-type STAT1, mutated STAT1, or antibody against STAT1 were incubated with interferon-gamma for 20 hours, followed by a further incubation with [3H]-thymidine for four hours.

RESULTS

JAK1, JAK2, and STAT1 were detected in whole cell lysates, suggesting that JAK-STAT signaling could be activated by interferon-gamma (INF-gamma). Using an antibody specific for tyrosine-phosphorylated STAT1, we detected signal in the INF-gamma-treated nuclear extracts, which showed translocation of phosphorylated STAT1 to the nucleus. [3H]-thymidine incorporation in the presence of INF-gamma was significantly lower than that of control in a dose-dependent manner. The introduction of wild-type STAT1 enhanced the effect of interferon-gamma and decreased [3H]-thymidine incorporation, whereas tyrosine-mutated (Y701F) STAT1 and SH2 domain (R602T)-mutated STAT1 reversed INF-gamma-induced suppression of [3H]-thymidine incorporation. Electroinjected antibody against STAT1 increased [3H]-thymidine incorporation upon stimulation with INF-gamma.

CONCLUSION

STAT1 activated by interferon-gamma suppresses mesangial cell proliferation.

AT(1)-signalling in vascular smooth muscle

Angiotensin II activates multiple signalling pathways in vascular smooth muscle. The precise pattern of signals and their relative importance to a particular functional response depends on both cell type and differentiation state. Although the contractile and trophic effects of Ang II are often thought of as distinct responses it is increasingly difficult to differentiate them in terms of signalling pathways. Since vasoconstriction and abnormal growth are both features of circulatory diseases such as hypertension and atherosclerosis a better understanding of the signalling pathways responsible for the vasoconstrictor and trophic actions of this peptide may help define novel therapeutic targets in cardiovascular disease.

Differential regulation of p27(Kip1) expression by mitogenic and hypertrophic factors: Involvement of transcriptional and posttranscriptional mechanisms

Platelet-derived growth factor-BB (PDGF-BB) acts as a full mitogen for cultured aortic smooth muscle cells (SMC), promoting DNA synthesis and cell proliferation. In contrast, angiotensin II (Ang II) induces cellular hypertrophy as a result of increased protein synthesis, but is unable to drive cells into S phase. In an effort to understand the molecular basis for this differential growth response, we have examined the downstream effects of PDGF-BB and Ang II on regulators of the cell cycle machinery in rat aortic SMC. Both PDGF-BB and Ang II were found to stimulate the accumulation of G(1) cyclins with similar kinetics. In addition, little difference was observed in the expression level of their catalytic partners, Cdk4 and Cdk2. However, while both factors increased the enzymatic activity of Cdk4, only PDGF-BB stimulated Cdk2 activity in late G(1) phase. The lack of activation of Cdk2 in Ang II-treated cells was causally related to the failure of Ang II to stimulate phosphorylation of the enzyme on threonine and to downregulate p27(Kip1) expression. By contrast, exposure to PDGF-BB resulted in a progressive and dramatic reduction in the level of p27(Kip1) protein. The time course of p27(Kip1) decline was correlated with a reduced rate of synthesis and an increased rate of degradation of the protein. Importantly, the repression of p27(Kip1) synthesis by PDGF-BB was associated with a marked attenuation of Kip1 gene transcription and a corresponding decrease in Kip1 mRNA accumulation. We also show that the failure of Ang II to promote S phase entry is not related to the autocrine production of transforming growth factor-beta1 by aortic SMC. These results identify p27(Kip1) as an important regulator of the phenotypic response of vascular SMC to mitogenic and hypertrophic stimuli.

Interaction of angiotensin II and the insulin-like growth factor system in vascular smooth muscle cells

We studied the effects and interactions of ANG II and the insulin-like growth factor (IGF) system in cultured rat aortic smooth muscle cells. ANG II (1 microM) and IGF-I (10 nM) stimulated both DNA and protein synthesis. The effects of the two peptides in combination were additive or more than additive. The AT(1) receptor antagonist losartan (10 and 100 microM) blocked their synergistic effect on DNA synthesis. IGF binding protein (IGFBP)-1 inhibited the effect of IGF-I but not that of ANG II on DNA synthesis. IGF-I stimulated gene expression of IGFBP-2 and IGFBP-4. ANG II decreased IGF-I, IGFBP-2, and IGFBP-4 transcripts but increased the IGF-I receptor transcript. IGF-I and ANG II in combination had similar effects on gene expression as ANG II alone. The IGFBP-2 and IGFBP-4 peptides could be detected in the conditioned medium. Our results show that ANG II and IGF-I have synergistic effects on vascular smooth muscle cells and that they interact in several ways.

Mechanisms regulating cAMP-mediated growth of bovine neonatal pulmonary artery smooth muscle cells

Neonatal pulmonary artery smooth muscle cells (PASMCs) exhibit enhanced growth capacity and increased growth responses to mitogenic stimuli compared with adult PASMCs. Because intracellular signals mediating enhanced growth responses in neonatal PASMCs are incompletely understood, we questioned whether 1) Gq agonists increase cAMP content and 2) increased cAMP is proproliferative. Endothelin-1 and angiotensin II increased both cAMP content and proliferation in neonatal but not in adult PASMCs. Inhibition of protein kinase C and protein kinase A activity nearly eliminated the endothelin-1- and angiotensin II-induced growth of neonatal PASMCs. Moreover, cAMP increased proliferation in neonatal but not in adult cells. Protein kinase C-stimulated adenylyl cyclase was expressed in both cell types, suggesting that insensitivity to stimulation of cAMP in adult cells was not due to decreased enzyme expression. Our data collectively indicate that protein kinase C stimulation of cAMP is a critical signal mediating proliferation of neonatal PASMCs that is absent in adult PASMCs and therefore may contribute to the unique proproliferative phenotype of these neonatal cells.

Raf-1 kinase activation by angiotensin II in adrenal glomerulosa cells: roles of Gi, phosphatidylinositol 3-kinase, and Ca2+ influx

Little is known of the mechanisms leading to mitogen-activated protein kinase (MAPK) activation via Gq-coupled receptors. We therefore examined the pathways by which angiotensin II (Ang II) activates Raf-1 kinase, an upstream intermediate in the pathway to MAPK, via the Gq-coupled AT1 angiotensin receptor in bovine adrenal glomerulosa (BAG) cells. Ang II caused a rapid and transient activation of Raf-1 that reached a peak at 5-10 min. Ang II was a potent stimulus of Raf-1 activation with an ED50 of 10 pM and a maximal response at 1 nM, although higher Ang II concentrations elicited a submaximal response. Ang II-stimulated Raf-1 activity was unaffected by down-regulation of protein kinase C and intracellular Ca2+ chelation (using BAPTA) but was partially inhibited by pertussis toxin, and was abolished by manumycin A. Removal of extracellular Ca2+ (by EGTA) or blockade of L type Ca2+ channels (by nifedipine), as well as inhibition of MEK-1 kinase (by PD98059), enhanced Raf-1 activity, whereas wortmannin (100 nM) inhibited approximately one half of Ang II-stimulated Raf-1 activity. Hence, Raf-1 kinase activation by Ang II in BAG cells is dependent on Ras, is mediated in part via Gi and phosphatidylinositol 3-kinase, and is negatively regulated via Ca2+ influx and a downstream signaling element(s).

Control of vascular smooth muscle cell growth in fowl

In adult domestic fowl, angiotensin (ANG) receptors are present in the vascular smooth muscles (VSM) and in the endothelium, mediating vasorelaxation via endothelium-derived relaxing factor/cGMP. ANG II-induced relaxation is minor in chicks and becomes more marked as they mature but diminishes in adult birds, whereas ANG II neither relaxes nor contracts endothelium-denuded aortae from mature chickens. The present study examines in cultured fowl aortic SM cells whether (1) ANG II stimulates or inhibits VSM cell growth and, if so, whether this growth-stimulatory or -inhibitory effect changes with maturation/aging, and (2) S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide donor, and cGMP attenuate the basal or stimulated VSM cell growth. [Asp1, Val5]ANG II (native fowl ANG II, 10(-6) M) markedly increased (increase from vehicle control, 226.5%; P < 0.01) [3H]thymidine (Thd) incorporation into DNA of quiescent VSM cells (first subculture) from 6-week-old chicks. This growth-stimulating effect was reduced with age (41.4, 29.6, and 3.2% at 9, 19, and 43 weeks of age, respectively). In contrast, platelet-derived growth factor (PDGF, 20 ng/ml) increased [3H]Thd incorporation similarly in chicks, pullets, and hens. Furthermore, ANG II significantly (45.9%, P < 0.01) attenuated the growth-promoting effect of fetal calf serum in cultured VSM cells from 6-week-old chicks. This inhibitory effect also decreased in older birds. ANG II showed neither a growth-stimulatory nor -inhibitory effect in cultured neointimal cells. SNAP attenuated dose dependently (20-60 microM) the basal and PDGF-induced VSM cell growth, whereas cGMP inhibited basal growth only at a high dose (100 microM). These results indicate that in fowl VSM cells, ANG II is mitogenic and antimitogenic in chicks but not in mature birds, suggesting that phenotypic modulation occurs in the ANG receptors/signaling mechanism with maturation/age or in neointimal cells, whereas the mitogenic mechanism via PDGF remains in both young and mature birds.

Effects of long-term intrarenal angiotensin II infusion on renal vascular responsiveness to vasoactive agents

1. We tested whether chronic intrarenal angiotensin II (AngII) infusion altered renal vascular responsiveness to vasoactive agents, which would provide evidence of vascular structural changes. 2. The renal blood flow (RBF) responses to renal arterial administration of bolus doses of acetylcholine, glyceryl trinitrate, AngII and noradrenaline were measured before commencement of and 1 day after cessation of 28 days intrarenal AngII infusion (0.5 ng/kg per min) in chronically instrumented conscious dogs. 3. The RBF responses to these vasoactive agents were unaltered by chronic intrarenal AngII infusion in conscious dogs. 4. These functional studies provide no evidence for renal vascular hypertrophy in response to chronic intrarenal AngII infusion in conscious dogs.

Culture and characterization of smooth muscle cells from porcine retinal microvessels

PURPOSE

To establish long-term cultures of retinal vascular smooth muscle cells for future studies of their functions under normal and diseased conditions.

METHODS

Smooth muscle cells (SMC) from porcine retinal microvessels were isolated and cultured.

RESULTS

Cells in culture retained the common biochemical characteristics of SMC propagated from other sources. The cells were large, polygonal, spindle shaped and demonstrated the presence of smooth muscle-specific alpha-actin. Post-confluent cultures showed the 'hill and valley' multilayer growth characteristics. However, the growth rate was lower and the population doubling time was significantly larger than those reported for SMC propagated from big vessels.

CONCLUSION

Retinal vascular SMC could be cultured separately from other cell types. The availability of this culture provides a unique model for functional and metabolic studies of the retinal vessels.

Effects of adenosine deaminase inhibition on blood pressure in old spontaneously hypertensive rats

Adenosine is an ubiquitously occurring endogenous nucleoside that via cell surface receptors exerts multiple antihypertensive actions, and mediates a number of biological responses that may reduce cardiovascular disease risk. Therefore modulation of endogenous levels of adenosine may offer beneficial effects in hypertension. The objective of this study was to determine whether inhibition of adenosine deaminase lowers blood pressure in spontaneously hypertensive rats (SHR). We investigated the effects of erythro-9-(2-hydroxyl-3-nonyl) adenine (EHNA), an adenosine deaminase inhibitor, on hemodynamic and renal parameters in 16-week-old and 36-week-old SHR and normotensive Wistar Kyoto rats (WKY) and in 36-week-old SHR and WKY pretreated with 1,3-dipropyl-8-p-sulfopheznylxanthine (DPSPX, an adenosine antagonist that does not enter the brain and is restricted to the extracellular space). Adenosine deaminase inhibition with EHNA (10 mg/kg, iv.) produced a marked fall in arterial blood pressure in older (MABP 162.0+/-7.6 mmHg and 120.7+/-11.7 mmHg for baseline and EHNA period, respectively; p<0.01), but not younger, SHR, whereas no effects on blood pressure were observed in age-matched normotensive WKY rats. EHNA did not affect renal hemodynamic and excretory function in any of six groups of animals. DPSPX blocked the antihypertensive effects of EHNA, suggesting that the effects of EHNA on blood pressure are mediated via peripheral adenosine receptors. Further studies are required to elucidate why inhibition of adenosine deaminase lowers blood pressure only in older SHR. The present data suggest that inhibition of adenosine deaminase may provide beneficial effects in older hypertensives and lead us to propose that design and use of extracellular adenosine deaminase inhibitors may offer cardiovascular protection in hypertension.

Angiotensin II activates mitogen-activated protein kinase via protein kinase C and Ras/Raf-1 kinase in bovine adrenal glomerulosa cells

Angiotensin II (Ang II) stimulates growth and mitogenesis in bovine adrenal glomerulosa cells, but little is known about the signaling pathways that mediate these responses. An analysis of the growth-promoting pathways in cultured bovine adrenal glomerulosa cells revealed that Ang II, acting via the AT1 receptor, caused rapid but transient activation of mitogen-activated protein kinase (MAPK), with an ED50 of 10-50 pM. Although neither Ca2+ influx nor Ca2+ release from intracellular stores was sufficient to activate MAPK, Ca2+ appeared to play a permissive role in this response. A major component of Ang II-induced MAPK activation was insensitive to pertussis toxin (PTX), although a minor PTX-sensitive component could not be excluded. Ang II also induced the rapid activation of ras and raf-1 kinase with time-courses that correlated with that of MAPK. Activation of protein kinase C (PKC) by phorbol 12-myristate 13-acetate was sufficient to activate both MAPK and raf-1 kinase. However, whereas PKC depletion had no effect on Ang II-induced raf-1 kinase activation, it attenuated Ang II-induced MAPK activation. Ang II also stimulated a mobility shift of raf-1, reflecting hyperphosphorylation of the kinase. However, unlike its activation, raf-1 hyperphosphorylation was dependent on PKC and its time-course correlated not with activation, but rather with deactivation of the kinase. Taken together, these findings indicate that Ang II stimulates multiple pathways to MAPK activation via PKC and ras/raf-1 kinase in bovine adrenal glomerulosa cells.

Angiotensin II and NGF differentially influence microtubule proteins in PC12W cells: role of the AT2 receptor

Angiotensin AT2 receptors have been shown to play a role in cell differentiation characterized by neurite outgrowth in neuronal cells of different origin. To further investigate AT2 receptor-mediated events leading to neurite formation, we examined the effect of AT2 receptor stimulation on the microtubule components, beta-tubulin, MAP1B and MAP2, by Western blot analysis and immunofluorescence in quiescent and nerve growth factor (NGF)-differentiated PC12W cells. These proteins are involved in neurite extension and neuronal maturation. Whereas NGF (0.5, 10, and 50 ng/ml) up-regulated these proteins after 3 days of stimulation, angiotensin II (ANG II; 10(-7) M) induced a different pattern. In quiescent PC12W cells, AT2 receptor stimulation up-regulated polymerized beta-tubulin and MAP2 but down-regulated MAP1B protein levels. In PC12W cells, differentiated by NGF (0.5 ng/ml), ANG II elevated polymerized beta-tubulin and reduced MAP1B. All ANG II effects were abolished by the AT2 receptor antagonist PD123177 (10(-5) M) but not affected by the AT1 receptor antagonist losartan (10(-5) M). These results implicate a specific role of AT2 receptors in cell differentiation and nerve regeneration via regulation of the cytoskeleton.

Heterogeneous smooth muscle cell population derived from small and larger arteries

Vascular lesion formations in such disease states as hypertension and atherosclerosis occur in a district-specific manner. Large conduit and small resistance arteries play district-specific roles in the regulation of organ perfusion. Using a culture method, we studied the morphology and growth of smooth muscle cells derived from small arteries (S-SMCs, less than 90 microm in internal diameter) and from larger arteries (L-SMCs, ranging from 800 to 900 microm) of the rat mesenteric arterial bed. S-SMCs showed a hill-and-valley pattern, whereas L-SMCs showed sheet or whorl formation. The majority of S-SMCs were smaller, bipolar-shaped; in contrast, the majority of L-SMCs were larger, polygonal-shaped. Actin fibers within S-SMCs were oriented in a bipolar manner from the nuclei, whereas those within L-SMCs had a radial appearance. [3H]Thymidine incorporation induced by serum, platelet-derived growth factor-AB (PDGF), or mechanical stretch was greater in S- vs L-SMCs. The population doubling time measured after the addition of serum or PDGF was shorter in S- vs L-SMCs. Thus, distinct morphological and growth phenotypes of SMCs exist in small and larger arteries of the same vascular bed.

G protein mRNA expression in renal microvessels from spontaneously hypertensive and Wistar-Kyoto rats

The exaggerated sensitivity of spontaneously hypertensive rat (SHR) renal microvasculature to angiotensin II (ANG II) may be due to an imbalance between the effectiveness of G alpha s-utilizing vasodilator pathways and vasoconstrictor pathways activated by ANG II (mediated by G alpha i-1, G alpha i-2, G alpha i-3, and G alpha q). Because the alteration appears to be distal to the hormone receptors and proximal to the effector adenylyl cyclase, we hypothesized that SHR have altered amounts of signal-transducing G proteins. This was examined by quantifying the steady-state mRNA levels of specific G alpha subunits in renal microvessels of 12- to 14-wk-old SHR and control Wistar-Kyoto (WKY) rats, using a quantitative-competitive polymerase chain reaction technique coupled to reverse transcription. No significant differences were detected in the absolute levels of G alpha s (0.96 +/- 0.35 vs. 0.74 +/- 0.25 amol/50 ng RNA) or in the relative levels of G alpha i-1 (0.44 +/- 0.05 vs. 0.48 +/- 0.13). G alpha i-2 (40.9 +/- 7.8 vs. 45.2 +/- 8.9), or G alpha i-3 (0.79 +/- 0.05 vs. 0.82 +/- 0.15) normalized to the level of G alpha s for WKY vs. SHR, respectively. The ratio of G alpha q to G alpha s tended to be higher in SHR, but this difference did not achieve statistical significance (0.41 +/- 0.08 vs. 1.04 +/- 0.32, P = 0.08). In conclusion, the steady-state levels of G alpha s, G alpha i-1, G alpha i-2, G alpha i-3, and G alpha q are similar in SHR and WKY renal microvasculature, suggesting that other components of the ANG II signal transduction mechanism are responsible for the enhanced renal vascular responsiveness in SHR.

Phosphodiesterases in the rat renal vasculature

The objective this investigation was to determine the relative importance of type I, III, and IV phosphodiesterases in the regulation of cyclic adenosine monophosphate (cAMP) in the renal circulation. In the first experimental series, four groups of isolated rat kidneys perfused with Tyrode's solution were stimulated with isoproterenol (3 microM) and then treated with increasing concentrations (from the approximately IC50 to 30 times the approximately IC50 in threefold increments) of one of four phosphodiesterase inhibitors: group 1, 3-isobutyl-1-methylxanthine, a "broad-spectrum" phosphodiesterase inhibitor (10-300 microM); group 2, Ro 20-1724, a selective type IV phosphodiesterase inhibitor (3-100 microM); group 3, 8-methoxymethyl-3-isobutyl-1-methylxanthine, a selective type I phosphodiesterase inhibitor (3-100 microM); and group 4, milrinone, a selective type III phosphodiesterase inhibitor (0.3-10 microM). In the second experimental series, five groups of cultured preglomerular (interlobular and afferent arteriolar) vascular smooth-muscle cells were stimulated with isoproterenol (1 microM) and treated with vehicle or supramaximal concentrations (30 times IC50) of either 3-isobutyl-1-methylxanthine (300 microM), Ro 20-1724 (100 microM), 8-methoxymethyl-3-isobutyl-1-methylxanthine (100 microM), or milrinone (10 microM). In perfused kidneys and cultured pre-glomerular vascular smooth-muscle cells, 3-isobutyl-1-methylxanthine and Ro 20-1724 similarly increased renal cAMP release and total cellular (extracellular + intracellular) cAMP levels, respectively. In contrast, neither 8-methoxymethyl-3-isobutyl-1-methylxanthine nor milrinone affected renal cAMP release or total cellular cAMP levels. These data indicate that in the renal circulation, type IV phosphodiesterase is the predominant phosphodiesterase isozyme.

Amphotericin B as an intracellular antioxidant: protection against 2,2'-azobis(2,4-dimethylvaleronitrile)-induced peroxidation of membrane phospholipids in rat aortic smooth muscle cells

The antifungal activity of amphotericin B (AmB) and its side-effects (e.g. nephrotoxicity and hemolytic action) are suggested to be associated with its prooxidant effects in target cells. To test this hypothesis, we have undertaken studies to examine the role of AmB in oxidative stress in cultured rat aortic smooth muscle cells (SMC) incubated in the absence or in the presence of a lipid-soluble azo-initiator of peroxyl radicals, 2,2'-azobis(2,4-dimethylvaleronitrile) (AMVN). No changes in the pattern of membrane phospholipids could be detected by two-dimensional high performance thin-layer chromatography (HPTLC) after oxidative stress induced by AMVN in which the cells remained viable, as judged by trypan blue exclusion. To improve the sensitivity of detection of oxidative stress in the cells, cis-parinaric acid (PnA) was incorporated biosynthetically into the membrane phospholipids [using PnA-human serum albumin (hSA) complex]. Incubation of the cells under aerobic conditions in the presence of up to 10 microM AmB showed no significant change in the pattern of PnA-labeled phospholipids, suggesting that AmB was not affecting the oxidative state of the cells. In contrast, treatment with AMVN (0.5 mM, incubation in the dark for 2 hr at 37 degrees--conditions in which the viability of the cells was maintained) caused a significant reduction of all fluorescently labeled phospholipid fractions separated by HPLC. When PnA-labeled cells were subjected to oxidative stress by incubation with 0.5 mM AMVN in the presence of AmB, the loss of fluorescent phospholipids was reduced in a concentration-dependent manner over a concentration range of 0.25 to 10 microM. Thus, AmB does not produce any prooxidant effect but rather acts as an intracellular antioxidant.

Angiotensin II antagonism and pre-glomerular arterial wall dimensions in the kidney of the spontaneously hypertensive rat

The effects of the angiotensin II type 1 receptor antagonist TCV-116 on the wall dimensions of the interlobular and arcuate arteries have been studied. SHR rats were treated with TCV-116 between 4 and 10 weeks, at which time their kidneys were perfusion-fixed and examined using stereological techniques. TCV-116 reduced arterial pressure and left ventricle/body weight ratio, but did not reduce renal arterial wall dimensions. For both arcuate and interlobular arteries, wall density/kidney ratio was significantly greater in the TCV-116 treated SHR than in untreated SHR and wall:lumen ratio was also significantly greater for the interlobular arteries in the TCV-116 treated rats. These findings are similar to those obtained previously using enalapril, and indicate that hypertrophy of the walls of these intra-renal arteries is not secondary to the elevated arterial pressure, unlike in other vascular beds.

Regulation of mitogenesis by kinins in arterial smooth muscle cells

Recent evidence suggests that bradykinin (BK) plays a role in regulating neointimal formation after vascular injury. The present study examined the mechanism whereby BK regulates platelet-derived growth factor (PDGF) AB-induced mitogenesis in smooth muscle cells from rat mesenteric artery. BK, but not other activators of phosphoinositidase C (e.g., angiotensin II), inhibited PDGF-stimulated mitogenesis. The B1 receptor agonist des-Arg9-BK (DABK) was more potent than the B2 agonist BK; smaller BK fragments had no activity. In studies in which the B2 receptor antagonist HOE-140 {D-Arg0[Hyp3,beta-(2-thienyl)-Ala5,D-Tic7,Oic 8]BK} and the B1 receptor antagonist DHOE [[D-Arg0,Hyp3,beta-(2-thienyl)-Ala5,D-Tic7,Oi c8,des-Arg9]BK] were used, both receptors independently mediated inhibition of PDGF-induced mitogenesis. There was no evidence for metabolism of BK to DABK. The rank potency for activating phosphoinositidase C and increasing intracellular Ca2+ (BK > DABK) was opposite that for inhibiting mitogenesis (DABK > BK). Inhibition of cyclooxygenase did not prevent the kinin-mediated inhibition. Kinetic analysis of the cell cycle effects of kinins on PDGF-stimulated mitogenesis revealed that continuous exposure to DABK or BK was inhibitory even when added shortly before the cells initiated DNA synthesis (S phase). However, short-term exposure (5-60 min) to DABK or BK was inhibitory only when added after exposure to PDGF. These data suggest that the B1 and B2 receptors potently inhibited PDGF-stimulated mitogenesis and proliferation by activating an alternative signal transduction cascade not involving phosphoinositidase C or prostaglandins. The inhibition occurred at a point late in progression of the cell cycle from G1 to S and was dependent on the presence of kinins after exposure to PDGF.

Chronic intrarenal infusion of low-dose angiotensin II in dogs increases arterial pressure without impairment of renal function

1. To determine whether chronic angiotensin II (AngII) infusion into the renal artery, at a dose which increases systemic arterial pressure, reduces glomerular filtration rate (GFR) and renal blood flow, AngII was infused at 0.5 ng/kg per min into the renal artery or intravenously in chronically instrumented dogs for 1 month. 2. Mean arterial pressure (MAP) rose significantly (P < 0.05) during the infusion of AngII into the renal artery (+7 +/- 2 mmHg on days 26-30). There were no significant changes in GFR or renal blood flow. When the same dose of AngII was infused intravenously, MAP did not change significantly (-2 +/- 2 mmHg) and there were no significant changes in GFR or in renal blood flow. 3. We conclude that AngII infused into the renal artery for 1 month, at a dose which was initially subpressor, causes a rise in arterial pressure that is not associated with impairment of renal function.

Interest and limits of in vitro studies in renal vascular endocrinology

Various in vitro preparations have been utilized to study the cellular activity of vasoactive agents on renal cortical microvessels and on mesangial cells. The receptors and the transduction pathways of bradykinin and atrial natriuretic factor were characterized on cultured cortical vascular smooth muscle cells from the rabbit kidney. A preparation of afferent arterioles that had been freshly isolated from the rat kidney was used to study the NO-dependent regulation of renin release. The influence of endothelin and angiotensin II on mesangial cell proliferation was evaluated, using cocultures of human endothelial and mesangial cells. These appropriate in vitro preparations have provided new insights on renal vascular endocrinology. However, extrapolation of in vitro data to in vivo physiology must be cautious because the phenotype of vascular cells often changes in culture conditions.

Peripheral vasculature in essential hypertension

1. Haemodynamic evidence shows that in essential hypertension minimum vascular resistance and vascular pressor response are increased and that the vascular reserve is decreased. 2. The haemodynamic changes are most easily explained in terms of a generalized narrowing of the vasculature and an increase in the ratio between the thickness of the tunica media and the lumen diameter (media: lumen ratio), with no change in the functional properties of the smooth muscle itself. 3. Histological and in vitro studies of resistance vessels confirm these predictions. Moreover, the evidence indicates that these changes are associated mainly with remodelling (rearrangement of the same amount of material) of the vessels, rather than growth. 4. Although the alteration in small artery structure is usually appropriate to the actual blood pressure, the structure appears not only to be a secondary adaptation, but is also dependent on other factors, including neurohumoral factors. 5. The available evidence shows that normalization of the resistance vessel structure (by increasing lumen diameter and decreasing the media:lumen ratio) should be achieved not by inhibition of growth but by (reverse) remodelling. Recent evidence from clinical investigations shows that this can be achieved in essential hypertensive patients treated with the angiotensin-converting enzyme inhibitor perindopril. 6. The role of the resistance vasculature as a primary determinant of blood pressure remains unclear. It is suggested that the requirement for normalization of resistance vascular structure is due to a need to increase the vascular reserve.