The platelet-derived growth factor isomers, PDGF-AA, PDGF-AB and PDGF-BB, induce contraction of vascular smooth muscle cells by different intracellular mechanisms

Impact of Imatinib on reducing the painful crisis in patients with sickle cell disease

INTRODUCTION

Sickle cell disease (SCD) is a common hemoglobinopathy worldwide that causes painful crises and hospitalization of patients. These attacks decrease survival and cause chronic end-organ damage in these patients.

HYPOTHESIS

For this reason, finding new treatment approaches could be helpful.

METHOD

In this study, Imatinib was applied as a mast cell inhibitor to reduce pain crises in these patients. Seven patients resistant to hydroxyurea and folic acid treatment and who had at least four painful crises per year with hospitalization were enrolled in this study with treatment with Imatinib (100 mg, twice daily). Subsequently, the number and duration of hospitalizations, analgesic requirement, the severity of chronic pain, and changes in the hematological parameters of these patients were evaluated before and after the treatment.

RESULTS

The data showed that the total number of hospitalizations and the entire duration of hospitalizations were reduced 16 times after treatment with Imatinib, without apparent changes in hematological parameters. Also, the demand for pethidine, tramadol, and nonsteroidal anti-inflammatory drugs (NSAIDs) was reduced in all patients. The average reduction in chronic pain was over 70%.

CONCLUSION

This study demonstrates that treatment with Imatinib in patients with SCD or sickle cell anemia (SCA) may be a suitable therapeutic option for reducing painful crises.

Tyrosine kinase inhibitors relax pulmonary arteries in human and murine precision-cut lung slices

BACKGROUND

Tyrosine kinase inhibitors (TKIs) inhibit the platelet derived growth factor receptor (PDGFR) and gain increasing significance in the therapy of proliferative diseases, e.g. pulmonary arterial hypertension (PAH). Moreover, TKIs relax pulmonary vessels of rats and guinea pigs. So far, it is unknown, whether TKIs exert relaxation in human and murine pulmonary vessels. Thus, we studied the effects of TKIs and the PDGFR-agonist PDGF-BB in precision-cut lung slices (PCLS) from both species.

METHODS

The vascular effects of imatinib (mice/human) or nilotinib (human) were studied in Endothelin-1 (ET-1) pre-constricted pulmonary arteries (PAs) or veins (PVs) by videomicroscopy. Baseline initial vessel area (IVA) was defined as 100%. With regard to TKI-induced relaxation, K⁺-channel activation was studied in human PAs (PCLS) and imatinib/nilotinib-related changes of cAMP and cGMP were analysed in human PAs/PVs (ELISA). Finally, the contractile potency of PDGF-BB was explored in PCLS (mice/human).

RESULTS

Murine PCLS: Imatinib (10 μM) relaxed ET-1-pre-constricted PAs to 167% of IVA. Vice versa, 100 nM PDGF-BB contracted PAs to 60% of IVA and pre-treatment with imatinib or amlodipine prevented PDGF-BB-induced contraction. Murine PVs reacted only slightly to imatinib or PDGF-BB. Human PCLS: 100 μM imatinib or nilotinib relaxed ET-1-pre-constricted PAs to 166% or 145% of IVA, respectively, due to the activation of K_ATP-, BK_Ca²⁺- or K_v-channels. In PVs, imatinib exerted only slight relaxation and nilotinib had no effect. Imatinib and nilotinib increased cAMP in human PAs, but not in PVs. In addition, PDGF-BB contracted human PAs/PVs, which was prevented by imatinib.

CONCLUSIONS

TKIs relax pre-constricted PAs/PVs from both, mice and humans. In human PAs, the activation of K⁺-channels and the generation of cAMP are relevant for TKI-induced relaxation. Vice versa, PDGF-BB contracts PAs/PVs (human/mice) due to PDGFR. In murine PAs, PDGF-BB-induced contraction depends on intracellular calcium. So, PDGFR regulates the tone of PAs/PVs. Since TKIs combine relaxant and antiproliferative effects, they may be promising in therapy of PAH.

PDGF-BB regulates the pulmonary vascular tone: impact of prostaglandins, calcium, MAPK- and PI3K/AKT/mTOR signalling and actin polymerisation in pulmonary veins of guinea pigs

Background

Platelet-derived growth factor (PDGF)-BB and its receptor PDGFR are highly expressed in pulmonary hypertension (PH) and mediate proliferation. Recently, we showed that PDGF-BB contracts pulmonary veins (PVs) and that this contraction is prevented by inhibition of PDGFR-β (imatinib/SU6668). Here, we studied PDGF-BB-induced contraction and downstream-signalling in isolated perfused lungs (IPL) and precision-cut lung slices (PCLS) of guinea pigs (GPs).

Methods

In IPLs, PDGF-BB was perfused after or without pre-treatment with imatinib (perfused/nebulised), the effects on the pulmonary arterial pressure (P_PA), the left atrial pressure (P_LA) and the capillary pressure (P_cap) were studied and the precapillary (R_pre) and postcapillary resistance (R_post) were calculated. Perfusate samples were analysed (ELISA) to detect the PDGF-BB-induced release of prostaglandin metabolites (TXA₂/PGI₂). In PCLS, the contractile effect of PDGF-BB was evaluated in pulmonary arteries (PAs) and PVs. In PVs, PDGF-BB-induced contraction was studied after inhibition of PDGFR-α/β, L-Type Ca²⁺-channels, ROCK/PKC, prostaglandin receptors, MAP2K, p38-MAPK, PI3K-α/γ, AKT/PKB, actin polymerisation, adenyl cyclase and NO. Changes of the vascular tone were measured by videomicroscopy. In PVs, intracellular cAMP was measured by ELISA.

Results

In IPLs, PDGF-BB increased P_PA, P_cap and R_post. In contrast, PDGF-BB had no effect if lungs were pre-treated with imatinib (perfused/nebulised). In PCLS, PDGF-BB significantly contracted PVs/PAs which was blocked by the PDGFR-β antagonist SU6668. In PVs, inhibition of actin polymerisation and inhibition of L-Type Ca²⁺-channels reduced PDGF-BB-induced contraction, whereas inhibition of ROCK/PKC had no effect. Blocking of EP_1/3- and TP-receptors or inhibition of MAP2K-, p38-MAPK-, PI3K-α/γ- and AKT/PKB-signalling prevented PDGF-BB-induced contraction, whereas inhibition of EP₄ only slightly reduced it. Accordingly, PDGF-BB increased TXA₂ in the perfusate, whereas PGI₂ was increased in all groups after 120 min and inhibition of IP-receptors did not enhance PDGF-BB-induced contraction. Moreover, PDGF-BB increased cAMP in PVs and inhibition of adenyl cyclase enhanced PDGF-BB-induced contraction, whereas inhibition of NO-formation only slightly increased it.

Conclusions

PDGF-BB/PDGFR regulates the pulmonary vascular tone by the generation of prostaglandins, the increase of calcium, the activation of MAPK- or PI3K/AKT/mTOR signalling and actin remodelling. More insights in PDGF-BB downstream-signalling may contribute to develop new therapeutics for PH.

STIM1 Knockout Enhances PDGF-Mediated Ca2+ Signaling through Upregulation of the PDGFR⁻PLCγ⁻STIM2 Cascade

Platelet-derived growth factor (PDGF) has mitogenic and chemotactic effects on fibroblasts. An increase in intracellular Ca²⁺ is one of the first events that occurs following the stimulation of PDGF receptors (PDGFRs). PDGF activates Ca²⁺ elevation by activating the phospholipase C gamma (PLCγ)-signaling pathway, resulting in ER Ca²⁺ release. Store-operated Ca²⁺ entry (SOCE) is the major form of extracellular Ca²⁺ influx following depletion of ER Ca²⁺ stores and stromal interaction molecule 1 (STIM1) is a key molecule in the regulation of SOCE. In this study, wild-type and STIM1 knockout mouse embryonic fibroblasts (MEF) cells were used to investigate the role of STIM1 in PDGF-induced Ca²⁺ oscillation and its functions in MEF cells. The unexpected findings suggest that STIM1 knockout enhances PDGFR–PLCγ–STIM2 signaling, which in turn increases PDGF-BB-induced Ca²⁺ elevation. Enhanced expressions of PDGFRs and PLCγ in STIM1 knockout cells induce Ca²⁺ release from the ER store through PLCγ–IP3 signaling. Moreover, STIM2 replaces STIM1 to act as the major ER Ca²⁺ sensor in activating SOCE. However, activation of PDGFRs also activate Akt, ERK, and JNK to regulate cellular functions, such as cell migration. These results suggest that alternative switchable pathways can be observed in cells, which act downstream of the growth factors that regulate Ca²⁺ signaling.

Nanoparticles combined with growth factors: recent progress and applications

Increasing attention has been focused on the applications of nanoparticles combined with growth factors (NPs/GFs) due to the substantial functions of GFs in regenerative medicine and disease treatments.

Effects of hesperetin on platelet-derived growth factor-BB-induced pulmonary artery smooth muscle cell proliferation

Hesperetin is a natural flavonoid, which has been reported to exert various biological activities and positive health effects on mammalian cells. The present study aimed to investigate the effects of hesperetin on the proliferation of primary cultured rat pulmonary artery smooth muscle cells (PASMCs), and to elucidate the possible underlying molecular mechanisms. The results of the present study indicated that hesperetin was able to inhibit the proliferation and DNA synthesis of platelet‑derived growth factor‑BB (PDGF‑BB)‑induced PASMCs in a dose‑ and time‑dependent manner, without exerting cell cytotoxicity. In addition, hesperetin blocked the progression of the cell cycle from G0/G1 to S phase, which was correlated with the decreased mRNA expression levels of cyclin D1, cyclin E, cyclin‑dependent kinase (CDK)2 and CDK4, and the increased mRNA expression levels of p27. Furthermore, the anti‑proliferative effects of hesperetin were associated with suppression of the AKT/glycogen synthase kinase (GSK)3β and p38 signaling pathway, but were not associated with the extracellular signal‑regulated kinases 1/2 and c‑Jun N‑terminal kinases signaling pathways. These results suggested that hesperetin may inhibit PDGFa‑BB‑induced PASMC proliferation via the AKT/GSK3β signaling pathway, and that it may possess therapeutic potential for the treatment of pulmonary vascular remodeling diseases.

Murrayafoline A Induces a G0/G1-Phase Arrest in Platelet-Derived Growth Factor-Stimulated Vascular Smooth Muscle Cells

The increased potential for vascular smooth muscle cell (VSMC) growth is a key abnormality in the development of atherosclerosis and post-angioplasty restenosis. Abnormally high activity of platelet-derived growth factor (PDGF) is believed to play a central role in the etiology of these pathophysiological situations. Here, we investigated the anti-proliferative effects and possible mechanism(s) of murrayafoline A, a carbazole alkaloid isolated from Glycosmis stenocarpa Guillamin (Rutaceae), on PDGF-BB-stimulated VSMCs. Murrayafoline A inhibited the PDGF-BB-stimulated proliferation of VSMCs in a concentration-dependent manner, as measured using a non-radioactive colorimetric WST-1 assay and direct cell counting. Furthermore, murrayafoline A suppressed the PDGF-BB-stimulated progression through G₀/G₁ to S phase of the cell cycle, as measured by [³H]-thymidine incorporation assay and cell cycle progression analysis. This anti-proliferative action of murrayafoline A, arresting cell cycle progression at G₀/G₁ phase in PDGF-BB-stimulated VSMCs, was mediated via down-regulation of the expression of cyclin D1, cyclin E, cyclin-dependent kinase (CDK)2, CDK4, and proliferating cell nuclear antigen (PCNA), and the phosphorylation of retinoblastoma protein (pRb). These results indicate that murrayafoline A may be useful in preventing the progression of vascular complications such as restenosis after percutaneous transluminal coronary angioplasty and atherosclerosis.

Beneficial effects of platelet-derived growth factor on hemorrhagic shock in rats and the underlying mechanisms

Studies have shown that local application of platelet-derived growth factor (PDGF) can be used for the treatment of acute and chronic wounds. We investigated if systemic application of PDGF has a protective effect on acute hemorrhagic shock in rats in the present study. Using hemorrhagic shock rats and isolated superior mesenteric arteries, the effects of PDGF-BB on hemodynamics, animal survival, and vascular reactivity as well as the roles of the gap junction proteins connexin (Cx)40 and Cx43, PKC, and Rho kinase were observed. PDGF-BB (1–15 μg/kg iv) significantly improved the hemodynamics and blood perfusion to vital organs (liver and kidney) as well as vascular reactivity and improved the animal survival in hemorrhagic shock rats. PDGF recovering shock-induced vascular hyporeactivity depended on the integrity of the endothelium and myoendothelial gap junction. Cx43 antisense oligodeoxynucleotide abolished these improving effects of PDGF, whereas Cx40 oligodeoxynucleotide did not. Further study indicated that PDGF increased the activity of Rho kinase and PKC as well as vascular Ca2+ sensitivity, whereas it did not interfere with the intracellular Ca2+ concentration in hypoxia-treated vascular smooth muscle cells. In conclusion, systemic application of PDGF-BB may exert beneficial effects on hemorrhagic shock, which are closely related to the improvement of vascular reactivity and hemodynamics. The improvement of PDGF-BB in vascular reactivity is vascular endothelium and myoendothelial gap junction dependent. Cx43, Rho kinase, and PKC play very important role in this process. These findings suggest that PDGF may be a potential measure to treat acute clinical critical diseases such as severe trauma, shock, and sepsis.

An ethanolic extract of Angelica gigas improves atherosclerosis by inhibiting vascular smooth muscle cell proliferation

The effects of an ethanolic extract of Angelica gigas (EAG) on the vascular smooth muscle cell (VSMC) proliferation and high-cholesterol diet-induced hypercholesterolemia and atherosclerosis were investigated. Rat aortic VSMCs were stimulated with platelet-derived growth factor-BB (25 ng/mL) for the induction of DNA synthesis and cell proliferation. EAG (1-10 µg/mL) significantly inhibited both the thymidine incorporation and cell proliferation in a concentration-dependent manner. Hypercholesterolemia was induced by feeding male New Zealand white rabbits with 0.5% cholesterol in diet for 10 weeks, during which EAG (1% in diet) was given for the final 8 weeks after 2-week induction of hypercholesterolemia. Hypercholesterolemic rabbits exhibited great increases in serum total cholesterol and low-density lipoproteins (LDL) levels, and finally severe atheromatous plaque formation covering 28.4% of the arterial walls. EAG significantly increased high-density lipoproteins (HDL), slightly decreased LDL, and potentially reduced the atheroma area to 16.6%. The results indicate that EAG attenuates atherosclerosis not only by inhibiting VASC proliferation, but also by increasing blood HDL levels. Therefore, it is suggested that EAG could be an alternative or an adjunct therapy for the improvement of hypercholesterolemia and atherosclerosis.

Fermented soshiho-tang with Lactobacillus plantarum enhances the antiproliferative activity in vascular smooth muscle cell

Background

Soshiho-tang (SST) is a traditional medicine widely used for the treatment of chronic hepatitis. SST has been shown to confer a variety of pharmacological activities, including prevention of hepatotoxicity, promotion of liver regeneration, and modulation of liver fibrosis. In this study, we investigated the antiproliferative activity of native and fermented (FSST) formulations of SST in vascular smooth muscle cells (VSMCs) and examined the potential underlying mechanisms driving these effects.

Methods

SST, along with preparations fermented with Lactobacillus plantarum KFRI-144 (S-A144), L. amylophilus KFRI-161 (S-A161) and L. bulgaricus KFRI-344 (S-A344), were investigated to determine their effects on the proliferation and viability of VSMCs, along with the signalling pathways underlying these effects.

Results

S-A144 exhibited a strong, dose-dependent inhibition of VSMC proliferation relative to untreated controls, but the others did not affect. In addition, S-A144 significantly decreased the phosphorylation of Akt and PLCγ1 in a dose-dependent manner and induced cell cycle arrest at the G₀/G₁ phase characterised by decreased expression of CDKs, cyclins and PCNA.

Conclusions

The findings suggest that S-A144 exhibit enhanced inhibition of PDGF-BB-induced VSMC proliferation comparison to S-AOR through the suppression of cell cycle progression and expression of cell cycle-related proteins, along with the downregulation of Akt phosphorylation.

Plasma BDNF and PDGF-AA levels are associated with high TCD velocity and stroke in children with sickle cell anemia

Sickle cell anemia (SCA) associated cerebrovascular disease includes vascular remodeling, abnormal cerebral blood flow (CBF) and infarction. We studied the relationships between plasma brain derived neurotropic factor (BDNF), platelet derived growth factors (PDGF-AA and -AB/BB) and high trans-cranial Doppler (TCD) velocity, an indication of CBF velocity. Baseline plasma samples from 39 children (19 SCA with abnormal/high TCD [SATCD], 13 SCA with normal TCD [SNTCD] and 7 healthy non-SCA), were assayed for BDNF, PDGF-AA and -AB/BB plus 11 other cytokines. The sensitivity, specificity and usefulness of these biomarkers for stroke prediction was investigated. All subject groups were of similar age and gender distribution. Mean BDNF was significantly higher among SATCD than SNTCD (p=0.004) as was mean PDGF-AA (p=0.001). Similarly, mean PDGF-AA was higher among SCA subjects who developed stroke than those who did not (p=0.012). Elevated BDNF and PDGF-AA were good predictors of the presence of abnormally high CBF velocity and were both associated with severity of anemia. Elevated PDGF-AA predicted risk for stroke development. Stroke incidence and high TCD velocity were associated with elevated BDNF and PDGF-AA. These findings suggest a role for BDNF and PDGF-AA in the patho-physiological mechanism of cerebrovascular disease in SCA.

Cigarette smoke extract stimulates rat pulmonary artery smooth muscle cell proliferation via PKC-PDGFB signaling

Accumulating evidence suggests a direct role for cigarette smoke in pulmonary vascular remodeling, which contributes to the development of pulmonary hypertension. However, the molecular mechanisms underlying this process remain poorly understood. Platelet-derived growth factor (PDGF) is a potential mitogen and chemoattractant implicated in several biological processes, including cell survival, proliferation, and migration. In this study, we investigated the effect of cigarette smoke extract (CSE) on cell proliferation of rat pulmonary artery smooth muscle cells (rPASMCs). We found that stimulation of rPASMCs with CSE significantly increased cell proliferation and promoted cell cycle progression from G1 phase to the S and G2 phases. CSE treatment also significantly upregulated the mRNA and protein levels of PDGFB and PDGFRβ. Our study also revealed that Rottlerin, an inhibitor of PKCδ signaling, prevented CSE-induced cell proliferation, attenuated the increase of S and G2 phase populations induced by CSE treatment, and downregulated PDGFB and PDGFRβ mRNA and protein levels in rPASMCs exposed to CSE. Collectively, our data demonstrated that CSE-induced cell proliferation of rPASMCs involved upregulation of the PKCδ-PDGFB pathway.

Platelet-derived growth factor (PDGF)-BB produces NO-mediated relaxation and PDGF receptor β-dependent tonic contraction in murine iliac lymph vessels

We studied the effects of PDGF-BB on changes in the diameters of murine lymph vessels with or without intact endothelium. PDGF-BB induced dilation of the lymph vessels with endothelium. Pretreatment with l-NAME or removal of the endothelium caused a significant attenuation in the PDGF-BB-induced dilation. PDGF-BB also produced dose-related reduction of the diameters of the lymph vessels without endothelium. To evaluate intracellular signal transduction and Ca(2+) -dependence of the PDGF-BB-induced tonic contraction, we investigated the effects of imatinib, GW5074 (an inhibitor of Raf-1 kinase), U-73122 (an inhibitor of phospholipase C), and xestospongin C on the PDGF-BB-induced reduction responses. All of these inhibitors caused a significant attenuation in the PDGF-BB-induced reduction response that was significantly decreased by treatment with Ca(2+) -free Krebs-bicarbonate solution or nifedipine. Higher concentrations of PDGF-BB produced a marked reduction of lymph vessel diameter within both high K(+) Krebs-bicarbonate solution and Ca(2+) -free high K(+) Krebs solution containing 1mM EGTA. These findings suggest that PDGF-BB induced endothelium-dependent NO-mediated relaxation of lymphatic smooth muscles in murine lymph vessels. PDGF receptor β-mediated tonic contraction of the muscles through increased Ca(2+) influx through the membrane and the release of membrane-bound and intracellular Ca(2+) .

Platelet-derived growth factor-induced severe and chronic vasoconstriction of cerebral arteries: proposed growth factor explanation of cerebral vasospasm

OBJECTIVE

After subarachnoid hemorrhage (SAH), platelet-derived growth factor-BB (PDGF-BB) is secreted in and around the cerebral arteries. To clarify the role of PDGF-BB in the development of vasospasm after SAH, we determined whether PDGF-BB alone can cause long-lasting vasoconstriction of a severity similar to that of vasospasm. In addition, the anti-vasospastic effect of trapidil, an antagonist of PDGF-BB function, was investigated.

METHODS

We infused recombinant PDGF-BB (10 microg/mL saline as the vehicle) (n = 14) into the subarachnoid space of rabbits and analyzed alterations in the caliber of the basilar artery using repeated angiography. To study the role of PDGF-BB on the development of vasospasm, trapidil was administered continuously starting 1 hour after SAH, on day 0 (0.63-1.25 mg/kg /h or vehicle) for 47 hours (n = 24), or after the full development of cerebral vasospasm on day 2 (3.0 mg/kg/h or vehicle) for 0.5 hours (n = 17), and alterations in the caliber of the basilar artery were monitored.

RESULTS

PDGF-BB caused long-lasting vasoconstriction, with maximum constriction of 56% (P < .001) of the control value (= 100%) on day 2, resembling vasospasm seen after SAH. Prolonged administration of intravenous trapidil, starting soon after SAH, prevented the development of vasospasm in a dose-dependent manner (P < .05, .01, or .001). Intravenous or intra-arterial administration of trapidil significantly dilated vasospasm (P < .01) on day 2, at least transiently.

CONCLUSION

PDGF-BB, a growth factor synthesized in the subarachnoid space after SAH, can cause severe and long-lasting vasoconstriction. Significant prevention and resolution of vasospasm can be achieved by the PDGF-BB antagonist trapidil. We propose that excessive production of PDGF-BB, essentially aiming to repair injured arteries, causes cerebral vasospasm. Although the half-life of trapidil in serum may be shorter than that of PDGFG-BB-derived spasmogenic signaling, trapidil is a candidate drug for constructing a new therapeutic modality for preventing and resolving vasospasm.

PDGF and cardiovascular disease

Platelet-derived growth factor (PDGF) was identified in a search for serum factors that stimulate smooth muscle cell (SMC) proliferation. During the development of lesions of atherosclerosis that can ultimately lead to vessel occlusion, SMC are stimulated by inflammatory factors to migrate from their normal location in the media. They accumulate within the forming lesion where they contribute to lesion expansion by proliferation and deposition of extracellular matrix. Different genetic manipulations in vascular cells combined with various inhibitory strategies have provided strong evidence for PDGF playing a prominent role in the migration of SMC into the neointima following acute injury and in atherosclerosis. Other activities of PDGF identified in vivo suggest additional functions for PDGF in the pathogenesis of cardiovascular disease.

Angiogenesis of gastrointestinal tumours and their metastases – a target for intervention?

Angiogenesis is an obligatory event for the growth of tumours beyond 2 mm in diameter, above which simple oxygen diffusion can no longer support the rapid proliferation of malignant cells. Angiogenesis is a fine balance between inhibitory and stimulatory factors, the knowledge of which offers novel targets for the treatment of gastrointestinal neoplasia. A literature search of Pubmed and Medline databases was undertaken, using the keywords colorectal cancer, pancreatic cancer, gastrointestinal cancer, angiogenesis and anti-angiogenesis therapy. It was found that angiogenesis in primary tumours is a sequential and highly complex cascade of molecular events resulting in the rapid exponential growth of the tumour. Hepatic metastases of primary tumours may be less reliant on traditional angiogenic pathways, by co-opting pre-existing hepatic vasculature. Research into angiogenesis has revealed many different sites that can be targeted by agents such as tyrosine kinase inhibitors. Many anti-angiogenic agents are undergoing preclinical evaluation, with only a few entering phase I and phase III clinical trials. However, early results suggest that anti-angiogenic therapy could be an important adjunct to conventional chemotherapy treatment of gastrointestinal neoplasia.

Biology of angiogenesis in tumors of the gastrointestinal tract

The realization that the growth and spread of tumors are dependent on angiogenesis has created new avenues of research designed to help us to better understand cancer biology and to facilitate the development of new therapeutic strategies. However, the process of angiogenesis consists of multiple, sequential, and interdependent steps with a myriad of positive and negative regulators of angiogenesis being involved. The survival of tumors and thus their metastases are dependent upon the balance of endogenous angiogenic and anti-angiogenic factors such that the outcome favors increased angiogenesis. Several growth factors have been identified that regulate angiogenesis in cancers of the gastrointestinal tract. These include pro-angiogenic factors like vascular endothelial growth factor (VEGF) and anti-angiogenic factors, i.e., thrombospondin. The following review provides a brief overview about the most important factors that are involved in the angiogenic process in tumors derived from colon, stomach, and pancreas. A thorough understanding of the role these factors play in the angiogenic process may lead to the development of novel therapeutic antineoplastic strategies.

Formation of caspase-3 complexes and fragmentation of caspase-12 during anisomycin-induced apoptosis in AKR-2B cells without aggregation of Apaf-1

Treatment of AKR-2B fibroblasts with anisomycin (10 microM) led to a rapid disintegration of the cells (t1/2 = 5 h) which was complete after 24 h. Cell death was associated with typical hallmarks of apoptosis like membrane blebbing, exposure of phophatidylserine on the cell surface, nuclear condensation and specific cleavage of rRNA. However, there was no dissipation of the mitochondrial potential and no intranucleosomal fragmentation. By affinity labeling with YVK(-bio)D.aomk in combination with immunostaining against activated caspase-3 analyzed by 2-D gel electrophoresis it was shown that caspase-3 is the dominant executioner caspase. Gel filtration experiments of cytosolic extract analyzed by Western blotting revealed the formation of high-molecular-weight complexes of caspase-3 (600 kDa and 250 kDa, respectively), but there was no complex formation of Apaf-1. Anisomycin treatment led to a strong activation of the stress kinases p38 kinases and the jun kinases, that was not sufficient for the activation of caspase-3 which required much higher concentrations. By using the selective inhibitors SB 203580 for p38 kinases and SP 600125 for c-jun kinases, respectively, it is shown that activation of these kinases is not necessary for cell death induced by anisomycin in AKR-2B cells. Furthermore, we disclose the activation of caspase-12 in AKR-2B cells following the addition of anisomycin. Caspase-12 zymogen present as a cytosolic complex (> 600 kDa) is activated by anisomycin leading to an uncomplexed cleaved enzyme. Since anisomycin treatment did neither lead to stress of the endoplasmic reticulum nor to a breakdown of intracellular Ca(2+)-stores, alternative pathways involved in the activation of caspases are discussed.

Broad-spectrum and selective serine protease inhibitors prevent expression of platelet-derived growth factor-BB and cerebral vasospasm after subarachnoid hemorrhage: vasospasm caused by cisternal injection of recombinant platelet-derived growth factor-BB

BACKGROUND AND PURPOSE

Plasma serine protease cascade, including the complement system and thrombin, is activated in the subarachnoid space during the acute phase after subarachnoid hemorrhage (SAH). To examine the effect of protease cascade-based inflammation and subsequent vascular repair in the development of cerebral vasospasm, we examined the effect of 2 synthetic serine protease inhibitors-FUT-175, an inhibitor of thrombin and the complement system, and argatroban, a selective inhibitor of thrombin-on the development of cerebral vasospasm in a rabbit SAH model.

METHODS

One hundred Japanese White male rabbits were used in the study. The SAH was simulated by a single injection of autologous arterial blood into the cisterna magna. To evaluate the development of cerebral vasospasm, the caliber of the basilar artery was measured on x-ray film before and at 2 days after SAH. Nine groups of rabbits (n=6 each) were treated with continuous intravenous injection of FUT-175 (2.5, 5, 10, or 20 mg/d), argatroban (1.25, 2.5, or 5 mg/d), or the same amount of saline (vehicle) for 48 hours, starting 40 minutes after SAH. Two days after SAH, the expression of homodimer of platelet-derived growth factor-BB (PDGF-BB) in the basilar artery was examined with immunohistochemical techniques. In 20 normal rabbits, 5 microg of recombinant PDGF-BB or vehicle was injected into the cisterna magna, and the basilar arteries were examined on angiograms for 48 hours.

RESULTS

Significant differences were observed in the caliber of the basilar arteries between the vehicle group and the groups with the 3 larger doses of FUT-175 (vehicle, 52+/-5.0%; 5 mg, 79+/-5.7%; 10 mg, 80+/-2.5%; 20 mg, 80+/-3.7%) and between the vehicle group and the groups with the 2 larger doses of argatroban (vehicle, 52+/-6.4%; 2.5 mg, 81+/-9.0%; 5 mg, 85+/-4.1%) (P<0.05). In the histological examination, administration of effective doses of FUT-175 or argatroban suppressed the expression of PDGF-BB in the endothelial and medial smooth muscle cell layers. Exogenous PDGF-BB caused delayed and prolonged vasoconstriction on normal basilar arteries.

CONCLUSIONS

Activation of the serine protease cascade and/or thrombin after SAH was demonstrated to play an essential role in the development of cerebral vasospasm. The expression of PDGF-BB-like protein in the arterial walls correlated with the development of cerebral vasospasm. Elevated PDGF-BB level in the subarachnoid space was found to induce delayed and chronic vasoconstriction.

Involvement of platelet-derived growth factor in disease: development of specific antagonists

Platelet-derived growth factor (PDGF) is a family of dimeric isoforms that stimulates, e.g., growth, chemotaxis and cell shape changes of various connective tissue cell types and certain other cells. The cellular effects of PDGF isoforms are exerted through binding to two structurally related tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation. This enables a number of SH2 domain containing signal transduction molecules to bind to the receptors, thereby initiating various signaling pathways. PDGF isoforms have important roles during the embryonic development, particularly in the formation of connective tissue in various organs. In the adult, PDGF stimulates wound healing. Overactivity of PDGF has been implicated in certain disorders, including fibrotic conditions, atherosclerosis, and malignancies. Different kinds of PDGF antagonists are currently being developed and evaluated in different animal disease models, as well as in clinical trials.

Calcium and growth responses of hyperresponsive airway smooth muscle to different isoforms of platelet-derived growth factor (PDGF)

Airway smooth muscle (ASM) mass is likely to be an important determinant of airway responsiveness. Highly inbred Fisher rats model innate hyperresponsiveness, and also have more ASM in vivo than control Lewis rats. Platelet derived growth factor (PDGF) is an important endogenous growth factor for ASM, and partially purified PDGF-AB causes enhanced growth of Fisher rat ASM cells, compared to Lewis cells. The aim of the present study was to determine the mitogenic effects of all three recombinant PDGF isoforms on ASM cells, and investigate the mechanisms of enhanced Fisher ASM growth responses. The potential mechanisms assessed include PDGF receptor expression and activation (tyrosine phoshorylation), and intracellular calcium (Ca2+) responses to PDGF isoforms. Fisher ASM cells had a greater mitogenic response to PDGF-AB and -AA, and a greater Ca2+ response to -BB than Lewis ASM cells. A Ca2+ response was not necessary for a mitogenic response, and the effects of PDGF isoforms on Ca2+ were not associated with their effects on growth. Therefore, we suggest that enhanced Fisher mitogenic response to PDGF-AA and -AB is not mediated by differences in Ca2+ signalling. Western analysis of the PDGF receptor indicated a similar expression of β-PDGF receptor in ASM cells from the two rat strains, but a greater expression of α-PDGF receptor in Fisher cells; however, phosphorylation of the PDGF receptor following growth stimulation did not differ between strains. This suggests a role for post-receptor signals, in addition to enhanced receptor expression, in the enhanced growth response of Fisher ASM cells to PDGF-AA and -AB.Key words: PDGF receptors, tyrosine phosphorylation, intracellular calcium, proliferation, airway smooth muscle cells.

Platelet-derived growth factor-BB stimulates hypertrophy of peritubular smooth muscle cells from rat testis in primary cultures

The tunica propria of seminiferous tubules contains a particular type of smooth muscle cell (myoid cells) arranged in a contractile epithelioid layer that is responsible for sperm and tubular fluid flow. Unlike other types of smooth muscle (SM) cells, highly purified populations of peritubular smooth muscle cells (PSMC) survive and maintain their contractile phenotype in primary cultures in controlled conditions. We used this culture model to investigate the response of the SM contractile phenotype to prolonged exposure to platelet-derived growth factor (PDGF), one of the main factors involved in vascular SM pathologies. We observed that 4-day continuous exposure of PSMC to PDGF-BB at nanomolar concentrations in plain medium enhances contractile phenotype traits and induces cell hypertrophy without inducing proliferation. In Northern and Western blotting experiments, SM-alpha-actin transcript and protein were found to be markedly increased in the PDGF-BB-treated samples, which is in line with the formation of conspicuous SM-alpha-actin-containing stress fibers. Moreover, binding sites for endothelin-1 were increased, and the calcium response to the contractile agonist, determined in single fura-2-loaded cells, was enhanced. In response to PDGF-BB, the cells underwent immediate, transient contraction, as seen in a scanning electron microscope, followed by a gradual increase in size, as evaluated by cytofluorometry, and enhancement of protein synthesis. The observed pattern of response to PDGF-BB was not accompanied by cell proliferation, as assessed by [3H]thymidine incorporation and direct cell counts. Unlike other SM cell types, in which proliferation and loss of contractile traits are induced by PDGF, chronic treatment of PSMC with this growth factor results in hypertrophy rather than hyperplasia.

Early intracellular signalling pathway of ethanol in vascular smooth muscle cells

1. ERKs belong to MAP kinase family and are activated by several growth and stress factors. Although ethanol has been shown to modulate ERK1 and ERK2 (p44(mapk) and p42(mapk)) activity, it can also act as an antiproliferative agent in various mammalian cells. Since the nature of the antiproliferative effect of ethanol in VSMCs has not been defined, we examined its effects on growth and on early intracellular events normally induced by growth factors in VSMCs. 2. Measurement of cytosolic Ca(2+) and pH in cell monolayers was performed using fura-2/AM and BCECF/AM, respectively. The effect of ethanol on VSMCs growth was assessed by [(3)H]-thymidine incorporation, by cell counting and by determination of the caspase 3 activity. Stimulation of ERK1 and ERK2 was examined by the chemiluminescence Western blotting method. The expression of c-fos was quantitated by Northern blotting. Determination of inositolphosphates was performed after labelling of VSMCs with myo-[2-(3)H]-inositol and separation of inositolphosphates by HPLC. 3. Ethanol (0.3 - 1.0% v v(-1), 17 - 170 mM) induced a dose-dependent maximal stimulation of p44(mapk)/p42(mapk) at 30 min and expression of c-fos mRNA with a maximum at 120 min. Intracellular events upstream to MAP kinase, like an increase in [Ca(2+)](i), activation of the Na(+)/H(+) exchanger and formation of phosphoinositol metabolites were also markedly activated by ethanol. Treatment of VSMCs with ethanol for 3 - 5 min induced an increase in DNA synthesis whereas treatment of the cells for more than 30 min was toxic. Caspase 3 activity was not modulated by ethanol treatment of VSMCs. 4. We may postulate that the activation of these mitogenic signals including the elevation of DNA synthesis reflects a cell effort to protect itself against the toxic effects of ethanol.

Mechanism of action and in vivo role of platelet-derived growth factor

Platelet-derived growth factor (PDGF) is a major mitogen for connective tissue cells and certain other cell types. It is a dimeric molecule consisting of disulfide-bonded, structurally similar A- and B-polypeptide chains, which combine to homo- and heterodimers. The PDGF isoforms exert their cellular effects by binding to and activating two structurally related protein tyrosine kinase receptors, denoted the alpha-receptor and the beta-receptor. Activation of PDGF receptors leads to stimulation of cell growth, but also to changes in cell shape and motility; PDGF induces reorganization of the actin filament system and stimulates chemotaxis, i.e., a directed cell movement toward a gradient of PDGF. In vivo, PDGF has important roles during the embryonic development as well as during wound healing. Moreover, overactivity of PDGF has been implicated in several pathological conditions. The sis oncogene of simian sarcoma virus (SSV) is related to the B-chain of PDGF, and SSV transformation involves autocrine stimulation by a PDGF-like molecule. Similarly, overproduction of PDGF may be involved in autocrine and paracrine growth stimulation of human tumors. Overactivity of PDGF has, in addition, been implicated in nonmalignant conditions characterized by an increased cell proliferation, such as atherosclerosis and fibrotic conditions. This review discusses structural and functional properties of PDGF and PDGF receptors, the mechanism whereby PDGF exerts its cellular effects, and the role of PDGF in normal and diseased tissues.

Platelet-derived growth factor-induced vasodilatation in mesenteric resistance arteries by nitric oxide: blunted response in spontaneous hypertension

Platelet-derived growth factor (PDGF) is a potent mitogen for vascular smooth-muscle cells, but its effects on vasomotion remain controversial. Both vasoconstriction and vasodilatation of isolated rat aortic rings have been reported. The effects of PDGF on responses of perfused mesenteric resistance arteries from normotensive Wistar-Kyoto and spontaneously hypertensive rats were studied by using a video dimension analyzer. PDGF receptor messenger RNA (mRNA) expression in endothelial cells isolated from mesenteric arteries of both normotensive and hypertensive rats was studied by reverse transcriptase-polymerase chain reaction (RT-PCR) analysis. In both normotensive and hypertensive rats, PDGF-BB concentration-dependently induced vasodilatation (maximal response, 25 +/- 4% and 13 +/- 4% at 10(-8) M, respectively; p < 0.05, normotensive vs. hypertensive rats). Endothelium removal or preincubation with N(omega)-nitro-L-arginine methyl ester, but not indomethacin, inhibited these relaxations, indicating that these vasodilatations are endothelium dependent and mediated by nitric oxide. RT-PCR analysis showed that both PDGF-alpha and -beta receptor mRNAs were present in endothelial cells of the mesenteric arteries of normotensive as well as hypertensive rats. In addition, relaxations induced by both PDGF-AA and -AB were significantly less than those induced by PDGF-BB in both strains, suggesting that vasodilatation is mediated mainly by the PDGF-beta receptor subtype. No vasoconstriction was observed after application of PDGF-BB to both normotensive and hypertensive mesenteric arteries with or without endothelium. In rat mesenteric resistance arteries, PDGF induces endothelium-dependent vasodilatation mediated by nitric oxide. At sites where PDGF is released or locally produced, therefore, the growth factor may participate in regulating vascular tone, and this endothelium-dependent regulation is attenuated in spontaneous hypertension.

Role of tyrosine phosphorylation in excitation-contraction coupling in vascular smooth muscle

Increasingly it is recognized that tyrosine phosphorylation plays an important part in the regulation of function in differentiated contractile vascular smooth muscle. Tyrosine kinases and phosphatases are present in large amounts in vascular smooth muscle and have been reported to influence a number of processes crucial to contraction, including ion channel gating, calcium homeostasis and sensitization of the contractile process to [Ca2+]i. This review summarizes current understanding regarding the role of tyrosine phosphorylation in excitation-contraction coupling in blood vessels.

Contrasting effects of platelet-derived growth factor (PDGF) isomers on mitogenesis, contraction and intracellular calcium concentration in human vascular smooth muscle

The present study was aimed at characterizing the responses of human vascular smooth muscle to all three dimeric isomers of platelet-derived growth factor (PDGF-AA, -AB and -BB) in terms of mitogenesis, contraction and intracellular calcium concentration. The potential of interaction between PDGF and endothelin-1 (ET-1) was also investigated. All three PDGF isoforms (0.1-20 ng mL-1) stimulated DNA synthesis in cultured human coronary artery and saphenous vein vascular smooth muscle cells (VSMC), measured by [3H]thymidine incorporation. PDGF-AB and -BB elicited comparable large increases in DNA synthesis of maximum 595 +/- 149% (P = 0.001, n = 9) and 576 +/- 17% (P < 0.001, n = 5), respectively, whereas PDGF-AA was only weakly mitogenic (61 +/- 16% increase; P < 0.05, n = 3). At a threshold concentration, PDGF acted in synergy with ET-1 to enhance DNA synthesis (816 +/- 337% increase; P < 0.05, n = 7). In contrast to mitogenesis, none of the three PDGF isomers had any effect on contraction of human saphenous veins in vitro, nor did they affect the contractile response to ET-1, 5-HT or the thromboxane mimetic U46619. The effects of the three PDGF isomers on intracellular calcium ([Ca2+]i) rises in cultured human VSMC were heterogeneous, with PDGF-BB inducing the largest increase in [Ca2+]i (442 +/- 53 nmol L-1) vs. PDGF-AB (290 +/- 28 nmol L-1), whilst PDGF-AA had no effect. Both the responses to PDGF-AB and-BB relied upon intracellular calcium release, whilst only PDGF-AB showed additional dependence on influx of extracellular calcium. In summary, PDGF is strongly mitogenic and comitogenic with ET-1, despite not being a vasoconstrictor, for human VSMC. Also, human VSMC showed heterogeneous responses to the three PDGF isoforms. These results implicate PDGF, and in particular the PDGF receptor-beta, as important role players in the development of vascular smooth muscle-mediated intimal thickening in humans.

Signal transduction via platelet-derived growth factor receptors

Platelet-derived growth factor (PDGF) exerts its stimulatory effects on cell growth and motility by binding to two related protein tyrosine kinase receptors. Ligand binding induces receptor dimerization and autophosphorylation, allowing binding and activation of cytoplasmic SH2-domain containing signal transduction molecules. Thereby, a number of different signaling pathways are initiated leading to cell growth, actin reorganization migration and differentiation. Recent observations suggest that extensive cross-talk occurs between different signaling pathways, and that stimulatory signals are modulated by inhibitory signals arising in parallel.

The role of platelet-derived growth factor-BB-induced increase in cytosolic free Ca2+ in activation of mitogen-activated protein kinase and DNA synthesis in vascular smooth muscle cells

BACKGROUND

Platelet derived growth factor (PDGF)-BB is an important vascular smooth muscle cell (VSMC) mitogen. PDGF-BB induces an increase in intracellular free calcium concentration ([Ca2+]i), an activation of mitogen-activated protein (MAP) kinase and an increase in DNA synthesis. The increase in [Ca2+]i is thought to be an important second messenger in the intracellular signalling cascade, leading to growth of VSMC.

OBJECTIVE

The aim of the present study was to elucidate the role of the PDGF-BB-induced increase in [Ca2+]i in the activation of MAP kinase and increase in DNA synthesis. Binding of [Ca2+]i was performed by the intracellular chelator bis-(2-amino-5-methylphenoxy) ethane-N,N,N',N'-tetraacetic acid tetraacetoxymethyl ester (MAPTAM).

METHODS

Ca2+ levels were measured by the Fura-2 method. MAP kinase activation was determined by Western blotting. DNA synthesis was determined by measurement of incorporation of [3H]-thymidine into the cell DNA.

RESULTS

Administration of 50 ng/ml PDGF-BB induced an increase in [Ca2+]i, an activation of MAP kinase and an increase in DNA synthesis. In bis-(2-amino-5-methylphenoxy) ethane-N,N,N'N'-tetraacetic acid tetraacetoxymethyl ester (MAPTAM)-treated cells the PDGF-BB-induced effect on [Ca2+]i was totally blunted, whereas no effect on MAP kinase activation and DNA synthesis could be observed.

CONCLUSIONS

These findings show that the effect of PDGF-BB on MAP kinase activation is independent of calcium level. [Ca2+]i might be implicated in the PDGF-BB-induced mitogenic process only in conjugation with other signalling components.

PDGF-BB decreases systolic blood pressure through an increase in macrovascular compliance in rats

The cardiovascular roles of platelet-derived growth factor (PDGF) were examined in anesthetized rats by monitoring blood pressure and in isolated blood vessels and heart preparations. Intravenous injection of PDGF-BB lowered blood pressure. The decrease in systolic pressure was greater than that in diastolic pressure, so the pulse pressure decreased. PDGF-AA and -AB, other isoforms of PDGF, did not have any effect on blood pressure. Pretreatment of rats with N(omega)-nitro-L-arginine methyl ester (L-NAME), an inhibitor of nitric oxide (NO) synthase, shortened duration of the hypotensive effect of PDGF-BB. The administration of L-arginine with L-NAME partially prevented the effect of L-NAME. PDGF-BB relaxed aortic rings precontracted with phenylephrine with a 50% effective concentration of 3 ng/ml. In contrast, in isolated mesenteric vascular preparations, the vasodilating activity of PDGF-BB was observed only at a high concentration (>12.5 ng/ml). In isolated heart preparations, PDGF-BB had no effect on the beat rate or contractile activity. These results suggest a new role of PDGF-BB that may contribute to the regulation in circulation through the increase in macrovascular compliance mediated by NO.

Structural changes of small resistance arteries in spontaneously hypertensive rats after treatment with various doses of lacidipine

OBJECTIVE

To evaluate the modifications of the morphology of mesenteric small resistance vessels in spontaneously hypertensive rats (SHR) induced by lacidipine treatment.

METHODS

Lacidipine was administered at three different dosages, 20, 10, and 0.3 mg/kg per day. Fifty rats were studied. Nine SHR and 11 Wistar-Kyoto (WKY) rats were not treated. Each lacidipine dose was administered to 10 SHR. The drug and the placebo were administered by gavage from age 4 to age 12 weeks. The blood pressure was measured noninvasively every week. The animals were killed when they were aged 13 weeks, and the relative left ventricular mass (left ventricular weight plus septum weight/body weight) was calculated. Small mesenteric resistance vessels were dissected and mounted on a micromyograph (Mulvany's technique), and morphological parameters of the vessels were studied (media thickness and media: lumen ratio).

RESULTS

The systolic blood pressure of SHR administered 20 and 10 mg/kg lacidipine per day was reduced significantly during the treatment period, whereas that of rats treated with 0.3 mg/kg lacidipine per day did not change. A significant reduction in media: lumen ratio was observed for all three groups of treated rats, including those to which 0.3 mg/kg lacidipine per day had been administered, and no reduction in systolic blood pressure could be detected. The relative left ventricular mass was reduced significantly only in rats to which 20 and 10 mg/kg lacidipine per day had been administered.

CONCLUSION

A significant reduction in magnitude of vascular structural alternations was observed even in SHR treated with a low, nonhypotensive dose of lacidipine.

Cholesterol enhances platelet-derived growth factor-BB-induced [Ca2+]i and DNA synthesis in rat aortic smooth muscle cells

In the present study, we describe possible mechanisms by which hypercholesterolemia may contribute to the development of cardiovascular diseases. Treatment of rat aortic smooth muscle cells for 20 hours with cholesterol-rich liposomes (500 micrograms/mL cholesterol, 100 micrograms/mL low-density lipoprotein) resulted in a 76 +/- 12% increase in total cholesterol content. The effects of cholesterol enrichment were examined by determination of changes in cell membrane fluidity. Fluidity of the cholesterol-enriched cell membranes was decreased at all temperatures between 15 degrees C and 40 degrees C. Changes in membrane fluidity in whole cell membranes represented changes in fluidity of microsomal membranes isolated by Percoll gradient ultracentrifugation. The basal [Ca2+]i and the maximal platelet-derived growth factor (PDGF)-BB-induced [Ca2+]i was elevated by 30% and 90% in cholesterol-enriched cells, respectively. In contrast, the resting pH, and the PDGF-BB-induced stimulation of the Na+/H+ exchange were not affected in cholesterol-enriched cells. The effect of PDGF-BB on [3H]thymidine incorporation in cholesterol-enriched cells was elevated by 40% in comparison with untreated cells. Our findings show that cellular cholesterol may be involved in the development of vascular diseases via modulation of the PDGF-induced increase in [Ca2+]i and DNA synthesis in vascular smooth muscle cells.

Platelet-derived growth factor (PDGF): actions and mechanisms in vascular smooth muscle

1. PDGF is a highly hydrophilic cationic glycoprotein (M(r) 28-35kDa) produced by platelets, monocyte/macrophages, endothelial cells and vascular smooth muscle cells under some conditions. 2. Since its original description, PDGF has attracted much attention and it is currently believed to play a role in atherosclerosis and other vascular pathologies. 3. This review describes the vascular biology of PDGF. It particularly focuses on recent findings regarding the intracellular signals activated by PDGF in the context of vascular smooth muscle cell proliferation, migration and, contraction.

Regulation of platelet-derived growth factor isoform-mediated expression of prostaglandin G/H synthase in mesangial cells

Incubation of rat renal mesangial cells with platelet-derived growth factor (PDGF) -AB or -BB led to a transient increase in prostaglandin G/H synthase-2 (PGHS-2) mRNA expression with a maximum after two hours. Expression of PGHS-1 mRNA remained unchanged during short term incubation, but was enhanced about twofold after 8 to 12 hours incubation with PDGF-AB or -BB. Enhanced PGHS activity was still observed after 24 hours. Nevertheless, PGE2 release from mesangial cells was not enhanced by PDGF, hinting to the availability of arachidonic acid as rate-limiting step. PDGF receptors are coupled to multiple signaling pathways, among them phospholipase C gamma PDGF-BB rapidly phoshorylated PLC gamma, while phosphorylation by PDGF-AB was barely detectable. The differential effect of PDGF-BB and PDGF-AB was also seen with respect to calcium signaling: PDGF-BB but not PDGF-AB induced release of Ca2+ from internal stores. Activation of PLC and the resulting transient release of Ca2+ were not considered to be essential for PGHS-2 mRNA induction as both PDGF isoforms were equally effective in mRNA induction. Both PDGF isoforms led to a Ca2+ influx resulting in a long lasting elevation of [Ca2+]i. Enhanced [Ca2+]i seemed to be related to PGHS-2 mRNA expression, because PDGF-induced PGHS-2 mRNA was significantly reduced under Ca2+ free conditions. Diacylglycerol, liberated by PLC, is an activator of protein kinase C (PKC). Down-regulation of PKC by overnight incubation with phorbol ester (0.1 microM) attenuated PGHS-2 mRNA induction by PDGF-AB and -BB. Involvement of PKC was substantiated by the PKC inhibitor H7, which interfered with PDGF-mediated PGHS-2 mRNA expression, while HA1004, a considerably specific inhibitor of protein kinases A and G, was without effect. Taken together, signaling pathways other than PLC gamma seem to be involved in activation of PKC and elevation of [Ca2+]i, which were shown to be essential elements of PDGF-mediated induction of PGHS-2 mRNA expression in mesangial cells.

Persistent Pulmonary Hypertension of the Newborn: Role of Nitric Oxide

Persistent pulmonary hypertension of the newborn (PPHN) is a common cause of respiratory failure in the full-term neonate. Molecular and cellular studies in vascular biology have revealed that endothelial-derived mediators play a critical role in the pathogenesis and treatment of PPHN. Endothelial-derived vasoconstrictors, like endothelin, may increase smooth muscle cell contractility and growth, leading to the physiologic and structural changes observed in the pulmonary arterioles of infants with this disease. On the other hand, decreased production of the endothelial-derived relaxing factor, nitric oxide, may exacerbate pulmonary vasoreactivity and lead to more severe pulmonary hypertension. Exogenous (inhaled) nitric oxide therapy reduces pulmonary vascular resistance and improves oxygenation. The safety and efficacy of this therapy in reducing the need for extracorporeal membrane oxygenation and decreasing long-term morbidity is being tested in several trials nationally and abroad. Understanding the basic mechanisms that regulate the gene expression and production of these vasoactive mediators will lead to improved preventive and therapeutic strategies for PPHN.

Platelet-derived growth factor causes sustained depletion of both inositol trisphosphate-sensitive and caffeine-sensitive intracellular calcium stores in vascular smooth muscle cells

Since the platelet-derived growth factor (PDGF)-induced increase in cellular inositol 1,4,5-trisphosphate (InsP3) has been found to decay to basal levels soon after the onset of PDGF exposure, it has been argued that activation of Ca2+ release from intracellular stores must be similarly transient. The possibility remains, however, that PDGF-induced release of stored Ca2+ is initiated and sustained by other second-messenger systems. To test the hypothesis that PDGF-BB initiates sustained Ca2+ release from cellular stores, we performed 4-hour 45Ca effluxes on monolayers of A7r5 vascular smooth muscle cells in small, continuously perfused chambers. Isoform PDGF-BB (5 ng/mL for 30 minutes or 30 ng/mL for 15 minutes) was added to the perfusate beginning at 30 minutes of efflux. A dose-related increase in 45Ca release was sustained as long as PDGF-BB was present. Detailed kinetic analysis and nonlinear least-squares fitting of the experimental data revealed that (1) PDGF-BB induced sustained increases of 2.86-fold (5 ng/mL) and 6.50-fold (30 ng/mL) in the rate constant governing Ca2+ release from intracellular stores, (2) the apparent Km for this effect was 13.4 +/- 1.31 ng PDGF-BB/mL, and (3) the entire agonist-releasable Ca2+ store (presumably sarcoplasmic reticulum) is sensitive to PDGF-BB. These data indicate that PDGF-BB causes a sustained depletion of intracellular Ca2+ stores by means of sustained activation of Ca2+ release and suggest that intraorganellar Ca2+ may be one of the signals that mediates long-term smooth muscle responses to PDGF.

Ca(2+)-permeable channel associated with platelet-derived growth factor receptor in mesangial cells

We used patch-clamp methods to study the effect of platelet-derived growth factor (PDGF) on Ca2+ entry in cultured rat glomerular mesangial cells. In cell-attached patches, application of 50 ng/ml PDGF-BB inside, but not outside, the pipette frequently induced channel openings. The unitary conductance was 0.67 +/- 0.09 pS (n = 8) with 110 mM Mn2+ and 1.03 +/- 0.19 pS (n = 11) with 110 mM Ca2+ as the charge carrier. Number of channels times open probability was 0.515 +/- 0.144 (n = 14) with intrapipette PDGF and 0.037 +/- 0.022 (n = 12) without. Channel kinetics were only slightly voltage dependent. There was no effect of replacing chloride with gluconate in excised inside-out patches, showing that the channel was cation selective. The permeability (P) ratio for PMn/PNa was 1.65 and for PCa/PNa was 1.24. With the use of amphotericin B " perforated" whole cell patches, PDGF induced a small inward current (-16.1 +/- 4.33 pA; n = 11, membrane potential = -70 mV) consistent with 3,000-4,000 channels/cell. In summary, we have described a very-low-conductance Ca(2+)-permeable channel in rat mesangial cells with the following properties. 1) Activation by PDGF-BB occurs only when applied in close proximity to the channel. 2) Once activated, open probability is only slightly voltage dependent. 3) Under normal circumstances, the channel would probably appear to be cation nonselective, but with a permeability to divalent more than monovalent cations. 4) This PDGF-induced channel could provide a ligand-gated pathway for Ca2+ entry into mesangial cells that does not require membrane depolarization.

Delayed development of hypertension after short-term nitrendipine treatment

In this study we evaluated the delayed effects of a calcium entry blocker on blood pressure and on vascular structural and functional alterations in mesenteric resistance arteries of spontaneously hypertensive rats (SHR). The calcium entry blocker nitrendipine was administered (30 mg/kg per day) according to three different schedules: in one group of SHR from 4 to 8 weeks of age (n = 12), in a second group from 8 to 12 weeks of age (n = 12), and in a third group from 4 to 12 weeks of age (n = 12). Twelve untreated SHR and 12 untreated Wistar-Kyoto rats served as controls. Half the animals of each group were killed at 13 weeks, and the remaining were killed at 38 weeks. After death, relative left ventricular mass was calculated. Vascular morphology and function (responses to norepinephrine and acetylcholine) in mesenteric small arteries were then assessed using a micromyographic technique. Nitrendipine treatment delayed the development of hypertension and determined the regression of structural alterations of mesenteric resistance arteries in SHR. These favorable effects were maintained for several weeks after treatment withdrawal, provided that treatment was started at 4 weeks of age. Considering the functional alterations of mesenteric arteries in SHR (responses to norepinephrine and acetylcholine), nitrendipine treatment determined an improvement of both these dysfunctions as long as reductions of the media-to-lumen ratio and blood pressure, respectively, were maintained.

Actions of platelet-derived growth factor isoforms in mesangial cells

Platelet-derived growth factor (PDGF) occurs as homodimers or heterodimers of related polypeptide chains PDGF-BB, -AA, and -AB. There are two receptors that bind PDGF, termed alpha and beta. The beta receptor recognizes PDGF B chain and is dimerized in response to PDGF BB. The alpha receptor recognizes PDGF B as well as A chains and can be dimerized by the three dimeric forms of PDGF AA, AB, and BB. To characterize PDGF receptor signaling mechanisms and biologic activities in human mesangial cells (MC), we explored the effects of the three PDGF isoforms on DNA synthesis, phospholipase C activation, and PDGF protooncogene induction. PDGF-BB homodimer and AB heterodimer induced a marked increase in DNA synthesis, activation of phospholipase C, and autoinduction of PDGF A and B chain mRNAs, whereas PDGF-AA homodimer was without effect. The lack of response to PDGF AA could be accounted for by down-regulation of the PDGF-alpha receptor since preincubation of MC with suramin restored PDGF AA-induced DNA synthesis. Ligand binding studies demonstrate specific binding of labeled PDGF BB and AB and to a lower extent PDGF AA isoforms to mesangial cells. These results are consistent with predominant expression of PDGF beta receptor in MC, which is linked to phospholipase-C activation. The potent biologic effects of PDGF-AB heterodimer in cells that express very few alpha receptors and do not respond to PDGF AA are somewhat inconsistent with the currently accepted model of PDGF receptor interaction and suggest the presence of additional mechanisms for PDGF isoform binding and activation.

Nitric oxide regulates the expression of vasoconstrictors and growth factors by vascular endothelium under both normoxia and hypoxia

The mechanisms by which hypoxia causes vasoconstriction in vivo are not known. Accumulating evidence implicates the endothelium as a key regulator of vascular tone. Hypoxia induces the expression and secretion of endothelin-1 (ET-1), a potent vasoconstrictor in cultured human endothelial cells. We report here that nitric oxide (NO), an endothelial-derived relaxing factor, modifies this induction of ET-1. Whereas low oxygen tension (PO2 = 20-30 Torr) increases ET-1 expression four- to eightfold above that seen at normal oxygen tension (PO2 = 150 Torr), sodium nitroprusside, which releases NO, suppresses this effect. This inhibition of hypoxia-induced ET-1 expression occurs within the first hour of exposure of cells to sodium nitroprusside. Moreover, when the endogenous constitutive levels of NO made by endothelial cells are suppressed using N-omega-nitro-L-arginine, a potent competitive inhibitor of NO synthase, the baseline levels of ET-1 produced in normoxic environments are increased three- to fourfold. The effects of hypoxia and the NO synthase inhibitor on ET-1 expression are additive. The regulation of ET-1 production by NO appears to be at the level of transcription. Similar effects of NO were observed on the expression of the PDGF-B chain gene. PDGF-B expression was suppressed by NO in a hypoxic environment and induced by N-omega-nitro-L-arginine in both normoxic and hypoxic environments. These findings suggest that in addition to its role as a vasodilator, NO may also influence vascular tone via the regulated reciprocal production of ET-1 and PDGF-B in the vasculature.

PDGF-AA effectively stimulates early events but has no mitogenic activity in AKR-2B mouse fibroblasts

The response of AKR-2B mouse fibroblasts, which express approximately equal numbers of platelet-derived growth factor (PDGF)-alpha and -beta receptors on their surface (V. Hoppe et al. Eur. J. Biochem. 187, 207-214, 1990) to all three isoforms of PDGF, was studied. All isoforms stimulated early events, i.e., receptor autophosphorylation on tyrosine, total cellular phosphorylation, increase in 32P-labeled phospholipid content, but there was no correlation between the extents measured for the different effects. Although rPDGF-AA effectively stimulated these early events, it was unable to induce [3H]thymidine incorporation and cell growth whereas rPDGF-BB and -AB stimulated the division of more than 90% of the cells. This activity was restored by addition of insulin-like growth factor I (IGF-I), which itself exhibited only a low mitogenic activity. rPDGF-AB or -BB did not require the presence of IGF-I to fully stimulate cells for [3H]thymidine incorporation and cell division. Apparently, rPDGF-AA induced only a "competence" state of the cells whereas rPDGF-AB or -BB was also able to initiate "progression". It is speculated that some early events occurring during the competence phase might be part of a "maintenance" program elicited by growth factors.