Prostaglandins E1 and E2 stimulate the proliferation of pulmonary artery smooth muscle cells

Differential regulation of vascular tone and remodeling via stimulation of type 2 and type 6 adenylyl cyclases in the ductus arteriosus

RATIONALE

Prostaglandin (PG)E(2), which increases intracellular cAMP via activation of adenylyl cyclases (ACs), induces vasodilation and hyaluronan-mediated intimal thickening (IT) in the ductus arteriosus (DA) during late gestation. After birth, however, differential regulation of vasodilation and IT is preferable for treatment of patients with patent DA and DA-dependent congenital cardiac malformations.

OBJECTIVE

Our objectives were to examine whether AC isoforms play differential roles in DA vasodilation and IT.

METHODS AND RESULTS

AC2 and AC6 were more highly expressed in rat DA than in the aorta during the perinatal period. AC6-targeted siRNA counteracted PGE(1)-induced hyaluronan production in rat DA smooth muscle cells. Overexpression of AC6 enhanced PGE(1)-induced hyaluronan production and induced IT in DA explants. Furthermore, IT of the DA was less marked in mice lacking AC6 than in wild-type and AC5-deficient mice. Stimulation of AC2 attenuated AC6-induced hyaluronan production via inhibition of the p38 mitogen-activated protein kinase pathway and AC6-induced IT of the DA. An AC2/6 activator, 6-[N-(2-isothiocyanatoethyl) aminocarbonyl] forskolin (FD1), did not induce hyaluronan-mediated IT in DA explants, although an AC5/6 activator, 6-[3-(dimethylamino)propionyl]-14,15-dihydroforskolin (FD6) did. Moreover, FD1 induced longer vasodilation of the DA than did PGE(1) without significant adverse effects in vivo.

CONCLUSIONS

AC6 is responsible for hyaluronan-mediated IT of the DA and AC2 inhibited AC6-induced hyaluronan production. Stimulation of both AC2 and AC6 by FD1 induced longer vasodilation without hyaluronan-mediated IT in the DA in vivo. FD1 may be a novel alternative therapy to currently available PGE therapy for patients with DA-dependent congenital heart disease.

Effects of IL-1beta, TNF-alpha, and macrophage migration inhibitory factor on prostacyclin synthesis in rat pulmonary artery smooth muscle cells

OBJECTIVE

Cytokines have been implicated in the pathophysiology of pulmonary hypertension. We sought to explore the possibility that prostacyclin is a link.

METHODOLOGY

We tested the effects of the cytokines interleukin-1beta (IL-1beta), tumour necrosis factor-alpha (TNF-alpha), and macrophage migration inhibitory factor (MIF) on arachidonic acid metabolism of pulmonary artery smooth muscle cells (PASMCs) with special regard to prostacyclin (PGI2) that protects against pulmonary hypertension. Cultured rat PASMCs were treated with IL-1beta, TNF-alpha, or MIF. Expression of prostacyclin synthase (PGIS) and cyclooxygenase-2 (COX-2) mRNAs, and PGI2 synthesis, were measured.

RESULTS

We found that PGIS mRNA expression was suppressed by high concentrations of TNF-alpha and MIF, while COX-2 mRNA was induced by all three cytokines tested. IL-1beta increased PGI2 production in a dose-dependent manner. TNF-alpha and MIF also increased PGI2 production, but to a far lesser degree at high concentrations. TNF-alpha paradoxically decreased PGI2 production at a low concentration.

CONCLUSIONS

These results suggest that TNF-alpha and MIF are potentially antagonistic to the action of PGI2 in rat PASMCs via down-regulation of PGIS mRNA. Simultaneous induction of COX-2 mRNA may further counteract the action of PGI2 by increasing the levels of eicosanoids other than PGI2.

PGE(2) stimulates vascular smooth muscle cell proliferation via the EP2 receptor

Prostaglandins released by injured vascular tissue can modulate smooth muscle cell (SMC) proliferation. The mechanism of action of PGE(2) was investigated with porcine coronary artery SMCs obtained by explant culture. DNA and RNA syntheses exhibited a concentration-dependent increase following treatment of quiescent SMCs with PGE(2), while PGI(2) had no effect. PGE(2) also elevated PCNA expression, bromodeoxyuridine incorporation, and cell number, indicative of a hyperplastic growth response. Furthermore, induction of c-fos expression required activation of both phosphatidylinositol 3-kinase and mitogen-activated protein kinase. Contrary to these data, treatment of proliferating cells with PGE(2) caused a reduction in DNA synthesis. A role for PKA in either growth stimulation or inhibition was excluded. Interestingly, only quiescent SMCs expressed EP2 receptors, and the selective EP2 receptor agonist butaprost confirmed that this receptor was essential for growth stimulation and possibly inhibition. These data suggest that the growth state-dependent actions of PGE(2) on SMC proliferation may be mediated via the EP2 receptor.

Effects of the prostanoids on the proliferation or hypertrophy of cultured murine aortic smooth muscle cells

Effects of the prostanoids on the growth of cultured aortic vascular smooth muscle cells (VSMCs) were examined using mice lacking prostanoid receptors. Proliferation of VSMCs was assessed by measuring [(3)H]-thymidine incorporation and the cell number, and their hypertrophy by [(14)C]-leucine incorporation and protein content. In VSMCs from wild-type mice, expressions of mRNAs for the EP(4) and TP were most abundant, followed by those for the IP, EP(3) and FP, when examined by competitive reverse transcriptase-PCR. Those for the EP(1), EP(2) and DP, however, could not be detected. AE1-329, an EP(4) agonist, and cicaprost, an IP agonist, inhibited platelet derived growth factor (PDGF)-induced proliferation of VSMCs from wild-type mice; these inhibitory effects disappeared completely in VSMCs from EP(4)(-/-) and IP(-/-) mice, respectively. In accordance with these effects, AE1-329 and cicaprost stimulated cAMP production in VSMCs from wild-type mice, which were absent in VSMCs from EP(4)(-/-) and IP(-/-) mice, respectively. Effects of PGE(2) on cell proliferation and adenylate cyclase were almost similar with those of AE1-329 in VSMCs from wild-type mice, which disappeared in VSMCs from EP(4)(-/-) mice. PGD(2) inhibited PDGF-induced proliferation of VSMCs from both wild-type and DP(-/-) mice to a similar extent. This action of PGD(2) was also observed in VSMCs from EP4(-/-) and IP(-/-) mice. In VSMCs from wild-type mice, I-BOP, a TP agonist, showed potentiation of PDGF-induced hypertrophy. I-BOP failed to show this action in VSMCs from TP(-/-) mice. The specific agonists for the EP(1), EP(2) or EP(3), and PGF(2)alpha showed little effect on the growth of VSMCs. These results show that PGE(2), PGI(2) and TXA(2) modulate PDGF-induced proliferation or hypertrophy of VSMCs via the EP(4), IP and TP, respectively, and that the inhibitory effect of PGD(2) on PDGF-induced proliferation is not mediated by the DP, EP(4) or IP.

Prostacyclin analogues differentially inhibit growth of distal and proximal human pulmonary artery smooth muscle cells

BACKGROUND

Prostacyclin has proved to be a beneficial treatment for patients with severe pulmonary hypertension. We postulated that the response may reflect, at least in part, inhibition of pulmonary artery smooth muscle cell (PASMC) growth.

METHODS AND RESULTS

Human PASMCs were derived from distal (<1-mm external diameter, n=8) and proximal (>8-mm external diameter, n=12) pulmonary arteries obtained at transplant surgery and pneumonectomy. The effects of the stable prostacyclin analogues on [methyl-(3)H]thymidine incorporation and cell proliferation were investigated by using immunohistochemically characterized cells. Distal cells proliferated faster than did proximal PASMCs and displayed a distinct sensitivity to cicaprost and iloprost. Both analogues inhibited thymidine uptake over 24 hours (20% to 60%, P<0.001; n=8) and abolished stimulation of DNA synthesis by platelet-derived growth factor-BB (10 ng/mL) in distal but not proximal cells. The inhibitory effect of cicaprost was mimicked by isoproterenol (10(-5) mol/L), forskolin (10(-5) mol/L), and dibutyryl cAMP (5x10(-4) mol/L) and was potentiated by the phosphodiesterase inhibitor 3-isobutyl-1-methylxanthine (5x10(-5) mol/L). Cicaprost (10(-10) to 10(-6) mol/L) inhibited the proliferation of PASMCs, which had been stimulated with either platelet-derived growth factor-BB or serum, and increased cAMP production. These effects were potentiated by 3-isobutyl-1-methylxanthine and attenuated by the adenylyl cyclase inhibitor 2',5'-dideoxyadenosine (10(-5) to 10(-4) mol/L).

CONCLUSIONS

++Cicaprost and iloprost inhibit DNA synthesis and proliferation to a greater extent in distal compared with proximal human PASMCs, acting at least in part via a cAMP-dependent mechanism. The results are consistent with the hypothesis that prostacyclin analogues inhibit vascular remodeling in pulmonary hypertension and demonstrate heterogeneity among human PASMCs.

Roles of vasodilatory prostaglandins in mitogenesis of vascular smooth muscle cells

Vasodilatory prostaglandins (PGI2, PGE1) and synthetic prostacyclin mimetics inhibit smooth muscle cell proliferation in vitro after stimulation by growth factors. Similar results are obtained in vivo after endothelial injury, suggesting that vasodilatory prostaglandins might also control smooth muscle cell proliferation in vivo. However, available data from clinical trials are conflicting and currently do not support the concept that these compounds might be successfully used to suppress excessive smooth muscle cell growth in response to tissue injury, specifically restenosis after PTCA. One possible explanation for these different results is an agonist-induced down-regulation of prostacyclin receptors in vascular smooth muscle cells. It is possible that enhanced endogenous prostacyclin biosynthesis, subsequent to induction of COX-2 and/or in relation to the formation of a neointima from media smooth muscle cells, might have a similar effect. There is still uncertainty regarding the cellular signal transduction pathways and their possibly complex interaction, although cAMP-dependent reactions are probably involved. In addition, vasodilatory prostaglandins might also interfere with the generation and action of other growth modulating factors, including PDGF, hepatocyte growth factor and nitric oxide. In conclusion, vasodilatory prostaglandins might be considered as growth modulating endogenous mediators in vascular smooth muscle cells.

Antimitotic actions of vasodilatory prostaglandins--clinical aspects

A variety of in-vitro antiatherosclerotic actions, among them those on vascular smooth muscle cells (mitotic activity, proliferation, extracellular matrix production), have been identified especially for PGE1 and PGI2, and proven in experimental animals. Ex-vivo data in humans are not yet available. We examined the effect of PGE1-, PGI2- and iloprost therapy of various duration (1-4 weeks) on smooth muscle cells (mitosis, proliferation, prostaglandin formation from exogenous and endogenous substrate) derived from vascular surgery samples. In-vivo PG-therapy decreases [3H]-thymidine incorporation as well as [35]S- and [14C]-proline uptake. These effects are dependent on the duration of treatment, PGE1 being trendwise more effective. Arachidonic acid conversion to PGI2 is significantly enhanced in activated smooth muscle cells of the plaque, both in the intima as well as in the media. Due to the activation of the gene for COX-2, the actual synthesis of PGI2 as well as the conversion rate to 6-oxo-PGF1 alpha are increased in activated smooth muscle cells, an effect being abolished by the PG's administered. It can thus be concluded that PG-therapy for advanced atherosclerosis seems to affect vascular smooth muscle cells beneficially, decreasing mitotic and proliferative activity as well as collagen and glycosaminoglycan synthesis. The somewhat less pronounced effect for PGI2 and iloprost could be explained by desensitization at the receptor level as preliminary findings suggest. This could become even more relevant if a long-term administrable stable (oral) analogue becomes available for routine therapy.

Endothelin-1 and cell proliferation in lung organ cultures. Implications for lung allografts

Endothelin-1 (ET-1) is found in bronchoalveolar lavage fluid in patients following lung transplantation. ET-1 causes contraction of isolated pulmonary vessels and bronchi and stimulates proliferation of smooth muscle cells in culture. Therefore, ET-1 could contribute to the smooth muscle hyperplasia and stromal proliferation seen in chronic rejection of lung allografts. Experiments were designed to determine whether (1) ET-1 stimulates proliferation of pulmonary tissue, (2) proliferation is increased in rejecting allotransplanted lungs, (3) endothelin-A receptors mediate the proliferative response, and (4) ET-1 is produced by activated infiltrating immunocompetent cells. Lung organ cultures were prepared from unoperated dogs and dogs with rejecting single lung allografts. Incubation of organ cultures from unoperated dogs with ET-1 (10(-9) to 10(-7) M)) increased positive staining for proliferation cell nuclear antigen (PCNA) in lung parenchyma. PCNA staining was not decreased by the endothelin-A antagonist BQ123 (10(-6) M). In addition, immunostaining for endothelin-B receptors was present in sections of unoperated but not rejecting lungs. PCNA staining in lung cultures from rejecting allotransplanted dogs was significantly greater than that from unoperated dogs. Positive immunohistochemical staining for ET-1 was found in mononuclear cells infiltrating rejecting transplanted lungs. In conclusion, exogenous ET-1 is mitogenic in lung organ cultures through receptors other than endothelin-A. Proliferation in rejecting transplanted lungs is increased compared with unoperated lungs. Mononuclear cells may be a source of endothelin-1 in the rejecting lung. ET-1, therefore could, in synergism with other cytokines, contribute to acute and chronic pathological changes seen in pulmonary rejection.

Cell cycle related inhibition of mouse vascular smooth muscle cell proliferation by prostaglandin E1: relationship between prostaglandin E1 and intracellular cAMP levels

Elucidation of the cellular and molecular mechanisms which regulate vascular smooth muscle cell proliferation is critical to the understanding of atherogenesis. The present studies were conducted to evaluate the relationship between prostaglandin E1 (PGE1) and cAMP in the regulation of DNA synthesis in mouse vascular smooth muscle cells (SMCs). Quiescent cultures of SMCs were challenged with 10% fetal bovine serum to initiate cell cycle transit and PGE1 (10 microM) or dibutyryl cAMP (1, 10, 100 microM) added at 0, 8, 16, 24, and 32 h. DNA synthesis as measured by [3H] thymidine incorporation and intracellular cAMP levels were measured 24 h following individual treatments. PGE1 modulated DNA synthesis in a cell cycle related fashion, with inhibition only observed in cells challenged 16 h or longer following initiation of cell cycle transit. The decrease in DNA synthesis induced by PGE1 was associated with increased intracellular cAMP levels at 16 and 24 h, but not 32 h. Exposure of SMCs to dibutyryl-cAMP also inhibited DNA synthesis in a cell cycle related fashion, with the most pronounced effect seen at 16 h. These results demonstrate that the effects of PGE1 are restricted to a defined period within the cell cycle following S phase entry and implicate modulation of intracellular cAMP levels in the inhibitory response.

Effects of prostaglandin E1 on human keratinocytes and dermal fibroblasts: a possible mechanism for the healing of skin ulcers

The effects of prostaglandin E1 (PGE1) on cell growth, cytokine production and interaction of cultured normal human keratinocytes (NHKs) and human dermal fibroblasts (HDFs) were investigated. When NHKs were treated with PGE1 directly, only a slight increase in cell growth and a transient decrease in interleukin 1 alpha (IL-1 alpha) secretion were observed. No IL-6 was detected either before or after PGE1 treatment. In addition, IL-8 and transforming growth factor alpha (TGF alpha) production were uninfluenced by PGE1. The response of HDFs to PGE1 differed from that of NHKs. Following PGE1 treatment, IL-1 alpha and TGF alpha from HDFs remained undetectable while IL-6 production was enhanced markedly. IL-8 production was also slightly enhanced. Exposure of HDFs to PGE1 for 96 hours significantly promoted cell proliferation. Two kinds of conditioned media (CM) were prepared by a brief feeding of HDFs with keratinocyte basic medium or Dulbecco's modified Eagle's medium supplemented with 5% FCS with or without PGE1. NHKs proliferated more rapidly in CM than in corresponding basic medium. Moreover, CM prepared with PGE1 treatment showed a stronger effect in promoting NHK proliferation than CM without PGE1 treatment. This promoting effect was inhibited by anti-human IL-6 monoclonal antibody dose-dependently. These results indicate that fibroblasts are more sensitive than keratinocytes in response to PGE1 and that, upon PGE1 stimulation, HDF-derived IL-6 may play an essential role in NHK cell proliferation which may at least partly account for the beneficial effects of PGE1 in the treatment of cutaneous ulcerations.

Low protein diet blunts the rise in glomerular gene expression in focal glomerulosclerosis

The present study was designed to assess whether expression of mRNA for extracellular matrix (ECM) components, metalloproteinases (MMP) and tissue inhibitor of metalloproteinases (TIMP) in glomeruli is affected by a low protein diet during the course of focal glomerulosclerosis (FGS). Puromycin aminonucleoside (PAN) was injected intraperitoneally in rats and the right kidney was removed on day 22. Nephrotic rats received successive intraperitoneal injections of PAN on days 27, 34, and 41. Control rats were subjected to a nephrectomy or a sham operation on day 22. Animals were divided into six groups. In group 1, the PAN-injected rats were fed a standard diet containing 22% protein. In group 2, the PAN-injected rats were fed a low protein diet containing 6% protein, starting on the same day as the first PAN injection. In group 3, the nephrectomized rats without PAN were fed a standard diet. In group 4, the nephrectomized rats without PAN were fed a low protein diet for the same period. In group 5, the sham operated rats were fed a standard diet. In group 6, the sham operated rats were fed a low protein diet for the same period. Rats were sacrificed on days 0, 60 or 80 after the initial PAN or saline injection. The percentage of sclerotic glomeruli in group 1 rats increased markedly with time, reaching 77% on day 80. The mRNA levels encoding for alpha 1(I), alpha 1(III), alpha 1(IV) collagen chains, laminin B1 and B2 chains, heparan sulfate proteoglycan (HSPG), MMP-2, TIMP-1 and TIMP-2 increased significantly as glomerulosclerosis progressed, whereas MMP-1 and MMP-3 mRNA levels were unchanged, and no MMP-9 mRNA was detected throughout the experiments. In group 2, the low protein diet reduced the prevalence of glomerulosclerosis and attenuated the increased mRNA expression for ECM components, MMP-2, TIMP-1 and TIMP-2 in FGS glomeruli. In groups 3 through 6, mRNA levels for ECM components decreased with age, whereas those for MMPs and TIMPs changed little throughout the experiments. Immunofluorescence studies revealed the accumulation of types I, III and IV collagens, laminin, and HSPG in the sclerotic area and low protein diet attenuated the accumulation of these proteins. These data suggest that glomerulosclerosis may result from an imbalance among ECM components, MMPs and TIMPs and that a low protein diet attenuates the otherwise increased levels of mRNA for ECM components, MMP-2, TIMP-1 and TIMP-2 in glomerulosclerosis.