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Proliferation of vascular smooth muscle cells (VSMC) plays a major role as an initiating event of atherosclerosis. Although estrogen directly inhibits the proliferation of VSMC, the mechanism has not been firmly established. In addition, the effect of raloxifene on VSMC remains unknown. 17Beta-estradiol (E(2)) and raloxifene significantly inhibited the growth of VSMC under growth-stimulated conditions. Since mitogen-activated protein (MAP) kinases have been implicated in VSMC proliferation, the role of MAP kinases in both the E(2)- and raloxifene-induced growth inhibition of VSMC was studied. Both E(2) and raloxifene caused rapid, transient phosphorylation and activation of p38 that was not affected by actinomycin D and was blocked by ICI 182,780. In contrast with p38 phosphorylation, extracellular signal-regulated protein kinase (ERK) phosphorylation was significantly inhibited and c-Jun N-terminal kinase (JNK) phosphorylation was not changed by E(2). Because VSMC expressed both estrogen receptor (ER) alpha and ERbeta, it is not known which of them mediates the E(2)-induced phosphorylation of p38. Although E(2) did not affect the p38 phosphorylation in A10 smooth muscle cells, which express ERbeta but not ERalpha, transfection of ERalpha expression vector into A10 cells rendered them susceptible to induction of p38 phosphorylation by E(2). We then examined whether E(2) and raloxifene induce apoptosis through a p38 cascade. Both E(2) and raloxifene induced apoptosis under growth-stimulated conditions. The p38 inhibitor SB 203580 completely blocked the E(2)-induced apoptosis. Our findings suggest that both E(2)- and raloxifene-induced inhibition of VSMC growth is due to induction of apoptosis through a p38 cascade whose activation is mediated by ERalpha via a nongenomic mechanism.

The presence and possible physiological roles of alpha-melanocyte-stimulating hormone (alpha-MSH) in the peripheral tissues of birds have not been established. By a combination of RT-PCR, immunocytochemistry and in situ hybridization, we have examined alpha-MSH expression in the eye of the chicken during development. In the 1-day-old chick, alpha-MSH was expressed in the retinal pigment epithelial (RPE) cells, and also at a lower level in the cone cells. The melanocortin receptor subtypes, CMC1, CMC4 and CMC5, were expressed in the layers of the choroid and the neural retina, but not in the RPE cells. It is probable that the RPE cells secrete alpha-MSH to exert paracrine effects on the choroid and neural retina. During embryonic development, alpha-MSH immunoreactivity in the RPE cells was initially detected at embryonic day 10, and increased in intensity as development proceeded. No cone cells were stained with anti-alpha-MSH antiserum in any of the embryonic stages tested. The immunoreactivities for two prohormone convertases, PC1 and PC2, were co-localized to the RPE cells with a pattern of staining similar to that of alpha-MSH. Despite containing alpha-MSH immunoreactivity, the RPE cells in 1-day-old chicks expressed no immunoreactivity for the endoproteases. Furthermore, in a 3-day-old chick, pro-opiomelanocortin mRNA was detectable by in situ hybridization only in the photoreceptor layer and not in the RPE cells. These results suggest that the RPE cells and the cone cells are intraocular sources of alpha-MSH in the embryonic and postnatal life of the chicken respectively. Embryonic expression of alpha-MSH in the RPE cells implies a possible role for the peptide in ocular development.

To investigate the molecular mechanisms of increased transcription of the insulin-like growth factor-binding protein-1 (IGFBP-1) gene in dietary protein-deprived animals, the cis-acting sequence that is involved in this regulation was analyzed. We first showed that IGFBP-1 gene transcription was up-regulated by amino acid deprivation in cultured liver cell lines: H4IIE and HuH-7. Since HuH-7 cells showed a greater increase in IGFBP-1 mRNA in response to amino acid deprivation, this cell line was used in further experiments. Using a promoter function assay, we found that up-regulation of promoter activity responding to amino acid deprivation was abolished by deleting the region between -112 and -81 bp from the cap site from the gene construct. This cis-acting region includes the insulin-responsive element (IRE) and glucocorticoid responsive element (GRE) of IGFBP-1. In summary, the present observation suggests that the 32-bp (-112 to -81) in the IGFBP-1 gene 5' promoter region is involved in the induction of the IGFBP-1 gene in response to amino acid deprivation.

The purpose of this study was to investigate the effects of physiologic levels of ghrelin on insulin secretion and insulin sensitivity (glucose disposal) in scheduled fed-sheep, using the hyperglycemic clamp and hyperinsulinemic euglycemic clamp respectively. Twelve castrated Suffolk rams (69.8 ± 0.6 kg) were conditioned to be fed alfalfa hay cubes (2% of body weight) once a day. Three hours after the feeding, synthetic ovine ghrelin was intravenously administered to the animals at a rate of 0.025 and 0.05 μg/kg body weight (BW) per min for 3 h. Concomitantly, the hyperglycemic clamp or the hyperinsulinemic euglycemic clamp was carried out. In the hyperglycemic clamp, a target glucose concentration was clamped at 100 mg/100 ml above the initial level. In the hyperinsulinemic euglycemic clamp, insulin was intravenously administered to the animals for 3 h at a rate of 2 mU/kg BW per min. Basal glucose concentrations (44± 1 mg/dl) were maintained by variably infusing 100 mg/dl glucose solution. In both clamps, plasma ghrelin concentrations were dose-dependently elevated and maintained at a constant level within the physiologic range. Ghrelin infusions induced a significant (ANOVA; P < 0.01) increase in plasma GH concentrations. In the hyperglycemic clamp, plasma insulin levels were increased by glucose infusion and were significantly (P < 0.05) greater in ghrelin-infused animals. In the hyperinsulinemic euglycemic clamp, glucose infusion rate, an index of insulin sensitivity, was not affected by ghrelin infusion. In conclusion, the present study has demonstrated for the first time that ghrelin enhances glucose-induced insulin secretion in the ruminant animal.

The proliferation of vascular smooth muscle cells (VSMC) is a crucial pathophysiological process in the development of atherosclerosis. Although estrogen is known to inhibit the proliferation of VSMC, the mechanism responsible for this effect remains to be elucidated. In addition, the effect of raloxifene on VSMC remains unknown. We have shown here that 17beta-estradiol (E(2)) and raloxifene significantly inhibited the platelet-derived growth factor (PDGF)-stimulated proliferation of cultured human VSMC. Flow cytometry demonstrated that PDGF-stimulated S-phase progression of the cell cycle in VSMC was also suppressed by E(2) or raloxifene. We found that PDGF-induced phosphorylation of retinoblastoma protein (pRb), whose hyperphosphorylation is a hallmark of the G1-S transition in the cell cycle, was significantly inhibited by E(2) and raloxifene. These effects were associated with a decrease in cyclin D1 expression, without a change in cyclin-dependent kinase 4 or cyclin-dependent kinase inhibitor, p27(kip1) expression. ICI 182,780 abolished the inhibitory effects of E(2) and raloxifene on PDGF-induced pRb phosphorylation. Next, we examined which estrogen receptor (ER) is necessary for these effects of E(2) and raloxifene. Since VSMC express both ERalpha and ERbeta, A10, a rat aortic smooth muscle cell line that expresses ERbeta but not ERalpha, was used. The dose-dependent stimulation of A10 cell proliferation by PDGF was not inhibited by E(2) or raloxifene in contrast to the results obtained in VSMC. Moreover, E(2) and raloxifene significantly inhibited the PDGF-induced cyclin D1 promoter activity in A10 cells transfected with cDNA for ERalpha but not in the parental cells. These results suggested that E(2) and raloxifene exert an antiproliferative effect in VSMC treated with PDGF, at least in part through inhibition of pRb phosphorylation, and that the inhibitory effects of E(2) and raloxifene may be mainly mediated by ERalpha.