Estradiol 17-beta represses insulin-like growth factor I receptor expression in smooth muscle cells from rabbit cardiac recipients

Autocrine activation of the local insulin-like growth factor I system is up-regulated by estrogen receptor (ER)-independent estrogen actions and accounts for decreased ER expression in type 2 diabetic mesangial cells

Autocrine activation of the IGF-I system in mesangial cells (MC) promotes glomerular scarring in a model of type 1 diabetes. Although estrogens protect against progressive nondiabetic glomerulosclerosis (GS), women with diabetes seem to loose the estrogen-mediated protection against cardiovascular disease. However, little is known about the local IGF-I system and its interactions with estrogens in the pathogenesis of type 2 diabetic GS. Therefore, we examined db/db B6 (db/db) mice, a model of type 2 diabetes and diabetic GS. The IGF-I system was activated in the glomeruli and MC of female diabetic db/db mice, but not in nondiabetic db/+ littermates. We found increased IGF-I receptor (IGFR) expression and activation, including activation of MAPK. Surprisingly, estrogens, via an estrogen receptor (ER)-independent mechanism(s), increased IGFR expression, IGFR and insulin receptor substrate phosphorylation, and extracellular signal-regulated kinase activation in db/db MC. In contrast, ER expression was decreased in MC and glomeruli of db/db mice. Treatment with a neutralizing antibody to IGF-I or the MAPK inhibitor PD98059 increased ER expression and transcriptional activity. This suggests that the local prosclerotic IGF-I system is activated in type 2 diabetes and diminishes ER-mediated protection against GS. Although estrogens may stimulate protective ER signaling, they also activate the IGF-I system via ER-independent mechanisms in db/db MC. The later estrogen effects appear to outweigh the antisclerotic effects of ER activation. This may in part account for loss of estrogen protection against the progression of diabetic GS in women with type 2 diabetes.

Estrogen regulates insulin-like growth factor 1, platelet-derived growth factor A and B, and their receptors in the vascular wall

BACKGROUND

Peptide growth factors induce vascular smooth muscle cell (SMC) proliferation and migration after vascular injury, leading to arterial stenosis. Estrogen provides vasculoprotective effects by regulating endothelial and vascular SMC function.

METHODS

We performed aortic denudations in male Wistar rats. One group received 17beta-estradiol, 0.25 mg/kg per day subcutaneously, and the other group vehicle. Growth factor and receptor mRNA in the aorta wall was quantitated at 15 minutes, 3 days, and 7 days after denudation. Western blotting and immunohistochemistry were used to quantify and localize the protein.

RESULTS

Aortic injury caused SMC proliferation in the intima and media, indicated by an increase in the number of intimal nuclei and area. Quantitative reverse-transcriptase polymerase chain reaction and Western blotting showed concomitant up-regulation of insulin-like growth factor (IGF)-1, platelet-derived growth factor (PDGF)-B, and PDGF-receptor (R)alpha. 17beta-estradiol significantly inhibited SMC proliferation and intimal thickening. Similarly, estrogen administration completely suppressed IGF-1 mRNA (P=0.004) and protein but had no effect on IGF-1R. Estrogen had virtually no effect on PDGF-A mRNA or protein levels; however, on day 7, it inhibited PDGF-Ralpha mRNA by 74% (P=0.005) and protein by 67%. On day 7, it also inhibited PDGF-B mRNA expression by 36% (P=0.04) but had little effect on protein. PDGF-Rbeta expression was unaffected by estrogen. Estradiol treatment reduced immunoreactivity of IGF-1, PDGF-A, PDGF-Ralpha, and PDGF-B in vascular lesions, whereas no changes were seen with respect to IGF-1R and PDGF-Rbeta.

CONCLUSIONS

Our findings demonstrate that estrogen regulates IGF-1, PDGF-A, PDGF-B, and PDGF-Ralpha, which may be related to the vasculoprotective effect of estrogen, but has no effect on IGF-1R or PDGF-Rbeta.

Estrogen-induced cardiorenal protection: potential cellular, biochemical, and molecular mechanisms

A number of cellular and biochemical processes are involved in the pathophysiology of glomerular and vascular remodeling, leading to renal and vascular disorders, respectively. Although estradiol protects the renal and cardiovascular systems, the mechanisms involved remain unclear. In this review we provide a discussion of the cellular, biochemical, and molecular mechanisms by which estradiol may exert protective effects on the kidneys and vascular wall. In this regard, we consider the possible role of genomic vs. nongenomic mechanisms and estrogen receptor-dependent vs. estrogen receptor-independent mechanisms in mediating the protective effects of estradiol on the renal and cardiovascular systems.

Estradiol down regulates expression of vasoactive intestinal polypeptide receptor type-1 in breast cancer cell lines

Three breast carcinoma cell lines were tested for 17beta-estradiol (E(2)) mediated regulation of vasoactive intestinal polypeptide receptor type-1 (VPAC(1)) expression. In all three, E(2) was found to down-regulate the mRNA level. We studied T47D cells in more details and found a 25 and 70% decrease in the VPAC(1) mRNA level upon 7 and 48 h of E(2) treatment, respectively. The number of vasoactive intestinal polypeptide (VIP) binding sites was reduced 66% upon treatment with E(2) for 72 h. After cycloheximide pretreatment, the E(2) mediated mRNA reduction was attenuated from 50% to 25% after 24 h suggesting the effect to be at least partly independent of protein synthesis. Experiments with the transcriptional inhibitor actinomycin D showed that E(2) did not influence the VPAC(1) mRNA half-life while nuclear run-on experiments indicated that E(2) decreased the VPAC(1) transcription rate. Two antiestrogens: ICI 182780 (ICI) and 4-hydroxy-tamoxifen (4-OHT) mediated a concentration dependent inhibition of E(2)'s effect on the mRNA level. Transient transfection with reporter-gene constructs containing various portions of the VPAC(1) 5'-flanking sequence revealed the most proximal 100 bp to be essential for the basal transcriptional activity. However, E(2) did not influence the expression of the reporter gene using up to 3250 bp of the VPAC(1) 5'-flariking region.

Upregulation of estrogen receptor-alpha expression in rabbit cardiac allograft

Estrogen receptor (ER) expression has been detected in different tissues, and estradiol-17beta treatment protects against experimental transplant arteriosclerosis. In this study, ER-alpha expression in the rabbit hearts and attached aortas before and after cardiac-aorta allograft transplantation was examined. Ten male New Zealand White rabbits were transplanted with cardiac-aorta allografts from male Dutch Belted rabbits. This transplant arteriosclerosis model uses a 0.5% cholesterol diet and immunosuppression with cyclosporin A (10 mg . kg-1 . d-1) until euthanatization 42 days later. The cardiac grafts with the attached aorta were harvested. Strong staining of ER-alpha protein was shown in the coronary arteries of the cardiac allografts by immunohistochemistry with the use of a mouse anti-human ER-alpha monoclonal antibody (ID5). In contrast, both the nongrafted hearts of the recipients and donor hearts expressed only weak staining. RNase protection assay with the use of a 32P-labeled ER-alpha antisense riboprobe (pOR 300) proved that the basal expression of ER-alpha mRNA is similar in the nongrafted aorta of both recipients and donors. A marked increase of ER-alpha mRNA was observed in the allograft aorta compared with the nongrafted aorta (289+/-69%, P<0. 02) by reverse transcription and polymerase chain reaction. The DNA sequence analysis confirmed that the polymerase chain reaction-amplified fragment corresponded to ER-alpha. This is the first observation of ER-alpha upregulation in the allograft vasculature and may relate to the allograft cardiovascular protective effects of estrogen.