Stromal estrogen receptor-α promotes tumor growth by normalizing an increased angiogenesis.

Estrogens directly promote the growth of breast cancers that express the estrogen receptor α (ERα). However, the contribution of stromal expression of ERα in the tumor microenvironment to the protumoral effects of estrogen has never been explored. In this study, we evaluated the molecular and cellular mechanisms by which 17ß-estradiol (E2) impacts the microenvironment and modulates tumor development of ERα-negative tumors. Using different mouse models of ER-negative cancer cells grafted subcutaneously into syngeneic ovariectomized immunocompetent mice, we found that E2 potentiates tumor growth, increases intratumoral vessel density, and modifies tumor vasculature into a more regularly organized structure, thereby improving vessel stabilization to prevent tumor hypoxia and necrosis. These E2-induced effects were completely abrogated in ERα-deficient mice, showing a critical role of host ERα. Notably, E2 did not accelerate tumor growth when ERα was deficient in Tie2-positive cells, even in mice grafted with wild-type bone marrow. These results were extended by clinical evidence of ERα-positive stromal cell labeling in the microenvironment of human breast cancers. Together, our findings therefore show that E2 promotes the growth of ERα-negative cancer cells through the activation of stromal ERα (extra-hematopoietic Tie-2 positive cells), which normalizes tumor angiogenesis and allows an adaptation of blood supply to tumors, thereby preventing hypoxia and necrosis. These findings significantly deepen mechanistic insights into the impact of E2 on tumor development with potential consequences for cancer treatment.

The transactivating function 1 of estrogen receptor alpha is dispensable for the vasculoprotective actions of 17beta-estradiol.

Full-length 66-kDa estrogen receptor alpha (ERalpha) stimulates target gene transcription through two activation functions (AFs), AF-1 in the N-terminal domain and AF-2 in the ligand binding domain. Another physiologically expressed 46-kDa ERalpha isoform lacks the N-terminal A/B domains and is consequently devoid of AF-1. Previous studies in cultured endothelial cells showed that the N-terminal A/B domain might not be required for estradiol (E2)-elicited NO production. To evaluate the involvement of ERalpha AF-1 in the vasculoprotective actions of E2, we generated a targeted deletion of the ERalpha A/B domain in the mouse. In these ERalphaAF-1(0) mice, both basal endothelial NO production and reendothelialization process were increased by E2 administration to a similar extent than in control mice. Furthermore, exogenous E2 similarly decreased fatty streak deposits at the aortic root from both ovariectomized 18-week-old ERalphaAF-1(+/+) LDLr(-/-) (low-density lipoprotein receptor) and ERalphaAF-1(0) LDLr (-/-) mice fed with a hypercholesterolemic diet. In addition, quantification of lesion size on en face preparations of the aortic tree of 8-month-old ovariectomized or intact female mice revealed that ERalpha AF-1 is dispensable for the atheroprotective action of endogenous estrogens. We conclude that ERalpha AF-1 is not required for three major vasculoprotective actions of E2, whereas it is necessary for the effects of E2 on its reproductive targets. Thus, selective ER modulators stimulating ERalpha with minimal activation of ERalpha AF-1 could retain beneficial vascular actions, while minimizing the sexual effects.

Prevention of skin flap necrosis by estradiol involves reperfusion of a protected vascular network.

Although 17beta-estradiol (E2) is protective in experimental models of myocardial and brain ischemia, its effect on skin ischemia remains unknown. Here, we assessed the protective effect of E2 in a mouse model of skin ischemia, mimicking the surgery of skin flaps. Whereas necrosis appeared in the half portion of the skin flap within 1 week after surgery in ovariectomized mice, it was reduced up to 10-fold when mice were pretreated with E2, at least 3 days before the surgery. The beneficial effect of E2 appeared to be attributable to an increase in skin survival, revealed by measuring viability of ex vivo explants and enhancement of the antiapoptotic Bcl-2 protein expression in vivo. This protective effect on the skin contributed to the protection of the vascular network and facilitated reperfusion, which was found to be accelerated in ovariectomized E2-treated mice, whereas hemorrhages were observed in untreated mice. E2 also increased expression of fibroblast growth factor-2 isoforms in the skin and circulating vascular endothelial growth factor in the serum. Finally, this protective effect of E2 was abolished in estrogen receptor-deficient mice (ERalpha(-/-)) but maintained in chimeric mice reconstituted with ERalpha-deficient bone marrow, indicating dispensable action of E2 in bone marrow-derived cells. This protective effect of E2 was mimicked by treatment with tamoxifen, a selective estrogen receptor modulator. In conclusion, we have demonstrated for the first time that E2 exerts a major preventive effect of skin flap necrosis through a prevention of ischemic-induced skin lesions, including those of the vascular network, which contributes to accelerate the reperfusion of the skin flap.

Deleting TCR alpha beta+ or CD4+ T lymphocytes leads to opposite effects on site-specific atherosclerosis in female apolipoprotein E-deficient mice.

Recent studies have demonstrated the importance of lymphocytes, especially CD4(+) T cells, in early lesions of atherosclerosis in hypercholesterolemic mice. However, the role of other T cell subpopulations, like CD8(+) T cells or TCR gamma delta T lymphocytes, is not yet clear. We have therefore generated apolipoprotein E-deficient mice genetically deficient in specific T lymphocyte subpopulations and measured atherosclerotic lesions in the aortic sinus and en face whole aorta preparation at 18 weeks and at 1 year of age. Whereas TCR gamma delta(+) T lymphocytes appeared to play a modest role, TCR alpha beta(+) T lymphocytes played a major role as their deficiency significantly prevented early and late atherosclerosis at all arterial sites. However, neither CD4(+) nor CD8(+) T cells induced any significant decrease of the lesions at the aortic sinus, suggesting that compensatory proatherogenic mechanisms are operating at this site. Interestingly, the absence of CD4(+) T cells led to a dramatic increase in early lesion abundance at the level of the descending thoracic and abdominal aorta, which was still obvious at 1 year. In conclusion, whereas the TCR alpha beta(+) lymphocyte subset in its whole contribute to aggravate both early and late atherosclerosis, the CD4(+) T subpopulation appears to be critically protective at the level of the lower part of the aorta.