Estradiol Augments the Production and Actions of Polymorphonuclear Cells to Promote Lymphangioleiomyomatosis (LAM) Progression

Affecting almost exclusively women, lymphangioleiomyomatosis (LAM) is a rare lung disease characterized by slowly growing, estrogen-sensitive metastatic smooth muscle cell-like adenomas that result in cystic lung changes and loss of pulmonary function. LAM tumors are caused by mutations in either TSC1 or TSC2 genes that induces defective inhibition of the mTORC1 pathway, leading to increased mTORC1 activity and augmented cell proliferation. We have previously reported that estrogen ablation in our uterine-specific Tsc2 knockout mouse, which grows tumors with characteristic LAM features and lung colonization potential, effects notable regression of tumors. Thus, estrogen is required for to maintain heightened mTORC1 activity and LAM-like tumor progression. Interestingly, the observed estrogen sensitivity in vivo is more markedly pronounced than that of our estrogen receptor-positive TSC2-null cells when stimulated with estradiol in vitro, suggesting that estradiol may act elsewhere—in mTORC1 independent manner—in vivo to promote LAM progression. Flow cytometry revealed large numbers of Ly-6C(int) Ly-6G(high) myeloid cells—polymorphonuclear cells or PMNs—in the blood and myometrial tumors of our uterine-specific Tsc2-null mice. Accordingly, we found that Tsc2-null tumors required PMNs for normal disease progression, as Gr-1 (Ly-6C/Ly-6G) depletion or inhibition of PMN recruitment reduced tumor growth. Therefore, we hypothesized that, in addition to direct effects of estrogen on tumor cells, estrogen might also stimulate tumor growth by promoting PMN production in the bone marrow and actions in the tumor microenvironment. Using bone marrow cultures, we found that estradiol is indeed a potent inducer of PMN production. This effect occurs equally in both male and female bone marrow. Employing both pharmacologic agents and bone marrow from ERα; knockout mice, we showed that ERα; is necessary for promoting a PMN fate for myeloid progenitors. Additionally, we have evidence implicating estrogen in the pro-tumorigenic function of PMNs co-cultured with TSC2-null cell lines. Overall, these data suggest that estradiol maybe facilitating crosstalk in LAM tumors, directly stimulating tumor cells while also promoting the production and actions of PMNs, which in turn promote tumor growth.