7409 Estrogen Receptor a (ERa) Signaling Mediates Pro-Tumor Neutrophil Activation in the Setting of Lymphangioleiomyomatosis (LAM)

Abstract Disclosure: K.E. O'Leary: None. E. Gibbons: None. B.M. Minor: None. T. Henson: None. S.R. Hammes: None. Lymphangioleiomyomatosis (LAM), is a rare disease marked by the irregular proliferation of smooth muscle-like cells containing tuberous sclerosis (TSC) gene mutations. The resultant tumor growth causes cyst formation in the lung parenchyma which leads to decline in respiratory function. Notably, LAM almost exclusively affects biological females and appears to be estrogen sensitive. Prior studies have suggested that LAM tumor cells may originate from the uterus, thus explaining the female sexual dimorphism and the estrogen sensitivity. However, recent work from our laboratory suggests that estradiol not only stimulates TSC2-null smooth muscle cells, but also promotes neutrophil production via estrogen receptor α (ERα) signaling in the bone marrow, which in turn stimulates TSC2-null tumor progression. The precise mechanism by which ERα signaling promotes neutrophil production is unknown, nor are the direct effects of ERα signaling in neutrophils well understood; therefore, here we investigated the role of ERα signaling in tumor associated neutrophil activation. We hypothesized that estradiol, in concert with tumor-derived factors, may augment pro-tumorigenic and immunosuppressive functions of neutrophils. To address our hypothesis, Ly6G+ neutrophils were isolated from the harvested bone marrow of both C57BL/6 control and ERα knockout mice. Tumor conditioned media (TCM) containing potential tumor-derived stimulating factors was generated from LTM3 myometrial cells derived from uterine-specific TSC2-null mice (a mouse model for LAM tumors). Isolated neutrophils were then cultured in either fresh cell culture media or TCM for 24 hours. mRNA was collected and real-time quantitative PCR performed to investigate changes in mRNA expression of several known neutrophil activation markers. Our results show ERα was required for full expression of neutrophil elastase (Elane), nitric oxide synthase 2 (Nos2), and programmed death-ligand 1 (Pdl1/Cd274), all markers of neutrophils activated to support tumor progression. In addition, capacity for ERα signaling led to suppression of the chemokine receptor Cxcr2 mRNA. Our results indicate that, in addition to stimulating neutrophil production in bone marrow, estradiol signaling through ERα receptors on neutrophils may have significant influence on the quality of tumor exposed neutrophil activation, promoting a pro-tumorigenic immunosuppressive phenotype. Presentation: 6/3/2024