Pro-Tumorigenic Role of Neutrophil Elastase in Lymphangioleiomyomatosis (LAM)

Abstract

Lymphangioleiomyomatosis (LAM) is an estrogen-sensitive lung disease found almost exclusively in women. LAM is characterized by the hyperproliferation of smooth muscle cells creating small tumors throughout the lungs, resulting in the formation of large cysts that replace normal alveolar space. Growth of these tumors and progression of the cyst development leads to loss of pulmonary function, and sometimes subsequent lung transplantation. LAM tumor cells contain mutations in one of the tuberous sclerosis genes (TSC1 or TSC2), leading to activation of the mTORC1 pathway. In fact, mTOR inhibitors are commonly used to treat LAM; however, these drugs are not always effective and have significant side effects, suggesting the need for new therapeutic targets. Additionally, tumors recur even after lung transplantation and LAM cells are found in circulating body fluids, suggesting a metastatic nature of LAM, and a question of the origin of the LAM cell. Due to LAM’s estrogen sensitivity, female specificity, and metastatic nature, we previously proposed that LAM cells originate from the uterine myometrium. We therefore designed a uterine-specific TSC2-null mouse model where all the mice generate uterine tumors characteristic of LAM and half develop lung metastases. Using RNASeq analysis of uterine tissue from this mouse model, when focusing on genes regulated by estrogen and TSC2, we discovered significant upregulation of inflammatory proteases such as Neutrophil Elastase (NE). NE is secreted by myeloid cells such as polymorphonuclear cells (PMNs) and has been reported to promote invasion, migration, and proliferation in various cancers. We found this to be true in LAM as well, as depleting myeloid cells with an antibody directed against PMNs, or inhibiting NE with the NE inhibitor, sivelestat, markedly decreased TSC2-null uterine tumor growth. NE is released when PMNs undergo Neutrophil Extracellular Trap release, or NETosis. NETosis has been shown to have a pro-tumorigenic role in various cancers and we are investigating the effects of NETosis in LAM. We have also generated a novel uterine-specific TSC2-null mouse in the background of no NE to determine whether uterine tumor burden and lung metastases are reduced in NE-null mice and if these mice have PMNs capable of undergoing NETosis in the absence of NE. Overall, our results suggest that NE release from PMNs is critical for LAM tumor development and may be a novel target for its treatment.