The Molecular and Genetic Pathogenesis of LAM

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Abstract Lymphangioleiomyomatosis (LAM) is a progressive multi-system disease of women characterized by cystic lung destruction, renal angiomyolipomas, and chylous pleural effusions. Lymphangiogenesis is prominent in pulmonary LAM nodules and serum VEGF-D levels above 800 pg/ml are a diagnostic biomarker of LAM. The majority of LAM cells carry bi-allelic inactivating mutations in the tuberous sclerosis complex (TSC) genes and circulating LAM cells with TSC2 loss of heterozygosity can be detected in the blood. The TSC protein complex inhibits the mammalian/mechanistic target of rapamycin (mTORC1) via the small GTPase Rheb. mTORC1 acts as a molecular sensor that regulates cell growth, metabolism, autophagy, and microRNA biogenesis. Pivotal clinical trials have demonstrated clinical benefit from treatment with sirolimus (Rapamycin) or its analogs (Rapalogs) in LAM and TSC. Collectively these data indicate that Rapamycin is an effective suppressive therapy for LAM. However, lung function decline resumes, and tumors regrow when the drug is discontinued. Therefore, therapy must be used chronically – perhaps lifelong. This highlights the urgent unmet need for novel therapeutic strategies in LAM and TSC to eliminate (rather than suppress) LAM cells, for novel biomarkers allowing personalization of therapy and to better understand genetic and clinical factors that may help to predict the severity of LAM. This UO1 brings together a unique team of leaders in lymphangioleiomyomatosis (LAM) and tuberous sclerosis complex (TSC) to address key unanswered questions with high clinical impact. First, identifying novel biomarkers of LAM. Using in vitro and in vivo models of LAM and single cell RNA sequencing from human LAM lungs, systematic analysis of the LAM cell “secretome” will elucidate the pathogenesis of LAM revealing novel prognostic biomarkers. Second, investigating novel mTORC1-independent pathways leading to LAM cell survival that could be therapeutically targeted to induce LAM cell death. Third, analysis of genetic modifiers of LAM and of potential cryptic generalized somatic mosaicism for TSC2 gene mutations to elucidate LAM pathogenesis and help identify patients at highest risk of progression.