mTOR-mediated Leiomyoma Growth in Uterine-specific Tsc2-null Mice is Exclusively Dependent on Estradiol Signaling - Implications in the Treatment of Lymphangioleiomyomatosis (LAM)

Thesis (Ph. D.)--University of Rochester. School of Medicine and Dentistry. Dept. of Pharmacology and Physiology, 2015.Lymphangioleiomyomatosis (LAM) is a devastating rare lung disease in which adenomas consisting of abnormal smooth-muscle cells grow within the lungs and progressively lead to loss of pulmonary function. The true origin of the LAM cell is unknown; however, important features provide us with clues. First, LAM cells contain inactivating mutations in genes encoding tuberous sclerosis complex (TSC) 1 or TSC2, proteins that limit cell growth through mammalian target of rapamycin complex1 (mTORC1) activity. Second, LAM cells appear to be metastatic. Third, LAM cells express estrogen and progesterone receptors as well as melanocytic-differentiation markers. Finally, LAM is found almost exclusively in women. Interestingly, LAM shares many features with uterine leiomyomas, benign tumors of myometrial cells. To test the hypothesis that LAM cells originate from uterine leiomyomas containing Tsc mutations, we developed a mouse model for leiomyoma and LAM by targeting uterine-specific Tsc2 deletion. 100% of uteri from uterine-specific Tsc2-null mice developed LAM-like leiomyomas by 18-24 weeks and approximately 50% of 28-34 week old mice developed smooth-muscle Tsc2-null tumors in the lungs. Uniquely, uterine Tsc2-null cells expressed melanocytic markers premelanosomal protein (PMEL) and Melan-A (MLANA), both considered hallmarks of LAM. Ten-weeks after eliminating estrogen production through oophorectomy or by aromatase inhibition using letrozole, Tsc2-null uteri had reduced mTORC1 activity and decreased myometrial proliferation, resulting in tumor regression and reversal of the uterine phenotype. Thus, loss of TSC2 is not sufficient to promote mTORC1-mediated leiomyoma growth without a continuous positive proliferative signal from estradiol. Mechanistically, we find that matrix metalloproteinases (MMP)-2 activity and MMP-9 expression are dependent on estrogen in the absence of TSC2. In-vivo fluorescent imaging using an MMP-sensitive optical biomarker showed higher signal specifically in leiomyomas, suggesting that MMP activity is primarily in Tsc2-null myometrial cells. Finally, we identified another melanocytic-related marker, glycoprotein NMB (GPNMB) that was over-expressed in Tsc2-null myometrial cells as well as in human LAM. Thus, GPNMB may be useful as a biomarker for LAM. Together, we suggest that lung LAM-like myometrial lesions may indeed originate from the uterus and that anti-estrogen therapy may be an effective means of treating not only leiomyoma, but LAM as well