Pulmonary LAM, a rare lung disease affecting predominantly women of childbearing age, is associated with mutations of the Tuberous Sclerosis Complex (TSC) tumor suppressor genes. LAM manifests by cystic lung destruction, spontaneous pneumothoraces and neoplastic LAM cell growth. Although LAM cell growth has been linked to upregulation of the mTORC1 activity that is amenable to rapamycin treatment, key questions remain, among the most important: 1) what is the mechanism of LAM cell neoplastic transformation and 2) how do these changes lead to lung cyst formation characteristic of LAM. We have developed a novel experimental TSC-null murine LAM model in which there is infiltration of TSC-null cells into the lung and these cells induce cystic morphological changes highly similar to those seen in human LAM. Importantly, inhibition of both mTORC1 and mTORC2 signaling with rapamycin and with simvastatin, respectively, inhibits TSC-null tumor growth and airspace enlargement. Our published and new data also show that TSC loss promotes LAM cell invasiveness, activates mTORC2, increases MMP-9 expression, downregulates membrane localization of E-cadherin through upregulation of Rac1 GTPase activity, and induces cell transformation. These data supports our central hypothesis that: loss of TSC induces cell transformation by mTORC2-dependent Rac1 activation that downregulates membrane localization of E-cadherin and upregulates MMP-9 expression. This, in turn, induces proteolytic destruction of extracellular matrix (ECM), alveolar cell apoptosis, an inflammatory cell infiltration leading to destruction of lung parenchyma, alveolar space enlargements and the loss of pulmonary function. These observations also lead to the translational hypothesis that pharmacological targeting of both mTORC2 and mTORC1 signaling will provide combinational therapy in pulmonary LAM. These studies will establish a mechanistic link between loss of TSC and alveolar destruction in LAM, and will provide insights about potential novel molecular targets and potential combinational therapy to treat LAM.
Pulmonary lymphangioleiomyomatosis (LAM), a rare lung disease affecting predominantly women of childbearing age, is associated with mutations of the Tuberous Sclerosis Complex (TSC) tumor suppressor genes. Little is known about how TSC loss in LAM cells induces lung cyst formation and whether cystic lung destruction in LAM can be ameliorated. In this proposal using our newly developed TSC-null female mouse LAM model, we will identify the cellular mechanisms of cystic lung destruction in LAM, provide insights about novel molecular targets, and will generate pre-clinical evidence for potential treatments of LAM.
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