TSC Proteins in the Lymphatic Vasculature

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Tuberous Sclerosis Complex (TSC) is a chronic disease that is caused by mutations in the genes TSC1 or TSC2. The disease affects 2 million people worldwide and there is no cure for TSC disease. Symptoms include formation of large tumors called hamartomas in various organs of the body, including the brain, the kidney, and the lung. One of the severe complications associated with these tumors is chylothorax, which is the accumulation of chyle in the space between the pleura and chest cavity. Chyle is a milky fluid that originates from lymphatic vessels draining dietary fats. Chylothorax can cause difficulty breathing, tachypnea, chest pain, respiratory failure, and death. Although chylothorax indicates malfunctioning lymphatic vessels in TSC patients, the current dogma is that tumors compress/obstruct the lymphatic vessels near the lung resulting in leakage, and it remains unknown whether TSC mutations in lymphatic endothelial cells are a causative factor of chylothorax. Thus, a significant unmet need is to determine whether lymphatic vessels are involved in TSC disease and delineate the pathological changes of the lymphatic vasculature due to TSC loss-of-function, which will identify new signaling pathways and molecular targets for this disease. Our preliminary data show that lymphatic-specific deletion of the Tsc genes in mice leads to chylothorax and is accompanied by a severe loss of lymphatic valves. These data suggest that the lymphatic vasculature is involved in TSC disease and regressing lymphatic valves allow lymph to flow backwards into the paravertebral and intercostal lymphatic capillaries, which causes lymph leakage from the thoracic duct into the chest cavity. Aim 1 will determine pathological changes in the lymphatic vasculature upon genetic deletion of Tsc genes, Aim 2 will identify the molecular mechanisms by which loss of Tsc1 or Tsc2 causes the loss of lymphatic valves, and Aim 3 will investigate novel approach to reverse lymphatic valve loss in the Tsc knockouts. It is highly anticipated that these aims will identify new pathogenic features of TSC disease and new signaling pathways affected by loss of TSC signaling.