Abstract 1576: Mesenchymal disruption of Tsc2 in mice results in highly vascular hamartomas.

Patients with tuberous sclerosis complex (TSC) suffer from the formation of multi-organbenign tumors. Skin tumors from TSC patients are characterized by increased vascularity, fibrosis, and overactivation of mTORC1 signaling due to inactivation of either of the tumor suppressor genes TSC1 or TSC2 in fibroblasts. The role of the TSC2 gene in cells of mesenchymal origin with respect to tumor formation still remains unclear. To investigate the roles of TSC2 in these cells, we used the cre/loxP system to conditionally disrupt mouse Tsc2 in tissues derived from mesenchymal cells. Mice with floxed Tsc2 alleles were mated with mice expressing the cre recombinase transgene under the control of a Prrx1 regulatory element (Prrx1-cre), which is selectively expressed in craniofacial and limb bud mesenchyme. Cells with homozygous Tsc2 floxed alleles expressing the Prrx1-cre transgene (termed here “Tsc2cKO mice”) efficiently eliminated Tsc2 expression from fibroblasts isolated from limb and ventral skin. An EYFP reporter transgene was also present to track cells expressing cre recombinase. Fibroblasts grown from the skin of Tsc2cKO mice expressed EYFP, lacked Tsc2 protein and had elevated levels of phosphorylated ribosomal protein S6, a marker of mTORC1 signaling. Tsc2cKO mice had shortened lifespan with a median survival between 5 and 6 months of age. Tumors were observed in spleen and forepaws of nearly all mice, and tumors involving the liver, skin, skeletal muscle, mediastinum, and kidney also occurred. These results were unexpected due to the lineage restriction of the Prrx1-cre transgene. Tumor formation began to appear on forepaws near the heel of the paw pad as early as 3 weeks of age. By 6 weeks of age the lesions generally showed a reddish appearance. In mice serially imaged by MRI, splenic tumors were apparent by 10-12 weeks of age and renal tumors were apparent by 7-8 weeks. Histologically, the forepaw, splenic, and hepatic tumors were benign fibrovascular proliferations with perivascular cells that stained with smooth muscle actin, most prominently in the spleen. Using ex vivo fluorescent imaging, EYFP fluorescence was not detected in internal organs of control mice containing Prrx1-cre, but strong fluorescence was observed in the splenic, hepatic, and renal tumors of Tsc2cKO mice. In summary, we have developed model system to study the role of Tsc2-deficient mesenchymal cells in hamartoma formation. Citation Format: Peter Klover, Rajesh Thangapazham, Shaowei Li, Jiro Kato, Stasia A. Anderson, Victoria Hoffman, Ji-an Wang, Joshua Bernstock, Elizabeth McCart, Joel Moss, Thomas Darling. Mesenchymal disruption of Tsc2 in mice results in highly vascular hamartomas. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 1576. doi:10.1158/1538-7445.AM2013-1576