Endothelial Snail1 in angiogenesis and tumorigenesis

Snail1 is a transcriptional factor with a great relevance in tumor development as it is required for epithelial to mesenchymal transition and activation of cancer-associated fibroblasts (CAF). In this thesis, we reported that tumor endothelial cells did also express Snail1, being key for angiogenesis, by promoting endothelial cell migration, invasion and tubulogenesis in vitro. Those roles are associated to Snail1 induction by FGF2 and VEGFA, leading to gene expression profile change in endothelial cells and modulation of their activation status. Specific Snail1 depletion in the endothelium of adult mice does not promote an overt phenotype; however, it controls angiogenesis and vessel morphology in Matrigel plug assay. Moreover, endothelium-specific Snail1 depletion in the MMTVPyMT breast cancer murine model delays the initiation of neoplasms, being less advanced and with a papillary morphology, which was corroborated by orthotopic breast tumor inoculation model. These in vivo effects are associated to the inability of Snail1-deficient endothelial cells to promote a full in vitro and in vivo activation of fibroblasts through a reduced FGF2 and CXCL12 signaling; as well as to sustain a complete in vivo angiogenesis, with wider and less invasive neo-vessels. Similar changes on tumor onset and morphology are observed by pretreatment on MMTV-PyMT mice with the angiogenic inhibitor bevacizumab. Checking those results in human breast tumor samples, we could recapitulate most of the findings of our mouse models. Altogether, these findings establish a new role for Snail1 in endothelial cells, not only in angiogenesis but also in tumor onset, development and phenotypeSnail1 es un factor de transcripción con gran relevancia en el desarrollo tumoral, siendo necesario para la transición epitelio-mesénquima y la activación de fibroblastos asociados al cáncer (CAF). En esta tesis, hemos reportado la expresión de Snail1 en células endoteliales de tumor, jugando un papel fundamental en angiogénesis, promoviendo su migración, invasión y tubulogenesis in vitro. Estas funciones están asociadas a la inducción de Snail1 por FGF2 y VEGF-A, que generan un cambio en el perfil de expresión génica en las células endoteliales y modulan su estado de activación. La depleción específica de Snail1 en el endotelio de ratones adultos no supone un cambio fenotípico evidente; sin embargo, sí controla la angiogénesis y la morfología de los vasos en ensayos de plugs de Matrigel. Además, la eliminación específica de Snail1 en el endotelio del modelo murino de tumores de mama espontáneos MMTV-PyMT provoca el retraso en la iniciación de tumores, siendo éstos menos avanzados y con una morfología papilar. Estos efectos in vivo están asociados a la incapacidad de las células endoteliales sin Snail1 de promover una activación completa de fibroblastos in vitro e in vivo, debido a una señalización reducida de las vías de FGF2 y CXCL12; ni de generar una angiogénesis completa in vivo, con neovasos más anchos y menos invasivos. Cambios similares en la aparición de tumores y en su morfología se observaron en ratones MMTV-PyMT pretratados con el antiangiógenico bevacizumab. En muestras humanas de cáncer de mama pudimos recapitular la mayoría de los descubrimientos de los modelos animales usados. En resumen, estos hallazgos establecen un nuevo papel para Snail1 en las células endoteliales, no solo en angiogénesis, sino también en la aparición tumoral, el desarrollo y el fenotipo del tumor

Snail1 expression in endothelial cells controls growth, angiogenesis and differentiation of breast tumors

Snail1 is a transcriptional factor required for epithelial to mesenchymal transition and activation of cancer-associated fibroblasts (CAF). Apart from that, tumor endothelial cells also express Snail1. Here, we have unraveled the role of Snail1 in this tissue in a tumorigenic context. Methods: We generated transgenic mice with an endothelial-specific and inducible Snail1 depletion. This murine line was crossed with MMTV-PyMT mice that develop mammary gland tumors and the consequence of Snail1 depletion in the endothelium were investigated. We also interfere Snail1 expression in cultured endothelial cells. Results: Specific Snail1 depletion in the endothelium of adult mice does not promote an overt phenotype; however, it delays the formation of mammary gland tumors in MMTV-PyMT mice. These effects are associated to the inability of Snail1-deficient endothelial cells to undergo angiogenesis and to enhance CAF activation in a paracrine manner. Moreover, tumors generated in mice with endothelium-specific Snail1 depletion are less advanced and show a papillary phenotype. Similar changes on onset and tumor morphology are observed by pretreatment of MMTV-PyMT mice with the angiogenic inhibitor Bevacizumab. Human breast papillary carcinomas exhibit a lower angiogenesis and present lower staining of Snail1, both in endothelial and stromal cells, compared with other breast neoplasms. Furthermore, human breast tumors datasets show a strong correlation between Snail1 expression and high angiogenesis. Conclusion: These findings show a novel role for Snail1 in endothelial cell activation and demonstrate that these cells impact not only on angiogenesis, but also on tumor onset and phenotype.This study was funded by grants awarded to AGH by Agencia Estatal de Investigación (AEI) and Fondos FEDER (SAF2016-76461-R) and AEI (PID2019-104695RB-100/AEI/10.13039/501100011033). We also acknowledge support from the Instituto Carlos III / FEDER (PIE15/00008; PT17/0015/0011) and the "Xarxa de Bancs de tumors” sponsored by Pla Director d'Oncologia de Catalunya (XBTC). DCG was recipient of an FPU predoctoral fellowship from Ministerio de Educació