Overexpression of Notch1 Ectodomain in Myeloid Cells Induces Vascular Malformations through a Paracrine Pathway

Xiujie Li^*, Ezequiel Calvo^*, Marc Cool^*, Pavel Chrobak^*, Denis G. Kay^* and Paul Jolicoeur^*

From the Laboratory of Molecular Biology,^* Clinical Research Institute of Montreal; the Department of Experimental Medicine, McGill University; and the Department of Microbiology and Immunology, Université de Montréal, Montreal, Quebec, Canada

We previously reported that truncation of Notch1 (N1) by provirusinsertion leads to overexpression of both the intracellular(N1^IC) and the extracellular (N1^EC) domains. We produced transgenic(Tg) mice expressing N1^EC in T cells and in cells of the myeloidlineage under the regulation of the CD4 gene. These CD4C/N1^ECTg mice developed vascular disease, predominantly in the liver:superficial distorted vessels, cavernae, lower branching ofparenchymal vessels, capillarized sinusoids, and aberrant smoothmuscle/endothelial cell topography. The disease developed inlethally irradiated normal mice transplanted with Tg bone marrowor fetal liver cells as well as in Rag^–/– Tg mice.In nude mice transplanted with fetal liver cells from (ROSA26x CD4C/N1^EC) F₁ Tg mice, abnormal vessels were of recipientorigin. Transplantation of Tg peritoneal macrophages into normalrecipients also induced abnormal vessels. These Tg macrophagesshowed impaired functions, and their conditioned medium inhibitedthe proliferation of liver sinusoid endothelial cells in vitro.The Egr-1 gene and some of its targets (Jag1, FIII, FXIII-A,MCP-1, and MCP-5), previously implicated in hemangioma or vascularmalformations, were overexpressed in Tg macrophages. These resultsshow that myeloid cells can be reprogrammed by N1^EC to inducevascular malformations through a paracrine pathway.