Induction Of Endothelial-to-mesenchymal Transition Research Articles

IL-1β and TGFβ2 synergistically induce endothelial to mesenchymal transition in an NFκB-dependent manner

Endothelial to mesenchymal transition (EndMT) contributes to fibrotic diseases. The main inducer of EndMT is TGFβ signaling. TGFβ2 is the dominant isoform in the physiological embryonic EndMT, but its role in the pathological EndMT in the context of inflammatory co-stimulation is not known. The aim of this study was to investigate TGFβ2-induced EndMT in the context of inflammatory IL-1β signaling. Co-stimulation with IL-1β and TGFβ2, but not TGFβ1, caused synergistic induction of EndMT. Also, TGFβ2 was the only TGFβ isoform that was progressively upregulated during EndMT. External IL-1β stimulation was dispensable once EndMT was induced. The inflammatory transcription factor NFκB was upregulated in an additive manner by IL-1β and TGFβ2 co-stimulation. Co-stimulation also led to the nuclear translocation of NFκB which was sustained over long-term treatment. Activation of NFκB was indispensable for the co-induction of EndMT. Our data suggest that the microenvironment at the verge between inflammation (IL-1β) and tissue remodeling (TGFβ2) can strongly promote the process of EndMT. Therefore our findings provide new insights into the mechanisms of pathological EndMT.

Abstract 2976: KSHV-initiated Notch activation leads to membrane-type-1 matrix metalloproteinase-dependent lymphatic endothelial-to-mesenchymal transition

Abstract Kaposi sarcoma (KS), an angioproliferative disease associated with Kaposi sarcoma herpesvirus (KSHV) infection, harbors a diversity of cell types ranging from endothelial to mesenchymal cells of unclear origin. Using a novel three-dimensional (3D) cell model, we have demonstrated that KSHV induces transcriptional reprogramming of primary lymphatic endothelial cells (LEC) to mesenchymal cells via endothelial-to-mesenchymal transition (EndMT). As EndMT induction has been described in response to activation of the TGF-beta or Notch pathways, inhibitor studies were used to decipher their roles in our 3D system. Inhibition of the Notch pathway dramatically attenuated the EndMT in KSHV infected LECs (K-LECs) in 3D whereas inhibition or activation of the TGF-β pathway did not have any effect. Two viral gene products, vFLIP and vGPCR, were found to trigger Notch signaling and lead to the KSHV-induced EndMT. As Notch activation has been shown to inhibit angiogenic and lymphangiogenic sprouting, we assessed the effect of VEGFA or -C stimulation on the 3D K-LECs. Interestingly, VEGFA/C stimulation induced a dramatic outgrowth of (lymph)angiogenic sprouts and inhibited the KSHV-induced EndMT in the 3D K-LECs. This suggests that the KSHV-induced Notch signaling and mesenchymal reprogramming can override the lymphangiogenic properties of LECs in the absence of VEGF-A/C stimulation. These results further corroborate the central role of Notch signaling as a critical determinant for the lymphangiogenic vs. mesenchymal fate of LECs. The 3D K-LEC transcriptome showed significant up-regulation of invasion related genes over the uninfected control. Intriguingly, comparison of the GEM profiles of the 3D K-LECs and KS biopsies, genes with similar co-regulation were found and included those involved both in EMT/EndMT and invasive processes. Using a panel of specific inhibitors we found a membrane associated matrix metalloproteinase MT1-MMP to be the major MMP involved in this process. Our data further identifies Notch as a previously unrecognized upstream regulator of MT1-MMP, and demonstrates that MT1-MMP as such is sufficient to induce EndMT in 3D cultured LECs. Mesenchymal markers and MT1-MMP were found co-distributed in the same cells with LANA in primary KS tumors suggesting that virus-induced EndMT may contribute to development of KS by giving rise to invasive cells, and providing the virus a permissive microenvironment for efficient spread of the viral genomes. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 2976. doi:1538-7445.AM2012-2976

Notch Initiates the Endothelial-to-Mesenchymal Transition in the Atrioventricular Canal through Autocrine Activation of Soluble Guanylyl Cyclase

The heart is the most common site of congenital defects, and valvuloseptal defects are the most common of the cardiac anomalies seen in the newborn. The process of endothelial-to-mesenchymal transition (EndMT) in the cardiac cushions is a required step during early valve development, and Notch signaling is required for this process. Here we show that Notch activation induces the transcription of both subunits of the soluble guanylyl cyclase (sGC) heterodimer, GUCY1A3 and GUCY1B3, which form the nitric oxide receptor. In parallel, Notch also promotes nitric oxide (NO) production by inducing Activin A, thereby activating a PI3-kinase/Akt pathway to phosphorylate eNOS. We thus show that the activation of sGC by NO through a Notch-dependent autocrine loop is necessary to drive early EndMT in the developing atrioventricular canal (AVC).