No evidence for vasculogenesis regulation by angiostatin during mouse embryonic stem cell differentiation

Bone Morphogenetic Protein 9 Regulates Early Lymphatic-Specified Endothelial Cell Expansion during Mouse Embryonic Stem Cell Differentiation

Exogenous cues involved in the regulation of the initial steps of lymphatic endothelial development remain largely unknown. We have used an in vitro model based on the co-culture of vascular precursors derived from mouse embryonic stem cell (ESC) differentiation and OP9 stromal cells to examine the first steps of lymphatic specification and expansion. We found that bone morphogenetic protein 9 (BMP9) induced a dose-dependent biphasic effect on ESC-derived vascular precursors. At low concentrations, below 1 ng/mL, BMP9 expands the LYVE-1-positive lymphatic progeny and activates the calcineurin phosphatase/NFATc1 signaling pathway. In contrast, higher BMP9 concentrations preferentially enhance the formation of LYVE-1-negative endothelial cells. This effect results from an OP9 stromal cell-mediated VEGF-A secretion. RNA-silencing experiments indicate specific involvement of ALK1 and ALK2 receptors in these different BMP9 responses. BMP9 at low concentrations may be a useful tool to generate lymphatic endothelial cells from stem cells for cell-replacement strategies.

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Low doses of BMP9 raise lymph-vasculogenesis during ESC differentiation

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NFATc1 signaling operates in BMP9-induced lymphatic endothelial cell expansion

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High doses of BMP9 increase LYVE-1-negative endothelial cell formation

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A specific differential involvement of ALK1 and ALK2 mediates the BMP9 effects

TGFβ1 inhibits lymphatic endothelial cell differentiation from mouse embryonic stem cells

The lymphatic vasculature is essential for the maintenance of tissue fluid, immune surveillance, and dissemination of metastasis. Recently, several models for lymphatic vascular research and markers specific for lymphatic endothelium have been characterized. Despite these significant achievements, our understanding of the early lymphatic development is still rather limited. The purpose of the study was to further define early lymphatic differentiation regulatory pathways. In the present study, we have developed conditions leading to lymphatic endothelial cell differentiation under both serum-rich and serum-free conditions, using the coculture system of Flk-1-positive vascular precursors derived from murine embryonic stem (ES) cells grown on an OP9 stromal cell layer. In this work, we also identified Transforming Growth Factor-β1 (TGFβ1) as a negative regulator of lymphvasculogenesis from ES-derived vascular progenitors. Finally, we could show that TGFβ1 addition decreases COUP-TFII and Sox18 mRNA levels, which are two transcription factors known to be involved in early lymphatic endothelial differentiation. Taken together these findings support the concept that manipulating the TGFβ signaling pathway may represent an interesting target to favor lymphatic endothelial cell expansion for cell replacement strategies.

Angiostatin anti-angiogenesis requires IL-12: the innate immune system as a key target

BACKGROUND

Angiostatin, an endogenous angiogenesis inhibitor, is a fragment of plasminogen. Its anti-angiogenic activity was discovered with functional assays in vivo, however, its direct action on endothelial cells is moderate and identification of definitive mechanisms of action has been elusive to date. We had previously demonstrated that innate immune cells are key targets of angiostatin, however the pathway involved in this immune-related angiogenesis inhibition was not known. Here we present evidence that IL-12, a principal TH1 cytokine with potent anti-angiogenic activity, is the mediator of angiostatin's activity.

METHODS

Function blocking antibodies and gene-targeted animals were employed or in vivo studies using the subcutaneous matrigel model of angiogenesis. Quantitative real-time PCR were used to assess modulation of cytokine production in vitro.

RESULTS

Angiostatin inhibts angiogenesis induced by VEGF-TNFalpha or supernatants of Kaposi's Sarcoma cells (a highly angiogenic and inflammation-associated tumor). We found that function-blocking antibodies to IL-12 reverted angiostatin induced angiogenesis inhibition. The use of KO animal models revealed that angiostatin is unable to exert angiogenesis inhibition in mice with gene-targeted deletions of either the IL-12 specific receptor subunit IL-12Rbeta2 or the IL-12 p40 subunit. Angiostatin induces IL-12 mRNA synthesis by human macrophages in vitro, suggesting that these innate immunity cells produce IL-12 upon angiostatin stimulation and could be a major cellular mediator.

CONCLUSION

Our data demonstrate that an endogenous angiogenesis inhibitor such as angiostatin act on innate immune cells as key targets in inflammatory angiogenesis. Angiostatin proves to be anti-angiogenic as an immune modulator rather than a direct anti-vascular agent. This article is dedicated to the memory of Prof Judah Folkman for his leadership and for encouragement of these studies.