Aberrant Activation of Notch1 Signaling in Glomerular Endothelium Induces Albuminuria.

RATIONALE: Glomerular capillaries are lined with a highly specialized fenestrated endothelium and contribute to the glomerular filtration barrier. The Notch signaling pathway is involved in regulation of glomerular filtration barrier, but its role in glomerular endothelium has not been investigated due to the embryonic lethality of animal models with genetic modification of Notch pathway components in the endothelium. OBJECTIVE: To determine the effects of aberrant activation of the Notch signaling in glomerular endothelium and the underlying molecular mechanisms. METHODS AND RESULTS: We established the ZEG-NICD1 (notch1 intracellular domain)/Tie2-tTA/Tet-O-Cre transgenic mouse model to constitutively activate Notch1 signaling in endothelial cells of adult mice. The triple transgenic mice developed severe albuminuria with significantly decreased VE-cadherin (vascular endothelial cadherin) expression in the glomerular endothelium. In vitro studies showed that either NICD1 (Notch1 intracellular domain) lentiviral infection or treatment with Notch ligand DLL4 (delta-like ligand 4) markedly reduced VE-cadherin expression and increased monolayer permeability of human renal glomerular endothelial cells. In addition, Notch1 activation or gene knockdown of VE-cadherin reduced the glomerular endothelial glycocalyx. Further investigation demonstrated that activated Notch1 suppression of VE-cadherin was through the transcription factors SNAI1 (snail family transcriptional repressor 1) and ERG (Ets related gene), which bind to the -373 E-box and the -134/-118 ETS (E26 transformation-specific) element of the VE-cadherin promoter, respectively. CONCLUSIONS: Our results reveal novel regulatory mechanisms whereby endothelial Notch1 signaling dictates the level of VE-cadherin through the transcription factors SNAI1 and ERG, leading to dysfunction of glomerular filtration barrier and induction of albuminuria. Graphic Abstract: A graphic abstract is available for this article.

TFPI from erythroblasts drives heme production in central macrophages promoting erythropoiesis in polycythemia.

Bleeding and thrombosis are known as common complications of polycythemia for a long time. However, the role of coagulation system in erythropoiesis is unclear. Here, we discover that an anticoagulant protein tissue factor pathway inhibitor (TFPI) plays an essential role in erythropoiesis via the control of heme biosynthesis in central macrophages. TFPI levels are elevated in erythroblasts of human erythroblastic islands with JAK2V617F mutation and hypoxia condition. Erythroid lineage-specific knockout TFPI results in impaired erythropoiesis through decreasing ferrochelatase expression and heme biosynthesis in central macrophages. Mechanistically, the TFPI interacts with thrombomodulin to promote the downstream ERK1/2-GATA1 signaling pathway to induce heme biosynthesis in central macrophages. Furthermore, TFPI blockade impairs human erythropoiesis in vitro, and normalizes the erythroid compartment in mice with polycythemia. These results show that erythroblast-derived TFPI plays an important role in the regulation of erythropoiesis and reveal an interplay between erythroblasts and central macrophages.

Hypoxia Inhibits Proliferation of Human Dermal Lymphatic Endothelial Cells via Downregulation of Carcinoembryonic Antigen-related Cell Adhesion Molecule 1 Expression.

OBJECTIVE: Lymphatic endothelial cell (LEC) proliferation is essential for lymphangiogenesis. Hypoxia induces lymphangiogenesis, but it directly inhibits LEC proliferation and the underlying mechanisms have not been fully understood. The aim of this study was to investigate the role of carcinoembryonic antigen-related cell adhesion molecule 1 (CEACAM1) in hypoxia-repressed LEC proliferation. METHODS: Human dermal lymphatic endothelial cells (HDLECs) were cultured under normoxic or hypoxic conditions, and cell proliferation was determined using MTT or CCK-8 assays. CEACAM1 expression was silenced by siRNA transfection. Activation of mitogen-activated protein kinases (MAPKs) was examined by Western blotting and blocked by specific inhibitors. RESULTS: Under hypoxia, HDLECs proliferation was suppressed and CEACAM1 expression was downregulated. Silence of CEACAM1 in normoxia inhibited HDLECs proliferation and did not further decrease proliferation in HDLECs in response to hypoxia, suggesting that CEACAM1 may mediate hypoxia-induced inhibition of HDLECs proliferation. In addition, silence of CEACAM1 increased phosphorylation of MAPK molecules: extracellular signal-regulated kinase (ERK), p38 MAPK and Jun N-terminal kinase (JNK) in HDLECs. However, only inhibition of the JNK pathway rescued the reduction of HDLEC proliferation induced by CEACAM1 silence. CONCLUSION: Our results suggested that hypoxia downregulates CEACAM1 expression by activation of the JNK pathway, leading to inhibition of HDLEC proliferation. These findings may help to understand the mechanisms of LEC-specific response to hypoxia and develop novel therapies for pathological lymphangiogenesis.

Pathophysiology of aged lymphatic vessels.

Lymphatic vessels maintain body homeostasis by recirculation of fluid and cells. Cell senescence induces lymphatic dysfunction. Impaired contractile function is caused by low muscle cell investiture and decrease of nitric oxide in aged lymphatic collectors, leading to poor drainage of lymph. Aging-induced loss of endothelial glycocalyx and production of inflammatory cytokines increases permeability of lymphatic vessels. In addition, aging-associated basal activation of mast cells delays immune response. In this review, we summarize the structural and pathological changes of aged lymphatic vessels, and discuss the underlying molecular mechanisms.