Notch-1 mediates hypoxia-induced angiogenesis in rheumatoid arthritis

Authors

  • Wei Gao,

    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
    Current affiliation:
    1. University of Malaya, Kuala Lumpur, Malaysia
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    • Drs. Gao and Sweeney contributed equally to this work.

  • Catherine Sweeney,

    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
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    • Drs. Gao and Sweeney contributed equally to this work.

  • Mary Connolly,

    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
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  • Aisling Kennedy,

    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
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  • Chin Teck Ng,

    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
    Current affiliation:
    1. University of Malaya, Kuala Lumpur, Malaysia
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  • Jennifer McCormick,

    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
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  • Douglas J. Veale,

    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
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  • Ursula Fearon

    Corresponding author
    1. Dublin Academic Medical Centre, St. Vincent's University Hospital, and University College Dublin, Dublin, Ireland
    • Department of Rheumatology, Dublin Academic Medical Centre, St. Vincent's University Hospital, Dublin 4, Ireland
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Abstract

Objective

To examine the effect of hypoxia on Notch-1 signaling pathway components and angiogenesis in inflammatory arthritis.

Methods

The expression and regulation of Notch-1, its ligand delta-like protein 4 (DLL-4) and downstream signaling components (hairy-related transcription factor 1 [HRT-1], HRT-2), and hypoxia-inducible factor 1α (HIF-1α) under normoxic and hypoxic conditions (1–3%) were assessed in synovial tissue specimens from patients with inflammatory arthritis and controls and in human dermal microvascular endothelial cells (HDMECs) by immunohistology, dual immunofluorescence staining (Notch-1/factor VIII), Western blotting, and real-time polymerase chain reaction. In vivo synovial tissue oxygen levels (tissue PO2) were measured under direct visualization at arthroscopy. HDMEC activation under hypoxic conditions in the presence of Notch-1 small interfering RNA (siRNA), the γ-secretase inhibitor DAPT, or dimethyloxalylglycine (DMOG) was assessed by Matrigel tube formation assay, migration assay, invasion assay, and matrix metalloproteinase 2 (MMP-2)/MMP-9 zymography.

Results

Expression of Notch-1, its ligand DLL-4, and HRT-1 was demonstrated in synovial tissue, with the strongest expression localized to perivascular/vascular regions. Localization of Notch-1 to synovial endothelium was confirmed by dual immunofluorescence staining. Notch-1 intracellular domain (NICD) expression was significantly higher in synovial tissue from patients with tissue PO2 of <20 mm Hg (<3% O2) than in those with tissue PO2 of >20 mm Hg (>3% O2). Exposure of HDMECs to 3% hypoxia induced HIF-1α and NICD protein expression and DLL-4, HRT-1, and HRT-2 messenger RNA expression. DMOG directly induced NICD expression, while Notch-1 siRNA inhibited hypoxia-induced HIF-1α expression, suggesting that Notch-1/HIF-1α signaling is bidirectional. Finally, 3% hypoxia–induced angiogenesis, endothelial cell migration, endothelial cell invasion, and proMMP-2 and proMMP-9 activities were inhibited by Notch-1 siRNA and/or the γ-secretase inhibitor DAPT.

Conclusion

Our findings indicate that Notch-1 is expressed in synovial tissue and that increased NICD expression is associated with low in vivo tissue PO2. Furthermore, Notch-1/HIF-1α interactions mediate hypoxia-induced angiogenesis and invasion in inflammatory arthritis.

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