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Regulation of Angiogenesis and Blood Supply

Rapidly dividing tumors, embryos, and wounded tissues require more oxygen than usual, lowering the oxygen concentration in the blood. At low oxygen or hypoxic conditions, an oxygen-sensitive transcription factor called the hypoxia-inducible factor 1 or HIF1 is activated. HIF1 is a dimeric protein of alpha (ɑ) and beta (β) subunits.  Under optimal oxygen conditions, HIF1β is present in the nucleus while HIF1ɑ remains in the cytosol. HIF1ɑ is hydroxylated by prolyl hydroxylase and factor...
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Updated: Jul 1, 2026

A Novel In vitro Model for Studying the Interactions Between Human Whole Blood and Endothelium
06:27

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Published on: November 21, 2014

Xenogeneic endothelial cells activate human prothrombin

J B Siegel1, S T Grey, B A Lesnikoski

  • 1Sandoz Center for Immunobiology, Department of Surgery, Beth Israel Deaconess Medical Center and Harvard Medical School, Boston, Massachusetts 02215, USA.

Transplantation
|October 27, 1997
PubMed
Summary
This summary is machine-generated.

Porcine endothelial cells generate significantly more thrombin than human cells, potentially hindering xenotransplantation. This blood coagulation barrier impacts the clinical use of transgenic porcine organs.

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In Vitro Microfluidic Disease Model to Study Whole Blood-Endothelial Interactions and Blood Clot Dynamics in Real-Time
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Area of Science:

  • Biomedical Engineering
  • Vascular Biology
  • Transplantation Immunology

Background:

  • Delayed xenograft rejection involves platelet activation and fibrin deposition, independent of complement.
  • Endothelial cells (EC) play a role in regulating coagulation pathways.

Purpose of the Study:

  • To investigate the capacity of xenogeneic endothelial cells to regulate thrombin generation.
  • To assess the impact of porcine endothelial cells on the coagulation cascade.

Main Methods:

  • Compared prothrombin conversion by quiescent and activated porcine aortic EC (PAEC) versus human aortic EC.
  • Measured thrombin generation using chromogenic assays, F1+2, and thrombin-antithrombin III complexes.
  • Investigated cross-species interactions involving thrombomodulin, thrombin, and protein C.

Main Results:

  • PAEC exhibited significantly higher prothrombin to thrombin conversion rates than human EC.
  • PAEC activation by human complement did not alter thrombin generation levels.
  • Identified cross-species incompatibilities in thrombomodulin-thrombin and protein C interactions, reducing activated protein C generation.

Conclusions:

  • Porcine endothelial cells generate high levels of thrombin, contributing to a coagulation barrier.
  • Cross-species incompatibilities in coagulation factor interactions pose a challenge for xenotransplantation.
  • These findings highlight a molecular barrier that may affect the clinical application of porcine organs.