Functional difference between membrane-bound and soluble human thrombomodulin

Area of Science:

• Xenotransplantation research
• Immunology
• Vascular biology

Background:

• Cloned pigs expressing human thrombomodulin (hTM) are developed for xenotransplantation to address coagulation incompatibilities.
• Recombinant soluble hTM (S-hTM) is approved for disseminated intravascular coagulation and may be useful.
• Understanding functional differences between membrane-bound hTM (MB-hTM) and S-hTM is critical for xenotransplantation strategies.

Purpose of the Study:

• To compare the functional differences between MB-hTM and S-hTM in endothelial cells.
• To determine the most effective strategy for utilizing both forms of hTM in xenotransplantation.

Main Methods:

• Compared coagulation and inflammation factors in hTM-expressing pig aortic endothelial cells (PAEC) versus nontransgenic PAEC.
• Utilized tumor necrosis factor-α activation and S-hTM.
• Assessed clotting time, pig tissue factor (TF), pig E-selectin, direct prothrombinase activity, activated protein C (APC) production, and thrombin generation.

Main Results:

• MB-hTM significantly suppressed pig TF, E-selectin expression, and direct prothrombinase activity, indicating strong anti-inflammatory effects.
• S-hTM demonstrated a more potent capacity to inhibit thrombin generation and produce APC compared to MB-hTM.
• MB-hTM exhibited anti-inflammatory functions and APC production comparable to human endothelial cells.

Conclusions:

• S-hTM treatment may benefit high-risk periods for excessive thrombin formation, such as ischemia reperfusion injury or severe infection/rejection.
• MB-hTM's anti-inflammatory properties and APC production suggest cloned pigs expressing hTM are vital for long-term graft endothelial cell stabilization.
• Combining MB-hTM and S-hTM strategies could optimize xenotransplantation outcomes.