Abstract 715: Transforming Growth Factor Beta Inhibition Attenuates Vein Graft Thrombosis
Background: Vein graft (VG) thrombosis remains an unresolved complication of surgically constructed bypass grafts. Thrombomodulin (TM), a critical member of the protein C anticoagulant pathway, is abundantly expressed by endothelium. Transforming growth factor-β (TGFβ), a stretch-responsive cytokine inhibits TM expression in human umbilical vein endothelial cells (HUVEC). We hypothesize that acute exposure to arterial pressure induces TGFβ expression in VG, and contributes to thrombosis by downregulating TM expression.
Methods & Results: Male New Zealand White rabbits underwent interpositional grafting of jugular vein segments into the carotid circulation. TM expression was reduced by 56±4%(p=0.01), while TGFβ expression increased by 349±36% (p=0.0002) 7 days after grafting as determined by quantitative PCR. In situ generation of activated protein C by VG was reduced by 59±10% (p=0.001) correlating with a 340± 85% (p=0.007) increase in local thrombin activity. To determine how vessel distention modulates TM and TGFβ expression, we externally stented vein segments prior to grafting. Stented VG decreased TGFβ expression by 180% (p<0.007) and increased TM expression by 47% (p=0.05) compared to unstented VG. Treatment with an anti-TGFβ antibody attenuated TM downregulation (p<0.005) and normalized bound thrombin activity in VG. To determine the source of TGFβ, HUVEC and vascular smooth muscle cells (HVSMC) were subjected to 10% cyclic strain for 24 hours. Direct stretching of HUVEC increased TM expression without affecting TGFβ expression. In contrast, stretching HVSMC increased TGFβ (259±49%;p=0.02) expression. To determine if paracrine release of TGFβ modulates endothelial TM expression, HUVEC were cultured onto stationary filters and co-incubated with strained HVSMC. TM expression was reduced in HUVEC by 92±3% (p=0.01) compared to HUVEC co-incubated with unstretched HVSMC. TM downregulation in HUVEC was attenuated by an anti-TGFβ antibody.
Conclusion: Stretch induced paracrine release of TGFβ markedly reduces TM expression and increases thrombin generation in VG. Treatment with a neutralizing anti-TGFβ antibody attenuates loss of TM and normalizes thrombin activity, suggesting a novel approach to modulating VG thrombosis.