Background: 

The endothelium plays a key role in maintaining vascular function and preventing cardiovascular diseases. After ischemia/reperfusion endothelial function is compromised by free oxygen-radicals. Furthermore TNFa is released mediating its effects via two receptor-subtypes. We analyzed the role of the endothelial TNF-receptor-subtypes TNF-R1 and TNF-R2 for superoxide production in hypoxia/reoxygenation (H/R) in vitro and endothelial function in ischemia/reperfusion (I/R) in vivo.

Methods: 

Endothelial function in vivo was assessed by measuring the acetylcholine-dependent vasodilation by intravital microscopy in arterioles of the cremaster muscle in mice. The influence of TNF-R1 and TNF-R2 on endothelial function after I/R (1h/1h) was investigated in wildtype (WT)-, TNF-R1- and TNF-R2 deficient mice. In vitro endothelial superoxide production was measured after H/R (1h/1h) in human microvascular endothelial cells (HMEC) by cytochrome C reduction after TNF-R1 knockdown via siRNA-transfection (50nM).

Results: 

WT mice showed a significant impairment of the endothelium-dependent vasodilation-capacity after I/R compared to normoxic conditions (n=4, p<0.05). TNF-R1 deficient mice after I/R injury showed a significantly better acetylcholine-response compared to WT mice (n=4, p<0.05). This effect could not be observed in TNF-R2 deficient mice. In HMEC after H/R superoxide production was significantly increased (n=15, p<0.01), whereas in cells transfected with TNF-R1-siRNA both basal and H/R induced superoxide production were reduced as compared to random-siRNA treated cells (n=15, p<0.01).

Conclusions: 

These data suggest that signaling through TNF-R1 is crucial for increased superoxide production in hypoxia/reoxygenation and therefore responsible for ischemia/reperfusion induced endothelial dysfunction in vivo.