Endothelial cell expression of tissue factor in sickle mice is augmented by hypoxia/reoxygenation and inhibited by lovastatin

Abnormal tissue factor (TF) expression has been demonstrated on blood monocytes and circulating endothelial cells in humans with sickle cell anemia. We have now studied sickle transgenic mice to help define the biology of endothelial TF expression in sickle disease. Using immunostaining of tissue sections, we find that this is confined almost exclusively to the pulmonary veins. About 15% and 13% of these exhibit TF-positive endothelium in the wild-type normal mouse and the normal human hemoglobin (HbA)-expressing control transgenic mouse, respectively. The mild sickle mouse is indistinguishable from normal (similar to 14% positive), but TF expression is significantly elevated in the moderate and severe mouse models of sickle disease (similar to 29% and similar to 41% positive, respectively). Exposure of the mild sickle mouse to hypoxia for 3 hours, followed by reoxygenation, converted its TF expression phenotype to that of the severe sickle mouse (similar to 36% positive). Pretreatment with lovastatin eliminated excessive expression of TF in the posthypoxic mild sickle mouse (similar to 16% positive) and in the more severe mouse at ambient air (similar to 21% positive). In addition to identifying tissue expression of endothelial TF in the sickle lung, these studies implicate reperfusion injury physiology in its expression and suggest a rationale for use of statins in sickle disease.