Protective and detrimental effects of neuroectodermal cell-derived tissue factor in mouse models of stroke.

Within the CNS, a dysregulated hemostatic response contributes to both hemorrhagic and ischemic strokes. Tissue factor (TF), the primary initiator of the extrinsic coagulation cascade, plays an essential role in hemostasis and also contributes to thrombosis. Using both genetic and pharmacologic approaches, we characterized the contribution of neuroectodermal (NE) cell TF to the pathophysiology of stroke. We used mice with various levels of TF expression and found that astrocyte TF activity reduced to ~5% of WT levels was still sufficient to maintain hemostasis after hemorrhagic stroke but was also low enough to attenuate inflammation, reduce damage to the blood-brain barrier, and improve outcomes following ischemic stroke. Pharmacologic inhibition of TF during the reperfusion phase of ischemic stroke attenuated neuronal damage, improved behavioral deficit, and prevented mortality of mice. Our data demonstrate that NE cell TF limits bleeding complications associated with the transition from ischemic to hemorrhagic stroke and also contributes to the reperfusion injury after ischemic stroke. The high level of TF expression in the CNS is likely the result of selective pressure to limit intracerebral hemorrhage (ICH) after traumatic brain injury but, in the modern era, poses the additional risk of increased ischemia-reperfusion injury after ischemic stroke.