Cerebral Microvascular Obstruction by Fibrin is Associated with Upregulation of PAI-1 Acutely after Onset of Focal Embolic Ischemia in Rats

Abstract

The mechanisms underlying cerebral microvascular perfusion deficit resulting from occlusion of the middle cerebral artery (MCA) require elucidation. We, therefore, tested the hypothesis that intravascular fibrin deposition in situ directly obstructs cerebral microcirculation and that local changes in type 1 plasminogen activator inhibitor (PAI-1) gene expression contribute to intravascular fibrin deposition after embolic MCA occlusion. Using laser-scanning confocal microscopy (LSCM) in combination with immunofluorescent staining, we simultaneously measured in three dimensions the distribution of microvascular plasma perfusion deficit and fibrin(ogen) immunoreactivity in a rat model of focal cerebral embolic ischemia (n ϭ 12). In addition, using in situ hybridization and immunostaining, we analyzed expression of PAI-1 in ischemic brain (n ϭ 13). A significant ( p Ͻ 0.05) reduction of cerebral microvascular plasma perfusion accompanied a significant ( p Ͻ 0.05) increase of intravascular and extravascular fibrin deposition in the ischemic lesion. Microvascular plasma perfusion deficit and fibrin deposition expanded concomitantly from the subcortex to the cortex during 1 and 4 hr of embolic MCA occlusion. Threedimensional analysis revealed that intravascular fibrin deposition directly blocks microvascular plasma perfusion. Vascular plugs contained erythrocytes, polymorphonuclear leukocytes, and platelets enmeshed in fibrin. In situ hybridization demonstrated induction of PAI-1 mRNA in vascular endothelial cells in the ischemic region at 1 hr of ischemia. PAI-1 mRNA significantly increased at 4 hr of ischemia. Immunohistochemical staining showed the same pattern of increased PAI-1 antigen in the endothelial cells. These data demonstrate, for the first time, that progressive intravascular fibrin deposition directly blocks cerebral microvascular plasma perfusion in the ischemic region during acute focal cerebral embolic ischemia, and upregulation of the PAI-1 gene in the ischemic lesion may foster fibrin deposition through suppression of fibrinolysis.

Tissue-Type Plasminogen Activator Crosses the Intact Blood-Brain Barrier by Low-Density Lipoprotein Receptor–Related Protein-Mediated Transcytosis

“…7 Surprisingly, intravenous injection of tPA in such stroke models still has a beneficial component through the degradation of endogenous deposits of fibrin that takes place in the ischemic tissue. 27,28 Another key point of the debate is the dose of tPA used to achieve reperfusion. Because human tPA (found in Actilyse) is 10-fold less efficient in activating rodent plasminogen than endogenous rodent tPA, the dose used in animals is usually 10 mg/kg, corresponding to 10-fold the dose used in humans, which leads to a complex interpretation of the data.…”

Novel Mouse Model of Monocular Amaurosis Fugax

“…Flat-mounted retinas show microthromboemboli (Figure 2), as observed in acute ischemic rat brains. 16 The early and transient upregulation of PAI1 triggers vascular fibrin deposition and contributes to the stabilization and growth of arterial thrombi by abolishing fibrinolysis. 4 We observed a decrease in PAI1 mRNA levels 1 hour after reperfusion.…”

Exosomes in stroke pathogenesis and therapy

“…Platelets, along with thrombin and fibrin resulting from tissue factoractivated blood coagulation, are the primary contributors to thrombus development at the site of the occluded artery (14,15). Concomitantly, occlusion of a major cerebral artery triggers development of secondary thrombosis in downstream microvessels, which causes dysfunction of cerebral endothelial cells, pericytes, and astrocytes and leads to disruption of the blood-brain barrier (BBB) and ischemic cell damage (16)(17)(18)(19). The evolution of downstream microvascular thrombosis is heterogeneous and continues for hours and is highly associated with the progression of ischemic neuronal death from reversible to irreversible damage (14,(16)(17)(18).…”