Kininogen deficiency protects from ischemic neurodegeneration in mice by reducing thrombosis, blood-brain barrier damage, and inflammation

Abstract

Thrombosis and inflammation are hallmarks of ischemic stroke still unamenable to therapeutic interventions. Highmolecular-weight kininogen (KNG) is a central constituent of the contact-kinin system which represents an interface between thrombotic and inflammatory circuits and is critically involved in stroke development. Kng Ϫ/Ϫ mice are protected from thrombosis after artificial vessel wall injury and lack the proinflammatory mediator bradykinin. We investigated the consequences of KNG deficiency in models of ischemic stroke. Kng Ϫ/Ϫ mice of either sex subjected to transient middle cerebral artery occlusion developed dramatically smaller brain infarctions and less severe neurologic deficits without an increase in infarct-associated hemorrhage. This protective effect was preserved at later stages of infarction as well as in elderly mice. Targeting KNG reduced thrombus formation in ischemic vessels and improved cerebral blood flow, and reconstitution of KNG-deficient mice with human KNG or bradykinin restored clot deposition and infarct susceptibility. Moreover, mice deficient in KNG showed less severe blood-brain barrier damage and edema formation, and the local inflammatory response was reduced compared with controls. Because KNG appears to be instrumental in pathologic thrombus formation and inflammation but dispensable for hemostasis, KNG inhibition may offer a selective and safe strategy for combating stroke and other thromboembolic diseases. (Blood. 2012;120(19): 4082-4092) IntroductionThe pathology of ischemic stroke is complex and involves a myriad of distinct molecular pathways and cellular interactions. Among these, progressive thrombus formation in the cerebral microvasculature is a key process that can cause secondary infarct growth despite successful recanalization of larger proximal brain vessels both under experimental conditions as well as in humans. 1,2 We recently identified the intrinsic coagulation cascade as a novel and safe antithrombotic target for the prevention and treatment of acute ischemic stroke. 3 Genetic depletion or pharmacologic blockade of coagulation factor XII (FXII), the origin of the intrinsic pathway, markedly reduced intracerebral thrombus formation and infarct growth in mice without increasing the risk of bleeding complications. 4,5 Clot formation was also significantly reduced in several in vitro models of thrombosis after FXII inhibition. 5 Current pathophysiologic concepts also emphasize the importance of inflammatory mechanisms in stroke. 6 The cerebral endothelium is activated early during the course of an ischemic event, leading to the up-regulation of cell adhesion molecules and successive trafficking of inflammatory cells (neutrophils, macrophages, T cells) from the blood stream into the brain parenchyma. Those cells attracted from the periphery in concert with resident cell populations (endothelial cells, microglia) secrete an array of soluble immune mediators such as cytokines and chemokines that perpetuate the inflammatory response to cause direct or indirect ti...

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