No abstract

Platelet activation and aggregation at sites of vascular injury are essential for primary hemostasis, but are also major pathomechanisms underlying myocardial infarction and stroke. Changes in [Ca 2؉ ] i are a central step in platelet activation. In nonexcitable cells, receptormediated depletion of intracellular Ca 2؉ stores triggers Ca 2؉ entry through storeoperated calcium (SOC) channels. STIM1 has been identified as an endoplasmic reticulum (ER)-resident Ca 2؉ sensor that regulates store-operated calcium entry (SOCE) in immune cells and platelets, but the identity of the platelet SOC channel has remained elusive. Orai1 (CRACM1) is the recently discovered SOC (CRAC) channel in T cells and mast cells but its role in mammalian physiology is unknown. Here we report that Orai1 is strongly expressed in human and mouse platelets. To test its role in blood clotting, we generated Orai1-deficient mice and found that their platelets display severely defective SOCE, agonist-induced Ca 2؉ responses, and impaired activation and thrombus formation under flow in vitro. As a direct consequence, Orai1 deficiency in mice results in resistance to pulmonary thromboembolism, arterial thrombosis, and ischemic brain infarction, but only mild bleeding time prolongation. These results establish Orai1 as the long-sought platelet SOC channel and a crucial mediator of ischemic cardiovascular and cerebrovascular events. IntroductionAt sites of vascular injury the subendothelial extracellular matrix (ECM) is exposed to the flowing blood and triggers sudden platelet activation and the formation of a fibrin-containing thrombus. This process is essential to prevent excessive posttraumatic blood loss, but if it occurs at sites of atherosclerotic plaque rupture it can also lead to vessel occlusion and the development of myocardial infarction or ischemic stroke, which are among the leading causes of mortality and severe disability in industrialized countries. 1,2 Therefore, the inhibition of platelet activation has become an important strategy to prevent or treat such acute ischemic events. 3 Platelet activation can occur through different signaling pathways that culminate in the activation of phospholipase C (PLC) isoforms and production of diacylglycerol (DAG) and inositol 1,4,5-triphosphate (IP 3 ). IP 3 binds its receptors on the membrane of the intracellular Ca 2ϩ stores and mediates Ca 2ϩ release into the cytosol. In platelets, the dense tubular system, referred to as sarcoplasmic reticulum (SR), is thought to be the major Ca 2ϩ store. The resulting decline in Ca 2ϩ store content in turn triggers a sustained influx of extracellular Ca 2ϩ by a mechanism known as store-operated Ca 2ϩ entry (SOCE). 4,5 Although SOCE has pharmacologically been well defined for more than a decade, not much was known about the underlying molecular machinery until recently, when stromal interaction molecule 1 (STIM1) was identified as a sarco/ endoplasmic (SR/ER)-store calcium sensor that controls SOCE in T cells and mast cells. [6][7][8][9] Shortly after that, ...

Background and Purpose-Brain edema is detrimental in ischemic stroke and its treatment options are limited. Kinins are proinflammatory peptides that are released during tissue injury.

No abstract

Kinins are proinflammatory and vasoactive peptides that are released during tissue damage and may contribute to neuronal degeneration, inflammation, and edema formation after brain injury by acting on discrete bradykinin receptors, B1R and B2R. We studied the expression of B1R and B2R and the effect of their inhibition on lesion size, blood-brain barrier (BBB) disruption, and inflammatory processes after a focal cryolesion of the right parietal cortex in mice. B1R and B2R gene transcripts were significantly induced in the lesioned hemispheres of wild-type mice (P<0.05). The volume of the cortical lesions and neuronal damage at 24 h after injury in B1R(-/-) mice were significantly smaller than in wild-type controls (2.5+/-2.6 versus 11.5+/-3.9 mm(3), P<0.001). Treatment with the B1R antagonist R-715 1 h after lesion induction likewise reduced lesion volume in wild-type mice (2.6+/-1.4 versus 12.2+/-6.1 mm(3), P<0.001). This was accompanied by a remarkable reduction of BBB disruption and tissue inflammation. In contrast, genetic deletion or pharmacological inhibition of B2R had no significant impact on lesion formation or the development of brain edema. We conclude that B1R inhibition may offer a novel therapeutic strategy after acute brain injuries.