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Recently it was shown that the hematophagous salivary gland protein agaphelin exhibits multiple antithrombotic effects without promoting the risk of bleeding. Agaphelin inhibits neutrophil elastase and thereby reduces cathepsin G-induced platelet aggregation. However, it is still unclear, whether pharmacological treatment with agaphelin in brain ischemia is protective and, regarding its bleeding risk, safe. To elucidate this issue, male C57BL/6 mice were subjected to 60 min of transient middle cerebral artery occlusion (tMCAO) and treated with 0.25 mg/kg agaphelin intravenously immediately after tMCAO. On day 1 and 7, infarct volume and functional neurological outcome were assessed by behavioural tests, histochemistry and magnetic resonance imaging. Thrombus formation, intracerebral bleeding risk, blood-brain barrier damage and the local inflammatory response were determined on day 1. This study shows for the first time a protective effect of agaphelin characterized by smaller infarct volume, reduced neurological deficits and reduced animal mortality. This protective effect was associated with reduced local thrombus formation, increased blood-brain barrier integrity and reduced brain inflammatory response. It is essential to mention that the protective effect of agaphelin was not linked to an increased risk of intracerebral bleeding. The promotion of brain tissue survival and inhibition of thromboinflammation identifies agaphelin as a promising treatment option in ischemic stroke, which considering the lack of bleeding risk should potentially be safe.

Platelets, anucleated megakaryocyte (MK)-derived cells, play a major role in hemostasis and arterial thrombosis. Although protein kinase casein kinase 2 (CK2) is readily detected in MKs and platelets, the impact of CK2-dependent signaling on MK/platelet (patho-)physiology has remained elusive. The present study explored the impact of the CK2 regulatory β-subunit on platelet biogenesis and activation. MK/platelet-specific genetic deletion of CK2β (ck2β-/- ) in mice resulted in a significant macrothrombocytopenia and an increased extramedullar megakaryopoiesis with an enhanced proportion of premature platelets. Although platelet life span was only mildly affected, ck2β-/- MK displayed an abnormal microtubule structure with a drastically increased fragmentation within bone marrow and a significantly reduced proplatelet formation in vivo. In ck2β-/- platelets, tubulin polymerization was disrupted, resulting in an impaired thrombopoiesis and an abrogated inositol 1,4,5-triphosphate receptor-dependent intracellular calcium (Ca2+) release. Presumably due to a blunted increase in the concentration of cytosolic Ca2+, activation-dependent increases of α and dense-granule secretion and integrin αIIbβ3 activation, and aggregation were abrogated in ck2β-/- platelets. Accordingly, thrombus formation and stabilization under high arterial shear rates were significantly diminished, and thrombotic vascular occlusion in vivo was significantly blunted in ck2β-/- mice, accompanied by a slight prolongation of bleeding time. Following transient middle cerebral artery occlusion, ck2β-/- mice displayed significantly reduced cerebral infarct volumes, developed significantly less neurological deficits, and showed significantly better outcomes after ischemic stroke than ck2βfl/fl mice. The present observations reveal CK2β as a novel powerful regulator of thrombopoiesis, Ca2+-dependent platelet activation, and arterial thrombosis in vivo.

Ischemic stroke is a predominant cause of disability worldwide, with thrombolytic or mechanical removal of the occlusion being the only therapeutic option. Reperfusion bears the risk of an acute deleterious calcium-dependent breakdown of the blood-brain barrier. Its mechanism, however, is unknown. Here, we identified type 5 NADPH oxidase (NOX5), a calciumactivated, ROS-forming enzyme, as the missing link. Using a humanized knockin (KI) mouse model and in vitro organotypic cultures, we found that reoxygenation or calcium overload increased brain ROS levels in a NOX5-dependent manner. In vivo, postischemic ROS formation, infarct volume, and functional outcomes were worsened in NOX5-KI mice. Of clinical and therapeutic relevance, in a human blood-barrier model, pharmacological NOX inhibition also prevented acute reoxygenationinduced leakage. Our data support further evaluation of poststroke recanalization in the presence of NOX inhibition for limiting stroke-induced damage.

Background and Purpose— T lymphocytes have recently been identified as key mediators of tissue damage in ischemic stroke. The interaction between very late antigen-4 (VLA-4) and vascular adhesion molecule-1 is crucial for the transvascular egress of T lymphocytes, and inhibition of this interaction by specific antibodies is a powerful strategy to combat autoimmune neuroinflammation. However, whether pharmacological blocking of T-lymphocyte trafficking is also protective during brain ischemia is still unclear. We investigated the efficacy of a monoclonal antibody directed against VLA-4 in mouse models of ischemic stroke. Methods— Transient and permanent middle cerebral artery occlusion was induced in male C57Bl/6 mice. Animals treated with a monoclonal anti-CD49d antibody (300 μg) 24 hours before or 3 hours after the onset of cerebral ischemia and stroke outcome, including infarct size, functional status, and mortality, were assessed between day 1 and day 7. The numbers of immune cells invading the ischemic brain were determined by immunocytochemistry and flow cytometry. Results— Blocking of VLA-4 significantly reduced the invasion of T lymphocytes and neutrophils on day 5 after middle cerebral artery occlusion and inhibited the upregulation of vascular adhesion molecule-1. However, the anti-CD49d antibody failed to influence stroke outcome positively irrespective of the model or the time point investigated. Conclusions— Pharmacological inhibition of the VLA-4/vascular adhesion molecule-1 axis in experimental stroke was ineffective in our hands. Our results cast doubt on the effectiveness of anti-CD49d as a stroke treatment. Further translational studies should be performed before testing anti–VLA-4 antibodies in patients with stroke.

Significance: Stroke, a leading cause of death and disability, poses a substantial burden for patients, relatives, and our healthcare systems. Only one drug is approved for treating stroke, and more than 30 contraindications exclude its use in 90% of all patients. Thus, new treatments are urgently needed. In this review, we discuss oxidative stress as a pathomechanism of poststroke neurodegeneration and the inhibition of its source, type 4 nicotinamide adenine dinucleotide phosphate (NADPH) oxidase (NOX4), as a conceptual breakthrough in stroke therapy. Recent Advances: Among potential sources of reactive oxygen species (ROS), the NOXes stand out as the only enzyme family that is solely dedicated to forming ROS. In rodents, three cerebrovascular NOXes exist: the superoxide-forming NOX1 and 2 and the hydrogen peroxide-forming NOX4. Studies using NOX1 knockout mice gave conflicting results, which overall do not point to a role for this isoform. Several reports find NOX2 to be relevant in stroke, albeit to variable and moderate degrees. In our hands, NOX4 is, by far, the major source of oxidative stress and neurodegeneration on ischemic stroke. Critical Issues: We critically discuss the tools that have been used to validate the roles of NOX in stroke. We also highlight the relevance of different animal models and the need for advanced quality control in preclinical stroke research. Future Directions: The development of isoform-specific NOX inhibitors presents a precious tool for further clarifying the role and drugability of NOX homologues. This could pave the avenue for the first clinically effective neuroprotectant applied poststroke, and even beyond this, stroke could provide a proof of principle for antioxidative stress therapy. Antioxid. Redox Signal. 00, 000-000.

Aberrant immune responses represent the underlying cause of central nervous system (CNS) autoimmunity, including multiple sclerosis (MS). Recent evidence implicated the crosstalk between coagulation and immunity in CNS autoimmunity. Here we identify coagulation factor XII (FXII), the initiator of the intrinsic coagulation cascade and the kallikrein–kinin system, as a specific immune cell modulator. High levels of FXII activity are present in the plasma of MS patients during relapse. Deficiency or pharmacologic blockade of FXII renders mice less susceptible to experimental autoimmune encephalomyelitis (a model of MS) and is accompanied by reduced numbers of interleukin-17A-producing T cells. Immune activation by FXII is mediated by dendritic cells in a CD87-dependent manner and involves alterations in intracellular cyclic AMP formation. Our study demonstrates that a member of the plasmatic coagulation cascade is a key mediator of autoimmunity. FXII inhibition may provide a strategy to combat MS and other immune-related disorders., Factor XII initiates the intrinsic blood coagulation cascade and the kinin system. Here the authors show that Factor XII is elevated in the blood of multiple sclerosis patients, activates dendritic cells via CD87 and cAMP, and its blockade inhibits immunopathology in a mouse model of the disease.

The main goal of ischemic stroke treatment is rapid recanalization of the occluded blood vessel to limit brain injury and to salvage threatened cerebral tissue. To achieve early vessel recanalization, thrombolysis using recombinant tissue-type plasminogen activator is currently the only approved pharmacological intervention. Only recently, endovascular therapy has made its way into the clinic extending the therapeutic time-window and increasing reperfusion rates. However, despite fast restoration of blood vessel patency, progressive stroke still develops in many patients, which has led to the concept of reperfusion injury. During the past decades, many studies have been addressing the mechanisms underlying ischemic stroke damage and cerebral reperfusion injury, but the picture remains far from complete.1 It has become clear that both thrombotic and inflammatory pathways are important pathophysiologic contributors to ischemic brain damage. At ischemic vascular lesions, blood platelets adhere and become activated, increasing the risk of secondary thrombotic events.2 At the same time, cerebral ischemia elicits a strong inflammatory response involving upregulation of cell adhesion molecules and cytokines as well as adhesion, activation, and transmigration of several subsets of leukocytes.3 Interestingly, emerging insights indicate an important link between these thrombotic and inflammatory pathways in stroke, which led to the concept of thromboinflammation in stroke pathology. In this review, we focus on recently discovered thromboinflammatory pathways of ischemic stroke and discuss the clinical potential of targeting thromboinflammation as a novel treatment strategy in stroke management. An overview of the key components is given in Tables I to III in the online-only Data Supplement. Collagen, von Willebrand factor (vWF), and platelet glycoprotein (GP) Ib together form an important axis that is crucial for initial platelet adhesion at sites of vascular injury.4 On exposure of the subendothelial matrix, platelets are able to adhere to exposed collagen via their collagen receptors GP …

Potassium channels can fulfill both beneficial and detrimental roles in neuronal damage during ischemic stroke. Earlier studies have characterized a neuroprotective role of the two-pore domain potassium channels KCNK2 (TREK1) and KCNK3 (TASK1). Protective neuronal hyperpolarization and prevention of intracellular Ca(2+) overload and glutamate excitotoxicity were suggested to be the underlying mechanisms. We here identify an unexpected role for the related KCNK5 channel in a mouse model of transient middle cerebral artery occlusion (tMCAO). KCNK5 is strongly upregulated on neurons upon cerebral ischemia, where it is most likely involved in the induction of neuronal apoptosis. Hypoxic conditions elevated neuronal expression levels of KCNK5 in acute brain slices and primary isolated neuronal cell cultures. In agreement, KCNK5 knockout mice had significantly reduced infarct volumes and improved neurologic function 24 h after 60 min of tMCAO and this protective effect was preserved at later stages of infarct development. KCNK5 deficiency resulted in a significantly reduced number of apoptotic neurons, a downregulation of pro-apoptotic and upregulation of anti-apoptotic factors. Results of adoptive transfer experiments of wild-type and Kcnk5 (-/-) immune cells into Rag1 (-/-) mice prior to tMCAO exclude a major role of KCNK5 in poststroke inflammatory reactions. In summary, KCNK5 expression is induced on neurons under ischemic conditions where it most likely exerts pro-apoptotic effects. Hence, pharmacological blockade of KCNK5 might have therapeutic potential in preventing ischemic neurodegeneration.

The blood-brain barrier (BBB) is an integral part of the neurovascular unit (NVU). The NVU is comprised of endothelial cells that are interconnected by tight junctions resting on a parenchymal basement membrane ensheathed by pericytes, smooth muscle cells and a layer of astrocyte end feet. Circulating blood cells, such as leukocytes, complete the NVU. BBB disruption is common in several neurological diseases, but the molecular mechanisms involved remain largely unknown. We analyzed the role of TWIK-related potassium channel-1 (TREK1, encoded by KCNK2) in human and mouse endothelial cells and the BBB. TREK1 was downregulated in endothelial cells by treatment with interferon-γ (IFN-γ) and tumor necrosis factor-α (TNF-α). Blocking TREK1 increased leukocyte transmigration, whereas TREK1 activation had the opposite effect. We identified altered mitogen-activated protein (MAP) kinase signaling, actin remodeling and upregulation of cellular adhesion molecules as potential mechanisms of increased migration in TREK1-deficient (Kcnk2(-/-)) cells. In Kcnk2(-/-) mice, brain endothelial cells showed an upregulation of the cellular adhesion molecules ICAM1, VCAM1 and PECAM1 and facilitated leukocyte trafficking into the CNS. Following the induction of experimental autoimmune encephalomyelitis (EAE) by immunization with a myelin oligodendrocyte protein (MOG)35-55 peptide, Kcnk2(-/-) mice showed higher EAE severity scores that were accompanied by increased cellular infiltrates in the central nervous system (CNS). The severity of EAE was attenuated in mice given the amyotrophic lateral sclerosis drug riluzole or fed a diet enriched with linseed oil (which contains the TREK-1 activating omega-3 fatty acid α-linolenic acid). These beneficial effects were reduced in Kcnk2(-/-) mice, suggesting TREK-1 activating compounds may be used therapeutically to treat diseases related to BBB dysfunction.

Based on non-hypothesis-driven approaches genetic evidence suggests that diseases are interrelated differently to our current organ-based ontology. In fact, common effector mechanisms, when affected or triggered seem to produce pathophenotypes in diverse organs or co-morbidities. This will lead eventually to a revised disease nomenclature and opens up entirely new approaches for diagnosis and treatment. In this context, we noted that a common cardiovascular target, the cGMP-forming Fe(II) haem protein, soluble guanylate cyclase (sGC), appears to be situated in a common mechanism network that is prominently relevant to stroke. Ischemic stroke is the second leading cause of death worldwide and the leading cause of disability. Despite this high medical need only a single drug is available but due to its limited time window and risk of bleeding 85% of all patients are excluded from treatment. As a possible add-on, vasoactive drugs however typically dilate normal blood vessels and cause a paradoxical “steal phenomenon” by both shunting blood to healthy vascular beds and a systemic blood pressure drop. Upon middle cerebral artery occlusion sGC protein and nitric oxide-stimulated activity in the ischemic hemisphere were dramatically down-regulated leading to a high proportion of oxidized and/or haem-free apo-sGC activity. Pharmacological targeting of apo-sGC in vitro under oxygen and glucose deprivation conveyed strong neuroprotection via ERK/CREB signalling. In vivo, post-stroke apo-sGC activation by two distinct members of this compound class augmented cerebral blood-flow whilst leaving systemic blood pressure unaffected, reduced infarct size and increased survival. Different apo-sGC activators are in advanced stages of clinical development for different cardiovascular indications. Systems biology and network medicine and our preliminary target validation suggest that they should be urgently tested for repurposing as first-in-class, mechanism-based neuroprotective drugs in stroke.

Ischemic stroke is the second leading cause of death worldwide and the leading cause of disability. Despite this high medical need only a single drug is available but due to its limited time window and risk of bleeding 85% of all patients are excluded from treatment. Here we address three different new targets in stroke highly related to oxidative stress. NADPH oxidase is one of the most important sources of reactive oxygen species, which has been recently considered as a promising target in ischemic stroke. Neuronal nitric oxide synthase (NOS1) has been also suggested as a possible target so that its partial inhibition can lead to neuroprotective effects. Similarly, NOX possibly acts by scavenging or toxifying NO to nitrating species and oxidising the NO receptor, soluble guanylate cyclase (sGC). This then diminishes physiological NO-cGMP signalling, a process that could be reversed in mice by so-called sGC activator compounds. Pharmacological targeting of apo-sGC in vitro under oxygen and glucose deprivation conveyed strong neuroprotection via PKG/ERK/CREB signalling pathway. In vivo, post-stroke apo-sGC activation by two distinct members of this compound class augmented cerebral blood-flow whilst leaving systemic blood pressure unaffected, reduced infarct size and increased survival. Thus, both inhibiting NOX/NOS-dependent oxidative stress and augmenting cGMP signalling are neuroprotective in stroke. Current and future experiments are aimed at validating these finding in a second rodent species for further preclinical and clinical development as first-in-class neuroprotective drugs.