The ketone body b-hydroxybutyrate (BHB) is an endogenous factor protecting against stroke and neurodegenerative diseases, but its mode of action is unclear. Here we show in a stroke model that the hydroxy-carboxylic acid receptor 2 (HCA 2 , GPR109A) is required for the neuroprotective effect of BHB and a ketogenic diet, as this effect is lost in Hca2 À / À mice. We further demonstrate that nicotinic acid, a clinically used HCA 2 agonist, reduces infarct size via a HCA 2 -mediated mechanism, and that noninflammatory Ly-6C Lo monocytes and/or macrophages infiltrating the ischemic brain also express HCA 2 . Using cell ablation and chimeric mice, we demonstrate that HCA 2 on monocytes and/or macrophages is required for the protective effect of nicotinic acid. The activation of HCA 2 induces a neuroprotective phenotype of monocytes and/or macrophages that depends on PGD 2 production by COX1 and the haematopoietic PGD 2 synthase. Our data suggest that HCA 2 activation by dietary or pharmacological means instructs Ly-6C Lo monocytes and/or macrophages to deliver a neuroprotective signal to the brain.

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Gene therapy critically relies on vectors that combine high transduction efficiency with a high degree of target specificity and that can be administered through a safe intravenous route. The lack of suitable vectors, especially for gene therapy of brain disorders, represents a major obstacle. Therefore, we applied an in vivo screening system of random ligand libraries displayed on adeno‐associated viral capsids to select brain‐targeted vectors for the treatment of neurovascular diseases. We identified a capsid variant showing an unprecedented degree of specificity and long‐lasting transduction efficiency for brain microvasculature endothelial cells as the primary target of selection. A therapeutic vector based on this selected viral capsid was used to markedly attenuate the severe cerebrovascular pathology of mice with incontinentia pigmenti after a single intravenous injection. Furthermore, the versatility of this selection system will make it possible to select ligands for additional in vivo targets without requiring previous identification of potential target‐specific receptors.

Pannexin 1 (Px1, Panx1) and pannexin 2 (Px2, Panx2) form largepore nonselective channels in the plasma membrane of cells and were suggested to play a role in the pathophysiology of cerebral ischemia. To directly test a potential contribution of pannexins in ischemia-related mechanisms, we performed experiments in Px1 −/− , Px2 −/− , and Px1 −/− Px2 −/− knockout mice. IL-1β release, channel function in astrocytes, and cortical spreading depolarization were not altered in Px1 −/− Px2 −/− mice, indicating that, in contrast to previous concepts, these processes occur normally in the absence of pannexin channels. However, ischemia-induced dye release from cortical neurons was lower, indicating that channel function in Px1 −/− Px2 −/− neurons was impaired. Furthermore, Px1 −/− Px2 −/− mice had a better functional outcome and smaller infarcts than wild-type mice when subjected to ischemic stroke. In conclusion, our data demonstrate that Px1 and Px2 underlie channel function in neurons and contribute to ischemic brain damage.ATP release | gap junctions | macrophage | middle cerebral artery occlusion | metabolic inhibition

Expression of the MAP kinase kinase kinase TAK1 in brain endothelial cells is needed for production of prostaglandin E2, and for induction of fever and sickness behavior, in response to peripheral inflammation.

Activation of the cannabinoid 2 receptor (CB(2)) reduces ischemic injury in several organs. However, the mechanisms underlying this protective action are unclear. In a mouse model of ischemic stroke, we show that the CB(2) agonist JWH-133 (1 mg . kg(-1) . d(-1)) decreases the infarct size measured 3 d after onset of ischemia. The neuroprotective effect of JWH-133 was lost in CB(2)-deficient mice, confirming the specificity of JWH-133. Analysis of bone marrow chimeric mice revealed that bone marrow-derived cells mediate the CB(2) effect on ischemic brain injury. CB(2) activation reduced the number of neutrophils in the ischemic brain as shown by FACS analysis and by measuring the levels of the neutrophil marker enzyme myeloperoxidase. Indeed, we found in vitro that CB(2) activation inhibits adherence of neutrophils to brain endothelial cells. JWH-133 (1 microM) also interfered with the migration of neutrophils induced by the endogenous chemokine CXCL2 (30 ng/ml) through activation of the MAP kinase p38. This effect on neutrophils is likely responsible for the neuroprotection mediated by JWH-133 because JWH-133 was no longer protective when neutrophils were depleted. In conclusion, our data demonstrate that by activating p38 in neutrophils, CB(2) agonists inhibit neutrophil recruitment to the brain and protect against ischemic brain injury.-Murikinati, S., Jüttler, E., Keinert, T., Ridder, D. A., Muhammad, S., Waibler, Z., Ledent, C., Zimmer, A., Kalinke, U., Schwaninger, M. Activation of cannabinoid 2 receptors protects against cerebral ischemia by inhibiting neutrophil recruitment.

Background and Purpose-Stroke is triggered by several risk factors, including influenza and other respiratory tract infections. However, it is unknown how and in which way influenza infection affects stroke outcome. Methods-We infected mice intranasally with human influenza A (H1N1) virus and occluded the middle cerebral artery to induce ischemic strokes. Infarct volume and intracerebral hemorrhage were determined by histology. To evaluate the integrity of the blood-brain barrier and inflammation, we measured various cytokines in vivo and in vitro and performed immunohistochemistry of leukocyte markers, collagen IV, immunoglobulins, and matrix metalloproteinase-9. Results-Influenza virus infection increased infarct size. Whereas changes in cardiovascular parameters did not explain this effect, we found evidence for an inflammatory mechanism. In influenza virus infection, the respiratory tract released cytokines into the blood, such as RANTES that induced macrophage inflammatory protein-2 and other inflammatory mediators in the ischemic brain. In infected mice, there was an increased number of neutrophils expressing the matrix metalloproteinase-9 in the ischemic brain. This was accompanied by severe disruption of the blood-brain barrier and an increased rate of intracerebral hemorrhages after tissue plasminogen activator treatment. To investigate the role of cytokines, we blocked cytokine release by using GTS-21, a selective agonist of the ␣7 nicotinic acetylcholine receptor. GTS-21 ameliorated ischemic brain damage and improved survival. Key Words: ␣7 nicotinic acetylcholine receptor Ⅲ cytokines Ⅲ influenza Ⅲ RANTES Ⅲ stroke S troke is a serious health problem that kills millions of people every year. Several risk factors, including influenza A virus infection, trigger stroke. It has been shown that seasonal variation in stroke incidence closely resembles the occurrence of respiratory tract and influenza virus infections. 1 Furthermore, patients with stroke have an increased rate of preceding respiratory tract infections 2,3 and conversely respiratory tract infections are followed by an increased stroke risk. 4 The interval between symptoms of respiratory tract infection and stroke is often approximately 3 days. 4 Moreover, influenza vaccination has been shown to reduce stroke risk 5,6 and stroke mortality. 7 If influenza triggers stroke, what is the effect of concomitant influenza on the pathogenic cascade leading from cerebral ischemia to tissue demise? Although hard to answer from clinical data, this question is of great importance for the treatment of stroke. Experimental studies have shown that systemic inflammation due to lipopolysaccharides may aggravate neuroinflammation in cerebral ischemia, 8 but the effect of a more naturalistic source of inflammation is unknown. In general, the interplay between systemic inflammation and stroke pathophysiology is highly relevant because stroke often occurs in a pre-existing state of inflammation due to atherosclerosis, obesity, or infection. 9 Previous preclinical...

Fever is a hallmark of inflammatory and infectious diseases. The febrile response is triggered by prostaglandin E 2 synthesis mediated by induced expression of the enzymes cyclooxygenase-2 (COX-2) and microsomal prostaglandin E synthase 1 (mPGES-1). The cellular source for pyrogenic PGE 2 remains a subject of debate; several hypotheses have been forwarded, including immune cells in the periphery and in the brain, as well as the brain endothelium. Here we generated mice with selective deletion of COX-2 and mPGES1 in brain endothelial cells. These mice displayed strongly attenuated febrile responses to peripheral immune challenge. In contrast, inflammationinduced hypoactivity was unaffected, demonstrating the physiological selectivity of the response to the targeted gene deletions. These findings demonstrate that PGE 2 synthesis in brain endothelial cells is critical for inflammation-induced fever.