Slit modulates cerebrovascular inflammation and mediates neuroprotection against global cerebral ischemia

Abstract

Cerebrovascular inflammation contributes to secondary brain injury following ischemia. Recent in vitro studies of cell migration and molecular guidance mechanisms have indicated that the Slit family of secreted proteins can exert repellant effects on leukocyte recruitment in response to chemoattractants. Utilizing intravital microscopy, we addressed the role of Slit in modulating leukocyte dynamics in the mouse cortical venular microcirculation in vivo following TNFα application or global cerebral ischemia. We also studied whether Slit affected neuronal survival in the mouse global ischemia model as well as in mixed neuronal-glial cultures subjected to oxygenglucose deprivation. We found that systemically administered Slit significantly attenuated cerebral microvessel leukocyte-endothelial adherence occurring 4 h after TNFα and 24 h after global cerebral ischemia. Administration of RoboN, the soluble receptor for Slit, exacerbated the acute chemotactic response to TNFα. These findings are indicative of a tonic repellant effect of endogenous Slit in brain under acute proinflammatory conditions. Three days of continuous systemic administration of Slit following global ischemia significantly attenuated the delayed neuronal death of hippocampal CA1 pyramidal cells. Moreover, Slit abrogated neuronal death in mixed neuronal-glial cultures exposed to oxygen-glucose deprivation. The ability of Slit to reduce the recruitment of immune cells to ischemic brain and to provide cytoprotective effects suggests that this protein may serve as a novel anti-inflammatory and neuroprotective target for stroke therapy.

Slit2 Regulates Attractive Eosinophil and Repulsive Neutrophil Chemotaxis through Differential srGAP1 Expression during Lung Inflammation

“…Additionally, neutralization of endogenous Slit2 binding to Robo1 by R5, but not isotype-matched irrelevant mIgG, decreased allergic airway inflammation, but increased endotoxin-induced lung inflammation. Our experimental findings are fully consistent with previously published reports (12)(13)(14)(15)(16)(17), demonstrating a pathological role for Slit-Robo signaling in modulating chemotaxis of neutrophils, macrophages, and T lymphocytes. These results collectively indicate the pathological importance of Slit-Robo signaling in inflammatory responses in vivo.…”

“…Furthermore, Slit-Robo signaling potently exaggerates eosinophil chemotaxis during allergic airway inflammation while drastically suppressing neutrophil chemotaxis during LPS-induced lung inflammation in vivo, as demonstrated by the studies using Slit2-Tg mice, R5 neutralizing mAb, and rSlit2 protein. These results collectively indicate a direct effect of Slit2 on chemotaxis of neutrophils and eosinophils during lung inflammation, which is fully consistent with previous reports (12)(13)(14)(15)(16)(17).…”

“…Much effort has been directed at identifying exogenous factors that can be used therapeutically to control inflammation (30,31). Notably, Slit2 has been shown to inhibit migration of neutrophils, lymphocytes, and macrophages in inflammatory responses (12)(13)(14)(15)(16)(17). In this study, we unexpectedly found that Slit-Robo signaling activated not only repulsive chemotaxis of neutrophils during endotoxin-induced lung inflammation, but also attractive chemotaxis of eosinophils during allergic airway inflammation.…”

“…Slit2 reportedly inhibits chemotaxis of neutrophils, macrophages, and T lymphocytes (12)(13)(14)(15)(16)(17). Although the mechanism by which Slit2 attenuates chemotaxis of these leukocytes is unknown, Slit2 has been shown to induce repulsion of migratory neuronal cells within the developing brain through a pathway involving Robo1, srGAP1, and Cdc42.…”

“…Engagement of Robo1 by Slit2 functions as a repellent in axon guidance and neuronal migration (8)(9)(10)(11), an endogenous inhibitor of leukocyte chemotaxis (12)(13)(14)(15)(16)(17), and a chemoattractant of vascular endothelial cells during vasculogenesis and angiogenesis (18)(19)(20)(21). In addition, Slit2 modulates migration of malignant tumor cells (22)(23)(24).…”