Slit modulates cerebrovascular inflammation and mediates neuroprotection against global cerebral ischemia

Recombinant Slit2 suppresses neuroinflammation and Cdc42-mediated brain infiltration of peripheral immune cells via Robo1-srGAP1 pathway in a rat model of germinal matrix hemorrhage

BACKGROUND

Germinal matrix hemorrhage (GMH) is a devastating neonatal stroke, in which neuroinflammation is a critical pathological contributor. Slit2, a secreted extracellular matrix protein, plays a repulsive role in axon guidance and leukocyte chemotaxis via the roundabout1 (Robo1) receptor. This study aimed to explore effects of recombinant Slit2 on neuroinflammation and the underlying mechanism in a rat model of GMH.

METHODS

GMH was induced by stereotactically infusing 0.3 U of bacterial collagenase into the germinal matrix of 7-day-old Sprague Dawley rats. Recombinant Slit2 or its vehicle was administered intranasally at 1 h after GMH and daily for 3 consecutive days. A decoy receptor recombinant Robo1 was co-administered with recombinant Slit2 after GMH. Slit2 siRNA, srGAP1 siRNA or the scrambled sequences were administered intracerebroventricularly 24 h before GMH. Neurobehavior, brain water content, Western blotting, immunofluorescence staining and Cdc42 activity assays were performed.

RESULTS

The endogenous brain Slit2 and Robo1 expressions were increased after GMH. Robo1 was expressed on neuron, astrocytes and infiltrated peripheral immune cells in the brain. Endogenous Slit2 knockdown by Slit2 siRNA exacerbated brain edema and neurological deficits following GMH. Recombinant Slit2 (rSlit2) reduced neurological deficits, proinflammatory cytokines, intercellular adhesion molecules, peripheral immune cell markers, neuronal apoptosis and Cdc42 activity in the brain tissue after GMH. The anti-neuroinflammation effects were reversed by recombinant Robo1 co-administration or srGAP1 siRNA.

CONCLUSIONS

Recombinant Slit2 reduced neuroinflammation and neuron apoptosis after GMH. Its anti-neuroinflammation effects by suppressing onCdc42-mediated brain peripheral immune cells infiltration was at least in part via Robo1-srGAP1 pathway. These results imply that recombinant Slit2 may have potentials as a therapeutic option for neonatal brain injuries.

Genomic signatures reveal selection in Lingxian white goose

Lingxian white goose (LXW) is a goose breed indigenous to China that is famous for its meat quality and fast growth. However, the genomic evidence underlying such excellent breeding characteristics remains poorly understood. Therefore, we performed whole-genome resequencing of 141 geese from 3 indigenous breeds to scan for selection signatures and detect genomic regions related to breed features of LXW. We identified 5 reproduction-related genes (SYNE1, ESR1, NRIP1, CCDC170, and ARMT1) in highly differentiated regions and 11 notable genes in 26 overlapping windows, some of which are responsible for meat quality (DHX15), growth traits (LDB2, SLIT2, and RBPJ), reproduction (KCNIP4), and unique immunity traits (DHX15 and SLIT2). These findings provide insights into the genetic characteristics of LXW and identify genes affecting important traits in LXW, which extends the genetic resources and basis for facilitating genetic improvement in domestic geese breeds.

Overexpression of Slit2 decreases neuronal excitotoxicity, accelerates glymphatic clearance, and improves cognition in a multiple microinfarcts model

Background

Cerebral microinfarcts (MIs) lead to progressive cognitive impairments in the elderly, and there is currently no effective preventative strategy due to uncertainty about the underlying pathogenic mechanisms. One possibility is the dysfunction of GABAergic transmission and ensuing excitotoxicity. Dysfunction of GABAergic transmission induces excitotoxicity, which contributes to stroke pathology, but the mechanism has kept unknown. The secreted leucine-rich repeat (LRR) family protein slit homologue 2 (Slit2) upregulates GABAergic activity and protects against global cerebral ischemia, but the neuroprotective efficacy of Slit2 against MIs has not been examined.

Methods

Middle-aged Wild type (WT) and Slit2-Tg mice were divided into sham and MI treatment groups. MIs were induced in parietal cortex by laser-evoked arteriole occlusion. Spatial memory was then compared between sham and MI groups using the Morris water maze (MWM) task. In addition, neuronal activity, blood brain barrier (BBB) permeability, and glymphatic clearance in peri-infarct areas were compared using two-photon imaging, while GABAergic transmission, microglial activation, neuronal loss, and altered cortical connectivity were compared by immunofluorescent staining or western blotting.

Results

Microinfarcts increased the amplitude and frequency of spontaneous intracellular Ca²⁺ signals, reduced neuronal survival and connectivity within parietal cortex, decreased the number of GABAergic interneurons and expression of vesicular GABA transporter (VGAT), induced neuroinflammation, and impaired both glymphatic clearance and spatial memory. Alternatively, Slit2 overexpression attenuated dysfunctional neuronal Ca²⁺ signaling, protected against neuronal death in the peri-infarct area as well as loss of parietal cortex connectivity, increased GABAergic interneuron number and VGAT expression, attenuated neuroinflammation, and improved both glymphatic clearance and spatial memory.

Conclusion

Our results strongly suggest that overexpression of Slit2 protected against the dysfunction in MIs, which is a potential therapeutic target for cognition impairment in the elderly.

The potential of Slit2 as a therapeutic target for central nervous system disorders

Introduction: Slit2 is an extracellular matrix protein that regulates migration of developing axons during central nervous system (CNS) development. Roundabout (Robo) receptors expressed by various cell types in the CNS, mediate intracellular signal transduction pathways for Slit2. Recent studies indicate that Slit2 plays important protective roles in a myriad of processes such as cell migration, immune response, vascular permeability, and angiogenesis in CNS pathologies. Areas covered: This review provides an overview of the diverse functions of Slit2 in CNS disorders and discusses the potential of Slit2 as a therapeutic target. We reviewed preclinical studies reporting the role of Slit2 in various CNS disease models, transgenic animal research, and rodent models that utilized Slit2 as a therapy. Expert opinion: Slit2 exerts a wide array of beneficial effects ranging from anti-migration, blood-brain barrier (BBB) protection, inhibition of peripheral immune cell infiltration, and anti-apoptosis in various disease models. However, a dual role of Slit2 in endothelial permeability has been observed in transgenic animals. Further research on Slit2 will be crucial including key issues such as effects of transgenic overexpression versus exogenous Slit2, function of Slit2 dependent on cellular expression of Robo receptors and the underlying pathology for potential clinical translation.

Amyloid-β oligomers in cellular models of Alzheimer's disease

Amyloid-β (Aβ) dysmetabolism is tightly associated with pathological processes in Alzheimer's disease (AD). Currently, it is thought that, in addition to Aβ fibrils that give rise to plaque formation, Aβ aggregates into non-fibrillar soluble oligomers (AβOs). Soluble AβOs have been extensively studied for their synaptotoxic and neurotoxic properties. In this review, we discuss physicochemical properties of AβOs and their impact on different brain cell types in AD. Additionally, we summarize three decades of studies with AβOs, providing a compelling bulk of evidence regarding cell-specific mechanisms of toxicity. Cellular models may lead us to a deeper understanding of the detrimental effects of AβOs in neurons and glial cells, putatively shedding light on the development of innovative therapies for AD.

Inhibition of miR-200b-3p alleviates hypoxia-ischemic brain damage via targeting Slit2 in neonatal rats

BACKGROUND

Brain damage in premature infants often occurs in very low birth weight infants (VLBW) as a result of hypoxia-ischemia and can lead to cognitive impairment and movement disorders. Many miRNAs have been demonstrated to participate in hypoxia-ischemic brain damage (HIBD). This study was designed to investigate the roles of miR-200b-3p in brain damage of neonatal rats induced by hypoxia-ischemia.

METHODS AND RESULTS

Three-day-old SD rats were used to establish the model of hypoxia-ischemic brain injury mimicking premature infants. RT-qPCR showed that miR-200b-3p was up-regulated in rat brains at the early stage following hypoxia-ischemic treatment. Bioinformatics analysis identified that Slit2 is a target gene of miR-200b-3p and luciferase reporter gene assay confirmed that miR-200b-3p can interact with and target Slit2 mRNA. Inhibition of miR-200b-3p by antagomir increased Slit2 expression at both the mRNA and protein levels in rat brains. TUNEL assay and transmission electron microscopy (TEM) analysis showed decreased numbers of apoptotic neurons in the hypoxia-ischemia-treated animals as a result of administration of miR-200b-3p antagomir. Administration of miR-200b-3p antagomir attenuated spatial and learning memory loss in the animals induced by hypoxia-ischemia as compared to controls.

CONCLUSION

Our study has demonstrated that Slit2 is a target gene of miR-200b-3p and that the hypoxia-ischemic brain damage in neonatal rats was alleviated by inhibiting miR-200b-3p via Slit2. miR-200b-3p may be a potential therapeutic target of HIBD for further investigation.

Recombinant Slit2 attenuates neuronal apoptosis via the Robo1-srGAP1 pathway in a rat model of neonatal HIE

Apoptosis following hypoxic-ischemic injury to the brain plays a major role in neuronal cell death. The neonatal brain is more susceptible to injury as the cortical neurons are immature and there are lower levels of antioxidants. Slit2, an extracellular matrix protein, has been shown to be neuroprotective in various models of neurological diseases. However, there is no information about the role of Slit2 in neonatal hypoxia-ischemia. In this study, we evaluated the effect of Slit2 and its receptor Robo1 in a rat model with neonatal HIE. 10-day old rat pups were used to create the neonatal HIE model. The right common carotid artery was ligated followed by 2.5 h of hypoxia. Recombinant Slit2 was administered intranasally 1 h post HI, recombinant Robo1 was used as a decoy receptor and administered intranasally 1h before HI and srGAP1-siRNA was administered intracerebroventricularly 24 h before HI. Brain infarct area measurement, short-term and long-term neurological function tests, Western blot, immunofluorescence staining, Fluoro-Jade C staining, Nissl staining and TUNEL staining were the assessments done following drug administration. Recombinant Slit2 administration reduced neuronal apoptosis and neurological deficits after neonatal HIE which were reversed by co-administration of recombinant Robo1 and srGAP1-siRNA administration. Recombinant Slit2 showed improved outcomes possibly via the robo1-srGAP1 pathway which mediated the inhibition of RhoA. In this study, the results suggest that Slit2 may help in attenuation of apoptosis and could be a therapeutic agent for treatment of neonatal hypoxic ischemic encephalopathy.

The Role of the Slit/Robo Signaling Pathway

The Slit family is a family of secreted proteins that play important roles in various physiologic and pathologic activities via interacting with Robo receptors. Slit/Robo signaling was first identified in the nervous system, where it functions in neuronal axon guidance; nevertheless, an increasing number of studies have shown that Slit/Robo signaling even regulates other activities, such as angiogenesis, inflammatory cell chemotaxis, tumor cell migration and metastasis. Although the precise role of the ligand-receptor in organisms has been obscure and the conclusions drawn are sometimes paradoxical, tremendous advances in understanding the Slit/Robo signaling pathway have been made. As such, our review summarizes the characteristics of the Slit/Robo signaling pathway and its role in various cell types.

Lung Tumorigenesis Alters the Expression of Slit2-exon15 Splicing Variants in Tumor Microenvironment

Slit2 expression is downregulated in various cancers, including lung cancer. We identified two Slit2 splicing variants at exon15—Slit2-WT and Slit2-ΔE15. In the RT-PCR analyses, the Slit2-WT isoform was predominantly expressed in all the lung cancer specimens and in their normal lung counterparts, whereas Slit2-ΔE15 was equivalently or predominantly expressed in 41% of the pneumothorax specimens. A kRas^G12D transgenic mice system was used to study the effects of tumorigenesis on the expressions of the Slit2-exon15 isoforms. The results revealed that a kRas^G12D-induced lung tumor increased the Slit2-WT/Slit2-ΔE15 ratio and total Slit2 expression level. However, the lung tumors generated via a tail vein injection of lung cancer cells decreased the Slit2-WT/Slit2-ΔE15 ratio and total Slit2 expression level. Interestingly, the lipopolysaccharide (LPS)-induced lung inflammation also decreased the Slit2-WT/Slit2-ΔE15 ratio. Since Slit2 functions as an anti-inflammatory factor, the expression of Slit2 increases in kRas^G12D lungs, which indicates that Slit2 suppresses immunity during tumorigenesis. However, an injection of lung cancer cells via the tail vein and the LPS-induced lung inflammation both decreased the Slit2 expression. The increased Slit2 in the tumor microenvironment was mostly Slit2-WT, which lacks growth inhibitory activity. Thus, the results of our study suggested that the upregulation of Slit2-WT, but not Slit2-ΔE15, in a cancer microenvironment is an important factor in suppressing immunity while not interfering with cancer growth.

Different Isoforms of the Neuronal Guidance Molecule Slit2 Directly Cause Chemoattraction or Chemorepulsion of Human Neutrophils

The movement of neutrophils between blood and tissues appears to be regulated by chemoattractants and chemorepellents. Compared with neutrophil chemoattractants, relatively little is known about neutrophil chemorepellents. Slit proteins are endogenously cleaved into a variety of N- and C-terminal fragments, and these fragments are neuronal chemorepellents and inhibit chemoattraction of many cell types, including neutrophils. In this report, we show that the ∼140-kDa N-terminal Slit2 fragment (Slit2-N) is a chemoattractant and the ∼110-kDa N-terminal Slit2 fragment (Slit2-S) is a chemorepellent for human neutrophils. The effects of both Slit2 fragments were blocked by Abs to the Slit2 receptor Roundabout homolog 1 or the Slit2 coreceptor Syndecan-4. Slit2-N did not appear to activate Ras but increased phosphatidylinositol 3,4,5-triphosphate levels. Slit2-N-induced chemoattraction was unaffected by Ras inhibitors, reversed by PI3K inhibitors, and blocked by Cdc42 and Rac inhibitors. In contrast, Slit2-S activated Ras but did not increase phosphatidylinositol 3,4,5-triphosphate levels. Slit2-S-induced chemorepulsion was blocked by Ras and Rac inhibitors, not affected by PI3K inhibitors, and reversed by Cdc42 inhibitors. Slit2-N, but not Slit2-S, increased neutrophil adhesion, myosin L chain 2 phosphorylation, and polarized actin formation and single pseudopods at the leading edge of cells. Slit2-S induced multiple pseudopods. These data suggest that Slit2 isoforms use similar receptors but different intracellular signaling pathways and have different effects on the cytoskeleton and pseudopods to induce neutrophil chemoattraction or chemorepulsion.

Overexpression of Slit2 improves function of the paravascular pathway in the aging mouse brain

Aging is associated with impairment of the paravascular pathway caused by the activation of astrocytes and depolarization of protein aquaporin-4 (AQP4) water channels, resulting in the accumulation of protein waste, including amyloid β (Aβ), in the brain parenchyma. The secreted glycoprotein slit guidance ligand 2 (Slit2) is important in regulating the function of the central nervous system and inflammatory response process. In the present study, 15-month-old Slit2 overexpression transgenic mice (Slit2-Tg mice) and two-photon fluorescence microscopy were used to evaluate the dynamic clearance of the paravascular pathway and the integrity of the blood-brain barrier (BBB). The reactivity of astrocytes, polarity of AQP4 and deposition of Aβ in the brain parenchyma were analyzed by immunofluorescence. A Morris water maze test was used to examine the effect of Slit2 on spatial memory cognition in aging mice. It was found that the overexpression of Slit2 improved the clearance of the paravascular pathway by inhibiting astrocyte activation and maintaining AQP4 polarity on the astrocytic endfeet in Slit2-Tg mice. In addition, Slit2 restored the disruption of the BBB caused by aging. The accumulation of Aβ was significantly reduced in the brain of Slit2-Tg mice. Furthermore, the water maze experiment showed that Slit2 improved spatial memory cognition in the aging mice. These results indicated that Slit2 may have the potential to be used in the prevention and treatment of neurodegenerative diseases in the elderly.

Recombinant Slit2 Reduces Surgical Brain Injury Induced Blood Brain Barrier Disruption via Robo4 Dependent Rac1 Activation in a Rodent Model

Brain tissue surrounding surgical resection site can be injured inadvertently due to procedures such as incision, retractor stretch, and electrocauterization when performing neurosurgical procedures, which is termed as surgical brain injury (SBI). Blood brain barrier (BBB) disruption due to SBI can exacerbate brain edema in the post-operative period. Previous studies showed that Slit2 exhibited vascular anti-permeability effects outside the brain. However, BBB protective effects of Slit2 following SBI has not been evaluated. The objective of this study was to evaluate whether recombinant Slit2 via its receptor roundabout4 (Robo4) and the adaptor protein, Paxillin were involved in reducing BBB permeability in SBI rat model. Our results showed that endogenous Slit2 increased in the surrounding peri-resection brain tissue post-SBI, Robo4 remained unchanged and Paxillin showed a decreasing trend. Recombinant Slit2 administered 1 h before injury increased BBB junction proteins, reduced BBB permeability, and decreased neurodeficits 24 h post-SBI. Furthermore, recombinant Slit2 administration increased Rac1 activity which was reversed by Robo4 and Paxillin siRNA. Our findings suggest that recombinant Slit2 reduced SBI-induced BBB permeability, possibly by stabilizing BBB tight junction via Robo4 mediated Rac1 activation. Slit2 may be beneficial for BBB protection during elective neurosurgeries.

Increased Expression of Slit2 and its Robo Receptors During Astroglial Scar Formation After Transient Focal Cerebral Ischemia in Rats

Slit2, a secreted glycoprotein, has recently been implicated in the post-ischemic astroglial reaction. The objective of this study was to investigate the temporal changes and cellular localization of Slit2 and its receptors, Robo1, Robo2, and Robo4, in a rat transient focal ischemia model induced by middle cerebral artery occlusion. We used double- and triple-immunolabeling to determine the cell-specific changes in Slit2 and its receptors during a 10-week post-ischemia period. The expression profiles of Slit2 and the Robo receptors shared overlapping expression patterns in sham-operated and ischemic striatum. Constitutive expression of Slit2 and Robo receptors was observed in striatal neurons with weak intensity, whereas in rats reperfused after ischemic insults, these immunoreactivities were increased in reactive astrocytes. Astroglial induction of Slit2 and Robo in the peri-infarct region was distinct on days 7-14 after reperfusion and thereafter increased progressively throughout the 10-week experimental period. Slit2 and Robo were prominently expressed in the perinuclear cytoplasm and main processes of reactive astrocytes forming the astroglial scar. This observation was confirmed by quantification of the mean fluorescence intensity of Slit2 and Robo receptors over reactive astrocytes localized at the edge of the infarct area. However, activated microglia/macrophages in the peri-infarct area were devoid of any specific labeling for Slit2 and Robo. Thus, our data revealed a selective and sustained induction of Slit2 and Robo in astrocytes localized throughout the astroglial scar after ischemic stroke, suggesting that Slit2/Robo signaling participates in glial scar formation and brain remodeling following ischemic injury.

Increased expression of Slit2 and its receptors Robo1 and Robo4 in reactive astrocytes of the rat hippocampus after transient forebrain ischemia

Slit2 is a secreted glycoprotein that was originally identified as a chemorepulsive factor in the developing brain; however, it was recently reported that Slit2 is associated with adult neuronal function including a variety of pathophysiological processes. To elucidate whether Slit2 is implicated in the pathophysiology of ischemic injury, we investigated the temporal changes and cellular localization of Slit2 and its predominant receptors, Robo1 and Robo4, for 28 days after transient forebrain ischemia. Slit2 and its receptors had similar overall expression patterns in the control and ischemic hippocampi. The ligand and receptors were constitutively expressed in hippocampal neurons in control animals; however, in animals with ischemic injury, their upregulation was detected in reactive astrocytes, but not in neurons or activated microglia, in the CA1 region. Astroglial induction of Slit2 and its receptors occurred by day 3 after reperfusion, and appeared to increase progressively until the final time point on day 28. Their temporal expression patterns overlapped with the time period in which reactive astrocytes undergo dynamic structural changes and appear hypertrophic in the ischemic hippocampus. The immunohistochemical data were consistent with the results of the immunoblot analyses, indicating that the expression of Slit2 and Robo increased progressively over the relatively long period of 28 days examined here. Collectively, these results suggest that Slit2/Robo signaling may be involved in regulating the astroglial reaction via autocrine or paracrine mechanisms in post-ischemic processes. Moreover, this may contribute to the dynamic morphological changes that occur in astrocytes in response to ischemic injury.

Recombinant Slit2 attenuates neuroinflammation after surgical brain injury by inhibiting peripheral immune cell infiltration via Robo1-srGAP1 pathway in a rat model

BACKGROUND AND PURPOSE

Peripheral immune cell infiltration to the brain tissue at the perisurgical site can promote neuroinflammation after surgical brain injury (SBI). Slit2, an extracellular matrix protein, has been reported to reduce leukocyte migration. This study evaluated the effect of recombinant Slit2 and the role of its receptor roundabout1 (Robo1) and its downstream mediator Slit-Robo GTPase activating protein 1 (srGAP1)-Cdc42 on peripheral immune cell infiltration after SBI in a rat model.

METHODS

One hundred and fifty-three adult male Sprague-Dawley rats (280-350 g) were used. Partial resection of right frontal lobe was performed to induce SBI. Slit2 siRNA was administered by intracerebroventricular injection 24h before SBI. Recombinant Slit2 was injected intraperitoneally 1h before SBI. Recombinant Robo1 used as a decoy receptor was co-administered with recombinant Slit2. srGAP1 siRNA was administered by intracerebroventricular injection 24h before SBI. Post-assessments included brain water content measurement, neurological tests, ELISA, Western blot, immunohistochemistry, and Cdc42 activity assay.

RESULTS

Endogenous Slit2 was increased after SBI. Robo1 was expressed by peripheral immune cells. Endogenous Slit2 knockdown worsened brain edema after SBI. Recombinant Slit2 administration reduced brain edema, neurological deficits, and pro-inflammatory cytokines after SBI. Recombinant Slit2 reduced peripheral immune cell markers cluster of differentiation 45 (CD45) and myeloperoxidase (MPO), as well as Cdc42 activity in the perisurgical brain tissue which was reversed by recombinant Robo1 co-administration and srGAP1 siRNA.

CONCLUSIONS

Recombinant Slit2 improved outcomes by reducing neuroinflammation after SBI, possibly by decreasing peripheral immune cell infiltration to the perisurgical site through Robo1-srGAP1 mediated inhibition of Cdc42 activity. These results suggest that Slit2 may be beneficial to reduce SBI-induced neuroinflammation.

Isoflurane post-conditioning protects primary cultures of cortical neurons against oxygen and glucose deprivation injury via upregulation of Slit2/Robo1

Different mechanisms have been suggested to contribute to isoflurane-mediated neuroprotection. Previous studies have suggested that the protein Slit can abrogate neuronal death in mixed neuronal-glial cultures exposed to oxygen-glucose deprivation (OGD) and reperfusion (OGD/R). We hypothesized that isoflurane increases the expression of Slit and its receptor Robo when cortical neurons are exposed to OGD/R. To test this hypothesis, we exposed primary cortical neurons to OGD for 90 min and reperfusion for 24h and investigated how isoflurane post-conditioning affected cell survival and expression of Slit2 and receptors Robo1 and Robo4. Cell survival increased after administration of isoflurane, as assessed by the lactate dehydrogenase assay, trypan blue analysis, and propidium iodide staining. Western blot analysis showed that cleaved caspase-3 was increased after OGD/R(P<0.01) but reduced by isoflurane post-conditioning. Real-time PCR and Western blot analysis showed that the expression levels of Slit2 and Robo1, but not Robo4, were increased after OGD/R (P<0.5) and increased even further by isoflurane post-conditioning (P<0.01). Our results suggest that isoflurane post-conditioning markedly attenuates apoptosis and necrosis of cortical neurons exposed to OGD/R possibly in part via elevation of Slit2 and Robo1 expression. These findings provide a novel explanation for the pleiotropic effects of isoflurane that could benefit the central nervous system.

Slit-Robo: a potential way to treat periodontitis

Slit is a secreted protein known to function through the Roundabout (Robo) receptor. Slit has recently been shown to be an endogenously available inhibitor of leukocyte chemotaxis and as a chemoattractant to recruit vascular endothelial cells to sites for angiogenesis both in vivo and in vitro. The initiation and progression of periodontal diseases, is the result of complex interactions between the colonizing bacteria in the periodontal pockets and host immune and inflammatory responses. Antibiotics such as tetracyclines are commonly used in the management of periodontal infections and yet, have shown modest success in reducing neutrophil-mediated injury. Angiogenesis is important for the maintenance of homeostatus of periodontal tissues. However, few studies have been reported about angiogenesis targeted treatment for periodontitis. Based on its angiogenesis promoting effect and leukocyte chemotaxis inhibition effect, we hypothesize that Slit can be an effective immunotherapeutic agent in the treatment of periodontitis.

Phenolic alkaloids from Menispermum dauricum rhizome protect against brain ischemia injury via regulation of GLT-1, EAAC1 and ROS generation

Menispermum dauricum rhizome has been widely used in China to treat various cardiovascular and thrombosis disorders. Some studies have reported that the phenolic alkaloids of Menispermum dauricum rhizome (PAM) have protective effects against brain ischemia injury, but the mechanism of this action remains to be clarified. In the present study, we investigated the possible mechanisms of action of PAM on experimental brain ischemia injury. Oxygen and glucose deprivation (OGD) in rat primary cortical cultures and middle cerebral artery occlusion in rats were used to mimic ischemia-reperfusion injury, respectively. The results suggested that PAM protected rat primary cortical cultures against OGD-reoxygenation induced cytotoxicity. PAM decreased extracellular glutamate content and markedly prevented the effects induced by OGD on protein level of GLT-1 and EAAC1 glutamate transporters. In addition, it reduced intracellular ROS generation. In vivo, PAM significantly reduced cerebral infarct area and ameliorated neurological functional deficits at different time points. Our findings revealed that the possible mechanism of action of PAM protected against brain ischemia injury involves regulation of GLT-1, EAAC1 and ROS generation.

A roundabout way to cancer

The Slit family of secreted proteins and their transmembrane receptor, Robo, were originally identified in the nervous system where they function as axon guidance cues and branching factors during development. Since their discovery, a great number of additional roles have been attributed to Slit/Robo signaling, including regulating the critical processes of cell proliferation and cell motility in a variety of cell and tissue types. These processes are often deregulated during cancer progression, allowing tumor cells to bypass safeguarding mechanisms in the cell and the environment in order to grow and escape to new tissues. In the past decade, it has been shown that the expression of Slit and Robo is altered in a wide variety of cancer types, identifying them as potential therapeutic targets. Further, studies have demonstrated dual roles for Slits and Robos in cancer, acting as both oncogenes and tumor suppressors. This bifunctionality is also observed in their roles as axon guidance cues in the developing nervous system, where they both attract and repel neuronal migration. The fact that this signaling axis can have opposite functions depending on the cellular circumstance make its actions challenging to define. Here, we summarize our current understanding of the dual roles that Slit/Robo signaling play in development, epithelial tumor progression, and tumor angiogenesis.

A novel role for Slit2/Robo1 axis in modulating HIV-1 replication in T cells

OBJECTIVE

Slit2 is a secreted glycoprotein that has been shown to possess anti-inflammatory properties. In addition, Slit2 has been shown to modulate CXCR4-mediated functional effects in T cells. However, its role in HIV-1 pathogenesis is not known. The objective of the current study is to analyze the role of Slit2 in modulating HIV-1 replication in T cells.

METHODS

The effect of endogenous Slit2 expression of HIV-1 replication in T cells was studied by transient overexpression or downregulation of Slit2. The role of exogenous Slit2 was studied by analyzing the effect of soluble Slit2 protein on HIV-1 replication in T-cell lines and peripheral blood mononuclear cells (PBMCs).

RESULTS

Studies on T-cell lines revealed a higher expression of Slit2 in Jurkat T cells compared with MT4 cells. We observed that downregulation of Slit2 in Jurkat T cells using Slit2-specific small inhibitor RNA enhanced HIV-1 replication. However, overexpression of Slit2 in MT4 cells and PBMCs reduced HIV-1 replication. As Slit2 is a secretory protein, we further analyzed the role of soluble Slit2 on HIV-1 virus replication using various cell lines and PBMCs. Our data indicated that exogenous Slit2 inhibited replication of both X4-tropic and R5-tropic HIV-1 viruses. Further studies revealed that Slit2 mediated its functional effects by binding to Robo1 receptor.

CONCLUSION

Taken together, our results describe Slit2/Robo1 axis as a novel modulator of HIV-1 replication in T cells. These studies may contribute to the understanding of the immunopathogenesis of HIV-1 infection.

Over-expression of Slit2 induces vessel formation and changes blood vessel permeability in mouse brain

AIM

To investigate the effect of the axon guidance cue Slit2 on the density of blood vessels and permeability of the blood-brain barrier in mouse brain.

METHODS

hSlit2 transgenic mouse line was constructed, and the phenotypes of the mice were compared with wild-type mice in respect to the lateral ventricle (LV), ventricle pressure, and the choroids plexus. An in vivo Miles permeability assay and an amyloid-β permeability assay were used to assess the permeability of brain blood vessels. Brain vessel casting and intracerebral hemorrhage models were built to investigate vessel density in the transgenic mice. An in vitro permeability assay was used to test whether Slit2 could change the permeability and tight junctions of blood vessel endothelial cells.

RESULTS

Hydrocephalus occurred in some transgenic mice, and a significantly larger lateral ventricle area and significantly higher ventricle pressure were observed in the transgenic mice. The transgenic mice displayed changed construction of the choroids plexus, which had more micro vessels, dilated vessels, gaps between epithelial cells and endothelial cells than wild-type mice. Slit2 significantly increased brain vessel density and the permeability of brain vessels to large molecules. These blood vessels were more sensitive to cues that induce brain hemorrhage. At the cellular level, Slit2 disturbed the integrity of tight junctions in blood vessel endothelial cells and improved the permeability of the endothelial cell layer. Thus, it promoted the entry of amyloid-β peptides from the serum into the central nervous system, where they bound to neurons.

CONCLUSION

Slit2 increases vessel density and permeability in the brains of transgenic mice. Thus, Slit2 induces numerous changes in brain vessels and the barrier system.

Slit-Robo signaling induces malignant transformation through Hakai-mediated E-cadherin degradation during colorectal epithelial cell carcinogenesis

The Slit family of guidance cues binds to Roundabout (Robo) receptors and modulates cell migration. We report here that ectopic expression of Slit2 and Robo1 or recombinant Slit2 treatment of Robo1-expressing colorectal epithelial carcinoma cells recruited an ubiquitin ligase Hakai for E-cadherin (E-cad) ubiquitination and lysosomal degradation, epithelial-mesenchymal transition (EMT), and tumor growth and liver metastasis, which were rescued by knockdown of Hakai. In contrast, knockdown of endogenous Robo1 or specific blockade of Slit2 binding to Robo1 prevented E-cad degradation and reversed EMT, resulting in diminished tumor growth and liver metastasis. Ectopic expression of Robo1 also triggered a malignant transformation in Slit2-positive human embryonic kidney 293 cells. Importantly, the expression of Slit2 and Robo1 was significantly associated with an increased metastatic risk and poorer overall survival in colorectal carcinoma patients. We conclude that engagement of Robo1 by Slit2 induces malignant transformation through Hakai-mediated E-cad ubiquitination and lysosomal degradation during colorectal epithelial cell carcinogenesis.

Repetitive hypoxia extends endogenous neurovascular protection for stroke

OBJECTIVE

Brief systemic hypoxia protects the rodent brain from subsequent ischemic injury, although the protection wanes within days. We hypothesized that the duration of ischemic tolerance could be extended from days to months by repeated intermittent hypoxia of varying magnitude and duration.

METHODS

Infarction volumes following a 60-minute transient middle cerebral artery occlusion were determined in adult male mice 2 days through 8 weeks after completion of a 2-week repetitive hypoxic preconditioning (RHP) protocol. Separate cohorts were studied for the protective effects of RHP on postischemic and cytokine-induced cerebrovascular inflammation, and for potential deleterious effects of the RHP stimulus itself.

RESULTS

RHP protection against transient focal stroke persisted for 8 weeks. Leukocyte adherence to cortical venules was attenuated in response to stroke, as well as following tumor necrosis factor-α administration, indicating that reductions in postischemic inflammation were not secondary to smaller infarct volumes. RHP reduced poststroke leukocyte diapedesis concomitant with a long-lasting downregulation of endothelial adhesion molecule mRNAs, and also reduced postischemic blood--brain barrier permeability to endogenous immunoglobulin G. RHP was without effect on hippocampal CA1 pyramidal cell viability, only transiently elevated hematocrit, and did not affect the magnitude of cerebral blood flow during and after ischemia.

INTERPRETATION

Taken together, our findings reveal a novel form of epigenetic neurovascular plasticity characterized by a prominent anti-inflammatory phenotype that provides protection against stroke many weeks longer than previously established windows of preconditioning-induced tolerance. Translating these endogenous protective mechanisms into therapeutics could afford sustained periods of cerebroprotection in subpopulations of individuals at identified risk for stroke.

Slit2 regulates attractive eosinophil and repulsive neutrophil chemotaxis through differential srGAP1 expression during lung inflammation

Directional migration of leukocytes is an essential step in leukocyte trafficking during inflammatory responses. However, the molecular mechanisms governing directional chemotaxis of leukocytes remain poorly understood. The Slit family of guidance cues has been implicated for inhibition of leuocyte migration. We report that Clara cells in the bronchial epithelium secreted Slit2, whereas eosinophils and neutrophils expressed its cell-surface receptor, Robo1. Compared to neutrophils, eosinophils exhibited a significantly lower level of Slit-Robo GTPase-activating protein 1 (srGAP1), leading to activation of Cdc42, recruitment of PI3K to Robo1, enhancment of eotaxin-induced eosinophil chemotaxis, and exaggeration of allergic airway inflammation. Notably, OVA sensitization elicited a Slit2 gradient at so-called bronchus-alveoli axis, with a higher level of Slit2 in the bronchial epithelium and a lower level in the alveolar tissue. Aerosol administration of rSlit2 accelerated eosinophil infiltration, whereas i.v. administered Slit2 reduced eosinophil deposition. In contrast, Slit2 inactivated Cdc42 and suppressed stromal cell-derived factor-1α-induced chemotaxis of neutrophils for inhibiting endotoxin-induced lung inflammation, which were reversed by blockade of srGAP1 binding to Robo1. These results indicate that the newly identified Slit2 gradient at the bronchus-alveoli axis induces attractive PI3K signaling in eosinophils and repulsive srGAP1 signaling in neutrophils through differential srGAP1 expression during lung inflammation.

Neutrophil elastase and neurovascular injury following focal stroke and reperfusion

Neutrophil elastase (NE) degrades basal lamina and extracellular matrix molecules, and recruits leukocytes during inflammation; however, a basic understanding of the role of NE in stroke pathology is lacking. We measured an increased number of extravascular NE-positive cells, as well as increased levels of tissue elastase protein and activity, following transient middle cerebral artery occlusion (tMCAo). Both pharmacologic inhibition of NE with ZN200355 (ZN), and genetic deletion of NE, significantly reduced infarct volume, blood-brain barrier disruption, vasogenic edema, and leukocyte-endothelial adherence 24 h after tMCAo. ZN also reduced infarct volume in MMP9-null mice following tMCAo. There were, however, no reductions in infarct volume or vasogenic edema in NE-null mice in two models of permanent middle cerebral artery occlusion. Our findings confirm the involvement of NE in neurovascular stroke pathology, when reperfusion allows neutrophils access to vulnerable brain, with pharmacologic or genetic inhibition of NE being both neuro- and vasculo-protective in this setting.