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Blast exposure elicits blood-brain barrier disruption and repair mediated by tight junction integrity and nitric oxide dependent processes.

ABSTRACT: Mild blast-induced traumatic brain injury (TBI) is associated with blood-brain barrier (BBB) disruption. However, the mechanisms whereby blast disrupts BBB integrity are not well understood. To address this issue BBB permeability to peripherally injected 14C-sucrose and 99mTc-albumin was quantified in ten brain regions at time points ranging from 0.25 to 72?hours. In mice, repetitive (2X) blast provoked BBB permeability to 14C-sucrose that persisted in specific brain regions from 0.25 to 72?hours. However, 99mTc-albumin revealed biphasic BBB disruption (open-closed-open) over the same interval, which was most pronounced in frontal cortex and hippocampus. This indicates that blast initiates interacting BBB disruption and reparative processes in specific brain regions. Further investigation of delayed (72?hour) BBB disruption revealed that claudin-5 (CLD5) expression was disrupted specifically in the hippocampus, but not in dorsal striatum, a brain region that showed no blast-induced BBB permeability to sucrose or albumin. In addition, we found that delayed BBB permeability and disrupted CLD5 expression were blocked by the nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester (L-NAME). These data argue that latent nitric oxide-dependent signaling pathways initiate processes that result in delayed BBB disruption, which are manifested in a brain-region specific manner.

SUBMITTER: Logsdon AF

PROVIDER: S-EPMC6063850 | biostudies-literature | 2018 Jul

REPOSITORIES: biostudies-literature

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Project description:Disruption of the blood-brain barrier (BBB) results in cerebral edema formation, which is a major cause for high mortality after traumatic brain injury (TBI). As anesthetic care is mandatory in patients suffering from severe TBI it may be important to elucidate the effect of different anesthetics on cerebral edema formation. Tight junction proteins (TJ) such as zonula occludens-1 (ZO-1) and claudin-5 (cl5) play a central role for BBB stability. First, the influence of the volatile anesthetics sevoflurane and isoflurane on in-vitro BBB integrity was investigated by quantification of the electrical resistance (TEER) in murine brain endothelial monolayers and neurovascular co-cultures of the BBB. Secondly brain edema and TJ expression of ZO-1 and cl5 were measured in-vivo after exposure towards volatile anesthetics in native mice and after controlled cortical impact (CCI). In in-vitro endothelial monocultures, both anesthetics significantly reduced TEER within 24 hours after exposure. In BBB co-cultures mimicking the neurovascular unit (NVU) volatile anesthetics had no impact on TEER. In healthy mice, anesthesia did not influence brain water content and TJ expression, while 24 hours after CCI brain water content increased significantly stronger with isoflurane compared to sevoflurane. In line with the brain edema data, ZO-1 expression was significantly higher in sevoflurane compared to isoflurane exposed CCI animals. Immunohistochemical analyses revealed disruption of ZO-1 at the cerebrovascular level, while cl5 was less affected in the pericontusional area. The study demonstrates that anesthetics influence brain edema formation after experimental TBI. This effect may be attributed to modulation of BBB permeability by differential TJ protein expression. Therefore, selection of anesthetics may influence the barrier function and introduce a strong bias in experimental research on pathophysiology of BBB dysfunction. Future research is required to investigate adverse or beneficial effects of volatile anesthetics on patients at risk for cerebral edema.

Project description:Rationale: Endothelial cells (ECs) line the inner surface of continuous capillaries and form a permselective barrier between blood and tissues to limit paracellular fluid and solute flux. The capillary barrier is maintained by intercellular tight junctions (TJs) which are regulated, in part, by differential activity of small GTPases. Tumor necrosis factor (TNF) causes TJ disassembly in a process dependent upon NF-κB-mediated gene expression. Activated (GTP-bound) RhoB has been identified as a downstream effector of TNF-induced leak both through Rho-associated coiled-coil kinase-mediated phosphorylation of RelA, enhancing TNF-induced NF-κB-mediated gene activation, and through sequestration of Rac1 away from the cell junction, preventing barrier restoration. To date, no TNF-induced, RhoB-selective GTP exchange factor (GEF) has been identified in ECs. Objective: Identify a TNF-induced RhoB specific GEF in capillary ECs. Method and Results: human dermal microvascular ECs (HDMECs) were used because they form TJs. Candidate GEFs were identified by whole transcriptome profiling of HDMECs with or without TNF stimulation. Fifty-seven of 73 known GEFs were expressed in HDMECs and 17 were significantly upregulated by TNF. Functional impact of each of the latter group was assessed by measuring the effects of depletion by short interfering RNA knockdown on TNF-induced reduction of trans-endothelial electrical resistance (TEER) of HDMEC monolayers. Depletions of ArhGEF10 or RhoB or double depletion of ArhGEF10/RhoB similarly decreased TNF-mediated reduction of TEER. ArhGEF10 knockdown prevented TNF-induced disruption of TJ proteins assessed by confocal microscopy. TNF-induced increases in the levels of activated RhoB in HDMEC lysates were markedly reduced with only minimal alterations in RhoA or RhoC activation. Finally, immunoisolated ArhGEF10 selectively catalyzed GTP exchange for GDP in RhoB, but not RhoA or RhoC, in vitro. Conclusion: ArhGEF10 is a TNF-induced RhoB-selective GEF for RhoB in cultured human capillary ECs that contributes to TJ disruption.

Project description:BackgroundSilver nanoparticles (Ag-NPs) can enter the brain and induce neurotoxicity. However, the toxicity of Ag-NPs on the blood-brain barrier (BBB) and the underlying mechanism(s) of action on the BBB and the brain are not well understood.MethodTo investigate Ag-NP suspension (Ag-NPS)-induced toxicity, a triple coculture BBB model of rat brain microvascular endothelial cells, pericytes, and astrocytes was established. The BBB permeability and tight junction protein expression in response to Ag-NPS, NP-released Ag ions, and polystyrene-NP exposure were investigated. Ultrastructural changes of the microvascular endothelial cells, pericytes, and astrocytes were observed using transmission electron microscopy (TEM). Global gene expression of astrocytes was measured using a DNA microarray.ResultsA triple coculture BBB model of primary rat brain microvascular endothelial cells, pericytes, and astrocytes was established, with the transendothelial electrical resistance values >200 Ω·cm(2). After Ag-NPS exposure for 24 hours, the BBB permeability was significantly increased and expression of the tight junction (TJ) protein ZO-1 was decreased. Discontinuous TJs were also observed between microvascular endothelial cells. After Ag-NPS exposure, severe mitochondrial shrinkage, vacuolations, endoplasmic reticulum expansion, and Ag-NPs were observed in astrocytes by TEM. Global gene expression analysis showed that three genes were upregulated and 20 genes were downregulated in astrocytes treated with Ag-NPS. Gene ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis showed that the 23 genes were associated with metabolic processes, biosynthetic processes, response to stimuli, cell death, the MAPK pathway, and so on. No GO term and KEGG pathways were changed in the released-ion or polystyrene-NP groups. Ag-NPS inhibited the antioxidant defense of the astrocytes by increasing thioredoxin interacting protein, which inhibits the Trx system, and decreasing Nr4a1 and Dusp1. Meanwhile, Ag-NPS induced inflammation and apoptosis through modulation of the MAPK pathway or B-cell lymphoma-2 expression or mTOR activity in astrocytes.ConclusionThese results draw our attention to the importance of Ag-NP-induced toxicity on the neurovascular unit and provide a better understanding of its toxicological mechanisms on astrocytes.

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Blast exposure elicits blood-brain barrier disruption and repair mediated by tight junction integrity and nitric oxide dependent processes.

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