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The blood-brain barrier after stroke: Structural studies and the role of transcytotic vesicles.

ABSTRACT: Blood-brain barrier breakdown worsens ischaemic damage, but it is unclear how molecules breach the blood-brain barrier in vivo. Using the obese ob/ob mouse as a model of enhanced blood-brain barrier breakdown, we investigated how stroke-induced structural changes to the microvasculature related to blood-brain barrier permeability. Ob/ob mice underwent middle cerebral artery occlusion, followed by 4 or 24 h reperfusion. Blood-brain barrier integrity was assessed using IgG and horseradish peroxidase staining, and blood-brain barrier structure by two-dimensional and three-dimensional electron microscopy. At 4 and 24 h post-stroke, ob/ob mice had increased ischaemic damage and blood-brain barrier breakdown compared to ob/- controls, and vessels from both genotypes showed astrocyte end-foot swelling and increased endothelial vesicles. Ob/ob mice had significantly more endothelial vesicles at 4 h in the striatum, where blood-brain barrier breakdown was most severe. Both stroke and genotype had no effect on tight junction structure visualised by electron microscopy, or protein expression in isolated microvessels. Astrocyte swelling severity did not correlate with tissue outcome, being unaffected by genotype or reperfusion times. However, the rare instances of vessel lumen collapse were always associated with severe astrocyte swelling in two-dimensional and three-dimensional electron microscopy. Endothelial vesicles were therefore the best spatial and temporal indicators of blood-brain barrier breakdown after cerebral ischaemia.

SUBMITTER: Haley MJ

PROVIDER: S-EPMC5322831 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Incomplete recovery of blood-brain barrier (BBB) function contributes to stroke outcomes. How the BBB recovers after stroke remains largely unknown. Emerging evidence suggests that epigenetic factors play a significant role in regulating post-stroke BBB recovery. This study aimed to evaluate the epigenetic and transcriptional profile of cerebral microvessels after thromboembolic (TE) stroke to define potential causes of limited BBB recovery. RNA-sequencing and reduced representation bisulfite sequencing (RRBS) analyses were performed using microvessels isolated from young (6 months) and old (18 months) mice seven days poststroke compared to age-matched sham controls. DNA methylation profiling of poststroke brain microvessels revealed 11,287 differentially methylated regions (DMR) in old and 9818 DMR in young mice, corresponding to annotated genes. These DMR were enriched in genes encoding cell structural proteins (e.g., cell junction, and cell polarity, actin cytoskeleton, extracellular matrix), transporters and channels (e.g., potassium transmembrane transporter, organic anion and inorganic cation transporters, calcium ion transport), and proteins involved in endothelial cell processes (e.g., angiogenesis/vasculogenesis, cell signaling and transcription regulation). Integrated analysis of methylation and RNA sequencing identified changes in cell junctions (occludin), actin remodeling (ezrin) as well as signaling pathways like Rho GTPase (RhoA and Cdc42ep4). Aging as a hub of aberrant methylation affected BBB recovery processes by profound alterations (hypermethylation and repression) in structural protein expression (e.g., claudin-5) as well as activation of a set of genes involved in endothelial to mesenchymal transformation (e.g., Sox9, Snai1), repression of angiogenesis and epigenetic regulation. These findings revealed that DNA methylation plays an important role in regulating BBB repair after stroke, through regulating processes associated with BBB restoration and prevalently with processes enhancing BBB injury.

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The blood-brain barrier after stroke: Structural studies and the role of transcytotic vesicles.

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