Project description:The blood-brain barrier (BBB) consists of specific physical barriers, enzymes and transporters, which together maintain the necessary extracellular environment of the central nervous system (CNS). The main physical barrier is found in the CNS endothelial cell, and depends on continuous complexes of tight junctions combined with reduced vesicular transport. Other possible constituents of the BBB include extracellular matrix, astrocytes and pericytes, but the relative contribution of these different components to the BBB remains largely unknown. Here we demonstrate a direct role of pericytes at the BBB in vivo. Using a set of adult viable pericyte-deficient mouse mutants we show that pericyte deficiency increases the permeability of the BBB to water and a range of low-molecular-mass and high-molecular-mass tracers. The increased permeability occurs by endothelial transcytosis, a process that is rapidly arrested by the drug imatinib. Furthermore, we show that pericytes function at the BBB in at least two ways: by regulating BBB-specific gene expression patterns in endothelial cells, and by inducing polarization of astrocyte end-feet surrounding CNS blood vessels. Our results indicate a novel and critical role for pericytes in the integration of endothelial and astrocyte functions at the neurovascular unit, and in the regulation of the BBB. The brain microvascular fragments were isolated from mice with different genotypes, each represented by 3-4 biological replicates. Genotypes 1-2: Platelet derived growth factor-B (PDGF-B) retention-motif knockout (pdgfbret/ret) represent the pericyte-deficient situation, and the heterozygous mice (pdgfbret/+) are used as controls. Genotypes 3-4: Hypomorphic PDGF-B mutants that rescue pdgfb-/- null mice, in which a one copy of a conditionally silent human PDGF-B transgene targeted to the Rosa 26 locus (R26P) is turned on by endothelial-specific expression of Cre recombinase. In this data set these mice are named as Tie2Cre, R26P+/0, pdgfb-/- (representing the pericyte-deficient situation). Mice wt for pdgfb (pdgfb+/+) and carrying one silent copy of R26P (R26P+/0), are used as controls. Genotype 5: Adult Notch3+/+ wildtype (WT).
Project description:Purpose: Pericytes, the mural cells of blood microvessels, have come into focus as regulators of microvascular development and function, but due to paucity of defining markers, the identification and functional characterization of PC remain problematic, and reported data are often controversial. Here, we used a new approach for the isolation of mural cell from mouse brain in combination with RNA-sequencing (RNA-seq) and previously published vascular transcriptome data to assemble a state-of-the-art catalogue of brain mural cell-enriched gene transcripts. Methods: We isolated double positive cells from the brain of Pdgfrb-eGFP/NG2-DsRed transgenic mice using FACS. Cells were lysed, RNA extracted and sequenced with next-generation sequencing (NGS). For comparison, we also determined the transcriptome of brain microvascular fragments (containing both endothelial cells and mural cells) isolated by mechanical tissue disintegration, collagenase digestion and immune-panning using anti-CD31 antibodies coupled to magnetic beads. The reads were aligned to the Ensembl mouse gene assembly (NCBIM37) using Tophat2 software (version 2.0.4). The duplicated reads were removed using the picard tool (version 1.92). To identify the genes significantly enriched in the pericyte samples as compared with microvascular samples, statistical tests were performed using the Cufflinks tool (version 2.2.1) Results: The result showed that mRNA transcripts representing 856 different genes were enriched more than two-fold in FACS isolated Pdgfrb-eGFP/NG2-DsRed double positive cells compared with whole microvascular fragments (False Discovery Rate < 0.05) The RNA from three FACS sorted brain mural cell samples and three whole brain microvascular samples isolated from three animals were processed and sequenced on the Illumina HiSeq 2500 platform in the sequencing facility in Uppsala University.