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Background and Purpose-Increased mortality after stroke is associated with brain edema formation and high plasma levels of the acute phase reactant C-reactive protein (CRP). The aim of this study was to examine whether CRP directly affects blood-brain barrier stability and to analyze the underlying signaling pathways. Methods-We used a cell coculture model of the blood-brain barrier and the guinea pig isolated whole brain preparation. Results-We could show that CRP at clinically relevant concentrations (10 to 20 g/mL) causes a disruption of the blood-brain barrier in both approaches. The results of our study further demonstrate CRP-induced activation of surface Fc␥ receptors CD16/32 followed by p38-mitogen-activated protein kinase-dependent reactive oxygen species formation by the NAD(P)H-oxidase. The resulting oxidative stress increased myosin light chain kinase activity leading to an activation of the contractile machinery. Blocking myosin light chain phosphorylation prevented the CRP-induced blood-brain barrier breakdown and the disruption of tight junctions. Conclusions-Our data identify a previously unrecognized mechanism linking CRP and brain edema formation and present a signaling pathway that offers new sites of therapeutic intervention.

The LDL family of receptors and its member LRP1 have classically been associated with a modulation of lipoprotein metabolism. Current studies, however, indicate diverse functions for this receptor in various aspects of cellular activities, including cell proliferation, migration, differentiation and survival. LRP1 is essential for normal neuronal function in the adult CNS, whereas the role of LRP1 in development remained unclear. Previously we have observed an upregulation of LewisX (LeX) glycosylated LRP1 in the stem cells of the developing cortex and demonstrated its importance for oligodendrocyte differentiation. In the current study we show that LeX-glycosylated LRP1 is also expressed in the stem cell compartment of the developing spinal cord and has broader functions in the developing CNS. We have investigated the basic properties of LRP1 conditional knockout on the neural stem/progenitor cells (NSPCs) from the cortex and the spinal cord, created by means of Cre-loxp mediated recombination in vitro. The functional status of LRP1-deficient cells has been studied using proliferation, differentiation and apoptosis assays. LRP1 deficient NSPCs from both CNS regions demonstrated altered differentiation profiles. Their differentiation capacity towards oligodendrocyte progenitor cells (OPCs), mature oligodendrocytes and neurons was reduced. In contrast, astrocyte differentiation was promoted. Moreover, LRP1 deletion had a negative effect on NSPCs proliferation and survival. Our observations suggest that LRP1 facilitates NSPCs differentiation via interaction with ApoE. Upon ApoE4 stimulation wild type NSPCs generated more oligodendrocytes, but LRP1 knockout cells showed no response. The effect of ApoE seems to be independent of cholesterol uptake, but is rather mediated by downstream MAPK and Akt activation.

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The blood-brain barrier (BBB) facilitates amyloid-b (Ab) exchange between the blood and the brain. Here, we found that the cellular prion protein (PrP c ), a putative receptor implicated in mediating Ab neurotoxicity in Alzheimer's disease (AD), participates in Ab transcytosis across the BBB. Using an in vitro BBB model, [ 125 I]-Ab 1À40 transcytosis was reduced by genetic knockout of PrP c or after addition of a competing PrP c -specific antibody. Furthermore, we provide evidence that PrP c is expressed in endothelial cells and, that monomeric Ab 1À40 binds to PrP c . These observations provide new mechanistic insights into the role of PrP c in AD.