The contribution of CXCL12-expressing radial glia cells to neuro-vascular patterning during human cerebral cortex development.

This study was conducted on human developing brain by laser confocal and transmission electron microscopy (TEM) to make a detailed analysis of important features of blood-brain barrier (BBB) microvessels and possible control mechanisms of vessel growth and differentiation during cerebral cortex vascularization. The BBB status of cortex microvessels was examined at a defined stage of cortex development, at the end of neuroblast waves of migration, and before cortex lamination, with BBB-endothelial cell markers, namely tight junction (TJ) proteins (occludin and claudin-5) and influx and efflux transporters (Glut-1 and P-glycoprotein), the latter supporting evidence for functional effectiveness of the fetal BBB. According to the well-known roles of astroglia cells on microvessel growth and differentiation, the early composition of astroglia/endothelial cell relationships was analyzed by detecting the appropriate astroglia, endothelial, and pericyte markers.

Plasma membrane-derived microvesicles released from tip endothelial cells during vascular sprouting.

During human foetal brain vascularization, activated CD31+/CD105+ endothelial cells are characterized by the emission of filopodial processes which also decorate the advancing tip of the vascular sprout. Together with filopodia, both the markers also reveal a number of plasma membrane-derived microvesicles (MVs) which are concentrated around the tip cell tuft of processes. At this site, MVs appear in tight contact with endothelial filopodia and follow these long processes, advancing into the surrounding neuropil to a possible cell target.

In vivo assessment of epichlorohydrin effects: the chorioallantoic membrane model.

Background: Previous studies on the effects of the epichlorohydrin (ECH) epoxide demonstrated this compound's toxicity and mutagenicity and suggested a carcinogenic activity also in humans. To gain a better understanding of ECH effects in vivo, the substance was tested on developing tissues utilizing the chick embryo chorioallantoic membrane (CAM) assay.

Material/methods: Gelatin sponges adsorbed with ECH were implanted onto nine-day CAMs.

Involvement of metalloprotease-2 in the development of human brain microvessels.

The involvement of the metalloprotease-2 (MMP-2) in vessel development was investigated in the human telencephalon by double immunoreactions with antibodies to the enzyme, latent (proMMP-2) and active (aMMP-2) forms, and an antibody against collagen type IV, a constitutive component of the extracellular matrix (ECM) of the vessel basal lamina. MMP-2 is expressed in both 12- and 18-week telencephalic vessels, the proenzyme being mainly localised in endothelial cells and the active form prevailing in alpha-actin-reactive periendothelial cells identified as pericytes. Endothelial cells intensely positive for aMMP-2 were revealed in some microvessels and appeared locally associated with discontinuities of the collagen basal lamina.

Immunolocalization of tight junction proteins in the adult and developing human brain.

The formation of endothelial tight junctions (TJs) is crucial in blood-brain barrier (BBB) differentiation, and the expression and targeting of TJ-associated proteins mark the beginning of BBB functions. Using confocal microscopy, this study analyzed endothelial TJs in adult human cerebral cortex and the fetal telencephalon and leptomeninges in order to compare the localization of two TJ-associated transmembrane proteins, occludin and claudin-5. In the arterioles and microvessels of adult brain, occludin and claudin-5 form continuous bands of endothelial immunoreactivity.

Effects of 6-aminonicotinamide gliotoxin on blood-brain barrier differentiation in the chick embryo cerebellum.

The hypothesis of astroglial cell involvement in prenatal setting up of the blood-brain barrier (BBB) has been examined by producing glial degeneration in cerebellum of chicken embryos submitted to the action of gliotoxin 6-aminonicotinamide (6-AN), which was applied onto the embryo chorioallantoic membrane during both early and late embryonic development. The effects of 6-AN on the cerebellum astroglial cells and microvessels were analysed under the light microscope by immunostaining for 3CB2 (chick-specific glial marker) and HT7 (chick-specific marker of BBB-provided brain endothelia), under the electron microscope, as well as by the vascular permeability tracer horseradish peroxidase. The results, showing good suitability of the 6-AN model also when applied in early embryonic development, demonstrated a correlation between perivascular glia depletion and endothelial barrier impairment and suggested that astroglia play a role in the BBB prenatal differentiation.

Differential expression of connexin43 in foetal, adult and tumour-associated human brain endothelial cells.

Connexin43 (Cx43), the main protein constituting the gap junctions between astrocytes, has previously been demonstrated in endothelial cells of somatic vessels where the intercellular coupling that it provides plays a role in endothelial proliferation and migration. In this study, Cx43 expression was analysed in human brain microvascular endothelial cells of the cortical plate of 18-week foetal telencephalon, in adult cerebral cortex and glioma (astrocytomas). The study was carried out by immunocytochemistry utilizing a Cx43 monoclonal antibody and a polyclonal antibody anti-GLUT1 (glucose transporter isoform 1) to identify the endothelial cells and to localize Cx43.

VEGF expression is developmentally regulated during human brain angiogenesis.

Vascular endothelial growth factor (VEGF) is a potent angiogenic factor working as an endothelial cell-specific mitogen and exerting a trophic effect on neurons and glial cells, both these activities being essential during central nervous system vascularisation, development and repair. The vascularisation of human telencephalon takes place by means of an angiogenic mechanism, which starts at the beginning of corticogenesis and actively proceeds up to the last neuronal migration, when the basic scheme of the vascular network has been drawn. Our study focused on VEGF during this critical developmental period with the aim of identifying the cells that express VEGF and of correlating the events of angiogenesis with the main events of cerebral cortex formation.

Expression of P-glycoprotein in human cerebral cortex microvessels.

P-Glycoprotein (P-gp) is an ATP-dependent efflux transporter that extrudes non-polar molecules, including cytotoxic substances and drugs, from the cells. It was initially found in cancer cells and then was shown to be a normal component of complex transport systems working at the blood-brain barrier (BBB). Previous studies have demonstrated that, in the brain, P-gp is localized on the luminal plasmalemma of BBB endothelial cells and that it may interact with the caveolar compartment of these cells.

Developmental changes of HT7 expression in the microvessels of the chick embryo brain.

The neurothelin/HT7 antigen is a chick-specific, cell-surface glycoprotein expressed by the brain endothelial cells and widely utilized in experimental studies as a marker of barrier-provided vessels. Previous immunohistochemical studies have demonstrated that HT7 is already expressed in the embryonic brain vessels and that it is first detectable on embryonic day 10 and developmentally regulated. In the present study, the vascular expression of HT7 was investigated in different regions of the central nervous system from the 5th day right up to the latest stage of the chick embryo development.