Immunolocalization of tight junction proteins in blood vessels in human germinal matrix and cortex

Abstract

Brain development occurs in a specialized environment maintained by a blood-brain barrier (BBB). An important structural element of the BBB is the endothelial tight junction (TJ). TJs are present during the embryonic period, but BBB impermeability accrues over an extended gestational interval. In studies of human premature infants, we used immunomicroscopy to determine if amounts of the TJ proteins ZO-1, claudin and occludin increase with gestational age in vessels of germinal matrix (GM) and cortex. By 24 weeks postconception (PC), TJ proteins were present in both GM and cortical vessels, but immunoreactivity in the GM of the youngest subjects was less than in older subjects. At 24 weeks PC, TJ protein immunoreactivity in GM vessels was less than in cortical vessels suggesting that TJ maturation progresses along a superficial to deep brain axis. This concept correlates with conclusions from previous analyses of the expression of brain endothelial cell alkaline phosphatase (AP) activity. AP appears in cortical vessels before appearing in deep white matter and GM vessels. Together, these data indicate that differentiation of some functional specializations is still in progress in GM vessels during the third trimester. This maturation could relate to the pathogenesis of germinal matrix hemorrhage-intraventricular hemorrhage.

Differential expression of the bone and the liver tissue non-specific alkaline phosphatase isoforms in brain tissues

“…We have shown here that brain endothelial cells, either of mouse (pMBMEC) or human (hCMEC/D3) origin, specifically express the TNAP isoform driven by the promoter specific for bone exon 1A. A role of TNAP in blood-brain-barrier (BBB) integrity endowed with transport systems or in a structural BBB element such as tight junctions is supported by data from the literature (Anstrom et al 2007;Calhau et al 2002;Risau et al 1986). In addition, as observed for other BBB markers (Lyck et al 2009), our data indicate the strong down-regulation of TNAP expression when pMBMEC mouse brain endothelial cells are maintained in culture for a few days, whereas in the human hCMEC/D3 endothelial cell line that retains its BBB characteristics in vitro (Weksler et al 2005), we have detected bone TNAP transcripts under various culture conditions (data not shown).…”

Vessel maturation schedule determines vulnerability to neuronal injuries of prematurity

“…17,21). It is noteworthy that tight-junction expression is also relatively delayed in human GM vessels (27) (but also see ref. 28 reporting no difference in tight-junction expression) and that their pericyte coverage also lags behind that of other cerebral vessels (29).…”

The gut microbiota influences blood-brain barrier permeability in mice

“…This implies that claudin-5 expression continues to increase during the postnatal period in offspring of pathogen-free mothers but not in offspring of germ-free mice. Although claudin-5 expression is present from early intrauterine life in the human brain, it is localized mostly in the endothelial cytoplasm and shifts toward the endothelial border during development to form tight junctions (32, 33). Furthermore, claudin-5 knockout mice appear to develop normally during intrauterine life with morphologically normal blood vessels but have a BBB impairment associated with increased permeability to small molecules (34).…”