Development of integrins in the vasculature of germinal matrix, cerebral cortex, and white matter of fetuses and premature infants.

Germinal matrix (GM) vasculature is selectively vulnerable to hemorrhage in premature infants during the first 48 hr of life. This is attributed to rapid angiogenesis of this brain region, resulting in formation of nascent vessels that show a paucity of pericytes and immaturity of extracellular matrix. Integrins are key regulators of angiogenesis and contribute to stabilization of cerebral vasculature by providing endothelial- and astrocyte-matrix adhesion. Therefore, we asked whether GM exhibited a distinct regional pattern of integrin expression that was dissimilar from that of the cerebral cortex and white matter in human fetuses and premature infants. To this end, we measured protein and gene expression of integrins in the GM, cortex, and white matter of human fetuses (15-22 weeks), premature infants (23-35 weeks), and mature infants (36-40 weeks). We found that protein levels of alpha5beta1 integrin were greater in the GM than in the cortex or white matter by 1.6-fold for both fetuses and premature infants. alpha5beta1 integrin mRNA expression was higher in the GM than in the cortex or white matter by 2-fold for fetuses but not for premature infants. alphaVbeta3, alphaVbeta5, alphaVbeta8, and alpha4beta1 integrin expression were comparable among GM, cortex, and white matter in fetuses and premature infants. Because alpha5beta1 integrin is a central regulator of angiogenesis, its elevation in the GM of fetuses and premature infants indicates that this might be a key activator of endothelial proliferation in this brain region. We speculate that selective alpha5beta1 integrin inhibition might suppress angiogenesis in the GM and thus prevent brain hemorrhage in premature infants. (c) 2009 Wiley-Liss, Inc.