Laminin Beta 2 Is Localized at the Sites of Blood–Brain Barrier and Its Disruption Is Associated With Increased Vascular Permeability, Histochemical, and Transcriptomic Study

Heterotrimeric extracellular matrix proteins laminins are mostly deposited at basal membranes and are important in repair and neoplasia. Here, we localize laminin beta 2 (<i>LAMB2</i>) at the sites of blood-brain barrier (BBB). Microvasculature (MV) of normal brain is endowed with complete <i>LAMB2</i> coverage. In contrast, its cognate protein laminin beta 1 (<i>LAMB1</i>) is absent in MV of normal brain but emerges at the sprouting tip of a growing vessels. Similarly, vascular proliferation in high-grade gliomas (HGG) is accompanied by marked overexpression of <i>LAMB1</i>, whereas <i>LAMB2</i> shows deficient deposition. We find that many brain pathologies with presence of post-gadolinium enhancement (PGE) on magnetic resonance imaging (MRI) show disruption of <i>LAMB2</i> vascular ensheathment. Inhibition of vascular endothelial growth factor signaling in HGG blocks angiogenesis, suppresses PGE in HGG, prevents expression of <i>LAMB1</i>, and restores LAMB2 vascular coverage. Analysis of single-cell RNA sequencing (scRNA-seq) databases shows that in quiescent brain <i>LAMB2</i> is predominantly expressed by BBB-associated pericytes (PCs) and endothelial cells (ECs), whereas neither cell types produce <i>LAMB1</i>. In contrast, in HGG, both <i>LAMB1</i> and <i>2</i> are overexpressed by endothelial precursor cells, a phenotypically unique immature group, specific to proliferating hyperplastic MV.