Vascular basement membrane laminins modulate functional zonation of cerebral microvessels

We investigated whether basement membrane (BM) laminins influence regional differences in the vasculature by performing single-cell RNA sequencing on cerebral blood vessels from mice lacking the major vascular laminins in endothelial and smooth muscle BMs, laminin α4 (<i>Lama4</i>^{<i>^-/-</i>} ) and laminin α5 (<i>Tek-cre:Lama5</i>^{<i>^-/-</i>}), and wild-type littermates. Our dataset expands existing cerebral vascular transcriptomic profiles and reveals that <i>Lama4</i>^{^<i>-/-</i>} endothelial cells exhibit increased arterial marker expression and reduced postcapillary venule identity. In vitro and in vivo studies indicated that compensatory upregulation of laminin α5 in <i>Lama4</i>^{<i>^-/-</i>} vessels enhances expression of junctional proteins (<i>Ocln</i>, <i>Cldn5</i>) and promotes vessel contractility via increased expression of contractile molecules in mural cells. Additionally, loss of <i>Lama4</i> upregulated expression of large artery markers (<i>Gja4</i>, <i>Dll4</i>, <i>Tgfb2</i>) and resulted in elevated autotaxin (<i>Enpp2</i>) levels, a key enzyme in lysophosphatidic acid production implicated in stroke. Accordingly, <i>Lama4</i>^{<i>^-/-</i>} mice exhibited worsened stroke outcomes, driven not by immune infiltration or junctional defects, but by increased vascular permeability likely mediated by autotaxin and/or activation of resident myeloid cells. Our data suggest that laminin α4/α5 ratios in vascular BMs affect functional zonation between arterioles, capillaries and postcapillary venules by modulating metabolic pathways in endothelial and mural cells, and indirectly influencing resident myeloid cells.