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 (Lama4^-/- ) and laminin α5 (Tek-cre:Lama5^-/-), and wild-type littermates. Our dataset expands existing cerebral vascular transcriptomic profiles and reveals that Lama4^-/- 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 Lama4^-/- vessels enhances expression of junctional proteins (Ocln, Cldn5) and promotes vessel contractility via increased expression of contractile molecules in mural cells. Additionally, loss of Lama4 upregulated expression of large artery markers (Gja4, Dll4, Tgfb2) and resulted in elevated autotaxin (Enpp2) levels, a key enzyme in lysophosphatidic acid production implicated in stroke. Accordingly, Lama4^-/- 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.