Abstract Body: Introduction. VWF is an endothelial protein with known roles in hemostasis and thrombosis. We previously demonstrated abnormal deposition of VWF in the mural layer of leptomeningeal collateral arterioles (LMCs) during flow-induced outward remodeling. Additionally, LMC remodeling was attenuated in VWF KO mice, suggesting a modulating role for VWF. We now test the hypothesis that intramural VWF potentiates LMC remodeling in response to sustained increased luminal flow.
Methods. VWF protein was infused into the cisterna magna (CM) of WT and VWF KO C57BL/6 mice (3-7 mos females) to deliver VWF to the perivascular space around the leptomeningeal arteries (2.5 mg/ml at 1 ul/min; 5-7ul total). To confirm successful delivery of VWF to the wall of the leptomeningeal vessels, brain surface preparations containing the cortical leptomeningeal vessels were “planed off” and evaluated for VWF and smooth muscle actin (SMA) immunofluorescence at one hour after VWF infusion (cohort 1). In a subsequent experiment, right common carotid artery ligation (rCCAL) was performed on VWF KO and WT mice to induce increased flow in collateral vessels supplying the right MCA territory (cohort 2). VWF or vehicle was injected via CM at 16 hours after the rCCAL. At 3 days post-rCCAL, the intact leptomeningeal vessel preparations were evaluated by immunofluorescence (Ki67 & SMA) and morphometric analyses.
Results. [Cohort 1] WT and VWF KO mice demonstrated exogenous VWF protein surrounding the leptomeningeal vessels and within the mural layer. VWF KO mice were used to distinguish between endogenous and exogenous VWF. [Cohort 2] At 3 days, rCCAL induced endothelial cell proliferation (Ki67+) and outward vascular remodeling of collateral vessels supplying rescue flow following carotid ligation. In the VWF infusion group, there was a significant increase in Ki67+ ECs, 14.1 ± 3.1 vs. 5.4 ± 1.2 per mm of vessel of the control group (p = 0.042). In VWF KO mice, VWF infusion also increased the number of Ki67+ ECs, showing 18.3 ± 3.2 vs. 6.1 ± 2.8 per mm of vessel in the control group (p < 0.0001). In both WT and VWF KO mice, VWF infusion promoted non-uniform LMC remodeling.
Conclusions. Our study demonstrates that VWF in the vascular wall of LMCs potentiates the adaptive response to increased luminal flow, albeit with irregular resulting vascular morphology. These finding suggest that the presence of intramural VWF may contribute to abnormal vascular remodeling in the brain.