Abstract 42: Von Willebrand Factor (vwf) Is Required For Outward Remodeling Of Leptomeningeal Collateral Arterioles Following Stroke.

Introduction: VWF is an endothelial glycoprotein with known roles in vascular hemostasis and thrombosis. We previously showed increased expression of VWF in leptomeningeal collateral arterioles (LMCs) that underwent outward remodeling in the post-stroke brain. Interestingly, recent studies indicate that VWF may act as a novel smooth muscle mitogen and contribute to smooth muscle proliferation. The present study tested the hypothesis that VWF is required for LMC outward remodeling in the post-stroke brain. Methods: Permanent distal middle cerebral artery occlusion (pdMCAO) was performed in C57BL6 WT mice (cohort 1; 4 mos, males) or VWF KO and WT mice (cohort 2; 10 mos, males). At 3 days after pdMCAO, the intact leptomeningeal vasculature was “planed off” for VWF immunofluorescence and morphometric analyses of LMCs and distalmost arterioles (DMAs) from the ipsilateral (ischemic) and contralateral hemispheres. VWF density in LMCs was normalized to the connected DMAs and presented as a fold difference. In a subset of samples, VWF location in LMCs was imaged by super-resolution microscopy (STED imaging, Nikon). Results: At 3 days post-stroke, WT mice of cohort 1 demonstrated significantly increased VWF expression in ipsilateral LMCs (5.34 ipsi LMC vs 1.89 contra LMCs; p<0.01, 35-50 vessels from 7 mice). Cohort 2 was used to evaluate the effect of VWF expression on LMC remodeling. Mean diameter of DMAs were similar between VWF KO and WT mice at 3 days post-stroke (32.6 ± 1.1 μm vs 33.3 ± 0.8 μm, p=NS). The LMC diameter was significantly increased in the WT mice (39.7 ± 1.7 μm), however, it was not significantly altered in VWF KO mice (35.1 ± 1.4 μm). Lastly, super-resolution imaging demonstrated increased VWF in the endothelial layer as well as in the smooth muscle layers of remodeled LMCs. Notably, VWF in the smooth muscle layer was evident as long “pillars” running perpendicular to the vessel lumen and extending several microns into the smooth muscle layer. Conclusions: Our study revealed novel evidence for the essential role of VWF in the outward remodeling of LMCs in the post-stroke brain. Our findings also provide direct evidence for VWF within the smooth muscle layer, supporting the potential role of VWF as a critical smooth muscle mitogen in LMC remodeling.