Positive and Negative Spatial Gradients of High Wall Shear Stress Have Different Effects on Endothelial Gene Expression

Intracranial aneurysms tend to form at bifurcation apices, where flow impingement causes high frictional force (or wall shear stress, WSS) and flow acceleration and deceleration that create positive and negative streamwise gradients in WSS (WSSG), respectively. In vivo, intracranial aneurysms initiate under high WSS and positive WSSG. Little is known about the responses of endothelial cells (ECs) to either positive or negative WSSG under high WSS conditions. We used cDNA microarrays to profile EC gene expression exposed to positive WSSG vs. negative WSSG for 24 hours in a flow chamber with converging and diverging channels, respectively. WSS varied between 3.5 and 28.4 Pa in each gradient channel. GO and biological pathway analysis indicated that positive WSSG favored proliferation, apoptosis, and extracellular matrix processing while decreasing expression of pro-inflammatory genes. A subset of characteristic genes was validated using qPCR: Genes for ADAMTS1, CKAP2 and NCEH1 had higher expression under positive WSSG compared to negative WSSG while TAGLN, THBS1, VCAM1, CCL2, and CSF2 had lower expression. To determine if these patterns of expression are also exhibited in vivo, we tested whether the extracellular matrix related protein ADAMTS1 and proliferation were modulated by positive WSSG during intracranial aneurysm initiation. An aneurysm was induced at the basiliar terminus in rabbits by bilateral carotid ligation. WSSG at the bifurcation was determined by computational fluid dynamic simulations from 3D angiography and mapped on immunofluorescence staining for ADAMTS1 and the proliferation marker, Ki-67. Endothelial ADAMTS1 protein and Ki-67 were significantly higher in regions with positive WSSG compared to adjacent sites where WSSG was negative. Our results indicate that WSSG can elicit distinct gene expression profiles in ECs. Increased matrix processing and high levels of proliferation under positive WSSG could contribute to intracranial aneurysm initiation by causing transient gaps in the endothelium or disrupting EC signals to smooth muscle cells.

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Dolan JM, Meng H, Sim FJ, Kolega J