Mechanotransduction of interstitial flow modulates vascular smooth muscle cell and fibroblast motility and phenotype in 2-D and 3-D

Vascular lesion formation often occurs in regions where the endothelium has been damaged and the transmural interstitial flow is elevated. Vascular smooth muscle cells (SMCs) and fibroblasts/myofibroblasts (FBs/MFBs) contribute to vascular repair or vascular lesion formation by migrating from the vessel media and adventitia into the site of the injury intima. During the damage period, vascular SMCs and FBs/MFBs are exposed to luminal blood flow (2-dimensional, 2-D) or elevated interstitial flow (3-D). Therefore, we hypothesize that the alterations of fluid flow during vascular injury modulate SMC and FB/MFB phenotype and motility, which may contribute to vascular remodeling and lesion formation.;To test this hypothesis, we first established a 3-D interstitial flow-cell migration system and then through a series of newly-designed experimental methods, we have generated following primary findings: (1) Interstitial flow can promote rat vascular SMC, FB, and MFB motility in collagen gels by upregulation of matrix metalloproteinase-13 (MMP-13) expression; (2) Flow-induced upregulation of MMP-13 is mediated by activation of extracellular signal-regulated kinase 1/2 (ERK1/2) mitogen-activated protein kinase (MAPK) and the downstream transcription factor, activating protein-1 (AP-1), specifically c-Jun; (3) Furthermore, cell surface heparan sulfate proteoglycans (HSPGs) mediate focal adhesion kinase (FAK) activation which regulates the ERK signaling cascade; (4) We propose a conceptual mechanotransduction model wherein surface HSPGs, with the synergism of integrin-mediated cell-matrix adhesions, sense interstitial flow and activate the FAK and ERK pathway, leading to upregulation of MMP and cell motility in 3-D.;In a differentiation study, we have found that: (1) 2-D laminar flow shear stress reduces expression of SMC marker genes in both SMCs and MFBs: alpha-smooth muscle actin (alpha-SMA), smooth muscle protein 22 (SM22), SM myosin heavy chain (SM-MHC), smoothelin, and calponin; (2) 3-D interstitial flow suppresses expression of SM-MHC, smoothelin, and calponin, but enhances expression of alpha-SMA and SM22; (3) The effects of laminar flow and interstitial flow on SMC marker expression is dependent on HSPG-mediated ERK activation.;Taken together, we propose that mechanotransduction of fluid flow may be involved in vascular remodeling and lesion formation by affecting SMC, FB, and MFB phenotype and motility. This is the first study to describe a flow-induced mechanotransduction mechanism in 3-D. This study has implications in understanding the flow-related mechanobiology in vascular lesion formation, tumor cell invasion, and stem cell differentiation.