title: Effect of shear stress on water and LDL transport through cultured endothelial cell monolayers.
abstract: Previous animal experiments have shown that the transport of LDL into arterial walls is shear stress dependent. However, little work has probed shear effects on LDL transport in vitro where conditions are well defined and mechanisms are more easily explored. Therefore, we measured shear induced water and LDL fluxes across cultured bovine aortic endothelial (BAEC) monolayers in vitro and developed a three-pore model to describe the transport dynamics. Cell apoptosis was quantified by TdT-mediated dUTP nick end labeling (TUNEL) assay. We also examined the role of nitric oxide (NO) in shear induced water and LDL fluxes by incubating BAEC monolayers with an NO synthase inhibitor, NG-monomethyl-L-arginine (L-NMMA). Our results show that direct exposure of endothelial monolayers to 12 dyn/cm2 shear stress for 3 h elicited a 2.37-fold increase in water flux (Jv), a 3.00-fold increase in LDL permeability (Pe), a 1.32-fold increase in LDL uptake, and a 1.68-fold increase in apoptotic rate. L-NMMA treatment of BAEC monolayers blocked shear induced Jv response, but had no significant effect on shear responses of Pe and cell apoptosis. A long time shear exposure (12 h) of endothelial monolayers reduced Pe and apoptotic rate close to the baseline. These results suggest that an acute change in shear stress from a static baseline state induces increases in water flux that are mediated by an NO dependent mechanism. On the other hand, the permeability of endothelial monolayers to LDL is enhanced by a short term-shear application and reduced nearly to the baseline level by a longer time shear exposure, positively correlated to the leaky junctions forming around apoptotic cells.
authors.affiliation: Key Laboratory for Biomechanics and Mechanobiology of Ministry of Education, School of Biological Science and Medical Engineering, Beihang University, Beijing, China; Department of Biomedical Engineering, The City College of The City University of New York, New York, USA.
authors.forename: Hongyan
authors.initials: H
authors.lastname: Kang
authors.affiliation: Department of Biomedical Engineering, The City College of The City University of New York, New York, USA.
authors.forename: Limary M
authors.initials: LM
authors.lastname: Cancel
authors.affiliation: Department of Biomedical Engineering, The City College of The City University of New York, New York, USA. Electronic address: tarbell@ccny.cuny.edu.
authors.forename: John M
authors.initials: JM
authors.lastname: Tarbell
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D001011:Aorta / Q000166:cytology; D017209:Apoptosis; D001692:Biological Transport; D015820:Cadherins / Q000032:analysis; D002417:Cattle; D002463:Cell Membrane Permeability; D002478:Cells, Cultured; D042783:Endothelial Cells / Q000378:metabolism*; D004730:Endothelium, Vascular / Q000166:cytology* / Q000378:metabolism; D008077:Lipoproteins, LDL / Q000378:metabolism*; D008954:Models, Biological; D009569:Nitric Oxide / Q000502:physiology; D012212:Rheology; D013314:Stress, Mechanical; D014867:Water / Q000378:metabolism*; D019323:omega-N-Methylarginine / Q000494:pharmacology; D000099152:Cadherin 5
chemical_list: D015703:Antigens, CD; D015820:Cadherins; D008077:Lipoproteins, LDL; D009569:Nitric Oxide; D014867:Water; D019323:omega-N-Methylarginine; D000099152:Cadherin 5
keywords: Bovine aortic endothelial cells; LDL permeability; Leaky junctions; Shear stress; Water flux