Systems biology of endothelial mechano-activated pathways
Author(s)Koo, Andrew Jia-An
Massachusetts Institute of Technology. Department of Biological Engineering.
C . Forbes Dewey, Jr. and Guillermo García-Cardeña.
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Multiple signaling pathways are employed by endothelial cells to differentially respond to distinct hemodynamic environments and acquire functional phenotypes, including regulation of inflammation, angiogenesis, blood coagulation, and the vascular tone. In order to understand how these pathways interact, this thesis applies a systems biology approach through a two-step process. First, we constructed an integrated mathematical model for shear-stress-induced nitric oxide (NO) production to assemble the current understanding of this signaling system. Second, we conducted experiments to define how shear stress dynamically modulates the expression of components of the endothelial glycocalyx, a mechanosensor that regulates shear-stressdependent NO production. Nitric oxide produced by vascular endothelial cells is an anti-inflammatory mediator and a potent vasodilator. In order to understand the rich diversity of responses observed experimentally in endothelial cells exposed to shear stress, we assembled four quantitative molecular pathways previously defined for shear-stress-induced NO production. In these pathways, endothelial nitric oxide synthase (eNOS) is activated (a) via calcium release, (b) via phosphorylation reactions, and (c) via enhanced protein expression. To these pathways we added (d) an additional pathway describing the actual NO production from the interactions of eNOS with its various protein partners. These pathways were then combined and simulated. The integrated model is able to describe the experimentally observed change in NO production with time following the application of fluid shear stress, and to predict the specific effects to the system following interventional pharmacological or genetic changes. Importantly, this model reflects the up-to-date understanding of the NO system and provides a platform to aggregate information in an additive way. The endothelial glycocalyx is a glycosaminoglycan layer located on the apical surface of vascular endothelial cells. Previous studies have documented a strong correlation between the glycocalyx expression, local hemodynamic environment, and atheroprotection. Based on these observations, we hypothesized that the expression of components of the endothelial glycocalyx is differentially regulated by distinct hemodynamic environments. In order to test this hypothesis, human endothelial cells were exposed to shear stress waveforms characteristic of atherosclerosis-resistant or atherosclerosis-susceptible regions of the human carotid, and the expression of several components of the glycocalyx was then assessed. Interestingly, we found that heparan sulfate expression is higher and evenly distributed on the apical surface of endothelial cells exposed to the atheroprotective waveform, and is irregularly present in cells exposed to the atheroprone waveform. Furthermore, the expression of a heparan sulfate proteoglycan, syndecan-1, is also differentially regulated by the two waveforms, and its suppression mutes the atheroprotective-flow-induced cell surface expression of heparan sulfate. Collectively, these data links distinct hemodynamic environments to the differential expression of critical components of the endothelial glycocalyx. Taken together, these projects present in this doctoral thesis increase our understanding of endothelial mechano-activated pathways, and have demonstrated how we could use systems biology approach to unravel complex biological problems.
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biological Engineering, February 2013"December 2012." Cataloged from PDF version of thesis.Includes bibliographical references.
DepartmentMassachusetts Institute of Technology. Department of Biological Engineering.
Massachusetts Institute of Technology