Systems biology of endothelial mechano-activated pathways

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Biological Engineering, February 2013"December 2012." Cataloged from PDF version of thesis.Includes bibliographical references.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.by Andrew Jia-An Koo.Ph.D

In Silico Modeling of Shear-Stress-Induced Nitric Oxide Production in Endothelial Cells through Systems Biology

Nitric oxide (NO) produced by vascular endothelial cells is a potent vasodilator and an antiinflammatory mediator. Regulating production of endothelial-derived NO is a complex undertaking, involving multiple signaling and genetic pathways that are activated by diverse humoral and biomechanical stimuli. To gain a thorough understanding of the rich diversity of responses observed experimentally, it is necessary to account for an ensemble of these pathways acting simultaneously. In this article, we have assembled four quantitative molecular pathways previously proposed for shear-stress-induced NO production. In these pathways, endothelial NO synthase is activated 1), via calcium release, 2), via phosphorylation reactions, and 3), via enhanced protein expression. To these activation pathways, we have added a fourth, a pathway describing actual NO production from endothelial NO synthase and its various protein partners. These pathways were combined and simulated using CytoSolve, a computational environment for combining independent pathway calculations. The integrated model is able to describe the experimentally observed change in NO production with time after the application of fluid shear stress. This model can also be used to predict the specific effects on the system after interventional pharmacological or genetic changes. Importantly, this model reflects the up-to-date understanding of the NO system, providing a platform upon which information can be aggregated in an additive way.National Institutes of Health (U.S.) (Grant R01HL090856)Singapore-MIT Alliance Computational and Systems Biology Progra

Heparan Sulfate Regrowth Profiles Under Laminar Shear Flow Following Enzymatic Degradation

The local hemodynamic shear stress waveforms present in an artery dictate the endothelial cell phenotype. The observed decrease of the apical glycocalyx layer on the endothelium in atheroprone regions of the circulation suggests that the glycocalyx may have a central role in determining atherosclerotic plaque formation. However, the kinetics for the cells’ ability to adapt its glycocalyx to the environment have not been quantitatively resolved. Here we report that the heparan sulfate component of the glycocalyx of HUVECs increases by 1.4-fold following the onset of high shear stress, compared to static cultured cells, with a time constant of 19 h. Cell morphology experiments show that 12 h are required for the cells to elongate, but only after 36 h have the cells reached maximal alignment to the flow vector. Our findings demonstrate that following enzymatic degradation, heparan sulfate is restored to the cell surface within 12 h under flow whereas the time required is 20 h under static conditions. We also propose a model describing the contribution of endocytosis and exocytosis to apical heparan sulfate expression. The change in HS regrowth kinetics from static to high-shear EC phenotype implies a differential in the rate of endocytic and exocytic membrane turnover.National Heart, Lung, and Blood Institute (Grant HL090856-01)Singapore-MIT Allianc

Global patient outcomes after elective surgery: prospective cohort study in 27 low-, middle- and high-income countries.

BACKGROUND: As global initiatives increase patient access to surgical treatments, there remains a need to understand the adverse effects of surgery and define appropriate levels of perioperative care. METHODS: We designed a prospective international 7-day cohort study of outcomes following elective adult inpatient surgery in 27 countries. The primary outcome was in-hospital complications. Secondary outcomes were death following a complication (failure to rescue) and death in hospital. Process measures were admission to critical care immediately after surgery or to treat a complication and duration of hospital stay. A single definition of critical care was used for all countries. RESULTS: A total of 474 hospitals in 19 high-, 7 middle- and 1 low-income country were included in the primary analysis. Data included 44 814 patients with a median hospital stay of 4 (range 2-7) days. A total of 7508 patients (16.8%) developed one or more postoperative complication and 207 died (0.5%). The overall mortality among patients who developed complications was 2.8%. Mortality following complications ranged from 2.4% for pulmonary embolism to 43.9% for cardiac arrest. A total of 4360 (9.7%) patients were admitted to a critical care unit as routine immediately after surgery, of whom 2198 (50.4%) developed a complication, with 105 (2.4%) deaths. A total of 1233 patients (16.4%) were admitted to a critical care unit to treat complications, with 119 (9.7%) deaths. Despite lower baseline risk, outcomes were similar in low- and middle-income compared with high-income countries. CONCLUSIONS: Poor patient outcomes are common after inpatient surgery. Global initiatives to increase access to surgical treatments should also address the need for safe perioperative care. STUDY REGISTRATION: ISRCTN5181700

Kuluttajabarometri maakunnittain 2000, 2. neljännes

Suomen virallinen tilasto (SVT

Use of failure-to-rescue to identify international variation in postoperative care in low-, middle- and high-income countries: a 7-day cohort study of elective surgery

This was an investigator-initiated study funded by Nestle Health Sciences through an unrestricted research grant and by a National Institute for Health Research (UK) Professorship held by R.P. The study was sponsored by Queen Mary University of London