In vitro microphysiological system for modeling vascular disease
Creators: Ji, Hayeun
Publisher: name: Columbia University
Year: 2018
Subjects: subject: Blood-vessels--Diseases
subject: Tissue engineering
subject: Physiology
subject: FOS: Biological sciences
subject: Biomedical engineering

description: In vitro microphysiological system utilizes engineered tissue constructs from human cells to model functional activity of human tissues or organs in both healthy and diseased state, thereby providing a more accurate drug screening than animal models prior to clinical trials. One essential component of an in vitro microphysiological system is a tissue engineered blood vessel (TEBV) that can accurately recapitulate the functional vasculature in vivo. This thesis first explores two most important considerations to a successful TEBV generation, the cell source and the fabrication method. To engineer a vascular tissue construct, an ideal cell source should demonstrate high availability and accurate vessel functionality. Mesenchymal stem cells (MSC) were explored due to their high availability, proliferation capacity, and capability to deposit adequate extracellular matrix (ECM) for cell sheet formation. Vascular smooth muscle cells (SMC) are the cell components that comprise the medial layer of native blood vessel, and thus optimal for demonstrating equivalent biological functionality. However, SMC are much harder to acquire through biopsy, and they have limited proliferative capacity and quick senescence. Therefore, an alternative cell source for SMC was obtained through direct reprogramming approach involving the induced overexpression of myocardin in more readily available human cell sources. The resulting reprogrammed SMC demonstrated close resemblance to the native SMC in terms of its phenotype, related gene and protein expression levels, and contractile function. Two different fabrication methods, nanopatterned cell sheets and dense collagen hydrogel, were explored to engineer a 1 mm inner diameter blood vessel. The fabricated TEBVs were then compared to that of the native blood vessel and each other in terms of its structure, mechanical properties, and vasoactive function in response to stimuli. 
      After selecting the most optimal cell source and fabrication method for developing a human cell-based TEBV for in vitro microphysiological system, the second part of this thesis assesses the capability of the designed TEBV to model a vascular disease for drug screening purposes. Marfan syndrome was selected as a model vascular disease due to its previous history of contradictory results from the animal models and human clinical trials using losartan, an angiotensin II receptor blocker, in terms of preventing aortic root dilation. TEBV fabricated using reprogrammed SMC from Marfan syndrome patient sample and dense collagen hydrogel showed reduced fibrillin deposition, increased vessel diameter and thickness, and reduced vasoconstriction levels when compared to the wild type TEBV, which is consistent with that observed in native vessels of Marfan syndrome patients. Losartan improved the function of Marfan syndrome TEBV, but still at reduced level when compared to that of the wild type. SB203580, a selective inhibitor of p53 MAPK that has been shown to be a better drug candidate than losartan in recent cell-based studies, showed improved TEBV function comparable to that of the wild type.  In overall, this thesis presents a successful development of a highly robust, patient-specific in vitro vascular model. An accurate recapitulation of a drug-induced physiological response in humans can speed up the drug screening process with higher efficiency, and this will eventually increase the chances of successful treatment for patients.