Date of Graduation

5-2018

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Cell & Molecular Biology (PhD)

Degree Level

Graduate

Department

Cell & Molecular Biology

Advisor/Mentor

Balachandran, Kartik

Committee Member

Wolchok, Jeffrey C.

Second Committee Member

Erf, Gisela F.

Third Committee Member

Thallapuranam, Suresh

Keywords

Aortic valve disease; Biomechanics; Cell behavior; Heart valves; Mechanism; Valve interstitial cells

Abstract

Our works aim to provide an insight into how aortic valve interstitial cells (VICs) respond to pathological shape and mechanical stimulation as well as the potential signaling pathway that mediates these responses, using a multiscale approach. A single cell model was developed to investigate the effect of altered shape on valve cell function as valve cells were reported to significantly deform during the cardiac cycle. Single VICs were controlled to take on features with different width-to-length aspect ratios that corresponded to the steady-state shapes adopted by VICs when stretched to 0%, 10% and 20%, respectively. It appeared that single VIC reorganized their cytoskeleton and increased cellular activities, including contractility, metabolism, proliferation and pathological activation, in response to shape alterations. This study provided a fundamental understanding of VIC behavior at single cell level. In order to further examine valve cell pathophysiology, a more physiologically-relevant 3-dimensional (3D) stretchable model was developed to better simulate natural heart valve environment. We developed and characterized a collagen-based scaffold for dynamic culture of heart VICs. This 3D scaffold was porous, biocompatible and mechanically robust. For this reason, it was utilized as a culture model for the subsequent cell signaling study where the role of fibroblast growth factor on valve cell biology was examined in the presence of mechanical stretching stimulation. Stretch magnitudes of 10% and 20% were used to mimic healthy and pathological conditions, respectively. We reported that the Akt/mTOR pathway was up-regulated at elevated 20% stretch which was associated with increased cell proliferation/metabolism. Treatment with fibroblast growth factor 1/ fibroblast growth factor 2 (FGF1/FGF2) significantly altered cellular responses such that they aided in cell proliferation at 10% stretch while reduced cell proliferation at 20% stretch. FGF1/FGF2 treatment was also able to reduce expression of activated markers in pathologically stretched cells, suggesting that FGF1/FGF2 signaling might be a potential target for drug therapies for heart valve treatment. Overall, this project provided a specific picture of how heart valve cells responded to pathological stimulations at multiscale levels and the involvement of FGF-receptor signaling. It is hoped that the knowledge gained from these studies could help to identify therapeutic targets for valvular disease treatment.

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