Undergraduate Honors Theses

Thesis Defended

Spring 2011

Document Type

Thesis

Department

Molecular, Cellular, & Developmental Biology

First Advisor

Dr. Kristi Anseth

Second Advisor

Dr. Leslie Leinwand

Abstract

Valvular Interstitial Cells (VICs) are the predominant cell population of mammalian heart valves. When the valve is damaged, VICs become activated to a myofibroblastic state and secrete a variety of matrix molecules in order to repair the valve structure. However, in aortic valve stenosis, the VICs differentiate to an osteoblastic state. This phenotype ultimately calcifies the valve resulting in valvular stenosis, which eventually requires valve transplantation for prolonged survival. It has been previously shown that this activation is modulated separately by the cytokine transforming growth factor beta-1 (TGF-β1) as well as mechanical properties of the extracellular microenvironment, notably the environmental modulus. In this investigation, hydrogels of soft and stiff moduli with varying surface concentrations of covalently tethered TGF-β1 were constructed in order to assess the effect of varying both environmental modulus and TGF-β1 concentration. On softer substrates, VICs exhibited a rounded morphology and clustered together. As a result, there was little variation in activation or cell density between different TGF-β1 conditions. On stiffer substrates, VICs exhibited a more spread morphology and higher cell density on all conditions compared to soft conditions. In response to varying levels of TGF-β1 surface concentrations, VICs increased in activation from 0 to 16 ng/cm2 TGF-β1, but then significantly decreased in activation from 16 to 32 ng/cm2. VICs were also seen to form nodules on 32 and 64 ng/cm2 TGF-β1 conditions but not on 0 and 16 ng/cm2 conditions. These results suggest there is a TGF-β1 concentration threshold between the 16 and 32 ng/cm2 below which VICs remain activated and in a myofibroblastic state and above which VICs progress to a disease-like state. However, further cellular characterizations are needed to confirm these conclusions.

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