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Abstract
Valvular interstitial cells (VICs) maintain functional heart valve structure and display
transient fibroblast and myofibroblast properties. Most cell characterization studies
have been performed on plastic dishes; while insightful, these systems are limited.
Thus, a matrix metalloproteinase (MMP) degradable poly(ethylene glycol) (PEG) hydrogel
system is proposed in this communication as a useful tool for characterizing VIC function
in 3D. When encapsulated, VICs attained spread morphology, and proliferated and migrated
as shown through real-time cell microscopy. Additionally, fibronectin derived pendant
RGD was incorporated into the system to promote integrin binding. As RGD concentration
increased from 0 to 2000 microM, VIC process extension and integrin alpha(v)beta(3)
binding increased within two days. By day 10, integrin binding was equalized between
conditions. VIC morphology and rate of process extension were also increased through
decreasing the hydrogel matrix density presented to the cells. VIC differentiation
in response to exogenously delivered transforming growth factor-beta1 (TGF-beta1)
was also examined within the hydrogel networks. TGF-beta1 increased expression of
alpha smooth muscle actin (alphaSMA) and collagen-1 at both the mRNA and protein level
by day 2 of culture, indicating myofibroblast differentiation, and was sustained over
the course of the study (2 weeks). These studies demonstrate the utility, flexibility,
and biological activity of this MMP-degradable system for the characterization of
VICs, an important cell population for tissue engineering viable valve replacements
and understanding valvular pathobiology.