Investigating the Role of Substrate Stiffness on Beta-Catenin Activation in Osteoblasts
Author(s)
Platt, Randall Jeffrey
Type
Thesis
Abstract
Cells are exposed to a myriad of signals from their microenvironment and the finely tuned
processing of these cues regulates cell survival, proliferation, and differentiation. Traditional
belief was that only soluble signaling factors governed cell behavior, but more recently, much
attention has been focused on the influence of mechanical and topographical cues. Although
many landmark observations have been published in this regard, still little is known about the
mechanisms behind cell response to physical cues.
This work stems from the previously reported observations that beta-catenin, a key cell
signaling molecule involved in bone development, is activated by acute mechanical stress. The
main aim of this work was to investigate the role of substrate stiffness on beta-catenin activation
in osteoblasts. Here, two polyacrylamide gel platforms are adapted that vary in Young's modulus
and act as adhesive substrates for cell attachment. Osteoblasts grown on these polyacrylamide
gels attach through cross-linked extracellular matrix proteins and 'sense' the underlying stiffness
of the substrate and change their intracellular biochemistry accordingly. It was found in this
work that the amount of total beta-catenin increases after 24 hours in osteoblasts cultured on
tissue culture plastic and polyacrylamide gels of 40 kPa. Moreover, the number of cell-cell
contacts directly influences the amount of total beta-catenin. It was also found that osteoblasts
grown on higher stiffness substrates have more active beta-catenin and less degraded beta-
catenin compared to lower stiffness substrates. The novel findings reported here advance the
proposal that beta-catenin is a participant in mechanosensing and also provides a new platform
for investigation and further insight into a mechanism of action.
processing of these cues regulates cell survival, proliferation, and differentiation. Traditional
belief was that only soluble signaling factors governed cell behavior, but more recently, much
attention has been focused on the influence of mechanical and topographical cues. Although
many landmark observations have been published in this regard, still little is known about the
mechanisms behind cell response to physical cues.
This work stems from the previously reported observations that beta-catenin, a key cell
signaling molecule involved in bone development, is activated by acute mechanical stress. The
main aim of this work was to investigate the role of substrate stiffness on beta-catenin activation
in osteoblasts. Here, two polyacrylamide gel platforms are adapted that vary in Young's modulus
and act as adhesive substrates for cell attachment. Osteoblasts grown on these polyacrylamide
gels attach through cross-linked extracellular matrix proteins and 'sense' the underlying stiffness
of the substrate and change their intracellular biochemistry accordingly. It was found in this
work that the amount of total beta-catenin increases after 24 hours in osteoblasts cultured on
tissue culture plastic and polyacrylamide gels of 40 kPa. Moreover, the number of cell-cell
contacts directly influences the amount of total beta-catenin. It was also found that osteoblasts
grown on higher stiffness substrates have more active beta-catenin and less degraded beta-
catenin compared to lower stiffness substrates. The novel findings reported here advance the
proposal that beta-catenin is a participant in mechanosensing and also provides a new platform
for investigation and further insight into a mechanism of action.
Date Issued
2011-08
Date Awarded
2011-10
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Stevens, Molly
Sponsor
Whitaker International Scholars and Fellows Program
Creator
Platt, Randall Jeffrey
Publisher Department
Materials
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Master of Philosophy (MPhil)