All ETDs from UAB

Advisory Committee Chair

Vladimir Parpura

Advisory Committee Members

Marcas M Bamman

Chenbei Chang

Lori L McMahon-Wakefield

Scott M Wilson

Document Type

Dissertation

Date of Award

2014

Degree Name by School

Doctor of Philosophy (PhD) Heersink School of Medicine

Abstract

Skeletal muscle fibers, although terminally differentiated, can change their features, such as contraction speed and endurance, and throughout adult life in response to variety of stimuli, like exercise. This process is called plasticity and is mainly regulated by the type of nerve activity. Over the past several decades, research has shown that the properties of myofibers are also determined during muscle development. Ultimately, the change in phenotype requires a change in gene expression which is, in turn, regulated by transcription factors (TFs). Basic helix-loop-helix (bHLH) TFs regulate myogenesis and the central role belongs to the myogenic differentiation 1 (MyoD), often called the "master switch" because it can activate the whole myogenic transcription program. My research is focused on the modulation of this master regulator utilizing its interaction with E12, one of MyoD's dimerization partners. I hypothesized that different configurations of MyoD and E12 will selectively activate muscle differentiation and affect cell phenotype. To minimize cell-to-cell variability and the effect of cell growth medium, I used a molecular biology approach to generate myotubes from mammalian C2C12 myoblasts in non-differentiation growth conditions using the expression of different MyoD and E12 combinations/configurations. This approach not only recapitulated the basics of muscle development and physiology, as the obtained myotubes showed qualities similar to those seen in striated muscle fibers in vivo, but also allowed for the synthesis of subpopulations of myotubes which assumed distinct morphology, myofibrillar development, Ca2+-dynamics, and glucose utilization. I showed that these features were modified in a specific manner, indicating several distinct modi operandi of gene expression regulation and documenting for the first time in live cells the activation of myogenic subprograms by MyoD. Additionally, the approach allows the production of a set of biomaterials with predetermined morphological/functional characteristics suitable for the building blocks of soft actuators in micro-scale biomimetic robotics, and can be embraced in reparative medicine to customize myo¬fiber properties for specific needs, as opposed to bulk muscle replacement. This methodology can be adopted for the engineering of other tissue types whose differentiation is governed by the principles of basic helix-loop-helix transcription factors, like the nervous or endocrine systems.

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