Temporal examination of myoglobin and myosin heavy chain expression patterns in vitro
Date
2020
Authors
Larson, Ashley Mari, author
Kanatous, Shane, advisor
Hamilton, Karyn, committee member
Mykles, Donald, committee member
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Abstract
Myoglobin is a hemoprotein expressed in vertebrate muscle that is typically known to follow an established oxidative muscle fiber type, found in aerobic muscles. However, more recent evidence has demonstrated changes in myoglobin expression without a change in fiber type, indicating myoglobin expression could be regulated by different pathways and may not always be dependent on a prior expressed fiber type. Myoglobin structure is characterized by a globin backbone that supports a nonprotein heme prosthetic group containing iron, which is responsible for the reversible binding of several ligands such as oxygen, nitric oxide, and carbon monoxide. Naturally, it has been implicated in oxygen transport and storage, nitric oxide and reactive oxygen species scavenging, and cellular lipid transport. Mixed lipid supplementation alone and coupled with hypoxia elevates skeletal muscle myoglobin levels, but it is unknown how these culture treatments affect myoglobin expression relative to the fiber type. Given the uncertainty of when myoglobin is expressed independently from oxidative fiber types, we aimed to determine when differentiating C2C12 cells begin to express myoglobin compared to when they express oxidative isoforms of myosin heavy chain when subjected to factors known to increase myoglobin expression; hypoxia, lipid and/or caffeine treatments. We found that under control and hypoxic conditions, regardless of lipid supplementation, myoglobin expression occurred before oxidative fiber expression. Conversely, cells receiving caffeine stimulation expressed myoglobin following oxidative fiber type expression. Cells exposed to hypoxia and lipid supplementation displayed elevated functional myoglobin expression compared to caffeine stimulated cells, suggesting that this combination of treatments may be more effective at increasing myoglobin than stimulation alone. Overall, the work presented here has determined conditions under which expression of myoglobin precedes oxidative fiber type expression and within these treatments, conditions that also increase functional myoglobin concentration. These findings can act as a step in the process to assist in revealing more about how myoglobin can be expressed in skeletal muscle. Examination of alternate routes of myoglobin expression that are not reliant on prior expression of a particular fiber type could yield potential therapeutic benefits of expressing myoglobin in tissues to combat ischemic diseases seen in humans.
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Subject
cell culture
lipids
skeletal muscle
hypoxia
caffeine
myoglobin