Abstract
Myostatin is a major factor involved in the regulation of skeletal muscle protein mass. High myostatin levels have been associated with an increase in myotube shrinkage. Enhanced myostatin expression is caused by pro-catabolic reactions involving compounds such as tumor necrosis factor (TNF)-α. The present study investigated the effects of agaro-oligosaccharides (AOSs) on hypercatabolism of myotubes exposed to TNF-α. C2C12 myotubes exposed to TNF-α in the presence or absence of AOSs. Myotube exposure to TNF-α resulted in a reduction in the amount of myosin heavy chain (MyHC) protein and a decrease in myotube diameter, which was associated with increased myostatin mRNA expression. AOSs prevented TNF-α-induced MyHC protein loss and restored normal myostatin mRNA levels, with agarobiose and agarotetraose effectively suppressing the hyperexpression of the mRNA. In addition, expression levels of the known myostatin inhibitors, latent transforming growth factor beta binding protein 3 (Ltbp3) and growth and differentiation factor-associated serum protein 1 (Gasp1) mRNAs, decreased more in TNF-α-induced myotubes than in the TNF-α-free control, possibly resulting in myostatin upregulation. However, AOSs restored nearly normal expression levels of Ltbp3 and Gasp1 mRNA, potentially suppressing myostatin expression. These findings suggest that AOSs could prevent myotube shrinkage induced by TNF-α.
Highlights
Skeletal muscle is the most abundant tissue in the human body and is critical for locomotion and metabolic adaptation
Myotube exposure to tumor necrosis factor (TNF)-α resulted in a reduction in the amount of myosin heavy chain (MyHC) protein and a decrease in myotube diameter, which was associated with increased myostatin mRNA expression
This study reports that AOSs derived from agar had inhibitory effects toward myotube shrinkage, and these effects were associated with a down-regulation of myostatin expression
Summary
Skeletal muscle is the most abundant tissue in the human body and is critical for locomotion and metabolic adaptation. It comprises approximately 40% - 50% of the human body by weight and is mainly maintained by a balance between protein synthesis and degradation. Muscle atrophy is defined as a decrease in the size of tissue or organ due to myotube shrinkage caused by the loss of organelles, cytoplasm, and proteins [2]. We investigated the inhibitory effects of AOSs on protein degradation and gene expressions related to myotube shrinkage induced by tumor necrosis factor (TNF)-α
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