Abstract
Ammonia is very toxic to the body and has detrimental effects on many different organ systems. Using cultured myoblast cells, we examined ammonia’s effect on myostatin expression, a negative regulator of skeletal muscle growth, and myotube diameters. The objective of this study was to examine how murine, avian, and fish cells respond to increasing levels of ammonia up to 50 mM. The murine myoblast cell line (C2C12), primary chick, and primary tilapia myoblast cells were cultured and then exposed to 10, 25, and 50 mM ammonium acetate, sodium acetate, and an untreated control for 24 h. High levels of ammonia were detrimental to the C2C12 cells, causing increased Myostatin (MSTN) expression and decreased myotube diameters between 10 and 25 mM (p < 0.002). Ammonia at 10 mM continued the positive myogenic response in the chick, with lower MSTN expression than the C2C12 cells and larger myotube diameters, but the myotube diameter at 50 mM ammonium acetate was significantly smaller than those at 10 and 25 mM (p < 0.001). However, chick myotubes at 50 mM were still significantly larger than the sodium acetate-treated and untreated control (p < 0.001). The tilapia cells showed no significant difference in MSTN expression or myotube diameter in response to increasing the concentrations of ammonia. Overall, these results confirm that increasing concentrations of ammonia are detrimental to mammalian skeletal muscle, while chick cells responded positively at lower levels but began to exhibit a negative response at higher levels, as the tilapia experienced no detrimental effects. The differences in ammonia metabolism strategies between fish, avian, and mammalian species could potentially contribute to the differences between species in response to high levels of ammonia. Understanding how ammonia affects skeletal muscle is important for the treatment of muscle wasting observed in liver failure patients.
Highlights
Myostatin (MSTN) is an important negative regulator of embryonic and postnatal skeletal muscle growth in mammalian, avian, and fish species [1,2]
PCR to was utilized levels to examine the relative fold of the gene of myogenic markers in response increasing of ammonium acetate forchange the mouse, chicken, expression myogenic markers response to increasing levels of ammonium for the mouse, and tilapia. of Previous studies foundinthat acetic acid and sodium acetate did not alteracetate myostatin expression chicken, and tilapia
Previous studies found that acetic acid and sodium acetate did not in murine myotubes, and any effects on gene expression are due to the hyperammonemia [29]
Summary
Myostatin (MSTN) is an important negative regulator of embryonic and postnatal skeletal muscle growth in mammalian, avian, and fish species [1,2]. The functioning of myostatin in mammalian and avian species has been more extensively studied than in fish species, but the presence of the double-muscling phenotype in myostatin-null fish indicates myostatin has a similar role in skeletal muscle regulation as it does in avian and mammalian species [8,10,11]. Despite similarities between mammalian and fish myostatin, there are multiple differences that open up possibilities for new roles of myostatin in fish, which remain unknown. The discrepancy between mammalian and fish myostatin makes it more difficult to extrapolate the precise functions of myostatin in fish based solely on studies on mammals
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