PSXII-6 Effect of ractopamine-HCl on the release of myokine FGF-21 in cultured primary bovine muscle cells.

Abstract Animal health and efficient muscle growth are essential for maintaining sustainable beef production. Myokine proteins, such as fibroblast growth factor 21 (FGF-21), regulate muscle growth, fiber type development, and attributes associated with health, as demonstrated in human and biomedical studies. Many of these studies center on myokine secretion with exercise and evaluate how myokines contribute to positive health benefits. However, there are few studies in livestock species that have evaluated myokine proteins and their potential benefits for animal production. In livestock, exercise is not used to increase muscle mass and improve health. Other methods are employed to enhance muscle growth, such as sympathetic activation with β-agonists, which mimic exercise to promote lean muscle accretion. This study evaluated how the β-agonist ractopamine HCl (RAC) influences gene expression and protein secretion of FGF-21 in cultures of primary bovine satellite cells (BSC). Cells were isolated from the semimembranosus muscle of 3-month (n = 3) and 11-month-old (n = 3) steers and cultured on Matrigel matrix in 10% fetal bovine serum growth media. Cells were cultured to 70% confluency, growth media was removed, and cells were washed with PBS. Differentiation media containing 3% horse serum was applied to cultures. Half of the cells received differentiation media with 10 µM RAC, while the other half received differentiation media without RAC, serving as the control (CON) group. This established experimental time zero, and from this time cells were imaged and collected along with media at 0, 12, 24, and 48 hours. At each timepoint media was collected from the cells to assess protein secretion using an ELISA. Upon media removal, cells were washed with cold 1x PBS and immediately collected for RNA isolation, which was processed for gene expression. The entire experiment was conducted in triplicate. Statistical analysis was performed in SAS using the GLIMMIX procedure to test CON versus RAC within an hour. The result of this study show that cells treated with RAC present a decrease (p ≤ 0.05) in FGF-21 gene expression compared to CON at all timepoints. These findings were contrary to expectations, as RAC was anticipated to mimic muscle activity and either sustain or increase FGF-21 gene expression of healthy muscle cells. While protein secretion for FGF-21 was detected, there were no significant differences (p ≥ 0.05) in protein secretion between CON and RAC. The effect of RAC on FGF-21 expression and secretion in cultured cells may not perfectly reflect its actions in vivo. The circulatory system regulates RAC distribution and clearance whereas in culture RAC exposure to the muscle cells endures continuously until collection. It would be beneficial to evaluate expression and secretion of multiple myokines in vivo following the administration of RAC, to ascertain their influence on muscle growth.