Direct actions of growth hormone in rainbow trout, Oncorhynchus mykiss, skeletal muscle cells in vitro

Authors: REID, ROSS - University Of Alabama; TURKMEN, SERHAT - University Of Alabama; Cleveland, Beth; BIGA, PEGGY - University Of Alabama

Submitted to: Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/6/2024
Publication Date: 8/9/2024
Citation: Reid, R., Turkmen, S., Cleveland, B.M., Biga, P. 2024. Direct actions of growth hormone in rainbow trout, Oncorhynchus mykiss, skeletal muscle cells in vitro. Comparative Biochemistry and Physiology - Part A: Molecular & Integrative Physiology. Volume 297(November 2024):111725. https://doi.org/10.1016/j.cbpa.2024.111725.
DOI: https://doi.org/10.1016/j.cbpa.2024.111725

Interpretive Summary: Characterizing physiological mechanisms regulating muscle growth in rainbow trout is critical for developing strategies that improve production efficiency by increasing muscle yield. The growth hormone (GH) - insulin-like growth factor (IGF) system is recognized for its growth-promoting actions in fish, primarily though GH actions in liver. However, it is unknown if GH directly affects mechanisms regulating growth in muscle tissue. To address this knowledge gap, we exposed rainbow trout muscle cells to GH and signaling pathway inhibitors and characterized the response of growth-promoting genes. Results indicated that GH had minimal impact on gene expression in muscle, suggesting that GH indirectly promotes muscle growth by stimulating IGF production in liver. Therefore, focusing on GH effects in liver is the most efficient approach to characterize the anabolic nature of this hormone in rainbow trout.

Technical Abstract: The growth hormone (GH)-insulin-like growth factor-1 (IGF-1) system regulates skeletal muscle growth and function. GH has a major function of targeting the liver to regulate IGF-1 production and release, and IGF-1 mediates the primary anabolic action of GH on growth. However, skeletal muscle is a target tissue of GH as evidenced by dynamic GH receptor expression, but it is unclear if GH elicits any direct actions on extrahepatic tissues as it is difficult to distinguish the effects of IGF-1 from GH. Fish growth regulation is complex compared to mammals, as genome duplication events have resulted in multiple isoforms of GHs, GHRs, IGFs, and IGFRs expressed in most fish tissues. This study investigated the potential for GH direct actions on fish skeletal muscle using an in vitro system, where rainbow trout myogenic precursor cells (MPCs) were cultured in normal and serum-deprived media, to mimic in vivo fasting conditions. Fasting reduces IGF-1signaling in the muscle, which is critical for disentangling the roles of GH from IGF-1. The direct effects of GH were analyzed by measuring changes in myogenic proliferation and differentiation genes, as well as genes regulating muscle growth and proteolysis. This study provides the first in-depth analysis of the direct actions of GH on serum-deprived fish muscle cells in vitro. Data suggest that GH induces the expression of markers for proliferation, early differentiation, and proteolysis in the presence of serum, but all observed GH action was blocked in serum-deprived conditions. Additionally, serum deprivation alone reduced the expression of several proliferation, differentiation, and proteolysis markers. Results also demonstrate dynamic gene expression response in the presence of GH and a JAK inhibitor in fed but not fasted conditions. These data provide a better understanding of GH signaling in relation to serum in trout muscle cells in vitro.