Abstract
(1) Background: l-leucine (Leu) plays a positive role in regulating protein turnover in skeletal muscle in mammal. However, the molecular mechanism for the effects of Leu on muscle growth and protein deposition is not clearly demonstrated in fish. This study investigated the effects of dietary Leu on growth performance and muscle growth, protein synthesis, and degradation-related signaling pathways of hybrid catfish (Pelteobagrus vachelli♀ × Leiocassis longirostris♂). (2) Methods: A total of 630 hybrid catfish (23.19 ± 0.20 g) were fed 6 different experimental diets containing graded levels of Leu at 10.0 (control), 15.0, 20.0, 25.0, 30.0, 35.0, and 40.0 g Leu kg-1 for 8 weeks. (3) Results: Results showed that dietary Leu increased percent weight gain (PWG), specific growth rate (SGR), FI (feed intake), feed efficiency (FE), protein efficiency ratio (PER), muscle fibers diameter, and muscle fibers density; up-regulated insulin-like growth factor I (IGF-I), insulin-like growth factor I receptor (IGF-IR), proliferating cell nuclear antigen (PCNA), myogenic regulation factors (MyoD, Myf5, MyoG, and Mrf4), and MyHC mRNA levels; increased muscle protein synthesis via regulating the AKT/TOR signaling pathway; and attenuated protein degradation via regulating the AKT/FOXO3a signaling pathway. (4) Conclusions: These results suggest that Leu has potential role to improve muscle growth and protein deposition in fish, which might be due to the regulation of IGF mRNA expression, muscle growth related gene, and protein synthesis and degradation-related signaling pathways. Based on the broken-line model, the Leu requirement of hybrid catfish (23.19-54.55 g) for PWG was estimated to be 28.10 g kg-1 of the diet (73.04 g kg-1 of dietary protein). These results will improve our understanding of the mechanisms responsible for muscle growth and protein deposition effects of Leu in fish.
Highlights
Aquaculture has become an agronomic activity with noticeable development around the world to respond to the increasing demand of aquatic products for human consumption [1]
Muscle growth is a complex, dynamic process involving both the recruitment of new muscle fibers and the growth of existing fibers [4], which is under the control of diverse regulatory factors such as insulin-like growth factors (IGFs), myogenic regulatory factors (MRFs), and myostatin (MSTN) [5]
The present results showed that dietary Leu up-regulated proliferating cell nuclear antigen (PCNA), myogenic factor 5 (Myf5), myoblast determination protein (MyoD), myogenic regulatory factor 4 (MRF4), MyoG, and MyHC mRNA expressions in fish
Summary
Aquaculture has become an agronomic activity with noticeable development around the world to respond to the increasing demand of aquatic products for human consumption [1]. The IGF-I is a key regulatory hormone that controls growth in vertebrates [6], which stimulates both proliferation and differentiation of myoblasts, as well as promoting myotube hypertrophy in vitro and in vivo [7,8,9]. The MRFs are muscle-specific basic helix–loop–helix transcription factors. They include myoblast determination protein (MyoD), myogenic factor 5 (Myf5), myogenin (MyoG), and myogenic regulatory factor 4 (MRF4) [10]. Myf and MyoD are mainly involved in muscle specification and trigger conversion of no muscle cells, such as fibroblasts, into muscle, whereas myogenin and MRF4 act later during myogenesis and allow myotube formation and maturation [11,12]. Leu deficiency results in depressed growth rate, low feed efficiency, and poor protein retention, as reported for large yellow croaker Pseudosciaena crocea [15], rainbow trout
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