Abstract
The ubiquitin proteasome system (UPS) is a highly regulated mechanism of intracellular protein degradation and turnover. To evaluate the effect of crowding stress on the UPS in fish, grass carp (Ctenopharyngodon idellus) were randomly reared at low stocking density (LSD, 0.9 kg m−2) or high stocking density (HSD, 5.9 kg m−2) for 70 days. The expression of the genes regulating UPS, stress-related parameters, and profiles of amino acid in white muscle as well as growth rate of fish reared at two stocking densities were investigated. Fish exhibited significantly higher growth rate in the LSD group compared to the HSD group. Serum concentrations of cortisol, total protein, and glucose did not vary significantly in fish between two groups. There was no significant difference in the mRNA levels of nrf2, keap1, and hsp90 in white muscle of fish stocked at two densities at the endpoint of the experiment. In the UPS pathway, the expressions of ub, chip, psmc1 in the LSD group were significantly higher than those in the HSD group (P < 0.05). Ubiquitinated protein level and the content of 3-Methylhistidine elevated significantly in the LSD group (P < 0.05). The mRNA levels of mafbx, murf1, and s6k1 in the LSD group were significantly higher than those in HSD group (P < 0.05). These results illustrate that the fish cultured in lower stocking density would exhibit a greater growth rate and a fast protein turnover in muscle.
Highlights
The ubiquitin proteasome system (UPS) is important for regulating protein degradation and function (Pickart and Eddins, 2004)
There were no significant differences in serum levels of cortisol, total protein (TP) and GLU between two groups (Table 3)
HSD did not cause a significantly increased in the Initial weight (g) Initial length Final weight (g) Final length Weight gain rate Specific growth rate Feed conversion efficiency Feed ration
Summary
The ubiquitin proteasome system (UPS) is important for regulating protein degradation and function (Pickart and Eddins, 2004). The function of UPS is involved in various cellular processes, such as signal transduction, metabolic regulation, cell cycle control, development, apoptosis, protein quality control, and antigen presentation (Glickman and Ciechanover, 2002; Flick and Kaiser, 2012; Sommer and Wolf, 2014). The conjugation process of ubiquitinylation is a complex reaction that requires ubiquitin (ub), ubiquitin activating enzyme (E1), ubiquitin conjugating enzyme (E2), and ubiquitin protein ligase (E3) (Romn and Reznick, 2016). E3 ligases have a central role in coupling ubiquitin to the targeted protein and generate the specificity of the mechanism (Jackson and Eldridge, 2002). Targeted protein is polyubiquitinated with the specificity determined by the E3
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