AUTHOR=Sun Yiqing , Liang Xiao , Chen Jie , Tang Rong , Li Li , Li Dapeng 

TITLE=Change in Ubiquitin Proteasome System of Grass Carp Ctenopharyngodon idellus Reared in the Different Stocking Densities

JOURNAL=Frontiers in Physiology

VOLUME=9

YEAR=2018

URL=https://www.frontiersin.org/journals/physiology/articles/10.3389/fphys.2018.00837

DOI=10.3389/fphys.2018.00837

ISSN=1664-042X

ABSTRACT=<p>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 (<italic>Ctenopharyngodon idellus</italic>) were randomly reared at low stocking density (LSD, 0.9 kg m<sup>−2</sup>) or high stocking density (HSD, 5.9 kg m<sup>−2</sup>) 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 <italic>nrf2</italic>, <italic>keap1</italic>, and <italic>hsp90</italic> in white muscle of fish stocked at two densities at the endpoint of the experiment. In the UPS pathway, the expressions of <italic>ub</italic>, <italic>chip</italic>, <italic>psmc1</italic> in the LSD group were significantly higher than those in the HSD group (<italic>P</italic> &lt; 0.05). Ubiquitinated protein level and the content of 3-Methylhistidine elevated significantly in the LSD group (<italic>P</italic> &lt; 0.05). The mRNA levels of <italic>mafbx</italic>, <italic>murf1</italic>, and <italic>s6k1</italic> in the LSD group were significantly higher than those in HSD group (<italic>P</italic> &lt; 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.</p>