Dietary soybean β-conglycinin suppresses growth performance and inconsistently triggers apoptosis in the intestine of juvenile grass carp (Ctenopharyngodon idella) in association with ROS-mediated MAPK signalling

The current study aimed to investigate the effects of dietary soybean beta-conglycinin on growth performance and intestine apoptosis in juvenile grass carp (Ctenopharyngodon idella). For fish fed with the 80 g beta-conglycinin/kg diet for 7 weeks, the specific growth rate and feed intake were decreased. In the proximal intestine, dietary beta-conglycinin did not induce DNA fragmentation, tended to decrease the reactive oxygen species (ROS) content, and decreased ROS-generating enzyme (NADPH oxidase [NOX]) activity. Subsequently, in the mid-intestine, dietary beta-conglycinin caused DNA fragmentation, tended to increase the ROS content, increased caspase-3, caspase-8 and caspase-9 activities, upregulated the mRNA levels of proapoptotic molecules (apoptotic protease-activating factor-1 [Apaf1] and Bcl-2-associated X protein [BAX]) and mitogen-activated protein kinase (MAPK)-related signal molecules (Jun N-terminal kinase (JNK) and p38 MAPK) and increased the protein levels of p38 MAPK and phospho-p38 MAPK. Moreover, in the distal intestine, dietary beta-conglycinin induced DNA fragmentation, elevated NOX activity and the ROS content and increased caspase-3, caspase-8 and caspase-9 activities, death ligand (TNF-alpha) mRNA expression level, and p38 MAPK and phospho-p38 MAPK protein levels. In summary, dietary soybean beta-conglycinin suppressed fish growth and inconsistently caused apoptosis among the different intestinal segments which was partially associated with ROS-mediated MAPK signalling.