Involvement of insulin-like growth factor binding proteins (IGFBPs) and activation of insulin/IGF-like signaling (IIS)-target of rapamycin (TOR) signaling cascade in pacific white shrimp, Litopenaeus vannamei exposed to acute low-salinity

Abstract

Acute low-salinity induces multiple stress responses and significantly impact the health of aquatic animals. However, the molecular regulation network and metabolic adaptation of low salinity stress in aquatic organisms remain unclear. The insulin-like growth factor binding proteins (IGFBPs) and insulin/IGF-like signaling (IIS)-target of rapamycin (TOR) signaling cascade are evolutionarily conserved regulators known to play crucial roles in response to various stressors. In this study, we used the euryhaline Pacific white shrimp (Litopenaeus vannamei) as a model organism to investigate the involvement of IGFBP and IIS-TOR signaling cascade in acute low-salinity response. We found seven LvIGFBPs and evaluated 18s as one of most stable internal reference genes under acute low salinity stress. The expression of LvIGFBP4, LvSIBD1, and LvSIBD2 was significantly increased after 6-hours 5‰ salinity treatment. LvSIBD2 was specifically expressed on the surface of gill branch axis. Acute low-salinity significantly induced the phosphorylation of Akt and S6K in the gill but not in the muscle. We found acute low-salinity increased the levels of total essential amino acids, including leucine and arginine, while decreasing the total non-essential amino acid levels in the gill. Furthermore, glucose and key metabolites in glycolysis and tricarboxylic acid cycle (TCA cycle) were increased, indicating remodeling of energy metabolism occurred. These results demonstrate the involvement of IGFBP and IIS-TOR signaling cascade in acute low-salinity response and provide new insights into understanding the mechanism of osmoregulation in euryhaline crustacean species.