Molecular characterization and expression of AMP-activated protein kinase in response to low-salinity stress in the Pacific white shrimp Litopenaeus vannamei

AMP-activated protein kinase (AMPK) serves as a major regulator of cellular energy metabolism by activating ATP production pathways and blocking ATP consumption. However, information on AMPK genes in aquatic animals is limited. In this study, three subunits of AMPK were cloned from the Pacific white shrimp Litopenaeus vannamei. The full-length cDNAs of the α, β and γ subunits were 1617, 1243 and 3467 bp long, respectively, with open reading frames of 1566, 873 and 2988 bp encoding for 521, 290 and 996 amino acids, respectively. Amino acid sequence alignments of the three subunits showed that the functional domains in the L. vannamei proteins retained the highest similarity with those of other animals, at 89%, 58%, and 75%, respectively. The expression levels of the three subunits were higher in the muscle and gills than in the eyestalk and hepatopancreas. The mRNA levels of AMPK-α and AMPK-β were up-regulated in the hepatopancreas and muscle after acute low-salinity stress at 3 psu for 6 h compared with control salinity at 20 psu. After 8-week salinity stress at 3 psu, AMPK-α and AMPK-β mRNA levels in the hepatopancreas were significantly higher than those of the control at 30 psu. However, in the muscle only AMPK-γ mRNA was significantly up-regulated at low salinity relative to controls. Muscle and hepatopancreas showed increases in AMPK protein after 6 h exposure to low salinity, but there were no differences seen after long term acclimation. The change patterns of protein were slightly differing from the mRNA patterns due to the distinguishing function of individual subunits of AMPK. These findings confirm that three AMPK subunits are present in L. vannamei and that all encode proteins with conserved functional domains. The three AMPK subunits are all regulated at the transcriptional and protein levels to manage excess energy expenditure during salinity stress.