Molecular effects of microcystin-LA toxicity in Tilapia ( Oreochromis niloticus )

A comprehensive understanding of microcystin (MC) effects and mode(s) of action(s) on aquatic biota has not been achieved yet. In the present study, Nile tilapia ( Oreochromis niloticus ) were sub-lethally exposed to the microcystin analogue MC-LA for 12, 24, 48 and 96 hours, and gene expression of PP1, PP2A, GST and actin were analyzed by quantitative PCR. Moreover, PP2A protein abundance profile was established by immunoblotting, while its biological function integrity was checked by a phosphatase enzymatic assay. PP2A activity was significantly reduced by MC-LA, indicating that MC acts as a PP2A inhibitor, similarly to what occurs in mammals. However, the positive (9.1-fold after 12h) feedback mechanism induced by PP2A gene , after exposure to sub-lethal MC-LA dose (1,000 µg.kg -1 ), did not counteract the complete PP2A catalytic activity inhibition that occurred concomitantly. A weaker inflammatory response in fish compared to mammals may be the reason why O. niloticus is able to tolerate such high concentrations of MC-LA when compared to mice.