HSP70 Downregulation by Pifithrin-? Upregulates Pro-Apoptotic Changes in Stressed Fish Hepatocytes

Estuarine grey mullet is very sensitive to several environmental factors. Apoptosis signal regulating kinase-1 (ASK1) activity is regulated at multiple levels, one of which is through inhibition by heat shock protein (HSP70). In this study, we investigated the inhibitory effect of pifithrin- in the hepatocytes of Mugil cephalus inhabiting Kovalam and Ennore estuaries. The level of total antioxidant capacity (TAC) and the expression of 4-hydroxy-2-nonenal (HNE), HSP70, HO-1, phospho-ERK and ASK1 were measured in hepatocytes of M. cephalus inhabiting Kovalam and Ennore estuaries with and without pifithrin- incubation. A significant increase in oxidative stress along with decrease in antioxidant status in hepatocytes of M. cephalus inhabiting Ennore estuary was observed, whereas pifithrin- incubation moderately alters the stress and antioxidant status. The level of HSP70 was inhibited by 39 % at 10 M of pifithrin- for 60 minutes. Pifithrin- enhances the generation of ROS, possibly by inhibiting the anti-oxidant actions of HSP70. An alteration in the expression of HSP70 by pifithrin- inhibitor causes downregulation of phospho-ERK and upregulation of ASK1 expression. These proapoptotic changes in the stressed fish hepatocytes indicate that HSP70 threshold is a key factor in fish survival under polluted environmental stress.