Impact of season on liver mitochondrial oxidative stress and the expression of HSP70 in grey mullets from contaminated estuary.

Heat shock proteins (HSPs) are the ubiquitous feature of cells in which these proteins cope with stress induced denaturation of other proteins. HSP70 is found to play a primary role in cellular defense under stress condition. In the present investigation, the seasonal impact on environmental stress induced mitochondrial HSP70 (mtHSP70) expression in the liver mitochondria was examined in grey mullets, Mugil cephalus living in the Ennore estuary (polluted site) was compared with the Kovalam estuary (unpolluted site) over the course of two seasons viz monsoon and summer from April 2006 to March 2008. Oxidative stress was determined along with mtHSP70 expression studies in fish liver mitochondria collected from these two estuaries for both the seasons. The liver mitochondria of grey mullet fish collected from polluted Ennore estuary showed increased levels of lipid peroxide and mtHSP70 expression along with decrease in total antioxidant capacity and glutathione redox ratio levels ((c) P < 0.05) when compared to unpolluted Kovalam estuary fish. In the fish liver mitochondria of Ennore estuary, there was significant seasonal variation ((b) P < 0.05) in both oxidative stress marker levels (34% increase) and mitochondrial HSP70 expression (33% increase) with increased level during summer season but the Kovalam estuary fish did not show any significant seasonal variation. In the Ennore estuary fish that are exposed to chronic environmental stress, the overexpression of liver mtHSP70 particularly during summer season may confer differential effects on the cell survival by protection against oxidative stress induced changes.