Influence of acclimation temperature on the induction of heat-shock protein 70 in the catfish Horabagrus brachysoma (Gunther)

Every organism responds to heat stress by synthesizing a group of evolutionarily conserved proteins called the heat-shock proteins (HSPs) that, by acting as molecular chaperones, protect the cell against the aggregation of denatured proteins and play a significant role in adaptation to temperature. The present study aimed to investigate the critical thermal maxima (CTMax) and the expression of HSP70 in different tissues (gill, brain, muscle and liver) of an endemic catfish Horabagrus brachysoma acclimated at either 20 or 30A degrees C for 30 days. To understand the HSP70 response, fish acclimated to the two temperatures were exposed to preset temperatures (26, 30, 34, 36 and 38A degrees C for 20A degrees C acclimated fish and 32, 34, 36, 38 and 40A degrees C for 30A degrees C acclimated fish) for 2 h, followed by 1 h recovery at their respective acclimation temperatures. The HSP70 levels in the gill, brain, muscle and liver tissues were determined by Western blotting of one-dimensional sodium dodecyl sulphate-polyacrylamide gel electrophoresis. A significant (P < 0.05) increase in the CTMax values was observed for fish acclimated at 30A degrees C (41.86 +/- A 0.39A degrees C) than those acclimated at 20A degrees C (39.13 +/- A 0.18A degrees C). HSP70 was detected in all the tissues with the highest level in the liver followed by intermediate levels in muscle and brain, and lowest level in gill tissue, irrespective of the acclimation temperatures (20 or 30A degrees C). The HSP70 levels were significantly higher (P < 0.05) in the tissues of fish acclimated at 30A degrees C than those acclimated at 20A degrees C. The mean induction temperature of HSP70 in all the tissues of fish acclimated at either 20 or 30A degrees C was 30 and 34A degrees C, respectively. The optimum temperature for HSP70 induction in all the tissues of fish acclimated at 20A degrees C was 36A degrees C, whereas for fish acclimated at 30A degrees C was 36A degrees C for gill and 38A degrees C for brain, muscle and liver. Decreased levels of HSP70 were noted in all the tissues of fish when exposed to temperatures that exceeded the optimum temperatures for HSP70 inductions. Overall results indicated that acclimation temperature influences both temperature tolerance and induction of HSP70 in H. brachysoma.