EFFECT OF HEAT-SHOCK ON NEURONAL CULTURES - IMPORTANCE OF PROTEIN-SYNTHESIS AND HSP72 INDUCTION FOR INDUCED TOLERANCE AND SURVIVAL

In this study the effects of 30 min heat-shock, ranging from 42 degree s C to 46 degrees C, on survival, protein synthesis and HSP72 expressi on were investigated in primary rat neuronal cultures. Heat-shock of 4 4 degrees C resulted in a complete, but transient inhibition of protei n synthesis which recovered within 24 h. 46 degrees C heat-shock resul ted in an irreversible inhibition of protein synthesis and complete ne uronal loss within 24 h. Cycloheximide treatment of neuronal cultures resulted in aggravation of neuronal cell damage after heat-shock of 44 degrees C, indicating that the capacity for recovery of the overall p rotein synthesis is an important survival factor. In addition, the red uction of neuronal cell damage mediated by heat conditioning was aboli shed by cycloheximide treatment, indicating that the function of new p roteins is important for induced thermotolerance. Induction of the str ictly inducible member of the heat-shock protein 70kDa family, HSP72, was found in those few astrocytes which were contaminating the neurona l cell cultures, but not in neurons. These results indicate that newly synthesised proteins other than HSP72 are likely to mediate neuronal protection following heat shock in our experiments. These findings rai se the possibility that induced tolerance may not necessarily be media ted by HSP72.