FOCAL CEREBRAL-ISCHEMIA INCREASES THE LEVELS OF SEVERAL CLASSES OF HEAT-SHOCK PROTEINS AND THEIR CORRESPONDING MESSENGER-RNAS

The induction of focal cerebral ischaemia in rats by middle cerebral a rtery occlusion has previously been shown to increase, over time, the mRNA levels of the heat shock proteins (HSPs) 27 and 70. However, the levels of HSP90 mRNA remain constant. In contrast, during global ischa emia, HSP70 and HSP90 mRNA levels are both raised, particularly in the CA1 neurons in the hippocampus, an area that is resistant to the insu lt in comparison to the surrounding regions. HSP27 mRNA is raised in t he neuroglia in the subregions of the hippocampus. However, the protei n levels of HSP27, 70 and 90 have not been characterised in focal isch aemia. With this data in mind, we have carried out a comparative study of HSP27, 56, 60, 70 and 90 mRNA and protein levels during focal cere bral ischaemia in rats, up to 24 h post-occlusion. We have shown that HSP70 and HSP27 mRNA levels are increased and also that HSP60 mRNA lev els (which had also not previously been characterised in this model of focal ischaemia) are significantly raised. HSP90 and HSP56 mRNAs were not significantly elevated. On Western blot analysis, the inducible H SP72 protein was first detected at 8 h post-occlusion, HSP27 protein w as detected only at 24 h post-occlusion and HSP60 protein, although co nstitutive, appeared to increase at 24 h post-occlusion. HSP56 protein levels appeared to rise on the occluded side, but HSP90 protein level s remained constant.