Distributions of Heat Shock Protein-70 mRNAs and Heat Shock Cognate Protein-70 mRNAs after Transient Global Ischemia in Gerbil Brain

Abstract

Distributions of heat shock protein (HSP)-70 mRNAs and heat shock cognate protein (HSC)-70 mRNAs after 10 min of transient global ischemia were investigated in gerbil forebrain by in situ hybridization using cloned cDNA probes selective for the mRNAs. Expression of HSP70 immunoreactivity was also examined in the same brains. In hippocampal CA1 neuronal cells, in which only a minimal induction of immunoreactive HSP70 protein was found, the strong hybridization for HSP70 mRNA disappeared at around 2 days before the death of CA1 cells became evident. Furthermore, in hippocampal CA3 cells, a striking induction of HSP70 mRNA was sustained even at 2 days along with a prominent accumulation of HSP70 immunoreactivity. In contrast to the case of HSP70 mRNA, HSC70 mRNA was present in most neuronal cells, especially dense in CA3 cells, of the sham brain. A co-induction of HSP70 and HSC70 mRNAs was observed in several cell populations after the reperfusion with a peak at 8 h, although the magnitude of HSC70 mRNA induction was lower than that of HSP70 mRNA, particularly in CA1 cells. The expression of HSC70 mRNA in CA1 cells also disappeared at around 2 days. All the induced signals of HSP70 and HSC70 mRNAs in other cell populations were diminished and returned to the sham level, respectively, by 7 days. These results are the first to show the time courses of distribution of HSP70 and HSC70 mRNAs and the immunoreactive HSP70 protein in the same gerbil brain after ischemia. The results suggest that the weak induction of HSP70 protein in CA1 cells, which may relate to the vulnerability of this cell population, is due to both translational and transcriptional deficits. The different roles under normal condition and the cooperative role in the recovery process from ischemic injury between HSP70 and HSC70, and the involvement of HSC70 in CA1 cell death, are suggested.