Induction of heat shock proteins and its effects on glial differentiation in rat C6 glioblastoma cells

Heat shock proteins (HSPs) are immediately expressed in neuronal and glial cellsunder various stressful conditions and play a protective role through molecularchaperones. We investigated the characteristics of the induction manner of hemeoxygenase-1 (HO-1) and HSP70 in rat C6 glioblastoma cells. In heat treatment (42'Cfor 30 min), C6 cells expressed high level of HO-1 and HSP70 mRNAs Within 30-60min, and their proteins at 3 hrs. Heat-induced expressions of HSPs mRNAs werecompletely inhibited with actinomycin D, suggesting the transcriptional regulation.Oxygen-glucose deprivation (OGD), cystine-free (inhibition of synthesis ofglutathione), cyto-toxic (ethanol, sodium butyrate) treatments resulted in differentexpression manners between H0-1 and HSP70, which suggested that H0-1 and HSP70play different protective roles against a variety kind of stressful conditions in glialcells. C6 cells can differentiate toward both astrocyte and oligodendrocyte directions.Treatment with dibutyryl cyclic AMP (cAMP) induces expression of glial fibrillaryacidic protein (GFAP), a marker of astrocytes, and treatment with retinoic acid (RA)induces expression of myelin proteolipid protein (PLP), a marker of oligodendrocytes,respectively.Heat treatment before the initiation of differentiation by RA reduced theRA-induced expression of PLP mRNA profoundly, but not in GFAP mRNA levelinduced by cAMP. Heat treatment after the initiation of differentiation by CAMP orRA accelerated the expression of GFAP or PLP mRNAs. Astroglial differentiation byCAMP reduced the heat-induced expressions of HSPs mRNAs, but no change withRA pre-treatment. These results suggested that HSPs may modulate the glialdifferentiation in the developing brain. On the contrary, glial differentiation may giveinfluence on the stress-induced HSPs expression. The timing of stressful damages,resulting in the expression of HSPs, on the developing brain is critically important forthe pathogenesis of glial lesion.In the heat-treated C6 cells, the expression of platelet-derived growth factor(PDGF) receptor-a mRNA was significantly decreased. HSPs may have ability toinduce the glial differentiation in part through down-regulation of the PDGF pathway