HSP70 Gene Expression in the Zebrafish Retina After Optic Nerve Injury: A Comparative Study Under Heat Shock Stresses

Abstract

Unlike mammals, fish retinal ganglion cells (RGCs) can regrow their axon and restore visual function after optic nerve injury (ONI), which is the best model for CNS repair. Heat shock protein 70 (HSP70) plays an important role for cell protection by various environmental stresses. HSP70 is transactivated by phosphorylated Heat shock factor-1 (pHSF-1). In this study, we investigate the expression of HSP70 and pHSF-1 after ONI and heat shock condition (at 37°C for 30 min) in zebrafish (ZF) retina. After ONI, HSP70 was increased for a long time in the RGCs during 0.5–24 h and then returned to the control level by 72 h. In contrast, HSP70 increased for a short time in all nuclear layers at 0.5–1 h, and then returned to control level by 3 h after heat shock. The level of HSF-1 mRNA was significantly increased in ZF retina 0.5–24 h after ONI, but not after heat shock. pHSF-1 was detected after both heat shock and ONI. These results indicate that the increased expression of HSP70 mRNA after ONI is caused by both activations of translocation of pHSF-1 and of transcription of HSF-1 mRNA in the nucleus, whereas the increased expression of HSP70 mRNA after heat shock is caused only by activation of pHSF-1 translocation into the nucleus.