Enhancement of FGF-1 release along with cytosolic proteins from rat astrocytes by hydrogen peroxide

Abstract

We previously observed that the production and release of fibroblast growth factor (FGF-1) are increased in rat astrocytes during in vitro long-term culture, that FGF-1 enhances the generation of apoE-containing high density lipoproteins (apoE/HDL), and that the wound healing of brain cryoinjury delays in apoE-deficient mouse. The detail mechanism underlying these phenomena remains unknown. In this study, we examined effects of oxidative stress on release of FGF-1 from cultured rat astrocytes.The treatment of rat astrocytes with 100µM hydrogen peroxide (H2O2) for 10min enhanced FGF-1 release without inducing apoptosis. The conditioned medium prepared from the cells cultured in a fresh medium after the treatment with H2O2 had the FGF-1-like activities, which enhanced cholesterol synthesis, signalings to phosphorylate Akt and ERK, and apoE secretion. The oxidative stress induced by H2O2 enhanced the release of cytosolic proteins such as HSP70 and HSP90 in addition to FGF-1. Antioxidants such as ascorbic acid and ebselen suppressed the release of cytosolic proteins induced by H2O2 treatment. The addition of lipoproteins such as low density lipoproteins (LDL), furthermore, canceled H2O2-induced release of FGF-1 and cytosolic proteins. Proteolysis of cytosolic proteins in the H2O2-treated rat astrocytes was enhanced in the presence of exogenous trypsin, which was attenuated by the pretreatment with LDL, suggesting that H2O2 increases the permeability of the membrane of cells, which was prevented by the addition of lipoproteins. These findings suggest that oxidative stress is one of the candidates which triggers FGF-1 release from astrocytes in the brain, and that the lipid homeostasis in the cell membrane may regulate H2O2-induced release of FGF-1.