FGF9-induced changes in cellular redox status and HO-1 upregulation are FGFR-dependent and proceed through both ERK and AKT to induce CREB and Nrf2 activation

Our previous studies demonstrated that fibroblast growth factor 9 (FGF9) protects cortical and dopaminergic neurons from 1-methyl-4-phenylpyridinium (MPP+)-induced oxidative insult by upregulation of gamma-glutamylcysteine synthetase (gamma-GCS) and heme oxygenase-1 (HO-1). However, the mechanisms responsible for FGF9-induced gamma-GCS and HO-1 upregulation remain uncharacterized. In the present study, we demonstrate the signaling pathways by which FGF9 upregulates HO-1 and gamma-GCS expression. We found that FGF9-induced HO-1 and gamma-GCS expression was prevented by PD173014, an inhibitor of the FGF receptor (FUR). FGF9 treatment induced the phosphorylation of FUR downstream signals of extracellular signal-regulated kinase 1/2 (ERK1/2) and AKT in a dose- and time-dependent manner. The inhibition of MEK/ERK1/2 or PI3K/AKT activity by U0126 or wortmannin, but not the inhibition of phospholipase C gamma by 1173122, prevented FGF9-induced gamma-GCS and HO-1 upregulation, changes in cellular redox status, and neuroprotection against MPP+ toxicity in primary cortical and dopaminergic neurons. Furthermore, FGF9 treatment enhanced the promoter activity of the cAMP-response element binding protein (CREB) and nuclear factor erythroid-derived 2-like 2 (Nrf2), and this phenomenon was blocked by PD173014 or 110126 or wortmannin. Knockdown of CREB and Nrf2 by shRNA blocked FGF9-induced gamma-GCS and HO-1 upregulation, but not ERK and AKT phosphorylation. An in vivo study consistently showed that FGF9 overexpression using a lentivirus delivery system induced ERK1/2 phosphorylation and HO-1 upregulation and protected dopaminergic neurons against MPP+ toxicity in rat substantia nigra. These results indicate that FGF9-induced HO-1 and gamma-GCS upregulation is mediated by binding to FGFR and activation of two parallel downstream signaling pathways, ERK and AKT, which reconverge to induce CREB and Nrf2 transcriptional activity. (C) 2015 Elsevier Inc. All rights reserved.