Age affects ERK1/2 and NRF2 signaling in the regulation of GCLC expression

We previously reported that activator protein‐1 (AP‐1) DNA binding activity was increased in vascular smooth muscle cells (VSMC) from old rats when exposed to high glucose or tumor necrosis factor (TNF‐α) (Li et al., 2003. J Cell Physiol 197:418–425). We have now examined the relationship between the age‐dependent activation of the ERK1/2–AP‐1 pathway and modulation of constitutive gene expression of the catalytic subunit of glutamate‐cysteine ligase (GCLC) in response to high glucose and TNF‐α. GCLC mRNA levels were higher in VSMC from old rats compared to young, a pattern consistent with its protein levels. To determine whether age‐related activation of ERK1/2‐AP‐1 signaling is responsible for the up‐regulation of GCLC, the MEK inhibitors, PD98059 and U0126, were used to block ERK1/2 in VSMC from old rats. An increase in GCLC with inhibitors was observed, diminishing the likelihood of ERK1/2‐AP‐1 activation as the up‐regulating signal for GCLC. However, the transcription factor Nrf2 was higher in nuclei and accompanied by increased Nrf2‐ARE binding in VSMC from old rats. Furthermore, MEK inhibitors increased nuclear Nrf2 and Nrf2/ARE binding. These data suggest opposing effects of Nrf2 and ERK1/2 signaling in the modulation of GCLC expression in old animals. J. Cell. Physiol. © 2006 Wiley‐Liss, Inc.