MAPK and JAK-STAT Signaling Pathways are Involved in the Oxidative Stress - Induced Decrease in Expression of Surfactant Protein Genes

Oxidative stress is generated by reactive oxygen species (ROS) including hydrogen peroxide (H2O2), hydroxyl radical (center dot OH) and superoxide anion (02), which are produced as by-products of cellular metabolism. An imbalance in cellular redox status is a potent pathogenic factor that contributes to various chronic inflammatory diseases. In this study, we demonstrate that H2O2 decreases surfactant protein A, B and ABCA3 mRNA level, and increases SP-D mRNA level in human pulmonary lung epithelial cells. The decreased mRNA level of SP-A and SP-B were significant with a maximum inhibition of 79 and 87%, respectively by 150 mu M H2O2 after 24 hrs of incubation. In addition, ABCA3 mRNA level was decreased with a maximum inhibition of 55% by 150 pM H2O2 after 12 hrs of incubation. In contrast, 150 pM H2O2 caused the SP-D mRNA level to increase to 200% of control after 8 hrs of incubation. The H2O2-induced gene repression or activation of SP-A, SP-B, SP-D and ABCA3 was blocked by pretreatment with the antioxidants N-acetyl-L-cysteine (NAC) and catalase. Furthermore, the inhibition of SP-A and SP-B was associated with reduced thyroid transcription factor -1 (TTF-1) DNA binding activity, and this reduced TTF-1 binding activity may be due to decreased TTF-1 protein expression level. The analyses of signal transduction pathways that may play a role in the regulation of gene expression by H2O2 using several specific inhibitors showed that U0126, an inhibitor of ERK1/2 upstream kinase MEK1/2, blocked both H2O2-induced inhibition of SP-A and SP-B gene expression, whereas SB203580, an inhibitor of p38 MAPK, partially blocked H2O2-mediated inhibition of SP-A gene expression but not SP-B expression. In contrast, AG-490, a specific inhibitor of JAK-STAT pathway, blocked H2O2-mediated inhibition of SP-B gene expression but not SP-A expression. Immunoblot analyses using specific phosphor-antibodies demonstrated that ERK1/2, p38 MAPK and STAT3 are phosphorylated by oxidative stress suggesting that H2O2-induced inhibition of SP-A and SP-B gene expression is associated with MAPK and JAK-STAT signaling pathway. These data, therefore, suggest that H2O2 affects SP-A and SP-B gene regulation by reducing TTF-1 DNA binding activity via MAPKs or STAT signaling pathways. Copyright (C) 2012 S. Karger AG, Basel