Heme oxygenase‐1 (HO‐1) is a stress‐inducible rate‐limiting enzyme in heme degradation, which confers cytoprotection against oxidative injury and provides a vital function in maintaining tissue homeostasis. Increasing reports have indicated that lipoteichoic acid (LTA) exerts as LPS as an immune system‐stimulating agent and plays a role in the pathogenesis of severe inflammatory responses induced by Gram‐positive bacteria infection. Here, we report that LTA is an inducer of HO‐1 and examine the signaling pathways by which LTA regulates HO‐1 expression in human tracheal smooth muscle cells (HTSMCs). LTA induced HO‐1 protein, mRNA expression, and HO‐1 promoter activity. LTA‐stimulated HO‐1 expression was attenuated by transfection with dominant negative mutants of Toll‐like receptor‐2 (TLR‐2) and MyD88, the NADPH oxidase inhibitor (DPI), the ROS scavenger (NAC), and transfection with siRNAs of Src and NF‐E2‐related factor 2 (Nrf2). LTA‐stimulated c‐Src phosphorylation, translocation of p47phox and Nrf2, and ROS production were attenuated by transfection with dominant negative mutants of TLR‐2, MyD88, and c‐Src, and by pretreatment with DPI or NAC. Further studies revealed that LTA induced TLR‐2, MyD88, c‐Src, and p47phox complex formation. These results demonstrated that in HTSMCs, LTA induced ROS generation through the TLR‐2/MyD88/c‐Src/NADPH oxidase pathway, in turn initiates the activation of Nrf2, and ultimately induces HO‐1 expression.

We explored the regulation of filaggrin, cyclooxygenase 2 (COX2) and prostaglandin E2 (PGE2) expression induced by urban particulate matter (PM) in human keratinocytes. In addition, we investigated the signaling pathways involved in PM-induced effects on COX2/PGE2 and filaggrin. PMs induced increases in COX2 expression and PGE2 production, and decreased filaggrin expression. These effects were attenuated by pretreatment with COX2 inhibitor and PGE2 receptor antagonist, or after transfection with siRNAs of the aryl hydrocarbon receptor (AhR), gp91phox and p47phox. Furthermore, PM-induced generation of reactive oxygen species (ROS) and NADPH oxidase activity was attenuated by pretreatment with an AhR antagonist (AhRI) or antioxidants. Moreover, Nox-dependent ROS generation led to phosphorylation of ERK1/2, p38, and JNK, which then activated the downstream molecules NF-κB and AP-1, respectively. In vivo studies in PMs-treated mice showed that AhRI and apocynin (a Nox2 inhibitor) had anti-inflammatory effects by decreasing COX2 and increasing filaggrin expression. Our results reveal for the first time that PMs-induced ROS generation is mediated through the AhR/p47 phox/NADPH oxidase pathway, which in turn activates ERK1/2, p38/NF-κB and JNK/AP-1, and which ultimately induces COX2 expression and filaggrin downregulation. Up-regulated expression of COX2 and production of PGE2 may lead to impairment of skin barrier function.

Oxidative stresses are believed to play an important role in the induction of both cell adhesion molecules and pro-inflammatory cytokines, a key event in a variety of inflammatory processes. The enzyme heme oxygenase-1 (HO-1) functions as an antioxidant and serves to protect against tissue injury. In this study, we report that HO-1 was induced in cultured human tracheal smooth muscle cells after either treatment with a potent inducer of HO-1 activity, cobalt protoporphyrin IX, or infection with a recombinant adenovirus that carries the human HO-1 gene. Overexpression of HO-1 protected against tumor necrosis factor (TNF)-␣-mediated airway inflammation via the down-regulation of oxidative stress, adhesion molecules, and interleukin-6 in both cultured human tracheal smooth muscle cells and the airways of mice. In addition, HO-1 overexpression inhibited TNF-␣-induced intercellular adhesion molecule-1 and vascular cell adhesion molecule-1 expression, adherence of THP-1 cells, generation of interleukin-6, p47 phox translocation, and nuclear factor-B activation. HO-1 overexpression also attenuated TNF-␣-induced oxidative stress, which was abrogated in the presence of both the HO-1 inhibitor, zinc protoporphyrin IX, as well as a carbon monoxide scavenger. In addition, HO-1 overexpression reduced the formation of a TNFR1/c-Src/p47 phox complex. These results suggest that HO-1 functions as a suppressor of TNF-␣ signaling, not only by inhibiting the expression of adhesion molecules and generation of interleukin-6, but also by diminishing intracellular reactive oxygen species production and nuclear factor-B activation in both cultured human tracheal smooth muscle cells and the airways of mice.

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