Regulation of caveolin-1 expression, nitric oxide production and tissue injury by tumor necrosis factor-α following ozone inhalation

Alveolar macrophages (AM) and inflammatory mediators including nitric oxide and peroxynitrite contribute to ozone-induced lung injury. The generation of these mediators is regulated, in part, by the transcription factor NF-kappa B. We previously demonstrated a critical role for NF-kappa B p50 in ozone-induced injury. In the present studies mechanisms regulating NF-kappa B activation in the lung after ozone inhalation were analyzed. Treatment of wild type (WT) mice with ozone (0.8 ppm, 3 h) resulted in a rapid increase in NF-kappa B binding activity in AM, which persisted for at least 12 h. This was not evident in mice lacking TNF alpha which are protected from ozone-induced injury; there was also no evidence of nitric oxide or peroxynitrite production in lungs from these animals. These data demonstrate that TNF alpha plays a role in NF-kappa B activation and toxicity. TNF alpha signaling involves PI-3-kinase (PI3K)/protein kinase B (PKB), and p44/42 MAP kinase (MAPK) which are important in NF-kappa B activation. Ozone Inhalation resulted in rapid and transient increases in p44/42 MAPK and PI3K/PKB in AM from WT mice, which was evident immediately after exposure. Caveolin-1. a transmembrane protein that negatively regulates PI3K/PKB and p44/42 MAPK signaling, was downregulated in AM from WT mice after ozone exposure. In contrast, ozone had no effect on caveolin-1, PI3K/PKB or p44/42 MAPK expression in AM from TNF alpha knockout mice. These data, together with our findings that TNF alpha suppressed caveolin-1 expression in cultured AM, suggest that TNF alpha and downstream signaling mediate activation of NF-kappa B and the regulation of inflammatory genes important in ozone toxicity, and that this process is linked to caveolin-1. (c) 2007 Elsevier Inc. All rights reserved.