Inflammatory gene transcription in human astrocytes exposed to hypoxia: roles of the nuclear factor-kappa B and autocrine stimulation

Mechanisms of hypoxia-induced activation of nuclear factor-kappaB (NF-kappa B) and inflammatory genes were investigated in fetal human astrocytes in cu lture. Astrocytes were subjected to interleukin-1 beta (IL-1 beta; 50-100 u /ml; 4-24 h), or to a 4-h hypoxia (<2%, O-2) followed by a 4-24-h reoxygena tion. NF-kappaB binding and transcriptional activity increased up to 10-fol d in astrocytes exposed to IL-1 beta, and up to 3-fold in astrocytes subjec ted to hypoxia followed by reoxygenation. Both IL-1 beta- mRNAs and protein s hypoxia-induced NF-kappaB activation were blocked by the proteasome inhib itor, MG-132. MG-132 inhibited IL-1 beta -induced up-regulation of IL-1 bet a and IL-8 mRNA and protein but increased hypoxia-stimulated expression/rel ease of IL-1 beta and IL-8. IL-1 receptor antagonist (IL-1Ra) blocked both hypoxic astrocyte-conditioned media-induced NF-kappaB activation and the ex pression/release of IL-1 beta and IL-8. Astrocytes subjected to hypoxia in the presence of IL-1Ra failed to activate NF-kappaB, but expressed elevated levels of IL-1 beta and IL-8. The data suggest that hypoxia/reoxygenation- induced up-regulation of IL-1 beta and IL-8 in human astrocytes has two com ponents, a NF-kappaB independent up-regulation during hypoxia, followed by amplification through autocrine IL-lp-induced NIF-kappaB activation during reoxygenation. (C) 2001 Elsevier Science B.V. All rights reserved.