Hypoxia-inducible factor 1/heme oxygenase 1 cascade as upstream signals in the prolife role of heat shock protein 70 at rostral ventrolateral medulla during experimental brain stem death

As the origin of a life-and-death signal that reflects central cardiovascular regulatory failure during brain stem death, the rostral ventrolateral medulla (RVLM) is a suitable neural substrate to delineate the cellular mechanisms of this fateful phenomenon. Based on a clinically relevant animal model that used the organophosphate pesticide mevinphos (Mev) as the experimental insult, we reported previously that heat shock protein 70 (HSP70) in RVLM plays a prolife role by ameliorating circulatory depression during brain stem death. Because Mev also elicits significant hypoxia in RVLM, this study evaluated the hypothesis that the hypoxia-inducible factor 1 (HIF-1)/heme oxygenase 1 (HO-1) cascade acts as upstream signals in the prolife role of HSP70 at RVLM during experimental brain stem death. In Sprague-Dawley rats maintained under propofol anesthesia, transcription activity assay or Western blot analysis revealed an enhancement of nuclear activity of HIF-1α or augmentation of HO-1 and HSP70 expression in RVLM preferentially during the prolife phase of Mev intoxication. Loss-of-function manipulations in RVLM using HIF-1α, HIF-1β, or HO-1 antiserum or antisense hif-1α or ho-1 oligonucleotide significantly antagonized the preferential upregulation of HSP70, depressed the sustained cardiovascular regulatory machinery during the prolife phase, and exacerbated circulatory depression during the prodeath phase. Immunoneutralization of HIF-1α also blunted the preferential increase in HO-1 expression. We conclude that the repertoire of cellular events in RVLM during the prolife phase in our Mev intoxication of brain stem death triggered by hypoxia entails sequential activation of HIF-1, HO-1, and HSP70, leading to neuroprotection by amelioration of cardiovascular depression.