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  • Publication
    Hypoxia: an alarm signal during intestinal inflammation
    (Nature Publishing Group, 2010-04-06) ;
    Intestinal epithelial cells that line the mucosal surface of the gastrointestinal tract are positioned between an anaerobic lumen and a highly metabolic lamina propria. As a result of this unique anatomy, intestinal epithelial cells function within a steep physiologic oxygen gradient relative to other cell types. Furthermore, during active inflammatory disease such as IBD, metabolic shifts towards hypoxia are severe. Studies in vitro and in vivo have shown that the activation of hypoxia-inducible factor (HIF) serves as an alarm signal to promote the resolution of inflammation in various mouse models of disease. Amelioration of disease occurs, at least in part, through transcriptional upregulation of nonclassic epithelial barrier genes. There is much interest in harnessing hypoxia-inducible pathways, including stabilizing HIF directly or via inhibition of prolyl hydroxylase enzymes, for therapy of IBD. In this Review, we discuss the signaling pathways involved in the regulation of hypoxia and discuss how hypoxia may serve as an endogenous alarm signal for the presence of mucosal inflammatory disease. We also discuss the pros and cons of targeting these pathways to treat patients with IBD.
      364Scopus© Citations 331
  • Publication
    Hypercapnia Suppresses the HIF-dependent Adaptive Response to Hypoxia
    Molecular oxygen and carbon dioxide are the primary gaseous substrate and product of oxidative metabolism, respectively. Hypoxia (low oxygen) and hypercapnia (high carbon dioxide) are co-incidental features of the tissue microenvironment in a range of pathophysiologic states, including acute and chronic respiratory diseases. The hypoxia-inducible factor (HIF) is the master regulator of the transcriptional response to hypoxia; however, little is known about the impact of hypercapnia on gene transcription. Because of the relationship between hypoxia and hypercapnia, we investigated the effect of hypercapnia on the HIF pathway. Hypercapnia suppressed HIF-α protein stability and HIF target gene expression both in mice and cultured cells in a manner that was at least in part independent of the canonical O2-dependent HIF degradation pathway. The suppressive effects of hypercapnia on HIF-α protein stability could be mimicked by reducing intracellular pH at a constant level of partial pressure of CO2 Bafilomycin A1, a specific inhibitor of vacuolar-type H(+)-ATPase that blocks lysosomal degradation, prevented the hypercapnic suppression of HIF-α protein. Based on these results, we hypothesize that hypercapnia counter-regulates activation of the HIF pathway by reducing intracellular pH and promoting lysosomal degradation of HIF-α subunits. Therefore, hypercapnia may play a key role in the pathophysiology of diseases where HIF is implicated.
      39Scopus© Citations 39