title: Hypoxia-induced renal epithelial cell death through caspase-dependent pathway: role of Bcl-2, Bcl-xL and Bax in tubular injury.
abstract: Although injury of epithelial cells has been reported to be responsible for renal disease such as acute renal failure, its molecular mechanisms are largely unknown. As hypoxia has been postulated as the initial trigger of epithelial injury, we studied the molecular mechanisms of apoptosis induced by hypoxia in human renal epithelial cells. Severe hypoxia caused epithelial cell death, accompanied by a significant increase in LDH release (p<0.01). In addition, hypoxic treatment of epithelial cells resulted in a significant increase in apoptotic cells as assessed by cell morphology (p<0.01). The apoptotic change in epithelial cells under hypoxic condition was also confirmed by a significant increase in caspase-3-like activity and release of cytochrome c (p<0.01). The decrease in epithelial cell number was completely abolished by addition of a wide-spectrum caspase inhibitor, Z-VAD, rather than Z-DEVD, a specific caspase-3 inhibitor (p<0.01). Thus, we further studied the molecular mechanisms of apoptosis induced by hypoxia. Anti-apoptotic factors, Bcl-2 and Bcl-xL, were significantly decreased in epithelial cells under a hypoxic condition as assessed by Western blotting (p<0.01). In contrast, hypoxia did not alter their location. Of particular importance, translocation of a proapoptotic factor, Bax, from the cytoplasm to the mitochondrial membrane was observed in response to hypoxia, whereas total Bax protein was not changed by hypoxia. Overall, this study demonstrated that hypoxia caused epithelial cell death induced by caspase-3-like activity-dependent apoptosis. The pro-apoptotic mechanisms of hypoxia in epithelial cells largely depend on a significant decrease in Bcl-2 and Bcl-xL. In addition, the present results demonstrate that translocation of Bax from the cytosol to the mitochondrial membrane occurred under hypoxia, thereby leading to pathological tissue destruction.
authors.affiliation: Division of Clinical Gene Therapy, Osaka University Graduate School of Medicine, 2-2 Yamada-oka, Suita 565-0871, Japan.
authors.forename: Kei
authors.initials: K
authors.lastname: Yamamoto
authors.forename: Naruya
authors.initials: N
authors.lastname: Tomita
authors.forename: Shin-ichi
authors.initials: S
authors.lastname: Yoshimura
authors.forename: Hironori
authors.initials: H
authors.lastname: Nakagami
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Taniyama
authors.forename: Keita
authors.initials: K
authors.lastname: Yamasaki
authors.forename: Toshio
authors.initials: T
authors.lastname: Ogihara
authors.forename: Ryuichi
authors.initials: R
authors.lastname: Morishita
mesh_terms: D017209:Apoptosis; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D015687:Cell Hypoxia / Q000502:physiology*; D045304:Cytochromes c / Q000378:metabolism; D004847:Epithelial Cells / Q000201:enzymology / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D007668:Kidney / Q000201:enzymology / Q000378:metabolism / Q000473:pathology*; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism*; D015398:Signal Transduction; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein
chemical_list: C494826:BAX protein, human; C494811:BCL2L1 protein, human; D019253:Proto-Oncogene Proteins c-bcl-2; D051028:bcl-2-Associated X Protein; D051020:bcl-X Protein; D045304:Cytochromes c; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases