OBJECTIVE: We have previously demonstrated that the transcription factor hypoxia-inducible factor 1 (HIF-1) promotes the onset of autophagy in chondrocytes. The overall goal of this study was to test the hypothesis that another HIF family transcription factor, HIF-2, modulates the induction of autophagy by chondrocytes. METHODS: Expression of HIF-1, HIF-2, and light chain 3 (LC3) in human and murine articular cartilage was visualized by immunohistochemistry. Suppression of HIF-2 was achieved using small interfering RNA technology. Assessments of autophagic flux and lysosomal activity, as well as ultrastructural analysis, were performed in chondrocytes in cell culture. RESULTS: HIF-2 was expressed abundantly by cells in human and murine articular cartilage and in the cartilage of mineralizing vertebrae from neonatal mice. Protein levels were reduced in articular cartilage from older mice, in end-plate cartilage from mice, and in chondrocytes from human osteoarthritic (OA) cartilage. HIF-2 was robustly expressed in the prehypertrophic cells of mouse growth cartilage. When HIF-2alpha was silenced, the generation of reactive oxygen species was found to be elevated, with a concomitant decrease in catalase and superoxide dismutase activity. Suppression of HIF-2 was associated with decreased Akt-1 and mammalian target of rapamycin activities, reduced Bcl-xL expression, and a robust autophagic response, even under nutrient-replete conditions. In these silenced chondrocytes, HIF-1 expression was elevated. Decreased HIF-2 expression was associated with autophagy in OA tissues and aging cartilage samples. The autophagic response of chondrocytes in HIF-2alpha-knockout mouse growth plate showed an elevated autophagic response throughout the plate. CONCLUSION: Based on these observations, we conclude that HIF-2 is a potent regulator of autophagy in maturing chondrocytes. Our data suggest that this protein acts as a brake on the autophagy-accelerator function of HIF-1.
OBJECTIVE: We have previously demonstrated that the transcription factor hypoxia-inducible factor 1 (HIF-1) promotes the onset of autophagy in chondrocytes. The overall goal of this study was to test the hypothesis that another HIF family transcription factor, HIF-2, modulates the induction of autophagy by chondrocytes. METHODS: Expression of HIF-1, HIF-2, and light chain 3 (LC3) in human and murinearticular cartilage was visualized by immunohistochemistry. Suppression of HIF-2 was achieved using small interfering RNA technology. Assessments of autophagic flux and lysosomal activity, as well as ultrastructural analysis, were performed in chondrocytes in cell culture. RESULTS: HIF-2 was expressed abundantly by cells in human and murinearticular cartilage and in the cartilage of mineralizing vertebrae from neonatal mice. Protein levels were reduced in articular cartilage from older mice, in end-plate cartilage from mice, and in chondrocytes from humanosteoarthritic (OA) cartilage. HIF-2 was robustly expressed in the prehypertrophic cells of mousegrowth cartilage. When HIF-2alpha was silenced, the generation of reactive oxygen species was found to be elevated, with a concomitant decrease in catalase and superoxide dismutase activity. Suppression of HIF-2 was associated with decreased Akt-1 and mammalian target of rapamycin activities, reduced Bcl-xL expression, and a robust autophagic response, even under nutrient-replete conditions. In these silenced chondrocytes, HIF-1 expression was elevated. Decreased HIF-2 expression was associated with autophagy in OA tissues and aging cartilage samples. The autophagic response of chondrocytes in HIF-2alpha-knockout mouse growth plate showed an elevated autophagic response throughout the plate. CONCLUSION: Based on these observations, we conclude that HIF-2 is a potent regulator of autophagy in maturing chondrocytes. Our data suggest that this protein acts as a brake on the autophagy-accelerator function of HIF-1.
Authors: Huafeng Zhang; Marta Bosch-Marce; Larissa A Shimoda; Yee Sun Tan; Jin Hyen Baek; Jacob B Wesley; Frank J Gonzalez; Gregg L Semenza Journal: J Biol Chem Date: 2008-02-15 Impact factor: 5.157
Authors: Marzia Scortegagna; Kan Ding; Yavuz Oktay; Arti Gaur; Frederick Thurmond; Liang-Jun Yan; Brett T Marck; Alvin M Matsumoto; John M Shelton; James A Richardson; Michael J Bennett; Joseph A Garcia Journal: Nat Genet Date: 2003-11-09 Impact factor: 38.330
Authors: Adam M Zahm; Jolene Bohensky; Christopher S Adams; Irving M Shapiro; Vickram Srinivas Journal: Cells Tissues Organs Date: 2011-05-19 Impact factor: 2.481
Authors: T Weng; Y Xie; L Yi; J Huang; F Luo; X Du; L Chen; C Liu; D Chen; L Chen Journal: Osteoarthritis Cartilage Date: 2014-07-04 Impact factor: 6.576