1. Autophagy in mineralizing tissues: Microenvironmental perspectives
- Author
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Jolene Bohensky, Irving M. Shapiro, Vickram Srinivas, and Adam M. Zahm
- Subjects
Cartilage, Articular ,Cell ,Regulator ,Environment ,Biology ,Article ,Bone and Bones ,Chondrocyte ,Calcification, Physiologic ,Chondrocytes ,Autophagy ,Basic Helix-Loop-Helix Transcription Factors ,medicine ,Growth Plate ,Molecular Biology ,PI3K/AKT/mTOR pathway ,Adenylate Kinase ,AMPK ,Cell Biology ,Cell biology ,Crosstalk (biology) ,medicine.anatomical_structure ,Osteocyte ,Hypoxia-Inducible Factor 1 ,Signal Transduction ,Developmental Biology - Abstract
Chondrocytes in the growth plate and articular cartilage, and osteocytes subsumed in Haversian bone exist in environmental niches that are characterized by a limited oxygen supply. In these tissues, cells display a hitherto unrecognized state in which there is evidence of autophagy. The autophagic condition serves to promote cell survival. When the response is triggered, the cell cannibalizes itself to generate energy; if extended, then it can activate Type II apoptosis. We opine that survival is dependent on niche conditions and regulated by crosstalk between mTOR, AMPK and HIF-1 and HIF-2. Recent studies suggest that HIF-2 is a potent regulator of chondrocyte autophagy and that this protein acts as a brake to the stimulatory function of HIF-1. Accordingly, the oxemic state of the tissue, its nutrient supply as well as the energetic state of the cells regulates autophagic flux. From a clinical viewpoint, it may be possible to enhance skeletal cell survival through drugs that modulate the autophagic state and prevent the induction of apoptosis.
- Published
- 2009
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