Autophagy in mineralizing tissues: microenvironmental perspectives

Cell Cycle. 2009 Feb 1;8(3):391-3. doi: 10.4161/cc.8.3.7545. Epub 2009 Feb 4.

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.

Publication types

  • Research Support, N.I.H., Extramural
  • Review

MeSH terms

  • Adenylate Kinase / metabolism
  • Autophagy / physiology*
  • Basic Helix-Loop-Helix Transcription Factors / metabolism
  • Bone and Bones / cytology
  • Bone and Bones / metabolism
  • Calcification, Physiologic*
  • Cartilage, Articular / cytology
  • Cartilage, Articular / physiology
  • Chondrocytes / cytology
  • Chondrocytes / physiology*
  • Environment*
  • Growth Plate / cytology
  • Growth Plate / physiology
  • Hypoxia-Inducible Factor 1 / metabolism
  • Signal Transduction / physiology

Substances

  • Basic Helix-Loop-Helix Transcription Factors
  • Hypoxia-Inducible Factor 1
  • endothelial PAS domain-containing protein 1
  • Adenylate Kinase