The role of HIF proteins in maintaining the metabolic health of the intervertebral disc

Nat Rev Rheumatol. 2021 Jul;17(7):426-439. doi: 10.1038/s41584-021-00621-2. Epub 2021 Jun 3.

Abstract

The physiologically hypoxic intervertebral disc and cartilage rely on the hypoxia-inducible factor (HIF) family of transcription factors to mediate cellular responses to changes in oxygen tension. During homeostatic development, oxygen-dependent prolyl hydroxylases, circadian clock proteins and metabolic intermediates control the activities of HIF1 and HIF2 in these tissues. Mechanistically, HIF1 is the master regulator of glycolytic metabolism and cytosolic lactate levels. In addition, HIF1 regulates mitochondrial metabolism by promoting flux through the tricarboxylic acid cycle, inhibiting downsteam oxidative phosphorylation and controlling mitochondrial health through modulation of the mitophagic pathway. Accumulation of metabolic intermediates from HIF-dependent processes contribute to intracellular pH regulation in the disc and cartilage. Namely, to prevent changes in intracellular pH that could lead to cell death, HIF1 orchestrates a bicarbonate buffering system in the disc, controlled by carbonic anhydrase 9 (CA9) and CA12, sodium bicarbonate cotransporters and an intracellular H+/lactate efflux mechanism. In contrast to HIF1, the role of HIF2 remains elusive; in disorders of the disc and cartilage, its function has been linked to both anabolic and catabolic pathways. The current knowledge of hypoxic cell metabolism and regulation of HIF1 activity provides a strong basis for the development of future therapies designed to repair the degenerative disc.

Publication types

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

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Transcription Factors / metabolism
  • Basic Helix-Loop-Helix Transcription Factors / physiology
  • Humans
  • Hypoxia / metabolism
  • Hypoxia-Inducible Factor 1 / metabolism
  • Hypoxia-Inducible Factor 1 / physiology*
  • Intervertebral Disc / metabolism*
  • Intervertebral Disc / physiology

Substances

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