Na + controls hypoxic signalling by the mitochondrial respiratory chain

Nature. 2020 Oct;586(7828):287-291. doi: 10.1038/s41586-020-2551-y. Epub 2020 Jul 29.

Abstract

All metazoans depend on the consumption of O2 by the mitochondrial oxidative phosphorylation system (OXPHOS) to produce energy. In addition, the OXPHOS uses O2 to produce reactive oxygen species that can drive cell adaptations1-4, a phenomenon that occurs in hypoxia4-8 and whose precise mechanism remains unknown. Ca2+ is the best known ion that acts as a second messenger9, yet the role ascribed to Na+ is to serve as a mere mediator of membrane potential10. Here we show that Na+ acts as a second messenger that regulates OXPHOS function and the production of reactive oxygen species by modulating the fluidity of the inner mitochondrial membrane. A conformational shift in mitochondrial complex I during acute hypoxia11 drives acidification of the matrix and the release of free Ca2+ from calcium phosphate (CaP) precipitates. The concomitant activation of the mitochondrial Na+/Ca2+ exchanger promotes the import of Na+ into the matrix. Na+ interacts with phospholipids, reducing inner mitochondrial membrane fluidity and the mobility of free ubiquinone between complex II and complex III, but not inside supercomplexes. As a consequence, superoxide is produced at complex III. The inhibition of Na+ import through the Na+/Ca2+ exchanger is sufficient to block this pathway, preventing adaptation to hypoxia. These results reveal that Na+ controls OXPHOS function and redox signalling through an unexpected interaction with phospholipids, with profound consequences for cellular metabolism.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Breast Neoplasms / metabolism
  • Breast Neoplasms / pathology
  • Calcium Phosphates / metabolism
  • Cell Line, Tumor
  • Chemical Precipitation
  • Electron Transport*
  • Humans
  • Hypoxia / metabolism*
  • Male
  • Membrane Fluidity
  • Mice, Inbred C57BL
  • Mitochondria / metabolism*
  • Mitochondrial Membranes / chemistry
  • Mitochondrial Membranes / metabolism
  • Mitochondrial Proteins / metabolism
  • Oxidative Phosphorylation
  • Rats
  • Rats, Wistar
  • Reactive Oxygen Species / metabolism
  • Second Messenger Systems*
  • Sodium / metabolism*
  • Sodium-Calcium Exchanger / metabolism

Substances

  • Calcium Phosphates
  • Mitochondrial Proteins
  • Reactive Oxygen Species
  • SLC8B1 protein, human
  • Sodium-Calcium Exchanger
  • calcium phosphate
  • Sodium