mTORC2 regulates renal tubule sodium uptake by promoting ENaC activity

J Clin Invest. 2015 Jan;125(1):117-28. doi: 10.1172/JCI73935. Epub 2014 Nov 21.

Abstract

The epithelial Na+ channel (ENaC) is essential for Na+ homeostasis, and dysregulation of this channel underlies many forms of hypertension. Recent studies suggest that mTOR regulates phosphorylation and activation of serum/glucocorticoid regulated kinase 1 (SGK1), which is known to inhibit ENaC internalization and degradation; however, it is not clear whether mTOR contributes to the regulation of renal tubule ion transport. Here, we evaluated the effect of selective mTOR inhibitors on kidney tubule Na+ and K+ transport in WT and Sgk1-/- mice, as well as in isolated collecting tubules. We found that 2 structurally distinct competitive inhibitors (PP242 and AZD8055), both of which prevent all mTOR-dependent phosphorylation, including that of SGK1, caused substantial natriuresis, but not kaliuresis, in WT mice, which indicates that mTOR preferentially influences ENaC function. PP242 also substantially inhibited Na+ currents in isolated perfused cortical collecting tubules. Accordingly, patch clamp studies on cortical tubule apical membranes revealed that mTOR inhibition markedly reduces ENaC activity, but does not alter activity of K+ inwardly rectifying channels (ROMK channels). Together, these results demonstrate that mTOR regulates kidney tubule ion handling and suggest that mTOR regulates Na+ homeostasis through SGK1-dependent modulation of ENaC activity.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Amiloride / pharmacology
  • Animals
  • Biological Transport
  • Endosomal Sorting Complexes Required for Transport / metabolism
  • Epithelial Sodium Channels / metabolism*
  • Female
  • Immediate-Early Proteins / metabolism
  • Indoles / pharmacology
  • Kidney Tubules, Distal / metabolism*
  • Male
  • Mechanistic Target of Rapamycin Complex 2
  • Membrane Potentials
  • Mice, 129 Strain
  • Mice, Inbred C57BL
  • Mice, Knockout
  • Multiprotein Complexes / physiology*
  • Nedd4 Ubiquitin Protein Ligases
  • Patch-Clamp Techniques
  • Phosphorylation
  • Protein Processing, Post-Translational
  • Protein Serine-Threonine Kinases / metabolism
  • Purines / pharmacology
  • Rats, Sprague-Dawley
  • Sirolimus / pharmacology
  • Sodium / metabolism*
  • TOR Serine-Threonine Kinases / metabolism
  • TOR Serine-Threonine Kinases / physiology*
  • Ubiquitin-Protein Ligases / metabolism

Substances

  • Endosomal Sorting Complexes Required for Transport
  • Epithelial Sodium Channels
  • Immediate-Early Proteins
  • Indoles
  • Multiprotein Complexes
  • Purines
  • Amiloride
  • Sodium
  • Nedd4 Ubiquitin Protein Ligases
  • Ubiquitin-Protein Ligases
  • mTOR protein, mouse
  • Mechanistic Target of Rapamycin Complex 2
  • Protein Serine-Threonine Kinases
  • TOR Serine-Threonine Kinases
  • serum-glucocorticoid regulated kinase
  • PP242
  • Sirolimus