ENaC Dysregulation Through Activation of MEK1/2 Contributes to Impaired Na+ Absorption in Lymphocytic Colitis

Inflamm Bowel Dis. 2016 Mar;22(3):539-47. doi: 10.1097/MIB.0000000000000646.


Background: Lymphocytic colitis (LC) causes watery diarrhea. We aimed to identify mechanisms of altered Na absorption and regulatory inputs in patients with LC by examining the epithelial Na channel (ENaC) function as the predominant Na transport system in human distal colon.

Methods: Epithelial Na channel function and regulation was analyzed in biopsies from sigmoid colon of patients with LC and in rat distal colon in Ussing chambers. ENaC-subunit expression was measured by real-time PCR and RNA sequencing. Correction factors for subepithelial resistance contributions were determined by impedance spectroscopy. Upstream regulators in LC were determined by RNA sequencing.

Results: Epithelial Na channel-mediated electrogenic Na transport was inhibited despite aldosterone stimulation in human sigmoid colon of patients with LC. The increase in γ-ENaC mRNA expression in response to aldosterone was MEK1/2-dependently reduced in LC, since it could be restored toward normal by MEK1/2 inhibition through U0126. Parallel experiments for identification of signaling in rat distal colon established MEK1/2 to be activated by a cytokine cocktail of TNFα, IFNγ, and IL-15, which were identified as the most important regulators in the upstream regulator analysis in LC.

Conclusions: In the sigmoid colon of patients with LC, the key effector cytokines TNFα, IFNγ, and IL-15 inhibited γ-ENaC upregulation in response to aldosterone through a MEK1/2-mediated pathway. This prevents ENaC to reach its maximum transport capacity and results in Na malabsorption which contributes to diarrhea.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Case-Control Studies
  • Colitis, Lymphocytic / genetics
  • Colitis, Lymphocytic / metabolism
  • Colitis, Lymphocytic / pathology*
  • Dielectric Spectroscopy
  • Electric Impedance
  • Epithelial Sodium Channels / genetics
  • Epithelial Sodium Channels / metabolism*
  • Female
  • Humans
  • Intestinal Mucosa / metabolism
  • Intestinal Mucosa / pathology
  • MAP Kinase Kinase 1 / genetics
  • MAP Kinase Kinase 1 / metabolism*
  • MAP Kinase Kinase 2 / genetics
  • MAP Kinase Kinase 2 / metabolism*
  • Male
  • Middle Aged
  • Rats
  • Rats, Wistar
  • Real-Time Polymerase Chain Reaction
  • Sodium / metabolism*
  • Tumor Necrosis Factor-alpha / genetics
  • Tumor Necrosis Factor-alpha / metabolism*


  • Epithelial Sodium Channels
  • Tumor Necrosis Factor-alpha
  • Sodium
  • MAP2K2 protein, human
  • MAP Kinase Kinase 1
  • MAP Kinase Kinase 2
  • MAP2K1 protein, human