title: PPARγ-induced stimulation of amiloride-sensitive sodium current in renal collecting duct principal cells is serum and insulin dependent.
abstract: OBJECTIVE
  Thiazolidinediones (TZDs), such as rosiglitazone or pioglitazone, are peroxisome proliferator-activated receptor gamma (PPARγ) agonists currently used in the treatment of type 2 diabetes. However, their clinical applicability is limited by common and severe side effects including strong water retention, edema and cardiac stroke. The precise mechanisms leading to these disorders are not clearly understood and remain controversial. While the nature of the disorders due to TZDs points to an increase in ENaC-mediated sodium reabsorption in the aldosterone-sensitive distal nephron, some studies suggested that this channel was not targeted by PPARγ agonists.
  
  
  METHODS
  Mouse cortical collecting duct cells were incubated in different types of culture medium and treated with or without rosiglitazone. Transepithelial Na(+) current was measured and the changes in SGK and Nedd4 expression were determined by immunoblotting.
  
  
  RESULTS
  Herein we demonstrate that rosiglitazone stimulates the amiloride-sensitive transepithelial sodium current in Collecting Duct Principal Cells after 3h and 24h treatment. This activation was dependent of both serum and insulin in culture medium and was mediated by SGK1/Nedd4-2 pathway stimulation. In these conditions, rosiglitazone induced SGK1 expression, Nedd4-2 phosphorylation and thus abolished ubiquitylation and internalization of ENaC channels. This mechanism explains most of the side effects of thiazolidinediones previously observed in humans and animals.
  
  
  CONCLUSIONS
  Our data show an increase in transepithelial sodium amiloride-sensitive current induced by a PPARγ agonist in presence of serum and insulin, thus confirming some in-vitro and in-vivo experiments while providing explanations for previous conflicting findings.
authors.affiliation: Department of Physiology and Biophysics, Faculty of Medicine and Health Sciences Université de Sherbrooke, Sherbrooke, Québec, Canada.
authors.forename: Ahmed
authors.initials: A
authors.lastname: Chraïbi
authors.forename: Stéphane
authors.initials: S
authors.lastname: Renauld
mesh_terms: D062565:Acid Sensing Ion Channels / Q000378:metabolism*; D000818:Animals; D002461:Cell Line, Transformed; D056827:Endosomal Sorting Complexes Required for Transport / Q000378:metabolism; D053503:Epithelial Sodium Channels / Q000378:metabolism*; D017874:Immediate-Early Proteins / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D007685:Kidney Tubules, Collecting / Q000378:metabolism*; D051379:Mice; D000075702:Nedd4 Ubiquitin Protein Ligases; D047495:PPAR gamma / Q000819:agonists / Q000378:metabolism*; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D000077154:Rosiglitazone; D044967:Serum; D015398:Signal Transduction / Q000187:drug effects; D045162:Thiazolidinediones / Q000494:pharmacology*; D044767:Ubiquitin-Protein Ligases / Q000378:metabolism; D000099184:Serum-Glucocorticoid Regulated Kinases
chemical_list: D062565:Acid Sensing Ion Channels; D056827:Endosomal Sorting Complexes Required for Transport; D053503:Epithelial Sodium Channels; D017874:Immediate-Early Proteins; D007328:Insulin; D000075702:Nedd4 Ubiquitin Protein Ligases; D047495:PPAR gamma; D017346:Protein Serine-Threonine Kinases; D000077154:Rosiglitazone; D045162:Thiazolidinediones; D044767:Ubiquitin-Protein Ligases; D000099184:Serum-Glucocorticoid Regulated Kinases; C000618483:Nedd4 protein, human; C000618485:Nedd4L protein, human; C000618461:Nedd4l protein, mouse