title: Indoxyl sulfate counteracts endothelial effects of erythropoietin through suppression of Akt phosphorylation.
abstract: BACKGROUND
  Erythropoietin (EPO) is used to treat anemia in patients with chronic kidney disease (CKD). A wide variation in individual response to EPO, however, is often observed, causing EPO resistance. EPO exhibits not only hematopoietic but also extra-hematopoietic functions such as endothelial effects. Indoxyl sulfate, a uremic toxin, is involved in endothelial dysfunction, and consequently, the pathogenesis of CKD-associated cardiovascular disease. The aim of the present study was to determine the effect of indoxyl sulfate on the extra-hematopoietic functions of EPO in human umbilical vein endothelial cells (HUVECs).
  
  
  RESULTS
  HUVECs were incubated with or without indoxyl sulfate or an Akt inhibitor, and then stimulated with or without EPO. Indoxyl sulfate suppressed EPO-induced survival/proliferation, anti-apoptosis function, phosphorylation of endothelial nitric oxide synthase, and the expression of thrombospondin-1, an erythroid-stimulating factor, in HUVECs. Although EPO induced phosphorylation of both Akt and extracellular signal-regulated kinases (ERK) in HUVECs, indoxyl sulfate suppressed phosphorylation of Akt but not ERK. An Akt kinase inhibitor or Akt small interfering RNA suppressed all the EPO-induced cellular effects in HUVECs. As a site of action of indoxyl sulfate on EPO signaling, indoxyl sulfate attenuated EPO-induced tyrosine phosphorylation of EPO receptor (EPOR) in HUVECs.
  
  
  CONCLUSIONS
  Indoxyl sulfate negatively regulates the EPOR-Akt pathway in endothelial cells, and might contribute to EPO resistance and endothelial dysfunction in patients with CKD.
authors: Department of Advanced Medicine for Uremia, Nagoya University School of Medicine, Nagoya, Japan.
authors: Yelixiati
authors: Y
authors: Adelibieke
authors: Hidehisa
authors: H
authors: Shimizu
authors: Shinichi
authors: S
authors: Saito
authors: Roumyana
authors: R
authors: Mironova
authors: Toshimitsu
authors: T
authors: Niwa
mesh_terms: D017209:Apoptosis / Q000187:drug effects; D049109:Cell Proliferation / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002478:Cells, Cultured; D004921:Erythropoietin / Q000494:pharmacology*; D061307:Human Umbilical Vein Endothelial Cells / Q000187:drug effects* / Q000201:enzymology; D006801:Humans; D007200:Indican / Q000494:pharmacology*; D052250:Nitric Oxide Synthase Type III / Q000378:metabolism; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D051057:Proto-Oncogene Proteins c-akt / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034622:RNA Interference; D017467:Receptors, Erythropoietin / Q000187:drug effects / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D019700:Thrombospondin 1 / Q000378:metabolism; D013997:Time Factors; D014162:Transfection
chemical_list: C554270:EPO protein, human; D047428:Protein Kinase Inhibitors; D017467:Receptors, Erythropoietin; D019700:Thrombospondin 1; D004921:Erythropoietin; C496314:NOS3 protein, human; D052250:Nitric Oxide Synthase Type III; D051057:Proto-Oncogene Proteins c-akt; D007200:Indican