title: Conditioned medium from renal tubular epithelial cells initiates differentiation of human mesenchymal stem cells.
abstract: OBJECTIVE
  Mesenchymal-epithelial interactions play a pivotal role in tubular morphogenesis and in maintaining the integrity of the kidney. During renal repair, similar mechanisms may regulate cellular reorganization and differentiation. We have hypothesized that soluble factors from proximal tubular epithelial cells (PTC) induce differentiation of adipose-derived adult mesenchymal stem cells (ASC). This hypothesis has been tested using cultured ASC and PTC.
  
  
  METHODS
  Conditioned medium was prepared from injured PTC and transferred to ASC cultures. ASC proliferation was analysed by a fluorometric and photometric assay. Signal transduction was analysed by phosphorylation of extracellular signal-regulated kinase 1 and 2 (ERK1/ERK2). Grade of ASC differentiation was assessed by morphological analysis and cell expression of characteristic markers.
  
  
  RESULTS
  Conditioned medium significantly induced proliferation and phosphorylation of ERK1/ERK2 of ASC. After 12 days of incubation, cell morphology changed to an epithelial-like monolayer. Expression of cytokeratin 18 was induced by conditioned medium, while alpha-smooth muscle actin, CD49a and CD90 expression decreased. These alterations strongly indicate onset of the differentiation process to the epithelial lineage. In summary, soluble factors from PTC induce signal transduction and differentiation of ASC.
  
  
  CONCLUSIONS
  Our study shows that conditioned medium from renal tubular epithelial cells provides a convenient source of inductive signals to initiate differentiation of ASC towards epithelial lineage. We deduce that these interactions may play an important role during renal repair mechanisms.
authors.affiliation: Division of Nephrology, Department of Internal Medicine III, John Wolfgang Goethe-University, Frankfurt, Germany. p.baer@em.uni-frankfurt.de
authors.forename: P C
authors.initials: PC
authors.lastname: Baer
authors.forename: J
authors.initials: J
authors.lastname: Bereiter-Hahn
authors.forename: C
authors.initials: C
authors.lastname: Missler
authors.forename: M
authors.initials: M
authors.lastname: Brzoska
authors.forename: R
authors.initials: R
authors.lastname: Schubert
authors.forename: S
authors.initials: S
authors.lastname: Gauer
authors.forename: H
authors.initials: H
authors.lastname: Geiger
mesh_terms: D015153:Blotting, Western; D002454:Cell Differentiation; D049109:Cell Proliferation; D017077:Culture Media, Conditioned; D004847:Epithelial Cells / Q000166:cytology / Q000201:enzymology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D007684:Kidney Tubules / Q000166:cytology* / Q000201:enzymology; D059630:Mesenchymal Stem Cells / Q000166:cytology*; D008856:Microscopy, Fluorescence; D010766:Phosphorylation
chemical_list: D017077:Culture Media, Conditioned; D048049:Extracellular Signal-Regulated MAP Kinases