title: Adiponectin is expressed and secreted by renal tubular epithelial cells.
abstract: BACKGROUND
  Adiponectin (ADPN) is predominantly produced by adipose tissue, and high ADPN levels have been detected in patients affected by proteinuric glomerulonephritis. In this study we investigate whether human tubular epithelial cells express and secrete ADPN.
  
  
  METHODS
  In human proximal tubular epithelial cells, HK-2, ADPN mRNA was evaluated by real-time PCR assay, while protein expression levels were measured by Western blot analysis and immunofluorescence assay. Moreover, renal ADPN distribution was assessed by immunohistochemical analysis of kidney biopsy samples from healthy patients. Finally, by ELISA, we measured ADPN concentrations in culture media of HK-2 cells treated with 10 µg/mL lipopolysaccharide (LPS).
  
  
  RESULTS
  Our analyses revealed that HK-2 cells express ADPN both in terms of mRNA and protein. These results were confirmed by the observed cytoplasmatic HK-2 intense immunoreactivity for ADPN antibody and by immunohistochemical analysis showing a diffuse ADPN distribution in normal kidney tissue. Furthermore, we observed that tubular cells secrete ADPN in the basal condition and, more interestingly, that this secretion significantly increases (p<0.05) upon LPS treatment in a time-dependent manner. Finally, immunohistochemical analysis of kidney biopsy samples obtained from patients affected by membranous and rapidly progressive glomerulonephritis showed a similar pattern of ADPN staining to that observed in healthy controls.
  
  
  CONCLUSIONS
  Our study demonstrates for the first time that renal tubular cells express and secrete ADPN, and their concentration increases upon inflammatory stimulus. These results suggest that in renal inflammatory diseases, tubular cells may contribute to the increase in circulating ADPN levels, triggering a feedback response in order to self-mitigate the inflammatory process.
authors.affiliation: Research Center Kidney and Transplantation, Annunziata Hospital Cosenza, Cosenza - Italy; and Health Center, University of Calabria, Calabria - Italy.
authors.forename: Anna
authors.initials: A
authors.lastname: Perri
authors.forename: Donatella
authors.initials: D
authors.lastname: Vizza
authors.forename: Danilo
authors.initials: D
authors.lastname: Lofaro
authors.forename: Paolo
authors.initials: P
authors.lastname: Gigliotti
authors.forename: Francesca
authors.initials: F
authors.lastname: Leone
authors.forename: Elvira
authors.initials: E
authors.lastname: Brunelli
authors.forename: Rocco
authors.initials: R
authors.lastname: Malivindi
authors.forename: Francesca
authors.initials: F
authors.lastname: De Amicis
authors.forename: Francesco
authors.initials: F
authors.lastname: Romeo
authors.forename: Roberto
authors.initials: R
authors.lastname: De Stefano
authors.forename: Teresa
authors.initials: T
authors.lastname: Papalia
authors.forename: Renzo
authors.initials: R
authors.lastname: Bonofiglio
mesh_terms: D052242:Adiponectin / Q000032:analysis / Q000235:genetics / Q000378:metabolism*; D002478:Cells, Cultured; D003470:Culture Media / Q000032:analysis; D004847:Epithelial Cells / Q000187:drug effects / Q000378:metabolism*; D006801:Humans; D007687:Kidney Tubules, Proximal / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D008070:Lipopolysaccharides / Q000494:pharmacology; D012333:RNA, Messenger / Q000032:analysis / Q000378:metabolism
chemical_list: D052242:Adiponectin; D003470:Culture Media; D008070:Lipopolysaccharides; D012333:RNA, Messenger