title: Urinary exosomes: a novel means to non-invasively assess changes in renal gene and protein expression.
abstract: BACKGROUND
  In clinical practice, there is a lack of markers for the non-invasive diagnosis and follow-up of kidney disease. Exosomes are membrane vesicles, which are secreted from their cells of origin into surrounding body fluids and contain proteins and mRNA which are protected from digestive enzymes by a cell membrane.
  
  
  METHODS
  Toxic podocyte damage was induced by puromycin aminonucleoside in rats (PAN). Urinary exosomes were isolated by ultracentrifugation at different time points during the disease. Exosomal mRNA was isolated, amplified, and the mRNA species were globally assessed by gene array analysis. Tissue-specific gene and protein expression was assessed by RT-qPCR analysis and immunohistochemistry.
  
  
  RESULTS
  Gene array analysis of mRNA isolated from urinary exosomes revealed cystatin C mRNA as one of the most highly regulated genes. Its gene expression increased 7.5-fold by day 5 and remained high with a 1.9-fold increase until day 10. This was paralleled by a 2-fold increase in cystatin C mRNA expression in the renal cortex. Protein expression in the kidneys also dramatically increased with de novo expression of cystatin C in glomerular podocytes in parts of the proximal tubule and the renal medulla. Urinary excretion of cystatin C increased approximately 2-fold.
  
  
  CONCLUSIONS
  In this proof-of-concept study, we could demonstrate that changes in urinary exosomal cystatin C mRNA expression are representative of changes in renal mRNA and protein expression. Because cells lining the urinary tract produce urinary exosomal cystatin C mRNA, it might be a more specific marker of renal damage than glomerular-filtered free cystatin C.
authors.affiliation: Department of Nephrology, University of Medicine and Pharmacy "I. Hatieganu", Cluj-Napoca, Romania.
authors.forename: Silvia
authors.initials: S
authors.lastname: Spanu
authors.affiliation: Division of Nephrology and Immunology, Uniklinik RWTH Aachen, Aachen, Germany.
authors.forename: Claudia R C
authors.initials: CR
authors.lastname: van Roeyen
authors.affiliation: IZKF, Uniklinik RWTH Aachen, Aachen, Germany.
authors.forename: Bernd
authors.initials: B
authors.lastname: Denecke
authors.affiliation: Division of Nephrology and Immunology, Uniklinik RWTH Aachen, Aachen, Germany.
authors.forename: Jürgen
authors.initials: J
authors.lastname: Floege
authors.affiliation: Division of Nephrology and Immunology, Uniklinik RWTH Aachen, Aachen, Germany.
authors.forename: Anja S
authors.initials: AS
authors.lastname: Mühlfeld
mesh_terms: D000818:Animals; D015415:Biomarkers; D055316:Cystatin C / Q000235:genetics / Q000652:urine*; D055354:Exosomes / Q000187:drug effects* / Q000235:genetics; D015870:Gene Expression / Q000187:drug effects*; D007668:Kidney / Q000187:drug effects* / Q000378:metabolism; D007672:Kidney Cortex / Q000187:drug effects / Q000378:metabolism; D008297:Male; D050199:Podocytes / Q000187:drug effects* / Q000378:metabolism; D011692:Puromycin Aminonucleoside / Q000633:toxicity*; D012333:RNA, Messenger / Q000652:urine; D051381:Rats; D017207:Rats, Sprague-Dawley; D015854:Up-Regulation
chemical_list: D015415:Biomarkers; D055316:Cystatin C; D012333:RNA, Messenger; D011692:Puromycin Aminonucleoside