title: Sirolimus and everolimus reduce albumin endocytosis in proximal tubule cells via an angiotensin II-dependent pathway.
abstract: BACKGROUND
  The proliferation signal inhibitors (PSIs) sirolimus (SRL) and everolimus (ERL) often induce proteinuria due to glomerular but also tubular dysfunction in transplant patients. The beneficial effect of angiotensin converting enzyme inhibitors (ACE-I) and angiotensin II (Ang II) type 1 receptor blockers (ARB) has been reported.
  
  
  OBJECTIVE
  This study aimed to investigate: (i) the role of an Ang II-dependent mechanism and Ang II type 1 receptor (AT(1)R) in the regulation of receptor-mediated albumin endocytosis on proximal tubular epithelial cells (PTEC) following PSI treatment; (ii) the specific roles of the albumin receptors cubilin and megalin in albumin binding and uptake in PTEC.
  
  
  METHODS
  A human renal PTEC line (HK-2) was used in the study. The binding of Alexa 488 conjugated albumin was measured by flow cytometry. Albumin uptake and the expression of cubilin and megalin were determined by cellular ELISA.
  
  
  RESULTS
  The administration of PSIs resulted in decreased albumin binding and uptake and downregulation of cubilin and megalin expression in PTEC. These effects were significantly reversed by the administration of an ACE-I (ramipril) or an ARB (losartan). Combined use of ramipril and losartan demonstrated additive effects on cubilin expression, but not on megalin expression or albumin binding and uptake.
  
  
  CONCLUSIONS
  Our findings suggest that decreased albumin endocytosis in PTECs following PSI treatment involve an Ang II-dependent pathway via AT(1)R. The albumin receptor megalin may play a more crucial role than cubulin, since its expression correlated directly with albumin uptake.
authors.affiliation: Department of Cardiology, Heart Transplant (HTx)-Research Laboratory, Swiss Cardiovascular Centre Bern, University Hospital Bern, Switzerland.
authors.forename: Melinda
authors.initials: M
authors.lastname: Oroszlán
authors.forename: Michael
authors.initials: M
authors.lastname: Bieri
authors.forename: Nathalie
authors.initials: N
authors.lastname: Ligeti
authors.forename: Anikó
authors.initials: A
authors.lastname: Farkas
authors.forename: Bernhard
authors.initials: B
authors.lastname: Meier
authors.forename: Hans-Peter
authors.initials: HP
authors.lastname: Marti
authors.forename: Paul
authors.initials: P
authors.lastname: Mohacsi
mesh_terms: D000418:Albumins / Q000378:metabolism; D000804:Angiotensin II / Q000378:metabolism; D002460:Cell Line; D015536:Down-Regulation / Q000187:drug effects / Q000276:immunology; D004359:Drug Therapy, Combination; D004705:Endocytosis / Q000187:drug effects / Q000276:immunology; D004847:Epithelial Cells / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism / Q000473:pathology; D000068338:Everolimus; D006801:Humans; D007166:Immunosuppressive Agents / Q000494:pharmacology*; D007687:Kidney Tubules, Proximal / Q000473:pathology*; D019808:Losartan / Q000494:pharmacology; D026561:Low Density Lipoprotein Receptor-Related Protein-2 / Q000096:biosynthesis / Q000235:genetics; D017257:Ramipril / Q000494:pharmacology; D044140:Receptor, Angiotensin, Type 1 / Q000378:metabolism; D011956:Receptors, Cell Surface / Q000096:biosynthesis / Q000235:genetics; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology; D020123:Sirolimus / Q000031:analogs & derivatives* / Q000494:pharmacology*
chemical_list: D000418:Albumins; D007166:Immunosuppressive Agents; D026561:Low Density Lipoprotein Receptor-Related Protein-2; D044140:Receptor, Angiotensin, Type 1; D011956:Receptors, Cell Surface; C029486:intrinsic factor-cobalamin receptor; D000804:Angiotensin II; D000068338:Everolimus; D019808:Losartan; D017257:Ramipril; D020123:Sirolimus