title: Tubular kidney injury molecule-1 in protein-overload nephropathy.
abstract: Kim-1, a recently discovered membrane protein, is undetectable in normal kidneys but markedly induced in proximal tubules after ischemic and toxic injury. The function of Kim-1 is unclear, but it is implicated in damage/repair processes. The Kim-1 ectodomain is cleaved by metalloproteinases and detectable in urine. We studied Kim-1 in a nontoxic, nonischemic, model of tubulointerstitial damage caused by acute proteinuria. Uninephrectomized (NX) rats received daily (ip) injections of 2 g BSA (NX+BSA, n = 12) or saline (NX, n = 6) for 3 wk. Kidneys were stained for various damage markers by immunohistochemistry (IHC). Kim-1 mRNA (RT-PCR, in situ hybridization), protein (IHC, Western blotting), and urinary Kim-1 (Luminex) were determined. Spatial relations between Kim-1 and other damage markers were studied by double labeling IHC. NX+BSA rats developed massive proteinuria (1,217 +/- 313 vs. 18 +/- 2 mg/day in NX, P < 0.001) and significant renal damage. Kim-1 mRNA was upregulated eightfold in NX+BSA (ratio Kim-1/beta-actin, 4.08 +/- 2.56 vs. 0.52 +/- 0.64 in NX, P < 0.001) and localized to damaged tubules. Kim-1 protein expression was markedly induced in NX+BSA (2.46 +/- 1.19 vs. 0.39 +/- 0.10% staining/field in NX, P < 0.001). Urinary Kim-1 was significantly elevated in NX+BSA (921 +/- 592 vs. 87 +/- 164 pg/ml in NX, P < 0.001) and correlated with tissue Kim-1 expression (r = 0.66, P =0.02). Kim-1 protein was found at the apical membrane of dilated nephrons. Kim-1 expression was limited to areas with inflammation (MØ), fibrosis (alpha-smooth muscle actin), and tubular damage (osteopontin), and only occasionally with tubular dedifferentiation (vimentin). These results implicate involvement of Kim-1 in the pathogenesis of proteinuria-induced renal damage/repair. Urinary Kim-1 levels may serve as a marker of proteinuria-induced renal damage.
authors.affiliation: Department of Pathology and Laboratory Medicine, University Medical Center Groningen and University of Groningen, Groningen, The Netherlands. m.m.van.timmeren@path.umcg.nl
authors.forename: Mirjan M
authors.initials: MM
authors.lastname: van Timmeren
authors.forename: Stephan J L
authors.initials: SJ
authors.lastname: Bakker
authors.forename: Vishal S
authors.initials: VS
authors.lastname: Vaidya
authors.forename: Veronique
authors.initials: V
authors.lastname: Bailly
authors.forename: Theo A
authors.initials: TA
authors.lastname: Schuurs
authors.forename: Jeffrey
authors.initials: J
authors.lastname: Damman
authors.forename: Coen A
authors.initials: CA
authors.lastname: Stegeman
authors.forename: Joseph V
authors.initials: JV
authors.lastname: Bonventre
authors.forename: Harry
authors.initials: H
authors.lastname: van Goor
mesh_terms: D000818:Animals; D015153:Blotting, Western; D015815:Cell Adhesion Molecules / Q000032:analysis / Q000235:genetics / Q000502:physiology* / Q000652:urine; D005786:Gene Expression Regulation; D007150:Immunohistochemistry; D007674:Kidney Diseases / Q000209:etiology* / Q000473:pathology / Q000503:physiopathology*; D007684:Kidney Tubules / Q000737:chemistry / Q000473:pathology / Q000503:physiopathology*; D008297:Male; D008565:Membrane Proteins / Q000032:analysis / Q000235:genetics / Q000502:physiology* / Q000652:urine; D011507:Proteinuria / Q000150:complications* / Q000503:physiopathology; D012333:RNA, Messenger / Q000032:analysis / Q000235:genetics; D051381:Rats; D017208:Rats, Wistar; D014746:Vimentin / Q000032:analysis
chemical_list: D015815:Cell Adhesion Molecules; D008565:Membrane Proteins; D012333:RNA, Messenger; D014746:Vimentin; C110936:Havcr1 protein, rat