Expression of gremlin, a bone morphogenetic protein antagonist, in glomerular crescents of pauci-immune glomerulonephritis.
BACKGROUND
Recent evidence in vitro and in vivo suggests that gremlin, a bone morphogenetic protein antagonist, is participating in tubular epithelial mesenchymal transition (EMT) in diabetic nephropathy as a downstream mediator of TGF-beta. Since EMT also occurs in parietal epithelial glomerular cells (PECs) leading to crescent formation, we hypothesized that gremlin could participate in this process. With this aim we studied its expression in 30 renal biopsies of patients with pauci-immune crescentic nephritis.


METHODS
Gremlin was detected by in situ hybridization (ISH) and immunohistochemistry (IMH) and TGF-beta by ISH and Smads by southwestern histochemistry (SWH). Phosphorylated Smad2, CTGF, BMP-7, PCNA, alpha-SMA, synaptopodin, CD-68, and phenotypic markers of PECs (cytokeratin, E-cadherin), were detected by IMH. In cultured human monocytes, gremlin and CTGF induction by TGF-beta was studied by western blot.


RESULTS
We observed strong expression of gremlin mRNA and protein in cellular and fibrocellular crescents corresponding to proliferating PECs and monocytes, in co-localization with TGF-beta. A marked over-expression of gremlin was also observed in tubular and infiltrating interstitial cells, correlating with tubulointerstitial fibrosis (r=0.59; P<0.01). A nuclear Smad activation in the same tubular cells, that are expressing TGF-beta and gremlin, was detected. In human cultured monocytes, TGF-beta induced gremlin production while CTGF expression was not detected.


CONCLUSIONS
We postulate that gremlin may play a role in the fibrous process in crescentic nephritis, both in glomerular crescentic and tubular epithelial cells. The co-localization of gremlin and TGF-beta expression found in glomeruli and tubular cells suggest that gremlin may be important in mediating some of the pathological effects of TGF-beta.
Mezzano
Sergio
S
Division Nephrology, School of Medicine, Universidad Austral, Valdivia, Chile. smezzano@uach.cl
Droguett
Alejandra
A
Burgos
M Eugenia
ME
Aros
Claudio
C
Ardiles
Leopoldo
L
Flores
Claudio
C
Carpio
Daniel
D
Carvajal
Gisselle
G
Ruiz-Ortega
Marta
M
Egido
Jesús
J
D015153:Blotting, Western; D019485:Bone Morphogenetic Proteins / Q000037:antagonists & inhibitors*; D049109:Cell Proliferation; D002478:Cells, Cultured; D005355:Fibrosis; D005921:Glomerulonephritis / Q000276:immunology* / Q000378:metabolism* / Q000473:pathology; D006651:Histocytochemistry; D006801:Humans; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D036341:Intercellular Signaling Peptides and Proteins / Q000096:biosynthesis / Q000235:genetics / Q000378:metabolism*; D007678:Kidney Glomerulus / Q000378:metabolism* / Q000473:pathology; D007684:Kidney Tubules / Q000378:metabolism / Q000473:pathology; D009000:Monocytes / Q000187:drug effects / Q000378:metabolism; D012333:RNA, Messenger / Q000378:metabolism; D014018:Tissue Distribution; D016212:Transforming Growth Factor beta / Q000378:metabolism / Q000494:pharmacology
D019485:Bone Morphogenetic Proteins; C486399:GREM1 protein, human; D036341:Intercellular Signaling Peptides and Proteins; D012333:RNA, Messenger; D016212:Transforming Growth Factor beta