Expression of Gremlin, a Bone Morphogenetic Protein Antagonist, in Human Diabetic Nephropathy
Universidad Austral de Chile, Ciudad de Valdivía, Los Ríos, Chile American Journal of Kidney Diseases
(Impact Factor: 5.9).
07/2005; 45(6):1034-9. DOI: 10.1053/j.ajkd.2005.03.014
We report the induction of gremlin, a bone morphogenetic protein antagonist, in cultured human mesangial cells exposed to high glucose and transforming growth factor beta (TGF-beta) levels in vitro and kidneys from diabetic rats in vivo.
Gremlin expression was assessed in human diabetic nephropathy by means of in situ hybridization, immunohistochemistry, and real-time polymerase chain reaction and correlated with clinical and pathological indices of disease.
Gremlin was not expressed in normal human adult kidneys. Conversely, abundant gremlin expression was observed in human diabetic nephropathy. Although some gremlin expression was observed in occasional glomeruli, gremlin expression was most prominent in areas of tubulointerstitial fibrosis, where it colocalized with TGF-beta expression. Gremlin messenger RNA levels correlated directly with renal dysfunction, determined by means of serum creatinine level, but not with proteinuria level. There was a strong correlation between gremlin expression and tubulointerstitial fibrosis score.
In aggregate, these results indicate that the developmental gene gremlin reemerges in the context of tubulointerstitial fibrosis in diabetic nephropathy and suggests a role for TFG-beta as an inducer of gremlin expression in this context.
Available from: Akio Morita
- "Abundant Gremlin expression also occurs in diabetic nephropathy  , occasionally in glomeruli, but most prominently in areas of tubulointerstitial fibrosis, where it colocalizes with TGF-í µí»½ and is directly correlated with renal dysfunction . BMP-7 and Gremlin are involved in renal development and diabetic nephropathy and undergo expression changes in the diabetic kidney  . Dolan and colleagues proposed that reactivation of Gremlin (and BMP-7) in the diabetic kidney is a novel therapeutic target for diabetic nephropathy, since administration of the Gremlin ligand BMP-7 is protective in models of progressive renal diseases . "
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ABSTRACT: Gremlin is an antagonist of bone morphogenetic protein (BMP) and a major driving force in skeletal modeling in the fetal stage. Several recent reports have shown that Gremlin is also involved in angiogenesis of lung cancer and diabetic retinopathy. The purpose of this study was to investigate the role of Gremlin in tumor angiogenesis in pituitary adenoma. Double fluorescence immunohistochemistry of Gremlin and CD34 was performed in pituitary adenoma tissues obtained during transsphenoidal surgery in 45 cases (7 PRLoma, 17 GHoma, 2 ACTHoma, and 2 TSHoma). Gremlin and microvascular density (MVD) were detected by double-immunofluorescence microscopy in CD34-positive vessels from tissue microarray analysis of 60 cases of pituitary adenomas (6 PRLoma, 23 GHoma, 22 NFoma, 5 ACTHoma, and 4 TSHoma). In tissue microarray analysis, MVD was significantly correlated with an increased Gremlin level (linear regression: P < 0.005, r (2) = 0.4958). In contrast, Gremlin expression showed no correlation with tumor subtype or Knosp score. The high level of expression of Gremlin in pituitary adenoma tissue with many CD34-positive vessels and the strong coherence of these regions indicate that Gremlin is associated with angiogenesis in pituitary adenoma cells.
Available from: Marta Ruiz-Ortega
- "To distinguish the human TG protein from the murine endogenous gremlin, a c-myc tag was fused to the GREM1 protein, and we used eGFP as reporter for transgene expression. In vitro experiments in EBNA293 cells were performed to detect the c-myc signal and showed an expression pattern consistent with GREM1 subcellular localization , ; in a similar pattern to that found in human renal biopsies –, where this protein is localized in cytoplasm and nucleus of the affected tubular epithelial cells. HK-2 cells transfected with pCDNA3-GREM1-c-myc-IRES-eGFP were positive for GREM1 (Figure 1b), which confirmed that eGFP could be used as a reporter for in vivo experiments and that c-myc could be used to differentiate human GREM1 in TG animals. "
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ABSTRACT: A growing number of patients are recognized worldwide to have chronic kidney disease. Glomerular and interstitial fibrosis are hallmarks of renal progression. However, fibrosis of the kidney remains an unresolved challenge, and its molecular mechanisms are still not fully understood. Gremlin is an embryogenic gene that has been shown to play a key role in nephrogenesis, and its expression is generally low in the normal adult kidney. However, gremlin expression is elevated in many human renal diseases, including diabetic nephropathy, pauci-immune glomerulonephritis and chronic allograft nephropathy. Several studies have proposed that gremlin may be involved in renal damage by acting as a downstream mediator of TGF-β. To examine the in vivo role of gremlin in kidney pathophysiology, we generated seven viable transgenic mouse lines expressing human gremlin (GREM1) specifically in renal proximal tubular epithelial cells under the control of an androgen-regulated promoter. These lines demonstrated 1.2- to 200-fold increased GREM1 expression. GREM1 transgenic mice presented a normal phenotype and were without proteinuria and renal function involvement. In response to the acute renal damage cause by folic acid nephrotoxicity, tubule-specific GREM1 transgenic mice developed increased proteinuria after 7 and 14 days compared with wild-type treated mice. At 14 days tubular lesions, such as dilatation, epithelium flattening and hyaline casts, with interstitial cell infiltration and mild fibrosis were significantly more prominent in transgenic mice than wild-type mice. Tubular GREM1 overexpression was correlated with the renal upregulation of profibrotic factors, such as TGF-β and αSMA, and with increased numbers of monocytes/macrophages and lymphocytes compared to wild-type mice. Taken together, our results suggest that GREM1-overexpressing mice have an increased susceptibility to renal damage, supporting the involvement of gremlin in renal damage progression. This transgenic mouse model could be used as a new tool for enhancing the knowledge of renal disease progression.
Available from: Raquel Rodrigues-Diez
- "Gremlin is a glycosylated , phosphorylated, secreted protein present both on the external cell surface and within the ER-Golgi compartments . In many human renal diseases induction of Gremlin has been described    . Several experimental studies have shown that Gremlin participates in renal damage  . "
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ABSTRACT: Gremlin is a developmental gene upregulated in human chronic kidney disease and in renal cells in response to transforming growth factor- β (TGF- β ). Epithelial mesenchymal transition (EMT) is one process involved in renal fibrosis. In tubular epithelial cells we have recently described that Gremlin induces EMT and acts as a downstream TGF- β mediator. Our aim was to investigate whether Gremlin participates in EMT by the regulation of the Smad pathway. Stimulation of human tubular epithelial cells (HK2) with Gremlin caused an early activation of the Smad signaling pathway (Smad 2/3 phosphorylation, nuclear translocation, and Smad-dependent gene transcription). The blockade of TGF- β , by a neutralizing antibody against active TGF- β , did not modify Gremlin-induced early Smad activation. These data show that Gremlin directly, by a TGF- β independent process, activates the Smad pathway. In tubular epithelial cells long-term incubation with Gremlin increased TGF- β production and caused a sustained Smad activation and a phenotype conversion into myofibroblasts-like cells. Smad 7 overexpression, which blocks Smad 2/3 activation, diminished EMT changes observed in Gremlin-transfected tubuloepithelial cells. TGF- β neutralization also diminished Gremlin-induced EMT changes. In conclusion, we propose that Gremlin could participate in renal fibrosis by inducing EMT in tubular epithelial cells through activation of Smad pathway and induction of TGF- β .
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