Expression of gremlin, a bone morphogenetic protein antagonist, in human diabetic nephropathy

Background: We report the induction of gremlin, a bone morphogenetic protein antagonist, in cultured human mesangial cells exposed to high glucose and transforming growth factor β (TGF-β) levels in vitro and kidneys from diabetic rats in vivo. Methods: 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. Results: 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-β 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. Conclusion: 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-β as an inducer of gremlin expression in this context.