RESUMO
Tubular injury is one of the important determinants of progressive renal failure in diabetic nephropathy (DN), and TGF-ß1 has been implicated in the pathogenesis of tubulointerstitial disease that characterizes proteinuric renal disease. The aim of this study was to identify novel therapeutic target molecules that play a role in the tubule damage of DN. We used an LC-MS/MS-based proteomic technique and human renal proximal epithelial cells (HRPTECs). Urine samples from Japanese patients with type 2 diabetes (n = 46) were used to quantify the candidate protein. Several proteins in HRPTECs in cultured media were observed to be driven by TGF-ß1, one of which was 33-kDa IGFBP7, which is a member of IGFBP family. TGF-ß1 up-regulated the expressions of IGFBP7 mRNA and protein in a dose- and time-dependent fashion via Smad2 and 4, but not MAPK pathways in HRPTECs. In addition, the knockdown of IGFBP7 restored the TGF-ß1-induced epithelial to mesenchymal transition (EMT). In the immunohistochemical analysis, IGFBP7 was localized to the cytoplasm of tubular cells but not that of glomerular cells in diabetic kidney. Urinary IGFBP7 levels were significantly higher in the patients with macroalbuminuria and were correlated with age (r = 0.308, p = 0.037), eGFR (r = -0.376, p = 0.01), urinary ß2-microglobulin (r = 0.385, p = 0.008), and urinary N-acetyl-beta-D-glucosaminidase (NAG) (r = 0.502, p = 0.000). A multivariate regression analysis identified urinary NAG and age as determinants associated with urinary IGFBP7 levels. In conclusion, our data suggest that TGF-ß1 enhances IGFBP7 via Smad2/4 pathways, and that IGFBP7 might be involved in the TGF-ß1-induced tubular injury in DN.
Assuntos
Nefropatias Diabéticas/metabolismo , Células Epiteliais/metabolismo , Proteínas de Ligação a Fator de Crescimento Semelhante a Insulina/metabolismo , Túbulos Renais Proximais/metabolismo , Proteína Smad2/metabolismo , Proteína Smad4/metabolismo , Fator de Crescimento Transformador beta1/metabolismo , Idoso , Diabetes Mellitus Tipo 2/metabolismo , Diabetes Mellitus Tipo 2/patologia , Nefropatias Diabéticas/patologia , Células Epiteliais/patologia , Feminino , Humanos , Túbulos Renais Proximais/patologia , Masculino , Pessoa de Meia-Idade , Proteômica , Transdução de SinaisRESUMO
AIM: In order to clarify the importance of Interleukin (IL)-18 in the development of diabetic nephropathy (DN), we evaluated the expressions of IL-18 in diabetic kidney. METHODS: We performed immmunohistochemical analysis of IL-18 and IL-18 receptor (IL-18 R) in human kidney tissue derived from 12 subjects with type 2 diabetes and overt nephropathy, and compared with those in 7 subjects with minimal change nephrotic syndrome (MCNS). In addition, we examined the regulation of IL-18 expression using human renal proximal tubular epithelial cells (HRPTECs) in culture. RESULTS: IL-18 expression in tubular cells was observed in higher rate (83%) in patients with diabetes, whereas one positive specimen (14.3%) for IL-18 in patients with MCNS. In contrast, IL-18 R was expressed in glomerular mesangial cells and endothelial cells as well as tubular cells, similarly in almost of both groups. Exposure to transforming growth factor beta (TGF-beta(1)) led to two-fold increase in IL-18 gene expression in HRPTECs, and mitogen-activated protein kinases (MAPK) inhibitors abolished TGF-beta(1)-induced IL-18 mRNA expression. Western blot analysis showed the IL-18 protein in HRPTECs. CONCLUSION: The present data indicate that IL-18 is overexpressed in human tubular epithelial cells in diabetic nephropathy, probably through the activation of MAPK pathways induced by TGF-beta(1).
