Connective Tissue Growth Factor Plays an Important Role in Advanced Glycation End Product–Induced Tubular Epithelial-to-Mesenchymal Transition

Abstract

Epithelial-to-mesenchymal transition (EMT) of tubular cells contributes to the renal accumulation of matrix protein that is associated with diabetic nephropathy. Both TGF-␤1 and advanced glycation end products (AGE) are able to induce EMT in cell culture. This study examined the role of the prosclerotic growth factor connective tissue growth factor (CTGF) as a downstream mediator of these processes. EMT was assessed by the expression of ␣-smooth muscle actin, vimentin, E-cadherin, and matrix proteins and the induction of a myofibroblastic phenotype. CTGF, delivered in an adenovirus or as recombinant human CTGF (250 ng/ml), was shown to induce a partial EMT. This was not blocked by neutralizing anti-TGF-␤1 antibodies, suggesting that this action was TGF-␤1 independent. NRK-52E cells that were exposed to AGE-modified BSA (AGE-BSA; 40 M) or TGF-␤1 (10 ng/ml) also underwent EMT. This was associated with the induction of CTGF gene and protein expression. Transfection with siRNA to CTGF was able to attenuate EMT-associated phenotypic changes after treatment with AGE or TGF-␤1. These in vitro effects correlate with the in vivo finding of increased CTGF expression in the diabetic kidney, which co-localizes on the tubular epithelium with sites of EMT. In addition, inhibition of AGE accumulation was able to reduce CTGF expression and attenuate renal fibrosis in experimental diabetes. These findings suggest that CTGF represents an important independent mediator of tubular EMT, downstream of the actions of AGE or TGF-␤1. This interaction is likely to play an important role in progressive diabetic nephropathy and strengthens the rationale to consider CTGF as a potential target for the treatment of diabetic nephropathy.

AGEs in human lens capsule promote the TGFβ2‐mediated EMT of lens epithelial cells: implications for age‐associated fibrosis

“…It is therefore possible that accumulated AGEs promote fibrosis in aged individuals and contribute to disease pathogenesis. Our study could explain why the fibrosis rate is higher in diabetes, for example, in the pathogenesis of diabetic nephropathy (Burns et al ., 2006). Furthermore, the similar effects of TGFβ1 and TGFβ2 on the AGE enhancement of EMT further suggests that basement membrane AGEs could play a role in TGFβ1‐mediated fibrosis, such as the cardiac and lung fibroses that occur in the diseases of these organs (Yuen et al ., 2010; Song et al ., 2011).…”

“…Several studies have suggested a role for AGEs in EMT; kidney tubular epithelial cell EMT and fibrosis, which occur in diabetic nephropathy, are mediated through engagement of the receptor for AGEs (RAGE) with AGEs, followed by the synthesis of connective tissue growth factor and can be inhibited by AGE inhibitors (Oldfield et al ., 2001; Burns et al ., 2006; Sugimoto et al ., 2007). The AGE–RAGE interaction also enhances TGFβ1 expression and induces fibrosis of the peritoneal membrane (De Vriese et al ., 2003).…”

Honokiol ameliorates renal fibrosis by inhibiting extracellular matrix and pro‐inflammatory factors in vivo and in vitro

“…Induction of TGF-b1 may convert tubular epithelial cells and fibroblasts into activated myofibroblasts, which may be responsible for increased deposition of interstitial matrix in response to TGF-b/Smad signaling. Furthermore, considerable evidence indicates that CTGF plays a pivotal role in TGF-b-dependent tubulointerstitial fibrosis (Gupta et al, 2000;Burns et al, 2006). CTGF mediates the up-regulation of collagen type I by TGF-b1 in mesangial cells and fibroblasts; however, it…”

The role of TGF-β and epithelial-to mesenchymal transition in diabetic nephropathy

“…The underlying pathology of EMT has since been observed in renal biopsies from diseased kidney where the proportion of cells undergoing transition correlated to both the level of serum creatinine and the degree of interstitial fibrosis [88]. Evidence for EMT in vivo has since been described in various forms of of CKD, including diabetic nephropathy [89] [90]. In diabetes, glomerular fibrosis is observed in the progression from incipient to overt nephropathy [6].…”