Pediatr Nephrol (2008) 23:1257–1267 deactivation of AT1R expression in IgAN would be expected. Here, we found a significantly greater expression of glomerular AGT protein and ang II peptides and a tendency for higher ACE protein levels and lower AT1R protein levels in pediatric IgAN compared with MGA patients, indicating that the glomerular AGT level may directly regulate the ang II activity under the coordination of ACE and AT1R expression and other ang II-producible enzyme activity. Various enzymes, including cathepsin and chymase, are involved in the RAS besides renin and ACE, which are classical enzyme synthesizing ang II from AGT [37]. Indeed, approximately 40% of the ang II found in the kidney is generated by ACE-independent pathways [38]. In any case, local levels of renin and ACE are not related to the synthesis of ang II in situations where AGT levels are very high [18, 20, 21]. Thus, the quantity of AGT might well be the most important element for the level of ang II production. Indeed, recent experimental studies using rat models of nephropathy indicated that enhanced intrarenal AGT expression is linked to the increased level of ang II production and contributes to the development of glomerular injury [20–22, 39]. We previously disclosed the mechanisms and the role of ang II-induced ECM deposition through MC [5, 6]. Ang II stimulates ECM synthesis through he induction of TGF-β expression in cultured rat MC [5] and affects the plasminogen activator/plasminogen activator inhibitor-1 system to result in accelerated deposition of ECM [6], which indicates that ang II can act as a potent fibrotic molecule independent of its effects on blood pressure. Ang II can also induce MC activation (α-SM actin positive) [39–42]. In addition, experimental and human studies have shown that the degree of mesangial cellularity is associated with a high sensitivity to beneficial effects of ACEi and ARB on glomerular structure and proteinuria, suggesting that the glomerular ang II level may contribute to proliferation of MC [43]. Thus, our findings obtained here that the level of glomerular ang II is associated with the levels of TGF-β and α-SM actin expression as well as glomerular injury characterized by cell proliferation and ECM accumulation are consistent with the recent view of ang II action. GEC damage and dysfunction are early features of many types of GN [44, 45]. Injury to GEC induces the secretion of various mediators, such as vasoactive substances, cyto- kines, and growth factors critical in the regulation of glomerular capillary tone and glomerular remodeling [19, 46–48]. Lee et al. demonstrated that GEC injury results in increased AGT and TGF-β mRNA by GEC and MC in the subtotal nephrectomized rat model, suggesting that acti- vated or injured endothelial cells synthesize AGT, trigger- ing a cascade of ang II, TGF-β, and ECM protein gene expression with resultant development of the glomerular sclerotic lesion [19]. Here we provide in vivo data showing a striking increase of GEC-AGT and ang II in patients with 1265 IgAN as well as in vitro data indicating the potential of GEC to synthesize AGT protein and stimulatory effects of ang II on GEC-AGT expression. Taken together, it seems likely that GEC plays a crucial role in the activation of local RAS, and self-amplifying properties of ang II production in GEC are associated with the glomerular hemodynamic changes and the development of progressive glomerular injury in human GN. In general, RAS inhibitors are commonly used by chronic IgAN patients with hypertension or those with heavy proteinuria or initial impairment of renal function. We should stress that glomerular RAS activation could occur in pediatric IgAN without heavy proteinuria, hyper- tension, and renal impairment. IgAN patients in this study had a short-term observation period from onset to time of renal biopsy, renal lesions, characterized with mesangial proliferative changes, low-grade interstitial fibrosis, and tubular atrophy, indicating that they were diagnosed at an early stage of IgAN [14, 49]. Thus, considering the accumulating evidence that ang II plays a critical role in MC activation as well as glomerular hemodynamic changes and development of glomerulosclerosis, early treatment with ACEi and/or ARB in pediatric IgAN, even in the absence of hypertension and/or severe proteinuria, is reasonable for preventing progression in IgAN. In conclusion, our study showed that activated glomerular AGT expression is likely to be involved in local RAS activation, leading to enhanced local ang II production, in pediatric IgAN with normal blood pressure and normal renal function and, thereby, may trigger a dangerous RAS cascade resulting in overproduction of TGF-β and progression of glomerular injury. Moreover, a self-amplification loop of GEC-AGT production with ang II stimulation seems to drive the further injury of nephritic glomeruli in IgAN patients. These data provide a rationale for early intervention with RAS inhibitors in pediatric IgAN patients even in the absence of hypertension and/or impairment of renal function to prevent progression of glomerular injury. Acknowledgments This work was supported by grants from the Japanese Ministry of Welfare (16591035, 18591189). We thank Dr. Hiroshi Kawachi and Dr. Fujio Shimizu (Niigata University, Niigata, Japan) for providing rabbit anti-TGF-β antibody. We also thank Dr. Toshiaki Sano and Mrs. Naomi Okamoto for their excellent technical assistance. Parts of this work were published in abstract form at the 39th Annual Meeting of the American Society of Nephrology, 14–19 November 2006. Open Access This article is distributed under the terms of the Creative Commons Attribution Noncommercial License which permits any noncommercial use, distribution, and reproduction in any medium, provided the original author(s) and source are credited.