Hepatocyte Nuclear Factor-1ß Induces Redifferentiation of Dedifferentiated Tubular Epithelial Cells.

Tubular epithelial cells (TECs) can be dedifferentiated by repetitive insults, which activate scar-producing cells generated from interstitial cells such as fibroblasts, leading to the accumulation and deposition of extracellular matrix molecules. The dedifferentiated TECs play a crucial role in the development of renal fibrosis. Therefore, renal fibrosis may be attenuated if dedifferentiated TECs are converted back to their normal state (re-epithelialization). However, the mechanism underlying the re-epithelialization remains to be elucidated. In the present study, TGF-ß1, a profibrotic cytokine, induced dedifferentiation of cultured TECs, and the dedifferentiated TECs were re-epithelialized by the removal of TGF-ß1 stimulation. In the re-epithelialization process, transcription factor hepatocyte nuclear factor 1, beta (HNF-1ß) was identified as a candidate molecule involved in inducing re-epithelialization by means of DNA microarray and biological network analysis. In functional validation studies, the re-epithelialization by TGF-ß1 removal was abolished by HNF-1ß knockdown. Furthermore, the ectopic expression of HNF-1ß in the dedifferentiated TECs induced the re-epithelialization without the inhibition of TGF-ß/Smad signaling, even in the presence of TGF-ß1 stimulation. In mouse renal fibrosis model, unilateral ureteral obstruction model, HNF-1ß expression in the TECs of the kidney was suppressed with fibrosis progression. Furthermore, the HNF-1ß downregulated TECs resulted in dedifferentiation, which was characterized by expression of nestin. In conclusion, HNF-1ß suppression in TECs is a crucial event for the dedifferentiation of TECs, and the upregulation of HNF-1ß in TECs has a potential to restore the dedifferentiated TECs into their normal state, leading to the attenuation of renal fibrosis.

Urinary neutrophil gelatinase-associated lipocalin levels reflect damage to glomeruli, proximal tubules, and distal nephrons.

Urinary neutrophil gelatinase-associated lipocalin (Ngal or lipocalin 2) is a very early and sensitive biomarker of kidney injury. Here we determined the origin and time course of Ngal appearance in several experimental and clinically relevant renal diseases. Urinary Ngal levels were found to be markedly increased in lipoatrophic- and streptozotocin-induced mouse models of diabetic nephropathy. In the latter mice, the angiotensin receptor blocker candesartan dramatically decreased urinary Ngal excretion. The reabsorption of Ngal by the proximal tubule was severely reduced in streptozotocin-induced diabetic mice, but upregulation of its mRNA and protein in the kidney was negligible, compared to those of control mice, suggesting that increased urinary Ngal was mainly due to impaired renal reabsorption. In the mouse model of unilateral ureteral obstruction, Ngal protein synthesis was dramatically increased in the dilated thick ascending limb of Henle and N was found in the urine present in the swollen pelvis of the ligated kidney. Five patients with nephrotic syndrome or interstitial nephritis had markedly elevated urinary Ngal levels at presentation, but these decreased in response to treatment. Our study shows that the urinary Ngal level may be useful for monitoring the status and treatment of diverse renal diseases reflecting defects in glomerular filtration barrier, proximal tubule reabsorption, and distal nephrons.

N-acetyl-seryl-aspartyl-lysyl-proline ameliorates the progression of renal dysfunction and fibrosis in WKY rats with established anti-glomerular basement membrane nephritis.

N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), which is hydrolyzed by angiotensin-converting enzyme, is a natural regulator of hematopoiesis. Here it is shown that Ac-SDKP inhibits TGF-beta action in mesangial cells. Because TGF-beta is thought to play a pivotal role in the development and progression of glomerulonephritis, the therapeutic effects of Ac-SDKP on an established model of renal dysfunction and histologic alteration in Wistar-Kyoto rats with anti-glomerular basement membrane nephritis was examined. Fourteen days after the induction of anti-glomerular basement membrane nephritis, the rats were treated subcutaneously with Ac-SDKP at a dose of 1 mg/kg per d for 4 wk. Treatment with Ac-SDKP significantly improved proteinuria and renal dysfunction, including increased plasma blood urea nitrogen and creatinine levels and decreased creatinine clearance. Histologic examination showed severe glomerulosclerosis and interstitial fibrosis in the vehicle-treated rats, whereas these histologic injuries were significantly ameliorated in rats that were treated with Ac-SDKP. The histologic improvements were accompanied by the suppression of gene and protein expression of fibronectin, interstitial collagen, and TGF-beta1 in the nephritic kidney. Furthermore, treatment with Ac-SDKP resulted in the inhibition of Smad2 phosphorylation, an increase in Smad7 expression in the kidney, and reduction of macrophage accumulation into the glomeruli and tubulointerstitium in nephritic rats. In conclusion, Ac-SDKP significantly ameliorated the progression of renal dysfunction and fibrosis even after the establishment of nephritis. The inhibitory effect of Ac-SDKP was mediated in part by the inhibition of TGF-beta/Smad signal transduction and the inflammatory response. These findings suggest that Ac-SDKP treatment may be a novel and useful therapeutic strategy for the treatment of progressive renal diseases.

N-acetyl-seryl-aspartyl-lysyl-proline prevents renal insufficiency and mesangial matrix expansion in diabetic db/db mice.

We have previously reported that N-acetyl-seryl-aspartyl-lysyl-proline (Ac-SDKP), which is a tetrapeptide hydrolyzed by ACE, inhibits the transforming growth factor-beta (TGF-beta)-induced expression of extracellular matrix proteins via inhibition of the Smad signaling in human mesangial cells. To test in vivo the antifibrotic efficacy of Ac-SDKP, we examined whether long-term Ac-SDKP treatment can prevent renal insufficiency and glomerulosclerosis in diabetic db/db mice. Diabetic db/db mice or nondiabetic db/m mice were treated with Ac-SDKP for 8 weeks using osmotic minipumps. The treatment with Ac-SDKP increased plasma Ac-SDKP concentrations by approximately threefold in both groups but did not affect the blood glucose levels. Histologically, the increased glomerular surface area, mesangial matrix expansion, and overproduction of extracellular matrix proteins in db/db mice were significantly inhibited by Ac-SDKP. Furthermore, Ac-SDKP treatment normalized the increased plasma creatinine value in db/db mice, whereas the albuminuria in Ac-SDKP-treated db/db mice was somewhat decreased as compared with nontreated db/db mice, although the difference was not statistically significant. In addition, the nuclear translocation of Smad3 was inhibited by Ac-SDKP. These results demonstrate that long-term Ac-SDKP treatment ameliorates renal insufficiency and glomerulosclerosis in db/db mice via inhibition of TGF-beta/Smad pathway, suggesting that Ac-SDKP could be useful in the treatment of diabetic nephropathy.