Diabetic nephropathy is a well-known complication of diabetes and is a leading cause of chronic renal failure in the Western world. It is characterized by the accumulation of extracellular matrix in the glomerular and tubulointerstitial compartments and by the thickening and hyalinization of intrarenal vasculature. The various cellular events and signaling pathways activated during diabetic nephropathy may be similar in different cell types. Such cellular events include excessive channeling of glucose intermediaries into various metabolic pathways with generation of advanced glycation products, activation of protein kinase C, increased expression of transforming growth factor β and GTP-binding proteins, and generation of reactive oxygen species. In addition to these metabolic and biochemical derangements, changes in the intraglomerular hemodynamics, modulated in part by local activation of the renin-angiotensin system, compound the hyperglycemia-induced injury. Events involving various intersecting pathways occur in most cell types of the kidney.

YS. p66Shc mediates high-glucose and angiotensin II-induced oxidative stress renal tubular injury via mitochondrial-dependent apoptotic pathway.

The role of tubular injury in diabetic nephropathy is relatively unknown, despite that apoptosis of tubular epithelial cells is commonly observed in human renal biopsies. The GTPase Ras-proximate-1 (Rap1b) is upregulated in the hyperglycemic state and is known to increase B-Raf, an antiapoptotic effector protein.In this study, the effects of high glucose on renal tubular apoptosis and the potential ability for Rap1b to ameliorate these effects were investigated. In the kidneys of diabetic mice, apoptotic tubular cells and dysmorphic mitochondria were observed, Bcl-2 expression was decreased, and Bax expression was increased. Total Rap1b expression was slightly increased, but its associated GTPase activity was significantly decreased. In vitro, high extracellular glucose led to decreased Bcl-2 expression, reduced Rap1b GTPase activity, and increased levels of both Bax and GTPase activating protein in a proximal tubular cell line (HK-2). These changes were accompanied by increased DNA fragmentation, decreased high molecular weight mitochondrial DNA, altered mitochondrial morphology and function, disrupted Bcl-2-Bax and Bcl-2-Rap1b interactions, and reduced cell survival. Overexpression of Rap1b partially prevents these abnormalities. Furthermore, the BH4 domain of Bcl-2 was found to be required for successful protein-protein interaction between Bcl-2 and Rap1b. In summary, these data suggest that Rap1b ameliorates glucose-induced mitochondrial dysfunction in renal tubular cells.

Tubulointerstitial injury leading to fibrosis is a common pathway of many renal diseases. During this type of injury, modeled by unilateral ureteral obstruction (UUO), cells undergo epithelial-to-mesenchymal transition (EMT), a process that is mediated by various cytokines that modulate the biology of extracellular matrix proteins. Here, we studied the tubulointerstitial nephritis antigen (TINag), a tubular basement membrane protein, in the UUO model of tubulointerstitial injury. We observed upregulation of type IV collagen but downregulation of both laminin and TINag in obstructed kidneys. TINag downregulation was a result of oxidative stress; in the proximal tubular epithelial cell line HK-2, TINag expression and its promoter activity decreased after treatment with H2O2. We identified multiple CCAAT/enhancer binding protein beta (C/EBP-beta) motifs in the TINag promoter and observed that oxidant stress perturbed interactions between TINag DNA and C/EBP-beta protein. Oxidant stress reduced nuclear translocation of C/EBP-beta in HK-2 cells, which was restored by antioxidants. In addition, overexpression of C/EBP-beta restored the H2O2-induced reduction of TINag promoter activity and expression. Furthermore, in vivo, renal obstruction reduced nuclear expression of C/EBP-beta. Cells grown on a TINag substratum maintained their normal epithelial phenotype and cytoskeletal organization, similar to those grown on type IV collagen, and demonstrated reduced synthesis of fibronectin. Taken together, these findings suggest that altered interactions between C/EBP-beta and TINag play a critical role in the pathophysiology of renal injury after obstruction.

Norcantharidin (NCTD), the demethylated analog of cantharidin isolated from Mylabris, is an anticancer drug routinely used against various human cancers in China. The aims of this study are to learn if NCTD has a protective action against severe proteinuria and consequent interstitial inflammation and fibrosis, and if the inhibition of nuclear factor-ĸB (NF-ĸB) and connective tissue growth factor (CTGF) by NCTD might be involved. Male Sprague-Dawley rats with protein overload nephropathy induced by intraperitoneally injected bovine serum albumin were used as a model. The histopathological examination of kidney tissue in the 9th week by light microscopy and scanning electron microscopy revealed that inflammatory cells had extensively infiltrated into the tubulointerstitial areas with interstitial fibrosis. The administration of NCTD at 0.1 mg/kg/day to the bovine-serum-albumin-injected animal models effectively reduced the proteinuria, and prevented the proteinuria-induced interstitial inflammation and fibrosis. Expressions of the NF-ĸB p65 subunit and CTGF, detected by immunohistochemistry, Western blotting and reverse-transcription polymerase chain reaction, were upregulated in protein overload nephropathy and were attenuated by NCTD. Inhibition of the expressions of the NF-ĸB p65 subunit and CTGF was one beneficial effect of NCTD. These results suggest that in addition to the antiproteinuric action of NCTD, due to its anti-inflammatory and antifibrotic effects as shown in the present study, it may become a therapeutic agent for proteinuria and its associated chronic inflammatory and fibrotic nephropathy.

Both HOCM (diatrizoate) and LOCM (iohexol) could cause renal tubular cell apoptosis in the kidneys damaged by glycerin. LOCM was less toxic to rat kidneys than HOCM. Caspase-3 and Ang II might play a role in renal tubular cell apoptosis induced by contrast media. Telmisartan protected the renal tissue from nephrotoxicity induced by contrast media.

Heat shock protein (HSP)47 is a collagen-specific molecular chaperone that is essential for the biosynthesis of collagen molecules. It is likely that increased levels of HSP47 contribute to the assembly of procollagen and thereby cause an excessive accumulation of collagens in disease processes associated with fibrosis. Although HSP47 promotes renal fibrosis, the underlying mechanism and associated signaling events have not been clearly delineated. We examined the role of HSP47 in renal fibrosis using a rat unilateral ureteral obstruction model and transforming growth factor (TGF)-β(1)-treated human proximal tubular epithelial (HK-2) cells. An upregulation of HSP47 in both in vivo and in vitro models was observed, which correlated with the increased synthesis of extracellular matrix (ECM) proteins and expression of tissue-type plasminogen activator inhibitor (PAI)-1. Blockade of HSP47 by short interfering RNA suppressed the expression of ECM proteins and PAI-1. In addition, TGF-β(1)-induced HSP47 expression in HK-2 cells was attenuated by ERK1/2 and JNK MAPK inhibitors. These data suggest that ERK1/2 and JNK signaling events are involved in modulating the expression of HSP47, the chaperoning effect of which on TGF-β(1) would ultimately contribute to renal fibrosis by enhancing the synthesis and deposition of ECM proteins.

Progressive renal tubulointerstitial fibrosis is a common final pathway of nearly all forms of chronic kidney disease. Many efforts have been done to arrest or prevent renal tubulointerstitial fibrosis but with little progress. Nowadays, few therapeutic agents are available in clinical use. Norcantharidin (NCTD) is of great benefit in anticancer treatment, by inducing cell apoptosis, inhibiting cell proliferation, in addition, blocking tumor metastasis and angiogenesis in cancer, whereas little attention is given to its relationship with other diseases. Our recent studies demonstrated that NCTD was protective against renal tubulointerstitial fibrosis both in vivo and in vitro. The underlying mechanisms may include modulation of TGF-β1/Smad signal cascade, inhibition of protein serine/threonine phosphatases (PPP) as well as NF-κB. NCTD may be a promising therapeutic agent for renal tubulointerstitial fibrosis. In the present article, we will review the action of NCTD in renal tubulointerstitial fibrosis and discuss its possible mechanisms.