BACKGROUND AND PURPOSE So far, there is only limited information about the regulation of the endogenous synthesis of hydrogen sulfide (H₂S), an important gaseous signalling molecule. This study was done to evaluate the redox‐dependent signalling events that regulate the expression of the H₂S synthesising enzyme cystathionine‐γ‐lyase (CSE) in rat mesangial cells.EXPERIMENTAL APPROACH The effects of platelet‐derived growth factor (PDGF)‐BB and antioxidants on CSE expression and activity in cultured rat renal mesangial cells were assessed. Activity of nuclear factor erythroid‐2‐related factor‐2 (Nrf2) was measured as the binding capacity to a radiolabelled consensus element by electrophoretic mobility shift assay (EMSA). Furthermore, CSE and Nrf2 expression was analysed in a rat model of anti‐Thy‐1‐induced glomerulonephritis by immunohistochemistry.KEY RESULTS Treatment of mesangial cells with PDGF‐BB resulted in a marked time‐ and dose‐dependent up‐regulation of CSE mRNA and protein levels, as well as CSE activity accompanied with increased formation of reactive oxygen species. Remarkably, co‐administration of antioxidants, such as N‐acetylcysteine, ebselen or diphenylene iodonium chloride, drastically reduced PDGF‐BB‐induced CSE expression. PDGF‐BB induced binding of Nrf2 to a corresponding consensus antioxidant element in a redox‐dependent manner. Furthermore, PDGF‐BB‐induced CSE expression in mouse mesangial cells was completely abolished in Nrf2 knockout mice compared with wild‐type mice. In a rat model of anti‐Thy‐1‐induced proliferative glomerulonephritis, we observed a marked up‐regulation of CSE protein paralleled by a stabilization of Nrf2 protein.CONCLUSIONS AND IMPLICATIONS PDGF‐BB regulated CSE via a redox‐mediated activation of Nrf2. Such action would aid the resolution of glomerular inflammatory diseases.LINKED ARTICLE This article is commented on by Gallyas, pp. 2228–2230 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476‐5381.2012.01976.x

Cytokines and nitric oxide (NO) stimulate rat mesangial cells to synthesize and secrete inflammatory mediators. To understand better the signaling pathways that contribute to this response, we exposed rat mesangial cells to the prototypic inflammatory cytokine IL-1β and analyzed the changes in the pattern of gene expression. IL-1β downregulated the gene encoding the matricellular glycoprotein secreted modular calcium-binding protein 1 (SMOC-1) in mesangial cells. Inflammatory cytokines attenuated SMOC-1 mRNA and protein expression through endogenous production of NO, which activated the soluble guanylyl cyclase. Silencing SMOC-1 expression with small interfering RNA decreased the formation of TGF-β, reduced SMAD binding to DNA, and decreased mRNA expression of genes regulated by TGF-β. In a rat model of anti–Thy-1 glomerulonephritis, glomerular SMOC-1 mRNA and protein decreased and inducible NO synthase expression increased simultaneously. Treatment of nephritic rats with the inducible NO synthase–specific inhibitor l-N⁶-(1-iminoethyl)-lysine prevented SMOC-1 downregulation. In summary, these data suggest that NO attenuates SMOC-1 expression in acute glomerular inflammation, thereby limiting TGF-β–mediated profibrotic signaling.

Renal glomerular diseases such as glomerulosclerosis and diabetic nephropathy often result in the loss of glomerular function and consequently end-stage renal disease. The glomerulus consists of endothelial cells, mesangial cells and glomerular epithelial cells also referred to as podocytes. A fine-tuned crosstalk between glomerular cells warrants control of growth factor synthesis and of matrix production and degradation, preserving glomerular structure and function. Hydrogen sulfide (H₂S) belongs together with nitric oxide (NO) and carbon monoxide (CO) to the group of gasotransmitters. During the last three decades, these higher concentration toxic gases have been found to be produced in mammalian cells in a well-coordinated manner. Recently, it became evident that H₂S and the other gasotransmitters share common targets as signalling devices that trigger mainly protective pathways. In several animal models, H₂S has been demonstrated as a protective factor in the context of kidney disorders, in particular of diabetic nephropathy. Here, we focus on the synthesis and action of H₂S in glomerular cells, its beneficial effects in the glomerulus and its action in the context of the other gaseous signalling molecules NO and CO.

PDGF and nitric oxide (NO) have been shown to participate in the progression of several forms of glomerulonephritis. A potential influence of NO on PDGF-mediated signaling cascades was therefore examined. Treatment of rat mesangial cells (MC) with the NO donors diethylenetriamine NO (DETA-NO) or spermine-NONOate resulted in a time- and dose-dependent upregulation of PDGF receptor α (PDGFRα) but not PDGFRβ mRNA levels. Administration of DETA-NO also induced PDGFRα protein expression that was paralleled also by an enhanced receptor phosphorylation. Further experiments using 3-(5-hydroxymethyl-2-furyl)-1-benzylindazole (YC-1), an activator of the soluble guanylyl cyclase (sGC), the membrane-soluble cyclic GMP (cGMP) analog 8-Bromo-PET-cGMP, and the inhibitors of sGC ODQ and NS2028 suggest that elevated cGMP levels are responsible for the effects of NO. Importantly, NO-dependent autophosphorylation of PDGFRα drastically augmented PDGF-AA–evoked phosphorylation of PKB/Akt, a classical downstream target of PDGFRα signaling. Furthermore, in a rat model of anti-Thy-1 glomerulonephritis, expression and phosphorylation of PDGFRα but not PDGFRβ expression was markedly reduced in nephritic animals that were treated with the inducible NO synthase inhibitor l-N⁶(1-iminoethyl)lysine(dihydrochloride) (L-NIL) compared with non-L-NIL–treated nephritic rats as demonstrated by Western blotting and immunohistochemistry. Taken together, the data suggest that NO modulates PDGFRα-triggered signaling in a cGMP-dependent manner by induction of PDGFRα expression in MC and in a rat model of mesangioproliferative glomerulonephritis. The mechanistic details of this regulation have to be elucidated in further experiments.