Downregulation of SPARC expression is mediated by nitric oxide in rat mesangial cells and during endotoxemia in the rat

Regulation of Cellular Redox Signaling by Matricellular Proteins in Vascular Biology, Immunology, and Cancer

SIGNIFICANCE

In contrast to structural elements of the extracellular matrix, matricellular proteins appear transiently during development and injury responses, but their sustained expression can contribute to chronic disease. Through interactions with other matrix components and specific cell surface receptors, matricellular proteins regulate multiple signaling pathways, including those mediated by reactive oxygen and nitrogen species and H2S. Dysregulation of matricellular proteins contributes to the pathogenesis of vascular diseases and cancer. Defining the molecular mechanisms and receptors involved is revealing new therapeutic opportunities. Recent Advances: Thrombospondin-1 (TSP1) regulates NO, H2S, and superoxide production and signaling in several cell types. The TSP1 receptor CD47 plays a central role in inhibition of NO signaling, but other TSP1 receptors also modulate redox signaling. The matricellular protein CCN1 engages some of the same receptors to regulate redox signaling, and ADAMTS1 regulates NO signaling in Marfan syndrome. In addition to mediating matricellular protein signaling, redox signaling is emerging as an important pathway that controls the expression of several matricellular proteins.

CRITICAL ISSUES

Redox signaling remains unexplored for many matricellular proteins. Their interactions with multiple cellular receptors remains an obstacle to defining signaling mechanisms, but improved transgenic models could overcome this barrier.

FUTURE DIRECTIONS

Therapeutics targeting the TSP1 receptor CD47 may have beneficial effects for treating cardiovascular disease and cancer and have recently entered clinical trials. Biomarkers are needed to assess their effects on redox signaling in patients and to evaluate how these contribute to their therapeutic efficacy and potential side effects. Antioxid. Redox Signal. 27, 874-911.

CD2-associated protein participates in podocyte apoptosis via PI3K/Akt signaling pathway

CD2-associated protein is one of the most important slit diaphragm proteins in maintaining podocyte integrity and reducing proteinuria. In the last 15 years, progressive researches have shown that CD2AP serves as an adaptor protein, plays essential roles in the podocyte cytoskeletal structure and signaling from the extracellular SD to the intracellular dynamic actin cytoskeleton. CD2AP deficient or transcript abnormality would lead to podocyte failure and proteinuric glomerular diseases. In this study, we demonstrate that CD2AP and p85 regulatory subunit of phosphoinositide 3-OH kinase (PI3K), recruit PI3K to the plasma membrane, and stimulate PI3K-dependent AKT signaling in podocytes the CD2AP-mediated AKT activity can regulate complex biological programs. PAN reduces Akt phosphorylation levels of GSK3β, LY294002 can promote podocyte apoptosis induced by PAN. Our findings suggest that the activation of PI3K/AKT signaling represents an essential component to maintain the functional integrity of podocytes. And PI3K/Akt signaling pathway play an important role in podocyte apoptosis.

Activity of matrix metallo proteinases (MMPs) and the tissue inhibitor of MMP (TIMP)-1 in electromagnetic field-exposed THP-1 cells

Matrix metalloproteinases (MMPs) and tissue inhibitors of MMPs (TIMPs) are the main determinants of tissue remodeling in both physiological and pathological processes. Metabolic processes, which generate oxidants and antioxidants can be influenced by environmental factors such as electromagnetic fields (EMF). We analyzed the effects of EMF on the activity and expression of MMPs in THP-1 cells. Cells were exposed to a 50 Hz, 1 mT EMF for 24 h and incubated with or without LPS. Our data indicate that THP-1 cells exposed to EMF causes a reduction of anti-oxidant enzyme activity and an enhancement of nitrogen intermediates involving the iNOS pathway. We then analyzed the role of nitration of TIMP-1 in increasing the activity of MMPs in EMF exposed cells. Molecular modeling tools were employed to identify the most plausible sites in the active conformation of TIMP-1; at least two protein sites, Y120 and Y38 and/or Y72 were identified. Reactive nitrogen species (RNS) may affect protein targets, such as TIMP-1, which are crucial for the regulation of MMP activities by oxidation of sulfydryl groups, or by nitration of tyrosine residues. These results may suggest a pathway connecting an imbalance of MMPs and their cognate inhibitor TIMP-1.

Nitric oxide inhibits glomerular TGF-beta signaling via SMOC-1

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-1beta and analyzed the changes in the pattern of gene expression. IL-1beta 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-beta, reduced SMAD binding to DNA, and decreased mRNA expression of genes regulated by TGF-beta. 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-N(6)-(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-beta-mediated profibrotic signaling.

Dexamethasone Prevents Podocyte Apoptosis Induced by Puromycin Aminonucleoside: Role of p53 and Bcl-2–Related Family Proteins

Nephrotic-range proteinuria is due to glomerular diseases characterized by podocyte injury. Glucocorticoids are the standard of care for most forms of nephrotic syndrome. However, the precise mechanisms underlying the beneficial effects of glucocorticoids on podocytes, beyond its general immunosuppressive and anti-inflammatory effects, are still unknown. This study tested the hypothesis that the synthetic glucocorticoid dexamethasone directly reduces podocyte apoptosis. Growth-restricted immortalized mouse podocytes in culture were exposed to puromycin aminonucleoside (PA) to induce apoptosis. Our results showed that dexamethasone significantly reduced PA-induced apoptosis by 2.81-fold. Dexamethasone also rescued podocyte viability when exposed to PA. PA-induced apoptosis was associated with increased p53 expression, which was completely blocked by dexamethasone. Furthermore, the inhibition of p53 by the p53 inhibitor pifithrin-alpha protected against PA-induced apoptosis. Dexamethasone also lowered the increase in the proapoptotic Bax, which was increased by PA, and increased expression of the antiapoptotic Bcl-xL protein. Moreover, the decrease in p53 by dexamethasone was associated with increased Bcl-xL levels. Podocyte apoptosis induced by PA was caspase-3 independent but was associated with the translocation of apoptosis-inducing factor (AIF) from the cytoplasm to nuclei. AIF translocation was inhibited by dexamethasone. These results show that PA-induced podocyte apoptosis is p53 dependent and associated with changes in Bcl-2-related proteins and AIF translocation. The protective effects of dexamethasone on PA-induced apoptosis were associated with decreasing p53, increasing Bcl-xL, and inhibition of AIF translocation. These novel findings provide new insights into the beneficial effects of corticosteroids on podocytes directly, independent of its immunosuppressive effects.

Nitric oxide upregulates induction of PDGF receptor-alpha expression in rat renal mesangial cells and in anti-Thy-1 glomerulonephritis

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 alpha (PDGFRalpha) but not PDGFRbeta mRNA levels. Administration of DETA-NO also induced PDGFRalpha 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 PDGFRalpha drastically augmented PDGF-AA-evoked phosphorylation of PKB/Akt, a classical downstream target of PDGFRalpha signaling. Furthermore, in a rat model of anti-Thy-1 glomerulonephritis, expression and phosphorylation of PDGFRalpha but not PDGFRbeta 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 PDGFRalpha-triggered signaling in a cGMP-dependent manner by induction of PDGFRalpha expression in MC and in a rat model of mesangioproliferative glomerulonephritis. The mechanistic details of this regulation have to be elucidated in further experiments.

Identification of manganese superoxide dismutase as a NO-regulated gene in rat glomerular mesangial cells by 2D gel electrophoresis

The course of inflammatory glomerular diseases is accompanied by changes in the expression of matrix-associated proteins, growth factors, and mediators in renal mesangial cells. Furthermore, the production of nitric oxide (NO) by the inducible isoform of nitric oxide synthase (iNOS) is enhanced after stimulation with pro-inflammatory cytokines. NO has been demonstrated to be a potent modulator of gene expression. To identify NO-regulated genes, we compared the expression patterns of mesangial cells treated for 24h with 500 microM (Z)-1-[2-(2-aminoethyl)-N-(2-ammonioethyl)amino]diazen-1-ium-1,2-diolate (DETA-NO) with those of un-stimulated controls by applying a proteomics approach. One protein found to be NO-modulated by 2D gel electrophoresis is the manganese superoxide dismutase (Mn-SOD). Immunoblot and Northern blot analysis demonstrated a dose- and time-dependent induction of Mn-SOD expression by S-nitroso-N-acetyl-D, L-penicillamine (SNAP) and DETA-NO on both the protein and the mRNA levels. An upregulation of Mn-SOD expression by NO was accompanied by an increased Mn-SOD activity. Immunoblots of extracts of IL-1beta-treated cells cultivated with or without the iNOS inhibitor N(G)-monomethyl-L-arginine and the inhibitor of soluble guanylyl cyclase (sGC) 1H-[1,2,4]oxadiazole[4,3-a]quinoxalin-1-one (ODQ) demonstrated that the upregulation of the Mn-SOD by NO is due to a NO-dependent activation of sGC. The upregulation of Mn-SOD mRNA expression by NO was confirmed in vivo by Northern blot analysis in kidneys from rats treated with lipopolysaccharide (LPS) either in presence or absence of the iNOS inhibitor N(6)-(1-iminoethyl)-L-lysine (l-NIL).

Nitric oxide and mechanisms of redox signaling

Regulation of signal transduction and gene expression is a multifaceted process involving ligands, receptors, and second messengers that trigger cascades of protein kinases and phosphatases and propagate the signal to the nucleus to alter gene expression. Reduction-oxidation (redox)-based regulatory pathways provide additional means of gating signal transduction, and redox-based regulation of gene expression emerges as a fundamental regulatory mechanism in living cells. The cellular redox state is reflected by the degree of oxidation (or reduction) of various redox-active molecules at a specific cellular location at any given time point. The ratio of oxidized/reduced redox species determines the redox potential, which may vary dramatically in time and in different compartments of a cell and consequently alter in a temporally and spatially dynamic process the activity of signaling enzymes that carry redox-active functional groups. Generation and action of free radicals such as nitric oxide, superoxide, and H(2)O(2) that paradigmatically highlight the impact of redox regulation on cellular signal transduction and gene expression are discussed with a special focus on the renal glomerular response to injury.

Biglycan, a nitric oxide-regulated gene, affects adhesion, growth, and survival of mesangial cells

During glomerular inflammation mesangial cells are the major source and target of nitric oxide that pro-foundly influences proliferation, adhesion, and death of mesangial cells. The effect of nitric oxide on the mRNA expression pattern of cultured rat mesangial cells was therefore investigated by RNA-arbitrarily-primed polymerase chain reaction. Employing this approach, biglycan expression turned out to be down-regulated time- and dose-dependently either by interleukin-1beta-stimulated endogenous nitric oxide production or by direct application of the exogenous nitric oxide donor, diethylenetriamine nitric oxide. There was a corresponding decline in the rate of biglycan biosynthesis and in the steady state level of this proteoglycan. In vivo, in a model of mesangioproliferative glomerulonephritis up-regulation of inducible nitric-oxide synthase mRNA was associated with reduced expression of biglycan in isolated glomeruli. Biglycan expression could be normalized, both in vitro and in vivo, by using a specific inhibitor of the inducible nitric-oxide synthase, l-N6-(l-iminoethyl)-l-lysine dihydrochloride. Further studies showed that biglycan inhibited cell adhesion on type I collagen and fibronectin because of its binding to these substrates. More importantly, biglycan protected mesangial cells from apoptosis by decreasing caspase-3 activity, and it counteracted the proliferative effects of platelet-derived growth factor-BB. These findings indicate a signaling role of biglycan and describe a novel pathomechanism by which nitric oxide modulates the course of renal glomerular disease through regulation of biglycan expression.

Nitric oxide increases the decay of matrix metalloproteinase 9 mRNA by inhibiting the expression of mRNA-stabilizing factor HuR

Dysregulation of extracellular matrix turnover is an important feature of many inflammatory processes. Rat renal mesangial cells express high levels of matrix metalloproteinase 9 (MMP-9) in response to inflammatory cytokines such as interleukin-1 beta. We demonstrate that NO does strongly destabilize MMP-9 mRNA, since different luciferase reporter gene constructs containing the MMP-9 3' untranslated region (UTR) displayed significant reduced luciferase activity in response to the presence of NO. Moreover, by use of an in vitro degradation assay we found that the cytoplasmic fractions of NO-treated cells contained a higher capacity to degrade MMP-9 transcripts than those obtained from control cells. An RNA electrophoretic mobility shift assay demonstrated that three of four putative AU-rich elements present in the 3' UTR of MMP-9 were constitutively occupied by the mRNA-stabilizing factor HuR and that the RNA binding was strongly attenuated by the presence of NO. The addition of recombinant glutathione transferase-HuR prevented the rapid decay of MMP-9 mRNA, whereas the addition of a neutralizing anti-HuR antibody caused an acceleration of MMP-9 mRNA degradation. Furthermore, the expression of HuR mRNA and protein was significantly reduced by exogenously and endogenously produced NO. These inhibitory effects were mimicked by the cGMP analog 8-bromo-cGMP and reversed by LY-83583, an inhibitor of soluble guanylyl cyclase. These results demonstrate that NO acts in a cGMP-dependent mechanism to inhibit the expression level of HuR, thereby reducing the stability of MMP-9 mRNA.

Nitric oxide down-regulates connective tissue growth factor in rat mesangial cells

BACKGROUND

Nitric oxide (NO) exerts complex regulatory actions on mesangial cell (MC) biology, such as inhibition of proliferation, adhesion or contractility and induction of apoptosis. In our previous studies the NO-donor S-nitroso-glutathione (GSNO) was found to be a potent inhibitor of MC growth. This effect was mediated at least in part by inhibitory effects of GSNO on the transcription factor early growth response gene-1 (Egr-1) [10]. We therefore were interested in the regulation of gene expression in MC after treatment with NO.

METHODS

To identify the genes that are regulated by NO in MC, gene expression was analyzed by representational difference analysis. Expression of connective tissue growth factor (CTGF) was studied by Northern and Western blot analyses.

RESULTS

Cultured rat MCs treated with GSNO for 8 hours were compared with unstimulated MCs and the CTGF mRNA was found to be down-regulated. The down-regulation was dose-dependent and transient, with a maximum inhibition seen after 6 hours. In parallel, down-regulation of CTGF protein by GSNO was observed by Western blot analysis. Other NO-donors such as S-nitroso-N-acetyl-D,L-penicillamine and spermine-NO showed similar effects. The induction of the inducible NO-synthase by TNF-alpha, IL-1beta and LPS provoked a transient down-regulation of CTGF mRNA, an effect that could be partially overcome by pretreatment with the NOS-inhibitor Nomega-nitro-l-arginine methyl ester. The observed NO-effect could be simulated by treatment with the stable cGMP analog 8br-cGMP, and was abolished by blocking the guanylyl cyclase with the inhibitor NS2028.

CONCLUSION

NO acts as a strong repressor of CTGF expression in cultured rat MC. Thus, in addition to its antiproliferative effects, NO potentially exerts antifibrotic activity by down-regulation of CTGF.

Changing gears in the course of glomerulonephritis by shifting superoxide to nitric oxide-dominated chemistry

The glomerular response to injury displays astonishingly uniform features that include infiltration with professional immune cells, activation and proliferation of resident glomerular cells and matrix expansion. Cross-communication of intrinsic mesangial cells with invading immune cells is crucial for the fate of glomerular injury: progression to glomerulosclerosis or resolution and repair. The formation of free radicals, particularly of nitric oxide and superoxide, are key events that initiate redox-based signal transduction and gene expression. The balance between these radicals constitutes redox-operated genetic switches that ensure self-limited inflammatory responses to tissue injury. The aberrant production of the mediators, however, may sustain matrix accumulation and result in irreversible alteration of glomerular structure and function.

Nitric oxide and mechanisms of redox signalling: matrix and matrix-metabolizing enzymes as prime nitric oxide targets

One of the greatest biomedical breakthroughs of the twentieth century was the discovery of endothelium-derived relaxing factor and its identification as nitric oxide (NO). NO has received special attention ever since: besides its potent vasodilatory and vasoprotective effects, NO was identified as a key player in innate immunity and was found to act as an unconventional type of neurotransmitter. This article focuses on mechanisms of NO signalling that form the basis of functional cell responses to accommodate changes in the cellular microenvironment. Redox-based regulation of signal transduction and, on a more long-term scale, changes in gene expression will be exemplified by NO-modulation of matrix components and matrix-metabolizing enzymes. It seems to be a safe bet that ongoing analyses of NO signalling and gene expression will provide a wealth of promising therapeutic targets in human diseases.

Nitric oxide induces MIP-2 transcription in rat renal mesangial cells and in a rat model of glomerulonephritis

Nitric oxide is a crucial mediator of several forms of glomerulonephritis. We examined the effects of NO on the mRNA expression pattern in glomerular mesangial cells by using a low-stringency reverse transcriptase-polymerase chain reaction method and detected a cDNA fragment that was induced by interleukin 1b (IL-1b) and further up-regulated by the NO donor diethylenetriamine-nitric oxide (DETA-NO). Each respective cDNA fragment was found to match with the cDNAs of rat macrophage inflammatory protein 2 (MIP-2) and GRO/cytokine-induced neutrophil chemoattractant 2b (CINC-2b). Further characterization of MIP-2 regulation by Northern blot analysis confirmed an NO- and IL-1b-dependent increase in MIP-2 mRNA levels. Moreover, inhibition of IL-1b-induced endogenous NO formation by the NO-synthase (NOS) inhibitor L-NMMA markedly attenuated MIP-2 protein expression. We cloned 770 bp of the 5'-flanking region of rat MIP-2 and fused this fragment to a luciferase reporter gene. Transfection of the construct into mesangial cells resulted in a 3.5-fold increase in luciferase activity in cells treated with DETA-NO when compared to controls, suggesting a transcriptional mechanism for NO-induced MIP-2 expression. Deletion and mutational analysis identified critical nuclear factor (NF)-kB and NF-IL-6 binding sites required for NO regulation of MIP-2. In vivo, inhibition of NO synthesis in the Thy-1.1 model of mesangioproliferative glomerulonephritis by the specific inducible-NOS inhibitor L-NIL resulted in a marked reduction of MIP-2 mRNA expression. Furthermore, infiltration of neutrophils into the glomerulus was dramatically attenuated in L-NIL-treated rats.