Inhibition of NADH/NADPH oxidase affects signal transduction by growth factor receptors in normal fibroblasts

Engineering Advanced In Vitro Models of Systemic Sclerosis for Drug Discovery and Development

Systemic sclerosis (SSc) is a complex multisystem disease with the highest case-specific mortality among all autoimmune rheumatic diseases, yet without any available curative therapy. Therefore, the development of novel therapeutic antifibrotic strategies that effectively decrease skin and organ fibrosis is needed. Existing animal models are cost-intensive, laborious and do not recapitulate the full spectrum of the disease and thus commonly fail to predict human efficacy. Advanced in vitro models, which closely mimic critical aspects of the pathology, have emerged as valuable platforms to investigate novel pharmaceutical therapies for the treatment of SSc. This review focuses on recent advancements in the development of SSc in vitro models, sheds light onto biological (e.g., growth factors, cytokines, coculture systems), biochemical (e.g., hypoxia, reactive oxygen species) and biophysical (e.g., stiffness, topography, dimensionality) cues that have been utilized for the in vitro recapitulation of the SSc microenvironment, and highlights future perspectives for effective drug discovery and validation.

The Role of Oxidative Stress in the Development of Systemic Sclerosis Related Vasculopathy

Systemic sclerosis (SSc) is a rare connective tissue disease characterized by autoimmunity, vasculopathy, and progressive fibrosis typically affecting multiple organs including the skin. SSc often is a lethal disorder, because effective disease-modifying treatment still remains unavailable. Vasculopathy with endothelial dysfunction, perivascular infiltration of mononuclear cells, vascular wall remodeling and rarefaction of capillaries is the hallmark of the disease. Most patients present with vasospastic attacks of the digital arteries referred to as 'Raynaud's phenomenon,' which is often an indication of an underlying widespread vasculopathy. Although autoimmune responses and inflammation are both found to play an important role in the pathogenesis of this vasculopathy, no definite initiating factors have been identified. Recently, several studies have underlined the potential role of oxidative stress in the pathogenesis of SSc vasculopathy thereby proposing a new aspect in the pathogenesis of this disease. For instance, circulating levels of reactive oxygen species (ROS) related markers have been found to correlate with SSc vasculopathy, the formation of fibrosis and the production of autoantibodies. Excess ROS formation is well-known to lead to endothelial cell (EC) injury and vascular complications. Collectively, these findings suggest a potential role of ROS in the initiation and progression of SSc vasculopathy. In this review, we present the background of oxidative stress related processes (e.g., EC injury, autoimmunity, inflammation, and vascular wall remodeling) that may contribute to SSc vasculopathy. Finally, we describe the use of oxidative stress related read-outs as clinical biomarkers of disease activity and evaluate potential anti-oxidative strategies in SSc.

Nuclear localization of Formyl-Peptide Receptor 2 in human cancer cells

Current models of G protein-coupled receptors (GPCRs) signaling describe binding of external agonists to cell surface receptors which, in turn, trigger several biological responses. New paradigms indicate that GPCRs localize to and signal at the nucleus, thus regulating distinct signaling cascades. The formyl-peptide receptor FPR2 belongs to the GPCR super-family and is coupled to PTX-sensitive Gi proteins. We show by western blot analysis, immunofluorescence experiments and radioligand binding assays that FPR2 is expressed at nuclear level in CaLu-6 and AGS cells. Nuclear FPR2 is a functional receptor, since it participates in intra-nuclear signaling, as assessed by decreased G protein-FPR2 association and enhanced ERK2, c-Jun and c-Myc phosphorylation upon stimulation of intact nuclei with the FPR2 agonist, WKYMVm. We analyzed FPR2 sequence for the search of a nuclear localization sequence (NLS) and we found a stretch of basic aminoacids (227-KIHKK-231) in the third cytoplasmic loop of the receptor. We performed single (K230A) and multiple (H229A/K230A/K231A) mutagenesis of NLS. The constructs were individually overexpressed in HEK293 cells and immunofluorescence and western blot analysis showed that nuclear localization or translocation of FPR2 depends on the integrity of the H(229) and K(231) residues within the NLS.

Oxidative damage and antioxidative therapy in systemic sclerosis

Systemic sclerosis (SSc) is an autoimmune connective tissue disorder of unknown etiology. This disease is characterized by a large variety of clinical patterns, which include the fibrosis of skin and visceral organs causing a variety of clinical manifestations. Genetic and environmental factors participate in the etiology of this disease; however, recently many studies underline the oxidative background influencing the course and complications of this disease. Reactive oxygen species (ROS) synthesized in SSc can mediate extra- and intracellular oxidative processes affecting endothelial cells and fibroblasts. The estimation of prooxidative markers in the pathogenesis of SSc can enable the identification of useful markers for disease activity and, thus, may help in planning appropriate therapy focusing on the fibrotic or vascular pattern. Recently, many attempts have been made to find antioxidative molecules (nutritional and pharmacological) reducing the prooxidant state in a variety of cells—mainly in endothelium and proliferating fibroblasts. This paper presents both the background of oxidative stress processes in systemic sclerosis mediated by different mechanisms and the evidence suggesting which of the dietary and pharmacological antioxidants can be used as therapeutic targets for this disease.

NADH: flavin oxidoreductase/NADH oxidase and ROS regulate microsclerotium development in Nomuraea rileyi

Based on transcriptome library, an NADH: flavinoxidore ductase/NADH oxidase gene (Nox) was cloned from Nomuraea rileyi. The 1,663-bp full-length cDNA contains an open reading frame of 1,233 bp coding 410 amino acids. The expression level of Nox was up-regulated and co-related to the intracellular H2O2 concentration during microsclerotium (MS) initiation. Rotenone inhibition showed that inhibition of Nox could cause a noticeable decrease in the MS yields. Silencing of Nox resulted in the MS yields, H2O2 and virulence decreased by 98.5, 38 and 21.5%, respectively. On the other hand, MS yields increased by 24.8-61% when induced by H2O2 or menadione. Furthermore, the reactive oxygen species (ROS) scavenger, ascorbic acid (up to 0.03 g ascorbic acid l(-1)), completely inhibited the formation of MS. In conclusion, the results obtained suggested that ROS promoted MS development, and that Nox was required for MS differentiation through regulation of intracellular H2O2 concentration. Besides, Nox had a great impact on the virulence in N. rileyi.

TNFα signals via p66(Shc) to induce E-Selectin, promote leukocyte transmigration and enhance permeability in human endothelial cells

Endothelial cells participate in inflammatory events leading to atherogenesis by regulating endothelial cell permeability via the expression of VE-Cadherin and β-catenin and leukocyte recruitment via the expression of E-Selectins and other adhesion molecules. The protein p66^Shc acts as a sensor/inducer of oxidative stress and may promote vascular dysfunction. The objective of this study was to investigate the role of p66^Shc in tumor necrosis factor TNFα-induced E-Selectin expression and function in human umbilical vein endothelial cells (HUVEC). Exposure of HUVEC to 50 ng/ml TNFα resulted in increased leukocyte transmigration through the endothelial monolayer and E-Selectin expression, in association with augmented phosphorylation of both p66^Shc on Ser³⁶ and the stress kinase c-Jun NH₂-terminal protein kinase (JNK)-1/2, and higher intracellular reactive oxygen species (ROS) levels. Overexpression of p66^Shc in HUVEC resulted in enhanced p66^Shc phosphorylation on Ser³⁶, increased ROS and E-Selectin levels, and amplified endothelial cell permeability and leukocyte transmigration through the HUVEC monolayer. Conversely, overexpression of a phosphorylation-defective p66^Shc protein, in which Ser³⁶ was replaced by Ala, did not augment ROS and E-Selectin levels, nor modify cell permeability or leukocyte transmigration beyond those found in wild-type cells. Moreover, siRNA-mediated silencing of p66^Shc resulted in marked reduction of E-Selectin expression and leukocyte transmigration. In conclusion, p66^Shc acts as a novel intermediate in the TNFα pathway mediating endothelial dysfunction, and its action requires JNK-dependent phosphorylation of p66^Shc on Ser³⁶.

Inhibition of NADPH oxidase 4-related signaling by sodium hydrosulfide attenuates myocardial fibrotic response

BACKGROUND

Myocardial fibrosis plays a pivotal role in the development of heart failure. Hydrogen sulfide (H2S) is an endogenous gasotransmitter with potent cardioprotective properties; however, whether H2S is involved in fibrotic process remains unknown. This study aimed to explore the role of H2S in the process of cardiac fibrosis and the underlying mechanisms.

METHODS

Myocardial infarction (MI) was established in rats by ligation of coronary artery. Activation of rat neonatal cardiac fibroblasts was induced by angiotensin II (Ang II). Fibrotic responses in ischemic myocardium and in Ang II-stimulated cardiac fibroblasts were examined. The effects of sodium hydrosulfide (NaHS, an exogenous H2S donor) on NADPH oxidase 4 (Nox4), reactive oxygen species (ROS) production, extracellular signal-regulated kinase 1/2 (ERK1/2) phosphorylation, heme oxygenase-1 (HO-1), and cystathionine γ-lyase (CSE) were tested to elucidate the protective mechanisms of H2S on fibrotic response.

RESULTS

NaHS treatment inhibited Ang II-induced expression of α-smooth muscle actin, connective tissue growth factor (CTGF), and type I collagen and upregulated expression of HO-1 in cardiac fibroblasts. Ang II-induced Nox4 expression in cardiac fibroblasts was quenched by NaHS and this was associated with a decreased ROS production and reduced ERK1/2 phosphorylation and CTGF expression. In vivo studies using MI model indicated that NaHS administration attenuated Nox4 expression and fibrotic response. Moreover, NaHS therapy also prevented cardiac inflammatory response accompanied by increases in HO-1 and CSE expression.

CONCLUSIONS

The beneficial effect of H2S, at least in part, was associated with a decrease of Nox4-ROS-ERK1/2 signaling axis and an increase in HO-1 expression.

Ionizing radiation-induced metabolic oxidative stress and prolonged cell injury

Cellular exposure to ionizing radiation leads to oxidizing events that alter atomic structure through direct interactions of radiation with target macromolecules or via products of water radiolysis. Further, the oxidative damage may spread from the targeted to neighboring, non-targeted bystander cells through redox-modulated intercellular communication mechanisms. To cope with the induced stress and the changes in the redox environment, organisms elicit transient responses at the molecular, cellular and tissue levels to counteract toxic effects of radiation. Metabolic pathways are induced during and shortly after the exposure. Depending on radiation dose, dose-rate and quality, these protective mechanisms may or may not be sufficient to cope with the stress. When the harmful effects exceed those of homeostatic biochemical processes, induced biological changes persist and may be propagated to progeny cells. Physiological levels of reactive oxygen and nitrogen species play critical roles in many cellular functions. In irradiated cells, levels of these reactive species may be increased due to perturbations in oxidative metabolism and chronic inflammatory responses, thereby contributing to the long-term effects of exposure to ionizing radiation on genomic stability. Here, in addition to immediate biological effects of water radiolysis on DNA damage, we also discuss the role of mitochondria in the delayed outcomes of ionization radiation. Defects in mitochondrial functions lead to accelerated aging and numerous pathological conditions. Different types of radiation vary in their linear energy transfer (LET) properties, and we discuss their effects on various aspects of mitochondrial physiology. These include short and long-term in vitro and in vivo effects on mitochondrial DNA, mitochondrial protein import and metabolic and antioxidant enzymes.

Effect of oxidative stress on protein tyrosine phosphatase 1B in scleroderma dermal fibroblasts

OBJECTIVE

Platelet-derived growth factor (PDGF) and its receptor, PDGFR, promote fibrosis in systemic sclerosis (SSc; scleroderma) dermal fibroblasts, and such cells in scleroderma skin lesions produce excessive reactive oxygen species (ROS). PDGFR is phosphorylated upon PDGF stimulation, and is dephosphorylated by protein tyrosine phosphatases (PTPs), including PTP1B. This study was undertaken to determine whether the thiol-sensitive PTP1B is affected by ROS in SSc dermal fibroblasts, thereby enhancing the phosphorylation of PDGFR and synthesis of type I collagen. This study also sought to investigate the effect of a thiol antioxidant, N-acetylcysteine (NAC), in SSc.

METHODS

Fibroblasts were isolated from the skin of patients with diffuse SSc and normal healthy donors for cell culture experiments and immunofluorescence analyses. A phosphate release assay was used to determine the activity of PTP1B.

RESULTS

Levels of ROS and type I collagen were significantly higher and amounts of free thiol were significantly lower in SSc fibroblasts compared to normal fibroblasts. After stimulation with PDGF, not only were PDGFR and ERK-1/2 phosphorylated to a greater extent, but also the ability to produce PTP1B was hampered in SSc fibroblasts. The activity of PTP1B was significantly inactivated in SSc fibroblasts as a result of cysteine oxidation by the raised levels of ROS, which was confirmed by the oxidation of multiple PTPs, including PTP1B, in SSc fibroblasts. Decreased expression of PTP1B in normal fibroblasts led to increased expression of type I collagen. Treatment of the cells with NAC restored the activity of PTP1B, improved the profile of PDGFR phosphorylation, decreased the numbers of tyrosine-phosphorylated proteins and levels of type I collagen, and scavenged ROS in SSc fibroblasts.

CONCLUSION

This study describes a new mechanism by which ROS may promote a profibrotic phenotype in SSc fibroblasts through the oxidative inactivation of PTP1B, leading to pronounced activation of PDGFR. The study also presents a novel molecular mechanism by which NAC may act on ROS and PTP1B to provide therapeutic benefit in SSc.

NADPH-oxidase-dependent reactive oxygen species mediate EGFR transactivation by FPRL1 in WKYMVm-stimulated human lung cancer cells

Cross talk between unrelated cell surface receptors, such as G-protein-coupled receptors (GPCR) and receptor tyrosine kinases (RTK), is a crucial signaling mechanism to expand the cellular communication network. We investigated the ability of the GPCR formyl peptide receptor-like 1 (FPRL1) to transactivate the RTK epidermal growth factor receptor (EGFR) in CaLu-6 cells. We observed that stimulation with WKYMVm, an FPRL1 agonist isolated by screening synthetic peptide libraries, induces EGFR tyrosine phosphorylation, p47(phox) phosphorylation, NADPH-oxidase-dependent superoxide generation, and c-Src kinase activity. As a result of EGFR transactivation, phosphotyrosine residues provide docking sites for recruitment and triggering of the STAT3 pathway. WKYMVm-induced EGFR transactivation is prevented by the FPRL1-selective antagonist WRWWWW, by pertussis toxin (PTX), and by the c-Src inhibitor PP2. The critical role of NADPH-oxidase-dependent superoxide generation in this cross-talk mechanism is corroborated by the finding that apocynin or a siRNA against p22(phox) prevents EGFR transactivation and c-Src kinase activity. In addition, WKYMVm promotes CaLu-6 cell growth, which is prevented by PTX and by WRWWWW. These results highlight the role of FPRL1 as a potential target of new drugs and suggest that targeting both FPRL1 and EGFR may yield superior therapeutic effects compared with targeting either receptor separately.

Potentiation of epithelial innate host responses by intercellular communication

The epithelium efficiently attracts immune cells upon infection despite the low number of pathogenic microbes and moderate levels of secreted chemokines per cell. Here we examined whether horizontal intercellular communication between cells may contribute to a coordinated response of the epithelium. Listeria monocytogenes infection, transfection, and microinjection of individual cells within a polarized intestinal epithelial cell layer were performed and activation was determined at the single cell level by fluorescence microscopy and flow cytometry. Surprisingly, chemokine production after L. monocytogenes infection was primarily observed in non-infected epithelial cells despite invasion-dependent cell activation. Whereas horizontal communication was independent of gap junction formation, cytokine secretion, ion fluxes, or nitric oxide synthesis, NADPH oxidase (Nox) 4-dependent oxygen radical formation was required and sufficient to induce indirect epithelial cell activation. This is the first report to describe epithelial cell-cell communication in response to innate immune activation. Epithelial communication facilitates a coordinated infectious host defence at the very early stage of microbial infection.

All body surfaces are covered by a single layer of epithelial cells. Epithelial cells form a physical barrier to separate the underlying sterile tissue from the environment. In addition, epithelial cells actively sense bacterial and viral infection. The recognition of pathogenic microorganisms results in cell stimulation and the secretion of soluble mediators that attract professional immune cells to the site of infection. This first line host defence works very efficiently despite the often low number of pathogens and the limited amount of mediators secreted per epithelial cell. We therefore investigated whether infection of one individual epithelial cell would result in activation of other, non-infected cells within a confluent epithelial monolayer resulting in a more substantial host response. Indeed, using the model of the gut pathogen Listeria monocytogenes and monitoring infection and epithelial activation at a single cell level, we can clearly show that the epithelial response is mainly mediated by non-infected cells. Also, we identify oxygen radicals as potential mediators to facilitate horizontal epithelial communication upon immune stimulation. Our results thus provide a novel concept of a coordinated epithelial host response upon microbial infection facilitated by horizontal epithelial communication.

Expression and signaling of formyl-peptide receptors in the brain

The human formyl-peptide receptor (FPR) and its variants FPRL1 and FPRL2 belong to the G-protein coupled seven transmembrane receptor (GPCR) family sensitive to pertussis toxin. FPR and FPRL1 were first detected in phagocytic leukocytes, and FPRL2 was found in monocytes and in dendritic cells. The three receptors were subsequently identified in other cell types or tissues, including neuronal cells and brain, where FPR and FPRL1 play a key role in angiogenesis, cell proliferation, protection against and cell death, as well as in neuroendocrine functions. Binding of different agonists to FPRs triggers several signaling pathways, activates NFkB and STAT3 transcriptional factors and induces the accumulation of the CDK inhibitors p21(waf1/cip1), p16(INK4) and p27(kip1). Signaling molecules, such as ERKs, JNK, PKC, p38MAPK, PLC and PLD are involved in these intracellular cascades. In this article we briefly review FPRs expression and signaling in neuronal cells.

Oxidative-dependent integration of signal transduction with intercellular gap junctional communication in the control of gene expression

Research on oxidative stress focused primarily on determining how reactive oxygen species (ROS) damage cells by indiscriminate reactions with their macromolecular machinery, particularly lipids, proteins, and DNA. However, many chronic diseases are not always a consequence of tissue necrosis, DNA, or protein damage, but rather to altered gene expression. Gene expression is highly regulated by the coordination of cell signaling systems that maintain tissue homeostasis. Therefore, much research has shifted to the understanding of how ROS reversibly control gene expression through cell signaling mechanisms. However, most research has focused on redox regulation of signal transduction within a cell, but we introduce a more comprehensive-systems biology approach to understanding oxidative signaling that includes gap junctional intercellular communication, which plays a role in coordinating gene expression between cells of a tissue needed to maintain tissue homeostasis. We propose a hypothesis that gap junctions are critical in modulating the levels of second messengers, such as low molecular weight reactive oxygen, needed in the transduction of an external signal to the nucleus in the expression of genes. Thus, any comprehensive-systems biology approach to understanding oxidative signaling must also include gap junctions, in which aberrant gap junctions have been clearly implicated in many human diseases.

FPRL1-mediated induction of superoxide in LL-37-stimulated IMR90 human fibroblast

Molecular mechanisms underlying the generation of reactive oxygen species in LL-37-stimulated cells are poorly understood. Previously, we demonstrated that in human fibroblasts the exposure to WKYMVm induced p47(phox) phosphorylation and translocation and, in turn, NADPH oxidase activation. These effects were mediated by the activation of the Formyl-peptide receptor-like 1 (FPRL1) and the downstream signaling involved ERKs phosphorylation and PKCalpha- and PKCdelta-activation. Since LL-37 uses FPRL1 as a receptor to mediate its action on several cell types, we investigated in LL-37-stimulated IMR90 cells molecular mechanisms involved in NADPH-dependent superoxide generation. The exposure to LL-37, which is expressed in fibroblasts, induced ERKs activation, p47(phox) phosphorylation and translocation as well as NADPH oxidase activation. These effects were prevented by pertussis toxin, PD098059 and WRWWWW, a FPRL1-selective antagonist. Furthermore, the stimulation with LL-37 of HEK293 cells, transfected to stably express FPRL1, induced a rapid activation of ERKs and p47(phox) phosphorylation.

The involvement of reactive oxygen species (ROS) in the cell cycle activation (G(0)-to-G(1) transition) of plant cells

Reactive oxygen species (ROS) are involved in various cellular processes in plants. Among those, resistance to abiotic stress, defence mechanisms and cell expansion have been intensively studied during the last years. We recently demonstrated that ROS, in concert with auxin, have a role in cell cycle activation of differentiated leaf cells.1 In this addendum we provide further evidence to show that oxidative stress/ROS accelerate auxin-mediated cell cycle entry (G(0)-to-G(1)) and may have a positive effect on the plant cell cycle machinery. A generalized model for concentration-dependent synergistic effect of auxin and ROS on differentiated plant cells is also shown.

Regulation of normal cell cycle progression by flavin-containing oxidases

Mechanisms underlying the role of reactive oxygen species (ROS) generated by flavin-containing oxidases in regulating cell cycle progression were examined in human and rodent fibroblasts. Incubation of confluent cell cultures with nontoxic/nonclastogenic concentrations of the flavoprotein inhibitor, diphenyleneiodonium (DPI), reduced nicotinamide adenine dinucleotide phosphate (NAD(P)H) oxidase activity and basal ROS levels, but increased proteolysis of cyclin D1, p21(Waf1) and phospho-p38(MAPK). When these cells were allowed to proliferate by subculture in DPI-free medium, an extensive G(1) delay was observed with concomitant activation of p53/p21(Waf1) signaling and reduced phosphorylation of mitogen-activated kinases. Compensation for decreased oxidant generation by simultaneous exposure to DPI and nontoxic doses of the ROS generators, gamma-radiation or t-butyl-hydroperoxide, attenuated the G(1) delay. Whereas the DPI-induced G(1) checkpoint was completely dependent on PHOX91, ATM and WAF1, it was only partially dependent on P53. Interestingly, G(1) to S progression was not affected when another flavin-containing enzyme, nitric oxide synthase, was inhibited nor was it associated with changes in mitochondrial membrane potential. Proliferating cells treated with DPI also experienced a significant but attenuated delay in G(2). We propose that ATM performs a critical function in mediating normal cellular proliferation that is regulated by nonphagocytic NAD(P)H oxidase enzymes activity, which may serve as a novel target for arresting cancer cells in G(1).

Protein kinase C-alpha and -delta are required for NADPH oxidase activation in WKYMVm-stimulated IMR90 human fibroblasts

The regulation of the activation of non phagocytic NADPH oxidase is poorly understood. Previously we demonstrated that in fibroblasts the exposure to WKYMVm induced p47(phox) phosphorylation and translocation and that these effects were mediated by ERKs activation. Protein kinase C (PKC) is reported to be involved in regulating the phosphorylation of NADPH oxidase components in polymorphonucleate cells stimulated via FPRL1 receptor, but its involvement in fibroblasts was not demonstrated. Therefore, we investigated in IMR90 cells exposed to WKYMVm the role of PKC isoenzymes in the activation of NADPH oxidase-like enzyme. Preincubation with general pharmacological inhibitors of PKC, before stimulation with WKYMVm, prevented the ERKs activation, p47(phox) phosphorylation and translocation. The analysis of cellular partitioning of PKC isoenzymes demonstrated that PKCalpha and PKCdelta translocated from the cytosolic to the membrane fraction upon stimulation with WKYMVm. Preincubation with Gö6976 or with rottlerin prevented the phosphorylation and translocation of NADPH oxidase regulatory subunit.

Redox regulation of platelet-derived-growth-factor-receptor: Role of NADPH-oxidase and c-Src tyrosine kinase

This study identifies some early events contributing to the redox regulation of platelet-derived growth factor receptor (PDGFr) activation and its signalling in NIH3T3 fibroblasts. We demonstrate for the first time that the redox regulation of PDGFr tyrosine autophosphorylation and its signalling are related to NADPH oxidase activity through protein kinase C (PKC) and phosphoinositide-3-kinase (PI3K) activation and H2O2 production. This event is also essential for complete PDGF-induced activation of c-Src kinase by Tyr416 phosphorylation, and the involvement of c-Src kinase on H2O2-induced PDGFr tyrosine phosphorylation is demonstrated, suggesting a role of this kinase on the redox regulation of PDGFr activation. Finally, it has been determined that not only PI3K activity, but also PKC activity, are related to NADPH oxidase activation due to PDGF stimulation in NIH3T3 cells, as it occurs in non-phagocyte cells. Therefore, we suggest a redox circuit whereby, upon PDGF stimulation, PKC, PI3K and NADPH oxidase activity contribute to complete c-Src kinase activation, thus promoting maximal phosphorylation and activation of PDGFr tyrosine phosphorylation.

Role of protein kinase C and oxidative stress in interleukin-1beta-induced human proximal tubule cell injury and fibrogenesis

BACKGROUND

Interleukin (IL)-1beta, a pro-inflammatory macrophage-derived cytokine, is implicated as a key mediator of interstitial fibrosis and tubular loss or injury in progressive renal insufficiency. This study investigates some of the mechanisms of action of IL-1beta on the proximal tubule.

METHODS

Confluent cultures of primary human proximal tubule cells (PTC) were incubated in serum-free media supplemented with either IL-1beta (0-4 ng/mL), phorbol-12-myristate 13-acetate (PMA, protein kinase C activator) (6.25-100 nmol/L), or vehicle (control), together with a non-specific protein kinase C inhibitor (H7), a specific protein kinase C inhibitor (BIM-1), an anti-oxidant (NAC) or a NADPH oxidase inhibitor (AEBSF).

RESULTS

Interleukin-1beta-treated PTC exhibited time-dependent increases in fibronectin secretion (ELISA), cell injury (LDH release) and reactive nitrogen species (RNS) release (Griess assay). Proximal tubule cell DNA synthesis (thymidine incorporation) was also significantly suppressed. The effects of IL-1beta, which were reproduced by incubation of PTC with PMA (6.25-100 nmol/L), were blocked by H7 but not by BIM-1. The anti-oxidant (4 mmol/L) partially blocked IL-1beta-induced fibronectin secretion by PTC, but did not affect IL-1beta-induced LDH release, RNS release or growth inhibition. The NADPH oxidase inhibitor (AEBSF) significantly attenuated all observed deleterious effects of IL-1beta on PTC.

CONCLUSION

Interleukin-1beta directly induces proximal tubule injury, extracellular matrix production and impaired growth. The anti-oxidant, NAC, appears to ameliorate part of the fibrogenic effect of IL-1beta on PTC through mechanisms that do not significantly involve protein kinase C activation or nitric oxide release.