Differential activation of mitogen-activated protein kinases in experimental mesangioproliferative glomerulonephritis

The Effect and Mechanism of Fufang Banbianlian Injection in the Treatment of Mesangial Proliferative Glomerulonephritis

OBJECTIVE

Mesangial proliferative glomerulonephritis (MsPGN) is an important cause of chronic kidney disease. Abnormal proliferation of mesangial cells and immune-inflammatory response are its important pathological manifestations. Currently, there is no ideal treatment for this disease. Fufang Banbianlian Injection (FBI) has anti-inflammatory, antioxidant, and immuneenhancing effects, and is mostly used for the treatment of bronchitis, pneumonia, and respiratory tract infections in children.

METHODS

A rat model of MsPGN was established and treated with FBI. The efficacy was tested through pathological experiments and urine protein quantification. Network pharmacology methods were used to predict the signaling pathways and key proteins that exert the efficacy of FBI, and were screened through molecular docking experiments. The active substances that work were verified through cell experiments.

RESULTS

The results confirmed that intervention with FBI can inhibit the proliferation of glomerular cells and reduce the infiltration of macrophages, thereby reducing the pathological damage of rats with mesangial proliferative nephritis; it has been found to have an obvious therapeutic effect. Molecular docking results have shown kaempferol (Kae), the main component of FBI, to have a good affinity for key targets. The results of in vitro verification experiments showed that FBI and its active ingredient Kae may play a therapeutic role by regulating the NF-κB signaling pathway in mesangial cells, inhibiting its activation and the secretion of proinflammatory cytokines.

CONCLUSION

Through network pharmacology, molecular docking, and experimental verification, it was confirmed that FBI and its active ingredient Kae can reduce the molecular mechanism of pathological damage of MsPGN by regulating the NF-κB signaling pathway and providing potential therapeutic drugs for the treatment of this disease.

Carvedilol through ß1-Adrenoceptor blockade ameliorates glomerulonephritis via inhibition of oxidative stress, apoptosis, autophagy, ferroptosis, endoplasmic reticulum stress and inflammation

Glomerulonephritis (GN) is one of the main causes of end stage renal disease and requires an effective treatment for inhibiting GN. Renal nerves through efferent (RENA) and afferent (RANA) innervation to glomeruli regulate the glomerular function. We delineated the role of RENA and RANA on anti-Thy1.1-induced GN. Female Wistar rats were divided into Control, Thy1.1 plus anti-Thy1.1, bilaterally renal nerve denervation (DNX) plus anti-Thy1.1, and topical capsaicin to bilateral renal nerves for selective ablation of RANA (DNAX) plus anti-Thy1.1. We examined RANA and RENA response to anti-Thy1.1 and compared the effect of DNX or DNAX on urinary oxidative stress, renal gp91, tyrosine hydroxylase (TH), calcitonin gene-related peptide (CGRP), apoptosis, autophagy, ferroptosis, antioxidant enzymes, endoplasmic reticulum (ER) stress and inflammation by western blot. Anti-Thy1.1 significantly enhanced RENA, but did not affect RANA. DNX significantly decreased TH and CGRP expression, whereas DNAX only reduced CGRP expression. Anti-Thy1.1 significantly increased glomerulosclerosis injury, urinary protein, electron paramagnetic resonance signals of alpha-(4-pyridyl-N-oxide)-N-tert-butylnitrone adducts, 8-isoprostane and nitrotyrosine levels, NADPH oxidase gp91phox (gp91), macrophage/monocyte (ED-1), GRP-78, Beclin-1/LC3-II, Bax/caspase-3/poly(ADP-ribose) polymerase expression, inflammatory cytokines levels and decreased renal Copper/Zinc superoxide dismutase, Cystine/glutamate transporter (xCT) and Glutathione peroxidase 4 (GPX4) expression vs. Control. The enhanced oxidative parameters or reduced antioxidant defense by anti-Thy1.1 were significantly attenuated by DNX but not DNAX. Additionally, oral ß1-adrenoceptor antagonist-Carvedilol at an early stage reduced anti-Thy1.1 increased proteinuria level and oxidative parameters. Our data suggest that DNX and ß1-adrenoceptor antagonist-Carvedilol efficiently attenuate oxidative stress, inflammation, ER stress, autophagy, ferroptosis and apoptosis in GN.

Ameliorate impacts of scopoletin against vancomycin-induced intoxication in rat model through modulation of Keap1-Nrf2/HO-1 and IκBα-P65 NF-κB/P38 MAPK signaling pathways: Molecular study, molecular docking evidence and network pharmacology analysis

Nephrotoxicity is an indication for the damage of kidney-specific detoxification and excretion mechanisms by exogenous or endogenous toxicants. Exposure to vancomycin predominantly results in renal damage and losing the control of body homeostasis. Vancomycin-treated rats (200 mg/kg/once daily, for seven consecutive days, i.p.) revealed significant increase in serum pivotal kidney function, oxidative stress, and inflammatory biomarkers. Histologically, vancomycin showed diffuse acute tubular necrosis, denudation of epithelium and infiltration of inflammatory cells in the lining tubular epithelium in cortical portion. In the existing study, the conservative consequences of scopoletin against vancomycin nephrotoxicity was investigated centering on its capacity to alleviate oxidative strain and inflammation through streamlining nuclear factor (erythroid-derived-2) like 2 (Nrf2)/heme oxygenase-1 (HO-1) signaling and prohibiting the nuclear factor kappa B (NF-κB)/mitogen-activated protein kinase (p38 MAPK) pathway. With respect to vancomycin group, scopoletin pretreatment (50 mg/kg/once daily, i.p.) efficiently reduced kidney function, oxidative stress biomarkers and inflammatory mediators. Moreover, histological and immunohistochemical examination of scopoletin-treated group showed remarkable improvement in histological structure and reduced vancomycin-induced renal expression of iNOS, NF-κB and p38 MAPK. In addition, scopoletin downregulated (Kelch Like ECH Associated Protein1) Keap1, P38MAPK and NF-κB expression levels while upregulated renal expression levels of regulatory protein (IκBα), Nrf2 and HO-1. Furthermore, molecular docking and network approach were constructed to study the prospect interaction between scopoletin and the targeted proteins that streamline oxidative stress and inflammatory pathways. The present investigations elucidated that scopoletin co-treatment with vancomycin may be a rational curative protocol for mitigation of vancomycin-induced renal intoxication.

Dissecting the Involvement of Ras GTPases in Kidney Fibrosis

Many different regulatory mechanisms of renal fibrosis are known to date, and those related to transforming growth factor-β1 (TGF-β1)-induced signaling have been studied in greater depth. However, in recent years, other signaling pathways have been identified, which contribute to the regulation of these pathological processes. Several studies by our team and others have revealed the involvement of small Ras GTPases in the regulation of the cellular processes that occur in renal fibrosis, such as the activation and proliferation of myofibroblasts or the accumulation of extracellular matrix (ECM) proteins. Intracellular signaling mediated by TGF-β1 and Ras GTPases are closely related, and this interaction also occurs during the development of renal fibrosis. In this review, we update the available in vitro and in vivo knowledge on the role of Ras and its main effectors, such as Erk and Akt, in the cellular mechanisms that occur during the regulation of kidney fibrosis (ECM synthesis, accumulation and activation of myofibroblasts, apoptosis and survival of tubular epithelial cells), as well as the therapeutic strategies for targeting the Ras pathway to intervene on the development of renal fibrosis.

Erlotinib can halt adenine induced nephrotoxicity in mice through modulating ERK1/2, STAT3, p53 and apoptotic pathways

Renal fibrosis is a failed regenerative process that facilitates chronic kidney disease progression. The current study was designed to study the effect of erlotinib, a receptor tyrosine kinase inhibitor, on the progression of renal fibrosis. The study included four groups of mice: control group; adenine group: received adenine (0.2% w/w) daily with food for 4 weeks; erlotinib group: received 80 mg/kg/day erlotinib orally (6 ml/kg/day, 1.3% w/v suspension in normal saline 0.9%) for 4 weeks; adenine + erlotinib group: received adenine and erlotinib concurrently. Kidney function and antioxidant biomarkers were measured. Renal expression of Bcl2 and p53 and histopathological changes (tubular injury and renal fibrosis) were scored. Renal tissue levels of transforming growth factor-β₁, p-ERK1/2 and p-STAT3 were measured. Results obtained showed significant decrease (P < 0.001) in serum creatinine, urea and uric acid in erlotinib + adenine group. Level of malondialdehyde was decreased significantly (P < 0.001) while reduced glutathione and catalase levels were increased (P < 0.01) by erlotinib concurrent administration. Erlotinib markedly reduced fibrosis and tubular injury and decreased TGF-β1, p-ERK1/2 and p-STAT3 (P < 0.5). In addition, expression level of Bcl-2 was elevated (P < 0.001) while that of p53-was reduced compared to adenine alone. Erlotinib can attenuate renal fibrosis development and progression through anti-fibrotic, antioxidant and anti-apoptotic pathways.

Sublytic C5b-9 Induces Glomerular Mesangial Cell Apoptosis through the Cascade Pathway of MEKK2-p38 MAPK-IRF-1-TRADD-Caspase 8 in Rat Thy-1 Nephritis

The apoptosis of glomerular mesangial cells (GMCs) in the early phase of rat Thy-1 nephritis (Thy-1N), a model of human mesangioproliferative glomerulonephritis (MsPGN), is primarily triggered by sublytic C5b-9. However, the mechanism of GMC apoptosis induced by sublytic C5b-9 remains unclear. In this study, we demonstrate that expressions of TNFR1-associated death domain-containing protein (TRADD) and IFN regulatory factor-1 (IRF-1) were simultaneously upregulated in the renal tissue of Thy-1N rats (in vivo) and in GMCs under sublytic C5b-9 stimulation (in vitro). In vitro, TRADD was confirmed to be a downstream gene of IRF-1, because IRF-1 could bind to TRADD gene promoter to promote its transcription, leading to caspase 8 activation and GMC apoptosis. Increased phosphorylation of p38 MAPK was verified to contribute to IRF-1 and TRADD production and caspase 8 activation, as well as to GMC apoptosis induced by sublytic C5b-9. Furthermore, phosphorylation of MEK kinase 2 (MEKK2) mediated p38 MAPK activation. More importantly, three sites (Ser^153/164/239) of MEKK2 phosphorylation were identified and demonstrated to be necessary for p38 MAPK activation. In addition, silencing of renal MEKK2, IRF-1, and TRADD genes or inhibition of p38 MAPK activation in vivo had obvious inhibitory effects on GMC apoptosis, secondary proliferation, and urinary protein secretion in rats with Thy-1N. Collectively, these findings indicate that the cascade axis of MEKK2-p38 MAPK-IRF-1-TRADD-caspase 8 may play an important role in GMC apoptosis following exposure to sublytic C5b-9 in rat Thy-1N.

Temporal and spatial regulation of cAMP signaling in disease: role of cyclic nucleotide phosphodiesterases

Since its discovery, cAMP has been proposed as one of the most versatile second messengers. The remarkable feature of cAMP to tightly control highly diverse physiological processes, including metabolism, homeostasis, secretion, muscle contraction, cell proliferation and migration, immune response, and gene transcription, is reflected by millions of different articles worldwide. Compartmentalization of cAMP in space and time, maintained by mainly phosphodiesterases, contributes to the maintenance of equilibrium inside the cell where one signal can trigger many different events. Novel cAMP sensors seem to carry out certain unexpected signaling properties of cAMP and thereby to permit delicate adaptations of biologic responses. Measuring space and time events with biosensors will increase our current knowledge on the pathophysiology of diseases, such as chronic obstructive pulmonary disease, asthma, cognitive impairment, cancer, and renal and heart failure. Further insights into the cAMP dynamics will help to optimize the pharmacological treatment for these diseases.

Expression of phosphorylated extracellular signal-regulated kinase in rat kidneys exposed to high +Gz

Exposure to high gravitational acceleration forces acting along the body axis from the head to the feet (+Gz) severely reduces blood flow to the visceral organs, including the kidneys. Extracellular signal-regulated kinase (ERK) figures predominantly in mediating kidney cell responses to a wide variety of stress-related stimuli. Though previous studies have shown the activation of ERK in some experimental models, the regulation of ERK associated with +Gz exposure has not yet been investigated. The aim of this study was to examine the effect of high +Gz exposure on ERK activation in the kidneys. Using a small animal centrifuge, eight male Sprague-Dawley rats were exposed to +10Gz or +13Gz three times for 3 minutes each. The bilateral kidneys were obtained from each rat, and the expression levels of phosphorylated ERK (p-ERK) were evaluated using immunohistochemistry. In the control group, the collecting duct epithelium displayed faint cytoplasmic staining with no nuclear staining of p-ERK. By contrast, rats exposed to +10Gz showed strong nuclear staining intensity for p-ERK. In the renal papilla, the epithelial cells of collecting ducts and thin segments of the loop of Henle exhibited strong nuclear immunoreactivity for p-ERK. Rats exposed to +13Gz also showed the same staining intensity and distribution of p-ERK expression as that of rats exposed to +10Gz. This study is the first to describe +Gz exposure-induced alteration in the expression of p-ERK in the kidneys. Our finding suggests that high +Gz exposure leads to the activation of ERK in the renal papilla.

Gain-of-function mutations in transient receptor potential C6 (TRPC6) activate extracellular signal-regulated kinases 1/2 (ERK1/2)

Gain-of-function mutations in the canonical transient receptor potential 6 (TRPC6) gene are a cause of autosomal dominant focal segmental glomerulosclerosis (FSGS). The mechanisms whereby abnormal TRPC6 activity results in proteinuria remain unknown. The ERK1/2 MAPKs are activated in glomeruli and podocytes in several proteinuric disease models. We therefore examined whether FSGS-associated mutations in TRPC6 result in activation of these kinases. In 293T cells and cultured podocytes, overexpression of gain-of-function TRPC6 mutants resulted in increased ERK1/2 phosphorylation, an effect dependent upon channel function. Pharmacologic inhibitor studies implicated several signaling mediators, including calmodulin and calcineurin, supporting the importance of TRPC6-mediated calcium influx in this process. Through medium transfer experiments, we uncovered two distinct mechanisms for ERK activation by mutant TRPC6, a cell-autonomous, EGF receptor-independent mechanism and a non-cell-autonomous mechanism involving metalloprotease-mediated release of a presumed EGF receptor ligand. The inhibitors KN-92 and H89 were able to block both pathways in mutant TRPC6 expressing cells as well as the prolonged elevation of intracellular calcium levels upon carbachol stimulation seen in these cells. However, these effects appear to be independent of their effects on calcium/calmodulin-dependent protein kinase II and PKA, respectively. Phosphorylation of Thr-70, Ser-282, and Tyr-31/285 were not necessary for ERK activation by mutant TRPC6, although a phosphomimetic TRPC6 S282E mutant was capable of ERK activation. Taken together, these results identify two pathways downstream of mutant TRPC6 leading to ERK activation that may play a role in the development of FSGS.

Bioinformatics analysis of proteomic profiles during the process of anti-Thy1 nephritis

Anti-Thy1 nephritis is a well-established experimental mesangial proliferative nephritis model. Exploring the molecular mechanisms of pathophysiology in anti-Thy1 nephritis may elucidate the pathogeneses of mesangial proliferation. We examined the roles and acting mechanisms of differentially expressed proteins (DEPs) by bioinformatics analysis of glomeruli proteomic profiles during the course of anti-Thy1 nephritis. In total, 108 DEPs were found by two-dimensional fluorescence difference gel electrophoresis (2D-DIGE), and 40 DEPs were identified by matrix-assisted laser desorption ionization/time of flight and liquid chromatography-MS. DEPs were classified into five clusters (Clusters 1-5), according to their expression trends using Cluster 3.0 software, involved in regulating biological processes such as the stress response, cell proliferation, apoptosis, energy metabolism, transport, and the actin cytoskeleton. The expression patterns of ten DEPs, distributed across five clusters, including AKR1A1, AGAT, ATP6V1B2, HIBADH, MDH1, MPST, NIT2, PRDX6, PSMB7, and TPI1, were validated by Western blotting. Based on Western blotting and immunohistochemistry, we also found that the DEP FHL2, which was primarily expressed in the mesangial region, was down-regulated on days 3 and 5, and up-regulated on day 10. In vitro, we found that FHL2 overexpression induced mesangial cell proliferation by increasing the number of S-phase cells and decreasing G2/M-phase cells, whereas inhibiting FHL2 had the opposite effect. This study explored novel DEPs and their expression patterns during anti-Thy1 nephritis, and elucidated FHL2's effect on mesangial cell proliferation. These results will contribute to our understanding of the pathogenesis of mesangial proliferation.

Tetrandrine down-regulates ERK/NF-κB signaling and inhibits activation of mesangial cells

OBJECTIVES

Tetrandrine (TET), a bisbenzylisoquinoline alkaloid isolated from Stephania tetrandra S. Moore of the Menispermaceae, possesses anti-inflammatory activity. We examined the effect of tetrandrine on interleukin-1β (IL-1β)-provoked inflammatory response in mesangial cells.

MATERIALS AND METHODS

Primary rat mesangial cells (PRMCs) were treated with IL-1β to induce inflammation to resemble glomerulonephritis. Cell viability, morphology and NO production were evaluated. Western blotting was applied for expression of matrix metalloproteinase-9 (MMP-9), inducible NO synthase (iNOS), extracellular signal-regulated kinase (ERK) and NF-κB-related molecules. Electrophoretic mobility shift assay was performed to examine the DNA-binding activity of NF-κB.

RESULTS

TET, at concentrations up to 10 μg/ml, had no significant effect on viability of PRMCs. At non-toxic concentrations, TET inhibited expression of phosphorylated ERK as well as phosphorylated IKK, enhanced degradation of IκBα and reduced the DNA-binding activity of NF-κB in IL-1β-primed PRMCs, suggesting an inhibitory effect on ERK/NF-κB signaling. TET attenuated the IL-1β-provoked expression of iNOS and release of NO. Moreover, both the protein expression and gelatinase activity of MMP-9, but not MMP-2, were markedly suppressed by TET.

SIGNIFICANCE

TET down-regulated ERK/NF-κB signaling and inhibited the expression of inflammatory mediators NO and MMP-9. Since these mediators appear to activate mesangial cells, TET may play an important role in prevention of glomerulonephritis.

Erk in kidney diseases

Acute or chronic kidney injury results from various insults and pathological conditions, and is accompanied by activation of compensatory repair mechanisms. Both insults and repair mechanisms are initiated by circulating factors, whose cellular effects are mediated by activation selective signal transduction pathways. Two main signal transduction pathways are activated during these processes, the phosphatidylinositol 3' kinase (PI-3K)/mammalian target of rapamycin (mTOR) and the mitogen-activated protein kinase (MAPK) cascades. This review will focus on the latter, and more specifically on the role of extracellular signal-regulated kinase (ERK) cascade in kidney injury and repair.

Endothelin signaling via guanine exchange factor C3G in renal glomerular mesangial cells

The guanine nucleotide exchange factor C3G is one of the mediators of endothelin-1 (ET-1) intracellular signaling cascades and is vital for kidney development and homeostasis. The aim of the current study was to analyze the specificity of ET-1-induced signaling via C3G in rat glomerular mesangial cells (GMC) and to investigate the biological significance of C3G during mesangioproliferative glomerulonephritis. In GMC, C3G expression was increased (1) in vivo after induction of the anti-Thy1 model of glomerulonephritis and (2) in cell culture experiments after fetal bovine serum incubation. To examine the consequences of C3G up-regulation, adenovirus-mediated gene transfer of C3G into cultured glomerular cells was done, and the GTP loading of the small G proteins Rap1 and R-Ras was analyzed. Overexpression of C3G in mesangial cells resulted in enhanced activation of Rap1, but failed to affect the GTP-bound status of R-Ras in ET-1-stimulated cells. C3G overexpression led to significant changes in GMC spreading and migration patterns in response to ET-1 stimulation and increased stress fiber formation, which was mimicked by Rap1A overexpression. Together, these findings suggest (1) the existence of regulatory mechanisms resulting in disease-related up-regulation of C3G in GMC and (2) that an increase in the C3G protein level may contribute to the resolution stage of mesangioproliferative glomerulonephritis by reducing GMC sensitivity to ET-1, modulating cellular motility, and actin dynamics.

siRNA-based therapy ameliorates glomerulonephritis

RNA interference by short interfering RNAs (siRNAs) holds promise as a therapeutic strategy, but use of siRNAs in vivo remains limited. Here, we developed a system to target delivery of siRNAs to glomeruli via poly(ethylene glycol)-poly(l-lysine)-based vehicles. The siRNA/nanocarrier complex was approximately 10 to 20 nm in diameter, a size that would allow it to move across the fenestrated endothelium to access to the mesangium. After intraperitoneal injection of fluorescence-labeled siRNA/nanocarrier complexes, we detected siRNAs in the blood circulation for a prolonged time. Repeated intraperitoneal administration of a mitogen-activated protein kinase 1 (MAPK1) siRNA/nanocarrier complex suppressed glomerular MAPK1 mRNA and protein expression in a mouse model of glomerulonephritis; this improved kidney function, reduced proteinuria, and ameliorated glomerular sclerosis. Furthermore, this therapy reduced the expression of the profibrotic markers TGF-beta1, plasminogen activator inhibitor-1, and fibronectin. In conclusion, we successfully silenced intraglomerular genes with siRNA using nanocarriers. This technique could aid the investigation of molecular mechanisms of renal disease and has potential as a molecular therapy of glomerular diseases.

Atorvastatin prevents gentamicin-induced renal damage in rats through the inhibition of p38-MAPK and NF-kappaB pathways

BACKGROUND AND AIMS

Gentamicin (GM) is still considered to be an important antibiotic against life-threatening, gram-negative bacterial infections despite its known nephrotoxic effects. We aimed to evaluate the potential protective effect of atorvastatin (ATO) against GM-induced nephrotoxicity in rats.

MATERIALS AND METHODS

The rats were randomly divided into five groups of six animals each: control, GM (100 mg/kg/day), ATO (10 mg/kg/day), GM + ATO, and GM + Vehicle. Kidney function tests, tissue oxidative stress parameters, and histopathological and immunohistochemical studies clarified GM nephrotoxicity.

RESULTS

GM caused a marked reduction in renal functions and increased oxidative stress parameters. Histopathological examination revealed tubular necrosis especially in the renal cortex in GM rats. On immunohistochemical evaluation, GM rat showed more intense expressions of mitogen-activated protein kinase (MAPK), nuclear factor kappa B (NF-kappaB), and inducible nitric oxide synthase (iNOS) compared with control. Kidney function tests and tissue oxidative stress parameters were normalized in the GM + ATO group. Histopathological and immunohistochemical pictures were also greatly ameliorated.

CONCLUSIONS

ATO acts in the kidney as a potent scavenger of free radicals to prevent the toxic effects of GM via the inhibition of MAPK and NF-kappaB signaling pathways and iNOS expression.

Effects of pomegranate juice on hyperoxaluria-induced oxidative stress in the rat kidneys

To evaluate the role of the inducible nitric oxide synthase (iNOS), selective nuclear factor-kB (NF-kB), and p38-mitogene-activated protein kinase (p38-MAPK) on hyperoxaluria-induced oxidative stress and stone formation in rat kidneys. The rats were divided into five groups: group 1, control group; group 2: ethylene glycol (EG) group; group 3: EG + pomegranate juice (PJ)-low group; group 4: EG + PJ-middle group; group 5: EG + PJ-high group. Rats were sacrificed on 7, 15, and 45 days. The iNOS expression, p65-NF-kB and p38-MAPK activity, and oxidative stress markers were evaluated in the kidney. Crystal depositions were evident on day 7, and mild and severe crystallization were observed on day 15 and 45 in EG group, respectively. There was limited or no crystal formation in rats in both middle- and high-dose PJ groups when compared to low-dose PJ group. Crystal depositions, iNOS, p38-MAPK and p65-NF-kB activity, and oxidative stress markers were found to be decreased by middle- and high-dose PJ treatment. PJ was found to have inhibitory effects on renal tubular cell injury and oxidative stress caused by oxalate crystals by reducing ROS, iNOS, p38-MAPK, and NF-kB expression.

ERK5 activation enhances mesangial cell viability and collagen matrix accumulation in rat progressive glomerulonephritis

The mitogen-activated protein kinase (MAPK) cascade plays an important role in the regulation of various cellular functions in glomerulonephritis (GN). Here, we investigated whether extracellular signal-regulated kinase 5 (ERK5), a member of the MAPK family, is involved in the pathogenesis of chronic mesangioproliferative GN, using a rat model induced by uninephrectomy and anti-Thy-1 antibody injection. Immunostaining of kidneys obtained at different time points revealed that phospho-ERK5 was weakly expressed in control glomeruli but dramatically increased in a typical mesangial pattern after 28 and 56 days of GN. A semiquantitative assessment indicated that glomerular phospho-ERK5 expression closely paralleled the accumulation of extracellular matrix (ECM), collagen type I, as well as glomerular expression of reactive oxygen species (ROS) and ANG II. On the other hand, phospho-ERK1/2 expression increased on day 7 during the phase of enhanced mesangial cell (MC) proliferation and decreased thereafter. H(2)O(2) and ANG II each induced ERK5 phosphorylation by cultured rat MCs. Costimulation with both H(2)O(2) and ANG II synergistically increased ERK5 phosphorylation in MCs. Cultured MCs transfected with ERK5-specific small interference RNA showed a significant decrease in H(2)O(2) or ANG II-induced cell viability and soluble collagen secretion compared with control cells. Treatment of GN rats with an ANG II type 1 receptor blocker resulted in significant decreases in phospho-ERK5 expression and collagen accumulation accompanied by remarkable histological improvement. Taken together, these results suggest that MC ERK5 phosphorylation by ANG II or H(2)O(2) enhances cell viability and ECM accumulation in an experimental model of chronic GN.

Activation of Erk1/2 and Akt following unilateral ureteral obstruction

Chronic unilateral ureteral obstruction is a well characterized model of renal injury leading to tubulointerstitial fibrosis and distinct patterns of cell proliferation and apoptosis in the obstructed kidney. In this study we assessed the contribution of the mitogen activated protein kinase (MAPK)-ERK1/2 and the phosphatidylinositol 3 kinase (PI3K)-Akt pathways to early renal changes following unilateral obstruction. Increased activation of small Ras GTPase and its downstream effectors ERK1/2 and Akt was detected in ligated kidneys. The use of specific pharmacological inhibitors to either ERK1/2 or Akt activation led to decreased levels of fibroblast-myofibroblast markers in the interstitium while inhibition of PI3K reduced the number of proliferating cells and the amount of interstitial extracellular matrix deposition. Treatment with an ERK1/2 inhibitor diminished the number of apoptotic tubule and interstitial cells. Our results suggest a role for the MAPK-ERK1/2 and PI3K-Akt systems in early changes induced by ureteral obstruction and that inhibition of these signaling pathways may provide a novel approach to prevent progression of renal fibrosis.

Differential ConA-enriched urinary proteome in rat experimental glomerular diseases

Glomerular diseases are leading causes of end-stage renal diseases worldwide. They are considered to be consequences of injury primarily to the three types of glomerular cells. Differential diagnosis typically relies on invasive biopsy findings. We expected that injuries of different glomerular cells would cause different changes in urinary proteome. The goal of this study was to identify differential urinary proteins distinguishing between injuries of different glomerular cells before significant histopathologic changes. Adriamycin nephropathy and Thy1.1 glomerulonephritis were employed as models with different primary impaired cells. ConA-enriched urinary glycoproteome on day3 were profiled by gel-free shotgun tandem mass spectrometry, and compared with self-healthy controls to identify differential urinary proteins for each model. By comparing the changes of the differential proteins between these two models, we identified 39 proteins with different directions of changes, which may potentially be useful in differentiation; and 7 proteins with the same direction of changes, which may be potential indicators of early renal damage. These differential proteins were of several origins: plasma proteins, proteins with urine or kidney specificity, proteins without tissue-specificity (mainly inflammatory mediators) etc. Our results may help better understand the effects of injuries of different glomerular cells at the initial stage, and lead to the discovery of novel early diagnostic markers for human focal segmental glomerulosclerosis (FSGS) and mesangioproliferative glomerulonephritis (MsPGN) which have the same primary impaired cells with adriamycin nephropathy and Thy1.1 glomerulonephritis, respectively.

Role of JNK in network formation of human lung microvascular endothelial cells

The signaling mechanisms in vasculogenesis and/or angiogenesis remain poorly understood, limiting the ability to regulate growth of new blood vessels in vitro and in vivo. Cultured human lung microvascular endothelial cells align into tubular networks in the three-dimensional matrix, Matrigel. Overexpression of MAPK phosphatase-1 (MKP-1), an enzyme that inactivates the ERK, JNK, and p38 pathways, inhibited network formation of these cells. Adenoviral-mediated overexpression of recombinant MKP-3 (a dual specificity phosphatase that specifically inactivates the ERK pathway) and dominant negative or constitutively active MEK did not attenuate network formation in Matrigel compared with negative controls. This result suggested that the ERK pathway may not be essential for tube assembly, a conclusion which was supported by the action of specific MEK inhibitor PD 184352, which also did not alter network formation. Inhibition of the JNK pathway using SP-600125 or l-stereoisomer (l-JNKI-1) blocked network formation, whereas the p38 MAPK blocker SB-203580 slightly enhanced it. Inhibition of JNK also attenuated the number of small vessel branches in the developing chick chorioallantoic membrane. Our results demonstrate a specific role for the JNK pathway in network formation of human lung endothelial cells in vitro while confirming that it is essential for the formation of new vessels in vivo.

Recombinant tissue factor pathway inhibitor induces apoptosis in cultured rat mesangial cells via its Kunitz-3 domain and C-terminal through inhibiting PI3-kinase/Akt pathway

Tissue factor pathway inhibitor (TFPI) is an endogenous inhibitor of tissue factor (TF) induced coagulation. In addition to its anticoagulation activity, TFPI has other functions such as antiproliferation and inducing apoptosis. In the present study, we investigated whether or not TFPI induced apoptosis in cultured rat mesangial cells (MsCs) and the possible signal pathway that involved in the apoptotic process. We demonstrated that recombinant TFPI (rTFPI) induced apoptosis in cultured MsCs via its Kunitz-3 domain and C-terminal in a dose- and time-dependent manner by Hoechst 33258 assay, flow cytometry, nucleosomal laddering of DNA, caspase 3 assay. Because the serine/threonine protein kinase Akt has attracted attention as a mediator of survival (anti-apoptotic) signal in MsCs, we investigated the expression of phosphospecific-Akt and its downstream signal phospho-IkappaB-alpha and some other signal molecules like Fas and bcl-2. The results indicated that the process of apoptosis triggered by rTFPI is, at least in part, actively conducted by rat MsCs possibly through PI3-Kinase-Akt signal pathway not by binding to tissue factor. Our findings suggest that rTFPI has the potential usefulness in inducing apoptosis of MsCs under inflammatory conditions.

Oxidative stress-mediated mesangial cell proliferation requires RAC-1/reactive oxygen species production and beta4 integrin expression

Lipid abnormalities and oxidative stress, by stimulating mesangial cell (MC) proliferation, can contribute to the development of diabetes-associated renal disease. In this study we investigated the molecular events elicited by oxidized low density lipoproteins (ox-LDL) in MC. We demonstrate that in MC cultured in the presence of ox-LDL, survival and mitogenic signals on Akt and Erk1/2 MAPK pathways are induced, respectively. Moreover, as shown by the expression of the dominant negative Rac-1 construct, we first report that ox-LDL-mediated cell survival and cell cycle progression depend on Rac-1 GTPase-mediated reactive oxygen species production and on epidermal growth factor receptor transactivation. By silencing Akt and blocking Erk1/2 MAPK pathways, we also demonstrate that these signals are downstream to Rac-1/reactive oxygen species production and epidermal growth factor receptor activation. Finally, by endogenous depletion of beta4 integrin, expressed in MC, we provide evidence that the expression of this adhesion molecule is essential for ox-LDL-mediated MC dysfunction. Our data identify a novel signaling pathway involved in oxidative stress-induced diabetes-associated renal disease and provide the rationale for therapeutically targeting beta4 integrin.

Roles of coagulation pathway and factor Xa in rat mesangioproliferative glomerulonephritis

Tissue factor initiates the extrinsic coagulation pathway by activating coagulation factor X to factor Xa, and factor V is a cofactor for the prothrombin activation by factor Xa. As factor Xa is known to promote the proliferation of mesangial cells in culture, the roles of the coagulation pathway and factor Xa were studied in an animal model of mesangioproliferative glomerulonephritis (MsPGN). MsPGN was induced in Wistar rats by an intravenous injection of anti-Thy 1.1 monoclonal antibody, OX-7. To clarify the role of factor Xa in MsPGN, a specific factor Xa inhibitor, DX-9065a, was injected intravenously at 2.5 or 10 mg/kg at the same time as OX-7, and kidney involvement was assessed by immunohistological analyses. We also examined p44/42 mitogen-activated protein (MAP) kinase activation. Time-course study revealed that expressions of tissue factor, factor V, and protease-activated receptor 2 (PAR2) were peaked on day 3, followed by factor X accumulation and mesangial proliferation. DX-9065a treatment significantly ameliorated proteinuria in a dose-dependent manner on day 8. Histological analyses showed a significant reduction in the size of glomeruli, the total number of glomerular cells, and crescent formation by DX-9065a treatment. Macrophage infiltration, which was rapidly observed on day 1 in disease control rats was not inhibited on days 1-3 by DX-9065a treatment, however it was suppressed on days 5-8. The deposition of fibrin, the number of PCNA-positive cells, and phosphorylation of p44/42 MAP kinase were markedly increased in the disease control group, whereas they were significantly reduced in the treatment group. Tissue factor and factor V induction may accelerate MsPGN through the activation and accumulation of factor X via proinflammatory and procoagulant mechanisms, and the inhibition of factor Xa would be a promising method to regulate the disease process.

Angiotensin II receptor blockade ameliorates mesangioproliferative glomerulonephritis in rats through suppression of CTGF and PAI-1, independently of the coagulation system

BACKGROUND

Previously we observed that the coagulation system promotes matrix protein accumulation through transforming growth factor (TGF)-beta and connective tissue growth factor (CTGF) expression in rat mesangioproliferative glomerulonephritis (MsPGN). Angiotensin II receptor blockers (ARBs) are known to suppress matrix accumulation in experimental MsPGN. In the present study, we investigated whether ARB suppresses MsPGN through inhibition of these profibrotic cytokines, and in relation to coagulation and fibrinolytic systems.

METHODS

MsPGN was induced in Wistar rats by intravenous injection of anti-Thy-1.1 monoclonal antibody, OX-7. As an ARB, olmesartan was orally administered in rat feed from the day of OX-7 injection (day 0) to day 8, when rats were sacrificed and kidney specimens were collected. The degrees of cellular proliferation, matrix production, coagulation factors, and inhibitory factor of fibrinolysis were evaluated.

RESULTS

Although blood pressure did not change in the normal, disease control, or treatment groups, the amount of urinary protein was significantly decreased in the ARB-treated groups, compared with the disease control group (p < 0.05). alpha-Smooth muscle actin expression was suppressed significantly in the treatment groups (p < 0.001). Blue-staining areas of trichrome, the number of proliferating cell nuclear antigen (PCNA)- or ED-1-positive cells, fibronectin and plasminogen activator inhibitor type 1 in glomeruli significantly decreased in the treatment groups (p < 0.05, respectively); however, fibrin-related antigen and factor V depositions were not suppressed in the treatment groups.

CONCLUSIONS

These results suggest that the ARB drug would ameliorate MsPGN in vivo, at least partly through CTGF and plasminogen activator inhibitor type 1 suppression, and independently of the local coagulation system in glomeruli.

Increased expression of p38 mitogen- activated protein kinase is related to the acute renal lesions induced by gentamicin

Mitogen-activated protein kinases (MAPK) may be involved in the pathogenesis of acute renal failure. This study investigated the expression of p-p38 MAPK and nuclear factor kappa B (NF-kappaB) in the renal cortex of rats treated with gentamicin. Twenty rats were injected with gentamicin, 40 mg/kg, i.m., twice a day for 9 days, 20 with gentamicin + pyrrolidine dithiocarbamate (PDTC, an NF-kappaB inhibitor), 14 with 0.15 M NaCl, i.m., twice a day for 9 days, and 14 with 0.15 M NaCl , i.m., twice a day for 9 days and PDTC, 50 mg kg(-1) day(-1), i.p., twice a day for 15 days. The animals were killed 5 and 30 days after the last of the injections and the kidneys were removed for histological, immunohistochemical and Western blot analysis and for nitrate determination. The results of the immunohistochemical study were evaluated by counting the p-p38 MAPK-positive cells per area of renal cortex measuring 0.05 mm2. Creatinine was measured by the Jaffé method in blood samples collected 5 and 30 days after the end of the treatments. Gentamicin-treated rats presented a transitory increase in plasma creatinine levels. In addition, animals killed 5 days after the end of gentamicin treatment presented acute tubular necrosis and increased nitrate levels in the renal cortex. Increased expression of p-p38 MAPK and NF-kappaB was also observed in the kidneys from these animals. The animals killed 30 days after gentamicin treatment showed residual areas of interstitial fibrosis in the renal cortex, although the expression of p-p38 MAPK in their kidneys did not differ from control. Treatment with PDTC reduced the functional and structural changes induced by gentamicin as well as the expression of p-p38 MAPK and NF-kappaB. The increased expression of p-p38 MAPK and NF-kappaB observed in these rats suggests that these signaling molecules may be involved in the pathogenesis of tubulointerstitial nephritis induced by gentamicin.

Inhibition of nuclear factor-kappaB activation attenuates tubulointerstitial nephritis induced by gentamicin

BACKGROUND

Animals treated with gentamicin can show residual areas of interstitial fibrosis in the renal cortex. This study investigated the expression of nuclear factor-kappaB (NF-kappaB), mitogen-activated protein (MAP) kinases and macrophages in the renal cortex and structural and functional renal changes of rats treated with gentamicin or gentamicin + pyrrolidine dithiocarbamate (PDTC), an NF-kappaB inhibitor.

METHODS

38 female Wistar rats were injected with gentamicin, 40 mg/kg, twice a day for 9 days, 38 with gentamicin + PDTC, and 28 with 0.15 M NaCl solution. The animals were killed 5 and 30 days after these injections and the kidneys were removed for histological and immunohistochemical studies. The results of the immunohistochemical studies were scored according to the extent of staining. The fractional interstitial area was determined by morphometry.

RESULTS

Gentamicin-treated rats presented a transitory increase in plasma creatinine levels. Increased ED-1, MAP kinases and NF-kappaB staining were also observed in the renal cortex from all gentamicin-treated rats compared to control (p < 0.05). The animals killed on day 30 also presented fibrosis in the renal cortex despite the recovery of renal function. Treatment with PDTC reduced the functional and structural changes induced by gentamicin.

CONCLUSIONS

These data show that inhibition of NF-kappaB activation attenuates tubulointerstitial nephritis induced by gentamicin.

Immunoliposome Targeting to Mesangial Cells: A Promising Strategy for Specific Drug Delivery to the Kidney

Mesangial cell-mediated nephropathies are a frequent cause of ESRD. Specific drug delivery to mesangial cells might be more effective and better tolerated than existing systemic treatments. Rat mesangial cells are characterized by Thy1.1 antigen expression. Therefore, OX7-coupled immunoliposomes (OX7-IL) were prepared by coupling liposomes with F(ab') fragments of OX7 mAb directed against Thy1.1 antigen. As the glomerular endothelium is fenestrated and no basement membrane separates glomerular capillaries from the mesangium, mesangial cells represent a particularly suitable target for drug delivery by OX7-IL. Therefore, the targeting efficacy of OX7-IL to mesangial cells was investigated. Specific targeting in vitro was obtained, and intravenous injection of OX-7-IL to rats showed a specific targeting of all mesangial cells in both kidneys. OX7-IL showed marked accumulation in the cytoplasm of rat mesangial cells, both in vitro and in vivo. This renal targeting was blocked when free OX7 F((ab')2) fragments were co-administered with OX7-IL. Rats that were given a single intravenous injection of low-dose doxorubicin encapsulated in OX7-IL showed extensive glomerular damage, whereas other parts of the kidney and other organs were spared. Free doxorubicin and the liposomal formulation of this agent had no effect. Thus, immunoliposomes are a very promising delivery system for the treatment of kidney diseases.

Y-box protein 1 mediates PDGF-B effects in mesangioproliferative glomerular disease

The pivotal role of PDGF-B for mesangioproliferative glomerular disease is well established. Here, Y-box protein-1 (YB-1) was identified as a downstream signaling target of PDGF-B. In healthy kidney cells, YB-1 was located predominantly within the nuclear compartment. Subsequent to PDGF-B infusion and in the course of anti-Thy1.1-induced mesangioproliferative glomerulonephritis, relocalization of YB-1 into the cytoplasm was observed. In experimental models that lack profound mesangial cell proliferation (e.g., Puromycin-nephrosis, passive Heyman nephritis, spontaneous normotensive nephrosclerosis, hyperlipidemic diabetic nephropathy), YB-1 remained nuclear. This translocation coincided with upregulation of YB-1 protein levels within the mesangial compartment. Increased YB-1 expression and subcellular shuttling was dependent on PDGF-B signaling via the mitogen-activated protein kinase pathway because these alterations were prevented by specific PDGF aptamers and the mitogen-activated protein kinase pathway inhibitor U0126. Furthermore, PDGF-B strongly induced YB-1 expression in vitro. This induction was important because RNAi-dependent knockdown of YB-1 abolished the mitogenic PDGF-B effect. Taken together, YB-1 seems to represent a specific and necessary PDGF-B target in mesangioproliferative glomerular disease.

Activation of STAT3/Smad1 is a key signaling pathway for progression to glomerulosclerosis in experimental glomerulonephritis

Mesangial cell proliferation is a significant event in the development of progressive glomerular injuries. However, the issue of how cell proliferation is involved in the development of glomerulosclerosis is unclear. Recently, we showed that the overexpression of type IV collagen (Col IV), a major component of mesangial extracellular matrix, is transcriptionally regulated by Smad1 in diabetic glomerulosclerosis. In this study, we have demonstrated the effect of the administration of an anti-platelet-derived growth factor (PDGF) beta-receptor antibody (APB5) blocking activation by the PDGF-B chain on rat glomerulonephritis and have examined the signaling pathways that regulate both glomerular cell proliferation and glomerulosclerosis in vivo and in vitro. Experimental mesangial proliferative glomerulonephritis (Thy1 GN) was induced by a single intravenous injection of anti-rat Thy-1.1 monoclonal antibody. In Thy1 GN, mesangial cell proliferation and the expression of Col IV peaked at day 6. Immunohistochemical staining for the expression of Smad1, phospho-Smad1 (pSmad1), and phospho-STAT3 (pSTAT3) revealed that the peak for glomerular Smad1 expression occurred at day 6, consistent with the peak for mesangial proliferation. The expression of pSmad1 was up-regulated at day 1, and the peak for glomerular pSmad1 expression occurred at day 4 of the disease. When treated with APB5, both mesangial proliferation and sclerosis were reduced significantly. The expression of Smad1, pSmad1, and pSTAT3 was also significantly reduced by the administration of APB5. PDGF induced both mesangial cell replication and Col IV synthesis in association with an increased expression of pSTAT3 and pSmad1 on cultured mesangial cells. In addition, APB5 reduced mesangial cell proliferation in association with decreased pSmad1, pSTAT3, and Col IV protein expressions in vitro. The introduction of dominant negative STAT3 significantly decreased the expression of Col IV in cultured mesangial cells. These data suggest that the activation of STAT3 and Smad1 participates in the developing process of glomerulosclerosis in experimental glomerulonephritis.

Caveolin-1 in mesangial cells suppresses MAP kinase activation and cell proliferation induced by bFGF and PDGF

BACKGROUND

Caveolin is a principal component of caveolae and regulates signaling in caveolae. Mesangial cells contain many caveolae, and thus manipulation of caveolin-1 expression level might be useful to control mesangial cell proliferation, which is an important aggravating factor in many renal diseases.

METHODS

In the present study, we transfected caveolin-1 cDNA to rat primary mesangial cells and MES13 cells, and examined the effects on Raf-extracellular signal-regulated protein kinase (ERK) kinase (MEK)-mitogen-activated protein (MAP) kinase pathway and cell proliferation stimulated by basic fibroblast growth factor (bFGF) and platelet-derived growth factor (PDGF). Activity of the kinases was analyzed by immunofluorescence labeling and Western blot analysis.

RESULTS

The overexpression of caveolin-1 inhibited the activation of Raf-1, MEK-1/2, and MAP kinase induced by either bFGF or PDGF. Furthermore, it suppressed the cell proliferation caused by the cytokines. The effect was specific to the Raf-MEK-MAP kinase pathway, because it did not influence activation of Smad2 induced by transforming growth factor-beta (TGF-beta). On the contrary, expression of a dominant-negative caveolin mutant, DGV-caveolin, augmented activation of MAP kinase.

CONCLUSION

The result showed that overexpression of caveolin-1 in mesangial cells suppresses MAP kinase activation and cell proliferation induced by bFGF and PDGF. Because bFGF and PDGF are two major cytokines involved in the mesangioproliferative nephritis, the result implies that introduction of caveolin-1 expression vector is a potential therapeutic tool for the disease.

The role of the vitamin K-dependent growth factor Gas6 in glomerular pathophysiology

PURPOSE OF REVIEW

The product of growth arrest-specific gene 6 (gas6) is a unique vitamin K-dependent growth-potentiating factor for vascular smooth muscle cells, and anticoagulant warfarin inhibits the activation process of the protein. It has been reported that Gas6 is also a mitogen for mesangial cells, and that warfarin inhibits mesangial cell proliferation by blocking the activation of Gas6. A recent series of studies has revealed the in-vivo roles of Gas6 and its receptor Axl in the progression of various kidney diseases. This review summarizes these studies and discusses the possible interventions targeting the Gas6/Axl pathway to prevent the progression of kidney diseases.

RECENT FINDINGS

The expression of Gas6 and Axl is upregulated in an acute model of glomerulonephritis in rats, and the interference of the Gas6/Axl pathway by warfarin or the extracellular domain of Axl inhibits the progression of diseases. Induction of chronic glomerulonephritis in Gas6 mice results in less mortality, proteinuria, and histological changes of kidneys compared to wild-type mice. Administration of recombinant Gas6 reverses these phenotypes. Expression of Gas6 is also upregulated in streptozotocin-induced diabetic nephropathy, and administration of low-dose warfarin decreases albuminuria and hypertrophy of glomeruli. Possible roles of Gas6 are also reported in renal allograft dysfunction of rats and humans.

SUMMARY

The importance of the Gas6/Axl pathway has been implicated in many types of kidney disease. Further investigations on the role of the Gas6/Axl pathway in human kidney diseases and the development of specific antagonists targeting the pathway are warranted.

PDGF-BB enhances alpha1beta1 integrin-mediated activation of the ERK/AP-1 pathway involved in collagen matrix remodeling by rat mesangial cells

Platelet-derived growth factor-BB (PDGF-BB) has been implicated in the pathogenesis of progressive glomerulonephritis (GN). Previous studies have reported that PDGF-BB stimulates mesangial cells (MCs)-induced collagen matrix remodeling through enhancement of alpha1beta1 integrin-dependent migratory activity. To determine the cell signaling pathway responsible for abnormal MC-related mesangial matrix remodeling in progressive GN, we studied the involvement of the extracellular signal-regulated kinase (ERK)/activator protein-1 (AP-1) pathway in PDGF-BB-enhanced collagen gel contraction. Western blotting and gel shift assay revealed that MC-induced gel contraction resulted in ERK activation in parallel with that of AP-1 binding, peaking at 4 h and lasting at least for 24 h. Application of the MEK inhibitor, U0126, and the c-jun/AP-1 inhibitor, curcumin, inhibited gel contraction and AP-1 activity, respectively, dose dependently. PDGF-BB enhanced not only gel contraction but ERK phosphorylation and AP-1 activity by MCs. Marked inhibitory effects on PDGF-BB-induced gel contraction and ERK/AP-1 activity were observed in the presence of either function blocking anti-alpha1- or anti-beta1-integrin antibody or U0126. Consistently, AP-1-inactive MCs expressing a dominant-negative mutant of c-jun showed a significant decrease of PDGF-BB-induced gel contraction as compared with mock-transfected MCs. Finally, migration assay showed that ERK/AP-1 activity is required for PDGF-BB-stimulated alpha1beta1 integrin-dependent MC migration to collagen I. These results indicated that PDGF-BB enhances alpha1beta1 integrin-mediated collagen matrix reorganization through the activation of the ERK/AP-1 pathway that is crucial for MC migration. We conclude that the ERK/AP-1 pathway plays an important role in PDGF-BB-induced alpha1beta1 integrin-dependent collagen matrix remodeling; therefore, the inhibition of its pathway may provide a novel approach to regulate abnormal collagen matrix remodeling in progressive GN.

Specific MAP-kinase blockade protects against renal damage in homozygous TGR(mRen2)27 rats

Angiotensin II (AngII) plays an important role in renal damage by acting on hemodynamics, cell-growth, proliferation, and fibrosis, mainly by effects on the AngII type 1 (AT(1)) receptor. The AT(1) receptor activates several intracellular signaling molecules such as mitogen-activated protein kinases extracellular signal-regulated kinase (ERK) and p38, but their role in AngII-mediated renal damage is not well characterized. We therefore investigated whether pharmacologic blockade of ERK and p38 could prevent renal damage in high-renin homozygous transgenic rats (Ren2), with the effects of an AT(1) receptor antagonist (AT(1)-RA) as a reference. Seven-week-old homozygous Ren2 rats were treated with low-dose AT(1)-RA candesartan, ERK inhibitor tyrphostin, or p38 inhibitor SB239063 for 4 weeks. Untreated Ren2 and SD rats served as controls. Blood pressure was measured at 7 and 11 weeks. At 11 weeks, plasma renin activity (PRA) and serum aldosterone were determined, and the animals were killed. Kidney sections were scored for glomerular and interstitial smooth muscle actin and glomerular desmin expression as early markers for renal damage. Mesangial matrix expansion was determined as a marker for structural damage. PRA and aldosterone levels were elevated in untreated Ren2 rats in comparison to SD controls. AT(1)-RA further increased PRA but decreased aldosterone. All parameters of renal damage were elevated in untreated Ren2 rats. Blood pressure was not elevated at week 7 in Ren2 and not affected by either treatment. Mild signs of hypertensive damage were found in untreated Ren2 rats. All interventions significantly diminished damage to glomerular epithelium and interstitium. In addition, AT(1) receptor and p38 blockade reduced mesangial matrix expansion. In homozygous Ren2 rats, renal damage was ameliorated by a nonhypotensive dose of an AT(1)-RA and, similarly, by blockade of ERK or p38. This suggests that ERK and p38 are involved in AngII-mediated renal damage.

Oxidative stress in the pathogenesis of experimental mesangial proliferative glomerulonephritis

Reactive oxygen species (ROS) are increasingly believed to be important intracellular signaling molecules in mitogenic pathways involved in the pathogenesis of glomerulonephritis (GN). We explored the effects of the antioxidants α-lipoic acid and N-acetyl-l-cysteine on ERK activation in cultured mesangial cells and the role of ERK activation in the severity of glomerular injury in a rat model of anti-Thy 1 GN. In cultured mesangial cells, growth factors stimulated ERK phosphorylation by 150–450%. Antioxidants reduced this increase by 50–60%. Induction of anti-Thy 1 nephritis in rats led to a 210% increase in glomerular ERK phosphorylation. This increase in phosphorylated ERK was reduced by 50% in animals treated with α-lipoic acid. Treatment with α-lipoic acid resulted in significant improvement of glomerular injury. Cellular proliferation was reduced by 100%, and the number of proliferating cell nuclear antigen-positive cells was reduced by 64%. The increased expression of glomerular transforming growth factor-β1 protein and mRNA in rats with anti-Thy 1 nephritis was significantly attenuated and mesangial cell transformation into myofibroblasts was completely prevented by treatment with α-lipoic acid. The effects of α-lipoic acid were at least partially due to inhibition of oxidative stress. In rats with anti-Thy 1 nephritis, ROS production was increased 400–500%, and this increase was inhibited by 55% by treatment with α-lipoic acid. We suggest that ROS may mediate glomerular injury by inducing ERK phosphorylation. α-Lipoic acid should be considered a potential therapeutic agent in certain types of human GN.

Renal Abnormalities in Mice Caused by Insufficiency of p38α

p38MAP kinase (p38) is activated by hypertonicity and has been implicated to play a pivotal role in the renal system in survival under hypertonic conditions, both in vitro and in vivo. Although there are many aspects of the molecular events via the p38 pathway, its contribution to renal physiology and pathophysiology remains unclear. To elucidate the physiological relevance of p38 in renal function, we performed histochemical and biochemical characterization of p38alpha+/- mice. Although p38alpha+/- mice appeared normal, they showed 24% higher water intake (P < 0.05) and 16% higher kidney weight to total body weight ratio (P < 0.01) at 21 weeks of age. Histological examination of the kidney showed abnormalities such as dilation of proximal convoluted tubules, vacuolar degeneration, focal interstitial fibrosis, and inflammation and enlargement of Bowman's capsule with advancing age. Taken together, these results suggest that p38alpha plays an important role in the structural and functional maintenance of the normal kidney and its insufficiency causes renal abnormalities.

Counteractive effects of HGF on PDGF-induced mesangial cell proliferation in a rat model of glomerulonephritis

Activation and proliferation of glomerular mesangial cells play an important role in the development of mesangioproliferative glomerulonephritis. We investigated the role of hepatocyte growth factor (HGF) in regulating activated mesangial cell proliferation. In glomeruli of normal rats, mesangial cells barely expressed the c-Met/HGF receptor. However, when mesangioproliferative glomerulonephritis was induced in rats by the administration of an anti-Thy 1.1 antibody, glomerular HGF expression transiently decreased along with mesangiolysis, and activation of mesangial cells was associated with upregulation of the c-Met receptor. Activated mesangial cells in culture also expressed the c-Met/HGF receptor. Although addition of HGF to cultured mesangial cells did not increase DNA synthesis, HGF did diminish PDGF-induced DNA synthesis. PDGF induced activation of ERK, which continued for at least 48 h. When PDGF and HGF were simultaneously added, HGF inhibited the prolonged activation of ERK, which suggests that early inactivation of PDGF-induced ERK may be involved in the inhibitory effect of HGF on mesangial cell proliferation. Furthermore, administration of HGF to rats with anti-Thy 1.1 nephritis resulted in a selective suppression of activated mesangial cell proliferation, and this suppressive effect was associated with attenuation of phosphorylated glomerular ERK. These results indicate that HGF counteracts PDGF-induced mesangial cell proliferation and functions as a negative regulator of activated mesangial cell proliferation.

Different effect of ouabain on endothelin-1-induced extracellular signal-regulated kinase stimulation in rat heart and tail artery

Endogenous ouabain may play a role in the control of cardiovascular system function. In this study, we investigated the effects of a long-term ouabain treatment on basal and endothelin-1 (ET-1)-induced phosphorylation of cardiac and vascular extracellular signal-regulated kinases 1 and 2 (ERK-1 and ERK-2), which are involved in several cardiac and vascular physiologic and pathologic conditions. Our results show that the hearts from ouabain-treated rats have a higher basal level of ERK-1 and ERK-2 phosphorylation compared with untreated rats. Perfusion of the hearts with ET-1 increased ERK-1 and ERK-2 phosphorylation both in ouabain-treated and in control rats, with a larger stimulatory effect in ouabain-treated animals. On the contrary, exposure of endothelium-free tail artery to ET-1 increased ERKs phosphorylation both in treated and untreated rats, but this effect was blunted in ouabain-treated rats. These findings demonstrate that ouabain treatment has opposite effects on basal and ET-1-induced ERKs phosphorylation in the heart and in the tail artery of the rat.

Differential contribution of three mitogen-activated protein kinases to PDGF-BB-induced mesangial cell proliferation and gene expression

This study examined the role of mitogen-activated protein (MAP) kinase in PDGF-BB-induced proliferation and gene expression of human mesangial cells (MC). PDGF-BB stimulation of MC increased mRNA for transforming growth factor-beta1 (TGF-beta1), monocyte chemoattractant protein-1 (MCP-1), and plasminogen activator inhibitor-1 (PAI-1) and increased the cell numbers. To inhibit activation of extracellular signal-regulated kinase (ERK), c-Jun amino-terminal kinase (JNK), and p38, MC were infected with recombinant adenovirus containing dominant-negative mutants of ERK, JNK, and p38 (Ad-DN-ERK, Ad-DN-JNK, Ad-DN-p38, respectively), respectively. Infection of MC with Ad-DN-ERK or Ad-DN-JNK inhibited PDGF-BB-induced increase in [(3)H]thymidine incorporation and cell numbers, whereas Ad-DN-p38 did not. Ad-DN-ERK inhibited MCP-1 and PAI-1 mRNA expression in MC, but not TGF-beta1. Ad-DN-JNK and Ad-DN-p38 inhibited TGF-beta1 and MCP-1 mRNA expression, but not PAI-1. The inhibition of activator protein-1 (AP-1) in MC, by adenovirus containing dominant-negative mutant of c-Jun (Ad-DN-c-Jun), inhibited PDGF-BB-induced cell proliferation and TGF-beta1, MCP-1, and PAI-1 expressions. Furthermore, Ad-DN-JNK or Ad-DN-p38, but not Ad-DN-ERK, attenuated PDGF-BB-induced AP-1 activation in MC, indicating the involvement of JNK and p38 in AP-1 activation. Our results indicated that ERK and JNK, but not p38, participated in PDGF-BB-induced MC proliferation. PDGF-BB-induced expression of TGF-beta1 was mediated by JNK and p38, MCP-1 expression was through ERK, JNK, and p38, whereas PAI-1 expression was due to only ERK. AP-1 activation, which was partially due to JNK and p38 activations, was involved in MC proliferation and these three gene expressions. Thus, three MAP kinases seem to contribute to progression of glomerular disease via different molecular mechanisms.

Bradykinin reduces growth factor-induced glomerular ERK1/2 phosphorylation

Several experimental data report both mitogenic and antimitogenic effects of bradykinin (BK). To conciliate these apparent opposite effects, we hypothesized that, depending on cell context activation, BK could reduce the mitogenic effect of growth factors. Therefore, in the present study we assessed the existence of possible negative cross talk between BK and potential pathogenic growth factors in freshly isolated rat glomeruli (IG). Next, we determined whether this cross talk could be pharmacologically recruited during angiotensin-converting enzyme (ACE) inhibition in the diabetic rat. In IG from normal rats, BK, via activation of the B(2) kinin receptor (B(2)R), causes a transient stimulation of ERK1/2 phosphorylation, whereas it inhibits ERK1/2 phosphorylation induced by IGF-1, PDGF-BB, VEGF, or basic FGF. The reduction of growth factor-induced ERK1/2 phosphorylation is abolished by an inhibitor of tyrosine phosphatase. In glomeruli from diabetic rats, hyperglycemia increased the phosphorylation level of ERK-1/2 as well as oxidative stress. The reversal of these events by ACE inhibition is mediated via B(2)R activation. These observations are consistent with a potential therapeutic role of BK and B(2)R during glomerulosclerosis.

In vivo identification of the mitogen-activated protein kinase cascade as a central pathogenic pathway in experimental mesangioproliferative glomerulonephritis

Evidence was recently provided for the activation of extracellular signal-regulated kinase (ERK), the best characterized mitogen-activated protein kinase, as an intracellular convergence point for mitogenic stimuli in animal models of glomerulonephritis (GN). In this study, in vivo ERK activity was blocked, with a pharmacologic inhibitor (U0126) of the ERK-activating kinase, in rats with mesangioproliferative GN. After injection of the monoclonal anti-Thy1.1 antibody (OX-7), the rats were treated (days 3 to 6) with low (10 mg/kg body wt) or high (100 mg/kg body wt) doses of U0126 administered intraperitoneally twice daily. On day 6 after induction of the disease, whole cortical tissue and isolated glomeruli were examined by using kinase activity assays, Western blot analyses, and immunohistochemical assays. Treatment with U0126 significantly reduced glomerular stimulation of ERK in anti-Thy1 GN. In the high dose-treated group, this downregulation was accompanied by a reduction in the number of glomerular mitotic figures, back to healthy control levels, and significant decreases in the numbers of total (P < 0.05) and 5-bromo-2'-deoxyuridine-positive (P < 0.05) glomerular cells. Immunohistochemical double-staining of renal sections demonstrated that mesangial cells were the major glomerular targets of U0126 in anti-Thy1 GN. These observations point to ERK as a putative intracellular mediator of the proliferative response in GN and suggest that pharmacologic treatments that interfere with the activation of ERK may be of potential therapeutic interest.

B2 receptor activation reduces Erk1 and Erk2 phosphorylation induced by insulin-like growth factor-1, platelet-derived growth factor-BB, and high glucose in rat isolated glomeruli

Several experimental data document an activation of the mitogen-activated protein kinases Erk1 and Erk2 by bradykinin (BK), an agonist of the kinin B2 receptor (B2R). In contrast, other reports showed an inhibitory modulation of mitogenesis by BK. Therefore, we explored in the isolated glomeruli the effect of B2R activation on the signaling of insulin-like growth factor-1 (IGF-1), platelet-derived growth factor-BB (PDGF-BB), and high glucose (HG), three factors that are believed to be involved in the development of glomerulosclerosis via the phosphorylation of Erk1 and Erk2. We observed that the activation of B2R negatively modulates the phosphorylation of Erk1 and Erk2 induced by IGF-1, PDGF-BB, and HG in the glomerulus. These effects are consistent with the hypothesis of a protective role for BK in the kidney during development of glomerulosclerosis and renal pathologies associated with a hyperproliferative state.

Increased expression of cell adhesion kinase beta in human and rat crescentic glomerulonephritis

Cell adhesion kinase beta (CAKbeta, also known as Pyk2/CadTK/RAFTK) is the second member of the focal adhesion kinase (FAK) subfamily. We examined the expression of CAKbeta in various human glomerulopathies by immunohistochemistry. Although CAKbeta expression in the normal kidney is confined to the brush border of the proximal tubule with no detectable glomerular staining, we found that glomerular crescents strongly expressed this kinase. Expression of CAKbeta was prominent in cellular crescents but was minimal in fibrocellular or fibrous crescents. Serial section analysis revealed that most CAKbeta-expressing cells were positive for cytokeratin but were negative for CD68 (a macrophage marker), suggesting that CAKbeta was expressed by parietal epithelium in the crescents. We also examined CAKbeta expression in a rat model of crescentic glomerulonephritis induced by anti-glomerular basement membrane antibody. Similar to human nephritis, enhanced expression of CAKbeta in glomerular crescents was apparent. Increased expression of CAKbeta also was confirmed by anti-CAKbeta immunoblotting and by real-time quantitative polymerase chain reaction. Previous studies have shown that CAKbeta is activated by various stimuli regulating cell growth and survival. Although our findings do not determine whether or not increased expression of CAKbeta is a primary event for the development of crescentic glomerulonephritis, further understanding of this pathway may be important to gain novel insights into the factors that promote crescent formation.

Involvement of p38 mitogen-activated protein kinase followed by chemokine expression in crescentic glomerulonephritis

p38 Mitogen-activated protein kinase (MAPK) is involved in the production and signal transduction of interleukin-1beta (IL-1beta), tumor necrosis factor-alpha, and chemokines in vitro. However, the crucial role of p38 MAPK in the inflammatory processes of crescentic glomerulonephritis in vivo remains to be investigated. We showed a dramatic decrease in IL-1beta-induced phosphorylation of p38 MAPK, not extracellular signal-regulated kinases 1/2 or jun NH2-terminal kinase, in rat cultured mesangial cells by FR167653. We explored the effects of FR167653 as a specific inhibitor of p38 MAPK on renal injury and subsequent renal expression of chemokines in a progressive experimental crescentic glomerulonephritis model in Wistar-Kyoto rats. Rats developed crescentic glomerulonephritis leading to glomerulosclerosis and interstitial fibrosis by 56 days after the administration of nephrotoxic sera. The number of phosphorylated p38 MAPK-positive cells, detected mainly in crescents, correlated well with the percentage of crescents and number of ED-1-positive cells. Phosphorylated p38 MAPK-positive cells were downregulated in glomeruli in rats with the daily subcutaneous administration of FR167653 for 6 days. Concomitantly, renal expression of macrophage inflammatory protein-1alpha and monocyte chemoattractant protein-1/monocyte chemotactic and activating factor was markedly reduced by day 6. The severity of glomerulosclerosis and interstitial fibrosis significantly decreased by day 56, and renal function was preserved. These results suggest that p38 MAPK phosphorylation is pivotal for crescentic glomerulonephritis, followed by the subsequent expression of renal chemokines. This study provides evidence that regulation of p38 MAPK is a novel appealing therapeutic target for crescentic glomerulonephritis.

Gas6 induces mesangial cell proliferation via latent transcription factor STAT3

Mesangial cell proliferation is essential for the pathogenesis and progression of glomerular disease. Previously, we showed that Gas6 plays a pivotal role in mesangial cell proliferation in vitro and in vivo. In the present study, we identified downstream targets of Gas6 signaling to examine the role in mesangial cell proliferation in vitro and in vivo. We found that Gas6 tyrosine phosphorylates STAT3 (signal transducers and activators of transcription) with concomitant translocation to the nucleus and induces STAT3-dependent transcriptional activation in cultured mesangial cells. Expressing dominant negative STAT3 inhibited Gas6-mediated transcriptional activation of STAT3 and abolished Gas6-induced mesangial cell proliferation. In a model of mesangial proliferative glomerulonephritis, STAT3 is phosphorylated in mesangial cells, and its phosphorylation peaks at day 8 after the injection of anti-Thy1.1 antibody. Inhibition of Gas6 by warfarin and the extracellular domain of its receptor, Axl, abolished phosphorylation of STAT3 in vivo. Thus, our in vitro and in vivo findings indicate that autocrine growth factor Gas6 induces mesangial cell proliferation via latent transcription factor STAT3. Therefore, STAT3 might be a new therapeutic target for kidney disease induced by mesangial proliferation.

Gas6 regulates mesangial cell proliferation through Axl in experimental glomerulonephritis

Proliferation of mesangial cells is a hallmark of glomerular disease, and understanding its regulatory mechanism is clinically important. Previously, we demonstrated that the product of growth arrest-specific gene 6 (Gas6) stimulates mesangial cell proliferation through binding to its cell-surface receptor Axl in vitro. We also showed that warfarin and the extracellular domain of Axl conjugated with Fc portion of human IgG1 (Axl-Fc) inhibit mesangial cell proliferation by interfering the Gas6/Axl pathway in vitro. In the present study, therefore, we examined in vivo roles of Gas6 and Axl in an experimental model of mesangial proliferative glomerulonephritis induced by the injection of anti-Thy1.1 antibody (Thy1 GN). In Thy1 GN, expression of Gas6 and Axl was markedly increased in glomeruli, and paralleled the progression of mesangial cell proliferation. Administration of warfarin or daily injection of Axl-Fc inhibited mesangial cell proliferation, and abolished the induction of platelet-derived growth factor-B mRNA and protein in Thy1 GN. Moreover, the anti-proliferative effect of warfarin was achieved at lower concentrations than those in routine clinical use. These findings indicate that the Gas6/Axl pathway plays a key role in mesangial cell proliferation in vivo, and could be a potentially important therapeutic target for the treatment of renal disease.

MAPK signaling and the kidney

Following an overview of the biochemistry of mitogen-activated protein kinase (MAPK) pathways, the relevance of these signaling events to specific models of renal cell function and pathophysiology, both in vitro and in vivo, will be emphasized. In in vitro model systems, events activating the principal MAPK families [extracellular signal-regulated and c-Jun NH(2)-terminal kinase and p38] have been best characterized in mesangial and tubular epithelial cell culture systems and include peptide mitogens, cytokines, lipid mediators, and physical stressors. Several in vivo models of proliferative or toxic renal injury are also associated with aberrant MAPK regulation. It is anticipated that elucidation of downstream effector signaling mechanisms and a clearer understanding of the immediate and remote upstream activating pathways, when applied to these highly clinically relevant model systems, will ultimately provide much greater insight into the basis for specificity now seemingly absent from these signaling events.