Role of platelet-derived growth factor in glomerular disease

The role of the mesangium in glomerular function

When discussing glomerular function, one cell type is often left out, the mesangial cell (MC), probably since it is not a part of the filtration barrier per se. The MCs are instead found between the glomerular capillaries, embedded in their mesangial matrix. They are in direct contact with the endothelial cells and in close contact with the podocytes and together they form the glomerulus. The MCs can produce and react to a multitude of growth factors, cytokines, and other signaling molecules and are in the perfect position to be a central hub for crosstalk communication between the cells in the glomerulus. In certain glomerular diseases, for example, in diabetic kidney disease or IgA nephropathy, the MCs become activated resulting in mesangial expansion. The expansion is normally due to matrix expansion in combination with either proliferation or hypertrophy. With time, this expansion can lead to fibrosis and decreased glomerular function. In addition, signs of complement activation are often seen in biopsies from patients with glomerular disease affecting the mesangium. This review aims to give a better understanding of the MCs in health and disease and their role in glomerular crosstalk and inflammation.

The Role of Platelets in Diabetic Kidney Disease

Diabetic kidney disease (DKD) is among the most common microvascular complications in patients with diabetes, and it currently accounts for the majority of end-stage kidney disease cases worldwide. The pathogenesis of DKD is complex and multifactorial, including systemic and intra-renal inflammatory and coagulation processes. Activated platelets play a pivotal role in inflammation, coagulation, and fibrosis. Mounting evidence shows that platelets play a role in the pathogenesis and progression of DKD. The potentially beneficial effects of antiplatelet agents in preventing progression of DKD has been studied in animal models and clinical trials. This review summarizes the current knowledge on the role of platelets in DKD, including the potential therapeutic effects of antiplatelet therapies.

Insights Into the Role of Platelet-Derived Growth Factors: Implications for Parkinson’s Disease Pathogenesis and Treatment

Parkinson’s disease (PD), the second most common neurodegenerative disease after Alzheimer’s disease, commonly occurs in the elderly population, causing a significant medical and economic burden to the aging society worldwide. At present, there are few effective methods that achieve satisfactory clinical results in the treatment of PD. Platelet-derived growth factors (PDGFs) and platelet-derived growth factor receptors (PDGFRs) are important neurotrophic factors that are expressed in various cell types. Their unique structures allow for specific binding that can effectively regulate vital functions in the nervous system. In this review, we summarized the possible mechanisms by which PDGFs/PDGFRs regulate the occurrence and development of PD by affecting oxidative stress, mitochondrial function, protein folding and aggregation, Ca2+ homeostasis, and cell neuroinflammation. These modes of action mainly depend on the type and distribution of PDGFs in different nerve cells. We also summarized the possible clinical applications and prospects for PDGF in the treatment of PD, especially in genetic treatment. Recent advances have shown that PDGFs have contradictory roles within the central nervous system (CNS). Although they exert neuroprotective effects through multiple pathways, they are also associated with the disruption of the blood–brain barrier (BBB). Our recommendations based on our findings include further investigation of the contradictory neurotrophic and neurotoxic effects of the PDGFs acting on the CNS.

Mesangioproliferative Kidney Diseases and Platelet-Derived Growth Factor-Mediated AXL Phosphorylation

RATIONALE & OBJECTIVE

Immunoglobulin A nephropathy (IgAN) is a common glomerular disease, with mesangial cell proliferation as a major feature. There is no disease-specific treatment. Platelet-derived growth factor (PDGF) contributes to the pathogenesis of IgAN. To better understand its pathogenic mechanisms, we assessed PDGF-mediated AXL phosphorylation in human mesangial cells and kidney tissue biopsy specimens.

STUDY DESIGN

Immunostaining using human kidney biopsy specimens and in vitro studies using primary human mesangial cells.

SETTING & PARTICIPANTS

Phosphorylation of AXL was assessed in cultured mesangial cells and 10 kidney-biopsy specimens from 5 patients with IgAN, 3 with minimal change disease, 1 with membranous nephropathy, and 1 with mesangioproliferative glomerulonephritis (GN).

PREDICTOR

Glomerular staining for phospho-AXL in kidney biopsy specimens of patients with mesangioproliferative diseases.

OUTCOMES

Phosphorylated AXL detected in biopsy tissues of patients with IgAN and mesangioproliferative GN and in cultured mesangial cells stimulated with PDGF.

ANALYTIC APPROACH

t test, Mann-Whitney test, and analysis of variance were used to assess the significance of mesangial cell proliferative changes.

RESULTS

Immunohistochemical staining revealed enhanced phosphorylation of glomerular AXL in IgAN and mesangioproliferative GN, but not in minimal change disease and membranous nephropathy. Confocal-microscopy immunofluorescence analysis indicated that mesangial cells rather than endothelial cells or podocytes expressed phospho-AXL. Kinomic profiling of primary mesangial cells treated with PDGF revealed activation of several protein-tyrosine kinases, including AXL. Immunoprecipitation experiments indicated association of AXL and PDGF receptor proteins. An AXL-specific inhibitor (bemcentinib) partially blocked PDGF-induced cellular proliferation and reduced phosphorylation of AXL and PDGF receptor and the downstream signals (AKT1 and ERK1/2).

LIMITATIONS

Small number of kidney biopsy specimens to correlate the activation of AXL with disease severity.

CONCLUSIONS

PDGF-mediated signaling in mesangial cells involves transactivation of AXL. Finding appropriate inhibitors to block PDGF-mediated transactivation of AXL may provide new therapeutic options for mesangioproliferative kidney diseases such as IgAN.

Serum IP-10 is useful for identifying renal and overall disease activity in pediatric systemic lupus erythematosus

BACKGROUND

Traditional serological biomarkers often fail to assess systemic lupus erythematosus (SLE) disease activity and discriminate lupus nephritis (LN). The aim of this study was to identify novel markers for evaluating renal and overall disease activity in Chinese patients with pediatric systemic lupus erythematosus (pSLE).

METHODS

The study included 46 patients with pSLE (35 girls, 11 boys; average age 13.3 ± 2.6 years) and 31 matched healthy controls (22 girls, 9 boys; average age 12.3 ± 2.4 years). The SLE Disease Activity Index (SLEDAI) and renal SLEDAI were used to assess disease activity. Nine different soluble mediators in plasma, including tumor necrosis factor alpha (TNF-α), platelet-derived growth factor-BB (PDGF-BB), interferon (IFN) gamma inducible protein 10 (IP-10), interleukin (IL)-1β, IFN-γ, IL-17A, IL-2, Fas and Fas ligand, were measured by Luminex assay and compared between patients with active and inactive pSLE as well as between patients with pSLE with active and inactive renal disease. Receiver operating characteristic curve analysis was used to measure the discrimination accuracy.

RESULTS

Of the 46 patients with pSLE, 30 (65.2%) had LN. These patients had significantly elevated levels of serum TNF-α, PDGF-BB, IP-10 and Fas. The serum levels of IP-10 were also significantly higher in patients with active pSLE. We found that IP-10 was also more sensitive and specific than conventional laboratory parameters, including anti-double-stranded DNA and complement components C3 and C4, for distinguishing active lupus from quiescent lupus. The serum level of IP-10 was also significantly increased in children with pSLE with active renal disease relative to those with inactive renal disease. There was also a positive correlation between serum IP-10 levels and renal SLEDAI scores as well as with 24 h urine protein.

CONCLUSIONS

Serum IP-10 is useful for identifying renal and overall disease activity in children with pSLE.

Sulforaphane mitigates muscle fibrosis in mdx mice via Nrf2-mediated inhibition of TGF-β/Smad signaling

Sulforaphane (SFN), an activator of NF-E2-related factor 2 (Nrf2), has been found to have an antifibrotic effect on liver and lung. However, its effects on dystrophic muscle fibrosis remain unknown. This work was undertaken to evaluate the effects of SFN-mediated activation of Nrf2 on dystrophic muscle fibrosis. Male mdx mice (age 3 mo) were treated with SFN by gavage (2 mg/kg body wt per day) for 3 mo. Experimental results demonstrated that SFN remarkably attenuated skeletal and cardiac muscle fibrosis as indicated by reduced Sirius Red staining and immunostaining of the extracellular matrix. Moreover, SFN significantly inhibited the transforming growth factor-β (TGF-β)/Smad signaling pathway and suppressed profibrogenic gene and protein expressions such as those of α-smooth muscle actin (α-SMA), fibronectin, collagen I, plasminogen activator inhibitor-1 (PAI-1), and tissue inhibitor metalloproteinase-1 (TIMP-1) in an Nrf2-dependent manner. Furthermore, SFN significantly decreased the expression of inflammatory cytokines CD45, TNF-α, and IL-6 in mdx mice. In conclusion, these results show that SFN can attenuate dystrophic muscle fibrosis by Nrf2-mediated inhibition of the TGF-β/Smad signaling pathway, which indicates that Nrf2 may represent a new target for dystrophic muscle fibrosis.

Permeability factors in idiopathic nephrotic syndrome: historical perspectives and lessons for the future

The term idiopathic nephrotic syndrome (iNS) traditionally covers minimal change disease and primary focal segmental glomerulosclerosis (FSGS), now thought to be separate disease entities. Clinical and experimental evidence suggest that circulating permeability factors are involved in their pathogenesis. In the past four decades, many investigators have searched for the responsible factors, thus far with little success. The recent report of the soluble urokinase plasminogen activator receptor as a causative factor in FSGS has received much attention, but again the initially promising findings were not confirmed. We describe the history of the search for permeability factors, discuss the pitfalls that are likely responsible for the lack of success and propose criteria that should be used in future studies when evaluating candidate permeability factors.

Platelet-derived growth factor-BB induces cystathionine γ-lyase expression in rat mesangial cells via a redox-dependent mechanism

BACKGROUND AND PURPOSE

So far, there is only limited information about the regulation of the endogenous synthesis of hydrogen sulfide (H(2) S), an important gaseous signalling molecule. This study was done to evaluate the redox-dependent signalling events that regulate the expression of the H(2) S synthesising enzyme cystathionine-γ-lyase (CSE) in rat mesangial cells.

EXPERIMENTAL APPROACH

The effects of platelet-derived growth factor (PDGF)-BB and antioxidants on CSE expression and activity in cultured rat renal mesangial cells were assessed. Activity of nuclear factor erythroid-2-related factor-2 (Nrf2) was measured as the binding capacity to a radiolabelled consensus element by electrophoretic mobility shift assay (EMSA). Furthermore, CSE and Nrf2 expression was analysed in a rat model of anti-Thy-1-induced glomerulonephritis by immunohistochemistry.

KEY RESULTS

Treatment of mesangial cells with PDGF-BB resulted in a marked time- and dose-dependent up-regulation of CSE mRNA and protein levels, as well as CSE activity accompanied with increased formation of reactive oxygen species. Remarkably, co-administration of antioxidants, such as N-acetylcysteine, ebselen or diphenylene iodonium chloride, drastically reduced PDGF-BB-induced CSE expression. PDGF-BB induced binding of Nrf2 to a corresponding consensus antioxidant element in a redox-dependent manner. Furthermore, PDGF-BB-induced CSE expression in mouse mesangial cells was completely abolished in Nrf2 knockout mice compared with wild-type mice. In a rat model of anti-Thy-1-induced proliferative glomerulonephritis, we observed a marked up-regulation of CSE protein paralleled by a stabilization of Nrf2 protein.

CONCLUSIONS AND IMPLICATIONS

PDGF-BB regulated CSE via a redox-mediated activation of Nrf2. Such action would aid the resolution of glomerular inflammatory diseases.

LINKED ARTICLE

This article is commented on by Gallyas, pp. 2228-2230 of this issue. To view this commentary visit http://dx.doi.org/10.1111/j.1476-5381.2012.01976.x.

Platelet-derived growth factor triggers PKA-mediated signalling by a redox-dependent mechanism in rat renal mesangial cells

Inflammatory glomerular kidney diseases are often accompanied with a massive production of reactive oxygen species (ROS) that affect the function of the glomerular filtration barrier and contribute to mesangiolysis via the induction of cell death in mesangial cells. Intriguingly, ROS also trigger fine-tuned signalling processes that affect gene expression and cell proliferation or migration. To define such redox-driven signalling devices, a proteomics approach was performed to identify the formation of protein complexes induced by ROS. To this end, protein lysates of human podocytes were treated with or without hydrogen peroxide (250 μM). Thereafter cell lysates were subjected to diagonal 2D gel electrophoresis and putative redox-affected proteins were analysed by MS/MS analysis. Among others, the regulatory subunit of protein kinase A (PKA) could be identified that forms homodimers under oxidative conditions. To evaluate whether ROS dependent dimerization of PKA also occurs in a more physiological setting, rat mesangial cells were treated with platelet-derived growth factor-BB (PDGF-BB) to induce ROS formation. This regimen resulted in a redox dependent dimerization of the R-subunits of PKA. To demonstrate whether PDGF-BB induced ROS formation affects PKA dependent pathways, the effects of PDGF-BB on phosphorylation of serine 157 of vasodilator stimulated protein (VASP) a classical target of PKA were analysed. Interestingly PDGF-BB induced VASP phosphorylation in a ROS dependent manner but independent of changes in cAMP levels. Taken together, we demonstrate a redox-mediated activation of PKA by PDGF-BB thus highlighting a physiological role of ROS as regulator of PKA activity in rat mesangial cells.

Dimethylfumarate attenuates renal fibrosis via NF-E2-related factor 2-mediated inhibition of transforming growth factor-β/Smad signaling

TGF-β plays a key role in the development of renal fibrosis. Suppressing the TGF-β signaling pathway is a possible therapeutic approach for preventing this disease, and reports have suggested that Nrf2 protects against renal fibrosis by inhibiting TGF-β signaling. This study examines whether dimethylfumarate (DMF), which stimulates Nrf2, prevents renal fibrosis via the Nrf2-mediated suppression of TGF-β signaling. Results showed that DMF increased nuclear levels of Nrf2, and both DMF and adenovirus-mediated overexpression of Nrf2 (Ad-Nrf2) decreased PAI-1, alpha-smooth muscle actin (α-SMA), fibronectin and type 1 collagen expression in TGF-β-treated rat mesangial cells (RMCs) and renal fibroblast cells (NRK-49F). Additionally, DMF and Ad-Nrf2 repressed TGF-β-stimulated Smad3 activity by inhibiting Smad3 phosphorylation, which was restored by siRNA-mediated knockdown of Nrf2 expression. However, downregulation of the antioxidant response element (ARE)-driven Nrf2 target genes such as NQO1, HO-1 and glutathione S-transferase (GST) did not reverse the inhibitory effect of DMF on TGF-β-induced upregulation of profibrotic genes or extracellular matrix proteins, suggesting an ARE-independent anti-fibrotic activity of DMF. Finally, DMF suppressed unilateral ureteral obstruction (UUO)-induced renal fibrosis and α-SMA, fibronectin and type 1 collagen expression in the obstructed kidneys from UUO mice, along with increased and decreased expression of Nrf2 and phospho-Smad3, respectively. In summary, DMF attenuated renal fibrosis via the Nrf2-mediated inhibition of TGF-β/Smad3 signaling in an ARE-independent manner, suggesting that DMF could be used to treat renal fibrosis.

A novel, dual role of CCN3 in experimental glomerulonephritis: pro-angiogenic and antimesangioproliferative effects

In contrast to factors that promote mesangial cell proliferation, little is known about their endogenous inhibitors. During experimental mesangioproliferative nephritis, expression of the glomerular CCN3 (nephroblastoma overexpressed gene [NOV]) gene is reduced before the proliferative phase and increased in glomeruli and serum when mesangial cell proliferation subsides. To further elucidate its role in mesangioproliferative glomerulonephritis, CCN3 systemically was overexpressed by muscle electroporation in healthy or nephritic rats. This increased CCN3 serum concentrations more than threefold for up to 56 days. At day 5 after disease induction, CCN3-transfected rats showed an increase in glomerular endothelial area and in mRNA levels of the pro-angiogenic factors vascular endothelial growth factor and PDGF-C. At day 7, CCN3 overexpression decreased mesangial cell proliferation, including expression of α-smooth muscle actin and matrix accumulation of fibronectin and type IV collagen. In progressive nephritis (day 56), overexpression of CCN3 resulted in decreased albuminuria, glomerulosclerosis, and reduced cortical collagen type I accumulation. In healthy rat kidneys, overexpression of CCN3 induced no morphologic changes but regulated glomerular gene transcripts (reduced transcription of PDGF-B, PDGF-D, PDGF-receptor-β, and fibronectin, and increased PDGF-receptor-α and PDGF-C mRNA). These data identify a dual role for CCN3 in experimental glomerulonephritis with pro-angiogenic and antimesangioproliferative effects. Manipulation of CCN3 may represent a novel approach to help repair glomerular endothelial damage and mesangioproliferative changes.

Activation of Src mediates PDGF-induced Smad1 phosphorylation and contributes to the progression of glomerulosclerosis in glomerulonephritis

Platelet-derived growth factor (PDGF) plays critical roles in mesangial cell (MC) proliferation in mesangial proliferative glomerulonephritis. We showed previously that Smad1 contributes to PDGF-dependent proliferation of MCs, but the mechanism by which Smad1 is activated by PDGF is not precisely known. Here we examined the role of c-Src tyrosine kinase in the proliferative change of MCs. Experimental mesangial proliferative glomerulonephritis (Thy1 GN) was induced by a single intravenous injection of anti-rat Thy-1.1 monoclonal antibody. In Thy1 GN, MC proliferation and type IV collagen (Col4) expression peaked on day 6. Immunohistochemical staining for the expression of phospho-Src (pSrc), phospho-Smad1 (pSmad1), Col4, and smooth muscle α-actin (SMA) revealed that the activation of c-Src and Smad1 signals in glomeruli peaked on day 6, consistent with the peak of mesangial proliferation. When treated with PP2, a Src inhibitor, both mesangial proliferation and sclerosis were significantly reduced. PP2 administration also significantly reduced pSmad1, Col4, and SMA expression. PDGF induced Col4 synthesis in association with increased expression of pSrc and pSmad1 in cultured MCs. In addition, PP2 reduced Col4 synthesis along with decreased pSrc and pSmad1 protein expression in vitro. Moreover, the addition of siRNA against c-Src significantly reduced the phosphorylation of Smad1 and the overproduction of Col4. These results provide new evidence that the activation of Src/Smad1 signaling pathway plays a key role in the development of glomerulosclerosis in experimental glomerulonephritis.

Transactivation of RON receptor tyrosine kinase by interaction with PDGF receptor beta during steady-state growth of human mesangial cells

Although it is well known that platelet-derived growth factor (PDGF) causes mesangial cell proliferation (presumably contributing to progression of glomerular disease), targeted inhibition of the PDGF receptor system has shown only limited efficacy against glomerular diseases. To examine whether this discrepancy is due to the involvement of other pathways, we used phosphorylated receptor tyrosine kinase arrays and found that RON (recepteur d'origine nantais) was phosphorylated while the PDGF receptor was dephosphorylated (thus inactive) in human mesangial cells (HMCs) at the time of cell cycle entry. Further, RON remained active during steady-state growth. Activation of RON was independent of its canonical ligand, macrophage-stimulating protein, but was mediated by transactivation from the PDGF-engaged PDGF receptor. Following stimulation with PDGF we found that the two receptors physically interacted. Knockdown of RON by siRNA increased the number of apoptotic cells without affecting the rate of DNA synthesis, suggesting that RON has anti-apoptotic functions. Immunohistochemical analysis found phosphorylated RON in glomerular lesions of patients with IgA nephropathy but not those with minimal change nephrotic syndrome, a disease not associated with mesangial proliferation. These results suggest that RON is involved in mesangial cell proliferation under both physiological and pathological conditions, and may be a relevant target for therapeutic intervention.

Imatinib suppresses cryoglobulinemia and secondary membranoproliferative glomerulonephritis

Imatinib is a receptor tyrosine kinase inhibitor that blocks the activity of c-Abl, c-Kit, and PDGF receptors. We tested the protective effects of imatinib in thymic stromal lymphopoietin transgenic mice, a model of cryoglobulinemia and associated membranoproliferative glomerulonephritis (MPGN), in which some glomerular manifestations likely result from PDGF receptor activation. Surprising, administration of imatinib beginning at weaning suppressed production of cryoglobulin, attenuating both the renal injury and systemic features of cryoglobulinemia. Flow cytometry suggested that inhibition of B cell development in the bone marrow likely caused the reduction in cryoglobulin production. In addition, administration of imatinib to thymic stromal lymphopoietin transgenic mice with established MPGN also diminished cryoglobulin production and reversed the renal and systemic lesions. These data suggest that treatment with imatinib may be a novel therapeutic approach for cryoglobulinemia and MPGN in humans.

The Lipoxin A4 receptor is coupled to SHP-2 activation: implications for regulation of receptor tyrosine kinases

Mesangial cell proliferation is pivotal to the pathology of glomerular injury in inflammation. We have previously reported that lipoxins, endogenously produced eicosanoids with anti-inflammatory and pro-resolution bioactions, can inhibit mesangial cell proliferation in response to several agents. This process is associated with elaborate receptor cross-talk involving modification receptor tyrosine kinase phosphorylation (McMahon, B., Mitchell, D., Shattock, R., Martin, F., Brady, H. R., and Godson, C. (2002) FASEB J. 16, 1817-1819). Here we demonstrate that the lipoxin A(4) (LXA(4)) receptor is coupled to activation and recruitment of the SHP-2 (SH2 domain-containing tyrosine phosphatase-2) within a lipid raft microdomain. Using site-directed mutagenesis of the cytosolic domain of the platelet-derived growth factor receptor beta (PDGFRbeta), we report that mutation of the sites for phosphatidylinositol 3-kinase (Tyr(740) and Tyr(751)) and SHP-2 (Tyr(763) and Tyr(1009)) recruitment specifically inhibit the effect of LXA(4) on the PDGFRbeta signaling; furthermore inhibition of SHP-2 expression with short interfering RNA constructs blocked the effect of LXA(4) on PDGFRbeta phosphorylation. We demonstrate that association of the PDGFRbeta with lipid raft microdomains renders it susceptible to LXA(4)-mediated dephosphorylation by possible reactivation of oxidatively inactivated SHP-2. These data further elaborate on the potential mechanisms underlying the anti-inflammatory, proresolution, and anti-fibrotic bioactions of lipoxins.

Fibroblast differentiation in wound healing and fibrosis

The contraction of granulation tissue from skin wounds was first described in the 1960s. Later it was discovered that during tissue repair, fibroblasts undergo a change in phenotype from their normal relatively quiescent state in which they are involved in slow turnover of the extracellular matrix, to a proliferative and contractile phenotype termed myofibroblasts. These cells show some of the phenotypic characteristics of smooth muscle cells and have been shown to contract in vitro. In the 1990s, a number of researchers in different fields showed that myofibroblasts are present during tissue repair or response to injury in a variety of other tissues, including the liver, kidney, and lung. During normal repair processes, the myofibroblastic cells are lost as repair resolves to form a scar. This cell loss is via apoptosis. In pathological fibroses, myofibroblasts persist in the tissue and are responsible for fibrosis via increased matrix synthesis and for contraction of the tissue. In many cases this expansion of the extracellular matrix impedes normal function of the organ. For this reason much interest has centered on the derivation of myofibroblasts and the factors that influence their differentiation, proliferation, extracellular matrix synthesis, and survival. Further understanding of how fibroblast differentiation and myofibroblast phenotype is controlled may provide valuable insights into future therapies that can control fibrosis and scarring.

The influence of rutin on the extracellular matrix in streptozotocin-induced diabetic rat kidney

We previously reported that rutin administration to streptozotocin (STZ)-induced diabetic rats decreased plasma glucose and increased plasma insulin levels. In this study, we have examined the role of rutin on matrix remodelling in the kidney of STZ-induced diabetic rats. STZ was administered intraperitoneally (50 mg kg(-1)) to male albino Wistar rats to induce experimental diabetes. Rutin (100 mg kg(-1)) was orally administered to normal and STZ-induced diabetic rats for a period of 45 days and its influence on the content of hydroxyproline and collagen and on the activity of matrix metalloproteinases (MMPs) were studied. We have also studied the levels of tissue inhibitors of metalloproteinases (TIMPs) in the kidney. STZ-induced diabetic control rats showed increased content of hydroxyproline and collagen, decreased activity of MMPs and increased levels of TIMPs in the kidney. These changes were positively modulated by rutin treatment in STZ-induced diabetic rats, thereby protecting the kidney. In normal rats treated with rutin, none of the parameters studied were significantly altered. From the results obtained, we could conclude that rutin influences MMPs and effectively protects kidney against STZ-induced damage in rats. The effects observed are due to the reduction of plasma glucose levels by rutin.

Transplanted mesenchymal stem cells accelerate glomerular healing in experimental glomerulonephritis

Bone marrow-derived cells contribute to glomerular cell turnover and repair, but the cell types involved are unknown. Whether rat mesenchymal stem cells (MSC) can accelerate recovery from damage in rat mesangioproliferative anti-Thy1.1 glomerulonephritis was studied. After injection into the left renal artery on day 2 after disease induction, fluorescently labeled MSC were detected in 20 to 50% of glomeruli and rare intrarenal vessels but not in the tubulointerstitium, in contralateral kidneys, or in medium controls. In control experiments, injected mesangial cells were detected less frequently in glomeruli in comparison with injected MSC. In nephritic outbred Wistar rats, MSC injection led to an approximately 50% reduction of mesangiolysis on days 4 and 6 after disease induction, accompanied by three- to four-fold higher intraglomerular cell proliferation on day 4 and more rapid mesangial reconstitution as detected by alpha-smooth muscle actin expression. Injection of MSC into tail veins or intra-arterial injection of mesangial cells instead of MSC failed to reproduce any of these findings. In inbred Lewis rats, anti-Thy1.1 nephritis followed an aggravated course with transient acute renal failure. Acute renal failure was ameliorated by MSC injection into the left renal artery on day 2 after disease induction. Again, MSC led to more rapid recovery from mesangiolysis, increased glomerular cell proliferation, and reduction of proteinuria by 28%. Double immunostaining of 5-bromo-2'-deoxyuridine-labeled MSC for endothelial, mesangial, or monocyte/macrophage antigens showed that 85 to 95% of MSC that localized in glomeruli on day 6 failed to express these markers. In vitro, MSC secreted high amounts of vascular endothelial growth factor and TGF-beta1 but not PDGF-BB. In conclusion, even low numbers of MSC can markedly accelerate glomerular recovery from mesangiolytic damage possibly related to paracrine growth factor release and not to differentiation into resident glomerular cell types or monocytes/macrophages.

Role of the JAK/STAT signaling pathway in diabetic nephropathy

Excessive cellular growth is a major contributor to pathological changes associated with diabetic nephropathy. In particular, high glucose-induced growth of glomerular mesangial cells is a characteristic feature of diabetes-induced renal complications. Glomerular mesangial cells respond to traditional growth factors, although in diabetes this occurs in the context of an environment enriched in both circulating vasoactive mediators and high glucose. For example, the vasoactive peptide ANG II has been implicated in the pathogenesis of diabetic renal disease, and recent findings suggest that high glucose and ANG II activate intracellular signaling processes, including the polyol pathway and generation of reactive oxygen species. These pathways activate the Janus kinase (JAK)/signal transducers and activators of transcription (STAT) signaling cascades in glomerular mesangial cells. Activation of the JAK/STAT signaling cascade can stimulate excessive proliferation and growth of glomerular mesangial cells, contributing to diabetic nephropathy. This review focuses on some of the key elements in the diabetic microenvironment, especially high glucose and the accumulation of advanced glycoxidation end products and considers their impact on ANG II and other vasoactive peptide-mediated signaling events in vitro and in vivo.

Inhibition of platelet-derived growth factor-induced mesangial cell proliferation by cyclooxygenase-2 overexpression is abolished through reactive oxygen species

Proliferation of mesangial cells (MC) is an early event in many forms of glomerulonephritis. We have previously shown that platelet-derived growth factor (PDGF)-induced proliferation of MC was inhibited by the overexpression of cyclooxygenase-2 (COX-2). Since reactive oxygen species (ROS) are important mediators of mitogenic signaling, we evaluated the role of ROS in the COX-2 induced growth arrest in MC. We demonstrate that ROS are reduced in COX-2 overexpressing MC. Intracellular elevation of ROS restored PDGF-induced proliferation, while the expression of the cyclin-dependent kinase inhibitors p21(cip1) and p27(kip1) were decreased in these cells. The data suggest that COX-2 decreases ROS formation which consequently leads to the PDGF-induced inhibition of MC proliferation.

Antagonism of PDGF-D by human antibody CR002 prevents renal scarring in experimental glomerulonephritis

Glomerular mesangial cell proliferation and/or matrix accumulation characterizes many progressive renal diseases. PDGF-D was identified recently as a novel mediator of mesangial cell proliferation in vitro and in vivo. This study investigated the long-term consequences of PDGF-D inhibition in vivo. Rats with progressive mesangioproliferative glomerulonephritis (uninephrectomy plus anti-Thy-1.1 antibody) received the PDGF-D-neutralizing, fully human mAb CR002 on days 3, 10, and 17 after disease induction. Glomerular mesangioproliferative changes on day 10 were significantly reduced by anti-PDGF-D treatment as compared with control antibody. Eight weeks after disease induction, anti-PDGF-D therapy significantly ameliorated focal segmental glomerulosclerosis, podocyte damage (de novo desmin expression), tubulointerstitial damage, and fibrosis as well as the accumulation of renal interstitial matrix including type III collagen and fibronectin. Treatment with anti-PDGF-D also reduced the cortical infiltration of monocytes/macrophages on day 56, possibly related to lower renal cortical complement activation (C5b-9 deposition) and/or reduced epithelial-to-mesenchymal transition (preserved cortical expression of E-cadherin and reduced expression of vimentin and alpha-smooth muscle actin). In conclusion, these data provide evidence for a causal role of PDGF-D in the pathogenesis of renal scarring and point to a new therapeutic approach to progressive mesangioproliferative renal disease.

Hypoxia regulates PDGF-B interactions between glomerular capillary endothelial and mesangial cells

BACKGROUND

Platelet-derived growth factor (PDGF)-B regulates mesangial cell and vessel development during embryogenesis, and contributes to the pathogenesis of adult renal and vascular diseases. Endothelial cell PDGF-B exerts paracrine effects on mesangial cells, but its regulation is not well defined. We examined the impact of hypoxia on PDGF-B-mediated interactions between glomerular endothelial and mesangial cells, a condition of potential relevance in developing, and diseased adult, kidneys.

METHODS

Glomerular endothelial or mesangial cells were subjected to hypoxia and responses compared to normoxic cells. Endothelial PDGF-B was studied by Northern and Western analysis. Mesangial proliferative responses to PDGF-B were assessed by (3)H-thymidine incorporation, and migration by a modified Boyden chamber assay. Hypoxia-induced changes in receptor specific binding capacity were studied by saturation binding assays.

RESULTS

Hypoxia stimulated increases in endothelial PDGF-B mRNA and protein. In normoxic mesangial cells, PDGF-B stimulated dose-dependent proliferation, but the proliferative response of hypoxic cells was two to three times greater. Exogenous PDGF-B also caused prompter migration in hypoxic mesangial cells. Mesangial cells were treated with endothelial cell-conditioned medium. More cells migrated when hypoxic cells were stimulated with hypoxic conditioned medium, than when normoxic cells were stimulated with normoxic conditioned medium. Preincubating conditioned medium with PDGF-B neutralizing antibody greatly decreased the chemoattractant activity. Binding studies demonstrated increased specific binding capacity in hypoxic cells.

CONCLUSION

Hypoxia enhances PDGF-B paracrine interactions between glomerular endothelial and mesangial cells. These hypoxia-regulated interactions may be important during glomerulogenesis in fetal life and during the pathogenesis of adult glomerular disease.

Post-inflammatory glomerular remodeling is influenced by transformed mesangial cells

To identify the role of transformed mesangial cells (MC) during glomerular remodeling, anti-thymocyte-1 (Thy1) nephritis; modified Thy1 nephritis (injections of anti-Thy1 antibody four times, weekly); and Thy1 nephritis treated with signal transduction inhibitor 571 (Thy1 + STI); were analyzed. At week 1 the index of MC proliferation in modified Thy1 nephritis and in mesangiolysis in Thy1 + STI nephritis was highest among the three models. From week 4, the index of alpha-smooth muscle actin (alpha-SMA) was significantly higher in modified Thy1 nephritis than the other two models. Production of the mesangial matrix including type IV collagen was increased in modified Thy1 but inhibited in Thy1 + STI nephritis. In contrast to modified Thy1 nephritis, the capillary numbers in glomeruli recovered to normal at week 4 in Thy1, and at week 8 in Thy1 + STI nephritis. At week 12, both the adhesive and sclerotic index was significantly higher in modified Thy1 than in the other two models. Data suggest that a moderate amount of mesangial matrix results in a complete repair of capillary loops. Overproduction of the mesangial matrix retards capillary remodeling and finally induces glomerulosclerosis. Insufficient mesangial matrix delays the repair of capillary loops. In conclusion, transformed MC may influence glomerular remodeling by changing the amount of mesangial matrix.

Aldosterone Stimulates Proliferation of Mesangial Cells by Activating Mitogen-Activated Protein Kinase 1/2, Cyclin D1, and Cyclin A

Recently, attention has been focused on the role of aldosterone in the pathophysiology of hypertension and cardiovascular disease. Several clinical and experimental data support the hypothesis that aldosterone contributes to the progression of renal injury. However, the molecular mechanisms of the effects of aldosterone in signal transduction and the cell-cycle progression of mesangial cells are not well known. For determining the signaling pathway of aldosterone in cultured mesangial cells, the effects of aldosterone on the mitogen-activated protein kinase 1/2 (MAPK1/2) pathway and the promoter activities of cyclin D1, cyclin A, and cyclin E were investigated. First, it was shown that the mineralocorticoid receptor (MR) was expressed in rat mesangial cells and glomeruli and that aldosterone stimulated the proliferation of mesangial cells via the MR and MAPK1/2 pathway. Next, it was demonstrated that aldosterone stimulated Ki-RasA, c-Raf kinase, MEK1/2, and MAPK1/2 in rat mesangial cells. Aldosterone induced cyclin D1 and cyclin A promoter activities and protein expressions, as well as the increments of CDK2 and CDK4 kinase activities. The presence of CYP11B2 and 11beta-HSD2 mRNA in rat mesangial cells also was shown. In conclusion, aldosterone seems to exert mainly MR-induced effects that stimulate c-Raf, MEK1/2, MAPK1/2, the activities of CDK2 and CDK4, and the cell-cycle progression in mesangial cells. MR antagonists may serve as a potential therapeutic approach to mesangial proliferative disease.

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

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

Epidermal growth factor receptor inhibition attenuates early kidney enlargement in experimental diabetes

BACKGROUND

Renal enlargement is an early feature of both human and experimental diabetes. Although the precise mechanisms underlying its development are incompletely understood, locally active growth factors have been suggested to have a key role. Having previously documented increased expression of the proproliferative and antiapoptotic growth factor, epidermal growth factor (EGF), in early diabetes-related kidney growth, the present study sought to evaluate its pathogenetic role by blocking its action with a specific inhibitor.

METHODS

Sprague-Dawley rats were randomized to receive streptozotocin (diabetic) or buffer (control) and then further randomized to receive either vehicle or the inhibitor of the EGF receptor tyrosine kinase, PKI 166 (100 mg/kg/day) for 2 days and 3 weeks following streptozotocin administration.

RESULTS

Experimental diabetes was associated with an increase in kidney weight and tubular epithelial cell proliferation as identified by increased expression of proliferating cell nuclear antigen (PCNA) and 5-bromo-2'-deoxyuridine (BrdU) incorporation. PKI 166 resulted in a 30% reduction in kidney weight in diabetic rats (P < 0.01) and reduced tubular epithelial cell proliferation (P < 0.01). In addition, EGF receptor inhibition also led to a 40% increase in tubular epithelial cell apoptosis at 3 weeks (P < 0.01). Diabetes-associated glomerular enlargement was similarly attenuated by PKI 166, although glomerular hyperfiltration was unaffected.

CONCLUSION

These findings suggest that the EGF-EGF receptor (EGFR) axis has a significant role in the development of early diabetes-related kidney growth. The impact of EGFR inhibition on the later development of renal dysfunction, however, remains to be determined.

Platelet-derived growth factor and platelet profiles in childhood nephrotic syndrome

The aim of the study was to investigate (1) whether there are any changes in release of platelet-derived growth factor AA (PDGF AA) in children with nephrotic syndrome without clinical thromboembolic symptoms 2; (2) whether serum PDGF AA correlates with the platelet count (PLT) and platelet indices; (3) whether prednisone therapy affects the serum PDGF AA and the PLT; (4) whether PDGF AA is a useful predictor of disease activity. The study involved two groups of children: 33 with nephrotic syndrome (I) who were evaluated twice (A during relapse and B after 2 weeks of prednisone treatment) and 34 healthy children (II). The serum concentration of PDGF was measured by ELISA. In group I/A the PLT (P<0.01) and platelet distribution width (P<0.05) were elevated, the mean platelet volume (MPV) (P<0.05) was decreased and the plateletcrit (P>0.05) was normal. In group I/B, the PLT was decreased and MPV increased. The concentration of PDGF AA was still increased and correlated negatively with the albumin concentration. Hence in children with nephrotic syndrome an increase in PLT, a decrease in MPV, and a higher concentration of PDGF were observed. Treatment of nephrotic syndrome with prednisone for 2 weeks is not sufficient to normalize platelet parameters. Further studies are necessary to confirm the role of PDGF AA in the hypercoagulation state in children with nephrotic syndrome.

NHERF2 increases platelet-derived growth factor-induced proliferation through PI-3-kinase/Akt-, ERK-, and Src family kinase-dependent pathway

Platelet-derived growth factor (PDGF) has multiple functions including inhibition of apoptosis and promotion of cell proliferation. In this study, we show that Na(+)/H(+) exchanger regulatory factor 2 (NHERF2) binds to the carboxyl-terminal PDZ domain-binding motif of the PDGF receptor through a PDZ domain-mediated interaction, and evaluate the consequence on PDGF-induced proliferation. Stable transfection with NHERF2 increased the PDGF-induced phosphorylation of ERK and Akt in Rat1 embryonic fibroblasts. The phosphorylation of Akt was blocked by pretreatment with LY294002, a PI-3-kinase inhibitor, in both Rat1/NHERF2 and Rat1/vector cells. In Rat1/vector cells, PDGF-induced phosphorylation of ERK was completely inhibited by pretreatment with PD98059, a MEK inhibitor. In contrast, the NHERF2-dependent increase of ERK phosphorylation was not affected by pretreatment with PD98059 in Rat1/NHERF2 cells. Thus, the NHERF2-dependent increase of ERK phosphorylation occurs in a MEK-independent fashion. Pretreatment with PP2, a specific inhibitor of Src family tyrosine kinase, completely blocked the NHERF2-dependent increase of the phosphorylation of ERK and Akt, suggesting that NHERF2 up-regulates Erk phosphorylation through a Src family kinase-dependent pathway. Consistent with these results, the PDGF-induced thymidine incorporation was increased in Rat1/NHERF2 cells, and the NHERF2-dependent increase of thymidine incorporation was prevented by treatment with LY294002 and PP2 but not with PD98059. These results suggest that NHERF2 stimulates PDGF-induced proliferation by increasing PI-3-kinase/Akt, MEKindependent ERK, and Src family kinase-mediated signaling pathways.

Role of cyclins in cAMP inhibition of glomerular mesangial cell proliferation

MC (mesangial cell) proliferation is closely linked to the progression of glomerular disease. It has been reported that cAMP effectors suppress MC proliferation, inhibiting activation of MAPK (mitogen-activated protein kinase). In fibroblasts, activation of MAPK induces the expression of type D cyclin, whereas, in MCs, this induction has not been shown. In the present study, we explored the effects of cAMP on MAPK and expression of cell-cycle-regulated proteins. PDGF (platelet-derived growth factor) stimulated MAPK activity, up-regulated protein levels of cyclin D1, CDK2 (cyclin-dependent kinase 2) and PCNA (proliferating cell nuclear antigen), decreased the protein level of p27 and increased DNA synthesis. Fsk (forskolin) or PD98059 suppressed PDGF-induced DNA synthesis. Both agents inhibited PDGF-stimulated mRNA and protein expression of cyclin D1 and CDK2. Fsk or PD98059 also inhibited protein expression of PCNA and blocked a decrease in p27 protein. Fsk induced the phosphorylation of Raf-1 at Ser259, which was inhibited by KT5720. These data suggest that cAMP inhibits MC proliferation through inhibition of MAPK activity, and this mechanism partly involves alteration in the levels of cell-cycle-regulated proteins.

Platelet-Derived Growth Factor Receptor Transactivation Mediates the Trophic Effects of Angiotensin II In Vivo

In addition to the modulation of vascular tone, angiotensin II (Ang II) has growth factor–like effects in vascular tissue. The mechanisms whereby Ang II mediates these trophic actions are incompletely understood but are thought to include effects on systemic blood pressure, stimulation of transforming growth factor-β (TGF-β) expression, and transactivation of growth factor receptor kinases. To investigate the role of platelet-derived growth factor receptor (PDGFR) transactivation in mediating the growth factor–like effects of Ang II we administered Ang II (200 ng/kg per minute) or saline to male Sprague-Dawley rats by osmotic minipump for 12 days and treated with imatinib mesylate, an inhibitor of the PDGFR tyrosine kinase. In addition to systolic blood pressure elevation, Ang II infusion led to increased vascular weight, media:lumen ratio, matrix expansion, and overexpression of TGF-β mRNA in mesenteric arteries. Without affecting blood pressure or PDGF ligand expression, imatinib attenuated the changes in vessel morphology but further increased TGF-β mRNA. Western blot analysis of mesenteric arterial tissue demonstrated the presence of the β- but not the α-isoform of PDGFR. Phosphorylation of PDGFR-β was increased by Ang II in vascular smooth muscle cells, and this was inhibited by imatinib. The findings of attenuation of vascular hypertrophy and matrix deposition by imatinib indicate that transactivation of the PDGFR in vivo contributes to the growth factor–like effects of Ang II, independent of its hemodynamic effects or its ability to induce TGF-β gene expression.

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.

Impact of renin angiotensin system blockade on renal function in health and disease: an end or a beginning?

Substantial reduction of functioning nephrons from any origin is followed by a relentless progression to chronic renal failure. This progression continues long after the acute nephropathy and its initiating events have subsided. Glomerular hypertension and hyperfiltration are the major contributors to this progressive nephron loss. Studies on the adverse effects of hemodynamic changes and attempts to define the modalities that slow the rate of progression of renal disease have been among the dominant trends in modern nephrology. Numerous animal studies as well as recent clinical trials indicate that blockade of the renin angiotensin system effectively retards progression of nephropathy from diverse origins.

A fully human monoclonal antibody (CR002) identifies PDGF-D as a novel mediator of mesangioproliferative glomerulonephritis

PDGF-B is of central importance in mesangioproliferative diseases. PDGF-D, a new PDGF isoform, like PDGF-B, signals through the PDGF betabeta-receptor. The present study first determined that PDGF-D is mitogenic for rat mesangial cells and is not inhibited by a PDGF-B antagonist. Low levels of PDGF-D mRNA were detected in normal rat glomeruli. After induction of mesangioproliferative nephritis in rats by anti-Thy 1.1 mAb, glomerular PDGF-D mRNA and protein expression increased significantly from days 4 to 9 in comparison with nonnephritic rats. Peak expression of PDGF-D mRNA occurred 2 d later than peak PDGF-B mRNA expression. In addition, PDGF-D serum levels increased significantly in the nephritic animals on day 7. For investigating the functional role of PDGF-D, neutralizing fully human mAb were generated using the XenoMouse technology. Rats with anti-Thy 1.1-induced nephritis were treated on days 3 and 5 with different amounts of a fully human PDGF-DD-specific neutralizing mAb (CR002), equal amounts of irrelevant control mAb, or PBS by intraperitoneal injection. Specific antagonism of PDGF-D led to a dose-dependent (up to 67%) reduction of glomerular cell proliferation. As judged by double immunostaining for 5-bromo-2'-deoxyuridine and alpha-smooth muscle actin, glomerular mesangial cell proliferation was reduced by up to 57%. Reduction of glomerular cell proliferation in the rats that received CR002 was not associated with reduced glomerular expression of PDGF-B mRNA. PDGF-D antagonism also led to reduced glomerular infiltration of monocytes/macrophages (day 5) and reduced accumulation of fibronectin (day 8). In contrast, no effect was noted in normal rats that received an injection of CR002. These data show that PDGF-D is overexpressed in mesangioproliferative states and can act as an auto-, para-, or even endocrine glomerular cell mitogen, indicating that antagonism of PDGF-D may represent a novel therapeutic approach to mesangioproliferative glomerulonephritides.

Eicosapentaenoic acid inhibits PDGF-induced mitogenesis and cyclin D1 expression via TGF-beta in mesangial cells

Eicosapentaenoic acid (EPA), an omega-3 polyunsaturated fatty acid derived from fish oil, is efficacious in glomerular diseases where mesangial proliferation is a key event. We examined the mechanisms of action of EPA on platelet-derived growth factor (PDGF)-stimulated rat mesangial cell mitogenesis. EPA dose-dependently inhibited PDGF-stimulated [(3)H]-thymidine incorporation. PDGF-induced PDGF receptor autophosphorylation, an initial event for PDGF signaling, was not affected by 2 micro g/ml EPA. Similarly, PDGF-stimulated activation of extracellular signal-regulated kinase (ERK) was not altered. On the other hand, EPA inhibited cyclin-dependent kinase 4 (CDK4) activation and cyclin D1 protein induction, a critical step for G1/S progression. TGF-beta secretion assessed by ELISA and bioassay was increased by EPA at 18 h. Coincubation with anti-TGF-beta antibody inhibited the EPA-induced suppression of [(3)H]-thymidine incorporation and cyclin D1 expression. SB203580, an inhibitor of p38, a downstream kinase of TGF-beta, did not affect EPA's growth inhibitory effect. These results demonstrate that EPA inhibits PDGF-stimulated mesangial cell mitogenesis and cyclin D1 expression via TGF-beta.

Preventive effect of sulphated colominic acid on P-selectin-dependent infiltration of macrophages in experimentally induced crescentic glomerulonephritis

Leucocytes infiltrate into renal tissue and are involved in the pathogenesis of crescentic glomerulonephritis. The initial event in the process of leucocyte infiltration is characterized by selectin-mediated leucocyte rolling on endothelial surface. Role of selectins in pathogenesis of glomerulonephritis has still been controversial. Sulphated glycolipids and sulphated polysaccharides interfere with the binding of P- and L-selectin with carbohydrate ligands on endothelial cells or on leucocytes. Here we evaluated the role of selectins and the preventive effects of sulphated colominic acid (SCA), a synthetic sulphated polysaccharide, on experimental crescentic glomerulonephritis in Wistar-Kyoto (WKY) rats. Crescentic glomerulonephritis was induced by injection of nephrotoxic serum (NTS) in WKY rats. Rats subsequently received intraperitoneal injection of saline, neutralizing or non-neutralizing monoclonal antibody (mAb) to rat P-selectin and L-selectin, SCA (5 or 10mg/kg/day) or nonsulphated colominic acid (CA) (10mg/kg/day) for 2 weeks. Localization of P-, E-selectin, ligands for L-selectin and intraglomerular leucocytes was examined by immunohistochemistry. Gene expression of platelet-derived growth factor (PDGF) B chain in glomeruli was quantified using real-time RT-PCR. P-selectin was highly expressed on glomerular endothelial cells after injection of NTS, whereas E-selectin and L-selectin ligands were not detected. Anti-P-selectin mAb, but not anti-L-selectin mAb, significantly reduced glomerular infiltration of macrophages, crescent formation, and proteinuria. SCA also reduced proteinuria, macrophage infiltration, and crescent formation in a dose-dependent manner. Furthermore, SCA suppressed gene expression of PDGF B chain in glomeruli. Our results indicate that P-selectin partially mediates glomerular infiltration of macrophage in experimental crescentic glomerulonephritis. Moreover, SCA may inhibit intraglomerular infiltration of macrophages by interfering with P-selectin-dependent adhesion pathway, and progression of experimental crescentic glomerulonephritis.

PDGF receptor-alpha deficiency in glomerular mesangial cells of tenascin-C knockout mice

Tenascin-C (TNC) knockout (TNKO) mice showed reduced proliferation of mesangial cells and abnormal restoration after habu-snake venom (HSV)-induced glomerulonephritis. In this study, we examined the relationship of TNC and platelet-derived growth factor receptor (PDGFR) in glomerular mesangial cells. TNC and PDGFR-alpha and -beta transcriptions were up-regulated in wild type (WT) mice after HSV injection, but in TNKO mice PDGFR-alpha transcription was not up-regulated. Immunohistochemistry showed that PDGFR-alpha was found in mesangial areas of colocalized alpha-smooth muscle actin, but in TNKO mice it was not detectable. In vitro studies showed that the expressions of PDGFR-alpha and -beta mRNA and protein in cultured glomerular mesangial cells (GMC) of TNKO mice were lower than those in WT GMC. These results suggest that failures of both TNC and PDGFR-alpha are a candidate for abnormal restoration of TNKO mice.

High glucose-enhanced activation of mesangial cell p38 MAPK by ET-1, ANG II, and platelet-derived growth factor

Mitogen-activated protein kinase (MAPK) p38 is activated in response to stress stimuli and growth factors relevant to the pathogenesis of diabetic nephropathy. We postulated that mesangial cells exposed to high glucose and to endothelin-1 (ET-1), angiotensin II (ANG II), and platelet-derived growth factor (PDGF) demonstrate enhanced p38 activity and subsequent activation of the cAMP responsive element binding (CREB) transcription factor. Primary rat mesangial cells exposed to 5.6 (NG) or 30 mM glucose (HG) or NG plus 24.4 mM sorbitol (osmotic control) for < or = 4 days were acutely stimulated with ET-1, ANG II, or PDGF. After 3 days of HG, p38 phosphorylation and kinase activity increased twofold (P < 0.05 vs. NG, n = 5). No change in p38 activity was observed with sorbitol. In HG, activation of p38 by ET-1, ANG II, or PDGF was enhanced compared with NG and was protein kinase C (PKC) independent. In HG, CREB phosphorylation in response to ET-1, ANG II, and PDGF stimulation was enhanced compared with NG and was abolished by p38 inhibition with SB202190. To conclude, in HG, mesangial cell p38 is activated, which in turn stimulates CREB phosphorylation. Furthermore, in HG, mesangial cell p38 responsiveness to ET-1, ANG II, and PDGF and consequent CREB phosphorylation are enhanced through a PKC-independent pathway, which may contribute to the pathogenesis of diabetic nephropathy.

Overexpression of brain natriuretic peptide in mice ameliorates immune-mediated renal injury

One of major causes of end-stage renal disease is glomerulonephritis, the treatment of which remains difficult clinically. It has already been shown that transgenic mice that overexpress brain natriuretic peptide (BNP), with a potent vasorelaxing and natriuretic property, have ameliorated glomerular injury after subtotal nephrectomy. However, the role of natriuretic peptides in immune-mediated renal injury still remains unknown. Therefore, the effects of chronic excess of BNP on anti-glomerular basement membrane nephritis induced in BNP-transgenic mice (BNP-Tg) were investigated and the mechanisms how natriuretic peptides act on mesangial cells in vitro were explored. After induction of nephritis, severe albuminuria (approximately 21-fold above baseline), tissue damage, including mesangial expansion and cell proliferation, and functional deterioration developed in nontransgenic littermates. In contrast, BNP-Tg exhibited much milder albuminuria (approximately fourfold above baseline), observed only at the initial phase, and with markedly ameliorated histologic and functional changes. Up-regulation of transforming growth factor-beta (TGF-beta) and monocyte chemoattractant protein-1 (MCP-1), as well as increased phosphorylation of extracellular signal-regulated kinase (ERK), were also significantly inhibited in the kidney of BNP-Tg. In cultured mesangial cells, natriuretic peptides counteracted the effects of angiotensin II with regard to ERK phosphorylation and fibrotic action. Because angiotensin II has been shown to play a pivotal role in the progression of nephritis through induction of TGF-beta and MCP-1 that may be ERK-dependent, the protective effects of BNP are likely to be exerted, at least partly, by antagonizing the renin-angiotensin system locally. The present study opens a possibility of a novel therapeutic potential of natriuretic peptides for treating immune-mediated renal injury.

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.

Ciprofibrate increases plasma concentration of platelet-derived growth factor AB in patients with advanced atherosclerosis and hyperlipidemia independently of its hypolipidemic effects

Fibrates, besides their hypolipidemic action, share alternative effects, such as decreased plasma fibrinogen and uric acid levels. Because of their complex action, additional effects have been investigated. A group of 23 patients with clinical signs of atherosclerosis and hyperlipoproteinemia was randomly allocated after a 1-month washout period and treated with either 100 mg/d of ciprofibrate or 100 mg/d of aspirin for 2 months. Patients were then treated with a combination of these two agents for the next 2 months. Ciprofibrate decreased plasma concentrations of triglycerides (-29%) and very-low-density lipoprotein cholesterol (-27%) in monotherapy and a larger reduction was observed if ciprofibrate was added to the aspirin therapy: triglycerides (-39%), very-low-density lipoprotein cholesterol (-33%), total cholesterol (-18%), low-density lipoprotein cholesterol (-17%), and increased high-density lipoprotein cholesterol (+36%). Ciprofibrate increased plasma levels of platelet-derived growth factor (PDGF) AB in both monotherapy patients (+162.9 pg/ml, +297%) and in aspirin-pretreated patients (+129.8 pg/ml, +134%); the increase of PDGF AB platelet store was significant only in aspirin-pretreated patients (+11.1 ng/ml, +51%). Aspirin in monotherapy did not modulate either plasma or platelet store of PDGF AB. Ciprofibrate did not inhibit thromboxane B 2 synthesis in platelets. Aspirin did not influence plasma thromboxane B 2 concentration at all, whereas it decreased thromboxane B 2 platelet production markedly in monotherapy (-85%) and in combination with ciprofibrate (-91%). Ciprofibrate increases PDGF AB content, which is amplified by aspirin pretreatment without correlation with its hypolipidemic action. The increase of PDGF production is suggested to participate in plaque stabilization.

Aminoguanidine ameliorates overexpression of prosclerotic growth factors and collagen deposition in experimental diabetic nephropathy

Profibrotic cytokines and the formation of advanced-glycation end products (AGE) have both been implicated in the pathogenesis of glomerulosclerosis in diabetic kidney disease. However, tubulointerstitial pathology is also an important determinant of progressive renal dysfunction in diabetic nephropathy. This study sought to investigate the expression of profibrotic growth factors and matrix deposition in the glomerulus and the tubulointerstitium and to examine the effect of blocking AGE formation in experimental diabetic nephropathy. Thirty-six male Sprague-Dawley rats were randomized into control and diabetic groups. Diabetes was induced in 24 rats by streptozotocin. Twelve diabetic rats were further randomized to receive the inhibitor of AGE formation, aminoguanidine (1 g/l drinking water). At 6 mo, experimental diabetes was associated with a three-fold increase in expression of transforming growth factor (TGF)-beta1 (P < 0.01 versus control) and five-fold increase in platelet-derived growth factor (PDGF)-B gene expression (P < 0.01 versus control) in the tubulointerstitium. In situ hybridization demonstrated a diffuse increase in both TGF-beta1 and PDGF-B mRNA in renal tubules. Aminoguanidine attenuated not only the overexpression of TGF-beta1 and PDGF-B but also reduced type IV collagen deposition in diabetic rats (P < 0.05). TGF-beta1 and PDGF mRNA within glomeruli were also similarly increased with diabetes and attenuated with aminoguanidine. The observed beneficial effects of aminoguanidine on the tubulointerstitium in experimental diabetes suggest that AGE-mediated expression of profibrotic cytokines may contribute to tubulointerstitial injury and the pathogenesis of diabetic nephropathy.

A vitamin D analog ameliorates glomerular injury on rat glomerulonephritis

OCT (22-oxa-calcitriol), a vitamin D analog, has been reported to show strong inhibitory effects on mesangial cell proliferation in vitro. In the present study, we report a study of the effect of OCT on anti-thy-1 glomerulonephritis. Both OCT and 1,25(OH)(2)D(3) significantly inhibited mesangial cell proliferation, the degree of glomerulosclerosis, and albuminuria at day 8 compared to the disease control group. The OCT-treated group showed normal calcium levels but the 1,25(OH)(2)D(3)-treated group showed higher levels. The disease control group showed a marked increase of type I and type IV collagens, and alpha-smooth muscle actin (alpha-SMA) compared to the normal group. The treatment of OCT or 1,25(OH)(2)D(3) significantly reduced the expression of these proteins. The mRNA of the glomeruli of anti-thy-1 model expressed significantly higher levels of type I and type IV collagens, and alpha-SMA at day 8 compared to normal rats. Treatment with OCT or 1,25(OH)(2)D(3) inhibited the mRNA expressions of type I and type IV collagens, as well as that of alpha-SMA. These data demonstrate that OCT inhibits mesangial cell proliferation and extracellular matrix expansion with a low calcemic activity. Disease control rats showed significantly increased levels of transforming growth factor-beta1 protein in the glomeruli, but treatment with OCT or 1,25(OH)(2)D(3) markedly reduced this expression. The levels of mRNA in glomeruli were also consistent with these protein levels. Therefore, the suppressive effect of OCT may be mediated by inhibition of transforming growth factor-beta1. The present results suggest that OCT has potential for use in therapeutic strategy for the treatment of glomerulonephritis without inducing hypercalcemia.

Glucocorticoids stimulate p21(CIP1) in mesangial cells and in anti-GBM glomerulonephritis

BACKGROUND

Glucocorticoids are widely used for the treatment of glomerulonephritis, but the mechanism of cell cycle inhibition by glucocorticoids is poorly understood at a molecular level.

METHODS

The effects of dexamethasone on cell cycle progression were examined in rat mesangial cells. To investigate the mechanisms of cell cycle inhibition by dexamethasone, we transfected the -2.3 kb p21(CIP1) promoter-CAT construct to mesangial cells using an electroporation

METHOD

We also examined whether glucocorticoids stimulate the expression of p21(CIP1) and inhibit cell proliferation in glomeruli of anti-glomerular basement membrane (GBM) glomerulonephritis in rats.

RESULTS

Dexamethasone inhibited 3H-thymidine uptake and the percentages of S and G2/M phases in rat mesangial cells. Dexamethasone stimulated CAT activity of the p21(CIP1) promoter 4.5-fold. Deletion analysis of the p21(CIP1) promoter revealed that the glucocorticoid-responsive region (GRE) is present between -1.4 and -1.1 kb upstream of the transcription initiation site. Dexamethasone inducibility of p21(CIP1) promoter activity requires the presence of the C/EBP alpha DNA binding site in the GRE of the p21(CIP1) promoter and C/EBP alpha protein. Intravenous injection of anti-GBM antibody caused mesangial proliferation, crescent formation, and proteinuria in rats. Ten days of administration of prednisolone (1 mg/kg/day) reduced proteinuria and inhibited mesangial cell proliferation and crescent formation. The glomerular-sieving method revealed that prednisolone increased p21(CIP1) expression in glomeruli.

CONCLUSION

These data suggest that the cell cycle arrest of mesangial cells is mediated by a functional link between the glucocorticoid receptor and the transcriptional control of p21(CIP1) not only in vitro but also in vivo. Our observations provide new insights into the molecular mechanisms of glucocorticoid action in glomerulonephritis.

Specific antagonism of PDGF prevents renal scarring in experimental glomerulonephritis

Glomerular mesangial cell proliferation and/or mesangial matrix accumulation characterizes many progressive renal diseases. Rats with progressive mesangioproliferative glomerulonephritis were treated from day 3 to day 7 after disease induction with a high-affinity oligonucleotide aptamer antagonist against platelet-derived growth factor-B chain (PDGF-B). In comparison with nephritic rats that received vehicle or a scrambled aptamer, treatment with the PDGF-B aptamer led to a significant reduction of mesangioproliferative changes, glomerular hypertrophy, podocyte damage, and glomerular macrophage influx on day 8. Both nephritic control groups subsequently developed progressive proteinuria and decreased renal function. On day 100, glomerulosclerosis, tubulointerstitial damage, glomerular and interstitial accumulation of types III and IV collagen, and overexpression of transforming growth factor-beta were widespread. All of these chronic changes were prevented in rats that received the PDGF-B aptamer, and their functional and morphologic parameters on day 100 were largely indistinguishable from non-nephritic rats. These data provide the first evidence for a causal role of PDGF in the pathogenesis of renal scarring and point to a new, highly effective therapeutic approach to progressive, in particular mesangioproliferative, renal disease.

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.