The role of lymphocytes in the experimental progressive glomerulonephritis

Immunosenescence: an unexplored role in glomerulonephritis

Immunosenescence is a natural ageing phenomenon with alterations in innate and especially adaptive immunity and contributes to reduced antimicrobial defence and chronic low‐grade inflammation. This is mostly reflected by an increase in organ‐directed and/or circulating reactive and cytolytic terminally differentiated T cells that have lost their expression of the costimulatory receptor CD28. Apart from being induced by a genetic predisposition, ageing or viral infections (particularly cytomegalovirus infection), immunosenescence is accelerated in many inflammatory diseases and uraemia. This translates into an enhancement of vascular inflammation and cardiovascular disease varying from endothelial dysfunction to plaque rupture. Emerging data point to a mechanistic role of CD28^null T cells in glomerulonephritis, where they initiate and propagate local inflammation in concordance with dendritic cells and macrophages. They are suitably equipped to escape immunological dampening by the absence of homing to lymph nodes, anti‐apoptotic properties and resistance to suppression by regulatory T cells. Early accumulation of senescent CD28^null T cells precedes glomerular or vascular injury, and targeting these cells could open avenues for early treatment interventions that aim at abrogating a detrimental vicious cycle.

Suppressor of Cytokine Signaling-1/STAT1 Regulates Renal Inflammation in Mesangial Proliferative Glomerulonephritis Models

Mesangial proliferative glomerulonephritis (MsGN) is a significant global threat to public health. Inflammation plays a crucial role in MsGN; however, the underlying mechanism remains unknown. Herein, we demonstrate that suppression of the cytokine signaling-1 (SOCS1)/signal transducer and activator of transcription 1 (STAT1) signaling pathway is associated with renal inflammation and renal injury in MsGN. Using MsGN rat (Thy1.1 GN) and mouse (Habu GN) models, renal SOCS1/STAT1 was determined to be associated with CD4+ T cell infiltration and related cytokines. In vitro, SOCS1 overexpression repressed IFN-γ-induced MHC class II and cytokine levels and STAT1 phosphorylation in mesangial cells. SOCS1 and STAT1 inhibitors significantly inhibited IFN-γ-induced CIITA promoter activity and MHC class II expression. In conclusion, our study emphasizes the pivotal role of the SOCS1/STAT1 axis in the regulation of inflammation in MsGN.

Role of immune cells in crystal-induced kidney fibrosis

Chronic kidney diseases can lead to kidney fibrosis, which can be considered a futile attempt of tissue healing to replaces functional kidney tissue with connective tissue, basically forming a scar. Chronic inflammation is a frequent cause of kidney fibrosis. Classical as well as recently discovered immune cell subsets and their molecular mediators have been intensively investigated for their contribution to kidney fibrosis and their potential as therapeutic targets. Here we review the current knowledge about the role of immune cells in crystal-induced renal fibrosis.

Expression and Role of CD166 in the Chronic Kidney Disease

BACKGROUND

CD166, an adhesion molecule of the immunoglobulin superfamily, is one of the crucial effectors that traffic lymphocytes into tissues. Till now, the expression and role of CD166 in the chronic kidney disease remains unknown.

OBJECTIVES

In the present study, we are to examine the expression of CD166 in the chronic kidney disease, and to explore its function with CD4+ T cells.

MATERIALS AND METHODS

CD166 expression was tested by Flow Cytometry (FACS) in the primary macrophages stimulated with LPS. In vivo, the expression of CD166 and CD4 were examined in the kidney tissues of adriamycin-induced nephropathy (AN) mice by immnohistochemistry. Macrophages and lymphocytes were co-cultured, the interaction between CD166 and CD4 was tested by immunofluorescent staining. Furthermore, the effects of CD166 on the activation and proliferation of T cells were explored.

RESULTS

In this study, CD166 expression was found to be upregulated on activated macrophages and glomerular endothelia in the adriamycin-induced nephropathy (AN) mice and CD4+ T cells were increased with CD166 expression in the AN mice. The interaction between macrophages and CD4+ T cells indicated that CD166 played a key role in the recruitment of lymphocytes in the chronic kidney disease, and neither proliferation nor activation of T cells was affected by CD166.

CONCLUSIONS

CD166 expressed on macrophages and endothelia in AN kidney, and the function was related to the recruitment of CD4+ T cells into inflamed kidney, indicating that CD166 may be a potential target for reducing the inflammatory infiltrates in the chronic kidney disease.

miR-34a regulates mesangial cell proliferation via the PDGFR-β/Ras-MAPK signaling pathway

The main pathological characteristic of glomerulonephritis is diffuse mesangial cell proliferation. MiR-34a is associated with the proliferation of various organs and cancer cells. However, the role of miR-34a in renal proliferation diseases is not clear. Therefore, this study aimed to elucidate the mechanism of miR-34a in the regulation of renal mesangial cell proliferation. The miR-34a expression level at different time points in an anti-Thy1 mesangial proliferative nephritis rat model was determined by qRT-PCR. The cell proliferation rate and cell cycle changes were measured in the in vitro cultured rat mesangial cells (RMCs). Our results suggested that miR-34a expression was negatively correlated with the degree of cell proliferation in the anti-Thy1 nephritis model. MiR-34a could extend the G0/G1 phase and block cell proliferation in RMCs. Dual-luciferase assay results showed that there were binding sites of miR-34a at 3′-UTR of platelet-derived growth factor receptor-β (PDGFR-β). MiR-34a can inhibit PDGFR-β protein expression at a post-transcriptional level, suppress Ras/MAPK signaling pathways, and down-regulate expression of cell cycle proteins at the G0/G1 phase, such as cyclin D1, CDK4/CDK6. In addition, miR-34a may also inhibit RMC proliferation by directly targeting cyclin E and CDK2. MiR-34a inhibits exogenous stimuli-induced proliferation of mesangial cells. Expression levels of phospho-PDGFR-β and phospho-MEK1 (an important downstream molecule in PDGFR-β-induced signaling pathway) were significantly increased in the anti-Thy-1 nephritis rat model. These results suggest that miR-34a may regulate RMC proliferation by directly inhibiting expressions of PDGFR-β, MEK1, and cell cycle proteins, cyclin E and CDK2.

Sublytic C5b-9 induces IL-6 and TGF-β1 production by glomerular mesangial cells in rat Thy-1 nephritis through p300-mediated C/EBPβ acetylation

CCAAT/enhancer-binding protein (C/EBPβ)-enhanced IL-6 and TGF-β1 promoter activity and p300-mediated C/EBPβ acetylation were involved in up-regulation of IL-6 and TGF-β1 expression in GMCs attacked by sublytic C5b-9. In detail, the elements of C/EBPβ binding to rat IL-6 and TGF-β1 promoter and 3 acetylated sites of rat C/EBPβ protein were first revealed. Furthermore, silencing the p300 or C/EBPβ gene in rat kidney significantly reduced the production of IL-6 and TGF-β1 and renal lesions in Thy-1N rats. Together, these data indicate that the mechanism of IL-6 and TGF-β1 production in renal tissue of Thy-1N rats is associated with sublytic C5b-9 up-regulated p300 and p300-mediated C/EBPβ acetylation as well as C/EBPβ-activated IL-6 and TGF-β1 genes.

Phenotypic change of macrophages in the progression of diabetic nephropathy; sialoadhesin-positive activated macrophages are increased in diabetic kidney

BACKGROUND

Inflammatory process is involved in pathogenesis of diabetic nephropathy, although the activation and phenotypic change of macrophages in diabetic kidney has remained unclear. Sialoadhesin is a macrophage adhesion molecule containing 17 extracellular immunoglobulin-like domains, and is an I-type lectin which binds to sialic acid ligands expressed on hematopoietic cells. The aim of this study is to clarify the activation and phenotypic change of macrophages in the progression of diabetic nephropathy.

METHODS

We examined the expression of surface markers for pan-macrophages, resident macrophages, sialoadhesin, major histocompatibility complex class II and α-smooth muscle actin in the glomeruli of diabetic rats using immunohistochemistry at 0, 1, 4, 12, and 24 weeks after induction of diabetes by streptozotocin. Expression of type IV collagen and the change of mesangial matrix area were also measured. The mechanism for up-regulated expression of sialoadhesin on macrophages was evaluated in vitro.

RESULTS

The number of macrophages was increased in diabetic glomeruli at 1 month after induction of diabetes and the increased number was maintained until 6 months. On the other hand, sialoadhesin-positive macrophages were increased during the late stage of diabetes concomitantly with the increase of α-smooth muscle actin-positive mesangial cells, mesangial matrix area and type IV collagen. Gene expression of sialoadhesin was induced by stimulation with interleukin (IL)-1β and tumor necrosis factor-α but not with IL-4, transforming growth factor-β and high glucose in cultured human macrophages.

CONCLUSION

The present findings suggest that sialoadhesin-positive macrophages may contribute to the progression of diabetic nephropathy.

Platelet recruitment to the inflamed glomerulus occurs via an alphaIIbbeta3/GPVI-dependent pathway

Recruitment of leukocytes to glomeruli is fundamental to the pathogenesis of many forms of glomerulonephritis. In a model of glomerulonephritis induced by in situ immune complex deposition, we previously observed that, in addition to leukocytes, platelets accumulate in glomerular capillaries, where they contribute to leukocyte recruitment. However, the mechanisms of platelet recruitment and the role of platelet-expressed P-selectin in leukocyte recruitment require further investigation. We used intravital microscopy to examine the mechanisms of platelet and leukocyte recruitment to glomeruli of mice following administration of an antibody against the glomerular basement membrane (anti-GBM antibody). Platelet recruitment was initiated within five minutes of administration of anti-GBM antibody. This was unaltered by inhibition of platelet GPIbalpha but was prevented by the absence of platelet GPVI. Fibrinogen was deposited in glomerular capillaries via a partially intercellular adhesion molecule 1 (ICAM-1)-dependent mechanism, and inhibition of alpha(IIb)beta(3), fibrinogen and ICAM-1 inhibited platelet recruitment. Notably, neutrophil depletion also reduced platelet accumulation, indicating a cooperative interaction underlying recruitment of platelets and neutrophils. Finally, using bone marrow chimeras to restrict expression of P-selectin to platelets or endothelial cells, platelet but not endothelial P-selectin was required for glomerular leukocyte recruitment. Together these data indicate that platelet recruitment in this model is dependent on the combined actions of GPVI and the alpha(IIb)beta(3)/fibrinogen/ICAM-1 pathway and that platelet P-selectin is crucial for subsequent leukocyte recruitment.

Activated macrophages down-regulate podocyte nephrin and podocin expression via stress-activated protein kinases

The development of proteinuria and glomerulosclerosis in kidney disease is associated with podocyte damage, including down-regulation of nephrin and podocin. Macrophages are known to induce renal injury, but the mechanisms involved are not fully understood. This study examined macrophage-mediated podocyte damage. Conditioned media (CM) from activated macrophages caused a 50-60% reduction in nephrin and podocin mRNA and protein expression in cultured mouse podocytes and rat glomeruli. This was abolished by a neutralizing anti-TNFalpha antibody. The addition of recombinant TNFalpha to podocytes or glomeruli caused a comparable reduction in podocyte nephrin and podocin expression to that of macrophage CM. Inhibition of c-Jun amino terminal kinase (JNK) or p38 kinase abolished the TNFalpha-induced reduction in nephrin and podocin expression. This study demonstrates that activated macrophages can induce podocyte injury via a TNFalpha-JNK/p38-dependent mechanism. This may explain, in part, the protective effects of JNK and p38 blockade in experimental kidney disease.

Dissociation of NEPH1 from nephrin is involved in development of a rat model of focal segmental glomerulosclerosis

Focal segmental glomerulosclerosis (FSGS) is a disease showing severe proteinuria, and the disease progresses to end-stage kidney failure in many cases. However, the pathogenic mechanism of FSGS is not well understood. The slit diaphragm (SD), which bridges the neighboring foot processes of glomerular epithelial cells, is understood to function as a barrier of the glomerular capillary wall. To investigate the role of SD dysfunction in the development of FSGS, we analyzed the expression of SD-associated molecules in rat adriamycin-induced nephropathy, a mimic of FSGS. The staining of the SD molecules nephrin, podocin, and NEPH1 had already shifted to a discontinuous dotlike pattern at the initiation phase of the disease, when neither proteinuria nor any morphological alterations were detected yet. The alteration of NEPH1 expression was the most evident among the molecules examined, and NEPH1 was dissociated from nephrin at the initiation phase. On day 28, when severe proteinuria was detected and sclerotic changes were already observed, alteration of the expressions of nephrin, podocin, and NEPH1 worsened, but no alteration in the expression of other SD-associated molecules or other podocyte molecules was detected. It is postulated that the dissociation of NEPH1 from nephrin initiates proteinuria and that the SD alteration restricted in these molecules plays a critical role in the development of sclerotic changes in FSGS.

Progression of chronic kidney disease: insights from animal models

PURPOSE OF REVIEW

Chronic kidney diseases are emerging as a worldwide public health problem. Clarification of the mechanisms underlying progression of proteinuric nephropathies received significant input from the generation of transgenic and knockout animals and from novel approaches to block mediators of injury. Reviewed here are advances in animal models used as a tool to address some relevant questions to the pathophysiology of human chronic nephropathies.

RECENT FINDINGS

Gene targeting in rodents identified podocyte loss as central event in the development of glomerulosclerosis. The trigger is dysfunction or absence of podocyte molecules that stabilize the slit diaphragm or anchor foot processes to the basement membrane. Sustained injury of the glomerular barrier to proteins is transmitted to the tubulointerstitial compartment leading to inflammation and fibrosis. Blocking NF-kappaB activity and chemokine signals in the kidney effectively interrupts such process. Growth factors produced by tubular cells and inflammatory cells contribute to interstitial fibrogenesis via myofibroblast activation.

SUMMARY

Development of genetically engineered animals and techniques to specifically manipulate cellular mediators has highlighted the determinants of glomerulosclerosis and tubulointerstitial injury. This knowledge will provide basis for novel interventions to protect the podocyte in chronic progressive glomerulopathies and to halt renal scarring and loss of function.

Expression of the novel co-stimulatory molecule B7-H4 by renal tubular epithelial cells

Crosstalk between T cells and renal tubular epithelial cells (TECs) in the pathogenesis of tubular lesions, the most important sign of progressive renal diseases, has not been clarified. Previous work has shown that TECs harbor co-stimulatory signals that promote T-cell activation, which induces tubular lesions. Nevertheless, the expression and functional role of B7-H4, a recently identified co-stimulatory ligand of the B7 superfamily, in pathologic human kidneys is unclear. We investigated the expression of B7-H4 on cryostat renal biopsies from patients with idiopathic membranous nephropathy (n=20), immunoglobulin A nephropathy (n=19), lupus nephritis (n=16), and acute renal allograft rejection (n=15) using immunohistochemistry. In addition, we also analyzed TEC-associated B7-H4 in the regulation of T-cell activation. Immunohistological staining revealed that B7-H4 antigen is restricted to tubular epithelium and that the protein is prominent in sections with severe tubular lesions, although no correlation was observed between tubular B7-H4 expression and levels of serum creatinine, serum urea nitrogen concentration, and 24-h proteinuria in each type of nephropathy. In vitro, mixed lymphocyte reactions revealed that TEC-related B7-H4 promotes cytokine (interleukin-2 and interferon-gamma) production and proliferation of co-cultured T cells. Interestingly, the secretion of interleukin-2 by C10 T cell hybridomas also increased when C10 cells were co-cultured with the B7-H4-transgenic murine TEC line, 3M-1-secreting tubular epithelial cells (MCT) in the presence of the antigen hen egg lysozyme. Our results clearly show that TEC-associated B7-H4 induces T-cell activation and we propose that B7-H4 is a potential activator that promotes tubular lesion.

Alpha2-adrenoceptor stimulation transforms immune responses in neuritis and blocks neuritis-induced pain

Neuropathic pain may be primarily driven by immune responses in peripheral nerves. Peripherally released catecholamines may exacerbate neuropathic pain and also modulate immune responses in a complex and sometimes opposing manner by actions on multiple adrenoceptor subtypes. We showed previously that injection of the alpha2-adrenoceptor agonist clonidine at the site of peripheral nerve injury reduces pain behavior and local tissue pro-inflammatory cytokine content in rats. The current study used a model of acute inflammatory neuritis to test the efficacy and mechanisms of action of alpha2-adrenoceptor stimulation to reduce pain. Zymosan, injected on the sciatic nerve, caused hypersensitivity to mechanical stimuli ipsilateral to injection and contralaterally, so-called mirror image pain. Ipsilateral hypersensitivity was inhibited dose-dependently by perineural injection of clonidine. Zymosan increased leukocyte number at the site of injection 3 d later as well as their content of interleukin 1alpha (IL-1alpha), IL-1beta, and IL-6. Perineural clonidine prevented both the increase in leukocyte number and cytokine expression induced by zymosan. Additionally, clonidine reduced the capacity of leukocytes to express pro-inflammatory cytokines as assessed by treatment of cells ex vivo with lipopolysaccharide, whereas no repression of IL-10 production occurred. Clonidine reduced the number of macrophages and lymphocytes as well as their expression of tumor necrosis factor alpha. All of the effects of clonidine were prevented by coadministration of an alpha2A-adrenoceptor-preferring antagonist. These results suggest that alpha2-adrenoceptor stimulation transforms cytokine gene expression, especially in macrophages and lymphocytes from a pro- to an anti-inflammatory profile in the setting of neuritis, likely relieving neuritis-induced pain by this mechanism.

TLR agonists regulate PDGF-B production and cell proliferation through TGF-beta/type I IFN crosstalk

Transforming growth factor-beta (TGF-beta) and type I interferon (IFN) autocrine/paracrine loops are recognized as key mediators of signaling cascades that control a variety of cellular functions. Here, we describe a novel mechanism by which Toll-like receptor (TLR) agonists utilize these two autocrine/paracrine loops to differentially regulate the induction of PDGF-B, a growth factor implicated in a number of diseases ranging from tumor metastasis to glomerulonephritis. We demonstrate that CpG-specific induction of PDGF-B requires activation of Smads through TGFbeta1 autocrine/paracrine signaling. In contrast, polyinosinic:polycytidylic acid strongly represses CpG's as well as its own intrinsic ability to induce PDGF-B mRNA through type I IFN-mediated induction of Smad7, a negative regulator of Smad3/4. Furthermore, we have shown that this crosstalk mechanism translates into similar regulation of mesangial cell proliferation. Thus, our results demonstrate the importance of crosstalk between TGF-beta and type I IFNs in determining the specificity of TLR-mediated gene induction.

The sialoadhesin (CD169) expressing a macrophage subset in human proliferative glomerulonephritis

BACKGROUND

Sialoadhesin (Sn; CD169) is a lectin-like receptor whose expression is restricted to subsets of tissue and inflammatory macrophages. We have previously identified accumulation of Sn+ macrophages as an important marker of disease progression versus remission in rat mesangial proliferative nephritis. The current study examined the significance of Sn+ macrophages in human proliferative glomerulonephritis.

METHODS

Frozen kidney sections from normal adult human kidney (n = 4) and pediatric nephropathy (n = 40) were stained for total macrophages (CD68+ cells), Sn+ macrophages, CD3+ T-cells and collagen type I by immunofluorescence. Leukocyte infiltration and the severity of glomerular lesions and interstitial damage were scored. A second protocol biopsy was performed in 27 cases and clinical and biopsy-based data obtained.

RESULTS

Sn+ macrophages were absent from glomeruli in normal adult human kidney and in thin basement membrane disease (n = 4), but were detected in 4 of 9 cases of purpura nephritis; 7 of 17 IgA nephropathy; 5 of 5 membranoproliferative glomerulonephritis, and 5 of 5 lupus nephritis. Sn+ macrophages were localized in areas of focal glomerular and interstitial damage. Two-colour immunostaining confirmed that Sn+ cells are a subset of total CD68+ macrophages. The number of glomerular Sn+ macrophages correlated with the degree of proteinuria and glomerular lesions (r = 0.44, P = 0.0045 and r = 0.82, P<0.0001; respectively), while interstitial Sn+ macrophages correlated with the degree of proteinuria and interstitial damage (r = 0.59, P<0.0001 and r = 0.75, P<0.0001; respectively). Combined immunostaining revealed that interstitial Sn+ macrophages and CD3+ T-cells co-localized in areas of tubulointerstitial damage with increased type I collagen deposition. There was significant correlation between the number of interstitial Sn+ macrophages and CD3+ T-cells (r = 0.74, P<0.0001). Most patients responded to a 2 year period of glucocorticoid therapy with a reduction in proteinuria and glomerular lesions and this correlated with the reduction in the number of glomerular Sn+ macrophages.

CONCLUSION

This study has identified Sn+ cells as a macrophage subset whose accumulation in the kidney correlates with proteinuria and histologic damage. These results, together with recent findings from animal studies, suggest that Sn+ macrophages may play an important role in progressive renal disease.