RORγt expression in Tregs promotes systemic lupus erythematosus via IL-17 secretion, alteration of Treg phenotype and suppression of Th2 responses

Systemic lupus erythematosus (SLE) is a common autoimmune disorder with a complex and poorly understood immunopathogenesis. However, a pathogenic role for the T helper type 17 (Th17) axis was demonstrated by many studies, while regulatory T cells (T_regs ) were shown to mediate protection. Recently, we and others characterized a novel and independent T cell population expressing both the T_reg characteristic transcription factor forkhead box protein 3 (FoxP3) and the Th17-defining retinoic acid receptor-related orphan nuclear receptor γt (RORγt). Studies in a model of acute glomerulonephritis unveiled potent regulatory, but also proinflammatory, functions of RORγt⁺ FoxP3⁺ T_regs . This bi-functional nature prompted us to suggest the name 'biT_regs '. Importantly, the pathogenic biT_reg effects were dependent upon expression of RORγt. We thus aimed to evaluate the contribution of RORγt⁺ FoxP3⁺ biT_regs to pristane-induced SLE and explored the therapeutic potential of interference with RORγt activation. Our analyses revealed expansion of IL-17 producing biT_regs in a distinctive time-course and organ-specific pattern, coincident with the development of autoimmunity and tissue injury. Importantly, specific ablation of RORγt activation in endogenous biT_regs resulted in significant amelioration of pristane-induced pulmonary vasculitis and lupus nephritis. As potential mechanisms underlying the observed protection, we found that secretion of IL-17 by biT_regs was abrogated completely in FoxP3^Cre  × RORC^fl/fl mice. Furthermore, T_regs showed a more activated phenotype after cell-specific inactivation of RORγt signalling. Finally, and remarkably, biT_regs were found to potently suppress anti-inflammatory Th2 immunity in a RORγt-dependent manner. Our study thus identifies biT_regs as novel players in SLE and advocates RORγt-directed interventions as promising therapeutic strategies.

UCH-L1 induces podocyte hypertrophy in membranous nephropathy by protein accumulation

Podocytes are terminally differentiated cells of the glomerular filtration barrier that react with hypertrophy in the course of injury such as in membranous nephropathy (MGN). The neuronal deubiquitinase ubiquitin C-terminal hydrolase L1 (UCH-L1) is expressed and activated in podocytes of human and rodent MGN. UCH-L1 regulates the mono-ubiquitin pool and induces accumulation of poly-ubiquitinated proteins in affected podocytes. Here, we investigated the role of UCH-L1 in podocyte hypertrophy and in the homeostasis of the hypertrophy associated "model protein" p27(Kip1). A better understanding of the basic mechanisms leading to podocyte hypertrophy is crucial for the development of specific therapies in MGN. In human and rat MGN, hypertrophic podocytes exhibited a simultaneous up-regulation of UCH-L1 and of cytoplasmic p27(Kip1) content. Functionally, inhibition of UCH-L1 activity and knockdown or inhibition of UCH-L1 attenuated podocyte hypertrophy by decreasing the total protein content in isolated glomeruli and in cultured podocytes. In contrast, UCH-L1 levels and activity increased podocyte hypertrophy and total protein content in culture, specifically of cytoplasmic p27(Kip1). UCH-L1 enhanced cytoplasmic p27(Kip1) levels by nuclear export and decreased poly-ubiquitination and proteasomal degradation of p27(Kip1). In parallel, UCH-L1 increased podocyte turnover, migration and cytoskeletal rearrangement, which are associated with known oncogenic functions of cytoplasmic p27(Kip1) in cancer. We propose that UCH-L1 induces podocyte hypertrophy in MGN by increasing the total protein content through altered degradation and accumulation of proteins such as p27(Kip1) in the cytoplasm of podocytes. Modification of both UCH-L1 activity and levels could be a new therapeutic avenue to podocyte hypertrophy in MGN.

A new role for the neuronal ubiquitin C-terminal hydrolase-L1 (UCH-L1) in podocyte process formation and podocyte injury in human glomerulopathies

Glomerular epithelial cell (podocyte) injury is characterized by foot process retraction, slit diaphragm reorganization, and degradation of podocyte-specific proteins. However, the mechanisms underlying podocyte injury are largely unknown. The ubiquitin C-terminal hydrolase-L1 (UCH-L1) is a key modulator of ubiquitin modification in neurons. Like neurons, UCH-L1 expression was associated with an undifferentiated status in cultured human podocytes, whereas differentiation and arborization decreased UCH-L1 and monoUb expression. Inhibition of UCH-L1 induced time and concentration-dependent process formation with alpha-actinin-4 distribution to the cell membrane and processes. An immunohistochemical approach was used to evaluate whether UCH-L1 expression was associated with podocyte injury in 15 different human glomerular diseases. Whereas normal kidneys expressed no UCH-L1 and little ubiquitin, a subset of human glomerulopathies associated with podocyte foot process effacement (membranous nephropathy, SLE class V, FSGS) de novo expressed UCH-L1 in podocyte cell bodies, nuclei, and processes. Interestingly, UCH-L1 expression correlated with podocyte ubiquitin content and internalization of the podocyte-specific proteins nephrin and alpha-actinin-4. In contrast, minimal change glomerulonephritis, a reversible disease, demonstrated minimal UCH-L1 and ubiquitin expression with intact alpha-actinin-4 but internalized nephrin. Glomerular kidney diseases typically not associated with foot process effacement (SLE class IV, ANCA+ necrotizing GN, amyloidosis, IgA nephritis) expressed intermediate to no UCH-L1 and ubiquitin. These studies show a role for UCH-L1 and ubiquitin modification in podocyte differentiation and injury.

Rapid development of severe end-organ damage in C57BL/6 mice by combining DOCA salt and angiotensin II

The C57BL/6 mouse strain serves as the genetic background of many transgenic and gene knockout models; however, this strain appears to be resistant to hypertension-induced renal injury. We developed a new model of hypertensive end-organ damage in C57BL/6 mice by combining deoxycorticosterone acetate (DOCA) and salt with angiotensin II infusion. The systolic blood pressure (SBP) was significantly elevated in DOCA salt-angiotensin II mice compared to control mice or mice treated individually with DOCA salt or angiotensin II. Hypertensive glomerular damage, increased expression of profibrotic and inflammatory genes, albuminuria, tubular casts, increased plasma cholesterol, cardiac hypertrophy, and fibrosis were found in mice treated with DOCA salt-angiotensin II. The SBP in the angiotensin II-infused group was further increased by increasing the infusion rate; only mild injury was observed in these mice, suggesting that blood pressure was not a causal factor. Removal of DOCA and the angiotensin pump lowered blood pressure to normal; however, albuminuria along with the glomerular and cardiac damage did not completely resolve. Our study describes a new model of hypertensive end-organ damage and repair in C57BL/6 mice.

Antihypertensive therapy upregulates renin and (pro)renin receptor in the clipped kidney of Goldblatt hypertensive rats

Recently, a (pro)renin receptor has been identified which mediates profibrotic effects independent of angiotensin II. Because antihypertensive therapy induces renal injury in the clipped kidney of two kidney-1-clip hypertensive rats, we examined the regulation of renin and the (pro)renin receptor in this model. Hypertensive Goldblatt rats were treated with increasing doses of the vasopeptidase inhibitor AVE 7688 after which the plasma renin and prorenin as well as the renal renin and (pro)renin receptor expression were measured. The vasopeptidase inhibitor dose-dependently lowered blood pressure, which was associated with a massive increase in plasma prorenin and renin as well as increased renal renin expression. The (pro)renin receptor was upregulated in the clipped kidney of the Goldblatt rat indicating a parallel upregulation of renin and its receptor in vivo. Immunohistochemistry showed a redistribution of renin upstream from the glomerulus in preglomerular vessels and renin staining in tubular cells. Expression of the (pro)renin receptor was increased in the vessels and tubules. This upregulation was associated with thickening of renin-positive vessels and tubulointerstitial damage. We propose that renin and the (pro)renin receptor may play a profibrotic role in the clipped kidney of Goldblatt rats treated for hypertension.

A new mouse model of immune-mediated podocyte injury

Podocytes play a major role in the initiation and progression of glomerular diseases and are a target of both immune-mediated and non-immune-mediated injury. To establish a mouse model of such injury, we preimmunized mice with Freunds adjuvant 5 days before intravenous injection of a rabbit polyclonal antibody directed against a murine podocyte cell line. For the next 7 weeks, we collected urine, serum, and kidney samples. Nephritic animals developed severe albuminuria, which was maximal on day 10. Histochemistry revealed diffuse mesangial matrix expansion. Mouse immunoglobulin G and complement were detected in a linear pattern along the glomerular filtration barrier and in the mesangial hinge region. Complement depletion, however, did not prevent proteinuria. Glomerular T cells were increased, whereas podocytes were significantly reduced. Glomerular foot processes were flattened in regions with mesangial matrix deposition as viewed by electron microscopy. Immunohistochemistry detected the injected anti-podocyte antibody exclusively at the glomerular tuft on all days examined. Immunoelectron microscopy localized the antibody to podocyte foot processes and the glomerular basement membrane, which was morphologically intact. This suggests that the podocyte was the main target of the antiserum. Our study establishes a new mouse model of immune-mediated podocyte injury.

A pitfall of glomerular sieving: profibrotic and matrix proteins derive from the Bowman's capsule and not the glomerular tuft in rats with renovascular hypertension

BACKGROUND

The glomeruli in the non-clipped kidney of rats with 2-kidney, 1-clip hypertension are a classical model for studying the mechanisms of glomerular injury.

METHODS

In the present study, we compared the glomerular expression of PAI-1 and collagen I alpha1 mRNA from glomeruli isolated by the classic technique of sieving with the recently developed technique of tissue laser microdissection. For quantification of mRNA from both methods, real-time PCR was used.

RESULTS

Real-time PCR revealed a 9.0 +/- 1.3- and a 7.1 +/- 0.2-fold induction of PAI-1 and collagen I alpha 1, respectively, in the glomeruli from hypertensive rats isolated by sieving. However, in situ hybridization and microdissection revealed that expression of both mRNAs was mainly from the Bowman's capsule and not from the glomerular tuft (10.7 +/- 1.3- and 7.2 +/- 0.6-fold higher induction in whole glomeruli compared with tuft alone).

CONCLUSION

This emphasizes that studies focusing on processes in the mesangium, endothelial cells or podocytes should not rely on glomeruli obtained by sieving. Rather, a technique like the laser microdissection or in situ hybridization should be applied which allows the clear separation of different glomerular and periglomerular compartments.

PDGF-B gene single-nucleotide polymorphisms are not predictive for disease onset or progression of IgA nephropathy

BACKGROUND

Few genetic factors have been identified that determine susceptibility to and progression of IgA-nephropathy (IgAN). Given that IgAN is usually characterized by mesangioproliferative glomerulonephritis and that PDGF-B is of central pathophysiological relevance in this process, we analyzed four single-nucleotide polymorphisms (SNPs) of the PDGF-B gene to evaluate a possible association of these SNPs with disease onset and progression, histological grading and responses to ACE inhibitor (ACEi) therapy.

METHODS

The total study population consisted of 195 IgAN patients (127 from southern Italy and 68 from northern Germany) and 200 healthy controls (100 from each region). All four SNPs were in Hardy-Weinberg equilibrium and genotype distributions did not differ between patients and controls in either region.

RESULTS

SNP distribution in Italian patients reaching end-stage renal disease (n=45) also was not significantly different from patients maintaining a serum creatinine below 1.2 mg/dl (n=60) during 5.6 +/- 5.5 years of follow-up. Furthermore, we failed to detect significant effects of any SNP on the slope of 1/serum creatinine, proteinuria level or the antiproteinuric response to ACEi. Additionally, particular PDGF-B genotypes did not correlate with histological grading using the Lee classification.

CONCLUSION

We conclude that none of the four PDGF-B SNPs is related to the onset of IgAN in two different populations and that none of them has a major influence on the course of IgAN.

Antihypertensive therapy induces compartment-specific chemokine expression and a Th1 immune response in the clipped kidney of Goldblatt hypertensive rats

The present study examined the pathogenesis of interstitial inflammation and fibrosis in antihypertensively treated rats with two-kidney, one-clip hypertension. Hypertensive rats were randomized into four groups: no treatment and moderate, intermediate, and intensified lowering of blood pressure with increasing doses of a vasopeptidase inhibitor for 6 wk. The vasopeptidase inhibitor dose dependently lowered blood pressure. The tubulointerstitial damage was accompanied by a diffuse infiltration of mononuclear cells and circumscript mononuclear inflammatory cell cluster formation consisting mainly of T cells and to a lesser degree of macrophages and B cells. Real-time PCR analyses showed a dose-dependent induction of MCP-1 and the Th1-type chemokines IP10 and Mig as well as their receptor CXCR3 and the Th1 cytokine IFN-γ. In situ hybridization and laser microdissection revealed a strong expression of these Th1-associated transcripts in the clusters and, in the case of MCP-1, also diffusely in the interstitium. The inflammation was accompanied by the appearance of myofibroblasts and synthesis of the fibrogenic factor plasminogen activator inhibitor-1 as well as the collagenase matrix metalloproteinase-2, leading to collagen I upregulation and interstitial scarring. No inflammation or fibrosis was found in normotensive rats treated with the vasopeptidase inhibitor. The renal injury in the clipped kidney is accompanied by compartment-specific chemokine expression and cell cluster formation of Th1 specificity associated with upregulation of fibrogenic proteins and matrix metalloproteinases. These findings suggest that the Th1 chemokines IP10 and Mig as well as their receptor CXCR3 are potential targets for therapeutic interventions in ischemic nephropathy.

Statin therapy in patients with chronic kidney disease: to use or not to use

Dyslipdemia is a common complication of chronic kidney disease (CKD) and contributes to high cardiovascular morbidity and mortality of CKD patients. Experimental studies have demonstrated that lipids induce glomerular and tubulointerstitial injury and that lipid-lowering treatments ameliorate renal injury. Therapy with statins not only has the potential to lower cardiovascular morbidity and mortality in patients with CKD but also to slow progression of renal disease. Whereas the guidelines for treatment of hyperlipidaemia in nonrenal patients are based on prospective, randomized, placebo-controlled mega-trials, such data are not available for CKD patients. This review outlines the limited information currently available on the effect of statins among patients with CKD and summarizes the ongoing randomized trials designed to address this question.

[Dysfunction of a kidney allograft with life-threatening results]

Post-transplant lymphoproliferative disease (PTLD) is a serious complication after organ transplantation. We describe the case of a 45-year old patient who developed an EBV associated B-cell lymphoma in a cadaveric renal allograft. This case underscores the importance of considering PTLD as possible differential diagnosis for allograft dysfunction. Careful diagnostic evaluation should be undertaken in patients who present with risk factors for development of PTLD such as high doses of immunosuppression for rejection therapy, suspicious EBV serologies or negative EBV serologies before transplantation. PTLD can be of donor or recipient origin. Independent of its origin PTLD needs an immediate therapy which depends on the histology of the lymphoma and on the clinical conditions of the patient. Therapeutic options are reduction of the immunosuppression, chemotherapy or radiation, administration of lymphocyte-specific antibodies or removal of the kidney allograft.

Erk 1,2 phosphorylates p27(Kip1): Functional evidence for a role in high glucose-induced hypertrophy of mesangial cells

AIMS/HYPOTHESIS

Mesangial cell hypertrophy is one of the earliest morphological abnormalities of diabetic nephropathy. We have previously shown that high glucose induces p27(Kip1) by a post-transcriptional mechanism and that mesangial cell hypertrophy depends on G(1)-phase arrest mediated by this CDK-inhibitor. However, it remains poorly understood how high glucose stimulates p27(Kip1) expression in mesangial cells.

METHODS

Mesangial cells were isolated from p27(Kip1) +/+ and -/- mice and characterized by light microscopy and immunohistochemistry. It was tested by Western blotting and autoradiography whether high glucose medium activates Erk 1,2 and whether this activation phosphorylates p27(Kip1). The three consensus phosphorylation sites of p27(Kip1) were mutated and these constructs were expressed in p27(Kip1) -/- mesangial cells. Hypertrophy was assessed by different methods.

RESULTS

High glucose stimulates phosphorylation of MAP kinases Erk 1,2 in p27(Kip1 )+/+ and -/- mesangial cells. Activation of Erk 1,2 leads to phosphorylation of p27(Kip1 )in vitro and in vivo. Mutations of serine(10) or threonine(187) still supported high glucose-induced hypertrophy. In contrast, a mutation of serine(178) converted the hypertrophic response into a proliferative phenotype. Mutation of serine(178) leads to the attenuated expression of p27(Kip1) protein in the presence of high glucose.

CONCLUSIONS/INTERPRETATION

Our study shows that high glucose stimulates Erk 1,2 that phosphorylate p27(Kip1) at serine(178) increasing its expression. This is an important molecular mechanism of high glucose-induced hypertrophy of mesangial cells.

Membran�se Glomerulonephritis

Membranous nephropathy remains the most common cause of nephrotic syndrome in adults. The common variant is idiopathic membranous nephropathy with no evidence of any known precipitating factors. Membranous nephropathy also occurs as a secondary form in association with inflammatory or neoplastic diseases. Prognosis is mostly favorable as shown by the frequency of spontaneous remissions which averages 30%, although about one-third of patients progress to end-stage renal failure. Risk factors for a poor prognosis include severe proteinuria, hypertension, older age, male gender and impaired renal function. Therapy should include an ACE-Inhibitor and/or angiotensin-II receptor blocker to lower proteinuria (blood pressure < or =130/80 mmHg). The majority of patients should be observed for six months whilst receiving conservative treatment before deciding about an immunosuppressive approach. The debate over its management continues today. Steroids alone are ineffective. Evidence-based medicine supports the use of cyclosporine or the Ponticelli regimen (monthly cycling routine of chlorambucil or cyclophosphamide alternating with prednisone).