[Show abstract][Hide abstract] ABSTRACT: C3 glomerulopathy (C3G) is a severe kidney disease for which no specific therapy exists. The causes of C3G are heterogeneous, and defective complement regulation is often linked to C3G pathogenesis. Copy number variations in the complement factor H-related (CFHR) gene cluster on chromosome 1q32 and CFHR5 mutant proteins associate with this disease. Here, we identified CFHR5 as a pattern recognition protein that binds to damaged human endothelial cell surfaces and to properdin, the human complement activator. We found the two N-terminal short consensus repeat domains of CFHR5 contact properdin and mediate dimer formation. These properdin-binding segments are duplicated in two mutant CFHR5 proteins, CFHR2-CFHR5Hyb from German patients with C3G and CFHR5Dup from Cypriot patients with C3G. Each of these mutated proteins assembled into large multimeric complexes and, compared to CFHR5, bound damaged human cell surfaces and properdin with greater intensity and exacerbated local complement activation. This enhanced surface binding and properdin recruitment was further evidenced in the mesangia of a transplanted and explanted kidney from a German patient with a CFHR2-CFHR5Hyb protein. Enhanced properdin staining correlated with local complement activation with C3b and C5b-9 deposition on the mesangial cell surface in vitro. This gain of function in complement activation for two disease-associated CFHR5 mutants describes a new disease mechanism of C3G, which is relevant for defining appropriate treatment options for this disorder.
Journal of the American Society of Nephrology 10/2015; DOI:10.1681/ASN.2015020212 · 9.34 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Based on new pathophysiological discoveries in recent years, a new classification of glomerulonephritis with dominant or codominant C3 deposits was introduced in 2010, which represents the essential subgroup of C3 glomerulopathy (C3G). Although secondary causes can lead to immune complex-mediated membranoproliferative glomerulonephritis (MPGN), the major trigger of C3G is primarily dysregulation of the alternative complement pathway, which can often become apparent in the form of MPGN as well as various light microscopic phenotypes. Knowledge of the underlying pathophysiology of the disease is of high relevance for a subsequent differentiation after assessment of secondary causes. Initiation of a comprehensive analysis of complement factors, antibody screening and genetic analyses, should be part of a subsequent diagnostic work-up. Even though systematic evidence from studies is lacking, knowledge of the individual pathophysiology provides a robust foundation for the application of available therapeutic approaches for these often rapidly progressing forms of kidney disease, which frequently recur after kidney transplantation. This overview summarizes the current state of knowledge in the form of a (national German) expert consensus on the state of the art diagnostic work-up for C3 dominant glomerulonephritis and MPGN.
Der Nephrologe 07/2015; 10(4):327-340. DOI:10.1007/s11560-014-0978-6
[Show abstract][Hide abstract] ABSTRACT: Reduced nephron number predisposes to hypertension and kidney disease. Interaction of the branching ureteric bud and surrounding mesenchymal cells determines nephron number. Since oxygen supply may be critical for intrauterine development, we tested whether hypoxia and hypoxia-inducible factor-1α (HIF-1α) influence nephrogenesis. We found that HIF-1α is required for branching of MDCK cells. In addition, culture of metanephric mouse kidneys with ureteric bud cell-specific stabilization or knockout of HIF-1α revealed a positive impact of HIF-1α on nephrogenesis. In contrast, widespread stabilization of HIF-1α in metanephric kidneys through hypoxia or HIF stabilizers impaired nephrogenesis, and pharmacological HIF inhibition enhanced nephrogenesis. Several lines of evidence suggest an inhibitory effect through the hypoxia response of mesenchymal cells. HIF-1α was expressed in mesenchymal cells during nephrogenesis. Expression of the anti-branching factors Bmp4 and Vegfa, secreted by mesenchymal cells, was increased upon HIF stabilization. The conditioned medium from hypoxic metanephric kidneys inhibited MDCK branching, which was partially rescued by Vegfa antibodies. Thus, the effect of HIF-1α on nephrogenesis appears context dependent. While HIF-1α in the ureteric bud is of importance for proper branching morphogenesis, the net effect of hypoxia-induced HIF activation in the embryonic kidney appears to be mesenchymal cell-dependent inhibition of ureter branching.Kidney International advance online publication, 22 July 2015; doi:10.1038/ki.2015.214.
Kidney International 07/2015; DOI:10.1038/ki.2015.214 · 8.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Rare autosomal dominant tubulointerstitial kidney disease is caused by mutations in the genes encoding uromodulin (UMOD), hepatocyte nuclear factor-1β (HNF1B), renin (REN), and mucin-1 (MUC1). Multiple names have been proposed for these disorders, including 'Medullary Cystic Kidney Disease (MCKD) type 2', 'Familial Juvenile Hyperuricemic Nephropathy (FJHN)', or 'Uromodulin-Associated Kidney Disease (UAKD)' for UMOD-related diseases and 'MCKD type 1' for the disease caused by MUC1 mutations. The multiplicity of these terms, and the fact that cysts are not pathognomonic, creates confusion. Kidney Disease: Improving Global Outcomes (KDIGO) proposes adoption of a new terminology for this group of diseases using the term 'Autosomal Dominant Tubulointerstitial Kidney Disease' (ADTKD) appended by a gene-based subclassification, and suggests diagnostic criteria. Implementation of these recommendations is anticipated to facilitate recognition and characterization of these monogenic diseases. A better understanding of these rare disorders may be relevant for the tubulointerstitial fibrosis component in many forms of chronic kidney disease.Kidney International advance online publication, 4 March 2015; doi:10.1038/ki.2015.28.
Kidney International 03/2015; 88(4). DOI:10.1038/ki.2015.28 · 8.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: In der Nachsorge nierentransplantierter Patienten kommt der nephropathologischen Begutachtung der Transplantatnierenbiopsie eine wesentliche Bedeutung zu. Die kontinuierliche Überarbeitung der diagnostischen Kriterien der Transplantatabstoßung durch die sog. BANFF-Konferenzen seit 1997 hat einen wesentlichen Anteil zur Systematisierung und damit zur Diagnosesicherheit beigetragen. Die letzte Überarbeitung 2013 mit dem Einschluss der C4d-negativen antikörpervermittelten Abstoßung schließt hier eine diagnostische Lücke, hat aber auch dazu beigetragen, dass mehr antikörpervermittelte Abstoßungen diagnostiziert werden. Die therapeutischen Optionen bei zellulären und antikörpervermittelten Abstoßungen sind multimodal, basieren jedoch auf geringer Evidenz. Zelluläre Rejektionen und akute/aktive humorale Rejektionen sind in der Regel dennoch gut behandelbar. Vor allem die chronisch, aktive humorale Rejektion stellt den Kliniker weiterhin vor große Herausforderungen, da viele der Therapieoptionen eingreifend und teuer sind und potenziell zu schweren Infektkomplikationen führen können. Der Artikel gibt eine Übersicht über die pathologischen Veränderungen entsprechend der BANFF-Klassifikation und erörtert spezifisch zu den unterschiedlichen Rejektionsformen die therapeutischen Optionen.
Der Nephrologe 03/2015; 10(2):113-123. DOI:10.1007/s11560-014-0912-y
[Show abstract][Hide abstract] ABSTRACT: To investigate whether bortezomib, a proteasome inhibitor approved for treatment of multiple myeloma, induces clinically relevant plasma cell (PC) depletion in patients with active, refractory systemic lupus erythematosus (SLE).
Twelve patients received a median of two (range 1-4) 21-day cycles of intravenous bortezomib (1.3 mg/m(2)) with the coadministration of dexamethasone (20 mg) for active SLE. Disease activity was assessed using the SLEDAI-2K score. Serum concentrations of anti-double-stranded DNA (anti-dsDNA) and vaccine-induced protective antibodies were monitored. Flow cytometry was performed to analyse peripheral blood B-cells, PCs and Siglec-1 expression on monocytes as surrogate marker for type-I interferon (IFN) activity.
Upon proteasome inhibition, disease activity significantly declined and remained stable for 6 months on maintenance therapies. Nineteen treatment-emergent adverse events occurred and, although mostly mild to moderate, resulted in treatment discontinuation in seven patients. Serum antibody levels significantly declined, with greater reductions in anti-dsDNA (∼60%) than vaccine-induced protective antibody titres (∼30%). Bortezomib significantly reduced the numbers of peripheral blood and bone marrow PCs (∼50%), but their numbers increased between cycles. Siglec-1 expression on monocytes significantly declined.
These findings identify proteasome inhibitors as a putative therapeutic option for patients with refractory SLE by targeting PCs and type-I IFN activity, but our results must be confirmed in controlled trials.
Published by the BMJ Publishing Group Limited. For permission to use (where not already granted under a licence) please go to http://group.bmj.com/group/rights-licensing/permissions.
Annals of the Rheumatic Diseases 02/2015; 74(7). DOI:10.1136/annrheumdis-2014-206016 · 10.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: For decades, ill-defined autosomal dominant renal diseases have been reported, which originate from tubular cells and lead to tubular atrophy and interstitial fibrosis. These diseases are clinically indistinguishable, but caused by mutations in at least four different genes: UMOD, HNF1B, REN, and, as recently described, MUC1. Affected family members show renal fibrosis in the biopsy and gradually declining renal function, with renal failure usually occurring between the third and sixth decade of life. Here we describe 10 families and define eligibility criteria to consider this type of inherited disease, as well as propose a practicable approach for diagnosis. In contrast to what the frequently used term 'Medullary Cystic Kidney Disease' implies, development of (medullary) cysts is neither an early nor a typical feature, as determined by MRI. In addition to Sanger and gene panel sequencing of the four genes, we established SNaPshot minisequencing for the predescribed cytosine duplication within a distinct repeat region of MUC1 causing a frameshift. A mutation was found in 7 of 9 families (3 in UMOD and 4 in MUC1), with one indeterminate (UMOD p.T62P). On the basis of clinical and pathological characteristics we propose the term 'Autosomal Dominant Tubulointerstitial Kidney Disease' as an improved terminology. This should enhance recognition and correct diagnosis of affected individuals, facilitate genetic counseling, and stimulate research into the underlying pathophysiology.Kidney International advance online publication, 26 March 2014; doi:10.1038/ki.2014.72.
Kidney International 03/2014; 86(3). DOI:10.1038/ki.2014.72 · 8.56 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Background Long-lived plasma cells secreting pathogenic autoantibodies may contribute to refractory disease courses of SLE, because long-lived plasma cells are resistant to conventional therapies (1). We showed that the proteasome inhibitor bortezomib, which is approved for the treatment of relapsed multiple myeloma, eliminates plasma cells including long-lived ones and ameliorates lupus nephritis in mouse models of SLE (2).
Objectives We collected data of all refractory SLE patients treated with bortezomib in our clinics to investigate the efficacy and potential side effects of bortezomib treatment in a case series.
Methods At 3 university centers we treated 13 patients with bortezomib, who had not sufficiently responded to tr did not tolerate conventional drugs. The patients had given informed consent to off-label treatment before they received bortezomib intravenously at a dose of 1.3 mg/m2 body surface at day 1, 4 and 8, some additionally at day 11. Most patients also received 20 mg of dexamethasone together with bortezomib. Treatment cycles were repeated up to four times with an time interval of usually 10 to 14 days in-between cycles. The following clinical and laboratory parameters were monitored: SLEDAI, urine sediment, circulating plasma cells, 24 hour-proteinuria, creatinine clearance, complement C3 and C4, antibodies to double-stranded (ds) DNA and ENA, vaccine antibody titers to hepatits B surface antigen and tetanus toxoid.
Results No serious side effects were observed upon bortezomib treatment. One patient experienced myalgias, fever and headache next day after the first 3 bortezomib applications. Three of seven patients who were treated with 4 bortezomib injections per cycle developed polyneuropathies, which were reversible upon discontinuation of treatment. One patient developed a reversible thrombocytopenia after 4 treatment cycles, no other relevant hematologic toxicities were observed. The disease activity score SLEDAI and anti-dsDNA antibody titers significantly decreased in all patients, in a few patients anti-dsDNA nearly disappeared, whereas ENAs were decreased by up to 50% only. In general, complement levels increased. In all patients with active lupus nephritis, proteinuria declined within 6 weeks of treatment; one patient reached normal protein excretion within 4 months. Protective vaccine antibody titers to hepatitis B surface antigen and tetanus toxoid decreased, but remained within the protective range. Total IgG levels slightly declined in most patients.
Conclusions The proteasome inhibitor bortezomib may provide an effective new therapy for refractory SLE. Pathogenic antibodies, but also protective antibody titers decline upon bortezomib treatment. Clinical trials should be initiated to explore the use of bortezomib as induction therapy in patients with refractory SLE.
Disclosure of Interest None Declared
Annals of the Rheumatic Diseases 01/2014; 71(Suppl 3):540-540. DOI:10.1136/annrheumdis-2012-eular.3150 · 10.38 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The renal disorder C3 glomerulopathy with dense deposit disease (C3G-DDD) pattern results from complement dysfunction and primarily affects children and young adults. There is no effective treatment, and patients often progress to end-stage renal failure. A small fraction of C3G-DDD cases linked to factor H or C3 gene mutations as well as autoantibodies have been reported. Here, we examined an index family with 2 patients with C3G-DDD and identified a chromosomal deletion in the complement factor H-related (CFHR) gene cluster. This deletion resulted in expression of a hybrid CFHR2-CFHR5 plasma protein. The recombinant hybrid protein stabilized the C3 convertase and reduced factor H-mediated convertase decay. One patient was refractory to plasma replacement and exchange therapy, as evidenced by the hybrid protein quickly returning to pretreatment plasma levels. Subsequently, complement inhibitors were tested on serum from the patient for their ability to block activity of CFHR2-CFHR5. Soluble CR1 restored defective C3 convertase regulation; however, neither eculizumab nor tagged compstatin had any effect. Our findings provide insight into the importance of CFHR proteins for C3 convertase regulation and identify a genetic variation in the CFHR gene cluster that promotes C3G-DDD. Monitoring copy number and sequence variations in the CFHR gene cluster in C3G-DDD and kidney patients with C3G-DDD variations will help guide treatment strategies.
The Journal of clinical investigation 12/2013; 124(1). DOI:10.1172/JCI71866 · 13.22 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The inhibitor of apoptosis protein survivin is a bifunctional molecule which regulates cellular division and survival. We have previously shown that survivin protein can be found at high concentrations in the adult kidney, particularly in the proximal tubules. Here, survivin is localized primarily at the apical membrane, a pattern which may indicate absorption of the protein. Several proteins in primary urine are internalised by megalin, an endocytosis receptor, which is in principle found in the same localization as survivin. Immunolabeling for survivin in different species confirmed survivin signal localising to the apical membrane of the proximal tubule. Immuno-electron microscopy also showed apical localisation of survivin in human kidneys. Furthermore, in polarised human primary tubular cells endogenous as well as external recombinant survivin stored in the apical region of the cells. Co-staining of survivin and megalin by immunohistochemistry and immuno-electron microscopy confirmed colocalization. Finally, by surface plasmon resonance we were able to demonstrate that survivin binds megalin and cubilin and that megalin knockout mice loose survivin through the urine. Survivin accumulates at the apical membrane of the renal tubule by reuptake, which is achieved by the endocytic receptor megalin, collaborating with cubilin. For this to occur, survivin will have to circulate in blood and be filtered into the primary urine. It is not known at this stage what the functional role of tubular survivin is. However, a small number of experimental and clinical reports implicate that renal survivin is important for functional integrity of the kidney.
[Show abstract][Hide abstract] ABSTRACT: The differential diagnosis of T cell-mediated rejection (TCMR) and BK-virus nephropathy (BKVN) in renal transplant biopsies is notoriously difficult. Therefore, attempts were made to differentiate between the two by characterizing the immune cell infiltrate. Using immunohistochemistry, the distribution of immune cell (sub)populations such as CD4(+) T helper (TH), TH1, TH2, CD8(+) cytotoxic T cells, regulatory T cells, B cells, plasma cells and follicular dendritic cells was determined in a total of 38 renal biopsy specimens. In addition, the expression of the HLA class I antigen presentation machinery (APM) components was investigated. In general, the frequency of T cells was higher than B cells, and TH cells outnumbered cytotoxic T cells with a predominance of TH2 over TH1 cells. In BKVN, a significantly higher number of plasma cells was observed (P = .028), and interstitial fibrosis and tubular atrophy was more pronounced in BKVN (P = .007) compared to TCMR. The expression of components of the HLA class I APM was not affected by the infection with BK virus compared to TCMR. These findings indicate a TH2 shift in renal transplants in the context of alloreactive and virus-induced inflammation maybe as a consequence of immunosuppression, which usually targets T cell reaction. The predominance of plasma cells might underline an important role of humoral immunity in BKVN. Moreover, BK virus does not seem to modulate the expression of HLA class I APM as a strategy of immune evasion.
Human pathology 03/2012; 43(9):1453-62. DOI:10.1016/j.humpath.2011.11.006 · 2.77 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Backgroundand objectives Long-lived memory plasma cells secreting pathogenic autoantibodies are resistant to conventional immunosuppression and B cell targeting therapies. Bortezomib, an approved drug for relapsing multiple myeloma, efficiently depletes short- and long-lived plasma cells and ameliorates nephritis in murine lupus models. Therefore, the authors studied the efficacy of bortezomib in refractory SLE patients in a case series.
Materials and methods At three university centers, 13 SLE patients refractory or intolerant to cyclophosphamide, MMF and/or rituximab were treated with bortezomib intravenously at a dose of 1.3 mg/m2 body surface area on days 1, 4, and 8 and, in some cases, on day 11. Most patients received 20mg of dexamethasone together with bortezomib. Treatment cycles were repeated up to four times with an interruption of usually 10 to 14 days between cycles. The following clinical and laboratory parameters were monitored: SLEDAI disease activity score, 24 h proteinuria, creatinine clearance, circulating plasma cells, complement C3 and C4, IgG, IgA, IgM, antibodies to dsDNA and ENA, and vaccine titers.
Results SLEDAI and antibody levels significantly decreased under bortezomib while complement levels increased. In seven patients with active nephritis, proteinuria declined within 6 weeks of treatment, and normalised after four months in one case. Anti-dsDNA antibodies decreased by up to 90%, anti-ENA and protective vaccine titers by up to 50%, and immunoglobulin levels by up to 30%. Circulating plasmablasts dropped substantially. Serious side effects were not observed. One patient experienced myalgia, fever and headache 1 day after the first 3 bortezomib doses. Three of five patients treated with four bortezomib injections per cycle developed polyneuropathies, which were reversible upon discontinuation of treatment. One patient developed reversible thrombocytopenia after four treatment cycles.
Conclusions The proteasome inhibitor bortezomib may effectively reduce disease activity in refractory SLE patients by depleting plasma cells. The data encourage initiation of clinical trials with bortezomib in refractory SLE and support the relevance of plasma cells in the pathogenesis of this autoimmune disease.
Annals of the Rheumatic Diseases 02/2012; 71(Suppl 1):A15-A16. DOI:10.1136/annrheumdis-2011-201230.34 · 10.38 Impact Factor