Role of factor H-related protein 3 in Pseudomonas aeruginosa bloodstream infections.

Pseudomonas aeruginosa is a leading cause of nosocomial bloodstream infections. The outcome of these infections depends on the virulence of the microorganism as well as host-related conditions and factors. The complement system plays a crucial role in defense against bloodstream infections. P. aeruginosa counteracts complement attack by recruiting Factor H (FH) that inhibits complement amplification on the bacterial surface. Factor H-related proteins (FHRs) are a group of plasma proteins evolutionarily related to FH that have been postulated to interfere this bacterial evasion mechanism. In this study, we demonstrate that FHR-3 competes with purified FH for binding to P. aeruginosa and identify EF-Tu as a common bacterial target for both complement regulator factors. Importantly, elevated levels of FHR-3 in human serum promote complement activation, leading to increased opsonization and killing of P. aeruginosa. Conversely, physiological concentrations of FHR-3 have no significant effect. Our findings suggest that FHR-3 may serve as a protective host factor against P. aeruginosa infections.

Factor H-related protein 1 in systemic lupus erythematosus.

Background: Factor H (FH) is a major soluble inhibitor of the complement system and part of a family comprising five related proteins (FHRs 1-5). Deficiency of FHR1 was described to be linked to an elevated risk of systemic lupus erythematosus (SLE). As FHR1 can partially antagonize the functionality of FH, an altered FHR1/FH ratio could not only enhance SLE vulnerability but also affect the disease expression. This study focuses on the analysis of FH and FHR1 at a protein level, and the occurrence of anti-FH autoantibodies (anti-FH) in a large cohort of SLE patients to explore their association with disease activity and/or expression. Methods: We assessed FH and FHR1 levels in plasma from 378 SLE patients compared to 84 healthy controls (normal human plasma, NHP), and sera from another cohort of 84 healthy individuals (normal human serum, NHS), using RayBio® CFH and CFHR1 ELISA kits. Patients were recruited by the Swiss SLE Cohort Study (SSCS). Unmeasurable FHR1 levels were all confirmed by Western blot, and in a subgroup of patients by PCR. Anti-FH were measured in SLE patients with non-detectable FHR1 levels and matched control patients using Abnova's CFH IgG ELISA kit. Results: Overall, FH and FHR1 levels were significantly higher in healthy controls, but there was no significant difference in FHR1/FH ratios between SLE patients and NHPs. However, SLE patients showed a significantly higher prevalence of undetectable FHR1 compared to all healthy controls (35/378 SLE patients versus 6/168 healthy controls; p= 0.0214, OR=2.751, 95% CI = 1.115 - 8.164), with a consistent trend across all ethnic subgroups. Levels of FH and FHR1, FHR1/FH ratios and absence of FHR1 were not consistently associated with disease activity and/or specific disease manifestations, but absence of FHR1 (primarily equivalent to CFHR1 deficiency) was linked to the presence of anti-FH in SLE patients (p=0.039). Conclusions: Deficiency of FHR1 is associated with a markedly elevated risk of developing SLE. A small proportion of FHR1-deficient SLE patients was found to have autoantibodies against FH but did not show clinical signs of microangiopathy.

Enhancement of complement-dependent cytotoxicity by linking factor-H derived short consensus repeats 19-20 to CD20 antibodies.

Antibody-mediated complement-dependent cytotoxicity (CDC) on malignant cells is regulated by several complement control proteins, including the inhibitory complement factor H (fH). fH consists of 20 short consensus repeat elements (SCRs) with specific functional domains. Previous research revealed that the fH-derived SCRs 19-20 (SCR1920) can displace full-length fH on the surface of chronic lymphocytic leukemia (CLL) cells, which sensitizes CLL cells for e.g. CD20-targeting therapeutic monoclonal antibody (mAb) induced CDC. Therefore, we constructed lentiviral vectors for the generation of cell lines that stably produce mAb-SCR-fusion variants starting from the clinically approved parental mAbs rituximab, obinutuzumab and ofatumumab, respectively. Flow-cytometry revealed that the modification of the mAbs by the SCRs does not impair the binding to CD20. Increased in vitro lysis potency compared to their parental mAbs was corroborated by showing specific and dose dependent target cell elimination by CDC when compared to their parental mAbs. Lysis of CLL cells was not affected by the depletion of NK cells, suggesting that antibody-dependent cellular cytotoxicity plays a minor role in this context. Overall, this study emphasizes the crucial role of CDC in the elimination of CLL cells by mAbs and introduces a novel approach for enhancing CDC by directly fusing fH SCR1920 with mAbs.

Complement-Coagulation Cross-talk: Factor H-mediated regulation of the Complement Classical Pathway activation by fibrin clots.

The classical pathway of the complement system is activated by the binding of C1q in the C1 complex to the target activator, including immune complexes. Factor H is regarded as the key downregulatory protein of the complement alternative pathway. However, both C1q and factor H bind to target surfaces via charge distribution patterns. For a few targets, C1q and factor H compete for binding to common or overlapping sites. Factor H, therefore, can effectively regulate the classical pathway activation through such targets, in addition to its previously characterized role in the alternative pathway. Both C1q and factor H are known to recognize foreign or altered-self materials, e.g., bacteria, viruses, and apoptotic/necrotic cells. Clots, formed by the coagulation system, are an example of altered self. Factor H is present abundantly in platelets and is a well-known substrate for FXIIIa. Here, we investigated whether clots activate the complement classical pathway and whether this is regulated by factor H. We show here that both C1q and factor H bind to the fibrin formed in microtiter plates and the fibrin clots formed under in vitro physiological conditions. Both C1q and factor H become covalently bound to fibrin clots, and this is mediated via FXIIIa. We also show that fibrin clots activate the classical pathway of complement, as demonstrated by C4 consumption and membrane attack complex detection assays. Thus, factor H downregulates the activation of the classical pathway induced by fibrin clots. These results elucidate the intricate molecular mechanisms through which the complement and coagulation pathways intersect and have regulatory consequences.

An unusual case of adult-onset still's disease complicated with anti-complement factor H antibodies associated atypical haemolytic uraemic syndrome.

BACKGROUND: Atypical haemolytic uremic syndrome (aHUS) is an uncommon form of thrombotic microangiopathy (TMA). However, it remains difficult to diagnose the disease early, given its non-specific and overlapping presentation to other conditions such as thrombotic thrombocytopenic purpura and typical HUS. It is also important to identify the underlying causes and to distinguish between primary (due to a genetic abnormality leading to a dysregulated alternative complement pathway) and secondary (often attributed by severe infection or inflammation) forms of the disease, as there is now effective treatment such as monoclonal antibodies against C5 for primary aHUS. However, primary aHUS with severe inflammation are often mistaken as a secondary HUS. We presented an unusual case of adult-onset Still's disease (AOSD) with macrophage activation syndrome (MAS), which is in fact associated with anti-complement factor H (anti-CFH) antibodies related aHUS. Although the aHUS may be triggered by the severe inflammation from the AOSD, the presence of anti-CFH antibodies suggests an underlying genetic defect in the alternative complement pathway, predisposing to primary aHUS. One should note that anti-CFH antibodies associated aHUS may not always associate with genetic predisposition to complement dysregulation and can be an autoimmune form of aHUS, highlighting the importance of genetic testing. CASE PRESENTATION: A 42 years old man was admitted with suspected adult-onset Still's disease. Intravenous methylprednisolone was started but patient was complicated with acute encephalopathy and low platelet. ADAMTS13 test returned to be normal and concurrent aHUS was eventually suspected, 26 days after the initial thrombocytopenia was presented. Plasma exchange was started and patient eventually had 2 doses of eculizumab after funding was approved. Concurrent tocilizumab was also used to treat the adult-onset Still's disease with MAS. The patient was eventually stabilised and long-term tocilizumab maintenance treatment was planned instead of eculizumab following haematology review. Although the aHUS may be a secondary event to MAS according to haematology opinion and the genetic test came back negative for the five major aHUS gene, high titre of anti-CFH antibodies was detected (1242 AU/ml). CONCLUSION: Our case highlighted the importance of prompt anti-CFH antibodies test and genetic testing for aHUS in patients with severe AOSD and features of TMA. Our case also emphasized testing for structural variants within the CFH and CFH-related proteins gene region, as part of the routine genetic analysis in patients with anti-CFH antibodies associated aHUS to improve diagnostic approaches.

Mapping the interaction sites of human and avian influenza A viruses and complement factor H.

The complement system is an innate immune mechanism against microbial infections. It involves a cascade of effector molecules that is activated via classical, lectin and alternative pathways. Consequently, many pathogens bind to or incorporate in their structures host negative regulators of the complement pathways as an evasion mechanism. Factor H (FH) is a negative regulator of the complement alternative pathway that protects "self" cells of the host from non-specific complement attack. FH has been shown to bind viruses including human influenza A viruses (IAVs). In addition to its involvement in the regulation of complement activation, FH has also been shown to perform a range of functions on its own including its direct interaction with pathogens. Here, we show that human FH can bind directly to IAVs of both human and avian origin, and the interaction is mediated via the IAV surface glycoprotein haemagglutinin (HA). HA bound to common pathogen binding footprints on the FH structure, complement control protein modules, CCP 5-7 and CCP 15-20. The FH binding to H1 and H3 showed that the interaction overlapped with the receptor binding site of both HAs, but the footprint was more extensive for the H3 HA than the H1 HA. The HA - FH interaction impeded the initial entry of H1N1 and H3N2 IAV strains but its impact on viral multicycle replication in human lung cells was strain-specific. The H3N2 virus binding to cells was significantly inhibited by preincubation with FH, whereas there was no alteration in replicative rate and progeny virus release for human H1N1, or avian H9N2 and H5N3 IAV strains. We have mapped the interaction between FH and IAV, the in vivo significance of which for the virus or host is yet to be elucidated.

Targeted complement inhibition using bispecific antibodies that bind local antigens and endogenous complement regulators.

Complement activation protects against infection but also contributes to pathological mechanisms in a range of clinical conditions such as autoimmune diseases and transplant rejection. Complement-inhibitory drugs, either approved or in development, usually act systemically, thereby increasing the risk for infections. We therefore envisioned a novel class of bispecific antibodies (bsAbs) which are capable of site-directed complement inhibition by bringing endogenous complement regulators in the vicinity of defined cell surface antigens. Here, we analyzed a comprehensive set of obligate bsAbs designed to crosslink a specific target with either complement regulator factor H (FH) or C4b-binding protein (C4BP). The bsAbs were assessed for their capacity to inhibit complement activation and cell lysis in an antigen-targeted manner. We observed that the bsAbs inhibited classical, lectin, and alternative pathway complement activation in which sufficient endogenous serum FH and C4BP could be recruited to achieve local inhibition. Importantly, the bsAbs effectively protected antigen-positive liposomes, erythrocytes, and human leukocytes from complement-mediated lysis. In conclusion, localized complement inhibition by bsAbs capable of recruiting endogenous human complement regulators (such as FH or C4BP) to cell surfaces potentially provides a novel therapeutic approach for the targeted treatment of complement-mediated diseases.

Anti-CFH-associated hemolytic uremic syndrome: do we still need plasma exchange?

BACKGROUND: Between 5 and 50% of atypical hemolytic uremic syndrome (aHUS) cases in children are caused by autoantibodies against complement factor H (CFH). Given the acquired autoimmune nature of the disease, plasma exchange (PE) and various immunosuppressive treatments have been used. More recently, eculizumab has been proposed. METHODS: In this multicenter, retrospective study, we report outcomes of 12 children with anti-FH antibody-associated HUS treated with eculizumab associated with various immunosuppressive regimens. RESULTS: Patients were treated with eculizumab for 15.5 [9.5;23.0] months and 3 received PE or IgG adsorption. Three patients received mycophenolate mofetil (MMF) alone, 1 patient received MMF and steroids, 1 patient received MMF and rituximab, 3 patients received MMF/steroids and rituximab, and 4 patients did not receive any immunosuppression. Anti-FH antibody levels significantly decreased but no difference was observed based on the immunosuppressive regimen. Eculizumab was discontinued in 7/10 patients after 11 [7.5;15.5] months and MMF in 6/8 patients after 36 [35;40] months. Anti-FH titers at MMF discontinuation ranged from 257 to 3425 UI/L. None of these patients relapsed and eGFR at last follow-up was above 70 mL/min/1.73 m2 in all patients. CONCLUSIONS: Eculizumab is effective and safe in inducing and maintaining remission in aHUS secondary to anti-FH antibodies and renders reduction of anti-FH titers less urgent. Anti-FH antibody titers decreased in most patients irrespective of the immunosuppressive treatment chosen, so that a strategy consisting of combining eculizumab with MMF monotherapy seems sufficient at least in non-Indian or less severe forms of anti-FH antibody-associated HUS.

Characterization of patients with aHUS and associated triggers or clinical conditions: A Global aHUS Registry analysis.

INTRODUCTION: Atypical haemolytic uremic syndrome (aHUS) is a rare form of thrombotic microangiopathy (TMA) associated with complement dysregulation; aHUS may be associated with other 'triggers' or 'clinical conditions'. This study aimed to characterize this patient population using data from the Global aHUS Registry, the largest collection of real-world data on patients with aHUS. METHODS: Patients enrolled in the Global aHUS Registry between April 2012 and June 2021 and with recorded aHUS-associated triggers or clinical conditions prior/up to aHUS onset were analysed. aHUS was diagnosed by the treating physician. Data were classified by age at onset of aHUS (< or ≥18 years) and additionally by the presence/absence of identified pathogenic complement genetic variant(s) and/or anti-complement factor H (CFH) antibodies. Genetically/immunologically untested patients were excluded. RESULTS: 1947 patients were enrolled in the Global aHUS Registry by June 2021, and 349 (17.9%) met inclusion criteria. 307/349 patients (88.0%) had a single associated trigger or clinical condition and were included in the primary analysis. Malignancy was most common (58/307, 18.9%), followed by pregnancy and acute infections (both 53/307, 17.3%). Patients with an associated trigger or clinical condition were generally more likely to be adults at aHUS onset. CONCLUSION: Our analysis suggests that aHUS-associated triggers or clinical conditions may be organized into clinically relevant categories, and their presence does not exclude the concurrent presence of pathogenic complement genetic variants and/or anti-CFH antibodies. Considering a diagnosis of aHUS with associated triggers or clinical conditions in patients presenting with TMA may allow faster and more appropriate treatment.

Promotion of an Antitumor Immune Program by a Tumor-specific, Complement-activating Antibody.

Tumor-targeting Abs can be used to initiate an antitumor immune program, which appears essential to achieve a long-term durable clinical response to cancer. We previously identified an anti-complement factor H (CFH) autoantibody associated with patients with early-stage non-small cell lung cancer. We cloned from their peripheral B cells an mAb, GT103, that specifically recognizes CFH on tumor cells. Although the underlying mechanisms are not well defined, GT103 targets a conformationally distinct CFH epitope that is created when CFH is associated with tumor cells, kills tumor cells in vitro, and has potent antitumor activity in vivo. In the effort to better understand how an Ab targeting a tumor epitope can promote an effective antitumor immune response, we used the syngeneic CMT167 lung tumor C57BL/6 mouse model, and we found that murinized GT103 (mGT103) activates complement and enhances antitumor immunity through multiple pathways. It creates a favorable tumor microenvironment by decreasing immunosuppressive regulatory T cells and myeloid-derived suppressor cells, enhances Ag-specific effector T cells, and has an additive antitumor effect with anti-PD-L1 mAb. Furthermore, the immune landscape of tumors from early-stage patients expressing the anti-CFH autoantibody is associated with an immunologically active tumor microenvironment. More broadly, our results using an mAb cloned from autoantibody-expressing B cells provides novel, to our knowledge, mechanistic insights into how a tumor-specific, complement-activating Ab can generate an immune program to kill tumor cells and inhibit tumor growth.

Triple-fusion protein (TriFu): A potent, targeted, enzyme-like inhibitor of all three complement activation pathways.

The introduction of a therapeutic anti-C5 antibody into clinical practice in 2007 inspired a surge into the development of complement-targeted therapies. This has led to the recent approval of a C3 inhibitory peptide, an antibody directed against C1s and a full pipeline of several complement inhibitors in preclinical and clinical development. However, no inhibitor is available that efficiently inhibits all three complement initiation pathways and targets host cell surface markers as well as complement opsonins. To overcome this, we engineered a novel fusion protein combining selected domains of the three natural complement regulatory proteins decay accelerating factor, factor H and complement receptor 1. Such a triple fusion complement inhibitor (TriFu) was recombinantly expressed and purified alongside multiple variants and its building blocks. We analyzed these proteins for ligand binding affinity and decay acceleration activity by surface plasmon resonance. Additionally, we tested complement inhibition in several in vitro/ex vivo assays using standard classical and alternative pathway restricted hemolysis assays next to hemolysis assays with paroxysmal nocturnal hemoglobinuria erythrocytes. A novel in vitro model of the alternative pathway disease C3 glomerulopathy was established to evaluate the potential of the inhibitors to stop C3 deposition on endothelial cells. Next to the novel engineered triple fusion variants which inactivate complement convertases in an enzyme-like fashion, stoichiometric complement inhibitors targeting C3, C5, factor B, and factor D were tested as comparators. The triple fusion approach yielded a potent complement inhibitor that efficiently inhibits all three complement initiation pathways while targeting to surface markers.

Abbreviated protocol of plasma exchanges for patients with anti-factor H associated hemolytic uremic syndrome.

BACKGROUND: Plasma exchanges (PEX) and immunosuppression are the cornerstone of management of anti-factor H (FH) antibody-associated atypical hemolytic uremic syndrome (aHUS), particularly if access to eculizumab is limited. The duration of therapy with PEX for anti-FH aHUS is empirical. METHODS: We compared the efficacy of abbreviated PEX protocol (10-12 sessions) in a prospective cohort of patients diagnosed with anti-FH aHUS (2020-2022), to standard PEX protocol (20-22 sessions) in a historical cohort (2016-2019; n = 65). Efficacy was defined as 70% decline in anti-FH titers or fall to ≤ 1300 AU/ml at 4 weeks. Patients in both cohorts received similar immunosuppression with oral prednisolone, IV cyclophosphamide (5 doses) and mycophenolate mofetil. Outcomes included efficacy, rates of hematological remission and adverse kidney outcomes at 1, 3 and 6 months. RESULTS: Of 23 patients, 8.2 ± 2.1 years old enrolled prospectively, two were excluded for significant protocol deviation. PEX was abbreviated in 18/21 (86%) patients to 11.5 ± 3.3 sessions. Abbreviation failed for lack of hematological remission by day 14 (n = 2) and persistent neurological manifestations (n = 1). All patients in whom PEX was abbreviated achieved > 70% reduction in anti-FH titers at day 28. The percentage fall in anti-FH titers was similar for the abbreviated vs. standard PEX protocols at 1, 3 and 6 months. At last follow-up, at median 50 months and 25 months for standard and abbreviated cohorts, the estimated GFR was similar at 104.8 ± 29.1 vs. 93.7 ± 53.4, respectively (P = 0.42). CONCLUSION: Abbreviation of the duration of PEX is feasible and efficacious in reducing anti-FH titers. Short-term outcomes were comparable in patients managed by abbreviated and standard PEX protocols.

Anti-factor H antibody and its role in atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome (aHUS) an important form of a thrombotic microangiopathy (TMA) that can frequently lead to acute kidney injury (AKI). An important subset of aHUS is the anti-factor H associated aHUS. This variant of aHUS can occur due to deletion of the complement factor H genes, CFHR1 and CFHR3, along with the presence of anti-factor H antibodies. However, it is a point of interest to note that not all patients with anti-factor H associated aHUS have a CFHR1/R3 deletion. Factor-H has a vital role in the regulation of the complement system, specifically the alternate pathway. Therefore, dysregulation of the complement system can lead to inflammatory or autoimmune diseases. Patients with this disease respond well to treatment with plasma exchange therapy along with Eculizumab and immunosuppressant therapy. Anti-factor H antibody associated aHUS has a certain genetic predilection therefore there is focus on further advancements in the diagnosis and management of this disease. In this article we discuss the baseline characteristics of patients with anti-factor H associated aHUS, their triggers, various treatment modalities and future perspectives.

Homodimeric Minimal Factor H: In Vivo Tracking and Extended Dosing Studies in Factor H Deficient Mice.

C3 glomerulopathy (C3G) is associated with dysregulation of the alternative pathway (AP) of complement and treatment options remain inadequate. Factor H (FH) is a potent regulator of the AP. An in-depth analysis of FH-related protein dimerised minimal (mini)-FH constructs has recently been published. This analysis showed that addition of a dimerisation module to mini-FH not only increased serum half-life but also improved complement regulatory function, thus providing a potential treatment option for C3G. Herein, we describe the production of a murine version of homodimeric mini-FH [mHDM-FH (mFH1-5^18-20^R1-2)], developed to reduce the risk of anti-drug antibody formation during long-term experiments in murine models of C3G and other complement-driven pathologies. Our analysis of mHDM-FH indicates that it binds with higher affinity and avidity to WT mC3b when compared to mouse (m)FH (mHDM-FH KD=505 nM; mFH KD=1370 nM) analogous to what we observed with the respective human proteins. The improved binding avidity resulted in enhanced complement regulatory function in haemolytic assays. Extended interval dosing studies in CFH-/- mice (5mg/kg every 72hrs) were partially effective and bio-distribution analysis in CFH-/- mice, through in vivo imaging technologies, demonstrates that mHDM-FH is preferentially deposited and remains fixed in the kidneys (and liver) for up to 4 days. Extended dosing using an AAV- human HDM-FH (hHDM-FH) construct achieved complete normalisation of C3 levels in CFH-/- mice for 3 months and was associated with a significant reduction in glomerular C3 staining. Our data demonstrate the ability of gene therapy delivery of mini-FH constructs to enhance complement regulation in vivo and support the application of this approach as a novel treatment strategy in diseases such as C3G.

Pediatric Atypical Hemolytic Uremic Syndrome Advances.

Atypical hemolytic uremic syndrome (aHUS) is a rare disorder characterized by dysregulation of the alternate pathway. The diagnosis of aHUS is one of exclusion, which complicates its early detection and corresponding intervention to mitigate its high rate of mortality and associated morbidity. Heterozygous mutations in complement regulatory proteins linked to aHUS are not always phenotypically active, and may require a particular trigger for the disease to manifest. This list of triggers continues to expand as more data is aggregated, particularly centered around COVID-19 and pediatric vaccinations. Novel genetic mutations continue to be identified though advancements in technology as well as greater access to cohorts of interest, as in diacylglycerol kinase epsilon (DGKE). DGKE mutations associated with aHUS are the first non-complement regulatory proteins associated with the disease, drastically changing the established framework. Additional markers that are less understood, but continue to be acknowledged, include the unique autoantibodies to complement factor H and complement factor I which are pathogenic drivers in aHUS. Interventional therapeutics have undergone the most advancements, as pharmacokinetic and pharmacodynamic properties are modified as needed in addition to their as biosimilar counterparts. As data continues to be gathered in this field, future advancements will optimally decrease the mortality and morbidity of this disease in children.

Complement Factor H-Related 3 Enhanced Inflammation and Complement Activation in Human RPE Cells.

Complement Factor H-Related 3 (FHR-3) is a major regulator of the complement system, which is associated with different diseases, such as age-related macular degeneration (AMD). However, the non-canonical local, cellular functions of FHR-3 remained poorly understood. Here, we report that FHR-3 bound to oxidative stress epitopes and competed with FH for interaction. Furthermore, FHR-3 was internalized by viable RPE cells and modulated time-dependently complement component (C3, FB) and receptor (C3aR, CR3) expression of human RPE cells. Independently of any external blood-derived proteins, complement activation products were detected. Anaphylatoxin C3a was visualized in treated cells and showed a translocation from the cytoplasm to the cell membrane after FHR-3 exposure. Subsequently, FHR-3 induced a RPE cell dependent pro-inflammatory microenvironment. Inflammasome NLRP3 activation and pro-inflammatory cytokine secretion of IL-1ß, IL-18, IL-6 and TNF-α were induced after FHR-3-RPE interaction. Our previously published monoclonal anti-FHR-3 antibody, which was chimerized to reduce immunogenicity, RETC-2-ximab, ameliorated the effect of FHR-3 on ARPE-19 cells. Our studies suggest FHR-3 as an exogenous trigger molecule for the RPE cell "complosome" and as a putative target for a therapeutic approach for associated degenerative diseases.

C3 Glomerulopathy and Related Disorders in Children: Etiology-Phenotype Correlation and Outcomes.

BACKGROUND AND OBJECTIVES: Membranoproliferative GN and C3 glomerulopathy are rare and overlapping disorders associated with dysregulation of the alternative complement pathway. Specific etiologic data for pediatric membranoproliferative GN/C3 glomerulopathy are lacking, and outcome data are based on retrospective studies without etiologic data. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: A total of 80 prevalent pediatric patients with membranoproliferative GN/C3 glomerulopathy underwent detailed phenotyping and long-term follow-up within the National Registry of Rare Kidney Diseases (RaDaR). Risk factors for kidney survival were determined using a Cox proportional hazards model. Kidney and transplant graft survival was determined using the Kaplan-Meier method. RESULTS: Central histology review determined 39 patients with C3 glomerulopathy, 31 with immune-complex membranoproliferative GN, and ten with immune-complex GN. Patients were aged 2-15 (median, 9; interquartile range, 7-11) years. Median complement C3 and C4 levels were 0.31 g/L and 0.14 g/L, respectively; acquired (anticomplement autoantibodies) or genetic alternative pathway abnormalities were detected in 46% and 9% of patients, respectively, across all groups, including those with immune-complex GN. Median follow-up was 5.18 (interquartile range, 2.13-8.08) years. Eleven patients (14%) progressed to kidney failure, with nine transplants performed in eight patients, two of which failed due to recurrent disease. Presence of >50% crescents on the initial biopsy specimen was the sole variable associated with kidney failure in multivariable analysis (hazard ratio, 6.2; 95% confidence interval, 1.05 to 36.6; P<0.05). Three distinct C3 glomerulopathy prognostic groups were identified according to presenting eGFR and >50% crescents on the initial biopsy specimen. CONCLUSIONS: Crescentic disease was a key risk factor associated with kidney failure in a national cohort of pediatric patients with membranoproliferative GN/C3 glomerulopathy and immune-complex GN. Presenting eGFR and crescentic disease help define prognostic groups in pediatric C3 glomerulopathy. Acquired abnormalities of the alternative pathway were commonly identified but not a risk factor for kidney failure.

Patient-specific iPSC-derived endothelial cells reveal aberrant p38 MAPK signaling in atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome (aHUS) is a rare disease associated with high morbidity and mortality. Existing evidence suggests that the central pathogenesis to aHUS might be endothelial cell damage. Nevertheless, the role of endothelial cell alterations in aHUS has not been well characterized and the underlying mechanisms remain unclear. Utilizing an induced pluripotent stem cell-derived endothelial cell (iPSC-EC) model, we showed that anti-complement factor H autoantibody-associated aHUS patient-specific iPSC-ECs exhibited an intrinsic defect in endothelial functions. Stimulation using aHUS serums exacerbated endothelial dysfunctions, leading to cell apoptosis in iPSC-ECs. Importantly, we identified p38 as a novel signaling pathway contributing to endothelial dysfunctions in aHUS. These results illustrate that iPSC-ECs can be a reliable model to recapitulate EC pathological features, thus providing a unique platform for gaining mechanistic insights into EC injury in aHUS. Our findings highlight that the p38 MAPK signaling pathway can be a therapeutic target for treatment of aHUS.