C3b protein (Complement Technology) serially diluted in NHS and coated on the plate instead of CRP was used for the preparation of the standard curve. the GoF mutations in complement C2. Keywords:complement system, aHUS, C3 glomerulopathy, complement C2, endothelial cells == Introduction == The etiology of rare kidney diseases such as C3 glomerulopathy (C3G) and atypical hemolytic uremic syndrome (aHUS) involves dysregulation of the complement system (1). The common etiologic factor is usually impairment of proteins engaged in the alternative complement pathway (AP), as this route is constantly active at a low level, and its further propagation depends on endogenous inhibition on self surfaces. Conversely, the classical and lectin complement pathways (CP/LP) need specific stimuli, and therefore loss of pathway regulation may not be sufficient for the occurrence of pathology. Elements of AP but not CP/LP are included in routine genetic diagnostics of glomerulopathies. Previously, our group identified the first-ever gain-of-function (GoF) mutation in the CP/LP convertase component, C2, in an aHUS patient (2). Substitution of serine 250 to cysteine renders CP/LP convertase insensitive to regulation by CD55 complement inhibitor, which significantly increases generation and deposition of C3 on target cells. Heterozygous S250C mutation in C2 was the only complement pathogenic variant found in this patient, who also carried the homozygous risk polymorphism in the promoter region of theMCPgene that encodes membrane-bound complement inhibitor CD46 (2,3). However, the mechanism that triggers the pathogenic scenario in the S250C mutation carrier remains unknown. Herein, we report the identification of the S250C mutation and another C2 GoF mutation, R249C, adjacent to the S250C mutation, in two other patients with chronic renal disease. We show that both GoF C2 variants increase the deposition of C3 in the presence of C-reactive protein (CRP), an acute phase protein that elevates its concentration in plasma up to 1 1,000 occasions upon contamination and/or inflammation (4). To investigate the potential contribution of R249C and S250C C2 proteins to the pathogenic mechanism, we have used immortalized glomerular endothelial cell cultures. == Methods == == Cells == The human lymphoma cell lines Raji and Ramos (both obtained from the American Type Culture Collection, ATCC) were cultured in RPMI 1640 medium with l-glutamine (ATCC) supplemented with 10% FBS (ATCC). Cells were cultivated at 37C and in humidified 5% CO2atmosphere. Raji cells with CD55 knockout were produced by CRISPR/Cas9 technology as described in (5). Immortalized human glomerular endothelial cells (iGEnC) (6) were cultured in EGM2-MV medium (Lonza) at 33C to activate the temperature-sensitive SV40LT transgene. Before the experiments, cells were transferred to 37C and kept for 5 days to ensure that the transgene was inactive. == Expression and Purification of C2 Variants == All C2 variants used in the current study were produced in HEK293 Freestyle cells (ThermoFisher) as described in (2,7). Similar to WT and S250C variants previously described, cDNA coding R249C sequence was codon-optimized, Rabbit Polyclonal to EGR2 codons for six histidine residues were added at 3, and all matrices were synthesized in the framework of GeneArt Synthesisservice by ThermoFisher. The construct was cloned into a pCEP4 vector and transfected using Freestyle Max reagent Azithromycin Dihydrate (ThermoFisher). One microgram of each C2 protein was separated in 12% polyacrylamide gel electrophoresis in reducing conditions and stained with Coomassie Brilliant blue. == Patients == Information about rare genetic variants in THBD, DGKE,C1QA,C1QB,C1QC,C1R,C1S,C2,C3,C4A,C4BPA,C4BPB,C5,C7,C8A,C8B,C8G,C9,CD46,CD55,CD59,CFB,CFD,CFH,CFHR1,CFHR3,CFHR4,CFHR5,CFI,CFP,CLU,CR1,CR2,FCN1,FCN2,FCN3,ITGAX,ITGB2,MASP1,MASP2,MBL2,SERPING1,VSIG4, andVTNgenes among aHUS and C3G patients were retrieved from the Spanish aHUS/C3G Registry. Diagnostics criteria and detailed methodology Azithromycin Dihydrate of next-generation sequencing with the following data analyses were described in detail in (2). == CDC and Classical Convertase Assays == Complement-dependent cytotoxicity (CDC) assay was performed Azithromycin Dihydrate in Raji cells as described in (8). Briefly, cells were loaded with 1mM calcein-AM (Sigma) for.