Csincsi Ádám I, Kopp Anne, Zöldi Miklós, Bánlaki Zsófia, Uzonyi Barbara, Hebecker Mario, Caesar Joseph J E, Pickering Matthew C, Daigo Kenji, Hamakubo Takao, Lea Susan M, Goicoechea de Jorge Elena, Józsi Mihály
Hungarian Academy of Sciences-Eötvös Loránd University "Lendület" Complement Research Group, Department of Immunology, Eötvös Loránd University, 1117 Budapest, Hungary;
Junior Research Group for Cellular Immunobiology, Leibniz Institute for Natural Product Research and Infection Biology-Hans Knöll Institute, 07745 Jena, Germany;
J Immunol. 2015 May 15;194(10):4963-73. doi: 10.4049/jimmunol.1403121. Epub 2015 Apr 8.
The physiological roles of the factor H (FH)-related proteins are controversial and poorly understood. Based on genetic studies, FH-related protein 5 (CFHR5) is implicated in glomerular diseases, such as atypical hemolytic uremic syndrome, dense deposit disease, and CFHR5 nephropathy. CFHR5 was also identified in glomerular immune deposits at the protein level. For CFHR5, weak complement regulatory activity and competition for C3b binding with the plasma complement inhibitor FH have been reported, but its function remains elusive. In this study, we identify pentraxin 3 (PTX3) as a novel ligand of CFHR5. Binding of native CFHR5 to PTX3 was detected in human plasma and the interaction was characterized using recombinant proteins. The binding of PTX3 to CFHR5 is of ∼2-fold higher affinity compared with that of FH. CFHR5 dose-dependently inhibited FH binding to PTX3 and also to the monomeric, denatured form of the short pentraxin C-reactive protein. Binding of PTX3 to CFHR5 resulted in increased C1q binding. Additionally, CFHR5 bound to extracellular matrix in vitro in a dose-dependent manner and competed with FH for binding. Altogether, CFHR5 reduced FH binding and its cofactor activity on pentraxins and the extracellular matrix, while at the same time allowed for enhanced C1q binding. Furthermore, CFHR5 allowed formation of the alternative pathway C3 convertase and supported complement activation. Thus, CFHR5 may locally enhance complement activation via interference with the complement-inhibiting function of FH, by enhancement of C1q binding, and by activating complement, thereby contributing to glomerular disease.
补体因子H（FH）相关蛋白的生理作用存在争议且了解甚少。基于遗传学研究，补体因子H相关蛋白5（CFHR5）与肾小球疾病有关，如非典型溶血尿毒综合征、致密物沉积病和CFHR5肾病。在蛋白质水平上，CFHR5也在肾小球免疫沉积物中被鉴定出来。对于CFHR5，已有报道称其具有较弱的补体调节活性以及与血浆补体抑制剂FH竞争C3b结合的能力，但其功能仍不明确。在本研究中，我们鉴定出五聚素3（PTX3）是CFHR5的一种新配体。在人血浆中检测到天然CFHR5与PTX3的结合，并使用重组蛋白对该相互作用进行了表征。与FH相比，PTX3与CFHR5的结合亲和力高约2倍。CFHR5以剂量依赖性方式抑制FH与PTX3的结合，也抑制FH与短五聚素C反应蛋白的单体、变性形式的结合。PTX3与CFHR5的结合导致C1q结合增加。此外，CFHR5在体外以剂量依赖性方式与细胞外基质结合，并与FH竞争结合。总之，CFHR5降低了FH在五聚素和细胞外基质上的结合及其辅因子活性，同时增强了C1q结合。此外，CFHR5促进了替代途径C3转化酶的形成并支持补体激活。因此，CFHR5可能通过干扰FH的补体抑制功能、增强C1q结合以及激活补体来局部增强补体激活，从而导致肾小球疾病。
