scholarly journals Deregulation of Factor H by Factor H-Related Protein 1 Depends on Sialylation of Host Surfaces

2021 ◽  
Vol 12 ◽  
Author(s):  
Arthur Dopler ◽  
Selina Stibitzky ◽  
Rachel Hevey ◽  
Marco Mannes ◽  
Mara Guariento ◽  
...  

To discriminate between self and non-self surfaces and facilitate immune surveillance, the complement system relies on the interplay between surface-directed activators and regulators. The dimeric modulator FHR-1 is hypothesized to competitively remove the complement regulator FH from surfaces that strongly fix opsonic C3b molecules—a process known as “deregulation.” The C-terminal regions of FH and FHR-1 provide the basis of this competition. They contain binding sites for C3b and host surface markers and are identical except for two substitutions: S1191L and V1197A (i.e., FH “SV”; FHR-1 “LA”). Intriguingly, an FHR-1 variant featuring the “SV” combination of FH predisposes to atypical hemolytic uremic syndrome (aHUS). The functional impact of these mutations on complement (de)regulation, and their pathophysiological consequences, have largely remained elusive. We have addressed these questions using recombinantly expressed wildtype, mutated, and truncated versions of FHR-1 and FH. The “SV” to “LA” substitutions did not affect glycosaminoglycan recognition and had only a small effect on C3b binding. In contrast, the two amino acids substantially affected the binding of FH and FHR-1 to α2,3-linked sialic acids as host surfaces markers, with the S-to-L substitution causing an almost complete loss of recognition. Even with sialic acid-binding constructs, notable deregulation was only detected on host and not foreign cells. The aHUS-associated “SV” mutation converts FHR-1 into a sialic acid binder which, supported by its dimeric nature, enables excessive FH deregulation and, thus, complement activation on host surfaces. While we also observed inhibitory activities of FHR-1 on C3 and C5 convertases, the high concentrations required render the physiological impact uncertain. In conclusion, the SV-to-LA substitution in the C-terminal regions of FH and FHR-1 diminishes its sialic acid-binding ability and results in an FHR-1 molecule that only moderately deregulates FH. Such FH deregulation by FHR-1 only occurs on host/host-like surfaces that recruit FH. Conversion of FHR-1 into a sialic acid binder potentiates the deregulatory capacity of FHR-1 and thus explains the pathophysiology of the aHUS-associated FHR-1 “SV” variant.

2021 ◽  
Vol 8 ◽  
Author(s):  
Lara Kollbrunner ◽  
Patricia Hirt-Minkowski ◽  
Javier Sanz ◽  
Elena Bresin ◽  
Thomas J. Neuhaus ◽  
...  

Lipoprotein glomerulopathy (LPG) is a rare inherited disease caused by mutations in the APOE gene, encoding apolipoprotein E (apoE). Atypical hemolytic uremic syndrome (aHUS) is a thrombotic microangiopathy (TMA) characterized by overactivation of the alternative complement pathway. Here we report the case of a 21-year-old man with LPG who developed aHUS. A functional complement assay demonstrated an overactivation of the complement system. Complementary genetic analysis revealed a homozygous aHUS risk allele for complement factor-H related 1 (CFHR1), CFHR1*B. To the best of our knowledge, this is the first report of an aHUS in a patient with LPG.


2018 ◽  
Vol 5 (3) ◽  
pp. 132-139
Author(s):  
Aleksandr V. Novikov

Atypical hemolytic-uremic syndrome (aHUS) is an ultra-rare (orphan) disease, a form of thrombotic microangiopathy, which arises from a disturbance of the activation of an alternative complement pathway. Pregnancy is a frequent trigger for the onset of obstetric aHUS. Against the background of the disease in pregnant women, there is a high risk of developing pre-eclampsia, acute renal damage and consequently maternal mortality. In the world over the past 5 years, the number of confirmed cases of aHUS has increased. However, this is due not so much to the increase in the occurence of the disease as to the improvement in the methods of its diagnosis. The genetic nature of the aHUS dictates the need to create modern sensitive tests for the study of the complement system: measurement of the plasma concentration of factor H and factor I, C3, C4, genetic screening of regulatory genes, and others. It is also necessary to develop new drugs that, along with Eculizumabum (Soliris®, Alexion Pharmaceuticals, Cheshire, CT, USA) would be used in the therapy of aHUS.


Blood ◽  
2016 ◽  
Vol 127 (22) ◽  
pp. 2701-2710 ◽  
Author(s):  
Satu Hyvärinen ◽  
Seppo Meri ◽  
T. Sakari Jokiranta

Key Points Sialic acids are critical for factor H–mediated complement regulation on endothelial cells, erythrocytes, and platelets. Impaired ability of factor H mutants to simultaneously bind sialic acid and C3b on cells explains their association with aHUS.


Author(s):  
Gillian Dekkers ◽  
Mieke Brouwer ◽  
Jorn Jeremiasse ◽  
Angela Kamp ◽  
Robyn M. Biggs ◽  
...  

AbstractThe complement system plays an important role in our innate immune system. Complement activation results in clearance of pathogens, immune complex and apoptotic cells. The host is protected from complement-mediated damage by several complement regulators. Factor H (FH) is the most important fluid-phase regulator of the alternative pathway of the complement system. Heterozygous mutations in FH are associated with complement-related diseases such as atypical hemolytic uremic syndrome (aHUS) and age-related macular degeneration.We recently described an agonistic anti-FH monoclonal antibody that can potentiate the regulatory function of FH. This antibody could serve as a potential new drug for aHUS patients and alternative to C5 blockade by Eculizumab. However, it is unclear whether this antibody can potentiate FH mutant variants in addition to wild type FH. Here, the functionality and potential of the agonistic antibody in the context of pathogenic aHUS-related FH mutant proteins was investigated. The binding affinity of recombinant WT FH, and the FH variants, W1183L, V1197A, R1210C, and G1194D to C3b was increased upon addition of the potentiating antibody and similarly, the decay accelerating activity of all mutants is increased. The potentiating anti-FH antibody is able to restore the surface regulatory function of most of the tested FH mutants to WT FH levels. In conclusion, our potentiating anti-FH is broadly active and able to enhance both WT FH function as well as most aHUS-associated FH variants tested in this study.


Blood ◽  
2010 ◽  
Vol 115 (2) ◽  
pp. 379-387 ◽  
Author(s):  
Iain Moore ◽  
Lisa Strain ◽  
Isabel Pappworth ◽  
David Kavanagh ◽  
Paul N. Barlow ◽  
...  

Abstract Factor H autoantibodies have been reported in approximately 10% of patients with atypical hemolytic uremic syndrome (aHUS) and are associated with deficiency of factor H–related proteins 1 and 3. In this study we examined the prevalence of factor H autoantibodies in the Newcastle cohort of aHUS patients, determined whether the presence of such autoantibodies is always associated with deficiency of factor H–related proteins 1 and 3, and examined whether such patients have additional susceptibility factors and/or mutations in the genes encoding complement regulator/activators. We screened 142 patients with aHUS and found factor H autoantibodies in 13 individuals (age 1-11 years). The presence of the autoantibodies was confirmed by Western blotting. By using multiplex ligation-dependent probe amplification we measured complement factor H–related (CFHR)1 and CFHR3 copy number. In 10 of the 13 patients there were 0 copies of CFHR1, and in 3 patients there were 2. In 3 of the patients with 0 copies of CFHR1 there was 1 copy of CFHR3, and these individuals exhibited a novel deletion incorporating CFHR1 and CFHR4. In 5 patients mutations were identified: 1 in CFH, 1 in CFI, 1 in CD46, and 2 in C3. The latter observation emphasizes that multiple concurrent factors may be necessary in individual patients for disease manifestation.


Nephron ◽  
2017 ◽  
Vol 138 (4) ◽  
pp. 324-327 ◽  
Author(s):  
Hironori Nakamura ◽  
Mariko Anayama ◽  
Mutsuki Makino ◽  
Yasushi Makino ◽  
Katsuhiko Tamura ◽  
...  

2011 ◽  
Vol 49 (1-2) ◽  
pp. 48-55 ◽  
Author(s):  
Saki Mukai ◽  
Yoshihiko Hidaka ◽  
Masako Hirota-Kawadobora ◽  
Kazuyuki Matsuda ◽  
Noriko Fujihara ◽  
...  

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