A genome-wide association study identifies key modulators of complement factor H binding to malondialdehyde-epitopes.

Genetic variants within complement factor H (CFH), a major alternative complement pathway regulator, are associated with the development of age-related macular degeneration (AMD) and other complementopathies. This is explained with the reduced binding of CFH or its splice variant factor H-like protein 1 (FHL-1) to self-ligands or altered self-ligands (e.g., malondialdehyde [MDA]-modified molecules) involved in homeostasis, thereby causing impaired complement regulation. Considering the critical role of CFH in inhibiting alternative pathway activation on MDA-modified surfaces, we performed an unbiased genome-wide search for genetic variants that modify the ability of plasma CFH to bind MDA in 1,830 individuals and characterized the mechanistic basis and the functional consequences of this. In a cohort of healthy individuals, we identified rs1061170 in CFH and the deletion of CFHR3 and CFHR1 as dominant genetic variants that modify CFH/FHL-1 binding to MDA. We further demonstrated that FHR1 and FHR3 compete with CFH for binding to MDA-epitopes and that FHR1 displays the highest affinity toward MDA-epitopes compared to CFH and FHR3. Moreover, FHR1 bound to MDA-rich areas on necrotic cells and prevented CFH from mediating its cofactor activity on MDA-modified surfaces, resulting in enhanced complement activation. These findings provide a mechanistic explanation as to why the deletion of CFHR3 and CFHR1 is protective in AMD and highlight the importance of genetic variants within the CFH/CFHR3/CFHR1 locus in the recognition of altered-self in tissue homeostasis.

Corrigendum: High Complement Factor H-Related (FHR)-3 Levels Are Associated With the Atypical Hemolytic-Uremic Syndrome-Risk Allele CFHR3 * B.

[This corrects the article DOI: 10.3389/fimmu.2018.00848.].

High Complement Factor H-Related (FHR)-3 Levels Are Associated With the Atypical Hemolytic-Uremic Syndrome-Risk Allele CFHR3*B.

Dysregulation of the complement alternative pathway (AP) is a major pathogenic mechanism in atypical hemolytic-uremic syndrome (aHUS). Genetic or acquired defects in factor H (FH), the main AP regulator, are major aHUS drivers that associate with a poor prognosis. FH activity has been suggested to be downregulated by homologous FH-related (FHR) proteins, including FHR-3 and FHR-1. Hence, their relative levels in plasma could be disease-relevant. The genes coding for FH, FHR-3, and FHR-1 (CFH, CFHR3, and CFHR1, respectively) are polymorphic and located adjacent to each other on human chromosome 1q31.3. We have previously shown that haplotype CFH(H3)-CFHR3*B-CFHR1*B associates with aHUS and reduced FH levels. In this study, we used a specific enzyme-linked immunosorbent assay to quantify FHR-3 in plasma samples from controls and patients with aHUS genotyped for the three known CFHR3 alleles (CFHR3*A, CFHR3*B, and CFHR3*Del). In the 218 patients carrying at least one copy of CFHR3, significant differences between CFHR3 genotype groups were found, with CFHR3*A/Del patients having the lowest FHR-3 concentration (0.684-1.032 µg/mL), CFHR3*B/Del and CFHR3*A/A patients presenting intermediate levels (1.437-2.201 µg/mL), and CFHR3*A/B and CFHR3*B/B patients showing the highest concentration (2.330-4.056 µg/mL) (p < 0.001). These data indicate that CFHR3*A is a low-expression allele, whereas CFHR3*B, associated with increased risk of aHUS, is a high-expression allele. Our study reveals that the aHUS-risk haplotype CFH(H3)-CFHR3*B-CFHR1*B generates twofold more FHR-3 than the non-risk CFH(H1)-CFHR3*A-CFHR1*A haplotype. In addition, FHR-3 levels were higher in patients with aHUS than in control individuals with the same CFHR3 genotype. These data suggest that increased plasma levels of FHR-3, altering the balance between FH and FHR-3, likely impact the FH regulatory functions and contribute to the development of aHUS.

Complement factor H, FHR-3 and FHR-1 variants associate in an extended haplotype conferring increased risk of atypical hemolytic uremic syndrome.

Atypical hemolytic uremic syndrome (aHUS) is a severe thrombotic microangiopathy affecting the renal microvasculature and is associated with complement dysregulation caused by mutations or autoantibodies. Disease penetrance and severity is modulated by inheritance of "risk" polymorphisms in the complement genes MCP, CFH and CFHR1. We describe the prevalence of mutations, the frequency of risk polymorphisms and the occurrence of anti-FH autoantibodies in a Spanish aHUS cohort (n=367). We also report the identification of a polymorphism in CFHR3 (c.721C>T; rs379370) that is associated with increased risk of aHUS (OR=1.78; CI 1.22-2.59; p=0.002), and is most frequently included in an extended risk haplotype spanning the CFH-CFHR3-CFHR1 genes. This extended haplotype integrates polymorphisms in the promoter region of CFH and CFHR3, and is associated with poorer evolution of renal function and decreased FH levels. The CFH-CFHR3-CFHR1 aHUS-risk haplotype seems to be the same as was previously associated with protection against meningococcal infections, suggesting that the genetic variability in this region is limited to a few extended haplotypes, each with opposite effects in various human diseases. These results suggest that the combination of quantitative and qualitative variations in the complement proteins encoded by CFH, CFHR3 and CFHR1 genes is key for the association of these haplotypes with disease.