Molecular basis for factor H and FHL-1 deficiency in an Italian family

Association of C-reactive protein and complement factor H gene polymorphisms with risk of lupus nephritis in Chinese population

BACKGROUND

Complement overactivation is a major driver of lupus nephritis (LN). Impaired interactions of C-reactive protein (CRP) with complement factor H (CFH) have been shown as a pathogenic mechanism that contributes to the overactivation of complement in LN. However, genetic variations of neither CRP nor CFH show consistent influences on the risk of LN.

AIM

To examine whether genetic variations of CRP and CFH in combination can improve the risk stratification in Chinese population.

METHODS

We genotyped six CRP single nucleotide polymorphisms (SNPs) (rs1205, rs3093062, rs2794521, rs1800947, rs3093077, and rs1130864) and three CFH SNPs (rs482934, rs1061170, and rs1061147) in 270 LN patients and 303 healthy subjects.

RESULTS

No linkage was found among CRP and CFH SNPs, indicating lack of genetic interactions between the two genes. Moreover, CRP and CFH SNPs, neither individually nor in combination, are associated with the risk or clinical manifestations of LN. Given the unambiguous pathogenic roles of the two genes.

CONCLUSION

These findings suggest that the biological effects of most genetic variations of CRP and CFH on their expressions or activities are not sufficient to influence the disease course of LN.

Genetic analysis of CFH and MCP in Egyptian patients with immune-complex proliferative glomerulonephritis

Glomerulonephritis (GN) is a complex disease with intricate underlying pathogenic mechanisms. The possible role of underlying complement dysregulation is not fully elucidated in some GN subsets, especially in the setting of autoimmunity or infection. In the current study, diagnosed cases of lupus nephritis (LN) and post-infectious GN (PIGN) were recruited for molecular genetic analysis and targeted next-generation DNA sequencing was performed for two main complement regulating genes: in the fluid phase; CFH, and on tissue surfaces; MCP. Three heterozygous pathogenic variants in CFH (Q172*, W701*, and W1096*) and one likely pathogenic heterozygous variant in MCP (C223R) have been identified in four of the studied LN cases. Additionally, among the several detected variants of uncertain significance, one novel variant (CFH:F614S) was identified in 74% of the studied LN cases and in 65% of the studied PIGN cases. This variant was detected for the first time in the Egyptian population. These findings suggest that subtle mutations may be present in complement regulating genes in patients with immune-complex mediated category of GN that may add to the disease pathogenesis. These findings also call for further studies to delineate the impact of these gene variants on the protein function, the disease course, and outcome.

Renal thrombotic microangiopathy associated to worse renal prognosis in Lupus Nephritis

INTRODUCTION

Renal thrombotic microangiopathy (rTMA) is one of many vascular findings in Lupus Nephritis (LN). However, the influence of rTMA on prognosis has not been well established. The objective of this study was to evaluate the clinical and pathological aspects of patients with lupus and rTMA in kidney biopsy.

METHODS

Analysis of medical reports and kidney biopsy of 253 patients with LN, between January 2012 and December 2018.

RESULTS

Among our 253 patients, 43 (17%) showed acute or chronic TMA lesions on kidney histology This group had a significantly lower estimated glomerular filtration rate (eGFR) at the time of biopsy (24.1 vs. 64.15 ml/min/1.73m2, p < 0.001), at 1 year of follow up (28.1 vs. 90.7 ml/min/1.73m2, p < 0.001), and at the end of follow up (25.4 vs. 81.55 ml/min/1.73m2, p < 0.001). More patients in the rTMA group reached the composite endpoint of eGFR < 15 mL/min/1.73m2 or death or dialysis (82.9% vs. 32.9%, p < 0.001). When comparing the classical clinical TMA features, the rTMA group had higher percentages of anemia, thrombocytopenia, low haptoglobin levels, but not higher lactate dehydrogenase (LDH) levels (> 214 U/L). Combining these variables in a definition of clinical TMA, the rTMA group had a statistically higher percentage of clinical TMA (20.9% vs. 4.33%, p = 0.001). As expected, TMA group showed higher systolic blood pressure (SBP) (130 vs 129.5 mmHg, p = 0.01). Concerning histopathological features, rTMA group had significantly higher activity (9.0 vs. 6.0, p = 0.001) and chronicity (4.0 vs. 3.0, p = 0.001) scores, also a higher percentage of patients presented with crescents (76.7% vs. 57.1%, p = 0.012).

CONCLUSIONS

The classical clinical TMA criteria were unable to predict the presence of tissue TMA, suggesting a probably renal-limited TMA that may occur independently of systemic evident factors. Therefore, renal biopsy remains the critical method for diagnosing an important prognostic feature.

The Genetics of Ultra-Rare Renal Disease

The complement-mediated renal diseases are a group of ultra-rare renal diseases that disproportionately affect children and young adults and frequently lead to irreversible renal failure. Genetic mutations in alternate pathway of complement genes are pathomechanistically involved in a significant number of these unique diseases. Here, we review our current understanding of the role of genetics in the primary complement-mediated renal diseases affecting children, with a focus on atypical hemolytic uremic syndrome and C3 glomerulopathy. Also, included is a brief discussion of the related diseases whose relationship to complement abnormality has been suspected but not yet confirmed. Advances in genetics have transformed both treatment and outcomes in these historically difficult to treat, highly morbid diseases.

Clinicopathological characteristics and outcomes of Chinese patients with scanty immune deposits lupus nephritis: a large cohort study from a single center

Objective. To assess clinicopathological characteristics of lupus nephritis patients with scanty immune deposits. Methods. The data of patients with scanty immune deposits lupus nephritis were retrospectively analyzed. Plasma ANCA and complement components were detected. Results. Among 316 cases with renal biopsy-proven lupus nephritis, 40 cases were diagnosed as scanty immune deposits. There were significantly higher value of serum creatinine (P = 0.002) and lower hemoglobin level (P = 0.009) and higher score of cellular crescents (P = 0.015) in scanty immune deposits group compared with immune complex deposits group. The frequency of positive plasma ANCA was significantly higher in scanty immune deposits group than that in immune complex deposits group (52.5% versus 10.1%, P < 0.001). As for comparisons of plasma complement components, there were significantly higher levels of C1q (P = 0.005) and Bb (P = 0.02) and lower level of factor H (P = 0.003) in scanty immune deposits group. The ratio of treatment failure was significantly higher in scanty immune deposits group than that in immune deposits group (42.5% versus 19.20%, P = 0.001). The renal outcomes were similar between the two groups. Conclusions. Patients with scanty immune deposits lupus nephritis had more severe kidney damage. ANCA and activation of complement alternative pathway might be involved in the pathogenesis of the disease.

The spectrum of renal thrombotic microangiopathy in lupus nephritis

INTRODUCTION

Among various lupus renal vascular changes, thrombotic microangiopathy (TMA) presented with the most severe clinical manifestations and high mortality. The pathogenesis of TMA in systemic lupus erythematosus (SLE) was complicated. The aim of this study was to assess clinical manifestations, laboratory characteristics, pathological features and risk factors for clinical outcomes of lupus nephritis patients co-existing with renal TMA in a large cohort in China.

METHODS

Clinical and renal histopathological data of 148 patients with biopsy-proven lupus nephritis were retrospectively analyzed. Serum complement factor H, A Disintegrin and Metalloprotease with Thrombospondin type I repeats 13 (ADAMTS-13) activity, antiphospholipid antibodies and C4d deposition on renal vessels were further detected and analyzed.

RESULTS

In the 148 patients with lupus nephritis, 36 patients were diagnosed as co-existing with renal TMA based on pathological diagnosis. Among the 36 TMA patients, their clinical diagnoses of renal TMA were as followings: 2 patients combining with thrombotic thrombocytopenic purpura-hemolytic uremic syndrome, 2 patients combining with anti-phospholipid syndrome, 2 patients with malignant hypertension, 1 patient with scleroderma and the other 29 patients presenting with isolated renal TMA. Compared with the non-renal TMA group, patients with renal TMA had significantly higher urine protein (7.09±4.64 vs. 4.75±3.13 g/24h, P=0.007) and serum creatinine (159, 86 to 215 vs. 81, 68 to 112 μmol/l, P<0.001), higher scores of total activity indices (AI) (P<0.001), endocapillary hypercellularity (P<0.001), subendothelial hyaline deposits (P=0.003), interstitial inflammation (P=0.005), glomerular leukocyte infiltration (P=0.006), total chronicity indices (CI) (P=0.033), tubular atrophy (P=0.004) and interstitial fibrosis (P=0.018). Patients with renal TMA presented with poorer renal outcome (P=0.005) compared with the non-TMA group. Renal TMA (hazard ratio (HR): 2.772, 95% confidence interval: 1.009 to 7.617, P=0.048) was an independent risk factor for renal outcome in patients with lupus nephritis. The renal outcome was poorer for those with both C4d deposition and decreased serum complement factor H in the TMA group (P=0.007).

CONCLUSIONS

There were various causes of renal TMA in lupus nephritis. Complement over-activation via both classical and alternative pathways might play an important role in the pathogenesis of renal TMA in lupus nephritis.

Serum complement factor H is associated with clinical and pathological activities of patients with lupus nephritis

OBJECTIVE

The aim of this study was to investigate serum complement factor H (CFH) and its associations with clinical and pathological features in patients with LN.

METHODS

Serum CFH was detected in 241 LN patients, 38 active and 11 inactive patients with SLE without clinical evidence of renal involvement and 51 normal controls. Serum CFH autoantibodies and CFH Tyr402His were screened in the 241 LN patients. CFH deposition in kidneys was detected in some patients.

RESULTS

Serum CFH levels in patients with LN at active phase were significantly lower than in 38 SLE patients or in normal controls. No serum anti-CFH autoantibodies were detected in patients with LN, and there was no significant difference in CFH Tyr402His distribution between patients with LN and normal controls. Glomerular expression of CFH was stronger than in normal controls. Serum CFH levels were mildly negatively associated with SLEDAI scores (r = -0.204, P = 0.001) and positively associated with serum C3 (r = 0.367, P < 0.001) and haemoglobulin levels (r = 0.193, P = 0.003). Patients with LN class III, subclass IV-S and those with thrombotic microangiopathy had the lowest serum CFH.

CONCLUSION

Serum CFH levels were associated with disease activity of LN.

Characterization of complement factor H-related (CFHR) proteins in plasma reveals novel genetic variations of CFHR1 associated with atypical hemolytic uremic syndrome

The factor H-related protein family (CFHR) is a group of minor plasma proteins genetically and structurally related to complement factor H (fH). Notably, deficiency of CFHR1/CFHR3 associates with protection against age-related macular degeneration and with the presence of anti-fH autoantibodies in atypical hemolytic uremic syndrome (aHUS). We have developed a proteomics strategy to analyze the CFHR proteins in plasma samples from controls, patients with aHUS, and patients with type II membranoproliferative glomerulonephritis. Here, we report on the identification of persons carrying novel deficiencies of CFHR1, CFHR3, and CFHR1/CFHR4A, resulting from point mutations in CFHR1 and CFHR3 or from a rearrangement involving CFHR1 and CFHR4. Remarkably, patients with aHUS lacking CFHR1, but not those lacking CFHR3, present anti-fH autoantibodies, suggesting that generation of these antibodies is specifically related to CFHR1 deficiency. We also report the characterization of a novel CFHR1 polymorphism, resulting from a gene conversion event between CFH and CFHR1, which strongly associates with aHUS. The risk allotype CFHR1*B, with greater sequence similarity to fH, may compete with fH, decreasing protection of cellular surfaces against complement damage. In summary, our comprehensive analyses of the CFHR proteins have improved our understanding of these proteins and provided further insights into aHUS pathogenesis.

Deficiency of the human complement regulatory protein factor H associated with low levels of component C9

We identified a 4-year-old Brazilian boy from a family of Japanese descent and history of consanguinity, who suffered from severe recurrent pneumonia. He carries factor H (FH) deficiency associated with reduced levels of component C9 and low serum levels of C3 and factor B. His mother also presented low levels of these proteins and factor I, while his father and sister had only lower levels of FH. Western blot assays confirmed the complete absence of FH and FHL-1 polypeptides in this patient. Sequencing of the proband's FH cDNA revealed a homozygous G453A substitution, encoding an Arg(127)His change. His mother, father and sister are heterozygous for this substitution. Despite the absence of FH in the plasma, this protein was detected in the patient's fibroblasts, suggesting that Arg(127) may be important for FH secretion. Low concentrations of C9 were detected in the proband serum but no mutations in the patient's C9 gene or promoter have been identified, suggesting that this is a consequence of uncontrolled complement activation and high C9 consumption.

Translational mini-review series on complement factor H: renal diseases associated with complement factor H: novel insights from humans and animals

Factor H is the major regulatory protein of the alternative pathway of complement activation. Abnormalities in factor H have been associated with renal disease, namely glomerulonephritis with C3 deposition including membranoproliferative glomerulonephritis (MPGN) and the atypical haemolytic uraemic syndrome (aHUS). Furthermore, a common factor H polymorphism has been identified as a risk factor for the development of age-related macular degeneration. These associations suggest that alternative pathway dysregulation is a common feature in the pathogenesis of these conditions. However, with respect to factor H-associated renal disease, it is now clear that distinct molecular defects in the protein underlie the pathogenesis of glomerulonephritis and HUS. In this paper we review the associations between human factor H dysfunction and renal disease and explore how observations in both spontaneous and engineered animal models of factor H dysfunction have contributed to our understanding of the pathogenesis of factor H-related renal disease.

An interactive web database of factor H-associated hemolytic uremic syndrome mutations: insights into the structural consequences of disease-associated mutations

Factor H (FH) is a central complement regulator comprised of 20 short complement repeat (SCR) domains. Nucleotide changes within this gene (CFH) have been observed in patients with hemolytic uremic syndrome (HUS), and also membranoproliferative glomerulonephritis and age-related macular degeneration. All parts of FH are affected, but many mutations are clustered in the C-terminal part of FH. Up to now, structural analyses of HUS have been based on SCR-20, a domain that is involved in FH interactions with C3b, heparin, and endothelial cells. In order to identify the structural and functional consequence of HUS mutations, further disease-associated mutations were analyzed in terms of homology and nuclear magnetic resonance (NMR) models for factor H SCR domains. An interactive web database of 54 human HUS-associated mutations and others was created from the literature (www.FH-HUS.org). This has comprehensive search and analysis tools, integrating phenotypic and genetic data with structural analysis. Each mutation can be highlighted on the SCR structure together with the patient FH and C3 levels where available. Two new insights were obtained from our collection of data. First, phenotypic data on FH clarify our previously-proposed classification of Type I and Type II disorders that both lead to HUS, where Type I affects FH secretion and folding, and Type II leads to expressed protein in plasma that is functionally defective. Second, the new mutations show more clearly that SCR domains from SCR-16 to SCR-19 are important for the ligand binding activities of FH as well as SCR-20. This FH web database will facilitate the interpretation of new mutations and polymorphisms when these are identified in patients, and it will clarify the functional role of FH.

Clinical aspects and molecular basis of primary deficiencies of complement component C3 and its regulatory proteins factor I and factor H

The complement system participates in both innate and acquired immune responses. Deficiencies in any of the protein components of this system are generally uncommon and require specialized services for diagnosis. Consequently, complement deficiencies are clinically underscored and may be more common than is normally estimated. As C3 is the major complement component and participates in all three pathways of activation, it is fundamental to understand all the clinical consequences observed in patients for which this protein is below normal concentration or absent in the serum. C3 deficiencies are generally associated with higher susceptibility to severe infections and in some cases with autoimmune diseases such as systemic lupus erythematosus. Here, we review the main clinical aspects and the molecular basis of primary C3 deficiency as well as the mutations in the regulatory proteins factor I and factor H that result in secondary C3 deficiencies. We also discuss the use of animal models to study these deficiencies.

Localization of the third heparin-binding site in the human complement regulator factor H1

Complement factor H (fH) plays a pivotal role in regulating the alternative pathway, allowing complement activation to proceed on foreign surfaces, whilst protecting surrounding host cell surfaces from complement-mediated damage. Host cell recognition is mediated by polyanions such as sialic acid and glycosaminoglycans (GAGs), which promote a high affinity interaction between fH and C3b deposited on host cell surfaces. Factor H is composed of 20 short consensus repeats (SCRs); two heparin-binding sites have been identified within SCR 7 and SCR 20 and a third site is thought to exist within or near SCR 13. Using an extensive series of recombinant fH fragments and heparin affinity chromatography, we have localized the third heparin-binding domain to SCR 9. A recombinant fH fragment containing both SCR 7 and SCR 9 exhibited higher affinity for heparin than SCR 7 alone, suggesting that the individual heparin-binding sites interact simultaneously with heparin to create a higher avidity interaction. Recombinant fragments containing SCR 9 bound to endothelial cells, indicating that this domain is capable of interacting with polyanions within a physiologically relevant environment. In addition, the three heparin-binding sites exhibited differences in their specificity for certain GAGs, suggesting that the individual binding domains may possess separate GAG recognition functions.

Phenotypic expression of factor H mutations in patients with atypical hemolytic uremic syndrome

We investigated the phenotypic expression of factor H mutations in two patients with atypical hemolytic uremic syndrome (HUS). Factor H in serum was assayed by rocket immunoelectrophoresis, immunoblotting, and double immunodiffusion and in tissue by immunohistochemistry. Functional activity was analyzed by hemolysis of sheep erythrocytes and binding to endothelial cells. A homozygous mutation in complement control protein (CCP) domain 10 of factor H was identified in an adult man who first developed membranoproliferative glomerulonephritis and later HUS. C3 levels were very low. The patient had undetectable factor H levels in serum and a weak factor H 150 kDa band. Double immunodiffusion showed partial antigenic identity with factor H in normal serum owing to the presence of factor H-like protein 1. Strong specific labeling for factor H was detected in glomerular endothelium, mesangium and in glomerular and tubular epithelium as well as in bone marrow cells. A heterozygous mutation in CCP 20 of factor H was found in a girl with HUS. C3 levels were moderately decreased at onset. Factor H levels were normal and a normal 150 kDa band was present. Double immunodiffusion showed antigenic identity with normal factor H. Factor H labeling was minimal in the renal cortex. Factor H dysfunction was demonstrated by increased sheep erythrocyte hemolysis and decreased binding to endothelial cells. In summary, two different factor H mutations associated with HUS were examined: in one, factor H accumulated in cells, and in the other, membrane binding was reduced.

Structural and functional characterization of factor H mutations associated with atypical hemolytic uremic syndrome

Genetic studies have demonstrated the involvement of the complement regulator factor H in nondiarrheal, nonverocytotoxin (i.e., atypical) cases of hemolytic uremic syndrome. Different factor H mutations have been identified in 10%-30% of patients with atypical hemolytic uremic syndrome (aHUS), and most of these mutations alter single amino acids in the C-terminal region of factor H. Although these mutations are considered to be responsible for the disease, the precise role that factor H plays in the pathogenesis of aHUS is unknown. We report here the structural and functional characterization of three different factor H proteins purified from the plasma of patients with aHUS who carry the factor H mutations W1183L, V1197A, or R1210C. Structural anomalies in factor H were found only in R1210C carriers; these individuals show, in their plasma, a characteristic high-molecular-weight factor H protein that results from the covalent interaction between factor H and human serum albumin. Most important, all three aHUS-associated factor H proteins have a normal cofactor activity in the proteolysis of fluid-phase C3b by factor I but show very low binding to surface-bound C3b. This functional impairment was also demonstrated in recombinant mutant factor H proteins expressed in COS7 cells. These data support the hypothesis that patients with aHUS carry a specific dysfunction in the protection of cellular surfaces from complement activation, offering new possibilities to improve diagnosis and develop appropriate therapies.

Factor H mutations in hemolytic uremic syndrome cluster in exons 18-20, a domain important for host cell recognition

Several recent studies have established an association between abnormalities of complement factor H (FH) and the development of hemolytic uremic syndrome (HUS). To identify the relative importance of mutations in FH as a cause of HUS, we have undertaken mutation screening of the FH gene in 19 familial and 31 sporadic patients with FH. Mutations were found in two familial and three sporadic patients, and these clustered in exons 18-20, a domain important for host recognition. Moreover, this study demonstrates that familial HUS is likely to be a heterogeneous condition.

Clustering of missense mutations in the C-terminal region of factor H in atypical hemolytic uremic syndrome

Hemolytic-uremic syndrome (HUS) is a microvasculature disorder leading to microangiopathic hemolytic anemia, thrombocytopenia, and acute renal failure. Most cases of HUS are associated with epidemics of diarrhea caused by verocytotoxin-producing bacteria, but atypical cases of HUS not associated with diarrhea (aHUS) also occur. Early studies describing the association of aHUS with deficiencies of factor H suggested a role for this complement regulator in aHUS. Molecular evidence of factor H involvement in aHUS was first provided by Warwicker et al., who demonstrated that aHUS segregated with the chromosome 1q region containing the factor H gene (HF1) and who identified a mutation in HF1 in a case of familial aHUS with normal levels of factor H. We have performed the mutational screening of the HF1 gene in a novel series of 13 Spanish patients with aHUS who present normal complement profiles and whose plasma levels of factor H are, with one exception, within the normal range. These studies have resulted in the identification of five novel HF1 mutations in four of the patients. Allele HF1 Delta exon2, a genomic deletion of exon 2, produces a null HF1 allele and results in plasma levels of factor H that are 50% of normal. T956M, W1183L, L1189R, and V1197A are missense mutations that alter amino acid residues in the C-terminal portion of factor H, within a region--SCR16-SCR20--that is involved in the binding to solid-phase C3b and to negatively charged cellular structures. This remarkable clustering of mutations in HF1 suggests that a specific dysfunction in the protection of cellular surfaces by factor H is a major pathogenic condition underlying aHUS.