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

ABSTRACT: 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.

SUBMITTER: Sanchez-Corral P

PROVIDER: S-EPMC378565 | biostudies-literature | 2002 Dec

REPOSITORIES: biostudies-literature

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

Sánchez-Corral Pilar P Pérez-Caballero David D Huarte Olatz O Simckes Ari M AM Goicoechea Elena E López-Trascasa Margarita M de Córdoba Santiago Rodríguez SR

American journal of human genetics 20021106 6

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 ...[more]

PMID: 12424708

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Project description:BackgroundThe hemolytic-uremic syndrome consists of the triad of microangiopathic hemolytic anemia, thrombocytopenia, and renal failure. The common form of the syndrome is triggered by infection with Shiga toxin-producing bacteria and has a favorable outcome. The less common form of the syndrome, called atypical hemolytic-uremic syndrome, accounts for about 10% of cases, and patients with this form of the syndrome have a poor prognosis. Approximately half of the patients with atypical hemolytic-uremic syndrome have mutations in genes that regulate the complement system. Genetic factors in the remaining cases are unknown. We studied the role of thrombomodulin, an endothelial glycoprotein with anticoagulant, antiinflammatory, and cytoprotective properties, in atypical hemolytic-uremic syndrome.MethodsWe sequenced the entire thrombomodulin gene (THBD) in 152 patients with atypical hemolytic-uremic syndrome and in 380 controls. Using purified proteins and cell-expression systems, we investigated whether thrombomodulin regulates the complement system, and we characterized the mechanisms. We evaluated the effects of thrombomodulin missense mutations associated with atypical hemolytic-uremic syndrome on complement activation by expressing thrombomodulin variants in cultured cells.ResultsOf 152 patients with atypical hemolytic-uremic syndrome, 7 unrelated patients had six different heterozygous missense THBD mutations. In vitro, thrombomodulin binds to C3b and factor H (CFH) and negatively regulates complement by accelerating factor I-mediated inactivation of C3b in the presence of cofactors, CFH or C4b binding protein. By promoting activation of the plasma procarboxypeptidase B, thrombomodulin also accelerates the inactivation of anaphylatoxins C3a and C5a. Cultured cells expressing thrombomodulin variants associated with atypical hemolytic-uremic syndrome had diminished capacity to inactivate C3b and to activate procarboxypeptidase B and were thus less protected from activated complement.ConclusionsMutations that impair the function of thrombomodulin occur in about 5% of patients with atypical hemolytic-uremic syndrome.

Project description:BACKGROUND AND OBJECTIVES: Atypical hemolytic uremic syndrome is characterized by vascular endothelial damage caused by complement dysregulation. Consistently, complement inhibition therapies are highly effective in most patients with atypical hemolytic uremic syndrome. Recently, it was shown that a significant percentage of patients with early-onset atypical hemolytic uremic syndrome carry mutations in diacylglycerol kinase-?, an intracellular protein with no obvious role in complement. These data support an alternative, complement-independent mechanism leading to thrombotic microangiopathy that has implications for treatment of early-onset atypical hemolytic uremic syndrome. To get additional insights into this new form of atypical hemolytic uremic syndrome, the diacylglycerol kinase-? gene in a cohort with atypical hemolytic uremic syndrome was analyzed. DESIGN, SETTING, PARTICIPANTS, & MEASUREMENTS: Eighty-three patients with early-onset atypical hemolytic uremic syndrome (<2 years) enrolled in the Spanish atypical hemolytic uremic syndrome registry between 1999 and 2013 were screened for mutations in diacylglycerol kinase-?. These patients were also fully characterized for mutations in the genes encoding factor H, membrane cofactor protein, factor I, C3, factor B, and thrombomodulin CFHRs copy number variations and rearrangements, and antifactor H antibodies. RESULTS: Four patients carried mutations in diacylglycerol kinase-?, one p.H536Qfs*16 homozygote and three compound heterozygotes (p.W322*/p.P498R, two patients; p.Q248H/p.G484Gfs*10, one patient). Three patients also carried heterozygous mutations in thrombomodulin or C3. Extensive plasma infusions controlled atypical hemolytic uremic syndrome recurrences and prevented renal failure in the two patients with diacylglycerol kinase-? and thrombomodulin mutations. A positive response to plasma infusions and complement inhibition treatment was also observed in the patient with concurrent diacylglycerol kinase-? and C3 mutations. CONCLUSIONS: Data suggest that complement dysregulation influences the onset and disease severity in carriers of diacylglycerol kinase-? mutations and that treatments on the basis of plasma infusions and complement inhibition are potentially useful in patients with combined diacylglycerol kinase-? and complement mutations. A comprehensive understanding of the genetic component predisposing to atypical hemolytic uremic syndrome is, therefore, critical to guide an effective treatment.

Dataset Information

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

Publications

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

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