Abstract
Atypical hemolytic uremic syndrome (aHUS) is frequently associated in humans with loss-of-function mutations in complement-regulating proteins or gain-of-function mutations in complement-activating proteins. Thus, aHUS provides an archetypal complement-mediated disease with which to model new therapeutic strategies and treatments. Herein, we show that, when transferred to mice, an aHUS-associated gain-of-function change (D1115N) to the complement-activation protein C3 results in aHUS. Homozygous C3 p.D1115N (C3KI) mice developed spontaneous chronic thrombotic microangiopathy together with hematuria, thrombocytopenia, elevated creatinine, and evidence of hemolysis. Mice with active disease had reduced plasma C3 with C3 fragment and C9 deposition within the kidney. Therapeutic blockade or genetic deletion of C5, a protein downstream of C3 in the complement cascade, protected homozygous C3KI mice from thrombotic microangiopathy and aHUS. Thus, our data provide in vivo modeling evidence that gain-of-function changes in complement C3 drive aHUS. They also show that long-term C5 deficiency is not accompanied by development of other renal complications (such as C3 glomerulopathy) despite sustained dysregulation of C3. Our results suggest that this preclinical model will allow testing of novel complement inhibitors with the aim of developing precisely targeted therapeutics that could have application in many complement-mediated diseases.
Highlights
Our understanding and treatment of complement-mediated diseases has grown exponentially over the last 20 years
C5 blockade protected C3KI mice from disease, and through longterm studies of C5 genetic deletion, we have shown that while increased C3 turnover continues through dysregulation of the alternative pathway, this does not evolve into a C3 glomerulopathy
This study demonstrates that transferring a disease-associated single-nucleotide substitution in C3, present in a family within the NRCTC atypical hemolytic uremic syndrome (aHUS) cohort, to murine C3 faithfully recapitulated the salient features of the human disease
Summary
Our understanding and treatment of complement-mediated diseases has grown exponentially over the last 20 years. CFH mutations typically cluster in exons 22 and 23 of CFH, which encode the C-terminal short consensus repeats (SCRs; referred to as complement control protein domains [CCPs]) 19–20 of FH [21, 22] This region is important for regulating C3b amplification on host cell and tissue surfaces, while the N-terminal region SCRs 1–4 are important for regulatory activity both in the fluid phase and on surfaces [21, 23]. Given that our model robustly recapitulates the clinical phenotype in humans, this allows us to translate our long-term studies in mice to humans — providing insight into the effects of chronic terminal pathway inhibition on the alternative pathway This C3 gain-of-function mouse model of aHUS provides an opportunity for anti-complement drug testing
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