Complement factor H–related hybrid protein deregulates complement in dense deposit disease
Qian Chen, Michael Wiesener, Hannes U. Eberhardt, Andrea Hartmann, Barbara Uzonyi, Michael Kirschfink, Kerstin Amann, Maike Buettner, Tim Goodship, Christian Hugo, Christine Skerka, Peter F. Zipfel
Qian Chen, Michael Wiesener, Hannes U. Eberhardt, Andrea Hartmann, Barbara Uzonyi, Michael Kirschfink, Kerstin Amann, Maike Buettner, Tim Goodship, Christian Hugo, Christine Skerka, Peter F. Zipfel
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Research Article Nephrology

Complement factor H–related hybrid protein deregulates complement in dense deposit disease

Abstract

The renal disorder C3 glomerulopathy with dense deposit disease (C3G-DDD) pattern results from complement dysfunction and primarily affects children and young adults. There is no effective treatment, and patients often progress to end-stage renal failure. A small fraction of C3G-DDD cases linked to factor H or C3 gene mutations as well as autoantibodies have been reported. Here, we examined an index family with 2 patients with C3G-DDD and identified a chromosomal deletion in the complement factor H–related (CFHR) gene cluster. This deletion resulted in expression of a hybrid CFHR2-CFHR5 plasma protein. The recombinant hybrid protein stabilized the C3 convertase and reduced factor H–mediated convertase decay. One patient was refractory to plasma replacement and exchange therapy, as evidenced by the hybrid protein quickly returning to pretreatment plasma levels. Subsequently, complement inhibitors were tested on serum from the patient for their ability to block activity of CFHR2-CFHR5. Soluble CR1 restored defective C3 convertase regulation; however, neither eculizumab nor tagged compstatin had any effect. Our findings provide insight into the importance of CFHR proteins for C3 convertase regulation and identify a genetic variation in the CFHR gene cluster that promotes C3G-DDD. Monitoring copy number and sequence variations in the CFHR gene cluster in C3G-DDD and kidney patients with C3G-DDD variations will help guide treatment strategies.

Authors

Qian Chen, Michael Wiesener, Hannes U. Eberhardt, Andrea Hartmann, Barbara Uzonyi, Michael Kirschfink, Kerstin Amann, Maike Buettner, Tim Goodship, Christian Hugo, Christine Skerka, Peter F. Zipfel

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Figure 3

The CFHR21,2-CFHR5 hybrid protein interacts with C3b.

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The CFHR21,2-CFHR5 hybrid protein interacts with C3b. (A) Recombinant ...
(A) Recombinant CFHR21,2-CFHR5 binds with higher intensity to the C3 activation products C3b than CFHR5 and CFHR2. CFHR21,2-CFHR5 also binds with higher intensity than factor H to C3b. BSA represents no interaction. (B) The competition effect of recombinant CFHR21,2-CFHR5 on factor H binding to immobilized C3b was assayed by ELISA. CFHR21,2-CFHR5 reduced factor H binding to immobilized C3b, and bound H was detected with factor H mAb T13. Factor H interaction with C3b alone was set to 100%; CFHR2 and CFHR5 were used in addition, and these 2 proteins showed minor effects on factor H binding. **P ≤ 0.01, ***P ≤ 0.001. (C) Serum-derived CFHR21,2-CFHR5 binds to and influences binding of factor H to C3b. Protein input. NHS alone or in combination with sera of patient no. 635 (20%:0%, 10%:10%, 5%:15%, 0%:20%, NHS/serum of patient no. 635) were separated by SDS-PAGE and detected by Western blotting. The 4 probes were absorbed to the immobilized C3b at a final serum concentration of 20%. CFHR21,2-CFHR5 and CFHR5 bound to C3b correlated with input levels (lanes 1–4). However, factor H binding to C3b correlated inversely with the levels of CFHR21,2-CFHR5 (lanes 1–4). No binding of CFHR2 was detected in this set up (lanes 1–4). The blot shown is representative of 3 independent experiments.