Complement factor H–related hybrid protein deregulates complement in dense deposit disease
Qian Chen, … , Christine Skerka, Peter F. Zipfel
Qian Chen, … , Christine Skerka, Peter F. Zipfel
Published December 16, 2013
Citation Information: J Clin Invest. 2014;124(1):145-155. https://doi.org/10.1172/JCI71866.
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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 4

The CFHR21,2-CFHR5 hybrid protein deregulates the C3 convertase.

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The CFHR21,2-CFHR5 hybrid protein deregulates the C3 convertase. (A) T...
(A) The alternative pathway C3 convertase C3bBb (Mg2+) was assembled, and attached Bb was measured by Western blotting. CFHR21,2-CFHR5 (10, 25, and 50 nM) increased Bb attachment and thus convertase formation (lanes 1–3), and CFHR2 and CFHR5 added at the same concentration had less effect (lanes 4–6 and 7–9, respectively). BSA had no effect (lanes 10–12). (B) Factor H–mediated convertase dissociation was dose-dependent for all 3 situations. In presence of CFHR21,2-CFHR5, more C3 convertases were formed and more resistant to factor H–mediated decay. (C) The convertase assembly and stability in presence of CFHR21,2-CFHR5, CFHR2, or CFHR5 were quantitated by ELISA. With CFHR21,2-CFHR5, convertase formation was enhanced by 69% and more resistant to factor H–mediated decay. The convertase assembly with BSA was sent to 100%. (D) Ba levels were determined in the supernatant after reaction. Ba levels, which were high in the presence of CFHR21,2-CFHR5 (50 nM) (lane 1), were slightly reduced when factor H was added (10 and 25 nM, lanes 2 and 3), the amount of Ba was higher as compared with the set up when factor H was added to C3 convertase in the absence of CFHR21,2-CFHR5 (BSA; lane 10–12). CFHR2 and CFHR5 alone did not influence the Ba levels significantly (lane 4–6 and lane 7–9). Blots shown in A and B were run in the same gels but were noncontiguous.