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Modeling C3 glomerulopathies: C3 convertase regulation on an extracellular matrix surface
Sofiya Pisarenka1,2, Nicole C Meyer1, Xue Xiao1
1Molecular Otolaryngology and Renal Research Laboratories, Caver College of Medicine, University of Iowa, Iowa City, IA, United States.
Insights
This study introduces a new in vitro model to study C3 glomerulopathies (C3G), a rare kidney disease. The model helps understand how complement alternative pathway (AP) overactivation drives C3G, aiding research into genetic and acquired factors.
Area of Science:
- Complement system biology
- Nephrology
- Immunology
Background:
- C3 glomerulopathies (C3G) are rare, complement-mediated kidney diseases.
- C3G frequently leads to end-stage renal disease (ESRD) within a decade.
- Overactivation of the complement alternative pathway (AP) drives C3G pathogenesis.
Purpose of the Study:
- To develop and validate an in vitro model for studying AP activation on a glycomatrix surface.
- To investigate the impact of genetic and acquired drivers of C3G using this novel model.
- To elucidate mechanisms of C3G pathogenesis, particularly C3 nephritic factor (C3Nef) involvement.
Main Methods:
- Developed an in vitro model using an extracellular matrix substitute (MaxGel) to reconstitute AP C3 convertase.
- Validated the model with properdin and Factor H (FH).
- Assessed the effects of genetic (mutants) and acquired (C3Nefs) drivers on C3 convertase activity and stability.
Main Results:
- C3 convertase formation on MaxGel was confirmed, regulated by properdin and FH.
- Factor B (FB) and FH mutants demonstrated impaired complement regulation.
- C3Nefs were shown to stabilize C3 convertase, revealing a novel pathogenic mechanism.
Conclusions:
- The developed ECM-based model provides a reproducible platform for evaluating complement system activity in C3G.
- This model enhances understanding of the diverse factors contributing to C3G.
- The findings offer insights into C3Nef-mediated C3G pathogenesis.
Introduction:
C3 glomerulopathies (C3G) are ultra-rare complement-mediated diseases that lead to end-stage renal disease (ESRD) within 10 years of diagnosis in ~50% of patients. Overactivation of the alternative pathway (AP) of complement in the fluid phase and on the surface of the glomerular endothelial glycomatrix is the underlying cause of C3G. Although there are animal models for C3G that focus on genetic drivers of disease, in vivo studies of the impact of acquired drivers are not yet possible.
Methods:
Here we present an in vitro model of AP activation and regulation on a glycomatrix surface. We use an extracellular matrix substitute (MaxGel) as a base upon which we reconstitute AP C3 convertase. We validated this method using properdin and Factor H (FH) and then assessed the effects of genetic and acquired drivers of C3G on C3 convertase.
Results:
We show that C3 convertase readily forms on MaxGel and that this formation was positively regulated by properdin and negatively regulated by FH. Additionally, Factor B (FB) and FH mutants impaired complement regulation when compared to wild type counterparts. We also show the effects of C3 nephritic factors (C3Nefs) on convertase stability over time and provide evidence for a novel mechanism of C3Nef-mediated C3G pathogenesis.
Discussion:
We conclude that this ECM-based model of C3G offers a replicable method by which to evaluate the variable activity of the complement system in C3G, thereby offering an improved understanding of the different factors driving this disease process.
