molecular signature of convertases activation in complement-mediated glomerulopathies – COMSIGN

Complement system is a major part of innate immunity and plays a role in cell homeostasis and mounting of adaptative immune response. Complement overactivation is increasingly implicated in pathophysiology of numerous kidney diseases. Among them, C3 glomerulopathy (C3G) is the prototype of disease mediated by complement alternative pathway (AP) activation related to overactivation of both key enzymes of the system C3 and C5 convertase. The disease is mainly acquired due to the presence of autoantibodies targeting complement protein, in particular C3Nef that recognizes and stabilizes the C3 convertase. C3G is a rare disease affecting children and young adults with a sex ratio of 1:1. In patients aged over 50, C3G is associated in more than 65% of cases with monoclonal immunoglobulin (Ig), that, in vitro, has been proved to directly enhance AP activation. Clinical presentation and prognosis are very heterogeneous. In the absence of efficient treatment, renal outcome remains poor: 50% of patients reach end stage renal disease (ESRD) after 8-10 years. There is no specific biomarkers identified as associated with high risk for progression to ESRD. Histological features associate C3 deposition and various degrees of intra renal inflammation that correlates with the severity of the disease.
PI preliminary results suggest that the equilibrium between C3 and C5 convertase activity correlates with severity of the disease and may be modulated by intrinsic properties of auto Ab. Moreover, preliminary results on transcriptomic analysis (from kidney biopsies) allowed to identify different clusters of intra renal immune response that correlated with renal survival. We hypothesize that physico-chemical properties of either polyclonal or monoclonal Ig modulate the balance of C3/C5 convertase activity, resulting in different degrees of intra renal immune cell infiltration that drive the severity of the disease.
Thanks to strong collaboration with clinicians and pathologists from department of nephrology, we dispose of large blood and renal tissue collection.
Using models of complement activation set up in the PI lab, the first objective is to depict fine molecular mechanisms underlying the balance between C3 and C5 convertases activity in presence of Ig from patients in order to identify biomarkers of convertases activity in blood (dosage of complement fragment cleavage by ELISA), renal tissue (immunostaining by IF and IHC) and urines (mass spectrometry). Second, we aim to determine the molecular signature of the immune response related to complement activation in kidney (transcriptomic analysis) and blood (lymphocyte phenotyping by flow cytometry), induced by complement overactivation, in order to correlate the profile convertases activity balance and immune cell response and renal prognosis. Third, we aim to determine biological and physico-chemical properties of polyclonal or monoclonal immunoglobulins that determine equilibrium between C3 and C5 convertase activation. For functional assays based on immunoglobulins purified from patients, we will use immunoglobulins purified from healthy donors matched on sex
The identification of specific biomarkers of complement activation but above all, of convertases balance combined to the identification of molecular signature of immune response related to complement activation will allow to establish an immunoscore in order to 1) stratify patients according to their risk for progression to ESRD, 2) to better define a personalized therapeutic strategy based on adapted immunosuppressive (either anti B cell or T cell therapy for instance) or adapted prescription of new complement inhibitors that are under development. Transposition of the new concept of immunoscore in other complement mediated kidney diseases will help clinicians to improve understanding of the role of complement in their pathophysiology and to better adapt the prescription of new complement inhibitors as best as possible.