complement and alarmin crosstalk in chronic inflammatory diseases – DYSALARM

Complement proteins have been considered for long to act only within this plasma-born enzymatic cascade, evolved to fight infections and to clean debris. Nevertheless, recent research, including from the DYSALARM partners, demonstrated that the complement proteins crosstalk with other systems and can act outside of the cascade, having independent, non-canonical functions. Dysfunctions of the components of the classical complement pathway (CP) C1q, C1r and C1s and of the multifunctional protein HMGB1 are associated with the chronic inflammatory disease Systemic Lupus Erythematosus (SLE). Genetic deficiency of these classical pathway proteins is rare, but are the strongest genetic risk for SLE, with more than 90% of the affected individuals developing the disease. Recent study explained the link between C1q deficiency and SLE with a complement cascade-unrelated function of C1q to be internalized by the T cells and to regulate their activation. How the deficiency of the serine proteases C1r and C1s leads to SLE remains unknown. The DYSALARM partners discovered that C1s has non-canonical functions, affecting genes transcription and proliferation. Furthermore, C1s cleaves HMGB1, potentially modifying its functions. Moreover, C1q and C1s, together with HMGB1, are targets for auto-antibodies (auto-Abs) in SLE, but their functional relevance is not fully understood or unexplored, respectively.
DYSALARM aims to explore at the fine molecular scale the non-canonical interactions of the complement proteins C1q and C1s, including with their recently discovered HMGB1 target. It will also explore at the cellular level the functional impacts of C1s deficiency and how it could be related to immune tolerance, exploring the interaction of SLE-target cell types, knockdown for C1s (epithelial, endothelial and fibroblasts) with T cells. In a preclinical study, the correlation with severity of the serum levels of these proteins and their auto-Abs directed will be analysed.
We expect to demonstrate for the first time how C1s (alone or in coordinated action with C1 components and HMGB1) affects cellular functions. By linking C1s and immune tolerance, beyond its canonical action of triggering the complement cascade, we aim to provide explanation why the C1s genetic deficiency is one of the strongest pre-disposing factors for SLE. The exploration of non-canonical action of the C1 complex subunits will be the breakthrough of this project and will have a major scientific impact, since it will allow to characterize previously unrecognized fundamental biological functions of these proteins.
The discovery of these novel, previously unexpected functions, raises the question whether the auto-Abs in SLE patients might create a functional deficiency of these proteins which will renew the interest on this question. Since the genetic deficiency of C1q, C1r and C1s leads nearly automatically to SLE, such functional deficiency could contribute to maintain the break of the immune tolerance, helping to understand the role of CP in the systemic auto-immunity. We will explore in the preclinical study whether these auto-Abs may serve as potential biomarker candidates for LN flares. Indeed, there is a real need for improved biological markers for the diagnosis/prognosis of active lupus forms, because these periods of illness are life threatening, and for new strategies to improve possible treatments, since there is currently no definite cure and patients need to be followed. Lastly, the molecular interplay between HMGB1 and C1 components is likely to play a role in a larger set of diseases, which may thus include several acute and chronic inflammatory diseases, cancer progression as well as neurologic disorders.
This interdisciplinary project associates 3 partners having a longstanding experience in the complement system. They gather complementary expertise, from basic molecular studies to clinical and pathophysiology research to answer the objectives of DYSALARM.