Complement is a humoral innate immune system that plays an important role in host defense and in bridging adaptive immunity. Under certain conditions, complement activation can also cause significant autologous tissue injury leading to complement-mediated diseases. Complement is activated via three different pathways; one of which is by the lectin pathway (LP) which is triggered by collagen-like soluble pattern recognition molecules (PRMs). Upon binding of PRMs to sugar molecules on microbes or altered self-tissues, a specific group of proteases called MASPs are activated. Activation of MASPs is the key step in LP complement activation and the ensuing host defense response or tissue injury consequence. The mechanism of action of MASPs in vivo has not been well understood and recent studies have revealed a surprising link between MASP3 and the alternative pathway (AP) complement activation. It has been shown that MASP3 plays an essential role in converting pro-factor D (FD) to mature active FD. The objectives of this proposal are two fold, 1) to understand whether MASP2 and MASP3 play significant roles in complement-mediated pathologies, and if so, whether targeting these enzyme represents a feasible therapeutic approach; and 2) to understand how FD activity is regulated in vivo by MASP3 and a putative serine protease inhibitor(s). To this end, we propose three specific aims in this project.
Specific aim 1. To use MASP2 KO mice and blocking mAbs and test the role of MASP2 and LP in complement-mediated diseases.
Specific aim 2. To use MASP3 KO mice and blocking mAbs and test the role of MASP3 in regulating AP complement activity and as a therapeutic target in AP complement-dependent diseases.
Specific aim 3. To test the hypothesis that maturation of pro-FD by MASP3 is not a default reaction, but rather a regulated process, and that constitutive, unregulated mature FD activity leads to AP complement consumption via Factor B cleavage which can be exploited therapeutically. These studies will provide proof of concept for therapeutically targeting MASP2 and MASP3, as well as add new fundamental knowledge on how FD and AP complement activity is regulated in vivo.
This project will produce mouse models to study two blood proteins called MASP3 and MASP2 which are part of the body?s natural immune system but could also participate in certain autoimmune and inflammatory diseases such as arthritis and kidney disease. The proposed studies will use mouse models in which these two proteins are experimentally eliminated so that their deficiency can be evaluated to see if their absence will make a difference in arthritis and kidney disease. We will also develop antibodies to these proteins and test such antibodies as drug prototypes to see if they will be effective in treating arthritis and kidney disease. These studies may lead to the development of novel therapeutics for unmet medical need in the area of inflammatory and autoimmune conditions.
