Complement in the Pathogenesis of Acute Chest Syndrome - Project Summary
Sickle Cell Disease (SCD) is characterized by vasoocclusion of blood vessels and chronic hemolytic anemia,
resulting in recurrent and episodic acute organ damage. Acute chest syndrome (ACS) is a leading cause of
hospitalization, requires intensive care, and is the most common cause of death in SCD. Despite this, ACS
continues to be managed only with supportive interventions, such as oxygen therapy, antibiotics, and red blood
cell transfusions that likely fail to directly treat the underlying pathophysiology of this condition. Thus, there is an
unmet need for better therapeutic interventions in ACS. Our long-term research objective is to define key
molecular factors that drive ACS pathogenesis and use this information to identify targets to prevent or treat this
condition. We initially demonstrated that patients with ACS exhibit increased levels of complement activation,
including alternative complement pathway (ACP) specific products. Furthermore, in select patients, complement
inhibition appears to reverse hemolysis and result in rapid clinical improvement. Our overarching hypothesis is
that hemolysis-induced activation of the ACP amplifies hemolysis, injures endothelial cells, and activates
neutrophils, thereby resulting in ACS in SCD. The key contribution of this proposal will be characterizing the role
of ACP in hemolysis and ACS in pre-clinical models. To accomplish this, we will define the mechanisms by which
complement contributes to the development of ACS (aim 1) by evaluating the influence and interaction of
complement with erythrocytes and endothelium using a complementary approach of novel pre-clinical animal
models, microfluidics, and in vitro assays to measure complement dysregulation. To accomplish this, we
generated a novel humanized sickle mouse model that is deficient in complement component C3 (SSC3KO),
which is protected from hemin-mediated ACS. In addition to this novel genetic model and microfluidics, we will
utilize high-dimensional flow cytometry to characterize the complement and neutrophil-dependent mechanisms
contributing to ACS (aim 2). Finally, we will test the efficacy of pharmacological inhibitors to inhibit complement
pathways to prevent or treat ACS (aim 3), by targeting the alternative (factor B) and terminal (C5) pathways to
prevent hemolysis, neutrophil activation, endothelial injury, and subsequent ACS. The contribution of this overall
proposal is expected to be significant because it will allow us to develop tools that can help predict the likelihood
of ACS and also potentially identify critical therapeutic targets designed to prevent or abort ACS. We anticipate
that the successful completion of these studies will define an essential contribution of complement activation to
the development of ACS and, more importantly, could lead to a paradigm shift in the mechanistic understanding
of hemolysis and complement in the pathophysiology of SCD.
