Pathophysiological impact of subtypes of eosinophil cell death

Project Summary Eosinophils (eos) are a subset of white blood cells that are involved in multiple immune diseases, broadly termed eosinophilic-associated diseases (EAD). Whether they are protective or contribute to disease pathology is not always clear. For instance, eos are central to fighting infections caused by parasites. However, in asthma they

have been shown to cause tissue damage, as well as participate in tissue repair and regeneration. Our lab has recently focused on eosinophilic heart disease, a serious consequence of hypereosinophilia in patients. The function of eos in physiology and pathology is often correlated with the extracellular presence of their cytoplasmic

contents. Indeed, in the mouse model of eosinophilic heart disease that we developed, we see the presence of extracellular eosinophil granules intimately associated with dying cardiomyocytes. Eos cytoplasmic contents are released through a process of degranulation. Various methods of degranulation including cytolysis, a non-

apoptotic cell death, have been characterized. Although cell death is a natural and essential process in the life cycle of all cells and organisms, the mechanism of cell death has significant impact on tissue homeostasis, immune response, and diseases. This is particularly true for terminally differentiated cells like eos, whose

accumulation at sites of disease is regulated by recruitment and survival versus cell death stimuli. There are several mechanisms of cell death, including apoptosis, accidental/non-regulated necrosis, and regulated necrosis. The latter is a spectrum of cell death types that are different from the classical type of necrosis in that

they are triggered by specific stimuli and mediated by specific signaling pathways. Importantly, this makes it a targetable process. Currently these cell death mechanisms have not been well characterized in eos. In my preliminary studies, I have generated in vitro models of multiple eosinophil cell death types, using diverse stimuli

(staurosporine, ligation of Fas receptor, TNF𝛼 in presence of apoptosis inhibitor, H2O2, calcium ionophore) and measuring different outcomes (expression of annexin V on outer plasma membrane leaflet, permeability to 7AAD, active caspase-3), which will be used to characterize mechanisms of eosinophil cell death.

Understanding mechanisms of eosinophil cell death that are destructive to tissue could provide novel targeted therapies for EAD. Our long-term goal is to develop novel rational therapies for EADs based on understanding of mechanisms of disease. The overall goal of this proposal is to define and characterize the different eos cell

death mechanisms and their impact on disease pathogenesis.