PROJECT SUMMARY
In 2019, methicillin-resistant Staphylococcus aureus infections were the basis of nearly 400,000 hospitalizations
per year with direct costs estimated at $1.7 billion. Furthermore, S. aureus is the leading cause of bacterial
endocarditis. Understanding host-pathogen interactions that skew disease outcome will facilitate the design of
efficacious therapeutic strategies. Neutrophils possess antimicrobial functions that are critical to the innate
immune response to S. aureus. Preliminary data show that neutrophils lacking calprotectin (CP), a highly
abundant immune protein expressed by neutrophils, exhibit altered mitochondrial homeostasis, where CP-
deficient neutrophils produce more mitochondrial superoxide in response to S. aureus compared to wild-type
neutrophils. As a result, CP-deficient neutrophils undergo elevated suicidal NETosis. In addition, increased
suicidal NETosis correlates with CP-deficient mice having lower bacterial burdens specifically within the heart
and increased survival during systemic S. aureus infection. This suggests that neutrophil and CP biology is
unique within the heart. Aim 1 will identify why the heart offers a unique niche for CP biology during S. aureus
infection. More specifically, we will address (i) whether cardiomyocyte function in CP-deficient mice is altered,
thereby skewing the neutrophil response and (ii) identify factors driving CP secretion/retention by neutrophils
during infection in the heart. These experiments are significant as they define the immunological and metabolic
environment of the heart, compared to other sites of infection, and the implications this has on CP and neutrophil
biology. Aim 2 will focus on the role of intracellular CP in altering mitochondrial homeostasis. We will specifically
test the role of CP in regulating mitochondrial metabolism and metal homeostasis, and downstream impacts this
has on neutrophil function. These experiments are significant because they identify CP as a molecular rheostat
for neutrophil function by controlling mitochondrial homeostasis, which may be broadly applicable to other cells
expressing CP during inflammation. This proposal provides critical scientific insights into the function of CP that
may be especially efficacious as a biological target for treating S. aureus infections of the heart. In addition, the
technological advancements achieved by this proposal will create a platform that can be applied to other
inflammatory diseases.