Impacts of diverse inflammatory stimuli on neutrophil behavior: extracellular vesicles, e-cigarettes, and nanoparticles

Neutrophils are the body’s front-line defenders against foreign insult and are key players in a variety of inflammatory conditions. This body of work examines the role of neutrophils in promoting pathology in three distinct inflammatory contexts. In the pro-inflammatory state provoked by breast cancer, neutrophils decondense their nuclei and release cytotoxic web-like structures known as neutrophil extracellular traps (NETs). NETs form most commonly via histone modifications facilitated by the enzyme PAD4. NETs are known to be a harbinger of disease progression and promote metastasis through capture of circulating tumor cells. It was hypothesized that breast tumors release small particles known as extracellular vesicles (EVs) into the circulation which interact with peripheral neutrophils to cause NET release. The first group of studies herein examined for the first time whether tumor-released EVs promote NET release in a PAD4- dependent manner, as well as whether PAD4 expression by the parent cell influences the capacity of EVs to promote NET formation. Altered neutrophil behavior is not unique to the inflammatory state of cancer. The second set of studies investigated the role of neutrophils in response to e-cigarette vapor (EC) exposure. Existing literature indicates that EC exposure dysregulates neutrophil function, promoting inflammation while compromising the ability to fight off infections. Neutrophil-platelet aggregates potentiate NET formation and can occlude small blood vessels, causing further inflammation and injury. Currently, no literature reports on the link between EC exposure and neutrophil interactions with platelets to form cellular aggregates, much less how the adhesion molecule P-selectin is involved in this process. It was observed that EC exposure potentiated neutrophil recruitment, neutrophil-platelet aggregates and vascular blockages in the pulmonary microcirculation following EC exposure and that these interactions were significantly abrogated through P-selectin blockade. The final set of studies explored NET formation at the intersection of toxicology and cancer. Often, neutrophils are ignored while designing novel nanoparticle (NP) contrast agents for cancer detection via magnetic resonance imaging (MRI). These studies investigated how NP metal oxide cargo and NP polymeric surface modification led to differential NET release, oxidative stress, and neutrophil cytokine release. Therefore, MRI contrast agents and more broadly, any NP intended for use in the circulation, should be designed with neutrophils in mind. These studies collectively provide a framework which illustrates the ubiquity of neutrophils in inflammation and offers novel insights into potential strategies for mitigating neutrophil-mediated pathology