Neutrophil Metabolic Rewiring in Severe and Mild COVID-19

SARS-CoV-2 infection can cause severe respiratory disease resulting in hospitalization and death in some people, but in others it causes a mild disease or is asymptomatic. The causes of severe COVID-19 are of profound public health importance. Severe COVID-19 is marked by an exacerbated innate immune response leading to hyperinflammation which damages host tissues. Broad inhibition of hyperinflammation by dexamethasone is a mainstay of severe COVID-19 treatment. However, more targeted therapeutic approaches to dampen hyperinflammation are lacking. Patients typically exhibit increased neutrophil numbers in the blood and lung, and increased formation of neutrophil extracellular traps. Previous work profiled the metabolome of plasma in severe COVID-19 patients and found several metabolic aberrations as compared to mild COVID-19 patients or healthy controls. However, the metabolome of immune cell populations in COVID-19 has not been characterized to our knowledge. In addition, it is not known if metabolic changes observed in severe COVID-19 mechanistically contribute to hyperinflammation and host tissue damage or if they are simply markers of pathology.

To understand how metabolism can regulate the innate immune system in COVID-19 and to explore possible therapeutic targets, we carried out a comprehensive metabolomic study of neutrophils purified from healthy controls, mild/moderate COVID-19 patients, and severe COVID-19 patients. Severe COVID-19 patients were defined as having Acute Respiratory Distress and being treated in the intensive care unit. Plasma from the same patients and healthy controls was also collected and metabolomics was performed to study how COVID-19 impacts the neutrophil and plasma metabolome in tandem.

Several metabolic pathways were significantly different between mild COVID-19 patients, severe COVID-19 patients, and healthy controls, consistent with rewired neutrophil and plasma metabolome in severe COVID-19. Differentially abundant metabolites belonged to central carbon metabolism, nucleotide metabolism, amino acid metabolism and other pathways. Variation in the PMN metabolome was largely independent from variation in the plasma metabolome. This suggests that processes internal to neutrophils drive changes in neutrophil metabolism. Metabolomics in 3 mouse models of hyperinflammation showed common or distinct metabolic features that change in inflammation compared to metabolomics of severe COVID-19 patients. Therefore changes in some metabolites comprise a general hyperinflammatory metabolic signature while others are more specific to severe COVID-19. Isotope tracing experiments were carried out to understand how nutrients were utilized in neutrophils in context of inflammation. We will describe mechanistic work testing whether metabolic features we observe in severe COVID-19 patients regulate the inflammatory response of human neutrophils.