Summary Neutrophils can function and survive in injured and infected tissues, where oxygen and metabolic substrates are limited. Using radioactive flux assays and LC-MS tracing with U- 13 C glucose, glutamine, and pyruvate, we observe that neutrophils require the generation of intracellular glycogen stores by gluconeogenesis and glycogenesis for effective survival and bacterial killing. These metabolic adaptations are dynamic, with net increases in glycogen stores observed following LPS challenge or altitude-induced hypoxia. Neutrophils from patients with chronic obstructive pulmonary disease have reduced glycogen cycling, resulting in impaired function. Metabolic specialization of neutrophils may therefore underpin disease pathology and allow selective therapeutic targeting.

Background: Acute respiratory distress syndrome (ARDS) is a severe critical condition with a high mortality that is currently in focus given that it is associated with mortality caused by coronavirus disease 2019 (COVID-19). Neutrophils play a key role in the lung injury characteristic of non-COVID-19 ARDS and there is also accumulating evidence of neutrophil mediated lung injury in patients who succumb to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Methods: We undertook a functional proteomic and metabolomic survey of circulating neutrophil populations, comparing patients with COVID-19 ARDS and non-COVID-19 ARDS to understand the molecular basis of neutrophil dysregulation. Results: Expansion of the circulating neutrophil compartment and the presence of activated low and normal density mature and immature neutrophil populations occurs in ARDS, irrespective of cause. Release of neutrophil granule proteins, neutrophil activation of the clotting cascade and upregulation of the Mac-1 platelet binding complex with formation of neutrophil platelet aggregates is exaggerated in COVID-19 ARDS. Importantly, activation of components of the neutrophil type I interferon responses is seen in ARDS following infection with SARS-CoV-2, with associated rewiring of neutrophil metabolism, and the upregulation of antigen processing and presentation. Whilst dexamethasone treatment constricts the immature low density neutrophil population, it does not impact upon prothrombotic hyperinflammatory neutrophil signatures. Conclusions: Given the crucial role of neutrophils in ARDS and the evidence of a disordered myeloid response observed in COVID-19 patients, this work maps the molecular basis for neutrophil reprogramming in the distinct clinical entities of COVID-19 and non-COVID-19 ARDS.

No abstract

Increasing evidence implicates the decline of microglial defensive responses in the progression of Alzheimer's disease (AD). Loss of function of genetic non-modifiable AD risk factors, as the triggering receptor expressed on myeloid cells 2 (TREM2) and the apolipoprotein E (APOE), associates with microglial dysfunction characterized by reduced clustering and survival around Aß plaques. However, the contribution of modifiable AD risk factors to microglial dysfunction is not known. We show here the concomitant activation of the HIF1-mediated stress response pathway and the transcription of aerobic respiration-related genes in Aß plaque-associated microglia (AßAM). We also demonstrate that AßAM mitochondria are elongated, a cellular response found in cells that maintain aerobic respiration under low nutrient and oxygen conditions, suggesting that HIF1 activation may be hijacking microglial mitochondrial metabolism.Overactivation of HIF1 induces microglial quiescence in cellulo, characterized by lower mitochondrial respiration and reduced proliferation. In vivo, overstabilization of HIF1, either genetically (von Hippel-Lindau deficient microglia) or by exposure to systemic hypoxia (mimicking vascular contributions to AD), reduces AßAM clustering and proliferation. We also observed increased Aß neuropathology in an AD mouse model exposed to hypoxia that mimics the loss of function of genetic AD risk genes. In the AD hippocampus, the upregulation of HIF1a and HIF1 target genes correlates with the presence of "nude" plaques (i.e., with reduced microglial coverage) in a hypoxia-prone brain area and the increase of Aß plaque-associated dystrophic neurites. Thus, low oxygen levels, a modifiable AD risk factor, disrupt microglial mitochondrial metabolism and converge with genetic susceptibility to cause AD microglial dysfunction.

No abstract

Background: Acute respiratory distress syndrome (ARDS) is a severe critical condition with a high mortality that is currently in focus given that it is associated with mortality caused by coronavirus disease 2019 (COVID-19). Neutrophils play a key role in the lung injury characteristic of non-COVID-19 ARDS and there is also accumulating evidence of neutrophil mediated lung injury in patients who succumb to infection with severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2). Methods: We undertook a functional proteomic and metabolomic survey of circulating neutrophil populations, comparing patients with COVID-19 ARDS and non-COVID-19 ARDS to understand the molecular basis of neutrophil dysregulation. Results: Expansion of the circulating neutrophil compartment and the presence of activated low and normal density mature and immature neutrophil populations occurs in ARDS, irrespective of cause. Release of neutrophil granule proteins, neutrophil activation of the clotting cascade and upregulation of the Mac-1 platelet binding complex with formation of neutrophil platelet aggregates is exaggerated in COVID-19 ARDS. Importantly, activation of components of the neutrophil type I interferon responses is seen in ARDS following infection with SARS-CoV-2, with associated rewiring of neutrophil metabolism, and the upregulation of antigen processing and presentation. Whilst dexamethasone treatment constricts the immature low density neutrophil population, it does not impact upon prothrombotic hyperinflammatory neutrophil signatures. Conclusions: Given the crucial role of neutrophils in ARDS and the evidence of a disordered myeloid response observed in COVID-19 patients, this work maps the molecular basis for neutrophil reprogramming in the distinct clinical entities of COVID-19 and non-COVID-19 ARDS.

In the originally published version of this article, an earlier draft of Figure 5 was mistakenly included. This has now been replaced with the final version, which includes data generated during the revision process. Updated figure panels now include bacterial killing of Staphylococcus aureus (SH1000) (Figure 5B), baseline ATP levels (Figure 5D), glycolytic response to SH1000 (Figures 5E and 5F), and tracing of U-13C glutamine into F1,6BP (Figure 5R). Figure 5G has been removed and replaced by 5E; 5L has been removed and replaced by 5D. The remaining panels have been renumbered in line with the figure legend and Results text. The figure legend in the originally published article is correct and corresponds to the updated figure. This error does not affect the data and conclusions of the paper. The authors sincerely apologize for any confusion that this error may have caused.

Hypoxemia is a defining feature of acute respiratory distress syndrome (ARDS), an often-fatal complication of pulmonary or systemic inflammation, yet the resulting tissue hypoxia, and its impact on immune responses, is often neglected. In the present study, we have shown that ARDS patients were hypoxemic and monocytopenic within the first 48 h of ventilation. Monocytopenia was also observed in mouse models of hypoxic acute lung injury, in which hypoxemia drove the suppression of type I interferon signaling in the bone marrow. This impaired monopoiesis resulted in reduced accumulation of monocyte-derived macrophages and enhanced neutrophil-mediated inflammation in the lung. Administration of colony-stimulating factor 1 in mice with hypoxic lung injury rescued the monocytopenia, altered the phenotype of circulating monocytes, increased monocyte-derived macrophages in the lung and limited injury. Thus, tissue hypoxia altered the dynamics of the immune response to the detriment of the host and interventions to address the aberrant response offer new therapeutic strategies for ARDS.