Obesity alters monocyte developmental trajectories to enhance metastasis.

Obesity is characterized by chronic systemic inflammation and enhances cancer metastasis and mortality. Obesity promotes breast cancer metastasis to lung in a neutrophil-dependent manner; however, the upstream regulatory mechanisms of this process remain unknown. Here, we show that obesity-induced monocytes underlie neutrophil activation and breast cancer lung metastasis. Using mass cytometry, obesity favors the expansion of myeloid lineages while restricting lymphoid cells within the peripheral blood. RNA sequencing and flow cytometry revealed that obesity-associated monocytes resemble professional antigen-presenting cells due to a shift in their development and exhibit enhanced MHCII expression and CXCL2 production. Monocyte induction of the CXCL2-CXCR2 axis underlies neutrophil activation and release of neutrophil extracellular traps to promote metastasis, and enhancement of this signaling axis is observed in lung metastases from obese cancer patients. Our findings provide mechanistic insight into the relationship between obesity and cancer by broadening our understanding of the interactive role that myeloid cells play in this process.

Visualizing NETosis Using a Novel Neutrophil Extracellular Trap-Specific Marker.

As the most abundant leukocyte in circulation, the neutrophil plays a far-reaching role in maintaining homeostasis. Within the context of disease, however, neutrophils can potentiate various pathophysiological mechanisms with disastrous consequences for patients. The role of the neutrophil in disease is complex with mechanisms like NETosis driving the progression of several pathologies. NETosis involves neutrophils extruding protein-decorated DNA webs called neutrophil extracellular traps (NETs), which facilitate the progression of inflammatory, non-infectious, and neoplastic pathologies. The need to visualize NETs has thus never been greater. Current approaches for visualizing NETs are limited in specificity and sensitivity, involving non-specific fluorescent DNA dyes or co-stains of neutrophil and DNA markers. Improved methodologies are needed to robustly distinguish NETs from other cell-free DNA. Excitingly, a novel NET-specific posttranslational modification involving cleavage on the N-terminus of histone H3 has recently been identified. Here, we demonstrate that this single marker is superior to the conventional use of the co-stain of the neutrophil marker, myeloperoxidase, and, the DNA marker, histone H3 citrullination in visualizing neutrophil NETosis. This is due to this single marker's unparalleled ability to identify, not only more NETs but also their formation at earlier stages of NETosis. Moreover, we additionally propose a stepwise mechanism of neutrophil NETosis in which a histone H3 cleavage event precedes histone H3 citrullination. Taken together, these results demonstrate a novel method for visualizing NETs, allowing for continued exploration of their multifaceted roles in immunity and disease.

The role of neutrophil extracellular traps in cancer progression and metastasis.

Neutrophil extracellular traps (NET) are the extracellular release of decondensed chromatin and granules known for their role in host defense against foreign pathogens. However, a novel and predominantly pro-tumorigenic role of NETs in cancer is emerging. Tumors induce NET formation through the secretion of an array of tumor and infection-derived factors. NET deposition favors tumor cell proliferation, immunosuppression and cancer-associated thrombosis. Moreover, NETs enhance metastasis by contributing to epithelial-to-mesenchymal transition. A mesenchymal transition in tumor cells potentiates their migratory and invasive abilities. Circulating NETs capture circulating tumor cells and increase vascular permeability, thereby promoting tumor cell intravasation and establishment of micrometastasis. NETs present in pre-metastatic niches serve as cytokines in the recruitment of tumor cells through CCDC25. Through NET-mediated laminin remodelling, dormant cells are reawakened favoring metastatic growth. Moreover, post-operative infection results in high NET deposition and exacerbates post-surgical cancer progression and recurrence. Anti-NET therapies are in use for autoimmune diseases and are now being investigated in the context of cancer. The hope is that anti-NET therapies may synergize with existing anti-cancer therapy to increase rate of response given their multi-faceted interplay in several domains of cancer progression.