Lung mesenchymal cells elicit lipid storage in neutrophils that fuel breast cancer lung metastasis

Acquisition of a lipid-laden phenotype by immune cells has been defined in infectious diseases and atherosclerosis, but remains largely uncharacterized in cancer. Here, in breast cancer models we found that neutrophils are induced to accumulate neutral lipids upon interaction with resident mesenchymal cells (MCs) in the pre-metastatic lung. Lung MCs elicit this process through repressing the adipose triglyceride lipase (ATGL) activity in neutrophils in prostaglandin E2-dependent and -independent manners. In vivo, neutrophil-specific deletion of genes encoding ATGL or ATGL inhibitory factors altered neutrophil lipid profiles and breast tumor lung metastasis in mice. Mechanistically, lipids stored in lung neutrophils are transported to metastatic tumor cells through a macropinocytosis-lysosome pathway, endowing the tumor cells with augmented survival and proliferative capacities. Pharmacological inhibition of macropinocytosis significantly reduced metastatic colonization by breast tumor cells in vivo. Collectively, our work reveals that neutrophils serve as an energy reservoir to fuel breast cancer lung metastasis.