Infiltrating myeloid cells in the central nervous system mediate cancer cachexia
Kevin G. Burfeind, Xinxia Zhu, Katherine A. Michaelis, Peter R. Levasseur, Mason A. Norgard and Daniel L. Marks
Papé Family Pediatric Research Institute, Oregon Health & Science University, Portland, OR
Cachexia is a devastating syndrome consisting of anorexia, involuntary weight loss, and fatigue. This syndrome is driven by chronic inflammation in the brain, yet cellular sources of cytokines in the central nervous system (CNS) remain unidentified. In our validated mouse model of pancreatic ductal adenocarcinoma (PDAC)-associated cachexia, we assessed for immune cell infiltration into the brain with flow cytometry and immunofluorescence. We assessed for chemokine expression in the brain using in situ hybridization and CCL2fl/fl mCherry reporter mice. Microglia-specific CCL2 knockout mice were generated by crossing CX3CR1Cre/ERT and CCL2fl/fl mice. Animals with PDAC had robust immune cell infiltration into the brain, even in early cachexia, as identified by an increase in CD45high cells with flow cytometry. While the cell infiltrate was dominated by myeloid cells throughout the course of cachexia, by mid/late cachexia, 63±2% of CD45high cells in the brains of PDAC mice were neutrophils. A large percentage of brain-infiltrating neutrophils expressed CCR2. Furthermore, neutrophil extracellular traps were present in the brain parenchyma in mice with PDAC but not in sham mice. Myeloid cells were present throughout the brain at 10 d.p.i, but were concentrated in the thalamus, choroid plexus, and cavum veli interpositi (CVI). Robust mRNA expression of the chemokine CCL2 was observed in the CVI during PDAC. CCL2 protein was exclusively expressed in meningeal, choroid plexus, and perivascular macrophages. CCR2 knockout (CCR2KO) mice had attenuated PDAC cachexia and a 43% decrease in neutrophil infiltration into the brain compared to WT PDAC mice. There was no difference either in brain-infiltrating monocytes or T-cells or in liver- or spleen-infiltrating neutrophils between genotypes. Lastly, mice with CCL2 deleted specifically from microglia experienced attenuated anorexia and neutrophil infiltration in the brain during PDAC compared to mice with intact CCL2 gene expression. Our results show that myeloid cell infiltration into the brain, controlled by the CCL2-CCR2 axis, is important in PDAC-associated cachexia, which provides a novel therapeutic target for this syndrome.