Murine macrophage choline metabolism underpins IL-4 polarization and RELMα up-regulation

Choline is an essential nutrient and in macrophages, mainly supports phosphatidylcholine (PC) synthesis. Cellular uptake and incorporation of choline into PC is critical for LPS-induced macrophage inflammation. Here, we examined choline metabolism in the context of IL-4 polarization of mouse macrophages in vitro and in vivo . Like LPS, IL-4 increased the levels of choline transporter-like protein 1, the rate of choline uptake, and incorporation into PC. Targeted lipidomics analysis revealed higher PC content in IL-4-polarized macrophages, with enrichment in low-saturated species. Pharmacological inhibition of choline metabolism significantly suppressed the transcription of certain hallmark IL-4 genes ( Retnla ) but not others ( Chil3, Mrc1, Arg1 ). Blocking choline metabolism diminished the expression and secretion of RELMα protein (encoded by Retnla ), while also limiting PD-L2 up-regulation and increasing PD-L1 expression. In vivo administration of RSM-932a, a choline kinase inhibitor, caused a dramatic shift in the peritoneal immune cell profile and up-regulated macrophage CD86 and PD-L1, while down-regulating CD206 and PD-L2. Strikingly, blocking choline metabolism lowered RELMα expression in multiple cell-types and tissues in naïve mice as well as mice infected with the helminth pathogens Heligmosomoides polygyrus and Nippostrongylus brasiliensis . There were no changes in pathogen burden or clearance in the two separate helminth models. In contrast, in dextran sulfate sodium-induced colitis, loss of colon length as a marker of inflammation was mitigated by choline metabolism inhibition. These data demonstrate a critical link between choline and macrophage effector functions and suggest that targeting choline metabolism could be leveraged to fine-tune immunopathology. ![Figure][1] ### Competing Interest Statement The authors have declared no competing interest. [1]: pending:yes