Voss-Willenbockel, H.; Leitner, F.; Wischnewski, S.; Ng, S.; Aina, K.; Metzdorf, K.; Penninger, J.; Gerritsen, H.; Taudte, R. V.; Schurich, A.; Steinert, M.; Cordes, T.

Citrate is a central metabolite linking tricarboxylic acid (TCA) cycle activity to energy and lipid metabolism and supports the synthesis of inflammatory mediators, including itaconate, in macrophages. While citrate is primarily generated endogenously, extracellular citrate levels are elevated under pathological conditions such as citrate transporter disorder. Cells import extracellular citrate through SLC13 transporters, including the sodium-dependent citrate transporter NaCT (encoded by SLC13A5). However, whether macrophages take up extracellular citrate and how this affects metabolism and function remains unclear. Here, we combined mass spectrometry and tracing approaches to investigate the metabolic fate of citrate in human macrophage cell lines, primary, and iPSC-derived macrophages. We demonstrate that cells take up extracellular citrate, which was enhanced under metabolic stress conditions. Exogenous citrate was not substantially utilized as a carbon source but selectively altered glutamine metabolism and responses to bacterial infection with Salmonella enterica Typhimurium and Legionella pneumophila Corby. Our work identifies extracellular citrate as a context-dependent regulator in macrophages that decouples uptake from metabolic utilization.