Citrate Compartmentalization Regulates Calcium Signaling and Cytokine Production in T Cells
Researchers have identified that cytosolic citrate — a metabolite transported from mitochondria — buffers free calcium ions in CD8+ T cells, suppressing cytokine production when glucose is abundant. When glucose is scarce or the citrate transporter SLC25A1 is blocked, calcium rises and activates NFAT transcription factors, sustaining cytokine expression. The finding reveals a metabolic checkpoint that could have implications for understanding immune suppression in tumors and for cancer immunotherapy.
A study posted to bioRxiv reports that the compartmentalization of citrate between mitochondria and the cytosol serves as a regulatory mechanism linking glucose metabolism to calcium-dependent immune signaling in effector CD8+ T cells. Under glucose-replete conditions, the mitochondrial citrate carrier SLC25A1 exports citrate into the cytosol, where it chelates free calcium and thereby dampens the nuclear translocation of NFAT-family transcription factors and reduces cytokine production. Conversely, when glucose is limited or SLC25A1 is pharmacologically or genetically inhibited, cytosolic citrate falls, free calcium rises, and NFAT-driven cytokine expression is sustained. The researchers extended their analysis to hundreds of human cancer cell lines, finding negative correlations between citrate-derived metabolites and calcium-dependent transcriptional programs, and also observed spatially organized signatures of this mechanism within human tumor tissue. The authors propose that cytosolic citrate functions as a broadly conserved metabolic rheostat, allowing mitochondria to adaptively tune cytokine expression and other calcium-dependent programs in response to local nutrient conditions. This work adds calcium signaling regulation to the known roles of SLC25A1 and may help explain why tumor-infiltrating T cells, which often face nutrient-poor microenvironments, can exhibit altered cytokine profiles.
What's missing
As a preprint, this study has not yet undergone peer review, so findings should be treated as preliminary. The authors do not detail the specific concentrations of cytosolic citrate required to meaningfully chelate calcium under physiological conditions, nor do they fully address whether the calcium-buffering effect of citrate is sufficient in magnitude to account for the observed transcriptional changes independent of other citrate-dependent pathways (e.g., histone acetylation via acetyl-CoA). The causal directionality in the cancer cell line correlational data is not established. In vivo validation in animal tumor models is not described in the abstract.
What different sources said
- bioRxivCenter
Citrate Compartmentalization Controls Calcium-Dependent Cytokine Production in Effector T Cells
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