Etomoxir Actions on Regulatory and Memory T Cells Are Independent of Cpt1a-Mediated Fatty Acid Oxidation

T cell subsets including effector (Teff), regulatory (Treg), and memory (Tmem) cells are characterized by distinct metabolic profiles that influence their differentiation and function. Previous research suggests that engagement of long-chain fatty acid oxidation (LC-FAO) supports Foxp3+ Treg cell and Tmem cell survival. However, evidence for this is mostly based on inhibition of Cpt1a, the rate-limiting enzyme for LC-FAO, with the drug etomoxir. Using genetic models to target Cpt1a specifically in T cells, we dissected the role of LC-FAO in primary, memory, and regulatory T cell responses. Here we show that the ACC2/Cpt1a axis is largely dispensable for Teff, Tmem, or Treg cell formation, and that the effects of etomoxir on T cell differentiation and function are independent of Cpt1a expression. Together our data argue that metabolic pathways other than LC-FAO fuel Tmem or Treg differentiation and suggest alternative mechanisms for the effects of etomoxir that involve mitochondrial respiration. [Display omitted] •Cpt1a mediates long-chain fatty acid oxidation (LC-FAO) in T cells•Cpt1a is not required for T effector (Teff) or T memory (Tmem) cell responses•Cpt1a is not required for CD4+ Treg homeostasis/differentiation/suppressive function•Etomoxir induces Cpt1a-independent off-target effects at concentrations >100 μM Using genetic models of Cpt1a deficiency, Raud et al. demonstrate that long-chain fatty acid oxidation is largely dispensable for T cell activation and generation of CD8+ T memory (Tmem) cells and CD4+ Treg cells, and observe that, at high concentrations, the Cpt1 inhibitor etomoxir presents off-target effects on cell metabolism.