SREBP1c modulates Treg immunobiology through a phospholipid-dependent adenosine pathway

Regulatory T cells (Tregs) maintain immune tolerance through mechanisms tightly coupled to cellular metabolism. Whereas glycolysis supports Treg migration, lipid metabolism sustains their suppressive phenotype. Here, we identify the sterol regulatory element-binding protein 1c (SREBP1c) as a central regulator of Treg immunobiology. Tregs from Srebp1c-deficient mice displayed impaired suppressive function, reduced frequencies in circulation and lymphoid tissues, and diminished expression of functional markers. These defects stemmed from intrinsic metabolic rewiring rather than systemic alterations, as both ex vivo Tregs (CD4+CD25hiFoxP3+) and in vitro-derived Tregs lacking Srebp1c were shifted toward glycolysis. Integrated transcriptomic and lipidomic analyses revealed that Srebp1c-deficient Tregs exhibited defective phospholipid remodeling, with an accumulation of lysophosphatidylcholines over phosphatidylcholines, which we attributed to enhanced cytosolic phospholipase A2 (cPLA2α) activity and disruption of the Lands cycle. Altered lipid composition impaired adenosine-mediated immunosuppression by reducing CD73 expression and extracellular adenosine generation. Accordingly, pharmacological inhibition of cPLA2α restored adenosine signaling, CD73 expression, and Treg suppressive capacity. Thus, by preserving phospholipid homeostasis, SREBP1c functions as an immunometabolic checkpoint that links lipid metabolism to adenosine-dependent Treg suppression.