Vitamin D supports activated CD4

Background: Vitamin D (VitD) is an important immunometabolic regulator of T cell function. Its active form, 1,25-dihydroxyvitamin D Methods: Human CD4 Results: VitD-treated cultures exhibited increased cell numbers despite reduced glucose uptake and lactate production, indicating proliferation partially independent of classical glycolytic metabolism. Proteomic analysis revealed increased expression of glutaminase, glutamate dehydrogenase, and CD38, together with enrichment of Selenium Metabolism and Selenoproteins and Nicotinate and Nicotinamide Metabolism, suggesting enhanced glutaminolysis and NAD+ remodeling. Consistently, tritiated and ¹³C-glutamine tracing demonstrated increased glutamine uptake and incorporation into glutamate, α-ketoglutarate, glucose, and inositol-related metabolites, supporting a glutaminolysis-dependent anabolic program rather than oxidative phosphorylation. Pharmacological inhibition of VDR (MeTC7, 1 nM), glutamine uptake (GPNA, 250 µM), or glutaminase activity (BPTES and compound 968, 5 µM) significantly reduced T cell expansion, highlighting glutamine metabolism as essential for the VitD-mediated cell expansion. Interestingly, prolonged cultures showed that VitD ultimately restricted proliferation at day 7; however, supplementation with glutamine and VitD restored cell expansion, suggesting that VitD promotes a metabolically restrained but adaptive proliferative state. Discussion: Overall, our findings identify glutaminolysis as a central metabolic pathway supporting VitD-induced CD4