Graduate Student/Graduate Research Assistant UT Hlth. San Antonio, United States
Introduction/Rationale: The lupus susceptibility locus Sle1 includes the Pbx1 gene, which is preferentially expressed in Tregs among CD4⁺ T cells. Its dominant-negative isoform Pbx1-d is overexpressed in Tregs from both human and murine lupus, contributing to Treg instability and loss of suppressive function. Pbx1 regulates the metabolism of cancer and mesangial cells, thus this study aimed to determine whether Pbx1-d regulates Treg function via metabolic reprogramming.
Methods: Metabolic profiling of Pbx1 WT, KO, and Pbx1-d overexpressing Tregs was performed using Seahorse metabolic assays. A dual-luciferase reporter assay was used to assess human and murine CamkIV promoter activation by Pbx1 isoforms. CRISPR-Cas9–mediated CamkIV knockdown was generated in CD4⁺ T cells, which will be polarized into induced Tregs (iTregs) and analyzed by Seahorse and in vitro suppression assays.
Results: Here, we showed that both Pbx1-d overexpressing and Pbx1-deficient murine Treg cells exhibit increased glycolysis and lower respiration to glycolysis ratio compared to WT cells. In addition, Pbx1 deficient Tregs have higher basal and maximum glycolytic capacity than WT independent of respiration. These results indicate that Pbx1 regulates Treg metabolism. We further showed that CamkIV, a glycolysis-driving gene overexpressed in lupus T cells and known to impair Treg function, is a direct Pbx1 transcriptional target with Pbx1-d inducing a higher expression relative to the normal Pbx1-b in both species. CamkIV-knockdown iTregs will be used to assess whether CamkIV deficiency rescues the metabolic and functional alterations driven by Pbx1-d.
Conclusion: Our findings suggest that Pbx1-d impairs Treg homeostasis by reprogramming cellular metabolism, at least in part through CamkIV upregulation. Understanding this mechanism could guide strategies to enhance Treg efficacy in adoptive therapies and to overcome intrinsic barriers limiting Treg function in autoimmune diseases.
