Purine metabolic pathway regulates regulatory T cell stability and function

Regulatory T cell (Treg) lymphatic migration and maintenance of transcription factor Foxp3 expression are required for suppressor function and allograft protection, and migrated Tregs express ectonucleotidase CD39 hi. Purine metabolism is implicated in Treg phenotype but the precise functions of purine metabolites on Treg function and stability have remained unclear. Sorted Foxp3+ Tregs were used to test Treg stability, migration, and cellular viability in a transendothelial migration (TEM) in vitro model. Intracellular metabolome of Tregs was analyzed by mass spectrometry, and differentially expressed metabolites between Tregs and exTregs were identified and tested. Foxp3 hiTregs displayed higher suppressive function and migration across LECs compared to Foxp3 loexTregs, but cellular viability was similar. Tregs showed differential metabolic profiles compared to exTregs, and the top 16 most differentially expressed metabolites involved the tricarboxylic acid cycle, polyamines, and purine metabolism. Ten metabolites including nicotinamide and inosine monophosphate (IMP) were downregulated, while six metabolites including putrescine, cadaverine, and N-acetylglycine were upregulated in Tregs compared to exTregs. A purine ectonucleotidase CD73 inhibitor decreased Treg conversion to exTregs and adenosine increased Treg migration and suppressive function concomitant with decreased exTreg conversion. Polyamine metabolites showed only subtle effects on exTreg conversion and migration. These results suggest that purine metabolism is a potent regulator that maintains Treg Foxp3 expression and suppressive function during Treg TEM and thus, could be a promising target for therapeutic interventions. NIH grant RO1 A1062765