The Heteromeric Dopamine Receptor D2:D3 Controls the Gut Recruitment and Suppressive Activity of Regulatory T-Cells.

Since colonic dopamine levels are markedly reduced during inflammatory bowel disease (IBD), we investigated how dopamine affects regulatory T-cells (Treg), which critically limit gut inflammation. Previously, we showed that the stimulation of the high-affinity dopamine receptor D3 (Drd3) impairs suppressive Treg activity and limits their recruitment into the colon upon gut inflammation. Here we study the role of the low-affinity dopamine receptor Drd2 in Treg. We find that mice harbouring Drd2-deficient T-cells developed more severe colitis induced by dextran sodium sulphate. The stimulation of Drd2 potentiated the suppressive Treg activity and increased their ability to reach the colonic tissue. A transcriptomic analysis of intestinal mucosa from IBD patients revealed an association with increased DRD3 and reduced DRD2 expression. Bioluminescence resonance energy transfer assays revealed that Drd2 and Drd3 form a heteromer. An in situ proximity ligation assay indicated that the Drd2:Drd3 heteromer was expressed on colonic Treg, and its expression was increased upon inflammation. Using peptides analogous to the transmembrane (TM) segments from Drd2 and Drd3 in bimolecular fluorescence complementation assays, we found TM peptides able to disassemble this heteromer. The heteromer disassembly dampened the suppressive Treg activity and impaired the recruitment of Treg into the colon upon inflammation. Our findings indicate that the Drd2:Drd3 heteromer constitutes a dopamine sensor that regulates suppressive Treg activity and their colonic recruitment.