The Heteromeric Complex Formed by Dopamine Receptor D5 and CCR9 Leads the Gut Homing of CD4+ T Cells Upon Inflammation

BACKGROUND AND AIMS: CD4(+) T cells constitute central players in inflammatory bowel diseases (IBDs), driving inflammation in the gut mucosa. Current evidence indicates that CCR9 and the integrin alpha 4 beta 7 are necessary and sufficient to imprint colonic homing on CD4(+) T cells upon inflammation. Interestingly, dopaminergic signaling has been previously involved in leukocyte homing. Despite dopamine levels are strongly reduced in the inflamed gut mucosa, the role of dopamine in the gut homing of T cells remains unknown. Here, we study how dopaminergic signaling affects T cells upon gut inflammation. METHODS: Gut inflammation was induced by transfer of naive T cells into Rag1(-/-) mice or by administration of dextran sodium sulfate. T cell migration and differentiation were evaluated by adoptive transfer of congenic lymphocytes followed by flow cytometry analysis. Protein interaction was studied by bioluminescence resonance energy transfer analysis, bimolecular fluorescence complementation, and in situ proximity ligation assays. RESULTS: We show the surface receptor providing colonic tropism to effector CD4(+) T cells upon inflammation is not CCR9 but the complex formed by CCR9 and the dopamine receptor D-5 (DRD5). Assembly of the heteromeric complex was demonstrated in vitro and in vivo using samples from mouse and human origin. The CCR9:DRD5 heteroreceptor was upregulated in the intestinal mucosa of IBD patients. Signaling assays confirmed that complexes behave differently than individual receptors. Remarkably, the disruption of CCR9:DRD5 assembly attenuated the recruitment of CD4(+) T cells into the colonic mucosa. CONCLUSIONS: Our findings describe a key homing receptor involved in gut inflammation and introduce a new cell surface module in immune cells: macromolecular complexes formed by G protein-coupled receptors integrating the sensing of multiple molecular cues.

Automated summary

This study reveals that the heteromeric complex formed by CCR9 and the dopamine receptor D-5 (DRD5) is the key receptor providing colonic tropism to effector CD4(+) T cells in gut inflammation, as opposed to CCR9 alone. The CCR9:DRD5 heteroreceptor is upregulated in the intestinal mucosa of IBD patients. Signaling assays demonstrate that these complexes behave differently than individual receptors.