Abstract 464: Molecular and Functional Interaction of the Angiotensin AT2-Receptor and the Receptor MAS

Abstract

The angiotensin AT2-receptor (AT2R) and the receptor MAS both mediate very similar tissue-protective actions. Furthermore, AT2R-antagonists have been reported to block effects of the MAS-agonist Ang 1-7. Therefore we speculated that a molecular association between these two receptors exists resulting in functional interactions. Fluorescence resonance energy transfer (FRET) with photobleaching was used for detection of a putative interaction between MAS and AT2R in HEK-293 cells transfected with vectors encoding MAS or AT2R fused in the C-terminus with CFP or YFP. In addition, functional interaction of AT2R and MAS was assessed in primary mouse astrocytes by determining the effect of respective agonists and antagonists on expression of mRNA encoding the chemokine receptor CX3CR1. There was significant FRET efficiency of 10.8±0.8% when AT2-YFP and MAS-CFP were co-expressed indicating heterodimerisation. Both, MAS and AT2R also formed homodimers (FRET efficiencies: 7.4±0.8% or 9.2±0.8%, respectively). No FRET efficiency was observed with an unrelated transmembrane receptor, and expression of non-fluorescent MAS and AT2R competed with FRET efficiencies, which both supports specificity of receptor interactions. Regarding putative functional interactions, AT2R-agonist induced increases in CX3CR1 mRNA expression were absent in astrocytes concomitantly treated with the MAS-antagonists A-779 or in Mas-deficient cells. Likewise, effects of the Mas agonist Ang 1-7 were undetectable in cells concomitantly treated with the AT2-antagonist PD123319 or in AT2-deficient cells. This study provides evidence that MAS and AT2 receptors form homo- and heterodimers. Heterodimerisation may be of functional relevance, because in primary mouse astrocytes, Mas and AT2 seemed only functional in the presence of the respective other receptor.