A Novel Allosteric Activator of Free Fatty Acid 2 Receptor Displays Unique G(i)-functional Bias

The short chain fatty acid receptor FFA2 is able to stimulate signaling via both G(i)- and G(q)/G(11)-promoted pathways. These pathways are believed to control distinct physiological end points but FFA2 receptor ligands appropriate to test this hypothesis have been lacking. Herein, we characterize AZ1729, a novel FFA2 regulator that acts as a direct allosteric agonist and as a positive allosteric modulator, increasing the activity of the endogenously produced short chain fatty acid propionate in G(i)-mediated pathways, but not at those transduced by G(q)/G(11). Using AZ1729 in combination with direct inhibitors of G(i) and G(q)/G(11) family G proteins demonstrated that although both arms contribute to propionate-mediated regulation of phospho-ERK1/2 MAP kinase signaling in FFA2-expressing 293 cells, the G(q)/G(11)-mediated pathway is predominant. We extend these studies by employing AZ1729 to dissect physiological FFA2 signaling pathways. The capacity of AZ1729 to act at FFA2 receptors to inhibit β-adrenoreceptor agonist-promoted lipolysis in primary mouse adipocytes and to promote chemotaxis of isolated human neutrophils confirmed these as FFA2 processes mediated by G(i) signaling, whereas, in concert with blockade by the G(q)/G(11) inhibitor FR900359, the inability of AZ1729 to mimic or regulate propionate-mediated release of GLP-1 from mouse colonic preparations defined this physiological response as an end point transduced via activation of G(q)/G(11).