Antidepressants interact with an LPA₃ receptor binding site: Functional and docking studies

The effects of the antidepressants imipramine, amitriptyline, and paroxetine on LPA₃ receptors were studied in cellulo, using receptor-transfected HEK 293 Flp-In TREx cells, and in silico, through docking simulations. These drugs showed a low affinity for LPA₃ receptors with lesser efficacy than LPA (paroxetine ≈ 60% and imipramine and amitriptyline ≈ 30%). When LPA-treated cells (with the agonist present) were challenged with antidepressants, paroxetine triggered a robust increase in intracellular calcium, whereas imipramine and amitriptyline decreased the calcium concentration below the baseline values. For ERK 1/2 phosphorylation, imipramine induced a rapid and potent increase, whereas amitriptyline and paroxetine reduced ERK 1/2 phosphorylation below the baseline level. Similarly, imipramine induced rapid and robust ERK phosphorylation in LPA-stimulated cells, whereas amitriptyline decreased ERK 1/2 phosphorylation. The effects of antidepressants on intracellular calcium and ERK phosphorylation required LPA₃ receptor expression; that is, in cells where expression was not induced, these actions were only marginal or absent. Activation with antidepressants leads to LPA₃ internalization, accompanied by dramatic morphological changes. Docking simulations showed that these drugs interact with the LPA₃ receptor pocket, termed the Upper Cavity. Although the agonist binding cavity was the same, the amino acids interacting with the various ligands were distinct because of their different chemical structures. This manuscript advances our knowledge of the mechanisms underlying the antidepressant effects on LPA₃ receptors, which may have potential therapeutic implications.