Analysis of Antidepressant Agonist Activity at LPA1, LPA2 and LPA3 lysophosphatidic acid receptors

Abstract

Besides inhibiting monoamine reuptake, antidepressants have been shown to affect a number of neurotransmitter receptor systems, at which they most often act as antagonists. We have previously shown that in neuronal and non‐neuronal cells different antidepressants, predominantly belonging to the tricyclic and tetracyclic classes, activate the LPA1 lysophosphatidic acid (LPA) receptor to induce proliferative and prosurvival signaling. In the present study we further characterize this unique agonist activity of antidepressants by examining their ability to activate two additional members of the LPA receptor family, LPA2 and LPA3, which display high sequence similarity to LPA1. The human LPA receptors were stably transfected in HEK293 cells (HEK293‐LPA1–3 cells), and their activation was monitored by measuring the phosphorylation/activation of ERK1/2 by Western blot. Exposure to LPA caused a concentration‐dependent increase of phospho‐ERK1/2 levels with EC50 values of 145, 210 and 45 nM in HEK293‐LPA1, ‐LPA2 and ‐LPA3 cells, respectively. As previously observed in other cell types endogenously expressing LPA receptors, amitriptyline, imipramine, clomipramine, desipramine, mianserin and mirtazapine effectively increased ERK1/2 phosphorylation in HEK293‐LPA1 cells. In HEK293 cells stably transfected with a LPA1 mutant (Q3.29A), which was unresponsive to LPA, the stimulatory effects of amitriptyline, clomipramine and mianserin were greatly suppressed, indicating the dependence on receptor structural integrity. Tricyclic antidepressants failed to stimulate ERK1/2 phosphorylation in HEK293‐LPA2 cells, whereas the tetracyclic compounds mianserin and mirtazapine displayed agonist activity, although with relative efficacies lower than those showed in HEK293‐LPA1 cells. Conversely, both tricyclic and tetracyclic antidepressants induced ERK1/2 activation in HEK293‐LPA3 cells. These data demonstrate that some classes of antidepressants can exert agonist activity at more than one LPA receptor, thus extending their spectrum of pharmacological activity. In particular, the present finding that antidepressants can activate LPA3, which is expressed in human hippocampus, amygdala, frontal cortex and in different peripheral tissues, suggests that this receptor can be a potential target for the therapeutic and adverse effects of these drugs.Support or Funding InformationUniversity of Cagliari FIR 2019