Antidepressant-induced Switch of β1-Adrenoceptor Trafficking as a Mechanism for Drug Action

Abstract

Reduction in surface ␤ 1 -adrenoceptor (␤1AR) density is thought to play a critical role in mediating the therapeutic long term effects of antidepressants. Since antidepressants are neither agonists nor antagonists for G protein-coupled receptors, receptor density must be regulated through processes independent of direct receptor activation. Endocytosis and recycling of the ␤1AR fused to green fluorescent protein at its carboxylterminus (␤1AR-GFP) were analyzed by confocal fluorescence microscopy of live cells and complementary ligand binding studies. In stably transfected C6 glioblastoma cells, ␤1AR-GFP displayed identical ligand-binding isotherms and adenylyl cyclase activation as native ␤1AR. Upon exposure to isoproterenol, a fraction of ␤1AR-GFP (10 -15%) internalized rapidly and colocalized with endocytosed transferrin receptors in an early endosomal compartment in the perinuclear region. Chronic treatment with the tricyclic antidepressant desipramine (DMI) did not affect internalization characteristics of ␤1AR-GFP when challenged with isoproterenol. However, internalized receptors were not able to recycle back to the cell surface in DMI-treated cells, whereas recycling of transferrin receptors was not affected. Endocytosed receptors were absent from structures that stained with fluorescently labeled dextran, and inhibition of lysosomal protease activity did not restore receptor recycling, indicating that ␤1AR-GFP did not immediately enter the lysosomal compartment. The data suggest a new mode of drug action causing a "switch" of receptor fate from a fast recycling pathway to a slowly exchanging perinuclear compartment. Antidepressant-induced reduction of receptor surface expression may thus be caused by modulation of receptor trafficking routes.Chronic treatment with most classes of antidepressants leads to a reduction in the number of central postsynaptic ␤-adrenoceptors (␤AR) 1 in vivo and of surface ␤AR density in cell cultures (1-4). This effect is reported to be specific for the ␤ 1 -adrenoceptor subtype (5, 6). ␤AR down-regulation is accompanied by decreased receptor-stimulated cAMP formation (7). The two major effects at the molecular level become apparent in vivo after 10 -20 days of drug administration and coincide with the onset of clinical antidepressant response in humans. Therefore ␤AR down-regulation and diminished cAMP response to catecholamines may relate to the therapeutic action of antidepressants.It has been proposed that the reduction in the number of functional ␤AR could be a regulatory response to the enhanced presence of norepinephrine in the synaptic cleft after acute inhibition of norepinephrine reuptake or of monoamine oxidase activity by antidepressants (1, 8). Some clinically effective antidepressants, however, neither influence norepinephrine reuptake nor inhibit monoamine oxidase activity but still cause a ␤AR down-regulation. Furthermore, this model fails to explain the observed time lag between the rapid drug-induced increase in intrasynaptic neurotransmitter concentrations ...

Antidepressants and Antipsychotic Drugs Colocalize with 5-HT3Receptors in Raft-Like Domains

“…For example, chronic administration of benzodiazepines induces internalization of the GABA A receptor (Tehrani and Barnes, 1997). Moreover, antidepressants (Koshikawa et al, 1987;Burgi et al, 2003;Riad et al, 2004) and antipsychotic drugs (Willins et al, 1999) may enhance receptor internalization/downregulation of 5-HT 1A receptors, 5-HT 2 receptors, or ␤-adrenoceptors (␤1AR), which all are G-protein-coupled receptors. However, only chronic treatment with DMI, but not acute doses of DMI, may cause downregulation of ␤1AR in vivo (Koshikawa et al, 1987;Burgi et al, 2003).…”

“…Moreover, antidepressants (Koshikawa et al, 1987;Burgi et al, 2003;Riad et al, 2004) and antipsychotic drugs (Willins et al, 1999) may enhance receptor internalization/downregulation of 5-HT 1A receptors, 5-HT 2 receptors, or ␤-adrenoceptors (␤1AR), which all are G-protein-coupled receptors. However, only chronic treatment with DMI, but not acute doses of DMI, may cause downregulation of ␤1AR in vivo (Koshikawa et al, 1987;Burgi et al, 2003). In our study, the noncompetitive antagonism of antidepressants at the 5-HT 3 receptor could be observed after short time exposure to the respective drugs and obviously was not conferred by an enhancement of receptor internalization as shown by immunofluorescence studies, assessment of receptor density in clathrin-coated vesicles, and electrophysiological recordings after coexpression of dynamin K44A, a dominantnegative mutant of dynamin I, which inhibits receptor internalization.…”

Astrocytic Adrenoceptors: A Major Drug Target in Neurological and Psychiatric Disorders?

“…Five days of treatment with 1 µM amytriptyline has no effect on isoproterenol-induced stimulation of cAMP formation but after at least two weeks of chronic treatment the stimulation is down-regulated by 25-30%, an effect that is shared by chronic treatment with the monoamine oxidase inhibitor tranylcypromine [152] but not with the antipsychotic haloperidol or the anti-anxiety-drug clonazepam. A downregulation of stimulated cAMP accumulation after chronic antidepressant treatment has been confirmed in C-6 glioma cells treated with either amitriptyline or desipamine [451][452][453]. A reduction of β-adrenergic receptor binding has also been observed in chronically treated C-6 glioma cells [451,454] and in freshly isolated astrocytes from rats treated chronically with desipramine [455].…”

Psychopharmaka und Diabetes

“…Für Desipramine aus der Gruppe der trizyklischen Antidepressiva konnte ein Einfluss auf die Dichte b-adrenerger Rezeptoren und den Rezeptortransport nachgewiesen werden [110]. Dies könnte einschneidende Veränderungen in der Energiehomöo-stase der Zelle zur Folge haben.…”