Pharmacologically diverse antidepressants facilitate TRKB receptor activation by disrupting its interaction with the endocytic adaptor complex AP-2

Abstract

Antidepressant drugs activate TRKB (tropomyosin-related kinase B), however it remains unclear whether these compounds employ a common mechanism for achieving this effect. We found by using mass spectrometry that the interaction of several proteins with TRKB was disrupted in the hippocampus of fluoxetine-treated animals (single intraperitoneal injection), including members of the AP-2 complex (adaptor protein complex-2) involved in vesicular endocytosis. The interaction of TRKB with the cargo-docking mu subunit of the AP-2 complex (AP2M) was disrupted by both acute and repeated fluoxetine treatment.However, while the coupling between full length TRKB and AP2M was disrupted by fluoxetine, the interaction between AP2M and the TRKB C-terminal peptide was resistant to this drug, indicating that the binding site targeted by fluoxetine must lie outside of the TRKB:AP2M interface. In addition to fluoxetine, other pharmacologically diverse antidepressants imipramine, rolipram, phenelzine, ketamine, and the ketamine metabolite 2R,6R-hydroxynorketamine (RR-HNK) also decreased the interaction between TRKB:AP2M in vitro , as measured by ELISA. Silencing the expression of AP2M in MG87.TRKB cell line led to increased surface positioning of TRKB and to a higher response to BDNF (brain-derived neurotrophic factor), observed as the levels of active TRKB. Moreover, animals haploinsufficient for the Ap2m1 gene displayed increased levels of active TRKB in vivo , as well as an enhanced cell surface expression of the receptor in cultured hippocampal neurons.Taken together, our data suggests that disruption of the TRKB:AP2M interaction is an effect shared by several antidepressants with diverse chemical structures and canonical modes of action.

Chondroitinase and Antidepressants Promote Plasticity by Releasing TRKB from Dephosphorylating Control of PTPσ in Parvalbumin Neurons

“…These data indicate that PTPσ interacts with TRKB. Furthermore, our previous proteomic study found PTPσ among the proteins that were immunoprecipitated with TRKB in hippocampal samples of the adult mouse brain ( Fred et al, 2019 ).…”

“…Cell-surface ELISA was conducted to assess PTPσ levels found on the cell surface as previously described ( Zheng et al, 2008 ; Fred et al, 2019 ). Briefly, cortical cells were cultivated in clear-bottom 96-well plates (ViewPlate 96, PerkinElmer).…”

Antidepressant drugs act by directly binding to TRKB neurotrophin receptors

“…Simulations predict that membrane lipids also participate in fluoxetine binding to TRKB. As TRKB exists as a multi-protein complex that also includes transmembrane proteins 66,67 , it is possible that other proteins and lipids participate in antidepressant binding to TRKB in cell-type and subcellular compartment dependent manner. Further characterization of this binding site may yield important information for discovery of new antidepressants with increased potency for plasticity-related behavioral effects.…”

Role of BDNF in the pathophysiology and treatment of depression: Activity‐dependent effects distinguish rapid‐acting antidepressants

“…Typical monoaminergic antidepressants are reported to rapidly increase the phosphorylation of TrkB, which has been used as a surrogate marker for increased BDNF activity (Saarelainen et al, 2003). However, recent studies demonstrate that these monoaminergic antidepressants rapidly activate TrkB receptors via interactions with other regulatory sites on the receptor, including the endocytic adaptor complex AP-2 (Fred et al, 2019) and a cholesterol regulatory site (Casarotto et al, 2019) that are independent of BDNF release. Importantly, the rapid effects of monoaminergic antidepressants on TrkB do not correspond with the time lag for the therapeutic response to these agents, and there is no direct evidence that these agents produce activity-dependent synaptic effects.…”