Antidepressant Activity And Its Mechanism Of Allosteric Modulation Of Sigma-1 Receptor

Part 1 SOMCL-668 manifests as an allosteric modulator ofsigma-1 receptorAims: Sigma-1 receptors are involved in the pathophysiological process of several neuropsychiatric diseases such as depression. Allosteric modulation represents an important mechanism for receptor functional regulation. Our previous work has confirmed that 3-methyl-phenyl-2, 3, 4, 5-tetrahydro-1H-benzo[d]azepin-7-ol(SOMCL-668) can promote the binding of 3H-(+)-pentazocine with the sigma-1 receptor in an allosteric manner. Herein, we further examined the functional allosteric effect of SOMCL-668 on sigma-1 receptors.Methods: The complex of Bip(binding immunoglobulin protein) and sigma-1 receptor in the HT22 cells was revealed by the immunostaining or immunoprecipitation, which was stimulated by SOMCL-668 alone or with(+)SKF-10047. Western blotting assay on the plasma membrane was performed to reveal the translocation of sigma-1 receptor treated with SOMCL-668 alone or in combination with(+)SKF-10047. Besides, the neurite outgrowth and release of BDNF(brain-derived neurotrophic factor) were investigated in the primary neuron culture.Results: SOMCL-668 alone did not significantly alter the association between sigma-1 receptor and Bip, the compound, however, significantly potentiated the effect of(+)SKF-10047 on sigma-1 receptor disassociation and translocation from Bip. Additionally, SOMCL-668 alone did not significantly alter neurite outgrowth or the secretion of BDNF. However, SOMCL-668 significantly potentiated(+)SKF-10047-stimulated neurite growth and production of BDNF.Conclusions: SOMCL-668 is an allosteric mofulator of sigma-1 receptor, which possesses the functional allosteric effect.Part II Allosteric modulation of sigma-1 receptor elicitsantidepressant activityAims: In the present study, we examined antidepressant activity and potential mechanisms of the latest identified novel and selective allosteric modulator of sigma-1 receptor SOMCL-668.Methods:(1) Forced swimming test(FST) and tail suspension test(TST) were used to evaluate the potential antidepressant effects of acute SOMCL-668 treatment.(2) The antidepressant effects of chronic application of SOMCL-668 were revealed through sucrose preference and open field test in the chronic unpredicted mild stress(CUMS) model. Western blotting assay was adopted to detect BDNF-GSK3β(glycogen synthase kinase 3β) pathway in the CUMS model.(3) Western blotting assay was performed to test whether sigma-1 receptor could regulate GSK3β(ser-9) phosphorylation.(4) Western blotting assay was performed to uncover whether SOMCL-668 regulated GSK3β(ser-9) phosphorylation, and whether GSK3β mediated the antidepressant activity of SOMCL-668.Results:(1) A single administration of SOMCL-668 decreased the immobility time in FST and TST in mice, which were abolished by pretreatment of sigma-1 receptor antagonist BD1047.(2) In the CUMS model, chronic application of SOMCL-668 rapidly ameliorated anhedonia- like behavior(within a week, rapid than venlafaxine), accompanying with the enhanced expression of BDNF and phosphorylation of GSK3β(ser-9) in the hippocampus.(3) Agonists or over-expression of sigma-1 receptor can increase the phosphorylation of GSK3β(ser-9), which was reversed by inhibition of Trk B receptor or AKT pathway. It suggests that sigma-1 receptor can regulate GSK3β activity.(4) SOMCL-668 rapidly promoted the phosphorylation of GSK3β(ser-9) in the mice hippocampus, which was abolished by sigma-1 receptor antagonist. SOMCL-668 also elevated the phosphorylation of GSK3β(ser-9) in the HT22 cells in an allosteric manner. However, this effect was disapper while the sigma-1 receptor was knockdown by the si RNA. Additonally, the antidepressant activity of SOMCL-668 was canceled by pretreatment with pharmacologic activator of GSK3β.Conclusions: SOMCL-668, a novel allosteric modulator of sigma-1 receptors, elicits a potent and rapid acting antidepressant effect, which may associated with BDNF-GSK3β pathway. The present data provides the first evidence that allosteric modulation of sigma-1 receptors may represent a new approach for antidepressant drug discovery.