ABSTRACT
Depression is accompanied by the activation of the inflammatory-response system, and increased production of proinflammatory cytokines may play a role in the pathophysiology of depressive disorders. Imipramine (IM), a tricyclic antidepressant drug, has recently been shown to promote neurogenesis and improve the survival rate of neurons in the hippocampus. However, whether IM elicits a neuroprotective or anti-inflammatory effect, or promotes the differentiation of neural stem cells (NSCs) remains to be elucidated. In this study, we cultured NSCs derived from the hippocampal tissues of adult rats as an in vitro model to evaluate the NSCs drug-modulation effects of IM. Our results showed that 3 microM IM treatment significantly increased the survival rate of NSCs, and up-regulated the mRNA and protein expression of brain-derived neurotrophic factor (BDNF) and Bcl-2 in Day-7 IM-treated NSCs. Similar to BDNF-treated effect, incubation of NSCs with 3 microM IM increased Bcl-2 protein levels and further prevented lipopolysaccharide (LPS)-induced apoptosis through the activation of the mitogen-activated protein kinase (MAPK)/extracellular-regulated kinase (ERK) pathway. Inhibition of BDNF expression with small interfering RNA (siRNA), or blocking the MAPK pathway with U0126 further significantly decreased Bcl-2 protein levels and abrogated the neuroprotective effects of IM against LPS-induced apoptosis in NSCs. In addition, the percentages of serotonin and MAP-2-positive neuronal cells in the Day 7 culture of IM-treated NSCs were significantly increased. By using microdialysis with high performance liquid chromatography-electrochemical detection, the functional release of serotonin in the process of serotoninergic differentiation of IM-treated NSCs was concomitantly increasing and mediated by the activation of the BDNF/MAPK/ERK pathway/Bcl-2 cascades. In sum, the study results indicate that IM can increase the neuroprotective effects, suppress the LPS-induced inflammatory process, and promote serotoninergic differentiation in NSCs via the modulation of the BDNF/MAPK/ERK pathway/Bcl-2 cascades.
Subject(s)
Adrenergic Uptake Inhibitors/pharmacology , Apoptosis/drug effects , Brain-Derived Neurotrophic Factor/metabolism , Imipramine/pharmacology , Mitogen-Activated Protein Kinase Kinases/metabolism , Neurons/drug effects , Signal Transduction/drug effects , Stem Cells/drug effects , Analysis of Variance , Animals , Cell Differentiation/drug effects , Cell Survival/drug effects , Cells, Cultured , Enzyme Inhibitors/pharmacology , Enzyme-Linked Immunosorbent Assay , Hippocampus/cytology , In Situ Nick-End Labeling , Lipopolysaccharides/pharmacology , Nerve Tissue Proteins/metabolism , Rats , Rats, Sprague-Dawley , Time FactorsABSTRACT
The hippocampus has long been associated with learning, memory, and modulation of emotional responses. Previous studies demonstrated that stress-induced loss of hippocampal neurons may contribute to the pathogenesis of depression. The recent observations supported that antidepressant drugs increase the production of serotoninergic neurotransmitter and they play a critical role in the initiation of neurogenesis in the hippocampus. In order to explore the possible new mechanism of the treatment of depression, we cultured neural stem cells (NSCs) derived from the hippocampus of adult rats as an in vitro model to evaluate the capabilities of neuroprotection and neural differentiation in NSCs by fluoxetine (FL) treatment. Our results showed that 20 microM FL treatment can significantly increase the proliferation rate of NSCs (p<0.05), and up-regulate the mRNA and protein expressions of Bcl-2 in Day-7 FL-treated NSCs (p<0.01). Using Bcl-2 gene silencing with small interfering RNA, our data verified that FL can prevent Fas ligand-induced caspase-dependent apoptosis in NSCs through the activation of Bcl-2. The in vitro observation and immunofluorescent study further demonstrated that FL treatment can stimulate the neurite development and serotoninergic differentiation of NSCs through the activation of Bcl-2. Using microdialysis with high performance liquid chromatography- electrochemical detection, the functional release of serotonin in the differentiating NSCs with FL treatment was increased and simultaneously regulated by the Bcl-2 expressions. In sum, the study results indicate that antidepressant administration can increase NSCs survival, promote the neurite development, and facilitate NSCs differentiating into the functional serotoninergic neurons via the modulation of Bcl-2 expression.
