The Molecular Mechanism Of Clomipramine On Neural Stem Cell/Progenitor Proliferation And Differentiation

Depression is a common and serious psychological disorder, affecting people of all ages, backgrounds, and ethnic groups. Psychologist Martin Seligman has called depression the "common cold" of psychological problems, because nearly everyone has suffered it at some time. In the United States, depression is extremely common and is one of the ten most frequently reported medical conditions. It is estimated that 9.5 percent of the population, or about 20.9 million American adults suffered from a depressive illness each year and that approximately 16% of the population were stricken with depression on at least one occasion in their lives. And indeed, it is currently the leading cause of disability in America as well as other countries, and is expected to become the second leading cause of disability in the world (after heart disease) by the year 2020, according to the WHO (World Health Organization). Depression can interfere with person's normal functioning, and frequently disrupt the work, social and family adjustment. The economic cost for this disorder is high, but the cost in human suffering cannot be estimated. It causes pain and suffering not only to those who have a disorder, but also to those who care about them. Serious depression can destroy family life as well as the life of the depressed person. There are a variety of antidepressant medications and psychotherapies that can be used to treat depressive disorders. People with moderate to severe depression most often benefit from antidepressants. Whereas, there is also need for safe, effective, and affordable alternative treatments for depression.The monoamine hypothesis of depression is a biological theory stating that depression is caused by the underactivity in the brain of monoamines, such as dopamine, serotonin, and norepinephrine. The hypothesis supposes that increasing the levels of these brain chemicals--known as neurotransmitters--could alleviate or completely reverse depression. The hypothesis has been a major focus of research in the pathophysiology and pharmacotherapy for over 50 years, and led to the development of new classes of drugs such as SSRIs (selective serotonin reuptake inhibitors). There are several classes of antidepressant, including the monoamine oxidase inhibitors (MAOIs), tricyclic antidepressants (TCAs). tetracyclic antidepressants (TeCAs), selective serotonin reuptake inhibitors (SSRIs), and serotonin-norepinephrine reuptake inhibitors (SNRIs). The clinical research showed that these antidepressants would upregulated the monoamine neurotransmitters to the nomal level in several minutes, but the depressive symptoms would be relieved after 4-6 weeks. So, the monoamine hypothesis could not elucidate the clinical pharmacological phenomenon.One very influential theme that emerged, only to gain momentum, is the neurogenesis-depression hypothesis. Generally, the idea is that adult hippocampal neurogenesis is protective against depression. But more direct evidence linking the hippocampus to mood has come from studies showing that manipulations to the hippocampus alter stress and anxiety-related behaviors. Daszuta, McEwen, and Duman discussed reduced adult neurogenesis as a potential factor in depression and mood disorders just before the decade. But the study that really got the field going was the finding that antidepressants can increase neurogenesis, by Malberg et al., in 2000. Within the next few years it was clear that every type of chemical antidepressant increased neurogenesis, as did electroconvulsive shock, as did environmental influences such as running and social housing, which are known to have antidepressant effects. Furthermore, factors that precipitate depression, such as chronic stress, potently downregulate neurogenesis. The neurotrophic factors promoting neurogenesis also have antidepressant effects. These findings are all consistent with the possibility that neurogenesis plays a role in depression, antidepressants/ECS/exercise/stress also have many other effects on the brain that could explain their effects on mood.Adult hippocampal neurogenesis has been implicated in cognitive and emotional processes, as well as in response to antidepressant treatment. However, little is known about how the adult stem cell lineage contributes to hippocampal structure and function and how this process is modulated by the animal's experience. The increase of neurogenesis might contribute to the behavioral effects of antidepressants. However, the mechanism by which antidepressants increase hippocampal neurogenesis is largely unknown. One paper show that fluoxetine exposure can promoted rat neural progenitors proliferating and differentiating in postnatal cerebellum possibly through the activation of 5HT (1A) receptors and ERK-CREB signaling in vitro. And many reseaches confirmed that the neurothrophic factors such as, BDNF, VEGF et al, maybe involved in the effect of antidepressant on neurogenesis. But if there are direct effect of antidepressant on neurogenesis, in other words, the proliferation and differentiation of neural progenitors? And the mechanism by which antidepressants increase hippocampal neurogenesis also merited further investigation.Eluminating the molecular mechanism of clomipramine on the proliferation and differentiation of neural progenitors will give more clues for developing new antidepressant. There has been increasing interest in examining intracellular signal transduction pathways that may regulate neurogenesis. For example, the cAMP cascade and the cAMP rsponse element-bind ing protein (CREB) have recently been implicated as processes that enhance survival of newborn neurons in the adult hippocampus. Because activation of the cAMP-CREB pathway increases the expression of BDNF in the hippocampus, which in turn in creases neurogenesis in the adult brain, it is plausible that this may be a pathway involved in neurogenesis modulation within depression and its treatment with antidepressants. It has indeed been suggested that CREB may serve as a convergence point for multiple classes of antidepressants drugs; however, to date very few studies have addressed this hypothesis.There appears to be sufficient evidence to justify continued investigation into a molecular link between adult hippocampal neurogenesis and depression. While it is probable that modulation of hippocampal neurogenesis contributes to the onset and alleviation of depression, much investigation is still needed into the mechanisms that may regulate this process. The articulation of precise and consistent definitions of study variables should lead to improved focus for research directions, as well as contributing to outcomes that can be meaningfully compared across studies.This paper elucidate the molecular mechanism of clomipramine on the proliferation and differentiation of neural progenitors in two parts:1) The direct effect and the right dose of clomipramine on the proliferation and differentiation of neural progenitors 2) the cell signaling and the target gene involved in the effect of clomipramine on neurogenesis.The results are presented as following:3) The direct effect of clomipramien on the neural progenitor d) Establish the steady culture systems of neural progenitors in vitroThe neural progenitors from hippocampus were consistent proliferated in vitro, and attached to the poly-L-lysine-coated culture plate and gradually migrated and differentiated into neurons, astrocytes and oligodentrocytes in the differentiation media (deprived of growth factors).e) Confirm the direct effect of clomipramine on the neural progenitors 2μM and 5μM clomipramine further promotes the proliferation of neural progenitors in the existent of bFGF and EGF. And in the differentiation media, the same dose of clomipramine also positively altered the differentiation of neural progenitors and showed the preference of astrocytes.4) the molecular mechanism of clomipramine on the neural progenitorsd) The different activation of the cell signaling molecules involved in the effectof clomipramine on the neural progenitors There are several signal pathway involved in the proliferation and differentiation of neural progenitors. Among these, c-Srk, Rsk, Erk et al are involved in the effect of clomipramine on neural progeniotors.e) Observation the proliferation of neural progenitors treated with clomipramine and the inhibitor of MEK and ERKThe PD 98059 and U0126 partly contradicted the effect of clomipramine on neural progenitorsf) Searching the relative target gene in the downstream of signaling pathway by Neurogenesis and Neural Stem Cells PCR Array. In 89 target gene, there is only GDNF mRNA were upregulated in 2μM clomipromine group compared with the 0μM group. But, there are Bone morphogenetic protein 15, Bone morphogenetic protein 8a, GDNF, Pleiotrophin mRNA were up-regulated, and only Neuropilin 1 were down-regulated.Conclusion:4.2μM and 5μM clomipramine can promote the proliferation and differentiation of neural progenitors 5. The ERK signaling pathway is involved in the effect of clomipramine on neural progeniotors.6. the downstream target gene of the ERK signaling pathway were GDNF, Bone morphogenetic protein 15, Bone morphogenetic protein 8a, Pleiotrophin, Neuropilin 1. The role of these target genes in the effect of clomipramine on neurogenesis is merited more investigation.