Yoshihiro Seki

Kyushu University, Fukuoka-shi, Fukuoka-ken, Japan

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Publications (15)51.76 Total impact

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    ABSTRACT: Background: Microglia are immune cells that release factors, including proinflammatory cytokines, nitric oxide (NO) and neurotrophins, following activation after disturbance in the brain. Elevation of intracellular Ca2+ concentration ([Ca2+]i) is important for microglial functions, such as the release of cytokines and NO from activated microglia. There is increasing evidence suggesting that pathophysiology of neuropsychiatric disorders is related to the inflammatory responses mediated by microglia. Brain-derived neurotrophic factor (BDNF) is a neurotrophin well known for its roles in the activation of microglia as well as in pathophysiology and/or treatment of neuropsychiatric disorders. Results: In this study, we sought to examine the underlying mechanism of BDNF-induced sustained increase in [Ca2+]i in rodent microglial cells. We observed that canonical transient receptor potential 3 (TRPC3) channels contribute to the maintenance of BDNF-induced sustained intracellular Ca2+ elevation. Immunocytochemical technique and flowcytometry also revealed that BDNF rapidly upregulated the surface expression of TRPC3 channels in rodent microglial cells. In addition, pretreatment with BDNF suppressed the production of NO induced by tumor necrosis factor α (TNFα), which was prevented by co-adiministration of a selective TRPC3 inhibitor. These suggest that BDNF induces sustained intracellular Ca2+ elevation through the upregulation of surface TRPC3 channels and TRPC3 channels could be important for the BDNF-induced suppression of the NO production in activated microglia. Conclusions: We show that TRPC3 channels could also play important roles in microglial functions, which might be important for the regulation of inflammatory responses, and may also be involved in the pathophysiology and/or the treatment of neuropsychiatric disorders.
    Journal of Biological Chemistry 05/2014; · 4.65 Impact Factor
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    ABSTRACT: Recent imaging studies have indicated that the pathophysiology of schizophrenia is closely related to white matter abnormalities and microglial activation. Additionally, recent clinical trials have suggested that atypical antipsychotics may have brain protective properties and that minocycline, an antibiotic with inhibitory effects on microglial activation, improves symptoms of schizophrenia. We have reported that not only atypical antipsychotics with dopamine D2 receptor (D2R) antagonism but also aripiprazole, a unique antipsychotic drug with D2R partial agonism, inhibit microglial activation in vitro. Thus, atypical antipsychotics may exert a beneficial influence on both microglia and oligodendrocytes, while the underlying mechanisms have not been clarified. Here, we investigated whether antipsychotics suppress oligodendrocyte damage by inhibiting microglial activation utilizing a co-culture model with microglia and oligodendrocytes. Pretreatment of aripiprazole and minocycline suppressed apoptosis of oligodendrocytes in the co-culture model with interferon-γ (IFN-γ)-activated microglia, while haloperidol, a traditional antipsychotic drug, did not. Aripiprazole and minocycline inhibited the production of tumor necrosis factor-alpha (TNF-α) from IFN-γ-activated microglia. Moreover, aripiprazole and minocycline attenuated the phosphorylation of signal transducer and activator of transcription 1 (STAT1) in microglia. Overall, our results suggest that aripiprazole and minocycline may have antipsychotic effects through reducing oligodendrocyte damage caused by microglial activation. These results put forward a novel therapeutic hypothesis in schizophrenia research. Future in vivo studies to confirm the present results should be performed.
    Schizophrenia Research 10/2013; · 4.59 Impact Factor
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    ABSTRACT: Bisphosphonate-related osteonecrosis of the jaw (BRONJ) is a serious side effect of nitrogen-containing bisphosphonate (NBP) use. Many studies have shown that BRONJ is limited to the jawbone and does not occur in the other bones. We hypothesized that BRONJ is related to local bacterial iections and involves the innate immune system. To examine the relationship between BRONJ and innate immunity, we examined the effects of NBPs on macrophages, one of the important cell types in innate immunity. The expression of toll-like receptor-4 (TLR4) in cells after pretreatment with zoledronic acid (ZOL) did not considerably differ from that in untreated control cells. However, cytokine levels and nitric oxide (NO) production increased after pretreatment with ZOL. Furthermore, ZOL induced NF-κB activation by enhancing IκB-α degradation. Lipopolysaccharide (LPS)-induced apoptosis also increased after pretreatment with ZOL. This effect was mediated by a reduction of suppressor of cytokine signaling-1 (SOCS1), which is a negative regulator of myeloid differentiation primary response gene 88 (MyD 88)-dependent signaling. These results suggest that ZOL induced excessive innate immune response and proinflammatory cytokine production and that these processes may be involved in the bone destruction observed in BRONJ.
    PLoS ONE 01/2013; 8(7):e67906. · 3.53 Impact Factor
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    ABSTRACT: Psychiatric disorders have long and dominantly been regarded to be induced by disturbances of neuronal networks including synapses and neurotransmitters. Thus, the effects of psychotropic drugs such as antipsychotics and antidepressants have been understood to modulate synaptic regulation via receptors and transporters of neurotransmitters such as dopamine and serotonin. Recently, microglia, immunological/inflammatory cells in the brain, have been indicated to have positive links to psychiatric disorders. Positron emission tomography (PET) imaging and postmortem studies have revealed microglial activation in the brain of neuropsychiatric disorders such as schizophrenia, depression and autism. Animal models of neuropsychiatric disorders have revealed the underlying microglial pathologies. In addition, various psychotropic drugs have been suggested to have direct effects on microglia. Until now, the relationship between microglia, neurotransmitters and psychiatric disorders has not well been understood. Therefore, in this review, at first, we summarize recent findings of interaction between microglia and neurotransmitters such as dopamine, serotonin, norepinephrine, acetylcholine and glutamate. Next, we introduce up-to-date knowledge of the effects of psychotropic drugs such as antipsychotics, antidepressants and antiepileptics on microglial modulation. Finally, we propose the possibility that modulating microglia may be a key target in the treatment of various psychiatric disorders. Further investigations and clinical trials should be conducted to clarify this perspective, using animal in vivo studies and imaging studies with human subjects.
    Current Medicinal Chemistry 11/2012; · 3.72 Impact Factor
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    ABSTRACT: An accumulating body of evidence point to the significance of neuroinflammation and immunogenetics also in schizophrenia. Recent genome-wide studies in schizophrenia suggest immune involvement in schizophrenia. Microglia are the resident macrophage of the brain and major players in innate immunity in the CNS. They respond rapidly to even minor pathological changes in the brain and may contribute directly to the neuronal degeneration by producing various pro-inflammatory cytokines and free radicals. In many aspects, the neuropathology of schizophrenia is closely associated with microglial activation. We and other researchers have shown the inhibitory effects of some typical or atypical antipsychotics on the release of inflammatory cytokines and free radicals from activated microglia, both of which are not only directly toxic to neurons but also cause a decrease in neurogenesis as well as white matter abnormalities in the brains of the patients with schizophrenia. The treatment through the inhibition of microglial activation may shed new light on the therapeutic strategy of schizophrenia.
    Progress in Neuro-Psychopharmacology and Biological Psychiatry 12/2011; · 3.55 Impact Factor
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    ABSTRACT: We previously developed a rat trigeminal motor neuron axotomy model involving masseter and temporal muscle resection to study pathological changes of the central nucleus after peripheral nerve injury caused by oral surgery. Because motor neurons are reported to be more vulnerable to axotomy in mice than rats, we compared the degeneration process of the trigeminal motor nucleus in the rat model with a similar mouse model. We removed masseter and temporal muscles of adult mice or rats. Animals were sacrificed at 3, 7, 14, 28, 42, and 56 days post-operation, and the trigeminal motor nuclei were histologically analyzed. Size reduction, but no neuronal loss, was seen in the trigeminal motor nuclei in both mice and rats. Time-dependent Noxa expression, starting at 1 week post-operation (wpo), was seen in the mouse model. By 8 wpo, mice expressed a higher level of Noxa than rats. Additionally, we noted persistent expression of cleaved caspase-3 in mice but not in rats. Conversely, apoptosis-inducing factor (AIF), which executes DNA fragmentation in the nucleus, was not translocated to the nucleus in either model. Our findings indicate differential activation of motor neuron apoptosis pathways after axotomy in mice and rats. Lack of activation of caspase-independent pathways and distal end denervation in our model might be related to the survival of motor neurons after axonal injury. These findings could be relevant to future neuroprotective strategies for peripheral nerve injury caused by oral surgeries.
    Journal of Oral Pathology and Medicine 11/2011; 41(4):354-60. · 2.06 Impact Factor
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    ABSTRACT: Altered antioxidant status has been implicated in schizophrenia. Microglia, major sources of free radicals such as superoxide (•O(2)(-)), play crucial roles in various brain pathologies. Recent postmortem and imaging studies have indicated microglial activation in the brain of schizophrenic patients. We previously demonstrated that atypical antipsychotics including aripiprazole significantly inhibited the release of nitric oxide and proinflammatory cytokines from interferon-γ-stimulated microglia in vitro. Antioxidative effects of antipsychotics via modulating microglial superoxide generation have never been reported. Therefore, we herein investigated the effects of antipsychotics on the •O(2)(-) generation from phorbol-myristate-acetate (PMA)-stimulated rodent microglia by the electron spin resonance (ESR) spectroscopy and also examined the intracellular mechanism by intracellular Ca(2+) imaging and immunostaining. Neuronal damage induced by microglial activation was also investigated by the co-culture experiment. Among various antipsychotics, only aripiprazole inhibited the •O(2)(-) generation from PMA-stimulated microglia. Aripiprazole proved to inhibit the •O(2)(-) generation through the cascade of protein kinase C (PKC) activation, intracellular Ca(2+) regulation and NADPH oxidase activation via cytosolic p47(phox) translocation to the plasma/phagosomal membranes. Formation of neuritic beading, induced by PMA-stimulated microglia, was attenuated by pretreatment of aripiprazole. D2R antagonism has long been considered as the primary therapeutic action for schizophrenia. Aripiprazole with D2R partial agonism is effective like other antipsychotics with fewer side effects, while aripiprazole's therapeutic mechanism itself remains unclear. Our results imply that aripiprazole may have psychotropic effects by reducing the microglial oxidative reactions and following neuronal reactions, which puts forward a novel therapeutic hypothesis in schizophrenia research.
    Schizophrenia Research 07/2011; 129(2-3):172-82. · 4.59 Impact Factor
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    ABSTRACT: Microglia are intrinsic immune cells that release factors, including proinflammatory cytokines, nitric oxide (NO) and neurotrophins, following activation after disturbance in the brain. Elevation of intracellular Ca(2+) concentration ([Ca(2+)]i) is important for microglial functions, such as the release of cytokines and NO from activated microglia. There is increasing evidence suggesting that pathophysiology of neuropsychiatric disorders is related to the inflammatory responses mediated by microglia. Brain-derived neurotrophic factor (BDNF) is a neurotrophin well known for its roles in the activation of microglia as well as in pathophysiology and/or treatment of neuropsychiatric disorders. We have recently reported that BDNF induces a sustained increase in [Ca(2+)]i through binding with the truncated TrkB receptor, resulting in activation of the PLC pathway and store-operated calcium entry (SOCE) in rodent microglial cells. Sustained activation of SOCE, possibly mediated by TRP channels, occurred after brief BDNF application and contributed to the maintenance of sustained [Ca(2+)]i elevation. Pretreatment with BDNF significantly suppressed the release of NO from activated microglia. Additionally, selective serotonin reuptake inhibitors (SSRIs), including paroxetine or sertraline, potentiated the BDNF-induced increase in [Ca(2+)]i in rodent microglial cells This article provides a review of recent findings on the role of BDNF in the pathophysiology of neuropsychiatric disorders, especially by focusing on its effect on intracellular Ca(2+) signaling in microglial cells.
    Mini Reviews in Medicinal Chemistry 06/2011; 11(7):575-81. · 2.87 Impact Factor
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    ABSTRACT: Schizophrenia is one of the most severe psychiatric diseases noted for its chronic and often debilitating processes; affecting approximately 1% of the world's population, while its etiology and therapeutic strategies still remain elusive. In the 1950s, the discovery of antipsychotic effects of haloperidol and chlorpromazine shifted the paradigm of schizophrenia. These drugs proved to be antagonists of dopamine D2 receptor (D2R), thus dopamine system dysfunction came to be hypothesized in the pathophysiology of schizophrenia, and D2R antagonism against dopamine neurons has been considered as the primary therapeutic target for schizophrenia. In addition, abnormalities of glutamatergic neurons have been indicated in the pathophysiology of schizophrenia. On the other hand, recent neuroimaging studies have shown that not only dementia but also schizophrenic patients have a significant volume reduction of some specific regions in the brain, which indicates that schizophrenia may involve some neurodegenerative process. Microglia, major sources of various inflammatory cytokines and free radicals such as superoxide and nitric oxide (NO) in the CNS, play a crucial role in a variety of neurodegenerative diseases such as dementia. Recent postmortem and positron emission computed tomography (PET) studies have indicated that activated microglia may be present in schizophrenic patients. Recent in vitro studies have suggested the anti-inflammatory effects of antipsychotics on microglial activation. In this article, we review the anti-inflammatory effects of antipsychotics on microglia, and propose a novel therapeutic hypothesis of schizophrenia from the perspective of microglial modulation.
    Mini Reviews in Medicinal Chemistry 06/2011; 11(7):565-74. · 2.87 Impact Factor
  • The Journal of neuropsychiatry and clinical neurosciences 01/2011; 23(4):E14-5. · 2.34 Impact Factor
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    ABSTRACT: Microglia are implicated in both neuroprotection and neurodegeneration, and are a key area of interest with respect to various CNS diseases. Until now, primary microglia prepared by various isolation methods have been widely used to investigate their role in CNS diseases. However, there are some problems with the current isolation methods, such as the numbers of animals required in order to obtain sufficient numbers of microglial cells due to low yields, and also the long periods of culture required. We herein describe a simple, high-yield method for isolating not only primary microglia, but also immortalized microglial cells. Our method allows for the isolation of an almost pure population of microglia with only two steps. First, a primary mixed neural culture was prepared from the brains of 3-day-old postnatal rats. Next, primary microglia were collected for 2 h by adhesion to Aclar plastic film. The average yield by this method was approximately 50 times higher than that of the conventional shaking method. Immortalized microglial cells could also be prepared based on this procedure. A plasmid vector encoding the SV40 large T antigen was transfected into the mixed neural culture using a calcium phosphate precipitation method. Then, proliferating immortalized microglia were collected after several weeks in a similar fashion. Several clones were obtained by limited dilution and one of the immortalized cell lines was designated SMK. The SMK cells exhibited markers specific for the microglia lineage, including Iba-1, CD11b, CD45, CD68, major histocompatibility complex (MHC) class I and MHC class II, but not for the astrocyte-specific markers, GFAP and glutamate aspartate transporter. SMK also showed phagocytic activity. In conclusion, this method resulted in a high-yield preparation of microglial cultures with ease and reproducibility.
    Neuropathology 11/2010; 31(3):215-22. · 1.91 Impact Factor
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    ABSTRACT: Microglia, which are a major glial component of the central nervous system (CNS), have recently been suggested to mediate neuroinflammation through the release of pro-inflammatory cytokines and nitric oxide (NO). Microglia are also known to play a critical role as resident immunocompetent and phagocytic cells in the CNS. Immunological dysfunction has recently been demonstrated to be associated with the pathophysiology of depression. However, to date there have only been a few studies on the relationship between microglia and depression. We therefore investigated if antidepressants can inhibit microglial activation in vitro. Our results showed that the selective serotonin reuptake inhibitors (SSRIs) paroxetine and sertraline significantly inhibited the generation of NO and tumor necrosis factor (TNF)-α from interferon (IFN)-γ-activated 6-3 microglia. We further investigated the intracellular signaling mechanism underlying NO and TNF-α release from IFN-γ-activated 6-3 microglia. Our results suggest that paroxetine and sertraline may inhibit microglial activation through inhibition of IFN-γ-induced elevation of intracellular Ca(2+). Our results suggest that the inhibitory effect of paroxetine and sertraline on microglial activation may not be a prerequisite for antidepressant function, but an additional beneficial effect.
    Progress in Neuro-Psychopharmacology and Biological Psychiatry 10/2010; 34(7):1306-16. · 3.55 Impact Factor
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    ABSTRACT: Microsurgical reconstruction techniques have allowed treatment of advanced head and neck carcinomas; however, it remains difficult to achieve long-term, functional reconstruction of the faciocervical muscles. To address this issue, in this we developed a rat trigeminal nerve denervation model that closely simulates the effects of oral surgery. The rat trigeminal nerve denervation model was developed by removing the masseter and temporal muscles, and degeneration process of the trigeminal motor nucleus was investigated by immunohistochemistry with particular focus on microglial/astrocytic reactions and motoneuron degeneration. Atrophy of the trigeminal motor nucleus was observed at 8 weeks after denervation. A microglial reaction peaked at 3 days post-operation, while an astrocytic reaction was evident within 2 weeks, and peaked around 4 weeks post-operation. Expression of the stress protein HSP27 and an autophagy marker Rab24 was also upregulated in the injured trigeminal motor nucleus. The results from this study suggest that this model is a practical and useful tool help to develop a further understanding of the pathology of the trigeminal motor nucleus after surgical denervation.
    Journal of Oral Pathology and Medicine 04/2009; 38(10):777-84. · 2.06 Impact Factor
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    ABSTRACT: Microglia are intrinsic immune cells that release factors, including proinflammatory cytokines, NO, and neurotrophins, following activation after disturbance in the brain. Elevation of intracellular Ca(2+) concentration ([Ca(2+)]i) is important for microglial functions, such as the release of cytokines and NO from activated microglia. There is increasing evidence suggesting that pathophysiology of neuropsychiatric disorders is related to the inflammatory responses mediated by microglia. Brain-derived neurotrophic factor (BDNF) is a neurotrophin well known for its roles in the activation of microglia as well as in pathophysiology and/or treatment of neuropsychiatric disorders. In this study, we observed that BDNF induced a sustained increase in [Ca(2+)]i through binding with the truncated tropomyosin-related kinase B receptor, resulting in activation of the PLC pathway and store-operated calcium entry in rodent microglial cells. RT-PCR and immunocytochemical techniques revealed that truncated tropomyosin-related kinase B-T1 receptors were highly expressed in rodent microglial cells. Sustained activation of store-operated calcium entry occurred after brief BDNF application and contributed to the maintenance of sustained [Ca(2+)]i elevation. Pretreatment with BDNF significantly suppressed the release of NO from activated microglia. Additionally, pretreatment of BDNF suppressed the IFN-gamma-induced increase in [Ca(2+)]i, along with a rise in basal levels of [Ca(2+)]i in rodent microglial cells. We show direct evidence that rodent microglial cells are able to respond to BDNF, which may be important for the regulation of inflammatory responses, and may also be involved in the pathophysiology and/or the treatment of neuropsychiatric disorders.
    The Journal of Immunology 01/2009; 183(12):7778-86. · 5.52 Impact Factor
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    ABSTRACT: The activation of the inflammatory/immunological response system is suggested to be related to the pathophysiology of schizophrenia. Aripiprazole is a novel atypical antipsychotic, which is a high-affinity dopamine D(2) receptor partial agonist. Atypical antipsychotics, all of which have dopamine D(2) receptor antagonism, have recently reported to have significantly inhibitory effects on interferon (IFN)-gamma-induced microglial activation in vitro. In the present study, we investigated whether or not aripiprazole also has anti-inflammatory effect on IFN-gamma-induced microglial activation. Not quinpirole, dopamine D(2) full agonist, but aripiprazole significantly inhibited the generation of nitric oxide (NO) and tumor necrosis factor (TNF)-alpha from IFN-gamma-activated microglia and suppressed the IFN-gamma-induced elevation of intracellular Ca(2+) concentrations ([Ca(2+)](i)) in murine microglial cells. Increased [Ca(2+)](i) has been reported to be required, but by itself not sufficient, for the release of NO and certain cytokines. As a result, we can speculate that aripiprazole may inhibit IFN-gamma-induced microglial activation through the suppression of IFN-gamma-induced elevation of [Ca(2+)](i) in microglia. Our results demonstrated that not only antipsychotics which have dopamine D(2) receptor antagonism but also aripiprazole have anti-inflammatory effects via the inhibition of microglial activation. Antipsychotics may therefore have a potentially useful therapeutic effect on patients with schizophrenia by reducing the microglial inflammatory reactions.
    Journal of Neurochemistry 01/2008; 106(2):815-25. · 3.97 Impact Factor