Kazue Hisaoka-Nakashima

Antidepressant acts on astrocytes leading to an increase in the expression of neurotrophic/growth factors: differential regulation of FGF-2 by noradrenaline.

Recently, multiple neurotrophic/growth factors have been proposed to play an important role in the therapeutic action of antidepressants. In this study, we prepared astrocyte- and neuron-enriched cultures from the neonatal rat cortex, and examined the changes in neurotrophic/growth factor expression by antidepressant treatment using real-time PCR. Treatment with amitriptyline (a tricyclic antidepressant) significantly increased the expression of fibroblast growth factor-2 (FGF-2), brain-derived neurotrophic factor, vascular endothelial growth factor and glial cell line-derived neurotrophic factor mRNA with a different time course in astrocyte cultures, but not in neuron-enriched cultures. Only the expression of FGF-2 was higher in astrocyte cultures than in neuron-enriched cultures. We focused on the FGF-2 production in astrocytes. Several different classes of antidepressants, but not non-antidepressants, also induced FGF-2 mRNA expression. Noradrenaline (NA) is known to induce FGF-2 expression in astrocyte cultures, as with antidepressants. Therefore, we also assessed the mechanism of NA-induced FGF-2 expression, in comparison to amitriptyline. NA increased the FGF-2 mRNA expression via α1 and β-adrenergic receptors; however, the amitriptyline-induced FGF-2 mRNA expression was not mediated via these adrenergic receptors. Furthermore, the amitriptyline-induced FGF-2 mRNA expression was completely blocked by cycloheximide (an inhibitor of protein synthesis), while the NA-induced FGF-2 mRNA was not. These data suggest that the regulation of FGF-2 mRNA expression by amitriptyline was distinct from that by NA. Taken together, antidepressant-stimulated astrocytes may therefore be important mediators that produce several neurotrophic/growth factors, especially FGF-2, through a monoamine-independent and a de novo protein synthesis-dependent mechanism.

Neuropathic Pain in Rats with a Partial Sciatic Nerve Ligation Is Alleviated by Intravenous Injection of Monoclonal Antibody to High Mobility Group Box-1

High mobility group box-1 (HMGB1) is associated with the pathogenesis of inflammatory diseases. A previous study reported that intravenous injection of anti-HMGB1 monoclonal antibody significantly attenuated brain edema in a rat model of stroke, possibly by attenuating glial activation. Peripheral nerve injury leads to increased activity of glia in the spinal cord dorsal horn. Thus, it is possible that the anti-HMGB1 antibody could also be efficacious in attenuating peripheral nerve injury-induced pain. Following partial sciatic nerve ligation (PSNL), rats were treated with either anti-HMGB1 or control IgG. Intravenous treatment with anti-HMGB1 monoclonal antibody (2 mg/kg) significantly ameliorated PSNL-induced hind paw tactile hypersensitivity at 7, 14 and 21 days, but not 3 days, after ligation, whereas control IgG had no effect on tactile hypersensitivity. The expression of HMGB1 protein in the spinal dorsal horn was significantly increased 7, 14 and 21 days after PSNL; the efficacy of the anti-HMGB1 antibody is likely related to the presence of HMGB1 protein. Also, the injury-induced translocation of HMGB1 from the nucleus to the cytosol occurred mainly in dorsal horn neurons and not in astrocytes and microglia, indicating a neuronal source of HMGB1. Markers of astrocyte (glial fibrillary acidic protein (GFAP)), microglia (ionized calcium binding adaptor molecule 1 (Iba1)) and spinal neuron (cFos) activity were greatly increased in the ipsilateral dorsal horn side compared to the sham-operated side 21 days after PSNL. Anti-HMGB1 monoclonal antibody treatment significantly decreased the injury-induced expression of cFos and Iba1, but not GFAP. The results demonstrate that nerve injury evokes the synthesis and release of HMGB1 from spinal neurons, facilitating the activity of both microglia and neurons, which in turn leads to symptoms of neuropathic pain. Thus, the targeting of HMGB1 could be a useful therapeutic strategy in the treatment of chronic pain.

Amitriptyline up-regulates connexin43-gap junction in rat cultured cortical astrocytes via activation of the p38 and c-Fos/AP-1 signalling pathway

Intercellular communication via gap junctions, comprised of connexin (Cx) proteins, allow for communication between astrocytes, which in turn is crucial for maintaining CNS homeostasis. The expression of Cx43 is decreased in post‐mortem brains from patients with major depression. A potentially novel mechanism of tricyclic antidepressants is to increase the expression and functioning of gap junctions in astrocytes.

History of the G Protein–Coupled Receptor (GPCR) Assays From Traditional to a State-of-the-Art Biosensor Assay

The G protein-coupled receptors (GPCRs) form the largest and the most versatile superfamily that share a seven-transmembrane-spanning architecture. GPCR-signaling is involved in vision, taste, olfaction, sympathetic/parasympathetic nervous functions, metabolism, and immune regulation, indicating that GPCRs are extremely important therapeutic targets for various diseases. Cellular dielectric spectroscopy (CDS) is a novel technology that employs a label-free, real-time and cell-based assay approach for the comprehensive pharmacological evaluation of cells that exogenously or endogenously express GPCRs. Among the biosensors that use CDS technology, the CellKey™ system not only detects the activation of GPCRs but also distinguishes between signals through different subtypes of the Gα protein (Gs, Gi/o, and Gq). In this review, we discuss the traditional assays and then introduce the principles by which the CellKey™ system evaluates GPCR activation, followed by a perspective on the advantages and future prospects of this system.

Tricyclic Antidepressant Amitriptyline-induced Glial Cell Line-derived Neurotrophic Factor Production Involves Pertussis Toxin-sensitive Gαi/o Activation in Astroglial Cells

Background: A significant non-neural, monoamine-independent mechanism underlies the antidepressant effect of amitriptyline. Results: Amitriptyline-evoked GDNF production is mediated by pertussis toxin (PTX)-sensitive Gαi/o. Conclusion: PTX-sensitive Gαi/o activation is critical for the cascade that underpins the biological effect of amitriptyline. Significance: Further elaboration of the intracellular mechanism of amitriptyline could lead to greater understanding of depression and novel antidepressant treatments. Further elaborating the mechanism of antidepressants, beyond modulation of monoaminergic neurotransmission, this study sought to elucidate the mechanism of amitriptyline-induced production of glial cell line-derived neurotrophic factor (GDNF) in astroglial cells. Previous studies demonstrated that an amitriptyline-evoked matrix metalloproteinase (MMP)/FGF receptor (FGFR)/FGFR substrate 2α (FRS2α)/ERK cascade is crucial for GDNF production, but how amitriptyline triggers this cascade remains unknown. MMP is activated by intracellular mediators such as G proteins, and this study sought to clarify the involvement of G protein signaling in amitriptyline-evoked GDNF production in rat C6 astroglial cells (C6 cells), primary cultured rat astrocytes, and normal human astrocytes. Amitriptyline-evoked GDNF mRNA expression and release were inhibited by pertussis toxin (PTX), a Gαi/o inhibitor, but not by NF449, a Gαs inhibitor, or YM-254890, a Gαq inhibitor. The activation of the GDNF production cascade (FGFR/FRS2α/ERK) was also inhibited by PTX. Deletion of Gαο1 and Gαi3 by RNAi demonstrated that these G proteins play important roles in amitriptyline signaling. G protein activation was directly analyzed by electrical impedance-based biosensors (CellKeyTM assay), using a label-free (without use of fluorescent proteins/probes or radioisotopes) and real time approach. Amitriptyline increased impedance, indicating Gαi/o activation that was suppressed by PTX treatment. The impedance evoked by amitriptyline was not affected by inhibitors of the GDNF production cascade. Furthermore, FGF2 treatment did not elicit any effect on impedance, indicating that amitriptyline targets PTX-sensitive Gαi/o upstream of the MMP/FGFR/FRS2α/ERK cascade. These results suggest novel targeting for the development of antidepressants.

Tumor necrosis factor-mediated downregulation of spinal astrocytic connexin43 leads to increased glutamatergic neurotransmission and neuropathic pain in mice.

Spinal cord astrocytes are critical in the maintenance of neuropathic pain. Connexin 43 (Cx43) expressed on spinal dorsal horn astrocytes modulates synaptic neurotransmission, but its role in nociceptive transduction has yet to be fully elaborated. In mice, Cx43 is mainly expressed in astrocytes, not neurons or microglia, in the spinal dorsal horn. Hind paw mechanical hypersensitivity was observed beginning 3days after partial sciatic nerve ligation (PSNL), but a persistent downregulation of astrocytic Cx43 in ipsilateral lumbar spinal dorsal horn was not observed until 7days post-PSNL, suggesting that Cx43 downregulation mediates the maintenance and not the initiation of nerve injury-induced hypersensitivity. Downregulation of Cx43 expression by intrathecal treatment with Cx43 siRNA also induced mechanical hypersensitivity. Conversely, restoring Cx43 by an adenovirus vector expressing Cx43 (Ad-Cx43) ameliorated PSNL-induced mechanical hypersensitivity. The sensitized state following PSNL is likely maintained by dysfunctional glutamatergic neurotransmission, as Cx43 siRNA-induced mechanical hypersensitivity was attenuated with intrathecal treatment of glutamate receptor antagonists MK801 and CNQX, but not neurokinin-1 receptor antagonist CP96345 or the Ca(2+) channel subunit α2δ1 blocker gabapentin. The source of this dysfunctional glutamatergic neurotransmission is likely decreased clearance of glutamate from the synapse rather than increased glutamate release into the synapse. Astrocytic expression of glutamate transporter GLT-1, but not GLAST, and activity of glutamate transport were markedly decreased in mice intrathecally injected with Cx43-targeting siRNA but not non-targeting siRNA. Glutamate release from spinal synaptosomes prepared from mice treated with either Cx43-targeting siRNA or non-targeting siRNA was unchanged. Intrathecal injection of Ad-Cx43 in PSNL mice restored astrocytic GLT-1 expression. The cytokine tumor necrosis factor (TNF) has been implicated in the induction of central sensitization, particularly through its actions on astrocytes, in the spinal cord following peripheral injury. Intrathecal injection of TNF in naïve mice induced the downregulation of both Cx43 and GLT-1 in spinal dorsal horn, as well as hind paw mechanical hypersensitivity, as observed in PSNL mice. Conversely, intrathecal treatment of PSNL mice with the TNF inhibitor etanercept prevented not only mechanical hypersensitivity but also the downregulation of Cx43 and GLT-1 expression in astrocytes. The current findings indicate that spinal astrocytic Cx43 are essential for the maintenance of neuropathic pain following peripheral nerve injury and suggest modulation of Cx43 as a novel target for developing analgesics for neuropathic pain.

The regulation of exon-specific brain-derived neurotrophic factor mRNA expression by protein kinase C in rat cultured dorsal root ganglion neurons

Although brain-derived neurotrophic factor (BDNF) is localized in primary sensory neurons and has crucial roles in nociceptive transduction, the mechanisms involved in regulation of BDNF exon-specific mRNA expression in dorsal root ganglion (DRG) neurons have yet to be determined. Rat primary cultures of DRG neurons were stimulated with phorbol-12-myristate-13-acetate (PMA), a potent activator of protein kinase C (PKC), which resulted in the robust expression of both BDNF mRNA and protein. Among each BDNF mRNA exon, it was found that exons I, IV and VI were especially induced after PMA stimulation. The induction of these exons was significantly blocked by Gö6983 (a broad spectrum PKC inhibitor), Gö6976 (a conventional PKCs and PKCμ inhibitor), and rottlerin (a PKCδ inhibitor), but not by a PKCε inhibitor. The effect of PMA on exons I and VI was blocked by either U0126 (a MAP kinase kinase (MEK) inhibitor) or SB202190 (a p38 inhibitor), and PMAs effect on exon IV was inhibited by U0126 but not by SB202190. Furthermore, the activation of cAMP-responsive element-binding protein (CREB) was associated with the induction of exons I and IV, and the activation of nuclear factor-κB (NF-κB) contributed to the induction of exons I, IV and VI. These results show that the activation of PKCs induces the expression of BDNF mRNA exons I, IV and VI through exon-specific mechanisms, including extracellular signal-regulated kinase, p38, CREB and NF-κB, in cultured DRG neurons. These data suggest multiple pathways in the expression of BDNF in nociceptive sensory neurons.

GDNF facilitates differentiation of the adult dentate gyrus-derived neural precursor cells into astrocytes via STAT3.

While the pro-neurogenic actions of antidepressants in the adult hippocampal dentate gyrus (DG) are thought to be one of the mechanisms through which antidepressants exert their therapeutic actions, antidepressants do not increase proliferation of neural precursor cells derived from the adult DG. Because previous studies showed that antidepressants increase the expression and secretion of glial cell line-derived neurotrophic factor (GDNF) in C6 glioma cells derived from rat astrocytes and GDNF increases neurogenesis in adult DG in vivo, we investigated the effects of GDNF on the proliferation, differentiation and apoptosis of cultured neural precursor cells derived from the adult DG. Data showed that GDNF facilitated the differentiation of neural precursor cells into astrocytes but had no effect on their proliferation or apoptosis. Moreover, GDNF increased the phosphorylation of STAT3, and both a specific inhibitor of STAT3 and lentiviral shRNA for STAT3 decreased their differentiation into astrocytes. Taken together, our findings suggest that GDNF facilitates astrogliogenesis from neural precursor cells in adult DG through activating STAT3 and that this action might indirectly affect neurogenesis.

Primary cultures of rat cortical microglia treated with nicotine increases in the expression of excitatory amino acid transporter 1 (GLAST) via the activation of the α7 nicotinic acetylcholine receptor

Although the clearance of glutamate from the synapse under physiological conditions is performed by astrocytic glutamate transporters, their expression might be diminished under pathological conditions. Microglia glutamate transporters, however, might serve as a back-up system when astrocytic glutamate uptake is impaired, and could have a prominent neuroprotective function under pathological conditions. In the current study, the effect of nicotine, well known as a neuroprotective molecule, on the function of glutamate transporters in cultured rat cortical microglia was examined. Reverse transcription polymerase chain reaction and pharmacological approaches demonstrated that, glutamate/aspartate transporter (GLAST), not glutamate transporter 1 (GLT-1), is the major functional glutamate transporter in cultured cortical microglia. Furthermore, the α7 subunit was demonstrated to be the key subunit comprising nicotinic acetylcholine (nACh) receptors in these cells. Treatment of cortical microglia with nicotine led to a significant increase of GLAST mRNA expression and (14)C-glutamate uptake in a concentration- and time-dependent manner, which were markedly inhibited by pretreatment with methyllycaconitine, a selective α7 nACh receptor antagonist. The nicotine-induced expression of GLAST mRNA and protein is mediated through an inositol trisphosphate (IP3) and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) depend intracellular pathway, since pretreatment with either xestospongin C, an IP3 receptor antagonist, or KN-93, a CaMKII inhibitor, blocked GLAST expression. Together, these findings indicate that activation of nACh receptors, specifically those expressing the α7 subunit, on cortical microglia could be a key mechanism of the neuroprotective effect of nACh receptor ligands such as nicotine.

Clock gene Per1 regulates the production of CCL2 and interleukin-6 through p38, JNK1 and NF-κB activation in spinal astrocytes.

It has been previously reported that spinal clock genes controlled under circadian rhythm contribute to the regulation of astrocytic function, which in turn is involved in diverse processes such as nociceptive transduction and the induction of inflammation. However, how clock genes expressed in spinal cord astrocytes are associated with the modulation of the inflammatory response is poorly understood. In the current study, the role of Period1 (Per1), one of clock genes, in the expression of chemokine (C-C motif) ligand 2 (CCL2) and interleukin-6 (IL-6), which are typical pro-inflammatory mediators produced by spinal astrocytes, was investigated. It was found that the knockdown of Per1 by using RNA interference led to a significant increase of the expression of CCL2 and IL-6 in cultured rat spinal astrocytes. Moreover, the silencing of the Per1 gene also increased the phosphorylation of p38, c-Jun N-terminal kinase (JNK) 1 and IκBα, and led to the translocation of p65 from the cytosol to the nucleus. The induction of CCL2 and IL-6 was significantly inhibited by treatment with the inhibitors of p38, JNK, and NF-κB. By contrast, the overexpression of PER1 by transfection vector significantly blocked the expression of CCL2 and IL-6, and the activation of p38, JNK, and NF-κB. Together, these results suggest that down-regulation of Per1 induced the phosphorylation of p38 and JNK1 and the subsequent activation of NF-κB, and that these events contribute to neuroinflammatory state in the spinal cord via the induction of the release of inflammatory mediators.