Yoki Nakamura

The Sigma-1 Receptor as a Pluripotent Modulator in Living Systems

The sigma-1 receptor (Sig-1R) is an endoplasmic reticulum (ER) protein that resides specifically in the mitochondria-associated endoplasmic reticulum (ER) membrane (MAM), an interface between ER and mitochondria. In addition to being able to translocate to the plasma membrane (PM) to interact with ion channels and other receptors, Sig-1R also occurs at the nuclear envelope, where it recruits chromatin-remodeling factors to affect the transcription of genes. Sig-1Rs have also been reported to interact with other membranous or soluble proteins at other loci, including the cytosol, and to be involved in several central nervous system (CNS) diseases. Here, we propose that Sig-1R is a pluripotent modulator with resultant multiple functional manifestations in living systems.

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.

Activation of transient receptor potential ankyrin 1 evokes nociception through substance P release from primary sensory neurons

J. Neurochem. (2012) 120, 1036–1047.

Paclitaxel and vinorelbine, evoked the release of substance P from cultured rat dorsal root ganglion cells through different PKC isoform-sensitive ion channels

Many patients suffer from serious adverse effects including respiratory distress and pulmonary edema during and after chemotherapy with paclitaxel or vinorelbine. These effects appear to be due to the activation of neurokinin-1 receptors. The present study investigated the influences of paclitaxel and vinorelbine on the substance P (sP) release from cultured dorsal root ganglion (DRG) cells using a radioimmunoassay. Both paclitaxel and vinorelbine evoked sP release in a dose- and time-dependent manner within 60 min at a concentration range of 0.1-10 microM. The sP release levels induced by the two drugs were attenuated by pretreatment with the protein kinase Cs (PKCs) inhibitors (bisindolylmaleimide I and Gö6976). Moreover, the paclitaxel- or vinorelbine-induced sP release was diminished in the absence of extracellular Ca2+ or the presence of LaCl3 (an extracellular Ca2+ influx blocker). A Ca2+ imaging assay further indicated that both paclitaxel and vinorelbine gradually increased the intracellular Ca2+ concentration, and these increases lasted for at least 15 min and were suppressed by Gö6976. Paclitaxel caused the membrane translocation of only PKCbeta within 10 min after stimulation, whereas vinorelbine induced the translocation of both PKCalpha and beta. The paclitaxel- and vinorelbine-induced sP release levels were separately inhibited by ruthenium red (a transient receptor potential (TRP) channel blocker) and gabapentin (an inhibitor of voltage-gated Ca2+ channels (VGCCs)). These findings suggest that paclitaxel and vinorelbine evoke the sP release from cultured DRG cells by the extracellular Ca2+ influx through TRP channels activated by PKCbeta and VGCCs activated by both PKCalpha and beta, respectively.

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.

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.

A β1/2 Adrenergic Receptor‐Sensitive Intracellular Signaling Pathway Modulates CCL2 Production in Cultured Spinal Astrocytes

The phosphorylation of c‐jun N‐terminal kinase (JNK) and the subsequent production of C–C chemokine CCL2 (monocyte chemoattractant protein; MCP‐1) in spinal astrocytes contribute to the initiation of neurological disorders including chronic pain. Astrocytes express neurotransmitter receptors which could be targeted to ameliorate neurological disorders. In the current study, the involvement of the β‐adrenergic system in the regulation of JNK activity and CCL2 production after stimulation with tumor necrosis factor (TNF)‐α, one of many initiators of neuroinflammation, was elucidated. Treatment of cultured spinal astrocytes with isoproterenol (a β‐adrenergic receptor agonist; 1 µM) reduced both TNF‐α‐induced JNK1 phosphorylation, as observed by Western blotting, and the subsequent increase of both CCL2 mRNA expression and CCL2 production, which were measured by real time‐PCR and ELISA, respectively. The effects of isoproterenol were completely blocked by pretreatment with either propranolol (a β‐adrenoceptor antagonist) or H89 (a protein kinase A [PKA] inhibitor). The current study revealed that the regulation of glycogen synthase kinase‐3β (GSK‐3β) activity is a crucial factor in the inhibitory action of isoproterenol. The TNF‐α‐induced JNK1 phosphorylation was significantly blocked by treatment with GSK‐3β inhibitors (either LiCl or TWS119), and stimulation of β‐adrenergic receptors induced the inhibition of GSK‐3β through the phosphorylation of Ser9. Moreover, treatment with isoproterenol markedly suppressed the TNF‐α‐induced increase of CCL2 mRNA expression and CCL2 production through a β‐adrenergic receptor‐PKA pathway mediated by GSK‐3β regulation. Thus, activation of β1/2 adrenergic receptors expressed in spinal astrocytes could be a novel method of moderating neurological disorders with endogenous catecholamines or selective agonists. J. Cell. Physiol. 229: 323–332, 2014.

Downregulation of connexin36 in mouse spinal dorsal horn neurons leads to mechanical allodynia

Connexin36 (Cx36), a component of neuronal gap junctions, is crucial for interneuronal communication and regulation. Gap junction dysfunction underlies neurological disorders, including chronic pain. Following a peripheral nerve injury, Cx36 expression in the ipsilateral spinal dorsal horn was markedly decreased over time, which paralleled the time course of hind paw tactile allodynia. Intrathecal (i.t.) injection of Cx36 siRNA (1 and 5 pg) significantly reduced the expression of Cx36 protein in the lumbar spinal cord, peaking 3 days after the injection, which corresponded with the onset of hind paw tactile allodynia. It is possible that some of the tactile allodynia resulting from Cx36 downregulation could be mediated through excitatory neuromodulators, such as glutamate and substance P. The Cx36 knockdown‐evoked tactile allodynia was significantly attenuated by i.t. treatment with the N‐methyl‐D‐aspartate glutamate receptor antagonist MK‐801 but not the substance P receptor antagonist CP96345. Immunohistochemistry showed that Cx36 was colocalized with glycine transporter‐2, a marker for inhibitory glycinergic spinal interneurons, but not with glutamate decarboxylase 67, a marker for inhibitory GABAergic spinal interneurons. The results indicate that spinal inhibition through glycinergic interneurons is reduced, leading to increased glutamatergic neurotransmission, as a result of Cx36 downregulation. The current data suggest that gap junction dysfunction underlies neuropathic pain and further suggest a novel target for the development of analgesics.

Perineural expression of high-mobility group box-1 contributes to long-lasting mechanical hypersensitivity via matrix metalloprotease-9 up-regulation in mice with painful peripheral neuropathy

High‐mobility group box‐1 (HMGB1) has been shown to be critical in the modulation of nociceptive transduction following a peripheral neuropathy. However, the precise role of peripherally expressed HMGB1 in neuropathic pain has yet to be fully elaborated. Following a partial sciatic nerve ligation (PSNL) in mice, a persistent ipsilateral up‐regulation of HMGB1 was observed from 3 to 21 days after PSNL, in paralleled with a robust ipsilateral hind paw mechanical hypersensitivity. Increased HMGB1 was detected in both infiltrating macrophages and proliferating Schwann cells in the ipsilateral nerve 14 days following PSNL. Repeated perineural treatment with anti‐HMGB1 antibody significantly ameliorated PSNL‐induced mechanical hypersensitivity. Several pronociceptive molecules, including matrix metalloprotease‐9 (MMP‐9), tumor necrosis factor‐α, interleukin‐1β (IL‐1β), and cyclooxygenase‐2, were up‐regulated in injured sciatic nerve 14 days following PSNL. Repeated perineural treatment with an anti‐HMGB1 antibody significantly suppressed expression of MMP‐9, but not other pronociceptive molecules. Perineural treatment with a selective MMP‐9 inhibitor ameliorated PSNL‐induced mechanical hypersensitivity. The current findings demonstrate that the maintenance of the neuropathic state following an injured nerve is dependent on the up‐regulation of HMGB1 and MMP‐9. Thus, blocking HMGB1 function in sciatic nerve could be a potent therapeutic strategy for the treatment of neuropathic pain.