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Inhibiting STAT3 in a murine model of human breast cancer-induced bone pain delays the onset of nociception.

Aggressive breast cancer subtypes utilize system x, a membrane antiporter, to import cystine for glutathione synthesis and maintenance of redox homeostasis, in turn releasing glutamate as a metabolic pro-nociceptive by-product. Metastatic breast cancers establish themselves at distal sites including bone, where changes in extracellular glutamate levels contribute to cancer-induced bone pain. We previously established that stearically blocking system x activity with sulfasalazine delays the onset of nociceptive behaviours and that xCT, the functional antiporter subunit, is positively regulated by signal transducer and activator of transcription 3 (STAT3). In the current investigation, a murine xenograft cancer-induced bone pain model was applied to examine whether pharmacological inhibition of phosphorylated STAT3 (pSTAT3) induces changes in nociception. A high glutamate-releasing, xCT/pSTAT3 over-expressing human breast cancer cell line was selected for injection into the distal epiphysis of the right femur of female nude mice. A 14-day regimen of intraperitoneal injections with either vehicle or the novel STAT3 inhibitor DR-1-55 commenced three weeks after initial intrafemoral bone injection. Nociceptive behaviours were temporally monitored by automated von Frey, dynamic weight bearing and open-field testing for the duration of the study, beginning at the baseline. Prior to sacrifice and at ethical end point, tumour-induced osteolytic lesions were radiographically assessed. Treatment with DR-1-55 significantly delayed the onset and severity of spontaneous and induced nociceptive behaviours, also decreasing human SLC7A11 ( xCT) mRNA levels in tumour-bearing limbs without altering osteolysis. In addition, two pro-inflammatory cytokines released by this cell line, interleukin 6 and interleukin 1β, were also down-regulated at the mRNA level in response to DR-1-55 treatment in vivo, with lower human interleukin 6 levels detected in the host circulation. This study demonstrates that targeting pSTAT3 may be a viable therapeutic means to manage cancer-induced bone pain, alone or in combination with stearic system x blockers.

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Trigeminal Nerve Transection-Induced Neuroplastic Changes in the Somatosensory and Insular Cortices in a Rat Ectopic Pain Model.

The primary sensory cortex processes competitive sensory inputs. Ablation of these competitive inputs induces neuroplastic changes in local cortical circuits. However, information concerning cortical plasticity induced by a disturbance of competitive nociceptive inputs is limited. Nociceptive information from the maxillary and mandibular molar pulps converges at the border between the ventral secondary somatosensory cortex (S2) and insular oral region (IOR); therefore, S2/IOR is a suitable target for examining the cortical changes induced by a disturbance of noxious inputs, which often causes neuropathic pain and allodynia. We focused on the plastic changes in S2/IOR excitation in a model of rats subjected to inferior alveolar nerve transection (IANX). Our optical imaging using a voltage-sensitive dye (VSD) revealed that the maxillary molar pulp stimulation-induced excitatory propagation was expanded one to two weeks after IANX at the macroscopic level. At the cellular level, based on Ca imaging using two-photon microscopy, the amplitude of the Ca responses and the number of responding neurons in S2/IOR increased in both excitatory and inhibitory neurons. The laser scanning photostimulation (LSPS) revealed that Layer II/III pyramidal and GABAergic fast-spiking neurons in S2/IOR received larger excitatory inputs from Layer IV in the IANX models, which supports the findings obtained by the macroscopic and microscopic optical imaging. Furthermore, the inhibitory postsynaptic inputs to the pyramidal neurons were decreased in the IANX models, suggesting suppression of inhibitory synaptic transmission onto excitatory neurons. These results suggest that IANX induces plastic changes in S2/IOR by changing the local excitatory and inhibitory circuits.

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Inflammatory and neuropathic gene expression signatures of chemotherapy-induced neuropathy induced by vincristine, cisplatin and oxaliplatin in C57BL/6J mice.

Vincristine, oxaliplatin, and cisplatin are commonly prescribed chemotherapeutic agents for the treatment of many tumors. However, a main side-effect is chemotherapy-induced peripheral neuropathy (CIPN), which may lead to changes in chemotherapeutic treatment. Although symptoms associated with CIPN are recapitulated by mouse models, there is limited knowledge of how these drugs affect the expression of genes in sensory neurons. The present study carried out a transcriptomic analysis of dorsal root ganglia (DRG) following vincristine, oxaliplatin, and cisplatin treatment with a view to gain insight into the comparative pathophysiological mechanisms of CIPN. RNA-Seq revealed 368, 295 and 256 differential expressed genes (DEGs) induced by treatment with vincristine, oxaliplatin and cisplatin, respectively and only five shared genes were dysregulated in all three groups. Cell type enrichment analysis and gene set enrichment analysis showed predominant effects on genes associated with the immune system after treatment with vincristine, while oxaliplatin treatment affected mainly neuronal genes. Treatment with cisplatin resulted in a mixed gene expression signature. Perspective: These results provide insight into the recruitment of immune responses to DRG and indicate enhanced neuro-inflammatory processes following administration of vincristine, oxaliplatin, and cisplatin. These gene expression signatures may provide insight into novel drug targets for treatment of CIPN.

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Cathepsin S acts via protease-activated receptor 2 to activate sensory neurons and induce itch-like behaviour.

Chronic itch is a debilitating condition characterised by excessive scratching and is a symptom frequently reported in skin diseases such as atopic dermatitis. It has been proposed that release of the cysteine protease Cathepsin S (CatS) from skin keratinocytes or immune cells resident in or infiltrating the skin could act as a pruritogen in chronic itch conditions. CatS is known to activate protease-activated receptor 2 (PAR2). We therefore hypothesised that enzymatic activation of neuronally expressed PAR2 by CatS was responsible for activation of sensory neurons and transmission of itch signals. Intradermally-injected human recombinant (hr)-CatS or the PAR2 agonist, SLIGRL-NH behaved as pruritogens by causing scratching behaviour in mice. Hr-CatS-induced scratching behaviour was prevented by CatS inhibitors and PAR2 antagonists and reduced by 50% in TRPV1 mice compared with wild-type mice, whilst no significant reduction in scratching behaviour was observed in TRPA1 mice. Cultured dorsal root ganglion (DRG) cells showed an increase in [Ca] following incubation with hr-CatS, and the percentage of neurons that responded to hr-CatS decreased in the presence of a PAR2 antagonist or in cultures of neurons from TRPV1 mice. Taken together, our results indicate CatS acts as a pruritogen via PAR2 activation in TRPV1-expressing sensory neurons.

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Preoperative anxiety induced glucocorticoid signaling reduces GABAergic markers in spinal cord and promotes postoperative hyperalgesia by affecting Npas4.

Preoperative anxiety is common in patients undergoing elective surgery and is closely related to postoperative hyperalgesia. In this study, a single prolonged stress (SPS) model was used to induce preoperative anxiety-like behavior in rats 24h before the surgery. We found that SPS exacerbated the postoperative pain and elevated the level of serum corticosterone (CORT). Previous studies have shown that glucocorticoid (GC) is associated with synaptic plasticity, and decreased spinal GABAergic activity can cause hyperalgesia in rodents. Here, SPS rats lumbar spinal cord showed reduced glutamic acid decarboxylase-65 (GAD65), glutamic acid decarboxylase-67 (GAD67), GABA type A receptor alpha 1 subunit (GABAA α1), and GABA type A receptor gamma 2 subunit (GABAA γ2) , indicating an impairment of GABAergic system. Furthermore, Neuronal PAS domain protein 4 (Npas4) was also reduced in rats after SPS stimulation, which has been reported to promote GABAergic synapse development. Then intraperitoneal injection of RU486 (a glucocorticoid receptor antagonist) rather than spironolactone (a mineralocorticoid receptor antagonist) was found to relieve SPS induced hyperalgesia and reverse Npas4 reduction and the impairment of GABAergic system. Further over-expressing Npas4 could also restore the damage of GABAergic system caused by SPS while interfering with Npas4 caused an opposite effect. Finally, after stimulation of rat primary spinal cord neurons with exogenous CORT in vitro, Npas4 and GABAergic markers were also down-regulated, and RU486 reversed that. Together, our results demonstrated that preoperative anxiety led to GABAergic system impairment in spinal cord and thus caused hyperalgesia due to glucocorticoid-induced down-regulation of Npas4.

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mTOR activation due to APPL1 deficiency exacerbates hyperalgesia via Rab5/Akt and AMPK signaling pathway in STZ-induced diabetic rats.

Painful diabetic neuropathy (PDN) is a common complication of diabetes mellitus with obscure underlying mechanisms. The adaptor protein APPL1 is critical in mediating the insulin sensitizing and insulin signaling. In neurons, APPL1 reportedly affects synaptic plasticity, while its role in the pathogenesis of PDN is masked. Our western blotting revealed significantly decreased APPL1 expression in the dorsal horn in streptozocin (STZ)-induced rats versus the control rats, coupled with concomitant mechanical and thermal hyperalgesia. Afterwards, the determination of exact localization of APPL1 in spinal cord by immunofluorescent staining assay revealed highly expressed APPL1 in the lamina of spinal dorsal horn in control rats, with the overexpression in neurons, microglia and underexpression in astrocytes. The APPL1 expression in laminae I and II was significantly downregulated in PDN rats. Additionally, APPL1 deficiency or overexpression contributed to the increase or decrease of Map and Bassoon, respectively. The localization and immunoactivity of APPL1 and mammalian target of rapamycin (mTOR) were determined in spinal dorsal horn in PDN rats and control rats by immunohistochemistry, suggesting pronounced decrease in APPL1 expression in the superficial layer of the spinal cord in PDN rats, with p-mTOR expression markedly augmented. APPL1 knockdown by infection with lentiviral vector facilitated the activation of mTOR and abrogated mechanical withdrawal threshold (MWT) values in PDN rats. Genetically overexpressed APPL1 significantly eliminated the activation of mTOR and resulted in the augmented MWT values and thermal withdrawal latency (TWL) values. Further, the APPL1 levels affect phosphorylation of adenosine monophosphate (AMP)-activated protein kinase (AMPK), and Akt, the phosphorylation of AMPK and Akt as well as the small GTPase, Rab5 expression in PDN rats. Our results uncovered a novel mechanism by which APPL1 deficiency facilitates the mTOR activation, and thus exacerbates the hyperalgesia in STZ-induced diabetic rats, presumably via the regulation of Rab5/Akt and AMPK signaling pathway.

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Specialized cutaneous Schwann cells initiate pain sensation.

An essential prerequisite for the survival of an organism is the ability to detect and respond to aversive stimuli. Current belief is that noxious stimuli directly activate nociceptive sensory nerve endings in the skin. We discovered a specialized cutaneous glial cell type with extensive processes forming a mesh-like network in the subepidermal border of the skin that conveys noxious thermal and mechanical sensitivity. We demonstrate a direct excitatory functional connection to sensory neurons and provide evidence of a previously unknown organ that has an essential physiological role in sensing noxious stimuli. Thus, these glial cells, which are intimately associated with unmyelinated nociceptive nerves, are inherently mechanosensitive and transmit nociceptive information to the nerve.

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Low-dose interleukin-2 reverses behavioral sensitization in multiple mouse models of headache disorders.

Headache disorders are highly prevalent and debilitating, with limited treatment options. Previous studies indicate that many pro-inflammatory immune cells contribute to headache pathophysiology. Given the well-recognized role of regulatory T (Treg) cells in maintaining immune homeostasis, we hypothesized that enhancing Treg function may be effective to treat multiple headache disorders. In a mouse model of chronic migraine, we observed that repeated nitroglycerin (NTG, a reliable trigger of migraine in patients) administration doubled the number of CD3 T cells in the trigeminal ganglia without altering the number of Treg cells, suggesting a deficiency in Treg-mediated immune homeostasis. We treated mice with low-dose interleukin-2 (ld-IL2) to preferentially expand and activate endogenous Treg cells. This not only prevented the development of NTG-induced persistent sensitization, but also completely reversed the established facial skin hyper-sensitivity resulting from repeated NTG administration. The effect of ld-IL2 was independent of mouse sex and/or strain. Importantly, ld-IL2 treatment did not alter basal nociceptive responses, and repeated usage did not induce tolerance. The therapeutic effect of ld-IL2 was abolished by Treg depletion and was recapitulated by Treg adoptive transfer. Furthermore, treating mice with ld-IL2 1-7 days after mild traumatic brain injury effectively prevented as well as reversed the development of behaviors related to acute and chronic post-traumatic headache. In a model of medication overuse headache, Ld-IL2 completely reversed the cutaneous hyper-sensitivity induced by repeated administration of sumatriptan. Collectively, the present study identifies ld-IL2 as a promising prophylactic for multiple headache disorders with a mechanism distinct from the existing treatment options.

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Aldosterone Synthase in Peripheral Sensory Neurons Contributes to Mechanical Hypersensitivity during Local Inflammation in Rats.

Aldosterone is believed to be synthesized exclusively in the adrenal gland through the processing enzyme aldosterone synthaseMineralocorticoid receptors are predominantly expressed in peripheral nociceptive neurons whose activation leads to increased neuronal excitability and mechanical sensitivity WHAT THIS ARTICLE TELLS US THAT IS NEW: Extra-adrenal production of aldosterone by aldosterone synthase within peripheral sensory neurons contributes to ongoing mechanical hypersensitivity via intrinsic activation of neuronal mineralocorticoid receptorsIntrathecally-applied aldosterone synthase inhibitor reduced aldosterone content in peripheral sensory neurons and subsequently attenuated enhanced mechanical hypersensitivity resulting from local inflammation BACKGROUND:: Recent emerging evidence suggests that extra-adrenal synthesis of aldosterone occurs (e.g., within the failing heart and in certain brain areas). In this study, the authors investigated evidence for a local endogenous aldosterone production through its key processing enzyme aldosterone synthase within peripheral nociceptive neurons.

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Acid and inflammatory sensitisation of naked mole-rat colonic afferent nerves.

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