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Zhang J, Gao L, Zhang Y, Wang H, Sun S, Wu L. Involvement of microglial P2X7 receptor in pain modulation. CNS Neurosci Ther 2024; 30:e14496. [PMID: 37950524 PMCID: PMC10805404 DOI: 10.1111/cns.14496] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/02/2023] [Revised: 08/23/2023] [Accepted: 10/02/2023] [Indexed: 11/12/2023] Open
Abstract
BACKGROUND Pain is a rapid response mechanism that compels organisms to retreat from the harmful stimuli and triggers a repair response. Nonetheless, when pain persists for extended periods, it can lead to adverse changes into in the individual's brain, negatively impacting their emotional state and overall quality of life. Microglia, the resident immune cells in the central nervous system (CNS), play a pivotal role in regulating a variety of pain-related disorders. Specifically, recent studies have shed light on the central role that microglial purinergic ligand-gated ion channel 7 receptor (P2X7R) plays in regulating pain. In this respect, the P2X7R on microglial membranes represents a potential therapeutic target. AIMS To expound on the intricate link between microglial P2X7R and pain, offering insights into potential avenues for future research. METHODS We reviewed 140 literature and summarized the important role of microglial P2X7R in regulating pain, including the structure and function of P2X7R, the relationship between P2X7R and microglial polarization, P2X7R-related signaling pathways, and the effects of P2X7R antagonists on pain regulation. RESULTS P2X7R activation is related to M1 polarization of microglia, while suppressing P2X7R can transfer microglia from M1 into M2 phenotype. And targeting the P2X7R-mediated signaling pathways helps to explore new therapy for pain alleviation. P2X7R antagonists also hold potential for translational and clinical applications in pain management. CONCLUSIONS Microglial P2X7R holds promise as a potential novel pharmacological target for clinical treatments due to its distinctive structure, function, and the development of antagonists.
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Affiliation(s)
- Jing Zhang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Diseases, Department of Pediatric Dentistry, School of StomatologyThe Fourth Military Medical UniversityXi'anShaanxiChina
| | - Lei Gao
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Diseases, Department of Pediatric Dentistry, School of StomatologyThe Fourth Military Medical UniversityXi'anShaanxiChina
| | - Yaoyuan Zhang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Diseases, Department of Pediatric Dentistry, School of StomatologyThe Fourth Military Medical UniversityXi'anShaanxiChina
| | - Haozhen Wang
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Diseases, Department of Pediatric Dentistry, School of StomatologyThe Fourth Military Medical UniversityXi'anShaanxiChina
| | - Shukai Sun
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Diseases, Department of Pediatric Dentistry, School of StomatologyThe Fourth Military Medical UniversityXi'anShaanxiChina
| | - Li‐an Wu
- State Key Laboratory of Oral & Maxillofacial Reconstruction and Regeneration, National Clinical Research Center for Oral Diseases, Department of Pediatric Dentistry, School of StomatologyThe Fourth Military Medical UniversityXi'anShaanxiChina
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Ballon Romero SS, Fuh LJ, Hung SY, Lee YC, Huang YC, Chien SY, Chen YH. Electroacupuncture exerts prolonged analgesic and neuroprotective effects in a persistent dental pain model induced by multiple dental pulp injuries: GABAergic interneurons-astrocytes interaction. Front Immunol 2023; 14:1213710. [PMID: 37954604 PMCID: PMC10639134 DOI: 10.3389/fimmu.2023.1213710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2023] [Accepted: 10/03/2023] [Indexed: 11/14/2023] Open
Abstract
Pain within the trigeminal system, particularly dental pain, is poorly understood. This study aimed to determine whether single or multiple dental pulp injuries induce persistent pain, its association with trigeminal central nociceptive pathways and whether electroacupuncture (EA) provides prolonged analgesic and neuroprotective effects in a persistent dental pain model. Models of single dental pulp injury (SDPI) and multiple dental pulp injuries (MDPI) were used to induce trigeminal neuropathic pain. The signs of dental pain-related behavior were assessed using the mechanical head withdrawal threshold (HWT). Immunofluorescence and western blot protocols were used to monitor astrocyte activation, changes in apoptosis-related proteins, and GABAergic interneuron plasticity. SDPI mice exhibited an initial marked decrease in HWT from days one to 14, followed by progressive recovery from days 21 to 42. From days 49 to 70, the HWT increased and returned to the control values. In contrast, MDPI mice showed a persistent decrease in HWT from days one to 70. MDPI increased glial fibrillary acidic protein (GFAP) and decreased glutamine synthetase (GS) and glutamate transporter-1 (GLT1) expression in the Vi/Vc transition zone of the brainstem on day 70, whereas no changes in astrocytic markers were observed on day 70 after SDPI. Increased expression of cleaved cysteine-aspartic protease-3 (cleaved caspase-3) and Bcl-2-associated X protein (Bax), along with decreased B-cell lymphoma/leukemia 2 (Bcl-2), were observed at day 70 after MDPI but not after SDPI. The downregulation of glutamic acid decarboxylase (GAD65) expression was observed on day 70 only after MDPI. The effects of MDPI-induced lower HWT from days one to 70 were attenuated by 12 sessions of EA treatment (days one to 21 after MDPI). Changes in astrocytic GFAP, GS, and GLT-1, along with cleaved caspase-3, Bax, Bcl-2, and GAD65 expression observed 70 days after MDPI, were reversed by EA treatment. The results suggest that persistent dental pain in mice was induced by MDPI but not by SDPI. This effect was associated with trigeminal GABAergic interneuron plasticity along with morphological and functional changes in astrocytes. EA exerts prolonged analgesic and neuroprotective effects that might be associated with the modulation of neuron-glia crosstalk mechanisms.
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Affiliation(s)
| | - Lih-Jyh Fuh
- School of Dentistry, College of Dentistry, China Medical University, Taichung, Taiwan
| | - Shih-Ya Hung
- Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan
- Division of Surgery, Department of Medical Research, China Medical University Hospital, Taichung, Taiwan
| | - Yu-Chen Lee
- Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan
- Department of Acupuncture, China Medical University Hospital, Taichung, Taiwan
| | - Yu-Chuen Huang
- Department of Medical Research, China Medical University Hospital, School of Chinese Medicine, China Medical University, Taichung, Taiwan
| | - Szu-Yu Chien
- Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan
| | - Yi-Hung Chen
- Graduate Institute of Acupuncture Science, China Medical University, Taichung, Taiwan
- Chinese Medicine Research Center, China Medical University, Taichung, Taiwan
- Department of Photonics and Communication Engineering, Asia University, Taichung, Taiwan
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Zhang J, Si J, Liang R, Lu Y, Shang H, Li X, Sun S, Wu LA. Ligand-gated ion channel P2X7 regulates hypoxia-induced factor-1α mediated pain induced by dental pulpitis in the medullary dorsal horn. Front Mol Neurosci 2022; 15:1015751. [PMID: 36385758 PMCID: PMC9644926 DOI: 10.3389/fnmol.2022.1015751] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/10/2022] [Accepted: 09/27/2022] [Indexed: 12/02/2022] Open
Abstract
Dental pulpitis often induces severe pain, and the molecular immune response is remarkable in both peripheral and central nervous system. Accumulating evidence indicates that activated microglia in the medullary dorsal horn (MDH) contribute to dental pulpitis induced pain. The P2X7 receptor plays an important role in driving pain and inflammatory processes, and its downstream target hypoxia-induced factor-1α (HIF-1α) has a crucial role in maintaining inflammation. However, the relationship between P2X7 and HIF-1α in dental inflammatory pain remains unclear. This study demonstrated that the degree of inflammation in the dental pulp tissue became more severe in a time-dependent manner by establishing a rat dental pulpitis model via pulp exposure. Meanwhile, the expression of P2X7, HIF-1α, IL-1β, and IL-18 in the MDH increased most on the seventh day when the pain threshold was the lowest in the dental pulpitis model. Furthermore, lipopolysaccharides (LPS) increased P2X7-mediated HIF-1α expression in microglia. Notably, the suppression of P2X7 caused less IL-1β and IL-18 release and lower HIF-1α expression, and P2X7 antagonist Brilliant Blue G (BBG) could alleviate pain behaviors of the dental pulpitis rats. In conclusion, our results provide further evidence that P2X7 is a key molecule, which regulates HIF-1α expression and inflammation in dental pulpitis-induced pain.
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Affiliation(s)
- Jing Zhang
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
| | - Jialin Si
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
| | - Rongrong Liang
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
- College of Life Sciences, Northwest University, Xi’an, China
| | - Yuxin Lu
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
| | - Hongwei Shang
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
| | - Xinwei Li
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
| | - Shukai Sun
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
- *Correspondence: Shukai Sun,
| | - Li-an Wu
- State Key Laboratory of Military Stomatology, Department of Pediatric Dentistry, National Clinical Research Center for Oral Diseases, School of Stomatology, The Fourth Military Medical University, Xi’an, China
- Li-an Wu,
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Mai L, Zhu X, Huang F, He H, Fan W. p38 mitogen-activated protein kinase and pain. Life Sci 2020; 256:117885. [PMID: 32485175 DOI: 10.1016/j.lfs.2020.117885] [Citation(s) in RCA: 40] [Impact Index Per Article: 10.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/27/2020] [Revised: 05/23/2020] [Accepted: 05/28/2020] [Indexed: 12/18/2022]
Abstract
Inflammatory and neuropathic pain is initiated by tissue inflammation and nerve injury, respectively. Both are characterized by increased activity in the peripheral and central nervous system, where multiple inflammatory cytokines and other active molecules activate different signaling pathways that involve in the development and/or maintenance of pain. P38 mitogen-activated protein kinase (MAPK) is one member of the MAPK family, which is activated in neurons and glia and contributes importantly to inflammatory and neuropathic pain. The aim of this review is to summarize the latest advances made about the implication of p38 MAPK signaling cascade in pain. It can deepen our understanding of the molecular mechanisms of pain and may help to offer new targets for pain treatment.
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Affiliation(s)
- Lijia Mai
- Department of Anesthesiology, Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen University, Guangzhou 510080, China; Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510080, China
| | - Xiao Zhu
- The Marine Biomedical Research Institute, Guangdong Medical University, Zhanjiang 524023, China
| | - Fang Huang
- Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510080, China
| | - Hongwen He
- Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510080, China
| | - Wenguo Fan
- Department of Anesthesiology, Guanghua School of Stomatology, Hospital of Stomatology, Sun Yat-sen University, Guangzhou 510080, China; Guangdong Provincial Key Laboratory of Stomatology, Guangzhou 510080, China.
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5
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Ballon Romero SS, Lee YC, Fuh LJ, Chung HY, Hung SY, Chen YH. Analgesic and Neuroprotective Effects of Electroacupuncture in a Dental Pulp Injury Model-A Basic Research. Int J Mol Sci 2020; 21:E2628. [PMID: 32283868 PMCID: PMC7178196 DOI: 10.3390/ijms21072628] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2020] [Revised: 04/02/2020] [Accepted: 04/05/2020] [Indexed: 12/18/2022] Open
Abstract
Irreversible pulpitis is an extremely painful condition and its consequence in the central nervous system (CNS) remains unclear. A mouse model of dental pulp injury (DPI) resembles the irreversible pulpitis profile in humans. This study sought to determine whether pain induced by DPI activates microglia and astrocytes in the trigeminal subnucleus caudalis (Vc), as well as increases levels of proinflammatory cytokines, and whether electroacupuncture (EA) can be a potential analgesic and neuroprotective therapy following DPI. Pain behavior was measured via head-withdrawal threshold (HWT) and burrowing behavior at days 1, 3, 7, 14 and 21 after DPI. A marked decrease in HWT and burrowing activity was observed from day 1 to 14 after DPI and no changes were seen on day 21. Microglial and astrocytes activation; along with high cytokine (TNFα, IL-1β, and IL-6) levels, were observed in the Vc at 21 days after DPI. These effects were attenuated by verum (local and distal) EA, as well as oral ibuprofen administration. The results suggest that DPI-induced pain and glial activations in the Vc and EA exert analgesic efficacy at both local and distal acupoints. Furthermore, verum (local and distal) EA might be associated with the modulations of microglial and astrocytes activation.
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Affiliation(s)
- Sharmely Sharon Ballon Romero
- Graduate Institute of Acupuncture Science, China Medical University, Taichung 40402, Taiwan; (S.S.B.R.); (Y.-C.L.); (H.-Y.C.); (S.-Y.H.)
| | - Yu-Chen Lee
- Graduate Institute of Acupuncture Science, China Medical University, Taichung 40402, Taiwan; (S.S.B.R.); (Y.-C.L.); (H.-Y.C.); (S.-Y.H.)
- Department of Acupuncture, China Medical University Hospital, Taichung 40447, Taiwan
- Chinese Medicine Research Center, China Medical University, Taichung 40402, Taiwan
| | - Lih-Jyh Fuh
- School of Dentistry, College of Dentistry, China Medical University; Taichung 40402, Taiwan;
| | - Hsin-Yi Chung
- Graduate Institute of Acupuncture Science, China Medical University, Taichung 40402, Taiwan; (S.S.B.R.); (Y.-C.L.); (H.-Y.C.); (S.-Y.H.)
| | - Shih-Ya Hung
- Graduate Institute of Acupuncture Science, China Medical University, Taichung 40402, Taiwan; (S.S.B.R.); (Y.-C.L.); (H.-Y.C.); (S.-Y.H.)
- Department of Medical Research, China Medical University Hospital, Taichung 40447, Taiwan
| | - Yi-Hung Chen
- Graduate Institute of Acupuncture Science, China Medical University, Taichung 40402, Taiwan; (S.S.B.R.); (Y.-C.L.); (H.-Y.C.); (S.-Y.H.)
- Chinese Medicine Research Center, China Medical University, Taichung 40402, Taiwan
- Department of Photonics and Communication Engineering, Asia University, Taichung 41354, Taiwan
- Brain Disease Research Center, China Medical University Hospital, Taichung 40447, Taiwan
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Peña-Ortega F. Clinical and experimental aspects of breathing modulation by inflammation. Auton Neurosci 2018; 216:72-86. [PMID: 30503161 DOI: 10.1016/j.autneu.2018.11.002] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2018] [Revised: 11/06/2018] [Accepted: 11/07/2018] [Indexed: 12/19/2022]
Abstract
Neuroinflammation is produced by local or systemic alterations and mediated mainly by glia, affecting the activity of various neural circuits including those involved in breathing rhythm generation and control. Several pathological conditions, such as sudden infant death syndrome, obstructive sleep apnea and asthma exert an inflammatory influence on breathing-related circuits. Consequently breathing (both resting and ventilatory responses to physiological challenges), is affected; e.g., responses to hypoxia and hypercapnia are compromised. Moreover, inflammation can induce long-lasting changes in breathing and affect adaptive plasticity; e.g., hypoxic acclimatization or long-term facilitation. Mediators of the influences of inflammation on breathing are most likely proinflammatory molecules such as cytokines and prostaglandins. The focus of this review is to summarize the available information concerning the modulation of the breathing function by inflammation and the cellular and molecular aspects of this process. I will consider: 1) some clinical and experimental conditions in which inflammation influences breathing; 2) the variety of experimental approaches used to understand this inflammatory modulation; 3) the likely cellular and molecular mechanisms.
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Affiliation(s)
- Fernando Peña-Ortega
- Departamento de Neurobiología del Desarrollo y Neurofisiología, Instituto de Neurobiología, Universidad Nacional Autónoma de México, Querétaro, QRO 76230, México.
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7
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Liu H, Zhao L, Gu W, Liu Q, Gao Z, Zhu X, Wu Z, He H, Huang F, Fan W. Activation of satellite glial cells in trigeminal ganglion following dental injury and inflammation. J Mol Histol 2018. [PMID: 29516260 DOI: 10.1007/s10735-018-9765-4] [Citation(s) in RCA: 24] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Satellite glial cells (SGCs), a peripheral neuroglial cell, surround neurons and form a complete envelope around individual sensory neurons in the trigeminal ganglia (TG), which may be involved in modulating neurons in inflammation. The purpose of this study was to determine the effect of dental injury and inflammation on SGCs in the TG. Pulp exposure (PX) was performed on the first maxillary molar of 28 rats. The neurons innervating injured tooth in TG were labeled by the retrograde transport of fluoro-gold (FG). Specimens were collected at 1, 3, 7, 14, 21 and 28 days after PX and stained immunohistochemically for glial fibrillary acid protein (GFAP), a marker of SGCs activation, in the TG. We observed that GFAP-immunoreactivity (IR) SGCs enclosed FG-labeled neurons increased in a time-dependent manner after PX. The neurons surrounded by GFAP-IR SGCs were mainly small and medium in size. The GFAP-IR SGCs encircled neurons increased significantly in the maxillary nerve region of the TG at 7-28 days following PX. The results show that dental injury and inflammation induced SGCs activation in the TG. It indicates that activation of SGCs might be implicated in the peripheral mechanisms of pain following dental injury and inflammation.
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Affiliation(s)
- Haichao Liu
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China
| | - Lei Zhao
- Department of Radiation Oncology, Sun Yat-sen University Cancer Center, State Key Laboratory of Oncology in South China, Collaborative Innovation Center for Cancer Medicine, Guangzhou, 510060, China
| | - Wenzhen Gu
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China
| | - Qin Liu
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China
| | - Zhixiong Gao
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China
| | - Xiao Zhu
- Guangdong Provincial Key Laboratory of Medical Molecular Diagnostics, Guangdong Medical University, Dongguan, 523808, China
| | - Zhi Wu
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China
| | - Hongwen He
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China
| | - Fang Huang
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China.
| | - Wenguo Fan
- Guangdong Provincial Key Laboratory of Stomatology, Guanghua School of Stomatology, Sun Yat-sen University, Guangzhou, 510080, China.
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8
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Liu CC, Cheng JT, Li TY, Tan PH. Integrated analysis of microRNA and mRNA expression profiles in the rat spinal cord under inflammatory pain conditions. Eur J Neurosci 2017; 46:2713-2728. [DOI: 10.1111/ejn.13745] [Citation(s) in RCA: 15] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2016] [Revised: 10/06/2017] [Accepted: 10/06/2017] [Indexed: 12/23/2022]
Affiliation(s)
- Chien Cheng Liu
- Department of Biological Sciences; National Sun Yat-sen University; No. 70 Lienhai Rd. Gushan Dist. Kaohsiung City 80424 Taiwan
- Department of Anesthesiology; E-Da Hospital/I-Shou University; Kaohsiung City Taiwan
| | - Jiin Tsuey Cheng
- Department of Biological Sciences; National Sun Yat-sen University; No. 70 Lienhai Rd. Gushan Dist. Kaohsiung City 80424 Taiwan
| | - Tien Yui Li
- Department of Anesthesiology; E-Da Hospital/I-Shou University; Kaohsiung City Taiwan
| | - Ping Heng Tan
- Department of Anesthesiology; Chi Mei Medical Center; No. 901 Zhonghua Rd. Yongkang Dist. Tainan City 71004 Taiwan
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Berta T, Qadri YJ, Chen G, Ji RR. Microglial Signaling in Chronic Pain with a Special Focus on Caspase 6, p38 MAP Kinase, and Sex Dependence. J Dent Res 2016; 95:1124-31. [PMID: 27307048 DOI: 10.1177/0022034516653604] [Citation(s) in RCA: 56] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Microglia are the resident immune cells in the spinal cord and brain. Mounting evidence suggests that activation of microglia plays an important role in the pathogenesis of chronic pain, including chronic orofacial pain. In particular, microglia contribute to the transition from acute pain to chronic pain, as inhibition of microglial signaling reduces pathologic pain after inflammation, nerve injury, and cancer but not baseline pain. As compared with inflammation, nerve injury induces much more robust morphologic activation of microglia, termed microgliosis, as shown by increased expression of microglial markers, such as CD11b and IBA1. However, microglial signaling inhibitors effectively reduce inflammatory pain and neuropathic pain, arguing against the importance of morphologic activation of microglia in chronic pain sensitization. Importantly, microglia enhance pain states via secretion of proinflammatory and pronociceptive mediators, such as tumor necrosis factor α, interleukins 1β and 18, and brain-derived growth factor. Mechanistically, these mediators have been shown to enhance excitatory synaptic transmission and suppress inhibitory synaptic transmission in the pain circuits. While early studies suggested a predominant role of microglia in the induction of chronic pain, further studies have supported a role of microglia in the maintenance of chronic pain. Intriguingly, recent studies show male-dominant microglial signaling in some neuropathic pain and inflammatory pain states, although both sexes show identical morphologic activation of microglia after nerve injury. In this critical review, we provide evidence to show that caspase 6-a secreted protease that is expressed in primary afferent axonal terminals surrounding microglia-is a robust activator of microglia and induces profound release of tumor necrosis factor α from microglia via activation of p38 MAP kinase. The authors also show that microglial caspase 6/p38 signaling is male dominant in some inflammatory and neuropathic pain conditions. Finally, the authors discuss the relevance of microglial signaling in chronic trigeminal and orofacial pain.
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Affiliation(s)
- T Berta
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA Pain Research Center, Department of Anesthesiology, University of Cincinnati Medical Center, Cincinnati, OH, USA
| | - Y J Qadri
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - G Chen
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA
| | - R R Ji
- Department of Anesthesiology, Duke University Medical Center, Durham, NC, USA Department of Neurobiology, Duke University Medical Center, Durham, NC, USA
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Lin JJ, Du Y, Cai WK, Kuang R, Chang T, Zhang Z, Yang YX, Sun C, Li ZY, Kuang F. Toll-like receptor 4 signaling in neurons of trigeminal ganglion contributes to nociception induced by acute pulpitis in rats. Sci Rep 2015. [PMID: 26224622 PMCID: PMC4519790 DOI: 10.1038/srep12549] [Citation(s) in RCA: 48] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022] Open
Abstract
Pain caused by acute pulpitis (AP) is a common symptom in clinical settings. However, its underlying mechanisms have largely remained unknown. Using AP model, we demonstrated that dental injury caused severe pulp inflammation with up-regulated serum IL-1β. Assessment from head-withdrawal reflex thresholds (HWTs) and open-field test demonstrated nociceptive response at 1 day post injury. A consistent up-regulation of Toll-like receptor 4 (TLR4) in the trigeminal ganglion (TG) ipsilateral to the injured pulp was found; and downstream signaling components of TLR4, including MyD88, TRIF and NF-κB, and cytokines such as TNF-α and IL-1β, were also increased. Retrograde labeling indicated that most TLR4 positve neuron in the TG innnervated the pulp and TLR4 immunoreactivity was mainly in the medium and small neurons. Double labeling showed that the TLR4 expressing neurons in the ipsilateral TG were TRPV1 and CGRP positive, but IB4 negative. Furthermore, blocking TLR4 by eritoran (TLR4 antagonist) in TGs of the AP model significantly down-regulated MyD88, TRIF, NF-κB, TNF-α and IL-1β production and behavior of nociceptive response. Our findings suggest that TLR4 signaling in TG cells, particularly the peptidergic TRPV1 neurons, plays a key role in AP-induced nociception, and indicate that TLR4 signaling could be a potential therapeutic target for orofacial pain.
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Affiliation(s)
- Jia-Ji Lin
- 1] Department of Neurology, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710004, China [2] Department of Neurobiology and Collaborative Innovation Center for Brain Science, School of Basic Medicine, The Fourth Military Medical University, Xi'an, 710032, China
| | - Yi Du
- 1] State Key Laboratory of Military Stomatology, Department of Operative Dentistry and Endodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, 710032,China [2] Department of Endodontics, Jinan Stomatological Hospital, Jinan, 250001, China
| | - Wen-Ke Cai
- 1] Department of Cardio-Thoracic Surgery, Kunming General Hospital of Chengdu Military Region, Kunming, 650000, China [2] Department of Neurology, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710004, China
| | - Rong Kuang
- State Key Laboratory of Military Stomatology, Department of Operative Dentistry and Endodontics, School of Stomatology, The Fourth Military Medical University, Xi'an, 710032,China
| | - Ting Chang
- Department of Neurology, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710004, China
| | - Zhuo Zhang
- Department of Neurology, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710004, China
| | - Yong-Xiang Yang
- Department of Neurology, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710004, China
| | - Chao Sun
- Department of Neurology, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710004, China
| | - Zhu-Yi Li
- Department of Neurology, Tangdu Hospital, The Fourth Military Medical University, Xi'an, 710004, China
| | - Fang Kuang
- Department of Neurobiology and Collaborative Innovation Center for Brain Science, School of Basic Medicine, The Fourth Military Medical University, Xi'an, 710032, China
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A chronic pain: inflammation-dependent chemoreceptor adaptation in rat carotid body. Respir Physiol Neurobiol 2011; 178:362-9. [PMID: 21397054 DOI: 10.1016/j.resp.2011.03.006] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2011] [Revised: 03/02/2011] [Accepted: 03/03/2011] [Indexed: 11/20/2022]
Abstract
Experiments in recent years have revealed labile electrophysiological and neurochemical phenotypes in primary afferent neurons exposed to specific stimulus conditions associated with the development of chronic pain. These studies collectively demonstrate that the mechanisms responsible for functional plasticity are primarily mediated by novel neuroimmune interactions involving circulating and resident immune cells and their secretory products, which together induce hyperexcitability in the primary sensory neurons. In another peripheral sensory modality, namely the arterial chemoreceptors, sustained stimulation in the form of chronic hypoxia (CH) elicits increased chemoafferent excitability from the mammalian carotid body. Previous studies which focused on functional changes in oxygen-sensitive type I cells in this organ have only partially elucidated the molecular and cellular mechanisms which initiate and control this adaptive response. Recent studies in our laboratory indicate a unique role for the immune system in regulating the chemo-adaptive response of the carotid body to physiologically relevant levels of hypoxia.
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Abstract
Microglia are resident brain cells that sense pathological tissue alterations. They can develop into brain macrophages and perform immunological functions. However, expression of immune proteins by microglia is not synonymous with inflammation, because these molecules can have central nervous system (CNS)-specific roles. Through their involvement in pain mechanisms, microglia also respond to external threats. Experimental studies support the idea that microglia have a role in the maintenance of synaptic integrity. Analogous to electricians, they are capable of removing defunct axon terminals, thereby helping neuronal connections to stay intact. Microglia in healthy CNS tissue do not qualify as macrophages, and their specific functions are beginning to be explored.
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Affiliation(s)
- Manuel B Graeber
- Brain and Mind Research Institute, University of Sydney, Camperdown, NSW 2050, Australia.
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