PRG-1 relieves pain and depressive-like behaviors in rats of bone cancer pain by regulation of dendritic spine in hippocampus

Spotlight on plasticity-related genes: Current insights in health and disease

The development of the central nervous system is highly complex, involving numerous developmental processes that must take place with high spatial and temporal precision. This requires a series of complex and well-coordinated molecular processes that are tighly controlled and regulated by, for example, a variety of proteins and lipids. Deregulations in these processes, including genetic mutations, can lead to the most severe maldevelopments. The present review provides an overview of the protein family Plasticity-related genes (PRG1-5), including their role during neuronal differentiation, their molecular interactions, and their participation in various diseases. As these proteins can modulate the function of bioactive lipids, they are able to influence various cellular processes. Furthermore, they are dynamically regulated during development, thus playing an important role in the development and function of synapses. First studies, conducted not only in mouse experiments but also in humans, revealed that mutations or dysregulations of these proteins lead to changes in lipid metabolism, resulting in severe neurological deficits. In recent years, as more and more studies have shown their involvement in a broad range of diseases, the complexity and broad spectrum of known and as yet unknown interactions between PRGs, lipids, and proteins make them a promising and interesting group of potential novel therapeutic targets.

Study on the Mechanisms of Glrα3 in Pain Sensitization of Endometriosis

Endometriosis, often associated with chronic pelvic pain, can lead to anxiety and depression. This study investigates the role and mechanism of Glycine receptor alpha 3 (Glrα3) in the central sensitization of pain in endometriosis, aiming to identify new therapeutic targets. Using a Glrα3 knockout mouse model of endometriosis, we employed behavioral tests, qPCR, immunofluorescence, Nissl staining, MRI, and Western blot to assess the involvement of Glrα3 in central pain sensitization. Our results indicate that endometriosis-induced hyperalgesia and anxiety-depressive-like behaviors are linked to increased Glrα3 expression. Chronic pain in endometriosis leads to gray matter changes in the sensory and insular cortices, with Glrα3 playing a significant role. The inhibition of Glrα3 alleviates pain, reduces neuronal abnormalities, and decreases glial cell activation. The absence of Glrα3 effectively regulates the central sensitization of pain in endometriosis by inhibiting glial cell activation and maintaining neuronal stability. This study offers new therapeutic avenues for the clinical treatment of endometriosis-related pain.

DExH-box helicase 9 modulates hippocampal synapses and regulates neuropathic pain

Experimental studies have shown that neuropathic pain impairs hippocampal synaptic plasticity. Here, we sought to determine the underlying mechanisms responsible for synaptic changes in neuropathic painful mouse hippocampal neurons. Beyond demonstrating proof-of-concept for the location of DExH-box helicase 9 (DHX9) in the nucleus, we found that it did exist in the cytoplasm and DHX9 depletion resulted in structural and functional changes at synapses in the hippocampus. A decrease of DHX9 was observed in the hippocampus after peripheral nerve injury; overexpression of DHX9 in the hippocampus significantly alleviated the nociceptive responses and improved anxiety behaviors. Mimicking DHX9 decrease evoked spontaneous pain behavioral symptoms and anxiety emotion in naïve mice. Mechanistically, we found that DHX9 bound to dendrin (Ddn) mRNA, which may have altered the level of synaptic- and dendritic-associated proteins. The data suggest that DHX9 contributes to synapses in hippocampal neurons and may modulate neuropathic pain and its comorbidity aversive emotion.

Specific inhibition of TET1 in the spinal dorsal horn alleviates inflammatory pain in mice by regulating synaptic plasticity

DNA demethylation mediated by ten-eleven translocation 1 (TET1) is a critical epigenetic mechanism in which gene expression is regulated via catalysis of 5-methylcytosine to 5-hydroxymethylcytosine. Previously, we demonstrated that TET1 is associated with the genesis of chronic inflammatory pain. However, how TET1 participates in enhanced nociceptive responses in chronic pain remains poorly understood. Here, we report that conditional knockout of Tet1 in dorsal horn neurons via intrathecal injection of rAAV-hSyn-Cre in Tet1fl/fl mice not only reversed the inflammation-induced upregulation of synapse-associated proteins (post-synaptic density protein 95 (PSD95) and synaptophysin (SYP)) in the dorsal horn but also ameliorated abnormalities in dendritic spine morphology and alleviated pain hypersensitivities. Pharmacological blockade of TET1 by intrathecal injection of a TET1-specific inhibitor-Bobcat 339-produced similar results, as did knockdown of Tet1 by intrathecal injection of siRNA. Thus, our data strongly suggest that increased TET1 expression during inflammatory pain upregulates the expression of multiple synapse-associated proteins and dysregulates synaptic morphology in dorsal horn neurons, suggesting that Tet1 may be a potential target for analgesic strategies.

Dorsoventral hippocampus distinctly modulates visceral sensitivity and anxiety behaviors in male IBS-like rats

Accumulating evidences suggest dysfunctions in the hippocampus are associated with chronic pain. Nevertheless, the role of hippocampal circuitry in pain memories and emotional responses is not yet fully understood. In this study, we utilized a comprehensive approach that combined electromyography (EMG), photochemical genetic techniques, and anxiety-related behavioral paradigms to investigate the involvement of dorsal hippocampus (DH) and ventral hippocampus (VH) in visceral sensitivity and anxiety behaviors in male rats. Our results demonstrated that IBS-like rats exhibited comorbid visceral hypersensitivity and anxiety, along with the number of activated neurons in the VH was higher than that in the DH. Manipulation of glutamatergic neurons in the hippocampus was identified as a crucial mechanism underlying the mediation of both visceral sensitivity and anxiety behaviors. Specifically, optogenetic activation of the DH induced both visceral hypersensitivity and anxiety, while activation of the VH induced anxiety but did not affect visceral sensitivity. Conversely, chemogenetic inhibition of the DH reduced both visceral hypersensitivity and anxiety, whereas inhibition of the VH alleviated anxiety but did not alleviate visceral hypersensitivity in IBS-like rats. Our study highlights the important role of early life stress in inducing visceral hypersensitivity and anxiety, and further elucidates the distinct functional contributions of the DH and VH to these behavioral changes. These findings provide a theoretical basis for the diagnosis and treatment of IBS, and suggest that targeting specific hippocampal neuron subtypes may represent a promising therapeutic approach.

Purinergic P2X7 receptor as a potential therapeutic target in depression

The elaborate mechanisms of depression have always been a research hotspot in recent years, and the pace of research has never ceased. The P2X7 receptor (P2X7R) belongs to one of the adenosine triphosphates (ATP)-gated cation channels that exist widely in brain tissues and play a prominent role in the regulation of depression-related pathology. To date, the role of purinergic P2X7R in the mechanisms underlying depression is not fully understood. In this review, we conclude that the purinergic receptor P2X7 is a potential therapeutic target for depression based on research results published over the past 5 years in Google Scholar and the National Library of Medicine (PubMed). Additionally, we introduced the functional characteristics of P2X7R and confirmed that excessive activation of P2X7R led to increased release of inflammatory cytokines, which eventually contributed to depression. Furthermore, the inhibition of P2X7R produced antidepressant-like effects in animal models of depression, further proving that P2X7R signalling mediates depression-like behaviours. Finally, we summarised related studies on drugs that exert antidepressant effects by regulating the expression of P2X7R. We hope that the conclusions of this review will provide information on the role of P2X7R in the neuropathophysiology of depression and novel therapeutic targets for the treatment of depression.

PLPPR4 haploinsufficiency causes neurodevelopmental disorders by disrupting synaptic plasticity via mTOR signalling

Phospholipid phosphatase related 4 (PLPPR4), a neuron-specific membrane protein located at the postsynaptic density of glutamatergic synapses, is a putative regulator of neuronal plasticity. However, PLPPR4 dysfunction has not been linked to genetic disorders. In this study, we report three unrelated patients with intellectual disability (ID) or autism spectrum disorder (ASD) who harbour a de novo heterozygous copy number loss of PLPPR4 in 1p21.2p21.3, a heterozygous nonsense mutation in PLPPR4 (NM_014839, c.4C > T, p.Gln2*) and a homozygous splice mutation in PLPPR4 (NM_014839: c.408 + 2 T > C), respectively. Bionano single-molecule optical mapping confirmed PLPPR4 deletion contains no additional pathogenic genes. Our results suggested that the loss of function of PLPPR4 is associated with neurodevelopmental disorders. To test the pathogenesis of PLPPR4, peripheral blood mononuclear cells obtained from the patient with heterozygous deletion of PLPPR4 were induced to specific iPSCs (CHWi001-A) and then differentiated into neurons. The neurons carrying the deletion of PLPPR4 displayed the reduced density of dendritic protrusions, shorter neurites and reduced axon length, suggesting the causal role of PLPPR4 in neurodevelopmental disorders. As the mTOR signalling pathway was essential for regulating the axon maturation and function, we found that mTOR signalling was inhibited with a higher level of p-AKT, p-mTOR and p-ERK1/2, decreased p-PI3K in PLPPR4-iPSCs neurons. Additionally, we found silencing PLPPR4 disturbed the mTOR signalling pathway. Our results suggested PLPPR4 modulates neurodevelopment by affecting the plasticity of neurons via the mTOR signalling pathway.

Pain in Huntington's disease and its potential mechanisms

Pain is common and frequent in many neurodegenerative diseases, although it has not received much attention. In Huntington's disease (HD), pain is often ignored and under-researched because attention is more focused on motor and cognitive decline than psychiatric symptoms. In HD progression, pain symptoms are complex and involved in multiple etiologies, particularly mental issues such as apathy, anxiety and irritability. Because of psychiatric issues, HD patients rarely complain of pain, although their bodies show severe pain symptoms, ultimately resulting in insufficient awareness and lack of research. In HD, few studies have focused on pain and pain-related features. A detailed and systemic pain history is crucial to assess and explore pain pathophysiology in HD. This review provides an overview concentrating on pain-related factors in HD, including neuropathology, frequency, features, affecting factors and mechanisms. More attention and studies are still needed in this interesting field in the future.

IGF/IGF-1R signal pathway in pain: a promising therapeutic target

Pain, one of the most important problems in the field of medicine and public health, has great research significance. Opioids are still the main drugs to relieve pain now. However, its application is limited due to its obvious side effects. Therefore, it is urgent to develop new drugs to relieve pain. Multiple studies have found that IGF/IGF-1R pathway plays an important role in the occurrence and development of pain. The regulation of IGF/IGF-1R pathway has obvious effect on pain. This review summarized and discussed the therapeutic potential of IGF/IGF-1R signal pathway for pain. It also summarized that IGF/IGF-1R regulates pain by acting on neuronal excitability, neuroinflammation, glial cells, apoptosis, etc. However, its mechanisms of occurrence and development in pain still need further study in the future. In conclusion, although more deep researches are needed, these studies indicate that IGF/IGF-1R signal pathway is a promising therapeutic target for pain.

Understanding the initiation, delivery and processing of bone cancer pain from the peripheral to the central nervous system

Bone cancer pain is a complex condition characterized by persistent, sudden, spontaneous pain accompanied by hyperalgesia that typically arises from bone metastases or primary bone tumors, causing severe discomfort and significantly diminishing cancer patients' quality of life and confidence in their ability to overcome the disease. It is widely known that peripheral nerves are responsible for detecting harmful stimuli, which are then transmitted to the brain via the spinal cord, resulting in the perception of pain. In the case of bone cancer, tumors and stromal cells within the bone marrow release various chemical signals, including inflammatory factors, colony-stimulating factors, chemokines, and hydrogen ions. Consequently, the nociceptors located at the nerve endings within the bone marrow sense these chemical signals, generating electrical signals that are then transmitted to the brain through the spinal cord. Subsequently, the brain processes these electrical signals in a complex manner to create the sensation of bone cancer pain. Numerous studies have investigated the transmission of bone cancer pain from the periphery to the spinal cord. However, the processing of pain information induced by bone cancer within the brain remains unclear. With the continuous advancements in brain science and technology, the brain mechanism of bone cancer pain would become more clearly understood. Herein, we focus on summarizing the peripheral nerve perception of the spinal cord transmission of bone cancer pain and provide a brief overview of the ongoing research regarding the brain mechanisms involved in bone cancer pain.

Assessing Orofacial Pain Behaviors in Animal Models: A Review

Orofacial pain refers to pain occurring in the head and face, which is highly prevalent and represents a challenge to clinicians, but its underlying mechanisms are not fully understood, and more studies using animal models are urgently needed. Currently, there are different assessment methods for analyzing orofacial pain behaviors in animal models. In order to minimize the number of animals used and maximize animal welfare, selecting appropriate assessment methods can avoid repeated testing and improve the reliability and accuracy of research data. Here, we summarize different methods for assessing spontaneous pain, evoked pain, and relevant accompanying dysfunction, and discuss their advantages and disadvantages. While the behaviors of orofacial pain in rodents are not exactly equivalent to the symptoms displayed in patients with orofacial pain, animal models and pain behavioral assessments have advanced our understanding of the pathogenesis of such pain.

Musical therapy attenuates neuroma pain by modifying leptin expression

BACKGROUND

Accumulating evidence reveals that music therapy appears to help patients with pain. However, there is a limited understanding of the underlying mechanisms. Several studies indicate that leptin level has a crucial relationship with acute and chronic pain. Herein, we evaluated the effects of music stimulation and the potential roles of adipokines (leptin) in pain behaviors.

METHODS

We used a tibial neuroma transposition (TNT) rat model to mimic neuroma pain. Adult male Sprague-Dawley rats were randomly assigned to one of the three groups (n = 6):group 1 (GC), TNT with white noise; group 2(GM), TNT with music; and group 3(GH), TNT. White noise and music stimulation was given once a day following surgery until the end of the study (42^nd day). Pain behavioral tests were carried out before surgery and on the 3^rd, 10^th, 14^th, 21^st, 28^th, 35^th, and 42^nd days after surgery. At the end of the observation period, we analyzed the histological samples of blood, spinal cord, and prefrontal cortex to investigate the role of leptin in pain behaviors modulated by white noise and sound stimulation.

RESULT

Music therapy might improve the pain of TNT rats. Music stimulation ameliorated paw withdrawal thermal latency (PWTL) from the 3^rd day after the surgery while the mechanical pain was improved 21 days after the operation.Music stimulation also increased leptin expression in the spinal cord, prefrontal cortex.White noise had no obvious effect.

CONCLUSION

Music therapy might improve the pain of TNT rats. Besides, music stimulation ameliorated TNT-induced pain behaviors and affected leptin expression.

Emerging roles of the P2X7 receptor in cancer pain

Cancer pain is the most prevalent symptom experienced by cancer patients. It substantially impacts a patient’s long-term physical and emotional health, making it a pressing issue that must be addressed. Purinergic receptor P2X7 (P2X7R) is a widely distributed and potent non-selective ATP-gated ion channel that regulates tumor proliferation, chronic pain, and the formation of inflammatory lesions in the central nervous system. P2X7R plays an essential role in cancer pain and complications related to cancer pain including depression and opioid tolerance. This review focuses on the structure and distribution of P2X7R, its role in diverse tissues in cancer pain, and the application of P2X7R antagonists in the treatment of cancer pain to propose new ideas for cancer pain management.

A Possible Causal Involvement of Neuroinflammatory, Purinergic P2X7 Receptors in Psychiatric Disorders

P2X7 receptors (Rs) are prominent members of the P2XR family, which after binding ATP, open non-selective cationic channels, thereby allowing the transmembrane passage of Na+, Ca²⁺, and K+. Long-lasting and repetitive stimulation of the receptor by its agonist leads to the formation of large membrane pores permeable for organic cations of up to 900 Da molecular size. These pores are believed to play a role in apoptosis and inflammation. P2X7Rs are located primarily at peripheral macrophages and microglial cells, the resident macrophages of the CNS. The coactivation of toll-like receptors 4 (TLR4) by lipopolysaccharide, a constituent of the cell membrane of gram-negative bacteria, and the P2X7R by ATP leads to the generation and release of the proinflammatory cytokines interleukin-1β (IL-1β), IL-6, and tumor necrosis factor-α. Together with the microglial release of chemokines, reactive oxygen and nitrogen species, proteases, and excitotoxic glutamate, these cytokines result in neurodegeneration. P2X7Rs were found not only to amplify various neurodegenerative illnesses, such as Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis, but also to participate in a range of psychiatric diseases, such as major depression, bipolar disorder, schizophrenia, and autism spectrum disorder. Based on the prevention/reversal of neuroinflammation, pharmacological antagonists of P2X7Rs and their genetic deletion in animal experiments counteract these deleterious psychiatric conditions. Hence, brain penetrant P2X7R antagonists are potential therapeutics for psychiatric diseases, although the available evidence still needs to be extended and validated by further clinical data.

Neuroinflammation in the medial prefrontal cortex exerts a crucial role in bone cancer pain

Bone cancer pain (BCP) is one of the most common types of pain in cancer patients which compromises the patient's functional status, quality of life, and survival. Central hyperalgesia has increasingly been identified as a crucial factor of BCP, especially in the medial prefrontal cortex (mPFC) which is the main cortical area involved in the process of pain and consequent negative emotion. To explore the genetic changes in the mPFC during BCP occurrence and find possible targets for prediction, we performed transcriptome sequencing of mPFC in the BCP rat model and found a total of 147 differentially expressed mRNAs (DEmRNAs). A protein-protein interaction (PPI) network revealed that the DEmRNAs mainly participate in the inflammatory response. Meanwhile, microglia and astrocytes were activated in the mPFC of BCP rats, further confirming the presence of neuroinflammation. In addition, Gene Ontology (GO) analysis showed that DEmRNAs in the mPFC are mainly involved in antigen processing, presentation of peptide antigen, and immune response, occurring in the MHC protein complex. Besides, the Kyoto Encyclopedia of Genes and Genomes (KEGG) analysis revealed that DEmRNAs are mainly enriched in the pathways of phagosome, staphylococcus aureus infection, and antigen processing, in which MHCII participate. Furthermore, immunostaining showed that MHCII is mainly located in the microglia. Microglia are believed to be involved in antigen processing, a key cause of BCP. In vivo, minocycline (MC) treatment inhibits the activation of microglia and reduces the expression of MHCII and proinflammatory cytokines, thereby alleviating BCP and pain-related anxiety. Taken together, our study identified differentially expressed genes in the BCP process and demonstrated that the activation of microglia participates in the inflammatory response and antigen process, which may contribute to BCP.

PRG-1 prevents neonatal stimuli-induced persistent hyperalgesia and memory dysfunction via NSF/Glu/GluR2 signaling

Neonatal repetitive noxious stimuli (RNS) has been shown to cause long-term harmful effects on nociceptive processing, learning, and memory which persist until adulthood. Plasticity-related gene 1 (PRG-1) regulates synaptic plasticity and functional reorganization in the brain during neuronal development. In this study, neonatal RNS rats were established by repetitive needle pricks to neonatal rats on all four feet to model repetitive pain exposure in infants. Neonatal RNS caused thermal hyperalgesia, mechanical allodynia, learning, and memory impairments which manifested in young rats and persisted until adulthood. Hippocampal PRG-1/N-ethylmaleimide sensitive fusion protein (NSF) interaction was determined to be responsible for the RNS-induced impairment via enhanced extracellular glutamate release and AMPAR GluR2 trafficking deficiency in a cell-autonomous manner. These pathways likely act synergistically to cause changes in dendritic spine density. Our findings suggest that PRG-1 prevents the RNS-induced hyperalgesia, learning, and memory impairment by regulating synaptic plasticity via NSF/Glu/GluR2 signaling.

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Neonatal RNS induced hyperalgesia, learning, and memory impairment until adulthood.

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PRG-1 attenuated RNS-induced impairments by dendritic spine regulation.

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PRG-1 prevents RNS-induced impairments via NSF/Glu/GluR2 signaling.

Basolateral Amygdala Reactive Microglia May Contribute to Synaptic Impairment and Depressive-Like Behavior in Mice with Bone Cancer Pain

Anxiety and depression induced by cancer-related pain disturb quality of life and willingness to survive. As a component of the limbic system, the basolateral amygdala (BLA) is critical for processing negative emotions. The reactive microglial engulfment of synapses may promote depression during adolescence. However, whether microglia phagocytose synapses to mediate cancer pain-induced depression remains unclear. The present study established a bone cancer-pain model to investigate the association between dendritic spine synapses and depressive-like behavior and explore the phagocytic function of microglia in the BLA. We found that tumor-bearing mice experienced postoperative pain-related depression, and their BLAs exhibited reactive microglia, as well as phagocytic synapses. The microglial inhibitor minocycline effectively mitigated depressive behavior, synaptic damage, and the phagocytic function of microglia. Our study implicates microglia-mediated synaptic loss in the BLA may act as the pathological basis of depressive-like behavior in bone cancer pain model.