Chronic pain induces nociceptive neurogenesis in dorsal root ganglia from Sox2‐positive satellite cells

8-shogaol derived from dietary ginger alleviated acute and inflammatory pain by targeting TRPV1

Ginger, a well-known spice plant, has been used widely in medicinal preparations for pain relief. However, little is known about its analgesic components and the underlying mechanism. Here, we ascertained, the efficacy of ginger ingredient 8-Shogaol (8S), on inflammatory pain and tolerance induced by morphine, and probed the role of TRPV1 in its analgesic action using genetic and electrophysiology approaches. Results showed that 8S effectively reduced nociceptive behaviors of mice elicited by chemical stimuli, noxious heat as well as inflammation, and antagonized morphine analgesic tolerance independent on opioid receptor function. Genetic deletion of TRPV1 significantly abolished 8S' analgesia action. Further calcium imaging and patch-clamp recording showed that 8S could specifically activate TRPV1 in TRPV1-expressing HEK293T cells and dorsal root ganglion (DRG) neurons. The increase of [Ca2+]i in DRG was primarily mediated through TRPV1. Mutational and computation studies revealed the key binding sites for the interactions between 8S and TRPV1 included Leu515, Leu670, Ile573, Phe587, Tyr511, and Phe591. Further studies showed that TRPV1 activation evoked by 8S resulted in channel desensitization both in vitro and in vivo, as may be attributed to TRPV1 degradation or TRPV1 withdrawal from the cell surface. Collectively, this work provides the first evidence for the attractive analgesia of 8S in inflammatory pain and morphine analgesic tolerance mediated by targeting pain-sensing TRPV1 channel. 8S from dietary ginger has potential as a candidate drug for the treatment of inflammatory pain.

Piezo1-Mediated Neurogenic Inflammatory Cascade Exacerbates Ventricular Remodeling After Myocardial Infarction

BACKGROUND

Heart failure is associated with a high rate of mortality and morbidity, and ventricular remodeling invariably precedes heart failure. Ventricular remodeling is fundamentally driven by mechanotransduction that is regulated by both the nervous system and the immune system. However, it remains unknown which key molecular factors govern the neuro/immune/cardio axis that underlies mechanotransduction during ventricular remodeling. Here, we investigated whether the mechanosensitive Piezo cation channel-mediated neurogenic inflammatory cascade underlies ventricular remodeling-related mechanotransduction.

METHODS

By ligating the left coronary artery of rats to establish an in vivo model of chronic myocardial infarction (MI), lentivirus-mediated thoracic dorsal root ganglion (TDRG)-specific Piezo1 knockdown rats and adeno-associated virus-PHP.S-mediated TDRG neuron-specific Piezo1 knockout mice were used to investigate whether Piezo1 in the TDRG plays a functional role during ventricular remodeling. Subsequently, neutralizing antibody-mediated TDRG IL-6 (interleukin-6) inhibition rats and adeno-associated virus-PHP.S-mediated TDRG neuron-specific IL-6 knockdown mice were used to determine the mechanism underlying neurogenic inflammation. Primary TDRG neurons were used to evaluate Piezo1 function in vitro.

RESULTS

Expression of Piezo1 and IL-6 was increased, and these factors were functionally activated in TDRG neurons at 4 weeks after MI. Both knockdown of TDRG-specific Piezo1 and deletion of TDRG neuron-specific Piezo1 lessened the severity of ventricular remodeling at 4 weeks after MI and decreased the level of IL-6 in the TDRG or heart. Furthermore, inhibition of TDRG IL-6 or knockdown of TDRG neuron-specific IL-6 also ameliorated ventricular remodeling and suppressed the IL-6 cascade in the heart, whereas the Piezo1 level in the TDRG was not affected. In addition, enhanced Piezo1 function, as reflected by abundant calcium influx induced by Yoda1 (a selective agonist of Piezo1), led to increased release of IL-6 from TDRG neurons in mice 4 weeks after MI.

CONCLUSIONS

Our findings point to a critical role for Piezo1 in ventricular remodeling at 4 weeks after MI and reveal a neurogenic inflammatory cascade as a previously unknown facet of the neuronal immune signaling axis underlying mechanotransduction.

Characterisation of GFAP-Expressing Glial Cells in the Dorsal Root Ganglion after Spared Nerve Injury

Satellite glial cells (SGCs), enveloping primary sensory neurons' somas in the dorsal root ganglion (DRG), contribute to neuropathic pain upon nerve injury. Glial fibrillary acidic protein (GFAP) serves as an SGC activation marker, though its DRG satellite cell specificity is debated. We employed the hGFAP-CFP transgenic mouse line, designed for astrocyte studies, to explore its expression within the peripheral nervous system (PNS) after spared nerve injury (SNI). We used diverse immunostaining techniques, Western blot analysis, and electrophysiology to evaluate GFAP+ cell changes. Post-SNI, GFAP+ cell numbers increased without proliferation, and were found near injured ATF3+ neurons. GFAP+ FABP7+ SGCs increased, yet 75.5% of DRG GFAP+ cells lacked FABP7 expression. This suggests a significant subset of GFAP+ cells are non-myelinating Schwann cells (nmSC), indicated by their presence in the dorsal root but not in the ventral root which lacks unmyelinated fibres. Additionally, patch clamp recordings from GFAP+ FABP7-cells lacked SGC-specific Kir4.1 currents, instead displaying outward Kv currents expressing Kv1.1 and Kv1.6 channels specific to nmSCs. In conclusion, this study demonstrates increased GFAP expression in two DRG glial cell subpopulations post-SNI: GFAP+ FABP7+ SGCs and GFAP+ FABP7- nmSCs, shedding light on GFAP's specificity as an SGC marker after SNI.

Transcriptome and secretome profiling of sensory neurons reveals sex differences in pathways relevant to insulin sensing and insulin secretion

Sensory neurons in the dorsal root ganglia (DRG) convey somatosensory and metabolic cues to the central nervous system and release substances from stimulated terminal endings in peripheral organs. Sex-biased variations driven by the sex chromosome complement (XX and XY) have been implicated in the sensory-islet crosstalk. However, the molecular underpinnings of these male-female differences are not known. Here, we aim to characterize the molecular repertoire and the secretome profile of the lower thoracic spinal sensory neurons and to identify molecules with sex-biased insulin sensing- and/or insulin secretion-modulating activity that are encoded independently of circulating gonadal sex hormones. We used transcriptomics and proteomics to uncover differentially expressed genes and secreted molecules in lower thoracic T5-12 DRG sensory neurons derived from sexually immature 3-week-old male and female C57BL/6J mice. Comparative transcriptome and proteome analyses revealed differential gene expression and protein secretion in DRG neurons in males and females. The transcriptome analysis identified, among others, higher insulin signaling/sensing capabilities in female DRG neurons; secretome screening uncovered several sex-specific candidate molecules with potential regulatory functions in pancreatic β cells. Together, these data suggest a putative role of sensory interoception of insulin in the DRG-islet crosstalk with implications in sensory feedback loops in the regulation of β-cell activity in a sex-biased manner. Finally, we provide a valuable resource of molecular and secretory targets that can be leveraged for understanding insulin interoception and insulin secretion and inform the development of novel studies/approaches to fathom the role of the sensory-islet axis in the regulation of energy balance in males and females.

Scientific and Regulatory Policy Committee Technical Review: Biology and Pathology of Ganglia in Animal Species Used for Nonclinical Safety Testing

Dorsal root ganglia (DRG), trigeminal ganglia (TG), other sensory ganglia, and autonomic ganglia may be injured by some test article classes, including anti-neoplastic chemotherapeutics, adeno-associated virus-based gene therapies, antisense oligonucleotides, nerve growth factor inhibitors, and aminoglycoside antibiotics. This article reviews ganglion anatomy, cytology, and pathology (emphasizing sensory ganglia) among common nonclinical species used in assessing product safety for such test articles (TAs). Principal histopathologic findings associated with sensory ganglion injury include neuron degeneration, necrosis, and/or loss; increased satellite glial cell and/or Schwann cell numbers; and leukocyte infiltration and/or inflammation. Secondary nerve fiber degeneration and/or glial reactions may occur in nerves, dorsal spinal nerve roots, spinal cord (dorsal and occasionally lateral funiculi), and sometimes the brainstem. Ganglion findings related to TA administration may result from TA exposure and/or trauma related to direct TA delivery into the central nervous system or ganglia. In some cases, TA-related effects may need to be differentiated from a spectrum of artifactual and/or spontaneous background changes.

Transient neurogenesis in ischemic cortex from Sox2+ astrocytes

The adult cortex has long been regarded as non-neurogenic. Whether injury can induce neurogenesis in the adult cortex is still controversial. Here, we report that focal ischemia stimulates a transient wave of local neurogenesis. Using 5'-bromo-2'-deoxyuridine labeling, we demonstrated a rapid generation of doublecortin-positive neuroblasts that died quickly in mouse cerebral cortex following ischemia. Nestin-Cre^ER-based cell ablation and fate mapping showed a small contribution of neuroblasts by subventricular zone neural stem cells. Using a mini-photothrombotic ischemia mouse model and retrovirus expressing green fluorescent protein labeling, we observed maturation of locally generated new neurons. Furthermore, fate tracing analyses using PDGFRα-, GFAP-, and Sox2-Cre^ER mice showed a transient wave of neuroblast generation in mild ischemic cortex and identified that Sox2-positive astrocytes were the major neurogenic cells in adult cortex. In addition, a similar upregulation of Sox2 and appearance of neuroblasts were observed in the focal ischemic cortex of Macaca mulatta. Our findings demonstrated a transient neurogenic response of Sox2-positive astrocytes in ischemic cortex, which suggests the possibility of inducing neuronal regeneration by amplifying this intrinsic response in the future.

The Similar and Distinct Roles of Satellite Glial Cells and Spinal Astrocytes in Neuropathic Pain

Preclinical studies have identified glial cells as pivotal players in the genesis and maintenance of neuropathic pain after nerve injury associated with diabetes, chemotherapy, major surgeries, and virus infections. Satellite glial cells (SGCs) in the dorsal root and trigeminal ganglia of the peripheral nervous system (PNS) and astrocytes in the central nervous system (CNS) express similar molecular markers and are protective under physiological conditions. They also serve similar functions in the genesis and maintenance of neuropathic pain, downregulating some of their homeostatic functions and driving pro-inflammatory neuro-glial interactions in the PNS and CNS, i.e., "gliopathy". However, the role of SGCs in neuropathic pain is not simply as "peripheral astrocytes". We delineate how these peripheral and central glia participate in neuropathic pain by producing different mediators, engaging different parts of neurons, and becoming active at different stages following nerve injury. Finally, we highlight the recent findings that SGCs are enriched with proteins related to fatty acid metabolism and signaling such as Apo-E, FABP7, and LPAR1. Targeting SGCs and astrocytes may lead to novel therapeutics for the treatment of neuropathic pain.

New Insights on the Role of Satellite Glial Cells

Satellite glial cells (SGCs) that surround sensory neurons in the peripheral nervous system ganglia originate from neural crest cells. Although several studies have focused on SGCs, the origin and characteristics of SGCs are unknown, and their lineage remains unidentified. Traditionally, it has been considered that SGCs regulate the environment around neurons under pathological conditions, and perform functions of supporting, nourishing, and protecting neurons. However, recent studies demonstrated that SGCs may have the characteristics of stem cells. After nerve injury, SGCs up-regulate the expression of stem cell markers and can differentiate into functional sensory neurons. Moreover, SGCs express several markers of Schwann cell precursors and Schwann cells, such as CDH19, MPZ, PLP1, SOX10, ERBB3, and FABP7. Schwann cell precursors have also been proposed as a potential source of neurons in the peripheral nervous system. The similarity in function and markers suggests that SGCs may represent a subgroup of Schwann cell precursors. Herein, we discuss the roles and functions of SGCs, and the lineage relationship between SGCs and Schwann cell precursors. We also describe a new perspective on the roles and functions of SGCs. In the DRG located on the posterior root of spinal nerves, satellite glial cells wrap around each sensory neuron to form an anatomically and functionally distinct unit with the sensory neurons. Following nerve injury, satellite glial cells up-regulate the expression of progenitor markers, and can differentiate into neurons.

The Roles of Imaging Biomarkers in the Management of Chronic Neuropathic Pain

Chronic neuropathic pain (CNP) affects around 10% of the general population and has a significant social, emotional, and economic impact. Current diagnosis techniques rely mainly on patient-reported outcomes and symptoms, which leads to significant diagnostic heterogeneity and subsequent challenges in management and assessment of outcomes. As such, it is necessary to review the approach to a pathology that occurs so frequently, with such burdensome and complex implications. Recent research has shown that imaging methods can detect subtle neuroplastic changes in the central and peripheral nervous system, which can be correlated with neuropathic symptoms and may serve as potential markers. The aim of this paper is to review available imaging methods used for diagnosing and assessing therapeutic efficacy in CNP for both the preclinical and clinical setting. Of course, further research is required to standardize and improve detection accuracy, but available data indicate that imaging is a valuable tool that can impact the management of CNP.

Morphological and phenotypical characteristics of porcine satellite glial cells of the dorsal root ganglia

Satellite glial cells (SGCs) of the dorsal root ganglia (DRG) ensure homeostasis and proportional excitability of sensory neurons and gained interest in the field of development and maintenance of neuropathic pain. Pigs represent a suitable species for translational medicine with a more similar anatomy and physiology to humans compared to rodents, and are used in research regarding treatment of neuropathic pain. Knowledge of anatomical and physiological features of porcine SGCs is prerequisite for interpreting potential alterations. However, state of knowledge is still limited. In the present study, light microscopy, ultrastructural analysis and immunofluorescence staining was performed. SGCs tightly surround DRG neurons with little vascularized connective tissue between SGC-neuron units, containing, among others, axons and Schwann cells. DRG were mainly composed of large sized neurons (∼59%), accompanied by fewer medium sized (∼36%) and small sized sensory neurons (∼6%). An increase of neuronal body size was concomitant with an increased number of surrounding SGCs. The majority of porcine SGCs expressed glutamine synthetase and inwardly rectifying potassium channel Kir 4.1, known as SGC-specific markers in other species. Similar to canine SGCs, marked numbers of porcine SGCs were immunopositive for glial fibrillary acidic protein, 2',3'-cyclic-nucleotide 3'-phosphodiesterase and the transcription factor Sox2. Low to moderate numbers of SGCs showed aquaporin 4-immunoreactivity (AQP4) as described for murine SGCs. AQP4-immunoreactivity was primarily found in SGCs ensheathing small and medium sized neuronal somata. Low numbers of SGCs were immunopositive for ionized calcium-binding adapter molecule 1, indicating a potential immune cell character. No immunoreactivity for common leukocyte antigen CD45 nor neural/glial antigen 2 was detected. The present study provides essential insights into the characteristic features of non-activated porcine SGCs, contributing to a better understanding of this cell population and its functional aspects. This will help to interpret possible changes that might occur under activating conditions such as pain.

Astragalus Mongholicus: A review of its anti-fibrosis properties

Background: Fibrosis-related diseases (FRD) include cerebral fibrosis, pulmonary fibrosis, cardiac fibrosis, liver fibrosis, renal fibrosis, peritoneal fibrosis, etc. The effects of fibrosis can be severe, resulting in organ dysfunction, functional decline, and even organ failure, which can cause serious health problems.

Aim: Currently, there is no effective modern medicine for anti-fibrosis in the clinics; however, Chinese medicine has a certain beneficial effect on treating such diseases. Astragalus Mongholicus (AM) has rich medicinal value, and its anti-fibrosis effect has been recently investigated. In recent years, more and more experimental studies have been conducted on the intervention of astragaloside IV (AS-IV), astragalus polysaccharide (APS), astragalus flavone, cycloastragalus alcohol, astragalus water extract and other pharmacological components in fibrosis-related diseases, attracting the interest of researchers. We aim to provide ideas for future research by summarizing recent research advances of AM in treating fibrosis-related diseases.

Methods: A literature search was conducted from the core collections of electronic databases such as Baidu Literature, Sciencen.com, Google Scholar, PubMed, and Science Direct using the above keywords and the pharmacological and phytochemical details of the plant.

Results: AM can be used to intervene in fibrosis-disease progression by regulating inflammation, oxidative stress, the immune system, and metabolism.

Conclusion: AS-IV, APS, and astragalus flavone were studied and discussed in detail. These components have high potential anti-fibrosis activity. Overall, this review aims to gain insight into the AM’s role in treating fibro-related diseases.

Peroxisome Metabolism Contributes to PIEZO2-Mediated Mechanical Allodynia

Mutations in the peroxisomal half-transporter ABCD1 cause X-linked adrenoleukodystrophy, resulting in elevated very long-chain fatty acids (VLCFA), progressive neurodegeneration and an associated pain syndrome that is poorly understood. In the nervous system of mice, we found ABCD1 expression to be highest in dorsal root ganglia (DRG), with satellite glial cells (SGCs) displaying higher expression than neurons. We subsequently examined sensory behavior and DRG pathophysiology in mice deficient in ABCD1 compared to wild-type mice. Beginning at 8 months of age, Abcd1-/y mice developed persistent mechanical allodynia. DRG had a greater number of IB4-positive nociceptive neurons expressing PIEZO2, the mechanosensitive ion channel. Blocking PIEZO2 partially rescued the mechanical allodynia. Beyond affecting neurons, ABCD1 deficiency impacted SGCs, as demonstrated by high levels of VLCFA, increased glial fibrillary acidic protein (GFAP), as well as genes disrupting neuron-SGC connectivity. These findings suggest that lack of the peroxisomal half-transporter ABCD1 leads to PIEZO2-mediated mechanical allodynia as well as SGC dysfunction. Given the known supportive role of SGCs to neurons, this elucidates a novel mechanism underlying pain in X-linked adrenoleukodystrophy.

Single-Dose Intrathecal Dorsal Root Ganglia Toxicity of Onasemnogene Abeparvovec in Cynomolgus Monkeys

Intravenous onasemnogene abeparvovec is approved for the treatment of spinal muscular atrophy in children < 2 years. For later-onset patients, intrathecal onasemnogene abeparvovec may be advantageous over intravenous administration. Recently, microscopic dorsal root ganglion (DRG) changes were observed in nonhuman primates (NHPs) following intrathecal onasemnogene abeparvovec administration. To characterize these DRG findings, two NHP studies evaluating intrathecal onasemnogene abeparvovec administration were conducted: a 12-month study with a 6-week interim cohort and a 13-week study with a 2-week interim cohort. The latter investigated the potential impact of prednisolone or rituximab plus everolimus on DRG toxicity. An additional 6-month, single-dose, intravenous NHP study conducted in parallel evaluated onasemnogene abeparvovec safety (including DRG toxicity) with or without prednisolone coadministration. Intrathecal onasemnogene abeparvovec administration was well tolerated and not associated with clinical observations. Microscopic onasemnogene abeparvovec-related changes were observed in the DRG and trigeminal ganglion (TG) and included mononuclear cell inflammation and/or neuronal degeneration, which was colocalized with high vector transcript expression at 6 weeks postdose. Incidence and severity of DRG changes were generally decreased after 52 weeks compared with 6 weeks postdose. Other onasemnogene abeparvovec-related microscopic findings of axonal degeneration, mononuclear cell infiltrates and/or gliosis in the spinal cord, dorsal spinal nerve root/spinal nerves, and/or peripheral nerves were absent or found at decreased incidences and/or severities after 52 weeks. DRG and/or TG microscopic findings following intravenous onasemnogene abeparvovec dosing included minimal to slight neuronal degeneration and mononuclear cell inflammation at 6 weeks and 6 months postdose. Nervous system microscopic findings following intrathecal onasemnogene abeparvovec (≥1.2 × 10¹³ vg/animal) trended toward resolution after 52 weeks, supporting nonprogression of changes, including in the DRG. Onasemnogene abeparvovec-related DRG findings were not associated with electrophysiology changes and were not ameliorated by prednisolone or rituximab plus everolimus coadministration. The pathogenesis is possibly a consequence of increased vector genome transduction and/or transgene expression.

Long non-coding RNA rhabdomyosarcoma 2-associated transcript contributes to neuropathic pain by recruiting HuR to stabilize DNA methyltransferase 3 alpha mRNA expression in dorsal root ganglion neuron

Introduction

Long non-coding RNAs (lncRNAs) act as key regulators in multiple human diseases. In particular, the dysfunction of lncRNAs in dorsal root ganglion (DRG) contributes to the pathogenesis of neuropathic pain (NP). Nevertheless, the role and mechanism of most lncRNAs in NP remain unclear.

Methods

Two classic chronic NP models, including L4 spinal nerve ligation (SNL) model and chronic constriction injury (CCI) of the sciatic nerve, were performed. Mechanical allodynia and heat hyperalgesia were used to evaluate neuropathic pain. DRG microinjection was used to deliver agents into DRG. qRT-PCR, immunofluorescence, immunoprecipitation, western blotting, siRNA transfection, AAV transduction were performed to investigate the phenotypes and molecular basis.

Results

Here, we discovered that Rmst as a lncRNA was specifically expressed in Atf3 ⁺ injured DRG neurons and significantly upregulated following peripheral nerve damage. Rmst overexpression by direct DRG injection of AAV5-Rmst causes neuropathic symptoms in the absence of nerve damage. Conversely, blocking Rmst expression in injured DRGs alleviated nerve injury-induced pain hypersensitivities and downregulated Dnmt3a expression. Furthermore, we found peripheral nerve damage induced Rmst increase could interact with RNA-binding protein HuR to stabilize the Dnmt3a mRNA.

Conclusion

Our findings reveal a crucial role of Rmst in damaged DRG neurons under NP condition and provide a novel target for drug development against NP.

Phenotypical changes of satellite glial cells in a murine model of GM1 -gangliosidosis

Satellite glial cells (SGCs) of dorsal root ganglia (DRG) react in response to various injuries in the nervous system. This study investigates reactive changes within SGCs in a murine model for G_M1‐gangliosidosis (G_M1). DRG of homozygous β‐galactosidase‐knockout mice and homozygous C57BL/6 wild‐type mice were investigated performing immunostaining on formalin‐fixed, paraffin‐embedded tissue. A marked upregulation of glial fibrillary acidic protein (GFAP), the progenitor marker nestin and Ki67 within SGCs of diseased mice, starting after 4 months at the earliest GFAP, along with intracytoplasmic accumulation of ganglioside within neurons and deterioration of clinical signs was identified. Interestingly, nestin‐positive SGCs were detected after 8 months only. No changes regarding inwardly rectifying potassium channel 4.1, 2, 3‐cyclic nucleotide 3‐phosphodiesterase, Sox2, doublecortin, periaxin and caspase3 were observed in SGCs. Iba1 was only detected in close vicinity of SGCs indicating infiltrating or tissue‐resident macrophages. These results indicate that SGCs of DRG show phenotypical changes during the course of G_M1, characterized by GFAP upregulation, proliferation and expression of a neural progenitor marker at a late time point. This points towards an important role of SGCs during neurodegenerative disorders and supports that SGCs represent a multipotent glial precursor cell line with high plasticity and functionality.

Voltage-Gated Sodium Channels: A Prominent Target of Marine Toxins

Voltage-gated sodium channels (VGSCs) are considered to be one of the most important ion channels given their remarkable physiological role. VGSCs constitute a family of large transmembrane proteins that allow transmission, generation, and propagation of action potentials. This occurs by conducting Na⁺ ions through the membrane, supporting cell excitability and communication signals in various systems. As a result, a wide range of coordination and physiological functions, from locomotion to cognition, can be accomplished. Drugs that target and alter the molecular mechanism of VGSCs’ function have highly contributed to the discovery and perception of the function and the structure of this channel. Among those drugs are various marine toxins produced by harmful microorganisms or venomous animals. These toxins have played a key role in understanding the mode of action of VGSCs and in mapping their various allosteric binding sites. Furthermore, marine toxins appear to be an emerging source of therapeutic tools that can relieve pain or treat VGSC-related human channelopathies. Several studies documented the effect of marine toxins on VGSCs as well as their pharmaceutical applications, but none of them underlined the principal marine toxins and their effect on VGSCs. Therefore, this review aims to highlight the neurotoxins produced by marine animals such as pufferfish, shellfish, sea anemone, and cone snail that are active on VGSCs and discuss their pharmaceutical values.

Spinal cord injury in mice impacts central and peripheral pathology in a severity-dependent manner

ABSTRACT

Chronic pain is a common medical complication experienced by those living with spinal cord injury (SCI) and leads to worsened quality of life. The pathophysiology of SCI pain is poorly understood, hampering the development of safe and efficacious therapeutics. We therefore sought to develop a clinically relevant model of SCI with a strong pain phenotype and characterize the central and peripheral pathology after injury. A contusion (50 kdyn) injury, with and without sustained compression (60 seconds) of the spinal cord, was carried out on female C57BL/6J mice. Mice with compression of the spinal cord exhibited significantly greater heat and mechanical hypersensitivity starting at 7 days post-injury, concomitant with reduced locomotor function, compared to those without compression. Immunohistochemical analysis of spinal cord tissue revealed significantly less myelin sparing and increased macrophage activation in mice with compression compared to those without. As measured by flow cytometry, immune cell infiltration and activation were significantly greater in the spinal cord (phagocytic myeloid cells and microglia) and dorsal root ganglia (Ly6C+ monocytes) following compression injury. We also decided to investigate the gastrointestinal microbiome, as it has been shown to be altered in SCI patients and has recently been shown to play a role in immune system maturation and pain. We found increased dysbiosis of the gastrointestinal microbiome in an injury severity-dependent manner. The use of this contusion-compression model of SCI may help advance the preclinical assessment of acute and chronic SCI pain and lead to a better understanding of mechanisms contributing to this pain.

Discrepancy in the Usage of GFAP as a Marker of Satellite Glial Cell Reactivity

Satellite glial cells (SGCs) surrounding the neuronal somas in peripheral sensory ganglia are sensitive to neuronal stressors, which induce their reactive state. It is believed that such induced gliosis affects the signaling properties of the primary sensory neurons and is an important component of the neuropathic phenotype leading to pain and other sensory disturbances. Efforts to understand and manipulate such gliosis relies on reliable markers to confirm induced SGC reactivity and ultimately the efficacy of targeted intervention. Glial fibrillary acidic protein (GFAP) is currently the only widely used marker for such analyses. However, we have previously described the lack of SGC upregulation of GFAP in a mouse model of sciatic nerve injury, suggesting that GFAP may not be a universally suitable marker of SGC gliosis across species and experimental models. To further explore this, we here investigate the regulation of GFAP in two different experimental models in both rats and mice. We found that whereas GFAP was upregulated in both rodent species in the applied inflammation model, only the rat demonstrated increased GFAP in SGCs following sciatic nerve injury; we did not observe any such GFAP upregulation in the mouse model at either protein or mRNA levels. Our results demonstrate an important discrepancy between species and experimental models that prevents the usage of GFAP as a universal marker for SGC reactivity.

Phenotypical peculiarities and species-specific differences of canine and murine satellite glial cells of spinal ganglia

Satellite glial cells (SGCs) are located in the spinal ganglia (SG) of the peripheral nervous system and tightly envelop each neuron. They preserve tissue homeostasis, protect neurons and react in response to injury. This study comparatively characterizes the phenotype of murine (mSGCs) and canine SGCs (cSGCs). Immunohistochemistry and immunofluorescence as well as 2D and 3D imaging techniques were performed to describe a SGC-specific marker panel, identify potential functional subsets and other phenotypical, species-specific peculiarities. Glutamine synthetase (GS) and the potassium channel Kir 4.1 are SGC-specific markers in murine and canine SG. Furthermore, a subset of mSGCs showed CD45 immunoreactivity and the majority of mSGCs were immunopositive for neural/glial antigen 2 (NG2), indicating an immune and a progenitor cell character. The majority of cSGCs were immunopositive for glial fibrillary acidic protein (GFAP), 2',3'-cyclic-nucleotide 3'-phosphodiesterase (CNPase) and Sox2. Therefore, cSGCs resemble central nervous system glial cells and progenitor cells. SGCs lacked expression of macrophage markers CD107b, Iba1 and CD204. Double labelling with GS/Kir 4.1 highlights the unique anatomy of SGC-neuron units and emphasizes the indispensability of further staining and imaging techniques for closer insights into the specific distribution of markers and potential colocalizations.

Satellite Glial Cells Give Rise to Nociceptive Sensory Neurons

Dorsal root ganglia (DRG) sensory neurons can transmit information about noxious stimulus to cerebral cortex via spinal cord, and play an important role in the pain pathway. Alterations of the pain pathway lead to CIPA (congenital insensitivity to pain with anhidrosis) or chronic pain. Accumulating evidence demonstrates that nerve damage leads to the regeneration of neurons in DRG, which may contribute to pain modulation in feedback. Therefore, exploring the regeneration process of DRG neurons would provide a new understanding to the persistent pathological stimulation and contribute to reshape the somatosensory function. It has been reported that a subpopulation of satellite glial cells (SGCs) express Nestin and p75, and could differentiate into glial cells and neurons, suggesting that SGCs may have differentiation plasticity. Our results in the present study show that DRG-derived SGCs (DRG-SGCs) highly express neural crest cell markers Nestin, Sox2, Sox10, and p75, and differentiate into nociceptive sensory neurons in the presence of histone deacetylase inhibitor VPA, Wnt pathway activator CHIR99021, Notch pathway inhibitor RO4929097, and FGF pathway inhibitor SU5402. The nociceptive sensory neurons express multiple functionally-related genes (SCN9A, SCN10A, SP, Trpv1, and TrpA1) and are able to generate action potentials and voltage-gated Na⁺ currents. Moreover, we found that these cells exhibited rapid calcium transients in response to capsaicin through binding to the Trpv1 vanilloid receptor, confirming that the DRG-SGC-derived cells are nociceptive sensory neurons. Further, we show that Wnt signaling promotes the differentiation of DRG-SGCs into nociceptive sensory neurons by regulating the expression of specific transcription factor Runx1, while Notch and FGF signaling pathways are involved in the expression of SCN9A. These results demonstrate that DRG-SGCs have stem cell characteristics and can efficiently differentiate into functional nociceptive sensory neurons, shedding light on the clinical treatment of sensory neuron-related diseases.

Chronic Pain Causes Peripheral and Central Responses in MIA-Induced TMJOA Rats

Chronic pain is the predominant symptom that drives temporomandibular joint osteoarthritis (TMJOA) patients to seek medical care; however, currently used treatment modalities remain less effective. This study aimed to investigate chronic pain and the peripheral and central responses in monoiodoacetate (MIA)-induced TMJOA rats. First, the appropriate dose of MIA was determined based on pain behavior assessment in rats. Alterations of the condylar structure in TMJOA rats were evaluated by histological staining and micro-computed tomography (micro-CT). Second, the period of TMJOA chronic pain was further explored by assessing the numbers of glial fibrillary acidic protein (GFAP)-positive astrocytes and ionized calcium-binding adaptor molecule 1 (IBA-1)-positive microglia in the trigeminal spinal nucleus (TSN) and performing nonsteroidal anti-inflammatory drug (NSAID) efficacy experiments. Finally, the expression of neurofilament 200 (NF200), calcitonin gene-related peptide (CGRP), and isolectin B4 (IB4) in the trigeminal ganglion (TG) and TSN was assessed by immunofluorescence. MIA at 4 mg/kg was considered an appropriate dose. Gradual MIA-induced alterations of the condylar structure were correlated with temporomandibular joint (TMJ) pain. The numbers of GFAP- and IBA-1-positive cells were increased at 2, 3, and 4 weeks after MIA injection. NSAIDs failed to alleviate pain behavior 10 days after MIA injection. CGRP and IB4 levels in the TG and TSN were upregulated at 2 and 4 weeks. These results suggest that TMJOA-related chronic pain emerged 2 weeks after MIA injection. CGRP- and IB4-positive afferents in both the peripheral and central nervous systems may be involved in MIA-induced TMJOA-related chronic pain in rats.

Antagonistic effects of IL-17 and Astragaloside IV on cortical neurogenesis and cognitive behavior after stroke in adult mice through Akt/GSK-3β pathway

We aimed to investigate the exact effect of IL-17 on regulating neural stem cells (NSCs) stemness and adult neurogenesis in ischemic cortex after stroke, how Astragaloside IV(As-IV) regulated IL-17 expression and the underlying mechanism. Photochemical brain ischemia model was established and IL-17 protein expression was observed at different time after stroke in WT mice. At 3 days after stroke, when IL-17 expression peaked, IL-17 knock out (KO) mice were used to observe cell proliferation and neurogenesis in ischemic cortex. Then, As-IV was administered intravenously to assess cell apoptosis, proliferation, neurogenesis, and cognitive deficits by immunochemistry staining, western blots, and animal behavior tests in WT mice. Furthermore, IL-17 KO mice and As-IV were used simultaneously to evaluate the mechanism of cell apoptosis and proliferation after stroke in vivo. Besides, in vitro, As-IV and recombinant mouse IL-17A was administered, respectively, into NSCs culture, and then their diameters, viable cell proliferation and pathway relevant protein was assessed. The results showed knocking out IL-17 contributed to regulating PI3K/Akt pathway, promoting NSCs proliferation, and neurogenesis after ischemic stroke. Moreover, As-IV treatment helped inhibit neural apoptosis, promote the neurogenesis and eventually relieve mice anxiety after stroke. Unsurprisingly, IL-17 protein expression could be downregulated by As-IV in vivo and in vitro and they exerted antagonistic effect on neurogenesis by regulating Akt/GSK-3β pathway, with significant regulation for apoptosis. In conclusion, IL-17 exerts negative effect on promoting NSCs proliferation, neurogenesis and cognitive deficits after ischemic stroke, which could be reversed by As-IV.

Astragaloside IV Exerts Cognitive Benefits and Promotes Hippocampal Neurogenesis in Stroke Mice by Downregulating Interleukin-17 Expression via Wnt Pathway

Background

Stroke remains a leading cause of adult disability and the demand for stroke rehabilitation services is growing, and Astragaloside IV (As IV), a primary bioactive compound of Radix Astragali : Astragalus mongholicus Bunge (Fabaceae), may be a promising stroke therapy.

Methods

To access the effect of As IV on adult mice after ischemic stroke, a photochemical ischemia model was established on C57BL/6 mice, which were intravenously administered As IV for three consecutive days later. And then the cognitive benefits and hippocampal neurogenesis were evaluated by Morris Water Maze (MWM) test, Golgi staining, and immunohistochemical staining in vivo and in vitro. Furthermore, to find out the underlying mechanism, interleukin-17 (IL-17) knockout (KO) mice were used, through RNA sequence (RNA-seq) analysis and immunohistochemistry. Then the mechanism of neurogenesis promoted by As IV was observed by western blot both in vivo and in vitro. Specifically, As IV, recombinant mouse IL-17A and IL-17F, and Wingless/integrated (Wnt)-expressing virus was administered respectively in neural stem cells (NSCs), and then their diameters and protein expression of Nestin, IL-17, and Wnt pathway relevant protein, were measured in vitro.

Results

Administering As IV resulted in significant amelioration of stroke-induced cognitive deficits. And more hippocampal neurons with normal morphology, significant increments in the length of the apical dendrites, and the density of their spines were observed in As IV-treated mice. Furthermore, the immunohistochemistry staining of DCX/BrdU and Sox2/Nestin showed As IV could promote hippocampal neurogenesis and NSC proliferation after ischemic stroke, as well as in vitro. For the mechanism underlying, IL-17 expression was downregulated significantly by As IV treatment and knocking out IL-17 was associated with nervous regeneration and synapse repair according to the analysis of RNA-seq. Consistent to As IV treatment, knocking out IL-17 showed some promotion on hippocampal neurogenesis and proliferation of NSCs, with activating Wnt pathway after stoke. Finally, in vitro, NSCs’ diameters and protein expression of Nestin, IL-17, and Wnt pathway were regulated by either administering As IV or inhibiting IL-17.

Conclusion

As IV stimulates hippocampal neurogenesis after stroke, thus potentially facilitates brain to remodel and repair by downregulating IL-17 expression via Wnt pathway.

Changes in the transcriptional fingerprint of satellite glial cells following peripheral nerve injury

Satellite glial cells (SGCs) are homeostatic cells enveloping the somata of peripheral sensory and autonomic neurons. A wide variety of neuronal stressors trigger activation of SGCs, contributing to, for example, neuropathic pain through modulation of neuronal activity. However, compared to neurons and other glial cells of the nervous system, SGCs have received modest scientific attention and very little is known about SGC biology, possibly due to the experimental challenges associated with studying them in vivo and in vitro. Utilizing a recently developed method to obtain SGC RNA from dorsal root ganglia (DRG), we took a systematic approach to characterize the SGC transcriptional fingerprint by using next-generation sequencing and, for the first time, obtain an overview of the SGC injury response. Our RNA sequencing data are easily accessible in supporting information in Excel format. They reveal that SGCs are enriched in genes related to the immune system and cell-to-cell communication. Analysis of SGC transcriptional changes in a nerve injury-paradigm reveal a differential response at 3 days versus 14 days postinjury, suggesting dynamic modulation of SGC function over time. Significant downregulation of several genes linked to cholesterol synthesis was observed at both time points. In contrast, regulation of gene clusters linked to the immune system (MHC protein complex and leukocyte migration) was mainly observed after 14 days. Finally, we demonstrate that, after nerve injury, macrophages are in closer physical proximity to both small and large DRG neurons, and that previously reported injury-induced proliferation of SGCs may, in fact, be proliferating macrophages.

The role of adenosine and P2Y receptors expressed by multiple cell types in pain transmission

The role of extracellular nucleotides and nucleosides as signaling molecules in cell-to-cell communication has now been clearly established. This is particularly true in the central and peripheral nervous system, where purines and pyrimidines are involved in both physiological and pathological interactions between neurons and surrounding glial cells. It can be thus foreseen that the purinergic system could represent a new potential target for the development of effective analgesics, also through the normalization of neuronal functions and the inhibition of glial cell activation. Research in the last 15 years has progressively confirmed this hypothesis, but no purinergic-based analgesics have reach the market so far; in the present review we have collected the more recent discoveries on the role of G protein-coupled P2Y nucleotide and of adenosine receptors expressed by both neurons and glial cells under painful conditions, and we have highlighted some of the challenges that must be faced to translate basic and preclinical studies to clinics.