Early transplantation of mesenchymal stem cells after spinal cord injury relieves pain hypersensitivity through suppression of pain-related signaling cascades and reduced inflammatory cell recruitment

Cerebrospinal fluid-contacting neurons: a promising source for adult neural stem cell transplantation in spinal cord injury treatment

Transplantation of adult neural stem cells (NSCs) is regarded as one of the most promising approaches for treating spinal cord injury (SCI). However, securing a sufficient and reliable source of adult NSCs remains one of the primary challenges in applying this method for SCI treatment. Cerebrospinal fluid-contacting neurons (CSF-cNs) act as adult NSCs and can be substantially expanded in vitro while maintaining their NSC characteristics even after 60 passages. When CSF-cNs are transplanted into the injury sites of SCI mice, they demonstrate high survival rates along with the ability to proliferate and differentiate into neurons, astrocytes, and oligodendrocytes. Additionally, significant improvements in motor function have been observed in SCI mice following the transplantation of CSF-cNs. These results suggest that CSF-cNs may represent a promising source of adult NSCs for transplantation therapy in SCI.

Emerging role of macrophages in neuropathic pain

Neuropathic pain is a complex syndrome caused by injury to the neurons, which causes persistent hypersensitivity and considerable inconvenience to the patient's whole life. Over the past two decades, the interaction between immune cells and neurons has been proven to play a crucial role in the development of neuropathic pain. Increasing studies have indicated the important role of macrophages for neuroinflammation and have shed light on the underlying molecular and cellular mechanisms. In addition, novel therapeutic methods targeting macrophages are springing up, which provide more options in our clinical treatment. Herein, we reviewed the characteristics of peripheral macrophages and their function in neuropathic pain, with the aim of better understanding how these cells contribute to pathological processes and paving the way for therapeutic approaches.

Translational potential statement

This review provides a comprehensive overview of the mechanisms underlying the interplay between the macrophages and nervous system during the progression of nerve injury. Additionally, it compiles existing intervention strategies targeting macrophages for the treatment of neuropathic pain. This information offers valuable insights for researchers seeking to address the challenge of this intractable pain.

Mesenchymal stem cells as a therapeutic strategy to combat oxidative stress-mediated neuropathic pain

Neuropathic pain, a chronic condition resulting from somatosensory system damage, remains a significant clinical challenge due to its complex pathophysiology and inadequate response to traditional therapies. Oxidative stress, characterized by an imbalance between free radicals production and antioxidant defenses, plays a pivotal role in the development and maintenance of neuropathic pain. Mesenchymal stem cells (MSCs) are multipotent stromal cells with the ability to differentiate into various cell types and possess immunomodulatory, anti-inflammatory, and regenerative properties, making them promising candidates for novel pain management strategies. Preclinical studies demonstrate that MSCs can reduce inflammation, scavenge reactive oxygen species (ROS), promote nerve regeneration, and modulate pain signaling pathways. Various administration routes, including intravenous and intrathecal, have been investigated to optimize MSC delivery and efficacy. Additionally, MSC-derived extracellular vesicles (EVs) represent a cell-free alternative with substantial therapeutic potential. Despite encouraging preclinical findings, further research is needed to refine MSC-based therapies, including the exploration of combination treatments and rigorous clinical trials, to translate these promising results into effective clinical applications for neuropathic pain relief. This review explores the therapeutic potential of MSCs in alleviating oxidative stress-mediated neuropathic pain.

Mesenchymal stem cell transplantation plays a role in relieving cancer pain

Tumors can invade, compress, and damage nerves, leading to persistent pain and seriously affecting the quality of life of patients. However, their treatment is challenging. Sensitization of peripheral receptors, abnormal activity of primary sensory neurons, activation of glial cells, enhanced inflammatory responses, and sensory information transmission contribute towards cancer pain. Therefore, considerable attention has been paid to exploring prospective methods to inhibit the occurrence of these factors and relieve cancer pain. Studies on different types of pains have revealed that the transplantation of functionally active cells into the host has the pharmacological effect of producing analgesia. Mesenchymal stem cells (MSCs) can act as small active pumps to reduce the expression of pain-related molecules and produce analgesic effects. Moreover, MSCs can establish complex communication networks with non-tumor and cancer cells in the microenvironment, interact with each other, and can be used as destinations for inflammation and tumor sites, affecting their potential for invasion and metastasis. This emphasizes the key role of MSCs in cancer and pain management. The pain relief mechanisms of MSCs include neuronutrition, neural protection, neural network reconstruction, immune regulation, and improvement of the inflammatory microenvironment around the nerve injury. All of these are beneficial for the recovery of injured or stimulated nerves and the reconstruction of neural function, and play a role in relieving pain. The pain treatment strategy of cell transplantation is to repair injured nerves and produce analgesic pharmacological properties that are different from those of painkillers and other physiotherapies. Although the therapeutic role of MSCs in cancer and pain is in its early stages, the therapeutic value of MSCs for cancer pain has great prospects. Therefore, in this study, we explored the possible mechanism between MSCs and cancer pain, the potential therapeutic role of therapeutic cells in cancer pain, and some problems and challenges.

Influential factors on stem cell therapy success in canine model of spinal cord Injury: A systematic review and meta-analysis

Spinal cord injury (SCI) is a serious medical condition. The search for an effective cure remains a persistent challenge. Current treatments, unfortunately, are unable to sufficiently improve neurological function, often leading to lifelong disability. This systematic review and meta-analysis evaluated the effectiveness of stem cell therapy for SCI using canine models. It also explored the optimal protocol for implementing stem cell therapy. A comprehensive search of studies was conducted from 2000 to October 2022. This study focused on five outcomes: motor function score, histopathology, IHC, western blot, and SEP. The results demonstrated a significant improvement in locomotion post-SCI in dogs treated with stem cell therapy. The therapy also led to an average increase of 3.15 points in the Olby score of the treated dogs compared to the control group. These findings highlights stem cell therapy's potential as a promising SCI treatment. The meta-analysis suggests that using bone marrow stem cells, undergoing neural differentiation in vitro, applying a surgical implantation or intrathecal route of administration, associating matrigel in combination with stem cells, and a waiting period of two weeks before starting treatment can enhance SCI treatment effectiveness.

Evidence-Based Clinical Practice Guidelines on Regenerative Medicine Treatment for Chronic Pain: A Consensus Report from a Multispecialty Working Group

Purpose

Injectable biologics have not only been described and developed to treat dermal wounds, cardiovascular disease, and cancer, but have also been reported to treat chronic pain conditions. Despite emerging evidence supporting regenerative medicine therapy for pain, many aspects remain controversial.

Methods

The American Society of Pain and Neuroscience (ASPN) identified the educational need for an evidence-based guideline on regenerative medicine therapy for chronic pain. The executive board nominated experts spanning multiple specialties including anesthesiology, physical medicine and rehabilitation, and sports medicine based on expertise, publications, research, and clinical practice. A steering committee selected preliminary questions, which were reviewed and refined. Evidence was appraised using the United States Preventive Services Task Force (USPSTF) criteria for evidence level and degree of recommendation. Using a modified Delphi approach, consensus points were distributed to all collaborators and each collaborator voted on each point. If collaborators provided a decision of "disagree" or "abstain", they were invited to provide a rationale in a non-blinded fashion to the committee chair, who incorporated the respective comments and distributed revised versions to the committee until consensus was achieved.

Results

Sixteen questions were selected for guideline development. Questions that were addressed included type of injectable biologics and mechanism, evidence in treating chronic pain indications (eg, tendinopathy, muscular pathology, osteoarthritis, intervertebral disc disease, neuropathic pain), role in surgical augmentation, dosing, comparative efficacy between injectable biologics, peri-procedural practices to optimize therapeutic response and quality of injectate, federal regulations, and complications with mitigating strategies.

Conclusion

In well-selected individuals with certain chronic pain indications, use of injectable biologics may provide superior analgesia, functionality, and/or quality of life compared to conventional medical management or placebo. Future high-quality randomized clinical trials are warranted with implementation of minimum reporting standards, standardization of preparation protocols, investigation of dose-response associations, and comparative analysis between different injectable biologics.

Bone Marrow Mesenchymal Stem Cells-Derived Extracellular Vesicle miR-208a-3p Alleviating Spinal Cord Injury via Regulating the Biological Function of Spinal Cord Neurons

We aim to explore the potential mechanism of bone marrow mesenchymal stem cells-derived extracellular vesicles (BMSCs-Exo) in improving spinal cord injury (SCI). Thirty male 12-week specific pathogen-free (SPF) Sprague-Dawley (SD) rats were used to construct SCI model in vivo. Ten male 12-week SPF SD rats were used to extract BMSCs. The Basso, Beattie, Bresnahan (BBB) score was used to evaluate the motor function of rats. Real-time fluorescence quantitative PCR (RT-PCR), western blot (WB), and double luciferase assay were used to explore the regulation between rno-miR-208a-3p and Cdkn1a (p21) in BMSCs. Primary spinal cord neurons were treated with lipopolysaccharide (100 ng/mL) for 30 min to mimic SCI in vitro. Compared with the model group (14 scores), BMSCs-Exo increased BBB score (19 scores) in SCI rats. Compared with the sham group, Cdkn1a was upregulated, whereas rno-miR-208a-3p was downregulated in the model group. However, compared with the model group, Cdkn1a was downregulated, whereas rno-miR-208a-3p was upregulated in the BMSCs-Exo group. In addition, rno-miR-208a-3p inhibited the expression of Cdkn1a via direct binding way. BMSCs-Exo-rno-miR-208a-3p promoted the proliferation of primary spinal neurons via inhibiting apoptosis in vitro. Moreover, BMSCs-Exo-rno-miR-208a-3p promoted cyclin D1, CDK6, and Bcl-2 and inhibited Bax expression in a cell model of SCI. In conclusion, BMSCs-Exo-carried rno-miR-208a-3p significantly protects rats from SCI via regulating the Cdkn1a pathway.

Optimization strategies for mesenchymal stem cell-based analgesia therapy: a promising therapy for pain management

Pain is a very common and complex medical problem that has a serious impact on individuals' physical and mental health as well as society. Non-steroidal anti-inflammatory drugs and opioids are currently the main drugs used for pain management, but they are not effective in controlling all types of pain, and their long-term use can cause adverse effects that significantly impair patients' quality of life. Mesenchymal stem cells (MSCs) have shown great potential in pain treatment. However, limitations such as the low proliferation rate of MSCs in vitro and low survival rate in vivo restrict their analgesic efficacy and clinical translation. In recent years, researchers have explored various innovative approaches to improve the therapeutic effectiveness of MSCs in pain treatment. This article reviews the latest research progress of MSCs in pain treatment, with a focus on methods to enhance the analgesic efficacy of MSCs, including engineering strategies to optimize the in vitro culture environment of MSCs and to improve the in vivo delivery efficiency of MSCs. We also discuss the unresolved issues to be explored in future MSCs and pain research and the challenges faced by the clinical translation of MSC therapy, aiming to promote the optimization and clinical translation of MSC-based analgesia therapy.

Neuroinflammation mechanism underlying neuropathic pain: the role of mesenchymal stem cell in neuroglia

Pain is an essential aspect of the body's physiological response to unpleasant noxious stimuli from either external sustained injuries or an internal disease condition that occurs within the body. Generally, pain is temporary. However, in patients with neuropathic pain, the experienced pain is persistent and uncontrollable, with an unsatisfactory treatment effectiveness. The activation of the immune system is a crucial factor in both central and peripheral neuropathic pain. The immune response plays an important role in the progression of the stages of neuropathic pain, and acts not only as pain mediators, but also produce analgesic molecules. Neuropathic pain has long been described as a result of dysfunctional nerve activities. However, there is substantial evidence indicating that the regulation of hyperalgesia is mediated by astrocytes and microglia activation. Mesenchymal stem cells currently hold an optimal potential in managing pain, as they can migrate to damaged tissues and have a robust immunosuppressive role for autologous or heterologous transplantation. Moreover, mesenchymal stem cells revealed their immunomodulatory capabilities by secreting growth factors and cytokines through direct cell interactions. The main idea underlying the use of mesenchymal stem cells in pain management is that these cells can replace damaged nerve cells by releasing neurotrophic factors. This property makes them the perfect option to modulate and treat neuropathic pain, which is notoriously difficult to treat.

Advances of the MAPK pathway in the treatment of spinal cord injury

Spinal cord injury (SCI) represents a complex pathology within the central nervous system (CNS), leading to severe sensory and motor impairments. It activates various signaling pathways, notably the mitogen-activated protein kinase (MAPK) pathway. Present treatment approaches primarily focus on symptomatic relief, lacking efficacy in addressing the underlying pathophysiological mechanisms. Emerging research underscores the significance of the MAPK pathway in neuronal differentiation, growth, survival, axonal regeneration, and inflammatory responses post-SCI. Modulating this pathway post-injury has shown promise in attenuating inflammation, minimizing apoptosis, alleviating neuropathic pain, and fostering neural regeneration. Given its pivotal role, the MAPK pathway emerges as a potential therapeutic target in SCI management. This review synthesizes current knowledge on SCI pathology, delineates the MAPK pathway's characteristics, and explores its dual roles in SCI pathology and therapeutic interventions. Furthermore, it addresses the existing challenges in MAPK research in the context of SCI, proposing solutions to overcome these hurdles. Our aim is to offer a comprehensive reference for future research on the MAPK pathway and SCI, laying the groundwork for targeted therapeutic strategies.

Molars to Medicine: A Focused Review on the Pre-Clinical Investigation and Treatment of Secondary Degeneration following Spinal Cord Injury Using Dental Stem Cells

Spinal cord injury (SCI) can result in the permanent loss of mobility, sensation, and autonomic function. Secondary degeneration after SCI both initiates and propagates a hostile microenvironment that is resistant to natural repair mechanisms. Consequently, exogenous stem cells have been investigated as a potential therapy for repairing and recovering damaged cells after SCI and other CNS disorders. This focused review highlights the contributions of mesenchymal (MSCs) and dental stem cells (DSCs) in attenuating various secondary injury sequelae through paracrine and cell-to-cell communication mechanisms following SCI and other types of neurotrauma. These mechanistic events include vascular dysfunction, oxidative stress, excitotoxicity, apoptosis and cell loss, neuroinflammation, and structural deficits. The review of studies that directly compare MSC and DSC capabilities also reveals the superior capabilities of DSC in reducing the effects of secondary injury and promoting a favorable microenvironment conducive to repair and regeneration. This review concludes with a discussion of the current limitations and proposes improvements in the future assessment of stem cell therapy through the reporting of the effects of DSC viability and DSC efficacy in attenuating secondary damage after SCI.

Preemptive administration of mesenchymal stem cells-derived conditioned medium can attenuate the development of neuropathic pain in rats via downregulation of proinflammatory cytokines

Neuropathic pain (NP) is a chronic condition characterized by persistent pain following nerve injury. It is a challenging clinical problem to manage due to limited treatment options. Mesenchymal stem cells (MSCs)-derived conditioned medium (CM) is a cell-free product that contains the secretome of MSCs and has been shown to have therapeutic potential in various inflammatory and degenerative disorders. Several animal studies have examined the antinociceptive effects of MSCs-CM on established neuropathic pain, but none have investigated the early prevention of neuropathic pain using MSCs-CM. Therefore, in this study, we tested whether preemptive administration of MSCs-CM could attenuate the development of NP in rats. To this end, NP was induced in Wistar rats using a chronic constriction injury (CCI) model (day 0), and then the animals were divided into four groups: Sham, CCI, CCI-Dulbecco's Modified Eagle Medium (DMEM), and CCI-CM. The CCI-CM group received 1 ml intraperitoneal administration of MSCs-CM on days - 1, 1, and 2, while the Sham, CCI, and CCI-DMEM groups received vehicle only (normal saline or DMEM). Mechanical withdrawal threshold and thermal withdrawal latency were assessed to evaluate pain sensitivities. In addition, the expression levels of proinflammatory cytokines (TNF-α and IL-1β) in the spinal cord tissues were measured using quantitative real-time PCR (qRT-PCR). The results demonstrated that preemptive treatment with MSCs-CM can significantly attenuate the development of NP, as evidenced by improved mechanical withdrawal threshold and thermal withdrawal latency in the CCI-CM group compared to the CCI and CCI-DMEM groups. Furthermore, the relative gene expression of proinflammatory cytokines TNF-α and IL-1β were significantly decreased in the spinal cord tissues of the CCI-CM group compared to the control groups. These findings suggest that preemptive administration of MSCs-CM can attenuate the development of NP in rats, partly due to the downregulation of proinflammatory cytokines.

Imbalance of Th1 and Th2 Cytokines and Stem Cell Therapy in Pathological Pain

The pathophysiological importance of T helper 1 (Th1) and Th2 cell cytokines in pathological pain has been highly debated in recent decades. However, the analgesic strategy targeting individual cytokines still has a long way to go for clinical application. In this review, we focus on the contributions of Th1 cytokines (TNF-α, IFN-γ, and IL-2) and Th2 cytokines (IL-4, IL-5, IL-10, and IL-13) in rodent pain models and human pain-related diseases. A large number of studies have shown that Th1 and Th2 cytokines have opposing effects on pain modulation. The imbalance of Th1 and Th2 cytokines might determine the final effect of pain generation or inhibition. However, increasing evidence indicates that targeting the individual cytokine is not sufficient for the treatment of pathological pain. It is practical to suggest a promising therapeutic strategy against the combined effects of Th1 and Th2 cytokines. We summarize the current advances in stem cell therapy for pain-related diseases. Preclinical and clinical studies show that stem cells inhibit proinflammatory cytokines and release enormous Th2 cytokines that exhibit a strong analgesic effect. Therefore, a shift of the imbalance of Th1 and Th2 cytokines induced by stem cells will provide a novel therapeutic strategy against intractable pain. It is extremely important to reveal the cellular and molecular mechanisms of stem cell-mediated analgesia. The efficiency and safety of stem cell therapy should be carefully evaluated in animal models and patients with pathological pain.

Stem cells and pain

Pain can be defined as an unpleasant sensory and emotional experience caused by either actual or potential tissue damage or even resemble that unpleasant experience. For years, science has sought to find treatment alternatives, with minimal side effects, to relieve pain. However, the currently available pharmacological options on the market show significant adverse events. Therefore, the search for a safer and highly efficient analgesic treatment has become a priority. Stem cells (SCs) are non-specialized cells with a high capacity for replication, self-renewal, and a wide range of differentiation possibilities. In this review, we provide evidence that the immune and neuromodulatory properties of SCs can be a valuable tool in the search for ideal treatment strategies for different types of pain. With the advantage of multiple administration routes and dosages, therapies based on SCs for pain relief have demonstrated meaningful results with few downsides. Nonetheless, there are still more questions than answers when it comes to the mechanisms and pathways of pain targeted by SCs. Thus, this is an evolving field that merits further investigation towards the development of SC-based analgesic therapies, and this review will approach all of these aspects.

Adipose-Derived Mesenchymal Stromal Cell Transplantation for Severe Spinal Cord Injury: Functional Improvement Supported by Angiogenesis and Neuroprotection

Mesenchymal stromal cell transplantation alone is insufficient when motor dysfunction is severe; combination therapy with rehabilitation could improve motor function. Here, we aimed to analyze the characteristics of adipose-derived MSCs (AD-MSCs) and determine their effectiveness in severe spinal cord injury (SCI) treatment. A severe SCI model was created and motor function were compared. The rats were divided into AD-MSC-transplanted treadmill exercise-combined (AD-Ex), AD-MSC-transplanted non-exercise (AD-noEx), PBS-injected exercise (PBS-Ex), and no PBS-injected exercise (PBS-noEx) groups. In cultured cell experiments, AD-MSCs were subjected to oxidative stress, and the effects on the extracellular secretion of AD-MSCs were investigated using multiplex flow cytometry. We assessed angiogenesis and macrophage accumulation in the acute phase. Spinal cavity or scar size and axonal preservation were assessed histologically in the subacute phase. Significant motor function improvement was observed in the AD-Ex group. Vascular endothelial growth factor and C-C motif chemokine 2 expression in AD-MSC culture supernatants increased under oxidative stress. Enhanced angiogenesis and decreased macrophage accumulation were observed at 2 weeks post-transplantation, whereas spinal cord cavity or scar size and axonal preservation were observed at 4 weeks. Overall, AD-MSC transplantation combined with treadmill exercise training improved motor function in severe SCI. AD-MSC transplantation promoted angiogenesis and neuroprotection.

Bibliometric and visual analysis of microglia-related neuropathic pain from 2000 to 2021

Background

Microglia has gradually gained researchers' attention in the past few decades and has shown its promising prospect in treating neuropathic pain. Our study was performed to comprehensively evaluate microglia-related neuropathic pain via a bibliometric approach.

Methods

We retrospectively reviewed publications focusing on microglia-related neuropathic pain from 2000 to 2021 in WoSCC. VOS viewer software and CiteSpace software were used for statistical analyses.

Results

A total of 2,609 articles were finally included. A steady increase in the number of relevant publications was observed in the past two decades. China is the most productive country, while the United States shares the most-cited and highest H-index country. The University of London, Kyushu University, and the University of California are the top 3 institutions with the highest number of publications. Molecular pain and Pain are the most productive and co-cited journals, respectively. Inoue K (Kyushu University) is the most-contributed researcher and Ji RR (Duke University) ranks 1st in both average citations per article and H-index. Keywords analyses revealed that pro-inflammatory cytokines shared the highest burst strength. Sex differences, neuroinflammation, and oxidative stress are the emerging keywords in recent years.

Conclusion

In the field of microglia-related neuropathic pain, China is the largest producer and the United States is the most influential country. The signaling communication between microglia and neurons has continued to be vital in this field. Sexual dimorphism, neuroinflammation, and stem-cell therapies might be emerging trends that should be closely monitored.

Stem cells therapeutic effect in a reserpine-induced fibromyalgia rat model: A possible NLRP3 inflammasome modulation with neurogenesis promotion in the cerebral cortex

Fibromyalgia is a chronic pain syndrome with a multifactorial pathophysiology affecting 2-8 % of the population.

AIMS

To investigate the therapeutic effects of bone marrow mesenchymal stem cells (BMSCs) against fibromyalgia-related cerebral cortex damage and the possible underlying mechanisms of action.

MATERIALS AND METHODS

Rats were randomly allocated into three groups; control, fibromyalgia and fibromyalgia treated with BMSCs groups. Physical and behavioural assessments were performed. Cerebral cortices were collected for biochemical and histological assessment.

KEY FINDINGS

Fibromyalgia group showed behavioural changes indicating presence of pain, fatigue, depression, and sleep disturbances. Moreover, biochemical biomarkers alterations were demonstrated by a significant decrease in brain monoamines and GSH levels, but MDA, NO, TNF-alpha, HMGB-1, NLRP3, and caspase-1 levels significantly increased. Furthermore, histological assessment revealed structural and ultrastructural alterations indicating neuronal and neuroglial degeneration with microglia activation, an increase in mast cell number and IL-1β immune-expression. Additionally, a significant decrease in Beclin-1 immune-expression, and blood brain barrier disruption were noticed. Interestingly, BMSCs administration significantly improved behavioural alterations, restored the reduced brain monoamines and oxidative stress markers, and reduced TNF-alpha, HMGB-1, NLRP3, and caspase-1 levels. Profoundly, cerebral cortices demonstrated improved histological structure, significant decrease in mast cell number and IL-1β immune-expression, besides a significant increase in Beclin-1 and DCX immune-expression.

SIGNIFICANCE

For the best of our knowledge, this is the first study showing ameliorative effects for BMSCs treatment in fibromyalgia-related cerebral cortical damage. The neurotherapeutic effects of BMSCs could be attributed to NLRP3 inflammasome signaling pathway inhibition, mast cell deactivation, and stimulation of neurogenesis and autophagy.

Mechanisms of analgesic effect of mesenchymal stem cells in osteoarthritis pain

Osteoarthritis (OA) is the most common musculoskeletal disease, and it is a major cause of pain, disability and health burden. Pain is the most common and bothersome presentation of OA, but its treatment is still suboptimal, due to the short-term action of employed analgesics and their poor adverse effect profile. Due to their regenerative and anti-inflammatory properties, mesenchymal stem cells (MSCs) have been extensively investigated as a potential therapy for OA, and numerous preclinical and clinical studies found a significant improvement in joint pathology and function, pain scores and/or quality of life after administration of MSCs. Only a limited number of studies, however, addressed pain control as the primary end-point or investigated the potential mechanisms of analgesia induced by MSCs. In this paper, we review the evidence reported in literature that support the analgesic action of MSCs in OA, and we summarize the potential mechanisms of these antinociceptive effects.

CircSmox knockdown alleviates PC12 cell apoptosis and inflammation in spinal cord injury by miR-340-5p/Smurf1 axis

BACKGROUND

Spinal cord injury (SCI) is a traumatic central nervous system disorder that leads to irreversible neurological dysfunction. Emerging evidence has shown that differentially expressed circular RNAs (circRNAs) after SCI is closely associated with the pathophysiological process. Herein, the potential function of circRNA spermine oxidase (circSmox) in functional recovery after SCI was investigated.

METHODS

Differentiated PC12 cells stimulated with lipopolysaccharide (LPS) were employed as an in vitro model for neurotoxicity research. Levels of genes and proteins were detected by quantitative real-time PCR and Western blot analysis. Cell viability and apoptosis were determined by CCK-8 assay and flow cytometry. Western blot analysis was used to detect the protein level of apoptosis-related markers. The levels of interleukin (IL)-1β, IL-6, IL-8, and tumor necrosis factor (TNF)-α. Dual-luciferase reporter, RIP, and pull-down assays were used to confirm the target relationship between miR-340-5p and circSmox or Smurf1 (SMAD Specific E3 Ubiquitin Protein Ligase 1).

RESULTS

LPS elevated the levels of circSmox and Smurf1, but decreased the levels of miR-340-5p in PC12 cells in a dose-dependent manner. Functionally, circSmox silencing alleviated LPS-induced apoptosis and inflammation in PC12 cells in vitro. Mechanistically, circSmox directly sponged miR-340-5p, which targeted Smurf1. Rescue experiments showed that miR-340-5p inhibition attenuated the neuroprotective effect of circSmox siRNA in PC12 cells. Moreover, miR-340-5p suppressed LPS-triggered neurotoxicity in PC12 cells, which was reversed by Smurf1 overexpression.

CONCLUSION

CircSmox enhances LPS-induced apoptosis and inflammation via miR-340-5p/Smurf1 axis, providing an exciting view of the potential involvement of circSmox in SCI pathogenesis.

Resolvin D1 attenuates mechanical allodynia after burn injury: Involvement of spinal glia, p38 mitogen-activated protein kinase, and brain-derived neurotrophic factor/tropomyosin-related kinase B signaling

Resolvin D1 (RvD1) suppresses inflammatory, postoperative, and neuropathic pain. The present study assessed the roles and mechanisms of RvD1 in mechanical allodynia after burn injury. A rat model of burn injury was established for analyses, and RvD1 was injected intraperitoneally. Pain behavior and the expression levels of spinal dorsal horn Iba-1 (microglia marker), GFAP (astrocyte marker), p-p38 mitogen-activated protein kinase (MAPK), brain-derived neurotrophic factor (BDNF), and tropomyosin-related kinase B (TrkB) were detected by behavioral and immunocytochemical assays. The results showed that RvD1 attenuated mechanical allodynia after burn injury, prevented microglial and astroglial activation, and downregulated p-p38 MAPK in microglia and BDNF/TrkB following burn injury. Similarly, inhibition of p38 MAPK and BDNF/TrkB signaling attenuated mechanical allodynia after burn injury. In addition, inhibition of p38 MAPK prevented spinal microglial activation and downregulated BDNF/TrkB following burn injury. Furthermore, inhibition of BDNF/TrkB signaling prevented spinal microglial activation and downregulated p-p38 MAPK within spinal microglia. Taken together, this study demonstrated that RvD1 might attenuate mechanical allodynia after burn injury by inhibiting spinal cord glial activation, microglial p38 MAPK, and BDNF/TrkB signaling in the spinal dorsal horn.

Cell therapy for neuropathic pain

Neuropathic pain (NP) is caused by a lesion or a condition that affects the somatosensory system. Pathophysiologically, NP can be ascribed to peripheral and central sensitization, implicating a wide range of molecular pathways. Current pharmacological and non-pharmacological approaches are not very efficacious, with over half of NP patients failing to attain adequate pain relief. So far, pharmacological and surgical treatments have focused primarily on symptomatic relief by modulating pain transduction and transmission, without treating the underlying pathophysiology. Currently, researchers are trying to use cell therapy as a therapeutic alternative for the treatment of NP. In fact, mounting pre-clinical and clinical studies showed that the cell transplantation-based therapy for NP yielded some encouraging results. In this review, we summarized the use of cell grafts for the treatment of NP caused by nerve injury, synthesized the latest advances and adverse effects, discussed the possible mechanisms to inform pain physicians and neurologists who are endeavoring to develop cell transplant-based therapies for NP and put them into clinical practice.

Evaluation of (R)-[11C]PK11195 PET/MRI for Spinal Cord-Related Neuropathic Pain in Patients with Cervical Spinal Disorders

Activated microglia are involved in secondary injury after acute spinal cord injury (SCI) and in development of spinal cord-related neuropathic pain (NeP). The aim of the study was to assess expression of translocator protein 18 kDa (TSPO) as an indicator of microglial activation and to investigate visualization of the dynamics of activated microglia in the injured spinal cord using PET imaging with (R)-[¹¹C]PK11195, a specific ligand for TSPO. In SCI chimeric animal models, TSPO was expressed mainly in activated microglia. Accumulation of (R)-[³H]PK11195 was confirmed in autoradiography and its dynamics in the injured spinal cord were visualized by (R)-[¹¹C]PK11195 PET imaging in the acute phase after SCI. In clinical application of (R)-[¹¹C]PK11195 PET/MRI of the cervical spinal cord in patients with NeP related to cervical disorders, uptake was found in cases up to 10 months after injury or surgery. No uptake could be visualized in the injured spinal cord in patients with chronic NeP at more than 1 year after injury or surgery, regardless of the degree of NeP. However, a positive correlation was found between standardized uptake value ratio and the severity of NeP, suggesting the potential of clinical application for objective evaluation of chronic NeP.

Novel therapeutic approach to slow down the inflammatory cascade in acute/subacute spinal cord injury: Early immune therapy with lipopolysaccharide enhanced neuroprotective effect of combinational therapy of granulocyte colony-stimulating factor and bone-marrow mesenchymal stem cell in spinal cord injury

Bone-marrow mesenchymal stem cells (BM-MSCs) have not yet proven any significant therapeutic efficacy in spinal cord injury (SCI) clinical trials, due to the hostile microenvironment of the injured spinal cord at the acute phase. This study aims to modulate the inflammatory milieu by lipopolysaccharide (LPS) and granulocyte colony-stimulating factor (G-CSF) to improve the BM-MSCs therapy. For this purpose, we determined the optimum injection time and sub-toxic dosage of LPS following a T10 contusion injury. Medium-dose LPS administration may result in a local anti-inflammatory beneficial role. This regulatory role is associated with an increase in NF-200-positive cells, significant tissue sparing, and improvement in functional recovery compared to the SCI control group. The second aim was to examine the potential ability of LPS and LPS + G-CSF combination therapy to modulate the lesion site before BM-MSC (1 × 105 cells) intra-spinal injection. Our results demonstrated combination therapy increased potency to enhance the anti-inflammatory response (IL-10 and Arg-1) and decrease inflammatory markers (TNF-α and CD86) and caspase-3 compared to BM-MSC monotherapy. Histological analysis revealed that combination groups displayed better structural remodeling than BM-MSC monotherapy. In addition, Basso-Beattie-Bresnahan (BBB) scores show an increase in motor recovery in all treatment groups. Moreover, drug therapy shows faster recovery than BM-MSC monotherapy. Our results suggest that a sub-toxic dose of LPS provides neuroprotection to SCI and can promote the beneficial effect of BM-MSC in SCI. These findings suggest that a combination of LPS or LPS + G-CSF prior BM-MSC transplantation is a promising approach for optimizing BM-MSC-based strategies to treat SCI. However, because of the lack of some methodological limitations to examine the survival rate and ultimate fate of transplanted BM-MSCs followed by LPS administration in this study, further research needs to be done in this area. The presence of only one-time point for evaluating the inflammatory response (1 week) after SCI can be considered as one of the limitations of this study. We believed that the inclusion of additional time points would provide more information about the effect of our combination therapy on the microglia/macrophage polarization dynamic at the injured spinal cord.

Local Environment Induces Differential Gene Expression in Regenerating Nerves

INTRODUCTION

Approximately 80% of amputations are complicated by neuromas. Methods for neuroma management include nerve translocation into bone and implantation into skeletal muscle grafts, which have also facilitated the development of regenerative neural interfaces to enable fixation of prosthetics with motor and sensory feedback. However, molecular-level differences between nerves in these environments have not been investigated. This study aimed to elucidate the physiology of regenerating nerves in different settings by assessing gene expression.

MATERIALS AND METHODS

New Zealand white rabbits underwent transfemoral amputation with sciatic nerve transposition into the femur or tacked to skeletal muscle. At 5 wk, ribonucleic acid (RNA) sequencing of samples of distal nerve terminating in bone or muscle and nerve of the contralateral limb (control) identified differentially expressed genes (DEGs) and biochemical pathways (α = 0.05).

RESULTS

Three samples of nerve housed in bone, four of nerve tacked to muscle, and seven naïve controls were analyzed. Relative to controls, nerve housed in bone had little within-group variation and 13,028 DEGs, and nerve tacked to muscle had dramatic within-group variation and 12,811 DEGs. These samples upregulated the following pathways: lysosome, phagosome, antigen processing/presentation, and cell adhesion molecule. Relative to nerve housed in bone, nerve tacked to muscle had 12,526 DEGs, demonstrating upregulation of pathways of B-cell receptor signaling, focal adhesion, natural killer-cell mediated cytotoxicity, leukocyte transendothelial migration, and extracellular matrix-receptor interactions.

CONCLUSIONS

Nerve housed in bone has a more predictable molecular profile than does nerve tacked to muscle. Thus, the intramedullary canal may provide a more reliable setting for neuroma prevention and neural interfacing.

Stem cells from human exfoliated deciduous teeth attenuate trigeminal neuralgia in rats by inhibiting endoplasmic reticulum stress

Background

The treatment of trigeminal neuralgia remains a challenging issue. Stem cells from human exfoliated deciduous teeth (SHED) provide optimized therapy for chronic pain. This study aimed to investigate the mechanisms underlying the attenuation of trigeminal neuralgia by SHED.

Methods

Trigeminal neuralgia was induced by chronic constriction injury of the infraorbital nerve. The mechanical threshold was assessed after model establishment and local SHED transplantation. Endoplasmic reticulum (ER) morphology and Caspase12 expression in trigeminal ganglion (TG) was evaluated as well. BiP expression was observed in PC12 cells induced by tunicamycin.

Results

The local transplantation of SHED could relieve trigeminal neuralgia in rats. Further, transmission electron microscopy revealed swelling of the ER in rats with trigeminal neuralgia. Moreover, SHED inhibited the tunicamycin-induced up-regulated expression of BiP mRNA and protein in vitro. Additionally, SHED decreased the up-regulated expression of Caspase12 mRNA and protein in the TG of rats caused by trigeminal neuralgia after chronic constriction injury of the infraorbital nerve mode.

Conclusions

This findings demonstrated that SHED could alleviate pain by relieving ER stress which provide potential basic evidence for clinical pain treatment.

Stem Cell-Based Therapeutic Strategies in Diabetic Wound Healing

Impaired wound healing and especially the “all-too-common” occurrence of associated diabetic foot ulcers (DFU) are becoming an increasingly urgent and deteriorating healthcare issue, which drastically impact the quality of life and further heighten the risks of infection and amputation in patients with diabetes mellitus. Amongst the multifactorial wound healing determinants, glycemic dysregulation has been identified to be the primary casual factor of poor wound healing. Unfortunately, current therapeutic modalities merely serve as moderate symptomatic relieves but often fail to completely restore the wound site to its pre-injury state and prevent further recurrence. Stem cell-based therapeutics have been employed for its promising potential to address the root of the problem as they not only exhibit the capacity for self-renewal and differentiation towards multiple lineages, but also have been disclosed to participate in mediating variant growth factors and cytokines. Herein we review the current literatures on the therapeutic benefits of using various kinds of stem cells, including embryonic stem cells (ESCs), induced pluripotent stem cells (iPSCs), mesenchymal stem cells (MSCs), and adipose-derived stem cells (ASCs) in diabetic wound healing by searching on the PubMed® Database for publications. This study shall serve as an overview of the current body of research with particular focus on autologous ASCs and the laboratory expandable iPSCs in hope of shedding more light on this attractive therapy so as to elevate the efficacy of wound healing that is almost always compromised in diabetic patients.

Stem Cell Therapy for Neuropathic Pain: A Bibliometric and Visual Analysis

Purpose

Neuropathic pain is intractable and current treatment modalities are ineffective to cure this intractable pain, which has become a global problem. In recent years, there have been an increasing number of studies on stem cell therapy for neuropathic pain that have shown enormous potential. Using a visual analysis approach of the existing literature on stem cell therapy for neuropathic pain, we hope to understand the current research status and hot issues in this field and to provide valuable predictions for future research in this field.

Methods

We used Citespace software to visually analyze 291 articles and reviews indexed by the Web of Science Core Collection Database exploring stem cell-based treatment of neuropathic pain from 1995 to 2021. The Gunnmap online world map evaluated the number of countries and regional articles separately. Microsoft Excel 2016 was used to generate a graph of trends in annual publications.

Results

Visualization analysis revealed that the number of publications has increased yearly. The top three countries in terms of number of articles published are United States, China, and Japan. Analysis of highly co-cited articles revealed that the contents of these articles primarily involved the expression of IL-1β, IL-10, NPY, TRPA1, p-p38, p-ERK1/2, TGF-β, PKCδ, CaMKIIɑ, P2X4, P2X7 and TNF-ɑ. Keywords and citation burst analysis demonstrated that activation, regeneration, chemotherapy, and expression are likely the research hotspots and future directions of stem cell research in neuropathic pain.

Conclusion

Stem cell therapy may be a potential means of future treatment of neuropathic pain. The study of the mechanisms underlying stem cell therapy for neuropathic pain is still a focus of future research.

Effects of mesenchymal stem cell transplantation on spinal cord injury patients

Spinal cord injury (SCI) is a traumatic injury with sensory and motor deficits that more than 1 million patients worldwide suffer from disability due to it. Many pharmacological therapies help reduce SCI-related injury and protect CNS from more damage but no current therapy could improve the axonal repair. In this regard, stem cell therapy is considered a regenerative method for SCI patient treatment. The neurotrophic and immunomodulatory factor secretion, differentiation, neuroprotecting, and remyelinating properties have made mesenchymal stem cells (MSCs) principally useful in this field. There are studies on the role of MSCs in patients suffering from SCI. However, low number of SCI patients and the lack of control groups in these studies, the cell transplantation appropriate methods, including cell source, dose, route of delivery, and transplantation timing, are various in trials. This study reviews the beneficial effects of MSC transplantation in SCI clinical studies with a special focus on the MSC properties and limitations of MSC transplantation.

Research on Differentiation of Bone Marrow Stromal Cells (BMSCs) Prompted by MicroRNA-124 and Effect on Inflammatory Reaction of Spinal Cord Injury Nerve Cells

The major feature of spinal cord injury (SCI) was the damage of nervous tissue in spinal cord. The damaged spinal cord was difficult to be repaired and regenerated. MicroRNA-124 could play a role in the repairing and recovering the injured tissue. The BMSCs could participate in repairing the damage. However, the regulatory effect of MicroRNA-124 on BMSCs and the inflammatory response of SCI was still not illustrated. These spinal cord nerve cells were assigned into group of mechanical damage, BMSCs and BMSCs with miR-124 overexpression followed by analysis of proliferation of nerve cells by MTT assay, apoptotic activity, expression of miR-124, GFAP and BDNF by Real time PCR, levels of TNF-α and IL-6 by ELISA as well as MDH and SOD activity. miR-124 mimics transfection significantly promoted BMSCs proliferation and increased ALK activity and the expression of GFAP and BDNF. In conclusion, the proliferation and differentiation of BMSCs could be regulated by miR-124. The inflammation and oxidative stress could be restrained so as to prompt the proliferation and repair of SCI cells and restrain apoptosis, indicating that it might be beneficial to recover the SCI.

From acute to long-term alterations in pain processing and modulation after spinal cord injury: mechanisms related to chronification of central neuropathic pain

ABSTRACT

A severe and debilitating consequence of a spinal cord injury (SCI) is central neuropathic pain (CNP). Our aim was to investigate the processes leading to CNP emergence and chronification by analyzing causal relationship over time between spinothalamic function, pain excitability, and pain inhibition after SCI. This longitudinal follow-up study included 53 patients with acute SCI and 20 healthy controls. Spinothalamic, pain excitability, and intrasegmental and extrasegmental pain inhibition indices were repeatedly evaluated at 1.5, 3, and 6 months post-SCI. Between- and within-group analyses were conducted among those patients who eventually developed CNP and those who did not. Healthy controls were evaluated twice for repeatability analysis. Patients who developed CNP, compared with those who did not, exhibited increased thermal thresholds (P < 0.05), reduced pain adaptation (P < 0.01), and conditioned pain modulation (P < 0.05), early post-injury, and the CNP group's manifestations remained worse throughout the follow-up. By contrast, allodynia frequency was initially similar across SCI groups, but gradually increased in the subacute phase onward only among the CNP group (P < 0.001), along with CNP emergence. Early worse spinothalamic and pain inhibition preceded CNP and predicted its occurrence, and early worse pain inhibition mediated the link between spinothalamic function and CNP. Crossover associations were observed between early and late pain inhibition and excitability. Inefficient intrasegmental and extrasegmental inhibition, possibly resulting from spinothalamic deafferentation, seems to ignite CNP chronification. Pain excitability probably contributes to CNP maintenance, possibly via further exhaustion of the inhibitory control. Preemptive treatment promoting antinociception early post-SCI may mitigate or prevent CNP.

Biomaterial and Therapeutic Approaches for the Manipulation of Macrophage Phenotype in Peripheral and Central Nerve Repair

Injury to the peripheral or central nervous systems often results in extensive loss of motor and sensory function that can greatly diminish quality of life. In both cases, macrophage infiltration into the injury site plays an integral role in the host tissue inflammatory response. In particular, the temporally related transition of macrophage phenotype between the M1/M2 inflammatory/repair states is critical for successful tissue repair. In recent years, biomaterial implants have emerged as a novel approach to bridge lesion sites and provide a growth-inductive environment for regenerating axons. This has more recently seen these two areas of research increasingly intersecting in the creation of 'immune-modulatory' biomaterials. These synthetic or naturally derived materials are fabricated to drive macrophages towards a pro-repair phenotype. This review considers the macrophage-mediated inflammatory events that occur following nervous tissue injury and outlines the latest developments in biomaterial-based strategies to influence macrophage phenotype and enhance repair.

Sodium tanshinone IIA sulfonate promotes spinal cord injury repair by inhibiting blood spinal cord barrier disruption in vitro and in vivo

Spinal cord injury (SCI) leads to microvascular damage and the destruction of the blood spinal cord barrier (BSCB), which can progress into secondary injuries, such as apoptosis and necrosis of neurons and glia, culminating in permanent neurological deficits. BSCB restoration is the primary goal of SCI therapy, although very few drugs can repair damaged barrier structure and permeability. Sodium tanshinone IIA sulfonate (STS) is commonly used to treat cardiovascular disease. However, the therapeutic effects of STS on damaged BSCB during the early stage of SCI remain uncertain. Therefore, we exposed spinal cord microvascular endothelial cells to H₂ O₂ and treated them with different doses of STS. In addition to protecting the cells from H₂ O₂ -induced apoptosis, STS also reduced cellular permeability. In the in vivo model of SCI, STS reduced BSCB permeability, relieved tissue edema and hemorrhage, suppressed MMP activation and prevented the loss of tight junction and adherens junction proteins. Our findings indicate that STS treatment promotes SCI recovery, and should be investigated further as a drug candidate against traumatic SCI.

Neuroinflammation in Primary Cultures of the Rat Spinal Dorsal Horn Is Attenuated in the Presence of Adipose Tissue-Derived Medicinal Signalling Cells (AdMSCs) in a Co-cultivation Model

Neuroinflammation within the superficial dorsal horn (SDH) of the spinal cord induces inflammatory pain with symptoms of hyperalgesia and allodynia. Glial activation and production of inflammatory mediators (e.g. cytokines) is associated with modulation of nociceptive signalling. In this context, medicinal signalling cells, e.g. obtained from adipose tissue (AdMSCs), gained attention due to their capacity to modulate the inflammatory response in several diseases, e.g. spinal cord injury. We applied the recently established mixed neuroglial primary cell culture of the rat SDH to investigate effects of AdMSCs on the inflammatory response of SDH cells. Following establishment of a co-cultivation system, we performed specific bioassays for tumour necrosis factor alpha (TNFα) and interleukin (IL)-6, RT-qPCR and immunocytochemistry to detect changes in cytokine production and glial activation upon inflammatory stimulation with lipopolysaccharide (LPS). LPS-induced expression and release of pro-inflammatory cytokines (TNFα, IL-6) by SDH cells was significantly attenuated in the presence of AdMSCs. Further evidence for anti-inflammatory capacities of AdMSCs derived from a blunted LPS-induced TNFα/IL-10 expression ratio and suppressed nuclear translocation of the inflammatory transcription factor nuclear factor kappa B (NFκB) in SDH microglial cells. Expression of IL-10, transforming growth factor beta (TGF-β) and TNFα-stimulated gene-6 (TSG-6) was detected in AdMSCs, which are putative candidates for anti-inflammatory capacities of these cells. We present a novel co-cultivation system of AdMSCs with neuroglial primary cultures of the SDH to investigate immunomodulatory effects of AdMSCs at a cellular level.

Bone Marrow Mesenchymal Stem Cells (BMSCs) Promote Neuronal Cell Repair in Spinal Cord Injury by Regulating Toll-Like Receptor 4/Nuclear Factor-Kappa B Signaling Pathway

SCI (SCI) poses a challenge to nerve cell repair strategies. SCI injury can lead to the development of inflammation, which in turn can exacerbate nerve cell damage. The TLR4/NF-kappa B signaling pathway is a common inflammatory signaling pathway. Since BMSCs are involved in injury repair, whether they can promote the repair of SCI neuronal cells have not been reported. Spinal cord nerve cells were cultured in vitro and divided into mechanical injury group and BMSCs group followed by analysis of cell proliferation activity and detection of altered apoptotic activity. Changes in the concentrations of IL-6 and IL-1β were measured by ELISA and cellular mitochondrial alterations was assessed by JG-B staining along with analysis of NF-kappa B, TLR4, related neurodevelopmental factor BDNF, and NGF expression by western blot. Mechanical damage to neuronal cells resulted in decreased cell proliferation, increased apoptotic activity, decreased cellular mitochondrial activity, increased TLR4 and NF-kappa B expression, decreased BDNF and NGF expression, as well as increased secertions of IL-6 and IL-1β (P < 0.05). In contrast, co-culture with BMSCs resulted in increased proliferation and decreased apoptosis of mechanically injured neuronal cells, increased cellular mitochondrial activity, with observation of the inverse changes in other factors (P < 0.05). In conclusion, BMSCs can suppress inflammation and promote repair of injured neuronal cells by inhibiting TLR4/NF-kappa B signaling.

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.

Optimizing Olfactory Ensheathing Cell Transplantation for Spinal Cord Injury Repair

Cell transplantation constitutes an important avenue for development of new treatments for spinal cord injury (SCI). These therapies are aimed at supporting neural repair and/or replacing lost cells at the injury site. To date, various cell types have been trialed, with most studies focusing on different types of stem cells or glial cells. Here, we review commonly used cell transplantation approaches for spinal cord injury (SCI) repair, with focus on transplantation of olfactory ensheathing cells (OECs), the glial cells of the primary olfactory nervous system. OECs are promising candidates for promotion of neural repair given that they support continuous regeneration of the olfactory nerve that occurs throughout life. Further, OECs can be accessed from the nasal mucosa (olfactory neuroepithelium) at the roof of the nasal cavity and can be autologously transplanted. OEC transplantation has been trialed in many animal models of SCI, as well as in human clinical trials. While several studies have been promising, outcomes are variable and the method needs improvement to enhance aspects such as cell survival, integration, and migration. As a case study, we include the approaches used by our team (the Clem Jones Centre for Neurobiology and Stem Cell Research, Griffith University, Nathan, QLD, Australia) to address the current problems with OEC transplantation and discuss how the therapeutic potential of OEC transplantation can be improved. Our approach includes discovery research to improve our knowledge of OEC biology, identifying natural and synthetic compounds to stimulate the neural repair properties of OECs, and designing three-dimensional cell constructs to create stable and transplantable cell structures.

Trends of Chitosan Based Delivery Systems in Neuroregeneration and Functional Recovery in Spinal Cord Injuries

Spinal cord injury (SCI) is one of the most complicated nervous system injuries with challenging treatment and recovery. Regenerative biomaterials such as chitosan are being reported for their wide use in filling the cavities, deliver curative drugs, and also provide adsorption sites for transplanted stem cells. Biomaterial scaffolds utilizing chitosan have shown certain therapeutic effects on spinal cord injury repair with some limitations. Chitosan-based delivery in stem cell transplantation is another strategy that has shown decent success. Stem cells can be directed to differentiate into neurons or glia in vitro. Stem cell-based therapy, biopolymer chitosan delivery strategies, and scaffold-based therapeutic strategies have been advancing as a combinatorial approach for spinal cord injury repair. In this review, we summarize the recent progress in the treatment strategies of SCI due to the use of bioactivity of chitosan-based drug delivery systems. An emphasis on the role of chitosan in neural regeneration has also been highlighted.

Bone mesenchymal stem cells attenuate resiniferatoxin-induced neuralgia via inhibiting TRPA1-PKCδ-P38/MAPK-p-P65 pathway in mice

Treatment of neuropathic pain (NP) resulting from nerve injury is one of the most complicated and challenging in modern practice. Pharmacological treatments for NP are not fully effectively and novel approaches are requisite. Recently, transplantation of bone mesenchymal stem cells (BMSCs) has represented a promising approach for pain relief and neural repair, but how it produces beneficial effects on resiniferatoxin (RTX) induced nerve injury is still unclear. Here, we identified the BMSCs' analgesic effects and their potential mechanisms of microglial cells activation on RTX induced neuralgia. Immunostaining, biochemical studies demonstrated that microglia rather than astrocyte cells activation involved in RTX induced mechanical hyperalgesia, whereas the GFP-labeled BMSCs alleviated this mechanical hyperalgesia. Moreover, pain-related TRPA1, PKCδ, CaMKIIɑ (Calcium/calmodulin dependent protein kinase II), P38/MAPK (mitogen-activated protein kinase), p-P65 activation and expression in the spinal cord were significantly inhibited after BMSC administration. In addition, BMSCs treated RTX mice displayed a lower density of mushroom dendritic spines. Our research suggested that activation of PKCδ-CaMKIIɑ-P38/MAPK-p-P65 pathway and mushroom dendritic spines abnormal increase in the spinal cord is the main mechanism of RTX induced neuropathic pain, and transplant of BMSCs to the damaged nerve may offer promising approach for neuropathic pain.

Identification of Regeneration and Hub Genes and Pathways at Different Time Points after Spinal Cord Injury

Spinal cord injury (SCI) is a neurological injury that can cause neuronal loss around the lesion site and leads to locomotive and sensory deficits. However, the underlying molecular mechanisms remain unclear. This study aimed to verify differential gene time-course expression in SCI and provide new insights for gene-level studies. We downloaded two rat expression profiles (GSE464 and GSE45006) from the Gene Expression Omnibus database, including 1 day, 3 days, 7 days, and 14 days post-SCI, along with thoracic spinal cord data for analysis. At each time point, gene integration was performed using "batch normalization." The raw data were standardized, and differentially expressed genes at the different time points versus the control were analyzed by Gene Ontology enrichment analysis, the Kyoto Encyclopedia of Genes and Genomes pathway analysis, and gene set enrichment analysis. A protein-protein interaction network was then built and visualized. In addition, ten hub genes were identified at each time point. Among them, Gnb5, Gng8, Agt, Gnai1, and Psap lack correlation studies in SCI and deserve further investigation. Finally, we screened and analyzed genes for tissue repair, reconstruction, and regeneration and found that Anxa1, Snap25, and Spp1 were closely related to repair and regeneration after SCI. In conclusion, hub genes, signaling pathways, and regeneration genes involved in secondary SCI were identified in our study. These results may be useful for understanding SCI-related biological processes and the development of targeted intervention strategies.

Mesenchymal stem cells and extracellular vesicles for the treatment of pain: Current status and perspectives

Mesenchymal stem/stromal cells (MSCs) are multipotent progenitor cells of mesodermal origin. Due to their capacity for self-renewal and differentiation into several cell types, MSCs have been extensively studied in experimental biology and regenerative medicine in recent years. Moreover, MSCs release extracellular vesicles (EVs), which might be partly responsible for their regenerative properties. MSCs regulate several processes in target cells via paracrine signalling, such as immunomodulation, anti-apoptotic signalling, tissue remodelling, angiogenesis and anti-fibrotic signalling. The aim of this review is to provide a detailed description of the functional properties of MSCs and EVs and their potential clinical applications, with a special focus on pain treatment. The analgesic, anti-inflammatory and regenerative properties of MSCs and EVs will be discussed for several diseases, such as neuropathic pain, osteoarthritis and spinal cord injury.

Fe3O4@Polydopamine-Labeled MSCs Targeting the Spinal Cord to Treat Neuropathic Pain Under the Guidance of a Magnetic Field

Purpose

Neuropathic pain causes great distress among patients; however, its response to traditional analgesia techniques remains sub-optimal. There has been progress in stem cell research for neuropathic pain treatment; however, effective homing remains problematic. This study aimed to establish Fe₃O₄@polydopamine(PDA)-labeled mesenchymal stem cells (MSCs); moreover, we aimed to guide MSCs using a magnetic field to the spinal cord segments showing pain-related responses to allow MSC homing and gathering, in advance, in order to fully employ their repair function.

Materials and Methods

Fe₃O₄@PDA-labeled MSCs were characterized using transmission electron microscopy. We analyzed the characteristics of MSCs, as well as the nanoparticle effects on MSC activity, differentiation, and proliferation, using the CCK-8 method, flow cytometry, and staining. Using rats, we performed behavioral tests of mechanical and thermal pain hypersensitivity. Serum inflammatory markers were detected using ELISA. Finally, changes in proteins associated with spinal cord pain were detected through quantitative reverse transcription PCR, histology, and immunohistochemistry.

Results

Fe₃O₄@PDA did not affect the characteristics and viability of MSCs. The magnetic field guidance improved the therapeutic effect of Fe₃O₄@PDA-labeled MSCs as indicated by the paw withdrawal threshold. Fe₃O₄@PDA-labeled MSCs decreased spinal nerve demyelination and c-Fos expression (a pain molecule); moreover, they inhibited microglia and astrocyte activation.

Conclusion

Fe₃O₄@PDA-labeled MSCs showed better homing to the spinal cord under magnetic field guidance. Moreover, they inhibited microglial and astrocyte activation, as well as played an early and continuous role in neuropathic pain treatment.

Stem Cell Therapy for Modulating Neuroinflammation in Neuropathic Pain

Neuropathic pain (NP) is a complex, debilitating, chronic pain state, heterogeneous in nature and caused by a lesion or disease affecting the somatosensory system. Its pathogenesis involves a wide range of molecular pathways. NP treatment is extremely challenging, due to its complex underlying disease mechanisms. Current pharmacological and nonpharmacological approaches can provide long-lasting pain relief to a limited percentage of patients and lack safe and effective treatment options. Therefore, scientists are focusing on the introduction of novel treatment approaches, such as stem cell therapy. A growing number of reports have highlighted the potential of stem cells for treating NP. In this review, we briefly introduce NP, current pharmacological and nonpharmacological treatments, and preclinical studies of stem cells to treat NP. In addition, we summarize stem cell mechanisms—including neuromodulation in treating NP. Literature searches were conducted using PubMed to provide an overview of the neuroprotective effects of stem cells with particular emphasis on recent translational research regarding stem cell-based treatment of NP, highlighting its potential as a novel therapeutic approach.

Revascularization After Traumatic Spinal Cord Injury

Traumatic spinal cord injury (SCI) is a complex pathological process. The initial mechanical damage is followed by a progressive secondary injury cascade. The injury ruptures the local microvasculature and disturbs blood-spinal cord barriers, exacerbating inflammation and tissue damage. Although endogenous angiogenesis is triggered, the new vessels are insufficient and often fail to function normally. Numerous blood vessel interventions, such as proangiogenic factor administration, gene modulation, cell transplantation, biomaterial implantation, and physical stimulation, have been applied as SCI treatments. Here, we briefly describe alterations and effects of the vascular system on local microenvironments after SCI. Therapies targeted at revascularization for SCI are also summarized.

Exosomes derived from miR-26a-modified MSCs promote axonal regeneration via the PTEN/AKT/mTOR pathway following spinal cord injury

Background

Exosomes derived from the bone marrow mesenchymal stem cell (MSC) have shown great potential in spinal cord injury (SCI) treatment. This research was designed to investigate the therapeutic effects of miR-26a-modified MSC-derived exosomes (Exos-26a) following SCI.

Methods

Bioinformatics and data mining were performed to explore the role of miR-26a in SCI. Exosomes were isolated from miR-26a-modified MSC culture medium by ultracentrifugation. A series of experiments, including assessment of Basso, Beattie and Bresnahan scale, histological evaluation, motor-evoked potential recording, diffusion tensor imaging, and western blotting, were performed to determine the therapeutic influence and the underlying molecular mechanisms of Exos-26a in SCI rats.

Results

Exos-26a was shown to promote axonal regeneration. Furthermore, we found that exosomes derived from miR-26a-modified MSC could improve neurogenesis and attenuate glial scarring through PTEN/AKT/mTOR signaling cascades.

Conclusions

Exosomes derived from miR-26a-modified MSC could activate the PTEN-AKT-mTOR pathway to promote axonal regeneration and neurogenesis and attenuate glia scarring in SCI and thus present great potential for SCI treatment.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02282-0.

Human spinal GABA neurons alleviate spasticity and improve locomotion in rats with spinal cord injury

Spinal cord injury (SCI) often results in spasticity. There is currently no effective therapy for spasticity. Here, we describe a method to efficiently differentiate human pluripotent stem cells from spinal GABA neurons. After transplantation into the injured rat spinal cord, the DREADD (designer receptors exclusively activated by designer drug)-expressing spinal progenitors differentiate into GABA neurons, mitigating spasticity-like response of the rat hindlimbs and locomotion deficits in 3 months. Administering clozapine-N-oxide, which activates the grafted GABA neurons, further alleviates spasticity-like response, suggesting an integration of grafted GABA neurons into the local neural circuit. These results highlight the therapeutic potential of the spinal GABA neurons for SCI.

Knockdown of lncRNA SNHG14 alleviates LPS-induced inflammation and apoptosis of PC12 cells by regulating miR-181b-5p

Spinal cord injury (SCI) is a traumatic central nervous system disorder that leads to permanent functional loss, and unavailable treatment of this disease results in poor quality of life. However, the specific role of long non-coding RNA small nucleolar RNA host gene 14 (lncRNA SNHG14) in SCI has not been fully studied. The aim of the current study was to investigate the role of SNHG14 and its regulatory mechanism in lipopolysaccharide (LPS)-induced PC-12 cells. LPS was used to stimulate PC-12 cells to simulate inflammatory injury following SCI in vitro. Cell viability and apoptosis were respectively assessed by Cell Counting Kit-8 assay and TUNEL assay. Western blotting was performed to detect the expressions of apoptosis-related proteins. The mRNA levels of SNHG14 and microRNA (miR)-181b-5p were detected by reverse transcription-quantitative PCR. The target of SNGH14 was predicted by bioinformatics analysis and subsequently validated by a luciferase reporter assay. ELISA was then used to detect the levels of inflammatory factors. The results indicated that LPS induced inflammation, decreased cell viability and increased the apoptosis of PC-12 cells. Interference of SNHG14 alleviated this type of injury of PC-12 cells. Bioinformatics prediction and luciferase reporter assay demonstrated that miR-181b-5p could directly bind to SNHG14. Moreover, mechanistic investigations revealed that the miR-181b-5p inhibitor could reverse the inhibitory effects of SNHG14 silencing on cell viability, inflammation and apoptosis of PC-12 cells. To conclude, the present results showed that SNHG14 knockdown alleviated PC-12 cell inflammation and apoptosis induced by LPS via regulating miR-181b-5p, which might provide a novel insight into the treatment of SCI.

The Comparative Effects of Mesenchymal Stem Cell Transplantation Therapy for Spinal Cord Injury in Humans and Animal Models: A Systematic Review and Meta-Analysis

Animal models have been used in preclinical research to examine potential new treatments for spinal cord injury (SCI), including mesenchymal stem cell (MSC) transplantation. MSC transplants have been studied in early human trials. Whether the animal models represent the human studies is unclear. This systematic review and meta-analysis has examined the effects of MSC transplants in human and animal studies. Following searches of PubMed, Clinical Trials and the Cochrane Library, published papers were screened, and data were extracted and analysed. MSC transplantation was associated with significantly improved motor and sensory function in humans, and significantly increased locomotor function in animals. However, there are discrepancies between the studies of human participants and animal models, including timing of MSC transplant post-injury and source of MSCs. Additionally, difficulty in the comparison of functional outcome measures across species limits the predictive nature of the animal research. These findings have been summarised, and recommendations for further research are discussed to better enable the translation of animal models to MSC-based human clinical therapy.