Cell-Free Extracts from Human Fat Tissue with a Hyaluronan-Based Hydrogel Attenuate Inflammation in a Spinal Cord Injury Model through M2 Microglia/Microphage Polarization

Hydrogel-based therapeutic strategies for spinal cord injury repair: Recent advances and future prospects

Spinal cord injury (SCI) is a debilitating condition that can result in significant functional impairment and loss of quality of life. There is a growing interest in developing new therapies for SCI, and hydrogel-based multimodal therapeutic strategies have emerged as a promising approach. They offer several advantages for SCI repair, including biocompatibility, tunable mechanical properties, low immunogenicity, and the ability to deliver therapeutic agents. This article provides an overview of the recent advances in hydrogel-based therapy strategies for SCI repair, particularly within the past three years. We summarize the SCI hydrogels with varied characteristics such as phase-change hydrogels, self-healing hydrogel, oriented fibers hydrogel, and self-assembled microspheres hydrogel, as well as different functional hydrogels such as conductive hydrogels, stimuli-responsive hydrogels, adhesive hydrogel, antioxidant hydrogel, sustained-release hydrogel, etc. The composition, preparation, and therapeutic effect of these hydrogels are briefly discussed and comprehensively evaluated. In the end, the future development of hydrogels in SCI repair is prospected to inspire more researchers to invest in this promising field.

Research Progress on Treating Spinal Cord Injury by Modulating the Phenotype of Microglia

Spinal cord injury (SCI) is a severe central nervous system disorder with no currently available effective treatment. Microglia are immune cells in the central nervous system that play crucial roles in the SCI occurrence, development, and recovery stages. They exhibit dynamic polarization over time and can switch between classical activation (M1) and alternative activation (M2) phenotypes to respond to environmental stimuli. The M1 phenotype is involved in initiating and sustaining inflammatory responses, while the M2 phenotype exerts anti-inflammatory effects and promotes tissue repair in damaged areas. Inhibiting M1 polarization and promoting M2 polarization have become hotspots in regulating neuroinflammation and treating SCI. This article provides a comprehensive review centered on modulating microglial polarization phenotypes for SCI treatment.

Cell-free adipose tissue extracts as a novel treatment for rosacea by downregulating TRPV1

Rosacea is a chronic inflammatory skin disease that typically affects the central facial area. Its main clinical symptoms include paroxysmal flushing, telangiectasia, and non-temporary erythema. Cell-free adipose tissue extracts (ATEs) are liquid components extracted from human adipose tissue that contain large amounts of growth factors. Despite the scar-reducing, anti-aging, and wound-healing effects of ATEs, the efficacy of ATEs in rosacea remains unknown. Therefore, the anti-rosacea effects of ATEs were investigated in human cathelicidin peptide (LL-37) induced rosacea mice and capsaicin (CAP)-stimulated HaCaT keratinocytes. In vitro, ATEs significantly reduced TRPV1 expression, intracellular calcium ions influx and the release of inflammatory factors (such as KLK5, IL-6, IL-8 and TNF-α) after intervening in CAP-stimulated cells. The in vivo results revealed that ATEs alleviated rosacea symptoms, such as erythema score, erythema area, transepidermal water loss, abnormal epidermal thickness, mast cell infiltration and telangiectasia upon downregulating TRPV1 and CD31 expression. Moreover, the up-regulated TRPV1 protein expression was also recovered by ATEs administration in vivo and in vitro. Meanwhile, ATEs demonstrated good biocompatibility. In summary, ATEs could be a potential therapeutic agent for rosacea by regulating inflammation and alleviating telangiectasia.

Fisetin Promotes Functional Recovery after Spinal Cord Injury by Inhibiting Microglia/Macrophage M1 Polarization and JAK2/STAT3 Signaling Pathway

Spinal cord injury (SCI) is one of the most serious health problems, with no effective therapy. Recent studies indicate that Fisetin, a natural polyphenolic flavonoid, exhibits multiple functions, such as life-prolonging, antioxidant, antitumor, and neuroprotection. However, the restorative effects of Fisetin on SCI and the underlying mechanism are still unclear. In the present study, we found that Fisetin reduced LPS-induced apoptosis and oxidative damage in PC12 cells and reversed LPS-induced M1 polarization in BV2 cells. Additionally, Fisetin safely and effectively promoted the motor function recovery of SCI mice by attenuating neurological damage and promoting neurogenesis at the lesion. Moreover, Fisetin administration inhibited glial scar formation, modulated microglia/macrophage polarization, and reduced neuroinflammation. Network pharmacology, RNA-seq, and molecular biology revealed that Fisetin inhibited the activation of the JAK2/STAT3 signaling pathway. Notably, Colivelin TFA, an activator of JAK2/STAT3 signaling, attenuated Fis-mediated neuroinflammation inhibition and therapeutic effects on SCI mice. Collectively, Fisetin promotes functional recovery after SCI by inhibiting microglia/macrophage M1 polarization and the JAK2/STAT3 signaling pathway. Thus, Fisetin may be a promising therapeutic drug for the treatment of SCI.

Transplantation of miR-145a-5p modified M2 type microglia promotes the tissue repair of spinal cord injury in mice

BACKGROUND

The traumatic spinal cord injury (SCI) can cause immediate multi-faceted function loss or paralysis. Microglia, as one of tissue resident macrophages, has been reported to play a critical role in regulating inflammation response during SCI processes. And transplantation with M2 microglia into SCI mice promotes recovery of motor function. However, the M2 microglia can be easily re-educated and changed their phenotype due to the stimuli of tissue microenvironment. This study aimed to find a way to maintain the function of M2 microglia, which could exert an anti-inflammatory and pro-repair role, and further promote the repair of spinal cord injury.

METHODS

To establish a standard murine spinal cord clip compression model using Dumont tying forceps. Using FACS, to sort microglia from C57BL/6 mice or CX3CR1GFP mice, and further culture them in vitro with different macrophage polarized medium. Also, to isolate primary microglia using density gradient centrifugation with the neonatal mice. To transfect miR-145a-5p into M2 microglia by Lipofectamine2000, and inject miR-145a-5p modified M2 microglia into the lesion sites of spinal cord for cell transplanted therapy. To evaluate the recovery of motor function in SCI mice through behavior analysis, immunofluorescence or histochemistry staining, Western blot and qRT-PCR detection. Application of reporter assay and molecular biology experiments to reveal the mechanism of miR-145a-5p modified M2 microglia therapy on SCI mice.

RESULTS

With in vitro experiments, we found that miR-145a-5p was highly expressed in M2 microglia, and miR-145a-5p overexpression could suppress M1 while promote M2 microglia polarization. And then delivery of miR-145a-5p overexpressed M2 microglia into the injured spinal cord area significantly accelerated locomotive recovery as well as prevented glia scar formation and neuron damage in mice, which was even better than M2 microglia transplantation. Further mechanisms showed that overexpressed miR-145a-5p in microglia inhibited the inflammatory response and maintained M2 macrophage phenotype by targeting TLR4/NF-κB signaling.

CONCLUSIONS

These findings indicate that transplantation of miR-145a-5p modified M2 microglia has more therapeutic potential for SCI than M2 microglia transplantation from epigenetic perspective.

Ginsenoside Rg1 Regulates Immune Microenvironment and Neurological Recovery After Spinal Cord Injury Through MYCBP2 Delivery via Neuronal Cell-Derived Extracellular Vesicles

Spinal cord injury (SCI) is a severe neurological condition that frequently leads to significant sensory, motor, and autonomic dysfunction. This study sought to delineate the potential mechanistic underpinnings of extracellular vesicles (EVs) derived from ginsenoside Rg1-pretreated neuronal cells (Rg1-EVs) in ameliorating SCI. These results demonstrated that treatment with Rg1-EVs substantially improved motor function in spinal cord-injured mice. Rg1-EVs enhance microglial polarization toward the M2 phenotype and repressed oxidative stress, thereby altering immune responses and decreasing inflammatory cytokine secretion. Moreover, Rg1-EVs substantially diminish reactive oxygen species accumulation and enhanced neural tissue repair by regulating mitochondrial function. Proteomic profiling highlighted a significant enrichment of MYCBP2 in Rg1-EVs, and functional assays confirmed that MYCBP2 knockdown counteracted the beneficial effects of Rg1-EVs in vitro and in vivo. Mechanistically, MYCBP2 is implicated in the ubiquitination and degradation of S100A9, thereby promoting microglial M2-phenotype polarization and reducing oxidative stress. Overall, these findings substantiated the pivotal role of Rg1-EVs in neuronal protection and functional recovery following SCI through MYCBP2-mediated ubiquitination of S100A9. This research offers novel mechanistic insights into therapeutic strategies against SCI and supports the clinical potential of Rg1-EVs.

Linkage of serum ITIH4 with Th2 signature cytokine, inflammation, exacerbation risk and severity in childhood asthma

Aim: ITIH4 has anti-inflammatory properties toward eosinophilic/neutrophilic inflammation. This study aimed to explore clinical value of ITIH4 in childhood asthma.Materials & methods: Serum ITIH4 and inflammatory cytokines were determined in 120 childhood asthma patients by enzyme-linked immunosorbent assay.Results: In the entire and acute exacerbation patients, ITIH4 positively associated with IFN-γ, but negatively related to proinflammatory cytokines. ITIH4 was lowest in patients with acute exacerbation, followed by chronic persistent, and highest in clinical remission. By receiver-operating characteristic analysis, ITIH4 potentially estimated acute exacerbation asthma risk. Moreover, ITIH4 negatively related to exacerbation severity in acute exacerbation patients.Conclusion: Serum ITIH4 negatively links with Th2 cell signature cytokine, proinflammatory cytokines, exacerbation risk and severity in childhood asthma.

Injectable, Electroconductive, Free Radical Scavenging Silk Fibroin/Black Phosphorus/Glycyrrhizic Acid Nanocomposite Hydrogel for Enhancing Spinal Cord Repair

Spinal cord injury (SCI) often leads to a severe permanent disability. A poor inflammatory microenvironment and nerve electric signal conduction block are the main reasons for difficulty in spinal cord nerve regeneration. In this study, black phosphorus (BP) and glycyrrhizic acid (GA) are integrated into methacrylate-modified silk fibroin (SF) to construct a bifunctional injectable hydrogel (SF/BP/GA) with appropriate conductivity and the ability to inhibit inflammation to promote neuronal regeneration after SCI. This work discovers that the SF/BP/GA hydrogel can reduce the oxidative damage mediated by oxygen free radicals, promote the polarization of macrophages toward the anti-inflammatory M2 phenotype, reduce the expression of inflammatory factors, and improve the inflammatory microenvironment. Moreover, it induces neural stem cell (NSC) differentiation and neurosphere formation, restores signal conduction at the SCI site in vivo, and ameliorates motor function in mice with spinal cord hemisection, revealing a significant neural repair effect. An injectable, electroconductive, free-radical-scavenging hydrogel is a promising therapeutic strategy for SCI repair.

Injectable Hydrogel System Incorporating Black Phosphorus Nanosheets and Tazarotene Drug for Enhanced Vascular and Nerve Regeneration in Spinal Cord Injury Repair

Spinal cord injury (SCI) often leads to cell death, vascular disruption, axonal signal interruption, and permanent functional damage. Currently, there are no clearly effective therapeutic options available for SCI. Considering the inhospitable SCI milieu typified by ischemia, hypoxia, and restricted neural regeneration, a novel injectable hydrogel system containing conductive black phosphorus (BP) nanosheets within a lipoic acid-modified chitosan hydrogel matrix (LAMC) is explored. The incorporation of tannic acid (TA)-modified BP nanosheets (BP@TA) into the LAMC hydrogel matrix significantly improved its conductivity. Further, by embedding a bicyclodextrin-conjugated tazarotene drug, the hydrogel showcased amplified angiogenic potential in vitro. In a rat model of complete SCI, implantation of LAMC/BP@TA hydrogel markedly improved the recovery of motor function. Immunofluorescence evaluations confirmed that the composite hydrogel facilitated endogenous angiogenesis and neurogenesis at the injury site. Collectively, this work elucidates an innovative drug-incorporated hydrogel system enriched with BP, underscoring its potential to foster vascular and neural regeneration.

MG53/GMs/HA-Dex neural scaffold promotes the functional recovery of spinal cord injury by alleviating neuroinflammation

The adverse microenvironment, including neuroinflammation, hinders the recovery of spinal cord injury (SCI). Regulating microglial polarization to alleviate neuroinflammation at the injury site is an effective strategy for SCI recovery. MG53 protein exerts obvious repair ability on multiple tissues damage, but with short half-life. In this study, we composited an innovative MG53/GMs/HA-Dex neural scaffold using gelatin microspheres (GMs), hyaluronic acid (HA), and dextran (Dex) loaded with MG53 protein. This novel neural scaffold could respond to MMP-2/9 protein and stably release MG53 protein with good physicochemical properties and biocompatibility. In addition, it significantly improved the motor function of SCI mice, suppressed M1 polarization of microglia and neuroinflammation, and promoted neurogenesis and axon regeneration. Further mechanistic experiments demonstrated that MG53/GMs/HA-Dex hydrogel inhibited the JAK2/STAT3 signaling pathway. Thus, this MG53/GMs/HA-Dex neural scaffold promotes the functional recovery of SCI mice by alleviating neuroinflammation, which provides a new intervention strategy for the neural regeneration and functional repair of SCI.

Cell-free fat extract regulates oxidative stress and alleviates Th2-mediated inflammation in atopic dermatitis

Atopic dermatitis (AD) is a common inflammatory skin disease that significantly affects patients' quality of life. This study aimed to evaluate the therapeutic potential of cell-free fat extract (FE) in AD. In this study, the therapeutic effect of DNCB-induced AD mouse models was investigated. Dermatitis scores and transepidermal water loss (TEWL) were recorded to evaluate the severity of dermatitis. Histological analysis and cytokines measurement were conducted to assess the therapeutic effect. Additionally, the ability of FE to protect cells from ROS-induced damage and its ROS scavenging capacity both in vitro and in vivo were investigated. Furthermore, we performed Th1/2 cell differentiation with and without FE to elucidate the underlying therapeutic mechanism. FE reduced apoptosis and cell death of HaCat cells exposed to oxidative stress. Moreover, FE exhibited concentration-dependent antioxidant activity and scavenged ROS both in vitro and vivo. Treatment with FE alleviated AD symptoms in mice, as evidenced by improved TEWL, restored epidermis thickness, reduced mast cell infiltration, decreased DNA oxidative damage and lower inflammatory cytokines like IFN-γ, IL-4, and IL-13. FE also inhibited the differentiation of Th2 cells in vitro. Our findings indicate that FE regulates oxidative stress and mitigates Th2-mediated inflammation in atopic dermatitis by inhibiting Th2 cell differentiation, suggesting that FE has the potential as a future treatment option for AD.

Human Adipose Tissue Lysate-Based Hydrogel for Lasting Immunomodulation to Effectively Improve Spinal Cord Injury Repair

The long-term inflammatory microenvironment is one of the main obstacles to inhibit acute spinal cord injury (SCI) repair. The natural adipose tissue-derived extracellular matrix hydrogel shows effective anti-inflammatory regulation because of its unique protein components. However, the rapid degradation rate and removal of functional proteins during the decellularization process impair the lasting anti-inflammation function of the adipose tissue-derived hydrogel. To address this problem, adipose tissue lysate provides an effective way for SCI repair due to its abundance of anti-inflammatory and nerve regeneration-related proteins. Thereby, human adipose tissue lysate-based hydrogel (HATLH) with an appropriate degradation rate is developed, which aims to in situ long-term recruit and induce anti-inflammatory M2 macrophages through sustainedly released proteins. HATLH can recruit and polarize M2 macrophages while inhibiting pro-inflammatory M1 macrophages regardless of human or mouse-originated. The axonal growth of neuronal cells also can be effectively improved by HATLH and HATLH-induced M2 macrophages. In vivo experiments reveal that HATLH promotes endogenous M2 macrophages infiltration in large numbers (3.5 × 105/100 µL hydrogel) and maintains a long duration for over a month. In a mouse SCI model, HATLH significantly inhibits local inflammatory response, improves neuron and oligodendrocyte differentiation, enhances axonal growth and remyelination, as well as accelerates neurological function restoration.

Pro-vasculogenic Fibers by PDA-Mediated Surface Functionalization Using Cell-Free Fat Extract (CEFFE)

Formation of adequate vascular network within engineered three-dimensional (3D) tissue substitutes postimplantation remains a major challenge for the success of biomaterials-based tissue regeneration. To better mimic the in vivo angiogenic and vasculogenic processes, nowadays increasing attention is given to the strategy of functionalizing biomaterial scaffolds with multiple bioactive agents. Aimed at engineering electrospun biomimicking fibers with pro-vasculogenic capability, this study was proposed to functionalize electrospun fibers of polycaprolactone/gelatin (PCL/GT) by cell-free fat extract (CEFFE or FE), a newly emerging natural "cocktail" of cytokines and growth factors extracted from human adipose tissue. This was achieved by having the electrospun PCL/GT fiber surface coated with polydopamine (PDA) followed by PDA-mediated immobilization of FE to generate the pro-vasculogenic fibers of FE-PDA@PCL/GT. It was found that the PDA-coated fibrous mat of PCL/GT exhibited a high FE-loading efficiency (∼90%) and enabled the FE to be released in a highly sustained manner. The engineered FE-PDA@PCL/GT fibers possess improved cytocompatibility, as evidenced by the enhanced cellular proliferation, migration, and RNA and protein expressions (e.g., CD31, vWF, VE-cadherin) in the human umbilical vein endothelial cells (huvECs) used. Most importantly, the FE-PDA@PCL/GT fibrous scaffolds were found to enormously stimulate tube formation in vitro, microvascular development in the in ovo chick chorioallantoic membrane (CAM) assay, and vascularization of 3D construct in a rat subcutaneous embedding model. This study highlights the potential of currently engineered pro-vasculogenic fibers as a versatile platform for engineering vascularized biomaterial constructs for functional tissue regeneration.

Engineered Macrophage Membrane-Coated Nanoparticles with Enhanced CCR2 Expression Promote Spinal Cord Injury Repair by Suppressing Neuroinflammation and Neuronal death

Spinal cord injury (SCI) is a severe neurological disorder characterized by significant disability and limited treatment options. Mitigating the secondary inflammatory response following the initial injury is the primary focus of current research in the treatment of SCI. CCL2 (C─C motif chemokine ligand 2) serves as the primary regulator responsible for inflammatory chemotaxis of the majority of peripheral immune cells, blocking the CCL2-CCR2 (C─C chemokine receptor type 2) axis has shown considerable therapeutic potential for inflammatory diseases, including SCI. In this study, it presents a multifunctional biomimetic nanoplatform (CCR2-MM@PLGA/Cur) specifically designed to target the CCL2-CCR2 axis, which consisted of an engineered macrophage membrane (MM) coating with enhanced CCR2 expression and a PLGA (poly (lactic-co-glycolic acid)) nanoparticle that encapsulated therapeutic drugs. CCR2 overexpression on MM not only enhanced drug-targeted delivery to the injury site, but also attenuated macrophage infiltration, microglia pro-inflammatory polarization, and neuronal apoptosis by trapping CCL2. Consequently, it facilitated neural regeneration and motor function recovery in SCI mice, enabling a comprehensive treatment approach for SCI. The feasibility and efficacy of this platform are confirmed through a series of in vitro and in vivo assays, offering new insights and potential avenues for further exploration in the treatment of SCI.

Administration with curcumin alleviates spinal cord ischemia-reperfusion injury by regulating anti-oxidative stress and microglia activation-mediated neuroinflammation via Nrf2/NF-κB axis

Spinal cord ischemia-reperfusion injury (SCII) ranks as the common complication after aortic surgery, usually leading to devastating post-operative paraplegia. Microglia over-activation and neuronal cell loss are key pathological features of SCII. Curcumin is involved in several I/R injuries. However, its underlying mechanism in SCII remains elusive. Here, curcumin attenuated oxygen and glucose deprivation/reoxygenation (OGD/R)-induced oxidative injury in PC12 neuronal cells by increasing cell viability, inhibiting cell apoptosis, lactate dehydrogenase, malondialdehyde levels, but elevating anti-oxidative superoxide dismutase and glutathione peroxidase levels. Furthermore, curcumin restrained OGD/R-evoked microglia M1 activation by decreasing microglia M1 polarization marker IBA-1 and iNOS transcripts. Moreover, the increased inflammatory cytokine levels of TNF-α and IL-6 in microglia under OGD/R conditions were suppressed after curcumin treatment. Importantly, neuronal cells incubated with a conditioned medium from OGD/R-treated microglia exhibited lower cell viability and higher apoptotic ratio, which were overturned when microglia were treated with curcumin. Intriguingly, curcumin could inhibit the activation of the NF-κB pathway by Nrf2 enhancement in OGD/R-treated PC12 cells and microglia. Notably, targeting Nrf2 signaling reversed the protective efficacy of curcumin against OGD/R-evoked oxidative insult in neuronal, microglia M1 activation, inflammatory response, and microglial activation-evoked neuronal death. In vivo, curcumin improved histopathologic injury and neurologic motor function in SCII rats and attenuated oxidative stress, microglia activation and neuroinflammation in spinal cord tissues, and activation of the Nrf2/NF-κB pathway. Thus, curcumin may alleviate SCII by mitigating I/R-evoked oxidative injury in neuron and microglia activation-induced neuroinflammation and neuron death through Nrf2/NF-κB signaling, supporting a promising therapeutic agent for SCII.

Emerging functions and therapeutic targets of IL-38 in central nervous system diseases

Interleukin (IL)-38 is a newly discovered cytokine of the IL-1 family, which binds various receptors (i.e., IL-36R, IL-1 receptor accessory protein-like 1, and IL-1R1) in the central nervous system (CNS). The hallmark physiological function of IL-38 is competitive binding to IL-36R, as does the IL-36R antagonist. Emerging research has shown that IL-38 is abnormally expressed in the serum and brain tissue of patients with ischemic stroke (IS) and autism spectrum disorder (ASD), suggesting that IL-38 may play an important role in neurological diseases. Important advances include that IL-38 alleviates neuromyelitis optica disorder (NMOD) by inhibiting Th17 expression, improves IS by protecting against atherosclerosis via regulating immune cells and inflammation, and reduces IL-1β and CXCL8 release through inhibiting human microglial activity post-ASD. In contrast, IL-38 mRNA is markedly increased and is mainly expressed in phagocytes in spinal cord injury (SCI). IL-38 ablation attenuated SCI by reducing immune cell infiltration. However, the effect and underlying mechanism of IL-38 in CNS diseases remain inadequately characterized. In this review, we summarize the biological characteristics, pathophysiological role, and potential mechanisms of IL-38 in CNS diseases (e.g., NMOD, Alzheimer's disease, ASD, IS, TBI, and SCI), aiming to explore the therapeutic potential of IL-38 in the prevention and treatment of CNS diseases.

PMN-incorporated multifunctional chitosan hydrogel for postoperative synergistic photothermal melanoma therapy and skin regeneration

Melanoma excision surgery is usually accompanied by neoplasm residual, tissue defect, and bacterial infection, resulting in high tumor recurrence and chronic wound. Nanocomposite hydrogels can satisfy the twin requirements of avoiding tumor recurrence and skin wound healing following skin melanoma surgery due to their photothermal anti-tumor and anti-bacterial activities. In this study, carboxymethyl chitosan, oxidized fucoidan and polyphenol-metal nanoparticle (PMN) of tannic acid capped gold nanoparticles were used to fabricate multifunctional nanocomposite hydrogels through Schiff base reaction. The prepared hydrogel demonstrated outstanding photothermal effect, and the controlled high temperature will rapidly kill melanoma cells as well as bacteria within 10 min. Good injectability, self-healing and adhesion combined with high reactive oxygen species (ROS) scavenging capacity, hemostasis and biocompatibility made this hydrogel platform perfect for the postoperative treatment of melanoma and promoting wound healing. With the assistance of NIR irradiance, hydrogel can inhibit tumor tissue proliferation and promote tumor cell apoptosis, thereby helping to prevent melanoma recurrence after surgical removal of tumors. Simultaneously, the irradiance heat and polyphenol component kill bacteria on the wound surface, eliminate ROS, inhibit inflammatory responses, and promote angiogenesis, collagen deposition, and skin regeneration, all of which help to speed up wound healing.

Application of Injectable Hydrogels as Delivery Systems in Spinal Cord Injury

Spinal cord injury (SCI) is a severe neurological injury caused by traffic accidents, trauma, or falls, which leads to significant loss of sensory, motor, and autonomous functions and seriously affects the patient's life quality. Although considerable progress has been made in mitigating secondary injury and promoting the regeneration/repair of SCI, the therapeutic effects need to be improved due to drug availability. Given their good biocompatibility, biodegradability, and low immunogenicity, injectable hydrogels can be used as delivery systems to achieve controlled release of drugs and other substances (cells and proteins, etc.), offering new hope for SCI repair. In this article, we summarized the types of injectable hydrogels, analyzed their application as delivery systems in SCI, and further discussed the mechanisms of hydrogels in the treatment of SCI, such as anti-inflammatory, antioxidant, anti-apoptosis, and pro-neurogenesis. Moreover, we highlighted the potential benefits of hydrogels in the treatment of SCI in combination with therapies, including the recent advances and achievements of these promising tools. Our review may offer new strategies for the development of SCI treatments based on injectable hydrogels as delivery systems.

Robust and Multifunctional Nanoparticles Assembled from Natural Polyphenols and Metformin for Efficient Spinal Cord Regeneration

The treatment of spinal cord injury (SCI) remains unsatisfactory owing to the complex pathophysiological microenvironments at the injury site and the limited regenerative potential of the central nervous system. Metformin has been proven in clinical and animal experiments to repair damaged structures and functions by promoting endogenous neurogenesis. However, in the early stage of acute SCI, the adverse pathophysiological microenvironment of the injury sites, such as reactive oxygen species and inflammatory factor storm, can prevent the activation of endogenous neural stem cells (NSCs) and the differentiation of NSCs into neurons, decreasing the whole repair effect. To address those issues, a series of robust and multifunctional natural polyphenol-metformin nanoparticles (polyphenol-Met NPs) were fabricated with pH-responsiveness and excellent antioxidative capacities. The resulting NPs possessed several favorable advantages: First, the NPs were composed of active ingredients with different biological properties, without the need for carriers; second, the pH-responsiveness feature could allow targeted drug delivery at the injured site; more importantly, NPs enabled drugs with different performances to exhibit strong synergistic effects. The results demonstrated that the improved microenvironment by natural polyphenols boosted the differentiation of activated NSCs into neurons and oligodendrocytes, which could efficiently repair the injured nerve structures and enhance the functional recovery of the SCI rats. This work highlighted the design and fabrication of robust and multifunctional NPs for SCI treatment via efficient microenvironmental regulation and targeted NSCs activation.

Recent progress and challenges in the treatment of spinal cord injury

Spinal cord injury (SCI) disrupts the structural and functional connectivity between the higher center and the spinal cord, resulting in severe motor, sensory, and autonomic dysfunction with a variety of complications. The pathophysiology of SCI is complicated and multifaceted, and thus individual treatments acting on a specific aspect or process are inadequate to elicit neuronal regeneration and functional recovery after SCI. Combinatory strategies targeting multiple aspects of SCI pathology have achieved greater beneficial effects than individual therapy alone. Although many problems and challenges remain, the encouraging outcomes that have been achieved in preclinical models offer a promising foothold for the development of novel clinical strategies to treat SCI. In this review, we characterize the mechanisms underlying axon regeneration of adult neurons and summarize recent advances in facilitating functional recovery following SCI at both the acute and chronic stages. In addition, we analyze the current status, remaining problems, and realistic challenges towards clinical translation. Finally, we consider the future of SCI treatment and provide insights into how to narrow the translational gap that currently exists between preclinical studies and clinical practice. Going forward, clinical trials should emphasize multidisciplinary conversation and cooperation to identify optimal combinatorial approaches to maximize therapeutic benefit in humans with SCI.

Hydrogel-based treatments for spinal cord injuries

Spinal cord injury (SCI) is characterized by damage resulting in dysfunction of the spinal cord. Hydrogels are common biomaterials that play an important role in the treatment of SCI. Hydrogels are biocompatible, and some have electrical conductivity that are compatible with spinal cord tissues. Hydrogels have a high drug-carrying capacity, allowing them to be used for SCI treatment through the loading of various types of active substances, drugs, or cells. We first discuss the basic anatomy and physiology of the human spinal cord and briefly discuss SCI and its treatment. Then, we describe different treatment strategies for SCI. We further discuss the crosslinking methods and classification of hydrogels and detail hydrogel biomaterials prepared using different processing methods for the treatment of SCI. Finally, we analyze the future applications and limitations of hydrogels for SCI. The development of biomaterials opens up new possibilities and options for the treatment of SCI. Thus, our findings will inspire scholars in related fields and promote the development of hydrogel therapy for SCI.

Thermos-responsive hydrogel system encapsulated engineered exosomes attenuate inflammation and oxidative damage in acute spinal cord injury

Introduction: Spinal cord injury (SCI) is a serious and disabling condition, and the effectiveness of conventional treatment is limited, such as supportive treatment and emergency surgery. Exosomes derived from umbilical cord mesenchymal stem cells (UCMSC-Exos) have potential therapeutic effects on SCI but are limited by delivery efficiency. Our study aimed to further investigate the therapeutic effects of miR-138-modified UCMSC-exosomes (Exos-138) following SCI. Methods: We developed an injectable triblock polymer of polyglycolic acid copolymer and polyethylene glycol (PLGA-PEG-PLGA)-loaded temperature-sensitive hydrogel of miR-138-modified stem cell exosomes and characterised its biocompatibility in vitro. In Sprague-Dawley rats with SCI, the hydrogel was injected into the injury site, behavioural scores were measured, and pathological analysis was conducted postoperatively to assess neurological recovery. Results: In vitro, our data demonstrated that miR-138-5p-modified UCMSC-Exos can reduce inflammation levels in BV-2 cells through the NLRP3-caspase1 signalling pathway and reduce neuronal apoptosis by downregulating intracellular reactive oxygen species levels through the Nrf2-keap1 signalling cascade. The results of in vivo experiments showed that the P-Exos-138 hydrogel promoted neurological recovery in rats with SCI. Discussion: Our study explored a novel exosome delivery system that can be a potential therapeutic strategy for SCI. Our study, currently, has theoretical value; however, it can serve as a basis for further investigations on the treatment approaches at various stages of SCI development in inflammation-dependent injury of the central nervous system.

Recent advance in bioactive hydrogels for repairing spinal cord injury: material design, biofunctional regulation, and applications

Functional hydrogels show potential application in repairing spinal cord injury (SCI) due to their unique chemical, physical, and biological properties and functions. In this comprehensive review, we present recent advance in the material design, functional regulation, and SCI repair applications of bioactive hydrogels. Different from previously released reviews on hydrogels and three-dimensional scaffolds for the SCI repair, this work focuses on the strategies for material design and biologically functional regulation of hydrogels, specifically aiming to show how these significant efforts can promoting the repairing performance of SCI. We demonstrate various methods and techniques for the fabrication of bioactive hydrogels with the biological components such as DNA, proteins, peptides, biomass polysaccharides, and biopolymers to obtain unique biological properties of hydrogels, including the cell biocompatibility, self-healing, anti-bacterial activity, injectability, bio-adhesion, bio-degradation, and other multi-functions for repairing SCI. The functional regulation of bioactive hydrogels with drugs/growth factors, polymers, nanoparticles, one-dimensional materials, and two-dimensional materials for highly effective treating SCI are introduced and discussed in detail. This work shows new viewpoints and ideas on the design and synthesis of bioactive hydrogels with the state-of-the-art knowledges of materials science and nanotechnology, and will bridge the connection of materials science and biomedicine, and further inspire clinical potential of bioactive hydrogels in biomedical fields.

Hydrogel Drug Delivery Systems for Bone Regeneration

With the in-depth understanding of bone regeneration mechanisms and the development of bone tissue engineering, a variety of scaffold carrier materials with desirable physicochemical properties and biological functions have recently emerged in the field of bone regeneration. Hydrogels are being increasingly used in the field of bone regeneration and tissue engineering because of their biocompatibility, unique swelling properties, and relative ease of fabrication. Hydrogel drug delivery systems comprise cells, cytokines, an extracellular matrix, and small molecule nucleotides, which have different properties depending on their chemical or physical cross-linking. Additionally, hydrogels can be designed for different types of drug delivery for specific applications. In this paper, we summarize recent research in the field of bone regeneration using hydrogels as delivery carriers, detail the application of hydrogels in bone defect diseases and their mechanisms, and discuss future research directions of hydrogel drug delivery systems in bone tissue engineering.

Research progress of hydrogels as delivery systems and scaffolds in the treatment of secondary spinal cord injury

Secondary spinal cord injury (SSCI) is the second stage of spinal cord injury (SCI) and involves vasculature derangement, immune response, inflammatory response, and glial scar formation. Bioactive additives, such as drugs and cells, have been widely used to inhibit the progression of secondary spinal cord injury. However, the delivery and long-term retention of these additives remain a problem to be solved. In recent years, hydrogels have attracted much attention as a popular delivery system for loading cells and drugs for secondary spinal cord injury therapy. After implantation into the site of spinal cord injury, hydrogels can deliver bioactive additives in situ and induce the unidirectional growth of nerve cells as scaffolds. In addition, physical and chemical methods can endow hydrogels with new functions. In this review, we summarize the current state of various hydrogel delivery systems for secondary spinal cord injury treatment. Moreover, functional modifications of these hydrogels for better therapeutic effects are also discussed to provide a comprehensive insight into the application of hydrogels in the treatment of secondary spinal cord injury.

Engineered exosomes enriched in netrin-1 modRNA promote axonal growth in spinal cord injury by attenuating inflammation and pyroptosis

BACKGROUND

Spinal cord injury (SCI) brings a heavy burden to individuals and society, and there is no effective treatment at present. Exosomes (EX) are cell secreted vesicles containing molecules such as nucleic acids and proteins, which hold promise for the treatment of SCI. Netrin-1 is an axon guidance factor that regulates neuronal growth. We investigated the effects of engineered EX enriched in netrin-1 chemically synthetic modified message RNA (modRNA) in treating SCI in an attempt to find a novel therapeutic approach for SCI.

METHODS

Netrin-1 modRNA was transfected into bone marrow mesenchymal stem cells to obtain EX enriched with netrin-1 (EX-netrin1). We built an inflammatory model in vitro with lipopolysaccharide (LPS) in vitro to study the therapeutic effect of EX-netrin1 on SCI. For experiments in vitro, ELISA, CCK-8 assay, immunofluorescence staining, lactate dehydrogenase release experiments test, real-time quantitative polymerase chain reaction, and western blot were conducted. At the same time, we constructed a rat model of SCI. MRI, hematoxylin-eosin and Nissl staining were used to assess the extent of SCI in rats.

RESULTS

In vitro experiments showed that EX had no effect on the viability of oligodendrocytes and PC12 cells. EX-netrin1 could attenuate LPS-induced inflammation and pyroptosis and accelerate axonal/dentritic growth in PC12 cells/oligodendrocytes. In addition, netrin-1 could activate the PI3K/AKT/mTOR signalling pathway upon binding to its receptor unc5b. When Unc5b and PI3K were inhibited, the effect of EX-netrin1 was weakened, which could be reversed by PI3K or mTOR activator. Our in vivo experiments indicated that EX-netrin1 could promote recovery in rats with SCI.

CONCLUSION

We found that EX-netrin1 regulated inflammation, pyroptosis and axon growth in SCI via the Unc5b/PI3K/AKT/mTOR pathway, which provides a new strategy for the treatment of SCI.

Sulforaphane Delays Intervertebral Disc Degeneration by Alleviating Endoplasmic Reticulum Stress in Nucleus Pulposus Cells via Activating Nrf-2/HO-1

Intervertebral disc degeneration (IVDD) is one of the main causes of low back pain, which brings heavy burdens to individuals and society. The mechanism of IVDD is complex and diverse. One of the important reasons is that the abnormal accumulation of reactive oxygen species (ROS) in nucleus pulposus cells (NPCs) leads to endoplasmic reticulum stress (ERS), which causes increased apoptosis of NPCs. Nuclear factor E2-related factor 2 (Nrf-2) and its downstream antioxidant proteins are key molecular switches for sensing oxidative stress and regulating antioxidant responses in cells. Sulforaphane (SFN), a natural compound derived from Brassicaceae plants, is a Nrf-2 agonist that displays potent antioxidant potential in vitro and in vivo. Here, we used advanced glycation end products (AGEs) to construct an in vitro degeneration model of NPCs, and we found that AGEs elevated ROS level in NPCs and caused severe ERS and apoptosis. While SFN can promote the entry of Nrf-2 into the nucleus and increase the expression level of heme oxygenase 1 (HO-1) in vitro, thus clearing the accumulated ROS in cells and alleviating ERS and cell apoptosis. Moreover, the protection of SFN on NPCs was greatly attenuated after HO-1 was inhibited. We also used AGEs to construct a rat IVDD model. Consistent with the in vitro experiments, SFN could attenuate ERS in NPCs in vivo and delay disc degeneration in rats. This study found that SFN can be used as a new and promising agent for the treatment of IVDD.

Biomaterials delivery strategies to repair spinal cord injury by modulating macrophage phenotypes

Spinal cord injury (SCI) causes tremendous harm to a patient's physical, mental, and financial health. Moreover, recovery of SCI is affected by many factors, inflammation is one of the most important as it engulfs necrotic tissue and cells during the early stages of injury. However, excessive inflammation is not conducive to damage repair. Macrophages are classified into either blood-derived macrophages or resident microglia based on their origin, their effects on SCI being two-sided. Microglia first activate and recruit blood-derived macrophages at the site of injury-blood-borne macrophages being divided into pro-inflammatory M1 phenotypes and anti-inflammatory M2 phenotypes. Among them, M1 macrophages secrete inflammatory factors such as interleukin-β (IL-β), tumor necrosis factor-α (TNF-α), IL-6, and interferon-γ (IFN-γ) at the injury site, which aggravates SCIs. M2 macrophages secrete IL-4, IL-10, IL-13, and neurotrophic factors to inhibit the inflammatory response and inhibit neuronal apoptosis. Consequently, modulating phenotypic differentiation of macrophages appears to be a meaningful therapeutic target for the treatment of SCI. Biomaterials are widely used in regenerative medicine and tissue engineering due to their targeting and bio-histocompatibility. In this review, we describe the effects of biomaterials applied to modulate macrophage phenotypes on SCI recovery and provide an outlook.

Cannabinoid receptor-2 attenuates neuroinflammation by promoting autophagy-mediated degradation of the NLRP3 inflammasome post spinal cord injury

Background

Neuroinflammation following spinal cord injury (SCI) results in prolonged neurological damage and locomotor dysfunction. Polarization of microglia is vital to regulation of neuroinflammation, although the underlying mechanisms have not yet been elucidated. Endocannabinoid receptor subtype 2 (CB2R) is reported to ameliorate neurodegeneration via immunomodulation activities. However, the underlying machinery in the context of SCI remains unclear.

Methods

A lipopolysaccharide-induced microglia inflammation model and a mouse model of SCI were employed to investigate the regulatory role of CB2R in the polarization of microglia in response to excess neuroinflammation. Markers of inflammation and autophagy were measured by Western blot analysis, immunofluorescence, flow cytometry, and enzyme-linked immunosorbent assays. Histological staining with hematoxylin and eosin, Nissl, and Luxol^® fast blue was conducted using commercial kits. The locomotor function of the hindlimbs of the experimental mice was evaluated with the Basso Mouse Scale, Louisville Swim Scale, and footprint assay.

Results

The results showed that CB2R promoted M2 differentiation, increased interleukin (IL)-10 expression, and inhibited M1 differentiation with decreased expression of IL-1β and IL-6. CB2R activation also increased ubiquitination of the NLRP3 inflammasome and interacted with the autophagy-related proteins p62 and microtubule-associated proteins 1B light chain 3. Treatment with the CB2R activator JWH-133 reduced loss of myelin, apoptosis of neurons, and glial scarring, leading to improved functional recovery of the hindlimbs, while the CB2R antagonist AM630 produced opposite results.

Conclusion

Taken together, these results suggested that CB2R activation attenuated neuroinflammation targeting microglial polarization by promoting NLRP3 clearance, thereby facilitating functional recovery post-SCI.

Forsythoside B attenuates neuro-inflammation and neuronal apoptosis by inhibition of NF-κB and p38-MAPK signaling pathways through activating Nrf2 post spinal cord injury

BACKGROUND

Spinal cord injury (SCI) is a ruinous neurological pathology that results in locomotor and sensory impairment. Neuro-inflammation and secondary neuronal apoptosis contribute to SCI, with anti-inflammatory therapies the focus of many SCI studies. Forsythoside B (FTS•B), a phenylethanoid glycoside extracted from the leaves of Lamiophlomis rotata Kudo, has been shown previously to have anti-inflammatory properties. Nevertheless, the therapeutic effect of FTS•B on neuro-inflammation after SCI is unknown.

METHODS

Neuro-inflammation was assessed by western blotting (WB), immunofluorescence (IF) staining, and enzyme-linked immunosorbent assay (ELISA) both in vitro and in vivo. Secondary neuronal apoptosis was simulated in a microglia-neuron co-culture model with the degree of apoptosis measured by WB, IF, and TUNEL staining. In vivo, FTS•B (10 mg/kg, 40 mg/kg) were intraperitoneally injected into SCI mice. Morphological changes following SCI were evaluated by Nissl, Hematoxylin-eosin, and Luxol Fast Blue staining. Basso Mouse Scale scores were used to evaluate locomotor function recovery.

RESULTS

FTS•B markedly decreased the levels of iNOS, COX-2 and signature mediators of inflammation. Phosphorylated p38 and nuclear factor-kappa B (NF-κB) were markedly decreased by FTS•B. Additionally, FTS•B-induced inhibition of NF-κB and p38-MAPK signaling pathways was reversed by Nrf2 downregulation. Administration of FTS•B also significantly reduced apoptosis-related protein levels indicating that FTS•B ameliorated secondary neuronal apoptosis. FTS•B administration inhibited glial scar formation, decreased neuronal death, tissue deficiency, alleviated demyelination, and promoted locomotor recovery.

CONCLUSION

FTS•B effectively attenuates neuro-inflammation and secondary neuronal apoptosis by inhibition of NF-κB and p38-MAPK signaling pathways through activating Nrf2 after SCI. This study demonstrates FTS•B to be a potential therapeutic for SCI.