Reverse Adverse Immune Microenvironments by Biomaterials Enhance the Repair of Spinal Cord Injury

The Role of Inflammatory Cascade and Reactive Astrogliosis in Glial Scar Formation Post-spinal Cord Injury

Reactive astrogliosis and inflammation are pathologic hallmarks of spinal cord injury. After injury, dysfunction of glial cells (astrocytes) results in glial scar formation, which limits neuronal regeneration. The blood-spinal cord barrier maintains the structural and functional integrity of the spinal cord and does not allow blood vessel components to leak into the spinal cord microenvironment. After the injury, disruption in the spinal cord barrier causes an imbalance of the immunological microenvironment. This triggers the process of neuroinflammation, facilitated by the actions of microglia, neutrophils, glial cells, and cytokines production. Recent work has revealed two phenotypes of astrocytes, A1 and A2, where A2 has a protective type, and A1 releases neurotoxins, further promoting glial scar formation. Here, we first describe the current understanding of the spinal cord microenvironment, both pre-, and post-injury, and the role of different glial cells in the context of spinal cord injury, which forms the essential update on the cellular and molecular events following injury. We aim to explore in-depth signaling pathways and molecular mediators that trigger astrocyte activation and glial scar formation. This review will discuss the activated signaling pathways in astrocytes and other glial cells and their collaborative role in the development of gliosis through inflammatory responses.

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.

Spatial multi-omics analysis of the microenvironment in traumatic spinal cord injury: a narrative review

Traumatic spinal cord injury (tSCI) is a severe injury to the central nervous system that is categorized into primary and secondary injuries. Among them, the local microenvironmental imbalance in the spinal cord caused by secondary spinal cord injury includes accumulation of cytokines and chemokines, reduced angiogenesis, dysregulation of cellular energy metabolism, and dysfunction of immune cells at the site of injury, which severely impedes neurological recovery from spinal cord injury (SCI). In recent years, single-cell techniques have revealed the heterogeneity of multiple immune cells at the genomic, transcriptomic, proteomic, and metabolomic levels after tSCI, further deepening our understanding of the mechanisms underlying tSCI. However, spatial information about the tSCI microenvironment, such as cell location and cell-cell interactions, is lost in these approaches. The application of spatial multi-omics technology can solve this problem by combining the data obtained from immunohistochemistry and multiparametric analysis to reveal the changes in the microenvironment at different times of secondary injury after SCI. In this review, we systematically review the progress of spatial multi-omics techniques in the study of the microenvironment after SCI, including changes in the immune microenvironment and discuss potential future therapeutic strategies.

Biomaterials targeting the microenvironment for spinal cord injury repair: progression and perspectives

Spinal cord injury (SCI) disrupts nerve pathways and affects sensory, motor, and autonomic function. There is currently no effective treatment for SCI. SCI occurs within three temporal periods: acute, subacute, and chronic. In each period there are different alterations in the cells, inflammatory factors, and signaling pathways within the spinal cord. Many biomaterials have been investigated in the treatment of SCI, including hydrogels and fiber scaffolds, and some progress has been made in the treatment of SCI using multiple materials. However, there are limitations when using individual biomaterials in SCI treatment, and these limitations can be significantly improved by combining treatments with stem cells. In order to better understand SCI and to investigate new strategies for its treatment, several combination therapies that include materials combined with cells, drugs, cytokines, etc. are summarized in the current review.

Advances in Conductive Hydrogel for Spinal Cord Injury Repair and Regeneration

Spinal cord injury (SCI) treatment represents a major challenge in clinical practice. In recent years, the rapid development of neural tissue engineering technology has provided a new therapeutic approach for spinal cord injury repair. Implanting functionalized electroconductive hydrogels (ECH) in the injury area has been shown to promote axonal regeneration and facilitate the generation of neuronal circuits by reshaping the microenvironment of SCI. ECH not only facilitate intercellular electrical signaling but, when combined with electrical stimulation, enable the transmission of electrical signals to electroactive tissue and activate bioelectric signaling pathways, thereby promoting neural tissue repair. Therefore, the implantation of ECH into damaged tissues can effectively restore physiological functions related to electrical conduction. This article focuses on the dynamic pathophysiological changes in the SCI microenvironment and discusses the mechanisms of electrical stimulation/signal in the process of SCI repair. By examining electrical activity during nerve repair, we provide insights into the mechanisms behind electrical stimulation and signaling during SCI repair. We classify conductive biomaterials, and offer an overview of the current applications and research progress of conductive hydrogels in spinal cord repair and regeneration, aiming to provide a reference for future explorations and developments in spinal cord regeneration strategies.

Role of the Osteocyte in Musculoskeletal Disease

PURPOSE OF THE REVIEW

The purpose of this review is to summarize the role of the osteocyte in muscle atrophy in cancer patients, sarcopenia, spinal cord injury, Duchenne's muscular dystrophy, and other conditions associated with muscle deterioration.

RECENT FINDINGS

One type of bone cell, the osteocyte, appears to play a major role in muscle and bone crosstalk, whether physiological or pathological. Osteocytes are cells living within the bone-mineralized matrix. These cells are connected to each other by means of dendrites to create an intricately connected network. The osteocyte network has been shown to respond to different types of stimuli such as mechanical unloading, immobilization, aging, and cancer by producing osteocytes-derived factors. It is now becoming clear that some of these factors including sclerostin, RANKL, TGF-β, and TNF-α have detrimental effects on skeletal muscle. Bone and muscle not only communicate mechanically but also biochemically. Osteocyte-derived factors appear to contribute to the pathogenesis of muscle disease and could be used as a cellular target for new therapeutic approaches.

Mesenchymal stem cells in the treatment of spinal cord injury: Mechanisms, current advances and future challenges

Spinal cord injury (SCI) has considerable impact on patient physical, mental, and financial health. Secondary SCI is associated with inflammation, vascular destruction, and subsequent permanent damage to the nervous system. Mesenchymal stem cells (MSCs) have anti-inflammatory properties, promoting vascular regeneration and the release neuro-nutrients, and are a promising strategy for the treatment of SCI. Preclinical studies have shown that MSCs promote sensory and motor function recovery in rats. In clinical trials, MSCs have been reported to improve the American Spinal Injury Association (ASIA) sensory and motor scores. However, the effectiveness of MSCs in treating patients with SCI remains controversial. MSCs promote tumorigenesis and ensuring the survival of MSCs in the hostile environment of SCI is challenging. In this article we examine the evidence on the pathophysiological changes occurring after SCI. We then review the underlying mechanisms of MSCs in the treatment of SCI and summarize the potential application of MSCs in clinical practice. Finally, we highlight the challenges surrounding the use of MSCs in the treatment of SCI and discuss future applications.

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.

Pathophysiology and Therapeutic Approaches for Spinal Cord Injury

Spinal cord injury (SCI) is a disabling condition that disrupts motor, sensory, and autonomic functions. Despite extensive research in the last decades, SCI continues to be a global health priority affecting thousands of individuals every year. The lack of effective therapeutic strategies for patients with SCI reflects its complex pathophysiology that leads to the point of no return in its function repair and regeneration capacity. Recently, however, several studies started to uncover the intricate network of mechanisms involved in SCI leading to the development of new therapeutic approaches. In this work, we present a detailed description of the physiology and anatomy of the spinal cord and the pathophysiology of SCI. Additionally, we provide an overview of different molecular strategies that demonstrate promising potential in the modulation of the secondary injury events that promote neuroprotection or neuroregeneration. We also briefly discuss other emerging therapies, including cell-based therapies, biomaterials, and epidural electric stimulation. A successful therapy might target different pathologic events to control the progression of secondary damage of SCI and promote regeneration leading to functional recovery.