Functional regeneration of respiratory pathways after spinal cord injury

A facilitatory role of astrocytes in axonal regeneration after acute and chronic spinal cord injury

Neuroscience dogma avers that astrocytic "scars" inhibit axonal regeneration after spinal cord injury (SCI). A recent report suggested however that astrocytes form "borders" around lesions that are permissive rather than inhibitory to axonal growth. We now provide further evidence supporting a facilitatory role of astrocytes in axonal regeneration after SCI. First, even 6months after SCI, injured axons are retained within regions of densely reactive astrocytes, in direct contact with astrocyte processes without being repelled. Second, 6 month-delayed implants of neural stem cells extend axons into reactive astrocyte borders surrounding lesions, densely contacting astrocyte surfaces. Third, bioengineered hydrogels implanted into sites of SCI re-orient reactive astrocytic processes to align along the rostral-to-caudal spinal cord axis resulting in successful regeneration into the lesion/scaffold in close association with astrocytic processes. Fourth, corticospinal axons regenerate into neural progenitor cells implanted six months after injury in close association with host astrocytic processes. Thus, astrocytes do not appear to inhibit axonal regeneration, and the close association of newly growing axons with astrocytic processes suggests a facilitatory role in axonal regeneration.

PTEN inhibition promotes robust growth of bulbospinal respiratory axons and partial recovery of diaphragm function in a chronic model of cervical contusion spinal cord injury

High spinal cord injury (SCI) leads to persistent and debilitating compromise in respiratory function. Cervical SCI not only causes the death of phrenic motor neurons (PhMNs) that innervate the diaphragm, but also damages descending respiratory pathways originating in the rostral ventral respiratory group (rVRG) located in the brainstem, resulting in denervation and consequent silencing of spared PhMNs located caudal to injury. It is imperative to determine whether interventions targeting rVRG axon growth and respiratory neural circuit reconnection are efficacious in chronic cervical contusion SCI, given that the vast majority of individuals are chronically-injured and most cases of SCI involve contusion-type damage to the cervical region. We therefore employed a rat model of chronic cervical hemicontusion to test therapeutic manipulations aimed at reconstructing damaged rVRG-PhMN-diaphragm circuitry to achieve recovery of respiratory function. At a chronic time point post-injury, we systemically administered: an antagonist peptide directed against phosphatase and tensin homolog (PTEN), a central inhibitor of neuron-intrinsic axon growth potential; an antagonist peptide directed against receptor-type protein tyrosine phosphatase sigma (PTPσ), another important negative regulator of axon growth capacity; or a combination of these two peptides. PTEN antagonist peptide (PAP4) promoted partial recovery of diaphragm motor activity out to nine months post-injury (though this effect depended on the anesthetic regimen used during recording), while PTPσ peptide did not impact diaphragm function after cervical SCI. Furthermore, PAP4 promoted robust growth of descending bulbospinal rVRG axons caudal to the injury within the denervated portion of the PhMN pool, while PTPσ peptide did not affect rVRG axon growth at this location that is critical to control of diaphragmatic respiratory function. In conclusion, we find that, when PTEN inhibition is targeted at a chronic time point following cervical contusion, our non-invasive PAP4 strategy can successfully promote significant regrowth of damaged respiratory neural circuitry and also partial recovery of diaphragm motor function.

The roles of circular RNAs in nerve injury and repair

Nerve injuries significantly impact the quality of life for patients, with severe cases posing life-threatening risks. A comprehensive understanding of the pathophysiological mechanisms underlying nerve injury is crucial to the development of effective strategies to promote nerve regeneration. Circular RNAs (circRNAs), a recently characterized class of RNAs distinguished by their covalently closed-loop structures, have been shown to play an important role in various biological processes. Numerous studies have highlighted the pivotal role of circRNAs in nerve regeneration, identifying them as potential therapeutic targets. This review aims to succinctly outline the latest advances in the role of circRNAs related to nerve injury repair and the underlying mechanisms, including peripheral nerve injury, traumatic brain injury, spinal cord injury, and neuropathic pain. Finally, we discuss the potential applications of circRNAs in drug development and consider the potential directions for future research in this field to provide insights into circRNAs in nerve injury repair.

Forelimb motor recovery by modulating extrinsic and intrinsic signaling as well as neuronal activity after the cervical spinal cord injury

Singular strategies for promoting axon regeneration and motor recovery after spinal cord injury (SCI) have been attempted with limited success. Here, we propose the combinatorial approach of deleting extrinsic and intrinsic factors paired with neural stimulation, will enhance adaptive axonal growth and motor recovery after SCI. We previously showed the deletion of RhoA and Pten in corticospinal neurons inhibits axon dieback and promotes axon sprouting after lumbar SCI. Here, we examined the effects of RhoA;Pten deletion coupled with neural stimulation after cervical SCI. This combinatorial approach promoted more boutons on injured corticospinal neurons in the spinal cord compared to sole RhoA;Pten deletion. Although RhoA;Pten deletion does not promote motor recovery in the forelimb after SCI, stimulating corticospinal neurons in those mice results in partial motor recovery. These results demonstrate that a combinatorial approach that pairs genetic modifications with neuronal stimulation can promote axon sprouting and motor recovery following SCI.

The top 100 most cited articles on axon regeneration from 2003 to 2023: a bibliometric analysis

Objective

In this study, we used a bibliometric and visual analysis to evaluate the characteristics of the 100 most cited articles on axon regeneration.

Methods

The 100 most cited papers on axon regeneration published between 2003 and 2023 were identified by searching the Web of Science Core Collection database. The extracted data included the title, author, keywords, journal, publication year, country, and institution. A bibliometric analysis was subsequently undertaken.

Results

The examined set of 100 papers collectively accumulated a total of 39,548 citations. The number of citations for each of the top 100 articles ranged from 215 to 1,604, with a median value of 326. The author with the most contributions to this collection was He, Zhigang, having authored eight papers. Most articles originated in the United States (n = 72), while Harvard University was the institution with the most cited manuscripts (n = 19). Keyword analysis unveiled several research hotspots, such as chondroitin sulfate proteoglycan, alternative activation, exosome, Schwann cells, axonal protein synthesis, electrical stimulation, therapeutic factors, and remyelination. Examination of keywords in the articles indicated that the most recent prominent keyword was "local delivery."

Conclusion

This study offers bibliometric insights into axon regeneration, underscoring that the United States is a prominent leader in this field. Our analysis highlights the growing relevance of local delivery systems in axon regeneration. Although these systems have shown promise in preclinical models, challenges associated with long-term optimization, agent selection, and clinical translation remain. Nevertheless, the continued development of local delivery technologies represents a promising pathway for achieving axon regeneration; however, additional research is essential to fully realize their potential and thereby enhance patient outcomes.

Collagen I is a critical organizer of scarring and CNS regeneration failure

Although axotomized neurons retain the ability to initiate the formation of growth cones and attempt to regenerate after spinal cord injury, the scar area formed as a result of the lesion in most adult mammals contains a variety of reactive cells that elaborate multiple extracellular matrix and enzyme components that are not suitable for regrowth 1,2 . Newly migrating axons in the vicinity of the scar utilize upregulated LAR family receptor protein tyrosine phosphatases, such as PTPσ, to associate with extracellular chondroitin sulphate proteoglycans (CSPGs), which have been discovered to tightly entrap the regrowing axon tip and transform it into a dystrophic non-growing endball. The scar is comprised of two compartments, one in the lesion penumbra, the glial scar, composed of reactive microglia, astrocytes and OPCs; and the other in the lesion epicenter, the fibrotic scar, which is made up of fibroblasts, pericytes, endothelial cells and inflammatory cells. While the fibrotic scar is known to be strongly inhibitory, even more so than the glial scar, the molecular determinants that curtail axon elongation through the injury core are largely uncharacterized. Here, we show that one sole member of the entire family of collagens, collagen I, creates an especially potent inducer of endball formation and regeneration failure. The inhibitory signaling is mediated by mechanosensitive ion channels and RhoA activation. Staggered systemic administration of two blood-brain barrier permeable-FDA approved drugs, aspirin and pirfenidone, reduced fibroblast incursion into the complete lesion and dramatically decreased collagen I, as well as CSPG deposition which were accompanied by axonal growth and considerable functional recovery. The anatomical substrate for robust axonal regeneration was provided by laminin producing GFAP + and NG2 + bridging cells that spanned the wound. Our results reveal a collagen I-mechanotransduction axis that regulates axonal regrowth in spinal cord injury and raise a promising strategy for rapid clinical application.

Link Protein 1 Is Involved in the Activity-Dependent Modulation of Perineuronal Nets in the Spinal Cord

One of the challenges of the mature nervous system is to maintain the stability of neural networks while providing a degree of plasticity to generate experience-dependent modifications. This plasticity-stability dynamism is regulated by perineuronal nets (PNNs) and is crucial for the proper functioning of the system. Previously, we found a relation between spinal PNNs reduction and maladaptive plasticity after spinal cord injury (SCI), which was attenuated by maintaining PNNs with activity-dependent therapies. Moreover, transgenic mice lacking the cartilage link protein 1 (Crtl1 KO mice) showed aberrant spinal PNNs and increased spinal plasticity. Therefore, the aim of this study is to evaluate the role of link protein 1 in the activity-dependent modulation of spinal PNNs surrounding motoneurons and its impact on the maladaptive plasticity observed following SCI. We first studied the activity-dependent modulation of spinal PNNs using a voluntary wheel-running protocol. This training protocol increased spinal PNNs in WT mice but did not modify PNN components in Crtl1 KO mice, suggesting that link protein 1 mediates the activity-dependent modulation of PNNs. Secondly, a thoracic SCI was performed, and functional outcomes were evaluated for 35 days. Interestingly, hyperreflexia and hyperalgesia found at the end of the experiment in WT-injured mice were already present at basal levels in Crtl1 KO mice and remained unchanged after the injury. These findings demonstrated that link protein 1 plays a dual role in the correct formation and in activity-dependent modulation of PNNs, turning it into an essential element for the proper function of PNN in spinal circuits.

Perineuronal Net Microscopy: From Brain Pathology to Artificial Intelligence

Perineuronal nets (PNN) are a special highly structured type of extracellular matrix encapsulating synapses on large populations of CNS neurons. PNN undergo structural changes in schizophrenia, epilepsy, Alzheimer's disease, stroke, post-traumatic conditions, and some other brain disorders. The functional role of the PNN microstructure in brain pathologies has remained largely unstudied until recently. Here, we review recent research implicating PNN microstructural changes in schizophrenia and other disorders. We further concentrate on high-resolution studies of the PNN mesh units surrounding synaptic boutons to elucidate fine structural details behind the mutual functional regulation between the ECM and the synaptic terminal. We also review some updates regarding PNN as a potential pharmacological target. Artificial intelligence (AI)-based methods are now arriving as a new tool that may have the potential to grasp the brain's complexity through a wide range of organization levels-from synaptic molecular events to large scale tissue rearrangements and the whole-brain connectome function. This scope matches exactly the complex role of PNN in brain physiology and pathology processes, and the first AI-assisted PNN microscopy studies have been reported. To that end, we report here on a machine learning-assisted tool for PNN mesh contour tracing.

Gibbs H, McCreedy DA, Alilain WJ, Crone SA. V2a neurons restore diaphragm function in mice following spinal cord injury

The specific roles that different types of neurons play in recovery from injury is poorly understood. Here, we show that increasing the excitability of ipsilaterally projecting, excitatory V2a neurons using designer receptors exclusively activated by designer drugs (DREADDs) restores rhythmic bursting activity to a previously paralyzed diaphragm within hours, days, or weeks following a C2 hemisection injury. Further, decreasing the excitability of V2a neurons impairs tonic diaphragm activity after injury as well as activation of inspiratory activity by chemosensory stimulation, but does not impact breathing at rest in healthy animals. By examining the patterns of muscle activity produced by modulating the excitability of V2a neurons, we provide evidence that V2a neurons supply tonic drive to phrenic circuits rather than increase rhythmic inspiratory drive at the level of the brainstem. Our results demonstrate that the V2a class of neurons contribute to recovery of respiratory function following injury. We propose that altering V2a excitability is a potential strategy to prevent respiratory motor failure and promote recovery of breathing following spinal cord injury.

PTEN inhibition promotes robust growth of bulbospinal respiratory axons and partial recovery of diaphragm function in a chronic model of cervical contusion spinal cord injury

High spinal cord injury (SCI) leads to persistent and debilitating compromise in respiratory function. Cervical SCI not only causes the death of phrenic motor neurons (PhMNs) that innervate the diaphragm, but also damages descending respiratory pathways originating in the rostral ventral respiratory group (rVRG) located in the brainstem, resulting in denervation and consequent silencing of spared PhMNs located caudal to injury. It is imperative to determine whether interventions targeting rVRG axon growth and respiratory neural circuit reconnection are efficacious in chronic cervical contusion SCI, given that the vast majority of individuals are chronically-injured and most cases of SCI involve contusion-type damage to the cervical region. We therefore employed a clinically-relevant rat model of chronic cervical hemicontusion to test therapeutic manipulations aimed at reconstructing damaged rVRG-PhMN-diaphragm circuitry to achieve recovery of respiratory function. At a chronic time point post-injury, we systemically administered: an antagonist peptide directed against phosphatase and tensin homolog (PTEN), a central inhibitor of neuron-intrinsic axon growth potential; an antagonist peptide directed against receptor-type protein tyrosine phosphatase sigma (PTPσ), another important negative regulator of axon growth capacity; or a combination of these two peptides. PTEN antagonist peptide (PAP4) promoted partial recovery of diaphragm motor activity out to nine months post-injury, while PTPσ peptide did not impact diaphragm function after cervical SCI. Furthermore, PAP4 promoted robust growth of descending bulbospinal rVRG axons caudal to the injury within the denervated portion of the PhMN pool, while PTPσ peptide did not affect rVRG axon growth at this location that is critical to control of diaphragmatic respiratory function. In conclusion, we find that, when PTEN inhibition is targeted at a chronic time point following cervical contusion that is most relevant to the SCI clinical population, our non-invasive PAP4 strategy can successfully promote significant regrowth of damaged respiratory neural circuitry and also partial recovery of diaphragm motor function.

HIGHLIGHTS

PTEN antagonist peptide promotes partial diaphragm function recovery in chronic cervical contusion SCI.PTPσ inhibitory peptide does not impact diaphragm function recovery in chronic cervical contusion SCI.PTEN antagonist peptide promotes growth of bulbospinal rVRG axons in chronic cervical contusion SCI.PTPσ peptide does not affect rVRG axon growth in chronic cervical contusion SCI.

Targeting the Microbiome to Improve Gut Health and Breathing Function After Spinal Cord Injury

Spinal cord injury (SCI) is a devastating condition characterized by impaired motor and sensory function, as well as internal organ pathology and dysfunction. This internal organ dysfunction, particularly gastrointestinal (GI) complications, and neurogenic bowel, can reduce the quality of life of individuals with an SCI and potentially hinder their recovery. The gut microbiome impacts various central nervous system functions and has been linked to a number of health and disease states. An imbalance of the gut microbiome, i.e., gut dysbiosis, contributes to neurological disease and may influence recovery and repair processes after SCI. Here we examine the impact of high cervical SCI on the gut microbiome and find that transient gut dysbiosis with persistent gut pathology develops after SCI. Importantly, probiotic treatment improves gut health and respiratory motor function measured through whole-body plethysmography. Concurrent with these improvements was a systemic decrease in the cytokine tumor necrosis factor-alpha and an increase in neurite sprouting and regenerative potential of neurons. Collectively, these data reveal the gut microbiome as an important therapeutic target to improve visceral organ health and respiratory motor recovery after SCI.

Research Highlights

Cervical spinal cord injury (SCI) causes transient gut dysbiosis and persistent gastrointestinal (GI) pathology.Treatment with probiotics after SCI leads to a healthier GI tract and improved respiratory motor recovery.Probiotic treatment decreases systemic tumor necrosis factor-alpha and increases the potential for sprouting and regeneration of neurons after SCI.The gut microbiome is a valid target to improve motor function and secondary visceral health after SCI.

Recovery of Forearm and Fine Digit Function After Chronic Spinal Cord Injury by Simultaneous Blockade of Inhibitory Matrix Chondroitin Sulfate Proteoglycan Production and the Receptor PTPσ

Spinal cord injuries (SCI), for which there are limited effective treatments, result in enduring paralysis and hypoesthesia, in part because of the inhibitory microenvironment that develops and limits regeneration/sprouting, especially during chronic stages. Recently, we discovered that targeted enzymatic removal of the inhibitory chondroitin sulfate proteoglycan (CSPG) component of the extracellular and perineuronal net (PNN) matrix via Chondroitinase ABC (ChABC) rapidly restored robust respiratory function to the previously paralyzed hemi-diaphragm after remarkably long times post-injury (up to 1.5 years) following a cervical level 2 lateral hemi-transection. Importantly, ChABC treatment at cervical level 4 in this chronic model also elicited improvements in gross upper arm function. In the present study, we focused on arm and hand function, seeking to highlight and optimize crude as well as fine motor control of the forearm and digits at lengthy chronic stages post-injury. However, instead of using ChABC, we utilized a novel and more clinically relevant systemic combinatorial treatment strategy designed to simultaneously reduce and overcome inhibitory CSPGs. Following a 3-month upper cervical spinal hemi-lesion using adult female Sprague Dawley rats, we show that the combined treatment had a profound effect on functional recovery of the chronically paralyzed forelimb and paw, as well as on precision movements of the digits. The regenerative and immune system related events that we describe deepen our basic understanding of the crucial role of CSPG-mediated inhibition via the PTPσ receptor in constraining functional synaptic plasticity at lengthy time points following SCI, hopefully leading to clinically relevant translational benefits.

Osteopontin enhances the effect of treadmill training and promotes functional recovery after spinal cord injury

In this study, we examined the combined impact of osteopontin (OPN) and treadmill training on mice with spinal cord injury (SCI). OPN was overexpressed by injecting AAV9-SPP1-GFP into the sensorimotor cortex, followed by a left incomplete C5 crush injury two weeks later. Mice (Ex or Ex + OPN group) were trained at 50% maximum running speed for 8 weeks. To analyze the effects, we used biotinylated dextran amine (BDA) for tracing the corticospinal tract (CST) and performed Western blotting and immunohistochemical methods to assess the activation of the mammalian target of rapamycin (mTOR). We also examined axonal regeneration and conducted behavioral tests to measure functional recovery. The results demonstrated that treadmill training promoted the expression of neurotrophic factors such as brain-derived neurotrophic factor (BNDF) and insulin-like growth factor I (IGF-1) and activated mTOR signaling. OPN amplified the effect of treadmill training on activating mTOR signaling indicated by upregulated phosphorylation of ribosomal protein S6 kinase (S6). The combination of OPN and exercise further promoted functional recovery and facilitated limited CST axonal regeneration which did not occur with treadmill training and OPN treatment alone. These findings indicate that OPN enhances the effects of treadmill training in the treatment of SCI and offer new therapeutic insights for spinal cord injury.

Changes in respiratory structure and function after traumatic cervical spinal cord injury: observations from spinal cord and brain

Respiratory difficulties and mortality following severe cervical spinal cord injury (CSCI) result primarily from malfunctions of respiratory pathways and the paralyzed diaphragm. Nonetheless, individuals with CSCI can experience partial recovery of respiratory function through respiratory neuroplasticity. For decades, researchers have revealed the potential mechanism of respiratory nerve plasticity after CSCI, and have made progress in tissue healing and functional recovery. While most existing studies on respiratory plasticity after spinal cord injuries have focused on the cervical spinal cord, there is a paucity of research on respiratory-related brain structures following such injuries. Given the interconnectedness of the spinal cord and the brain, traumatic changes to the former can also impact the latter. Consequently, are there other potential therapeutic targets to consider? This review introduces the anatomy and physiology of typical respiratory centers, explores alterations in respiratory function following spinal cord injuries, and delves into the structural foundations of modified respiratory function in patients with CSCI. Additionally, we propose that magnetic resonance neuroimaging holds promise in the study of respiratory function post-CSCI. By studying respiratory plasticity in the brain and spinal cord after CSCI, we hope to guide future clinical work.

The Promising Role of a Zebrafish Model Employed in Neural Regeneration Following a Spinal Cord Injury

Spinal cord injury (SCI) is a devastating event that results in a wide range of physical impairments and disabilities. Despite the advances in our understanding of the biological response to injured tissue, no effective treatments are available for SCIs at present. Some studies have addressed this issue by exploring the potential of cell transplantation therapy. However, because of the abnormal microenvironment in injured tissue, the survival rate of transplanted cells is often low, thus limiting the efficacy of such treatments. Many studies have attempted to overcome these obstacles using a variety of cell types and animal models. Recent studies have shown the utility of zebrafish as a model of neural regeneration following SCIs, including the proliferation and migration of various cell types and the involvement of various progenitor cells. In this review, we discuss some of the current challenges in SCI research, including the accurate identification of cell types involved in neural regeneration, the adverse microenvironment created by SCIs, attenuated immune responses that inhibit nerve regeneration, and glial scar formation that prevents axonal regeneration. More in-depth studies are needed to fully understand the neural regeneration mechanisms, proteins, and signaling pathways involved in the complex interactions between the SCI microenvironment and transplanted cells in non-mammals, particularly in the zebrafish model, which could, in turn, lead to new therapeutic approaches to treat SCIs in humans and other mammals.

Temporal dynamics of microglia-astrocyte interaction in neuroprotective glial scar formation after intracerebral hemorrhage

The role of glial scar after intracerebral hemorrhage (ICH) remains unclear. This study aimed to investigate whether microglia-astrocyte interaction affects glial scar formation and explore the specific function of glial scar. We used a pharmacologic approach to induce microglial depletion during different ICH stages and examine how ablating microglia affects astrocytic scar formation. Spatial transcriptomics (ST) analysis was performed to explore the potential ligand-receptor pair in the modulation of microglia-astrocyte interaction and to verify the functional changes of astrocytic scars at different periods. During the early stage, sustained microglial depletion induced disorganized astrocytic scar, enhanced neutrophil infiltration, and impaired tissue repair. ST analysis indicated that microglia-derived insulin like growth factor 1 (IGF1) modulated astrocytic scar formation via mechanistic target of rapamycin (mTOR) signaling activation. Moreover, repopulating microglia (RM) more strongly activated mTOR signaling, facilitating a more protective scar formation. The combination of IGF1 and osteopontin (OPN) was necessary and sufficient for RM function, rather than IGF1 or OPN alone. At the chronic stage of ICH, the overall net effect of astrocytic scar changed from protective to destructive and delayed microglial depletion could partly reverse this. The vital insight gleaned from our data is that sustained microglial depletion may not be a reasonable treatment strategy for early-stage ICH. Inversely, early-stage IGF1/OPN treatment combined with late-stage PLX3397 treatment is a promising therapeutic strategy. This prompts us to consider the complex temporal dynamics and overall net effect of microglia and astrocytes, and develop elaborate treatment strategies at precise time points after ICH.

Biomimetic scaffold-based stem cell transplantation promotes lung regeneration

Therapeutic options are limited for severe lung injury and disease as the spontaneous regeneration of functional alveolar is terminated owing to the weakness of the inherent stem cells and the dyscrasia of the niche. Umbilical cord mesenchymal-derived stem cells (UC-MSCs) have been applied to clinical trials to promote lung repair through stem cell niche restruction. However, the application of UC-MSCs is hampered by the effectiveness of cell transplantation with few cells homing to the injury sites and poor retention, survival, and proliferation in vivo. In this study, we constructed an artificial three-dimensional (3D) biomimetic scaffold-based MSCs implant to establish a beneficial regeneration niche for endogenous stem cells in situ lung regeneration. The therapeutic potential of 3D biomimetic scaffold-based MSCs implants was evaluated by 3D culture in vitro. And RNA sequencing (RNA-Seq) was mapped to explore the gene expression involved in the niche improvement. Next, a model of partial lung resection was established in rats, and the implants were implanted into the operative region. Effects of the implants on rat resected lung injury repair were detected. The results revealed that UC-MSCs loaded on biomimetic scaffolds exerted strong paracrine effects and some UC-MSCs migrated to the lung from scaffolds and had long-term retention to suppress inflammation and fibrosis in residual lungs and promoted vascular endothelial cells and alveolar type II epithelial cells to enter the scaffolds. Then, under the guidance of the ECM-mimicking structures of scaffolds and the stimulation of the remaining UC-MSCs, vascular and alveolar-like structures were formed in the scaffold region. Moreover, the general morphology of the operative lung was also restored. Taken together, the artificial 3D biomimetic scaffold-based MSCs implants induce in situ lung regeneration and recovery after lung destruction, providing a promising direction for tissue engineering and stem cell strategies in lung regeneration.

Therapeutic Strategies Targeting Respiratory Recovery after Spinal Cord Injury: From Preclinical Development to Clinical Translation

High spinal cord injuries (SCIs) lead to permanent functional deficits, including respiratory dysfunction. Patients living with such conditions often rely on ventilatory assistance to survive, and even those that can be weaned continue to suffer life-threatening impairments. There is currently no treatment for SCI that is capable of providing complete recovery of diaphragm activity and respiratory function. The diaphragm is the main inspiratory muscle, and its activity is controlled by phrenic motoneurons (phMNs) located in the cervical (C3-C5) spinal cord. Preserving and/or restoring phMN activity following a high SCI is essential for achieving voluntary control of breathing. In this review, we will highlight (1) the current knowledge of inflammatory and spontaneous pro-regenerative processes occurring after SCI, (2) key therapeutics developed to date, and (3) how these can be harnessed to drive respiratory recovery following SCIs. These therapeutic approaches are typically first developed and tested in relevant preclinical models, with some of them having been translated into clinical studies. A better understanding of inflammatory and pro-regenerative processes, as well as how they can be therapeutically manipulated, will be the key to achieving optimal functional recovery following SCIs.

Narrative review of roles of astrocytes in subarachnoid hemorrhage

Background and Objective

Astrocytes play an important role in healthy brain function, including the development and maintenance of blood-brain barrier (BBB), structural support, brain homeostasis, neurovascular coupling and secretion of neuroprotective factors. Reactive astrocytes participate in various pathophysiology after subarachnoid hemorrhage (SAH) including neuroinflammation, glutamate toxicity, brain edema, vasospasm, BBB disruption, cortical spreading depolarization (SD).

Methods

We searched PubMed up to 31 May, 2022 and evaluated the articles for screening and inclusion for subsequent systemic review. We found 198 articles with the searched terms. After exclusion based on the selection criteria, we selected 30 articles to start the systemic review.

Key Content and Findings

We summarized the response of astrocytes induced by SAH. Astrocytes are critical for brain edema formation, BBB reconstruction and neuroprotection in the acute stage of SAH. Astrocytes clear extracellular glutamate by increasing the uptake of glutamate and Na+/K+ ATPase activity after SAH. Neurotrophic factors released by astrocytes contribute to neurological recovery after SAH. Meanwhile, Astrocytes also form glial scars which hinder axon regeneration, produce proinflammatory cytokines, free radicals, and neurotoxic molecules.

Conclusions

Preclinical studies showed that therapeutic targeting the astrocytes response could have a beneficial effect in ameliorating neuronal injury and cognitive impairment after SAH. Clinical trials and preclinical animal studies are still urgently needed in order to determine where astrocytes stand in various pathway of brain damage and repair after SAH and, above all, to develop therapeutic approaches which benefit patient outcomes.

Behavioral regulation by perineuronal nets in the prefrontal cortex of the CNTNAP2 mouse model of autism spectrum disorder

Autism spectrum disorders (ASDs) arise from altered development of the central nervous system, and manifest behaviorally as social interaction deficits and restricted and repetitive behaviors. Alterations to parvalbumin (PV) expressing interneurons have been implicated in the neuropathological and behavioral deficits in autism. In addition, perineuronal nets (PNNs), specialized extracellular matrix structures that enwrap the PV-expressing neurons, also may be altered, which compromises neuronal function and susceptibility to oxidative stress. In particular, the prefrontal cortex (PFC), which regulates several core autistic traits, relies on the normal organization of PNNs and PV-expressing cells, as well as other neural circuit elements. Consequently, we investigated whether PNNs and PV-expressing cells were altered in the PFC of the CNTNAP2 knockout mouse model of ASD and whether these contributed to core autistic-like behaviors in this model system. We observed an overexpression of PNNs, PV-expressing cells, and PNNs enwrapping PV-expressing cells in adult CNTNAP2 mice. Transient digestion of PNNs from the prefrontal cortex (PFC) by injection of chondroitinase ABC in CNTNAP2 mutant mice rescued some of the social interaction deficits, but not the restricted and repetitive behaviors. These findings suggest that the neurobiological regulation of PNNs and PVs in the PFC contribute to social interaction behaviors in neurological disorders including autism.

AAV Vector Mediated Delivery of NG2 Function Neutralizing Antibody and Neurotrophin NT-3 Improves Synaptic Transmission, Locomotion, and Urinary Tract Function after Spinal Cord Contusion Injury in Adult Rats

NG2 is a structurally unique transmembrane chondroitin sulfate proteoglycan (CSPG). Its role in damaged spinal cord is dual. NG2 is considered one of key inhibitory factors restricting axonal growth following spinal injury. Additionally, we have recently detected its novel function as a blocker of axonal conduction. Some studies, however, indicate the importance of NG2 presence in the formation of synaptic contacts. We hypothesized that the optimal treatment would be neutralization of inhibitory functions of NG2 without its physical removal. Acute intraspinal injections of anti-NG2 monoclonal antibodies reportedly prevented an acute block of axonal conduction by exogenous NG2. For prolonged delivery of NG2 function neutralizing antibody, we have developed a novel gene therapy: adeno-associated vector (AAV) construct expressing recombinant single-chain variable fragment anti-NG2 antibody (AAV-NG2Ab). We examined effects of AAV-NG2Ab alone or in combination with neurotrophin NT-3 in adult female rats with thoracic T10 contusion injuries. A battery of behavioral tests was used to evaluate locomotor function. In vivo single-cell electrophysiology was used to evaluate synaptic transmission. Lower urinary tract function was assessed during the survival period using metabolic chambers. Terminal cystometry, with acquisition of external urethral sphincter activity and bladder pressure, was used to evaluate bladder function. Both the AAV-NG2Ab and AAV-NG2Ab combined with AAV-NT3 treatment groups demonstrated significant improvements in transmission, locomotion, and bladder function compared with the control (AAV-GFP) group. These functional improvements associated with improved remyelination and plasticity of 5-HT fibers. The best results were observed in the group that received combinational AAV-NG2Ab+AAV-NT3 treatment.SIGNIFICANCE STATEMENT We recently demonstrated beneficial, but transient, effects of neutralization of the NG2 proteoglycan using monoclonal antibodies delivered intrathecally via osmotic mini-pumps after spinal cord injury. Currently, we have developed a novel gene therapy tool for prolonged and clinically relevant delivery of a recombinant single-chain variable fragment anti-NG2 antibody: AAV-rh10 serotype expressing scFv-NG2 (AAV-NG2Ab). Here, we examined effects of AAV-NG2Ab combined with transgene delivery of Neurotrophin-3 (AAV-NT3) in adult rats with thoracic contusion injuries. The AAV-NG2Ab and AAV-NG2Ab+AAV-NT3 treatment groups demonstrated significant improvements of locomotor function and lower urinary tract function. Beneficial effects of this novel gene therapy on locomotion and bladder function associated with improved transmission to motoneurons and plasticity of axons in damaged spinal cord.

Remodeling Microenvironment for Endogenous Repair through Precise Modulation of Chondroitin Sulfate Proteoglycans Following Spinal Cord Injury

The fluid-filled cystic cavity sealed by a dense scar developed following traumatic spinal cord injury (SCI) has been a major obstacle to neural regeneration and functional recovery. Here the transected lesion is bridged using a functional self-assembling peptide (F-SAP) hydrogel loaded with membrane-permeable intracellular sigma peptide (ISP) and intracellular LAR peptide (ILP), targeted at perturbing chondroitin sulfate proteoglycan (CSPG) inhibitory signaling. As compared to F-SAP hydrogel loaded with chondroitinase ABC, the F-SAP+ISP/ILP promotes a beneficial anti-inflammatory response via manipulation of microglia/macrophages infiltration and assembly of extracellular matrix (ECM) molecules into fibrotic matrix rather than scarring tissues. The remodeled ECM creates a permissive environment that supports axon regrowth and the formation of synaptic connections with neurons derived from endogenous neural stem cells. The remodeled networks contribute to functional recovery, as demonstrated by improved hind limb movements and electrophysiological properties. This work proposes a unique mechanism that ECM remodeling induced by CSPG-manipulation-based anti-inflammation can construct a permissive environment for neural regeneration, and shed light on the advancement of manipulation of cascading cellular and molecular events potential for endogenous repair of SCI.

Regulation of axonal regeneration after mammalian spinal cord injury

One hundred years ago, Ramón y Cajal, considered by many as the founder of modern neuroscience, stated that neurons of the adult central nervous system (CNS) are incapable of regenerating. Yet, recent years have seen a tremendous expansion of knowledge in the molecular control of axon regeneration after CNS injury. We now understand that regeneration in the adult CNS is limited by (1) a failure to form cellular or molecular substrates for axon attachment and elongation through the lesion site; (2) environmental factors, including inhibitors of axon growth associated with myelin and the extracellular matrix; (3) astrocyte responses, which can both limit and support axon growth; and (4) intraneuronal mechanisms controlling the establishment of an active cellular growth programme. We discuss these topics together with newly emerging hypotheses, including the surprising finding from transcriptomic analyses of the corticospinal system in mice that neurons revert to an embryonic state after spinal cord injury, which can be sustained to promote regeneration with neural stem cell transplantation. These gains in knowledge are steadily advancing efforts to develop effective treatment strategies for spinal cord injury in humans.

Forced Remyelination Promotes Axon Regeneration in a Rat Model of Spinal Cord Injury

Spinal cord injuries result in the loss of motor and sensory functions controlled by neurons located at the site of the lesion and below. We hypothesized that experimentally enhanced remyelination supports axon preservation and/or growth in the total spinal cord transection in rats. Multifocal demyelination was induced by injection of ethidium bromide (EB), either at the time of transection or twice during transection and at 5 days post-injury. We demonstrated that the number of oligodendrocyte progenitor cells (OPCs) significantly increased 14 days after demyelination. Most OPCs differentiated into mature oligodendrocytes by 60-90 dpi in double-EB-injected rats; however, most axons were remyelinated by Schwann cells. A significant number of axons passed the injury epicenter and entered the distant segments of the spinal cord in the double-EB-injected rats. Moreover, some serotoninergic fibers, not detected in control animals, grew caudally through the injury site. Behavioral tests performed at 60-90 dpi revealed significant improvement in locomotor function recovery in double-EB-injected rats, which was impaired by the blockade of serotonin receptors, confirming the important role of restored serotonergic fibers in functional recovery. Our findings indicate that enhanced remyelination per se, without substantial inhibition of glial scar formation, is an important component of spinal cord injury regeneration.

Natural and targeted circuit reorganization after spinal cord injury

A spinal cord injury disrupts communication between the brain and the circuits in the spinal cord that regulate neurological functions. The consequences are permanent paralysis, loss of sensation and debilitating dysautonomia. However, the majority of circuits located above and below the injury remain anatomically intact, and these circuits can reorganize naturally to improve function. In addition, various neuromodulation therapies have tapped into these processes to further augment recovery. Emerging research is illuminating the requirements to reconstitute damaged circuits. Here, we summarize these natural and targeted reorganizations of circuits after a spinal cord injury. We also advocate for new concepts of reorganizing circuits informed by multi-omic single-cell atlases of recovery from injury. These atlases will uncover the molecular logic that governs the selection of 'recovery-organizing' neuronal subpopulations, and are poised to herald a new era in spinal cord medicine.

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.

Expression and regulatory network of long noncoding RNA in rats after spinal cord hemisection injury

Long noncoding RNAs (lncRNAs) participate in a variety of biological processes and diseases. However, the expression and function of lncRNAs after spinal cord injury has not been extensively analyzed. In this study of right side hemisection of the spinal cord at T10, we detected the expression of lncRNAs in the proximal tissue of T10 lamina at different time points and found 445 lncRNAs and 6522 mRNA were differentially expressed. We divided the differentially expressed lncRNAs into 26 expression trends and analyzed Profile 25 and Profile 2, the two expression trends with the most significant difference. Our results showed that the expression of 68 lncRNAs in Profile 25 rose first and remained high 3 days post-injury. There were 387 mRNAs co-expressed with the 68 lncRNAs in Profile 25. The co-expression network showed that the co-expressed genes were mainly enriched in cell division, inflammatory response, FcγR-mediated cell phagocytosis signaling pathway, cell cycle and apoptosis. The expression of 56 lncRNAs in Profile2 first declined and remained low after 3 days post-injury. There were 387 mRNAs co-expressed with the 56 lncRNAs in Profile 2. The co-expression network showed that the co-expressed genes were mainly enriched in the chemical synaptic transmission process and in the signaling pathway of neuroactive ligand-receptor interaction. The results provided the expression and regulatory network of the main lncRNAs after spinal cord injury and clarified their co-expressed gene enriched biological processes and signaling pathways. These findings provide a new direction for the clinical treatment of spinal cord injury.

A Localized Materials-Based Strategy to Non-Virally Deliver Chondroitinase ABC mRNA Improves Hindlimb Function in a Rat Spinal Cord Injury Model

Spinal cord injury often results in devastating consequences for those afflicted, with very few therapeutic options. A central element of spinal cord injuries is astrogliosis, which forms a glial scar that inhibits neuronal regeneration post-injury. Chondroitinase ABC (ChABC) is an enzyme capable of degrading chondroitin sulfate proteoglycan (CSPG), the predominant extracellular matrix component of the glial scar. However, poor protein stability remains a challenge in its therapeutic use. Messenger RNA (mRNA) delivery is an emerging gene therapy technology for in vivo production of difficult-to-produce therapeutic proteins. Here, mineral-coated microparticles as an efficient, non-viral mRNA delivery vehicles to produce exogenous ChABC in situ within a spinal cord lesion are used. ChABC production reduces the deposition of CSPGs in an in vitro model of astrogliosis, and direct injection of these microparticles within a glial scar forces local overexpression of ChABC and improves recovery of motor function seven weeks post-injury.

Respiratory plasticity following spinal cord injury: perspectives from mouse to man

The study of respiratory plasticity in animal models spans decades. At the bench, researchers use an array of techniques aimed at harnessing the power of plasticity within the central nervous system to restore respiration following spinal cord injury. This field of research is highly clinically relevant. People living with cervical spinal cord injury at or above the level of the phrenic motoneuron pool at spinal levels C3-C5 typically have significant impairments in breathing which may require assisted ventilation. Those who are ventilator dependent are at an increased risk of ventilator-associated co-morbidities and have a drastically reduced life expectancy. Pre-clinical research examining respiratory plasticity in animal models has laid the groundwork for clinical trials. Despite how widely researched this injury is in animal models, relatively few treatments have broken through the preclinical barrier. The three goals of this present review are to define plasticity as it pertains to respiratory function post-spinal cord injury, discuss plasticity models of spinal cord injury used in research, and explore the shift from preclinical to clinical research. By investigating current targets of respiratory plasticity research, we hope to illuminate preclinical work that can influence future clinical investigations and the advancement of treatments for spinal cord injury.

Extra Cellular Matrix Remodeling: An Adjunctive Target for Spinal Cord Injury and Intervertebral Disc Degeneration

The extracellular matrix (ECM) is a protein-and-carbohydrate meshwork that supports a variety of biological structures and processes, from tissue development and elasticity to the preservation of organ structures. ECM composition is different in each organ. It is a remarkably dynamic 3-dimensional structure that's constantly changing to maintain tissue homeostasis. This review aims to describe the involvement of ECM components in the remodeling process of spinal cord injury (SCI) and intervertebral disc degeneration (IVDD). Here, we have also described the current ECM-based therapeutic targets, which can be explored for ECM remodeling SCI is a neurological condition with intense influences resulting from a trauma inflicted on the spinal cord. SCI leads to damage to the intact ECM that leads to regeneration failure. IVDD mainly occurs due to aging and trauma. Various ECM components enable fragmentation of the disc and are thereby involved in disc degeneration. ECM manipulation can be used as an adjunct treatment in SCI and IVDD. Current treatment approaches for SCI and IVDD are conservative and unsatisfactory. Targeting ECM remodeling as an adjunct therapy may result in better disease outcomes.

Investigating Dynamics of the Spinal Cord Injury Adjustment Model: Mediation Model Analysis

Spinal cord injury (SCI) is a severe neurological injury that results in damage to multiple bodily systems. SCI rehabilitation requires a significant focus on improving adjustment to the injury. This paper presents a detailed description of the Spinal Cord Injury Adjustment Model (SCIAM), which clarifies how individuals adjust to SCI and contends that adjustment to SCI is a multifactorial process involving non-linear dynamic adaptation over time. Evidence supporting SCIAM is also discussed. Mediation analyses were conducted to test the mediator dynamics proposed by the model. The analyses tested the relationship between two moderators (self-care and secondary health conditions), mediators (two self-efficacy items and appraisal of quality of life or QoL), and positive versus negative vitality/mental health as outcomes. Results showed that higher self-efficacy and perceived QoL was related to greater independence in self-care and reduced negative impacts of secondary health conditions. This study supported the mediation role of self-efficacy and other appraisals such as perceived QoL in enhancing self-care and buffering the negative impact of health challenges. In conclusion, it is important to employ a holistic model such as SCIAM to conceptualise and increase understanding of the process of adjustment following a severe neurological injury such as SCI.

Chronic muscle recordings reveal recovery of forelimb function in spinal injured female rats after cortical epidural stimulation combined with rehabilitation and chondroitinase ABC

Cervical level spinal cord injury (SCI) can severely impact upper limb muscle function, which is typically assessed in the clinic using electromyography (EMG). Here, we established novel preclinical methodology for EMG assessments of muscle function after SCI in awake freely moving animals. Adult female rats were implanted with EMG recording electrodes in bicep muscles and received bilateral cervical (C7) contusion injuries. Forelimb muscle activity was assessed by recording maximum voluntary contractions during a grip strength task and cortical motor evoked potentials in the biceps. We demonstrate that longitudinal recordings of muscle activity in the same animal are feasible over a chronic post-injury time course and provide a sensitive method for revealing post-injury changes in muscle activity. This methodology was utilized to investigate recovery of muscle function after a novel combination therapy. Cervical contused animals received intraspinal injections of a neuroplasticity-promoting agent (lentiviral-chondroitinase ABC) plus 11 weeks of cortical epidural electrical stimulation (3 h daily, 5 days/week) and behavioral rehabilitation (15 min daily, 5 days/week). Longitudinal monitoring of voluntary and evoked muscle activity revealed significantly increased muscle activity and upper limb dexterity with the combination treatment, compared to a single treatment or no treatment. Retrograde mapping of motor neurons innervating the biceps showed a predominant distribution across spinal segments C5-C8, indicating that treatment effects were likely due to neuroplastic changes in a mixture of intact and injured motor neurons. Thus, longitudinal assessments of muscle function after SCI correlate with skilled reach and grasp performance and reveal functional benefits of a novel combination therapy.

Laryngeal and swallow dysregulation following acute cervical spinal cord injury

Laryngeal function is vital to airway protection. While swallow is mediated by the brainstem, mechanisms underlying increased risk of dysphagia after cervical spinal cord injury (SCI) are unknown. We hypothesized that loss of descending phrenic drive affects swallow and breathing differently, and loss of ascending spinal afferent information alters swallow regulation. We recorded electromyograms from upper airway and chest wall muscles in freely breathing pentobarbital-anesthetized cats and rats. Inspiratory laryngeal activity increased ~two-fold following C2 lateral-hemisection. Ipsilateral to the injury, crural diaphragm EMG amplitude was reduced during breathing (62 ± 25% change post-injury), but no animal had complete termination of activity; 75% of animals increased contralateral diaphragm recruitment, but this did not reach significance. During swallow, laryngeal adductor and pharyngeal constrictor muscles increased activity, and diaphragm activity was bilaterally suppressed. This was unexpected because of the ipsilateral-specific response during breathing. Swallow-breathing coordination was also disrupted and more swallows occurred during early expiration. Finally, to determine if the chest wall is a major source of feedback for laryngeal regulation, we performed T1 total transections in rats. As in the C2 lateral-hemisection, inspiratory laryngeal recruitment was the first feature noted. In contrast to the C2 lateral-hemisection, diaphragmatic drive increased after T1 transection. Overall, we found that SCI alters laryngeal drive during swallow and breathing, and reduced swallow-related diaphragm activity. Our results show behavior-specific effects, suggesting SCI affects swallow more than breathing, and emphasizes the need for additional studies on the effects of ascending afferents from the spinal cord on laryngeal function.

Chondroitin sulfate proteoglycans prevent immune cell phenotypic conversion and inflammation resolution via TLR4 in rodent models of spinal cord injury

Chondroitin sulfate proteoglycans (CSPGs) act as potent inhibitors of axonal growth and neuroplasticity after spinal cord injury (SCI). Here we reveal that CSPGs also play a critical role in preventing inflammation resolution by blocking the conversion of pro-inflammatory immune cells to a pro-repair phenotype in rodent models of SCI. We demonstrate that enzymatic digestion of CSPG glycosaminoglycans enhances immune cell clearance and reduces pro-inflammatory protein and gene expression profiles at key resolution time points. Analysis of phenotypically distinct immune cell clusters revealed CSPG-mediated modulation of macrophage and microglial subtypes which, together with T lymphocyte infiltration and composition changes, suggests a role for CSPGs in modulating both innate and adaptive immune responses after SCI. Mechanistically, CSPG activation of a pro-inflammatory phenotype in pro-repair immune cells was found to be TLR4-dependent, identifying TLR4 signalling as a key driver of CSPG-mediated immune modulation. These findings establish CSPGs as critical mediators of inflammation resolution failure after SCI in rodents, which leads to prolonged inflammatory pathology and irreversible tissue destruction.

The Role and Modulation of Spinal Perineuronal Nets in the Healthy and Injured Spinal Cord

Rather than being a stable scaffold, perineuronal nets (PNNs) are a dynamic and specialized extracellular matrix involved in plasticity modulation. They have been extensively studied in the brain and associated with neuroprotection, ionic buffering, and neural maturation. However, their biological function in the spinal cord and the effects of disrupting spinal PNNs remain elusive. The goal of this review is to summarize the current knowledge of spinal PNNs and their potential in pathological conditions such as traumatic spinal cord injury (SCI). We also highlighted interventions that have been used to modulate the extracellular matrix after SCI, targeting the glial scar and spinal PNNs, in an effort to promote regeneration and stabilization of the spinal circuits, respectively. These concepts are discussed in the framework of developmental and neuroplastic changes in PNNs, drawing similarities between immature and denervated neurons after an SCI, which may provide a useful context for future SCI research.

Advancing Peripheral Nerve Graft Transplantation for Incomplete Spinal Cord Injury Repair

Peripheral nerves have a propensity for axon growth and regeneration that the central nervous system lacks (CNS). However, CNS axons can also grow long distances if introduced to a graft harvested from a peripheral nerve (PNGs), which is the rationale for using PNGs as repair strategy for injuries of the spinal cord. From a clinical perspective, PNGs provide interesting possibilities with potential to repair the injured spinal cord. First, there are numerous options to harvest autologous grafts associated with low risk for the patient. Second, a PNG allow axons to grow considerable distances and can, by the surgical procedure, be navigated to specific target sites in the CNS. Furthermore, a PNG provides all necessary biological substrates for myelination of elongating axons. A PNG can thus be suited to bridge axons long distances across an injury site and restore long tracts in incomplete SCI. Experimentally, locomotor functions have been improved transplanting a PNG after incomplete injury. However, we still know little with regard to the formation of new circuitries and functional outcome in association to when, where, and how grafts are inserted into the injured spinal cord, especially for sensory functions. In this perspective, we discuss the advantages of PNG from a clinical and surgical perspective, the need for adding/repairing long tracts, how PNGs are best applied for incomplete injuries, and the unexplored areas we believe are in need of answers.

Diaphragmatic Activity and Respiratory Function Following C3 or C6 Unilateral Spinal Cord Contusion in Mice

The majority of spinal cord injuries (SCIs) are cervical (cSCI), leading to a marked reduction in respiratory capacity. We aimed to investigate the effect of hemicontusion models of cSCI on both diaphragm activity and respiratory function to serve as preclinical models of cervical SCI. Since phrenic motoneuron pools are located at the C3-C5 spinal level, we investigated two models of preclinical cSCI mimicking human forms of injury, namely, one above (C3 hemicontusion-C3HC) and one below phrenic motoneuron pools (C6HC) in wild-type swiss OF-1 mice, and we compared their effects on respiratory function using whole-body plethysmography and on diaphragm activity using electromyography (EMG). At 7 days post-surgery, both C3HC and C6HC damaged spinal cord integrity above the lesion level, suggesting that C6HC potentially alters C5 motoneurons. Although both models led to decreased diaphragmatic EMG activity in the injured hemidiaphragm compared to the intact one (-46% and -26% in C3HC and C6HC, respectively, both p = 0.02), only C3HC led to a significant reduction in tidal volume and minute ventilation compared to sham surgery (-25% and -20% vs. baseline). Moreover, changes in EMG amplitude between respiratory bursts were observed post-C3HC, reflecting a change in phrenic motoneuronal excitability. Hence, C3HC and C6HC models induced alteration in respiratory function proportionally to injury level, and the C3HC model is a more appropriate model for interventional studies aiming to restore respiratory function in cSCI.

Effects of Chronic High-Frequency rTMS Protocol on Respiratory Neuroplasticity Following C2 Spinal Cord Hemisection in Rats

Simple Summary

High spinal cord injuries (SCIs) are known to lead to permanent diaphragmatic paralysis, and to induce deleterious post-traumatic inflammatory processes following cervical spinal cord injury. We used a noninvasive therapeutic tool (repetitive transcranial magnetic stimulation (rTMS)), to harness plasticity in spared descending respiratory circuit and reduce the inflammatory processes. Briefly, the results obtained in this present study suggest that chronic high-frequency rTMS can ameliorate respiratory dysfunction and elicit neuronal plasticity with a reduction in deleterious post-traumatic inflammatory processes in the cervical spinal cord post-SCI. Thus, this therapeutic tool could be adopted and/or combined with other therapeutic interventions in order to further enhance beneficial outcomes.

Abstract

High spinal cord injuries (SCIs) lead to permanent diaphragmatic paralysis. The search for therapeutics to induce functional motor recovery is essential. One promising noninvasive therapeutic tool that could harness plasticity in a spared descending respiratory circuit is repetitive transcranial magnetic stimulation (rTMS). Here, we tested the effect of chronic high-frequency (10 Hz) rTMS above the cortical areas in C2 hemisected rats when applied for 7 days, 1 month, or 2 months. An increase in intact hemidiaphragm electromyogram (EMG) activity and excitability (diaphragm motor evoked potentials) was observed after 1 month of rTMS application. Interestingly, despite no real functional effects of rTMS treatment on the injured hemidiaphragm activity during eupnea, 2 months of rTMS treatment strengthened the existing crossed phrenic pathways, allowing the injured hemidiaphragm to increase its activity during the respiratory challenge (i.e., asphyxia). This effect could be explained by a strengthening of respiratory descending fibers in the ventrolateral funiculi (an increase in GAP-43 positive fibers), sustained by a reduction in inflammation in the C1–C3 spinal cord (reduction in CD68 and Iba1 labeling), and acceleration of intracellular plasticity processes in phrenic motoneurons after chronic rTMS treatment. These results suggest that chronic high-frequency rTMS can ameliorate respiratory dysfunction and elicit neuronal plasticity with a reduction in deleterious post-traumatic inflammatory processes in the cervical spinal cord post-SCI. Thus, this therapeutic tool could be adopted and/or combined with other therapeutic interventions in order to further enhance beneficial outcomes.

Down-regulating Circular RNA Prkcsh suppresses the inflammatory response after spinal cord injury

Circular RNAs (circRNAs) are a class of conserved, endogenous non-coding RNAs that are involved in transcriptional and post-transcriptional gene regulation and are highly enriched in the nervous system. They participate in the survival and differentiation of multiple nerve cells, and may even promote the recovery of neurological function after stroke. However, their role in the inflammatory response after spinal cord injury remains unclear. In the present study, we established a mouse model of T9 spinal cord injury using the modified Allen’s impact method, and identified 16,013 circRNAs and 960 miRNAs that were differentially expressed after spinal cord injury. Of these, the expression levels of circPrkcsh were significantly different between injured and sham-treated mice. We then treated astrocytes with tumor necrosis factor-α in vitro to simulate the inflammatory response after spinal cord injury. Our results revealed an elevated expression of circPrkcsh with a concurrent decrease in miR-488 expression in injured cells. We also found that circPrkcsh regulated the expression of the inflammation-related gene Ccl2. Furthermore, in tumor necrosis factor-α-treated astrocytes, circPrkcsh knockdown decreased the expression of Ccl2 by upregulating miR-488 expression, and reduced the secretion of inflammatory cytokines in vitro. These findings suggest that differentially expressed circRNAs participate in the inflammatory response after spinal cord injury and act as the regulators of certain microRNAs. Furthermore, circPrkcsh may be used as an miR-488 sponge to regulate Ccl2 expression, which might provide a new potential therapy for SCI. The study was approved by the Animal Ethics Committee of Shandong University of China (approval No. KYLL-20170303) on March 3, 2017.

Chondroitin sulfate expression around motoneurons changes after complete spinal transection of neonatal rats

Hind limb locomotor activity spontaneously recovers after complete spinal transection (CST) in neonatal rats, but the mechanisms underlying the recovery are poorly understood. The perineuronal net (PNN) surrounding the neuronal cell bodies comprises an extracellular matrix that regulates neuronal plasticity during development. Here, we examined the expression of chondroitin sulfate (CS), a major component of the PNN, on motoneurons after CST in neonatal rats, and compared it with that in juvenile rats, in which hindlimb locomotor activity does not recover spontaneously. The spinal cord was transected at the mid-thoracic level in neonatal (postnatal day 5 [P5] and P10) and juvenile (P15 and P20) rats. Two weeks after CST, the percentage of motoneurons surrounded by chondroitin sulfate C (CS-C) - positive structures was significantly lower in rats with CST at P10 than in intact rats, and tended to be higher in rats with CST at P15 than in intact rats. The percentage of motoneurons with CS-A - positive structures was significantly lower in rats with CST at P15 than in intact rats. These findings suggest that CS-A and CS-C are differentially expressed in the PNNs in rats with CST. The decrease in CS-C - positive PNNs might facilitate the formation of new synaptic contacts to motoneurons, resulting in the recovery of the hindlimb locomotor activity in rats with CST during the neonatal period.

Phrenic motor neuron survival below cervical spinal cord hemisection

Cervical spinal cord injury (cSCI) severs bulbospinal projections to respiratory motor neurons, paralyzing respiratory muscles below the injury. C2 spinal hemisection (C2Hx) is a model of cSCI often used to study spontaneous and induced plasticity and breathing recovery post-injury. One key assumption is that C2Hx dennervates motor neurons below the injury, but does not affect their survival. However, a recent study reported substantial bilateral motor neuron death caudal to C2Hx. Since phrenic motor neuron (PMN) death following C2Hx would have profound implications for therapeutic strategies designed to target spared neural circuits, we tested the hypothesis that C2Hx minimally impacts PMN survival. Using improved retrograde tracing methods, we observed no loss of PMNs at 2- or 8-weeks post-C2Hx. We also observed no injury-related differences in ChAT or NeuN immunolabeling within labelled PMNs. Although we found no evidence of PMN loss following C2Hx, we cannot rule out neuronal loss in other motor pools. These findings address an essential prerequisite for studies that utilize C2Hx as a model to explore strategies for inducing plasticity and/or regeneration within the phrenic motor system, as they provide important insights into the viability of phrenic motor neurons as therapeutic targets after high cervical injury.

Flexible triboelectric nanogenerator based on polyester conductive cloth for biomechanical energy harvesting and self-powered sensors

As a new nanotechnology of mechanical energy harvesting and self-powered sensing, triboelectric nanogenerators (TENGs) have been explored as a new path of using various low-frequency disordered mechanical energies in the surrounding environment to provide power and/or sensing. However, the research of TENGs that provide full flexibility and environmental friendliness is still limited. Herein, a flexible single-electrode TENG (S-TENG) based on polyester conductive cloth as the working electrode is developed to harvest human motion energy for powering light emitting diodes (LEDs) and portable electronics. The flat conductive cloth was wrapped in a flexible elastomer. Defatted cowhide was firstly selected as a friction positive charge material for TENGs. When the size of the fabricated S-TENG is 40 × 100 mm², high output performance has been achieved and it can generate an open-circuit voltage of 534 V and a power density of 230 mW m^-2 at an operation frequency of 3.0 Hz. After integrating with a rectifier, the S-TENG can power 240 LEDs, charge various capacitors, and drive an electronic watch or a calculator. Moreover, the S-TENG can harvest the biomechanical energy of wrist movement, hand tapping, and human walking. Meanwhile, the S-TENG as a self-powered sensor can be employed to monitor subtle signals of human physiological activities, such as finger motion, facial masseter activity, and diaphragmatic breathing. Additionally, the S-TENG can be attached to clothes (such as wool coats, polyamide sweaters) to harvest the energy of cuff movement. Therefore, this work provides new insights for clean power sources of skin-mounted electronics and promotes the development of a sustainable energy supply for wearable and portable electronics.

Perspectives in the Cell-Based Therapies of Various Aspects of the Spinal Cord Injury-Associated Pathologies: Lessons from the Animal Models

Traumatic injury of the spinal cord (SCI) is a devastating neurological condition often leading to severe dysfunctions, therefore an improvement in clinical treatment for SCI patients is urgently needed. The potential benefits of transplantation of various cell types into the injured spinal cord have been intensively investigated in preclinical SCI models and clinical trials. Despite the many challenges that are still ahead, cell transplantation alone or in combination with other factors, such as artificial matrices, seems to be the most promising perspective. Here, we reviewed recent advances in cell-based experimental strategies supporting or restoring the function of the injured spinal cord with a particular focus on the regenerative mechanisms that could define their clinical translation.

Combination of Drugs and Cell Transplantation: More Beneficial Stem Cell-Based Regenerative Therapies Targeting Neurological Disorders

Cell transplantation therapy using pluripotent/multipotent stem cells has gained attention as a novel therapeutic strategy for treating neurodegenerative diseases, including Parkinson’s disease, Alzheimer’s disease, Huntington’s disease, ischemic stroke, and spinal cord injury. To fully realize the potential of cell transplantation therapy, new therapeutic options that increase cell engraftments must be developed, either through modifications to the grafted cells themselves or through changes in the microenvironment surrounding the grafted region. Together these developments could potentially restore lost neuronal function by better supporting grafted cells. In addition, drug administration can improve the outcome of cell transplantation therapy through better accessibility and delivery to the target region following cell transplantation. Here we introduce examples of drug repurposing approaches for more successful transplantation therapies based on preclinical experiments with clinically approved drugs. Drug repurposing is an advantageous drug development strategy because drugs that have already been clinically approved can be repurposed to treat other diseases faster and at lower cost. Therefore, drug repurposing is a reasonable approach to enhance the outcomes of cell transplantation therapies for neurological diseases. Ideal repurposing candidates would result in more efficient cell transplantation therapies and provide a new and beneficial therapeutic combination.

Plasticity of the Injured Spinal Cord

Complete spinal cord injury (SCI) leads to permanent motor, sensitive and sensory deficits. In humans, there is currently no therapy to promote recovery and the only available treatments include surgical intervention to prevent further damage and symptomatic relief of pain and infections in the acute and chronic phases, respectively. Basically, the spinal cord is classically viewed as a nonregenerative tissue with limited plasticity. Thereby the establishment of the “glial” scar which appears within the SCI is mainly described as a hermetic barrier for axon regeneration. However, recent discoveries have shed new light on the intrinsic functional plasticity and endogenous recovery potential of the spinal cord. In this review, we will address the different aspects that the spinal cord plasticity can take on. Indeed, different experimental paradigms have demonstrated that axonal regrowth can occur even after complete SCI. Moreover, recent articles have demonstrated too that the “glial” scar is in fact composed of several cellular populations and that each of them exerts specific roles after SCI. These recent discoveries underline the underestimation of the plasticity of the spinal cord at cellular and molecular levels. Finally, we will address the modulation of this endogenous spinal cord plasticity and the perspectives of future therapeutic opportunities which can be offered by modulating the injured spinal cord microenvironment.

Exosomes Derived from Nerve Stem Cells Loaded with FTY720 Promote the Recovery after Spinal Cord Injury in Rats by PTEN/AKT Signal Pathway

Background

Spinal cord injury (SCI) remains a challenge owing to limited therapies. The exosome of neural stem cells (NSCs-Exos) and FTY720 transplantation could improve SCI effectively. However, the effect and mechanism of NSCs-Exos combined with FTY720 (FTY720-NSCs-Exos) transplantation in the treatment of SCI are not fully understood.

Methods

Sprague Dawley rats (8-week-old) were used to establish the SCI model, followed by the treatment of NSCs-Exos, FTY720, and FTY720-NSCs-Exos. The effect of FTY720, NSCs-Exos, and FTY720-NSCs-Exos combination treatment on hindlimb function, pathological changes, apoptosis activity, and the expression of spinal edema-related proteins and apoptosis-related proteins in SCI models were investigated by BBB scoring, HE staining, TUNEL staining and immunohistochemistry, and Western blotting. Meanwhile, the effect of these treatments on spinal cord microvascular endothelial cells (SCMECs) was detected under hypoxic circumstance.

Results

Our results found that FTY720-NSCs-Exos could alleviate pathological alterations and ameliorate the hindlimb function and oxygen insufficiency in model mice after SCI. In addition, exosomes could ameliorate the morphology of neurons, reduce inflammatory infiltration and edema, decrease the expression of Bax and AQP-4, upregulate the expression of claudin-5 and Bcl-2, and inhibit cell apoptosis. At the same time, in vitro experiments showed that FTY720-NSCs-Exos could protect the barrier of SCMECs under hypoxic circumstance, and the mechanism is related to PTEN/AKT pathway.

Conclusion

FTY720-NSCs-Exos therapy displayed a positive therapeutic effect on SCI by regulating PTEN/AKT pathway and offered a new therapy for SCI.

Intermittent Hypoxia Induces Greater Functional Breathing Motor Recovery as a Fixed Rather Than Varied Duration Treatment after Cervical Spinal Cord Injury in Rats

Intermittent hypoxia treatment (IH) has been shown to improve respiratory function in both pre-clinical animal models and human subjects following spinal cord injury (SCI), historically consisting of alternating and equal intervals of hypoxic and normoxic exposure. We describe such a procedure as fixed duration IH (FD-IH) and modulation of its severity, intermittency, and post-injury time-point of application differentially affects expression of breathing motor plasticity. As such, the established IH protocol exhibits similarity to instrumental conditioning and can be described as behavioral training through reinforcement. Findings from the field of operant conditioning, a form of more advanced learning, inspire the consideration that FD-IH protocols may be improved through exchanging fixed for varied durations of hypoxia between reinforcement. Thus, we hypothesized that varied duration intermittent hypoxia treatment (VD-IH) would induce greater breathing motor recovery ipsilateral to injury than FD-IH after cervical SCI in rats. To test this hypothesis, we treated animals with VD-IH or FD-IH for 5 days at 1 week and at 8 weeks following cervical SCI, then assessed breathing motor output by diaphragm electromyography (EMG) recording, and compared between groups. At 1 week post-injury, VD-IH-exposed animals trended slightly toward exhibiting greater levels of respiratory recovery in the hemidiaphragm ipsilateral to lesion than did FD-IH-treated animals, but at 8 weeks FD-IH produced significantly greater respiratory motor output than did VD-IH. Thus, these results identify a novel sensitivity of respiratory motor function to variations in the IH protocol that may lead to development of more effective treatments following SCI.

Chondroitinase ABC/galectin-3 fusion proteins with hyaluronan-based hydrogels stabilize enzyme and provide targeted enzyme activity for neural applications

Objective. Chondroitinase ABC (ChABC) has emerged as a promising therapeutic agent for central nervous system regeneration. Despite multiple beneficial outcomes for regeneration, translation of this enzyme is challenged by poor pharmacokinetics, localization, and stability.Approach. This study explored the function andin vitroapplication of engineered ChABC fused to galectin-3 (Gal3). Two previously developed ChABC-Gal3 oligomers (monomeric and trimeric) were evaluated for functionality and kinetics, then applied to anin vitrocellular outgrowth model using dorsal root ganglia (DRGs). The fusions were combined with two formulations of hyaluronan (HA)-based scaffolds to determine the extent of active enzyme release compared to wild type (WT) ChABC.Main Results. Monomeric and trimeric ChABC-Gal3 maintained digestive capabilities with kinetic properties that were substrate-dependent for chondroitin sulfates A, B, and C. The fusions had longer half-lives at 37 °C on the order of seven fold for monomer and twelve fold for trimer compared to WT. Both fusions were also effective at restoring DRG outgrowthin vitro. To create a combination approach, two triple-component hydrogels containing modified HA were formulated to match the mechanical properties of native spinal cord tissue and to support astrocyte viability (>80%) and adhesion. The hydrogels included collagen-I and laminin mixed with either 5 mg ml^-1of glycidyl methacrylate HA or 3 mg ml^-1Hystem. When combined with scaffolds, ChABC-Gal3 release time was lengthened compared to WT. Both fusions had measurable enzymatic activity for at least 10 d when incorporated in gels, compared to WT that lost activity after 1 d. These longer term release products from gels maintained adequate function to promote DRG outgrowth.Significance. Results of this study demonstrated cohesive benefits of two stabilized ChABC-Gal3 oligomers in combination with HA-based scaffolds for neural applications. Significant improvements to ChABC stability and release were achieved, meriting future studies of ChABC-Gal3/hydrogel combinations to target neural regeneration.