Timing and duration of anti-alpha4beta1 integrin treatment after spinal cord injury: effect on therapeutic efficacy

Single cell profiling of CD45+ spinal cord cells reveals microglial and B cell heterogeneity and crosstalk following spinal cord injury

Background

Immune cells play crucial roles after spinal cord injury (SCI). However, incomplete knowledge of immune contributions to injury and repair hinders development of SCI therapies. We leveraged single-cell observations to describe key populations of immune cells present in the spinal cord and changes in their transcriptional profiles from uninjured to subacute and chronic stages of SCI.

Methods

Deep-read single-cell sequencing was performed on CD45+ cells from spinal cords of uninjured and injured Swiss-webster mice. After T9 thoracic contusion, cells were collected 3-, 7-, and 60-day post-injury (dpi). Subpopulations of CD45+ immune cells were identified informatically, and their transcriptional responses characterized with time. We compared gene expression in spinal cord microglia and B cell subpopulations with those in published models of disease and injury. Microglia were compared with Disease Associated Microglia (DAM) and Injury Responsive Microglia (IRM). B cells were compared to developmental lineage states and to an Amyotrophic Lateral Sclerosis (ALS) model.

Results

In uninjured and 7 dpi spinal cord, most CD45+ cells isolated were microglia while chronically B cells predominated. B cells accumulating in the spinal cord following injury included immature B to mature stages and were predominantly found in the injury zone. We defined diverse subtypes of microglia and B cells with altered gene expression with time after SCI. Spinal cord microglia gene expression indicates differences from brain microglia at rest and in inflammatory states. Expression analysis of signaling ligand–receptor partners identified microglia–B cell interactions at acute and chronic stages that may be involved in B cell recruitment, retention, and formation of ectopic lymphoid follicles.

Conclusions

Immune cell responses to SCI have region-specific aspects and evolve with time. Developmentally diverse populations of B cells accumulate in the spinal cord following injury. Microglia at subacute stages express B cell recruitment factors, while chronically, they express factors predicted to reduce B cell inflammatory state. In the injured spinal cord, B cells create ectopic lymphoid structures, and express secreted factors potentially acting on microglia. Our study predicts previously unidentified crosstalk between microglia and B cells post-injury at acute and chronic stages, revealing new potential targets of inflammatory responses for SCI repair warranting future functional analyses.

The emerging role of mechanical and topographical factors in the development and treatment of nervous system disorders: dark and light sides of the force

Nervous system diseases are the subject of intensive research due to their association with high mortality rates and their potential to cause irreversible disability. Most studies focus on targeting the biological factors related to disease pathogenesis, e.g. use of recombinant activator of plasminogen in the treatment of stroke. Nevertheless, multiple diseases such as Parkinson’s disease and Alzheimer’s disease still lack successful treatment. Recently, evidence has indicated that physical factors such as the mechanical properties of cells and tissue and topography play a crucial role in homeostasis as well as disease progression. This review aims to depict these factors’ roles in the progression of nervous system diseases and consequently discusses the possibility of new therapeutic approaches. The literature is reviewed to provide a deeper understanding of the roles played by physical factors in nervous system disease development to aid in the design of promising new treatment approaches.

Intranasal Delivery of Mesenchymal Stem Cell Derived Exosomes Loaded with Phosphatase and Tensin Homolog siRNA Repairs Complete Spinal Cord Injury

Individuals with spinal cord injury (SCI) usually suffer from permanent neurological deficits, while spontaneous recovery and therapeutic efficacy are limited. Here, we demonstrate that when given intranasally, exosomes derived from mesenchymal stem cells (MSC-Exo) could pass the blood brain barrier and migrate to the injured spinal cord area. Furthermore, MSC-Exo loaded with phosphatase and tensin homolog small interfering RNA (ExoPTEN) could attenuate the expression of PTEN in the injured spinal cord region following intranasal administrations. In addition, the loaded MSC-Exo considerably enhanced axonal growth and neovascularization, while reducing microgliosis and astrogliosis. The intranasal ExoPTEN therapy could also partly improve structural and electrophysiological function and, most importantly, significantly elicited functional recovery in rats with complete SCI. The results imply that intranasal ExoPTEN may be used clinically to promote recovery for SCI individuals.

Potential immunotherapies for traumatic brain and spinal cord injury

Traumatic injury of the central nervous system (CNS) including brain and spinal cord remains a leading cause of morbidity and disability in the world. Delineating the mechanisms underlying the secondary and persistent injury versus the primary and transient injury has been drawing extensive attention for study during the past few decades. The sterile neuroinflammation during the secondary phase of injury has been frequently identified substrate underlying CNS injury, but as of now, no conclusive studies have determined whether this is a beneficial or detrimental role in the context of repair. Recent pioneering studies have demonstrated the key roles for the innate and adaptive immune responses in regulating sterile neuroinflammation and CNS repair. Some promising immunotherapeutic strategies have been recently developed for the treatment of CNS injury. This review updates the recent progress on elucidating the roles of the innate and adaptive immune responses in the context of CNS injury, the development and characterization of potential immunotherapeutics, as well as outstanding questions in this field.

Are the emergence of affective disturbances in neuropathic pain states contingent on supraspinal neuroinflammation?

Neuro-immune interactions contribute to the pathogenesis of neuropathic pain due to peripheral nerve injury. A large body of preclinical evidence supports the idea that the immune system acts to modulate the sensory symptoms of neuropathy at both peripheral and central nervous system sites. The potential involvement of neuro-immune interactions in the highly debilitating affective disturbances of neuropathic pain, such as depression, anhedonia, impaired cognition and reduced motivation has received little attention. This is surprising given the widely accepted view that sickness behaviour, depression, cognitive impairment and other neuropsychiatric conditions can arise from inflammatory mechanisms. Moreover, there is a set of well-described immune-to-brain transmission mechanisms that explain how peripheral inflammation can lead to supraspinal neuroinflammation. In the last 5years increasing evidence has emerged that peripheral nerve injury induces supraspinal changes in cytokine or chemokine expression and alters glial cell activity. In this systematic review, based on strong preclinical evidence, we advance the argument that the emergence of affective disturbances in neuropathic pain states are contingent on pro-inflammatory mediators in the interconnected hippocampal-medial prefrontal circuitry that subserve affective behaviours. We explore how dysregulation of inflammatory mediators in these networks may result in affective disturbances through a wide variety of neuromodulatory mechanisms. There are also promising results from clinical trials showing that anti-inflammatory agents have efficacy in the treatment of a variety of neuropsychiatric conditions including depression and appear suited to sub-groups of patients with elevated pro-inflammatory profiles. Thus, although further research is required, aggressively targeting supraspinal pro-inflammatory mediators at critical time-points in appropriate clinical populations is likely to be a novel avenue to treat debilitating affective disturbances in neuropathic conditions.

Current therapeutic strategies for inflammation following traumatic spinal cord injury

Damage from spinal cord injury occurs in two phases – the trauma of the initial mechanical insult and a secondary injury to nervous tissue spared by the primary insult. Apart from damage sustained as a result of direct trauma to the spinal cord, the post-traumatic inflammatory response contributes significantly to functional motor deficits exacerbated by the secondary injury. Attenuating the detrimental aspects of the inflammatory response is a promising strategy to potentially ameliorate the secondary injury, and promote significant functional recovery. This review details how the inflammatory component of secondary injury to the spinal cord can be treated currently and in the foreseeable future.

Acupuncture for treatment of secondary osteoporosis in patients with spinal cord injury: a controlled study

OBJECTIVE

We explored the effect of adjunctive acupuncture on secondary osteoporosis in patients with spinal cord injury (SCI).

METHODS

Patients with subacute SCI were recruited and divided into two groups by patient choice: group 1 patients received standard combination therapy and group 2 patients received combination therapy plus acupuncture for 3 months. The concentrations of IgG, IgM and tumour necrosis factor α (TNFα) in serum and the bone mineral density were measured before and after treatment.

RESULT

The decrease in the concentration of TNFα and IgM in patients in group 2 compared with those in group 1 was statistically significant. The IgG level showed no significant change in either group. Bone mineral density increased more after adjunctive acupuncture, but the difference was not significant.

CONCLUSIONS

Further research is needed to determine whether acupuncture as an adjunct to combination therapy can reduce osteoporosis in patients with subacute SCI.

TRIAL REGISTRATION NUMBER

P153-2008-36.

Dehydration affects spinal cord cross-sectional area measurement on MRI in healthy subjects

STUDY DESIGN

This was a prospective cohort observational study.

OBJECTIVE

To determine the effect of dehydration and rehydration on spinal cord cross-sectional area (CSA) measurement on magnetic resonance imaging (MRI).

SETTING

MRI Research Centre, University of British Columbia, Canada.

METHODS

Ten healthy subjects (aged 21-32 years) were scanned on a 3T MRI scanner at four time points: (1) baseline, (2) rescan after 1 h, (3) the next day after fasting for a minimum of 14 h and (4) after rehydration with 1.5 l of water over the course of 1 h. Two independent, established semi-automatic CSA measurement techniques (one based on two-dimensional (2D) edge detection, the other on three-dimensional (3D) surface fitting) were applied to a 3D T1-weighted scan of each subject at each time point, with the operator blinded to scan order. The percentage change in CSA from baseline to each subsequent time point was calculated. One-tailed paired t-tests were used to assess the significance of the changes from baseline.

RESULTS

A decrease in CSA following dehydration was detected by both measurement methods, with a mean change of -0.654% (s.d.=0.778, P<0.05) and -0.650% (s.d.=1.071, P<0.05) for the first and second methods, respectively.

CONCLUSION

Dehydration can confound CSA measurements on MRI. The magnitude of the effect is significant relative to short-term pathological changes that have been observed in diseases such as multiple sclerosis.

Inflammatory monocytes and the pathogenesis of viral encephalitis

Monocytes are a heterogeneous population of bone marrow-derived cells that are recruited to sites of infection and inflammation in many models of human diseases, including those of the central nervous system (CNS). Ly6C^hi/CCR2^hi inflammatory monocytes have been identified as the circulating precursors of brain macrophages, dendritic cells and arguably microglia in experimental autoimmune encephalomyelitis; Alzheimer’s disease; stroke; and more recently in CNS infection caused by Herpes simplex virus, murine hepatitis virus, Theiler’s murine encephalomyelitis virus, Japanese encephalitis virus and West Nile virus. The precise differentiation pathways and functions of inflammatory monocyte-derived populations in the inflamed CNS remains a contentious issue, especially in regard to the existence of monocyte-derived microglia. Furthermore, the contributions of monocyte-derived subsets to viral clearance and immunopathology are not well-defined. Thus, understanding the pathways through which inflammatory monocytes migrate to the brain and their functional capacity within the CNS is critical to inform future therapeutic strategies. This review discusses some of the key aspects of inflammatory monocyte trafficking to the brain and addresses the role of these cells in viral encephalitis.

The role of the immune system in the generation of neuropathic pain

Persistent pain is a sequela of several neurological conditions with a primary immune basis, such as Guillain-Barré syndrome and multiple sclerosis. Additionally, diverse forms of injury to the peripheral or the central nervous systems--whether traumatic, metabolic, or toxic--result in substantial recruitment and activation of immune cells. This response involves the innate immune system, but evidence also exists of T-lymphocyte recruitment, and in some patient cohorts antibodies to neuronal antigens have been reported. Mediators released by immune cells, such as cytokines, sensitise nociceptive signalling in the peripheral and central nervous systems. Preclinical data suggest an immune pathogenesis of neuropathic pain, but clinical evidence of a central role of the immune system is less clear. An important challenge for the future is to establish to what extent this immune response initiates or maintains neuropathic pain in patients and thus whether it is amenable to therapy.

Nerve transfers for the restoration of hand function after spinal cord injury

Spinal cord injury (SCI) remains a significant public health problem. Despite advances in understanding of the pathophysiological processes of acute and chronic SCI, corresponding advances in translational applications have lagged behind. Nerve transfers using an expendable nearby motor nerve to reinnervate a denervated nerve have resulted in more rapid and improved functional recovery than traditional nerve graft reconstructions following a peripheral nerve injury. The authors present a single case of restoration of some hand function following a complete cervical SCI utilizing nerve transfers.

Achieving CNS axon regeneration by manipulating convergent neuro-immune signaling

After central nervous system (CNS) trauma, axons have a low capacity for regeneration. Regeneration failure is associated with a muted regenerative response of the neuron itself, combined with a growth-inhibitory and cytotoxic post-injury environment. After spinal cord injury (SCI), resident and infiltrating immune cells (especially microglia/macrophages) contribute significantly to the growth-refractory milieu near the lesion. By targeting both the regenerative potential of the axon and the cytotoxic phenotype of microglia/macrophages, we may be able to improve CNS repair after SCI. In this review, we discuss molecules shown to impact CNS repair by affecting both immune cells and neurons. Specifically, we provide examples of pattern recognition receptors, integrins, cytokines/chemokines, nuclear receptors and galectins that could improve CNS repair. In many cases, signaling by these molecules is complex and may have contradictory effects on recovery depending on the cell types involved or the model studied. Despite this caveat, deciphering convergent signaling pathways on immune cells (which affect axon growth indirectly) and neurons (direct effects on axon growth) could improve repair and recovery after SCI. Future studies must continue to consider how regenerative therapies targeting neurons impact other cells in the pathological CNS. By identifying molecules that simultaneously improve axon regenerative capacity and drive the protective, growth-promoting phenotype of immune cells, we may discover SCI therapies that act synergistically to improve CNS repair and functional recovery.

Delayed intrathecal delivery of RhoA siRNA to the contused spinal cord inhibits allodynia, preserves white matter, and increases serotonergic fiber growth

RhoA is a key regulator of the actin cytoskeleton that is upregulated after spinal cord injury (SCI). We analyzed different methods for siRNA delivery and developed siRNAs targeting RhoA (siRhoA) for SCI treatment. Cy 3.5-labeled siRNA delivered at the time of SCI yielded fluorescence in several cell types in the injury site. Intraspinal injections of chemically stabilized siRhoA into the spinal cord of injured rats reduced RhoA protein levels after 1 week and improved hindlimb walking over 6 weeks. To explore a less invasive route, we tested intrathecal injection of Cy 3.5-labeled siRNA via lumbar puncture 1 day after SCI, which resulted in robust uptake in the T9-T10 injury site. Lumbar injection of siRhoA 1 day after SCI reduced RhoA mRNA and protein levels 3 days after injection. Although siRhoA treatment did not yield significant improvement in locomotion, it decreased tactile hypersensitivity significantly compared to controls. Histological analysis at 8 weeks showed significant improvement in white matter sparing with siRhoA compared to control siRNA. siRhoA treatment also resulted in less accumulation of ED1+macrophages, increased PKC-γ immunoreactivity in the corticospinal tract rostral to the injury site, and increased serotonergic fiber growth 12 mm caudal to the contusion site. The ability of siRhoA to preserve white matter and promote serotonergic axonal regrowth caudal to the injury site is likely to suppress allodynia. This provides justification for considering clinical development of RhoA inhibitors to treat SCI sub-acutely to reduce allodynia, which occurs frequently in SCI patients.

The systemic inflammatory response after spinal cord injury in the rat is decreased by α4β1 integrin blockade

Abstract The systemic inflammatory response syndrome (SIRS) follows spinal cord injury (SCI) and causes damage to the lungs, kidney, and liver due to an influx of inflammatory cells from the circulation. After SCI in rats, the SIRS develops within 12 h and is sustained for at least 3 days. We have previously shown that blockade of CD11d/CD18 integrin reduces inflammation-driven secondary damage to the spinal cord. This treatment reduces the SIRS after SCI. In another study we found that blockade of α4β1 integrin limited secondary cord damage more effectively than blockade of CD11d/CD18. Therefore we considered it important to assess the effects of anti-α4β1 treatment on the SIRS in the lung, kidney, and liver after SCI. An anti-α4 antibody was given IV at 2 h after SCI at the fourth thoracic segment and the effects on the organs were evaluated at 24 h post-injury. The migration of neutrophils into the lungs and liver was markedly reduced and all three organs contained fewer macrophages. In the lungs and liver, the activation of the oxidative enzymes myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS), cyclooxygenase-2 (COX-2), and gp91(phox), the production of free radicals, lipid peroxidation, and cell death were substantially and similarly reduced. Treatment effects were less robust in the kidney. Overall, the efficacy of the anti-α4β1 treatment did not differ greatly from that of the anti-CD11d antibody, although details of the results differed. The SIRS after SCI impedes recovery, and attenuation of the SIRS with an anti-integrin treatment is an important, clinically-relevant finding.

The challenges of long-distance axon regeneration in the injured CNS

Injury to the central nervous system (CNS) that results in long-tract axonal damage typically leads to permanent functional deficits in areas innervated at, and below, the level of the lesion. The initial ischemia, inflammation, and neurodegeneration are followed by a progressive generation of scar tissue, dieback of transected axons, and demyelination, creating an area inhibitory to regrowth and recovery. Two ways to combat this inhibition is to therapeutically target the extrinsic and intrinsic properties of the axon-scar environment. Scar tissue within and surrounding the lesion site can be broken down using an enzyme known as chondroitinase. Negative regulators of adult neuronal growth, such as Nogo, can be neutralized with antibodies. Both therapies greatly improve functional recovery in animal models. Alternatively, modifying the intrinsic growth properties of CNS neurons through gene therapy or pharmacotherapy has also shown promising axonal regeneration after injury. Despite these promising therapies, the main challenge of long-distance axon regeneration still remains; achieving a level of functional and organized connectivity below the level of the lesion that mimics the intact CNS.

Emerging concepts in myeloid cell biology after spinal cord injury

Traumatic spinal cord injury (SCI) affects the activation, migration, and function of microglia, neutrophils and monocyte/macrophages. Because these myeloid cells can positively and negatively affect survival of neurons and glia, they are among the most commonly studied immune cells. However, the mechanisms that regulate myeloid cell activation and recruitment after SCI have not been adequately defined. In general, the dynamics and composition of myeloid cell recruitment to the injured spinal cord are consistent between mammalian species; only the onset, duration, and magnitude of the response vary. Emerging data, mostly from rat and mouse SCI models, indicate that resident and recruited myeloid cells are derived from multiple sources, including the yolk sac during development and the bone marrow and spleen in adulthood. After SCI, a complex array of chemokines and cytokines regulate myelopoiesis and intraspinal trafficking of myeloid cells. As these cells accumulate in the injured spinal cord, the collective actions of diverse cues in the lesion environment help to create an inflammatory response marked by tremendous phenotypic and functional heterogeneity. Indeed, it is difficult to attribute specific reparative or injurious functions to one or more myeloid cells because of convergence of cell function and difficulties in using specific molecular markers to distinguish between subsets of myeloid cell populations. Here we review each of these concepts and include a discussion of future challenges that will need to be overcome to develop newer and improved immune modulatory therapies for the injured brain or spinal cord.

Anti-CD11d monoclonal antibody treatment for rat spinal cord compression injury

This study was initiated due to an NIH "Facilities of Research-Spinal Cord Injury" contract to support independent replication of published studies. Transient blockage of the CD11d/CD18 integrin has been reported to reduce secondary neuronal damage as well as to improve functional recovery after spinal cord injury (SCI) in rats. The purpose of this study was to determine whether treatment with an anti-CD11d monoclonal antibody (mAb) would improve motor performance, reduce pain and histopathological damage in animals following clip-compression injury as reported. Adult male Wistar rats (250g) were anesthetized with isoflurane, and the T12 spinal cord exposed by T10 and T11 dorsal laminectomies followed by a 60s period of clip compression utilizing a 35g clip. Control animals received an isotype-matched irrelevant antibody (1B7) while the treated group received the anti-CD11d mAb (217L; 1.0mg/kg) systemically. Open-field locomotion and sensory function were assessed and animals were perfusion-fixed at twelve weeks after injury for quantitative histopathological analysis. As compared to 1B7, 217L treated animals showed an overall non-significant trend to better motor recovery. All animals showed chronic mechanical allodynia and anti-CD11d mAb treatment did not significantly prevent its development. Histopathological analysis demonstrated severe injury to gray and white matter after compression with a non-significant trend in anti-CD11d protection compared to control animals for preserved myelin. Although positive effects with the anti-CD11d mAb treatment have been reported after compressive SCI, it is suggested that this potential treatment requires further investigation before clinical trials in spinal cord injured patients are implemented.

The timing of surgical decompression for spinal cord injury

Research into the pathophysiological mechanisms of spinal cord injury (SCI) has resulted in a classification scheme of primary and secondary injury. Primary injury refers to the destructive nature of the initial impact and the subsequent shearing, penetrating, and compressive forces that injure the delicate neural tissue. Secondary injury refers to a complex array of pathophysiologial processes – including ischemia, inflammation, excitotoxicity, and oxidative cell damage – that contribute to the ultimate loss of neural tissue. While our understanding of secondary mechanisms improves with continued research, novel treatments for SCI are currently being developed with a foundation rooted in halting deleterious secondary mechanisms. In this article, we will review the current evidence for surgical decompression as a treatment for SCI. Emerging evidence and a growing consensus among surgeons are in support of early surgical intervention to help minimize the secondary damage caused by compression of the spinal cord after trauma.