Graft of pre-injured sural nerve promotes regeneration of corticospinal tract and functional recovery in rats with chronic spinal cord injury

Respiratory axon regeneration in the chronically injured spinal cord

Promoting the combination of robust regeneration of damaged axons and synaptic reconnection of these growing axon populations with appropriate neuronal targets represents a major therapeutic goal following spinal cord injury (SCI). A key impediment to achieving this important aim includes an intrinsic inability of neurons to extend axons in adult CNS, particularly in the context of the chronically-injured spinal cord. We tested whether an inhibitory peptide directed against phosphatase and tensin homolog (PTEN: a central inhibitor of neuron-intrinsic axon growth potential) could restore inspiratory diaphragm function by reconnecting critical respiratory neural circuitry in a rat model of chronic cervical level 2 (C2) hemisection SCI. We found that systemic delivery of PTEN antagonist peptide 4 (PAP4) starting at 8 weeks after C2 hemisection promoted substantial, long-distance regeneration of injured bulbospinal rostral Ventral Respiratory Group (rVRG) axons into and through the lesion and back toward phrenic motor neurons (PhMNs) located in intact caudal C3-C5 spinal cord. Despite this robust rVRG axon regeneration, PAP4 stimulated only minimal recovery of diaphragm function. Furthermore, re-lesion through the hemisection site completely removed PAP4-induced functional improvement, demonstrating that axon regeneration through the lesion was responsible for this partial functional recovery. Interestingly, there was minimal formation of putative excitatory monosynaptic connections between regrowing rVRG axons and PhMN targets, suggesting that (1) limited rVRG-PhMN synaptic reconnectivity was responsible at least in part for the lack of a significant functional effect, (2) chronically-injured spinal cord presents an obstacle to achieving synaptogenesis between regenerating axons and post-synaptic targets, and (3) addressing this challenge is a potentially-powerful strategy to enhance therapeutic efficacy in the chronic SCI setting. In conclusion, our study demonstrates a non-invasive and transient pharmacological approach in chronic SCI to repair the critically-important neural circuitry controlling diaphragmatic respiratory function, but also sheds light on obstacles to circuit plasticity presented by the chronically-injured spinal cord.

Low‑frequency pulsed electromagnetic field promotes functional recovery, reduces inflammation and oxidative stress, and enhances HSP70 expression following spinal cord injury

Low-frequency pulsed electromagnetic fields (LPEMFs) have been reported to be protective for multiple diseases. However, whether the administration of LPEMFs inhibits inflammation and oxidative stress following spinal cord injury requires further investigation. In the current study, a contusion spinal cord injury model was used and LPEMFs administration was applied to investigate the molecular changes, including inflammation, oxidative stress and heat shock protein 70 (HSP70) levels. The results revealed that LPEMFs significantly promoted functional recovery following spinal cord injury, as demonstrated by an increased Basso, Beattie and Bresnahan score. The results demonstrated that LPEMFs decreased the expression of inflammatory factors, including tumor necrosis factor-α, interleukin-1β and nuclear factor-κB. Additionally, LPEMFs exposure reduced the levels of inducible nitric oxide synthase and reactive oxygen species, and upregulated the expression of catalase and superoxide dismutase. Furthermore, treatment with LPEMFs significantly enhanced the expression of HSP70 in spinal cord-injured rats. Overall, the present study revealed that LPEMFs promote functional recovery following spinal cord injury, potentially by modulating inflammation, oxidative stress and HSP70.

Immunohistochemical assessment of rat nerve isografts and immunosuppressed allografts

OBJECTIVE

Autologous peripheral nerve grafts are commonly used clinically as a treatment for peripheral nerve injuries. However, in research using an autologous graft is not always feasible due to loss of function, which in many cases is assessed to determine the efficacy of the peripheral nerve graft. In addition, using allografts for research require the use of an immunosuppressant, which creates unwanted side effects and another variable within the experiment that can affect regeneration. The objective of this study was to analyze graft rejection in peripheral nerve grafts and the effects of cyclosporine A (CSA) on axonal regeneration.

METHODS

Peripheral nerve grafts in inbred Lewis rats were compared with Sprague-Dawley (SD) rats to assess graft rejection, CSA side effects, immune responses, and regenerative capability. Macrophages and CD8+ cells were labeled to determine graft rejection, and neurofilaments were labeled to determine axonal regeneration.

RESULTS

SD rats without CSA had significantly more macrophages and CD8+ cells compared to Lewis autografts, Lewis isografts, and SD allografts treated with CSA. Lewis autografts, Lewis isografts, and SD autografts had significantly more regenerated axons than SD rat allografts. Moreover, allografts in immunosuppressed SD rats had significantly less axons than Lewis rat autograft and isografts.

DISCUSSION

Autografts have long been the gold standard for treating major nerve injuries and these data suggest that even though CSA is effective at reducing graft rejection, axon regeneration is still superior in autografts versus immunosuppressed allografts.

The Morphofunctional Effect of the Transplantation of Bone Marrow Stromal Cells and Predegenerated Peripheral Nerve in Chronic Paraplegic Rat Model via Spinal Cord Transection

Functional recovery following spinal cord injury (SCI) is limited by poor axonal and cellular regeneration as well as the failure to replace damaged myelin. Employed separately, both the transplantation of the predegenerated peripheral nerve (PPN) and the transplantation of bone marrow stromal cells (BMSCs) have been shown to promote the regrowth and remyelination of the damaged central axons in SCI models of hemisection, transection, and contusion injury. With the aim to test the effects of the combined transplantation of PPN and BMSC on regrowth, remyelination, and locomotor function in an adult rat model of spinal cord (SC) transection, 39 Fischer 344 rats underwent SC transection at T9 level. Four weeks later they were randomly assigned to traumatic spinal cord injury (TSCI) without treatment, TSCI + Fibrin Glue (FG), TSCI + FG + PPN, and TSCI + FG + PPN + BMSCs. Eight weeks after, transplantation was carried out on immunofluorescence and electron microscope studies. The results showed greater axonal regrowth and remyelination in experimental groups TSCI + FG + PPN and TSCI + FG + PPN + BMSCs analyzed with GAP-43, neuritin, and myelin basic protein. It is concluded that the combined treatment of PPN and BMSCs is a favorable strategy for axonal regrowth and remyelination in a chronic SC transection model.

Dissociated predegenerated peripheral nerve transplants for spinal cord injury repair: a comprehensive assessment of their effects on regeneration and functional recovery compared to Schwann cell transplants

Several recent studies suggest that predegenerated nerves (PDNs) or dissociated PDNs (dPDNs) can improve behavioral and histological outcomes following transplantation into the injured rat spinal cord. In the current study we tested the efficacy of dPDN transplantation by grafting cells isolated from the sciatic nerve 7 days after crush. We did not replicate one study, but rather assessed what appeared, based on five published reports, to be a reported robust effect of dPDN grafts on corticospinal tract (CST) regeneration and locomotor recovery. Using a standardized rodent spinal cord injury model (200 kD IH contusion) and transplantation procedure (injection of GFP⁺ cells 7 days post-SCI), we demonstrate that dPDN grafts survive within the injured spinal cord and promote the ingrowth of axons to a similar extent as purified Schwann cell (SC) grafts. We also demonstrate for the first time that while both dPDN and SC grafts promote the ingrowth of CGRP axons, neither graft results in mechanical or thermal hyperalgesia. Unlike previous studies, dPDN grafts did not promote long-distance axonal growth of CST axons, brainstem spinal axons, or ascending dorsal column sensory axons. Moreover, using a battery of locomotor tests (Basso Beattie Bresnahan [BBB] score, BBB subscore, inked footprint, Catwalk, and ladderwalk), we failed to detect any beneficial effects of dPDN transplantation on the recovery of locomotor function after SCI. We conclude that dPDN transplants are not sufficient to promote CST regeneration or locomotor recovery after SCI.

Transplantation of autologous activated Schwann cells in the treatment of spinal cord injury: six cases, more than five years of follow-up

Schwann cells (SCs) are the main glial cells of the peripheral nervous system, which can promote neural regeneration. Grafting of autologous SCs is one of the well-established and commonly performed procedures for peripheral nerve repair. With the aim to improve the clinical condition of patients with spinal cord injury (SCI), a program of grafting autologous activated Schwann cells (AASCs), as well as a series of appropriate neurorehabilitation programs, was employed to achieve the best therapeutic effects. We selected six patients who had a history of SCI before transplantation. At first, AASCs were obtained by prior ligation of sural nerve and subsequently isolated, cultured, and purified in vitro. Then the patients accepted an operation of laminectomy and cell transplantation, and no severe adverse event was observed in any of these patients. Motor and sensitive improvements were evaluated by means of American Spinal Injury Association (ASIA) grading and Functional Independence Measure (FIM); bladder and urethral function were determined by clinical and urodynamic examination; somatosensory evoked potentials (SSEPs) and motor evoked potentials (MEPs) were used to further confirm the functional recovery following transplantation. The patients were followed up for more than 5 years. All of the patients showed some signs of improvement in autonomic, motor, and sensory function. So we concluded that AASC transplantation might be feasible, safe, and effective to promote neurorestoration of SCI patients.

Combination of activated Schwann cells with bone mesenchymal stem cells: the best cell strategy for repair after spinal cord injury in rats

AIM

We aim to explore the repair effect of combined cell therapy using activated Schwann cells (ASCs) and bone mesenchymal stem cells (BMSCs) in traumatic spinal cord injury (SCI) in rats.

MATERIALS & METHODS

ASCs and BMSCs were used for combined transplantation to treat acute SCI in rats, both of which can be obtained from SCI patients. ASCs were obtained by prior ligation of saphenous nerve and BMSCs by flush of the marrow cavity with Dulbecco's modified Eagle's medium solution. Our experiment in vitro confirmed that ASCs promoted BMSCs to differentiate into mature neural cells. It also indicates that BMSCs hold the potential to repair CNS injury. ASCs and BMSCs were co-transplanted into the injured epicenter of spinal cord made by the New York University (NYU) impactor machine using a 10 g × 50 mm drop weight. Complete ASCs, BMSCs and Dulbecco's modified Eagle's medium were also transplanted in rats with SCI as a control. Recovery of rat's hindlimb function was serially evaluated by Basso, Beattie, Bresnahan locomotor rating scale and footprint analysis. Changes of neurological potential were recorded by nerve electrophysiologic test. Improvement in the microenvironment of the injured spinal cord was evaluated by hematoxylin and eosin staining, glial fibrillary acidic protein staining, biotinylated dextran amine anterograde tracing and electron microscopy.

RESULTS

Using biotinylated dextran amine anterograde tracing, we demonstrated that there were more regenerative axons of corticospinal tract surrounding and passing through the injured cavity to the caudal cord in the ASC-BMSC co-graft group than those in the other three groups, and we also confirmed this further by quantitative analysis. Immunostaining for glial fibrillary acidic protein showed the smallest population of astrocytes in the injury epicenter in the ASC-BMSC group compared with the other three groups. Relatively complete myelin sheaths and organelles were found in the ASC-BMSC group compared with the other three groups under electron microscopy.

CONCLUSION

Effective co-transplantation of ASCs and BMSCs promotes functional recovery in rats' hindlimbs and reduces the formation of glial scar, and remyelinates the injured axons as compared with the other three groups. This conclusion was also supported by the observation of immunohistochemistry staining and electron microscopy, suggesting the possible clinical application for the treatment of spinal injury.

Chondroitinase combined with rehabilitation promotes recovery of forelimb function in rats with chronic spinal cord injury

Chondroitinase ABC (ChABC) in combination with rehabilitation has been shown to promote functional recovery in acute spinal cord injury. For clinical use, the optimal treatment window is concurrent with the beginning of rehabilitation, usually 2-4 weeks after injury. We show that ChABC is effective when given 4 weeks after injury combined with rehabilitation. After C4 dorsal spinal cord injury, rats received no treatment for 4 weeks. They then received either ChABC or penicillinase control treatment followed by hour-long daily rehabilitation specific for skilled paw reaching. Animals that received both ChABC and task-specific rehabilitation showed the greatest recovery in skilled paw reaching, approaching similar levels to animals that were treated at the time of injury. There was also a modest increase in skilled paw reaching ability in animals receiving task-specific rehabilitation alone. Animals treated with ChABC and task-specific rehabilitation also showed improvement in ladder and beam walking. ChABC increased sprouting of the corticospinal tract, and these sprouts had more vGlut1(+ve) presynaptic boutons than controls. Animals that received rehabilitation showed an increase in perineuronal net number and staining intensity. Our results indicate that ChABC treatment opens a window of opportunity in chronic spinal cord lesions, allowing rehabilitation to improve functional recovery.

Macrophage presence is essential for the regeneration of ascending afferent fibres following a conditioning sciatic nerve lesion in adult rats

BACKGROUND

Injury to the peripheral branch of dorsal root ganglia (DRG) neurons prior to injury to the central nervous system (CNS) DRG branch results in the regeneration of the central branch. The exact mechanism mediating this regenerative trigger is not fully understood. It has been proposed that following peripheral injury, the intraganglionic inflammatory response by macrophage cells plays an important role in the pre-conditioning of injured CNS neurons to regenerate. In this study, we investigated whether the presence of macrophage cells is crucial for this type of regeneration to occur. We used a clodronate liposome technique to selectively and temporarily deplete these cells during the conditioning phase of DRG neurons.

RESULTS

Retrograde and anterograde tracing results indicated that in macrophage-depleted animals, the regenerative trigger characteristic of pre-conditioned DRG neurons was abolished as compared to injury matched-control animals. In addition, depletion of macrophage cells led to: (i) a reduction in macrophage infiltration into the CNS compartment even after cellular repopulation, (ii) astrocyte up-regulation at rostral regions and down-regulation in brain derived neurotrophic factor (BDNF) concentration in the serum.

CONCLUSION

Activation of macrophage cells in response to the peripheral nerve injury is essential for the enhanced regeneration of ascending sensory neurons.

ProBDNF inhibits infiltration of ED1+ macrophages after spinal cord injury

The central nervous system (CNS) does not regenerate partly due to the slow clearance of debris from the degenerated myelin sheath by Wallerian degeneration. The mechanism underlying the inefficiency in myelin clearance is not clear. Here we showed that endogenous proBDNF may inhibit the infiltration of ED1+ inflammatory cells after spinal cord injury. After injury, proBDNF and its receptors sortilin and p75NTR are expressed in the spinal cord as determined by Western blots and immunocytochemistry. ProBDNF and mature BDNF were released from macrophages in vitro. Macrophages in vivo (ED1+) and isolated in vitro (CD11b+) express moderate levels of proBDNF, sortilin and p75NTR. ProBDNF suppressed the migration of isolated macrophages in vitro and the antibody to proBDNF enhanced the migration. Suppression of proBDNF in vivo by administering the antiserum to the prodomain of BDNF after spinal cord injury (SCI) increased the infiltration of macrophages and increased number of neurons in the injured cord. BBB tests showed that the treatment of the antibody to proBDNF improved the functional recovery after spinal cord injury. Our data suggest that proBDNF is a suppressing factor for macrophage migration and infiltration and may play a detrimental role after SCI.

Strategies to restore motor functions after spinal cord injury

This review presents recent advances in the development of strategies to restore posture and locomotion after spinal cord injury (SCI). A set of strategies focusing on the lesion site includes prevention of secondary damages, promotion of axonal sprouting/regeneration, and replacement of lost cells. Other strategies focus on spinal central pattern generators (CPGs). Training promotes functional recovery by enhancing the plasticity of CPGs and these sublesional networks can be reactivated by means of pharmacological or electrical stimulation. It is now clear that substantial functional recovery will require a combination of strategies adapted to each phase following SCI. Finally, improvements in the understanding of the mechanisms underlying spasticity may lead to new treatments of this disabling complication affecting patients with SCI.

Intraspinal cord graft of autologous activated Schwann cells efficiently promotes axonal regeneration and functional recovery after rat's spinal cord injury

Basic research in spinal cord injury (SCI) has made great strides in recent years, and some new insights and strategies have been applied in promoting effective axonal regrowth and sprouting. However, a relatively safe and efficient transplantation technique remains undetermined. This study, therefore, was aimed to address a question of how to graft Schwann cells to achieve the best possible therapeutic effects. To clarify the issue, the rats were subjected to spinal cord injury at T10. Autologous activated Schwann cells (AASCs) were obtained by prior ligation of saphenous nerve and subsequently isolated and purified in vitro and then grafted into spinal cord-injured rats via three different routes (group I: intravenous, group II: intrathecal and group III: intraspinal cord). Neurologic function was serially evaluated by Basso, Beattie, Bresnahan locomotor rating scale and footprint analysis. We also evaluated the migration of the transplanted cells at 2 weeks after transplantation. Using biotinylated dextran amine (BDA) anterograde tracing, we demonstrated that more regenerative axons of corticospinal tract (CST) surrounding the injured cavity in group III than those in the other two groups, and we also confirmed it further by quantitative analysis. The microenvironment surrounding the injured spinal cord has been improved to the greatest extent in group III, as determined by immunohistological staining. Relatively complete myelin sheaths and more neurofilaments in axons were found in groups II and III than those in group I under electron microscopy. The results showed that intraspinal cord injection of AASCs promoted recovery of hindlimb locomotor function of injured rats more efficiently than the other grafting routes. In addition, intact myelin sheaths and sufficient neurofilaments in axons were not adequate for full functional recovery after SCI, suggesting that reestablishment of normal synaptic connection is indispensable. The findings in this study strongly suggest that transplantation of AASCs directly into the spinal cord may be one of the promising candidates for potential scaffold for injured spinal cord, and such strategy of transplantation of AASCs could be hopeful to treat patients with SCI.