The corticospinal tract (CST) is a major descending pathway contributing to the control of voluntary movement in mammals. During the last decades anatomical and electrophysiological studies have ...demonstrated significant reorganization in the CST after spinal cord injury (SCI) in animals and humans. In animal models of SCI, anatomical evidence showed corticospinal sprouts rostral and caudal to the lesion and their integration into intraspinal axonal circuits. Electrophysiological data suggested that indirect connections from the primary motor cortex to forelimb motoneurons, via brainstem nuclei and spinal cord interneurons, or direct connections from slow uninjured corticospinal axons, might contribute to the control of movement after a CST injury. In humans with SCI, post mortem spinal cord tissue revealed anatomical changes in the CST some of which were similar but others markedly different from those found in animal models of SCI. Human electrophysiological studies have provided ample evidence for corticospinal reorganization after SCI that may contribute to functional recovery. Together these studies have revealed a large plastic capacity of the CST after SCI. There is also a limited understanding of the relationship between anatomical and electrophysiological changes in the CST and control of movement after SCI. Increasing our knowledge of the role of CST plasticity in functional restoration after SCI may support the development of more effective repair strategies.
Spinal cord injury (SCI) causes immediate damage to the nervous tissue accompanied by loss of motor and sensory function. The limited self-repair competence of injured nervous tissue underscores the ...need for reparative interventions to recover function after SCI. The vasculature of the spinal cord plays a crucial role in SCI and repair. Ruptured and sheared blood vessels in the injury epicenter and blood vessels with a breached blood-spinal cord barrier (BSCB) in the surrounding tissue cause bleeding and inflammation, which contribute to the overall tissue damage. The insufficient formation of new functional vasculature in and near the injury impedes endogenous tissue repair and limits the prospect of repair approaches. Limiting the loss of blood vessels, stabilizing the BSCB, and promoting the formation of new blood vessels are therapeutic targets for spinal cord repair. Inflammation is an integral part of injury-mediated vascular damage, which has deleterious and reparative consequences. Inflammation and the formation of new blood vessels are intricately interwoven. Biomaterials can be effectively used for promoting and guiding blood vessel formation or modulating the inflammatory response after SCI, thereby governing the extent of damage and the success of reparative interventions. This review deals with the vasculature after SCI, the reciprocal interactions between inflammation and blood vessel formation, and the potential of biomaterials to support revascularization and immunomodulation in damaged spinal cord nervous tissue.
The ability of intraspinal bone marrow stromal cell (BMSC) transplants to elicit repair is thought to result from paracrine effects by secreted trophic factors including brain-derived neurotrophic ...factor (BDNF). Here we used gene therapy to increase or silence BDNF production in BMSCs to investigate the role of BDNF in BMSC-mediated neuroprotection. In a spinal cord organotypic culture, BMSC-conditioned medium significantly enhanced spinal motoneuron survival by 64% compared with culture medium only. Only conditioned medium of BDNF-hypersecreting BMSCs sustained this neuroprotective effect. In a rat model of spinal cord contusion, a BDNF-dependent neuroprotective effect was confirmed; only with a subacute transplant of BDNF-hypersecreting BMSCs were significantly more spared motoneurons found at 4 weeks postinjury compared with vehicle controls. Spared nervous tissue volume was improved by 68% with both control BMSCs and BDNF-hypersecreting BMSCs. In addition, blood vessel density in the contusion with BDNF-hypersecreting BMSCs was 35% higher compared with BMSC controls and sixfold higher compared with vehicle controls. BDNF-silenced BMSCs did not survive the first week of transplantation, and no neuroprotective effect was found at 4 weeks after transplantation. Together, our data broaden our understanding of the role of BDNF in BMSC-mediated neuroprotection and successfully exploit BDNF dependency to enhance anatomical spinal cord repair.
Pre-clinical and clinical studies revealed that mesenchymal stromal cell (MSC) transplants elicit tissue repair. Conditioning MSC prior to transplantation may boost their ability to support repair. ...We investigated macrophage-derived inflammation as a means to condition MSC by comprehensively analyzing their transcriptome and secretome. Conditioning MSC with macrophage-derived inflammation resulted in 3208 differentially expressed genes, which were annotated with significantly enriched GO terms for 1085 biological processes, 85 cellular components, and 79 molecular functions. Inflammation-mediated conditioning increased the secretion of growth factors that are key for tissue repair, including vascular endothelial growth factor, hepatocyte growth factor, nerve growth factor and glial-derived neurotrophic factor. Furthermore, we found that inflammation-mediated conditioning induces transcriptomic changes that challenge the viability and mobility of MSC. Our data support the notion that macrophage-derived inflammation stimulates MSC to augment their paracrine repair-supporting activity. The results suggest that inflammatory pre-conditioning enhances the therapeutic potential of MSC transplants.
The Schwann cell is one of the most widely studied cell types for repair of the spinal cord. These cells play a crucial role in endogenous repair of peripheral nerves due to their ability to ...dedifferentiate, migrate, proliferate, express growth promoting factors, and myelinate regenerating axons. Following trauma to the spinal cord, Schwann cells migrate from the periphery into the injury site, where they apparently participate in endogenous repair processes. For transplantation into the spinal cord, large numbers of Schwann cells are necessary to fill injury-induced cystic cavities. Several culture systems have been developed that provide large, highly purified populations of Schwann cells. Importantly, the development of in vitro systems to harvest human Schwann cells presents a unique opportunity for autologous transplantation in the clinic. In animal models of spinal cord injury (SCI), grafting Schwann cells or peripheral nerve into the lesion site has been shown to promote axonal regeneration and myelination. However, axons do not regenerate beyond the transplant due to the inhibitory nature of the glial scar surrounding the injury. To overcome the glial scar inhibition, additional approaches such as increasing the intrinsic capacity of axons to regenerate and/or removal of the inhibitory molecules associated with reactive astrocytes and/or oligodendrocyte myelin should be incorporated. Clearly, Schwann cells have great potential for repair of the injured spinal cord, but they need to be combined with other interventions to maximize axonal regeneration and functional recovery.
Spinal cord injury causes immediate damage of nervous tissue accompanied by the loss of motor and sensory function. The limited self-repair ability of damaged nervous tissue underlies the need for ...reparative interventions to restore function after spinal cord injury. Blood vessels play a crucial role in spinal cord injury and repair. Injury-induced loss of local blood vessels and a compromised blood–brain barrier contribute to inflammation and ischemia and thus to the overall damage to the nervous tissue of the spinal cord. Lack of vasculature and leaking blood vessels impede endogenous tissue repair and limit prospective repair approaches. A reduction of blood vessel loss and the restoration of blood vessels so that they no longer leak might support recovery from spinal cord injury. The promotion of new blood vessel formation (i.e., angio- and vasculogenesis) might aid repair but also incorporates the danger of exacerbating tissue loss and thus functional impairment. The delicate interplay between cells and molecules that govern blood vessel repair and formation determines the extent of damage and the success of reparative interventions. This review deals with the cellular and molecular mechanisms underlying the role of blood vessels in spinal cord injury and repair.
Regenerated cerebrospinal axons are considered to be involved in the spontaneous recovery of swimming ability following a spinal cord injury in adult zebrafish. We employed behavioral analysis, ...neuronal tracing, and immunocytochemistry to determine the exact temporal relationship between swimming ability and regenerated cerebrospinal axon number in adult zebrafish with a complete spinal cord transection. Between two and eight weeks post-lesion, swimming gradually improved to 44% of sham-injured zebrafish. Neurons within the reticular formation, magnocellular octaval nucleus, and nucleus of the medial longitudinal fascicle grew their axon across and at least four millimeters beyond the lesion. The largest increases in swimming ability and number of regenerated cerebrospinal axons were observed between two and four weeks post-lesion. Regression analyses revealed a significant correlation between swimming ability and the number of regenerated axons. Our results indicate the involvement of cerebrospinal axons in swimming recovery after spinal cord injury in adult zebrafish.
Aligned, electrospun polymer fibers have shown considerable promise in directing regenerating axons in vitro and in vivo. However, in several studies, final electrospinning parameters are presented ...for producing aligned fiber scaffolds, and alignment where minimal fiber crossing occurs is not achieved. Highly aligned species are necessary for neural tissue engineering applications to ensure that axonal extension occurs through a regenerating environment efficiently. Axonal outgrowth on fibers that deviate from the natural axis of growth may delay axonal extension from one end of a scaffold to the other. Therefore, producing aligned fiber scaffolds with little fiber crossing is essential. In this study, the contributions of four electrospinning parameters (collection disk rotation speed, needle size, needle tip shape and syringe pump flow rate) were investigated thoroughly with the goal of finding parameters to obtain highly aligned electrospun fibers made from poly-L-lactic acid (PLLA). Using an 8 wt% PLLA solution in chloroform, a collection disk rotation speed of 1000 revolutions per minute (rpm), a 22 gauge, sharp-tip needle and a syringe pump rate of 2 ml h(-1) produced highly aligned fiber (1.2-1.6 microm in diameter) scaffolds verified using a fast Fourier transform and a fiber alignment quantification technique. Additionally, the application of an insulating sheath around the needle tip improved the rate of fiber deposition (electrospinning efficiency). Optimized scaffolds were then evaluated in vitro using embryonic stage nine (E9) chick dorsal root ganglia (DRGs) and rat Schwann cells (SCs). To demonstrate the importance of creating highly aligned scaffolds to direct neurite outgrowth, scaffolds were created that contained crossing fibers. Neurites on these scaffolds were directed down the axis of the aligned fibers, but neurites also grew along the crossed fibers. At times, these crossed fibers even stopped further axonal extension. Highly aligned PLLA fibers generated under optimized electrospinning conditions guided neurite and SC growth along the aligned fibers. Schwann cells demonstrated the bipolar phenotype seen along the fibers. Using a novel technique to determine fiber density, an increase in fiber density correlated to an increase in the number of neurites, but average neurite length was not statistically different between the two different fiber densities. Together, this work presents methods by which to produce highly aligned fiber scaffolds efficiently and techniques for assessing neurite outgrowth on different fiber scaffolds, while suggesting that crossing fibers may be detrimental in fostering efficient, directed axonal outgrowth.
Abstract Cell therapy for nervous tissue repair is limited by low transplant survival. We investigated the effects of a polyurethane-based reverse thermal gel, poly(ethylene glycol)–poly(serinol ...hexamethylene urethane) (ESHU) on bone marrow stromal cell (BMSC) transplant survival and repair using a rat model of spinal cord contusion. Transplantation of BMSCs in ESHU at three days post-contusion resulted in a 3.5-fold increase in BMSC survival at one week post-injury and a 66% increase in spared nervous tissue volume at four weeks post-injury. These improvements were accompanied by enhanced hindlimb motor and sensorimotor recovery. In vitro, we found that ESHU protected BMSCs from hydrogen peroxide-mediated death, resulting in a four-fold increase in BMSC survival with two-fold fewer BMSCs expressing the apoptosis marker, caspase 3 and the DNA oxidation marker, 8-oxo-deoxyguanosine. We argue that ESHU protected BMSCs transplanted is a spinal cord contusion from death thereby augmenting their effects on neuroprotection leading to improved behavioral restoration. The data show that the repair effects of intraneural BMSC transplants depend on the degree of their survival and may have a widespread impact on cell-based regenerative medicine.
Axons fail to regenerate in the injured spinal cord, limiting motor and autonomic recovery and contributing to long-term morbidity. Endogenous inhibitors, including those on residual myelin, ...contribute to regeneration failure. One inhibitor, myelin-associated glycoprotein (MAG), binds to sialoglycans and other receptors on axons. MAG inhibition of axon outgrowth in some neurons is reversed by treatment with sialidase, an enzyme that hydrolyzes sialic acids and eliminates MAG—sialoglycan binding. We delivered recombinant sialidase intrathecally to rats following a spinal cord contusive injury. Sialidase (or saline solution) was infused to the injury site continuously for 2 wk and then motor behavior, autonomic physiology, and anatomic outcomes were determined 3 wk later. Sialidase treatment significantly enhanced hindlimb motor function, improved bulbospinally mediated autonomic reflexes, and increased axon sprouting. These findings validate sialoglycans as therapeutic targets and sialidase as a candidate therapy for spinal cord injury.
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