Biodegradable chitin conduit tubulation combined with bone marrow mesenchymal stem cell transplantation for treatment of spinal cord injury by reducing glial scar and cavity formation

Syntaphilin Inactivation Can Enhance Axonal Mitochondrial Transport to Improve Spinal Cord Injury

Mitochondria are important organelle of eukaryotic cells. They consists of a large number of different proteins that provide most of the ATP and supply power for the growth, function, and regeneration of neurons. Therefore, smitochondrial transport ensures that adequate ATP is supplied for metabolic activities. Spinal cord injury (SCI), a detrimental condition, has high morbidity and mortality rates. Currently, the available treatments only provide symptomatic relief for long-term disabilities. Studies have implicated mitochondrial transport as a critical factor in axonal regeneration. Hence, enhancing mitochondrial transports could be beneficial for ameliorating SCI. Syntaphilin (Snph) is a mitochondrial docking protein that acts as a "static anchor," and its inhibition enhances mitochondrial transports. Therefore, Snph as a key mediator of mitochondrial transports, may contribute to improving axonal regeneration following SCI. Herein, we examine Snph's biological effects and its relation to mitochondrial pathway. Then, we elaborate on mitochondrial transports after SCI, the possible role of Snph in SCI, and some possible therapeutic approaches by Snph.

Clinical Trials Targeting Secondary Damage after Traumatic Spinal Cord Injury

Spinal cord injury (SCI) often causes loss of sensory and motor function resulting in a significant reduction in quality of life for patients. Currently, no therapies are available that can repair spinal cord tissue. After the primary SCI, an acute inflammatory response induces further tissue damage in a process known as secondary injury. Targeting secondary injury to prevent additional tissue damage during the acute and subacute phases of SCI represents a promising strategy to improve patient outcomes. Here, we review clinical trials of neuroprotective therapeutics expected to mitigate secondary injury, focusing primarily on those in the last decade. The strategies discussed are broadly categorized as acute-phase procedural/surgical interventions, systemically delivered pharmacological agents, and cell-based therapies. In addition, we summarize the potential for combinatorial therapies and considerations.

Chitin scaffold combined with autologous small nerve repairs sciatic nerve defects

Although autologous nerve transplantation is the gold standard for treating peripheral nerve defects, it has many clinical limitations. As an alternative, various tissue-engineered nerve grafts have been developed to substitute for autologous nerves. In this study, a novel nerve graft composed of chitin scaffolds and a small autologous nerve was used to repair sciatic nerve defects in rats. The novel nerve graft greatly facilitated regeneration of the sciatic nerve and myelin sheath, reduced atrophy of the target muscle, and effectively restored neurological function. When the epineurium of the small autogenous nerve was removed, the degree of nerve regeneration was similar to that which occurs after autogenous nerve transplantation. These findings suggest that our novel nerve graft might eventually be a new option for the construction of tissue-engineered nerve scaffolds. The study was approved by the Research Ethics Committee of Peking University People's Hospital (approval No. 2019PHE27) on October 18, 2019.

Stem Cell Therapy for Spinal Cord Injury

Traumatic spinal cord injury (SCI) results in direct and indirect damage to neural tissues, which results in motor and sensory dysfunction, dystonia, and pathological reflex that ultimately lead to paraplegia or tetraplegia. A loss of cells, axon regeneration failure, and time-sensitive pathophysiology make tissue repair difficult. Despite various medical developments, there are currently no effective regenerative treatments. Stem cell therapy is a promising treatment for SCI due to its multiple targets and reactivity benefits. The present review focuses on SCI stem cell therapy, including bone marrow mesenchymal stem cells, umbilical mesenchymal stem cells, adipose-derived mesenchymal stem cells, neural stem cells, neural progenitor cells, embryonic stem cells, induced pluripotent stem cells, and extracellular vesicles. Each cell type targets certain features of SCI pathology and shows therapeutic effects via cell replacement, nutritional support, scaffolds, and immunomodulation mechanisms. However, many preclinical studies and a growing number of clinical trials found that single-cell treatments had only limited benefits for SCI. SCI damage is multifaceted, and there is a growing consensus that a combined treatment is needed.

Recent Advances in the Regenerative Approaches for Traumatic Spinal Cord Injury: Materials Perspective

Spinal cord injury (SCI) is a devastating health condition that may lead to permanent disabilities and death. Understanding the pathophysiological perspectives of traumatic SCI is essential to define mechanisms that can help in designing recovery strategies. Since central nervous system tissues are notorious for their deficient ability to heal, efforts have been made to identify solutions to aid in restoration of the spinal cord tissues and thus its function. The two main approaches proposed to address this issue are neuroprotection and neuro-regeneration. Neuroprotection involves administering drugs to restore the injured microenvironment to normal after SCI. As for the neuro-regeneration approach, it focuses on axonal sprouting for functional recovery of the injured neural tissues and damaged axons. Despite the progress made in the field, neural regeneration treatment after SCI is still unsatisfactory owing to the disorganized way of axonal growth and extension. Nanomedicine and tissue engineering are considered promising therapeutic approaches that enhance axonal growth and directionality through implanting or injecting of the biomaterial scaffolds. One of these recent approaches is nanofibrous scaffolds that are used to provide physical support to maintain directional axonal growth in the lesion site. Furthermore, these preferable tissue-engineered substrates can afford axonal regeneration by mimicking the extracellular matrix of the neural tissues in terms of biological, chemical, and architectural characteristics. In this review, we discuss the regenerative approach using nanofibrous scaffolds with a focus on their fabrication methods and their properties that define their functionality performed to heal the neural tissue efficiently.

An injectable heparin-Laponite hydrogel bridge FGF4 for spinal cord injury by stabilizing microtubule and improving mitochondrial function

Rationale: Spinal cord injury (SCI) remains a critical clinical challenge. The controlled release of FGF4, a novel neuroprotective factor, from a versatile Laponite hydrogel to the injured site was a promising strategy to promote axon regeneration and motor functional recovery after SCI.

Methods: Characterization of Laponite, Laponite/Heparin (Lap/Hep) and Laponite/Heparin loaded with FGF4 (Lap/Hep@FGF4) hydrogels were measured by rheometer. Multiple comprehensive evaluations were used to detect motor functional recovery and the axonal rehabilitation after Lap/Hep@FGF4 treatment in vivo (SCI rat model). Moreover, microtubule dynamic and energy transportation, which regulated axonal regeneration was evaluated by Lap/Hep@FGF4 gel in vitro (primary neuron).

Results: FGF4 released from Lap/Hep gel locally achieves strong protection and regeneration after SCI. The Lap/Hep@FGF4 group revealed remarkable motor functional recovery and axonal regrowth after SCI through suppressing inflammatory reaction, increasing remyelination and reducing glial/fibrotic scars. Furthermore, the underlying mechanism of axonal rehabilitation were demonstrated via enhancing microtubule stability and regulating mitochondrial localization after Lap/Hep@FGF4 treatment.

Conclusion: This promising sustained release system provides a synergistic effective approach to enhance recovery after SCI underlying a novel mechanism of axonal rehabilitation, and shows a translational prospect for the clinical treatment of SCI.

Transplantation of human bone marrow-derived clonal mesenchymal stem cells reduces fibrotic scar formation in a rat spinal cord injury model

This study aimed to evaluate the therapeutic effect on tissue repair and scar formation of human bone marrow-derived clonal mesenchymal stem cells (hcMSCs) homogeneously isolated by using a subfractionation culturing method, in comparison with the non-clonal MSCs (hMSCs), in a rat spinal cord injury (SCI) model. The SCI was made using a vascular clip at the T9 level. Cells were transplanted into the lesion site 3 days after injury. A functional test was performed over 4 weeks employing a BBB score. Rats were killed for histological analysis at 3 days, 1 week and 4 weeks after injury. The transplantation of hMSCs and hcMSCs significantly reduced lesion size and the fluid-filled cavity at 4 weeks in comparison with the control group injected with phosphate buffered saline (PBS) (p < 0.01). Transplantation of hcMSCs showed more axons reserved than that of hMSCs in the lesion epicentre filled with non-neuronal tissues. In addition, hMSCs and hcMSCs clearly reduced the inflammatory reaction and intraparenchymal hemorrhaging, compared with the PBS group. Interestingly, hcMSCs largely decreased Col IV expression, one of the markers of fibrotic scars. hcMSCs yielded therapeutic effects more than equal to those of hMSCs on the SCI. Both hMSCs and hcMSCs created an increase in axon regeneration and reduced scar formation around the SCI lesion. Copyright © 2017 John Wiley & Sons, Ltd.

Enhanced axonal regeneration by transplanted Wnt3a-secreting human mesenchymal stem cells in a rat model of spinal cord injury

BACKGROUND

While pure mesenchymal stem cell (MSC) treatment for spinal cord injury (SCI) is known to be safe, its efficacy is insufficient. Therefore, gene-modified stem cells are being developed to enhance the effect of pure MSCs. We investigated the effect of stem cell therapy through the transfection of a Wnt3a-producing gene that stimulates axonal regeneration.

METHOD

MSCs obtained from the human umbilical cord blood (hMSCs) were multiplied, cultivated, and transfected with the pLenti-Wnt3a-GFP viral vector to produce Wnt3a-secreting hMSCs. A total of 50 rats were injured with an Infinite Horizon impactor at the level of the T7-8 vertebrae. Rats were divided into five groups according to the transplanted material: (1) phosphate-buffered saline injection group (sham group, n = 10); (Pertz et al. Proc Natl Acad Sci USA 105:1931-1936, 39) Wnt3a protein injection group (Wnt3a protein group, n = 10); (3) hMSC transplantation group (MSC group, n = 10); (4) hMSCs transfected with the pLenti vector transplantation group (pLenti-MSC group, n = 10); (5) hMSCs transfected with the pLenti+Wnt3a vector transplantation group (Wnt3a-MSC group, n = 10). Behavioral tests were performed daily for the first 3 days after injury and then weekly for 8 weeks. The injured spinal cords were extracted, and axonal regeneration markers including choline acetyltransferase (ChAT), growth-associated protein 43 (GAP43), and microtubule-associated protein 2 (MAP2) were investigated by immunofluorescence, RT-PCR, and western blotting.

RESULTS

Seven weeks after the transplantation (8 weeks after SCI), rats in the Wnt3a-MSC group achieved significantly higher average scores in the motor behavior tests than those in the other groups (p < 0.05). Immunofluorescent stains showed greater immunoreactivity of ChAT, GAP43, and MAP2 in the Wnt3a-MSC group than in the other groups. RT-PCR and western blots revealed greater expression of these proteins in the Wnt3a-MSC group than in the other groups (p < 0.05).

CONCLUSIONS

Wnt3a-secreting hMSC transplantation considerably improved neurological recovery and axonal regeneration in a rat SCI model.

Biomaterials and cells for neural tissue engineering: Current choices

The treatment of nerve injuries has taken a new dimension with the development of tissue engineering techniques. Prior to tissue engineering, suturing and surgery were the only options for effective treatment. With the advent of tissue engineering, it is now possible to design a scaffold that matches the exact biological and mechanical properties of the tissue. This has led to substantial reduction in the complications posed by surgeries and suturing to the patients. New synthetic and natural polymers are being applied to test their efficiency in generating an ideal scaffold. Along with these, cells and growth factors are also being incorporated to increase the efficiency of a scaffold. Efforts are being made to devise a scaffold that is biodegradable, biocompatible, conducting and immunologically inert. The ultimate goal is to exactly mimic the extracellular matrix in our body, and to elicit a combination of biochemical, topographical and electrical cues via various polymers, cells and growth factors, using which nerve regeneration can efficiently occur.

A Thermosensitive Heparin-Poloxamer Hydrogel Bridges aFGF to Treat Spinal Cord Injury

Acidic fibroblast growth factor (aFGF) exerts a protective effect on spinal cord injury (SCI) but is limited by the lack of physicochemical stability and the ability to cross the blood spinal cord barrier (BSCB). As promising biomaterials, hydrogels contain substantial amounts of water and a three-dimensional porous structure and are commonly used to load and deliver growth factors. Heparin can not only enhance growth factor loading onto hydrogels but also can stabilize the structure and control the release behavior. Herein, a novel aFGF-loaded thermosensitive heparin-poloxamer (aFGF-HP) hydrogel was developed and applied to provide protection and regeneration after SCI. To assess the effects of the aFGF-HP hydrogel, BSCB restoration, neuron and axonal rehabilitation, glial scar inhibition, inflammatory response suppression, and motor recovery were studied both in vivo and in vitro. The aFGF-HP hydrogels exhibited sustained release of aFGF and protected the bioactivity of aFGF in vitro. Compared to groups intravenously administered either drug-free HP hydrogel or aFGF alone, the aFGF-HP hydrogel group revealed prominent and attenuated disruption of the BSCB, reduced neuronal apoptosis, reactive astrogliosis, and increased neuron and axonal rehabilitation both in vivo and in vitro. This work provides an effective approach to enhance recovery after SCI and provide a successful strategy for SCI protection.

Mechanisms responsible for the inhibitory effects of epothilone B on scar formation after spinal cord injury

Scar formation after spinal cord injury is regarded as an obstacle to axonal regeneration and functional recovery. Epothilone B provides moderate microtubule stabilization and is mainly used for anti-tumor therapy. It also reduces scar tissue formation and promotes axonal regeneration after spinal cord injury. The aim of the present study was to investigate the effect and mechanism of the microtubule-stabilizing reagent epothilone B in decreasing fibrotic scarring through its action on pericytes after spinal cord injury. A rat model of spinal cord injury was established via dorsal complete transection at the T10 vertebra. The rats received an intraperitoneal injection of epothilone B (0.75 mg/kg) at 1 and 15 days post-injury in the epothilone B group or normal saline in the vehicle group. Neuron-glial antigen 2, platelet-derived growth factor receptor β, and fibronectin protein expression were dramatically lower in the epothilone B group than in the vehicle group, but β-tubulin protein expression was greater. Glial fibrillary acidic protein at the injury site was not affected by epothilone B treatment. The Basso, Beattie, and Bresnahan locomotor scores were significantly higher in the epothilone B group than in the vehicle group. The results of this study demonstrated that epothilone B reduced the number of pericytes, inhibited extracellular matrix formation, and suppressed scar formation after spinal cord injury.

Phenotypic changes of Schwann cells on the proximal stump of injured peripheral nerve during repair using small gap conduit tube

Dedifferentiation of Schwann cells is an important feature of the response to peripheral nerve injury and specific negative myelination regulators are considered to have a major role in this process. However, most experiments have focused on the distal nerve stump, where the Notch signaling pathway is strongly associated with Schwann cell dedifferentiation and repair of the nerve. We observed the phenotypic changes of Schwann cells and changes of active Notch signaling on the proximal stump during peripheral nerve repair using small gap conduit tubulization. Eighty rats, with right sciatic nerve section of 4 mm, were randomly assigned to conduit bridging group and control group (epineurium suture). Glial fibrillary acidic protein expression, in myelinating Schwann cells on the proximal stump, began to up-regulate at 1 day after injury and was still evident at 5 days. Compared with the control group, Notch1 mRNA was expressed at a higher level in the conduit bridging group during the first week on the proximal stump. Hes1 mRNA levels in the conduit bridging group significantly increased compared with the control group at 3, 5, 7 and 14 days post-surgery. The change of the Notch intracellular domain shared a similar trend as Hes1 mRNA expression. Our results confirmed that phenotypic changes of Schwann cells occurred in the proximal stump. The differences in these changes between the conduit tubulization and epineurium suture groups correlate with changes in Notch signaling. This suggests that active Notch signaling might be a key mechanism during the early stage of neural regeneration in the proximal nerve stump.

Immunomodulatory and angiogenic responses induced by graphene oxide scaffolds in chronic spinal hemisected rats

Attractive physic-chemical features of graphene oxide (GO) and promising results in vitro with neural cells encourage its exploration for biomedical applications including neural regeneration. Fueled by previous findings at the subacute state, we herein investigate for the first time chronic tissue responses (at 30 days) to 3D scaffolds composed of partially reduced GO (rGO) when implanted in the injured rat spinal cord. These studies aim to define fibrotic, inflammatory and angiogenic changes at the lesion site induced by the chronic implantation of these porous structures. Injured animals receiving no scaffolds show badly structured lesion zones and more cavities than those carrying rGO materials, thus pointing out a significant role of the scaffolds in injury stabilization and sealing. Notably, GFAP(+) cells and pro-regenerative macrophages are evident at their interface. Moreover, rGO scaffolds support angiogenesis around and, more importantly, inside their structure, with abundant and functional new blood vessels in whose proximities inside the scaffolds some regenerated neuronal axons are found. On the contrary, lesion areas without rGO scaffolds show a diminished quantity of blood vessels and no axons at all. These findings provide a foundation for the usefulness of graphene-based materials in the design of novel biomaterials for spinal cord repair and encourage further investigation for the understanding of neural tissue responses to this kind of materials in vivo.

Transplantation of human telomerase reverse transcriptase gene-transfected Schwann cells for repairing spinal cord injury

Transfection of the human telomerase reverse transcriptase (hTERT) gene has been shown to increase cell proliferation and enhance tissue repair. In the present study, hTERT was transfected into rat Schwann cells. A rat model of acute spinal cord injury was established by the modified free-falling method. Retrovirus PLXSN was injected at the site of spinal cord injury as a vector to mediate hTERT gene-transfected Schwann cells (1 × 10(10)/L; 10 μL) or Schwann cells (1 × 10(10)/L; 10 μL) without hTERT gene transfection. Between 1 and 4 weeks after model establishment, motor function of the lower limb improved in the hTERT-transfected group compared with the group with non-transfected Schwann cells. Terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling and reverse transcription-polymerase chain reaction results revealed that the number of apoptotic cells, and gene expression of aquaporin 4/9 and matrix metalloproteinase 9/2 decreased at the site of injury in both groups; however, the effect improved in the hTERT-transfected group compared with the Schwann cells without hTERT transfection group. Hematoxylin and eosin staining, PKH26 fluorescent labeling, and electrophysiological testing demonstrated that compared with the non-transfected group, spinal cord cavity and motor and sensory evoked potential latencies were reduced, while the number of PKH26-positive cells and the motor and sensory evoked potential amplitude increased at the site of injury in the hTERT-transfected group. These findings suggest that transplantation of hTERT gene-transfected Schwann cells repairs the structure and function of the injured spinal cord.

Bridging the lesion-engineering a permissive substrate for nerve regeneration

Biomaterial-based strategies to restore connectivity after lesion at the spinal cord are focused on bridging the lesion and providing an favourable substrate and a path for axonal re-growth. Following spinal cord injury (SCI) a hostile environment for neuronal cell growth is established by the activation of multiple inhibitory mechanisms that hamper regeneration to occur. Implantable scaffolds can provide mechanical support and physical guidance for axon re-growth and, at the same time, contribute to alleviate the hostile environment by the in situ delivery of therapeutic molecules and/or relevant cells. Basic research on SCI has been contributing with the description of inhibitory mechanisms for regeneration as well as identifying drugs/molecules that can target inhibition. This knowledge is the background for the development of combined strategies with biomaterials. Additionally, scaffold design is significantly evolving. From the early simple hollow conduits, scaffolds with complex architectures that can modulate cell fate are currently being tested. A number of promising pre-clinical studies combining scaffolds, cells, drugs and/or nucleic acids are reported in the open literature. Overall, it is considered that to address the multi-factorial inhibitory environment of a SCI, a multifaceted therapeutic approach is imperative. The progress in the identification of molecules that target inhibition after SCI and its combination with scaffolds and/or cells are described and discussed in this review.