Combining acellular nerve allografts with brain-derived neurotrophic factor transfected bone marrow mesenchymal stem cells restores sciatic nerve injury better than either intervention alone

Bone marrow mesenchymal stem cells in treatment of peripheral nerve injury

Peripheral nerve injury (PNI) is a common neurological disorder and complete functional recovery is difficult to achieve. In recent years, bone marrow mesenchymal stem cells (BMSCs) have emerged as ideal seed cells for PNI treatment due to their strong differentiation potential and autologous transplantation ability. This review aims to summarize the molecular mechanisms by which BMSCs mediate nerve repair in PNI. The key mechanisms discussed include the differentiation of BMSCs into multiple types of nerve cells to promote repair of nerve injury. BMSCs also create a microenvironment suitable for neuronal survival and regeneration through the secretion of neurotrophic factors, extracellular matrix molecules, and adhesion molecules. Additionally, BMSCs release pro-angiogenic factors to promote the formation of new blood vessels. They modulate cytokine expression and regulate macrophage polarization, leading to immunomodulation. Furthermore, BMSCs synthesize and release proteins related to myelin sheath formation and axonal regeneration, thereby promoting neuronal repair and regeneration. Moreover, this review explores methods of applying BMSCs in PNI treatment, including direct cell transplantation into the injured neural tissue, implantation of BMSCs into nerve conduits providing support, and the application of genetically modified BMSCs, among others. These findings confirm the potential of BMSCs in treating PNI. However, with the development of this field, it is crucial to address issues related to BMSC therapy, including establishing standards for extracting, identifying, and cultivating BMSCs, as well as selecting application methods for BMSCs in PNI such as direct transplantation, tissue engineering, and genetic engineering. Addressing these issues will help translate current preclinical research results into clinical practice, providing new and effective treatment strategies for patients with PNI.

Mesencephalic astrocyte-derived neurotrophic factor promotes axonal regeneration and the motor function recovery after sciatic nerve injury

Peripheral nerve injuries have common clinical problems that are often accompanied by sensory and motor dysfunction and failure of axonal regeneration. Although various therapeutic approaches have been attempted, full functional recovery and axonal regeneration are rarely achieved in patients. In this study, we investigated the effects of recombinant adeno-associated virus (AAV) of mesencephalic astrocyte-derived neurotrophic factor (AAV-MANF) or placental growth factor (AAV-PlGF) transduced into mesenchymal stem cells (hMSC-MANF and hMSC-PlGF), which were then transplanted using human decellularized nerves (HDN) into sciatic nerve injury model. Our results showed that both AAV-MANF and AAV-PlGF were expressed in MSCs transplanted into the injury site. Behavioral measurements performed 2, 4, 6, 8, and 12 weeks after injury indicated that MANF facilitated the rapid and improved recovery of sensory and motor functions than PlGF. In addition, immunohistochemical analysis was used to quantitatively analyze the myelination of neurofilaments, Schwann cells, and regrowth axons. Both hMSC-MANF and hMSC-PlGF increased axon numbers and immunoreactive areas of axons and Schwann cells compared with the hMSC-GFP group. However, hMSC-MANF significantly improved the thickness of axons and Schwann cells compared with hMSC-PlGF. G-ratio analysis also showed a marked increase in axon myelination in axons thicker than 2.0 μm treated with MANF than that treated with PlGF. Our study suggests that transplantation of hMSC transduced with AAV-MANF has a potential to provide a novel and efficient strategy for promoting functional recovery and axonal regeneration in peripheral nerve injury.

Localized delivery of brain-derived neurotrophic factor from PLGA microspheres promotes peripheral nerve regeneration in rats

Background

Repair of peripheral nerve defect presents a considerable challenge for reconstructive surgeons. The aim of this study is to develop a brain-derived neurotrophic factor (BDNF) from poly(D,L-lactide-co-glycolide) (PLGA) microspheres for the treatment of the peripheral nerve defect.

Method

BDNF microspheres were prepared by using an oil-in-water emulsification-solvent evaporation method. The morphology, particle size, encapsulation efficiency, drug loading and sustained release performance of microspheres was observed and calculated. Adipose mesenchymal stem cells (ADSCs) were isolated and expanded. ADSCs were divided into four groups: control, BDNF, blank microsphere and BDNF microsphere groups. Cell count kit-8 (CCK-8) assays were used to assess cell proliferation. Cell migration was determined by Transwell assays. Twenty-eight male Sprague–Dawley rats underwent transection damage model on the right sciatic nerve. The wet weight ratio of the gastrocnemius muscle was calculated by comparing the weight of the gastrocnemius muscle from the operated side to that of the normal side. Neuroelectrophysiological testing was performed to assess nerve function recovery. Nerve regeneration was evaluated by histological analysis and immunohistochemical staining.

Results

The microspheres were spherical and had uniform size (46.38 ± 1.00 μm), high encapsulation efficiency and high loading capacity. In vitro release studies showed that BDNF-loaded microspheres had good sustained release characteristics. The duration of BDNF release was extended to more than 50 days. BDNF or BDNF microsphere promote the proliferation and migration of ADSCs than control group (P < 0.05). Compared with control group, BDNF significantly decreased the nerve conduction velocity (NCV) and compound amplitude (AMP) (P < 0.05). The nerve fibers in the BDNF microsphere group were closely arranged and uniformly distributed than control group.

Conclusion

BDNF/PLGA sustained-release microsphere could promote the migration of ADSCs and promoted neural differentiation of ADSCs. Moreover, BDNF/PLGA sustained-release microsphere ameliorated nerve conduction velocity and prevented neuralgic amyotrophy.

Cell-Enhanced Acellular Nerve Allografts for Peripheral Nerve Reconstruction: A Systematic Review and a Meta-Analysis of the Literature

BACKGROUND

Peripheral nerve reconstruction is a difficult problem to solve. Acellular nerve allografts (ANAs) have been widely tested and are a promising alternative to the autologous gold standard. However, current reconstructive methods still yield unpredictable and unsuccessful results. Consequently, numerous studies have been carried out studying alternatives to plain ANAs, but it is not clear if nerve regeneration potential exists between current biological, chemical, and physical enrichment modes.

OBJECTIVE

To systematically review the effects of cell-enhanced ANAs on regeneration of peripheral nerve injuries.

METHODS

PubMed, ScienceDirect, Medline, and Scopus databases were searched for related articles published from 2007 to 2017. Inclusion criteria of selected articles consisted of (1) articles written in English; (2) the topic being cell-enhanced ANAs in peripheral nerve regeneration; (3) an in vivo study design; and (4) postgrafting neuroregenerative assessment of results. Exclusion criteria included all articles that (1) discussed central nervous system ANAs; (2) consisted of xenografts as the main topic; and (3) consisted of case series, case reports or reviews.

RESULTS

Forty papers were selected, and categorization included the animal model; the enhancing cell types; the decellularization method; and the neuroregenerative test performed. The effects of using diverse cellular enhancements combined with ANAs are discussed and also compared with the other treatments such as autologous nerve graft, and plain ANAs.

CONCLUSION

ANAs cellular enhancement demonstrated positive effects on recovery of nerve function. Future research should include clinical translation, in order to increase the level of evidence available on peripheral nerve reconstruction.

Novel approaches using mesenchymal stem cells for curing peripheral nerve injuries

Peripheral nerve injury (PNI) is a common life-changing disability of peripheral nervous system with significant socioeconomic consequences. Conventional therapeutic approaches for PNI have several drawbacks such as need to autologous nerve scarifying, surplus surgery, and difficult accessibility to donor nerve; therefore, other therapeutic strategies such as mesenchymal stem cells (MSCs) therapy are getting more interesting. MSCs have been proved to be safe and efficient in numerous degenerative diseases of central and peripheral nervous systems. In this paper, we review novel biotechnological advancements in treating PNI using MSCs.

Comparable functional motor outcomes after repair of peripheral nerve injury with an elastase-processed allograft in a rat sciatic nerve model

BACKGROUND

A bridging nerve autograft is the gold standard for the repair of segmental nerve injury that cannot be repaired directly. However, limited availability and donor site morbidity remain major disadvantages of autografts. Here, a nerve allograft decellularized with elastase was compared with an autograft regarding functional motor outcome in a rat sciatic segmental nerve defect model. Furthermore, the effect of storage on this allograft was studied.

METHODS

Sixty-six Lewis rats (250-300 g) underwent a 10-mm sciatic nerve reconstruction using either a cold- (n = 22) or frozen-stored (n = 22) decellularized nerve allograft or an autograft (n = 22). Sprague-Dawley rats (300-350 g) served as full major histocompatibility complex-mismatched donors. Functional motor outcome was evaluated after 12 and 16 weeks. Ankle angle, compound muscle action potential (CMAP), isometric tetanic force, wet muscle weight, and histomorphometry were tested bilaterally.

RESULTS

For CMAP and isometric tetanic force, no significant differences were observed between groups. In contrast, for ankle angle, histomorphometry and muscle weight, the cold-stored allograft performed comparable to the autograft, while the frozen-stored allograft performed significantly inferior to the autograft. At week 16, ankle angle was 88.0 ± 3.1% in the cold-stored group, 77.4 ± 3.6% in the frozen-stored group, and 74.1 ± 3.1% in the autograft group (P < .001); At week 16, the muscle weight showed a recovery up to 71.1 ± 4.8% in the autograft group, 67.0 ± 6.6% in the cold-stored group, and 64.7 ± 3.7% in the frozen-stored group (P < .05).

CONCLUSIONS

A nerve allograft decellularized with elastase, if stored under the right conditions, results in comparable functional motor outcomes as the gold standard, the autograft.

Transplantation of Embryonic Spinal Cord Derived Cells Helps to Prevent Muscle Atrophy after Peripheral Nerve Injury

Injuries to peripheral nerves are frequent in serious traumas and spinal cord injuries. In addition to surgical approaches, other interventions, such as cell transplantation, should be considered to keep the muscles in good condition until the axons regenerate. In this study, E14.5 rat embryonic spinal cord fetal cells and cultured neural progenitor cells from different spinal cord segments were injected into transected musculocutaneous nerve of 200–300 g female Sprague Dawley (SD) rats, and atrophy in biceps brachii was assessed. Both kinds of cells were able to survive, extend their axons towards the muscle and form neuromuscular junctions that were functional in electromyographic studies. As a result, muscle endplates were preserved and atrophy was reduced. Furthermore, we observed that the fetal cells had a better effect in reducing the muscle atrophy compared to the pure neural progenitor cells, whereas lumbar cells were more beneficial compared to thoracic and cervical cells. In addition, fetal lumbar cells were used to supplement six weeks delayed surgical repair after the nerve transection. Cell transplantation helped to preserve the muscle endplates, which in turn lead to earlier functional recovery seen in behavioral test and electromyography. In conclusion, we were able to show that embryonic spinal cord derived cells, especially the lumbar fetal cells, are beneficial in the treatment of peripheral nerve injuries due to their ability to prevent the muscle atrophy.

Molecular examination of bone marrow stromal cells and chondroitinase ABC-assisted acellular nerve allograft for peripheral nerve regeneration

The present study aimed to evaluate the molecular mechanisms underlying combinatorial bone marrow stromal cell (BMSC) transplantation and chondroitinase ABC (Ch-ABC) therapy in a model of acellular nerve allograft (ANA) repair of the sciatic nerve gap in rats. Sprague Dawley rats (n=24) were used as nerve donors and Wistar rats (n=48) were randomly divided into the following groups: Group I, Dulbecco's modified Eagle's medium (DMEM) control group (ANA treated with DMEM only); Group II, Ch-ABC group (ANA treated with Ch-ABC only); Group III, BMSC group (ANA seeded with BMSCs only); Group IV, Ch-ABC + BMSCs group (Ch-ABC treated ANA then seeded with BMSCs). After 8 weeks, the expression of nerve growth factor, brain-derived neurotrophic factor and vascular endothelial growth factor in the regenerated tissues were detected by reverse transcription-quantitative polymerase chain reaction and immunohistochemistry. Axonal regeneration, motor neuron protection and functional recovery were examined by immunohistochemistry, horseradish peroxidase retrograde neural tracing and electrophysiological and tibialis anterior muscle recovery analyses. It was observed that combination therapy enhances the growth response of the donor nerve locally as well as distally, at the level of the spinal cord motoneuron and the target muscle organ. This phenomenon is likely due to the propagation of retrograde and anterograde transport of growth signals sourced from the graft site. Collectively, growth improvement on the donor nerve, target muscle and motoneuron ultimately contribute to efficacious axonal regeneration and functional recovery. Thorough investigation of molecular peripheral nerve injury combinatorial strategies are required for the optimization of efficacious therapy and full functional recovery following ANA.

Acellular allogeneic nerve grafting combined with bone marrow mesenchymal stem cell transplantation for the repair of long-segment sciatic nerve defects: biomechanics and validation of mathematical models

We hypothesized that a chemically extracted acellular allogeneic nerve graft used in combination with bone marrow mesenchymal stem cell transplantation would be an effective treatment for long-segment sciatic nerve defects. To test this, we established rabbit models of 30 mm sciatic nerve defects, and treated them using either an autograft or a chemically decellularized allogeneic nerve graft with or without simultaneous transplantation of bone marrow mesenchymal stem cells. We compared the tensile properties, electrophysiological function and morphology of the damaged nerve in each group. Sciatic nerves repaired by the allogeneic nerve graft combined with stem cell transplantation showed better recovery than those repaired by the acellular allogeneic nerve graft alone, and produced similar results to those observed with the autograft. These findings confirm that a chemically extracted acellular allogeneic nerve graft combined with transplantation of bone marrow mesenchymal stem cells is an effective method of repairing long-segment sciatic nerve defects.

Neural Progenitor-Like Cells Induced from Human Gingiva-Derived Mesenchymal Stem Cells Regulate Myelination of Schwann Cells in Rat Sciatic Nerve Regeneration

Regeneration of peripheral nerve injury remains a major clinical challenge. Recently, mesenchymal stem cells (MSCs) have been considered as potential candidates for peripheral nerve regeneration; however, the underlying mechanisms remain elusive. Here, we show that human gingiva‐derived MSCs (GMSCs) could be directly induced into multipotent NPCs (iNPCs) under minimally manipulated conditions without the introduction of exogenous genes. Using a crush‐injury model of rat sciatic nerve, we demonstrate that GMSCs transplanted to the injury site could differentiate into neuronal cells, whereas iNPCs could differentiate into both neuronal and Schwann cells. After crush injury, iNPCs, compared with GMSCs, displayed superior therapeutic effects on axonal regeneration at both the injury site and the distal segment of the injured sciatic nerve. Mechanistically, transplantation of GMSCs, especially iNPCs, significantly attenuated injury‐triggered increase in the expression of c‐Jun, a transcription factor that functions as a major negative regulator of myelination and plays a central role in dedifferentiation/reprogramming of Schwann cells into a progenitor‐like state. Meanwhile, our results also demonstrate that transplantation of GMSCs and iNPCs consistently increased the expression of Krox‐20/EGR2, a transcription factor that governs the expression of myelin proteins and facilitates myelination. Altogether, our findings suggest that transplantation of GMSCs and iNPCs promotes peripheral nerve repair/regeneration, possibly by promoting remyelination of Schwann cells mediated via the regulation of the antagonistic myelination regulators, c‐Jun and Krox‐20/EGR2. Stem Cells Translational Medicine2017;6:458–470

Repair of peripheral nerve defects with chemically extracted acellular nerve allografts loaded with neurotrophic factors-transfected bone marrow mesenchymal stem cells

Chemically extracted acellular nerve allografts loaded with brain-derived neurotrophic factor-transfected or ciliary neurotrophic factor-transfected bone marrow mesenchymal stem cells have been shown to repair sciatic nerve injury better than chemically extracted acellular nerve allografts alone, or chemically extracted acellular nerve allografts loaded with bone marrow mesenchymal stem cells. We hypothesized that these allografts compounded with both brain-derived neurotrophic factor- and ciliary neurotrophic factor-transfected bone marrow mesenchymal stem cells may demonstrate even better effects in the repair of peripheral nerve injury. We cultured bone marrow mesenchymal stem cells expressing brain-derived neurotrophic factor and/or ciliary neurotrophic factor and used them to treat sciatic nerve injury in rats. We observed an increase in sciatic functional index, triceps wet weight recovery rate, myelin thickness, number of myelinated nerve fibers, amplitude of motor-evoked potentials and nerve conduction velocity, and a shortened latency of motor-evoked potentials when allografts loaded with both neurotrophic factors were used, compared with allografts loaded with just one factor. Thus, the combination of both brain-derived neurotrophic factor and ciliary neurotrophic factor-transfected bone marrow mesenchymal stem cells can greatly improve nerve injury.