Nerve Repair Using Decellularized Nerve Grafts in Rat Models. A Review of the Literature

End-to-side neurorrhaphy in the reconstruction of peripheral segmental neural loss: an experimental study

PURPOSE

To evaluate the effects on peripheral neural regeneration of the end-to-side embracing repair technique compared to the autograft repair technique in Wistar rats.

METHODS

Fifteen male Wistar rats were divided into three groups with five animals each: denervated group (GD), autograft group (GA), and embracing group (EG). For the evaluation, the grasping test, electroneuromyography (ENMG), and muscle weight assessment were used.

RESULTS

Muscle weight assessment and ENMG did not show significant neural regeneration at the end of 12 weeks in the DG and GE groups, but only in GA. The grasping test showed an increase in strength between the surgery and the fourth week in all groups, and only the GA maintained this trend until the 12th week.

CONCLUSIONS

The present study indicates that the neural regeneration observed in the end-to-side embracing neurorrhaphy technique, in the repair of segmental neural loss, is inferior to autograft repair in Wistar rats.

Limited Nerve Regeneration across Acellular Nerve Allografts (ANAs) Coincides with Changes in Blood Vessel Morphology and the Development of a Pro-Inflammatory Microenvironment

The use of acellular nerve allografts (ANAs) to reconstruct long nerve gaps (>3 cm) is associated with limited axon regeneration. To understand why ANA length might limit regeneration, we focused on identifying differences in the regenerative and vascular microenvironment that develop within ANAs based on their length. A rat sciatic nerve gap model was repaired with either short (2 cm) or long (4 cm) ANAs, and histomorphometry was used to measure myelinated axon regeneration and blood vessel morphology at various timepoints (2-, 4- and 8-weeks). Both groups demonstrated robust axonal regeneration within the proximal graft region, which continued across the mid-distal graft of short ANAs as time progressed. By 8 weeks, long ANAs had limited regeneration across the ANA and into the distal nerve (98 vs. 7583 axons in short ANAs). Interestingly, blood vessels within the mid-distal graft of long ANAs underwent morphological changes characteristic of an inflammatory pathology by 8 weeks post surgery. Gene expression analysis revealed an increased expression of pro-inflammatory cytokines within the mid-distal graft region of long vs. short ANAs, which coincided with pathological changes in blood vessels. Our data show evidence of limited axonal regeneration and the development of a pro-inflammatory environment within long ANAs.

Beyond the limiting gap length: peripheral nerve regeneration through implantable nerve guidance conduits

Peripheral nerve damage results in the loss of sensorimotor and autonomic functions, which is a significant burden to patients. Furthermore, nerve injuries greater than the limiting gap length require surgical repair. Although autografts are the preferred clinical choice, their usage is impeded by their limited availability, dimensional mismatch, and the sacrifice of another functional donor nerve. Accordingly, nerve guidance conduits, which are tubular scaffolds engineered to provide a biomimetic environment for nerve regeneration, have emerged as alternatives to autografts. Consequently, a few nerve guidance conduits have received clinical approval for the repair of short-mid nerve gaps but failed to regenerate limiting gap damage, which represents the bottleneck of this technology. Thus, it is still necessary to optimize the morphology and constituent materials of conduits. This review summarizes the recent advances in nerve conduit technology. Several manufacturing techniques and conduit designs are discussed, with emphasis on the structural improvement of simple hollow tubes, additive manufacturing techniques, and decellularized grafts. The main objective of this review is to provide a critical overview of nerve guidance conduit technology to support regeneration in long nerve defects, promote future developments, and speed up its clinical translation as a reliable alternative to autografts.

Myelin histology: a key tool in nervous system research

The myelin sheath is a lipoprotein-rich, multilayered structure capable of increasing conduction velocity in central and peripheral myelinated nerve fibers. Due to the complex structure and composition of myelin, various histological techniques have been developed over the centuries to evaluate myelin under normal, pathological or experimental conditions. Today, methods to assess myelin integrity or content are key tools in both clinical diagnosis and neuroscience research. In this review, we provide an updated summary of the composition and structure of the myelin sheath and discuss some histological procedures, from tissue fixation and processing techniques to the most used and practical myelin histological staining methods. Considering the lipoprotein nature of myelin, the main features and technical details of the different available methods that can be used to evaluate the lipid or protein components of myelin are described, as well as the precise ultrastructural techniques.

Role of transforming growth factor-β in peripheral nerve regeneration

Injuries caused by trauma and neurodegenerative diseases can damage the peripheral nervous system and cause functional deficits. Unlike in the central nervous system, damaged axons in peripheral nerves can be induced to regenerate in response to intrinsic cues after reprogramming or in a growth-promoting microenvironment created by Schwann cells. However, axon regeneration and repair do not automatically result in the restoration of function, which is the ultimate therapeutic goal but also a major clinical challenge. Transforming growth factor (TGF) is a multifunctional cytokine that regulates various biological processes including tissue repair, embryo development, and cell growth and differentiation. There is accumulating evidence that TGF-β family proteins participate in peripheral nerve repair through various factors and signaling pathways by regulating the growth and transformation of Schwann cells; recruiting specific immune cells; controlling the permeability of the blood-nerve barrier, thereby stimulating axon growth; and inhibiting remyelination of regenerated axons. TGF-β has been applied to the treatment of peripheral nerve injury in animal models. In this context, we review the functions of TGF-β in peripheral nerve regeneration and potential clinical applications.

The Medial Antebrachial Cutaneous Nerve Is a Low-Morbidity Alternative to the Standard Sural Nerve Autograft

BACKGROUND

Nerve interposition grafting is an important technique in nerve reconstructive surgery that is used when a primary repair is not feasible without significant tension. This study sought to evaluate the long-term morbidity of the medial antebrachial cutaneous (MABC) nerve as an alternative donor nerve in comparison with sural nerve harvest.

METHODS

A single surgeon and institution retrospective chart review was performed to identify all patients who underwent nerve autografting using the sural and MABC as donor nerves between January 1, 2000 and December 31, 2019. Surveys assessed overall patient satisfaction with surgery, as well as donor and recipient site morbidity, satisfaction, pain, numbness, and cold sensitivity.

RESULTS

Of the 73 patients contacted, 54 agreed to participate, and 43 of 73 (58.9%) ultimately completed the survey: 28 MABC (65.1%) and 15 sural (34.9%). There were no significant differences between the sural and MABC groups in overall satisfaction with surgery, donor and recipient site satisfaction, pain, cold sensitivity, and effect on quality of life. Even though 66.7% of sural donor sites and 75% of MABC donor sites had residual numbness, the effect this had on quality of life was very low (2 and 3, respectively).

CONCLUSION

The MABC is a safe alternative to the traditional sural nerve autograft. A small subset of patients undergoing nerve autograft harvest will experience long-term morbidity in the form of pain. Conversely, the more common presence of numbness is not reported as bothersome.

Decellularized Graft for Repairing Severe Peripheral Nerve Injuries in Sheep

BACKGROUND AND OBJECTIVES

Peripheral nerve injuries resulting in a nerve defect require surgical repair. The gold standard of autograft (AG) has several limitations, and therefore, new alternatives must be developed. The main objective of this study was to assess nerve regeneration through a long gap nerve injury (50 mm) in the peroneal nerve of sheep with a decellularized nerve allograft (DCA).

METHODS

A 5-cm long nerve gap was made in the peroneal nerve of sheep and repaired using an AG or using a DCA. Functional tests were performed once a month and electrophysiology and echography evaluations at 6.5 and 9 months postsurgery. Nerve grafts were harvested at 9 months for immunohistochemical and morphological analyses.

RESULTS

The decellularization protocol completely eliminated the cells while preserving the extracellular matrix of the nerve. No significant differences were observed in functional tests of locomotion and pain response. Reinnervation of the tibialis anterior muscles occurred in all animals, with some delay in the DCA group compared with the AG group. Histology showed a preserved fascicular structure in both AG and DCA; however, the number of axons distal to the nerve graft was higher in AG than in DCA.

CONCLUSION

The decellularized graft assayed supported effective axonal regeneration when used to repair a 5-cm long gap in the sheep. As expected, a delay in functional recovery was observed compared with the AG because of the lack of Schwann cells.

Nerve regeneration using decellularized tissues: challenges and opportunities

In tissue engineering, the decellularization of organs and tissues as a biological scaffold plays a critical role in the repair of neurodegenerative diseases. Various protocols for cell removal can distinguish the effects of treatment ability, tissue structure, and extracellular matrix (ECM) ability. Despite considerable progress in nerve regeneration and functional recovery, the slow regeneration and recovery potential of the central nervous system (CNS) remains a challenge. The success of neural tissue engineering is primarily influenced by composition, microstructure, and mechanical properties. The primary objective of restorative techniques is to guide existing axons properly toward the distal end of the damaged nerve and the target organs. However, due to the limitations of nerve autografts, researchers are seeking alternative methods with high therapeutic efficiency and without the limitations of autograft transplantation. Decellularization scaffolds, due to their lack of immunogenicity and the preservation of essential factors in the ECM and high angiogenic ability, provide a suitable three-dimensional (3D) substrate for the adhesion and growth of axons being repaired toward the target organs. This study focuses on mentioning the types of scaffolds used in nerve regeneration, and the methods of tissue decellularization, and specifically explores the use of decellularized nerve tissues (DNT) for nerve transplantation.

Cell-free therapy based on extracellular vesicles: a promising therapeutic strategy for peripheral nerve injury

Peripheral nerve injury (PNI) is one of the public health concerns that can result in a loss of sensory or motor function in the areas in which injured and non-injured nerves come together. Up until now, there has been no optimized therapy for complete nerve regeneration after PNI. Exosome-based therapies are an emerging and effective therapeutic strategy for promoting nerve regeneration and functional recovery. Exosomes, as natural extracellular vesicles, contain bioactive molecules for intracellular communications and nervous tissue function, which could overcome the challenges of cell-based therapies. Furthermore, the bioactivity and ability of exosomes to deliver various types of agents, such as proteins and microRNA, have made exosomes a potential approach for neurotherapeutics. However, the type of cell origin, dosage, and targeted delivery of exosomes still pose challenges for the clinical translation of exosome therapeutics. In this review, we have focused on Schwann cell and mesenchymal stem cell (MSC)-derived exosomes in nerve tissue regeneration. Also, we expressed the current understanding of MSC-derived exosomes related to nerve regeneration and provided insights for developing a cell-free MSC therapeutic strategy for nerve injury.

Comprehensive ex vivo and in vivo preclinical evaluation of novel chemo enzymatic decellularized peripheral nerve allografts

As a reliable alternative to autografts, decellularized peripheral nerve allografts (DPNAs) should mimic the complex microstructure of native nerves and be immunogenically compatible. Nevertheless, there is a current lack of decellularization methods able to remove peripheral nerve cells without significantly altering the nerve extracellular matrix (ECM). The aims of this study are firstly to characterize ex vivo, in a histological, biochemical, biomechanical and ultrastructural way, three novel chemical-enzymatic decellularization protocols (P1, P2 and P3) in rat sciatic nerves and compared with the Sondell classic decellularization method and then, to select the most promising DPNAs to be tested in vivo. All the DPNAs generated present an efficient removal of the cellular material and myelin, while preserving the laminin and collagen network of the ECM (except P3) and were free from any significant alterations in the biomechanical parameters and biocompatibility properties. Then, P1 and P2 were selected to evaluate their regenerative effectivity and were compared with Sondell and autograft techniques in an in vivo model of sciatic defect with a 10-mm gap, after 15 weeks of follow-up. All study groups showed a partial motor and sensory recovery that were in correlation with the histological, histomorphometrical and ultrastructural analyses of nerve regeneration, being P2 the protocol showing the most similar results to the autograft control group.

Evaluation of peripheral nerve regeneration in Murphy Roths Large mouse strain following transection injury

Aim: Murphy Roths Large (MRL/MpJ) mice have demonstrated the ability to heal with minimal or no scar formation in several tissue types. In order to identify a novel animal model, this study sought to evaluate whether this attribute applies to peripheral nerve regeneration. Materials & methods: This was a two-phase study. 6-week-old male mice were divided into two interventional groups: nerve repair and nerve graft. The MRL/MpJ was compared with the C57BL/6J strain for evaluation of both functional and histological outcomes. Results: MRL/MpJ strain demonstrated superior axon myelination and less scar formation, however functional outcomes did not show significant difference between strains. Conclusion: Superior histological outcomes did not translate into superior peripheral nerve regeneration in MRL/MpJ strain.

Orthopedic Surgical Management of Complicated Congenital Popliteal Pterygium Syndrome: A Case Report

Introduction

Popliteal pterygium syndrome (PPS) is a rare autosomal-dominant condition that causes fixed flexion deformity of the knee. The popliteal webbing and shortening of the surrounding soft tissue could limit the functionality of the affected limb unless it is surgically corrected. We reported a case of PPS in a pediatric patient encountered in our hospital.

Case

A 10-month-old boy came with a congenital abnormally flexed left knee with bilateral undescended testis and syndactyly of the left foot. The left popliteal pterygium extending from the buttock to the calcaneus was observed, with an associated fixed flexion contracture of the knee and equine position of the ankle. Normal vascular anatomy was seen in the angiographic CT scan; therefore, multiple Z-plasty and fibrotic band excision were performed. The sciatic trunk was exposed on the popliteal level, and the fascicular segment was excised from the distal stump and sutured to the proximal stump under the microscope to extend the sciatic nerve for approximately 7 cm. No postoperative complications were reported. Multiple tendons and soft tissue reconstruction were performed when the patient was 2-year-old to correct the adductus and equine deformity of the left foot.

Discussion

Surgical correction for popliteal pterygium demands staged techniques to deal with the shortened structure. In our case, multiple Z-plasty were performed, and the fibrotic band was excised until its base with meticulous consideration of the underlying neurovascular bundle. Fascicular shifting technique for sciatic nerve lengthening can be considered in unilateral popliteal pterygium with difficulty extending the knee due to shortened sciatic nerve. The unfavorable outcome of nerve conduction disturbance resulting from the procedure may be multifactorial. Still, the existing foot deformity, including a certain degree of pes equinovarus could be treated by multiple soft tissue reconstructions and adequate rehabilitation to achieve the desired outcome.

Conclusion

Multiple soft tissue procedures resulted in acceptable functional outcomes. However, the nerve grafting procedure is still a challenging task. Further study is required to explore the technique in optimizing the nerve grafting procedure for popliteal pterygium.

Advancement of Electrospun Nerve Conduit for Peripheral Nerve Regeneration: A Systematic Review (2016-2021)

Peripheral nerve injury (PNI) is a worldwide problem which hugely affects the quality of patients' life. Nerve conduits are now the alternative for treatment of PNI to mimic the gold standard, autologous nerve graft. In that case, with the advantages of electrospun micro- or nano-fibers nerve conduit, the peripheral nerve growth can be escalated, in a better way. In this systematic review, we focused on 39 preclinical studies of electrospun nerve conduit, which include the in vitro and in vivo evaluation from animal peripheral nerve defect models, to provide an update on the progress of the development of electrospun nerve conduit over the last 5 years (2016-2021). The physical characteristics, biocompatibility, functional and morphological outcomes of nerve conduits from different studies would be compared, to give a better strategy for treatment of PNI.

Repair of Long Nerve Defects with a New Decellularized Nerve Graft in Rats and in Sheep

Decellularized nerve allografts (DC) are an alternative to autografts (AG) for repairing severe peripheral nerve injuries. We have assessed a new DC provided by VERIGRAFT. The decellularization procedure completely removed cellularity while preserving the extracellular matrix. We first assessed the DC in a 15 mm gap in the sciatic nerve of rats, showing slightly delayed but effective regeneration. Then, we assayed the DC in a 70 mm gap in the peroneal nerve of sheep compared with AG. Evaluation of nerve regeneration and functional recovery was performed by clinical, electrophysiology and ultrasound tests. No significant differences were found in functional recovery between groups of sheep. Histology showed a preserved fascicular structure in the AG while in the DC grafts regenerated axons were grouped in small units. In conclusion, the DC was permissive for axonal regeneration and allowed to repair a 70 mm long gap in the sheep nerve.

Apoptosis-Decellularized Peripheral Nerve Scaffold Allows Regeneration across Nerve Gap

Peripheral nerve injury results in loss of motor and sensory function distal to the nerve injury and is often permanent in nerve gaps longer than 5 cm. Autologous nerve grafts (nerve autografts) utilize patients' own nerve tissue from another part of their body to repair the defect and are the gold standard in care. However, there is a limited autologous tissue supply, size mismatch between donor nerve and injured nerve, and morbidity at the site of nerve donation. Decellularized cadaveric nerve tissue alleviates some of these limitations and has demonstrated success clinically. We previously developed an alternative apoptosis-assisted decellularization process for nerve tissue. This new process may result in an ideal scaffold for peripheral nerve regeneration by gently removing cells and antigens while preserving delicate topographical cues. In addition, the apoptosis-assisted process requires less active processing time and is inexpensive. This study examines the utility of apoptosis-decellularized peripheral nerve scaffolds compared to detergent-decellularized peripheral nerve scaffolds and isograft controls in a rat nerve gap model. Results indicate that, at 8 weeks post-injury, apoptosis-decellularized peripheral nerve scaffolds perform similarly to detergent-decellularized and isograft controls in both functional (muscle weight recovery, gait analysis) and histological measures (neurofilament staining, macrophage infiltration). These new apoptosis-decellularized scaffolds hold great promise to provide a less expensive scaffold for nerve injury repair, with the potential to improve nerve regeneration and functional outcomes compared to current detergent-decellularized scaffolds.

Efficacy of Nerve-Derived Hydrogels to Promote Axon Regeneration Is Influenced by the Method of Tissue Decellularization

Injuries to large peripheral nerves are often associated with tissue defects and require reconstruction using autologous nerve grafts, which have limited availability and result in donor site morbidity. Peripheral nerve-derived hydrogels could potentially supplement or even replace these grafts. In this study, three decellularization protocols based on the ionic detergents sodium dodecyl sulfate (P1) and sodium deoxycholate (P2), or the organic solvent tri-n-butyl phosphate (P3), were used to prepare hydrogels. All protocols resulted in significantly decreased amounts of genomic DNA, but the P2 hydrogel showed the best preservation of extracellular matrix proteins, cytokines, and chemokines, and reduced levels of sulfated glycosaminoglycans. In vitro P1 and P2 hydrogels supported Schwann cell viability, secretion of VEGF, and neurite outgrowth. Surgical repair of a 10 mm-long rat sciatic nerve gap was performed by implantation of tubular polycaprolactone conduits filled with hydrogels followed by analyses using diffusion tensor imaging and immunostaining for neuronal and glial markers. The results demonstrated that the P2 hydrogel considerably increased the number of axons and the distance of regeneration into the distal nerve stump. In summary, the method used to decellularize nerve tissue affects the efficacy of the resulting hydrogels to support regeneration after nerve injury.

Peripheral Nerve Decellularization for In Vitro Extracellular Matrix Hydrogel Use: A Comparative Study

The rise of tissue-engineered biomaterials has introduced more clinically translatable models of disease, including three-dimensional (3D) decellularized extracellular matrix (dECM) hydrogels. Specifically, decellularized nerve hydrogels have been utilized to model peripheral nerve injuries and disorders in vitro; however, there lacks standardization in decellularization methods. Here, rat sciatic nerves of varying preparations were decellularized using previously established methods: sodium deoxycholate (SD)-based, 3-((3-cholamidopropyl)dimethylammonio)-1-propanesulfonate (CHAPS)-based, and apoptosis-mediated. These nerves were characterized for cellular debris removal, ECM retention, and low cytotoxicity with cultured Schwann cells. The best preparations of each decellularization method were digested into dECM hydrogels, and rheological characterization, gelation kinetics, and confocal reflectance imaging of collagen fibril assembly were performed. It was determined that the SD-based method with nerve epineurial removal best maintained the overall ECM composition and mechanical properties of physiological peripheral nerves while efficiently stripping the scaffolds of tissue-specific cells and debris. This method was then utilized as a culture platform for quiescent Schwann cells and cancer-nerve crosstalk. Hydrogel-embedded Schwann cells were found to have high viability and act in a more physiologically relevant manner than those cultured in monolayers, and the hydrogel platform allowed for the activation of Schwann cells following treatment with cancer secreted factors. These findings establish a standard for peripheral nerve decellularization for usage as a dECM hydrogel testbed for in vitro peripheral nerve disease modeling and may facilitate the development of treatments for peripheral nerve disease and injury.

Waste-derived biomaterials as building blocks in the biomedical field

Recent developments in the biomedical arena have led to the fabrication of innovative biomaterials by utilizing bioactive molecules obtained from biological wastes released from fruit and beverage processing industries, and fish, meat, and poultry industries. These biological wastes that end up in water bodies as well as in landfills are an affluent source of animal- and plant-derived proteins, bio ceramics and polysaccharides such as collagens, gelatins, chitins, chitosans, eggshell membrane proteins, hydroxyapatites, celluloses, and pectins. These bioactive molecules have been intricately designed into scaffolds and dressing materials by utilizing advanced technologies for drug delivery, tissue engineering, and wound healing relevance. These biomaterials are environment-friendly, biodegradable, and biocompatible, and show excellent tissue regeneration attributes. Additionally, being cost-effective they can reduce the burden on the healthcare system as well as provide a sustainable solution to waste management. In this review, the current trends in the utilization of plant and animal waste-derived biomaterials in various biomedical fields are considered along with a separate section on their applications as xenografts.

A novel decellularized nerve graft for repairing peripheral nerve long gap injury in the rat

Decellularized nerve allografts are an alternative to autograft for repairing severe nerve injuries, since they have higher availability and do not induce rejection. In this study, we have assessed the regenerative potential of a novel decellularization protocol for human and rat nerves for repairing nerve resections, compared to the gold standard autograft. A 15-mm gap in the sciatic nerve was repaired with decellularized rat allograft (DC-RA), decellularized human xenograft (DC-HX), or fresh autograft (AG). Electrophysiology tests were performed monthly to evaluate muscle reinnervation, whereas histological and immunohistochemical analyses of the grafts were evaluated at 4 months. A short-term study was also performed to compare the differences between the two decellularized grafts (DC-RA and DC-HX) in early phases of regeneration. The decellularization process eliminated cellularity while preserving the ECM and endoneurial tubules of both rat and human nerves. Higher amount of reinnervation was observed in the AG group compared to the DC-RA group, while only half of the animals of the DC-HX showed distal muscle reinnervation. The number of regenerating myelinated axons in the mid-graft was similar between AG and DC-RA and lower in DC-HX graft, but significantly lower in both DC grafts distally. At short term, fibroblasts repopulated the DC-RA graft, supporting regenerated axons, whereas an important fibrotic reaction was observed around DC-HX grafts. In conclusion, the decellularized allograft sustained regeneration through a long gap in the rat although at a slower rate compared to the ideal autograft, whereas regeneration was limited or even failed when using a decellularized xenograft.

Preparation of decellularized optic nerve grafts

BACKGROUND

Decellularized tissues based on well-conserved extracellular matrices (ECMs) are a common area of research in tissue engineering. Although several decellularization protocols have been suggested for several types of tissues, studies on the optic nerve have been limited.

METHODS

We report decellularization protocol with different detergent for the preparation of acellular optic nerve and tissues were examined. DNA, glycosaminoglycan (GAG), and collagen content of the groups were evaluated with biochemical analyses and examined with histological staining. Mechanical properties, chemical components as well as cytotoxic properties of tissues were compared.

RESULTS

According to the results, it was determined that TX-100 (Triton X-100) was insufficient in decellularization when used alone. In addition, it was noticed that 85% of GAG content was preserved by using TX-100 and TX-100-SD (sodium deoxycholate), while this ratio was calculated as 30% for SDS. In contrast, the effect of the decellularization protocols on ECM structure of the tissues was evaluated by scanning and transmission electron microscopy (SEM and TEM) and determined their mechanical properties. Cytotoxicity analyses were exhibited minimum 95% cell viability for all groups, suggesting that there are no cytotoxic properties of the methods on L929 mouse fibroblast cells.

CONCLUSIONS

The combination of TX-100-SD and TX-100-SDS (sodium dodecyl sulfate) were was determined as the most effective methods to the literature for optic nerve decellularization.

Functional and immunological peculiarities of peripheral nerve allografts

This review addresses the accumulating evidence that live (not decellularized) allogeneic peripheral nerves are functionally and immunologically peculiar in comparison with many other transplanted allogeneic tissues. This is relevant because live peripheral nerve allografts are very effective at promoting recovery after segmental peripheral nerve injury via axonal regeneration and axon fusion. Understanding the immunological peculiarities of peripheral nerve allografts may also be of interest to the field of transplantation in general. Three topics are addressed: The first discusses peripheral nerve injury and the potential utility of peripheral nerve allografts for bridging segmental peripheral nerve defects via axon fusion and axon regeneration. The second reviews evidence that peripheral nerve allografts elicit a more gradual and less severe host immune response allowing for prolonged survival and function of allogeneic peripheral nerve cells and structures. Lastly, potential mechanisms that may account for the immunological differences of peripheral nerve allografts are discussed.

Peripheral Nerve Basic Science Research-What Is Important for Hand Surgeons to Know?

Peripheral nerve injury and regeneration continue to be extensively studied through basic science research using animal models. A translational gap remains between basic science research and clinical application. The importance of peripheral nerve regeneration in basic science research depends on the design of the study, the outcome measures, and the time of regeneration selected. The purpose of this article is to provide an overview of the importance of the design and outcome measures of peripheral nerve basic science research, for hand surgeons to understand for potential clinical translation.

Biomimicry in 3D printing design: implications for peripheral nerve regeneration

Nerve guide conduits (NGCs) connect dissected nerve stumps and effectively repair short-range peripheral nerve defects. However, for long-range defects, autografts show better therapeutic effects, despite intrinsic limitations. Recent evidence shows that biomimetic design is essential for high-performance NGCs, and 3D printing is a promising fabricating technique. The current work includes a brief review of the challenges for peripheral nerve regeneration. The authors propose a potential solution using biomimetic 3D-printed NGCs as alternative therapies. The assessment of biomimetic designs includes microarchitecture, mechanical property, electrical conductivity and biologics inclusion. The applications of 3D printing in preparing NGCs and present strategies to improve therapeutic effects are also discussed.

Regenerative Potential of Platelet-Rich Fibrin Releasate Combined with Adipose Tissue-Derived Stem Cells in a Rat Sciatic Nerve Injury Model

Sciatic nerve injuries, not uncommon in trauma with a limited degree of functional recovery, are considered a persistent clinical, social, and economic problem worldwide. Accumulating evidence suggests that stem cells can promote the tissue regeneration through various mechanisms. The aim of the present study was to investigate the role of adipose tissue–derived stem cells (ADSCs) and combine with platelet-rich fibrin releasate (PRFr) in the regeneration of sciatic nerve injury in rats. Twenty-four Sprague-Dawley rats were randomly assigned to four groups, a blade was used to transect the left hindlimb sciatic nerve, and silicon tubes containing one of the following (by injection) were used to bridge the nerve proximal and distal ends (10-mm gap): group 1: untreated controls; group 2: PRFr alone; group 3: ADSCs alone; group 4: PRFr + ADSCs-treated. Walking function was assessed in horizontal rung ladder apparatus to compare the demands of the tasks and test sensitivity at 1-mo interval for a total of 3 mo. The gross inspection and histological examination was performed at 3 mo post transplantation. Overall, PRFr + ADSCs-treated performed better compared with PRFr or ADSCs injections alone. Significant group differences of neurological function were observed in ladder rung walking tests in all treated groups compared to that of untreated controls (P < 0.05). This injection approach may provide a successfully employed technique to target sciatic nerve defects in vivo, and the combined strategy of ADSCs with PRFr appears to have a superior effect on nerve repair.

Comparison of Decellularization Protocols to Generate Peripheral Nerve Grafts: A Study on Rat Sciatic Nerves

In critical nerve gap repair, decellularized nerve allografts are considered a promising tissue engineering strategy that can provide superior regeneration results compared to nerve conduits. Decellularized nerves offer a well-conserved extracellular matrix component that has proven to play an important role in supporting axonal guiding and peripheral nerve regeneration. Up to now, the known decellularized techniques are time and effort consuming. The present study, performed on rat sciatic nerves, aims at investigating a novel nerve decellularization protocol able to combine an effective decellularization in short time with a good preservation of the extracellular matrix component. To do this, a decellularization protocol proven to be efficient for tendons (DN-P1) was compared with a decellularization protocol specifically developed for nerves (DN-P2). The outcomes of both the decellularization protocols were assessed by a series of in vitro evaluations, including qualitative and quantitative histological and immunohistochemical analyses, DNA quantification, SEM and TEM ultrastructural analyses, mechanical testing, and viability assay. The overall results showed that DN-P1 could provide promising results if tested in vivo, as the in vitro characterization demonstrated that DN-P1 conserved a better ultrastructure and ECM components compared to DN-P2. Most importantly, DN-P1 was shown to be highly biocompatible, supporting a greater number of viable metabolically active cells.

Effective decellularization of human nerve matrix for regenerative medicine with a novel protocol

Injuries to the peripheral nerves represent a frequent cause of permanent disability in adults. The repair of large nerve lesions involves the use of autografts, but they have several inherent limitations. Overcoming these limitations, the use of decellularized nerve matrix has emerged as a promising treatment in tissue regenerative medicine. Here, we generate longer human decellularized nerve segments with a novel decellularization method, using nonionic, zwitterionic, and enzymatic incubations. Efficiency of decellularization was measured by DNA quantification and cell remnant analysis (myelin, S100, neurofilament). The evaluation of the extracellular matrix (collagen, laminin, and glycosaminoglycans) preservation was carried out by enzyme-linked immunosorbent assay (ELISA) or biochemical methods, along with histological and immunofluorescence analysis. Moreover, biomechanical properties and cytocompatibility were tested. Results showed that the decellularized nerves generated with this protocol have a concentration of DNA below the threshold of 50 ng/mg of dry tissue. Furthermore, myelin, S100, and MHCII proteins were absent, although some neurofilament remnants could be observed. Moreover, extracellular matrix proteins were well maintained, as well as the biomechanical properties, and the decellularized nerve matrix did not generate cytotoxicity. These results show that our method is effective for the generation of decellularized human nerve grafts. The generation of longer decellularized nerve segments would allow the understanding of the regenerative neurobiology after nerve injuries in both clinical assays and bigger animal models. Effective decellularization of human nerve matrix for regenerative medicine with a novel protocol. Combination of zwitterionic, non-ionic detergents, hyperosmotic solution and nuclease enzyme treatment remove cell remnants, maintain collagen, laminin and biomechanics without generating cytotoxic leachables.

Histological, Biomechanical, and Biological Properties of Genipin-Crosslinked Decellularized Peripheral Nerves

Acellular nerve allografts (ANGs) represent a promising alternative in nerve repair. Our aim is to improve the structural and biomechanical properties of biocompatible Sondell (SD) and Roosens (RS) based ANGs using genipin (GP) as a crosslinker agent ex vivo. The impact of two concentrations of GP (0.10% and 0.25%) on Wistar rat sciatic nerve-derived ANGs was assessed at the histological, biomechanical, and biocompatibility levels. Histology confirmed the differences between SD and RS procedures, but not remarkable changes were induced by GP, which helped to preserve the nerve histological pattern. Tensile test revealed that GP enhanced the biomechanical properties of SD and RS ANGs, being the crosslinked RS ANGs more comparable to the native nerves used as control. The evaluation of the ANGs biocompatibility conducted with adipose-derived mesenchymal stem cells cultured within the ANGs confirmed a high degree of biocompatibility in all ANGs, especially in RS and RS-GP 0.10% ANGs. Finally, this study demonstrates that the use of GP could be an efficient alternative to improve the biomechanical properties of ANGs with a slight impact on the biocompatibility and histological pattern. For these reasons, we hypothesize that our novel crosslinked ANGs could be a suitable alternative for future in vivo preclinical studies.

Electrospun Fiber Scaffolds for Engineering Glial Cell Behavior to Promote Neural Regeneration

Electrospinning is a fabrication technique used to produce nano- or micro- diameter fibers to generate biocompatible, biodegradable scaffolds for tissue engineering applications. Electrospun fiber scaffolds are advantageous for neural regeneration because they mimic the structure of the nervous system extracellular matrix and provide contact guidance for regenerating axons. Glia are non-neuronal regulatory cells that maintain homeostasis in the healthy nervous system and regulate regeneration in the injured nervous system. Electrospun fiber scaffolds offer a wide range of characteristics, such as fiber alignment, diameter, surface nanotopography, and surface chemistry that can be engineered to achieve a desired glial cell response to injury. Further, electrospun fibers can be loaded with drugs, nucleic acids, or proteins to provide the local, sustained release of such therapeutics to alter glial cell phenotype to better support regeneration. This review provides the first comprehensive overview of how electrospun fiber alignment, diameter, surface nanotopography, surface functionalization, and therapeutic delivery affect Schwann cells in the peripheral nervous system and astrocytes, oligodendrocytes, and microglia in the central nervous system both in vitro and in vivo. The information presented can be used to design and optimize electrospun fiber scaffolds to target glial cell response to mitigate nervous system injury and improve regeneration.

Fundamentals and Current Strategies for Peripheral Nerve Repair and Regeneration

A body of evidence indicates that peripheral nerves have an extraordinary yet limited capacity to regenerate after an injury. Peripheral nerve injuries have confounded professionals in this field, from neuroscientists to neurologists, plastic surgeons, and the scientific community. Despite all the efforts, full functional recovery is still seldom. The inadequate results attained with the "gold standard" autograft procedure still encourage a dynamic and energetic research around the world for establishing good performing tissue-engineered alternative grafts. Resourcing to nerve guidance conduits, a variety of methods have been experimentally used to bridge peripheral nerve gaps of limited size, up to 30-40 mm in length, in humans. Herein, we aim to summarize the fundamentals related to peripheral nerve anatomy and overview the challenges and scientific evidences related to peripheral nerve injury and repair mechanisms. The most relevant reports dealing with the use of both synthetic and natural-based biomaterials used in tissue engineering strategies when treatment of nerve injuries is envisioned are also discussed in depth, along with the state-of-the-art approaches in this field.

Tissue Engineered Bands of Büngner for Accelerated Motor and Sensory Axonal Outgrowth

Following peripheral nerve injury comprising a segmental defect, the extent of axon regeneration decreases precipitously with increasing gap length. Schwann cells play a key role in driving axon re-growth by forming aligned tubular guidance structures called bands of Büngner, which readily occurs in distal nerve segments as well as within autografts - currently the most reliable clinically-available bridging strategy. However, host Schwann cells generally fail to infiltrate large-gap acellular scaffolds, resulting in markedly inferior outcomes and motivating the development of next-generation bridging strategies capable of fully exploiting the inherent pro-regenerative capability of Schwann cells. We sought to create preformed, implantable Schwann cell-laden microtissue that emulates the anisotropic structure and function of naturally-occurring bands of Büngner. Accordingly, we developed a biofabrication scheme leveraging biomaterial-induced self-assembly of dissociated rat primary Schwann cells into dense, fiber-like three-dimensional bundles of Schwann cells and extracellular matrix within hydrogel micro-columns. This engineered microtissue was found to be biomimetic of morphological and phenotypic features of endogenous bands of Büngner, and also demonstrated 8 and 2× faster rates of axonal extension in vitro from primary rat spinal motor neurons and dorsal root ganglion sensory neurons, respectively, compared to 3D matrix-only controls or planar Schwann cells. To our knowledge, this is the first report of accelerated motor axon outgrowth using aligned Schwann cell constructs. For translational considerations, this microtissue was also fabricated using human gingiva-derived Schwann cells as an easily accessible autologous cell source. These results demonstrate the first tissue engineered bands of Büngner (TE-BoBs) comprised of dense three-dimensional bundles of longitudinally aligned Schwann cells that are readily scalable as implantable grafts to accelerate axon regeneration across long segmental nerve defects.

Fabrication and evaluation of an optimized acellular nerve allograft with multiple axial channels

Acellular nerve allografts are promising alternatives to autologous nerve grafts, but still have many drawbacks which greatly limit their curative effects. Here, we developed an optimized acellular nerve allograft with multiple axial channels by a modified decellularization method. These allografts were confirmed to preserve more extracellular matrix components and factors, and remove cellular components effectively. Meanwhile, macrochannels and microchannels were introduced to optimize internal microstructure of allografts, which increases porosity and water absorption, without significant loss of mechanical strength. The in vitro experiments demonstrated that the multichannel allografts showed superior ability of facilitating proliferation and penetration of Schwann cells. Additionally, in the in vivo experiments, the multichannel allografts were used to bridge 10 mm rat sciatic nerve defects. They exhibited better capacity to guide regenerative nerve fibers through the defective segment and restore innervation of target organs, thus achieving better recovery of muscle and motor function, in comparison with conventional acellular allografts. These findings indicate that this multichannel acellular nerve allograft has great potential for clinical application and provides a new prospective for future investigations of nerve regeneration. STATEMENT OF SIGNIFICANCE: Acellular nerve allografts, with preservation of natural extracellular matrix, are officially approved to repair peripheral nerve injury in some countries. However, bioactive component loss and compact internal structure result in variable clinical effects of conventional acellular allografts. In the present study, we fabricated an optimized acellular nerve allograft with multiple axial channels, which could both enable decellularization to be easily accomplished and reduce the amount of detergents in the preparation process. Characterization of the multichannel acellular allografts was confirmed to have better preservation of ECM bioactive molecules and regenerative factors. Efficiency evaluation showed the multichannel allografts could facilitate Schwann cells to migrate inside them in vitro, and enhance regrowth and myelination of axons as well as recovery of muscle and motor function in vivo.

Preclinical Validation of SilkBridgeTM for Peripheral Nerve Regeneration

Silk fibroin (Bombyx mori) was used to manufacture a nerve conduit (SilkBridge^TM) characterized by a novel 3D architecture. The wall of the conduit consists of two electrospun layers (inner and outer) and one textile layer (middle), perfectly integrated at the structural and functional level. The manufacturing technology conferred high compression strength on the device, thus meeting clinical requirements for physiological and pathological compressive stresses. As demonstrated in a previous work, the silk material has proven to be able to provide a valid substrate for cells to grow on, differentiate and start the fundamental cellular regenerative activities in vitro and, in vivo, at the short time point of 2 weeks, to allow the starting of regenerative processes in terms of good integration with the surrounding tissues and colonization of the wall layers and of the lumen with several cell types. In the present study, a 10 mm long gap in the median nerve was repaired with 12 mm SilkBridge^TM conduit and evaluated at middle (4 weeks) and at longer time points (12 and 24 weeks). The SilkBridge^TM conduit led to a very good functional and morphological recovery of the median nerve, similar to that observed with the reference autograft nerve reconstruction procedure. Taken together, all these results demonstrated that SilkBridge^TM has an optimized balance of biomechanical and biological properties, which allowed proceeding with a first-in-human clinical study aimed at evaluating safety and effectiveness of using the device for the reconstruction of digital nerve defects in humans.

Development of vascularized nerve scaffold using perfusion-decellularization and recellularization

INTRODUCTION

Vascularized nerve grafts (VNG) may offer an advantage in peripheral nerve regeneration by avoiding ischemic damage and central necrosis observed in non-VNG, particularly for the treatment of large and long nerve defects. However, surgical complexity, donor site morbidity and limited nerve availability remain important drawbacks for the clinical use of VNG. Here we explore the potential of perfusion-decellularization for bioengineering a VNG to be used in peripheral nerve reconstruction.

METHODS

Porcine sciatic nerves were surgically procured along with their vascular pedicle attached. The specimens were decellularized via perfusion-decellularization and preservation of the extracellular matrix (ECM), vascular patency and tissue cytokine contents were examined. Scaffold reendothelialization was conducted with porcine aortic endothelial cells in a perfusion-bioreactor.

RESULTS

Morphologic examination of decellularized VNG and analysis of the DNA content demonstrated cell clearance whereas ECM content and structures of the nerve fascicles were preserved. Using 3D micro-computed tomography imaging we observed optimal vasculature preservation in decellularized scaffolds, down to the capillary level. Cytokine quantification demonstrated measurable levels of growth factors after decellularization. Endothelial cell engraftment of the large caliber vessels was observed in reendothelialized scaffolds.

CONCLUSIONS

In this study we provide evidence that perfusion-decellularization can be used to create vascularized nerve scaffolds in which the vasculature and the ECM component are well preserved. As compared to non-vascularized conduits, engineered vascularized nerve scaffolds may represent an ideal approach for promoting better nerve regeneration in larger nerve defect reconstructions.

Modification of tubular chitosan-based peripheral nerve implants: applications for simple or more complex approaches

Surgical treatment of peripheral nerve injuries is still a major challenge in human clinic. Up to now, none of the well-developed microsurgical treatment options is able to guarantee a complete restoration of nerve function. This restriction is also effective for novel clinically approved artificial nerve guides. In this review, we compare surgical repair techniques primarily for digital nerve injuries reported with relatively high prevalence to be valuable attempts in clinical digital nerve repair and point out their advantages and shortcomings. We furthermore discuss the use of artificial nerve grafts with a focus on chitosan-based nerve guides, for which our own studies contributed to their approval for clinical use. In the second part of this review, very recent future perspectives for the enhancement of tubular (commonly hollow) nerve guides are discussed in terms of their clinical translatability and ability to form three-dimensional constructs that biomimick the natural nerve structure. This includes materials that have already shown their beneficial potential in in vivo studies like fibrous intraluminal guidance structures, hydrogels, growth factors, and approaches of cell transplantation. Additionally, we highlight upcoming future perspectives comprising co-application of stem cell secretome. From our overview, we conclude that already simple attempts are highly effective to increase the regeneration supporting properties of nerve guides in experimental studies. But for bringing nerve repair with bioartificial nerve grafts to the next level, e.g. repair of defects > 3 cm in human patients, more complex intraluminal guidance structures such as innovatively manufactured hydrogels and likely supplementation of stem cells or their secretome for therapeutic purposes may represent promising future perspectives.

Decellularized skeletal muscles display neurotrophic effects in three-dimensional organotypic cultures

Skeletal muscle decellularization allows the generation of natural scaffolds that retain the extracellular matrix (ECM) mechanical integrity, biological activity, and three‐dimensional (3D) architecture of the native tissue. Recent reports showed that in vivo implantation of decellularized muscles supports muscle regeneration in volumetric muscle loss models, including nervous system and neuromuscular junctional homing. Since the nervous system plays pivotal roles during skeletal muscle regeneration and in tissue homeostasis, support of reinnervation is a crucial aspect to be considered. However, the effect of decellularized muscles on reinnervation and on neuronal axon growth has been poorly investigated. Here, we characterized residual protein composition of decellularized muscles by mass spectrometry and we show that scaffolds preserve structural proteins of the ECM of both skeletal muscle and peripheral nervous system. To investigate whether decellularized scaffolds could per se attract neural axons, organotypic sections of spinal cord were cultured three dimensionally in vitro, in presence or in absence of decellularized muscles. We found that neural axons extended from the spinal cord are attracted by the decellularized muscles and penetrate inside the scaffolds upon 3D coculture. These results demonstrate that decellularized scaffolds possess intrinsic neurotrophic properties, supporting their potential use for the treatment of clinical cases where extensive functional regeneration of the muscle is required.

Detergent-based decellularized peripheral nerve allografts: An in vivo preclinical study in the rat sciatic nerve injury model

Nerve autograft is the gold standard technique to repair critical nerve defects, but efficient alternatives are needed. The present study evaluated the suitability of our novel Roosens-based (RSN) decellularized peripheral nerve allografts (DPNAs) in the repair of 10-mm sciatic nerve defect in rats at the functional and histological levels after 12 weeks. These DPNAs were compared with the autograft technique (AUTO) and Sondell (SD) or Hudson (HD) based DPNAs. Clinical and functional assessments demonstrated a partial regeneration in all operated animals. RSN-based DPNAs results were comparable with SD and HD groups and closely comparable with the AUTO group without significant differences (p > .05). Overall hematological studies confirmed the biocompatibility of grafted DPNAs. In addition, biochemistry revealed some signs of muscle affection in all operated animals. These results were confirmed by the loss of weight and volume of the muscle and by muscle histology, especially in DPNAs. Histology of repaired nerves confirmed an active nerve tissue regeneration and partial myelination along with the implanted grafts, being the results obtained with HD and RSN-based DPNAs comparable with the AUTO group. Finally, this in vivo study suggests that our novel RSN-based DPNAs supported a comparable tissue regeneration, along the 10-mm nerve gap, after 12-week follow-up to HD DPNAs, and both were superior to SD group and closely comparable with autograft technique. However, further improvements are needed to overcome the efficacy of the nerve autograft technique.

Long-Term Outcomes of Donor Site Morbidity After Sural Nerve Graft Harvesting

Purpose

Although nerve autografts have been considered the standard treatment for peripheral nerve defects, limited studies have reported long-term outcomes of nerve harvesting over 15 years after surgery. This study aimed to evaluate the long-term outcomes of donor site morbidity after sural nerve graft harvesting.

Methods

Thirteen patients for whom more than 15 years had passed after harvesting of the sural nerve for peripheral nerve defects were included. Mean follow-up was 29.5 years. Sensory disturbances and difficulty in performing foot movements immediately after surgery and currently were evaluated on a 10-point scale. Influences on daily living and work and current satisfaction with the autologous sural nerve graft were evaluated.

Results

Sensory disturbances and difficulty in movement tended to improve; however, the differences between time points were not significant. Influences on activities of daily living and work were mild, and the satisfaction level for autologous sural nerve graft was high.

Conclusions

Although donor site morbidity after sural nerve graft harvesting persisted for a long time after surgery, foot symptoms and functional impairment were mild.

Type of study/level of evidence

Therapeutic V.

Animal models used to study direct peripheral nerve repair: a systematic review

Objective:

Peripheral nerve repair is required after traumatic injury. This common condition represents a major public health problem worldwide. Recovery after nerve repair depends on several factors, including the severity of the injury, the nerve involved, and the surgeon’s technical skills. Despite the precise microsurgical repair of nerve lesions, adequate functional recovery is not always achieved and, therefore, the regeneration process and surgical techniques are still being studied. Pre-clinical animal models are essential for this research and, for this reason, the focus of the present systematic review (according to the PRISMA statement) was to analyze the different animal models used in pre-clinical peripheral nerve repair studies.

Data sources:

Original articles, published in English from 2000 to 2018, were collected using the Web of Science, Scopus, and PubMed databases.

Data selection:

Only preclinical trials on direct nerve repair were included in this review. The articles were evaluated by the first two authors, in accordance with predefined data fields.

Outcome measures:

The primary outcomes included functional motor abilities, daily activity and regeneration rate. Secondary outcomes included coaptation technique and animal model.

Results:

This review yielded 267 articles, of which, after completion of the screening, 49 studies were analyzed. There were 1425 animals in those 49 studies, being rats, mice, guinea pigs, rabbits, cats and dogs the different pre-clinical models. The nerves used were classified into three groups: head and neck (11), forelimb (8) and hindlimb (30). The techniques used to perform the coaptation were: microsuture (46), glue (12), laser (8) and mechanical (2). The follow-up examinations were histology (43), electrophysiological analysis (24) and behavioral observation (22).

Conclusion:

The most widely used animal model in the study of peripheral nerve repair is the rat. Other animal models are also used but the cost-benefit of the rat model provides several strengths over the others. Suture techniques are currently the first option for nerve repair, but the use of glues, lasers and bioengineering materials is increasing. Hence, further research in this field is required to improve clinical practice.

The Combination of Adipose-derived Schwann-like Cells and Acellular Nerve Allografts Promotes Sciatic Nerve Regeneration and Repair through the JAK2/STAT3 Signaling Pathway in Rats

Schwann cells (SCs) combined with acellular nerve allografts (ANAs) effectively promote the regeneration and repair of peripheral nerves, but the exact mechanism has not been fully elucidated. However, the disadvantages of SCs include their limited source and slow rate of expansion in vitro. Previous studies have found that adipose-derived stem cells have the ability to differentiate into Schwann-like cells. Therefore, we speculated that Schwann-like cells combined with ANAs could profoundly facilitate nerve regeneration and repair. The aim of the present study was to investigate the cellular and molecular mechanisms of regeneration and repair. In this study, tissue-engineered nerves were first constructed by adipose-derived Schwann-like cells and ANAs to bridge missing sciatic nerves. Then, the rats were randomly divided into five groups (n = 12 per group): a Control group; a Model group; an ADSC group; an SC-L group; and a DMEM group. Twelve weeks postsurgery, behavioral function tests and molecular biological techniques were used to evaluate the function of regenerated nerves and the relevant molecular mechanisms after sciatic nerve injury (SNI). The results showed that adipose-derived Schwann-like cells combined with ANAs markedly promoted sciatic nerve regeneration and repair. These findings also demonstrated that the expression of neurotrophic factors (NFs) was increased, and the expression of Janus activated kinase2 (JAK2)/P-JAK2, signal transducer and activator of transcription-3 (STAT3)/P-STAT3 was decreased in the spinal cord after SNI. Therefore, these results suggested that highly expressed NFs in the spinal cord could promote nerve regeneration and repair by inhibiting activation of the JAK2/STAT3 signaling pathway.

KLF7 overexpression in bone marrow stromal stem cells graft transplantation promotes sciatic nerve regeneration

OBJECTIVE

Our previous study demonstrated that the transcription factor, Krüppel-like Factor 7 (KLF7), stimulates axon regeneration following peripheral nerve injury. In the present study, we used a gene therapy approach to overexpress KLF7 in bone marrow-derived stem/stromal cells (BMSCs) as support cells, combined with acellular nerve allografts (ANAs) and determined the potential therapeutic efficacy of a KLF7-transfected BMSC nerve graft transplantation in a rodent model for sciatic nerve injury and repair.

APPROACH

We efficiently transfected BMSCs with adeno-associated virus (AAV)-KLF7, which were then seeded in ANAs for bridging sciatic nerve defects.

MAIN RESULTS

KLF7 overexpression promotes proliferation, survival, and Schwann-like cell differentiation of BMSCs in vitro. In vivo, KLF7 overexpression promotes transplanted BMSCs survival and myelinated fiber regeneration in regenerating ANAs; however, KLF7 did not improve Schwann-like cell differentiation of BMSCs within in the nerve grafts. KLF7-BMSCs significantly upregulated expression and secretion of neurotrophic factors by BMSCs, including nerve growth factor, ciliary neurotrophic factor, brain-derived neurotrophic factor, and glial cell line-derived neurotrophic factor in regenerating ANA. KLF7-BMSCs also improved motor axon regeneration, and subsequent neuromuscular innervation and prevention of muscle atrophy. These benefits were associated with increased motor functional recovery of regenerating ANAs.

SIGNIFICANCE

Our findings suggest that KLF7-BMSCs promoted peripheral nerve axon regeneration and myelination, and ultimately, motor functional recovery. The mechanism of KLF7 action may be related to its ability to enhance transplanted BMSCs survival and secrete neurotrophic factors rather than Schwann-like cell differentiation. This study provides novel foundational data connecting the benefits of KLF7 in neural injury and repair to BMSC biology and function, and demonstrates a potential combination approach for the treatment of injured peripheral nerve via nerve graft transplant.