Chemokine platelet factor 4 accelerates peripheral nerve regeneration by regulating Schwann cell activation and axon elongation

Schwann cells in peripheral nerves react to traumatic nerve injury by attempting to grow and regenerate.Howeve r,it is unclear what factors play a role in this process.In this study,we searched a GEO database and found that expression of platelet factor 4 was markedly up-regulated after sciatic nerve injury.Platelet factor is an important molecule in cell apoptosis,diffe rentiation,survival,and proliferation.Further,polymerase chain reaction and immunohistochemical staining confirmed the change in platelet factor 4 in the sciatic nerve at different time points after injury.Enzyme-linked immunosorbent assay confirmed that platelet factor 4 was secreted by Schwann cells.We also found that silencing platelet factor 4 decreased the proliferation and migration of primary cultured Schwann cells,while exogenously applied platelet factor 4 stimulated Schwann cell prolife ration and migration and neuronal axon growth.Furthermore,knocking out platelet factor 4 inhibited the prolife ration of Schwann cells in injured rat sciatic nerve.These findings suggest that Schwann cell-secreted platelet factor 4 may facilitate peripheral nerve repair and regeneration by regulating Schwann cell activation and axon growth.Thus,platelet factor 4 may be a potential therapeutic target for traumatic peripheral nerve injury.

Translational bioengineering strategies for peripheral nerve regeneration:opportunities,challenges,and novel concepts

Peripheral nerve injuries remain a challenging problem in need of better treatment strategies.Despite best efforts at surgical reconstruction and postoperative rehabilitation,patients are often left with persistent,debilitating motor and sensory deficits.There are currently no therapeutic strategies proven to enhance the regenerative process in humans.A clinical need exists for the development of technologies to promote nerve regeneration and improve functional outcomes.Recent advances in the fields of tissue engineering and nanotechnology have enabled biomaterial scaffolds to modulate the host response to tissue repair through tailored mechanical,chemical,and conductive cues.New bioengineered approaches have enabled targeted,sustained delivery of protein therapeutics with the capacity to unlock the clinical potential of a myriad of neurotrophic growth factors that have demonstrated promise in enhancing regenerative outcomes.As such,further exploration of combinatory strategies leveraging these technological advances may offer a pathway towards clinically translatable solutions to advance the care of patients with peripheral nerve injuries.This review first presents the various emerging bioengineering strategies that can be applied for the management of nerve gap injuries.We cover the rationale and limitations for their use as an alternative to autografts,focusing on the approaches to increase the number of regenerating axons crossing the repair site,and facilitating their growth towards the distal stump.We also discuss the emerging growth factor-based therapeutic strategies designed to improve functional outcomes in a multimodal fashion,by accelerating axonal growth,improving the distal regenerative environment,and preventing end-organs atrophy.

Potential application of let-7a antagomir in injured peripheral nerve regeneration

Neurotrophic factors,particularly nerve growth factor,enhance neuronal regeneration.However,the in vivo applications of nerve growth factor are largely limited by its intrinsic disadvantages,such as its short biological half-life,its contribution to pain response,and its inability to cross the blood-brain barrier.Considering that let-7(human miRNA)targets and regulates nerve growth factor,and that let-7 is a core regulator in peripheral nerve regeneration,we evaluated the possibilities of let-7 application in nerve repair.In this study,anti-let-7a was identified as the most suitable let-7 family molecule by analyses of endogenous expression and regulatory relationship,and functional screening.Let-7a antagomir demonstrated biosafety based on the results of in vivo safety assessments and it entered into the main cell types of the sciatic nerve,including Schwann cells,fibroblasts and macrophages.Use of hydrogel effectively achieved controlled,localized,and sustained delivery of let-7a antagomir.Finally,let-7a antagomir was integrated into chitosan conduit to construct a chitosan-hydrogel scaffold tissue-engineered nerve graft,which promoted nerve regeneration and functional recovery in a rat model of sciatic nerve transection.Our study provides an experimental basis for potential in vivo application of let-7a.

Hypoxic pre-conditioned adipose-derived stem/progenitor cells embedded in fibrin conduits promote peripheral nerve regeneration in a sciatic nerve graft model

Recent results emphasize the supportive effects of adipose-derived multipotent stem/progenitor cells(ADSPCs)in peripheral nerve recovery.Cultivation under hypoxia is considered to enhance the release of the regenerative potential of ADSPCs.This study aimed to examine whether peripheral nerve regeneration in a rat model of autologous sciatic nerve graft benefits from an additional custom-made fibrin conduit seeded with hypoxic pre-conditioned(2%oxygen for 72 hours)autologous ADSPCs(n=9).This treatment mode was compared with three others:fibrin conduit seeded with ADSPCs cultivated under normoxic conditions(n=9);non-cell-carrying conduit(n=9);and nerve autograft only(n=9).A 16-week follow-up included functional testing(sciatic functional index and static sciatic index)as well as postmortem muscle mass analyses and morphometric nerve evaluations(histology,g-ratio,axon density,and diameter).At 8 weeks,the hypoxic pre-conditioned group achieved significantly higher sciatic functional index/static sciatic index scores than the other three groups,indicating faster functional regeneration.Furthermore,histologic evaluation showed significantly increased axon outgrowth/branching,axon density,remyelination,and a reduced relative connective tissue area.Hypoxic pre-conditioned ADSPCs seeded in fibrin conduits are a promising adjunct to current nerve autografts.Further studies are needed to understand the underlying cellular mechanism and to investigate a potential application in clinical practice.

Transplantation of mesenchymal stem cells from human umbilical cord versus human umbilical cord blood for peripheral nerve regeneration

BACKGROUND： Mesenchymal stem cells （MSCs） appear to be a good alternative to Schwann cells in the treatment of peripheral nerve injury. Fetal stem cells, like umbilical cord blood （UCB） and umbilical cord （UC） stem cells, have several advantages over adult stem cells. OBJECTIVE： To assess the effects of UC-derived MSCs （UCMSCs） and UCB-derived MSCs （UCBMSCs） in repair of sciatic nerve defects. DESIGN, TIME AND SETTING： A randomized controlled animal experiment was performed at the laboratory of Department of Oral and Maxillofacial Surgery, Seoul National University Dental Hospital, from July to December 2009. MATERIALS： UCMSCs were provided by the Research Institute of Biotechnology, Dongguk University. UCBMSCs were provided by the Laboratory of Stem Cells and Tumor Biology, College of Veterinary Medicine, Seoul National University. Dulbecco＇s modified Eagle＇s medium （DMEM） was purchased from Gibco-BRL, USA. METHODS： Seven-week-old Sprague-Dawley rats were randomly and evenly divided into three groups： DMEM, UCBMSCs, and UCMSCs. A 10-mm defect in the left sciatic nerve was constructed in all rats. DMEM （15 μL） containing 1×10^6 UCBMSCs or UCMSCs was injected into the gap between nerve stumps, with the surrounding epineurium as a natural conduit. For the DMEM group, simple DMEM was injected. MAIN OUTCOME MEASURES： At 7 weeks after sciatic nerve dissection, dorsal root ganglia neurons were labeled by fluorogold retrograde labeling. At 8 weeks, electrophysiology and histomorphometry were performed. At 2, 4, 6, and 8 weeks after surgery, sciatic nerve function was evaluated using gait analysis. RESULTS： The UCBMSCs group and the UCMSCs group exhibited similar sciatic nerve function and electrophysiological indices, which were better than the DMEM group, as measured by gait analysis （P 〈 0.05）. Fluorogold retrograde labeling of sciatic nerve revealed that the UCBMSCs group demonstrated a higher number of labeled neurons; however, the differences were not significant. Histomorphometric indices were similar in the UCBMSCs and UCMSCs groups, and total axon counts, particularly axon density （P 〈 0.05）, were significantly greater in the UCBMSCs and UCMSCs groups than in the DMEM group. CONCLUSION： Transplanting either UCBMSCs or UCMSCs into axotomized sciatic nerves could accelerate and promote sciatic nerve regeneration over 8 weeks. Both treatments had similar effects on nerve regeneration.

The Achyranthes bidentata polypeptide k fraction enhances neuronal growth in vitro and promotes peripheral nerve regeneration after crush injury in vivo

We have previously shown that Achyranthes bidentata polypeptides （ABPP）, isolated from Achyranthes bidentata Blume （a medicinal herb）, exhibit neurotrophic and neuroprotective effects on the nervous system. To identify the major active component of ABPP, and thus optimize the use of ABPP, we used reverse-phase high performance liquid chromatography to separate ABPP. We obtained 12 fractions, among which the fraction of ABPPk demonstrated the strongest neuroactivity. Immunocytochemistry and western blot analysis showed that ABPPk promoted neurite growth in cultured dorsal root ganglion explant and dorsal root ganglion neurons, which might be associated with activation of Erk1/2. A combination of behavioral tests, electrophysiological assessment, and histomorphometric analysis indicated that ABPPk enhanced nerve regeneration and function restoration in a mouse model of crushed sciatic nerve. All the results suggest that ABPPk, as the key component of ABPP, can be used for peripheral nerve repair to yield better outcomes than ABPP.

Sustained release of exosomes loaded into polydopamine-modified chitin conduits promotes peripheral nerve regeneration in rats

Exosomes derived from mesenchymal stem cells are of therapeutic interest because of their important role in intracellular communication and biological regulation.On the basis of previously studied nerve conduits,we designed a polydopamine-modified chitin conduit loaded with mesenchymal stem cell-derived exosomes that release the exosomes in a sustained and stable manner.In vitro experiments revealed that rat mesenchymal stem cell-derived exosomes enhanced Schwann cell proliferation and secretion of neurotrophic and growth factors,increased the expression of Jun and Sox2 genes,decreased the expression of Mbp and Krox20 genes in Schwann cells,and reprogrammed Schwann cells to a repair phenotype.Furthermore,mesenchymal stem cell-derived exosomes promoted neurite growth of dorsal root ganglia.The polydopamine-modified chitin conduits loaded with mesenchymal stem cell-derived exosomes were used to bridge 2 mm rat sciatic nerve defects.Sustained release of exosomes greatly accelerated nerve healing and improved nerve function.These findings confirm that sustained release of mesenchymal stem cell-derived exosomes loaded into polydopamine-modified chitin conduits promotes the functional recovery of injured peripheral nerves.

Stimulating effect of thyroid hormones in peripheral nerve regeneration:research history and future direction toward clinical therapy

Injury to peripheral nerves is often observed in the clinic and severe injuries may cause loss of motor and sensory functions.Despite extensive investigation,testing various surgical repair techniques and neurotrophic molecules,at present,a satisfactory method to ensuring successful recovery does not exist.For successful molecular therapy in nerve regeneration,it is essential to improve the intrinsic ability of neurons to survive and to increase the speed of axonal outgrowth.Also to induce Schwann cell phenotypical changes to prepare the local environment favorable for axonal regeneration and myelination.Therefore,any molecule that regulates gene expression of both neurons and Schwann cells could play a crucial role in peripheral nerve regeneration.Clinical and experimental studies have reported that thyroid hormones are essential for the normal development and function of the nervous system,so they could be candidates for nervous system regeneration.This review provides an overview of studies devoted to testing the effect of thyroid hormones on peripheral nerve regeneration.Also it emphasizes the importance of combining biodegradable tubes with local administration of triiodothyronine for future clinical therapy of human severe injured nerves.We highlight that the local and single administration of triiodothyronine within biodegradable nerve guide improves significantly the regeneration of severed peripheral nerves,and accelerates functional recovering.This technique provides a serious step towards future clinical application of triiodothyronine in human severe injured nerves.The possible regulatory mechanism by which triiodothyronine stimulates peripheral nerve regeneration is a rapid action on both axotomized neurons and Schwann cells.

Polydopamine-modified chitin conduits with sustained release of bioactive peptides enhance peripheral nerve regeneration in rats

The introduction of neurotrophic factors into injured peripheral nerve sites is beneficial to peripheral nerve regeneration.However,neurotrophic facto rs are rapidly degraded in vivo and obstruct axonal regeneration when used at a supraphysiological dose,which limits their clinical benefits.Bioactive mimetic peptides have been developed to be used in place of neurotrophic factors because they have a similar mode of action to the original growth fa ctors and can activate the equivalent receptors but have simplified sequences and structures.In this study,we created polydopamine-modified chitin conduits loaded with brain-derived neurotrophic factor mimetic peptides and vascular endothelial growth fa ctor mimetic peptides(Chi/PDA-Ps).We found that the Chi/PDA-Ps conduits were less cytotoxic in vitro than chitin conduits alone and provided sustained release of functional peptides.In this study,we evaluated the biocompatibility of the Chi/P DA-Ps conduits.Brain-derived neurotrophic factor mimetic peptide and vascular endothelial growth fa ctor mimetic peptide synergistically promoted prolife ration of Schwann cells and secretion of neurotrophic factors by Schwann cells and attachment and migration of endothelial cells in vitro.The Chi/P DA-Ps conduits were used to bridge a 2 mm gap between the nerve stumps in rat models of sciatic nerve injury.We found that the application of Chi/PDA-Ps conduits could improve the motor function of rats and reduce gastrocnemius atrophy.The electrophysiological results and the microstructure of regenerative nerves showed that the nerve conduction function and re myelination was further resto red.These findings suggest that the Chi/PDA-Ps conduits have great potential in peripheral nerve injury repair.

Nerve bundle formation during the promotion of peripheral nerve regeneration:collagenⅥ-neural cell adhesion molecule 1 interaction

The formation of nerve bundles,which is partially regulated by neural cell adhesion molecule 1(NCAM1),is important for neural network organization during peripheral nerve regeneration.However,little is known about how the extracellular matrix(ECM)microenvironment affects this process.Here,we seeded dorsal root ganglion tissue blocks on different ECM substrates of peripheral nerve ECM-derived matrixgel,Matrigel,laminin 521,collagen I,and collagen IV,and observed well-aligned axon bundles growing in the peripheral nerve ECM-derived environment.We confirmed that NCAM1 is necessary but not sufficient to trigger this phenomenon.A protein interaction assay identified collagen VI as an extracellular partner of NCAM1 in the regulation of axonal fasciculation.Collagen VI interacted with NCAM1 by directly binding to the FNIII domain,thereby increasing the stability of NCAM1 at the axolemma.Our in vivo experiments on a rat sciatic nerve defect model also demonstrated orderly nerve bundle regeneration with improved projection accuracy and functional recovery after treatment with 10 mg/m L Matrigel and 20μg/m L collagen VI.These findings suggest that the collagen VI-NCAM1 pathway plays a regulatory role in nerve bundle formation.This study was approved by the Animal Ethics Committee of Guangzhou Medical University(approval No.GY2019048)on April 30,2019.

Preparation and Characterization of Poly Lactic Acid/Graphene Oxide/Nerve Growth Factor Scaffold with Electrical Stimulation for Peripheral Nerve Regeneration in vitro

A novel conductive drug-loading system was prepared by using an improved emulsion electrostatic spinning method which contained polylactic acid (PLA),graphene oxide (GO),and nerve growth factor (NGF) coated with bovine serum albumin (BSA) nanoparticles.Firstly,the structure,mechanical properties,morphology and electrical conductivity of PLA/GO electro spun fiber membranes with different GO ratios were characterized.PLA/GO scaffolds can exhibit superior porosity,hydrophilic and biomechanical properties when the GO incorporation rate is 0.5%.The addition of GO in the PLA/GO electro spun fiber membranes can also create appropriate pH environment for the repair of injured nerve when the GO incorporation rate is above 0.5%.Secondly,PLA/GO/BSA/Genipin/NGF particles (with a ratio of BSA/NGF=3:1) prepared by modified emulsion electro spinning method will release more NGF than PLA/GO/NGF particles.In addition,PLA/0.5%GO/NGF scaffold can maintain its structure stability for at least 8 weeks observed by scanning electron microscope (SEM).Moreover,the degradation of PLA/0.5%GO/NGF scaffold is consistent with its weight loss.Finally,in vitro assay confirmes that PLA/GO composite scaffold exhibits low cytotoxicity to RSC96 cells.Cellular results have demonstrated that PLA/0.5%GO/NGF sustained-release drug sustained-release system with appropriate electrical stimulation (ES) can promote PC12 cell proliferation,and it can maintain its differentiation capability for at least 3 weeks.In conclusion,PLA/0.5%GO/NGF sustained-release drug sustained-release system can maintain its biological activity for at least 3 weeks and promote cell proliferation with appropriate ES.

Fibrin glue repair leads to enhanced axonal elongation during early peripheral nerve regeneration in an in vivo mouse model

Microsurgical suturing is the gold standard of nerve coaptation. Although literature on the usefulness of fibrin glue as an alternative is becoming increasingly available, it remains contradictory. Furthermore, no data exist on how both repair methods might influence the morphological aspects（arborization; branching） of early peripheral nerve regeneration. We used the sciatic nerve transplantation model in thy-1 yellow fluorescent protein mice（YFP; n = 10）. Pieces of nerve（1cm） were grafted from YFP-negative mice（n = 10） into those expressing YFP. We performed microsuture coaptations on one side and used fibrin glue for repair on the contralateral side. Seven days after grafting, the regeneration distance, the percentage of regenerating and arborizing axons, the number of branches per axon, the coaptation failure rate, the gap size at the repair site and the time needed for surgical repair were all investigated. Fibrin glue repair resulted in regenerating axons travelling further into the distal nerve. It also increased the percentage of arborizing axons. No coaptation failure was detected. Gap sizes were comparable in both groups. Fibrin glue significantly reduced surgical repair time. The increase in regeneration distance, even after the short period of time, is in line with the results of others that showed faster axonal regeneration after fibrin glue repair. The increase in arborizing axons could be another explanation for better functional and electrophysiological results after fibrin glue repair. Fibrin glue nerve coaptation seems to be a promising alternative to microsuture repair.

New insights on the standardization of peripheral nerve regeneration quantitative analysis

Peripheral nerves form a complex network connecting the central nervous system and the body. Injuries to peripheral nerves often lead to partial or complete loss of motor, sen- sory and autonomic functions, thus interfering with many aspects of an individual＇s life.

Neuregulin 1 isoforms could be an effective therapeutic candidate to promote peripheral nerve regeneration

Traumatic injuries of peripheral nerves represent common casualties and their social impact is considerably high. Although peripheral nerves retain a good regeneration potential, the clinical outcome after nerve lesion is far from being satisfactory and functional recovery is almost never complete, especially in the case of large nerve defects, that result in loss or diminished sensitivity and/or motor activity of the innervated target organs. Therefore, to improve the outcome after nerve damage, or in peripheral neuropathies, there is a need for further research in nerve repair and regeneration to identify factors that promote axonal regrowth, remvelination and target reinnervation.

PDLLA/β-TCP/HA/CHS/NGF Sustained-release Conduits for Peripheral Nerve Regeneration

Using nerve guide conduits (NGCs) to promote the regeneration of PNI is a feasible alternative to autograft.Compared with NGCs made of single material,composite NGCs have a greater development prospect.Our previous research has confirmed that poly(D,L-lactic acid)/β-tricalcium phosphate/hyaluronic acid/chitosan/nerve growth factor (PDLLA/β-TCP/HA/CHS/NGF) NGCs have excellent physical and chemical properties,which can slowly release NGF and support cell adhesion and proliferation.In this study,PDLLA/β-TCP/HA/CHS/NGF NGCs were prepared and used to bridge a 10 mm sciatic nerve defect in 200-250 g Sprague-Dawley (SD) rat to verify the performance of the NGCs in vivo.Substantial improvements in nerve regeneration were observed after using the PDLLA/β-TCP/HA/CHS/NGF NGCs based on gross post-operation observation,triceps wet weight analysis and nerve histological assessment.In vivo studies illustrate that the PDLLA/β-TCP/HA/CHS/NGF sustained-release NGCs can effectively promote peripheral nerve regeneration,and the effect is similar to that of autograft.

Tubular conduits,cell-based therapy and exercise to improve peripheral nerve regeneration

Peripheral nerve injuries （PNI） are a major clinical prob- lem. In general, PNI results from motor vehicle accidents, lacerations with sharp objects, penetrating trauma （gunshot wounds） and stretching or crushing trauma and fractures. It is estimated that PNI occur in 2.8% of trauma patients and this number reaches 5% if plexus and root lesions are in- cluded. However, due to lack of recent epidemiological stud- ies, these data probably underestimate the actual number of nerve injuries

Peripheral nerve regeneration research Why is it getting so “cool”?

More than twenty years ago, when I first started working on plasticity and regeneration in the peripheral nervous system, I had the feeling of being part of a little, though lively, scientific community that was rarther isolated in the world of neuroscience which appeared to me as almost only focused on central nervous system. Since then, things have progressively changed very much and, today, interest in the regeneration in the peripheral nervous system, and especially in its main component. Le. the peripheral nerves （Geuna S, Raimondo S, Ronchi G, et al. Histology of the peripheral nerve and changes occurring during nerve regeneration. Int Rev Neurobiol. 2009;87：27-46.）, is sprading tremendouslty among both basic and clinical neuroscientists.

Potential of the use of an antioxidant compound to promote peripheral nerve regeneration after injury

The peripheral nervous system is a vital part of the body because it transfers information to coordinate all actions.Peripheral nerve injuries are detrimental to the proper function of this system and can cause loss of sense and movement.It is of utmost importance to research approaches to the treatment of peripheral nerve damage because such injuries can drastically change a person’s life,

Preparation and Evaluation of an Injectable Chitosan-Hyaluronic Acid hydrogel for Peripheral Nerve Regeneration

The aim of this study was to obtain the fillers in the lumen of hollow nerve conduits（NCs） to improve the microenvironment of nerve regeneration. A p H-induced injectable chitosan（CS）-hyaluronic acid（HA） hydrogel for nerve growth factor（NGF） sustained release was developed. Its properties were characterized by gelation time, FT-IR, SEM, in vitro swelling and degradation. Furthermore, the in vitro NGF release profiles and cell biocompatibility were also investigated. The experimental results show that the CS-HA aqueous solution can undergo a rapid gelation 3 minutes after its environmental p H is changed to 7.4. The CSHA hydrogel has interconnected channels with a controllable pore diameter and with a porosity of about 80%. It has a favorable swelling behavior and can be degraded by about 70% within 8 weeks in vitro and is suitable for NGF release. The CS-HA/NGF hydrogel exhibits a lower cytotoxicity and is in favor of the adhesion and proliferation of the BMMSCs cells. It is indicated that the CS-HA/NGF will be a promising candidate for neural tissue engineering.

Territory maximization hypothesis during peripheral nerve regeneration

Territory awareness refers to the notion that an organism lives in a territory, considers this territory its own, and prevents entry of other organisms. Generally, an organism maximizes its territory for best survival advantages, which subsequently allows for species continuation.