Enhancement of regeneration with glia cell line-derived neurotrophic factor-transduced human amniotic fluid mesenchymal stem cells after sciatic nerve crush injury

Advances in Genetic Reprogramming: Prospects from Developmental Biology to Regenerative Medicine

The foundations of cell reprogramming were laid by Yamanaka and co-workers, who showed that somatic cells can be reprogrammed into pluripotent cells (induced pluripotency). Since this discovery, the field of regenerative medicine has seen advancements. For example, because they can differentiate into multiple cell types, pluripotent stem cells are considered vital components in regenerative medicine aimed at the functional restoration of damaged tissue. Despite years of research, both replacement and restoration of failed organs/ tissues have remained elusive scientific feats. However, with the inception of cell engineering and nuclear reprogramming, useful solutions have been identified to counter the need for compatible and sustainable organs. By combining the science underlying genetic engineering and nuclear reprogramming with regenerative medicine, scientists have engineered cells to make gene and stem cell therapies applicable and effective. These approaches have enabled the targeting of various pathways to reprogramme cells, i.e., make them behave in beneficial ways in a patient-specific manner. Technological advancements have clearly supported the concept and realization of regenerative medicine. Genetic engineering is used for tissue engineering and nuclear reprogramming and has led to advances in regenerative medicine. Targeted therapies and replacement of traumatized , damaged, or aged organs can be realized through genetic engineering. Furthermore, the success of these therapies has been validated through thousands of clinical trials. Scientists are currently evaluating induced tissue-specific stem cells (iTSCs), which may lead to tumour-free applications of pluripotency induction. In this review, we present state-of-the-art genetic engineering that has been used in regenerative medicine. We also focus on ways that genetic engineering and nuclear reprogramming have transformed regenerative medicine and have become unique therapeutic niches.

Can amniotic fluid protect developing fetal lungs against the harmful effects of oxidative stress?

BACKGROUND

Preterm births cause fetuses to be born without completing the development of their organs. Due to this undesirable situation, it is the pulmonary tissue which has to be most exposed to harmful effects of extrauterine environment. Early disappearance of the prophylactic and constructive effects of amniotic fluid (AF) on developing tissues, such as pulmonary tissue, facilitates the formation of pulmonary morbidities resulting from oxygen. Setting out from this knowledge, we wanted, in addition to assessing the beneficent effects of AF on pulmonary tissue, to study the importance of AF in morbidities of this tissue thought to originate from oxygen.

METHODS

In this experimental study, while the study group was made up of the fetuses of pregnant rats exposed to hyperbaric oxygen, (hyperoxic pregnant rat fetuses-HPRF), the control group was formed of the fetuses of the rats pregnant in the usual room setting (normoxic pregnant rat fetuses-NPRF). The pulmonary and hepatic tissues taken from the fetuses of these pregnant rats on the 21st day of their pregnancy were compared biochemically and histologically. For biochemical assessment, total glutathione (tGSH), catalase (CAT), malondialdehyde (MDA), tumor necrosis factor-alpha (TNF-α) values and for histopathological assessment, apoptosis, alveolar wall count (AWC), vena centralis count (VCC) were included.

RESULTS

Statistical significance was found in the pulmonary tissue values of tGSH on behalf of NPRF, and MDA on behalf of HPRF (p < 0.05). In liver tissue, statistical significance was detected in tGSH and CAT values in favor of NPRF and in MDA, and TNF-α values in favor of HPRF (p < 0.05).

DISCUSSION

: Our study has demonstrated that AF protects the pulmonary tissue from the harmful effects of oxygen in the intrauterine period. In addition, our data have suggested that the pulmonary tissue's being deprived of the useful effects of AF owing to premature birth may be an important trigger in the occurrence of the pulmonary morbidities thought to result from oxygen.

Stem cell, Granulocyte-Colony Stimulating Factor and/or Dihexa to promote limb function recovery in a rat sciatic nerve damage-repair model: Experimental animal studies

Background

Optimizing nerve regeneration and re-innervation of target muscle/s is the key for improved functional recovery following peripheral nerve damage. We investigated whether administration of mesenchymal stem cell (MSC), Granulocyte-Colony Stimulating Factor (G-CSF) and/or Dihexa can improve recovery of limb function following peripheral nerve damage in rat sciatic nerve transection-repair model.

Materials and methods

There were 10 experimental groups (n = 6–8 rats/group). Bone marrow derived syngeneic MSCs (2 × 10⁶; passage≤6), G-CSF (200–400 μg/kg b.wt.), Dihexa (2–4 mg/kg b.wt.) and/or Vehicle were administered to male Lewis rats locally via hydrogel at the site of nerve repair, systemically (i.v./i.p), and/or to gastrocnemius muscle. The limb sensory and motor functions were assessed at 1–2 week intervals post nerve repair until the study endpoint (16 weeks).

Results

The sensory function in all nerve boundaries (peroneal, tibial, sural) returned to nearly normal by 8 weeks (Grade 2.7 on a scale of Grade 0–3 [0 = No function; 3 = Normal function]) in all groups combined. The peroneal nerve function recovered quickly with return of function at one week (∼2.0) while sural nerve function recovered rather slowly at four weeks (∼1.0). Motor function at 8–16 weeks post-nerve repair as determined by walking foot print grades significantly (P < 0.05) improved with MSC + G-CSF or MSC + Dihexa administrations into gastrocnemius muscle and mitigated foot flexion contractures.

Conclusions

These findings demonstrate MSC, G-CSF and Dihexa are promising candidates for adjunct therapies to promote limb functional recovery after surgical nerve repair, and have implications in peripheral nerve injury and limb transplantation. IACUC No.215064.

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G-CSF in combination with MSCs improved limb function recovery in sciatic nerve transection- repair model.

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Dihexa in combination with MSC improved limb function recovery in sciatic nerve transection- repair model.

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Foot flexion contractures were reduced with G-CSF & MSC or Dihexa & MSC administration into target muscle gastrocnemius.

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MSC, G-CSF or Dihexa combination therapy is attractive, feasible & promising in peripheral nerve injury repair and have implications in limb transplantation.

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The findings warrant further investigation to understand the cellular/molecular mechanisms.

The Roles of Different Stem Cells in Premature Ovarian Failure

Premature ovarian failure (POF) is characterized by amenorrhea, hypergonadotropism and hypoestrogenism before the age of 40, which affects 1% of women in the general population. POF is complex and heterogeneous due to its pathogenetic mechanisms. It is one of the significant causes of female infertility. Although many treatments are available for POF, these therapies are less efficient and trigger many side effects. Therefore, to find effective therapeutics for POF is urgently required. Due to stem cells having self-renewal and regeneration potential, they may be effective for the treatment of ovarian failure and consequently infertility. Recent studies have found that stem cells therapy may be able to restore the ovarian structure and function in animal models of POF and provide an effective treatment method. The present review summarizes the biological roles and the possible signaling mechanisms of the different stem cells in POF ovary. Further study on the precise mechanisms of stem cells on POF may provide novel insights into the female reproduction, which not only enhances the understanding of the physiological roles but also supports effective therapy for recovering ovarian functions against infertility.

"Stem cell therapy to promote limb function recovery in peripheral nerve damage in a rat model" - Experimental research

Background

Optimizing nerve regeneration and mitigating muscle atrophy are the keys to successful outcomes in peripheral nerve damage. We investigated whether mesenchymal stem cell (MSC) therapy can improve limb function recovery in peripheral nerve damage.

Materials and methods

We used sciatic nerve transection/repair (SNR) and individual nerve transection/repair (INR; branches of sciatic nerve - tibial, peroneal, sural) models to study the effect of MSCs on proximal and distal peripheral nerve damages, respectively, in male Lewis rats. Syngeneic MSCs (5 × 10⁶; passage≤6) or saline were administered locally and intravenously. Sensory/motor functions (SF/MF) of the limb were assessed.

Results

Rat MSCs (>90%) were CD29⁺, CD90⁺, CD34⁻, CD31⁻ and multipotent. Total SF at two weeks post-SNR & INR with or without MSC therapy was ∼1.2 on a 0–3 grading scale (0 = No function; 3 = Normal); by 12 weeks it was 2.6–2.8 in all groups (n ≥ 9/group). MSCs accelerated SF onset. At eight weeks post-INR, sciatic function index (SFI), a measure of MF (0 = Normal; −100 = Nonfunctional) was −34 and −77 in MSC and vehicle groups, respectively (n ≥ 9); post-SNR it was −72 and −92 in MSC and vehicle groups, respectively. Long-term MF (24 weeks) was apparent in MSC treated INR (SFI -63) but not in SNR (SFI -100). Gastrocnemius muscle atrophy was significantly reduced (P < 0.05) in INR. Nerve histomorphometry revealed reduced axonal area (P < 0.01) but no difference in myelination (P > 0.05) in MSC treated INR compared to the naive contralateral nerve.

Conclusion

MSC therapy in peripheral nerve damage appears to improve nerve regeneration, mitigate flexion-contractures, and promote limb functional recovery.

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Mesenchymal stem cell (MSC) therapy improved limb functional recovery.

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MSCs improved nerve regeneration and mitigated foot flexion-contractures.

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Limb muscle atrophy was significantly reduced in individual nerve repair (INR).

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Functional recovery in distal nerve repair (INR) was superior to proximal (SNR).

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MSC therapy is attractive, feasible & promising in peripheral nerve injury repair.

Advances in stem cell treatment for sciatic nerve injury

INTRODUCTION

The sciatic nerve is one of the peripheral nerves that is most prone to injuries. After injury, the connection between the nervous system and the distal organs is disrupted, and delayed treatment results in distal organ atrophy and total disability. Regardless of great advances in the fields of neurosurgery, biological sciences, and regenerative medicine, total functional recovery is yet to be achieved.

AREAS COVERED

Cell-based therapy for the treatment of peripheral nerve injuries (PNIs) has brought a new perspective to the field of regenerative medicine. Having the ability to differentiate into neural and glial cells, stem cells enhance neural regeneration after PNIs. Augmenting axonal regeneration, remyelination, and muscle mass preservation are the main mechanisms underlying stem cells' beneficial effects on neural regeneration.

EXPERT OPINION

Despite the usefulness of employing stem cells for the treatment of PNIs in pre-clinical settings, further assessments are still needed in order to translate this approach into clinical settings. Mesenchymal stem cells, especially adipose-derived stem cells, with the ability of autologous transplantation, as well as easy harvesting procedures, are speculated to be the most promising source to be used in the treatment of PNIs.

Concise Review: Amniotic Fluid Stem Cells: The Known, the Unknown, and Potential Regenerative Medicine Applications

The amniotic fluid has been identified as an untapped source of cells with broad potential, which possess immunomodulatory properties and do not have the ethical and legal limitations of embryonic stem cells. CD117(c-Kit)+ cells selected from amniotic fluid have been shown to differentiate into cell lineages representing all three embryonic germ layers without generating tumors, making them ideal candidates for regenerative medicine applications. Moreover, their ability to engraft in injured organs and modulate immune and repair responses of host tissues, suggest that transplantation of such cells may be useful for the treatment of various degenerative and inflammatory diseases. Although significant questions remain regarding the origin, heterogeneous phenotype, and expansion potential of amniotic fluid stem cells, evidence to date supports their potential role as a valuable stem cell source for the field of regenerative medicine. Stem Cells 2017;35:1663-1673.

Stem Cell Transplantation for Peripheral Nerve Regeneration: Current Options and Opportunities

Peripheral nerve regeneration is a complicated process highlighted by Wallerian degeneration, axonal sprouting, and remyelination. Schwann cells play an integral role in multiple facets of nerve regeneration but obtaining Schwann cells for cell-based therapy is limited by the invasive nature of harvesting and donor site morbidity. Stem cell transplantation for peripheral nerve regeneration offers an alternative cell-based therapy with several regenerative benefits. Stem cells have the potential to differentiate into Schwann-like cells that recruit macrophages for removal of cellular debris. They also can secrete neurotrophic factors to promote axonal growth, and remyelination. Currently, various types of stem cell sources are being investigated for their application to peripheral nerve regeneration. This review highlights studies involving the stem cell types, the mechanisms of their action, methods of delivery to the injury site, and relevant pre-clinical or clinical data. The purpose of this article is to review the current point of view on the application of stem cell based strategy for peripheral nerve regeneration.

The Present and Future for Peripheral Nerve Regeneration

Peripheral nerve injury can have a potentially devastating impact on a patient's quality of life, resulting in severe disability with substantial social and personal cost. Refined microsurgical techniques, advances in peripheral nerve topography, and a better understanding of the pathophysiology and molecular basis of nerve injury have all led to a decisive leap forward in the field of translational neurophysiology. Nerve repair, nerve grafting, and nerve transfers have improved significantly with consistently better functional outcomes. Direct nerve repair with epineural microsutures is still the surgical treatment of choice when a tension-free coaptation in a well-vascularized bed can be achieved. In the presence of a significant gap (>2-3 cm) between the proximal and distal nerve stumps, primary end-to-end nerve repair often is not possible; in these cases, nerve grafting is the treatment of choice. Indications for nerve transfer include brachial plexus injuries, especially avulsion type, with long distance from target motor end plates, delayed presentation, segmental loss of nerve function, and broad zone of injury with dense scarring. Current experimental research in peripheral nerve regeneration aims to accelerate the process of regeneration using pharmacologic agents, bioengineering of sophisticated nerve conduits, pluripotent stem cells, and gene therapy. Several small molecules, peptides, hormones, neurotoxins, and growth factors have been studied to improve and accelerate nerve repair and regeneration by reducing neuronal death and promoting axonal outgrowth. Targeting specific steps in molecular pathways also allows for purposeful pharmacologic intervention, potentially leading to a better functional recovery after nerve injury. This article summarizes the principles of nerve repair and the current concepts of peripheral nerve regeneration research, as well as future perspectives. [Orthopedics. 2017; 40(1):e141-e156.].

Human amniotic fluid: a source of stem cells for possible therapeutic use

Stem cells are undifferentiated cells with the capacity for differentiation. Amniotic fluid cells have emerged only recently as a possible source of stem cells for clinical purposes. There are no ethical or sampling constraints for the use of amniocentesis as a standard clinical procedure for obtaining an abundant supply of amniotic fluid cells. Amniotic fluid cells of human origin proliferate rapidly and are multipotent with the potential for expansion in vitro to multiple cell lines. Tissue engineering technologies that use amniotic fluid cells are being explored. Amniotic fluid cells may be of clinical benefit for fetal therapies, degenerative disease, and regenerative medicine applications. We present a comprehensive review of the evolution of human amniotic fluid cells as a possible modality for therapeutic use.

Dual Inhibition of Activin/Nodal/TGF-β and BMP Signaling Pathways by SB431542 and Dorsomorphin Induces Neuronal Differentiation of Human Adipose Derived Stem Cells

Damage to the nervous system can cause devastating diseases or musculoskeletal dysfunctions and transplantation of progenitor stem cells can be an excellent treatment option in this regard. Preclinical studies demonstrate that untreated stem cells, unlike stem cells activated to differentiate into neuronal lineage, do not survive in the neuronal tissues. Conventional methods of inducing neuronal differentiation of stem cells are complex and expensive. We therefore sought to determine if a simple, one-step, and cost effective method, previously reported to induce neuronal differentiation of embryonic stem cells and induced-pluripotent stem cells, can be applied to adult stem cells. Indeed, dual inhibition of activin/nodal/TGF-β and BMP pathways using SB431542 and dorsomorphin, respectively, induced neuronal differentiation of human adipose derived stem cells (hADSCs) as evidenced by formation of neurite extensions, protein expression of neuron-specific gamma enolase, and mRNA expression of neuron-specific transcription factors Sox1 and Pax6 and matured neuronal marker NF200. This process correlated with enhanced phosphorylation of p38, Erk1/2, PI3K, and Akt1/3. Additionally, in vitro subcutaneous implants of SB431542 and dorsomorphin treated hADSCs displayed significantly higher expression of active-axonal-growth-specific marker GAP43. Our data offers novel insights into cell-based therapies for the nervous system repair.

A Mini Overview of Isolation, Characterization and Application of Amniotic Fluid Stem Cells

Amniotic fluid represents rich sources of stem cells that can be used in treatments for a wide range of diseases. Amniotic fluid- stem cells have properties intermediate between embryonic and adult mesenchymal stem cells which make them particularly attractive for cellular regeneration and tissue engineering. Furthermore, scientists are interested in these cells because they come from the amniotic fluid that is routinely discarded after birth. In this review we give a brief introduction of amniotic fluid followed by a description of the cells present within this fluid and aim to summarize the all existing isolation methods, culturing, characterization and application of these cells. Finally, we elaborate on the differentiation and potential for these cells to promote regeneration of various tissue defects, including fetal tissue, the nervous system, heart, lungs, kidneys, bones, and cartilage in the form of table.

Is there a role for neurotrophic factors and their receptors in augmenting the neuroprotective effect of (-)-epigallocatechin-3-gallate treatment of sciatic nerve crush injury?

This study analyzed and compared the effects of EGCG treatment on the expression of NTFs and NTF receptors expression in the sciatic nerve and the L3-L6 spinal cord segments at the early phase of regeneration following sciatic nerve crush injury. Analysis of BDNF, GDNF and NT3 neurotropic factors and Trk-B, Trk-C and NGFR-p75 receptors in neurons in the spinal cord of CRUSH and CRUSH + EGGC rats showed significant (p < 0.0001) decrease compared to NAÏVE and SHAM at day 1, 3, 7 and 14 after nerve injury. EGCG treatment significantly (p < 0.0001) increased the BDNF, GDN, NT3, Trk-B, Trk-C and NGFR-p75 immunostaining in the L3-L6 spinal cord compared to CRUSH animals. Also, EGCG treatment significantly increased the Trk-B protein concentration and Trk-B, NT3 and Trk-C gene expression in the spinal cords compared to CRUSH group. However, at day 1 and 3 post nerve injury, EGCG treatment significantly decreased the NGFR-p75 expression compared to CRUSH rats. In the sciatic nerve, EGCG treatment significantly (p < 0.01) increased the Trk-B and NGFR-p75 protein concentration in the controls. EGCG treatment significantly (p < 0.0001) increased the Trk-B, Trk-C and NGFR-p75 mRNA gene expressions in the sciatic nerves compared to CRUSH group. Only at day 1, CRUSH + EGCG animals displayed significant rise in the sciatic nerves NT3 gene expression compared to CRUSH group. Our data suggest that the EGCG neuroprotective effect on the spinal cord neurons may be mediated through the modulation of NTFs and NTF receptors following nerve crush injury in a rat model.

Stem cells from amniotic fluid--Potential for regenerative medicine

Regenerative medicine has recently been established as an emerging field focussing on repair, replacement or regeneration of cells, tissues and whole organs. The significant recent advances in the field have intensified the search for novel sources of stem cells with potential for therapy. Recently, researchers have identified the amniotic fluid as an untapped source of stem cells that are multipotent, possess immunomodulatory properties and do not have the ethical and legal limitations of embryonic stem cells. Stem cells from the amniotic fluid have been shown to differentiate into cell lineages representing all three embryonic germ layers without generating tumours, which make them an ideal candidate for tissue engineering applications. In addition, their ability to engraft in injured organs and modulate immune and repair responses of host tissues suggest that transplantation of such cells may be useful for the treatment of various degenerative and inflammatory diseases affecting major tissues/organs. This review summarises the evidence on amniotic fluid cells over the past 15 years and explores the potential therapeutic applications of amniotic fluid stem cells and amniotic fluid mesenchymal stem cells.

Topical Review: Use of Fetal Tissue in Foot and Ankle Surgery

Fetal tissues are well known for their therapeutic potential. They contain numerous growth factors, cytokines, and matrix components that promote regeneration of tissues while downregulating inflammation and scar formation. As a result, use of these treatments has expanded over the previous 20 years throughout various surgical specialties, including orthopaedics. With improved methods of sterilization, processing, and storage, surgeons need to be informed about the potential benefits of fetal tissue in foot and ankle surgery. The aim of this review is to provide a brief historical background, basic anatomy and physiology, and a current review of the literature in regard to chronic wounds, diabetic foot ulcerations, plantar fasciitis, tendon repair, adhesion prevention, nerve repair, and bone healing.

LEVELS OF EVIDENCE

Level V: Expert Opinion.

Autologous nerve graft repair of different degrees of sciatic nerve defect: stress and displacement at the anastomosis in a three-dimensional fnite element simulation model

In the repair of peripheral nerve injury using autologous or synthetic nerve grafting, the magnitude of tensile forces at the anastomosis affects its response to physiological stress and the ultimate success of the treatment. One-dimensional stretching is commonly used to measure changes in tensile stress and strain; however, the accuracy of this simple method is limited. Therefore, in the present study, we established three-dimensional finite element models of sciatic nerve defects repaired by autologous nerve grafts. Using PRO E 5.0 finite element simulation software, we calculated the maximum stress and displacement of an anastomosis under a 5 N load in 10-, 20-, 30-, 40-mm long autologous nerve grafts. We found that maximum displacement increased with graft length, consistent with specimen force. These findings indicate that three-dimensional finite element simulation is a feasible method for analyzing stress and displacement at the anastomosis after autologous nerve grafting.

Therapeutic efficacy of amniotic membrane stem cells and adipose tissue stem cells in rats with chemically induced ovarian failure

The present study was conducted to compare between the therapeutic efficacies of human amniotic membrane-derived stem cells (hAM-MSCs) vs. adipose tissue derived stem cells (AD-MSCs) in cyclophosphamide (CTX)-induced ovarian failure in rats. Forty-eight adult female rats were included in the study; 10 rats were used as control group. Thirty-eight rats were injected with CTX to induce ovarian failure and divided into four groups: ovarian failure (IOF) (IOF group), IOF + phosphate buffer saline (PBS group), IOF + hAM-MSCs group and IOF + AD-MSCs group. Serum levels of FSH and estradiol (E2) were assessed. Histopathological examination of the ovarian tissues was performed and quantitative gene expressions of Oct-4, Stra8 and integrin beta-1 genes were conducted by quantitative real time PCR. Results showed that IOF and IOF + PBS rat groups exhibited decreased ovarian follicles, increased interstitial fibrosis with significant decrease of serum E2, significant increase serum FSH level and significant down-regulation of Stra8 and integrin beta-1. In hAM-MSCs and AD-MSCs rat groups, there were increased follicles and corpora with evident the presence of oocytes, significant increase in serum E2, significant decrease in serum FSH levels (in hAM-MSCs treated group only) and significant up-regulation of the three studied genes with higher levels in hAM-MSCs treated rats group when compared to AD-MSCs treated rats group. In Conclusion, administration of either hAM-derived MSCs or AD-MSCs exerts a significant therapeutic efficacy in chemotherapy induced ovarian insult in rats. hAM-MSCs exert higher therapeutic efficacy as compared to AD-MSCs.

Improved neurological outcome by intramuscular injection of human amniotic fluid derived stem cells in a muscle denervation model

Purpose

The skeletal muscle develops various degrees of atrophy and metabolic dysfunction following nerve injury. Neurotrophic factors are essential for muscle regeneration. Human amniotic fluid derived stem cells (AFS) have the potential to secrete various neurotrophic factors necessary for nerve regeneration. In the present study, we assess the outcome of neurological function by intramuscular injection of AFS in a muscle denervation and nerve anastomosis model.

Materials and Methods

Seventy two Sprague-Dawley rats weighing 200–250 gm were enrolled in this study. Muscle denervation model was conducted by transverse resection of a sciatic nerve with the proximal end sutured into the gluteal muscle. The nerve anastomosis model was performed by transverse resection of the sciatic nerve followed by four stitches reconnection. These animals were allocated to three groups: control, electrical muscle stimulation, and AFS groups.

Results

NT-3 (Neurotrophin 3), BDNF (Brain derived neurotrophic factor), CNTF (Ciliary neurotrophic factor), and GDNF (Glia cell line derived neurotrophic factor) were highly expressed in AFS cells and supernatant of culture medium. Intra-muscular injection of AFS exerted significant expression of several neurotrophic factors over the distal end of nerve and denervated muscle. AFS caused high expression of Bcl-2 in denervated muscle with a reciprocal decrease of Bad and Bax. AFS preserved the muscle morphology with high expression of desmin and acetylcholine receptors. Up to two months, AFS produced significant improvement in electrophysiological study and neurological functions such as SFI (sciatic nerve function index) and Catwalk gait analysis. There was also significant preservation of the number of anterior horn cells and increased nerve myelination as well as muscle morphology.

Conclusion

Intramuscular injection of AFS can protect muscle apoptosis and likely does so through the secretion of various neurotrophic factors. This protection furthermore improves the nerve regeneration in a long term nerve anastomosis model.

Strain and stress variations in the human amniotic membrane and fresh corpse autologous sciatic nerve anastomosis in a model of sciatic nerve injury

A 10-mm long sciatic nerve injury model was established in fresh normal Chinese patient cadavers. Amniotic membrane was harvested from healthy maternal placentas and was prepared into multilayered, coiled, tubular specimens. Sciatic nerve injury models were respectively anastomosed using the autologous cadaveric sciatic nerve and human amniotic membrane. Tensile test results showed that maximal loading, maximal displacement, maximal stress, and maximal strain of sciatic nerve injury models anastomosed with human amniotic membrane were greater than those in the autologous nerve anastomosis group. The strain-stress curves of the human amniotic membrane and sciatic nerves indicated exponential change at the first phase, which became elastic deformation curves at the second and third phases, and displayed plastic deformation curves at the fourth phase, at which point the specimens lost their bearing capacity. Experimental findings suggested that human amniotic membranes and autologous sciatic nerves exhibit similar stress-strain curves, good elastic properties, and certain strain and stress capabilities in anastomosis of the injured sciatic nerve.

Augmenting peripheral nerve regeneration using stem cells: A review of current opinion

Outcomes following peripheral nerve injury remain frustratingly poor. The reasons for this are multifactorial, although maintaining a growth permissive environment in the distal nerve stump following repair is arguably the most important. The optimal environment for axonal regeneration relies on the synthesis and release of many biochemical mediators that are temporally and spatially regulated with a high level of incompletely understood complexity. The Schwann cell (SC) has emerged as a key player in this process. Prolonged periods of distal nerve stump denervation, characteristic of large gaps and proximal injuries, have been associated with a reduction in SC number and ability to support regenerating axons. Cell based therapy offers a potential therapy for the improvement of outcomes following peripheral nerve reconstruction. Stem cells have the potential to increase the number of SCs and prolong their ability to support regeneration. They may also have the ability to rescue and replenish populations of chromatolytic and apoptotic neurons following axotomy. Finally, they can be used in non-physiologic ways to preserve injured tissues such as denervated muscle while neuronal ingrowth has not yet occurred. Aside from stem cell type, careful consideration must be given to differentiation status, how stem cells are supported following transplantation and how they will be delivered to the site of injury. It is the aim of this article to review current opinions on the strategies of stem cell based therapy for the augmentation of peripheral nerve regeneration.

Gene delivery in tissue engineering and regenerative medicine

As a promising strategy to aid or replace tissue/organ transplantation, gene delivery has been used for regenerative medicine applications to create or restore normal function at the cell and tissue levels. Gene delivery has been successfully performed ex vivo and in vivo in these applications. Excellent proliferation capabilities and differentiation potentials render certain cells as excellent candidates for ex vivo gene delivery for regenerative medicine applications, which is why multipotent and pluripotent cells have been intensely studied in this vein. In this review, gene delivery is discussed in detail, along with its applications to tissue engineering and regenerative medicine. A definition of a stem cell is compared to a definition of a stem property, and both provide the foundation for an in-depth look at gene delivery investigations from a germ lineage angle.

Stress and strain analysis on the anastomosis site sutured with either epineurial or perineurial sutures after simulation of sciatic nerve injury

The magnitude of tensile stress and tensile strain at an anastomosis site under physiological stress is an important factor for the success of anastomosis following suturing in peripheral nerve injury treatment. Sciatic nerves from fresh adult cadavers were used to create models of sciatic nerve injury. The denervated specimens underwent epineurial and perineurial suturing. The elastic modulus (40.96 ± 2.59 MPa) and Poisson ratio (0.37 ± 0.02) of the normal sciatic nerve were measured by strain electrical measurement. A resistance strain gauge was pasted on the front, back, left, and right of the edge of the anastomosis site after suturing. Strain electrical measurement results showed that the stress and strain values of the sciatic nerve following perineurial suturing were lower than those following epineurial suturing. Scanning electron microscopy revealed that the sciatic nerve fibers were disordered following epineurial compared with perineurial suturing. These results indicate that the effect of perineurial suturing in sciatic nerve injury repair is better than that of epineurial suturing.

Neuroprotective effects of GDNF-expressing human amniotic fluid cells

Brain injury continues to be one of the leading causes of disability worldwide. Despite decades of research, there is currently no pharmacologically effective treatment for preventing neuronal loss and repairing the brain. As a result, novel therapeutic approaches, such as cell-based therapies, are being actively pursued to repair tissue damage and restore neurological function after injury. In this study, we examined the neuroprotective potential of amniotic fluid (AF) single cell clones, engineered to secrete glial cell derived neurotrophic factor (AF-GDNF), both in vitro and in a surgically induced model of brain injury. Our results show that pre-treatment with GDNF significantly increases cell survival in cultures of AF cells or cortical neurons exposed to hydrogen peroxide. Since improving the efficacy of cell transplantation depends on enhanced graft cell survival, we investigated whether AF-GDNF cells seeded on polyglycolic acid (PGA) scaffolds could enhance graft survival following implantation into the lesion cavity. Encouragingly, the AF-GDNF cells survived longer than control AF cells in serum-free conditions and continued to secrete GDNF both in vitro and following implantation into the injured motor cortex. AF-GDNF implantation in the acute period following injury was sufficient to activate the MAPK/ERK signaling pathway in host neural cells in the peri-lesion area, potentially boosting endogenous neuroprotective pathways. These results were complemented with promising trends in beam walk tasks in AF-GDNF/PGA animals during the 7 day timeframe. Further investigation is required to determine whether significant behavioural improvement can be achieved at a longer timeframe.

Morphological differences in skeletal muscle atrophy of rats with motor nerve and/or sensory nerve injury

Skeletal muscle atrophy occurs after denervation. The present study dissected the rat left ventral root and dorsal root at L_4-6 or the sciatic nerve to establish a model of simple motor nerve injury, sensory nerve injury or mixed nerve injury. Results showed that with prolonged denervation time, rats with simple motor nerve injury, sensory nerve injury or mixed nerve injury exhibited abnormal behavior, reduced wet weight of the left gastrocnemius muscle, decreased diameter and cross-sectional area and altered ultrastructure of muscle cells, as well as decreased cross-sectional area and increased gray scale of the gastrocnemius muscle motor end plate. Moreover, at the same time point, the pathological changes were most severe in mixed nerve injury, followed by simple motor nerve injury, and the changes in simple sensory nerve injury were the mildest. These findings indicate that normal skeletal muscle morphology is maintained by intact innervation. Motor nerve injury resulted in larger damage to skeletal muscle and more severe atrophy than sensory nerve injury. Thus, reconstruction of motor nerves should be considered first in the clinical treatment of skeletal muscle atrophy caused by denervation.

Comparison of viscoelasticity between normal human sciatic nerve and amniotic membrane

Sciatic nerve tissue was obtained from the gluteus maximus muscle segment of normal human cadavers and amniotic membrane tissue was obtained from healthy human puerperant placentas. Both tissues were analyzed for their stress relaxation and creep properties to determine suitability for transplantation applications. Human amniotic membrane and sciatic nerve tissues had similar tendencies for stress relaxation and creep properties. The stress value of the amniotic membrane stress relaxation group decreased to a greater extent compared with the sciatic nerve stress relaxation group. Similarly, the stress value of the amniotic membrane creep group increased to a greater extent compared with the sciatic nerve creep group. The stress relaxation curve for human amniotic membrane and sciatic nerve showed a logarithm correlation, while the creep curve showed an exponential correlation. These data indicate that amniotic membrane tissue has better stress relaxation and creep properties compared with sciatic nerve tissue.

Viscoelasticity of repaired sciatic nerve by poly(lactic-co-glycolic acid) tubes

Medical-grade synthetic poly(lactic-co-glycolic acid) polymer can be used as a biomaterial for nerve repair because of its good biocompatibility, biodegradability and adjustable degradation rate. The stress relaxation and creep properties of peripheral nerve can be greatly improved by repair with poly(lactic-co-glycolic acid) tubes. Ten sciatic nerve specimens were harvested from fresh corpses within 24 hours of death, and were prepared into sciatic nerve injury models by creating a 10 mm defect in each specimen. Defects were repaired by anastomosis with nerve autografts and poly(lactic-co-glycolic acid) tubes. Stress relaxation and creep testing showed that at 7 200 seconds, the sciatic nerve anastomosed by poly(lactic-co-glycolic acid) tubes exhibited a greater decrease in stress and increase in strain than those anastomosed by nerve autografts. These findings suggest that poly(lactic-co-glycolic acid) exhibits good viscoelasticity to meet the biomechanical require-ments for a biomaterial used to repair sciatic nerve injury.

Amniotic fluid stem cells prevent follicle atresia and rescue fertility of mice with premature ovarian failure induced by chemotherapy

Chemotherapy used to treat cancer may cause irreversible premature ovarian failure (POF). Of late, amniotic fluid stem cells (AFSCs) provide a novel source for regenerative medicine because of their primitive stage, low immunogenicity, and easy accessibility. In this study, we isolated AFSCs from transgenic mice that ubiquitously express enhanced green fluorescence protein (EGFP). These AFSCs exhibited morphologies, immunophenotypes, and mesoderm trilineage differentiation potentials similar to mesenchymal stem cells (MSCs). Further, AFSCs proliferated faster than MSCs and expressed OCT4, a marker for pluripotency. To investigate their potential in recovering fertility in POF model, AFSCs were transplanted into the ovaries of mice with POF six weeks post induction using chemotherapeutic drugs, busulfan and cyclophosphamide. AFSCs could rescue the reproductive ability of mice with POF by preventing follicle atresia and sustaining the healthy follicles. Notably, the transplanted AFSCs did not differentiate into granulosa and germline cells in vivo. After one month, the decreased numbers of transplanted AFSCs accompanied with the reduced beneficial effects indicated that the therapeutic efficacy were directly from AFSCs. These findings demonstrated the therapeutic effects of AFSCs and suggested the promise of AFSCs for treating infertility and POF caused by chemotherapy.

SOX9 as a Predictor for Neurogenesis Potentiality of Amniotic Fluid Stem Cells

Preclinical studies of amniotic fluid-derived cell therapy have been successful in the research of neurodegenerative diseases, peripheral nerve injury, spinal cord injury, and brain ischemia. Transplantation of human amniotic fluid stem cells (AFSCs) into rat brain ventricles has shown improvement in symptoms of Parkinson's disease and also highlighted the minimal immune rejection risk of AFSCs, even between species. Although AFSCs appeared to be a promising resource for cell-based regenerative therapy, AFSCs contain a heterogeneous pool of distinct cell types, rendering each preparation of AFSCs unique. Identification of predictive markers for neuron-prone AFSCs is necessary before such stem cell-based therapeutics can become a reality. In an attempt to identify markers of AFSCs to predict their ability for neurogenesis, we performed a two-phase study. In the discovery phase of 23 AFSCs, we tested ZNF521/Zfp521, OCT6, SOX1, SOX2, SOX3, and SOX9 as predictive markers of AFSCs for neural differentiation. In the validation phase, the efficacy of these predictive markers was tested in independent sets of 18 AFSCs and 14 dental pulp stem cells (DPSCs). We found that high expression of SOX9 in AFSCs is associated with good neurogenetic ability, and these positive correlations were confirmed in independent sets of AFSCs and DPSCs. Furthermore, knockdown of SOX9 in AFSCs inhibited their neuronal differentiation. In conclusion, the discovery of SOX9 as a predictive marker for neuron-prone AFSCs could expedite the selection of useful clones for regenerative medicine, in particular, in neurological diseases and injuries.

Neural tissue engineering options for peripheral nerve regeneration

Tissue engineered nerve grafts (TENGs) have emerged as a potential alternative to autologous nerve grafts, the gold standard for peripheral nerve repair. Typically, TENGs are composed of a biomaterial-based template that incorporates biochemical cues. A number of TENGs have been used experimentally to bridge long peripheral nerve gaps in various animal models, where the desired outcome is nerve tissue regeneration and functional recovery. So far, the translation of TENGs to the clinic for use in humans has met with a certain degree of success. In order to optimize the TENG design and further approach the matching of TENGs with autologous nerve grafts, many new cues, beyond the traditional ones, will have to be integrated into TENGs. Furthermore, there is a strong requirement for monitoring the real-time dynamic information related to the construction of TENGs. The aim of this opinion paper is to specifically and critically describe the latest advances in the field of neural tissue engineering for peripheral nerve regeneration. Here we delineate new attempts in the design of template (or scaffold) materials, especially in the context of biocompatibility, the choice and handling of support cells, and growth factor release systems. We further discuss the significance of RNAi for peripheral nerve regeneration, anticipate the potential application of RNAi reagents for TENGs, and speculate on the possible contributions of additional elements, including angiogenesis, electrical stimulation, molecular inflammatory mediators, bioactive peptides, antioxidant reagents, and cultured biological constructs, to TENGs. Finally, we consider that a diverse array of physicochemical and biological cues must be orchestrated within a TENG to create a self-consistent coordinated system with a close proximity to the regenerative microenvironment of the peripheral nervous system.

Neurotrauma and mesenchymal stem cells treatment: From experimental studies to clinical trials

Mesenchymal stem cell (MSC) therapy has attracted the attention of scientists and clinicians around the world. Basic and pre-clinical experimental studies have highlighted the positive effects of MSC treatment after spinal cord and peripheral nerve injury. These effects are believed to be due to their ability to differentiate into other cell lineages, modulate inflammatory and immunomodulatory responses, reduce cell apoptosis, secrete several neurotrophic factors and respond to tissue injury, among others. There are many pre-clinical studies on MSC treatment for spinal cord injury (SCI) and peripheral nerve injuries. However, the same is not true for clinical trials, particularly those concerned with nerve trauma, indicating the necessity of more well-constructed studies showing the benefits that cell therapy can provide for individuals suffering the consequences of nerve lesions. As for clinical trials for SCI treatment the results obtained so far are not as beneficial as those described in experimental studies. For these reasons basic and pre-clinical studies dealing with MSC therapy should emphasize the standardization of protocols that could be translated to the clinical set with consistent and positive outcomes. This review is based on pre-clinical studies and clinical trials available in the literature from 2010 until now. At the time of writing this article there were 43 and 36 pre-clinical and 19 and 1 clinical trials on injured spinal cord and peripheral nerves, respectively.

Amniotic mesenchymal stem cells display neurovascular tropism and aid in the recovery of injured peripheral nerves

Recently, we reported that human amniotic membrane-derived mesenchymal stem cells (AMMs) possess great angiogenic potential. In this study, we determined whether local injection of AMMs ameliorates peripheral neuropathy. AMMs were transplanted into injured sciatic nerves. AMM injection promoted significant recovery of motor nerve conduction velocity and voltage amplitude compared to human adipose-derived mesenchymal stem cells. AMM implantation also augmented blood perfusion and increased intraneural vascularity. Whole-mount fluorescent imaging analysis demonstrated that AMMs exhibited higher engraftment and endothelial incorporation abilities in the sciatic nerve. In addition, the higher expression of pro-angiogenic factors was detected in AMMs injected into the peripheral nerve. Therefore, these data provide novel therapeutic and mechanistic insights into stem cell biology, and AMM transplantation may represent an alternative therapeutic option for treating peripheral neuropathy.

The potential of mesenchymal stem cells derived from amniotic membrane and amniotic fluid for neuronal regenerative therapy

The mesenchymal stem cells (MSCs), which are derived from the mesoderm, are considered as a readily available source for tissue engineering. They have multipotent differentiation capacity and can be differentiated into various cell types. Many studies have demonstrated that the MSCs identified from amniotic membrane (AM-MSCs) and amniotic fluid (AF-MSCs) are shows advantages for many reasons, including the possibility of noninvasive isolation, multipotency, self-renewal, low immunogenicity, anti-inflammatory and nontumorigenicity properties, and minimal ethical problem. The AF-MSCs and AM-MSCs may be appropriate sources of mesenchymal stem cells for regenerative medicine, as an alternative to embryonic stem cells (ESCs). Recently, regenerative treatments such as tissue engineering and cell transplantation have shown potential in clinical applications for degenerative diseases. Therefore, amnion and MSCs derived from amnion can be applied to cell therapy in neuro-degeneration diseases. In this review, we will describe the potential of AM-MSCs and AF-MSCs, with particular focus on cures for neuronal degenerative diseases.

RECENT DEVELOPMENTS IN THERAPIES WITH STEM CELLS FROM AMNIOTIC FLUID AND PLACENTA

Significant advances in the field of regenerative medicine have intensified the search for novel sources of stem cells with potential for therapy. Although embryonic and adult tissues can be used for the isolation of pluripotent stem cells, significant limitations including ethical concerns, complexity of isolation/culture and tumorigenicity have hindered translation of laboratory findings to clinical practice.

Therapeutic potential of amniotic fluid-derived cells for treating the injured nervous system

There is a need for improved therapy for acquired brain injury, which has proven resistant to treatment by numerous drugs in clinical trials and continues to represent one of the leading causes of disability worldwide. Research into cell-based therapies for the treatment of brain injury is growing rapidly, but the ideal cell source has yet to be determined. Subpopulations of cells found in amniotic fluid, which is readily obtained during routine amniocentesis, can be easily expanded in culture, have multipotent differentiation capacity, are non-tumourigenic, and avoid the ethical complications associated with embryonic stem cells, making them a promising cell source for therapeutic purposes. Beneficial effects of amniotic fluid cell transplantation have been reported in various models of nervous system injury. However, evidence that amniotic fluid cells can differentiate into mature, functional neurons in vivo and incorporate into the existing circuitry to replace lost or damaged neurons is lacking. The mechanisms by which amniotic fluid cells improve outcomes after experimental nervous system injury remain unclear. However, studies reporting the expression and release of neurotrophic, angiogenic, and immunomodulatory factors by amniotic fluid cells suggest they may provide neuroprotection and (or) stimulate endogenous repair and remodelling processes in the injured nervous system. In this paper, we address recent research related to the neuronal differentiation of amniotic fluid-derived cells, the therapeutic efficacy of these cells in animal models of nervous system injury, and the possible mechanisms mediating the positive outcomes achieved by amniotic fluid cell transplantation.

Amniotic fluid as a source of pluripotent and multipotent stem cells for organ regeneration

PURPOSE OF REVIEW

Amniotic fluid, due to its contact to the fetus during development, is considered an important diagnostic tool to evaluate the health status of the fetus during pregnancy. However, amniotic fluid also contains a heterogeneous cellular population that can be safely collected by amniocentesis and easily cultured. Many different cell types have been found within amniotic fluid and currently some of them are being tested for their possible use for cellular therapy.

RECENT FINDINGS

Potential of pluripotent and multipotent cells isolated from the amniotic fluid has been tested and in-vitro differentiations toward various cell types have been successfully performed. Furthermore, in-vivo studies are highlighting the benefits and mechanisms of amniotic fluid cells for therapy, with particular focus on kidney and lung diseases.

SUMMARY

Amniotic fluid may represent a precious source for easily and safely retrievable cell types that may be used for regenerative medicine purposes.

Sciatic nerve regeneration by cocultured Schwann cells and stem cells on microporous nerve conduits

Cell transplantation is a useful therapy for treating peripheral nerve injuries. The clinical use of Schwann cells (SCs), however, is limited because of their limited availability. An emerging solution to promote nerve regeneration is to apply injured nerves with stem cells derived from various tissues. In this study, different types of allogeneic cells including SCs, adipose-derived adult stem cells (ASCs), dental pulp stem cells (DPSCs), and the combination of SCs with ASCs or DPSCs were seeded on nerve conduits to test their efficacy in repairing a 15-mm-long critical gap defect of rat sciatic nerve. The regeneration capacity and functional recovery were evaluated by the histological staining, electrophysiology, walking track, and functional gait analysis after 8 weeks of implantation. An in vitro study was also performed to verify if the combination of cells led to synergistic neurotrophic effects (NGF, BDNF, and GDNF). Experimental rats receiving conduits seeded with a combination of SCs and ASCs had the greatest functional recovery, as evaluated by the walking track, functional gait, nerve conduction velocity (NCV), and histological analysis. Conduits seeded with cells were always superior to the blank conduits without cells. Regarding NCV and the number of blood vessels, conduits seeded with SCs and DPSCs exhibited better values than those seeded with DPSCs only. Results from the in vitro study confirmed the synergistic NGF production from the coculture of SCs and ASCs. It was concluded that coculture of SCs with ASCs or DPSCs in a conduit promoted peripheral nerve regeneration over a critical gap defect.

Applications of amniotic membrane and fluid in stem cell biology and regenerative medicine

The amniotic membrane (AM) and amniotic fluid (AF) have a long history of use in surgical and prenatal diagnostic applications, respectively. In addition, the discovery of cell populations in AM and AF which are widely accessible, nontumorigenic and capable of differentiating into a variety of cell types has stimulated a flurry of research aimed at characterizing the cells and evaluating their potential utility in regenerative medicine. While a major focus of research has been the use of amniotic membrane and fluid in tissue engineering and cell replacement, AM- and AF-derived cells may also have capabilities in protecting and stimulating the repair of injured tissues via paracrine actions, and acting as vectors for biodelivery of exogenous factors to treat injury and diseases. Much progress has been made since the discovery of AM and AF cells with stem cell characteristics nearly a decade ago, but there remain a number of problematic issues stemming from the inherent heterogeneity of these cells as well as inconsistencies in isolation and culturing methods which must be addressed to advance the field towards the development of cell-based therapies. Here, we provide an overview of the recent progress and future perspectives in the use of AM- and AF-derived cells for therapeutic applications.

Functions of neurotrophins and growth factors in neurogenesis and brain repair

The identification and isolation of multipotent neural stem and progenitor cells in the brain, giving rise to neurons, astrocytes, and oligodendrocytes initiated many studies in order to understand basic mechanisms of endogenous neurogenesis and repair mechanisms of the nervous system and to develop novel therapeutic strategies for cellular regeneration therapies in brain disease. A previous review (Trujillo et al., Cytometry A 2009;75:38-53) focused on the importance of extrinsic factors, especially neurotransmitters, for directing migration and neurogenesis in the developing and adult brain. Here, we extend our review discussing the effects of the principal growth and neurotrophic factors as well as their intracellular signal transduction on neurogenesis, fate determination and neuroprotective mechanisms. Many of these mechanisms have been elucidated by in vitro studies for which neural stem cells were isolated, grown as neurospheres, induced to neural differentiation under desired experimental conditions, and analyzed for embryonic, progenitor, and neural marker expression by flow and imaging cytometry techniques. The better understanding of neural stem cells proliferation and differentiation is crucial for any therapeutic intervention aiming at neural stem cell transplantation and recruitment of endogenous repair mechanisms.

Dual regeneration of muscle and nerve by intravenous administration of human amniotic fluid-derived mesenchymal stem cells regulated by stromal cell-derived factor-1α in a sciatic nerve injury model

OBJECT

Human amniotic fluid-derived mesenchymal stem cells (AFMSCs) have been shown to promote peripheral nerve regeneration. The expression of stromal cell-derived factor-1α (SDF-1α) in the injured nerve exerts a trophic effect by recruiting progenitor cells that promote nerve regeneration. In this study, the authors investigated the feasibility of intravenous administration of AFMSCs according to SDF-1α expression time profiles to facilitate neural regeneration in a sciatic nerve crush injury model.

METHODS

Peripheral nerve injury was induced in 63 Sprague-Dawley rats by crushing the left sciatic nerve using a vessel clamp. The animals were randomized into 1 of 3 groups: Group I, crush injury as the control; Group II, crush injury and intravenous administration of AFMSCs (5 × 10(6) cells for 3 days) immediately after injury (early administration); and Group III, crush injury and intravenous administration of AFMSCs (5 × 10(6) cells for 3 days) 7 days after injury (late administration). Evaluation of neurobehavior, electrophysiological study, and assessment of regeneration markers were conducted every week after injury. The expression of SDF-1α and neurotrophic factors and the distribution of AFMSCs in various time profiles were also assessed.

RESULTS

Stromal cell-derived factor-1α increased the migration and wound healing of AFMSCs in vitro, and the migration ability was dose dependent. Crush injury induced the expression of SDF-1α at a peak of 10-14 days either in nerve or muscle, and this increased expression paralleled the expression of its receptor, chemokine receptor type-4 (CXCR-4). Most AFMSCs were distributed to the lung during early or late administration. Significant deposition of AFMSCs in nerve and muscle only occurred in the late administration group. Significantly enhanced neurobehavior, electrophysiological function, nerve myelination, and expression of neurotrophic factors and acetylcholine receptor were demonstrated in the late administration group.

CONCLUSIONS

Amniotic fluid-derived mesenchymal stem cells can be recruited by expression of SDF-1α in muscle and nerve after nerve crush injury. The increased deposition of AFMSCs paralleled the expression profiles of SDF-1α and its receptor CXCR-4 in either muscle or nerve. Administration of AFMSCs led to improvements in neurobehavior and expression of regeneration markers. Intravenous administration of AFMSCs may be a promising alternative treatment strategy in peripheral nerve disorder.

Human adipose-derived mesenchymal stem cells systemically injected promote peripheral nerve regeneration in the mouse model of sciatic crush

Mesenchymal stem cells (MSCs) represent a promising therapeutic approach in nerve tissue engineering. To date, the local implantation of MSC in injured nerves has been the only route of administration used. In case of multiple sites of injury, the systemic administration of cells capable of reaching damaged nerves would be advisable. In this regard, we found that an intravenous administration of adipose-derived MSC (ASC) 1 week after sciatic nerve crush injury, a murine model of acute axonal damage, significantly accelerated the functional recovery. Sciatic nerves from ASC-treated mice showed the presence of a restricted number of undifferentiated ASC together with a significant improvement in fiber sprouting and the reduction of inflammatory infiltrates for up to 3 weeks. Besides the immune modulatory effect, our results show that ASC may contribute to peripheral nerve regeneration because of their ability to produce in culture neuroprotective factors such as insulin-like growth factor I, brain-derived neurotrophic factor, or basic fibroblast growth factor. In addition to this production in vitro, we interestingly found that the concentration of glial-derived neurotrophic factor (GDNF) was significantly increased in the sciatic nerves in mice treated with ASC. Since no detectable levels of GDNF were observed in ASC cultures, we hypothesize that ASC induced the local production of GDNF by Schwann cells. In conclusion, we show that systemically injected ASC have a clear therapeutic potential in an acute model of axonal damage. Among the possible mechanisms promoting nerve regeneration, our results rule out a process of trans-differentiation and rather suggest the relevance of a bystander effect, including the production of in situ molecules, which, directly or indirectly through a cross-talk with local glial cells, may modulate the local environment with the down-regulation of inflammation and the promotion of axonal regeneration.

Recruitment by SDF-1α of CD34-positive cells involved in sciatic nerve regeneration

Object

Increased integration of CD34+ cells in injured nerve significantly promotes nerve regeneration, but this effect can be counteracted by limited migration and short survival of CD34+ cells. SDF-1α and its receptor mediate the recruitment of CD34+ cells involved in the repair mechanism of several neurological diseases. In this study, the authors investigate the potentiation of CD34+ cell recruitment triggered by SDF-1α and the involvement of CD34+ cells in peripheral nerve regeneration.

Methods

Peripheral nerve injury was induced in 147 Sprague-Dawley rats by crushing the left sciatic nerve with a vessel clamp. The animals were allocated to 3 groups: Group 1, crush injury (controls); Group 2, crush injury and local application of SDF-1α recombinant proteins; and Group 3, crush injury and local application of SDF-1α antibody. Electrophysiological studies and assessment of regeneration markers were conducted at 4 weeks after injury; neurobehavioral studies were conducted at 1, 2, 3, and 4 weeks after injury. The expression of SDF-1α, accumulation of CD34+ cells, immune cells, and angiogenesis factors in injured nerves were evaluated at 1, 3, 7, 10, 14, 21, and 28 days after injury.

Results

Application of SDF-1α increased the migration of CD34+ cells in vitro, and this effect was dose dependent. Crush injury induced the expression of SDF-1α, with a peak of 10–14 days postinjury, and this increased expression of SDF-1α paralleled the deposition of CD34+ cells, expression of VEGF, and expression of neurofilament. These effects were further enhanced by the administration of SDF-1α recombinant protein and abolished by administration of SDF-1α antibody. Furthermore, these effects were consistent with improvement in measures of neurological function such as sciatic function index, electrophysiological parameters, muscle weight, and myelination of regenerative nerve.

Conclusions

Expression of SDF-1α facilitates recruitment of CD34+ cells in peripheral nerve injury. The increased deposition of CD34+ cells paralleled significant expression of angiogenesis factors and was consistent with improvement of neurological function. Utilization of SDF-1α for enhancing the recruitment of CD34+ cells involved in peripheral nerve regeneration may be considered as an alternative treatment strategy in peripheral nerve disorders.