Additive manufacturing of Schwann cell-laden collagen/alginate nerve guidance conduits by freeform reversible embedding regulate neurogenesis via exosomes secretion towards peripheral nerve regeneration

Peripheral nerve injury is a common clinical problem that could be debilitating to one's quality of life. The complex nerve guidance conduits (NGCs) with cells in order to improve nerve regeneration. Therefore, we used freeform reversible embedding of suspended hydrogels to fabricate Schwann cells (SCs)-laden collagen/alginate (Col/Alg) NGCs. First, we evaluated Col influence on the characteristics of NGCs. After which, Wharton's jelly mesenchymal stem cells (WJMSC) are seeded onto the inner channel of NGCs and evaluated neural regeneration behaviors. Results indicated the SCs-laden NGCs with 2.5 % Col found the highest proliferation and secretion of neurotrophic protein. Furthermore, co-culture of SCs promoted differentiation of WJMSC as seen from the increased neurogenic-related protein in NGCs. To determine the molecular mechanism between SCs and WJMSC, we demonstrated the neurotrophic factors secreted by SCs act on tropomyosin receptor kinase A (TrkA) receptors of WJMSC to promote nerve regeneration. In addition, our study demonstrated SCs-derived exosomes had a critical role in regulating neural differentiation of WJMSC. Taken together, this study demonstrates the fabrication of SCs-laden Col/Alg NGCs for nerve regeneration and understanding regarding the synergistic regenerative mechanisms of different cells could bring us a step closer for clinical treatment of large nerve defects.

Self-Closing Stretchable Cuff Electrodes for Peripheral Nerve Stimulation and Electromyographic Signal Recording

The cuff electrode can be wrapped in the columnar or tubular biological tissue for physiological signal detection or stimulation regulation. The reliable and non-excessive interfaces between the electrode and complex tissue are critical. Here, we propose a self-closing stretchable cuff electrode, which is able to self-close onto the bundles of tissues after dropping water. The curliness is realized by the mechanical stress mismatch between different layers of the elastic substrate. The material of the substrate can be selected to match the modulus of the target tissue to achieve minimal constraint on the tissue. Moreover, the self-closing structure keeps the cuff electrode free from any extra mechanical locking structure. For in vivo testing, both sciatic nerve stimulation to drive muscles and electromyographic signal monitoring around a rat's extensor digitorum longus for 1 month prove that our proposed electrode conforms well to the curved surface of biological tissue.

Polydopamine-Decorated PLCL Conduit to Induce Synergetic Effect of Electrical Stimulation and Topological Morphology for Peripheral Nerve Regeneration

Due to the limited self-repairing capacity after peripheral nerve injuries (PNI), artificial nerve conduits are widely applied to facilitate neural regeneration. Exogenous electrical stimulation (ES) that is carried out by the conductive conduit regulates the biological behavior of Schwann cells (SCs). Meanwhile, a longitudinal surface structure counts to guide axonal growth to accelerate the end-to-end connection. Currently, there are no conduits equipped with both electrical conduction and axon-guiding surface structure. Herein, a biodegradable, conductive poly(l-lactide-co-caprolactone)/graphene (PLCL/GN) composite conduit is designed. The conduit with 20.96 ± 1.26 MPa tensile strength has a micropatterned surface of 20 µm groove fabricated by microimprint technology and self-assembled polydopamine (PDA). In vitro evaluation shows that the conduits with ES effectively stimulate the directional cell migration, adhesion, and elongation, and enhance neuronal expression of SCs. The rat sciatic nerve crush model demonstrates that the conductive micropatterned conduit with ES promotes the growth of myelin sheath, faster nerve regeneration, and 20-fold functional recovery in vivo. These discoveries prove that the PLCL(G)/PDA/GN composite conduit is a promising tool for PNI treatment by providing the functional integration of physical guidance, biomimetic biological regulation, and bioelectrical stimulation, which inspires a novel therapeutic approach for nerve regeneration in the future.

Artificial Nerve Containing Stem Cells, Vascularity and Scaffold; Review of Our Studies

To promote nerve regeneration within a conduit (tubulation), we have performed studies using a tube model based on four important concepts for tissue engineering: vascularity, growth factors, cells, and scaffolds. A nerve conduit containing a blood vascular pedicle (vessel-containing tube) accelerated axon regeneration and increased the axon regeneration distance; however, it did not increase the number or diameter of the axons that regenerated within the tube. A vessel-containing tube with bone-marrow-derived mesenchymal stem cell (BMSC) transplantation led to the increase in the number and diameter of regenerated axons. Intratubularly transplanted decellularized allogenic nerve basal lamellae (DABLs) worked as a frame to maintain the fibrin matrix structure containing neurochemical factors and to anchor the transplanted stem cells within the tube. For the clinical application of nerve conduits, they should exhibit capillary permeability, biodegradability, and flexibility. Nerbridge® (Toyobo Co. Ltd., Osaka, Japan) is a commercially available artificial nerve conduit. The outer cylinder is a polyglycolic acid (PGA) fiber mesh and possesses capillary permeability. We used the outer cylinder of Nerbridge as a nerve conduit. A 20-mm sciatic nerve deficit was bridged by the PGA mesh tube containing DABLs and BMSCs, and the resulting nerve regeneration was compared with that obtained through a 20-mm autologous nerve graft. A neve-regeneration rate of about 70%-80% was obtained in 20-mm-long autologous nerve autografts using the new conduits.

Local delivery of tacrolimus using electrospun poly-ϵ-caprolactone nanofibres suppresses the T-cell response to peripheral nerve allografts

Objective.Repair of nerve gap injuries can be achieved through nerve autografting, but this approach is restricted by limited tissue supply and donor site morbidity. The use of living nerve allografts would provide an abundant tissue source, improving outcomes following peripheral nerve injury. Currently this approach is not used due to the requirement for systemic immunosuppression, to prevent donor-derived cells within the transplanted nerve causing an immune response, which is associated with severe adverse effects. The aim of this study was to develop a method for delivering immunosuppression locally, then to test its effectiveness in reducing the immune response to transplanted tissue in a rat model of nerve allograft repair.Approach.A coaxial electrospinning approach was used to produce poly-ϵ-caprolactone fibre sheets loaded with the immunosuppressant tacrolimus. The material was characterised in terms of structure and tacrolimus release, then testedin vivothrough implantation in a rat sciatic nerve allograft model with immunologically mismatched host and donor tissue.Main results.Following successful drug encapsulation, the fibre sheets showed nanofibrous structure and controlled release of tacrolimus over several weeks. Materials containing tacrolimus (and blank material controls) were implanted around the nerve graft at the time of allograft or autograft repair. The fibre sheets were well tolerated by the animals and tacrolimus release resulted in a significant reduction in lymphocyte infiltration at 3 weeks post-transplantation.Significance.These findings demonstrate proof of concept for a novel nanofibrous biomaterial-based targeted drug delivery strategy for immunosuppression in peripheral nerve allografting.

Morphological Methods to Evaluate Peripheral Nerve Fiber Regeneration: A Comprehensive Review

Regeneration of damaged peripheral nerves remains one of the main challenges of neurosurgery and regenerative medicine, a nerve functionality is rarely restored, especially after severe injuries. Researchers are constantly looking for innovative strategies for tackling this problem, with the development of advanced tissue-engineered nerve conduits and new pharmacological and physical interventions, with the aim of improving patients' life quality. Different evaluation methods can be used to study the effectiveness of a new treatment, including functional tests, morphological assessment of regenerated nerve fibers and biomolecular analyses of key factors necessary for good regeneration. The number and diversity of protocols and methods, as well as the availability of innovative technologies which are used to assess nerve regeneration after experimental interventions, often makes it difficult to compare results obtained in different labs. The purpose of the current review is to describe the main morphological approaches used to evaluate the degree of nerve fiber regeneration in terms of their usefulness and limitations.

Saltatory conduction and intrinsic electrophysiological properties at the nodes of ranvier of Aα/β-afferent fibers and Aα-efferent fibers in rat sciatic nerves

Large-diameter myelinated fibers in sciatic nerves are composed of both Aα/β-afferent fibers and Aα-efferent fibers to convey sensory and motor impulses, respectively, via saltatory conduction for rapid leg responses. Saltatory conduction and electrophysiological properties at the nodes of Ranvier (NRs) of these sciatic nerve fibers have not been directly studied. We used ex vivo sciatic nerve preparations from rats and applied patch-clamp recordings at the NRs of both Aα/β-afferent fibers and Aα-efferent fibers in the sciatic nerves to characterize their saltatory conduction and intrinsic electrophysiological properties. The velocity and frequency of saltatory conduction in both types of fibers were similar. Resting membrane potentials (RMPs), input resistance, action potential (AP) threshold, and AP rheobase were also not significantly different at the NRs of the two types of fibers in the sciatic nerves. In comparison with Aα/β-afferent fibers, Aα-efferent fibers in the sciatic nerves show higher amplitude and broader width of APs at their NRs. At the NRs of both types of fibers, depolarizing voltages evoked transient inward currents followed by non-inactivating outward currents, and the inward currents and non-inactivating outward currents at the NRs were not significantly different between the two types of fibers. Using AP-clamp, inward currents during AP upstroke were found to be insignificant difference, but amplitudes of non-inactivating outward currents during AP repolarization were significantly lower at the NRs of Aα-efferent fibers than at the NRs of Aα/β-afferent fibers in the sciatic nerves. Collectively, saltatory conduction, ionic currents, and intrinsic electrophysiological properties at the NRs of Aα/β-afferent fibers and Aα-efferent fibers in the sciatic nerves are generally similar, but some differences were also observed.

Influences of Repair Site Tension and Conduit Splinting on Peripheral Nerve Reconstruction

BACKGROUND

We investigated the use of a conduit splinting technique to mitigate tension at the coaptation site of a rodent nerve defect model to determine the optimal reconstruction method for segmental nerve defects.

METHODS

A rat sciatic nerve segmental defect model was created by excising 5mm of the sciatic nerve unilaterally. Four groups of 10 rats were each reconstructed using 1 of 4 techniques: primary repair, repair with conduit splinting, reverse isograft with conduit splinting, and reverse isograft without splinting. Functional outcomes were assessed at 6 weeks by measurement of Sciatic Functional Index (SFI), and sciatic nerves were harvested at the nonsurvival surgery. Histomorphologic measurements were reported as a value normalized to the average measurements of the control side. The primary outcomes were assessment of nerve continuity and the proportion of nerve fibers in the regenerating nerve compared with the uninjured side.

RESULTS

The number of repair site rupture rates was lower when a conduit splint was used-less than half of the primary repairs under tension remained intact at 6 weeks. No difference was seen in axon number, size, and density between primary repairs and those augmented by conduit splints, but worse functional outcomes and more debris were present compared with the intact primary repairs.

CONCLUSIONS

Nerve conduit splinting reduced rupture rates, particularly for nerve repairs associated with a segmental defect. No significant difference was seen in the number of axons among techniques. Primary nerve repair under tension that did not rupture demonstrated superior SFI.

The effect of a gap concept on peripheral nerve recovery in modified epineurial neurorrhaphy: An experimental study in rats

BACKGROUND

Several factors such as surgical approach that only consider topographic anatomy; inadequate fascicular alignment, extraepineurial sprouting in the repair zone; contact of axons with the suture area are the disadvantages of epineurial neurorrhaphy. Accordingly, axonal mismatch, neuroma, and unfavorable nerve recovery become inevitable. Neurotropism is the theory clarifying appropriate matching of the nerve fibers independently without needing surgical approach. The studies comparing the primary nerve repair with the nerve defects bridged in different ways demonstrated better outcomes of nerve recovery in the groups with a nerve gap. In this study, we aimed to demonstrate the effects of the gap concept in primary nerve repair bridged by own epineurium. We hypothesized that this technique will provide better results in terms of peripheral nerve recovery and will significantly eliminate the occurrence of a neuroma, which is quite possible in epineurial neurorrhaphy.

MATERIALS AND METHODS

A total of 35 Wistar female rats weighing 200 ~ 250 g were randomly divided into five groups each with seven rats. Sham controls constituted Group 1, while the rats with epineural neurorrhaphy were included in Group 2. The remaining three groups were the study groups. In Group 3, after the sciatic nerve transection, epineurium of the distal segment was sleeved and preserved. A 2-mm axonal segment was removed from the epineurium free distal ending and no any procedure was applied to the proximal ending of the transected sciatic nerve. Epineuriums of the both sides were approximated and repaired. In Group 4, a 2-mm axonal segment was removed from the proximal ending of the sciatic nerve after preservation of epineurium and no any procedure was applied to the distal part of sciatic nerve. Epineuriums of the both sides were approximated and repaired. In addition, in Group 5, after epineuriums were sleeved in the both distal and proximal stumps, a 1-mm nerve segment was removed from both endings and epineuriums were repaired in the middle bridging a 2-mm axonal gap again. After a 3 months follow-up period Sciatic Functional Index (SFI) was measured by walking track analysis; the area under the evoked compound muscle action potential (CMAP) and latency periods were calculated via electromyographic (EMG) analysis; and histopathological evaluation were performed to compare the parameters of edema, fibrosis, inflammation, vascularization, axonal degeneration, axonal density, myelination, disorganization, and neuroma occurrence. Vascular structures and nerve fibers were counted at ×200 magnification: +1, +2, and +3 indicated the presence of 0-15, 16-30, and >30 structures, respectively. For uncountable parameters (edema, disorganization, myelination, fibrosis, and inflammation): +1 indicated mild, +2 indicated moderate, and +3 indicated severe.

RESULTS

The differences between the groups with axonal gap repair and epineural neurorrhaphy were not significant regarding to SFI. The areas under CMAP were as follows: 27.9 ± 5.9 (Δ = 12.1%) in Group 1; 16.5 ± 5.5 (Δ = 6.3%) in Group 2; 14.1 ± 6.2 (Δ = 4.8%) in group 3; 13.8 ± 2.3 (Δ = 9.2%) in Group 4, and 22.5 ± 18.3 (Δ = 2.2%) in Group 5. Group 5 (1 mm gap in the distal +1 mm gap in the proximal segments) had a significantly better result in terms of the area under CMAP with the value of 22.5 ± 18.3 m/Mv (p = .031). Axonal density was 0.9 ± 0.6 (Δ = 2.2%) in Group 2, 2.4 ± 0.3 (Δ = 5.1%) in Group 3, 2.8 ± 0.1 (Δ = 7.7%) in Group 4, and 2.8 ± 0.2 (Δ = 4.8%) in Group 5. Myelination was 1.1 ± 0.5 (Δ = 3.4%) in group 2, 2.2 ± 0.2 (Δ = 6.7%) in group 3, 2.4 ± 0.4 (Δ = 6.0%) in Group 4, and 2.7 ± 0.3 (Δ = 4.6%) in Group 5. Disorganization was 2.3 ± 0.4 (Δ = 4.1%) in Group 2, 1.2 ± 0.2 (Δ = 7.7%) in Group 3, 1.3 ± 0.2 (Δ = 6.5%) in Group 4, and 1 ± 0.3 (Δ = 5.9%) in Group 5. And, neuroma occurrence was found 2.2 ± 0.6 (Δ = 2.8%) in Group 2 and 0.3 ± 0.2 (Δ = 0.1%) in Group 4 while neuroma was not encountered in Group 3 and Group 5. Comparison between the epineurial neurorrhaphy group and the groups with axonal defect revealed the statistically significant results in the factors of axonal density (p = .001), myelination (p = .028), disorganization (p = .016) and neuroma (p = .001).

CONCLUSIONS

Creating axonal gap bridged by own epineurium showed favorable results comparing with epineurial neurorrhaphy. Resection of a 1 mm axonal segment from the proximal and distal stumps following the epineurial sleeve procedure and performing the epineurium- only repair can facilitate the nerve regeneration. The feasibility of the described technique has been demonstrated in a small rat model and must be further validated in larger animals before clinical testing.

Spatio-temporal feature extraction in sensory electroneurographic signals

The recording and analysis of peripheral neural signal can provide insight for various prosthetic and bioelectronics medicine applications. However, there are few studies that investigate how informative features can be extracted from population activity electroneurographic (ENG) signals. In this study, five feature extraction frameworks were implemented on sensory ENG datasets and their classification performance was compared. The datasets were collected in acute rat experiments where multi-channel nerve cuffs recorded from the sciatic nerve in response to proprioceptive stimulation of the hindlimb. A novel feature extraction framework, which incorporates spatio-temporal focus and dynamic time warping, achieved classification accuracies above 90% while keeping a low computational cost. This framework outperformed the remaining frameworks tested in this study and has improved the discrimination accuracy of the sensory signals. Thus, this study has extended the tools available to extract features from sensory population activity ENG signals. This article is part of the theme issue 'Advanced neurotechnologies: translating innovation for health and well-being'.

Preparation of Rat Sciatic Nerve for Ex Vivo Neurophysiology

Ex vivo preparations enable the study of many neurophysiological processes in isolation from the rest of the body while preserving local tissue structure. This work describes the preparation of rat sciatic nerves for ex vivo neurophysiology, including buffer preparation, animal procedures, equipment setup and neurophysiological recording. This work provides an overview of the different types of experiments possible with this method. The outlined method aims to provide 6 h of stimulation and recording on extracted peripheral nerve tissue in tightly controlled conditions for optimal consistency in results. Results obtained using this method are A-fibre compound action potentials (CAP) with peak-to-peak amplitudes in the millivolt range over the entire duration of the experiment. CAP amplitudes and shapes are consistent and reliable, making them useful to test and compare new electrodes to existing models, or the effects of interventions on the tissue, such as the use of chemicals, surgical alterations, or neuromodulatory stimulation techniques. Both conventional commercially available cuff electrodes with platinum-iridium contacts and custom-made conductive elastomer electrodes were tested and gave similar results in terms of nerve stimulus strength-duration response.

A comparison of extraneural approaches for selective recording in the peripheral nervous system

The peripheral nervous system is a key target for the development of neural interfaces. However, recording from the peripheral nerves can be challenging especially when chronic implantation is desired. Nerve cuffs are frequently employed using either two or three contacts to provide a single recording channel. Advancements in manufacturing technology have enabled multi-contact cuffs, enabling measurement of both temporal (i.e., velocity) and spatial information (i.e., spatial location). Selective techniques have been developed with different time resolutions but it is unclear how the number of contacts and their spatial configuration affect their performance. Thus, this paper investigates two extraneural recording techniques (LDA and spatiotemporal signatures) and compares them using recordings made from the sciatic nerve of rats using high density (HD, 56 contact), reduced-HD (16 contacts), and low density (LD, 16 contact) datasets. Performance of the two techniques was evaluated using classification accuracy and F₁-score. Both techniques show an expected improvement in classification accuracy with the spatiotemporal signature approach showing a 21.6 (LD to HD) - 24.6% (reduced HD to HD) increase and the LDA approach showing a 2.9 (reduced HD to HD) - 41.3% (LD to HD) increase and had comparable results in both the LD and HD datasets.

Evaluation of Pneumatic Insertion Stability of Utah Slanted Electrode Arrays in Rat Sciatic Nerve

The Utah Electrode Array (UEA) and its variants (e.g., the Utah Slanted Electrode Array, or USEA) have been prominent contributors to advances in the field of neural engineering over the past decade. The most common means of inserting UEA and USEA devices into neural tissue is pneumatic insertion performed by an insertion wand and a pneumatic controller. As design changes from the well-established standards occur to better suit specialized surgical applications, it becomes essential to verify that the alterations do not compromise the structural integrity of the device during insertion. This paper characterizes and demonstrates the reliability of specialized USEAs and insertion wands designed for auditory nerve implants following pneumatic insertion into a rat sciatic nerve. The results show that proposed changes in the USEA form factor and pneumatic insertion ergonomics do not compromise implant stability and device structural viability.

Improvement of sciatic nerve regeneration by multichannel nanofibrous membrane-embedded electro-conductive conduits functionalized with laminin

Multichannel structures in the design of nerve conduits offer potential advantages for regeneration of damaged nerves. However, lack of biochemical cues and electrical stimulation could hamper satisfactory nerve regeneration. The aim of this study was to simultaneously evaluate the effects of topographical, biological, and electrical cues on sciatic nerve regeneration. Accordingly, a series of multichannel nerve conduit was made using longitudinally-aligned laminin-coated poly (lactic-co-glycolic acid) (PLGA)/carbon nanotubes (CNT) nanofibers (NF, mean diameter: 455 ± 362 nm) in the lumen and randomly-oriented polycaprolactone (PCL) NF (mean diameter: 340 ± 200 nm) on the outer surface. In vitro studies revealed that the materials were nontoxic and able to promote cell attachment and proliferation on nanofibers and on fibrin gel. To determine the influence of laminin as biological and CNT as electrical cues on nerve regeneration, either of hollow PCL conduits, PLGA NF-embedded, PLGA/CNT NF-embedded or laminin-coated PLGA/CNT NF-embedded PCL conduits were implanted in rats. A new surgery method was utilized and results were compared with an autograft. The results of motor and sensory tests in addition to histopathological examination of the regenerated nerves demonstrated the formation of nerve fibers in laminin-coated PLGA/CNT NF-embedded PCL conduits. Results suggested that these conduits have the potential to improve sciatic nerve regeneration. Graphical abstract.

Reversible CD8 T cell-neuron cross-talk causes aging-dependent neuronal regenerative decline

Aging is associated with increased prevalence of axonal injuries characterized by poor regeneration and disability. However, the underlying mechanisms remain unclear. In our experiments, RNA sequencing of sciatic dorsal root ganglia (DRG) revealed significant aging-dependent enrichment in T cell signaling both before and after sciatic nerve injury (SNI) in mice. Lymphotoxin activated the transcription factor NF-κB, which induced expression of the chemokine CXCL13 by neurons. This in turn recruited CXCR5+CD8+ T cells to injured DRG neurons overexpressing major histocompatibility complex class I. CD8+ T cells repressed the axonal regeneration of DRG neurons via caspase 3 activation. CXCL13 neutralization prevented CXCR5+CD8+ T cell recruitment to the DRG and reversed aging-dependent regenerative decline, thereby promoting neurological recovery after SNI. Thus, axonal regeneration can be facilitated by antagonizing cross-talk between immune cells and neurons.

Ultraflexible and Stretchable Intrafascicular Peripheral Nerve Recording Device with Axon-Dimension, Cuff-Less Microneedle Electrode Array

Peripheral nerve mapping tools with higher spatial resolution are needed to advance systems neuroscience, and potentially provide a closed-loop biomarker in neuromodulation applications. Two critical challenges of microscale neural interfaces are 1) how to apply them to small peripheral nerves, and 2) how to minimize chronic reactivity. A flexible microneedle nerve array (MINA) is developed, which is the first high-density penetrating electrode array made with axon-sized silicon microneedles embedded in low-modulus thin silicone. The design, fabrication, acute recording, and chronic reactivity to an implanted MINA, are presented. Distinctive units are identified in the rat peroneal nerve. The authors also demonstrate a long-term, cuff-free, and suture-free fixation manner using rose bengal as a light-activated adhesive for two time-points. The tissue response is investigated at 1-week and 6-week time-points, including two sham groups and two MINA-implanted groups. These conditions are quantified in the left vagus nerve of rats using histomorphometry. Micro computed tomography (micro-CT) is added to visualize and quantify tissue encapsulation around the implant. MINA demonstrates a reduction in encapsulation thickness over previously quantified interfascicular methods. Future challenges include techniques for precise insertion of the microneedle electrodes and demonstrating long-term recording.

A Highly Miniaturized, Chronically Implanted ASIC for Electrical Nerve Stimulation

We present a wireless, fully implantable device for electrical stimulation of peripheral nerves consisting of a powering coil, a tuning network, a Zener diode, selectable stimulation parameters, and a stimulator IC, all encapsulated in biocompatible silicone. A wireless RF signal at 13.56 MHz powers the implant through the on-chip rectifier. The ASIC, designed in TSMC's 180 nm MS RF G process, occupies an area of less than 1.2 mm². The IC enables externally selectable current-controlled stimulation through an on-chip read-only memory with a wide range of 32 stimulation parameters (90-750 µA amplitude, 100 µs or 1 ms pulse width, 15 or 50 Hz frequency). The IC generates the constant current waveform using an 8-bit binary weighted DAC and an H-Bridge. At the most power-hungry stimulation parameter, the average power consumption during a stimulus pulse is 2.6 mW with a power transfer efficiency of ∼5.2%. In addition to benchtop and acute testing, we chronically implanted two versions of the device (a design with leads and a leadless design) on two rats' sciatic nerves to verify the long-term efficacy of the IC and the full system. The leadless device had the following dimensions: height of 0.45 cm, major axis of 1.85 cm, and minor axis of 1.34 cm, with similar dimensions for the device with leads. Both devices were implanted and worked for experiments lasting from 21-90 days. To the best of our knowledge, the fabricated IC is the smallest constant-current stimulator that has been tested chronically.

Proteomic quantitative study of dorsal root ganglia and sciatic nerve in type 2 diabetic mice

OBJECTIVE

Peripheral neuropathy is the most common and debilitating complication of type 2 diabetes, leading to sensory loss, dysautonomia, hyperalgesia, and spontaneous noxious sensations. Despite the clinical and economic burden of diabetic neuropathy, no effective treatment is available. More preclinical research must be conducted in order to gain further understanding of the aetiology of the disease and elucidate new therapeutic targets.

METHODS

The proteome of lumbar dorsal root ganglia and sciatic nerve of BKS-db/db mice, which contain a mutation of the leptin receptor and are an established type 2 diabetes model, was characterized for the first time by tandem mass tag labelling and mass spectrometry analysis.

RESULTS

Proteomic analysis showed differentially expressed proteins grouped into functional clusters in db/db peripheral nerves compared to control mice, underlining reduced glycolytic and TCA cycle metabolism, higher lipid catabolism, upregulation of muscle-like proteins in DRG and downregulation in SCN, increased cytoskeleton-related proteins, a mild dysregulation of folding chaperones, activation of acute-phase and inflammatory response, and alterations in glutathione metabolism and oxidative stress related proteins.

CONCLUSIONS

Our data validate previous transcriptomic and metabolomic results and uncover new pathways altered in diabetic neuropathy. Our results point out that energetic deficiency could represent the main mechanism of neurodegeneration observed in diabetic neuropathy. These findings may provide important information to select appropriate targets to develop new therapeutic strategies.

Neurotransmission Recovery by Melatonin Measured by CMAP

Compound muscle action potential (CMAP) recordings provide a sensitive electromyographic approach to measure nerve conduction and assess neuromuscular junction functionality in humans and rodents. In humans, it represents a diagnostic tool for neuromuscular disorders. In rodents, this approach is widely employed to dissect the molecular mechanisms driving peripheral nerve degeneration/regeneration, as well as to evaluate the effect of candidate pro-regenerative compounds. The method described here allows recording CMAP from the gastrocnemius muscle of mice after sciatic nerve stimulation. We report some representative traces of CMAP recorded from adult, healthy mice, after sciatic nerve compression and during neurotransmission recovery stimulated by melatonin administration.

Effects of dapagliflozin on peripheral sympathetic nerve activity in standard chow- and high-fat-fed rats after a glucose load

To clarify the effects of long-term administration of SGLT2 inhibitor, a hypoglycemic agent, on basal sympathetic nerve activity (SNA) and on SNA under development of insulin resistance, we measured peripheral SNA in response to a glucose load in standard chow- (SCF) and high-fat-fed (HFF) rats treated with or without dapagliflozin for 7 weeks. We conducted an intravenous glucose administration (IVGA), and evaluated SNA microneurographically recorded in the unilateral sciatic nerve. Dapagliflozin did not affect the steady state action potential (AP) rate just before the IVGA (baseline) in both the SCF and HFF rats. After the IVGA, in the SCF rats, the AP rate in dapagliflozin-treated group transiently decreased within 20 min after the IVGA, and was significantly lower (P < 0.05) than non-treated group for 60 min. In the HFF rats, no significant difference was seen in the AP rate between dapagliflozin-treated and non-treated groups. The rate in the dapagliflozin-treated group after the IVGA was significantly lower (P < 0.05) than the baseline whereas such difference was not found in the non-treated group. In conclusion, dapagliflozin attenuate SNA in response to glucose load, and that the SNA response is different between standard chow-fed- and high-fat-fed rats.

Lycorine improves peripheral nerve function by promoting Schwann cell autophagy via AMPK pathway activation and MMP9 downregulation in diabetic peripheral neuropathy

Diabetic peripheral neuropathy (DPN) is the most common complication of diabetes mellitus and no effective therapy is approved. Here, lycorine, a natural alkaloid, was identified as a potential drug for DPN by the bioinformatics analysis of GEO datasets and Connectivity Map database. Lycorine administration improved peripheral nerve function and autophagy-associated proteins of diabetic mice. Again, in vitro high glucose-cultured rat Schwann cells (RSC96) showed enhanced autophagosome marker LC3-II with the treatment of lycorine. Additionally, beclin-1 and Atg3 were decreased in high glucose-stimulated RSC96 cells, which were reversed by lycorine treatment. Furthermore, DPN-associated differentially expressed genes (DEGs) from GEO datasets and lycorine-drug targets from PubChem and PharmMapper were visually analyzed and revealed that MMP9 was both DPN-associated DEGs and lycorine-drug target. Functional enrichment analysis of MMP9-relevant genes showed that cell energy metabolism was involved. Moreover, lycorine reduced high glucose-enhanced MMP9 expression in RSC96 cells. Overexpression of MMP9 attenuated lycorine-induced the expression of beclin-1, Atg3 and LC3-II in high glucose-cultured RSC96 cells. In addition, AMPK pathway activation was confirmed in lycorine-treated high glucose-cultured RSC96 cells. Then AMPK pathway inhibition attenuated lycorine-reduced MMP9 expression in high glucose-treated RSC96 cells. Molecular docking analysis revealed that lycorine bound the domain of AMPK containing Thr 172 site, which affected AMPK (Thr 172) phosphorylation. Finally, AMPK pathway activation and MMP9 downregulation were also revealed in the sciatic nerves of diabetic mice administrated with lycorine. Taken together, lycorine was advised to promote Schwann cell autophagy via AMPK pathway activation and MMP9 downregulation-induced LC3-II transformation in diabetic peripheral neuropathy.

Development of a conduit of PLGA-gelatin aligned nanofibers produced by electrospinning for peripheral nerve regeneration

A promising alternative to conventional nerve grafting is the use of artificial grafts made from biodegradable and biocompatible materials and support cells. The aim of this study has been to produce a biodegradable nerve conduit and investigate the cytocompatibility with stem cells and its regeneration promoting properties in a rat animal model. A poly (lactic-co-glycolic acid) (PLGA) conduit of aligned nanofibers was produced by the electrospinning method, functionalized with gelatin and seeded either with mouse embryonic stem cells (mESCs) or with human mesenchymal stem cells (SHED). The cell proliferation and viability were analyzed in vitro. The conduits were implanted in a rat model of sciatic nerve lesion by transection. The functional recovery was monitored for 8 weeks using the Sciatic Functional Index (SFI) and histological analyses were used to assess the nerve regeneration. Scaffolds of aligned PLGA fibers with an average diameter of 0.90 ± 0.36 μm and an alignment coefficient of 0.817 ± 0.07 were produced. The treatment with gelatin increased the fiber diameter to 1.05 ± 0.32 μm, reduced the alignment coefficient to 0.655 ± 0.045 and made the scaffold very hydrophilic. The cell viability and Live/dead assay showed that the stem cells remained viable and proliferated after 7 days in culture. Confocal images of phalloidin/DAPI staining showed that the cells adhered and proliferated widely, in fully adaptation with the biomaterial. The SFI values of the group that received the conduit were similar to the values of the control lesioned group. In conclusion, conduits composed of PLGA-gelatin nanofibers were produced and promoted a very good interaction with the stem cells. Although in vitro studies have shown this biomaterial to be a promising biomaterial for the regeneration of nerve tissue, in vivo studies of this graft have not shown significant improvements in nerve regeneration.

Functional Outcomes of Nerve Allografts Seeded with Undifferentiated and Differentiated Mesenchymal Stem Cells in a Rat Sciatic Nerve Defect Model

BACKGROUND

Mesenchymal stem cells have the potential to produce neurotrophic growth factors and establish a supportive microenvironment for neural regeneration. The purpose of this study was to determine the effect of undifferentiated and differentiated mesenchymal stem cells dynamically seeded onto decellularized nerve allografts on functional outcomes when used in peripheral nerve repair.

METHODS

In 80 Lewis rats, a 10-mm sciatic nerve defect was reconstructed with (1) autograft, (2) decellularized allograft, (3) decellularized allograft seeded with undifferentiated mesenchymal stem cells, or (4) decellularized allograft seeded with mesenchymal stem cells differentiated into Schwann cell-like cells. Nerve regeneration was evaluated over time by cross-sectional tibial muscle ultrasound measurements, and at 12 and 16 weeks by isometric tetanic force measurements, compound muscle action potentials, muscle mass, histology, and immunofluorescence analyses.

RESULTS

At 12 weeks, undifferentiated mesenchymal stem cells significantly improved isometric tetanic force measurement and compound muscle action potential outcomes compared to decellularized allograft alone, whereas differentiated mesenchymal stem cells significantly improved compound muscle action potential outcomes. The autografts outperformed both stem cell groups histologically at 12 weeks. At 16 weeks, functional outcomes normalized between groups. At both time points, the effect of undifferentiated versus differentiated mesenchymal stem cells was not significantly different.

CONCLUSIONS

Undifferentiated and differentiated mesenchymal stem cells significantly improved functional outcomes of decellularized allografts at 12 weeks and were similar to autograft results in the majority of measurements. At 16 weeks, outcomes normalized as expected. Although differences between both cell types were not statistically significant, undifferentiated mesenchymal stem cells improved functional outcomes of decellularized nerve allografts to a greater extent and had practical benefits for clinical translation by limiting preparation time and costs.

Administration of Purified Exosome Product in a Rat Sciatic Serve Reverse Autograft Model

BACKGROUND

The nerve autograft remains the gold standard when reconstructing peripheral nerve defects. However, although autograft repair can result in useful functional recovery, poor outcomes are common, and better treatments are needed. The purpose of this study was to evaluate the effect of purified exosome product on functional motor recovery and nerve-related gene expression in a rat sciatic nerve reverse autograft model.

METHODS

Ninety-six Sprague-Dawley rats were divided into three experimental groups. In each group, a unilateral 10-mm sciatic nerve defect was created. The excised nerve was reversed and used to reconstruct the defect. Group I animals received the reversed autograft alone, group II animals received the reversed autograft with fibrin glue, and group III animals received the reversed autograft with purified exosome product suspended in the fibrin glue. The animals were killed at 3 and 7 days and 12 and 16 weeks after surgery. Evaluation included compound muscle action potentials, isometric tetanic force, tibialis anterior muscle wet weight, nerve regeneration-related gene expression, and nerve histomorphometry.

RESULTS

At 16 weeks, isometric tetanic force was significantly better in group III (p = 0.03). The average axon diameter of the peroneal nerve was significantly larger in group III at both 12 and 16 weeks (p = 0.015 at 12 weeks; p < 0.01 at 16 weeks). GAP43 and S100b gene expression was significantly up-regulated by purified exosome product.

CONCLUSIONS

Local administration of purified exosome product demonstrated improved nerve regeneration profiles in the reverse sciatic nerve autograft rat model. Thus, purified exosome product may have beneficial effects on nerve regeneration, gene profiles, and motor outcomes.