Development of ibuprofen-loaded electrospun materials suitable for surgical implantation in peripheral nerve injury

The development of nerve wraps for use in the repair of peripheral nerves has shown promise over recent years. A pharmacological effect to improve regeneration may be achieved by loading such materials with therapeutic agents, for example ibuprofen, a non-steroidal anti-inflammatory drug with neuroregenerative properties. In this study, four commercially available polymers (polylactic acid (PLA), polycaprolactone (PCL) and two co-polymers containing different ratios of PLA to PCL) were used to fabricate ibuprofen-loaded nerve wraps using blend electrospinning. In vitro surgical handling experiments identified a formulation containing a PLA/PCL 70/30 molar ratio co-polymer as the most suitable for in vivo implantation. In a rat model, ibuprofen released from electrospun materials significantly improved the rate of axonal growth and sensory recovery over a 21-day recovery period following a sciatic nerve crush. Furthermore, RT-qPCR analysis of nerve segments revealed that the anti-inflammatory and neurotrophic effects of ibuprofen may still be observed 21 days after implantation. This suggests that the formulation developed in this work could have potential to improve nerve regeneration in vivo.

Potential of dental pulp stem cells and their products in promoting peripheral nerve regeneration and their future applications

Peripheral nerve injury (PNI) seriously affects people's quality of life. Stem cell therapy is considered a promising new option for the clinical treatment of PNI. Dental stem cells, particularly dental pulp stem cells (DPSCs), are adult pluripotent stem cells derived from the neuroectoderm. DPSCs have significant potential in the field of neural tissue engineering due to their numerous advantages, such as easy isolation, multidifferentiation potential, low immunogenicity, and low transplant rejection rate. DPSCs are extensively used in tissue engineering and regenerative medicine, including for the treatment of sciatic nerve injury, facial nerve injury, spinal cord injury, and other neurodegenerative diseases. This article reviews research related to DPSCs and their advantages in treating PNI, aiming to summarize the therapeutic potential of DPSCs for PNI and the underlying mechanisms and providing valuable guidance and a foundation for future research.

Unveiling adcyap1 as a protective factor linking pain and nerve regeneration through single-cell RNA sequencing of rat dorsal root ganglion neurons

BACKGROUND

Severe peripheral nerve injury (PNI) often leads to significant movement disorders and intractable pain. Therefore, promoting nerve regeneration while avoiding neuropathic pain is crucial for the clinical treatment of PNI patients. However, established animal models for peripheral neuropathy fail to accurately recapitulate the clinical features of PNI. Additionally, researchers usually investigate neuropathic pain and axonal regeneration separately, leaving the intrinsic relationship between the development of neuropathic pain and nerve regeneration after PNI unclear. To explore the underlying connections between pain and regeneration after PNI and provide potential molecular targets, we performed single-cell RNA sequencing and functional verification in an established rat model, allowing simultaneous study of the neuropathic pain and axonal regeneration after PNI.

RESULTS

First, a novel rat model named spared nerve crush (SNC) was created. In this model, two branches of the sciatic nerve were crushed, but the epineurium remained unsevered. This model successfully recapitulated both neuropathic pain and axonal regeneration after PNI, allowing for the study of the intrinsic link between these two crucial biological processes. Dorsal root ganglions (DRGs) from SNC and naïve rats at various time points after SNC were collected for single-cell RNA sequencing (scRNA-seq). After matching all scRNA-seq data to the 7 known DRG types, we discovered that the PEP1 and PEP3 DRG neuron subtypes increased in crushed and uncrushed DRG separately after SNC. Using experimental design scRNA-seq processing (EDSSP), we identified Adcyap1 as a potential gene contributing to both pain and nerve regeneration. Indeed, repeated intrathecal administration of PACAP38 mitigated pain and facilitated axonal regeneration, while Adcyap1 siRNA or PACAP6-38, an antagonist of PAC1R (a receptor of PACAP38) led to both mechanical hyperalgesia and delayed DRG axon regeneration in SNC rats. Moreover, these effects can be reversed by repeated intrathecal administration of PACAP38 in the acute phase but not the late phase after PNI, resulting in alleviated pain and promoted axonal regeneration.

CONCLUSIONS

Our study reveals that Adcyap1 is an intrinsic protective factor linking neuropathic pain and axonal regeneration following PNI. This finding provides new potential targets and strategies for early therapeutic intervention of PNI.

Application of Electrical Stimulation to Enhance Axon Regeneration Following Peripheral Nerve Injury

Enhancing axon regeneration is a major focus of peripheral nerve injury research. Although peripheral axons possess a limited ability to regenerate, their functional recovery is very poor. Various activity-based therapies like exercise, optical stimulation, and electrical stimulation as well as pharmacologic treatments can enhance spontaneous axon regeneration. In this protocol, we use a custom-built cuff to electrically stimulate the whole sciatic nerve for an hour prior to transection and repair. We used a Thy-1-YFP-H mouse to visualize regenerating axon profiles. We compared the regeneration of axons from nerves that were electrically stimulated to nerves that were not stimulated (untreated). Electrically stimulated nerves had longer axon growth than the untreated nerves. We detail how variations of this method can be used to measure acute axon growth.

PGC-1α Inhibits Schwann Cell Dedifferentiation and Delays Peripheral Nerve Degeneration by Targeting PON1

PPARγ coactivator-1 alpha (PGC-1α) is an essential transcription factor co-activator that regulates gene transcription and neural regeneration. Schwann cells, which are unique glial cells in peripheral nerves that dedifferentiate after peripheral nerve injury (PNI) and are released from degenerative nerves. Wallerian degeneration is a series of stereotypical events that occurs in response to nerve fibers after PNI. The role of PGC-1α in Schwann cell dedifferentiation and Wallerian degeneration is not yet clear. As Wallerian degeneration plays a crucial role in PNI, we conducted a study to determine whether PGC-1α has an effect on peripheral nerve degeneration after injury. We examined the expression of PGC-1α after sciatic nerve crush or transection using Western blotting and found that PGC-1α expression increased after PNI. Then we utilized ex vivo and in vitro models to investigate the effects of PGC-1α inhibition and activation on Schwann cell dedifferentiation and nerve degeneration. Our findings indicate that PGC-1α negatively regulates Schwann cell dedifferentiation and nerve degeneration. Through the use of RNA-seq, siRNA/plasmid transfection and reversal experiments, we identified that PGC-1α targets inhibit the expression of paraoxonase 1 (PON1) during Schwann cell dedifferentiation in degenerated nerves. In summary, PGC-1α plays a crucial role in preventing Schwann cell dedifferentiation and its activation can reduce peripheral nerve degeneration by targeting PON1. PGC-1α inhibits Schwann cell dedifferentiation and peripheral nerve degeneration. PGC-1α negatively regulates Schwann cell dedifferentiation and peripheral nerve degeneration after injury by targeting PON1.

A favorable suture method for size-mismatched nerve transfer: comparison with standard perineural suture in an experimental rat study

BACKGROUND

In nerve transfer for peripheral nerve injury, it is sometimes necessary to suture size-mismatched nerves. In 1993, a favorable suture method called the Ochiai suture method for size-mismatched nerve transfer was reported. However, there is currently a lack of substantial evidence beyond the original report. Therefore, this study aimed to verify the advantages of using the Ochiai suture method for size-mismatched nerve transfer.

METHODS

A total of 18 rats were evaluated in this study and randomly divided into two groups. All rats underwent femoral to sciatic nerve transfer. Specifically, group A (n = 10) underwent the Ochiai suture method, while group B (n = 8) underwent the perineural suture method. After 12 weeks postoperatively, we conducted the sciatic functional index (SFI) test, measured muscle wet-weight, and performed histological evaluations. All data were compared between the two groups, with Welch's t test for normally distributed data and Mann-Whitney's U test for non-normally distributed data. Statistical significance was set at p < 0.05.

RESULTS

The mean number of axons was significantly greater in group A than in group B at 5 mm distal to the stump (p = 0.04). Additionally, the average axonal diameter was significantly greater in group A than in group B at 5 mm and 10 mm distal to the stump (p < 0.01 and p < 0.01, respectively). However, the SFI test and measured muscle wet-weight values showed no significant differences between the two groups.

CONCLUSIONS

Our study revealed that the Ochiai suture method for size-mismatched nerve transfer in rats increases the regenerative axon numbers and diameters. These findings suggest that the Ochiai suture method could be a valuable approach for achieving effective motor function restoration in cases of size-mismatched nerve transfer.

Functional and structural synaptic remodeling mechanisms underlying somatotopic organization and reorganization in the thalamus

The somatosensory system organizes the topographic representation of body maps, termed somatotopy, at all levels of an ascending hierarchy. Postnatal maturation of somatotopy establishes optimal somatosensation, whereas deafferentation in adults reorganizes somatotopy, which underlies pathological somatosensation, such as phantom pain and complex regional pain syndrome. Here, we focus on the mouse whisker somatosensory thalamus to study how sensory experience shapes the fine topography of afferent connectivity during the critical period and what mechanisms remodel it and drive a large-scale somatotopic reorganization after peripheral nerve injury. We will review our findings that, following peripheral nerve injury in adults, lemniscal afferent synapses onto thalamic neurons are remodeled back to immature configuration, as if the critical period reopens. The remodeling process is initiated with local activation of microglia in the brainstem somatosensory nucleus downstream to injured nerves and heterosynaptically controlled by input from GABAergic and cortical neurons to thalamic neurons. These fruits of thalamic studies complement well-studied cortical mechanisms of somatotopic organization and reorganization and unveil potential intervention points in treating pathological somatosensation.

HIF-1α-induced upregulation of m6A reader IGF2BP1 facilitates peripheral nerve injury recovery by enhancing SLC7A11 mRNA stabilization

The recovery of peripheral nerve injury (PNI) is not ideal in clinic. Our previous study revealed that hypoxia treatment promoted PNI repair by inhibiting ferroptosis. The aim of this study was to investigate the underlying molecular mechanism of HIF-1α in hypoxia-PNI recovery. M6A dot blot was used to determine the total level of m6A modification. Besides, HIF-1α small interfering RNA (siRNA) or IGF2BP1 overexpression vector was transfected into dorsal root ganglion (DRG) neurons to alter the expression of HIF-1α and IGF2BP1. Subsequently, MeRIP-PCR analysis was applied to validate the m6A methylation level of SLC7A11. We demonstrated the hypoxia stimulated HIF-1α-dependent expression of IGF2BP1 and promoted the overall m6A methylation levels of DRG neurons. Overexpression of HIF-1α increased the expressions of neurotrophic factors including nerve growth factor (NGF), brain-derived neurotrophic factor (BDNF), and glial-derived neurotrophic factor (GDNF), which could be effectively reversed by siRNA knockdown of IGF2BP1. Moreover, upregulation of HIF-1α contributed to the m6A methylation level and mRNA stabilization of SLC7A11. This study revealed that the HIF-1α/IGF2BP1/SLC7A11 regulatory axis facilitated the recovery of injured DRG neurons. Our findings suggest a novel insight for the m6A methylation modification in PNI recovery.

Transcription Factor BCL11A Regulates Schwann Cell Behavior During Peripheral Nerve Regeneration

Nerve injury-induced Schwann cell dedifferentiation helps to construct a favorable microenvironment for axon growth. Transcription factors regulate cell reprogramming and thus may be critical for Schwann cell phenotype switch during peripheral nerve regeneration. Here, we show that transcription factor B-cell lymphoma/leukemia 11A (BCL11A) is up-regulated in Schwann cells of injured peripheral nerves. Bcl11a silencing suppresses Schwann cell viability, decreases Schwann cell proliferation and migration rates, and impairs the debris clearance ability of Schwann cells. Reduced Bcl11a in injured peripheral nerves results in restricted axon elongation and myelin wrapping, leading to recovery failure. Mechanistically, we demonstrate that BCL11A may mediate Schwann cell activity through binding to the promoter of nuclear receptor subfamily 2 group F member 2 (Nr2f2) and regulating Nr2f2 expression. Collectively, we conclude that BCL11A is essential for Schwann cell activation and peripheral nerve regeneration, providing a potential therapeutic target for the treatment of peripheral nerve injury.

Gelatin nanofiber-reinforced decellularized amniotic membrane promotes axon regeneration and functional recovery in the surgical treatment of peripheral nerve injury

Effective recovery of peripheral nerve injury (PNI) after surgical treatment relies on promoting axon regeneration and minimizing the fibrotic response. Decellularized amniotic membrane (dAM) has unique features as a natural matrix for promoting PNI repair due to its pro-regenerative extracellular matrix (ECM) structure and anti-inflammatory properties. However, the fragile nature and rapid degradation rate of dAM limit its widespread use in PNI surgery. Here we report an engineered composite membrane for PNI repair by combining dAM with gelatin (Gel) nanofiber membrane to construct a Gel nanofiber-dAM composite membrane (Gel-dAM) through interfacial bonding. The Gel-dAM showed enhanced mechanical properties and reduced degradation rate, while retaining maximal bioactivity and biocompatibility of dAM. These factors led to improved axon regeneration, reduced fibrotic response, and better functional recovery in PNI repair. As a fully natural materials-derived off-the-shelf matrix, Gel-dAM exhibits superior clinical translational potential for the surgical treatment of PNI.

Effects of RNA m6A writer METTL3 and hDPSCs on the peripheral nerve regeneration: In vitro and in vivo study

PURPOSE

This study aimed to investigate whether RNA m6A participated in the differentiation and proliferation of dental pulp stem cells and improved peripheral nerve regeneration using a rat model of crushed mental nerve injury.

MATERIALS AND METHODS

The components of RNA m6A were analyzed through qRT-PCR, while cell proliferation of different groups, including over-expression METTL3 (OE-METTL3) hDPSCs group, knock-down METTL3 (KD-METTL3) hDPSCs group and hDPSCs group in vitro, was clarified by MTT assay. Five groups were designed, namely, Control group, Sham group, hDPSCs group, OE-METTL3 group and KD-METTL3 group. After crushed right mental nerve injury, cells of different groups were transplanted into the lesion area (6 ul in volume). At one, two and three weeks later, histomorphometric analysis and sensory test were conducted in vivo.

RESULTS

qRT-PCR results showed that "METTL3" was participated in the differentiation of dental pulp stem cells. There were differences (P < 0.05) between OE-METTL3 group and control group in MTT results in the third, fourth and sixth days. Moreover, the sensory test revealed significant differences (P < 0.05) in difference score and gap score between OE-METTL3 group and KD-METTL3 group in the first and third weeks. The axon counts and retrograde labeled neurons significantly increased in OE-METTL3 group compared with KD-METTL3 group.

CONCLUSIONS

These results demonstrated that RNA m6A participated in the differentiation and proliferation of dental pulp stem cells, and that OE-METTL3 group exhibited the greater ability to improve peripheral nerve regeneration than KD-METTL3 group and hDPSCs group.

Astrocyte senescence-like response related to peripheral nerve injury-induced neuropathic pain

BACKGROUND

Peripheral nerve damage causes neuroinflammation, which plays a critical role in establishing and maintaining neuropathic pain (NeP). The mechanisms contributing to neuroinflammation remain poorly elucidated, and pharmacological strategies for NeP are limited. Thus, in this study, we planned to explore the possible link between astrocyte senescence and NeP disorders following chronic sciatic nerve injury.

METHODS

An NeP animal model was established by inducing chronic constrictive injury (CCI) to the sciatic nerve in adult rats. A senolytic drug combination of dasatinib and quercetin was gavaged daily from the first postoperative day until the end of the study. Paw mechanical withdrawal threshold (PMWT) and paw thermal withdrawal latency (PTWL) were evaluated to assess behaviors in response to pain in the experimental rats. Senescence-associated β-galactosidase staining, western blot analysis, and immunofluorescence were applied to examine the levels of proinflammatory factors and severity of the senescence-like response in the spinal cord. Lipopolysaccharide (LPS) was administered to induce senescence of spinal astrocytes in primary cultures in vitro, to explore the potential impacts of senescence on the secretion of proinflammatory factors. Furthermore, single-cell RNA sequencing (scRNA-seq) was conducted to identify senescence-related molecular responses in spinal astrocytes under neuropathic pain.

RESULTS

Following sciatic nerve CCI, rats exhibited reduced PMWT and PTWL, increased levels of spinal proinflammatory factors, and an enhanced degree of senescence in spinal astrocytes. Treatment with dasatinib and quercetin effectively attenuated spinal neuroinflammation and mitigated the hypersensitivities of the rats subjected to sciatic nerve CCI. Mechanistically, the dasatinib-quercetin combination reversed senescence in LPS-stimulated primary cultured astrocytes and decreased the levels of proinflammatory factors. The scRNA-seq data revealed four potential senescence-related genes in the spinal astrocyte population, and the expression of clusterin (CLU) protein was validated via in vitro experiments.

CONCLUSION

The findings indicate the potential role of astrocyte senescence in neuroinflammation following peripheral nerve injury, and suggest that targeting CLU activation in astrocytes might provide a novel therapeutic strategy to treat NeP.

Evaluation of motor and sensory neuron populations in a mouse median nerve injury model

BACKGROUND

Peripheral nerves can regenerate and restore function after injury but this process is hindered by many factors including chronic denervation, motor end-plate resorption and Schwann cell senescence. Forelimb injury models in rodents are becoming increasingly popular as they more accurately reflect the physiology and biomechanics of upper extremity nerve injuries. However several aspects of this surgical model remain poorly characterized.

NEW METHOD

C57Bl/6 mice underwent enumeration of median nerve motor and sensory neuron pools using retrograde labeling with or without nerve transection. Distal histomorphometry of uninjured mouse median nerves was also examined. Baseline reference values of volitional forelimb grip strength measurements were determined and the rate of neural elongation was also estimated.

RESULTS

We identified 1363 ± 165 sensory and 216 ± 16 motor neurons within the uninjured dorsal root ganglia (DRG) and ventral spinal cord, respectively. Eight days following injury, approximately 34% of motoneurons had elongated a distance of 5 mm beyond the repair site 8 days following injury. Volitional grip strength decreased 50% with unilateral median nerve transection and was negligible with contralateral flexor tendon tenotomy.

COMPARISON WITH EXISTING METHOD

Our spinal cord and DRG harvesting technique presented here was technically straightforward and reliable. Estimates of motor and sensory neuron numbers for the mouse median nerve compared favourably with studies using intramuscular injection of retrograde neurotracer. Histomorphometry data was consistent with and reinforced reference values in the literature.

CONCLUSIONS

This study provides data that further develops an increasingly popular surgical model for studying peripheral nerve injury and repair.

Challenges in Nerve Repair and Reconstruction

Peripheral nerve injuries may substantially impair a patient's function and quality of life. Despite appropriate treatment, outcomes often remain poor. Direct repair remains the standard of care when repair is possible without excessive tension. For larger nerve defects, nerve autografting is the gold standard. However, a considerable challenge is donor site morbidity. Processed nerve allografts and conduits are other options, but evidence supporting their use is limited to smaller nerves and shorter gaps. Nerve transfer is another technique that has seen increasing popularity. The future of care may include novel biologics and pharmacologic therapy to enhance regeneration.

Neural tissue-engineered prevascularization in vivo enhances peripheral neuroregeneration via rapid vascular inosculation

Neural tissue engineering techniques typically face a significant challenge, simulating complex natural vascular systems that hinder the clinical application of tissue-engineered nerve grafts (TENGs). Here, we report a subcutaneously pre-vascularized TENG consisting of a vascular endothelial growth factor-induced host vascular network, chitosan nerve conduit, and inserted silk fibroin fibers. Contrast agent perfusion, tissue clearing, microCT scan, and blood vessel 3D reconstruction were carried out continuously to prove whether the regenerated blood vessels were functional. Moreover, histological and electrophysiological evaluations were also applied to investigate the efficacy of repairing peripheral nerve defects with pre-vascularized TENG. Rapid vascular inosculation of TENG pre-vascularized blood vessels with the host vascular system was observed at 4 ​d bridging the 10 ​mm sciatic nerve defect in rats. Transplantation of pre-vascularized TENG in vivo suppressed proliferation of vascular endothelial cells (VECs) while promoting their migration within 14 ​d post bridging surgery. More importantly, the early vascularization of TENG drives axonal regrowth by facilitating bidirectional migration of Schwann cells (SCs) and the bands of Büngner formation. This pre-vascularized TENG increased remyelination, promoted recovery of electrophysiological function, and prevented atrophy of the target muscles when observed 12 weeks post neural transplantation. The neural tissue-engineered pre-vascularization technique provides a potential approach to discover an individualized TENG and explore the innovative neural regenerative process.

A grooved conduit combined with decellularized tissues for peripheral nerve regeneration

Peripheral nerve injury (PNI) is a common and severe clinical disease worldwide, which leads to a poor prognosis because of the complicated treatments and high morbidity. Autologous nerve grafting as the gold standard still cannot meet the needs of clinical nerve transplantation because of its low availability and limited size. The development of artificial nerve conduits was led to a novel direction for PNI treatment, while most of the currently developed artificial nerve conduits was lack biochemical cues to promote nerve regeneration. In this study, we designed a novel composite neural conduit by inserting decellularized the rat sciatic nerve or kidney in a poly (lactic-co-glycolic acid) (PLGA) grooved conduit. The nerve regeneration effect of all samples was analyzed using rat sciatic nerve defect model, where decellularized tissues and grooved PLGA conduit alone were used as controls. The degree of nerve regeneration was evaluated using the motor function, gastrocnemius recovery, and morphological and histological assessments suggested that the combination of a grooved conduit with decellularized tissues significantly promoted nerve regeneration compared with decellularized tissues and PLGA conduit alone. It is worth to note that the grooved conduits containing decellularized nerves have a promotive effect similar to that of autologous nerve grafting, suggesting that it could be an artificial nerve conduit used for clinical practice in the future.

Human platelet lysate stimulates neurotrophic properties of human adipose-derived stem cells better than Schwann cell-like cells

BACKGROUND

Trauma-associated peripheral nerve injury is a widespread clinical problem causing sensory and motor disabilities. Schwann cells (SCs) contribute to nerve regeneration, mainly by secreting nerve growth factor (NGF) and brain-derived neurotrophic factor. In the last years, adipose-derived stem cells (ASCs) differentiated into SCs (SC-ASCs) were considered as promising cell therapy. However, the cell trans-differentiation process has not been effectively showed and presents several drawbacks, thus an alternative approach for increasing ASCs neurotrophic properties is highly demanded. In the context of human cell-based therapies, Good Manufacturing Practice directions indicate that FBS should be substituted with a xenogeneic-free supplement, such as Human Platelet Lysate (HPL). Previously, we demonstrated that neurotrophic properties of HPL-cultured ASCs were superior compared to undifferentiated FBS-cultured ASCs. Therefore, as following step, here we compared the neurotrophic properties of differentiated SC-like ASCs and HPL-cultured ASCs.

METHODS

Both cell groups were investigated for gene expression level of neurotrophic factors, their receptors and neuronal markers. Moreover, the expression of nestin was quantitatively evaluated by flow cytometry. The commitment toward the SC phenotype was assessed with immunofluorescence pictures. Proteomics analysis was performed on both cells and their conditioned media to compare the differential protein profile. Finally, neurotrophic abilities of both groups were evaluated with a functional co-culture assay, assessing dorsal root ganglia survival and neurite outgrowth.

RESULTS

HPL-cultured ASCs demonstrated higher gene expression of NGF and lower expression of S100B. Moreover, nestin was present in almost all HPL-cultured ASCs and only in one quarter of SC-ASCs. Immunofluorescence confirmed that S100B was not present in HPL-cultured ASCs. Proteomics analysis validated the higher expression of nestin and the increase in cytoskeletal and ECM proteins involved in neural regeneration processes. The co-culture assay highlighted that neurite outgrowth was higher in the presence of HPL-ASCs or their conditioned medium compared to SC-ASCs.

CONCLUSIONS

All together, our results show that HPL-ASCs were more neurotrophic than SC-ASCs. We highlighted that the HPL triggers an immature neuro-induction state of ASCs, while keeping their stem properties, paving the way for innovative therapies for nerve regeneration.

Impaired motor unit recovery and maintenance in a knock-in mouse model of ALS-associated Kif5a variant

Kinesin family member 5A (KIF5A) is an essential, neuron-specific microtubule-associated motor protein responsible for the anterograde axonal transport of various cellular cargos. Loss of function variants in the N-terminal, microtubule-binding domain are associated with hereditary spastic paraplegia and hereditary motor neuropathy. These variants result in a loss of the ability of the mutant protein to process along microtubules. Contrastingly, gain of function splice-site variants in the C-terminal, cargo-binding domain of KIF5A are associated with amyotrophic lateral sclerosis (ALS), a neurodegenerative disease involving death of upper and lower motor neurons, ultimately leading to degradation of the motor unit (MU; an alpha motor neuron and all the myofibers it innervates) and death. These ALS-associated variants result in loss of autoinhibition, increased procession of the mutant protein along microtubules, and altered cargo binding. To study the molecular and cellular consequences of ALS-associated variants in vivo, we introduced the murine homolog of an ALS-associated KIF5A variant into C57BL/6 mice using CRISPR-Cas9 gene editing which produced mutant Kif5a mRNA and protein in neuronal tissues of heterozygous (Kif5a+/c.3005+1G>A; HET) and homozygous (Kif5ac.3005+1G>A/c.3005+1G>A; HOM) mice. HET and HOM mice appeared normal in behavioral and electrophysiological (compound muscle action potential [CMAP] and MU number estimation [MUNE]) outcome measures at one year of age. When subjected to sciatic nerve injury, HET and HOM mice have delayed and incomplete recovery of the MUNE compared to wildtype (WT) mice suggesting an impairment in MU repair. Moreover, aged mutant Kif5a mice (aged two years) had reduced MUNE independent of injury, and exacerbation of the delayed and incomplete recovery after injury compared to aged WT mice. These data suggest that ALS-associated variants may result in an impairment of the MU to respond to biological challenges such as injury and aging, leading to a failure of MU repair and maintenance. In this report, we present the behavioral, electrophysiological and pathological characterization of mice harboring an ALS-associated Kif5a variant to understand the functional consequences of KIF5A C-terminal variants in vivo.

Additive manufacturing of peripheral nerve conduits - Fabrication methods, design considerations and clinical challenges

Tissue-engineered nerve guidance conduits (NGCs) are a viable clinical alternative to autografts and allografts and have been widely used to treat peripheral nerve injuries (PNIs). Although these NGCs are successful to some extent, they cannot aid in native regeneration by improving native-equivalent neural innervation or regrowth. Further, NGCs exhibit longer recovery period and high cost limiting their clinical applications. Additive manufacturing (AM) could be an alternative to the existing drawbacks of the conventional NGCs fabrication methods. The emergence of the AM technique has offered ease for developing personalized three-dimensional (3D) neural constructs with intricate features and higher accuracy on a larger scale, replicating the native feature of nerve tissue. This review introduces the structural organization of peripheral nerves, the classification of PNI, and limitations in clinical and conventional nerve scaffold fabrication strategies. The principles and advantages of AM-based techniques, including the combinatorial approaches utilized for manufacturing 3D nerve conduits, are briefly summarized. This review also outlines the crucial parameters, such as the choice of printable biomaterials, 3D microstructural design/model, conductivity, permeability, degradation, mechanical property, and sterilization required to fabricate large-scale additive-manufactured NGCs successfully. Finally, the challenges and future directions toward fabricating the 3D-printed/bioprinted NGCs for clinical translation are also discussed.

Engineered hydrogels for peripheral nerve repair

Peripheral nerve injury (PNI) is a complex disease that often appears in young adults. It is characterized by a high incidence, limited treatment options, and poor clinical outcomes. This disease not only causes dysfunction and psychological disorders in patients but also brings a heavy burden to the society. Currently, autologous nerve grafting is the gold standard in clinical treatment, but complications, such as the limited source of donor tissue and scar tissue formation, often further limit the therapeutic effect. Recently, a growing number of studies have used tissue-engineered materials to create a natural microenvironment similar to the nervous system and thus promote the regeneration of neural tissue and the recovery of impaired neural function with promising results. Hydrogels are often used as materials for the culture and differentiation of neurogenic cells due to their unique physical and chemical properties. Hydrogels can provide three-dimensional hydration networks that can be integrated into a variety of sizes and shapes to suit the morphology of neural tissues. In this review, we discuss the recent advances of engineered hydrogels for peripheral nerve repair and analyze the role of several different therapeutic strategies of hydrogels in PNI through the application characteristics of hydrogels in nerve tissue engineering (NTE). Furthermore, the prospects and challenges of the application of hydrogels in the treatment of PNI are also discussed.

Heme-binding protein 1 delivered via pericyte-derived extracellular vesicles improves neurovascular regeneration in a mouse model of cavernous nerve injury

As a peripheral nerve injury disease, cavernous nerve injury (CNI) caused by prostate cancer surgery and other pelvic surgery causes organic damage to cavernous blood vessels and nerves, thereby significantly attenuating the response to phosphodiesterase-5 inhibitors. Here, we investigated the role of heme-binding protein 1 (Hebp1) in erectile function using a mouse model of bilateral CNI, which is known to promote angiogenesis and improve erection in diabetic mice. We found a potent neurovascular regenerative effect of Hebp1 in CNI mice, demonstrating that exogenously delivered Hebp1 improved erectile function by promoting the survival of cavernous endothelial-mural cells and neurons. We further found that endogenous Hebp1 delivered by mouse cavernous pericyte (MCP)-derived extracellular vesicles promoted neurovascular regeneration in CNI mice. Moreover, Hebp1 achieved these effects by reducing vascular permeability through regulation of claudin family proteins. Our findings provide new insights into Hebp1 as a neurovascular regeneration factor and demonstrate its potential therapeutic application to various peripheral nerve injuries.

Biomechanical microenvironmental stimulating effect of pulsed electromagnetic field on the regeneration of crush injured rat sciatic nerve

This study evaluated the biomechanical microenvironmental stimulating effect of pulsed electromagnetic field (PEMF) on the regeneration of crush-injured rat sciatic nerve, when combined with bone marrow mesenchymal stem cells (BMSCs) and recombinant human nerve growth factor (rhNGF-β), in the form of an adenoviral vector-mediated NGF. Sprague-Dawley rats were equally distributed into six groups; PBS, BMSC, NGF-Ad + BMSC, PEMF + PBS, PEMF + BMSC and PEMF + NGF-Ad + BMSC. The PBS group received PBS (volume: 10μL/rat), the BMSC group with BMSCs (1 × 106 cell/10 μL/rat) and NGF-Ad group with the rhNGF-β Ad infected BMSCs (1 × 106 cell/10 μL/rat) immediate after right sciatic nerve crush injury. The PEMF groups were exposed to PEMF of 1mT, 50 Hz, 1 h/day. The rats were observed for 3 weeks. PEMF alone did not showed the positive effect compared with negative control group. The groups transplanted with BMSCs showed higher axonal regeneration compared with the groups without transplantation of the cells whether BMSC was infected with NGF-Ad or not and whether the animals received PEMF. PEMF + NGF-Ad + BMSC group showed the significantly highest number of axons than the other groups. Functionally, all groups showed marked improvement at 3 weeks postoperatively although the difference was not statistically significant among the groups. PEMF showed the positive effect when combined with BMSC and NGF-ad in aspect of number of axons. Therefore, combining the microenvironment stimulation methods of PEMF and conventional methods such as transplantation of stem cells and growth factor could be considered for the regeneration methods in the nerve damage.

Time course of functional recovery after 1 cm sciatic nerve resection in rats with or without surgical intervention - measured by grip strength and locomotor activity

The rat sciatic nerve (SN) is the most frequently used model in experimental research on peripheral nerve injuries. Within the broad range of evaluation methods to determine the experimental outcome, recovery of behavior represents the major criterion to assess functional regeneration. The grasping test indicates when recovery begins and its improvement with time. However, lesions of the SN have yet remained unstudied with this method. Therefore, rats received a SN resection and were divided into experimental groups: 1) control with lesion only, 2) nerve bridge, and 3) autograft. During weekly sessions, the grasping test measured the grip strength, and the locomotor behavior was assessed in the open field. Finally, the nerves were prepared for electrophysiology and histomorphometry. Autograft recovered grasping after 7 weeks with the strongest improvement afterwards. Nerve tube allowed grasping by week 12. Control animals did not recover. In the open field, no differences were observed between the groups. Recordings were possible only in the autograft group, which could be explained by higher number of regenerated fibers. This study indicates that grasping data correspond with physiological and anatomical findings. We conclude that the grasping test is a valid method to evaluate functional recovery after SN resection in rats.

Promising application of a novel biomaterial, light chain of silk fibroin combined with NT3, in repairment of rat sciatic nerve defect injury

Autologous nerve transplantation is the gold standard for treating peripheral nerve defects, but it is associated with defects such as insufficient donor and secondary injury. Artificial nerve guidance conduits (NGCs) are now considered promising alternatives for bridging long nerve gaps, although exploring new biomaterials to construct NGCs remains challenging. Silk fibroin (SF) has good biocompatibility and can self-assemble in aqueous solutions¹. However, the lack of proximal neurotrophic factors after nerve injury is a major concern, leading to incomplete nerve regeneration. In this study, NT-3, a neurotrophin that promotes neuronal survival and differentiation, was bound to the light chain of silk fibroin (FIBL) in two ways: one was directly bound to FIBL (FIBL-NT3) and the other was a polypeptides-linker (FIBL-Linker-NT3). The design aimed to take advantage of silk fiber's character of self-assembly of heavy-light chains and test whether a flexible linker with NT3 molecule is easy to be a NT3 dimer, the active form. In vitro studies indicated that FIBL-Linker-NT3 combined with SF membranes promoted axon growth in adult rat dorsal root ganglion (DRG) neurons. Then we tested if FIBL-Linker-NT3 could self-assemble with the SF heavy chain (SFH). DTT (Dithiothreitol) was used to break the disulfide bonds between the SF light and heavy chains, and the light-chain protein was removed via dialysis. SFH was assembled using FIBL-Linker-NT3, as evidenced by the western blotting results that showed a high molecular band corresponding to SFH-FIBL-Linker-NT3. Chitosan scaffolds have been identified to provide a suitable microenvironment, so a chitosan/SF-FIBL-Linker-NT3 conduit was also constructed. Nerve transplantation of this conduit was evaluated in vivo in a rat sciatic nerve defect model. Immunohistochemical assays showed that the chitosan/SF-FIBL-Linker-NT3 group was superior to the chitosan/PBS, SF, PBS + FIBL-Linker-NT3 groups in nerve regeneration. In addition, the chitosan/SF-FIBL-Linker-NT3 conduit-transplanted group exhibited better recovery in terms of neurite length, sciatic functional index value, sensitivity to heat, time on the rotarod, wet weight ratio, cross-sectional area, compound muscle action potential, number of myelin layers, and myelin thickness in the nerve. Taking together, our study identified that FIBL-Linker-NT3 could promote axonal growth and regeneration in vivo and in vitro and is a promising candidate biomaterial for artificial NGCs.

Down-regulation miR-146a-5p in Schwann cell-derived exosomes induced macrophage M1 polarization by impairing the inhibition on TRAF6/NF-κB pathway after peripheral nerve injury

BACKGROUND

Both Schwann cell-derived exosomes (SC-Exos) and macrophagic sub-phenotypes are closely related to the regeneration and repair after peripheral nerve injury (PNI). However, the crosstalk between them is less clear.

OBJECTIVE

We aim to investigate the roles and underlying mechanisms of exosomes from normoxia-condition Schwann cell (Nor-SC-Exos) and from post-injury oxygen-glucose-deprivation-condition Schwann cell in regulating macrophagic sub-phenotypes and peripheral nerve injury repair.

METHOD

Both Nor-SC-Exos and OGD-SC-Exos were extracted through ultracentrifugation, identified by transmission electron microscopy (TEM), Nanosight tracking analysis (NTA) and western blotting. High-throughput sequencing was performed to explore the differential expression of microRNAs in both SC-Exos. In vitro, RAW264.7 macrophage was treated with two types of SC-Exos, M1 macrophagic markers (IL-10, Arg-1, TGF-β1) and M2 macrophagic markers (IL-6, IL-1β, TNF-α) were detected by enzyme-linked Immunosorbent Assay (ELISA) or qRT-PCR, and the expression of CD206, iNOS were detected via cellular immunofluorescence (IF) to judge macrophage sub-phenotypes. Dorsal root ganglion neurons (DRGns) were co-cultured with RAW264.7 cells treated with Nor-SC-Exos and OGD-SC-Exos, respectively, to explore their effect on neuron growth. In vivo, we established a sciatic nerve crush injury rat model. Nor-SC-Exos and OGD-SC-Exos were locally injected into the injury site. The mRNA expression of M1 macrophagic markers (IL-10, Arg-1, TGF-β1) and M2 macrophagic markers (IL-6, IL-1β, TNF-α) were detected by qRT-PCR to determine the sub-phenotype of macrophages in the injury site. IF was used to detect the expression of MBP and NF200, reflecting the myelin sheath and axon regeneration, and sciatic nerve function index (SFI) was measured to evaluate function repair.

RESULT

In vitro, Nor-SC-Exos promoted macrophage M2 polarization, increased anti-inflammation factors secretion, and facilitated axon elongation of DRGns. OGD-SC-Exos promoted M1 polarization, increased pro-inflammation factors secretion, and restrained axon elongation of DRGns. High-throughput sequencing and qRT-PCR results found that compared with Nor-SC-Exos, a shift from anti-inflammatory (pro-M2) to pro-inflammatory (pro-M1) of OGD-SC-Exos was closely related to the down-regulation of miR-146a-5p and its decreasing inhibition on TRAF6/NF-κB pathway after OGD injury. In vivo, we found Nor-SC-Exos and miR-146a-5p mimic promoted regeneration of myelin sheath and axon, and facilitated sciatic function repair via targeting TRAF6, while OGD-SC-Exos and miR-146a-5p inhibitor restrained them.

CONCLUSION

Our study confirmed that miR-146a-5p was significantly decreased in SC-Exos under the ischemia-hypoxic microenvironment of the injury site after PNI, which mediated its shift from promoting macrophage M2 polarization (anti-inflammation) to promoting M1 polarization (pro-inflammation), thereby limiting axonal regeneration and functional recovery.