Enhanced Immune Response in Immunodeficient Mice Improves Peripheral Nerve Regeneration Following Axotomy

The intersection of the nervous system and breast cancer

Breast cancer (BC) represents a paradigm of heterogeneity, manifesting as a spectrum of molecular subtypes with divergent clinical trajectories. It is fundamentally characterized by the aberrant proliferation of malignant cells within breast tissue, a process modulated by a myriad of factors that govern its progression. Recent endeavors outline the interplay between BC and the nervous system, illuminate the complex symbiosis between neural structures and neoplastic cells, and elucidate nerve dependence as a cornerstone of BC progression. This includes the neural modulations on immune response, neurovascular formation, and multisystem interactions. Such insights have unveiled the critical impact of neural elements on tumor dynamics and patient prognosis. This revelation beckons a deeper exploration into the neuro-oncological interface, potentially unlocking novel therapeutic vistas. This review endeavors to delineate the intricate mechanisms between the nervous system and BC, aiming to accentuate the implications and therapeutic strategies of this intersection for tumor evolution and the formulation of innovative therapeutic approaches.

Progress in methods for evaluating Schwann cell myelination and axonal growth in peripheral nerve regeneration via scaffolds

Peripheral nerve injury (PNI) is a neurological disorder caused by trauma that is frequently induced by accidents, war, and surgical complications, which is of global significance. The severity of the injury determines the potential for lifelong disability in patients. Artificial nerve scaffolds have been investigated as a powerful tool for promoting optimal regeneration of nerve defects. Over the past few decades, bionic scaffolds have been successfully developed to provide guidance and biological cues to facilitate Schwann cell myelination and orientated axonal growth. Numerous assessment techniques have been employed to investigate the therapeutic efficacy of nerve scaffolds in promoting the growth of Schwann cells and axons upon the bioactivities of distinct scaffolds, which have encouraged a greater understanding of the biological mechanisms involved in peripheral nerve development and regeneration. However, it is still difficult to compare the results from different labs due to the diversity of protocols and the availability of innovative technologies when evaluating the effectiveness of novel artificial scaffolds. Meanwhile, due to the complicated process of peripheral nerve regeneration, several evaluation methods are usually combined in studies on peripheral nerve repair. Herein, we have provided an overview of the evaluation methods used to study the outcomes of scaffold-based therapies for PNI in experimental animal models and especially focus on Schwann cell functions and axonal growth within the regenerated nerve.

Micron track chitosan conduit fabricated by 3D-printed model topography provides bionic microenvironment for peripheral nerve regeneration

The micron track conduit (MTC) and nerve factor provide a physical and biological model for simulating peripheral nerve growth and have potential applications for nerve injury. However, it has rarely been reported that they synergize on peripheral nerves. In this study, we used bioderived chitosan as a substrate to design and construct a neural repair conduit with micron track topography using threedimensional (3D) printing topography. We loaded the MTC with neurotrophin-3 (NT-3) to promote the regeneration of sensory and sympathetic neurons in the peripheral nervous system. We found that the MTC@NT3 composite nerve conduit mimicked the microenvironment of peripheral nerves and promoted axonal regeneration while inducing the targeted growth of Schwann cells, which would promote functional recovery in rats with peripheral nerve injury. Artificial nerve implants with functional properties can be developed using the strategy presented in this study.

Next-generation RNA sequencing elucidates transcriptomic signatures of pathophysiologic nerve regeneration

The cellular and molecular underpinnings of Wallerian degeneration have been robustly explored in laboratory models of successful nerve regeneration. In contrast, there is limited interrogation of failed regeneration, which is the challenge facing clinical practice. Specifically, we lack insight on the pathophysiologic mechanisms that lead to the formation of neuromas-in-continuity (NIC). To address this knowledge gap, we have developed and validated a novel basic science model of rapid-stretch nerve injury, which provides a biofidelic injury with NIC development and incomplete neurologic recovery. In this study, we applied next-generation RNA sequencing to elucidate the temporal transcriptional landscape of pathophysiologic nerve regeneration. To corroborate genetic analysis, nerves were subject to immunofluorescent staining for transcripts representative of the prominent biological pathways identified. Pathophysiologic nerve regeneration produces substantially altered genetic profiles both temporally and in the mature neuroma microenvironment, in contrast to the coordinated genetic signatures of Wallerian degeneration and successful regeneration. To our knowledge, this study presents as the first transcriptional study of NIC pathophysiology and has identified cellular death, fibrosis, neurodegeneration, metabolism, and unresolved inflammatory signatures that diverge from pathways elaborated by traditional models of successful nerve regeneration.

All the PNS is a Stage: Transplanted Bone Marrow Cells Play an Immunomodulatory Role in Peripheral Nerve Regeneration

SUMMARY STATEMENT

Bone marrow cell transplant has proven to be an effective therapeutic approach to treat peripheral nervous system injuries as it not only promoted regeneration and remyelination of the injured nerve but also had a potent effect on neuropathic pain.

Brief Electrical Stimulation Accelerates Axon Regeneration and Promotes Recovery Following Nerve Transection and Repair in Mice

BACKGROUND

Clinical outcomes following nerve injury repair can be inadequate. Pulsed-current electrical stimulation (ES) is a therapeutic method that facilitates functional recovery by accelerating axon regeneration. However, current clinical ES protocols involve the application of ES for 60 minutes during surgery, which can increase operative complexity and time. Shorter ES protocols could be a strategy to facilitate broader clinical adoption. The purpose of the present study was to determine if a 10-minute ES protocol could improve outcomes.

METHODS

C57BL/6J mice were randomized to 3 groups: no ES, 10 minutes of ES, and 60 minutes of ES. In all groups, the sciatic nerve was transected and repaired, and, in the latter 2 groups, ES was applied after repair. Postoperatively, changes to gene expression from dorsal root ganglia were measured after 24 hours. The number of motoneurons regenerating axons was determined by retrograde labeling at 7 days. Histomorphological analyses of the nerve were performed at 14 days. Function was evaluated serially with use of behavioral tests up to 56 days postoperatively, and relative muscle weight was evaluated.

RESULTS

Compared with the no-ES group, both ES groups demonstrated increased regeneration-associated gene expression within dorsal root ganglia. The 10-minute and 60-minute ES groups demonstrated accelerated axon regeneration compared with the no-ES group based on increased numbers of labeled motoneurons regenerating axons (mean difference, 202.0 [95% confidence interval (CI), 17.5 to 386.5] and 219.4 [95% CI, 34.9 to 403.9], respectively) and myelinated axon counts (mean difference, 559.3 [95% CI, 241.1 to 877.5] and 339.4 [95% CI, 21.2 to 657.6], respectively). The 10-minute and 60-minute ES groups had improved behavioral recovery, including on grid-walking analysis, compared with the no-ES group (mean difference, 11.9% [95% CI, 3.8% to 20.0%] and 10.9% [95% CI, 2.9% to 19.0%], respectively). There was no difference between the ES groups in measured outcomes.

CONCLUSIONS

A 10-minute ES protocol accelerated axon regeneration and facilitated functional recovery.

CLINICAL RELEVANCE

The brief (10-minute) ES protocol provided similar benefits to the 60-minute protocol in an acute sciatic nerve transection/repair mice model and merits further studies.

Bionic microenvironment-inspired synergistic effect of anisotropic micro-nanocomposite topology and biology cues on peripheral nerve regeneration

Anisotropic topographies and biological cues can simulate the regenerative microenvironment of nerve from physical and biological aspects, which show promising application in nerve regeneration. However, their synergetic influence on injured peripheral nerve is rarely reported. In the present study, we constructed a bionic microenvironment-inspired scaffold integrated with both anisotropic micro-nanocomposite topographies and IKVAV peptide. The results showed that both the topographies and peptide displayed good stability. The scaffolds could effectively induce the orientation growth of Schwann cells and up-regulate the genes and proteins relevant to myelination. Last, three signal pathways including the Wnt/β-catenin pathway, the extracellular signal-regulated kinase/mitogen-activated protein pathway, and the transforming growth factor-β pathway were put forward, revealing the main path of synergistic effects of anisotropic micro-nanocomposite topographies and biological cues on neuroregeneration. The present study may supply an important strategy for developing functional of artificial nerve implants.

The Neuropeptide Cortistatin Alleviates Neuropathic Pain in Experimental Models of Peripheral Nerve Injury

Neuropathic pain is one of the most severe forms of chronic pain caused by the direct injury of the somatosensory system. The current drugs for treating neuropathies have limited efficacies or show important side effects, and the development of analgesics with novel modes of action is critical. The identification of endogenous anti-nociceptive factors has emerged as an attractive strategy for designing new pharmacological approaches to treat neuropathic pain. Cortistatin is a neuropeptide with potent anti-inflammatory activity, recently identified as a natural analgesic peptide in several models of pain evoked by inflammatory conditions. Here, we investigated the potential analgesic effect of cortistatin in neuropathic pain using a variety of experimental models of peripheral nerve injury caused by chronic constriction or partial transection of the sciatic nerve or by diabetic neuropathy. We found that the peripheral and central injection of cortistatin ameliorated hyperalgesia and allodynia, two of the dominant clinical manifestations of chronic neuropathic pain. Cortistatin-induced analgesia was multitargeted, as it regulated the nerve damage-induced hypersensitization of primary nociceptors, inhibited neuroinflammatory responses, and enhanced the production of neurotrophic factors both at the peripheral and central levels. We also demonstrated the neuroregenerative/protective capacity of cortistatin in a model of severe peripheral nerve transection. Interestingly, the nociceptive system responded to nerve injury by secreting cortistatin, and a deficiency in cortistatin exacerbated the neuropathic pain responses and peripheral nerve dysfunction. Therefore, cortistatin-based therapies emerge as attractive alternatives for treating chronic neuropathic pain of different etiologies.

Unilateral facial injection of Botulinum neurotoxin A attenuates bilateral trigeminal neuropathic pain and anxiety-like behaviors through inhibition of TLR2-mediated neuroinflammation in mice

Objectives

In this study, we investigated the possible analgesic effects of Botulinum toxin type A (BoNT/A) on trigeminal neuralgia (TN). A modified TN mouse model was established by chronic constriction injury of the distal infraorbital nerve (dIoN-CCI) in mice, and the possible roles of microglia toll-like receptor 2 (TLR2) and neuroinflammation was investigated.

Methods

Male C57BL/6 mice were divided into 3 groups, including sham group, vehicle-treated TN group and BoNT/A-treated TN group. Bilateral mechanical pain hypersensitivity, anxiety-like and depressive-like behaviors were evaluated by using von Frey test, open field, elevated plus-maze testing, and forced swimming test in mice, respectively. The mRNA or protein expression levels of toll-like receptors (TLRs), glia activation markers and proinflammatory factors in the trigeminal nucleus caudalis (TNC) were tested by RT-qPCR, immunofluorescence and Western blotting. We also tested the pain behaviors of TN in Tlr2^−/− mice.

Results

We found that unilateral subcutaneous injection of BoNT/A into the whisker pad on the ipsilateral side of dIoN-CCI mice significantly attenuated bilateral mechanical pain hypersensitivity and anxiety-like behaviors induced by dIoN-CCI surgery in mice. The dIoN-CCI surgery significantly up-regulated the expression of TLR2, MyD88, CD11b (a microglia marker), IL-1β, TNF-α and IL-6 in the ipsilateral TNC in mice, and BoNT/A injection significantly inhibited the expression of these factors. Immunostaining results confirmed that BoNT/A injection significantly inhibited the microglia activation in the ipsilateral TNC in dIoN-CCI mice. TLR2 deficiency also alleviated bilateral mechanical pain hypersensitivity and the up-regulation of MyD88 expression in the TNC of dIoN-CCI mice.

Conclusion

These results indicate that unilateral injection of BoNT/A attenuated bilateral mechanical pain hypersensitivity and anxiety-like behaviors in dIoN-CCI mice, and the analgesic effects of BoNT/A may be associated with the inhibition of TLR2-mediated neuroinflammation in the TNC.

Gene set enrichment analysis and protein-protein interaction network analysis after sciatic nerve injury

Background

Peripheral nerves are able to regenerate spontaneously after injury. An increasing number of studies have investigated the mechanism of peripheral nerve regeneration and attempted to find potential therapeutic targets. The various bioinformatics analysis tools available, gene set enrichment analysis (GSEA) and protein-protein interaction (PPI) networks can effectively screen the crucial targets of neuroregeneration.

Methods

GSEA and PPI networks were constructed through ingenuity pathway analysis and sequential gene expression validation ex vitro to investigate the molecular processes at 1, 4, 7, and 14 days following sciatic nerve transection in rats.

Results

Immune response and the activation of related canonical pathways were classified as crucial biological events. Additionally, neural precursor cell expressed developmentally downregulated 4-like (NEDD4L), neuregulin 1 (NRG1), nuclear factor of activated T cells 2 (NFATC2), midline 1 (MID1), GLI family zinc finger 2 (GLI2), and ventral anterior homeobox 1 (VAX1), which were jointly involved in both immune response and axonal regeneration, were screened and their mRNA and protein expressions following nerve injury were validated. Among them, the expression of VAX1 continuously increased following nerve injury, and it was considered to be a potential therapeutic target.

Conclusions

The combined use of GSEA and PPI networks serves as a valuable way to identify potential therapeutic targets for neuroregeneration.

Cbp-dependent histone acetylation mediates axon regeneration induced by environmental enrichment in rodent spinal cord injury models

After a spinal cord injury, axons fail to regenerate in the adult mammalian central nervous system, leading to permanent deficits in sensory and motor functions. Increasing neuronal activity after an injury using electrical stimulation or rehabilitation can enhance neuronal plasticity and result in some degree of recovery; however, the underlying mechanisms remain poorly understood. We found that placing mice in an enriched environment before an injury enhanced the activity of proprioceptive dorsal root ganglion neurons, leading to a lasting increase in their regenerative potential. This effect was dependent on Creb-binding protein (Cbp)-mediated histone acetylation, which increased the expression of genes associated with the regenerative program. Intraperitoneal delivery of a small-molecule activator of Cbp at clinically relevant times promoted regeneration and sprouting of sensory and motor axons, as well as recovery of sensory and motor functions in both the mouse and rat model of spinal cord injury. Our findings showed that the increased regenerative capacity induced by enhancing neuronal activity is mediated by epigenetic reprogramming in rodent models of spinal cord injury. Understanding the mechanisms underlying activity-dependent neuronal plasticity led to the identification of potential molecular targets for improving recovery after spinal cord injury.

Immunomodulation by dimethyl fumarate treatment improves mouse sciatic nerve regeneration

Traumatic injury to the peripheral nervous system (PNS) often generates sensorimotor deficits that impair the quality of life of the patient. The success of nerve regeneration is related to tissue clearance and the formation of a microenvironment that sustains and stimulates axon growth up to the target. In this sense, macrophages are important for axon and myelin debris removal, neovascularization and the production of neurotrophic factors. Macrophage activation is improved by T helper (Th) lymphocytes, whose role remains few explored upon traumatic nerve injuries. Dimethyl fumarate (DMF) is the first-line drug for the treatment of multiple sclerosis due to its neuroprotective, anti-inflammatory and immunomodulatory properties. DMF improves nerve regeneration via antioxidant and cytoprotective cell signaling pathways. However, the direct activity on the cell immune response following nerve axotomy requires further investigation. In the present study, we evaluated DMF activity on Th cells and macrophage polarization, axonal regeneration and motor recovery following sciatic nerve crush in mice. For this aim, operated animals received DMF or vehicle once a day, starting at 3 days postinjury (dpi). Using an in vivo cell migration assay, we observed reduced lymphocyte infiltration in the nerves of DMF-treated mice at 7 dpi. Flow cytometry revealed DMF-responsive lymphocyte polarization from the pro- (Th1) to anti-inflammatory (Th2) phenotype at 7 dpi but not at 14 dpi. No effect was observed on macrophage polarization (from M1 to M2), although DMF reduced the frequency of the proinflammatory M1 subset from 7 to 14 dpi. Quantification of neurofilament (axon marker) and growth-associated protein 43 (GAP-43) immunolabeling showed improved axonal regeneration under DMF treatment at 14 dpi. Better motor recovery was observed in the DMF-treated group, as verified by an automated walking track test. Overall, our data reinforce the pro-regenerative capacity of DMF after traumatic nerve injury based on downmodulation of the proinflammatory immune response.

Critical roles of astrocytic-CCL2-dependent monocyte infiltration in a DJ-1 knockout mouse model of delayed brain repair

Monocyte-derived macrophages play a role in the repair of the injured brain. We previously reported that a deficiency of the Parkinson's disease (PD)-associated gene DJ-1 delays repair of brain injury produced by stereotaxic injection of ATP, a component of damage-associated molecular patterns. Here, we show that a DJ-1 deficiency attenuates monocyte infiltration into the damaged brain owing to a decrease in C-C motif chemokine ligand 2 (CCL2) expression in astrocytes. Like DJ-1-knockout (KO) mice, CCL2 receptor (CCR2)-KO mice showed defects in monocyte infiltration and delayed recovery of brain injury, as determined by 9.4 T magnetic resonance imaging analysis and immunostaining for tyrosine hydroxylase and glial fibrillary acid protein. Notably, transcriptome analyses showed that genes related to regeneration and synapse formation were similarly downregulated in injured brains of DJ-1-KO and CCR2-KO mice compared with the injured wild-type brain. These results indicate that defective astrogliosis in DJ-1-KO mice is associated with decreased CCL2 expression and attenuated monocyte infiltration, resulting in delayed repair of brain injury. Thus, delayed repair of brain injury could contribute to the development of PD. MAIN POINTS: A DJ-1 deficiency attenuates infiltration of monocytes owing to a decrease in CCL2 expression in astrocytes, which in turn led to delay in repair of brain injury.

Improved mouse sciatic nerve regeneration following lymphocyte cell therapy

Traumatic injury to the peripheral nervous system (PNS) is the most common cause of acquired nerve damage and impairs the quality of life of patients. The success of nerve regeneration depends on distal stump degeneration, tissue clearance and remodeling, processes in which the immune system participates. We previously reported improved motor recovery in sciatic nerve crush mice following adoptive transfer of lymphocytes, which migrated to the lesion site. However, lymphocyte activity and the nerve tissue response remain unexplored. Thus, in the present study, we evaluated sciatic nerve regeneration and T cell polarization in lymphocyte recipient mice. Splenic lymphocytes were isolated from mice 14 days after sciatic nerve crush and transferred to axotomized animals three days postinjury. Immediate lymphocyte migration to the crushed nerve was confirmed by in vivo imaging. Phenotyping of T helper (Th) cells by flow cytometry revealed an increased frequency of the proinflammatory Th1 and Th17 cell subsets in recipient mice at 7 days and showed that the frequency of these cells remained unchanged for up to 21 days. Moreover, nerve regeneration was improved upon cell therapy, as shown by sustained immunolabeling of axons, Schwann cells, growth-associated protein 43 and BDNF from 14 to 28 days after lesion. Macrophage and IgG immunolabeling were also higher in cell-transferred mice at 14 and 21 days following nerve crush. Functionally, we observed better sensory recovery in the lymphocyte-treated group. Overall, our data demonstrate that enhanced inflammation early after nerve injury has beneficial effects for the regenerative process, improving tissue clearance and axonal regrowth towards the target organs.

Low-Level Laser Effect on Peripheral Sciatic Regeneration Under the Systemic Inflammatory Condition of Periodontal Disease

Introduction: Periodontal disease (PD) is an inflammatory condition, which leads to tooth loss and promotes a systemic inflammatory state that can aggravate the nerve degeneration. As laser therapy may stimulate regeneration, this study aimed to evaluate the effect of the low-level laser (LLL) on peripheral nerve regeneration under the systemic inflammatory condition of PD. Methods: Thirry-two male rats were used, distributed in 4 groups: nerve injury (NIG); periodontal disease with nerve injury (PDNI); nerve injury and treatment (TNIG); periodontal disease with nerve injury and treatment (PDNIT). On the 7th day of the experiment, the animals had ligatures placed around the lower first molars. On the 22nd day, they underwent peripheral nerve damage, and on the 25th day, the LLL treatment was initiated, performed for two weeks. The sciatic functional index (SFI) was evaluated with subsequent euthanasia of all the animals on the 37th day of the experiment. The sciatic nerve was collected for morphological and oxidative stress analysis and the hemi jaws for radiographic analysis. Results: Regarding the SFI, there was no difference among the groups in the first evaluation (EV) pre-injury; as for theEV2, after injury, all the groups presented a decrease in these values, which remained in post-treatment. For the morphology of the PDNI, nerve tissue presented larger diameter fibers, whereas, for NIT and PDNIT, fibers had smaller diameters with endoneurial organization. When it comes to the antioxidant system, there was an increase in protein concentration, higher superoxide activity, and decreased glutathione transferase activity in the treated groups. Catalase and cholinesterase did not differ between the groups, and lipoperoxidation (LPO) increased in the PD groups. For the mandible radiographic analysis, it was possible to verify the induction of PD. Conclusion: As for the used parameters, the low-level laser was not effective in increasing the nociceptive threshold, but it contributed to the regeneration of nerve fibers, although the inflammation was still present in the site. However, the treatment was effective in protecting cells against oxidative damage due to increased SOD and increased protein, although the decrease in GST demonstrates the inhibition of this stage of the antioxidant system.

Miconazole alleviates peripheral nerve crush injury by mediating a macrophage phenotype change through the NF-κB pathway

BACKGROUND

Peripheral nerve injury (PNI) causes motor and sensory defects, has strong impact on life quality and still has no effective therapy. Miconazole is one of the most widely used antifungal drugs; the aims of the study were to investigate the effects of miconazole during sciatic nerve regeneration in a mouse model of sciatic nerve crush injury.

METHODS

We established peripheral nerve crush model and investigated the effects of miconazole by multiple aspects. We further studied the potential mechanism of action of miconazole by Western blotting, fluorescence immunohistochemistry, and PCR analysis.

RESULTS

Miconazole improves the symptoms of crushed nerve by improving inflammatory cell infiltration and demyelinating myelin of sciatic nerve. Affected by miconazole, the proportion of inflammatory M1 macrophages in the distal part of the sciatic nerve was reduced, and the proportion of anti-inflammatory M2 macrophages was increased. Finally, the neuroprotective properties of miconazole may be regulated by the nuclear factor (NF)-κB pathway.

CONCLUSIONS

Our data suggest that miconazole can effectively alleviate PNI, and the mechanism involves mediating a phenotype change of M1/ M2 macrophages. Thus, miconazole may represent a potential therapeutic intervention for nerve crush injury.

Local FK506 delivery at the direct nerve repair site improves nerve regeneration

INTRODUCTION

The objective of this study is to assess the efficacy of local tacrolimus (FK506) delivery to improve outcomes in the setting of nerve transection injury.

METHODS

FK506 embedded poly(lactide-co-caprolactone) films capable of extended, localized release of FK506 were developed. FK506 rate of release testing and bioactivity assay was performed. Mouse sciatic nerve transection and direct repair model was used to evaluate the effect extended, local delivery of FK506 had on nerve regeneration outcomes.

RESULTS

Linear release of FK506 was observed for 30 days and released FK506 matched control levels of neurite extension in the dorsal root ganglion assay. Groups treated with local FK506 had greater gastrocnemius muscle weight, foot electromyogram, and number of axons distal of the repair site than non-FK506 groups.

DISCUSSION

Results of this study indicate that extended, localized delivery of FK506 to nerve injuries can improve nerve regeneration outcomes in a mouse sciatic nerve transection and repair.

MIF/CD74 axis participates in inflammatory activation of Schwann cells following sciatic nerve injury

Based on deep RNA sequencing of distal segments of lesioned sciatic nerves, a huge number of differentially expression genes (DEGs) were thus obtained and functionally analyzed. The inflammatory response was denoted as one of most significant biological processes following sciatic nerve injury. In the present study, ingenuity pathway analysis (IPA) demonstrated that macrophage migration inhibitory factor (MIF) was identified as a core regulator of inflammatory response through interaction with CD74 membrane receptor. By establishment of rat sciatic nerve transection model, we displayed that MIF was upregulated following sciatic nerve axotomy, in colocalization with Schwann cells (SCs). MIF promoted migration, proliferation, together with inflammatory responses of SCs in vitro. Immunoprecipitation showed that MIF interacted with CD74 receptor, through which to activate intracellular ERK and JNK signaling pathways. Interference of CD74 receptor using specific siRNA showed that the transcription of proinflammatory cytokines including TNF-α, IL-1β, as well as cytokine receptor TLR4 in SCs was significantly attenuated, supporting an participation of MIF/CD74 signal axis in SCs inflammatory response. The data provide a novel role of MIF in eliciting inflammatory response of peripheral nerve injury, which might be beneficial for precise therapy of peripheral nerve inflammation.

The accumulation of T cells within acellular nerve allografts is length-dependent and critical for nerve regeneration

Repair of traumatic nerve injuries can require graft material to bridge the defect. The use of alternatives to bridge the defect, such as acellular nerve allografts (ANAs), is becoming more common and desired. Although ANAs support axon regeneration across short defects (<3 cm), axon regeneration across longer defects (>3 cm) is limited. It is unclear why alternatives, including ANAs, are functionally limited by length. After repairing Lewis rat nerve defects using short (2 cm) or long (4 cm) ANAs, we showed that long ANAs have severely reduced axon regeneration across the grafts and contain Schwann cells with a unique phenotype. But additionally, we found that long ANAs have disrupted angiogenesis and altered leukocyte infiltration compared to short ANAs as early as 2 weeks after repair. In particular, long ANAs contained fewer T cells compared to short ANAs. These outcomes were accompanied with reduced expression of select cytokines, including IFN-γ and IL-4, within long versus short ANAs. T cells within ANAs did not express elevated levels of IL-4, but expressed elevated levels of IFN-γ. We also directly assessed the contribution of T cells to regeneration across nerve grafts using athymic rats. Interestingly, T cell deficiency had minimal impact on axon regeneration across nerve defects repaired using isografts. Conversely, T cell deficiency reduced axon regeneration across nerve defects repaired using ANAs. Our data demonstrate that T cells contribute to nerve regeneration across ANAs and suggest that reduced T cells accumulation within long ANAs could contribute to limiting axon regeneration across these long ANAs.

Granulocyte-macrophage colony-stimulating factor improves mouse peripheral nerve regeneration following sciatic nerve crush

Peripheral nerve injuries severely impair patients' quality of life as full recovery is seldom achieved. Upon axonal disruption, the distal nerve stump undergoes fragmentation, and myelin breaks down; the subsequent regeneration progression is dependent on cell debris removal. In addition to tissue clearance, macrophages release angiogenic and neurotrophic factors that contribute to axon growth. Based on the importance of macrophages for nerve regeneration, especially during the initial response to injury, we treated mice with granulocyte-macrophage colony-stimulating factor (GM-CSF) at various intervals after sciatic nerve crushing. Sciatic nerves were histologically analyzed at different time intervals after injury for the presence of macrophages and indicators of regeneration. Functional recovery was followed by an automated walking track test. We found that GM-CSF potentiated early axon growth, as indicated by the enhanced expression of growth-associated protein at 7 days postinjury. Inducible nitric oxide synthase expression increased at the beginning and at the end of the regenerative process, suggesting that nitric oxide is involved in axon growth and pruning. As expected, GM-CSF treatment stimulated macrophage infiltration, which increased at 7 and 14 days; however, it did not improve myelin clearance. Instead, GM-CSF stimulated early brain-derived neurotrophic factor (BDNF) production, which peaked at 7 days. Locomotor recovery pattern was not improved by GM-CSF treatment. The present results suggest that GM-CSF may have beneficial effects on early axonal regeneration.

Counteracting roles of MHCI and CD8+ T cells in the peripheral and central nervous system of ALS SOD1G93A mice

BACKGROUND

The major histocompatibility complex I (MHCI) is a key molecule for the interaction of mononucleated cells with CD8⁺T lymphocytes. We previously showed that MHCI is upregulated in the spinal cord microglia and motor axons of transgenic SOD1^G93A mice.

METHODS

To assess the role of MHCI in the disease, we examined transgenic SOD1^G93A mice crossbred with β2 microglobulin-deficient mice, which express little if any MHCI on the cell surface and are defective for CD8⁺ T cells.

RESULTS

The lack of MHCI and CD8⁺ T cells in the sciatic nerve affects the motor axon stability, anticipating the muscle atrophy and the disease onset. In contrast, MHCI depletion in resident microglia and the lack of CD8⁺ T cell infiltration in the spinal cord protect the cervical motor neurons delaying the paralysis of forelimbs and prolonging the survival of SOD1^G93A mice.

CONCLUSIONS

We provided straightforward evidence for a dual role of MHCI in the peripheral nervous system (PNS) compared to the CNS, pointing out regional and temporal differences in the clinical responses of ALS mice. These findings offer a possible explanation for the failure of systemic immunomodulatory treatments and suggest new potential strategies to prevent the progression of ALS.

Transcriptomic Landscapes of Immune Response and Axonal Regeneration by Integrative Analysis of Molecular Pathways and Interactive Networks Post-sciatic Nerve Transection

Potential interaction between immune response and axonal regeneration has recently attracted much attention in peripheral nervous system (PNS). Previously, global mRNA expression changes in proximal nerve segments were profiled and merely focused on the differentially change of the key biological processes. To further uncover molecular mechanisms of peripheral nerve regeneration, here we focused on the interaction between immune response and axonal regeneration that associated with specific molecular pathways and interactive networks following sciatic nerve transection. To offer an outline of the specific molecular pathways elaborating axonal regeneration and immune response, and to figure out the molecular interaction between immune response and axonal regeneration post-sciatic nerve transection, we carried out comprehensive approaches, including gene expression profiling plus multi-level bioinformatics analysis and then further experimental validation. Alcam, Nrp1, Nrp2, Rac1, Creb1, and Runx3 were firstly considered as the key or hub genes of the protein-protein interaction (PPI) network in rat models of sciatic nerve transection, which are highly correlated with immune response and axonal regeneration. Our work provide a new way to figure out molecular mechanism of peripheral nerve regeneration and valuable resources to figure out the molecular courses which outline neural injury-induced micro-environmental variation to discover novel therapeutic targets for axonal regeneration.

Adipose Tissue Graft Improves Early but not Late Stages of Nerve Regeneration

AIM

The aim of the study was to assess the effect of autologous fat graft on nerve regeneration by means of immunohistochemistry.

MATERIALS AND METHODS

The rat sciatic nerve was used; complete transection followed by primary neurorrhaphy was performed on both hind legs, on the left side a processed fat graft was applied, surrounding the nerve. Nerve biopsies were collected and immunohistochemical procedures were performed for glial fibrillary acidic protein (GFAP) and for neurofilament-associated protein(NFAP).

RESULTS

At 4 weeks, GFAP-positive cells were observed in the connective tissue formed between the two nerve endings on the left side only. At 10 weeks, GFAP-positive structures were present and exhibited a tendency to become linear on both sides, with an increased density on the left. NFAP-positive expression was present in the left treated limb with a disorganized pattern.

CONCLUSION

Adipose tissue led to the stimulation of GFAP-positive Schwann cells, which could have a positive impact on nerve regeneration in the clinical setting.

Impact of peripheral immune status on central molecular responses to facial nerve axotomy

When facial nerve axotomy (FNA) is performed on immunodeficient recombinase activating gene-2 knockout (RAG-2^-/-) mice, there is greater facial motoneuron (FMN) death relative to wild type (WT) mice. Reconstituting RAG-2^-/- mice with whole splenocytes rescues FMN survival after FNA, and CD4+ T cells specifically drive immune-mediated neuroprotection. Evidence suggests that immunodysregulation may contribute to motoneuron death in amyotrophic lateral sclerosis (ALS). Immunoreconstitution of RAG-2^-/- mice with lymphocytes from the mutant superoxide dismutase (mSOD1) mouse model of ALS revealed that the mSOD1 whole splenocyte environment suppresses mSOD1 CD4+ T cell-mediated neuroprotection after FNA. The objective of the current study was to characterize the effect of CD4+ T cells on the central molecular response to FNA and then identify if mSOD1 whole splenocytes blocked these regulatory pathways. Gene expression profiles of the axotomized facial motor nucleus were assessed from RAG-2^-/- mice immunoreconstituted with either CD4+ T cells or whole splenocytes from WT or mSOD1 donors. The findings indicate that immunodeficient mice have suppressed glial activation after axotomy, and cell transfer of WT CD4+ T cells rescues microenvironment responses. Additionally, mSOD1 whole splenocyte recipients exhibit an increased astrocyte activation response to FNA. In RAG-2^-/- + mSOD1 whole splenocyte mice, an elevation of motoneuron-specific Fas cell death pathways is also observed. Altogether, these findings suggest that mSOD1 whole splenocytes do not suppress mSOD1 CD4+ T cell regulation of the microenvironment, and instead, mSOD1 whole splenocytes may promote motoneuron death by either promoting a neurotoxic astrocyte phenotype or inducing Fas-mediated cell death pathways. This study demonstrates that peripheral immune status significantly affects central responses to nerve injury. Future studies will elucidate the mechanisms by which mSOD1 whole splenocytes promote cell death and if inhibiting this mechanism can preserve motoneuron survival in injury and disease.

Strain-specific Differences in the Effects of Lymphocytes on the Development of Insulin Resistance and Obesity in Mice

Obesity is characterized as a chronic, low-grade inflammatory disease owing to the infiltration of the adipose tissue by macrophages. Although the role of macrophages in this process is well established, the role of lymphocytes in the development of obesity and metabolism remains less well defined. In the current study, we fed WT and Rag1-/- male mice, of C57BL/6J and BALB/c backgrounds, high-fat diet (HFD) or normal diet for 15 wk. Compared with WT mice, Rag1-/- mice of either of the examined strains were found less prone to insulin resistance after HFD, had higher metabolic rates, and used lipids more efficiently, as shown by the increased expression of genes related to fatty acid oxidation in epidydimal white adipose tissue. Furthermore, Rag1-/- mice had increased Ucp1 protein expression and associated phenotypic characteristics indicative of beige adipose tissue in subcutaneous white adipose tissue and increased Ucp1 expression in brown adipose tissue. As with inflammatory and other physiologic responses previously reported, the responses of mice to HFD show strain-specific differences, with increased susceptibility of C57BL/6J as compared with BALB/c strain. Our findings unmask a crucial role for lymphocytes in the development of obesity and insulin resistance, in that lymphocytes inhibit efficient dissipation of energy by adipose tissue. These strain-associated differences highlight important metabolic factors that should be accommodated in disease modeling and drug testing.

The Emerging Role of the Major Histocompatibility Complex Class I in Amyotrophic Lateral Sclerosis

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease affecting upper and lower motoneurons (MNs). The etiology of the disease is still unknown for most patients with sporadic ALS, while in 5–10% of the familial cases, several gene mutations have been linked to the disease. Mutations in the gene encoding Cu, Zn superoxide dismutase (SOD1), reproducing in animal models a pathological scenario similar to that found in ALS patients, have allowed for the identification of mechanisms relevant to the ALS pathogenesis. Among them, neuroinflammation mediated by glial cells and systemic immune activation play a key role in the progression of the disease, through mechanisms that can be either neuroprotective or neurodetrimental depending on the type of cells and the MN compartment involved. In this review, we will examine and discuss the involvement of major histocompatibility complex class I (MHCI) in ALS concerning its function in the adaptive immunity and its role in modulating the neural plasticity in the central and peripheral nervous system. The evidence indicates that the overexpression of MHCI into MNs protect them from astrocytes’ toxicity in the central nervous system (CNS) and promote the removal of degenerating motor axons accelerating collateral reinnervation of muscles.

Transcriptional Profiling at High Temporal Resolution Reveals Robust Immune/Inflammatory Responses during Rat Sciatic Nerve Recovery

After peripheral nerve injury, immune/inflammatory responses are triggered, which are critical for nerve regeneration. Despite their importance, the underlying molecular changes in immune/inflammatory responses remain largely unknown. In this study, we systematically analyzed differentially expressed genes in immune/inflammatory-related pathways at high temporal resolution and experimentally validated gene expression changes with RT-PCR following sciatic nerve crush in rats. We found that immune/inflammatory reactions not only occur in the acute injury but also remained activated over two weeks after injury. Detailed bioinformatic studies suggested that multiple immune/inflammatory pathways, including agranulocyte adhesion and diapedesis, granulocyte adhesion and diapedesis, IL-6 signaling, and IL-10 signaling, were sustained activated during nerve degeneration and regeneration. Our current study expands our understanding of the molecular basis of altered immune/inflammatory-related pathways following injury and thus might offer the possibility of targeting related molecules as therapeutic intervention for peripheral nerve regeneration.