Biology of the human blood-nerve barrier in health and disease

Animal models of immune-mediated demyelinating polyneuropathies

Immune-mediated demyelinating polyneuropathies (IMDPs) are rare disorders in which dysregulated adaptive immune responses cause peripheral nerve demyelinating inflammation and axonal injury in susceptible individuals. Despite significant advances in understanding IMDP pathogenesis guided by patient data and representative mammalian models, specific therapies are lacking. Significant knowledge gaps in IMDP pathogenesis still exist, e.g. precise antigen(s) and mechanisms that initially trigger immune system activation and identification of large population disease susceptibility factors. The initial directional cues for antigen-specific effector or autoreactive leukocyte trafficking into peripheral nerves are also unknown. An overview of current animal models, with emphasis on the experimental autoimmune neuritis and spontaneous autoimmune peripheral polyneuropathy models, is provided. Insights on the initial directional cues for peripheral nerve tissue specific autoimmunity using a novel Major Histocompatibility Complex class II conditional knockout mouse strain are also discussed, suggesting an essential research tool to study cell- and time-dependent adaptive immunity in autoimmune diseases.

Intravenous immunoglobulin alleviates Japanese encephalitis virus-induced peripheral neuropathy by inhibiting the ASM/ceramide pathway

Japanese encephalitis virus (JEV) infection is considered a global public health emergency. Severe peripheral neuropathy caused by JEV infection has increased disability and mortality rates in recent years. Because there are very few therapeutic options for JEV infection, prompt investigations of the ability of clinically safe, efficacious and globally available drugs to inhibit JEV infection and ameliorate peripheral neuropathy are urgently needed. In this study, we found that high doses of intravenous immunoglobulin, a function inhibitor of acid sphingomyelinase (FIASMA), inhibited acid sphingomyelinase (ASM) and ceramide activity in the serum and sciatic nerve of JEV-infected rats, reduced disease severity, reversed electrophysiological and histological abnormalities, significantly reduced circulating proinflammatory cytokine levels, inhibited Th1 and Th17 cell proliferation, and suppressed the infiltration of inflammatory CD4 + cells into the sciatic nerve. It also maintained the peripheral nerve-blood barrier without causing severe clinical side effects. In terms of the potential mechanisms, ASM was found to participate in immune cell differentiation and to activate immune cells, thereby exerting proinflammatory effects. Therefore, immunoglobulin is a FIASMA that reduces abnormal immune responses and thus targets the ASM/ceramide system to treat peripheral neuropathy caused by JEV infection.

Miniaturized therapeutic systems for ultrasound-modulated drug delivery to the central and peripheral nervous system

Ultrasound is a promising technology to address challenges in drug delivery, including limited drug penetration across physiological barriers and ineffective targeting. Here we provide an overview of the significant advances made in recent years in overcoming technical and pharmacological barriers using ultrasound-assisted drug delivery to the central and peripheral nervous system. We commence by exploring the fundamental principles of ultrasound physics and its interaction with tissue. The mechanisms of ultrasonic-enhanced drug delivery are examined, as well as the relevant tissue barriers. We highlight drug transport through such tissue barriers utilizing insonation alone, in combination with ultrasound contrast agents (e.g., microbubbles), and through innovative particulate drug delivery systems. Furthermore, we review advances in systems and devices for providing therapeutic ultrasound, as their practicality and accessibility are crucial for clinical application.

CD163+ macrophages monitor enhanced permeability at the blood-dorsal root ganglion barrier

In dorsal root ganglia (DRG), macrophages reside close to sensory neurons and have largely been explored in the context of pain, nerve injury, and repair. However, we discovered that most DRG macrophages interact with and monitor the vasculature by sampling macromolecules from the blood. Characterization of the DRG vasculature revealed a specialized endothelial bed that transformed in molecular, structural, and permeability properties along the arteriovenous axis and was covered by macrophage-interacting pericytes and fibroblasts. Macrophage phagocytosis spatially aligned with peak endothelial permeability, a process regulated by enhanced caveolar transcytosis in endothelial cells. Profiling the DRG immune landscape revealed two subsets of perivascular macrophages with distinct transcriptome, turnover, and function. CD163+ macrophages self-maintained locally, specifically participated in vasculature monitoring, displayed distinct responses during peripheral inflammation, and were conserved in mouse and man. Our work provides a molecular explanation for the permeability of the blood-DRG barrier and identifies an unappreciated role of macrophages as integral components of the DRG-neurovascular unit.

Role of transforming growth factor-β in peripheral nerve regeneration

Injuries caused by trauma and neurodegenerative diseases can damage the peripheral nervous system and cause functional deficits. Unlike in the central nervous system, damaged axons in peripheral nerves can be induced to regenerate in response to intrinsic cues after reprogramming or in a growth-promoting microenvironment created by Schwann cells. However, axon regeneration and repair do not automatically result in the restoration of function, which is the ultimate therapeutic goal but also a major clinical challenge. Transforming growth factor (TGF) is a multifunctional cytokine that regulates various biological processes including tissue repair, embryo development, and cell growth and differentiation. There is accumulating evidence that TGF-β family proteins participate in peripheral nerve repair through various factors and signaling pathways by regulating the growth and transformation of Schwann cells; recruiting specific immune cells; controlling the permeability of the blood-nerve barrier, thereby stimulating axon growth; and inhibiting remyelination of regenerated axons. TGF-β has been applied to the treatment of peripheral nerve injury in animal models. In this context, we review the functions of TGF-β in peripheral nerve regeneration and potential clinical applications.

Blood-nerve barrier enhances chronic postsurgical pain via the HIF-1α/ aquaporin-1 signaling axis

BACKGROUND

Blood nerve barrier (BNB) participates in the development of neuropathic pain. AQP1 is involved in peripheral pain perception and is negatively correlated with HIF-1α phenotype, which regulates endothelial permeability. However, the role of HIF-1α-AQP1-mediated BNB dysfunction in Chronic Postsurgical Pain (CPSP) has not been reported.

METHODS

Male Sprague-Dawley rats were randomized into 5 groups: (i) Naive group; (ii) Sham group; (iii) SMIR group: skin/muscle incision and retraction for one hour. Behavioral tests were performed for the three groups, BNB vascular permeability and western blotting were conducted to determine HIF-1α and AQP1 protein expression. (iv) The SMIR + HIF-1α inhibitor group; (v) SMIR + DMSO group. Rats in the two groups were administered with HIF-1α inhibitor (2ME2) or DMSO intraperitoneally on the third day post-SMIR surgery followed by performance of behavioral tests, BNB permeability assessment, and determination of HIF-1α, AQP1 and NF200 protein levels.

RESULTS

The permeability of BNB was significantly increased and the expression of AQP1 was downregulated on the 3rd and 7th days post-operation. AQP1 is mainly located in neurons and NF200, CGRP-positive nerve fibers. HIF-1α was highly expressed on the third day post-operation. HIF-1α inhibitor reversed the decrease in AQP1 expression and increase in NF200 expression, barrier permeability and hyperalgesia induced by SMIR on the 3rd day post-surgery.

CONCLUSIONS

Early dysfunction of BNB mediated by HIF-1α/AQP1 activated by SMIR may be an important mechanism to promote acute postoperative painful transformation of CPSP. Preadaptive protection of endothelial cells around nerve substructures may be an important countermeasure to inhibit CPSP transformation. Early impairment of BNB function mediated by HIF-1α/AQP1 activated by SMIR may be an important mechanism for promoting acute postoperative pain transformation of CPSP.

Twelve protections evolved for the brain, and their roles in extending its functional life

As human longevity has increased, we have come to understand the ability of the brain to function into advanced age, but also its vulnerability with age, apparent in the age-related dementias. Against that background of success and vulnerability, this essay reviews how the brain is protected by (by our count) 12 mechanisms, including: the cranium, a bony helmet; the hydraulic support given by the cerebrospinal fluid; the strategically located carotid body and sinus, which provide input to reflexes that protect the brain from blood-gas imbalance and extremes of blood pressure; the blood brain barrier, an essential sealing of cerebral vessels; the secretion of molecules such as haemopexin and (we argue) the peptide Aβ to detoxify haemoglobin, at sites of a bleed; autoregulation of the capillary bed, which stabilises metabolites in extracellular fluid; fuel storage in the brain, as glycogen; oxygen storage, in the haemoprotein neuroglobin; the generation of new neurones, in the adult, to replace cells lost; acquired resilience, the stress-induced strengthening of cell membranes and energy production found in all body tissues; and cognitive reserve, the ability of the brain to maintain function despite damage. Of these 12 protections, we identify 5 as unique to the brain, 3 as protections shared with all body tissues, and another 4 as protections shared with other tissues but specialised for the brain. These protections are a measure of the brain's vulnerability, of its need for protection. They have evolved, we argue, to maintain cognitive function, the ability of the brain to function despite damage that accumulates during life. Several can be tools in the hands of the individual, and of the medical health professional, for the lifelong care of our brains.

Neurofluids and the glymphatic system: anatomy, physiology, and imaging

First described in 2012, the glymphatic system is responsible for maintaining homeostasis within the central nervous system, including nutrient delivery, waste clearance, and consistency of the ionic microenvironment. It is comprised of glial cells and barrier systems that modulate neurofluid production, circulation, and exchange. Experimental interrogation of neurofluid dynamics is restricted to ex vivo and in vitro studies in animals and humans, therefore diagnostic imaging plays an important role in minimally invasive evaluation. This review article will synthesize current knowledge and theories regarding neurofluid circulation and implications for neuroimaging. First, we will discuss the anatomy of the neurogliovascular unit, including paravascular and perivascular pathways of fluid exchange. In addition, we will summarize the structure and function of barrier systems including the blood-brain, blood-cerebrospinal fluid, and brain-cerebrospinal fluid barriers. Next, we will mention physiologic factors that yield normal variations in neurofluid circulation, and how various disease pathologies can disrupt glymphatic drainage pathways. Lastly, we will cover the spectrum of diagnostic imaging and interventional techniques with relevance to glymphatic structure, flow, and function. We conclude by highlighting current barriers and future directions for translational imaging and applications to neurologic disorders.

Primary perineuritis, a rare but treatable neuropathy: Review of perineurial anatomy, clinicopathological features, and differential diagnosis

The perineurium surrounds each fascicle in peripheral nerves, forming part of the blood-nerve barrier. We describe its normal anatomy and function. "Perineuritis" refers to both a nonspecific histopathological finding and more specific clinicopathological entity, primary perineuritis (PP). Patients with PP are often assumed to have nonsystemic vasculitic neuropathy until nerve biopsy is performed. We systematically reviewed the literature on PP and developed a differential diagnosis for histopathologically defined perineuritis. We searched PubMed, Embase, Scopus, and Web of Science for "perineuritis." We identified 20 cases (11 M/9F) of PP: progressive, unexplained neuropathy with biopsy showing perineuritis without vasculitis or other known predisposing condition. Patients ranged in age from 18 to 75 (mean 53.7) y and had symptoms 2-24 (median 4.5) mo before diagnosis. Neuropathy was usually sensory-motor (15/20), painful (18/19), multifocal (16/20), and distal-predominant (16/17) with legs more affected than arms. Truncal numbness occurred in 6/17; 10/18 had elevated cerebrospinal fluid (CSF) protein. Electromyography (EMG) and nerve conduction studies (NCS) demonstrated primarily axonal changes. Nerve biopsies showed T-cell-predominant inflammation, widening, and fibrosis of perineurium; infiltrates in epineurium in 10/20 and endoneurium in 7/20; and non-uniform axonal degeneration. Six had epithelioid cells. 19/20 received corticosteroids, 8 with additional immunomodulators; 18/19 improved. Two patients did not respond to intravenous immunoglobulin (IVIg). At final follow-up, 13/16 patients had mild and 2/16 moderate disability; 1/16 died. Secondary causes of perineuritis include leprosy, vasculitis, neurosarcoidosis, neuroborreliosis, neurolymphomatosis, toxic oil syndrome, eosinophilia-myalgia syndrome, and rarer conditions. PP appears to be an immune-mediated, corticosteroid-responsive disorder. It mimics nonsystemic vasculitic neuropathy. Cases with epithelioid cells might represent peripheral nervous system (PNS)-restricted forms of sarcoidosis.

Microanatomical findings with relevance to trigeminal ganglion enhancement on post-contrast T1-weighted magnetic resonance images in dogs

Introduction

Trigeminal ganglion contrast enhancement (TGCE) is reported to be a normal and a common finding on magnetic resonance imaging studies of dogs, cats and humans. The intent of the present study was to describe the anatomical characteristics of the trigeminal ganglion, its surrounding structures, and histological features that are relevant to explain or hypothesize on the reason for TGCE on T1-weighted post-contrast MRI studies of the brain in dogs.

Methods

Eight dog cadavers were dissected to study the anatomy of the trigeminal ganglion. The presence and anatomy of vessels was studied by dissection and by histological techniques. Two trigeminal ganglia were isolated and stained with hematoxylin-eosin (HE). Two other trigeminal ganglia included in the trigeminal canal and trigeminal cavity were decalcified with formic acid/formalin for 12 weeks and stained with HE to study the related vessels. Additionally, a corrosion cast was obtained from a separate canine specimen.

Results

Leptomeninges and a subarachnoid space were identified at the level of the trigeminal nerve roots and the trigeminal ganglion. No subarachnoid space was identified and leptomeninges were no longer present at the level of the three trigeminal nerve branches. Small arterial vessels ran to and supplied the trigeminal ganglion, passing through the dura mater. No venous plexus was visualized at the level of the trigeminal ganglion in the dissections. A complex arterial vascular network was identified within the leptomeningeal covering of the trigeminal ganglion and was best appreciated in the corrosion cast. Histological examination revealed small-to moderate-sized blood vessels located in the epineurium around the ganglion; from there a multitude of arterioles penetrated into the perineurium. Small endoneurial branches and capillaries penetrated the ganglion and the trigeminal nerve branches.

Discussion

Limitations to this study include the limited number of canine specimens included and the lack of electron microscopy to further support current hypotheses included in our discussion. In conclusion, this study provides further support to the theory that TGCE in dogs may be due an incomplete blood-nerve barrier or blood-ganglion barrier at the interface between the central nervous system and the peripheral nervous system.

Stabilizing the neural barrier - A novel approach in pain therapy

Chronic and neuropathic pain are a widespread burden. Incomplete understanding of underlying pathomechanisms is one crucial factor for insufficient treatment. Recently, impairment of the blood nerve barrier (BNB) has emerged as one key aspect of pain initiation and maintenance. In this narrative review, we discuss several mechanisms and putative targets for novel treatment strategies. Cells such as pericytes, local mediators like netrin-1 and specialized proresolving mediators (SPMs), will be covered as well as circulating factors including the hormones cortisol and oestrogen and microRNAs. They are crucial in either the BNB or similar barriers and associated with pain. While clinical studies are still scarce, these findings might provide valuable insight into mechanisms and nurture development of therapeutic approaches.

COVID-19 as a trigger of Guillain-Barré syndrome: A review of the molecular mechanism

Severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) caused a pandemic with serious complications. After coronavirus disease 2019 (COVID-19), several post-acute COVID-19 syndromes (PACSs) and long-COVID sequels were reported. PACSs involve many organs, including the nervous, gustatory, and immune systems. One of the PACSs after SARS-CoV-2 infection and vaccination is Guillain-Barré syndrome (GBS). The incidence rate of GBS after SARS-CoV-2 infection or vaccination is low. However, the high prevalence of COVID-19 and severe complications of GBS, for example, autonomic dysfunction and respiratory failure, highlight the importance of post-COVID-19 GBS. It is while patients with simultaneous COVID-19 and GBS seem to have higher admission rates to the intensive care unit, and demyelination is more aggressive in post-COVID-19 GBS patients. SARS-CoV-2 can trigger GBS via several pathways like direct neurotropism and neurovirulence, microvascular dysfunction and oxidative stress, immune system disruption, molecular mimicry, and autoantibody production. Although there are few molecular studies on the molecular and cellular mechanisms of GBS occurrence after SARS-CoV-2 infection and vaccination, we aimed to discuss the possible pathomechanism of post-COVID-19 GBS by gathering the most recent molecular evidence.

Biomechanics Characterization of Autonomic and Somatic Nerves by High Dynamic Closed-Loop MEMS force sensing

The biomechanics of peripheral nerves are determined by the blood-nerve barrier (BNB), together with the epineural barrier, extracellular matrix, and axonal composition, which maintain structural and functional stability. These elements are often ignored in the fabrication of penetrating devices, and the implant process is traumatic due to the mechanical distress, compromising the function of neuroprosthesis for sensory-motor restoration in amputees. Miniaturization of penetrating interfaces offers the unique opportunity of decoding individual nerve fibers associated to specific functions, however, a main issue for their implant is the lack of high-precision standardization of insertion forces. Current automatized electromechanical force sensors are available; however, their sensitivity and range amplitude are limited (i.e. mN), and have been tested only in-vitro. We previously developed a high-precision bi-directional micro-electromechanical force sensor, with a closed-loop mechanism (MEMS-CLFS), that while measuring with high-precision (-211.7μN to 211.5μN with a resolution of 4.74nN), can be used in alive animal. Our technology has an on-chip electrothermal displacement sensor with a shuttle beam displacement amplification mechanism, for large range and high-frequency resolution (dynamic range of 92.9 dB), which eliminates the adverse effect of flexural nonlinearity measurements, observed with other systems, and reduces the mechanical impact on delicate biological tissue. In this work, we use the MEMS-CLFS for in-vivo bidirectional measurement of biomechanics in somatic and autonomic nerves. Furthermore we define the mechanical implications of irrigation and collagen VI in the BNB, which is different for both autonomic and somatic nerves (~ 8.5-8.6 fold density of collagen VI and vasculature CD31+ in the VN vs ScN). This study allowed us to create a mathematical approach to predict insertion forces. Our data highlights the necessity of nerve-customization forces to prevent injury when implanting interfaces, and describes a high precision MEMS technology and mathematical model for their measurements.

Drug Permeability: From the Blood-Brain Barrier to the Peripheral Nerve Barriers

Drug delivery into the peripheral nerves and nerve roots has important implications for effective local anesthesia and treatment of peripheral neuropathies and chronic neuropathic pain. Similar to drugs that need to cross the blood-brain barrier (BBB) and blood-spinal cord barrier (BSCB) to gain access to the central nervous system (CNS), drugs must cross the peripheral nerve barriers (PNB), formed by the perineurium and blood-nerve barrier (BNB) to modulate peripheral axons. Despite significant progress made to develop effective strategies to enhance BBB permeability in therapeutic drug design, efforts to enhance drug permeability and retention in peripheral nerves and nerve roots are relatively understudied. Guided by knowledge describing structural, molecular and functional similarities between restrictive neural barriers in the CNS and peripheral nervous system (PNS), we hypothesize that certain CNS drug delivery strategies are adaptable for peripheral nerve drug delivery. In this review, we describe the molecular, structural and functional similarities and differences between the BBB and PNB, summarize and compare existing CNS and peripheral nerve drug delivery strategies, and discuss the potential application of selected CNS delivery strategies to improve efficacious drug entry for peripheral nerve disorders.

Exploring Pro-Inflammatory Immunological Mediators: Unraveling the Mechanisms of Neuroinflammation in Lysosomal Storage Diseases

Lysosomal storage diseases are a group of rare and ultra-rare genetic disorders caused by defects in specific genes that result in the accumulation of toxic substances in the lysosome. This excess accumulation of such cellular materials stimulates the activation of immune and neurological cells, leading to neuroinflammation and neurodegeneration in the central and peripheral nervous systems. Examples of lysosomal storage diseases include Gaucher, Fabry, Tay–Sachs, Sandhoff, and Wolman diseases. These diseases are characterized by the accumulation of various substrates, such as glucosylceramide, globotriaosylceramide, ganglioside GM2, sphingomyelin, ceramide, and triglycerides, in the affected cells. The resulting pro-inflammatory environment leads to the generation of pro-inflammatory cytokines, chemokines, growth factors, and several components of complement cascades, which contribute to the progressive neurodegeneration seen in these diseases. In this study, we provide an overview of the genetic defects associated with lysosomal storage diseases and their impact on the induction of neuro-immune inflammation. By understanding the underlying mechanisms behind these diseases, we aim to provide new insights into potential biomarkers and therapeutic targets for monitoring and managing the severity of these diseases. In conclusion, lysosomal storage diseases present a complex challenge for patients and clinicians, but this study offers a comprehensive overview of the impact of these diseases on the central and peripheral nervous systems and provides a foundation for further research into potential treatments.

Oxygen-Glucose Deprivation Decreases the Motility and Length of Axonal Mitochondria in Cultured Dorsal Root Ganglion Cells of Rats

Controlling axonal mitochondria is important for maintaining normal function of the neural network. Oxygen-glucose deprivation (OGD), a model used for mimicking ischemia, eventually induces neuronal cell death similar to axonal degeneration. Axonal mitochondria are disrupted during OGD-induced neural degeneration; however, the mechanism underlying mitochondrial dysfunction has not been completely understood. We focused on the dynamics of mitochondria in axons exposed to OGD; we observed that the number of motile mitochondria significantly reduced in 1 h following OGD exposure. In our observation, the decreased length of stationary mitochondria was affected by the following factors: first, the halt of motile mitochondria; second, the fission of longer stationary mitochondria; and third, a transformation from tubular to spherical shape in OGD-exposed axons. Motile mitochondria reduction preceded stationary mitochondria fragmentation in OGD exposure; these conditions induced the decrease of stationary mitochondria in three different ways. Our results suggest that mitochondrial morphological changes precede the axonal degeneration while ischemia-induced neurodegeneration.

Sonic Hedgehog Signaling Pathway: A Role in Pain Processing

Pain, as one of the most prevalent clinical symptoms, is a complex physiological and psychological activity. Long-term severe pain can become unbearable to the body. However, existing treatments do not provide satisfactory results. Therefore, new mechanisms and therapeutic targets need to be urgently explored for pain management. The Sonic hedgehog (Shh) signaling pathway is crucial in embryonic development, cell differentiation and proliferation, and nervous system regulation. Here, we review the recent studies on the Shh signaling pathway and its action in multiple pain-related diseases. The Shh signaling pathway is dysregulated under various pain conditions, such as pancreatic cancer pain, bone cancer pain, chronic post-thoracotomy pain, pain caused by degenerative lumbar disc disease, and toothache. Further studies on the Shh signaling pathway may provide new therapeutic options for pain patients.

Contribution of microvascular dysfunction to chronic pain

There is growing evidence that microvascular dysfunction is a pathology accompanying various injuries and conditions that produce chronic pain and may represent a significant contributing factor. Dysfunction that occurs within each component of the microvasculature, including arterioles, capillaries and venules impacts the health of surrounding tissue and produces pathology that can both initiate pain and influence pain sensitivity. This mini review will discuss evidence for a critical role of microvascular dysfunction or injury in pathologies that contribute to chronic pain conditions such as complex regional pain syndrome (CRPS) and fibromyalgia.

Thiotepa-based high-dose chemotherapy with autologous stem cell transplantation for neurolymphomatosis

Neurolymphomatosis (NL) is a rare clinical entity characterized by lymphomatous infiltration of the peripheral nervous system. According to recent retrospective data, consolidative high-dose chemotherapy (HDC) with autologous stem cell transplantation (ASCT) may be beneficial for NL. However, few reports to date have discussed optimal conditioning regimens. Herein, we report two cases of NL in patients with relapsed intravascular large B-cell lymphoma who received consolidative thiotepa-containing HDC-ASCT. Case 1: A 56-year-old woman who relapsed 2 months after the first complete remission (CR) and underwent ASCT. Case 2: A 65-year-old woman who relapsed 8 months after the first CR and underwent ASCT. Both patients engrafted. Time to neutrophil engraftment was 10 and 12 days after HDC-ASCT, and CR was sustained for 26 and 18 months, respectively, as of the last follow-up. Although there is little evidence supporting the utility of thiotepa-based HDC-ASCT in patients with NL, the results of this case report suggest that further studies are warranted to determine its efficacy in this setting.

Blood-nerve barrier disruption and coagulation system activation induced by mechanical compression injury participate in the peripheral sensitization of trigeminal neuralgia

Introduction

The aim of this study was to investigate the effect and possible mechanisms of the blood-nerve barrier (BNB) and the coagulation-anticoagulation system in modulating the mechanical allodynia in a trigeminal neuralgia (TN) rat model induced by chronic compression of the trigeminal root entry zone (TREZ).

Methods

Von Frey filaments were applied to determine the orofacial mechanical allodynia threshold. The BNB permeability was evaluated by Evans blue extravasation test. Immunohistochemical staining and laser confocal microscopy were used to measure the length of the depletion zones of the nodes of Ranvier in the TREZ, the diameter of nerve fibers and the length of the nodal gap. The transcriptional levels of prothrombin and endogenous thrombin inhibitor protease nexin-1 (PN-1) in the TREZ of TN rats were assessed by RT-qPCR. A Western blotting assay was performed to detect the expression of paranodal proteins neurofascin-155 (NF155) and neurofascin-125 (NF125) in the TREZ. The spatiotemporal expression pattern of thrombin activated receptor (i.e. protease activated receptor 1, PAR1) in TREZ were defined by immunostaining and immunoblotting assays. PAR1 receptor inhibitors SCH79797 were administrated to TN rats to analyze the effect of thrombin-PAR1 on orofacial hyperalgesia.

Results

A compression injury of a rat's TREZ successfully induced TN-like behavior and was accompanied by the destruction of the permeability of the BNB and the promotion of prothrombin and thrombin inhibitor protease nexin-1 (PN-1) expression. The expression of the paranodal proteins neurofascin-155 (NF155) and neurofascin-125 (NF125) was increased, while the nodal gap length of the nodes of Ranvier was widened and the length of node-depleted zones was shortened. Moreover, the expression of PAR1 within the TREZ was upregulated at an early stage of TN, and administration of the PAR1 antagonist SCH79797 effectively ameliorated orofacial mechanical allodynia.

Conclusion

A compression injury of the TREZ increased the permeability of the BNB and induced disturbances in the local coagulation-anticoagulation system, concomitant with the structural changes in the nodes of Ranvier, thrombin-PAR1 may play a critical role in modulating orofacial mechanical hyperalgesia in a TN rat model.

The peripheral Epac1/p-Cav-1 pathway underlies the disruption of the vascular endothelial barrier following skin/muscle incision and retraction-induced chronic postsurgical pain

Background

Vascular endothelial barrier disruption is pivotal in the development of acute and chronic pain. Here, we demonstrate a previously unidentified molecular mechanism in which activation of the peripheral Epac1/p-Cav-1 pathway accelerated the disruption of the vascular endothelial barrier, thereby promoting chronic postsurgical pain (CPSP).

Methods

We established a rat model of CPSP induced by skin/muscle incision and retraction (SMIR). Pain behaviors were assessed by the mechanical withdrawal threshold (MWT) at different times. Local muscle tissues around the incision were isolated to detect the vascular permeability and the expression of Epac1 and Cav-1. They were assessed by western blot and immunofluorescence staining.

Results

SMIR increased vascular endothelial permeability and the number of macrophages and endothelial cells in the muscle tissues around the incision. The peripheral upregulation of Epac1 was macrophage-derived, whereas that of p-Cav-1 was both macrophage and endothelial cell-derived in the SMIR model. Moreover, the Epac1 agonist 8-pCPT could induce mechanical sensitivity, increase the expression of p-Cav-1, and disrupt vascular endothelial barrier in normal rats. The Epac1 inhibitor CE3F4 attenuated established SMIR-induced mechanical hyperalgesia, the upregulation of p-Cav-1 and vascular endothelial barrier. Finally, we showed that intrathecal injection of Cav-1siRNA relieved SMIR-induced mechanical allodynia, but had no effects of the expression of Epac1.

Conclusions

Collectively, these results revealed a molecular mechanism for modulating CPSP through the peripheral Epac1/Cav-1 pathway. Importantly, targeting Epac1/Cav-1 signaling might be a potential treatment for CPSP.

Pro-inflammatory cytokines and leukocyte integrins associated with chronic neuropathic pain in traumatic and inflammatory neuropathies: Initial observations and hypotheses

Leukocyte infiltration and persistence within peripheral nerves have been implicated in chronic nociception pathogenesis in murine peripheral neuropathy models. Endoneurial cytokine and chemokine expression contribute to leukocyte infiltration and maintenance of a pro-inflammatory state that delays peripheral nerve recovery and promotes chronic pain behaviors in these mice. However, there has been a failure to translate murine model data into safe and effective treatments for chronic neuropathic pain in peripheral neuropathy patients, or develop reliable biomarkers that may help diagnose or determine treatment responses in affected patients. Initial work showed that persistent sciatic nerve CD11b+ CD45+ leukocyte infiltration was associated with disease severity in three mouse models of inflammatory and traumatic peripheral neuropathies, implying a direct contributing role in disease pathogenesis. In support of this, CD11b+ leukocytes were also seen in the sural nerve biopsies of chronic neuropathic pain patients with three different peripheral neuropathies. Systemic CD11b antagonism using a validated function-neutralizing monoclonal antibody effectively treated chronic nociception following unilateral sciatic nerve crush injury (a representative traumatic neuropathy model associated with axonal degeneration and increased blood-nerve barrier permeability) and does not cause drug addiction behaviors in adult mice. These data suggest that CD11b could be an effective molecular target for chronic neuropathic pain treatment in inflammatory and traumatic peripheral neuropathies. Despite known murine peripheral neuropathy model limitations, our initial work suggests that early expression of pro-inflammatory cytokines, such as tissue inhibitor of metalloproteinases-1 may predict subsequent chronic nociception development following unilateral sciatic nerve crush injury. Studies aligning animal model investigation with observational data from well-characterized human peripheral neuropathies, including transcriptomics and proteomics, as well as animal model studies using a human clinical trial design should foster the identification of clinically relevant biomarkers and effective targeted treatments with limited addiction potential for chronic neuropathic pain in peripheral neuropathy patients.

The macrophage: a key player in the pathophysiology of peripheral neuropathies

Macrophages are present in all mammalian tissues and coexist with various cell types in order to respond to different environmental cues. However, the role of these cells has been underestimated in the context of peripheral nerve damage. More importantly, macrophages display divergent characteristics, associated with their origin, and in response to the modulatory effects of their microenvironment. Interestingly, the advent of new techniques such as fate mapping and single-cell transcriptomics and their synergistic use has helped characterize in detail the origin and fate of tissue-resident macrophages in the peripheral nervous system (PNS). Furthermore, these techniques have allowed a better understanding of their functions from simple homeostatic supervisors to chief regulators in peripheral neuropathies. In this review, we summarize the latest knowledge about macrophage ontogeny, function and tissue identity, with a particular focus on PNS-associated cells, as well as their interaction with reactive oxygen species under physiological and pathological conditions. We then revisit the process of Wallerian degeneration, describing the events accompanying axon degeneration, Schwann cell activation and most importantly, macrophage recruitment to the site of injury. Finally, we review these processes in light of internal and external insults to peripheral nerves leading to peripheral neuropathies, the involvement of macrophages and the potential benefit of the targeting of specific macrophages for the alleviation of functional defects in the PNS.

Impact of Neurofascin on Chronic Inflammatory Demyelinating Polyneuropathy via Changing the Node of Ranvier Function: A Review

The effective conduction of action potential in the peripheral nervous system depends on the structural and functional integrity of the node of Ranvier and paranode. Neurofascin (NF) plays an important role in the conduction of action potential in a saltatory manner. Two subtypes of NF, NF186, and NF155, are involved in the structure of the node of Ranvier. In patients with chronic inflammatory demyelinating polyneuropathy (CIDP), anti-NF antibodies are produced when immunomodulatory dysfunction occurs, which interferes with the conduction of action potential and is considered the main pathogenic factor of CIDP. In this study, we describe the assembling mechanism and anatomical structure of the node of Ranvier and the necessary cell adhesion molecules for its physiological function. The main points of this study are that we summarized the recent studies on the role of anti-NF antibodies in the changes in the node of Ranvier function and its impact on clinical manifestations and analyzed the possible mechanisms underlying the pathogenesis of CIDP.

State of the Art and Advances in Peripheral Nerve Surgery

This review is intended to describe and actualize the basic knowledge of the three basic entities that affect the peripheral nerve system and can be treated by surgery: nerve trauma, chronic nerve compressions, and tumors.Regarding trauma, emphasis is given on the timing of surgery, given the fact that the moment in which the surgery is performed and the employed microsurgical reconstruction technique are the most important factors in the final result. Open lesions with associated nerve injury should be managed with an early exploration carried out before 7 days. Closed injuries are usually deferred, with few exceptions, from 3 to 6 months after the trauma.In turn, chronic compressions require an appropriate clinical, neurophysiological, and imaging diagnosis. Isolated sensory symptoms can be treated actively though without surgery: motor signs like atrophy should be regarded as a sign for immediate surgery, as a deferred treatment might cause an irreversible nerve and muscular damage. Endoscopic approaches are a valuable tool for treatment in selected neuropathies.Finally, nerve tumors demand a thorough preoperative evaluation, as benign tumors are treated in a very different way when compared to malignant lesions. Benign tumors can usually be safely and completely resected without sacrificing the nerve of origin. When malignancy is confirmed, extensive resection to optimize patient survival is the main objective, potentially at the expense of neurological function. This may then be followed by adjuvant radiation and/or chemotherapy, depending on the nature of the tumor and the completeness of resection attained. The role of nerve biopsy remains controversial, and several modern diagnostic techniques might be helpful.

Neurologic complications of acute myeloid leukemia. Diagnostic approach and therapeutic modalities

Acute myeloid leukemia (AML) comprises a heterogeneous group of aggressive blood malignancies that arise from clonal expansion of malignant hematopoietic precursor cells in the bone marrow. Neurologic manifestations of these malignancies are manifolds. AML is the most common form of acute leukemia in adults and this review describes the neurologic complications in this age group. Neurologic symptoms and signs may develop in AML either from a direct neoplastic involvement of the central or the peripheral nervous system or as an indirect effect of the disease process. Direct involvement of the nervous system includes invasion of the central or the peripheral nervous system (parenchymal and leptomeningeal dissemination, myeloid sarcoma, neuroleukemiosis). Thrombotic and hemorrhagic events are common manifestations of indirect involvement of the nervous system and they are the outcome of hyperleukocytosis, thrombocytopenia and coagulopathy. Many neurologic complications are iatrogenic and include diverse categories such as lumbar puncture and intrathecal or systemic chemotherapy and targeted therapies, radiotherapy and allogeneic stem cell transplantation. Most neurologic manifestations require urgent treatment and confer a poor prognosis. This review describes the neurologic complications of acute myeloid malignancies in the era of contemporary treatment. Those manifestations require expert consideration of their origin as they are being identified with increasing frequency as patients survive longer.

Effects of early rehabilitation nursing intervention on nerve function and daily living in patients with stroke hemiplegia

OBJECTIVE

To explore the effects of early rehabilitation nursing on the rehabilitation of stroke hemiplegia patients.

METHODS

A total of 80 patients with stroke admitted to Ningxiang People's Hospital were selected as the research subjects for analysis. Among them, 40 patients received early rehabilitation nursing intervention after admission and were enrolled in the observation group. The other 40 patients received only general nursing intervention who were enrolled in the control group. National Institutes of Health Stroke Scale (NIHSS) and Ruminative responses scale (RRS) were used to evaluate the nerve function of the two groups of patients before and after treatment. Fugl-Meyer motor function assessment (FMA) was applied to evaluate their athletic ability, and activity of daily living (ADL) score and Barthel index were utilized to evaluate their living ability. The adverse reactions and nursing satisfaction were compared between the two groups.

RESULTS

After treatment, NIHSS score and RRS score in the observation group were lower than those in the control group (P<0.05). FMA score, ADL score and Barthel index were higher in the observation group than those of the control group (P<0.05). After treatment, NIHSS score and RRS score were both lower than those before treatment (P<0.05), while FMA score, ADL score and Barthel index were higher than those before treatment (P<0.05). There was no difference in the incidence of adverse reactions between the two groups (P>0.05). The nursing satisfaction of the observation group was higher than that of the control group (P<0.05).

CONCLUSION

Early rehabilitation nursing can effectively improve the nerve function, athletic ability and living ability of stroke hemiplegia patients, which is worth popularizing in clinic.

Peripheral nervous system manifestations of Shiga toxin-producing E. coli-induced haemolytic uremic syndrome in children

Background

The Neurological involvement is the most common extra-renal complication of Shiga toxin-producing E. coli-hemolytic uremic syndrome (HUS) or typical HUS. On brain magnetic resonance examination, main neurological signs encompass acute lesions of the basal ganglia and the white matter, which could usually regress after Eculizumab infusion. In contrast, peripheral nervous system (PNS) manifestations in typical HUS are very rare and, when occurring, they require a careful management of neurological sequelae and an intensive multidisciplinary neuro-rehabilitation program.

Case presentation

Here, we present two pediatric cases of severe and complicated typical HUS with PNS manifestations who required therapeutic treatment and an intensive multidisciplinary neuro-rehabilitation program.

In both cases, PNS manifestations were followed by the recovery from typical HUS-related severe central neurological damage and manifested mainly with marked bilateral motor deficit and hyporeflexia/areflexia in the lower limbs. The peripheral polyneuropathy was treated with immunosuppressive therapy (methylprednisolone boluses, i.v. immunoglobulins, plasma exchange), followed by a prolonged intensive neuro-rehabilitation program. After 8 months of rehabilitation, both patients gained complete functional recovery.

Conclusions

PNS manifestations during typical HUS are a rare event and potentially leading to severe disability. A timely clinical assessment is mandatory to set up a prompt therapeutic and rehabilitation program and to obtain a complete clinical and functional recovery.

Phase 0 Clinical Trial of Everolimus in Patients with Vestibular Schwannoma or Meningioma

Inhibition of mTORC1 signaling has been shown to diminish growth of meningiomas and schwannomas in preclinical studies, and clinical data suggest that everolimus, an orally administered mTORC1 inhibitor, may slow tumor progression in a subset of patients with neurofibromatosis type 2 (NF2) with vestibular schwannoma. To assess the pharmacokinetics, pharmacodynamics, and potential mechanisms of treatment resistance, we performed a presurgical (phase 0) clinical trial of everolimus in patients undergoing elective surgery for vestibular schwannoma or meningiomas. Eligible patients with meningioma or vestibular schwannoma requiring tumor resection enrolled on study received everolimus 10 mg daily for 10 days immediately prior to surgery. Everolimus blood levels were determined immediately before and after surgery. Tumor samples were collected intraoperatively. Ten patients completed protocol therapy. Median pre- and postoperative blood levels of everolimus were found to be in a high therapeutic range (17.4 ng/mL and 9.4 ng/mL, respectively). Median tumor tissue drug concentration determined by mass spectrometry was 24.3 pg/mg (range, 9.2-169.2). We observed only partial inhibition of phospho-S6 in the treated tumors, indicating incomplete target inhibition compared with control tissues from untreated patients (P = 0.025). Everolimus led to incomplete inhibition of mTORC1 and downstream signaling. These data may explain the limited antitumor effect of everolimus observed in clinical studies for patients with NF2 and will inform the design of future preclinical and clinical studies targeting mTORC1 in meningiomas and schwannomas.

Brain Barriers and brain fluids research in 2020 and the fluids and barriers of the CNS thematic series on advances in in vitro modeling of the blood-brain barrier and neurovascular unit

This editorial discusses advances in brain barrier and brain fluid research in 2020. Topics include: the cerebral endothelium and the neurovascular unit; the choroid plexus; the meninges; cerebrospinal fluid and the glymphatic system; disease states impacting the brain barriers and brain fluids; drug delivery to the brain. This editorial also highlights the recently completed Fluids Barriers CNS thematic series entitled, Advances in in vitro modeling of the bloodbrain barrier and neurovascular unit. Such in vitro modeling is progressing rapidly.

Transcriptional profiling of mouse peripheral nerves to the single-cell level to build a sciatic nerve ATlas (SNAT)

Peripheral nerves are organ-like structures containing diverse cell types to optimize function. This interactive assembly includes mostly axon-associated Schwann cells, but also endothelial cells of supporting blood vessels, immune system-associated cells, barrier-forming cells of the perineurium surrounding and protecting nerve fascicles, and connective tissue-resident cells within the intra-fascicular endoneurium and inter-fascicular epineurium. We have established transcriptional profiles of mouse sciatic nerve-inhabitant cells to foster the fundamental understanding of peripheral nerves. To achieve this goal, we have combined bulk RNA sequencing of developing sciatic nerves up to the adult with focused bulk and single-cell RNA sequencing of Schwann cells throughout postnatal development, extended by single-cell transcriptome analysis of the full sciatic nerve both perinatally and in the adult. The results were merged in the transcriptome resource Sciatic Nerve ATlas (SNAT: https://www.snat.ethz.ch). We anticipate that insights gained from our multi-layered analysis will serve as valuable interactive reference point to guide future studies.

Severe acute respiratory syndrome coronavirus 2 infection reaches the human nervous system: How?

Without protective and/or therapeutic agents the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection known as coronavirus disease 2019 is quickly spreading worldwide. It has surprising transmissibility potential, since it could infect all ages, gender, and human sectors. It attacks respiratory, gastrointestinal, urinary, hepatic, and endovascular systems and can reach the peripheral nervous system (PNS) and central nervous system (CNS) through known and unknown mechanisms. The reports on the neurological manifestations and complications of the SARS-CoV-2 infection are increasing exponentially. Herein, we enumerate seven candidate routes, which the mature or immature SARS-CoV-2 components could use to reach the CNS and PNS, utilizing the within-body cross talk between organs. The majority of SARS-CoV-2-infected patients suffer from some neurological manifestations (e.g., confusion, anosmia, and ageusia). It seems that although the mature virus did not reach the CNS or PNS of the majority of patients, its unassembled components and/or the accompanying immune-mediated responses may be responsible for the observed neurological symptoms. The viral particles and/or its components have been specifically documented in endothelial cells of lung, kidney, skin, and CNS. This means that the blood-endothelial barrier may be considered as the main route for SARS-CoV-2 entry into the nervous system, with the barrier disruption being more logical than barrier permeability, as evidenced by postmortem analyses.

Rapid and efficient immunomagnetic isolation of endothelial cells from human peripheral nerves

Endothelial cells (ECs) have gained an increased scientific focus since they were reported to provide guidance for Schwann cells and subsequently following axons after nerve injuries. However, previous protocols for the isolation of nerve-derived ECs from human nerves are ineffective regarding time and yield. Therefore, we established a novel and efficient protocol for the isolation of ECs from human peripheral nerves by means of immunomagnetic CD31-antibody conjugated Dynabeads and assessed the purity of the isolated cells. The easy-to-follow and time-effective isolation method allows the isolation of > 95% pure ECs. The isolated ECs were shown to express highly specific EC marker proteins and revealed functional properties by formation of CD31 and VE-cadherin positive adherens junctions, as well as ZO-1 positive tight-junctions. Moreover, the formation of capillary EC-tubes was observed in-vitro. The novel protocol for the isolation of human nerve-derived ECs allows and simplifies the usage of ECs in research of the human blood-nerve-barrier and peripheral nerve regeneration. Additionally, a potential experimental application of patient-derived nerve ECs in the in-vitro vascularization of artificial nerve grafts is feasible.

Hedging against Neuropathic Pain: Role of Hedgehog Signaling in Pathological Nerve Healing

The peripheral nervous system has important regenerative capacities that regulate and restore peripheral nerve homeostasis. Following peripheral nerve injury, the nerve undergoes a highly regulated degeneration and regeneration process called Wallerian degeneration, where numerous cell populations interact to allow proper nerve healing. Recent studies have evidenced the prominent role of morphogenetic Hedgehog signaling pathway and its main effectors, Sonic Hedgehog (SHH) and Desert Hedgehog (DHH) in the regenerative drive following nerve injury. Furthermore, dysfunctional regeneration and/or dysfunctional Hedgehog signaling participate in the development of chronic neuropathic pain that sometimes accompanies nerve healing in the clinical context. Understanding the implications of this key signaling pathway could provide exciting new perspectives for future research on peripheral nerve healing.

Recent Advances in Extracellular Vesicles as Drug Delivery Systems and Their Potential in Precision Medicine

Extracellular vesicles (EVs) are membrane-bilayered nanoparticles released by most cell types. Recently, an enormous number of studies have been published on the potential of EVs as carriers of therapeutic agents. In contrast to systems such as liposomes, EVs exhibit less immunogenicity and higher engineering potential. Here, we review the most relevant publications addressing the potential and use of EVs as a drug delivery system (DDS). The information is divided based on the key steps for designing an EV-mediated delivery strategy. We discuss possible sources and isolation methods of EVs. We address the administration routes that have been tested in vivo and the tissue distribution observed. We describe the current knowledge on EV clearance, a significant challenge towards enhancing bioavailability. Also, EV-engineering approaches are described as alternatives to improve tissue and cell-specificity. Finally, a summary of the ongoing clinical trials is performed. Although the application of EVs in the clinical practice is still at an early stage, a high number of studies in animals support their potential as DDS. Thus, better treatment options could be designed to precisely increase target specificity and therapeutic efficacy while reducing off-target effects and toxicity according to the individual requirements of each patient.