Myelinated Axons Research Articles

Ladder-based resistance training with the progression of training load altered the tibial nerve ultrastructure and muscle fiber area without altering the morphology of the postsynaptic compartment.

Scientific evidence regarding the effect of different ladder-based resistance training (LRT) protocols on the morphology of the neuromuscular system is scarce. Therefore, the present study aimed to compare the morphological response induced by different LRT protocols in the ultrastructure of the tibial nerve and morphology of the motor endplate and muscle fibers of the soleus and plantaris muscles of young adult Wistar rats. Rats were divided into groups: sedentary control (control, n = 9), a predetermined number of climbs and progressive submaximal intensity (fixed, n = 9), high-intensity and high-volume pyramidal system with a predetermined number of climbs (Pyramid, n = 9) and lrt with a high-intensity pyramidal system to exhaustion (failure, n = 9). myelinated fibers and myelin sheath thickness were statistically larger in pyramid, fixed, and failure. myelinated axons were statistically larger in pyramid than in control. schwann cell nuclei were statistically larger in pyramid, fixed, and failure. microtubules and neurofilaments were greater in pyramid than in control. morphological analysis of the postsynaptic component of the plantar and soleus muscles did not indicate any significant difference. for plantaris, the type i myofibers were statistically larger in the pyramid and fixed compared to control. the pyramid, fixed, and failure groups for type ii myofibers had larger csa than control. for soleus, the type i myofibers were statistically larger in the pyramid than in control. pyramid and fixed had larger csa for type ii myofibers than control and failure. the pyramid and fixed groups showed greater mass progression delta than the failure. We concluded that the LRT protocols with greater volume and progression of accumulated mass elicit more significant changes in the ultrastructure of the tibial nerve and muscle hypertrophy without endplate changes.

Nerve guide conduits promote nerve regeneration under a combination of electrical stimulation and RSCs combined with stem cell differentiation.

Nerve guide conduits (NGCs) offer a promising alternative to traditional tools for regenerating peripheral nerves. The efficacy of nerve regeneration and functional recovery is heavily dependent on the electrical, chemical, and physical properties of NGCs. A bionic melt electrowriting (MEW) NGC loaded with placental derived mesenchymal stem cells (PDMSCs) has been developed. Our study introduces a novel approach by utilizing Schwann cells induced from placental mesenchymal stem cells (PDMSCs), showcasing their potential in enhancing nerve regeneration when integrated with conductive nerve guidance conduits. Schwann cells (SCs) are crucial for nerve regeneration, and while various stem cells, including bone marrow stromal cells (BMSCs), have been investigated as sources of SCs for NGC loading, they are often limited by ethical concerns and restricted availability. PDMSCs, however, offer the advantages of widespread sourcing and unique ability to differentiate into SCs, making them an attractive alternative for NGC applications. This NGC utilizes an electrostatic direct writing technique employing polycaprolactone (PCL) for the sheath and a crimped fiber scaffold made of polypyrrole (PPY) incorporated with PDMSCs for its internal structure. The bionic PC-NGC loaded with PDMSCs exhibits favorable characteristics including permeability, mechanical stability, and electrical conductivity. The PPY component effectively transmits physiological nerve signals, thereby promoting nerve regeneration, while the PDMSCs differentiate into Schwann cells, creating a conducive environment for nerve regeneration. This research innovatively combines PDMSCs, known for their wide availability and SC differentiation potential, with a bionic NGC to enhance the treatment of peripheral nerve injuries (PNIs). In vitro evaluations have confirmed the excellent biocompatibility of the materials used. Animal experiments using a rat model with sciatic nerve injury demonstrated that the PC-NGC significently facilitated peripheral nerve regeneration. This was evidenced by improvements in axonal myelination, increased muscle mass, enhanced sciatic nerve function index, and positive electrophysiological findings. These outcomes are comparable to those achieved through autologous transplantation. Characterized by its layered oriented fibers, the bionic PC-NGC integrates multi-scale and multifunctional biomaterials with PDMSCs to effectively address peripheral nerve injuries (PNIs). The use of this printed NGC stimulates neuronal cell growth, thereby accelerating nerve regeneration. This innovative approach in tissue engineering presents a promising clinical treatment strategy for PNIs.

Theta burst stimulation promotes nestin expression in experimental autoimmune encephalomyelitis

Background/Aim. Multiple sclerosis (MS) is an immune-mediated disease of the nervous system in which the myelin sheath is destroyed during the process of neurodegeneration. Experimental autoimmune encephalomyelitis (EAE) is an animal model of MS in which preservation of myelin and remyelination of axons can improve neuron survival. The aim of the study was to evaluate the activation capacity of neuronal tissue by autoimmune inflammation and treatment with intermittent (i) theta burst stimulation (TBS)- iTBS or continuous TBS (cTBS) based on the expression profiles of nestin in astrocytes, oligodendrocytes, and neurons. Methods. Two forms of TBS - iTBS and cTBS - were used to extend the period during which axons can be remyelinated. It was investigated how iTBS or cTBS protocols affect the expression profiles of nestin with glial fibrillary acidic protein, myelin basic protein (MBP), and neuronal nuclear protein in rat spinal cord. Changes at the molecular level were monitored using the immunofluorescence method. Results. The obtained results showed that both protocols (iTBS and cTBS) increased the expression of nestin and MBP and reduced astrogliosis in the spinal cord of EAE rats. Conclusion. The therapeutic potential of TBS in EAE contributes to the improvement of the intrinsic ability to recover from spinal cord injury.

Mesenchymal Stem Cell-Derived Exosomes Promote Recovery of The Facial Nerve Injury through Regulating Macrophage M1 and M2 Polarization by Targeting the P38 MAPK/NF-Κb Pathway.

Facial nerve (FN) injury seriously affects human social viability and causes a heavy economic and social burden. Although mesenchymal stem cell-derived exosomes (MSC-Exos) promise therapeutic benefits for injury repair, there has been no evaluation of the impact of MSC-Exos administration on FN repair. Herein, we explore the function of MSC-Exos in the immunomodulation of macrophages and their effects in repairing FN injury. An ultracentrifugation technique was used to separate exosomes from the MSC supernatant. Administrating MSC-Exos to SD rats via local injection after FN injury promoted axon regeneration and myelination and alleviated local and systemic inflammation. MSC-Exos facilitated M2 polarization and reduced the M1-M2 polarization ratio. miRNA sequencing of MSC-Exos and previous literature showed that the MAPK/NF-κb pathway was a downstream target of macrophage polarization. We confirmed this hypothesis both in vivo and in vitro. Our findings show that MSC-Exos are a potential candidate for treating FN injury because they may have superior benefits for FN injury recovery and can decrease inflammation by controlling the heterogeneity of macrophages, which is regulated by the p38 MAPK/NF-κb pathway.

Oligodendrocyte-derived LGI3 and its receptor ADAM23 organize juxtaparanodal Kv1 channel clustering for short-term synaptic plasticity

Neurodevelopmental disorders, such as intellectual disability (ID), epilepsy, and autism, involve altered synaptic transmission and plasticity. Functional characterization of their associated genes is vital for understanding physio-pathological brain functions. LGI3 is a recently recognized ID-associated gene encoding a secretory protein related to an epilepsy-gene product, LGI1. Here, we find that LGI3 is uniquely secreted from oligodendrocytes in the brain and enriched at juxtaparanodes of myelinated axons, forming nanoscale subclusters. Proteomic analysis using epitope-tagged Lgi3 knockin mice shows that LGI3 uses ADAM23 as a receptor and selectively co-assembles with Kv1 channels. A lack of Lgi3 in mice disrupts juxtaparanodal clustering of ADAM23 and Kv1 channels and suppresses Kv1-channel-mediated short-term synaptic plasticity. Collectively, this study identifies an extracellular organizer of juxtaparanodal Kv1 channel clustering for finely tuned synaptic transmission. Given the defective secretion of the LGI3 missense variant, we propose a molecular pathway, the juxtaparanodal LGI3-ADAM23-Kv1 channel, for understanding neurodevelopmental disorders.

Clinical concentration of sevoflurane had no short-term effect on the myelin sheath in prefrontal cortex of aged marmosets.

The fragile brain includes both the developing brain in childhood and the deteriorating brain in elderly. While the effects of general anesthesia on the myelin sheath of developing brain have been well-documented, limited research has explored its impact on degenerating brain in elderly individuals. In our study, aged marmosets in control group were only anesthetized with 6-8% sevoflurane and 100% oxygen (2 L/min) for 1-2 min for anesthesia induction. In addition to anesthesia induction, the anesthesia group was exposed to a clinical concentration of sevoflurane (1.5-2%) for 6 h to maintain anesthesia. After anesthesia, scanning electron microscopy (SEM) and artificial intelligence-assisted image analysis were utilized to observe the effects of general anesthesia on the myelin sheath in prefrontal cortex (PFC) of aged marmosets. Compared with the control group, our findings revealed no evidence that 6 h of sevoflurane general anesthesia altered the thickness of myelin sheath, the diameter of myelinated axons, and the g-ratio in prefrontal cortex of aged marmosets. Clinical concentration of sevoflurane may have no short-term effect on the myelin sheath in prefrontal cortex of aged marmosets.

Preclinical Efficacy of Peripheral Nerve Regeneration by Schwann Cell-like Cells Differentiated from Human Tonsil-Derived Mesenchymal Stem Cells in C22 Mice.

Charcot-Marie-Tooth disease (CMT) is a hereditary disease with heterogeneous phenotypes and genetic causes. CMT type 1A (CMT1A) is a type of disease affecting the peripheral nerves and is caused by the duplication of the peripheral myelin protein 22 (PMP22) gene. Human tonsil-derived mesenchymal stem cells (TMSCs) are useful for stem cell therapy in various diseases and can be differentiated into Schwann cell-like cells (TMSC-SCs). We investigated the potential of TMSC-SCs called neuronal regeneration-promoting cells (NRPCs) for peripheral nerve and muscle regeneration in C22 mice, a model for CMT1A. We transplanted NRPCs manufactured in a good manufacturing practice facility into the bilateral thigh muscles of C22 mice and performed behavior and nerve conduction tests and histological and ultrastructural analyses. Significantly, the motor function was much improved, the ratio of myelinated axons was increased, and the G-ratio was reduced by the transplantation of NRPCs. The sciatic nerve and gastrocnemius muscle regeneration of C22 mice following the transplantation of NRPCs downregulated PMP22 overexpression, which was observed in a dose-dependent manner. These results suggest that NRPCs are feasible for clinical research for the treatment of CMT1A patients. Research applying NRPCs to other peripheral nerve diseases is also needed.

An adeno-associated viral labeling approach to visualize the meso- and microanatomy of mechanosensory afferents and autonomic innervation of the rat urinary bladder.

The urinary bladder is supplied by a rich network of sensory and autonomic axons, commonly visualized by immunolabeling for neural markers. This approach demonstrates overall network patterning but is less suited to understanding the structure of individual motor and sensory terminals within these complex plexuses. There is a further limitation visualizing the lightly myelinated (A-delta) class of sensory axons that provides the primary mechanosensory drive for initiation of voiding. Whereas most unmyelinated sensory axons can be revealed by immunolabeling for specific neuropeptides, to date no unique neural marker has been identified to immunohistochemically label myelinated visceral afferents. We aimed to establish a non-surgical method to visualize and map myelinated afferents in the bladder in rats. We found that in rats, the adeno-associated virus (AAV), AAV-PHP.S, which shows a high tropism for the peripheral nervous system, primarily transduced myelinated dorsal root ganglion neurons, enabling us to identify the structure and regional distribution of myelinated (mechanosensory) axon endings within the muscle and lamina propria of the bladder. We further identified the projection of myelinated afferents within the pelvic nerve and lumbosacral spinal cord. A minority of noradrenergic and cholinergic neurons in pelvic ganglia were transduced, enabling visualization and regional mapping of both autonomic and sensory axon endings within the bladder. Our study identified a sparse labeling approach for investigating myelinated sensory and autonomic axon endings within the bladder and provides new insights into the nerve-bladder interface.

Insights and improvements in correspondence between axonal volume fraction measured with diffusion-weighted MRI and electron microscopy.

Biophysical diffusion-weighted imaging (DWI) models are increasingly used in neuroscience to estimate the axonal water fraction ( ), which in turn is key for noninvasive estimation of the axonal volume fraction ( ). These models require thorough validation by comparison with a reference method, for example, electron microscopy (EM). While EM studies often neglect the unmyelinated axons and solely report the fraction of myelinated axons, in DWI both myelinated and unmyelinated axons contribute to the DWI signal. However, DWI models often include simplifications, for example, the neglect of differences in the compartmental relaxation times or fixed diffusivities, which in turn might affect the estimation of . We investigate whether linear calibration parameters (scaling and offset) can improve the comparability between EM- and DWI-based metrics of . To this end, we (a) used six DWI models based on the so-called standard model of white matter (WM), including two models with fixed compartmental diffusivities (e.g., neurite orientation dispersion and density imaging, NODDI) and four models that fitted the compartmental diffusivities (e.g., white matter tract integrity, WMTI), and (b) used a multimodal data set including ex vivo diffusion DWI and EM data in mice with a broad dynamic range of fibre volume metrics. We demonstrated that the offset is associated with the volume fraction of unmyelinated axons and the scaling factor is associated with different compartmental and can substantially enhance the comparability between EM- and DWI-based metrics of . We found that DWI models that fitted compartmental diffusivities provided the most accurate estimates of the EM-based . Finally, we introduced a more efficient hybrid calibration approach, where only the offset is estimated but the scaling is fixed to a theoretically predicted value. Using this approach, a similar one-to-one correspondence to EM was achieved for WMTI. The method presented can pave the way for use of validated DWI-based models in clinical research and neuroscience.

Filtering property of myelinated internode can change neural information representability and might trigger a compensatory action during demyelination

In this paper, for the first time, we showed that an Internode Segment (INS) of a myelinated axon acts as a lowpass filter, and its filter characteristics depend on the number of myelin turns. Consequently, we showed how the representability of a neural signal could be altered with myelin loss in pathological conditions involving demyelinating diseases. Contrary to the traditionally held viewpoint that myelin geometry of an INS is optimised for maximising Conduction Velocity (CV) of Action Potential (AP), our theory provides an alternative viewpoint that myelin geometry of an INS is optimised for maximizing representability of the stimuli a fibre is meant to carry. Subsequently, we show that this new viewpoint could explain hitherto unexplained experimentally observed phenomena such as, shortening of INS length during demyelination and remyelination, and non-uniform distribution of INS in the central nervous system fibres and associated changes in diameter of nodes of ranvier along an axon. Finally, our theory indicates that a compensatory action could take place during demyelination up to a certain number of loss of myelin turns to preserve the neural signal representability by simultaneous linear scaling of the length of an INS and the inner radius of the fibre.

Severe central nervous system demyelination in Sanfilippo disease.

Chronic progressive neuroinflammation is a hallmark of neurological lysosomal storage diseases, including mucopolysaccharidosis III (MPS III or Sanfilippo disease). Since neuroinflammation is linked to white matter tract pathology, we analyzed axonal myelination and white matter density in the mouse model of MPS IIIC HgsnatP304L and post-mortem brain samples of MPS III patients. Brain and spinal cord tissues of human MPS III patients, 6-month-old HgsnatP304L mice and age- and sex-matching wild type mice were analyzed by immunofluorescence to assess levels of myelin-associated proteins, primary and secondary storage materials, and levels of microgliosis. Corpus callosum (CC) region was studied by transmission electron microscopy to analyze axon myelination and morphology of oligodendrocytes and microglia. Mouse brains were analyzed ex vivo by high-filed MRI using Diffusion Basis Spectrum Imaging in Python-Diffusion tensor imaging algorithms. Analyses of CC and spinal cord tissues by immunohistochemistry revealed substantially reduced levels of myelin-associated proteins including Myelin Basic Protein, Myelin Associated Glycoprotein, and Myelin Oligodendrocyte Glycoprotein. Furthermore, ultrastructural analyses revealed disruption of myelin sheath organization and reduced myelin thickness in the brains of MPS IIIC mice and human MPS IIIC patients compared to healthy controls. Oligodendrocytes (OLs) in the CC of MPS IIIC mice were scarce, while examination of the remaining cells revealed numerous enlarged lysosomes containing heparan sulfate, GM3 ganglioside or "zebra bodies" consistent with accumulation of lipids and myelin fragments. In addition, OLs contained swollen mitochondria with largely dissolved cristae, resembling those previously identified in the dysfunctional neurons of MPS IIIC mice. Ex vivo Diffusion Basis Spectrum Imaging revealed compelling signs of demyelination (26% increase in radial diffusivity) and tissue loss (76% increase in hindered diffusivity) in CC of MPS IIIC mice. Our findings demonstrate an important role for white matter injury in the pathophysiology of MPS III. This study also defines specific parameters and brain regions for MRI analysis and suggests that it may become a crucial non-invasive method to evaluate disease progression and therapeutic response.

Nodopathy: clinic, diagnosis, treatment. Clinical description

AIM: Evaluation of the significance and possibilities of laboratory-instrumental diagnostic methods in establishing the diagnosis and selection of targeted therapy in patients with nodopathies.
 MATERIALS AND METHODS: System analysis of data from foreign and domestic literature with the presentation of a clinical case.
 RESULTS: Polyneuropathies are classified as demyelinating or axonal based on electrophysiological studies. However, in 2015, in addition to axonal and demyelinating neuropathies, it was proposed to distinguish a separate pathophysiological group — nodopathies. The pathogenesis of nodopathies may differ depending on the type of ion channels involved in the process, but always leads to a loss of excitability of the axon membrane; in the nodal region the membrane becomes inexcitable. Such neuropathies are characterized by transient conduction blocks followed by the development of axonal degeneration. Typical examples of nodopathies are acute motor axonal neuropathy, as well as multifocal motor neuropathy. Current pathophysiological understanding of specialized nodal regions (nodes of Ranvier) and associated axoglial proteins is growing. Hypotheses have been put forward about their role in the pathogenesis of immune-mediated attack on the peripheral myelinated axon. Recently, high titers of antibodies directed against a number of key adhesion molecules have been identified in both acute and chronic inflammatory neuropathies. These facts add to the differences in differential diagnosis between axonal and demyelinating peripheral neuropathies. New disease classification schemes based on seropositivity, improved electrophysiological and ultrasound classification, and identification of putative underlying pathological targets and mechanisms are being rapidly developed.
 CONCLUSION: Using our clinical example, we demonstrated the capabilities of laboratory and instrumental diagnostic methods in establishing a diagnosis in a patient with one of the forms of nodopathies — multifocal motor neuropathy.

Identifying glial cell‐surface proteins critical in normal brain aging

AbstractBackgroundGlial cells play a variety of supportive functions to facilitate effective neural communication, including maintaining an effective immune response, myelination of axons, and maintaining extracellular homeostasis. Glia also display age‐related transcriptomic and morphological alterations, and glial cell metabolism is altered in Alzheimer’s Disease (AD). Fully characterizing age‐related alterations to the cell‐surface proteosome of glial cells in both healthy and pathogenic forms of brain aging could provide further insight into how neuron‐glia interactions facilitate brain aging and identify novel biomarkers and treatment targets of AD.MethodWe performed tissue‐specific in‐situ cell surface proteomics on young (5‐day old) and aged (50‐day old) D. melanogaster utilizing the protocol developed by Li et al. (2020) with the Repo driver to target glial cells. From this, we identified 19 genes of interest with the most significant age‐related increase in protein expression and performed a broad genetic screen to identify how knockdown of genes upregulated with age in glial cells impacted fly lifespan. For this, we utilized the Repo‐GS‐UAS system to screen several transgenic D. melanogaster RNAi lines for the genes of interest, with 2‐3 RNAi lines per gene.ResultBased on a Gene Ontology (GO) analysis of the most upregulated candidate genes, we observed that most were associated with cell localization and transport. Additionally, from our preliminary screen, we have identified five top candidate genes of interest that, when knocked down, appear to increase average fly lifespan relative to the controls. Currently, we are in the process of validating the initial lifespan results, repeating lifespan screens of the top candidate genes in a new glial GS line and a glial Gal4 line.ConclusionWe have identified genes that appear to extend lifespan when knocked down and could serve as targets for further study. These results can provide a basis of understanding healthy brain aging and could serve as a basis of comparison to AD models.

APOE4 impairs myelination via cholesterol dysregulation in oligodendrocytes

AbstractBackgroundAPOE4 is the strongest genetic risk factor for late‐onset Alzheimer’s disease (AD), yet the cellular and molecular mechanisms by which APOE4 contributes to AD risk remain largely unknownMethodWe performed single‐nuclear RNAsequencing from the prefrontal cortex (Brodmann’s Area 10) of thirty‐two individuals, 12 APOE3/3 and 12 APOE3/4 carriers each, and one subgroup with 8 APOE4/4 carriers, and validated hypotheses using mouse models and patient‐derived iPSC lines.ResultDifferential expression and pathway analysis revealed that APOE4 is strongly associated with dysregulation of cholesterol homeostasis across multiple cell types, with oligodendrocytes being the most impacted. Strikingly, in human and mouse brains, APOE4 oligodendrocytes contained aberrant intracellular accumulations of cholesterol, whereas in non‐carriers, cholesterol preferentially localized to the oligodendrocyte cell membrane along myelinated neuronal tracts. Mass‐spectrometry‐based lipidomic analysis further revealed that APOE4 oligodendrocytes and APOE4 human post‐mortem brain tissue had elevated levels of cholesteryl esters, associated with intracellular storage of cholesterol as lipid droplets. Cholesterol transport and bioavailability are rate‐limiting steps in axonal myelination. Consistent with this, we discovered both APOE4 human and mouse brains were hypomyelinated relative to non‐carriers. We found that a small molecule known to facilitate cholesterol transport reduced cholesterol accumulation in APOE4 oligodendrocytes, increased axonal myelination, and improved memory in APOE4 mice.ConclusionThese results provide a transcriptional atlas of cell‐type specific APOE4 effects in the human brain. Our results demonstrate that cholesterol homeostasis in oligodendrocytes is highly dysregulated in APOE4 oligodendrocytes and identify hypomyelination as a key APOE4‐associated phenotype. Collectively, these data establish a functional link between APOE4, cholesterol homeostasis, and myelination that presents new therapeutic opportunities for Alzheimer’s disease.

Interplay Between Genes from Peroxisome Biogenesis and Integrated Stress Response Pathways is Significantly Associated with Alzheimer’s Disease

AbstractBackgroundPeroxisomes are single‐membrane organelles involved among other things in ether‐phospholipids production that plays an important role in axon myelination in the central nervous system. Disruptions in cytosolic receptor PEX5L (involved in protein import into peroxisome matrix) may lead to peroxisome malfunctioning and disturbance of myelin homeostasis, which, in turn, may contribute to developing Alzheimer’s disease (AD). Experimental studies showed that peroxisome dysfunction is associated with activation of the integrative stress response (ISR). Recent studies provide evidence that the EIF2AK4 gene, a sensor of amino acid deprivation in ISR, is involved in the AD regulation. It is, however, unclear whether interplay between PEX5L and EIF2A4 is associated with AD.MethodTo test the association of the interplay between PEX5L and EIF2AK4 genes with the late‐onset‐AD, we analyzed the Health and Retirement Study (HRS) data using logistic regression model with the interaction term. Education, sex, smoking status, and first five principal components were included as observed covariates. The binary AD outcome was defined as “0” if AD onset was at any age, and as “1” if a person survived to age 85+ and did not get AD during the life. Linkage Disequilibrium test and SNP‐clumping procedure were used to reduce number of tests in SNPxSNP interaction analysis.ResultInteractions between SNPs in fifteen SNP pairs (one SNP in EIF2AK4 gene and another in PEX5L gene) were significantly associated with decreased odds of AD, with effect sizes (β coefficients before the interaction term) ranging between 0.62‐0.69, and p‐values between 1.64E‐04 ‐ 2.12E‐05, with Bonferroni correction threshold = 1.67E‐04. Six SNPs from PEX5L (rs1404271, rs11708154, rs59018122, rs9836757, rs76133869, rs6443674) and five SNPs from EIF2AK4 (rs3207297, rs2279579, rs2291625, rs12591842, rs117584784) participated in such interactions.ConclusionIn this study, interactions between SNPs in EIF2AK4 and PEX5L genes were significantly associated with lower odds of AD in HRS participants. Our findings support the idea that the interplay between genes involved in cellular stress response pathway and peroxisome biogenesis can play a protective role in AD. These results also demonstrate how the knowledge from experimental research can be translated to human applications population‐based studies of AD.

Potential of an artificial nerve graft containing Schwann cells for the treatment of a 20-mm nerve defect in rats.

In a previous study, the authors showed that the migration of Schwann cells (SCs) through end-to-side (ETS) neurorrhaphy promotes axonal regrowth within an acellular nerve graft. In the present study, the authors investigated whether a similar strategy using an artificial nerve (AN) would allow reconstruction of a long nerve gap (20 mm) in rats. Forty-eight 8- to 12-week-old Sprague Dawley rats were divided into control (AN) and experimental (SC migration-induced AN [SCiAN]) groups. Prior to the experiment, the ANs used in the SCiAN group were populated in vivo with SCs over a 4-week period by ETS neurorrhaphy onto the sciatic nerve. In both groups, a 20-mm sciatic nerve defect was reconstructed in an end-to-end fashion using 20-mm ANs. Sections from the nerve graft and distal sciatic nerve in both groups underwent assessments at 4 weeks for SC migration by immunohistochemical analysis and quantitative reverse transcription-polymerase chain reaction. At 16 weeks, axonal elongation was assessed by immunohistochemical analysis, histomorphometry, and electron microscopy. The number of myelinated fibers was counted, the g-ratio was calculated, and myelin sheath thickness and axon diameter were measured. Furthermore, functional recovery was evaluated at 16 weeks using the Von Frey filament test for sensory recovery and by calculating the muscle fiber area for motor recovery. The area occupied by SCs at 4 weeks and by axons at 16 weeks was significantly larger in the SCiAN group than in the AN group. Histomorphometric evaluation of the distal sciatic nerve revealed a significantly greater number of axons. At 16 weeks, plantar perception in the SCiAN group was significantly better, demonstrating improvement in sensory function. However, no tibialis anterior muscle motor improvement was observed in either group. The induction of SC migration into an AN by ETS neurorrhaphy is a useful technique for repairing 20-mm nerve defects in rats, with better nerve regeneration and sensory recovery. No motor recovery was observed in either group; however, motor recovery might require a longer period of time than the lifespan of the AN used in this study. Future studies should investigate whether structural and material reinforcement of the AN, to lower its decomposition rate, can improve functional recovery.

Alzheimer’s disease biomarker‐related phospho‐tau 181 signals localize to demyelinated axons of parvalbumin‐positive GABAergic interneurons in App knock‐in mouse

AbstractBackgroundTau proteins phosphorylated at Thr181 (p‐tau 181) in cerebrospinal fluid and blood is a sensitive biomarker for Alzheimer’s disease (AD). An increase in p‐tau 181 level well correlates with Aβ pathology and precedes neurofibrillary tangle formation in the early stage of AD, though the relationship between p‐tau 181 and Aβ‐mediated pathology is less well understood. We have recently reported that p‐tau 181 signals are detected in the axonal structures and represent axonal abnormality around Aβ plaques in the cortex of App knock‐in mouse model of Aβ amyloidosis (AppNLGF mice). However, from which neuronal subtype(s) these p‐tau 181‐positive axons are originated remains elusive. In this study, we aimed to determine which neuronal subtype(s) express p‐tau 181 in the axons.MethodTo investigate the localization of p‐tau 181 signals in the brains of aged (24‐month‐old) AppNLGF and wild‐type mice, we prepared frozen brain sections and co‐immunostained with antibodies against p‐tau 181 and myeline basic protein (MBP), the glutamatergic neuronal vesicle marker vesicular glutamate transporter 1 (VGLUT1), the GABAergic neuronal vesicle marker vesicular GABA transporter (VGAT), the inhibitory neuron marker parvalbumin, the cholinergic neuronal vesicle marker vesicular acetylcholine transporter (VAChT), or the noradrenergic neuronal vesicle marker norepinephrine transporter (NET).ResultHistochemical analyses revealed that p‐tau 181 signals were not overlapped with axons of unmyelinated cholinergic nor noradrenergic neurons, but well colocalized with myelinated axons of parvalbumin‐positive GABAergic interneurons, but not of glutamatergic neurons. Interestingly, the density of unmyelinated axons was significantly decreased in AppNLGF mice, while that of glutamatergic, GABAergic or p‐tau 181‐positive axons was less affected. Instead, myelin sheaths surrounding p‐tau 181‐positive axons were significantly reduced in AppNLGF mice.ConclusionThis study suggests that p‐tau 181 signals may represent axonal abnormality of parvalbumin‐positive GABAergic interneurons with disrupted myelin sheaths in brains of mouse model of Aβ pathology.

The role of myelin in neurodegeneration: implications for drug targets and neuroprotection strategies.

Myelination of axons in the central nervous system offers numerous advantages, including decreased energy expenditure for signal transmission and enhanced signal speed. The myelin sheaths surrounding an axon consist of a multi-layered membrane that is formed by oligodendrocytes, while specific glycoproteins and lipids play various roles in this formation process. As beneficial as myelin can be, its dysregulation and degeneration can prove detrimental. Inflammation, oxidative stress, and changes in cellular metabolism and the extracellular matrix can lead to demyelination of these axons. These factors are hallmark characteristics of certain demyelinating diseases including multiple sclerosis. The effects of demyelination are also implicated in primary degeneration in diseases such as glaucoma and Alzheimer's disease, as well as in processes of secondary degeneration. This reveals a relationship between myelin and secondary processes ofneurodegeneration, including resultant degeneration following traumatic injury and transsynaptic degeneration. The role of myelin in primary and secondary degeneration is also of interest in the exploration of strategies and targets for remyelination, including the use of anti-inflammatory molecules or nanoparticles to deliver drugs. Although the use of these methods in animal models of diseases have shown to be effective in promoting remyelination, very few clinical trials in patients have met primary end points. This may be due to shortcomings or considerations that are not met while designing a clinical trial that targets remyelination. Potential solutions include diversifying disease targets and requiring concomitant interventions to promote rehabilitation.

Evaluating purified exosome product and its role in neurologic and functional recovery following spinal cord injury in female rats

Introduction Exosomes represent extracellular vesicles that mediate intercellular interactions and have been extensively studied for their therapeutic potential. Purified exosomes product (PEP) from human plasma is reported to aid in tissue repair but has never been evaluated as a potential therapy for spinal cord injury (SCI). Objective We aim to investigate the effects of PEP on axon myelination, reduction in cavity size, and functional improvements in rats following SCI. Methods Following T9-T10 laminectomy and contusion to the spinal cord, female rats received either intrathecal (IT) PEP, IT ringer-lactate solution (RL), intravenous (IV) PEP, or IV RL one day post injury. Rats underwent behavioral assessments each week for 10 weeks following SCI. After 10 weeks, histological evaluations were performed to quantity axon myelination and cavity size. Results The IT PEP group had significantly (P ≤ 0.05) more myelinated axons 1000 μm rostral to the injury, at the epicenter, and 1000 μm caudal of the injury (34.3 ± 3.1, 27.7 ± 2.1, and 32.0 ± 1.7, respectively) compared to the IT RL group (27.3 ± 2.5, 17.3 ± 2.5, and 23.3 ± 2.5, respectively). In addition, IT PEP rats had significantly reduced cavity size at the injury epicenter compared to controls (28.31%±1.74% vs. 34.39%±3.78%, respectively). Lastly, functional improvements were observed and sustained beginning at the 31 days following injury. The IV PEP group did not show sustained functional improvement compared to the IV RL rats. Conclusion Our results suggest that IT PEP injection may yield beneficial effects following SCI. However, further studies are warranted to investigate the role of PEP following SCI and to optimize its potential for clinical translation.

Bond-selective full-field optical coherence tomography.

Optical coherence tomography (OCT) is a label-free, non-invasive 3D imaging tool widely used in both biological research and clinical diagnosis. Conventional OCT modalities can only visualize specimen tomography without chemical information. Here, we report a bond-selective full-field OCT (BS-FF-OCT), in which a pulsed mid-infrared laser is used to modulate the OCT signal through the photothermal effect, achieving label-free bond-selective 3D sectioned imaging of highly scattering samples. We first demonstrate BS-FF-OCT imaging of 1 µm PMMA beads embedded in agarose gel. Next, we show 3D hyperspectral imaging of up to 75 µm of polypropylene fiber mattress from a standard surgical mask. We then demonstrate BS-FF-OCT imaging on biological samples, including cancer cell spheroids and C. elegans. Using an alternative pulse timing configuration, we finally demonstrate the capability of BS-FF-OCT on imaging a highly scattering myelinated axons region in a mouse brain tissue slice.