Axonal Transection Research Articles

Development of a 3-dimensional organotypic model with characteristics of peripheral sensory nerves

We developed a rat dorsal root ganglion (DRG)-derived sensory nerve organotypic model by culturing DRG explants on an organoid culture device. With this method, a large number of organotypic cultures can be produced simultaneously with high reproducibility simply by seeding DRG explants derived from rat embryos. Unlike previous DRG explant models, this organotypic model consists of a ganglion and an axon bundle with myelinated A fibers, unmyelinated C fibers, and stereo-myelin-forming nodes of Ranvier. The model also exhibits Ca2+ signaling in cell bodies in response to application of chemical stimuli to nerve terminals. Further, axonal transection increases the activating transcription factor 3 mRNA level in ganglia. Axons and myelin are shown to regenerate 14days following transection. Our sensory organotypic model enables analysis of neuronal excitability in response to pain stimuli and tracking of morphological changes in the axon bundle over weeks.

Recovery of walking after paralysis by regenerating characterized neurons to their natural target region.

Axon regeneration can be induced across anatomically complete spinal cord injury (SCI), but robust functional restoration has been elusive. Whether restoring neurological functions requires directed regeneration of axons from specific neuronal subpopulations to their natural target regions remains unclear. To address this question, we applied projection-specific and comparative single-nucleus RNA sequencing to identify neuronal subpopulations that restore walking after incomplete SCI. We show that chemoattracting and guiding the transected axons of these neurons to their natural target region led to substantial recovery of walking after complete SCI in mice, whereas regeneration of axons simply across the lesion had no effect. Thus, reestablishing the natural projections of characterized neurons forms an essential part of axon regeneration strategies aimed at restoring lost neurological functions.

Changes in serum cytokine profile and deficit severity in patients with relapsing-remitting multiple sclerosis.

In experimental autoimmune encephalomyelitis, neurological deficit correlates with axonal loss and the CD8+ T cells are a likely mediator of axonal damage. In relapsing-remitting multiple sclerosis, there is a correlation of the immune inflammatory activity in the lesion foci with the axon transection.

Assessment of Thyroid Functions in Multiple Sclerosis Patients Treated with Disease Modifying Therapies

Background:
 Multiple sclerosis is a chronic disease believed to be the result of autoimmune disorders of the central nervous system, characterised by inflammation, demyelination, and axonal transection, affecting primarily young adults. Disease modifying therapies have become widely used, and the rapid development of these drugs highlighted the need to update our knowledge on their short- and long-term safety profile.
 Objective:
 The study aim is to evaluate the impact of disease-modifying treatments on thyroid functions and thyroid autoantibodies with subsequent effects on the outcome of the disease.
 Materials and Methods:
 A retro prospective study enrolled 45 patients who were registered and diagnosed in the Multiple Sclerosis Clinic according to the revised McDonald criteria (2017). Blood samples for thyroid functions and thyroid autoantibody tests were taken before, 3 months and after 6 months from the start of disease modifying therapy. The Expanded Disability Status Scale was used to assess the severity of the disease before and after 6 months of receiving treatment.
 Results:
 45 patients with the mean age of 33.3 years, a standard deviation (SD) of ± 9.5 years were enrolled in this study. (64.4%) patients’ age was between 20 - 39 years.
 The mean free T3 decreased significantly, while the mean anti-TPO and anti-TG increased after three months compared to its baseline level.
 After six months of treatment, the mean free T4 decreased significantly, while the mean TSH increased compared to its baseline level. There were no statistically significant correlations between the baseline (EDSS) score and after 6 months of therapy.
 Conclusion
 Thyroid hormone dysfunction and thyroid autoimmune antibody levels that changed in response to interferon beta therapy in patients with multiple sclerosis may be temporary and not associated with poor outcomes.

Active shrinkage protects neurons following axonal transection

Trauma, vascular events, or neurodegenerative processes can lead to axonal injury and eventual transection (axotomy). Neurons can survive axotomy, yet the underlying mechanisms are not fully understood. Excessive water entry into injured neurons poses a particular risk due to swelling and subsequent death. Using invitro and invivo neurotrauma model systems based on laser transection and surgical nerve cut, we demonstrated that axotomy triggers actomyosin contraction coupled with calpain activity. As a consequence, neurons shrink acutely to force water out through aquaporin channels preventing swelling and bursting. Inhibiting shrinkage increased the probability of neuronal cell death by about 3-fold. These studies reveal a previously unrecognized cytoprotective response mechanism to neurotrauma and offer a fresh perspective on pathophysiological processes in the nervous system.

Repair of traumatic lesions to the plasmalemma of neurons and other cells: Commonalities, conflicts, and controversies.

Neuroscientists and Cell Biologists have known for many decades that eukaryotic cells, including neurons, are surrounded by a plasmalemma/axolemma consisting of a phospholipid bilayer that regulates trans-membrane diffusion of ions (including calcium) and other substances. Cells often incur plasmalemmal damage via traumatic injury and various diseases. If the damaged plasmalemma is not rapidly repaired within minutes, activation of apoptotic pathways by calcium influx often results in cell death. We review publications reporting what is less-well known (and not yet covered in neuroscience or cell biology textbooks): that calcium influx at the lesion sites ranging from small nm-sized holes to complete axonal transection activates parallel biochemical pathways that induce vesicles/membrane-bound structures to migrate and interact to restore original barrier properties and eventual reestablishment of the plasmalemma. We assess the reliability of, and problems with, various measures (e.g., membrane voltage, input resistance, current flow, tracer dyes, confocal microscopy, transmission and scanning electron microscopy) used individually and in combination to assess plasmalemmal sealing in various cell types (e.g., invertebrate giant axons, oocytes, hippocampal and other mammalian neurons). We identify controversies such as plug versus patch hypotheses that attempt to account for currently available data on the subcellular mechanisms of plasmalemmal repair/sealing. We describe current research gaps and potential future developments, such as much more extensive correlations of biochemical/biophysical measures with sub-cellular micromorphology. We compare and contrast naturally occurring sealing with recently-discovered artificially-induced plasmalemmal sealing by polyethylene glycol (PEG) that bypasses all natural pathways for membrane repair. We assess other recent developments such as adaptive membrane responses in neighboring cells following injury to an adjacent cell. Finally, we speculate how a better understanding of the mechanisms involved in natural and artificial plasmalemmal sealing is needed to develop better clinical treatments for muscular dystrophies, stroke and other ischemic conditions, and various cancers.

Temporal single-cell atlas of non-neuronal retinal cells reveals dynamic, coordinated multicellular responses to central nervous system injury.

Non-neuronal cells are key to the complex cellular interplay that follows central nervous system insult. To understand this interplay, we generated a single-cell atlas of immune, glial and retinal pigment epithelial cells from adult mouse retina before and at multiple time points after axonal transection. We identified rare subsets in naive retina, including interferon (IFN)-response glia and border-associated macrophages, and delineated injury-induced changes in cell composition, expression programs and interactions. Computational analysis charted a three-phase multicellular inflammatory cascade after injury. In the early phase, retinal macroglia and microglia were reactivated, providing chemotactic signals concurrent with infiltration of CCR2+ monocytes from the circulation. These cells differentiated into macrophages in the intermediate phase, while an IFN-response program, likely driven by microglia-derived type I IFN, was activated across resident glia. The late phase indicated inflammatory resolution. Our findings provide a framework to decipher cellular circuitry, spatial relationships and molecular interactions following tissue injury.

Nav1.7 P610T mutation in two siblings with persistent ocular pain after corneal axon transection: impaired slow inactivation and hyperexcitable trigeminal neurons.

Despite extensive study, the mechanisms underlying pain after axonal injury remain incompletely understood. Pain after corneal refractive surgery provides a model, in humans, of the effect of injury to trigeminal afferent nerves. Axons of trigeminal ganglion neurons that innervate the cornea are transected by laser-assisted in situ keratomileusis (LASIK). Although most patients do not experience postoperative pain, a small subgroup develop persistent ocular pain. We previously carried out genomic analysis and determined that some patients with persistent pain after axotomy of corneal axons during refractive surgery carry mutations in genes that encode the electrogenisome of trigeminal ganglion neurons, the ensemble of ion channels and receptors that regulate excitability within these cells, including SCN9A, which encodes sodium channel Nav1.7, a threshold channel abundantly expressed in sensory neurons that has been implicated in a number of pain-related disorders. Here, we describe the biophysical and electrophysiological profiling of the P610T Nav1.7 mutation found in two male siblings with persistent ocular pain after refractive surgery. Our results indicate that this mutation impairs the slow inactivation of Nav1.7. As expected from this proexcitatory change in channel function, we also demonstrate that this mutation produces increased spontaneous activity in trigeminal ganglion neurons. These findings suggest that this gain-of-function mutation in Nav1.7 may contribute to pain after injury to the axons of trigeminal ganglion neurons.NEW & NOTEWORTHY Mechanisms underlying pain after axonal injury remain elusive. A small subgroup of patients experience pain after corneal refractive surgery, providing a human pain model after well-defined injury to axons. Here we analyze a mutation (P610T) in Nav1.7, a threshold sodium channel expressed in nociceptors, found in two siblings with persistent ocular pain after refractive surgery. We show that it impairs channel slow inactivation, thereby triggering inappropriate repetitive activity in trigeminal ganglion axons that signal eye pain.

Alterations of the axon initial segment in multiple sclerosis grey matter.

Grey matter damage has been established as a key contributor to disability progression in multiple sclerosis. Aside from neuronal loss and axonal transections, which predominate in cortical demyelinated lesions, synaptic alterations have been detected in both demyelinated plaques and normal-appearing grey matter, resulting in functional neuronal damage. The axon initial segment is a key element of neuronal function, responsible for action potential initiation and maintenance of neuronal polarity. Despite several reports of profound axon initial segment alterations in different pathological models, among which experimental auto-immune encephalomyelitis, whether the axon initial segment is affected in multiple sclerosis is still unknown. Using immunohistochemistry, we analysed axon initial segments from control and multiple sclerosis tissue, focusing on layer 5/6 pyramidal neurons in the neocortex and Purkinje cells in the cerebellum and performed analysis on the parameters known to control neuronal excitability, i.e. axon initial segment length and position. We found that the axon initial segment length was increased only in pyramidal neurons of inactive demyelinated lesions, compared with normal appearing grey matter tissue. In contrast, in both cell types, the axon initial segment position was altered, with an increased soma-axon initial segment gap, in both active and inactive demyelinated lesions. In addition, using a computational model, we show that this increased gap between soma and axon initial segment might increase neuronal excitability. Taken together, these results show, for the first time, changes of axon initial segments in multiple sclerosis, in active as well as inactive grey matter lesions in both neocortex and cerebellum, which might alter neuronal function.

EP-273 Magnetic nanoparticle administration to a model of penetrating neurotrauma in vitro

Abstract Introduction/Aims Functional recovery in penetrating traumatic brain injury (pTBI) is hampered due to the lack of clinically approved regenerative therapies. Although a surgical emergency, pTBI management is largely supportive, with no targeted neuroregenerative therapies. Reactive gliotic and neuroinflammatory responses with a lack of spontaneous axonal regeneration represent a major barrier to repair. Emergent nanotechnologies including magnetic nanoparticles (MNPs) show promise to attenuate such responses through immunomodulation, with potential of delivery of neurotherapeutic molecules to lesion sites during surgical intervention. However, there is a lack of high throughput, neuropathomimetic, models for nano/biomaterial testing in experimental neurology. Our group recently showed glial cell interactions with a surgical biomaterial scaffold (DuraGen PlusTM) in a novel in vitro model of pTBI. Methods Mice cerebral cortices were extracted and cultured 8–10 days in vitro (DIV) using previous methodology (Basit et al, Mat Sci Eng C, 2021) with a modified chemical medium. At 8 DIV, a sterile pipette was used for transection of the culture simulating penetrating injury in vitro with injection of carboxymethyl dextran-coated magnetic nanoparticles and polyethylene glycol-coated magnetic nanoparticles into the lesion site. MNP-neural cell responses were evaluated using immunocytochemistry methods. Results Our model demonstrates hallmark reactive gliotic responses, immune cell infiltration and axonal transection in injury sites. We demonstrate preferential and competitive microglial uptake of delivered MNPs versus other neural cell types (p<0.05, n=5). Conclusion The model is adaptable to study neural cell responses to range of materials, offering high versatility for testing promising surgical neuromaterial based therapeutic interventions in experimental clinically relevant research.

The metalloprotease ADM-4/ADAM17 promotes axonal repair.

Axonal fusion is an efficient means of repair following axonal transection, whereby the regenerating axon fuses with its own separated axonal fragment to restore neuronal function. Despite being described over 50 years ago, its molecular mechanisms remain poorly understood. Here, we demonstrate that the Caenorhabditis elegans metalloprotease ADM-4, an ortholog of human ADAM17, is essential for axonal fusion. We reveal that animals lacking ADM-4 cannot repair their axons by fusion, and that ADM-4 has a cell-autonomous function within injured neurons, localizing at the tip of regrowing axon and fusion sites. We demonstrate that ADM-4 overexpression enhances fusion to levels higher than wild type, and that the metalloprotease and phosphatidylserine-binding domains are essential for its function. Last, we show that ADM-4 interacts with and stabilizes the fusogen EFF-1 to allow membranes to merge. Our results uncover a key role for ADM-4 in axonal fusion, exposing a molecular target for axonal repair.

Neuroinflammation and Scarring After Spinal Cord Injury: Therapeutic Roles of MSCs on Inflammation and Glial Scar.

Transected axons are unable to regenerate after spinal cord injury (SCI). Glial scar is thought to be responsible for this failure. Regulating the formation of glial scar post-SCI may contribute to axonal regrow. Over the past few decades, studies have found that the interaction between immune cells at the damaged site results in a robust and persistent inflammatory response. Current therapy strategies focus primarily on the inhibition of subacute and chronic neuroinflammation after the acute inflammatory response was executed. Growing evidences have documented that mesenchymal stem cells (MSCs) engraftment can be served as a promising cell therapy for SCI. Numerous studies have shown that MSCs transplantation can inhibit the excessive glial scar formation as well as inflammatory response, thereby facilitating the anatomical and functional recovery. Here, we will review the effects of inflammatory response and glial scar formation in spinal cord injury and repair. The role of MSCs in regulating neuroinflammation and glial scar formation after SCI will be reviewed as well.

SARM1-mediated wallerian degeneration: A possible mechanism underlying organophosphorus-induced delayed neuropathy

Some organophosphorus compounds (OPs) can cause a type of delayed neurotoxicity in human being, which is known as organophosphorus-induced delayed neuropathy (OPIDN). Signs and symptoms of the patients include tingling and sensory loss of the hands and feet, followed by progressive muscle weakness in the lower and upper limbs, and ataxia. Pathologically, OPIDN are characterized by distal sensorimotor axonopathy due to the distal axonal degeneration of nerve tracts located in central and peripheral nervous systems. The morphological pattern of the distal axonopathy is similar to Wallerian degeneration that occurs after nerve injury in vitro. It is generally acknowledged that inhibition and subsequent aging of neuropathy target esterase (NTE) is required for the occurrence of OPIDN. However, the underlying mechanisms through which NTE triggers axonal degeneration in OPIDN is still largely unclear. Recently, sterile alpha and toll/interleukin receptor motif-containing protein 1（SARM1) has been identified as a key player in Wallerian degeneration. In physical and chemical transection of axons, SARM1 was found to promotes axon degeneration by hydrolyzing NAD+. By contrast, SARM1 deficiency could prevent neuron degeneration in response to a wide range of insults. Furthermore, SARM1 can also translocate to mitochondria and cause mitochondrial damage, thus triggering axon degeneration and neuron death. These findings suggested the existence of a pathway in axonal degeneration that might be targeted therapeutically. Here, we hypothesize that SARM1 activation after NTE inhibition and aging might be an etiological factor in OPIDN that regulates Wallerian-like degeneration. Analysing SARM1 mediated NAD degeneration pathway and its upstream activators in OPIDN could contribute to the development of novel therapies to treat OPIDN.

Remyelination Trials: Are We Expecting the Unexpected?

Neuroaxonal loss is believed to underpin the progressive disability that characterizes multiple sclerosis (MS). While focal inflammatory demyelination is a principal cause of acute axonal transection and subsequent axonal degeneration, the gradual attrition of permanently demyelinated axons may also contribute to tissue damage, particularly in the progressive phase of the disease. Therefore, remyelination is considered a putative neuroprotective strategy. In this article, we review the potential pitfalls of remyelination trials, provide a framework for their appropriate design and temper the expectations, at times unrealistic, of researchers, regulators and the pharmaceutical industry.

Intraspinal Administration of Netrin-1 Promotes Locomotor Recovery after Complete Spinal Cord Transection.

Complete spinal cord lesions interrupt the connection of all axonal projections with their neuronal targets below and above the lesion site. In particular, the interruption of connections with the neurons at lumbar segments after thoracic injuries impairs voluntary body control below the injury. The failure of spontaneous regrowth of transected axons across the lesion prevents the reconnection and reinnervation of the neuronal targets. At present, the only treatment in humans that has proven to promote some degree of locomotor recovery is physical therapy. The success of these strategies, however, depends greatly on the type of lesion and the level of preservation of neural tissue in the spinal cord after injury. That is the reason it is key to design strategies to promote axonal regrowth and neuronal reconnection. Here, we test the use of a developmental axon guidance molecule as a biological agent to promote axonal regrowth, axonal reconnection, and recovery of locomotor activity after spinal cord injury (SCI). This molecule, netrin-1, guides the growth of the corticospinal tract (CST) during the development of the central nervous system. To assess the potential of this molecule, we used a model of complete spinal cord transection in rats, at thoracic level 10-11. We show that in situ delivery of netrin-1 at the epicenter of the lesion: (1) promotes regrowth of CST through the lesion and prevents CST dieback, (2) promotes synaptic reconnection of regenerated motor and sensory axons, and (3) preserves the polymerization of the neurofilaments in the sciatic nerve axons. These anatomical findings correlate with a significant recovery of locomotor function. Our work identifies netrin-1 as a biological agent with the capacity to promote the functional repair and recovery of locomotor function after SCI. These findings support the use of netrin-1 as a therapeutic intervention to be tested in humans.

Current Advances in Comprehending Dynamics of Regenerating Axons and Axon-Glia Interactions after Peripheral Nerve Injury in Zebrafish.

Following an injury, axons of both the central nervous system (CNS) and peripheral nervous system (PNS) degenerate through a coordinated and genetically conserved mechanism known as Wallerian degeneration (WD). Unlike central axons, severed peripheral axons have a higher capacity to regenerate and reinnervate their original targets, mainly because of the favorable environment that they inhabit and the presence of different cell types. Even though many aspects of regeneration in peripheral nerves have been studied, there is still a lack of understanding regarding the dynamics of axonal degeneration and regeneration, mostly due to the inherent limitations of most animal models. In this scenario, the use of zebrafish (Danio rerio) larvae combined with time-lapse microscopy currently offers a unique experimental opportunity to monitor the dynamics of the regenerative process in the PNS in vivo. This review summarizes the current knowledge and advances made in understanding the dynamics of the regenerative process of PNS axons. By using different tools available in zebrafish such as electroablation of the posterior lateral line nerve (pLLn), and laser-mediated transection of motor and sensory axons followed by time-lapse microscopy, researchers are beginning to unravel the complexity of the spatiotemporal interactions among different cell types during the regenerative process. Thus, understanding the cellular and molecular mechanisms underlying the degeneration and regeneration of peripheral nerves will open new avenues in the treatment of acute nerve trauma or chronic conditions such as neurodegenerative diseases.

Combining task-based rehabilitative training with PTEN inhibition promotes axon regeneration and upper extremity skilled motor function recovery after cervical spinal cord injury in adult mice

BackgroundConditional deletion of Pten in corticospinal neurons promotes axon sprouting and regeneration after spinal cord injury (SCI). However, regeneration studies targeted on PTEN inhibition seldom show motor function recovery. The promotion of functional recovery can be improved by rehabilitative training under a use-dependent plasticity mechanism. PurposeTo investigate the combined effects of PTEN inhibition and rehabilitative training on axon regeneration and subsequent motor functional improvement after cervical spinal cord injury. MethodsLentiviral particles (Lenti-PTEN-RNAi or Lenti-Scrambled-EGFP) were injected into the right sensorimotor mouse cortex in four experimental groups (PTEN RNAi + Training, PTEN RNAi, Control + Training, Control). Two weeks after injection, all mouse groups received a left C5 crush injury. We performed task-based rehabilitative training for 4 weeks on the PTEN RNAi + Training and Control + Training groups. Biotinylated dextran amine (BDA) was used for anterograde tracing of the dorsal corticospinal tract (dCST). We analysed axonal regeneration through immunohistochemical methods. A battery of behavioral tests was employed to assess functional recovery at Day3 and every other week after injury. ResultsCombining rehabilitative training with PTEN inhibition induced more axon regeneration and synapse reformation in the spinal cord caudal to the lesion site. Rostral to the lesion, the transected dCST axons sprouted into gray matter upon contact. Furthermore, forelimb function was found to be improved after combination therapy during behavioral testing. ConclusionCombining task-based rehabilitative training with PTEN inhibition further promotes axon regeneration, synaptic plasticity and reorganization of the neural network, with significant improvement in forelimb skilled motor function after cervical spinal cord injury. Our study provides new therapeutic insights for spinal cord injury management in the future.

Perilesional neurodegenerative injury in multiple sclerosis: Relation to focal lesions and impact on disability

BackgroundAxonal injury is the primary source of irreversible neurological decline in persons with multiple sclerosis (pwMS). Identifying and quantifying myelin and axonal loss in lesional and perilesional tissue in vivo is fundamental for a better understanding of multiple sclerosis (MS) outcomes and patient impairment. Using advanced magnetic resonance imaging (MRI) methods, consisting of selective inversion recovery quantitative magnetization transfer imaging (SIR-qMT) and multi-compartment diffusion MRI with the spherical mean technique (SMT), we conducted a cross-sectional pilot study to assess myelin and axonal damage in the normal appearing white matter (NAWM) surrounding chronic black holes (cBHs) and how this pathology correlates with disability in vivo. We hypothesized that lesional axonal transection propagates tissue injury in the surrounding NAWM and that the degree of this injury is related to patient disability. MethodsEighteen pwMS underwent a 3.0 Tesla conventional clinical MRI, inclusive of T1 and T2 weighted protocols, as well as SIR-qMT and SMT. Regions of interests (ROIs) were manually delineated in cBHs, NAWM neighboring cBHs (perilesional NAWM), distant ipsilateral NAWM and contra-lateral distant NAWM. SIR-qMT-derived macromolecular-to-free pool size ratio (PSR) and SMT-derived apparent axonal volume fraction (Vax) were extracted to infer on myelin and axonal content, respectively. Group differences were assessed using mixed-effects regression models and correlation analyses were obtained by bootstrapping 95% confidence interval. ResultsIn comparison to perilesional NAWM, both PSR and Vax values were reduced in cBHs (p < 0.0001) and increased in distant contra-lateral NAWM ROIs (p < 0.001 for PSR and p < 0.0001 for Vax) but not ipsilateral NAWM (p = 0.176 for PSR and p = 0.549 for Vax). Vax values measured in cBHs correlated with those in perilesional NAWM (Pearson rho = 0.63, p < 0.001). No statistically relevant associations were seen between PSR/Vax values and clinical and/or MRI metrics of the disease with the exception of cBH PSR values, which correlated with the Expanded Disability Status Scale (Pearson rho = −0.63, p = 0.03). ConclusionsOur results show that myelin and axonal content, detected by PSR and Vax, are reduced in perilesional NAWM, as a function of the degree of focal cBH axonal injury. This finding is indicative of an ongoing anterograde/retrograde degeneration and suggests that treatment prevention of cBH development is a key factor for preserving NAWM integrity in surrounding tissue. It also suggests that measuring changes in perilesional areas over time may be a useful measure of outcome for proof-of-concept clinical trials on neuroprotection and repair. PSR and Vax largely failed to capture associations with clinical and MRI characteristics, likely as a result of the small sample size and cross-sectional design, however, longitudinal assessment of a larger cohort may unravel the impact of this pathology on disease progression.

A new neutrophil subset promotes CNS neuron survival and axon regeneration.

Transected axons typically fail to regenerate in the central nervous system (CNS), resulting in chronic neurological disability in individuals with traumatic brain or spinal cord injury, glaucoma and ischemic reperfusion injury of the eye. Although neuroinflammation is often depicted as detrimental, there is growing evidence that alternatively activated, reparative leukocyte subsets and their products can be deployed to improve neurological outcomes. In the current study we identify a unique granulocyte subset, with characteristics of an immature neutrophil, that had neuroprotective properties and drove CNS axon regeneration in vivo, in part via secretion of a cocktail of growth factors. This pro-regenerative neutrophil promoted repair in the optic nerve and spinal cord, demonstrating its relevance across CNS compartments and neuronal populations. Our findings could ultimately lead to the development of novel immunotherapies that reverse CNS damage and restore lost neurological function across a spectrum of diseases.

Deletion of CD38 and supplementation of NAD+ attenuate axon degeneration in a mouse facial nerve axotomy model

Following facial nerve axotomy, nerve function is not fully restored even after reconstruction. This may be attributed to axon degeneration/neuronal death and sustained neuroinflammation. CD38 is an enzyme that catalyses the hydrolysis of nicotinamide adenine dinucleotide (NAD+) and is a candidate molecule for regulating neurodegeneration and neuroinflammation. In this study, we analyzed the effect of CD38 deletion and NAD+ supplementation on neuronal death and glial activation in the facial nucleus in the brain stem, and on axon degeneration and immune cell infiltration in the distal portion of the facial nerve after axotomy in mice. Compared with wild-type mice, CD38 knockout (KO) mice showed reduced microglial activation in the facial nucleus, whereas the levels of neuronal death were not significantly different. In contrast, the axon degeneration and demyelination were delayed, and macrophage accumulation was reduced in the facial nerve of CD38 KO mice after axotomy. Supplementation of NAD+ with nicotinamide riboside slowed the axon degeneration and demyelination, although it did not alter the level of macrophage infiltration after axotomy. These results suggest that CD38 deletion and supplementation of NAD+ may protect transected axon cell-autonomously after facial nerve axotomy.