Wallerian degeneration of the ipsilateral middle cerebellar peduncle after lower pontine paramedian infarct diagnosed by magnetic resonance imaging

We reported a case of Wallerian degeneration of the unilateral middle cerebellar peduncle (MCP) that developed after ipsilateral paramedian lower pontine infarction. The patient was a 70-year-old woman with right hemiparesis and dysarthria. Using a 3-Tesla scanner, cranial magnetic resonance imaging was performed, and an infarct was found at the left paramedian lower pons. Seven months later, an abnormal signal was found at the central portion of the left MCP, indicative of Wallerian degeneration of the pontocerebellar tract (PCT). There was no abnormality at the contralateral MCP. Usually, Wallerian degeneration of the bilateral MCPs may develop after unilateral paramedian pontine infarction, because bilateral PCTs cross each other at the midline of the basis pontis. In the present case, however, Wallerian degeneration was found at only the ipsilateral MCP. The contralateral PCT was not affected because the PCT runs in the craniocaudal direction, and our patient had a lower pontine infarct. The location of the pontine infarct (affected PCT) and the Wallerian degeneration of the side of the MCP were well correlated.

Long noncoding RNA H19 regulates degeneration and regeneration of injured peripheral nerves

Our previous studies have shown that long noncoding RNA (lncRNA) H19 is upregulated in injured rat sciatic nerve during the process of Wallerian degeneration, and that it promotes the migration of Schwann cells and slows down the growth of dorsal root ganglion axons. However, the mechanism by which lncRNA H19 regulates neural repair and regeneration after peripheral nerve injury remains unclear. In this study, we established a Sprague-Dawley rat model of sciatic nerve transection injury. We performed in situ hybridization and found that at 4-7 days after sciatic nerve injury, lncRNA H19 was highly expressed. At 14 days before injury, adeno-associated virus was intrathecally injected into the L4-L5 foramina to disrupt or overexpress lncRNA H19. After overexpression of lncRNA H19, the growth of newly formed axons from the sciatic nerve was inhibited, whereas myelination was enhanced. Then, we performed gait analysis and thermal pain analysis to evaluate rat behavior. We found that lncRNA H19 overexpression delayed the recovery of rat behavior function, whereas interfering with lncRNA H19 expression improved functional recovery. Finally, we examined the expression of lncRNA H19 downstream target SEMA6D, and found that after lncRNA H19 overexpression, the SEMA6D protein level was increased. These findings suggest that lncRNA H19 regulates peripheral nerve degeneration and regeneration through activating SEMA6D in injured nerves. This provides a new clue to understand the role of lncRNA H19 in peripheral nerve degeneration and regeneration.

Traumatic Axonal Injury in the Optic Nerve: The Selective Role of SARM1 in the Evolution of Distal Axonopathy

Traumatic axonal injury (TAI), thought to be caused by rotational acceleration of the head, is a prevalent neuropathology in traumatic brain injury (TBI). TAI in the optic nerve is a common finding in multiple blunt-force TBI models and hence a great model to study mechanisms and treatments for TAI, especially in view of the compartmentalized anatomy of the visual system. We have previously shown that the somata and the proximal, but not distal, axons of retinal ganglion cells (RGC) respond to DLK/LZK blockade after impact acceleration of the head (IA-TBI). Here, we explored the role of the sterile alpha and TIR-motif containing 1 (SARM1), the key driver of Wallerian degeneration (WD), in the progressive breakdown of distal and proximal segments of the optic nerve following IA-TBI with high-resolution morphological and classical neuropathological approaches. Wild type and Sarm1 knockout (KO) mice received IA-TBI or sham injury and were allowed to survive for 3, 7, 14, and 21 days. Ultrastructural and microscopic analyses revealed that TAI in the optic nerve is characterized by variable involvement of individual axons, ranging from apparent early disconnection of a subpopulation of axons to a range of ongoing axonal and myelin perturbations. Traumatic axonal injury resulted in the degeneration of a population of axons distal and proximal to the injury, along with retrograde death of a subpopulation of RGCs. Quantitative analyses on proximal and distal axons and RGC somata revealed that different neuronal domains exhibit differential vulnerability, with distal axon segments showing more severe degeneration compared with proximal segments and RGC somata. Importantly, we found that Sarm1 KO had a profound effect in the distal optic nerve by suppressing axonal degeneration by up to 50% in the first 2 weeks after IA-TBI, with a continued but lower effect at 3 weeks, while also suppressing microglial activation. Sarm1 KO had no evident effect on the initial traumatic disconnection and did not ameliorate the proximal optic axonopathy or the subsequent attrition of RGCs, indicating that the fate of different axonal segments in the course of TAI may depend on distinct molecular programs within axons.

Evaluation of the Aging Effect on Peripheral Nerve Regeneration: A Systematic Review

INTRODUCTION

Peripheral nerve injuries have been associated with increased healthcare costs and decreased patients' quality of life. Aging represents one factor that slows the speed of peripheral nervous system (PNS) regeneration. Since cellular homeostasis imbalance associated with aging lead to an increased failure in nerve regeneration in mammals of advanced age, this systematic review aims to determine the main molecular and cellular mechanisms involved in peripheral nerve regeneration in aged murine models after a peripheral nerve injuries.

METHODS

Following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, a literature search of 4 databases was conducted in July 2022 for studies comparing the peripheral nerve regeneration capability between young and aged murine models.

RESULTS

After the initial search yielded 744 publications, ten articles fulfilled the inclusion criteria. These studies show that age-related changes such as chronic inflammatory state, delayed macrophages' response to injury, dysfunctional Schwann Cells (SCs), and microenvironment alterations cause a reduction in the regenerative capability of the PNS in murine models. Furthermore, identifying altered gene expression patterns of SC after nerve damage can contribute to the understanding of physiological modifications produced by aging.

CONCLUSIONS

The interaction between macrophages and SC plays a crucial role in the nerve regeneration of aged models. Therefore, studies aimed at developing new and promising therapies for nerve regeneration should focus on these cellular groups to enhance the regenerative capabilities of the PNS in elderly populations.

Zebrafish cutaneous injury models reveal that Langerhans cells engulf axonal debris in adult epidermis

Somatosensory neurons extend enormous peripheral axons to the skin, where they detect diverse environmental stimuli. Somatosensory peripheral axons are easily damaged due to their small caliber and superficial location. Axonal damage results in Wallerian degeneration, creating vast quantities of cellular debris that phagocytes must remove to maintain organ homeostasis. The cellular mechanisms that ensure efficient clearance of axon debris from stratified adult skin are unknown. Here, we established zebrafish scales as a tractable model to study axon degeneration in the adult epidermis. Using this system, we demonstrated that skin-resident immune cells known as Langerhans cells engulf the majority of axon debris. In contrast to immature skin, adult keratinocytes did not significantly contribute to debris removal, even in animals lacking Langerhans cells. Our study establishes a powerful new model for studying Wallerian degeneration and identifies a new function for Langerhans cells in maintenance of adult skin homeostasis following injury. These findings have important implications for pathologies that trigger somatosensory axon degeneration.

Electrical stimulation accelerates Wallerian degeneration and promotes nerve regeneration after sciatic nerve injury

Following peripheral nerve injury (PNI), Wallerian degeneration (WD) in the distal stump can generate a microenvironment favorable for nerve regeneration. Brief low-frequency electrical stimulation (ES) is an effective treatment for PNI, but the mechanism underlying its effect on WD remains unclear. Therefore, we hypothesized that ES could enhance nerve regeneration by accelerating WD. To verify this hypothesis, we used a rat model of sciatic nerve transection and provided ES at the distal stump of the injured nerve. The injured nerve was then evaluated after 1, 4, 7, 14 and 21 days post injury (dpi). The results showed that ES significantly promoted the degeneration and clearance of axons and myelin, and the dedifferentiation of Schwann cells. It upregulated the expression of BDNF and NGF and increased the number of monocytes and macrophages. Through transcriptome sequencing, we systematically investigated the effect of ES on the molecular processes involved in WD at 4 dpi. Evaluation of nerves bridged using silicone tubing after transection showed that ES accelerated early axonal and vascular regeneration while delaying gastrocnemius atrophy. These results demonstrate that ES promotes nerve regeneration by accelerating WD and upregulating the expression of neurotrophic factors.

Glycolytic System in Axons Supplement Decreased ATP Levels after Axotomy of the Peripheral Nerve

Wallerian degeneration (WD) occurs in the early stages of numerous neurologic disorders, and clarifying WD pathology is crucial for the advancement of neurologic therapies. ATP is acknowledged as one of the key pathologic substances in WD. The ATP-related pathologic pathways that regulate WD have been defined. The elevation of ATP levels in axon contributes to delay WD and protects axons. However, ATP is necessary for the active processes to proceed WD, given that WD is stringently managed by auto-destruction programs. But little is known about the bioenergetics during WD. In this study, we made sciatic nerve transection models for GO-ATeam2 knock-in rats and mice. We presented the spatiotemporal ATP distribution in the injured axons with in vivo ATP imaging systems, and investigated the metabolic source of ATP in the distal nerve stump. A gradual decrease in ATP levels was observed before the progression of WD. In addition, the glycolytic system and monocarboxylate transporters (MCTs) were activated in Schwann cells following axotomy. Interestingly, in axons, we found the activation of glycolytic system and the inactivation of the tricarboxylic acid (TCA) cycle. Glycolytic inhibitors, 2-deoxyglucose (2-DG) and MCT inhibitors, a-cyano-4-hydroxycinnamic acid (4-CIN) decreased ATP and enhanced WD progression, whereas mitochondrial pyruvate carrier (MPC) inhibitors (MSDC-0160) did not change. Finally, ethyl pyruvate (EP) increased ATP levels and delayed WD. Together, our findings suggest that glycolytic system, both in Schwann cells and axons, is the main source of maintaining ATP levels in the distal nerve stump.

Regulation of the V-ATPase subunit ATP6V0D2 and its role in demyelination after peripheral nerve injury

After peripheral nerve injury, demyelinating Schwann cells discharge myelin debris and macrophages execute myelin degradation, leading to demyelination of degenerating axons, which is essential for efficient nerve regeneration. In this study, we show that vacuolar-type proton ATPase subunit d2 (Atp6v0d2) is among the most highly upregulated genes in degenerating mouse sciatic nerves after nerve injury using microarray analysis. ATP6V0D2 is mostly expressed in macrophages of injured nerves. Atp6v0d2 knockout mice display delayed peripheral nerve demyelination and significantly attenuated myelin lipid digestion after nerve injury. However, macrophage recruitment and Schwann cell dedifferentiation are unaffected by loss of Atp6v0d2 expression. Taken together, these data demonstrate that ATP6V0D2 in macrophages is specifically required for demyelination during Wallerian degeneration.

Rapid and effective fusion repair of severed digital nerves using neurorrhaphy and bioengineered solutions including polyethylene glycol: A case report

Peripheral nerve injuries (PNIs) that consist of simple nerve severance often result in severe motor impairment and permanent loss of function. Such patients face significant costs and pose major burdens to healthcare systems. Currently, the most promising surgical technique to achieve the best clinical outcome after such PNIs is immediate primary coaptation of severed nerve ends by microsutures (neurorrhaphy). However, recovery is often poor and delayed for many months due to Wallerian degeneration (WD) and slow (1-2 mm/day) axonal outgrowths from severed proximal axons that may not properly reinnervate denervated afferent/efferent targets that have atrophied. In contrast, recent pre-clinical studies using polyethylene glycol (PEG) to facilitate primary nerve repair have greatly improved the rate and extent of sensory and motor recovery and prevented much WD and muscle atrophy. That is, PEG-fused axons rapidly establish proximal-distal axoplasmic/axolemmal continuity, which do not undergo WD and maintain the structure and function of neuromuscular junction (NMJ). PEG-fused axons rapidly reinnervate denervated NMJs, thereby preventing muscle atrophy associated with monthslong denervation due to slowly regenerating axonal outgrowths. We now describe PEG-mediated fusion repair of a digital nerve in each of two patients presenting with a digital laceration resulting in total loss of sensation. The first patient's tactile perception improved markedly at 3 days postoperatively (PO). Two-point discrimination improved from greater than 10 mm at initial presentation to 4 mm at 11-week PO, and the Semmes-Weinstein monofilament score improved from greater than 6.65 to 2.83 mm, a near-normal level. The second patient had severe PO edema and scar development requiring a hand compression glove and scar massage, which began improving at 11-week PO. The sensory function then improved for 4 months PO, with both two-point discrimination and Semmes-Weinstein scores approaching near-normal levels at the final follow-up. These case study data are consistent with data from animal models. All these data suggest that PEG-fusion technologies could produce a paradigm shift from the current clinical practice of waiting days to months to repair ablation PNIs with autografts, anucleated nerve allografts, or conduits in which the patient outcome is solely dependent upon axon regeneration over months or years.

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

SUMMARY STATEMENT

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

Neuromuscular disease: 2023 update

This review highlights ten important advances in the neuromuscular disease field that were reported in 2022. As with prior updates in this article series, the overarching topics include (i) advances in understanding of fundamental neuromuscular biology; (ii) new / emerging diseases; (iii) advances in understanding of disease etiology and pathogenesis; (iv) diagnostic advances; and (v) therapeutic advances. Within this general framework, the individual disease entities that are discussed in more detail include neuromuscular complications of COVID-19 (another look at the topic first covered in the 2021 and 2022 reviews), DNAJB4-associated myopathy, NMNAT2-deficient hereditary axonal neuropathy, Guillain-Barré syndrome, sporadic inclusion body myositis, and amyotrophic lateral sclerosis. In addition, the review highlights a few other advances (including new insights into mechanisms of fiber maturation during muscle regeneration and fiber rebuilding following reinnervation, improved genetic testing methods for facioscapulohumeral and myotonic muscular dystrophies, and the use of SARM1 inhibitors to block Wallerian degeneration) that will be of significant interest for clinicians and researchers who specialize in neuromuscular disease.

Peripheral neuropathy caused by fenugreek (Trigonella foenum-graecum) straw intoxication in cattle and experimental reproduction in sheep and goats

Trigonella foenum-graecum (fenugreek) is a legume widely used as a food supplement in humans and less frequently in ruminants. Toxicity has been described sporadically in ruminants grazing mature fenugreek plants or stubble; however, the pathological features are unclear. This report describes a natural outbreak of intoxication in cattle fed fenugreek straw and the experimental reproduction using 8 sheep and 8 goats. Affected cattle presented clinical signs approximately 1 month after consuming the straw and 100 of 400 cattle (25%) were affected, of which 60 of 100 (60%) died or were euthanized. Clinical signs were characterized by proprioceptive positioning defects with abnormal postures and weakness of hindlimbs. Forelimbs were also affected in severely affected animals, and cattle became recumbent. Locomotion was characterized by trembling, and some cattle showed high-stepping movements of their forelimbs and knuckled over in their fetlocks. Experimental intoxication induced clinical signs only in sheep and were similar to cattle, although with signs starting in the forelegs. Gross and microscopic lesions were similar in spontaneous and experimental intoxications. Macroscopic changes corresponded with muscular hemorrhages and edema, mainly surrounding the peripheral nerves. Microscopic examination only demonstrated lesions in the distal peripheral nerves, which included edema, hemorrhages, and Wallerian degeneration. Neurofilament immunohistochemistry revealed altered axon labeling and S100 showed a decrease in myelin intensity and loss of its typical compact arrangement around axons. Biochemical and hematological abnormalities included elevated levels of muscle and liver enzymes and thrombocytopenia. These findings indicate that fenugreek straw induces peripheral neuropathy in cattle and sheep, but not in goats.

Motor and somatosensory degenerative myelopathy responsive to pantothenic acid in piglets

This report describes 2 events of degenerative myelopathy in 4- to 27-day-old piglets, with mortality rates reaching 40%. Sows were fed rations containing low levels of pantothenic acid. Piglets presented with severe depression, weakness, ataxia, and paresis, which were more pronounced in the pelvic limbs. No significant gross lesions were observed. Histologically, there were degeneration and necrosis of neurons in the spinal cord, primarily in the thoracic nucleus in the thoracic and lumbar segments, and motor neurons in nucleus IX of the ventral horn in the cervical and lumbar intumescence. Minimal-to-moderate axonal and myelin degeneration was observed in the dorsal funiculus of the spinal cord and in the dorsal and ventral nerve roots. Immunohistochemistry demonstrated depletion of acetylcholine neurotransmitters in motor neurons and accumulation of neurofilaments in the perikaryon of neurons in the thoracic nucleus and motor neurons. Ultrastructurally, the thoracic nucleus neurons and motor neurons showed dissolution of Nissl granulation. The topographical distribution of the lesions indicates damage to the second-order neurons of the spinocerebellar tract, first-order axon cuneocerebellar tract, and dorsal column-medial lemniscus pathway as the cause of the conscious and unconscious proprioceptive deficit, and damage to the alpha motor neuron as the cause of the motor deficit. Clinical signs reversed and no new cases occurred after pantothenic acid levels were corrected in the ration, and piglets received parenteral administration of pantothenic acid. This study highlights the important and practical use of detailed neuropathological analysis to refine differential diagnosis.

Traumatic axonopathy in spinal tracts after impact acceleration head injury: Ultrastructural observations and evidence of SARM1-dependent axonal degeneration

Traumatic axonal injury (TAI) and the associated axonopathy are common consequences of traumatic brain injury (TBI) and contribute to significant neurological morbidity. It has been previously suggested that TAI activates a highly conserved program of axonal self-destruction known as Wallerian degeneration (WD). In the present study, we utilize our well-established impact acceleration model of TBI (IA-TBI) to characterize the pathology of injured myelinated axons in the white matter tracks traversing the ventral, lateral, and dorsal spinal columns in the mouse and assess the effect of Sterile Alpha and TIR Motif Containing 1 (Sarm1) gene knockout on acute and subacute axonal degeneration and myelin pathology. In silver-stained preparations, we found that IA-TBI results in white matter pathology as well as terminal field degeneration across the rostrocaudal axis of the spinal cord. At the ultrastructural level, we found that traumatic axonopathy is associated with diverse types of axonal and myelin pathology, ranging from focal axoskeletal perturbations and focal disruption of the myelin sheath to axonal fragmentation. Several morphological features such as neurofilament compaction, accumulation of organelles and inclusions, axoskeletal flocculation, myelin degeneration and formation of ovoids are similar to profiles encountered in classical examples of WD. Other profiles such as excess myelin figures and inner tongue evaginations are more typical of chronic neuropathies. Stereological analysis of pathological axonal and myelin profiles in the ventral, lateral, and dorsal columns of the lower cervical cord (C6) segments from wild type and Sarm1 KO mice at 3 and 7 days post IA-TBI (n = 32) revealed an up to 90% reduction in the density of pathological profiles in Sarm1 KO mice after IA-TBI. Protection was evident across all white matter tracts assessed, but showed some variability. Finally, Sarm1 deletion ameliorated the activation of microglia associated with TAI. Our findings demonstrate the presence of severe traumatic axonopathy in multiple ascending and descending long tracts after IA-TBI with features consistent with some chronic axonopathies and models of WD and the across-tract protective effect of Sarm1 deletion.

Adaptive autophagy reprogramming in Schwann cells during peripheral demyelination

The myelin sheath is an essential structure for the rapid transmission of electrical impulses through axons, and peripheral myelination is a well-programmed postnatal process of Schwann cells (SCs), the myelin-forming peripheral glia. SCs transdifferentiate into demyelinating SCs (DSCs) to remove the myelin sheath during Wallerian degeneration after axonal injury and demyelinating neuropathies, and macrophages are responsible for the degradation of myelin under both conditions. In this study, the mechanism by which DSCs acquire the ability of myelin exocytosis was investigated. Using serial ultrastructural evaluation, we found that autophagy-related gene 7-dependent formation of a "secretory phagophore (SP)" and tubular phagophore was necessary for exocytosis of large myelin chambers by DSCs. DSCs seemed to utilize myelin membranes for SP formation and employed p62/sequestosome-1 (p62) as an autophagy receptor for myelin excretion. In addition, the acquisition of the myelin exocytosis ability of DSCs was associated with the decrease in canonical autolysosomal flux and was demonstrated by p62 secretion. Finally, this SC demyelination mechanism appeared to also function in inflammatory demyelinating neuropathies. Our findings show a novel autophagy-mediated myelin clearance mechanism by DSCs in response to nerve damage.

Bortezomib-induced neurotoxicity in human neurons is the consequence of nicotinamide adenine dinucleotide depletion

The proteosome inhibitor bortezomib has revolutionized the treatment of multiple hematologic malignancies, but in many cases, its efficacy is limited by a dose-dependent peripheral neuropathy. We show that human induced pluripotent stem cell (hiPSC)-derived motor neurons and sensory neurons provide a model system for the study of bortezomib-induced peripheral neuropathy, with promising implications for furthering the mechanistic understanding of and developing treatments for preventing axonal damage. Human neurons in tissue culture displayed distal-to-proximal neurite degeneration when exposed to bortezomib. This process coincided with disruptions in mitochondrial function and energy homeostasis, similar to those described in rodent models of bortezomib-induced neuropathy. Moreover, although the degenerative process was unaffected by inhibition of caspases, it was completely blocked by exogenous nicotinamide adenine dinucleotide (NAD+), a mediator of the SARM1-dependent axon degeneration pathway. We demonstrate that bortezomib-induced neurotoxicity in relevant human neurons proceeds through mitochondrial dysfunction and NAD+ depletion-mediated axon degeneration, raising the possibility that targeting these changes might provide effective therapeutics for the prevention of bortezomib-induced neuropathy and that modeling chemotherapy-induced neuropathy in human neurons has utility.

The role of corticospinal and extrapyramidal pathways in motor impairment after stroke

Anisotropy of descending motor pathways has repeatedly been linked to the severity of motor impairment following stroke-related damage to the corticospinal tract. Despite promising findings consistently tying anisotropy of the ipsilesional corticospinal tract to motor outcome, anisotropy is not yet utilized as a biomarker for motor recovery in clinical practice as several methodological constraints hinder a conclusive understanding of degenerative processes in the ipsilesional corticospinal tract and compensatory roles of other descending motor pathways. These constraints include estimating anisotropy in voxels with multiple fibre directions, sampling biases and confounds due to ageing-related atrophy. The present study addressed these issues by combining diffusion spectrum imaging with a novel compartmentwise analysis approach differentiating voxels with one dominant fibre direction (one-directional voxels) from voxels with multiple fibre directions. Compartmentwise anisotropy for bihemispheric corticospinal and extrapyramidal tracts was compared between 25 chronic stroke patients, 22 healthy age-matched controls, and 24 healthy young controls and its associations with motor performance of the upper and lower limbs were assessed. Our results provide direct evidence for Wallerian degeneration along the entire length of the ipsilesional corticospinal tract reflected by decreased anisotropy in descending fibres compared with age-matched controls, while ageing-related atrophy was observed more ubiquitously across compartments. Anisotropy of descending ipsilesional corticospinal tract voxels showed highly robust correlations with various aspects of upper and lower limb motor impairment, highlighting the behavioural relevance of Wallerian degeneration. Moreover, anisotropy measures of two-directional voxels within bihemispheric rubrospinal and reticulospinal tracts were linked to lower limb deficits, while anisotropy of two-directional contralesional rubrospinal voxels explained gross motor performance of the affected hand. Of note, the relevant extrapyramidal structures contained fibres crossing the midline, fibres potentially mitigating output from brain stem nuclei, and fibres transferring signals between the extrapyramidal system and the cerebellum. Thus, specific parts of extrapyramidal pathways seem to compensate for impaired gross arm and leg movements incurred through stroke-related corticospinal tract lesions, while fine motor control of the paretic hand critically relies on ipsilesional corticospinal tract integrity. Importantly, our findings suggest that the extrapyramidal system may serve as a compensatory structural reserve independent of post-stroke reorganization of extrapyramidal tracts. In summary, compartment-specific anisotropy of ipsilesional corticospinal tract and extrapyramidal tracts explained distinct aspects of motor impairment, with both systems representing different pathophysiological mechanisms contributing to motor control post-stroke. Considering both systems in concert may help to develop diffusion imaging biomarkers for specific motor functions after stroke.

A Therapeutic Strategy for Lower Motor Neuron Disease and Injury Integrating Neural Stem Cell Transplantation and Functional Electrical Stimulation in a Rat Model

Promising treatments for upper motor neuron disease are emerging in which motor function is restored by brain–computer interfaces and functional electrical stimulation. At present, such technologies and procedures are not applicable to lower motor neuron disease. We propose a novel therapeutic strategy for lower motor neuron disease and injury integrating neural stem cell transplantation with our new functional electrical stimulation control system. In a rat sciatic nerve transection model, we transplanted embryonic spinal neural stem cells into the distal stump of the peripheral nerve to reinnervate denervated muscle, and subsequently demonstrated that highly responsive limb movement similar to that of a healthy limb could be attained with a wirelessly powered two-channel neurostimulator that we developed. This unique technology, which can reinnervate and precisely move previously denervated muscles that were unresponsive to electrical stimulation, contributes to improving the condition of patients suffering from intractable diseases of paralysis and traumatic injury.

Coordinated NADPH oxidase/hydrogen peroxide functions regulate cutaneous sensory axon de- and regeneration

Tissue wounding induces cutaneous sensory axon regeneration via hydrogen peroxide (H2O2) that is produced by the epithelial NADPH oxidase, Duox1. Sciatic nerve injury instead induces axon regeneration through neuronal uptake of the NADPH oxidase, Nox2, from macrophages. We therefore reasoned that the tissue environment in which axons are damaged stimulates distinct regenerative mechanisms. Here, we show that cutaneous axon regeneration induced by tissue wounding depends on both neuronal and keratinocyte-specific mechanisms involving H2O2 signaling. Genetic depletion of H2O2 in sensory neurons abolishes axon regeneration, whereas keratinocyte-specific H2O2 depletion promotes axonal repulsion, a phenotype mirrored in duox1 mutants. Intriguingly, cyba mutants, deficient in the essential Nox subunit, p22Phox, retain limited axon regenerative capacity but display delayed Wallerian degeneration and axonal fusion, observed so far only in invertebrates. We further show that keratinocyte-specific oxidation of the epidermal growth factor receptor (EGFR) at a conserved cysteine thiol (C797) serves as an attractive cue for regenerating axons, leading to EGFR-dependent localized epidermal matrix remodeling via the matrix-metalloproteinase, MMP-13. Therefore, wound-induced cutaneous axon de- and regeneration depend on the coordinated functions of NADPH oxidases mediating distinct processes following injury.

The chemical biology of NAD+ regulation in axon degeneration

During axon degeneration, NAD⁺ levels are largely controlled by two enzymes: nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) and sterile alpha and toll interleukin motif containing protein 1 (SARM1). NMNAT2, which catalyzes the formation of NAD⁺ from NMN and ATP, is actively degraded leading to decreased NAD⁺ levels. SARM1 activity further decreases the concentration of NAD⁺ by catalyzing its hydrolysis to form nicotinamide and a mixture of ADPR and cADPR. Notably, SARM1 knockout mice show decreased neurodegeneration in animal models of axon degeneration, highlighting the therapeutic potential of targeting this novel NAD⁺ hydrolase. This review discusses recent advances in the SARM1 field, including SARM1 structure, regulation, and catalysis as well as the identification of the first SARM1 inhibitors.

Differences in the localization of AQP1 and expression patterns of AQP isoforms in rat and mouse sciatic nerve and changes in rat AQPs expression after nerve crush injury

In the peripheral nervous system aquaporins (AQPs) have been reported in both peripheral neurons and glial cells. Previously we described the precise localization of AQP1 in the rat sciatic nerve, which is present in both Remak and myelin Schwann cells, and is enriched in the Schmidt-Lanterman incisures. In this work, we found that AQP1 in mouse is only present in Remak cells, showing a different localization between these species. However, after nerve crush injury the level of AQP1 mRNA expression remains constant at all times studied in rat and mouse. We then performed RT-PCR of nine AQP (AQP1-9) isoforms from rat and mouse sciatic nerve, we found that in rat only five AQPs are present (AQP1, AQP4, AQP5, AQP7 and AQP9), whereas in mouse all AQPs except AQP8 are expressed. Then, we studied the expression by RT-PCR of AQPs in rat after nerve crush injury, showing that AQP1, AQP4 and AQP7 expression remain constant at all times studied, while AQP2, AQP5 and AQP9 are upregulated after injury. Therefore, these two closely related rodents show different AQP1 localization and have different AQPs expression patterns in the sciatic nerve, possibly due to a difference in the regulation of these AQPs. The expression of AQP1 in Remak cells supports the involvement of AQP1 in pain perception. Also, in rat the upregulation of AQP2, AQP5 and AQP7 after nerve injury suggests a possible role for these AQPs in promoting regeneration following injury.

Diffusion restriction in the corticospinal tract and the corpus callosum of term neonates with hypoxic-ischemic encephalopathy

BACKGROUND

Diffusion-weighted imaging performed shortly after brain injury has been shown to facilitate visualization of acute corticospinal tract injury known as "pre-Wallerian degeneration."

OBJECTIVE

The aim of this study was to determine whether diffusion restriction in the corticospinal tract and corpus callosum occurs within the first 2 weeks after birth in neonates with neonatal hypoxic-ischemic encephalopathy.

MATERIALS AND METHODS

We enrolled a consecutive series of 66 infants diagnosed with hypoxic-ischemic encephalopathy who underwent MRI. We evaluated diffusion-weighted imaging (DWI) and apparent diffusion coefficient (ADC) values to assess the presence of restricted diffusion in the corticospinal tract and corpus callosum. Next, we compared ADC values in the corticospinal tract and in the splenium and genu of the corpus callosum of infants with abnormal pattern on MRI with those of control infants, who showed a normal pattern on MRI. We attempted to follow all infants with hypoxic-ischemic encephalopathy until 18 months of age and assess them using a standardized neurologic examination.

RESULTS

After exclusions, we recruited 25 infants with abnormal MRI and 20 with normal MRI (controls). Among these 45 neonates, pre-Wallerian degeneration was visualized in the corticospinal tract in 10 neonates and in the corpus callosum in 12. The ADC values in the corticospinal tract in the first week were significantly lower than they were in the second week. Infants with pre-Wallerian degeneration in the corticospinal tract showed an unfavorable outcome.

CONCLUSION

Pre-Wallerian degeneration was visualized in the corticospinal tract and corpus callosum and was associated with extensive brain injury caused by hypoxic-ischemic encephalopathy. The changes in signal were observed to evolve over time within the first 2 weeks. The clinical outcome of infants having pre-Wallerian degeneration in the corticospinal tract was unfavorable.

Of axons that struggle to make ends meet: Linking axonal bioenergetic failure to programmed axon degeneration

Axons are the long, fragile, and energy-hungry projections of neurons that are challenging to sustain. Together with their associated glia, they form the bulk of the neuronal network. Pathological axon degeneration (pAxD) is a driver of irreversible neurological disability in a host of neurodegenerative conditions. Halting pAxD is therefore an attractive therapeutic strategy. Here we review recent work demonstrating that pAxD is regulated by an auto-destruction program that revolves around axonal bioenergetics. We then focus on the emerging concept that axonal and glial energy metabolism are intertwined. We anticipate that these discoveries will encourage the pursuit of new treatment strategies for neurodegeneration.