RESUMEN
Neutrophils are a vital part of the innate immune system. Many of their functions eliminate bacteria & viruses, like neutrophil extracellular traps (NETs), which trap bacteria, enhancing macrophage phagocytosis. It was surprising when it was demonstrated that neutrophils are a part of Wallerian degeneration, a process that is essential for nerve regeneration after a nerve injury. It is not known what signals attract neutrophils into the nerve and how they aid Wallerian degeneration. Neutrophils accumulate in the distal nerve within one day after an injury and are found in the nerve from one to three days. We demonstrate that CXCR2 mediates the trafficking of neutrophils into the distal nerve, and without CXCR2 Wallerian degeneration, as indicated by luxol fast blue staining, was reduced seven days after a sciatic nerve crush or transection injury. NETs were detected in the distal nerve after a sciatic nerve transection. NET formation has been shown to require protein arginine deiminase 4 (PAD4), which citrullinates histone 3. Inhibiting PAD4 reduced NET formation significantly in the distal nerve at two days and myelin clearance at seven days indicating that NETs aid myelin clearance. These results demonstrate another function for NETs other than clearing pathogens. Neutrophils have been detected after injuries to the central nervous system and diseases in humans and animal models. Our results demonstrate neutrophils aid myelin clearance, suggesting a role for their presence in central nervous system injuries and diseases.
Asunto(s)
Trampas Extracelulares , Vaina de Mielina , Neutrófilos , Traumatismos de los Nervios Periféricos , Receptores de Interleucina-8B , Degeneración Walleriana , Neutrófilos/metabolismo , Neutrófilos/inmunología , Animales , Receptores de Interleucina-8B/metabolismo , Trampas Extracelulares/metabolismo , Ratones , Vaina de Mielina/metabolismo , Vaina de Mielina/patología , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patología , Degeneración Walleriana/inmunología , Traumatismos de los Nervios Periféricos/metabolismo , Traumatismos de los Nervios Periféricos/inmunología , Ratones Endogámicos C57BL , Masculino , FemeninoRESUMEN
Neuritin, also known as candidate plasticity gene 15 (CPG15), was first identified as one of the activity-dependent gene products in the brain. Previous studies have been reported that Neuritin induces neuritogenesis, neurite arborization, neurite outgrowth and synapse formation, which are involved in the development and functions of the central nervous system. However, the role of Neuritin in peripheral nerve injury is still unknown. Given the importance and necessity of Schwann cell dedifferentiation response to peripheral nerve injury, we aim to investigate the molecular mechanism of Neuritin steering Schwann cell dedifferentiation during Wallerian degeneration (WD) in injured peripheral nerve. Herein, using the explants of sciatic nerve, an ex vivo model of nerve degeneration, we provided evidences indicating that Neuritin vividly accelerates Schwann cell dedifferentiation. Moreover, we found that Neuritin promotes Schwann cell demyelination as well as axonal degeneration, phagocytosis, secretion capacity. In summary, we first described Neuritin acts as a positive regulator for Schwann cell dedifferentiation and WD after peripheral nerve injury.
Asunto(s)
Desdiferenciación Celular , Neuropéptidos , Fosfatidilinositol 3-Quinasas , Proteínas Proto-Oncogénicas c-akt , Células de Schwann , Nervio Ciático , Transducción de Señal , Serina-Treonina Quinasas TOR , Degeneración Walleriana , Células de Schwann/metabolismo , Células de Schwann/patología , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patología , Animales , Serina-Treonina Quinasas TOR/metabolismo , Proteínas Proto-Oncogénicas c-akt/metabolismo , Fosfatidilinositol 3-Quinasas/metabolismo , Neuropéptidos/metabolismo , Neuropéptidos/genética , Nervio Ciático/lesiones , Nervio Ciático/metabolismo , Nervio Ciático/patología , Proteínas Ligadas a GPI/metabolismo , Proteínas Ligadas a GPI/genética , Ratas , Traumatismos de los Nervios Periféricos/metabolismo , Traumatismos de los Nervios Periféricos/patología , Ratas Sprague-Dawley , Axones/metabolismo , Axones/patología , Masculino , Fagocitosis , RatonesRESUMEN
Spinal cord contusion injury results in Wallerian degeneration of spinal cord axonal tracts, which are necessary for locomotor function. Axonal swelling and loss of axonal density at the contusion site, characteristic of Wallerian degeneration, commence within hours of injury. Tempol, a superoxide dismutase mimetic, was previously shown to reduce the loss of spinal cord white matter and improve locomotor function in an experimental model of spinal cord contusion, suggesting that tempol treatment might inhibit Wallerian degeneration of spinal cord axons. Here, we report that tempol partially inhibits Wallerian degeneration, resulting in improved locomotor recovery. We previously reported that Wallerian degeneration is reduced by inhibitors of aldose reductase (AR), which converts glucose to sorbitol in the polyol pathway. We observed that tempol inhibited sorbitol production in the injured spinal cord to the same extent as the AR inhibitor, sorbinil. Tempol also prevented post-contusion upregulation of AR (AKR1B10) protein expression within degenerating axons, as previously observed for AR inhibitors. Additionally, we hypothesized that tempol inhibits axonal degeneration by preventing loss of the glutathione pool due to polyol pathway activity. Consistent with our hypothesis, tempol treatment resulted in greater glutathione content in the injured spinal cord, which was correlated with increased expression and activity of gamma glutamyl cysteine ligase (γGCL; EC 6.3.2.2), the rate-limiting enzyme for glutathione synthesis. Administration of the γGCL inhibitor buthionine sulfoximine abolished all observed effects of tempol administration. Together, these results support a pathological role for polyol pathway activation in glutathione depletion, resulting in Wallerian degeneration after spinal cord injury (SCI). Interestingly, methylprednisolone, oxandrolone, and clenbuterol, which are known to spare axonal tracts after SCI, were equally effective in inhibiting polyol pathway activation. These results suggest that prevention of AR activation is a common target of many disparate post-SCI interventions.
Asunto(s)
Aldehído Reductasa , Óxidos N-Cíclicos , Glutatión , Marcadores de Spin , Traumatismos de la Médula Espinal , Degeneración Walleriana , Animales , Degeneración Walleriana/metabolismo , Degeneración Walleriana/tratamiento farmacológico , Aldehído Reductasa/antagonistas & inhibidores , Aldehído Reductasa/metabolismo , Óxidos N-Cíclicos/farmacología , Traumatismos de la Médula Espinal/metabolismo , Traumatismos de la Médula Espinal/tratamiento farmacológico , Ratas , Glutatión/metabolismo , Ratas Sprague-Dawley , Femenino , Activación Enzimática/efectos de los fármacos , Fármacos Neuroprotectores/farmacología , Superóxido Dismutasa/metabolismo , Superóxido Dismutasa/efectos de los fármacos , Antioxidantes/farmacología , Modelos Animales de EnfermedadRESUMEN
Neurotoxic organophosphorus compounds can induce a type of delayed neuropathy in humans and sensitive animals, known as organophosphorus-induced delayed neuropathy (OPIDN). OPIDN is characterized by axonal degeneration akin to Wallerian-like degeneration, which is thought to be caused by increased intra-axonal Ca2+ concentrations. This study was designed to investigate that deregulated cytosolic Ca2+ may function downstream of mitodysfunction in activating Wallerian-like degeneration and necroptosis in OPIDN. Adult hens were administrated a single dosage of 750â¯mg/kg tri-ortho-cresyl phosphate (TOCP), and then sacrificed at 1â¯day, 5â¯day, 10â¯day and 21â¯day post-exposure, respectively. Sciatic nerves and spinal cords were examined for pathological changes and proteins expression related to Wallerian-like degeneration and necroptosis. In vitro experiments using differentiated neuro-2a (N2a) cells were conducted to investigate the relationship among mitochondrial dysfunction, Ca2+ influx, axonal degeneration, and necroptosis. The cells were co-administered with the Ca2+-chelator BAPTA-AM, the TRPA1 channel inhibitor HC030031, the RIPK1 inhibitor Necrostatin-1, and the mitochondrial-targeted antioxidant MitoQ along with TOCP. Results demonstrated an increase in cytosolic calcium concentration and key proteins associated with Wallerian degeneration and necroptosis in both in vivo and in vitro models after TOCP exposure. Moreover, co-administration with BATPA-AM or HC030031 significantly attenuated the loss of NMNAT2 and STMN2 in N2a cells, as well as the upregulation of SARM1, RIPK1 and p-MLKL. In contrast, Necrostatin-1 treatment only inhibited the TOCP-induced elevation of p-MLKL. Notably, pharmacological protection of mitochondrial function with MitoQ effectively alleviated the increase in intracellular Ca2+ following TOCP and mitigated axonal degeneration and necroptosis in N2a cells, supporting mitochondrial dysfunction as an upstream event of the intracellular Ca2+ imbalance and neuronal damage in OPIDN. These findings suggest that mitochondrial dysfunction post-TOCP intoxication leads to an elevated intracellular Ca2+ concentration, which plays a pivotal role in the initiation and development of OPIDN through inducing SARM1-mediated axonal degeneration and activating the necroptotic signaling pathway.
Asunto(s)
Calcio , Pollos , Mitocondrias , Necroptosis , Degeneración Walleriana , Animales , Necroptosis/efectos de los fármacos , Calcio/metabolismo , Mitocondrias/efectos de los fármacos , Mitocondrias/metabolismo , Mitocondrias/patología , Degeneración Walleriana/inducido químicamente , Degeneración Walleriana/patología , Degeneración Walleriana/metabolismo , Femenino , Ratones , Tritolilfosfatos/toxicidad , Médula Espinal/efectos de los fármacos , Médula Espinal/metabolismo , Médula Espinal/patología , Nervio Ciático/efectos de los fármacos , Nervio Ciático/patología , Síndromes de Neurotoxicidad/patología , Síndromes de Neurotoxicidad/metabolismo , Síndromes de Neurotoxicidad/etiología , Compuestos Organofosforados/toxicidad , Compuestos Organofosforados/farmacología , Línea Celular TumoralRESUMEN
Sterile alpha and TIR motif-containing 1 (SARM1) is a protein involved in programmed death of injured axons. Following axon injury or a drug-induced insult, the TIR domain of SARM1 degrades the essential molecule nicotinamide adenine dinucleotide (NAD+), leading to a form of axonal death called Wallerian degeneration. Degradation of NAD+ by SARM1 is essential for the Wallerian degeneration process, but accumulating evidence suggest that other activities of SARM1, beyond the mere degradation of NAD+, may be necessary for programmed axonal death. In this study we show that the TIR domains of both human and fruit fly SARM1 produce 1''-2' and 1''-3' glycocyclic ADP-ribose (gcADPR) molecules as minor products. As previously reported, we observed that SARM1 TIR domains mostly convert NAD+ to ADPR (for human SARM1) or cADPR (in the case of SARM1 from Drosophila melanogaster). However, we now show that human and Drosophila SARM1 additionally convert ~0.1-0.5% of NAD+ into gcADPR molecules. We find that SARM1 TIR domains produce gcADPR molecules both when purified in vitro and when expressed in bacterial cells. Given that gcADPR is a second messenger involved in programmed cell death in bacteria and likely in plants, we propose that gcADPR may play a role in SARM1-induced programmed axonal death in animals.
Asunto(s)
NAD , Degeneración Walleriana , Animales , Humanos , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patología , NAD/metabolismo , Drosophila melanogaster/metabolismo , Axones/metabolismo , Bacterias/metabolismo , Adenosina Difosfato Ribosa/metabolismo , Proteínas del Dominio Armadillo/genética , Proteínas del Dominio Armadillo/metabolismo , Proteínas del Citoesqueleto/genética , Proteínas del Citoesqueleto/metabolismoRESUMEN
Iron accumulates in the neural tissue during peripheral nerve degeneration. Some studies have already been suggested that iron facilitates Wallerian degeneration (WD) events such as Schwann cell de-differentiation. On the other hand, intracellular iron levels remain elevated during nerve regeneration and gradually decrease. Iron enhances Schwann cell differentiation and axonal outgrowth. Therefore, there seems to be a paradox in the role of iron during nerve degeneration and regeneration. We explain this contradiction by suggesting that the increase in intracellular iron concentration during peripheral nerve degeneration is likely to prepare neural cells for the initiation of regeneration. Changes in iron levels are the result of changes in the expression of iron homeostasis proteins. In this review, we will first discuss the changes in the iron/iron homeostasis protein levels during peripheral nerve degeneration and regeneration and then explain how iron is related to nerve regeneration. This data may help better understand the mechanisms of peripheral nerve repair and find a solution to prevent or slow the progression of peripheral neuropathies.
Asunto(s)
Enfermedades del Sistema Nervioso Periférico , Humanos , Enfermedades del Sistema Nervioso Periférico/metabolismo , Degeneración Nerviosa , Nervios Periféricos , Degeneración Walleriana/metabolismo , Neuronas/metabolismoRESUMEN
PPARγ coactivator-1 alpha (PGC-1α) is an essential transcription factor co-activator that regulates gene transcription and neural regeneration. Schwann cells, which are unique glial cells in peripheral nerves that dedifferentiate after peripheral nerve injury (PNI) and are released from degenerative nerves. Wallerian degeneration is a series of stereotypical events that occurs in response to nerve fibers after PNI. The role of PGC-1α in Schwann cell dedifferentiation and Wallerian degeneration is not yet clear. As Wallerian degeneration plays a crucial role in PNI, we conducted a study to determine whether PGC-1α has an effect on peripheral nerve degeneration after injury. We examined the expression of PGC-1α after sciatic nerve crush or transection using Western blotting and found that PGC-1α expression increased after PNI. Then we utilized ex vivo and in vitro models to investigate the effects of PGC-1α inhibition and activation on Schwann cell dedifferentiation and nerve degeneration. Our findings indicate that PGC-1α negatively regulates Schwann cell dedifferentiation and nerve degeneration. Through the use of RNA-seq, siRNA/plasmid transfection and reversal experiments, we identified that PGC-1α targets inhibit the expression of paraoxonase 1 (PON1) during Schwann cell dedifferentiation in degenerated nerves. In summary, PGC-1α plays a crucial role in preventing Schwann cell dedifferentiation and its activation can reduce peripheral nerve degeneration by targeting PON1. PGC-1α inhibits Schwann cell dedifferentiation and peripheral nerve degeneration. PGC-1α negatively regulates Schwann cell dedifferentiation and peripheral nerve degeneration after injury by targeting PON1.
Asunto(s)
Arildialquilfosfatasa , Traumatismos de los Nervios Periféricos , Humanos , Arildialquilfosfatasa/metabolismo , Arildialquilfosfatasa/farmacología , Desdiferenciación Celular , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patología , Células de Schwann , Nervio Ciático/patología , Traumatismos de los Nervios Periféricos/patología , Regeneración Nerviosa/fisiologíaRESUMEN
Wallerian axonal degeneration (WD) does not occur in the nematode C. elegans, in contrast to other model animals. However, WD depends on the NADase activity of SARM1, a protein that is also expressed in C. elegans (ceSARM/ceTIR-1). We hypothesized that differences in SARM between species might exist and account for the divergence in WD. We first show that expression of the human (h)SARM1, but not ceTIR-1, in C. elegans neurons is sufficient to confer axon degeneration after nerve injury. Next, we determined the cryoelectron microscopy structure of ceTIR-1 and found that, unlike hSARM1, which exists as an auto-inhibited ring octamer, ceTIR-1 forms a readily active 9-mer. Enzymatically, the NADase activity of ceTIR-1 is substantially weaker (10-fold higher Km) than that of hSARM1, and even when fully active, it falls short of consuming all cellular NAD+. Our experiments provide insight into the molecular mechanisms and evolution of SARM orthologs and WD across species.
Asunto(s)
Axones , Caenorhabditis elegans , Animales , Humanos , Axones/metabolismo , Caenorhabditis elegans/metabolismo , Microscopía por Crioelectrón , Neuronas/metabolismo , Proteínas del Dominio Armadillo/metabolismo , NAD+ Nucleosidasa/metabolismo , Degeneración Walleriana/metabolismoRESUMEN
Significance: The remarkable geometry of the axon exposes it to unique challenges for survival and maintenance. Axonal degeneration is a feature of peripheral neuropathies, glaucoma, and traumatic brain injury, and an early event in neurodegenerative diseases. Since the discovery of Wallerian degeneration (WD), a molecular program that hijacks nicotinamide adenine dinucleotide (NAD+) metabolism for axonal self-destruction, the complex roles of NAD+ in axonal viability and disease have become research priority. Recent Advances: The discoveries of the protective Wallerian degeneration slow (WldS) and of sterile alpha and TIR motif containing 1 (SARM1) activation as the main instructive signal for WD have shed new light on the regulatory role of NAD+ in axonal degeneration in a growing number of neurological diseases. SARM1 has been characterized as a NAD+ hydrolase and sensor of NAD+ metabolism. The discovery of regulators of nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) proteostasis in axons, the allosteric regulation of SARM1 by NAD+ and NMN, and the existence of clinically relevant windows of action of these signals has opened new opportunities for therapeutic interventions, including SARM1 inhibitors and modulators of NAD+ metabolism. Critical Issues: Events upstream and downstream of SARM1 remain unclear. Furthermore, manipulating NAD+ metabolism, an overdetermined process crucial in cell survival, for preventing the degeneration of the injured axon may be difficult and potentially toxic. Future Directions: There is a need for clarification of the distinct roles of NAD+ metabolism in axonal maintenance as contrasted to WD. There is also a need to better understand the role of NAD+ metabolism in axonal endangerment in neuropathies, diseases of the white matter, and the early stages of neurodegenerative diseases of the central nervous system. Antioxid. Redox Signal. 39, 1167-1184.
Asunto(s)
Enfermedades Neurodegenerativas , Enfermedades del Sistema Nervioso Periférico , Humanos , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patología , NAD/metabolismo , Enfermedades del Sistema Nervioso Periférico/metabolismo , Axones/metabolismo , Enfermedades Neurodegenerativas/metabolismoRESUMEN
The cellular and molecular underpinnings of Wallerian degeneration have been robustly explored in laboratory models of successful nerve regeneration. In contrast, there is limited interrogation of failed regeneration, which is the challenge facing clinical practice. Specifically, we lack insight on the pathophysiologic mechanisms that lead to the formation of neuromas-in-continuity (NIC). To address this knowledge gap, we have developed and validated a novel basic science model of rapid-stretch nerve injury, which provides a biofidelic injury with NIC development and incomplete neurologic recovery. In this study, we applied next-generation RNA sequencing to elucidate the temporal transcriptional landscape of pathophysiologic nerve regeneration. To corroborate genetic analysis, nerves were subject to immunofluorescent staining for transcripts representative of the prominent biological pathways identified. Pathophysiologic nerve regeneration produces substantially altered genetic profiles both temporally and in the mature neuroma microenvironment, in contrast to the coordinated genetic signatures of Wallerian degeneration and successful regeneration. To our knowledge, this study presents as the first transcriptional study of NIC pathophysiology and has identified cellular death, fibrosis, neurodegeneration, metabolism, and unresolved inflammatory signatures that diverge from pathways elaborated by traditional models of successful nerve regeneration.
Asunto(s)
Tejido Nervioso , Neuroma , Traumatismos de los Nervios Periféricos , Humanos , Transcriptoma , Degeneración Walleriana/metabolismo , Regeneración Nerviosa/genética , Tejido Nervioso/metabolismo , Neuroma/patología , Análisis de Secuencia de ARN , Nervio Ciático/lesiones , Traumatismos de los Nervios Periféricos/genética , Traumatismos de los Nervios Periféricos/patología , Microambiente TumoralRESUMEN
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.
Asunto(s)
Axones , Degeneración Walleriana , Animales , Ratas , Ratones , Axotomía , Axones/metabolismo , Degeneración Walleriana/metabolismo , Nervio Ciático/metabolismo , Adenosina Trifosfato/metabolismo , Regeneración Nerviosa/fisiologíaRESUMEN
Nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2) is an evolutionarily conserved nicotinamide adenine dinucleotide (NAD+) synthase located in the cytoplasm and Golgi apparatus. NMNAT2 has an important role in neurodegenerative diseases, malignant tumors, and other diseases that seriously endanger human health. NMNAT2 exerts a neuroprotective function through its NAD synthase activity and chaperone function. Among them, the NMNAT2-NAD+-Sterile alpha and Toll/interleukin-1 receptor motif-containing 1 (SARM1) axis is closely related to Wallerian degeneration. Physical injury or pathological stimulation will cause a decrease in NMNAT2, which activates SARM1, leading to axonal degeneration and the occurrence of amyotrophic lateral sclerosis (ALS), Alzheimer's disease, peripheral neuropathy, and other neurodegenerative diseases. In addition, NMNAT2 exerts a cancer-promoting role in solid tumors, including colorectal cancer, lung cancer, ovarian cancer, and glioma, and is closely related to tumor occurrence and development. This paper reviews the chromosomal and subcellular localization of NMNAT2 and its basic biological functions. We also summarize the NMNAT2-related signal transduction pathway and the role of NMNAT2 in diseases. We aimed to provide a new perspective to comprehensively understand the relationship between NMNAT2 and its associated diseases.
Asunto(s)
Enfermedades Neurodegenerativas , Nicotinamida-Nucleótido Adenililtransferasa , Humanos , Axones , NAD/metabolismo , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patología , Enfermedades Neurodegenerativas/patología , Progresión de la Enfermedad , Nicotinamida-Nucleótido Adenililtransferasa/genética , Nicotinamida-Nucleótido Adenililtransferasa/metabolismoRESUMEN
Upon trauma, the adult murine peripheral nervous system (PNS) displays a remarkable degree of spontaneous anatomical and functional regeneration. To explore extrinsic mechanisms of neural repair, we carried out single-cell analysis of naïve mouse sciatic nerve, peripheral blood mononuclear cells, and crushed sciatic nerves at 1 day, 3 days, and 7 days following injury. During the first week, monocytes and macrophages (Mo/Mac) rapidly accumulate in the injured nerve and undergo extensive metabolic reprogramming. Proinflammatory Mo/Mac with a high glycolytic flux dominate the early injury response and rapidly give way to inflammation resolving Mac, programmed toward oxidative phosphorylation. Nerve crush injury causes partial leakiness of the blood-nerve barrier, proliferation of endoneurial and perineurial stromal cells, and entry of opsonizing serum proteins. Micro-dissection of the nerve injury site and distal nerve, followed by single-cell RNA-sequencing, identified distinct immune compartments, triggered by mechanical nerve wounding and Wallerian degeneration, respectively. This finding was independently confirmed with Sarm1-/- mice, in which Wallerian degeneration is greatly delayed. Experiments with chimeric mice showed that wildtype immune cells readily enter the injury site in Sarm1-/- mice, but are sparse in the distal nerve, except for Mo. We used CellChat to explore intercellular communications in the naïve and injured PNS and report on hundreds of ligand-receptor interactions. Our longitudinal analysis represents a new resource for neural tissue regeneration, reveals location- specific immune microenvironments, and reports on large intercellular communication networks. To facilitate mining of scRNAseq datasets, we generated the injured sciatic nerve atlas (iSNAT): https://cdb-rshiny.med.umich.edu/Giger_iSNAT/.
Asunto(s)
Traumatismos de los Nervios Periféricos , Degeneración Walleriana , Ratones , Animales , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patología , Leucocitos Mononucleares , Nervio Ciático/metabolismo , Degeneración Nerviosa , Compresión Nerviosa , Traumatismos de los Nervios Periféricos/metabolismo , Regeneración Nerviosa , Proteínas del Citoesqueleto/metabolismo , Proteínas del Dominio Armadillo/metabolismoRESUMEN
Neurodegeneration arising from aging, injury, or diseases has devastating health consequences. Whereas neuronal survival and axon degeneration have been studied extensively, much less is known about how neurodegeneration affects dendrites, in part due to the limited assay systems available. To develop an assay for dendrite degeneration and repair, we used photo-switchable caspase-3 (caspase-Light-Oxygen-Voltage-sensing [caspase-LOV]) in peripheral class 4 dendrite arborization (c4da) neurons to induce graded neurodegeneration by adjusting illumination duration during development and adulthood in Drosophila melanogaster. We found that both developing and mature c4da neurons were able to survive while sustaining mild neurodegeneration induced by moderate caspase-LOV activation. Further, we observed active dendrite addition and dendrite regeneration in developing and mature c4da neurons, respectively. Using this assay, we found that the mouse Wallerian degeneration slow (WldS) protein can protect c4da neurons from caspase-LOV-induced dendrite degeneration and cell death. Furthermore, our data show that WldS can reduce dendrite elimination without affecting dendrite addition. In summary, we successfully established a photo-switchable assay system in both developing and mature neurons and used WldS as a test case to study the mechanisms underlying dendrite regeneration and repair.
Asunto(s)
Dendritas/metabolismo , Drosophila melanogaster , Animales , Caspasas/metabolismo , Técnicas Citológicas/métodos , Proteínas de Drosophila/genética , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/metabolismo , Ratones , Neuronas/metabolismo , Degeneración Walleriana/metabolismoRESUMEN
Wallerian degeneration (WD) is a conserved axonal self-destruction program implicated in several neurological diseases. WD is driven by the degradation of the NAD+ synthesizing enzyme NMNAT2, the buildup of its substrate NMN, and the activation of the NAD+ degrading SARM1, eventually leading to axonal fragmentation. The regulation and amenability of these events to therapeutic interventions remain unclear. Here we explored pharmacological strategies that modulate NMN and NAD+ metabolism, namely the inhibition of the NMN-synthesizing enzyme NAMPT, activation of the nicotinic acid riboside (NaR) salvage pathway and inhibition of the NMNAT2-degrading DLK MAPK pathway in an axotomy model in vitro. Results show that NAMPT and DLK inhibition cause a significant but time-dependent delay of WD. These time-dependent effects are related to NMNAT2 degradation and changes in NMN and NAD+ levels. Supplementation of NAMPT inhibition with NaR has an enhanced effect that does not depend on timing of intervention and leads to robust protection up to 4 days. Additional DLK inhibition extends this even further to 6 days. Metabolite analyses reveal complex effects indicating that NAMPT and MAPK inhibition act by reducing NMN levels, ameliorating NAD+ loss and suppressing SARM1 activity. Finally, the axonal NAD+/NMN ratio is highly predictive of cADPR levels, extending previous cell-free evidence on the allosteric regulation of SARM1. Our findings establish a window of axon protection extending several hours following injury. Moreover, we show prolonged protection by mixed treatments combining MAPK and NAMPT inhibition that proceed via complex effects on NAD+ metabolism and inhibition of SARM1.
Asunto(s)
Nicotinamida Fosforribosiltransferasa/antagonistas & inhibidores , Nicotinamida-Nucleótido Adenililtransferasa , Degeneración Walleriana , Animales , Proteínas del Dominio Armadillo/metabolismo , Axones/patología , Proteínas del Citoesqueleto/metabolismo , Humanos , Mamíferos/metabolismo , NAD/metabolismo , Degeneración Nerviosa/patología , Nicotinamida-Nucleótido Adenililtransferasa/metabolismo , Inhibidores de Proteínas Quinasas , Degeneración Walleriana/metabolismoRESUMEN
Wallerian degeneration (WD) is a well-known process by which degenerating axons and myelin are cleared after nerve injury. Although organophosphate-induced delayed neuropathy (OPIDN) is characterized by Wallerian-like degeneration of long axons in human and sensitive animals, the precise pathological mechanism remains unclear. In this study, we cultured embryonic chicken dorsal root ganglia (DRG) neurons, the model of OPIDN in vitro, to investigate the underlying mechanism of axon degeneration induced by tri-ortho-cresyl phosphate (TOCP), an OPIDN inducer. The results showed that TOCP exposure time- and concentration-dependently induced a serious degeneration and fragmentation of the axons from the DRG neurons. A collapse of mitochondrial membrane potential and a dramatic depletion of ATP levels were found in the DRG neurons after TOCP treatment. In addition, nicotinamide nucleotide adenylyl transferase 2 (NMNAT2) expression and nicotinamide adenine dinucleotide (NAD+) level was also found to be decreased in the DRG neurons exposed to TOCP. However, the TOCP-induced Wallerian degeneration in the DRG neurons could be inhibited by ATP supplementation. And exogenous NAD+ or NAD+ processor nicotinamide riboside can rescue TOCP-induced ATP deficiency and prevent TOCP-induced axon degeneration of the DRG neurons. These findings may shed light on the pathophysiological mechanism of TOCP-induced axonal damages, and implicate the potential application of NAD+ to treat OPIDN.
Asunto(s)
Enfermedades del Sistema Nervioso Periférico , Tritolilfosfatos , Adenosina Trifosfato/metabolismo , Animales , Axones , Pollos , Ganglios Espinales , NAD/metabolismo , Neuronas , Organofosfatos/metabolismo , Fosfatos , Tritolilfosfatos/metabolismo , Tritolilfosfatos/toxicidad , Degeneración Walleriana/inducido químicamente , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patologíaRESUMEN
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.
Asunto(s)
Enfermedades Neurodegenerativas , Degeneración Walleriana , Axones/metabolismo , Axones/patología , Metabolismo Energético , Humanos , Enfermedades Neurodegenerativas/metabolismo , Enfermedades Neurodegenerativas/patología , Degeneración Walleriana/metabolismo , Degeneración Walleriana/patologíaRESUMEN
Injury to the spinal cord is devastating. Studies have implicated Wallerian degeneration as the main cause of axonal destruction in the wake of spinal cord injury. Therefore, the suppression of Wallerian degeneration could be beneficial for spinal cord injury treatment. Sterile alpha and armadillo motif-containing protein 1 (SARM1) is a key modulator of Wallerian degeneration, and its impediment can improve spinal cord injury to a significant degree. In this report, we analyze the various signaling domains of SARM1, the recent findings on Wallerian degeneration and its relation to axonal insults, as well as its connection to SARM1, the mitogen-activated protein kinase (MAPK) signaling, and the survival factor, nicotinamide mononucleotide adenylyltransferase 2 (NMNAT2). We then elaborate on the possible role of SARM1 in spinal cord injury and explicate how its obstruction could potentially alleviate the injury.
Asunto(s)
Proteínas del Dominio Armadillo/metabolismo , Proteínas del Citoesqueleto/metabolismo , Degeneración Walleriana/metabolismo , Axones/metabolismo , Humanos , Transducción de Señal , Traumatismos de la Médula Espinal/terapia , Degeneración Walleriana/fisiopatologíaRESUMEN
After injury, severed dendrites and axons expose the "eat-me" signal phosphatidylserine (PS) on their surface while they break down. The degeneration of injured axons is controlled by a conserved Wallerian degeneration (WD) pathway, which is thought to activate neurite self-destruction through Sarm-mediated nicotinamide adenine dinucleotide (NAD+) depletion. While neurite PS exposure is known to be affected by genetic manipulations of NAD+, how the WD pathway coordinates both neurite PS exposure and self-destruction and whether PS-induced phagocytosis contributes to neurite breakdown in vivo remain unknown. Here, we show that in Drosophila sensory dendrites, PS exposure and self-destruction are two sequential steps of WD resulting from Sarm activation. Surprisingly, phagocytosis is the main driver of dendrite degeneration induced by both genetic NAD+ disruptions and injury. However, unlike neuronal Nmnat loss, which triggers PS exposure only and results in phagocytosis-dependent dendrite degeneration, injury activates both PS exposure and self-destruction as two redundant means of dendrite degeneration. Furthermore, the axon-death factor Axed is only partially required for self-destruction of injured dendrites, acting in parallel with PS-induced phagocytosis. Lastly, injured dendrites exhibit a unique rhythmic calcium-flashing that correlates with WD. Therefore, both NAD+-related general mechanisms and dendrite-specific programs govern PS exposure and self-destruction in injury-induced dendrite degeneration in vivo.
Asunto(s)
Dendritas/metabolismo , Fagocitosis , Células Receptoras Sensoriales/metabolismo , Degeneración Walleriana/etiología , Degeneración Walleriana/metabolismo , Animales , Drosophila , Proteínas de Drosophila/deficiencia , Técnica del Anticuerpo Fluorescente , Técnicas de Silenciamiento del Gen , Degeneración Nerviosa , Nicotinamida-Nucleótido Adenililtransferasa/deficiencia , Fosfatidilserinas/metabolismo , Degeneración Walleriana/patologíaRESUMEN
Hundreds of millions of people worldwide suffer from peripheral nerve damage resulting from car accidents, falls, industrial accidents, residential accidents, and wars. The purpose of our study was to further investigate the effects of Wallerian degeneration (WD) after rat sciatic nerve injury and to screen for critical long noncoding RNAs (lncRNAs) in WD. We found H19 to be essential for nerve degeneration and regeneration and to be highly expressed in the sciatic nerves of rats with WD. lncRNA H19 potentially impaired the recovery of sciatic nerve function in rats. H19 was mainly localized in the cytoplasm of Schwann cells (SCs) and promoted their migration. H19 promoted the apoptosis of dorsal root ganglion (DRG) neurons and slowed the growth of DRG axons. The lncRNA H19 may play a role in WD through the Wnt/ß-catenin signaling pathway and is coexpressed with a variety of crucial mRNAs during WD. These data provide further insight into the molecular mechanisms of WD.