Adult motor neuron apoptosis is mediated by nitric oxide and Fas death receptor linked by DNA damage and p53 activation

The Role of Hydrogen Sulfide in the Localization and Expression of p53 and Cell Death in the Nervous Tissue in Traumatic Brain Injury and Axotomy

Traumatic brain injury (TBI) is one of the leading causes of disability and death worldwide. It is characterized by various molecular-cellular events, with the main ones being apoptosis and damage to axons. To date, there are no clinically effective neuroprotective drugs. In this study, we examined the role of hydrogen sulfide (H2S) in the localization and expression of the key pro-apoptotic protein p53, as well as cell death in the nervous tissue in TBI and axotomy. We used a fast donor (sodium sulphide, Na2S) H2S and a classic inhibitor (aminooxyacetic acid, AOAA) of cystathionine β-synthase (CBS), which is a key enzyme in H2S synthesis. These studies were carried out on three models of neurotrauma in vertebrates and invertebrates. As a result, it was found that Na2S exhibits a pronounced neuroprotective effect that reduces the number of TUNEL-positive neurons and glial cells in TBI and apoptotic glia in axotomy. This effect could be realized through the Na2S-dependent decrease in the level of p53 in the cells of the nervous tissue of vertebrates and invertebrates, which we observed in our study. We also observed the opposite effect when using AOAA, which indicates the important role of CBS in the regulation of p53 expression and death of neurons and glial cells in TBI and axotomy.

Hypothermic Protection in Neocortex Is Topographic and Laminar, Seizure Unmitigating, and Partially Rescues Neurons Depleted of RNA Splicing Protein Rbfox3/NeuN in Neonatal Hypoxic-Ischemic Male Piglets

The effects of hypothermia on neonatal encephalopathy may vary topographically and cytopathologically in the neocortex with manifestations potentially influenced by seizures that alter the severity, distribution, and type of neuropathology. We developed a neonatal piglet survival model of hypoxic-ischemic (HI) encephalopathy and hypothermia (HT) with continuous electroencephalography (cEEG) for seizures. Neonatal male piglets received HI-normothermia (NT), HI-HT, sham-NT, or sham-HT treatments. Randomized unmedicated sham and HI piglets underwent cEEG during recovery. Survival was 2-7 days. Normal and pathological neurons were counted in different neocortical areas, identified by cytoarchitecture and connectomics, using hematoxylin and eosin staining and immunohistochemistry for RNA-binding FOX-1 homolog 3 (Rbfox3/NeuN). Seizure burden was determined. HI-NT piglets had a reduced normal/total neuron ratio and increased ischemic-necrotic/total neuron ratio relative to sham-NT and sham-HT piglets with differing severities in the anterior and posterior motor, somatosensory, and frontal cortices. Neocortical neuropathology was attenuated by HT. HT protection was prominent in layer III of the inferior parietal cortex. Rbfox3 immunoreactivity distinguished cortical neurons as: Rbfox3-positive/normal, Rbfox3-positive/ischemic-necrotic, and Rbfox3-depleted. HI piglets had an increased Rbfox3-depleted/total neuron ratio in layers II and III compared to sham-NT piglets. Neuronal Rbfox3 depletion was partly rescued by HT. Seizure burdens in HI-NT and HI-HT piglets were similar. We conclude that the neonatal HI piglet neocortex has: (1) suprasylvian vulnerability to HI and seizures; (2) a limited neuronal cytopathological repertoire in functionally different regions that engages protective mechanisms with HT; (3) higher seizure burden, insensitive to HT, that is correlated with more panlaminar ischemic-necrotic neurons in the somatosensory cortex; and (4) pathological RNA splicing protein nuclear depletion that is sensitive to HT. This work demonstrates that HT protection of the neocortex in neonatal HI is topographic and laminar, seizure unmitigating, and restores neuronal depletion of RNA splicing factor.

A distinct circular DNA profile intersects with proteome changes in the genotoxic stress-related hSOD1G93A model of ALS

BACKGROUND

Numerous genes, including SOD1, mutated in familial and sporadic amyotrophic lateral sclerosis (f/sALS) share a role in DNA damage and repair, emphasizing genome disintegration in ALS. One possible outcome of chromosomal instability and repair processes is extrachromosomal circular DNA (eccDNA) formation. Therefore, eccDNA might accumulate in f/sALS with yet unknown function.

METHODS

We combined rolling circle amplification with linear DNA digestion to purify eccDNA from the cervical spinal cord of 9 co-isogenic symptomatic hSOD1G93A mutants and 10 controls, followed by deep short-read sequencing. We mapped the eccDNAs and performed differential analysis based on the split read signal of the eccDNAs, referred as DifCir, between the ALS and control specimens, to find differentially produced per gene circles (DPpGC) in the two groups. Compared were eccDNA abundances, length distributions and genic profiles. We further assessed proteome alterations in ALS by mass spectrometry, and matched the DPpGCs with differentially expressed proteins (DEPs) in ALS. Additionally, we aligned the ALS-specific DPpGCs to ALS risk gene databases.

RESULTS

We found a six-fold enrichment in the number of unique eccDNAs in the genotoxic ALS-model relative to controls. We uncovered a distinct genic circulome profile characterized by 225 up-DPpGCs, i.e., genes that produced more eccDNAs from distinct gene sequences in ALS than under control conditions. The inter-sample recurrence rate was at least 89% for the top 6 up-DPpGCs. ALS proteome analyses revealed 42 corresponding DEPs, of which 19 underlying genes were itemized for an ALS risk in GWAS databases. The up-DPpGCs and their DEP tandems mainly impart neuron-specific functions, and gene set enrichment analyses indicated an overrepresentation of the adenylate cyclase modulating G protein pathway.

CONCLUSIONS

We prove, for the first time, a significant enrichment of eccDNA in the ALS-affected spinal cord. Our triple circulome, proteome and genome approach provide indication for a potential importance of certain eccDNAs in ALS neurodegeneration and a yet unconsidered role as ALS biomarkers. The related functional pathways might open up new targets for therapeutic intervention.

Oxidative DNA Damage in the Pathophysiology of Spinal Cord Injury: Seems Obvious, but Where Is the Evidence?

Oxidative stress occurs at various phases of spinal cord injury (SCI), promoting detrimental processes such as free radical injury of proteins, nucleic acids, lipids, cytoskeleton, and organelles. Oxidative DNA damage is likely a major contributor to the pathogenesis of SCI, as a damaged genome cannot be simply turned over to avert detrimental molecular and cellular outcomes, most notably cell death. Surprisingly, the evidence to support this hypothesis is limited. There is some evidence that oxidative DNA damage is increased following SCI, mainly using comet assays and immunohistochemistry. However, there is great variability in the timing and magnitude of its appearance, likely due to differences in experimental models, measurement techniques, and the rigor of the approach. Evidence indicates that 8-oxodG is most abundant at 1 and 7 days post-injury (dpi), while DNA strand breaks peak at 7 and 28 dpi. The DNA damage response seems to be characterized by upregulation of PCNA and PARP1 but downregulation of APEX1. Significant improvements in the analysis of oxidative DNA damage and repair after SCI, including single-cell analysis at time points representative for each phase post-injury using new methodologies and better reporting, will uncover the role of DNA damage and repair in SCI.

NO-Dependent Mechanisms of p53 Expression and Cell Death in Rat’s Dorsal Root Ganglia after Sciatic-Nerve Transection

Peripheral-nerve injury is a frequent cause of disability. Presently, no clinically effective neuroprotectors have been found. We have studied the NO-dependent expression of p53 in the neurons and glial cells of the dorsal root ganglia (DRG) of a rat’s spinal cord, as well as the role of NO in the death of these cells under the conditions of axonal stress, using sciatic-nerve axotomy as a model. It was found out that axotomy led to the nuclear–cytoplasmic redistribution of p53 in neurons, 24 h after trauma. The NO donor led to a considerable increase in the level of p53 in nuclei and, to a smaller degree, in the cytoplasm of neurons and karyoplasm of glial cells 4 and 24 h after axotomy. Application of a selective inhibitor of inducible NO-synthase (iNOS) provided the opposite effect. Introduction of the NO donor resulted in a significant increase in cell death in the injured ipsilateral DRG, 24 h and 7 days after trauma. The selective inhibitor of iNOS demonstrated a neuroprotective effect. Axotomy was shown to upregulate the iNOS in nuclei and cytoplasm of DRG cells. The NO-dependent expression of p53, which is particularly achieved through iNOS activation, is believed to be a putative signaling mechanism of neural and glial-cell death after axotomy.

Potential of Cellular Therapy for ALS: Current Strategies and Future Prospects

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by progressive upper and lower motor neuron (MN) degeneration with unclear pathology. The worldwide prevalence of ALS is approximately 4.42 per 100,000 populations, and death occurs within 3-5 years after diagnosis. However, no effective therapeutic modality for ALS is currently available. In recent years, cellular therapy has shown considerable therapeutic potential because it exerts immunomodulatory effects and protects the MN circuit. However, the safety and efficacy of cellular therapy in ALS are still under debate. In this review, we summarize the current progress in cellular therapy for ALS. The underlying mechanism, current clinical trials, and the pros and cons of cellular therapy using different types of cell are discussed. In addition, clinical studies of mesenchymal stem cells (MSCs) in ALS are highlighted. The summarized findings of this review can facilitate the future clinical application of precision medicine using cellular therapy in ALS.

Nitric oxide inhibits endothelial cell apoptosis by inhibiting cysteine-dependent SOD1 monomerization

Endothelial cell apoptosis is an important pathophysiology in many cardiovascular diseases. The gasotransmitter nitric oxide (NO) is known to regulate cell survival and apoptosis. However, the mechanism underlying the effect of NO remains unclear. In this research, by targeting cytosolic copper/zinc superoxide dismutase (SOD1) monomerization, we aimed to explore how NO inhibited endothelial cell apoptosis. We showed that treatment with the NO synthase (NOS) inhibitor nomega‐nitro‐l‐arginine methyl ester hydrochloride (L‐NAME) significantly decreased the endogenous NO content of endothelial cells, facilitated the formation of SOD1 monomers, inhibited dismutase activity, and promoted reactive oxygen species (ROS) accumulation in human umbilical vein endothelial cells (HUVECs); by contrast, supplementation with the NO donor sodium nitroprusside (SNP) upregulated NO content, prevented the formation of SOD1 monomers, enhanced dismutase activity, and reduced ROS accumulation in L‐NAME‐treated HUVECs. Mechanistically, tris(2‐carboxyethyl) phosphine hydrochloride (TCEP), a specific reducer of cysteine thiol, increased SOD1 monomer formation, thus preventing the NO‐induced increase in dismutase activity and the decrease in ROS. Furthermore, SNP inhibited HUVEC apoptosis caused by the decrease in endogenous NO, whereas TCEP abolished this protective effect of SNP. In summary, our data reveal that NO protects endothelial cells against apoptosis by inhibiting cysteine‐dependent SOD1 monomerization to enhance SOD1 activity and inhibit oxidative stress.

DNA Damage and Repair Deficiency in ALS/FTD-Associated Neurodegeneration: From Molecular Mechanisms to Therapeutic Implication

Emerging studies reveal that neurodegenerative disorders, including amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), are commonly linked to DNA damage accumulation and repair deficiency. Neurons are particularly vulnerable to DNA damage due to their high metabolic activity, relying primarily on oxidative phosphorylation, which leads to increased reactive oxygen species (ROS) generation and subsequent DNA damage. Efficient and timely repair of such damage is critical for guarding the integrity of genomic DNA and for cell survival. Several genes predominantly associated with RNA/DNA metabolism have been implicated in both ALS and FTD, suggesting that the two diseases share a common underlying pathology with varied clinical manifestations. Recent studies reveal that many of the gene products, including RNA/DNA binding proteins (RBPs) TDP-43 and FUS are involved in diverse DNA repair pathways. A key question in the etiology of the ALS/FTD spectrum of neurodegeneration is the mechanisms and pathways involved in genome instability caused by dysfunctions/mutations of those RBP genes and their consequences in the central nervous system. The understanding of such converging molecular mechanisms provides insights into the underlying etiology of the rapidly progressing neurodegeneration in ALS/FTD, while also revealing novel DNA repair target avenues for therapeutic development. In this review, we summarize the common mechanisms of neurodegeneration in ALS and FTD, with a particular emphasis on the DNA repair defects induced by ALS/FTD causative genes. We also highlight the consequences of DNA repair defects in ALS/FTD and the therapeutic potential of DNA damage repair-targeted amelioration of neurodegeneration.

The Atr-Chek1 pathway inhibits axon regeneration in response to Piezo-dependent mechanosensation

Atr is a serine/threonine kinase, known to sense single-stranded DNA breaks and activate the DNA damage checkpoint by phosphorylating Chek1, which inhibits Cdc25, causing cell cycle arrest. This pathway has not been implicated in neuroregeneration. We show that in Drosophila sensory neurons removing Atr or Chek1, or overexpressing Cdc25 promotes regeneration, whereas Atr or Chek1 overexpression, or Cdc25 knockdown impedes regeneration. Inhibiting the Atr-associated checkpoint complex in neurons promotes regeneration and improves synapse/behavioral recovery after CNS injury. Independent of DNA damage, Atr responds to the mechanical stimulus elicited during regeneration, via the mechanosensitive ion channel Piezo and its downstream NO signaling. Sensory neuron-specific knockout of Atr in adult mice, or pharmacological inhibition of Atr-Chek1 in mammalian neurons in vitro and in flies in vivo enhances regeneration. Our findings reveal the Piezo-Atr-Chek1-Cdc25 axis as an evolutionarily conserved inhibitory mechanism for regeneration, and identify potential therapeutic targets for treating nervous system trauma.

Identification of SNPs Associated with Stress Response Traits within High Stress and Low Stress Lines of Japanese Quail

Mitigation of stress is of great importance in poultry production, as chronic stress can affect the efficiency of production traits. Selective breeding with a focus on stress responses can be used to combat the effects of stress. To better understand the genetic mechanisms driving differences in stress responses of a selectively bred population of Japanese quail, we performed genomic resequencing on 24 birds from High Stress (HS) and Low Stress (LS) lines of Japanese quail using Illumina HiSeq 2 × 150 bp paired end read technology in order to analyze Single Nucleotide Polymorphisms (SNPs) within the genome of each line. SNPs are common mutations that can lead to genotypic and phenotypic variations in animals. Following alignment of the sequencing data to the quail genome, 6,364,907 SNPs were found across both lines of quail. 10,364 of these SNPs occurred in coding regions, from which 2886 unique, non-synonymous SNPs with a SNP% ≥ 0.90 and a read depth ≥ 10 were identified. Using Ingenuity Pathway Analysis, we identified genes affected by SNPs in pathways tied to immune responses, DNA repair, and neurological signaling. Our findings support the idea that the SNPs found within HS and LS lines of quail could direct the observed changes in phenotype.

Anticancer potential of nitric oxide (NO) in neuroblastoma treatment

The most common extracranial solid tumor in childhood, paediatric neuroblastoma, is frequently diagnosed at advanced stages and identified as high risk. High risk neuroblastoma is aggressive and unpredictable, resulting in poor prognosis and only ∼40% five-year survival rates. Herein, nitric oxide (NO) delivered via the S-nitrosothiol, S-nitrosoglutathione (GSNO), is explored as an anticancer therapeutic in various neuroblastoma lines. After 24 h of treatment with GSNO, cell viability assays, as assessed by resazurin and MTT ((3-4,5-dimethylthiazol-2-yl)-2,5-diphyltetrazolium bromide), consistently identified a moderate, ∼13-29%, decrease in metabolic activity, colony formation assays revealed notably significant reduction of clonogenic activity, and cytotoxicity assays revealed a visibly significant reduction of total number of cells and live cells as well as an increase in number of dead cells in treated cells versus untreated cells. Thrillingly, RNA-sequence analysis provided highly valuable information regarding the differentially expressed genes in treated samples versus control samples as well as insight into the mechanism of action of NO as an anticancer therapeutic. Favorably, the collective results from these analyses exhibited tumoricidal, non-tumour promoting, and discriminatory characteristics, illuminating the feasibility and significance of NO as a cytotoxic adjuvant in neuroblastoma treatment.

Skeletal Muscle-Restricted Expression of Human SOD1 in Transgenic Mice Causes a Fatal ALS-Like Syndrome

Amyotrophic lateral sclerosis (ALS) is a fatal heterogeneous neurodegenerative disease that causes motor neuron (MN) loss and skeletal muscle paralysis. It is uncertain whether this degeneration of MNs is triggered intrinsically and is autonomous, or if the disease initiating mechanisms are extrinsic to MNs. We hypothesized that skeletal muscle is a primary site of pathogenesis in ALS that triggers MN degeneration. Some inherited forms of ALS are caused by mutations in the superoxide dismutase-1 (SOD1) gene, that encodes an antioxidant protein, so we created transgenic (tg) mice expressing wild-type-, G37R-, and G93A-human SOD1 gene variants only in skeletal muscle. Presence of human SOD1 (hSOD1) protein in skeletal muscle was verified by western blotting, enzyme activity gels, and immunofluorescence in myofibers and satellite cells. These tg mice developed limb weakness and paresis with motor deficits, limb and chest muscle wasting, diaphragm atrophy, and age-related fatal disease with a lifespan shortening of 10–16%. Brown and white adipose tissue also became wasted. Myofibers of tg mice developed crystalline-like inclusions, individualized sarcomere destruction, mitochondriopathy with vesiculation, DNA damage, and activated p53. Satellite cells became apoptotic. The diaphragm developed severe loss of neuromuscular junction presynaptic and postsynaptic integrity, including decreased innervation, loss of synaptophysin, nitration of synaptophysin, and loss of nicotinic acetylcholine receptor and scaffold protein rapsyn. Co-immunoprecipitation identified hSOD1 interaction with rapsyn. Spinal cords of tg mice developed gross atrophy. Spinal MNs formed cytoplasmic and nuclear inclusions, axonopathy, mitochondriopathy, accumulated DNA damage, activated p53 and cleaved caspase-3, and died. Tg mice had a 40–50% loss of MNs. This work shows that hSOD1 in skeletal muscle is a driver of pathogenesis in ALS, that involves myofiber and satellite cell toxicity, and apparent muscle-adipose tissue disease relationships. It also identifies a non-autonomous mechanism for MN degeneration explaining their selective vulnerability as likely a form of target-deprivation retrograde neurodegeneration.

Sigma 1 receptor as a therapeutic target for amyotrophic lateral sclerosis

Amyotrophic lateral sclerosis (ALS) is an adult disease causing a progressive loss of upper and lower motoneurons, muscle paralysis and early death. ALS has a poor prognosis of 3-5 years after diagnosis with no effective cure. The aetiopathogenic mechanisms involved include glutamate excitotoxicity, oxidative stress, protein misfolding, mitochondrial alterations, disrupted axonal transport and inflammation. Sigma non-opioid intracellular receptor 1 (sigma 1 receptor) is a protein expressed in motoneurons, mainly found in the endoplasmic reticulum (ER) on the mitochondria-associated ER membrane (MAM) or in close contact with cholinergic postsynaptic sites. MAMs are sites that allow the assembly of several complexes implicated in essential survival cell functions. The sigma 1 receptor modulates essential mechanisms for motoneuron survival including excitotoxicity, calcium homeostasis, ER stress and mitochondrial dysfunction. This review updates sigma 1 receptor mechanisms and its alterations in ALS, focusing on MAM modulation, which may constitute a novel target for therapeutic strategies. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.6/issuetoc.

Genome-Protecting Compounds as Potential Geroprotectors

Throughout life, organisms are exposed to various exogenous and endogenous factors that cause DNA damages and somatic mutations provoking genomic instability. At a young age, compensatory mechanisms of genome protection are activated to prevent phenotypic and functional changes. However, the increasing stress and age-related deterioration in the functioning of these mechanisms result in damage accumulation, overcoming the functional threshold. This leads to aging and the development of age-related diseases. There are several ways to counteract these changes: 1) prevention of DNA damage through stimulation of antioxidant and detoxification systems, as well as transition metal chelation; 2) regulation of DNA methylation, chromatin structure, non-coding RNA activity and prevention of nuclear architecture alterations; 3) improving DNA damage response and repair; 4) selective removal of damaged non-functional and senescent cells. In the article, we have reviewed data about the effects of various trace elements, vitamins, polyphenols, terpenes, and other phytochemicals, as well as a number of synthetic pharmacological substances in these ways. Most of the compounds demonstrate the geroprotective potential and increase the lifespan in model organisms. However, their genome-protecting effects are non-selective and often are conditioned by hormesis. Consequently, the development of selective drugs targeting genome protection is an advanced direction.

DNA damage accumulates and responses are engaged in human ALS brain and spinal motor neurons and DNA repair is activatable in iPSC-derived motor neurons with SOD1 mutations

DNA damage is implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS). However, relationships between DNA damage accumulation, DNA damage response (DDR), and upper and lower motor neuron vulnerability in human ALS are unclear; furthermore, it is unknown whether epigenetic silencing of DNA repair pathways contributes to ALS pathogenesis. We tested the hypotheses that DNA damage accumulates in ALS motor neurons along with diminished DDR, and that DNA repair genes undergo hypermethylation. Human postmortem CNS tissue was obtained from ALS cases (N = 34) and age-matched controls without neurologic disease (N = 15). Compared to age-matched controls, abasic sites accumulated in genomic DNA of ALS motor cortex and laser capture microdissection-acquired spinal motor neurons but not in motor neuron mitochondrial DNA. By immunohistochemistry, DNA damage accumulated significantly in upper and lower motor neurons in ALS cases as single-stranded DNA and 8-hydroxy-deoxyguanosine (OHdG) compared to age-matched controls. Significant DDR was engaged in ALS motor neurons as evidenced by accumulation of c-Abl, nuclear BRCA1, and ATM activation. DNA damage and DDR were present in motor neurons at pre-attritional stages and throughout the somatodendritic attritional stages of neurodegeneration. Motor neurons with DNA damage were also positive for activated p53 and cleaved caspase-3. Gene-specific promoter DNA methylation pyrosequencing identified the DNA repair genes Ogg1, Apex1, Pnkp and Aptx as hypomethylated in ALS. In human induced-pluripotent stem cell (iPSC)-derived motor neurons with familial ALS SOD1 mutations, DNA repair capacity was similar to isogenic control motor neurons. Our results show that vulnerable neurons in human ALS accumulate DNA damage, and contrary to our hypothesis, strongly activate and mobilize response effectors and DNA repair genes. This DDR in ALS motor neurons involves recruitment of c-Abl and BRCA1 to the nucleus in vivo, and repair of DNA double-strand breaks in human ALS motor neurons with SOD1 mutations in cell culture.

Neonatal Brain Injury and Genetic Causes of Adult-Onset Neurodegenerative Disease in Mice Interact With Effects on Acute and Late Outcomes

Neonatal brain damage and age-related neurodegenerative disease share many common mechanisms of injury involving mitochondriopathy, oxidative stress, excitotoxicity, inflammation, and neuronal cell death. We hypothesized that genes causing adult-onset neurodegeneration can influence acute outcome after CNS injury at immaturity and on the subsequent development of chronic disability after early-life brain injury. In two different transgenic (Tg) mouse models of adult-onset neurodegenerative disease, a human A53T-α-synuclein (hαSyn) model of Parkinson's disease (PD) and a human G93A-superoxide dismutase-1(hSOD1) model of amyotrophic lateral sclerosis (ALS), mortality and survivor morbidity were significantly greater than non-Tg mice and a Tg mouse model of Alzheimer's disease after neonatal traumatic brain injury (TBI). Acutely after brain injury, hαSyn neonatal mice showed a marked enhancement of protein oxidative damage in forebrain, brain regional mitochondrial oxidative metabolism, and mitochondriopathy. Extreme protein oxidative damage was also observed in neonatal mutant SOD1 mice after TBI. At 1 month of age, neuropathology in forebrain, midbrain, and brainstem of hαSyn mice with neonatal TBI was greater compared to sham hαSyn mice. Surviving hαSyn mice with TBI showed increased hαSyn aggregation and nitration and developed adult-onset disease months sooner and died earlier than non-injured hαSyn mice. Surviving hSOD1 mice with TBI also developed adult-onset disease and died sooner than non-injured hSOD1 mice. We conclude that mutant genes causing PD and ALS in humans have significant impact on mortality and morbidity after early-life brain injury and on age-related disease onset and proteinopathy in mice. This study provides novel insight into genetic determinants of poor outcomes after acute injury to the neonatal brain and how early-life brain injury can influence adult-onset neurodegenerative disease during aging.

Network-centric medicine for peripheral nerve injury: Treating the whole to boost endogenous mechanisms of neuroprotection and regeneration

Peripheral nerve injuries caused by accidents may lead to paralysis, sensory disturbances, anaesthesia, and lack of autonomic functions. Functional recovery after disconnection of the motoneuronal soma from target tissue with proximal rupture of axons is determined by several factors: motoneuronal soma viability, proper axonal sprouting across inhibitory zones and elongation toward specific muscle, effective synapse contact rebuilding, and prevention of muscle atrophy. Therapies, such as adjuvant drugs with pleiotropic effects, that promote functional recovery after peripheral nerve injury are needed. Toward this aim, we designed a drug discovery workflow based on a network-centric molecular vision using unbiased proteomic data and neural artificial computational tools. Our focus is on boosting intrinsic capabilities of neurons for neuroprotection; this is in contrast to the common approach based on suppression of a pathobiological pathway known to be associated with disease condition. Using our workflow, we discovered neuroheal, a combination of two repurposed drugs that promotes motoneuronal soma neuroprotection, is anti-inflammatory, enhances axonal regeneration after axotomy, and reduces muscle atrophy. This drug discovery workflow has thus yielded a therapy that is close to its clinical application.

Tubulation repair mitigates misdirection of regenerating motor axons across a sciatic nerve gap in rats

The repair of peripheral nerve laceration injury to obtain optimal function recovery remains a big challenge in the clinic. Misdirection of regenerating axons to inappropriate target, as a result of forced mismatch of endoneurial sheaths in the case of end-to-end nerve anastomosis or nerve autografting, represents one major drawback that limits nerve function recovery. Here we tested whether tubulation repair of a nerve defect could be beneficial in terms of nerve regeneration accuracy and nerve function. We employed sequential retrograde neuronal tracing to assess the accuracy of motor axon regeneration into the tibial nerve after sciatic nerve laceration and entubulation in adult Sprague-Dawley rats. In a separate cohort of rats with the same sciatic nerve injury/repair protocols, we evaluated nerve function recovery behaviorally and electrophysiologically. The results showed that tubulation repair of the lacerated sciatic nerve using a 3-6-mm-long bioabsorbable guidance conduit significantly reduced the misdirection of motor axons into the tibial nerve as compared to nerve autografting. In addition, tubulation repair ameliorated chronic flexion contracture. This study suggests that tubulation repair of a nerve laceration injury by utilizing a bioresorbable nerve guidance conduit represents a potential substitute for end-to-end epineurial suturing and nerve autografting.

Effect of nitric oxide to axonal degeneration in multiple sclerosis via downregulating monocarboxylate transporter 1 in oligodendrocytes

Multiple sclerosis (MS) is a neurodegenerative disease of the central nervous system (CNS). Axonal degeneration, one of the main pathological characteristics of MS, is affected by nitric oxide (NO). In turn, NO induces mitochondrial dysfunction of neurons and glial cells. Inadequate glucose causes monocarboxylate transporter 1 (MCT1) to transfer lactate from oligodendrocytes (OLs) to neurons, which decreases MCT1 and results in energy substrate deficit (mainly lactate) in axons. The condition gradually leads to axonal degeneration. This study proposes that NO-induced MCT1 down-regulation in OLs may be involved in the pathological process of axonal degeneration, which eventually leads to MS.

TDP-43/FUS in motor neuron disease: Complexity and challenges

Amyotrophic lateral sclerosis (ALS), a common motor neuron disease affecting two per 100,000 people worldwide, encompasses at least five distinct pathological subtypes, including, ALS-SOD1, ALS-C9orf72, ALS-TDP-43, ALS-FUS and Guam-ALS. The etiology of a major subset of ALS involves toxicity of the TAR DNA-binding protein-43 (TDP-43). A second RNA/DNA binding protein, fused in sarcoma/translocated in liposarcoma (FUS/TLS) has been subsequently associated with about 1% of ALS patients. While mutations in TDP-43 and FUS have been linked to ALS, the key contributing molecular mechanism(s) leading to cell death are still unclear. One unique feature of TDP-43 and FUS pathogenesis in ALS is their nuclear clearance and simultaneous cytoplasmic aggregation in affected motor neurons. Since the discoveries in the last decade implicating TDP-43 and FUS toxicity in ALS, a majority of studies have focused on their cytoplasmic aggregation and disruption of their RNA-binding functions. However, TDP-43 and FUS also bind to DNA, although the significance of their DNA binding in disease-affected neurons has been less investigated. A recent observation of accumulated genomic damage in TDP-43 and FUS-linked ALS and association of FUS with neuronal DNA damage repair pathways indicate a possible role of deregulated DNA binding function of TDP-43 and FUS in ALS. In this review, we discuss the different ALS disease subtypes, crosstalk of etiopathologies in disease progression, available animal models and their limitations, and recent advances in understanding the specific involvement of RNA/DNA binding proteins, TDP-43 and FUS, in motor neuron diseases.

Enforced DNA repair enzymes rescue neurons from apoptosis induced by target deprivation and axotomy in mouse models of neurodegeneration

It is unknown whether DNA damage accumulation is an upstream instigator or secondary effect of the cell death process in different populations of adult postmitotic neurons in the central nervous system. In two different mouse models of injury-induced neurodegeneration characterized by relatively synchronous accumulation of mitochondria, oxidative stress, and DNA damage prior to neuronal apoptosis, we enforced the expression of human 8-oxoguanine DNA glycosylase (hOGG1) and human apurinic-apyrimidinic endonuclease-1/Ref1 (hAPE) using recombinant adenoviruses (Ad). Thalamic lateral geniculate neurons and lumbar spinal cord motor neurons were transduced by Ad-hOGG1 and Ad-hAPE injections into the occipital cortex and skeletal muscle, respectively, prior to their target deprivation- and axotomy-induced retrograde apoptosis. Enforced expression of hOGG1 and hAPE in thalamus and spinal cord was confirmed by western blotting and immunohistochemistry. In injured populations of neurons in thalamus and spinal cord, a DNA damage response (DDR) was registered, as shown by localization of phospho-activated p53, Rad17, and replication protein A-32 immunoreactivities, and this DDR was attenuated more effectively by enforced hAPE expression than by hOGG1 expression. Enforced expression of hOGG1 and hAPE significantly protected thalamic neurons and motor neurons from retrograde apoptosis induced by target deprivation and axotomy. We conclude that a DDR response is engaged pre-apoptotically in different types of injured mature CNS neurons and that DNA repair enzymes can regulate the survival of retrogradely dying neurons, suggesting that DNA damage and activation of DDR are upstream mechanisms for this form of adult neurodegeneration in vivo, thus identifying DNA repair as a therapeutic target for neuroprotection.

Statins Trigger Mitochondrial Reactive Oxygen Species-Induced Apoptosis in Glycolytic Skeletal Muscle

AIMS

Although statins are the most widely used cholesterol-lowering agents, they are associated with a variety of muscle complaints. The goal of this study was to characterize the effects of statins on the mitochondrial apoptosis pathway induced by mitochondrial oxidative stress in skeletal muscle using human muscle biopsies as well as in vivo and in vitro models.

RESULTS

Statins increased mitochondrial H2O2 production, the Bax/Bcl-2 ratio, and TUNEL staining in deltoid biopsies of patients with statin-associated myopathy. Furthermore, atorvastatin treatment for 2 weeks at 10 mg/kg/day in rats increased H2O2 accumulation and mRNA levels and immunostaining of the Bax/Bcl-2 ratio, as well as TUNEL staining and caspase 3 cleavage in glycolytic (plantaris) skeletal muscle, but not in oxidative (soleus) skeletal muscle, which has a high antioxidative capacity. Atorvastatin also decreased the GSH/GSSG ratio, but only in glycolytic skeletal muscle. Cotreatment with the antioxidant, quercetin, at 25 mg/kg/day abolished these effects in plantaris. An in vitro study with L6 myoblasts directly demonstrated the link between mitochondrial oxidative stress following atorvastatin exposure and activation of the mitochondrial apoptosis signaling pathway.

INNOVATION

Treatment with atorvastatin is associated with mitochondrial oxidative stress, which activates apoptosis and contributes to myopathy. Glycolytic muscles are more sensitive to atorvastatin than oxidative muscles, which may be due to the higher antioxidative capacity in oxidative muscles.

CONCLUSION

There is a link between statin-induced mitochondrial oxidative stress and activation of the mitochondrial apoptosis signaling pathway in glycolytic skeletal muscle, which may be associated with statin-associated myopathy.

Clinical and neurobiological advances in promoting regeneration of the ventral root avulsion lesion

Root avulsions due to traction to the brachial plexus causes complete and permanent loss of function. Until fairly recent, such lesions were considered impossible to repair. Here we review clinical repair strategies and current progress in experimental ventral root avulsion lesions. The current gold standard in patients with a root avulsion is nerve transfer, whereas reimplantation of the avulsed root into the spinal cord has been performed in a limited number of cases. These neurosurgical repair strategies have significant benefit for the patient but functional recovery remains incomplete. Developing new ways to improve the functional outcome of neurosurgical repair is therefore essential. In the laboratory, the molecular and cellular changes following ventral root avulsion and the efficacy of intervention strategies have been studied at the level of spinal motoneurons, the ventral spinal root and peripheral nerve, and the skeletal muscle. We present an overview of cell-based pharmacological and neurotrophic factor treatment approaches that have been applied in combination with surgical reimplantation. These interventions all demonstrate neuroprotective effects on avulsed motoneurons, often accompanied with various degrees of axonal regeneration. However, effects on survival are usually transient and robust axon regeneration over long distances has as yet not been achieved. Key future areas of research include finding ways to further extend the post-lesion survival period of motoneurons, the identification of neuron-intrinsic factors which can promote persistent and long-distance axon regeneration, and finally prolonging the pro-regenerative state of Schwann cells in the distal nerve.

Releasing 'brakes' to nerve regeneration: intrinsic molecular targets

Restoring critical neuronal architecture after peripheral nerve injury is challenging. Although immediate regenerative responses to peripheral axon injury involve the synthesis of regeneration-associated proteins in neurons and Schwann cells, an unfavorable balance between growth facilitatory and growth inhibitory signaling impairs the growth continuum of injured peripheral nerves. Molecules involved with the signaling network of tumor suppressors play crucial roles in shifting the balance between growth and restraint during axon regeneration. An understanding of the molecular framework of tumor suppressor molecules in injured neurons and its impact on stage-specific regeneration events may expose therapeutic intervention points. In this review we discuss how signaling networks of the specific tumor suppressors PTEN, Rb1, p53, p27 and p21 are altered in injured peripheral nerves and how this impacts peripheral nerve regeneration. Insights into the roles and importance of these pathways may open new avenues for improving the neurological deficits associated with nerve injury.

Antitumoral gene-based strategy involving nitric oxide synthase type III overexpression in hepatocellular carcinoma

Hepatocellular carcinoma develops in cirrhotic liver. The nitric oxide (NO) synthase type III (NOS-3) overexpression induces cell death in hepatoblastoma cells. The study developed gene therapy designed to specifically overexpress NOS-3 in cultured hepatoma cells, and in tumors derived from orthotopically implanted tumor cells in fibrotic livers. Liver fibrosis was induced by CCl4 administration in mice. The first-generation adenoviruses were designed to overexpress NOS-3 or green fluorescent protein, and luciferase complementary DNA under the regulation of murine alpha-fetoprotein (AFP) and Rous Sarcoma Virus (RSV) promoters, respectively. Both adenovirus and Hepa 1-6 cells were used for in vitro and in vivo experiments. Adenoviruses were administered through the tail vein 2 weeks after orthotopic tumor cell implantation. AFP-NOS-3/RSV-luciferase increased oxidative-related DNA damage, p53, CD95/CD95L expression and caspase-8, -9 and -3 activities in cultured Hepa 1-6 cells. The increased expression of CD95/CD95L and caspase-8 activity was abolished by Nω-nitro-l-arginine methyl ester hydrochloride, p53 and CD95 small interfering RNA. AFP-NOS-3/RSV-luciferase adenovirus increased cell death markers, and reduced cell proliferation of established tumors in fibrotic livers. The increase of oxidative/nitrosative stress induced by NOS-3 overexpression induced DNA damage, p53, CD95/CD95L expression and cell death in hepatocellular carcinoma cells. The effectiveness of the gene therapy has been demonstrated in vitro and in vivo.

Regulation of cell death receptor S-nitrosylation and apoptotic signaling by Sorafenib in hepatoblastoma cells

Nitric oxide (NO) plays a relevant role during cell death regulation in tumor cells. The overexpression of nitric oxide synthase type III (NOS-3) induces oxidative and nitrosative stress, p53 and cell death receptor expression and apoptosis in hepatoblastoma cells. S-nitrosylation of cell death receptor modulates apoptosis. Sorafenib is the unique recommended molecular-targeted drug for the treatment of patients with advanced hepatocellular carcinoma. The present study was addressed to elucidate the potential role of NO during Sorafenib-induced cell death in HepG2 cells. We determined the intra- and extracellular NO concentration, cell death receptor expression and their S-nitrosylation modifications, and apoptotic signaling in Sorafenib-treated HepG2 cells. The effect of NO donors on above parameters has also been determined. Sorafenib induced apoptosis in HepG2 cells. However, low concentration of the drug (10nM) increased cell death receptor expression, as well as caspase-8 and -9 activation, but without activation of downstream apoptotic markers. In contrast, Sorafenib (10 µM) reduced upstream apoptotic parameters but increased caspase-3 activation and DNA fragmentation in HepG2 cells. The shift of cell death signaling pathway was associated with a reduction of S-nitrosylation of cell death receptors in Sorafenib-treated cells. The administration of NO donors increased S-nitrosylation of cell death receptors and overall induction of cell death markers in control and Sorafenib-treated cells. In conclusion, Sorafenib induced alteration of cell death receptor S-nitrosylation status which may have a relevant repercussion on cell death signaling in hepatoblastoma cells.

Identification of the Avulsion-Injured Spinal Motoneurons

In laboratory studies, counting the spinal motoneurons that survived axonal injury is a major method to estimate the severity and regenerative capacity of the injured motoneurons after the axonal injury and rehabilitation surgery. However, the typical motoneuron marker, the choline acetyltransferase (ChAT), could not be detected in the injured motoneurons within the first 3–4 weeks postinjury. It is necessary to explore the useful and reliable specific phenotypic markers to assess the fate of injured motoneurons in axonal injury. Here, we used the fluorogold to retrograde trace the injured motoneurons in the spinal cord and studied the expression patterns of the alpha-motoneuron marker, the neuronal nuclei DNA-binding protein (NeuN) and the peripheral nerve injury marker, the activating transcriptional factor (ATF-3), and the oxidative stress marker, the neuronal nitric oxide synthase (nNOS) within the first 4 weeks of the root avulsion of the right brachial plexus (BPRA) in the adult male Sprague-Dawley rats. Our results showed that ATF-3 was rapidly induced and sustained to express only in the nuclei of the fluorogold-labeled injured motoneurons but none in the unaffected motoneurons from the 24 h of the injury; meanwhile, the NeuN almost disappeared in the avulsion-affected motoneurons within the first 4 weeks. The nNOS was not detected in the motoneurons until the second week of the injury. On the basis of the present data, we suggest that ATF-3 labels avulsion-injured motoneurons while NeuN and nNOS are poor markers within the first 4 weeks of BPRA.

Evaluation of Avulsion-Induced Neuropathology in Rat Spinal Cords with 18F-FDG Micro-PET/CT

Brachial plexus root avulsion (BPRA) leads to dramatic motoneuron death and glial reactions in the corresponding spinal segments at the late stage of injury. To protect spinal motoneurons, assessment of the affected spinal segments should be done at an earlier stage of the injury. In this study, we employed ¹⁸F-FDG small-animal PET/CT to assess the severity of BPRA-induced cervical spinal cord injuries. Adult Sprague-Dawley rats were randomly treated and divided into three groups: Av+NS (brachial plexus root avulsion (Av) treated with normal saline), Av+GM1 (treated with monosialoganglioside), and control. At time points of 3 day (d), 1 week (w), 2 w, 4 w and 8 w post-injury, ¹⁸F-FDG micro-PET/CT scans and neuropathology assessments of the injured spinal roots, as well as the spinal cord, were performed. The outcomes of the different treatments were compared. The results showed that BPRA induced local bleeding and typical Wallerian degeneration of the avulsed roots accompanied by ¹⁸F-FDG accumulations at the ipsilateral cervical intervertebral foramen. BPRA-induced astrocyte reactions and overexpression of neuronal nitric oxide synthase in the motoneurons correlated with higher ¹⁸F-FDG uptake in the ipsilateral cervical spinal cord during the first 2 w post-injury. The GM1 treatment reduced BPRA-induced astrocyte reactions and inhibited the de novo nNOS expressions in spinal motoneurons. The GM1 treatment also protected spinal motoneurons from avulsion within the first 4 w post-injury. The data from this study suggest that ¹⁸F-FDG PET/CT could be used to assess the severity of BPRA-induced primary and secondary injuries in the spinal cord. Furthermore, GM1 is an effective drug for reducing primary and secondary spinal cord injuries following BPRA.

NF-κB regulates caspase-4 expression and sensitizes neuroblastoma cells to Fas-induced apoptosis

Found in neurons and neuroblastoma cells, Fas-induced apoptosis and accompanied activation of NF-κB signaling were thought to be associated with neurodegenerative diseases. However, the detailed functions of NF-κB activation in Fas killing and the effect of NF-κB activation on its downstream events remain unclear. Here, we demonstrated that agonistic Fas antibody induces cell death in a dose-dependent way and NF-κB signaling is activated as well, in neuroblastoma cells SH-EP1. Unexpectedly, NF-κB activation was shown to be pro-apoptotic, as suggested by the reduction of Fas-induced cell death with either a dominant negative form of IκBα (DN-IκBα) or an IκB kinase-specific inhibitor. To our interest, when analyzing downstream events of NF-κB signaling, we found that DN-IκBα only suppressed the expression of caspase-4, but not other caspases. Vice versa, enhancement of NF-κB activity by p65 (RelA) overexpression increased the expression of caspase-4 at both mRNA and protein levels. More directly, results from dual luciferase reporter assay demonstrated the regulation of caspase-4 promoter activity by NF-κB. When caspase-4 activity was blocked by its dominant negative (DN) form, Fas-induced cell death was substantially reduced. Consistently, the cleavage of PARP and caspase-3 induced by Fas was also reduced. In contrast, the cleavage of caspase-8 remained unaffected in caspase-4 DN cells, although caspase-8 inhibitor could rescue Fas-induced cell death. Collectively, these data suggest that caspase-4 activity is required for Fas-induced cell apoptosis and caspase-4 may act upstream of PARP and caspase-3 and downstream of caspase-8. Overall, we demonstrate that NF-κB can mediate Fas-induced apoptosis through caspase-4 protease, indicating that caspase-4 is a new mediator of NF-κB pro-apoptotic pathway in neuroblastoma cells.

Down-regulation of apurinic/apyrimidinic endonuclease 1 (APE1) in spinal motor neurones under oxidative stress

AIM

Apurinic/apyrimidinic endonuclease 1 (APE1) is an intermediate enzyme in base excision repair which is important for removing damaged nucleotides under normal and pathological conditions. Accumulation of damaged bases causes genome instability and jeopardizes cell survival. Our study is to examine APE1 regulation under oxidative stress in spinal motor neurones which are vulnerable to oxidative insult.

METHODS

We challenged the motor neurone-like cell line NSC-34 with hydrogen peroxide and delineated APE1 function by applying various inhibitors. We also examined the expression of APE1 in spinal motor neurones after spinal root avulsion in adult rats.

RESULTS

We showed that hydrogen peroxide induced APE1 down-regulation and cell death in a differentiated motor neurone-like cell line. Inhibiting the two functional domains of APE1, namely, DNA repair and redox domains potentiated hydrogen peroxide induced cell death. We further showed that p53 phosphorylation early after hydrogen peroxide treatment might contribute to the down-regulation of APE1. Our in vivo results similarly showed that APE1 was down-regulated after root avulsion injury in spinal motor neurones. Delay of motor neurone death suggested that APE1 might not cause immediate cell death but render motor neurones vulnerable to further oxidative insults.

CONCLUSION

We conclude that spinal motor neurones down-regulate APE1 upon oxidative stress. This property renders motor neurones susceptible to continuous challenge of oxidative stress in pathological conditions.

Axotomy-induced target disconnection promotes an additional death mechanism involved in motoneuron degeneration in amyotrophic lateral sclerosis transgenic mice

The target disconnection theory of amyotrophic lateral sclerosis (ALS) pathogenesis suggests that disease onset is initiated by a peripheral pathological event resulting in neuromuscular junction loss and motoneuron (MN) degeneration. Presymptomatic mSOD1(G93A) mouse facial MN (FMN) are more susceptible to axotomy-induced cell death than wild-type (WT) FMN, which suggests additional CNS pathology. We have previously determined that the mSOD1 molecular response to facial nerve axotomy is phenotypically regenerative and indistinguishable from WT, whereas the surrounding microenvironment shows significant dysregulation in the mSOD1 facial nucleus. To elucidate the mechanisms underlying the enhanced mSOD1 FMN loss after axotomy, we superimposed the facial nerve axotomy model on presymptomatic mSOD1 mice and investigated gene expression for death receptor pathways after target disconnection by axotomy vs. disease progression. We determined that the TNFR1 death receptor pathway is involved in axotomy-induced FMN death in WT and is partially responsible for the mSOD1 FMN death. In contrast, an inherent mSOD1 CNS pathology resulted in a suppressed glial reaction and an upregulation in the Fas death pathway after target disconnection. We propose that the dysregulated mSOD1 glia fail to provide support the injured MN, leading to Fas-induced FMN death. Finally, we demonstrate that, during disease progression, the mSOD1 facial nucleus displays target disconnection-induced gene expression changes that mirror those induced by axotomy. This validates the use of axotomy as an investigative tool in understanding the role of peripheral target disconnection in the pathogenesis of ALS.

Retrograde response in axotomized motoneurons: nitric oxide as a key player in triggering reversion toward a dedifferentiated phenotype

The adult brain retains a considerable capacity to functionally reorganize its circuits, which mainly relies on the prevalence of three basic processes that confer plastic potential: synaptic plasticity, plastic changes in intrinsic excitability and, in certain central nervous system (CNS) regions, also neurogenesis. Experimental models of peripheral nerve injury have provided a useful paradigm for studying injury-induced mechanisms of central plasticity. In particular, axotomy of somatic motoneurons triggers a robust retrograde reaction in the CNS, characterized by the expression of plastic changes affecting motoneurons, their synaptic inputs and surrounding glia. Axotomized motoneurons undergo a reprograming of their gene expression and biosynthetic machineries which produce cell components required for axonal regrowth and lead them to resume a functionally dedifferentiated phenotype characterized by the removal of afferent synaptic contacts, atrophy of dendritic arbors and an enhanced somato-dendritic excitability. Although experimental research has provided valuable clues to unravel many basic aspects of this central response, we are still lacking detailed information on the cellular/molecular mechanisms underlying its expression. It becomes clear, however, that the state-switch must be orchestrated by motoneuron-derived signals produced under the direction of the re-activated growth program. Our group has identified the highly reactive gas nitric oxide (NO) as one of these signals, by providing robust evidence for its key role to induce synapse elimination and increases in intrinsic excitability following motor axon damage. We have elucidated operational principles of the NO-triggered downstream transduction pathways mediating each of these changes. Our findings further demonstrate that de novo NO synthesis is not only "necessary" but also "sufficient" to promote the expression of at least some of the features that reflect reversion toward a dedifferentiated state in axotomized adult motoneurons.

Lithium enhances survival and regrowth of spinal motoneurons after ventral root avulsion

Background

During the clinical treatment of the brachial plexus root avulsion (BPRA), reimplantation surgery can not completely repair the motor function of the hand because the axonal growth velocity of the spinal motoneurons (MNs) is too slow to re-innervate the intrinsic hand muscles before muscle atrophy. Here, we investigated whether lithium can enhance the regenerative capacity of the spinal MNs in a rat model of BPRA.

Results

The avulsion and immediate reimplantation of the C7 and C8 ventral roots were performed and followed with daily intraperitoneal administration of a therapeutic concentrationof LiCl. After a 20 week long-term rehabilitation, the motor function recovery of the injured forepaw was studied by a grasping test. The survival and regeneration of MNs were checked by choline acetyltransferase (ChAT) immunofluorescence and by Fluoro-Gold (FG) retrograde labeling through the median and ulnar nerves of the ventral horn MNs. The number and diameter of the nerve fibers in the median nerve were assessed by toluidine blue staining. Our results showed that lithium plus reimplantation therapy resulted in a significantly higher grasping strength of the digits of the injured forepaw. Lithium plus reimplantation allowed 45.1% ± 8.11% of ChAT-positive MNs to survive the injury and increased the number and diameter of nerve fibers in the median nerve. The number of FG-labeled regenerative MNs was significantly elevated in all of the reimplantation animals. Our present data proved that lithium can enhance the regenerative capacity of spinal MNs.

Conclusions

These results suggest that immediate administration of lithium could be used to assist reimplantation surgery in repairing BPRA injuries in clinical treatment.

Glycoursodeoxycholic acid reduces matrix metalloproteinase-9 and caspase-9 activation in a cellular model of superoxide dismutase-1 neurodegeneration

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease that affects mainly motor neurons (MNs). NSC-34 MN-like cells carrying the G93A mutation in human superoxide dismutase-1 (hSOD1(G93A)) are a common model to study the molecular mechanisms of neurodegeneration in ALS. Although the underlying pathways of MN failure still remain elusive, increased apoptosis and oxidative stress seem to be implicated. Riluzole, the only approved drug, only slightly delays ALS progression. Ursodeoxycholic acid (UDCA), as well as its glycine (glycoursodeoxycholic acid, GUDCA) and taurine (TUDCA) conjugated species, have shown therapeutic efficacy in neurodegenerative models and diseases. Pilot studies in ALS patients indicate safety and tolerability for UDCA oral administration. We explored the mechanisms associated with superoxide dismutase-1 (SOD1) accumulation and MN degeneration in NSC-34/hSOD1(G93A) cells differentiated for 4 days in vitro (DIV). We examined GUDCA efficacy in preventing such pathological events and in restoring MN functionality by incubating cells with 50 μM GUDCA at 0 DIV and at 2 DIV, respectively. Increased cytosolic SOD1 inclusions were observed in 4 DIV NSC-34/hSOD1(G93A) cells together with decreased mitochondria viability (1.2-fold, p < 0.01), caspase-9 activation (1.8-fold, p < 0.05), and apoptosis (2.1-fold, p < 0.01). GUDCA exerted preventive effects (p < 0.05) while also reduced caspase-9 levels when added at 2 DIV (p < 0.05). ATP depletion (2-fold, p < 0.05), increased nitrites (1.6-fold, p < 0.05) and metalloproteinase-9 (MMP-9) activation (1.8-fold, p < 0.05), but no changes in MMP-2, were observed in the extracellular media of 4 DIV NSC-34/hSOD1(G93A) cells. GUDCA inhibited nitrite production (p < 0.05) while simultaneously prevented and reverted MMP-9 activation (p < 0.05), but not ATP depletion. Data highlight caspase-9 and MMP-9 activation as key pathomechanisms in ALS and GUDCA as a promising therapeutic strategy for slowing disease onset and progression.

Electroacupuncture treatment contributes to the downregulation of neuronal nitric oxide synthase and motoneuron death in injured spinal cords following root avulsion of the brachial plexus

This study was performed in order to investigate the effect of electroacupuncture (EA) on motoneurons and the expression of neuronal nitric oxide synthase (nNOS) following brachial plexus root avulsion (BPRA). A total of 40 female Sprague-Dawley rats underwent BPRA (5th cervical-1st thoracic) and were randomly divided into the avulsion plus EA stimulation (AV+EA) and AV groups. The AV+EA group received a continuous 20-Hz asymmetric bidirectional disperse-dense wave at the acupuncture points (acupoints) of Dazhui (DU4) and Shousanli (LI10) for 15 min on alternate days until the animals were sacrificed, at 1, 2, 3 and 6 weeks. The AV group received no treatment. The cryostat sections of the 7th cervical segments were prepared and stained with neuronal nitric oxide synthase nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) and histochemically stained and counterstained with neutral red (NR). The number of nNOS-positive motoneurons on the lesion side and survived motoneurons on both sides of the 7th cervical segments were blindly counted and compared between the two groups. The results demonstrated that the number of nNOS-positive motoneurons was significantly lower in the AV+EA group compared with that in the AV group and the percentage of survived motoneurons was significantly higher compared with that of the AV group at 2 and 3 weeks. However, the number of nNOS-positive motoneurons and the percentage of survived motoneurons were not significantly different between the two groups at 1 and 6 weeks. These results indicated that, during the early period after BPRA, EA stimulation at the acupoints of Dazhui (DU4) and Shousanli (LI10) may significantly reduce the number of nNOS-positive motoneurons and protect against motoneuron death.

Mitochondrial permeability transition pore regulates Parkinson's disease development in mutant α-synuclein transgenic mice

Parkinson's disease (PD) is a movement disorder caused by neurodegeneration in neocortex, substantia nigra and brainstem, and synucleinopathy. Some inherited PD is caused by mutations in α-synuclein (αSyn), and inherited and idiopathic PD is associated with mitochondrial perturbations. However, the mechanisms of pathogenesis are unresolved. We characterized a human αSyn transgenic mouse model and tested the hypothesis that the mitochondrial permeability transition pore (mPTP) is involved in the disease mechanisms. C57BL/6 mice expressing human A53T-mutant αSyn driven by a thymic antigen-1 promoter develop a severe, age-related, fatal movement disorder involving ataxia, rigidity, and postural instability. These mice develop synucleinopathy and neocortical, substantia nigra, and cerebello-rubro-thalamic degeneration involving mitochondriopathy and apoptotic and non-apoptotic neurodegeneration. Interneurons undergo apoptotic degeneration in young mice. Mutant αSyn associated with dysmorphic neuronal mitochondria and bound voltage-dependent anion channels. Genetic ablation of cyclophilin D, an mPTP modulator, delayed disease onset, and extended lifespans of mutant αSyn mice. Thus, mutant αSyn transgenic mice on a C57BL/6 background develop PD-like phenotypes, and the mPTP is involved in their disease mechanisms.

Chromatin modifications associated with DNA double-strand breaks repair as potential targets for neurological diseases

The integrity of the genome is continuously challenged by both endogenous and exogenous DNA damaging agents. Neurons, due to their post-mitotic state, high metabolism, and longevity are particularly prone to the accumulation of DNA lesions. Indeed, DNA damage has been suggested as a major contributor to both age-associated neurodegenerative diseases and acute neurological injury. The DNA damage response is a key factor in maintaining genome integrity. It relies on highly dynamic posttranslational modifications of the chromatin and DNA repair proteins to allow signaling, access, and repair of the lesion. Drugs that modulate the activity of the enzymes responsible for these modifications have emerged as attractive therapeutic compounds to treat neurodegeneration. In this review, we discuss the role of DNA double-strand breaks and abnormal chromatin modification patterns in a range of neurodegenerative conditions, and the chromatin modifiers that might ameliorate them. Finally, we suggest that understanding the epigenetic modifications specific to neuronal DNA repair is crucial for the development of efficient neurotherapeutic strategies.

Aberrant regulation of DNA methylation in amyotrophic lateral sclerosis: a new target of disease mechanisms

Amyotrophic lateral sclerosis (ALS) is the third most common adult-onset neurodegenerative disease. A diagnosis is fatal owing to degeneration of motor neurons in brain and spinal cord that control swallowing, breathing, and movement. ALS can be inherited, but most cases are not associated with a family history of the disease. The mechanisms causing motor neuron death in ALS are still unknown. Given the suspected complex interplay between multiple genes, the environment, metabolism, and lifestyle in the pathogenesis of ALS, we have hypothesized that the mechanisms of disease in ALS involve epigenetic contributions that can drive motor neuron degeneration. DNA methylation is an epigenetic mechanism for gene regulation engaged by DNA methyltransferase (Dnmt)-catalyzed methyl group transfer to carbon-5 in cytosine residues in gene regulatory promoter and nonpromoter regions. Recent genome-wide analyses have found differential gene methylation in human ALS. Neuropathologic assessments have revealed that motor neurons in human ALS show significant abnormalities in Dnmt1, Dnmt3a, and 5-methylcytosine. Similar changes are seen in mice with motor neuron degeneration, and Dnmt3a was found abundantly at synapses and in mitochondria. During apoptosis of cultured motor neuron-like cells, Dnmt1 and Dnmt3a protein levels increase, and 5-methylcytosine accumulates. Enforced expression of Dnmt3a, but not Dnmt1, induces degeneration of cultured neurons. Truncation mutation of the Dnmt3a catalytic domain and Dnmt3a RNAi blocks apoptosis of cultured neurons. Inhibition of Dnmt catalytic activity with small molecules RG108 and procainamide protects motor neurons from excessive DNA methylation and apoptosis in cell culture and in a mouse model of ALS. Thus, motor neurons can engage epigenetic mechanisms to cause their degeneration, involving Dnmts and increased DNA methylation. Aberrant DNA methylation in vulnerable cells is a new direction for discovering mechanisms of ALS pathogenesis that could be relevant to new disease target identification and therapies for ALS.

Skeletal muscle calpain acts through nitric oxide and neural miRNAs to regulate acetylcholine release in motor nerve terminals

Cholinergic overactivity in diseases of neuromuscular transmission elicits a retrograde signal resembling homeostatic synaptic plasticity that downregulates transmitter release. Understanding this compensatory pathway could provide insights into novel therapeutic avenues and molecular mechanisms underlying learning and memory. Here we identify nitric oxide as a possible source of this signal in pathological human and mouse muscle samples and link this signaling pathway to changes in synaptic function in the neuromuscular junction. We further show that neuronal nitric oxide synthase is regulated by cholinergic excess through activation of skeletal muscle calpain and its effect on Cdk5 and CaMKII, leading to direct modulation of presynaptic function. Finally, we show that this signaling pathway acts through specific miRNA control of presynaptic vesicle protein expression. The control of presynaptic miRNA levels by postsynaptic activity represents a novel mechanism for the modulation of synaptic activity in normal or pathological conditions.

P2X7 receptor-induced death of motor neurons by a peroxynitrite/FAS-dependent pathway

The P2X7 receptor/channel responds to extracellular ATP and is associated with neuronal death and neuroinflammation in spinal cord injury and amyotrophic lateral sclerosis. Whether activation of P2X7 directly causes motor neuron death is unknown. We found that cultured motor neurons isolated from embryonic rat spinal cord express P2X7 and underwent caspase-dependent apoptosis when exposed to exceptionally low concentrations of the P2X7 agonist 2'(3')-O-(4-Benzoylbenzoyl)-ATP. The P2X7 inhibitors BBG, oATP, and KN-62 prevented 2'(3')-O-(4-Benzoylbenzoyl)-ATP-induced motor neuron death. The endogenous P2X7 agonist ATP induced motor neuron death at low concentrations (1-100 μM). High concentrations of ATP (1 mM) paradoxically became protective due to degradation in the culture media to produce adenosine and activate adenosine receptors. P2X7-induced motor neuron death was dependent on neuronal nitric oxide synthase-mediated production of peroxynitrite, p38 activation, and autocrine FAS signaling. Taken together, our results indicate that motor neurons are highly sensitive to P2X7 activation, which triggers apoptosis by activation of the well-established peroxynitrite/FAS death pathway in motor neurons.

Inhibitory effect of carbazolequinone derivatives on lipopolysaccharide and interferon-γ-induced nitric oxide production in mouse macrophage RAW264.7 cells

Objectives

The aim of this study was to examine the mechanism underlying the inhibitory effect of our synthesized carbazolequinone derivatives on nitric oxide (NO) production in activated macrophages.

Methods

Lipopolysaccharide (LPS) and interferon-γ (IFN-γ)-stimulated RAW264.7 macrophages were treated with carbazolequinone derivatives. The NO and prostaglandin E2 (PGE2) levels in cell culture supernatants fractions were measured by Greiss and ELISA assay, respectively. The expression of inducible NO synthase (iNOS) and cyclooxygenase-2 (COX-2) was assessed by the real-time RT-PCR method. Nuclear factor kappa B (NF-κB) activation was detected by an NF-κB-dependent luciferase reporter assay.

Key findings

Our synthesized carbazolequinone derivatives (7-methoxy-2-methylcarbazole-1,4-quinone, 6-methoxy-2-methylcarbazole-1,4-quinone and 6-chloro-2-methylcarbazole-1,4-quinone) significantly inhibited LPS/IFN-γ-induced NO production and iNOS expression in RAW264.7 cells. They also inhibited the LPS/IFN-γ-mediated induction of COX-2 expression and PGE2 production. In addition, the LPS/IFN-γ-induced transcription activity of NF-κB was attenuated. Using the RAW264.7-tsAM5NE co-culture system, we found that these carbazolequinone derivatives protected neuronally differentiated tsAM5NE cells from NO-induced cell death by inhibiting the production of NO.

Conclusions

These results suggest that the three carbazolequinone derivatives inhibit LPS/IFN-γ-induced NO production via iNOS and COX-2 downregulation due to NF-κB inhibition. Therefore, these three carbazolequinone derivatives may be useful for developing a new drug against NO-mediated neurodegenerative diseases.

Simvastatin induces caspase-dependent apoptosis and activates P53 in OCM-1 cells

Simvastatin is a cholesterol-lowering drug which exhibits numerous pleiotropic effects including anti-cancer activity. Yet, the anti-cancer effects in choroidal melanoma remain poorly characterized. Therefore, in this study, we investigated the effects of simvastatin on OCM-1 cells growth, apoptosis and cycle. Simvastatin showed an inhibitory effects on OCM-1 cells viability in dose-dependent (2-10 μM) and time-dependent (24-72 h) manner. Further study suggested that simvastatin-induced inhibition OCM-1 cells proliferation was associated with G1 phase arrest, decreased protein and mRNA expression of proliferation marker cyclin D1, cyclin E, cyclin dependent kinase (CDK)2 and increased expression of CDK inhibitory protein P21. In addition, simvastatin resulted in an increase in levels of reactive oxygen species (ROS) in OCM-1 cells and simvastatin significantly triggered apoptosis in OCM-1 cells, which was characterized by increased chromatin condensation, activation of caspase-9 and cleaved-caspase-3, increased expression mitochondrion-related apoptosis protein of P53, Bax and decreased expression of Bcl2 and iASPP. Collectively, our study demonstrated that simvastatin can efficiently inhibit proliferation and induce apoptosis in OCM-1 cells.

Motor neuron degeneration in a mouse model of seipinopathy

Heterozygosity for missense mutations (N88S/S90L) in BSCL2 (Berardinelli–Seip congenital lipodystrophy type 2)/Seipin is associated with a broad spectrum of motoneuron diseases. To understand the underlying mechanisms how the mutations lead to motor neuropathy, we generated transgenic mice with neuron-specific expression of wild-type (tgWT) or N88S/S90L mutant (tgMT) human Seipin. Transgenes led to the broad expression of WT or mutant Seipin in the brain and spinal cord. TgMT, but not tgWT, mice exhibited late-onset altered locomotor activities and gait abnormalities that recapitulate symptoms of seipinopathy patients. We found loss of alpha motor neurons in tgMT spinal cord. Mild endoreticular stress was present in both tgMT and tgWT neurons; however, only tgMT mice exhibited protein aggregates and disrupted Golgi apparatus. Furthermore, autophagosomes were significantly increased, along with elevated light chain 3 (LC3)-II level in tgMT spinal cord, consistent with the activation of autophagy pathway in response to mutant Seipin expression and protein aggregation. These results suggest that induction of autophagy pathway is involved in the cellular response to mutant Seipin in seipinopathy and that motoneuron loss is a key pathogenic process underlying the development of locomotor abnormalities.

Targeting hepatoma using nitric oxide donor strategies

AIMS

The study evaluated the role of increased intracellular nitric oxide (NO) concentration using NO donors or stably NO synthase-3 (NOS-3) overexpression during CD95-dependent cell death in hepatoma cells. The expression of cell death receptors and caspase activation, RhoA kinase activity, NOS-3 expression/activity, oxidative/nitrosative stress, and p53 expression were analyzed. The antitumoral activity of NO was also evaluated in the subcutaneous implantation of NOS-3-overexpressing hepatoma cells, as well NO donor injection into wild-type hepatoma-derived tumors implanted in xenograft mouse models.

RESULTS

NO donor increased CD95 expression and activation of caspase-8 and 3 in HepG2, Huh7, and Hep3B cells. NOS-3 overexpression increased oxidative/nitrosative stress, p53 and CD95 expression, cellular Fas-associated death domain (FADD)-like IL-1beta converting enzyme (FLICE) inhibitory protein long (cFLIP(L)) and its short isoform (cFLIP(S)) shift, and cell death in HepG2 (4TO-NOS) cells. The inhibition of RhoA kinase and p53 knockdown using RNA interference reduced cell death in 4TO-NOS cells. The supplementation with hydrogen peroxide (H(2)O(2)) increased NOS-3 activity and cell death in 4TO-NOS cells. NOS-3 overexpression or NO donor injection into hepatoma-derived tumors reduced the size and increased p53 and cell death receptor expression in nude mice.

INNOVATION AND CONCLUSIONS

The increase of intracellular NO concentration promoted oxidative and nitrosative stress, Rho kinase activity, p53 and CD95 expression, and cell death in cultured hepatoma cells. NOS-3-overexpressed HepG2 cells or intratumoral NO donor administration reduced tumor cell growth and increased the expression of p53 and cell death receptors in tumors developed in a xenograft mouse model.

Differential gene expression in the axotomized facial motor nucleus of presymptomatic SOD1 mice

Previously, we compared molecular profiles of one population of wild-type (WT) mouse facial motoneurons (FMNs) surviving with FMNs undergoing significant cell death after axotomy. Regardless of their ultimate fate, injured FMNs respond with a vigorous pro-survival/regenerative molecular response. In contrast, the neuropil surrounding the two different injured FMN populations contained distinct molecular differences that support a causative role for glial and/or immune-derived molecules in directing contrasting responses of the same cell types to the same injury. In the current investigation, we utilized the facial nerve axotomy model and a presymptomatic amyotrophic lateral sclerosis (ALS) mouse (SOD1) model to experimentally mimic the axonal die-back process observed in ALS pathogenesis without the confounding variable of disease onset. Presymptomatic SOD1 mice had a significant decrease in FMN survival compared with WT, which suggests an increased susceptibility to axotomy. Laser microdissection was used to accurately collect uninjured and axotomized facial motor nuclei of WT and presymptomatic SOD1 mice for mRNA expression pattern analyses of pro-survival/pro-regeneration genes, neuropil-specific genes, and genes involved in or responsive to the interaction of FMNs and non-neuronal cells. Axotomized presymptomatic SOD1 FMNs displayed a dynamic pro-survival/regenerative response to axotomy, similar to WT, despite increased cell death. However, significant differences were revealed when the axotomy-induced gene expression response of presymptomatic SOD1 neuropil was compared with WT. We propose that the increased susceptibility of presymptomatic SOD1 FMNs to axotomy-induced cell death and, by extrapolation, disease progression, is not intrinsic to the motoneuron, but rather involves a dysregulated response by non-neuronal cells in the surrounding neuropil.