Neurodegenerative disease. Oxidative stress and motorneuron disease

Roxithromycin exposure induces motoneuron malformation and behavioral deficits of zebrafish by interfering with the differentiation of motor neuron progenitor cells

Roxithromycin (ROX), a commonly used macrolide antibiotic, is extensively employed in human medicine and livestock industries. Due to its structural stability and resistance to biological degradation, ROX persists as a resilient environmental contaminant, detectable in aquatic ecosystems and food products. However, our understanding of the potential health risks to humans from continuous ROX exposure remains limited. In this study, we used the zebrafish as a vertebrate model to explore the potential developmental toxicity of early ROX exposure, particularly focusing on its effects on locomotor functionality and CaP motoneuron development. Early exposure to ROX induces marked developmental toxicity in zebrafish embryos, significantly reducing hatching rates (n=100), body lengths (n=100), and increased malformation rates (n=100). The zebrafish embryos treated with a corresponding volume of DMSO (0.1%, v/v) served as vehicle controls (veh). Moreover, ROX exposure adversely affected the locomotive capacity of zebrafish embryos, and observations in transgenic zebrafish Tg(hb9:eGFP) revealed axonal loss in motor neurons, evident through reduced or irregular axonal lengths (n=80). Concurrently, abnormal apoptosis in ROX-exposed zebrafish embryos intensified alongside the upregulation of apoptosis-related genes (bax, bcl2, caspase-3a). Single-cell sequencing further disclosed substantial effects of ROX on genes involved in the differentiation of motor neuron progenitor cells (ngn1, olig2), axon development (cd82a, mbpa, plp1b, sema5a), and neuroimmunity (aplnrb, aplnra) in zebrafish larvae (n=30). Furthermore, the CaP motor neuron defects and behavioral deficits induced by ROX can be rescued by administering ngn1 agonist (n=80). In summary, ROX exposure leads to early-life abnormalities in zebrafish motor neurons and locomotor behavior by hindering the differentiation of motor neuron progenitor cells and inducing abnormal apoptosis.

Therapy development for spinal muscular atrophy: perspectives for muscular dystrophies and neurodegenerative disorders

BACKGROUND

Major efforts have been made in the last decade to develop and improve therapies for proximal spinal muscular atrophy (SMA). The introduction of Nusinersen/Spinraza™ as an antisense oligonucleotide therapy, Onasemnogene abeparvovec/Zolgensma™ as an AAV9-based gene therapy and Risdiplam/Evrysdi™ as a small molecule modifier of pre-mRNA splicing have set new standards for interference with neurodegeneration.

MAIN BODY

Therapies for SMA are designed to interfere with the cellular basis of the disease by modifying pre-mRNA splicing and enhancing expression of the Survival Motor Neuron (SMN) protein, which is only expressed at low levels in this disorder. The corresponding strategies also can be applied to other disease mechanisms caused by loss of function or toxic gain of function mutations. The development of therapies for SMA was based on the use of cell culture systems and mouse models, as well as innovative clinical trials that included readouts that had originally been introduced and optimized in preclinical studies. This is summarized in the first part of this review. The second part discusses current developments and perspectives for amyotrophic lateral sclerosis, muscular dystrophies, Parkinson's and Alzheimer's disease, as well as the obstacles that need to be overcome to introduce RNA-based therapies and gene therapies for these disorders.

CONCLUSION

RNA-based therapies offer chances for therapy development of complex neurodegenerative disorders such as amyotrophic lateral sclerosis, muscular dystrophies, Parkinson's and Alzheimer's disease. The experiences made with these new drugs for SMA, and also the experiences in AAV gene therapies could help to broaden the spectrum of current approaches to interfere with pathophysiological mechanisms in neurodegeneration.

Pogostemon cablin as ROS Scavenger in Oxidant-induced Cell Death of Human Neuroglioma Cells

Reactive oxygen species (ROS) have been implicated in the pathogenesis of a wide range of acute and long-term neurodegenerative diseases. This study was undertaken to examine the efficacy of Pogostemon cablin, a well-known herb in Korean traditional medicine, on ROS-induced brain cell injury. Pogostemon cablin effectively protected human neuroglioma cell line A172 against both the necrotic and apoptotic cell death induced by hydrogen peroxide (H₂O₂). The effect of Pogostemon cablin was dose dependent at concentrations ranging from 0.2 to 5 mg ml⁻¹. Pogostemon cablin significantly prevented depletion of cellular ATP and activation of poly ADP-ribose polymerase induced by H₂O₂. The preservation of functional integrity of mitochondria upon the treatment of Pogostemon cablin was also confirmed by 3-(4,5-dimethyl-2-thiazyl)-2,5-diphenyl-2-H-tetrazolium bromide assay. Furthermore, Pogostemon cablin significantly prevented H₂O₂-induced release of cytochrome c into cytosol. Determination of intracellular ROS showed that Pogostemon cablin might exert its role as a powerful scavenger of intracellular ROS. The present study suggests the beneficial effect of Pogostemon cablin on ROS-induced neuroglial cell injury. The action of Pogostemon cablin as a ROS-scavenger might underlie the mechanism.

Enprofylline protects motor neurons from in vitro excitotoxic challenge

BACKGROUND

The death of motor neurons in amyotrophic lateral sclerosis (ALS) is believed to result, in part, from unrestrained activation of glutamate receptors (excitotoxicity). In some in vitro models, excitotoxic death only occurs if motor neurons develop in the presence of the growth factor, brain-derived neurotrophic factor (BDNF).

OBJECTIVE

Since the increased vulnerability of motor neurons evoked by BDNF is mediated by activation of TrkB, we sought to identify pharmacological agents that can block this pathway. Adenosine receptors are known to transactivate Trk receptors, leading us to examine the effects of manipulating of adenosine receptor signaling on Trk signaling and excitotoxic sensitivity.

METHODS

Spinal cord cultures were treated with adenosine receptor agonists and antagonists. The biochemical effects on Trk signaling and excitotoxic motor neuron death were examined.

RESULTS

We show here that adenosine A(2a) antagonists can reduce activation of Trk receptors and are neuroprotective. Conversely, activating adenosine A(2a) receptors in the absence of BDNF signaling makes motor neurons vulnerable to excitotoxic challenge.

CONCLUSION

Selective, high-affinity adenosine A(2a) antagonists merit consideration as therapeutic agents for the treatment of ALS.

The radical scavenger CR-6 protects SH-SY5Y neuroblastoma cells from oxidative stress-induced apoptosis: effect on survival pathways

Reactive oxygen species (ROS) and oxidative stress have long been linked to cell death of neurons in many neurodegenerative conditions. However, the exact molecular mechanisms triggered by oxidative stress in neurodegeneration are at present unclear. In the current work we have used the human neuroblastoma SH-SY5Y cell line as a model for studying the molecular events occurring after inducing apoptosis with H2O2. We show that treatment of SH-SY5Y cells with H2O2 up-regulates survival pathways during early stages of apoptosis. Subsequently, the decline of anti-apoptotic protein levels leads to the activation of the calcium-dependent proteases calpains and the cysteine proteases caspases. Additionally, we demonstrate that CR-6 (3,4-dihydro-6-hydroxy-7-methoxy-2,2-dimethyl-1(2H)-benzopyran) acts as a scavenger of ROS and prevents apoptosis by enhancing and prolonging up-regulation of survival pathways. Furthermore, we show that pre-treatment of SH-SY5Y cells with a cocktail containing CR-6, the pan-caspase inhibitor zVAD-fmk (zVal-Ala-Asp-fluoro-methylketone) and the calpain inhibitor SJA6017 confers almost total protection against apoptosis. In summary, the present work characterizes the molecular mechanisms involved in oxidative stress-induced apoptosis in SH-SY5Y cells. Our findings highlight the relevance of CR-6, alone or in combination with other drugs, as potential therapeutic strategy for the treatment of neurodegenerative diseases.

Role of ERK in Hydrogen Peroxide-Induced Cell Death of Human Glioma Cells

Oxidative stress is known to induce cell death in a wide variety of cell types, apparently by modulating intracellular signaling pathways. Activation of extracellular signal-regulated kinase (ERK) in oxidative stress remains controversial. In some cellular systems, the ERK activation is associated with protection against oxidative stress, while in other system, the ERK activation is involved in apoptotic cell death. The present study was undertaken to examine the role of ERK activation in H2O2-induced cell death of human glioma (A172) cells. H2O2 resulted in a time- and dose-dependent cell death, which was largely attributed to apoptosis. H2O2 treatment caused marked sustained activation of ERK. The ERK activation and cell death induced by H2O2 was prevented by catalase, the hydrogen peroxide scavenger, and U0126, an inhibitor of ERK upstream kinase MEK1/2. Transient transfection with constitutive active MEK1, an upstream activator of ERK1/2, increased H2O2-induced cell death, whereas transfection with dominant-negative mutants of MEK1 decreased the cell death. The ERK activation and cell death caused by H2O2 was inhibited by antioxidants (N-acetylcysteine and trolox), Ras inhibitor, and suramin. H2O2 produced depolarization of mitochondrial membrane potential and its effect was prevented by catalase and U0126. Taken together, these findings suggest that growth factor receptor/Ras/MEK/ERK signaling pathway plays an active role in mediating H2O2-induced apoptosis of human glioma cells and functions upstream of mitochondria-dependent pathway to initiate the apoptotic signal.

CNTF promotes survival of retinal ganglion cells after induction of ocular hypertension in rats: the possible involvement of STAT3 pathway

We examined the neuroprotective effect of ciliary neurotrophic factor (CNTF) on retinal ganglion cells (RGCs) in a rat glaucoma model with increased intraocular pressure (IOP) and studied the CNTF-mediated activation of Janus kinase/signal transducer and activator of transcription (JAK-STAT) pathway. Elevated IOP was induced by laser photocoagulation of the episcleral and limbal veins. The survival of RGCs was studied using Fluoro-Gold labelled in ocular hypertensive eyes with or without CNTF intravitreal injection. Immunochemical staining and immunoblot analysis for CNTF and phosphorylated STAT3 (pSTAT3) were performed. There was a significant and progressive loss of RGCs in the retinas following the induction of elevated IOP. A single intravitreal injection of 2 microg in 2 microL CNTF significantly protected RGCs up to 4 weeks. pSTAT3 was only transiently expressed in ocular hypertensive eyes. However, in eyes treated with CNTF, pSTAT3 was observed up to 2 weeks after the induction of elevated IOP. In ocular hypertensive eyes, CNTF-positive cells were found in the inner nuclear layer (INL), and there was a transient increase in the pSTAT3 cells in the ganglion cell layer and INL. Immunoblots showed that STAT3 was transiently phosphorylated after IOP increase, but with an injection of CNTF, pSTAT3 protein was observed up to 2 weeks after hypertensive glaucoma induction. Laser-induced chronic ocular hypertension in rats resulted in the death of RGCs and a transient activation of STAT3 in the retina. Intravitreal injection of CNTF showed a significant protection of RGCs, and the JAK-STAT signalling could be one of the important pathways that underlie the mechanism of CNTF neuroprotection in this rat glaucoma model.

H2O2-induced cell death in human glioma cells: role of lipid peroxidation and PARP activation

Reactive oxygen species (ROS) have been implicated in the pathogenesis of a number of neurodegenerative disorders. However, the underlying mechanism of ROS-induced cell injury remains to be defined. This study was undertaken to examine the role of lipid peroxidation and poly (ADP-ribose) polymerase (PARP) activation in H2O2-induced cell death in A172 cells, a human glioma cell line. H2O2 induced a dose- and time-dependent cell death. The cell death was prevented by thiols (dithiothreitol and glutathione), iron chelators (deferoxamine and phenanthroline), H2O2 scavengers (catalase and pyruvate), and a hydroxyl radical scavenger (dimethylthiourea). Antioxidants N,N'-diphenyl-p-phenylenediamine (DPPD) and Trolox had no effect on the H2O2-induced cell death. Lipid peroxidation did not increase in human glioma cells exposed to H2O2. The PARP inhibitor 3-aminobenzamide prevented the cell death induced by H2O2. The PARP activity was increased by H2O2 and the H2O2 effect was prevented by 3-aminobenzamide, dithiothreitol, and phenanthroline. The ATP depletion induced by H2O2 was prevented by catalase, dithiothreitol, phenanthroline, and 3-aminobenzamide, but not by DPPD. These results indicate that the H2O2-induced cell death is mediated by PARP activation but not by lipid peroxidation in human glioma cells.

Therapeutic benefits of putrescine-modified catalase in a transgenic mouse model of familial amyotrophic lateral sclerosis

Dominant mutations in the copper/zinc superoxide dismutase (SOD1) gene have been observed in 15-20% of familial amyotrophic lateral sclerosis (FALS) cases. The mechanism by which SOD1 mutations result in motor neuron degeneration in FALS mice partly involves oxidative damage and an increased peroxidase activity of the mutant SOD1. A new therapeutic approach designed to eliminate the substrate of this peroxidase activity was examined in two lines of transgenic mice expressing the FALS-linked mutation glycine to alanine (G93A). We investigated the ability of putrescine-modified catalase (PUT-CAT), an antioxidant enzyme that removes hydrogen peroxide and has increased permeability at the blood-brain barrier, to modify the time course of the SOD1 mutation-induced motor neuron disease in these FALS mice. Continuous, subcutaneous administration of PUT-CAT significantly delayed the age at which onset of clinical disease occurred (indicated by loss of splay and/or tremors of hindlimbs) in a high-expressor line of FALS transgenic mice. Intraperitoneal injection of PUT-CAT given two times per week also significantly delayed the onset of clinical disease in a low-expressor line of FALS mice. PUT-CAT also significantly delayed the age at which clinical weakness developed (quantified by measuring the shortening of stride length) in both lines of FALS animals. No significant changes were observed in the survival times of the high-expressor FALS mice in any of the treatment groups. However, a trend toward a prolongation of survival was observed in the PUT-CAT-treated low-expressor FALS mice. These results support the role of free radical-mediated damage in the cascade of events leading to motor neurodegeneration in FALS and indicate that PUT-CAT interacts with a critical step in this cascade to delay the onset of clinical disease as well as the development of clinical weakness in FALS transgenic mice.

Plasma pharmacokinetics, nervous system biodistribution and biostability, and spinal cord permeability at the blood-brain barrier of putrescine-modified catalase in the adult rat

Free radical-mediated oxidative damage has been proposed to be an underlying mechanism in several neurodegenerative disorders. Previous investigations in our laboratory have shown that putrescine-modified catalase (PUT-CAT) has increased permeability at the blood-brain (BBB) and blood-nerve barriers with retained enzymatic activity after parenteral administration when compared to native catalase (CAT). The goals of the present study were to examine the plasma stability, spinal cord BBB permeability, nervous system biodistribution, and spinal cord enzyme activity of CAT and PUT-CAT after parenteral administration in the adult rat. TCA precipitation and chromatographic analyses revealed that CAT and PUT-CAT were found intact in the plasma and in the central nervous system (CNS) after iv, ip, or sc bolus injections. The highest percentages of intact CAT or PUT-CAT proteins were found in the plasma after iv administration, and similar percentages of intact CAT or PUT-CAT were found in the CNS following all three types of administration. Increases of 2.4- to 4.7-fold in permeability at the BBB and similar increases in the levels of intact PUT-CAT were found in different brain regions compared to the levels of CAT. A 2.4-fold higher level of intact PUT-CAT compared to that of CAT (P < 0.05) was found in the spinal cord 60 min after a sc bolus injection. CAT enzyme activity in the spinal cord was 50% higher (P < 0.05) in rats treated with PUT-CAT continuously for 1 week by subcutaneously implanted, osmotic pumps than the activity found in rats treated with PBS. These results provide evidence that intact, enzymatically active PUT-CAT is efficiently delivered to the nervous system following iv, ip, and sc administration and suggest that sc administration of PUT-CAT may be effective in treating neurodegenerative disorders in which the underlying mechanisms involve the action of free radicals and oxidative damage.

Alzheimer's disease and oxidative stress: implications for novel therapeutic approaches

Alzheimer's disease (AD) is a progressive neurodegenerative disorder with a deadly outcome. AD is the leading cause of senile dementia and although the pathogenesis of this disorder is not known, various hypotheses have been developed based on experimental data accumulated since the initial description of this disease by Alois Alzheimer about 90 years ago. Most approaches to explain the pathogenesis of AD focus on its two histopathological hallmarks, the amyloid beta protein- (A(beta)-) loaded senile plaques and the neurofibrillary tangles, which consist of the filament protein tau. Various lines of genetic evidence support a central role of A(beta) in the pathogenesis of AD and an increasing number of studies show that oxidation reactions occur in AD and that A(beta) may be one molecular link between oxidative stress and AD-associated neuronal cell death. A(beta) itself can be neurotoxic and can induce oxidative stress in cultivated neurons. A(beta) is, therefore, one player in the concert of oxidative reactions that challenge neurons besides inflammatory reactions which are also associated with the AD pathology. Consequently, antioxidant approaches for the prevention and therapy of AD are of central interest. Experimental as well as clinical data show that lipophilic antioxidants, such as vitamin E and estrogens, are neuroprotective and may help patients suffering from AD. While an additional intensive elucidation of the cellular and molecular events of neuronal cell death in AD will, ultimately, lead to novel drug targets, various antioxidants are already available for a further exploitation of their preventive and therapeutic potential. reserved

Calcium and S100B regulation of p53-dependent cell growth arrest and apoptosis

In glial C6 cells constitutively expressing wild-type p53, synthesis of the calcium-binding protein S100B is associated with cell density-dependent inhibition of growth and apoptosis in response to UV irradiation. A functional interaction between S100B and p53 was first demonstrated in p53-negative mouse embryo fibroblasts (MEF cells) by sequential transfection with the S100B and the temperature-sensitive p53Val135 genes. We show that in MEF cells expressing a low level of p53Val135, S100B cooperates with p53Val135 in triggering calcium-dependent cell growth arrest and cell death in response to UV irradiation at the nonpermissive temperature (37.5 degreesC). Calcium-dependent growth arrest of MEF cells expressing S100B correlates with specific nuclear accumulation of the wild-type p53Val135 conformational species. S100B modulation of wild-type p53Val135 nuclear translocation and functions was confirmed with the rat embryo fibroblast (REF) cell line clone 6, which is transformed by oncogenic Ha-ras and overexpression of p53Val135. Ectopic expression of S100B in clone 6 cells restores contact inhibition of growth at 37.5 degreesC, which also correlates with nuclear accumulation of the wild-type p53Val135 conformational species. Moreover, a calcium ionophore mediates a reversible G1 arrest in S100B-expressing REF (S100B-REF) cells at 37.5 degreesC that is phenotypically indistinguishable from p53-mediated G1 arrest at the permissive temperature (32 degreesC). S100B-REF cells proceeding from G1 underwent apoptosis in response to UV irradiation. Our data support a model in which calcium signaling and S100B cooperate with the p53 pathways of cell growth inhibition and apoptosis.

Cysteine oxidation in the mitogenic S100B protein leads to changes in phosphorylation by catalytic CKII-alpha subunit

The glial-derived calcium-binding protein S100B can be secreted to act as a neurotrophic factor or a mitogen, stimulating proliferation of glial cells. The extracellular S100B activities rely on the oxidation of the protein cysteine residues (Kligman, D., and Marshak, D. R. (1985) Proc. Natl. Acad. Sci. U. S. A. 82, 7136-7139; Winningham-Major, F., Staecker, J. L., Barger, S. W., Coats, S., and Van Eldik, L. J. (1989) J. Cell Biol. 109, 3063-3071). Here we show that oxidation of the S100B cysteine residues, Cys-68 and Cys-84, induces a conformational change in the protein structure, unmasking a canonical CKII phosphorylation site located within the typical EF-hand calcium-binding site IIbeta. Intrasubunit disulfide-bridged S100B monomer and disulfide-bonded S100B dimer are phosphorylated by the catalytic CKII-alpha subunit on Ser-62 with a Km of 0.5 microM and a Vmax of 10 pmol/min/100 pmol of S100B. Oxidized S100B is the best in vitro CKII-alpha substrate identified so far. Next we show that intrasubunit disulfide-bridged S100B monomer is the most potent S100B species to stimulate [3H]thymidine uptake by C6 glial cells in culture. In addition, the phosphorylated intrasubunit disulfide-bridged S100B monomer retains apparent mitogenic activity toward C6 glial cells, and hence, 32P-labeled S100B should be a useful probe for characterizing the mechanisms by which extracellular oxidized S100B functions. Finally, we show that formation of intrasubunit disulfide-bridged S100B monomer is stimulated by peroxynitrite anion, suggesting that production of mitogenic S100B species could be enhanced in neuropathology associated with peroxynitrite anion production.

Menadione-induced tau dephosphorylation in cultured human neuroblastoma cells

Oxidative stress has been implicated in the mechanism of aging and neurodegenerative disorders such as Alzheimer's disease (AD). Menadione causes oxidative stress by generating reactive oxygen species through its redox cycling and these free radicals are detoxified subsequently at the expense of intracellular thiol homeostasis. In non-neuronal cells, the cytoskeleton is a prime target of menadione-induced thiol oxidation. We used cultured human neuroblastoma MSN cells in this study to determine how tau proteins in neuronal cells are affected by menadione exposure. Menadione caused a dose-dependent thiol oxidation in these cells just like their non-neuronal counterparts. A prominent consequence of such oxidative insult in these neuronal cells was tau dephosphorylation. This dephosphorylation resulted in disappearance of phosphorylated 57-kDa tau with a concomitant emergence of 53-kDa tau whose full-length nature is indicated by its reactivity with antibodies Alz 50, Tau-1 and Tau-46. Immunochemical analyses using phosphorylation-dependent immunoprobes Tau-1 and PHF-1 with the aid of alkaline phosphatase demonstrated that 53-kDa tau was derived from dephosphorylation of 57-kDa tau. Despite its effect on thiol oxidation, menadione treatment did not lead to cytoskeletal changes reminiscent of the neurofibrillary tangles of AD. The data thus indicate that tau dephosphorylation constitutes a major feature of the menadione-induced oxidative injury in these neuronal cells.

The roles of hydrogen peroxide and superoxide as messengers in the activation of transcription factor NF-kappa B

BACKGROUND

The inducible, higher eukaryotic transcription factor NF-kappa B is activated by a variety of stimuli. Several lines of evidence have suggested that reactive oxygen intermediates (ROIs) serve as messengers for most if not all of these stimuli. To identify the relevant ROI species and to gain more direct evidence for an involvement of ROIs as messengers, we investigated whether changes in the levels of enzymes that control intracellular ROI levels affect the activation of NF-kappa B.

RESULTS

Cell lines stably overexpressing the H2O2-degrading enzyme catalase were deficient in activating NF-kappa B in response to tumor necrosis factor alpha (TNF) or okadaic acid. The catalase inhibitor aminotriazol restored NF-kappa B induction. In contrast, stable overexpression of cytoplasmic Cu/Zn-dependent superoxide dismutase (SOD), which enhances the production of H2O2 from superoxide, potentiated NF-kappa B activation. The level of cytoplasmic NF-kappa B-I kappa B complex was unchanged, indicating that synthesis of NF-kappa B was not affected.

CONCLUSIONS

Our data show that one ROI species, H2O2 acts as a messenger in the TNF- and okadaic acid-induced post-translational activation of NF-kappa B. Superoxide is only indirectly involved, as a source for H2O2. These data explain the inhibitory effects of many antioxidative compounds on the activation of NF-kappa B and its target genes. H2O2 is overproduced in response to various stimuli, and normal levels of catalase appear insufficient to remove it completely. H2O2 can therefore accumulate and act as an intracellular messenger molecule in the response to pathogens.