Differential lipid peroxidation, Mn superoxide, and bcl-2 expression contribute to the maturation-dependent vulnerability of oligodendrocytes to oxidative stress

Selenoprotein I is indispensable for ether lipid homeostasis and proper myelination

Selenoprotein I (SELENOI) catalyzes the final reaction of the CDP-ethanolamine branch of the Kennedy pathway, generating the phospholipids phosphatidylethanolamine (PE) and plasmenyl-PE. Plasmenyl-PE is a key component of myelin and is characterized by a vinyl ether bond that preferentially reacts with oxidants, thus serves as a sacrificial antioxidant. In humans, multiple loss-of-function mutations in genes affecting plasmenyl-PE metabolism have been implicated in hereditary spastic paraplegia, including SELENOI. Herein, we developed a mouse model of nervous system-restricted SELENOI deficiency that circumvents embryonic lethality caused by constitutive deletion and recapitulates phenotypic features of hereditary spastic paraplegia. Resulting mice exhibited pronounced alterations in brain lipid composition, which coincided with motor deficits and neuropathology including hypomyelination, elevated reactive gliosis, and microcephaly. Further studies revealed increased lipid peroxidation in oligodendrocyte lineage cells and disrupted oligodendrocyte maturation both in vivo and in vitro. Altogether, these findings detail a critical role for SELENOI-derived plasmenyl-PE in myelination that is of paramount importance for neurodevelopment.

Oxidative stress involvement in the molecular pathogenesis and progression of multiple sclerosis: a literature review

Multiple sclerosis (MS) is an autoimmune debilitating disease of the central nervous system caused by a mosaic of interactions between genetic predisposition and environmental factors. The pathological hallmarks of MS are chronic inflammation, demyelination, and neurodegeneration. Oxidative stress, a state of imbalance between the production of reactive species and antioxidant defense mechanisms, is considered one of the key contributors in the pathophysiology of MS. This review is a comprehensive overview of the cellular and molecular mechanisms by which oxidant species contribute to the initiation and progression of MS including mitochondrial dysfunction, disruption of various signaling pathways, and autoimmune response activation. The detrimental effects of oxidative stress on neurons, oligodendrocytes, and astrocytes, as well as the role of oxidants in promoting and perpetuating inflammation, demyelination, and axonal damage, are discussed. Finally, this review also points out the therapeutic potential of various synthetic antioxidants that must be evaluated in clinical trials in patients with MS.

Distribution and Localization of Mahogunin Ring Finger 1 in the Mouse Central Nervous System

Mahogunin ring finger 1 (MGRN1), an E3 ubiquitin, is involved in several physiological and neuropathological processes. Although mgrn1 mRNA is widely distributed in the central nervous system (CNS), detailed information on its cellular and subcellular localization is lacking and its physiological role remains unclear. In this study, we aimed to determine the distribution of MGRN1 in the mouse CNS using a newly produced antibody against MGRN1. We found that the MGRN1 protein was expressed in most neuronal cell bodies. An intense MGRN1 expression was also observed in the neuropil of the gray matter in different regions of the CNS, including the main olfactory bulb, cerebral cortex, caudate, putamen, thalamic nuclei, hypothalamic nuclei, medial eminence, superior colliculus, hippocampus, dentate gyrus, and spinal cord. Contrastingly, no MGRN1 expression was observed in glial cells. Double fluorescence and immunoelectron microscopic analyses revealed the intracellular distribution of MGRN1 in pre-synapses and near the outer membrane of the mitochondria in neurons. These findings indicate that MGRN1 is more widely expressed throughout the CNS; additionally, the intracellular expression of MGRN1 suggests that it may play an important role in synaptic and mitochondrial functions.

Cuprizone-induced Demyelination in Mouse Brain is not due to Depletion of Copper

The cuprizone (CPZ) model allows the study of the biochemical processes underlying nonautoimmune-mediated demyelination, remyelination, and chronic white matter disease progression. CPZ is a copper (Cu) chelator that chiefly causes oligodendrocyte apoptosis in the corpus callosum and cerebellum when administered in the mouse diet. While disruption of Cu homeostasis is known to cause neurodegeneration (as is observed in Wilson’s and Menkes disease), no consensus exists to date as to CPZ’s mechanism of action. We sought to determine whether CPZ-induced pathology is due to Cu depletion as is generally believed. Cu supplementation in chow, in stoichiometric excess to the added CPZ, did not reduce CPZ-induced demyelination in C57Bl/6 mice. Moreover, equivalent doses of other known Cu chelators neocuproine and D-penicillamine (D-Pen) failed to induce central nervous system (CNS) demyelination. Since administration of D-Pen in the treatment of Wilson’s disease can induce hypocupremia, we next sought to recreate penicillamine-induced Cu deficiency to compare with purported CPZ-induced Cu deficiency. The resulting clinical phenotype and histopathology were unlike that of CPZ. D-Pen-treated mice exhibited digit paralysis, tail flaccidity, subcutaneous hemorrhaging, and optic and sciatic neuropathy, all of which were prevented with Cu supplementation. No demyelination of the corpus callosum or cerebellum was observed, even with D-Pen doses tenfold higher than CPZ. Intriguingly, addition of D-Pen to the CPZ diet paradoxically prevented demyelination in a dose-dependent manner.

Oxidative stress and impaired oligodendrocyte precursor cell differentiation in neurological disorders

Oligodendrocyte precursor cells (OPCs) account for 5% of the resident parenchymal central nervous system glial cells. OPCs are not only a back-up for the loss of oligodendrocytes that occurs due to brain injury or inflammation-induced demyelination (remyelination) but are also pivotal in plastic processes such as learning and memory (adaptive myelination). OPC differentiation into mature myelinating oligodendrocytes is controlled by a complex transcriptional network and depends on high metabolic and mitochondrial demand. Mounting evidence shows that OPC dysfunction, culminating in the lack of OPC differentiation, mediates the progression of neurodegenerative disorders such as multiple sclerosis, Alzheimer's disease and Parkinson's disease. Importantly, neurodegeneration is characterised by oxidative and carbonyl stress, which may primarily affect OPC plasticity due to the high metabolic demand and a limited antioxidant capacity associated with this cell type. The underlying mechanisms of how oxidative/carbonyl stress disrupt OPC differentiation remain enigmatic and a focus of current research efforts. This review proposes a role for oxidative/carbonyl stress in interfering with the transcriptional and metabolic changes required for OPC differentiation. In particular, oligodendrocyte (epi)genetics, cellular defence and repair responses, mitochondrial signalling and respiration, and lipid metabolism represent key mechanisms how oxidative/carbonyl stress may hamper OPC differentiation in neurodegenerative disorders. Understanding how oxidative/carbonyl stress impacts OPC function may pave the way for future OPC-targeted treatment strategies in neurodegenerative disorders.

Curcumin promotes oligodendrocyte differentiation and their protection against TNF-α through the activation of the nuclear receptor PPAR-γ

Curcumin is a compound found in the rhizome of Curcuma longa (turmeric) with a large repertoire of pharmacological properties, including anti-inflammatory and neuroprotective activities. The current study aims to assess the effects of this natural compound on oligodendrocyte progenitor (OP) differentiation, particularly in inflammatory conditions. We found that curcumin can promote the differentiation of OPs and to counteract the maturation arrest of OPs induced by TNF-α by a mechanism involving PPAR-γ (peroxisome proliferator activated receptor), a ligand-activated transcription factor with neuroprotective and anti-inflammatory capabilities. Furthermore, curcumin induces the phosphorylation of the protein kinase ERK1/2 known to regulate the transition from OPs to immature oligodendrocytes (OLs), by a mechanism only partially dependent on PPAR-γ. Curcumin is also able to raise the levels of the co-factor PGC1-α and of the cytochrome c oxidase core protein COX1, even when OPs are exposed to TNF-α, through a PPAR-γ-mediated mechanism, in line with the known ability of PPAR-γ to promote mitochondrial integrity and functions, which are crucial for OL differentiation to occur. Altogether, this study provides evidence for a further mechanism of action of curcumin besides its well-known anti-inflammatory properties and supports the suggested therapeutic potential of this nutraceutical in demyelinating diseases.

Redox imbalance induced by docetaxel in the neuroblastoma SH-SY5Y cells: a study of docetaxel-induced neuronal damage

Objectives

In cancer survivors, chemotherapy-associated adverse neurological effects are described as side effects in non-targeted tissue. We investigated the role of redox-imbalance in neuronal damage by a relative low dose of Docetaxel (DTX).

Methods

The neuroblastoma cells (SH-SY5Y cells) were exposed to DTX at a dose of 1.25 nM for 6 h. Antioxidant defenses (i.e. ascorbic acid, glutathione, and catalase) and lipid oxidation products (i.e. F₂-isoprostanes) were evaluated. To investigate cell ultrastructure and tubulin localisation, transmission electron microscopy (TEM) and immunofluorescence techniques were applied.

Results

In the SH-SY5Y cells, DTX induced a significant reduction of total glutathione (P < 0.001) and ascorbic acid (P < 0.05), and an increase in both total F₂-Isoprostanes (P < 0.05) and catalase activity (P < 0.05), as compared to untreated cells. Additionally, TEM showed a significant increase in cells with apoptotic characteristics. Immunolocalisation of tubulin showed a compromised cytoskeletal organisation.

Discussion

The investigated sublethal dose of DTX, to which non-targeted cells may be exposed throughout the duration of chemotherapy treatment, induces a redox imbalance resulting in a specific modulation of the antioxidant response. This study provides new insights into DTX-induced cellular mechanisms useful for evaluating whether the concomitant use of antioxidants associated with chemotherapy mitigates chemotherapy side effects in cancer survivors.

NRF2 and PPAR-γ Pathways in Oligodendrocyte Progenitors: Focus on ROS Protection, Mitochondrial Biogenesis and Promotion of Cell Differentiation

An adequate protection from oxidative and inflammatory reactions, together with the promotion of oligodendrocyte progenitor (OP) differentiation, is needed to recover from myelin damage in demyelinating diseases. Mitochondria are targets of inflammatory and oxidative insults and are essential in oligodendrocyte differentiation. It is known that nuclear factor-erythroid 2-related factor/antioxidant responsive element (NRF2/ARE) and peroxisome proliferator-activated receptor gamma/PPAR-γ response element (PPAR-γ/PPRE) pathways control inflammation and overcome mitochondrial impairment. In this study, we analyzed the effects of activators of these pathways on mitochondrial features, protection from inflammatory/mitochondrial insults and cell differentiation in OP cultures, to depict the specificities and similarities of their actions. We used dimethyl-fumarate (DMF) and pioglitazone (pio) as agents activating NRF2 and PPAR-γ, respectively, and two synthetic hybrids acting differently on the NRF2/ARE pathway. Only DMF and compound 1 caused early effects on the mitochondria. Both DMF and pio induced mitochondrial biogenesis but different antioxidant repertoires. Moreover, pio induced OP differentiation more efficiently than DMF. Finally, DMF, pio and compound 1 protected from tumor necrosis factor-alpha (TNF-α) insult, with pio showing faster kinetics of action and compound 1 a higher activity than DMF. In conclusion, NRF2 and PPAR-γ by inducing partially overlapping pathways accomplish complementary functions aimed at the preservation of mitochondrial function, the defense against oxidative stress and the promotion of OP differentiation.

Adenosine A2A receptor stimulation restores cell functions and differentiation in Niemann-Pick type C-like oligodendrocytes

Niemann Pick type C (NPC) disease is a rare neurovisceral disorder. Mutations in npc1 gene induce an intracellular accumulation of unesterified cholesterol in the endosomal/lysosomal system causing cell death. We recently showed that stimulation of adenosine A_2A receptors (A_2AR) restores cholesterol accumulation in late endosomes/lysosomes in human NPC fibroblasts and neural cell lines transiently transfected with NPC1 siRNA, suggesting that these receptors might be targeted to contrast the disease. Since NPC1 disease is characterized by dysmyelination and maturational arrest of oligodendrocyte progenitors (OPs), in this study, we investigated whether A_2AR stimulation could promote oligodendrocyte differentiation and myelin formation, thus overcoming these important neurological abnormalities. We developed a NPC1 pharmacological model, in which primary cultures of OPs are exposed to a cholesterol transport inhibitor to induce a NPC1-like phenotype characterized by several typical features such as (i) cholesterol accumulation, (ii) altered mitochondrial morphology and membrane potential, (iii) defect of autophagy and (iv) maturation arrest. The A_2AR agonist CGS21680 normalized all NPC1-like features. The ability of CGS21680 of rescuing OP from maturational arrest and promoting their differentiation to mature OL, suggests that A_2AR stimulation might be exploited to correct dysmyelination in NPC1, further supporting their therapeutic potential in the disease.

Functional Characterization of Human ProNGF and NGF Mutants: Identification of NGF P61SR100E as a "Painless" Lead Investigational Candidate for Therapeutic Applications

Background

Nerve Growth Factor (NGF) holds a great therapeutic promise for Alzheimer's disease, diabetic neuropathies, ophthalmic diseases, dermatological ulcers. However, the necessity for systemic delivery has hampered the clinical applications of NGF due to its potent pro-nociceptive action. A “painless” human NGF (hNGF R100E) mutant has been engineered. It has equal neurotrophic potency to hNGF but a lower nociceptive activity. We previously described and characterized the neurotrophic and nociceptive properties also of the hNGF P61S and P61SR100E mutants, selectively detectable against wild type hNGF. However, the reduced pain-sensitizing potency of the “painless” hNGF mutants has not been quantified.

Objectives and Results

Aiming at the therapeutic application of the “painless” hNGF mutants, we report on the comparative functional characterization of the precursor and mature forms of the mutants hNGF R100E and hNGF P61SR100E as therapeutic candidates, also in comparison to wild type hNGF and to hNGF P61S. The mutants were assessed by a number of biochemical, biophysical methods and assayed by cellular assays. Moreover, a highly sensitive ELISA for the detection of the P61S-tagged mutants in biological samples has been developed. Finally, we explored the pro-nociceptive effects elicited by hNGF mutants in vivo, demonstrating an expanded therapeutic window with a ten-fold increase in potency.

Conclusions

This structure-activity relationship study has led to validate the concept of developing painless NGF as a therapeutic, targeting the NGF receptor system and supporting the choice of hNGF P61S R100E as the best candidate to advance in clinical development. Moreover, this study contributes to the identification of the molecular determinants modulating the properties of the hNGF “painless” mutants.

Cellular and molecular neuropathology of the cuprizone mouse model: clinical relevance for multiple sclerosis

The cuprizone mouse model allows the investigation of the complex molecular mechanisms behind nonautoimmune-mediated demyelination and spontaneous remyelination. While it is generally accepted that oligodendrocytes are specifically vulnerable to cuprizone intoxication due to their high metabolic demands, a comprehensive overview of the etiology of cuprizone-induced pathology is still missing to date. In this review we extensively describe the physico-chemical mode of action of cuprizone and discuss the molecular and enzymatic mechanisms by which cuprizone induces metabolic stress, oligodendrocyte apoptosis, myelin degeneration and eventually axonal and neuronal pathology. In addition, we describe the dual effector function of the immune system which tightly controls demyelination by effective induction of oligodendrocyte apoptosis, but in contrast also paves the way for fast and efficient remyelination by the secretion of neurotrophic factors and the clearance of cellular and myelinic debris. Finally, we discuss the many clinical symptoms that can be observed following cuprizone treatment, and how these strengthened the cuprizone model as a useful tool to study human multiple sclerosis, schizophrenia and epilepsy.

Pathophysiology and neuroprotection of global and focal perinatal brain injury: lessons from animal models

BACKGROUND

Arterial ischemic stroke occurs more frequently in term newborns than in the elderly, and brain immaturity affects mechanisms of ischemic injury and recovery. The susceptibility to injury of the brain was assumed to be lower in the perinatal period as compared with childhood. This concept was recently challenged by clinical studies showing marked motor disabilities after stroke in neonates, with the severity of motor and cortical sensory deficits similar in both perinatal and childhood ischemic stroke. Our understanding of the triggers and the pathophysiological mechanisms of perinatal stroke has greatly improved in recent years, but many factors remain incompletely understood.

METHODS

In this review, we focus on the pathophysiology of perinatal stroke and on therapeutic strategies that can protect the immature brain from the consequences of stroke by targeting inflammation and brain microenvironment.

RESULTS

Studies in neonatal rodent models of cerebral ischemia have suggested a potential role for soluble inflammatory molecules as important modulators of injury and recovery. A great effort is underway to investigate neuroprotective molecules based on our increasing understanding of the pathophysiology.

CONCLUSION

In this review, we provide a comprehensive summary of new insights concerning pathophysiology of focal and global perinatal brain injury and their implications for new therapeutic approaches.

The nuclear receptor peroxisome proliferator-activated receptor-γ promotes oligodendrocyte differentiation through mechanisms involving mitochondria and oscillatory Ca2+ waves

Peroxisome proliferator-activated receptor-γ (PPAR-γ) is one of the most studied nuclear receptor since its identification as a target to treat metabolic and neurological diseases. In addition to exerting anti-inflammatory and neuroprotective effects, PPAR-γ agonists, such as the insulin-sensitizing drug pioglitazone, promote the differentiation of oligodendrocytes (OLs), the myelin-forming cells of the central nervous system (CNS). In addition, PPAR-γ agonists increase OL mitochondrial respiratory chain activity and OL's ability to respond to environmental signals with oscillatory Ca2+ waves. Both OL maturation and oscillatory Ca2+ waves are prevented by the mitochondrial inhibitor rotenone and restored by PPAR-γ agonists, suggesting that PPAR-γ promotes myelination through mechanisms involving mitochondria.

Stem cell therapy and curcumin synergistically enhance recovery from spinal cord injury

Acute traumatic spinal cord injury (SCI) is marked by the enhanced production of local cytokines and pro-inflammatory substances that induce gliosis and prevent reinnervation. The transplantation of stem cells is a promising treatment strategy for SCI. In order to facilitate functional recovery, we employed stem cell therapy alone or in combination with curcumin, a naturally-occurring anti-inflammatory component of turmeric (Curcuma longa), which potently inhibits NF-κB. Spinal cord contusion following laminectomy (T9–10) was performed using a weight drop apparatus (10 g over a 12.5 or 25 mm distance, representing moderate or severe SCI, respectively) in Sprague-Dawley rats. Neural stem cells (NSC) were isolated from subventricular zone (SVZ) and transplanted at the site of injury with or without curcumin treatment. Functional recovery was assessed by BBB score and body weight gain measured up to 6 weeks following SCI. At the conclusion of the study, the mass of soleus muscle was correlated with BBB score and body weight. Stem cell therapy improved recovery from moderate SCI, however, it had a limited effect on recovery after severe SCI. Curcumin stimulated NSC proliferation in vitro, and in combination with stem cell therapy, induced profound recovery from severe SCI as evidenced by improved functional locomotor recovery, increased body weight, and soleus muscle mass. These findings demonstrate that curcumin in conjunction with stem cell therapy synergistically improves recovery from severe SCI. Furthermore, our results indicate that the effect of curcumin extends beyond its known anti-inflammatory properties to the regulation of stem cell proliferation.

Muscarinic receptor subtypes as potential targets to modulate oligodendrocyte progenitor survival, proliferation, and differentiation

Acetylcholine (ACh) is a major neurotransmitter but also an important signaling molecule in neuron-glia interactions. Expression of ACh receptors has been reported in several glial cell populations, including oligodendrocytes (OLs). Nonetheless, the characterization of muscarinic receptors in these cells, as well as the description of the cholinergic effects at different stages of OL development, is still incomplete. In this study, we characterized the pattern of expression of muscarinic receptor subtypes in primary cultures of rat oligodendrocyte progenitor cells (OPC) and mature OLs, at both mRNA and protein levels. We found that muscarinic receptor expression is developmentally regulated. M1, M3, and M4 receptors were the main subtypes expressed in OPC, whereas all receptor subtypes were expressed at low levels in mature OLs. Exposure of OPC to muscarine enhanced cell proliferation, an effect mainly due to M1, M3, and M4 receptor subtypes as demonstrated by pharmacological competition with selective antagonists. Conversely, M2 receptor activation impaired OPC survival. In line with the mitogenic activity, muscarinic receptor activation increased the expression of platelet derived growth factor receptor α. Muscarine stimulation increased CX32 and myelin basic protein expression, left unaffected that of myelin proteolipid protein (PLP), and decreased member of the family of epidermal growth factor receptor (EGFR) ErbB3/ErbB4 receptor expression indicating a predominant role of muscarinic receptors in OPC. These findings suggest that ACh may contribute to the maintenance of an immature proliferating progenitor pool and impair the progression toward mature stage. This hypothesis is further supported by increased expression of Notch-1 in OL on muscarinic activation.

Improvement of hypoxia-ischemia-induced white matter injury in immature rat brain by ethyl pyruvate

Ethyl pyruvate (EP) has been reported to be neuroprotective in several models of brain injury, yet its influence on periventricular leukomalacia still remains elusive. Here we investigated whether repeated administration of EP could protect against white matter injury after hypoxia-ischemia (HI) (right common carotid artery ligation and 6 % O2 for 60 min) in post-natal 3 day rat pups. EP was injected (50 mg/kg, intraperitoneally) 10 min, 1 and 24 h after HI insult. Treatment with EP significantly reduced HI-induced ventricular enlargement, loss of developing oligodendrocytes, and hypomyelination. We further demonstrated a marked inhibitory effect of EP on inflammatory responses, as indicated by the decreased number of activated microglia and astrocytes and the reduced release of proinflammatory cytokines. Moreover, EP down-regulated the expression of cleaved caspase-3 and Bax, and up-regulated Bcl-2 expression after HI exposure. In conclusion, our results demonstrated that EP was able to provide potent protection on white matter injury through blocking the cerebral inflammatory responses and modulating the apoptotic death program of oligodendrocytes, indicating a potential neuroprotective agent in neonatal brain injury.

Molecular mechanisms of oligodendrocyte injury in multiple sclerosis and experimental autoimmune encephalomyelitis

New evidence has emerged over the last decade indicating that oligodendrocyte injury in multiple sclerosis (MS) is not a single unified phenomenon but rather a spectrum of processes ranging from massive immune destruction to a subtle cell death in the absence of significant inflammation. Experimentally, protection of oligodendrocytes against inflammatory injury results in protection against experimental autoimmune encephalitis, the animal model of multiple sclerosis. In this review, we will discuss the molecular mechanisms regulating oligodendrocyte injury and inflammatory demyelination. We draw attention to the injurious role of IFN-γ signaling in oligodendrocytes and the pro-inflammatory effect of their death. In conclusion, studying the molecular mechanisms of oligodendrocyte injury is likely to provide new perspective on the pathogenesis of MS and a rationale for cell protective therapies.

Regulation of Glial Cell Functions by PPAR-gamma Natural and Synthetic Agonists

In the recent years, the peroxisome proliferator-activated receptor-γ (PPAR-γ), a well known target for type II diabetes treatment, has received an increasing attention for its therapeutic potential in inflammatory and degenerative brain disorders. PPAR-γ agonists, which include naturally occurring compounds (such as long chain fatty acids and the cyclopentenone prostaglandin 15-deoxy Δ^12,14 prostaglandin J₂), and synthetic agonists (among which the thiazolidinediones and few nonsteroidal anti-inflammatory drugs) have shown anti-inflammatory and protective effects in several experimental models of Alzheimer's and Parkinson's diseases, amyotrophic lateral sclerosis, multiple sclerosis and stroke, as well as in few clinical studies. The pleiotropic effects of PPAR-γ agonists are likely to be mediated by several mechanisms involving anti-inflammatory activities on peripheral immune cells (macrophages and lymphocytes), as well as direct effects on neural cells including cerebral vascular endothelial cells, neurons, and glia. In the present article, we will review the recent findings supporting a major role for PPAR-γ agonists in controlling neuroinflammation and neurodegeneration through their activities on glial cells, with a particular emphasis on microglial cells as major macrophage population of the brain parenchyma and main actors in brain inflammation.

Reduction of spinal cord ischemia/reperfusion injury with simvastatin in rats

BACKGROUND

Surgery of the thoracic or thoracoabdominal aorta may cause spinal cord ischemia and subsequent paraplegia. However, conventional strategies for preventing paraplegia due to spinal cord ischemia provide insufficient protection and cause additional side effects. We hypothesized that simvastatin, a drug recently shown to be neuroprotective against brain ischemia/reperfusion, would be neuroprotective in a rat spinal cord ischemia/reperfusion model.

METHODS

Rats were randomly assigned to simvastatin, vehicle, or sham-surgery (sham) groups (n = 6 per group). Simvastatin (10 mg/kg) or vehicle was administered subcutaneously once daily for 7 days before aortic balloon occlusion, and once at 24 hours after reperfusion. Spinal cord ischemia was induced by balloon inflation of a 2F Fogarty catheter in the thoracic aorta, and the proximal mean arterial blood pressure was maintained at 40 mm Hg for 12 minutes. The sham group received the same operation without inflation of the balloon. Ischemic injury was assessed by hindlimb motor function using the Motor Deficit Index score at 6 to 48 hours after ischemic reperfusion, and histological assessment of the spinal cord was performed 48 hours after reperfusion.

RESULTS

The Motor Deficit Index scores at 24 and 48 hours after reperfusion were significantly improved in the simvastatin group compared with the vehicle group (P = 0.021 and P = 0.023, respectively). Furthermore, there were significantly more normal motor neurons in the simvastatin group than in the vehicle group (P = 0.037). The percentage area of white matter vacuolation was significantly smaller in the simvastatin group than in the vehicle group (P = 0.030).

CONCLUSIONS

Simvastatin treatment can attenuate hindlimb motor dysfunction and histopathological changes in spinal cord ischemia/reperfusion injury in rats.

Antioxidant defense and apoptotic effectors in ascorbic acid and β-glycerophosphate-induced osteoblastic differentiation

MC3T3-E1 cells grown in the presence of ascorbic acid and β-glycerophosphate (AA/β-GP) express alkaline phosphatase and produce an extensive collagenous extracellular matrix. Differentiated MC3T3-E1 cells are more sensitive to hydrogen peroxide-induced oxidative stress than undifferentiated cells. In this study, we compared the profile of antioxidant enzymes and molecular markers of apoptosis in undifferentiated and differentiated MC3T3-E1 cells (cell differentiation was induced by treatment with AA/β-GP). Differentiated osteoblasts showed lower expression and activity of catalase, glutathione S-transferase and glutathione peroxidase. The total superoxide dismutase activity and the expression of Cu/Zn superoxide dismutase were also lower, while the expression of Mn superoxide dismutase was higher in differentiated osteoblasts. The level of malondialdehyde, a widely used marker for oxidative stress, was lower in the AA/β-GP group compared with control cells, but this difference was not significant. Western blotting showed that treatment with AA/β-GP increased the Bax/Bcl-2 ratio used as an index of cellular vulnerability to apoptosis. In addition, the activities of caspases 3, 8 and 9 and cleaved poly (ADP) ribose polymerase were significantly higher in differentiated cells. These findings provide new insights into how changes in the activities of major antioxidant enzymes and in the signaling pathways associated with apoptosis may influence the susceptibility of bone cells to oxidative stress.

Taking pain out of NGF: a "painless" NGF mutant, linked to hereditary sensory autonomic neuropathy type V, with full neurotrophic activity

During adulthood, the neurotrophin Nerve Growth Factor (NGF) sensitizes nociceptors, thereby increasing the response to noxious stimuli. The relationship between NGF and pain is supported by genetic evidence: mutations in the NGF TrkA receptor in patients affected by an hereditary rare disease (Hereditary Sensory and Autonomic Neuropathy type IV, HSAN IV) determine a congenital form of severe pain insensitivity, with mental retardation, while a mutation in NGFB gene, leading to the aminoacid substitution R100W in mature NGF, determines a similar loss of pain perception, without overt cognitive neurological defects (HSAN V). The R100W mutation provokes a reduced processing of proNGF to mature NGF in cultured cells and a higher percentage of neurotrophin secreted is in the proNGF form. Moreover, using Surface Plasmon Resonance we showed that the R100W mutation does not affect NGF binding to TrkA, while it abolishes NGF binding to p75NTR receptors. However, it remains to be clarified whether the major impact of the mutation is on the biological function of proNGF or of mature NGF and to what extent the effects of the R100W mutation on the HSAN V clinical phenotype are developmental, or whether they reflect an impaired effectiveness of NGF to regulate and mediate nociceptive transmission in adult sensory neurons. Here we show that the R100 mutation selectively alters some of the signaling pathways activated downstream of TrkA NGF receptors. NGFR100 mutants maintain identical neurotrophic and neuroprotective properties in a variety of cell assays, while displaying a significantly reduced pain-inducing activity in vivo (n = 8–10 mice/group). We also show that proNGF has a significantly reduced nociceptive activity, with respect to NGF. Both sets of results jointly contribute to elucidating the mechanisms underlying the clinical HSAN V manifestations, and to clarifying which receptors and intracellular signaling cascades participate in the pain sensitizing action of NGF.

Neuroprotective effect of oligodendrocyte precursor cell transplantation in a long-term model of periventricular leukomalacia

Perinatal white matter injury, or periventricular leukomalacia (PVL), is the most common cause of brain injury in premature infants and is the leading cause of cerebral palsy. Despite increasing numbers of surviving extreme premature infants and associated long-term neurological morbidity, our understanding and treatment of PVL remains incomplete. Inflammation- or ischemia/hypoxia-based rodent models, although immensely valuable, are largely restricted to reproducing short-term features of up to 3 weeks after injury. Given the long-term sequelae of PVL, there is a need for subchronic models that will enable testing of putative neuroprotective therapies. Here, we report long term characterization of a neonatal inflammation-induced rat model of PVL. We show bilateral ventriculomegaly, inflammation, reactive astrogliosis, injury to pre-oligodendrocytes, and neuronal loss 8 weeks after injury. We demonstrate neuroprotective effects of oligodendrocyte precursor cell transplantation. Our findings present a subchronic model of PVL and highlight the tissue protective effects of oligodendrocyte precursor cell transplants that demonstrate the potential of cell-based therapy for PVL.

Peroxisome proliferator-activated receptor-gamma agonists promote differentiation and antioxidant defenses of oligodendrocyte progenitor cells

Several lines of evidence suggest that peroxisome proliferator-activated receptor-gamma (PPAR-gamma) agonists may control brain inflammation and, therefore, may be useful for the treatment of human CNS inflammatory conditions. The PPAR-gamma agonists delay the onset and ameliorate clinical manifestations in animal demyelinating disease models, in which the beneficial effects are thought to be mainly related to anti-inflammatory effects on peripheral and brain immune cells. Direct effects on neurons, oligodendrocytes, and other CNS resident cells cannot be excluded, however. To analyze potential direct actions of PPAR-gamma agonists on oligodendrocytes, we investigated the effects of both natural (15-deoxy Delta prostaglandin J2) and synthetic (pioglitazone) PPAR-gamma agonists in primary cultures of rat oligodendrocyte progenitor cells. The PPAR-gamma agonists promoted oligodendrocyte progenitor cell differentiation and enhanced their antioxidant defenses by increasing levels of catalase and copper-zinc superoxide dismutase while maintaining the overall homeostasis of the glutathione system. Protective effects were abolished in the presence of the specific PPAR-gamma antagonist GW9662, indicating that they are specifically dependent on PPAR-gamma. These observations suggest that in addition to their known anti-inflammatory effects, PPAR-gamma agonists may protect oligodendrocyte progenitor cells by preserving their integrity and favoring their differentiation into myelin-forming cells. Thus, PPAR-gamma may promote recovery from demyelination by direct effects on oligodendrocytes.

Inhibition of gelatinase activity reduces neural injury in an ex vivo model of hypoxia-ischemia

Perinatal hypoxia-ischemia (H-I) often manifests as cognitive and/or motor disturbances that appear early in development. Growing evidence indicates that neuroinflammation may exacerbate H-I injury. Resident microglia release proinflammatory cytokines and proteases in response to ischemia. Matrix metalloproteinases (MMPs), in particular, activate cytokines and degrade basement membrane proteins. These actions ultimately permit entry of peripheral leukocytes into the CNS neuropil, enhancing neuroinflammation and cell death. Currently, the relative contributions of resident and peripheral immune cells to ischemic brain injury are unclear. The present study employed an ex vivo model of H-I through oxygen glucose deprivation (OGD) to identify the cellular localization of MMP-9 in organotypic hippocampal slices from rat, and to determine whether inhibiting gelatin-degrading MMPs affords neuroprotection in the absence of peripheral immune cells. Immunohistochemistry revealed ubiquitous neuronal MMP-9 expression in both normoxic and hypoxic slices. Increased MMP-9 expression was detected in CD11b-positive microglia after 48 h exposure to OGD relative to normoxic controls. Consistent with these data, in situ zymography showed increased gelatinolytic activity after OGD. Gelatin-cleaved fluorescence localized to astrocytic processes and somata of various cellular morphologies. Treatment with either the MMP inhibitor AG3340 (prinomastat) or minocycline dampened OGD-induced gelatinolytic activity and neural injury, as measured by Fluoro-Jade staining, relative to vehicle controls. These results show that resident microglia, in the absence of peripheral immune cells, were sufficient to enhance neural injury after OGD in the organotypic hippocampal slice. Additionally, these effects were associated with upregulation or secretion of MMP-9, and were blocked after treatment with either the gelatinase-selective compound AG3340 or the anti-inflammatory compound minocycline. These data, coupled with the effectiveness of these compounds previously shown in vivo, support the selective targeting of gelatin-degrading MMPs and activated microglia as potential therapeutic approaches to combat neonatal H-I injury.

Delayed administration of a matrix metalloproteinase inhibitor limits progressive brain injury after hypoxia-ischemia in the neonatal rat

Background

Hypoxia-ischemia (H-I) can produce widespread neurodegeneration and deep cerebral white matter injury in the neonate. Resident microglia and invading leukocytes promote lesion progression by releasing reactive oxygen species, proteases and other pro-inflammatory mediators. After injury, expression of the gelatin-degrading matrix metalloproteinases (MMPs), MMP-2 and MMP-9, are thought to result in the proteolysis of extracellular matrix (ECM), activation of cytokines/chemokines, and the loss of vascular integrity. Thus, therapies targeting ECM degradation and progressive neuroinflammation may be beneficial in reducing H-I – induced neuropathy. Minocycline has MMP-inhibitory properties and is both anti-inflammatory and neuroprotective. AG3340 (prinomastat) is an MMP inhibitor with high selectivity for the gelatinases. The purpose of this study was to determine whether these compounds could limit H-I – induced injury when administered at a delayed time point.

Methods

Sprague-Dawley rats were exposed to H-I at postnatal day 7 (P7), consisting of unilateral carotid artery ligation followed by 90 min exposure to 8% O₂. Minocycline, AG3340, or vehicle were administered once daily for 6 days, beginning 24 hours after insult. Animals were sacrificed at P14 for neurohistological assessments. Immunohistochemistry was performed to determine the degree of reactive astrogliosis and immune cell activation/recruitment. Neural injury was detected using the Fluoro-Jade stain, a marker that identifies degenerating cells.

Results

CD11b and glial fibrillary acidic protein (GFAP) immunopositive cells increased in ipsilateral cortex after treatment with vehicle alone, demonstrating microglia/macrophage recruitment and reactive astrogliosis, respectively. Fluoro-Jade staining was markedly increased throughout the fronto-parietal cortex, striatum and hippocampus. Treatment with minocycline or AG3340 inhibited microglia/macrophage recruitment, attenuated astrogliosis and reduced Fluoro-Jade staining when compared to vehicle alone.

Conclusion

The selective gelatinase inhibitor AG3340 showed equal efficacy in reducing neural injury and dampening neuroinflammation when compared to the anti-inflammatory compound minocycline. Thus, MMP-2 and MMP-9 may be viable therapeutic targets to treat neonatal brain injury.

Developmental stage of oligodendrocytes determines their response to activated microglia in vitro

Background

Oligodendrocyte progenitor cells (OPCs) and mature oligodendrocytes are both lost in central nervous system injury and disease. Activated microglia may play a role in OPC and oligodendrocyte loss or replacement, but it is not clear how the responses of OPCs and oligodendrocytes to activated microglia differ.

Methods

OPCs and microglia were isolated from rat cortex. OPCs were induced to differentiate into oligodendrocytes with thyroid hormone in defined medium. For selected experiments, microglia were added to OPC or oligodendrocyte cultures. Lipopolysaccharide was used to activate microglia and microglial activation was confirmed by TNFα ELISA. Cell survival was assessed with immunocytochemistry and cell counts. OPC proliferation and oligodendrocyte apoptosis were also assessed.

Results

OPCs and oligodendrocytes displayed phenotypes representative of immature and mature oligodendrocytes, respectively. Activated microglia reduced OPC survival, but increased survival and reduced apoptosis of mature oligodendrocytes. Activated microglia also underwent cell death themselves.

Conclusion

Activated microglia may have divergent effects on OPCs and mature oligodendrocytes, reducing OPC survival and increasing mature oligodendrocyte survival. This may be of importance because activated microglia are present in several disease states where both OPCs and mature oligodendrocytes are also reacting to injury. Activated microglia may simultaneously have deleterious and helpful effects on different cells after central nervous system injury.

Oxidative stress and excitotoxicity: a therapeutic issue in multiple sclerosis?

There is increasing evidence that multiple sclerosis (MS) is not only characterized by immune mediated inflammatory reactions but also by neurodegenerative processes. In neurodegenerative diseases, neuronal and axonal loss is mediated by oxidative stress and excitotoxicity which constitute a final common toxic pathway. Importantly, peroxynitrite is the key mediator of those two intertwined pathomechanisms. In MS, peroxynitrite is consistently associated with active lesions and produces highly toxic nitrating and oxidizing radical species that alter lipid, protein, DNA and mitochondrial structures and functions. During the remitting phase, peroxynitrite participates to neuron and oligodendrocyte damage in association with inflammatory processes. During the chronic phase, peroxynitrite contributes to self-perpetuating mechanisms responsible for disease progression. Neutralization of oxidative stress and excitotoxicity, and in particular of peroxynitrite derived free radicals, might represent a therapeutic approach to provide neuroprotection in MS.

Characterization of mature rat oligodendrocytes: a proteomic approach

Oligodendrocytes are glial cells responsible for the synthesis and maintenance of myelin in the central nervous system (CNS). Oligodendrocytes are vulnerable to damage occurring in a variety of neurological diseases. Understanding oligodendrocyte biology is crucial for the dissemination of de- and remyelination mechanisms. The goal of the present study is the construction of a protein database of mature rat oligodendrocytes. Post-mitotic oligodendrocytes were isolated from mature Wistar rats and subjected to immunocytochemistry. Proteins were extracted and analyzed by means of two-dimensional gel electrophoresis and two-dimensional liquid chromatography, both coupled to mass spectrometry. The combination of the gel-based and gel-free approach resulted in confident identification of a total of 200 proteins. A minority of proteins were identified in both proteomic strategies. The identified proteins represent a variety of functional groups, including novel oligodendrocyte proteins. The results of this study emphasize the power of the applied proteomic strategy to study known or to reveal new proteins and to investigate their regulation in oligodendrocytes in different disease models.

Hypoxia-ischemia preferentially triggers glutamate depletion from oligodendroglia and axons in perinatal cerebral white matter

Ischemia is implicated in periventricular white matter injury (PWMI), a lesion associated with cerebral palsy. PWMI features selective damage to early cells of the oligodendrocyte lineage, a phenomenon associated with glutamate receptor activation. We have investigated the distribution of glutamate in rat periventricular white matter at post-natal day 7. Immuno-electron microcopy was used to identify O4(+) oligodendroglia in control rats, and a similar approach was employed to stain glutamate in these cells before and after 90 mins of hypoxia-ischemia. This relatively brief period of hypoxia-ischemia produced mild cell injury, corresponding to the early stages of PWMI. Glutamate-like reactivity was higher in oligodendrocytes than in other cell types (2.13+/-0.25 counts/microm(2)), and declined significantly during hypoxia-ischemia (0.93+/-0.15 counts/microm(2): P<0.001). Astrocytes had lower glutamate levels (0.7+/-0.07 counts/microm(2)), and showed a relatively small decline during hypoxia-ischemia. Axonal regions contained high levels of glutamate (1.84+/-0.20 counts/microm(2)), much of which was lost during hypoxia-ischemia (0.72+/-0.20 counts/microm(2): P>0.001). These findings suggest that oligodendroglia and axons are the major source of extracellular glutamate in developing white matter during hypoxia-ischemia, and that astrocytes fail to accumulate the glutamate lost from these sources. We also examined glutamate levels in the choroid plexus. Control glutamate levels were high in both choroid epithelial (1.90+/-0.20 counts/microm(2)), and ependymal cells (2.20+/-0.28 counts/microm(2)), and hypoxia-ischemia produced a large fall in ependymal glutamate (0.97+/-0.08 counts/microm(2): P>0.001). The ependymal cells were damaged by the insult and represent a further potential source of glutamate during ischemia.

Lipid Peroxidation During Human Cerebral Myelination

The critical period of human cerebral myelination is characterized by rapid production of cellular membranes. We hypothesize that this period is subject to the "physiological" generation of free radicals resulting in lipid peroxidation (LPO). In this study, oxidative markers were examined in developing human parietal white matter using 4-hydroxy-2-nonenal (HNE) protein adducts as an indicator of LPO. Immunocytochemistry showed an increase in HNE-positive glia from 40 gestational weeks to 1.5 postnatal years encompassing the peak period of myelin sheath synthesis at this site. Western blots showed a distinct pattern of HNE-modified proteins at fetal/term ages 26 to 42 gestational weeks and a second, different pattern at 45 gestational weeks to 2.5 postnatal years. Proteins modified by HNE in the latter period, corresponding to active myelination, were identified using mass spectrometry. The most prominent category of HNE modification included cytoskeletal proteins such as tubulins and neurofilaments. Other categories included cell type-specific proteins for mature oligodendrocytes and astrocytes and proteins involved in cell cycle and energy metabolism. We conclude that human brain development involves basal levels of oxidative stress and resulting LPO and that these processes target different proteins in an age-specific manner, thereby likely playing distinct roles during different periods of brain maturation.

Selective vulnerability of preterm white matter to oxidative damage defined by F2-isoprostanes

Periventricular white matter injury (PWMI) is the leading cause of cerebral palsy and chronic neurological disability in survivors of prematurity. Despite the large number of affected children, the pathogenetic mechanisms related to PWMI remain controversial. Through studies of 33 human autopsy brains, we determined that early PWMI was related to oxidative damage that particularly targeted the oligodendrocyte lineage, whereas other neuronal and glial cell types were markedly more resistant. F(2)-isoprostanes, an arachidinate metabolite/lipid peroxidation marker of oxidative damage, were significantly increased in early PWMI lesions but not in cerebral cortex. That deleterious lipid peroxidation accompanied early PWMI was supported by similar increases in F(2)-isoprostanes levels in the cerebral cortex from term infants with hypoxic-ischemic cortical injury. Detection of F(4)-neuroprostanes, a neuronal-specific oxidative damage marker, confirmed that neuroaxonal elements were resistant to injury in cerebral cortex and white matter. Significant protein nitration was not detected in PWMI lesions by 3-nitrotyrosine staining. Significant cellular degeneration was confirmed in early PWMI lesions by terminal deoxynucleotidyltransferase-mediated dUTP nick end labeling and a marked depletion of oligodendrocyte progenitors of 71 +/- 8%. Hence, the predilection of preterm infants for PWMI is related to selective lipid peroxidation-mediated injury of cerebral white matter and targeted death of oligodendrocyte progenitors.

Exposure to ethanol induces oxidative damage in the pituitary gland

Chronic exposure of pubertal male rats to ethanol results in a decline in serum testosterone and decreased or inappropriately normal serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) levels suggesting a functional defect in the pituitary. The molecular mechanisms behind this disorder are undefined. A role for ethanol-induced oxidative damage in the pathophysiology is supported by studies in liver, muscle, and heart of experimental animals, but there is limited evidence in the pituitary. We examined markers of oxidative damage to lipids and proteins in pituitaries from rats consuming ethanol for 5, 10, 20, 30, and 60 days in addition to markers of damage to nucleic acids in pituitaries after 60 days of ethanol exposure. There were increases in 8-oxo-deoxyguanosine immunoreactivity, a marker of oxidative damage to nucleic acids, and an overall increase in malondialdehyde and 4-hydroxynonenal, markers of lipid peroxidation. Protein carbonylation and protein nitrotyrosination, markers of protein oxidation, were significantly increased after 30 days and 60 days of ethanol consumption, respectively. After 60 days of ethanol exposure, TUNEL assay revealed that cell death in the ethanol-treated pituitaries was not significantly different from that in the pair-fed controls at the time of examination. We also measured serum testosterone, FSH, and LH after ethanol consumption for 5, 10, 20, 30, and 60 days. Through 5 to 60 days of ethanol exposure, testosterone levels were consistently lower whereas LH and FSH were inappropriately unchanged, suggesting pituitary malfunction. These results provide evidence for ethanol-induced oxidative damage at the pituitary level, which may contribute to pituitary dysfunction.

Cytokine toxicity to oligodendrocyte precursors is mediated by iron

Inflammatory processes play a key role in the pathogenesis of a number of common neurodegenerative disorders such as Alzheimer's disease (AD), Parkinson's disease (PD), and multiple sclerosis (MS). Abnormal iron accumulation is frequently noted in these diseases and compelling evidence exists that iron is involved in inflammatory reactions. Histochemical stains for iron repeatedly demonstrate that oligodendrocytes, under normal conditions, stain more prominently than any other cell type in the brain. Therefore, we examined the hypothesis that cytokine toxicity to oligodendrocytes is iron mediated. Oligodendrocytes in culture were exposed to interferon-gamma (IFN-gamma), interleukin-1beta (IL-1beta), and tumor necrosis factor-alpha (TNF-alpha). Toxicity was observed in a dose-dependent manner for IFN-gamma and TNF-alpha. IL-1beta was not toxic in the concentrations used in this study. The toxic concentration of IFN-gamma, and TNF-alpha was lower if the cells were iron loaded, but iron loading had no effect on the toxicity of IL-1beta. These data provide insight into the controversy regarding the toxicity of cytokines to oligodendrocytes by revealing that iron status of these cells will significantly impact the outcome of cytokine treatment. The exposure of oligodendrocytes to cytokines plus iron decreased mitochondrial membrane potential but activation of caspase 3 is limited. The antioxidant, TPPB, which targets mitochondria, protected the oligodendrocytes from the iron-mediated cytotoxicity, providing further support that mitochondrial dysfunction may underlie the iron-mediated cytokine toxicity. Therapeutic strategies involving anti-inflammatory agents have met with limited success in the treatment of demyelinating disorders. A better understanding of these agents and the contribution of cellular iron status to cytokine toxicity may help develop a more consistent intervention strategy.

Developmental lag in superoxide dismutases relative to other antioxidant enzymes in premyelinated human telencephalic white matter

Periventricular leukomalacia (PVL) involves free radical injury to developing oligodendrocytes (OLs), resulting from ischemia/reperfusion, particularly between 24 and 32 gestational weeks. Using immunocytochemistry and Western blots, we tested the hypothesis that this vulnerability to free radical toxicity results, in part, from developmental lack of superoxide dismutases (SOD)-1 and -2, catalase, and glutathione peroxidase (GPx) in the telencephalic white matter of the human fetus. During the period of greatest PVL risk and through term (> or = 37 weeks), expression of both SODs (for conversion of O2- to H2O2) significantly lagged behind that of catalase and GPx (for breakdown of H2O2), which, in contrast, superseded adult levels by 30 gestational weeks. Our data indicate that a developmental "mismatch" in the sequential antioxidant enzyme cascade likely contributes to the vulnerability to free radical toxicity of the immature cerebral white matter, which is "unprepared" for the transition from a hypoxic intrauterine to an oxygen-rich postnatal environment. All enzymes, localized to astrocytes and OLs, had higher-than-adult expression at 2 to 5 postnatal months (peak of myelin sheath synthesis), suggesting an adaptive mechanism to protect against lipid peroxidation during myelin sheath (lipid) synthesis. The previously unrecognized dissociation between the expression of the SODs and that of catalase and GPx in the fetal period has potential implications for future antioxidant therapy in PVL.

Developmental up-regulation of MnSOD in rat oligodendrocytes confers protection against oxidative injury

Periventricular leukomalacia, the predominant pathological lesion underlying cerebral palsy in premature infants, is thought to be the result of hypoxic-ischemic injury to the cerebral white matter. The main cell type injured is the developing oligodendrocyte (OL), which has been shown to be more sensitive than mature OLs to both excitotoxic and oxidative mechanisms of injury. A maturation dependence of OL vulnerability to cystine deprivation-induced glutathione depletion has been previously demonstrated in culture. We hypothesized that mitochondria could be involved in this toxicity by generating superoxide and that increased superoxide dismutase (SOD) activity in mature OLs may account for their greater resistance. Cystine deprivation toxicity was found to be associated with mitochondrial dysfunction and intracellular superoxide accumulation in developing OLs. CuZnSOD protein expression and enzyme activity was similar along the OL lineage. In contrast, MnSOD was up-regulated in mature OLs, as manifested by a 53% increase in its expression and a four-fold increase in its activity. Overexpressing MnSOD in developing OLs was associated with a protective effect on mitochondrial membrane potential and a decrease in cell death induced by mild cystine deprivation. The greater challenge presented by total cystine deprivation was resistant to MnSOD overexpression and appeared to be related to hydrogen peroxide toxicity. These data suggest a primary involvement of superoxide in glutathione depletion toxicity in developing OLs, and suggest an important role for MnSOD in the resistance observed in mature OLs.

Cytotoxicity of the E(2)-isoprostane 15-E(2t)-IsoP on oligodendrocyte progenitors

Oxidant stress plays a significant role in the pathogenesis of periventricular leukomalacia (PVL). Isoprostanes (IsoPs) are bioactive products of lipid peroxidation abundantly generated during hypoxic-ischemic injuries. Because loss of oligodendrocytes (OLs) occurs early in PVL, we hypothesized that IsoPs could induce progenitor OL death. 15-E(2t)-IsoP but not 15-F(2t)-IsoP elicited a concentration-dependent death of progenitor OLs by oncosis and not by apoptosis, but exerted minimal effects on mature OLs. 15-E(2t)-IsoP-induced cytotoxicity could not be explained by its conversion into cyclopentenones, because PGA(2) was hardly cytotoxic. On the other hand, thromboxane A(2) (TxA(2)) synthase inhibitor CGS12970 and cyclooxygenase inhibitor ibuprofen attenuated 15-E(2t)-IsoP-induced cytotoxicity. Susceptibility of progenitor OLs was independent of TxA(2) receptor (TP) expression, which was far less in progenitor than in mature OLs. However, TxA(2) synthase was detected in precursor but not in mature OLs, and TxA(2) mimetic U46619 induced hydroperoxides generation and progenitor OL death. The glutathione synthesis enhancer N-acetylcysteine prevented 15-E(2t)-IsoP-induced progenitor cell death. Depletion of glutathione in mature OLs with buthionine sulfoximine rendered them susceptible to cytotoxicity of 15-E(2t)-IsoP. These novel data implicate 15-E(2t)-IsoP as a product of oxidative stress that may contribute in the genesis of PVL.

α-Phenyl-n-tert-butyl-nitrone attenuates hypoxic–ischemic white matter injury in the neonatal rat brain

White matter of the neonatal brain is highly sensitive to hypoxic-ischemic insult. The susceptibility of premature oligodendrocytes (OLs) to free radicals (FRs) produced during hypoxia-ischemia (HI) has been proposed as one of the mechanisms involved. To test this hypothesis, and to further investigate if the FR scavenger alpha-phenyl-N-tert-butyl-nitrone (PBN) attenuates hypoxic-ischemic white matter damage (WMD), postnatal day 4 (P4) SD rats were subjected to bilateral common carotid artery ligation (BCAL), followed by 8% oxygen exposure for 20 min. Pathological changes were evaluated on P6 and P9, 2 and 5 days after the HI insult. HI caused severe WMD including rarefaction, necrosis and cavity formation in the corpus callosum, external and internal capsule areas. OL injury was evidenced by degeneration of O4 positive OLs on P6. Disrupted myelination was verified by decreased immunostaining of myelin basic protein (MBP) on P9. Axonal injury was demonstrated by increased amyloid precursor protein (APP) immunostaining on both P6 and P9. Two lipid peroxidation end products, malondialdehyde (MDA) and 4-hydroxynonenal (4-HNE), showed a one-fold elevation within 1-24 h following HI. 4-HNE immunostaining was found to specifically localize in the white matter area. Furthermore, pyknotic O4+ OLs were double-labeled with 4-HNE. These findings suggest that FRs are involved in the pathogenesis of neonatal WMD. PBN (100 mg/kg, i.p.) treatment alleviated the pathological changes of WMD following HI. It improved the survival of O4 positive OLs, attenuated hypomyelination and reduced axonal damage. PBN treatment also decreased the brain concentration of MDA/4-HNE and positive 4-HNE staining in the white matter area. These findings indicate that in the current WMD model, PBN protects both OLs and axons, the two main components in the white matter, from neonatal HI insult. FR scavenging appears to be the primary mechanism underlying its neuroprotective effect.

Selective vulnerability in the developing central nervous system

Selective patterns of cerebral injury are observed after a variety of insults at different ages during development. Distinct populations of cells demonstrate selective vulnerability during these specific developmental stages, which may account for the observed patterns of injury. We review the evidence that injury to preoligodendrocytes and subplate neurons contributes to periventricular white matter injury in preterm infants, whereas thalamic neuronal cell vulnerability and neuronal nitric oxide synthase-expressing striatal interneurons resistance result in deep gray nuclei damage in the term infant. The unique roles of particular mechanisms including oxidative stress, glutamatergic neurotransmission, and programmed cell death are discussed in the context of this selective vulnerability.