Elizabeth Gray

Elevated activity and microglial expression of myeloperoxidase in demyelinated cerebral cortex in multiple sclerosis.

Recent studies have revealed extensive cortical demyelination in patients with progressive multiple sclerosis (MS). Demyelination in gray matter lesions is associated with activation of microglia. Macrophages and microglia are known to express myeloperoxidase (MPO) and generate reactive oxygen species during myelin phagocytosis in the white matter. In the present study we examined the extent of microglial activation in the cerebral cortex and the relationship of microglial activation and MPO activity to cortical demyelination. Twenty‐one cases of neuropathologically confirmed multiple sclerosis, with 34 cortical lesions, were used to assess microglial activation. HLA‐DR immunolabeling of activated microglia was significantly higher in demyelinated MS cortex than control cortex and, within the MS cohort, was significantly greater within cortical lesions than in matched non‐demyelinated areas of cortex. In homogenates of MS cortex, cortical demyelination was associated with significantly elevated MPO activity. Immunohistochemistry revealed MPO in CD68‐positive microglia within cortical plaques, particularly toward the edge of the plaques, but not in microglia in adjacent non‐demyelinated cortex. Cortical demyelination in MS is associated with increased activity of MPO, which is expressed by a CD68‐positive subset of activated microglia, suggesting that microglial production of reactive oxygen species is likely to be involved in cortical demyelination.

The PPAR-gamma agonist pioglitazone protects cortical neurons from inflammatory mediators via improvement in peroxisomal function

BackgroundInflammation is known to play a pivotal role in mediating neuronal damage and axonal injury in a variety of neurodegenerative disorders. Among the range of inflammatory mediators, nitric oxide and hydrogen peroxide are potent neurotoxic agents. Recent evidence has suggested that oligodendrocyte peroxisomes may play an important role in protecting neurons from inflammatory damage.MethodsTo assess the influence of peroxisomal activation on nitric oxide mediated neurotoxicity, we investigated the effects of the peroxisomal proliferator activated receptor (PPAR) gamma agonist, pioglitazone in primary cortical neurons that were either exposed to a nitric oxide donor or co-cultured with activated microglia.ResultsPioglitazone protected neurons and axons against both nitric-oxide donor-induced and microglia-derived nitric oxide-induced toxicity. Moreover, cortical neurons treated with this compound showed a significant increase in the protein and gene expression of PPAR-gamma, which was associated with a concomitant increase in the enzymatic activity of catalase. In addition, the protection of neurons and axons against hydrogen peroxide-induced toxicity afforded by pioglitazone appeared to be dependent on catalase.ConclusionsCollectively, these observations provide evidence that modulation of PPAR-gamma activity and peroxisomal function by pioglitazone attenuates both NO and hydrogen peroxide-mediated neuronal and axonal damage suggesting a new therapeutic approach to protect against neurodegenerative changes associated with neuroinflammation.

Elevated myeloperoxidase activity in white matter in multiple sclerosis

Recent studies have revealed extensive axonal damage in patients with progressive multiple sclerosis (MS). Axonal damage can be caused by a plethora of factors including the release of proteolytic enzymes and cytotoxic oxidants by activated immune cells and glia within the lesion. Macrophages and microglia are known to express myeloperoxidase (MPO) and generate reactive oxygen species during myelin phagocytosis in the white matter. In the present study we have measured MPO levels in post-mortem homogenates of demyelinated and non-demyelinated regions of white matter from nine patients with MS and seven controls, and assessed MPO immunoreactivity within MS brain. In homogenates of MS white matter, demyelination was associated with significantly elevated MPO activity when compared to controls. Immunohistochemistry showed MPO to be expressed mainly by macrophages within and adjacent to plaques. Demyelination in MS is associated with increased activity of MPO, suggesting that this production of reactive oxygen species may contribute to axonal injury within plaques.

Inflammatory Cytokine Induced Regulation of Superoxide Dismutase 3 Expression by Human Mesenchymal Stem Cells

Increasing evidence suggests that bone marrow derived-mesenchymal stem cells (MSCs) have neuroprotective properties and a major mechanism of action is through their capacity to secrete a diverse range of potentially neurotrophic or anti-oxidant factors. The recent discovery that MSCs secrete superoxide dismutase 3 (SOD3) may help explain studies in which MSCs have a direct anti-oxidant activity that is conducive to neuroprotection in both in vivo and in vitro. SOD3 attenuates tissue damage and reduces inflammation and may confer neuroprotective effects against nitric oxide-mediated stress to cerebellar neurons; but, its role in relation to central nervous system inflammation and neurodegeneration has not been extensively investigated. Here we have performed a series of experiments showing that SOD3 secretion by human bone marrow-derived MSCs is regulated synergistically by the inflammatory cytokines TNF-alpha and IFN-gamma, rather than through direct exposure to reactive oxygen species. Furthermore, we have shown SOD3 secretion by MSCs is increased by activated microglial cells. We have also shown that MSCs and recombinant SOD are able to increase both neuronal and axonal survival in vitro against nitric oxide or microglial induced damage, with an increased MSC-induced neuroprotective effect evident in the presence of inflammatory cytokines TNF-alpha and IFN-gamma. We have shown MSCs are able to convey these neuroprotective effects through secretion of soluble factors alone and furthermore demonstrated that SOD3 secretion by MSCs is, at least, partially responsible for this phenomenon. SOD3 secretion by MSCs maybe of relevance to treatment strategies for inflammatory disease of the central nervous system.

Purkinje cell fusion and binucleate heterokaryon formation in multiple sclerosis cerebellum

A major conceptual consideration in both endogenous and therapeutic central nervous system repair is how damaged (or senescent) neurons, given their often enormously complex and extensive network of connections, can possibly be replaced. The recent observation of fusion of circulating bone marrow cells with, in particular, cerebellar Purkinje cells, as well as the subsequent formation of stable heterokaryons, offers a tantalizing potential solution to this difficulty. Here, we have explored Purkinje cell fusion and heterokaryon formation in the human brain and the influence of central nervous system inflammation. We analysed post-mortem cerebellum tissue from patients who had multiple sclerosis and from appropriate controls. Purkinje cells were analysed for heterokaryon formation using immunohistochemistry techniques and chromosome composition using fluorescence in situ hybridization. For the first time in humans we show a disease-related increase in Purkinje cell fusion and heterokaryon formation. We have shown that heterokaryon formation takes place in control subjects, and that the frequency of this event is considerably increased in patients with multiple sclerosis, the prototypical inflammatory brain disease, with ~0.4% of Purkinje cells being binucleate heterokaryons. No mononucleate polyploid Purkinje cell heterokaryons were found. The observation that heterokaryon formation in the cerebellum occurs as part of the central nervous system inflammatory reaction suggests a potential mechanism of neural repair. It also suggests an exciting new avenue for therapeutic intervention, as enhancement or manipulation of fusion events may have a therapeutic role in cellular protection in multiple sclerosis.

Peroxisome proliferator-activated receptor-α agonists protect cortical neurons from inflammatory mediators and improve peroxisomal function

Inflammation is known to cause significant neuronal damage and axonal injury in many neurological disorders. Among the range of inflammatory mediators, nitric oxide is a potent neurotoxic agent. Recent evidence has suggested that cellular peroxisomes may be important in protecting neurons from inflammatory damage. To assess the influence of peroxisomal activation on nitric oxide‐mediated neurotoxicity, we investigated the effects of the peroxisomal proliferator‐activated receptor (PPAR)‐α agonist fenofibrate on cortical neurons exposed to a nitric oxide donor or co‐cultured with activated microglia. Fenofibrate protected neurons and axons against both nitric oxide donor‐induced and microglia‐derived nitric oxide‐induced toxicity. Moreover, cortical neurons treated with this compound showed a significant increase in gene expression of ABCD3 (the gene encoding for peroxisomal membrane protein‐70), with a concomitant increase in protein levels of PPAR‐α and catalase, which was associated with a functional increase in the activity of this enzyme. Collectively, these observations provide evidence that modulation of PPAR‐α activity and peroxisomal function by fenofibrate attenuates nitric oxide‐mediated neuronal and axonal damage, suggesting a new therapeutic approach to protect against neurodegenerative changes associated with neuroinflammation.

Elevated Matrix Metalloproteinase-9 and Degradation of Perineuronal Nets in Cerebrocortical Multiple Sclerosis Plaques

Matrix metalloproteinases (MMPs) degrade extracellular matrix; MMP activity, particularly of MMP-9, is elevated in the white matter in multiple sclerosis (MS) patients. The cerebral cortical extracellular matrix includes perineuronal nets (PNs) that surround parvalbumin-positive neurons (PV-positive neurons) and are important for their function. We measured active and total MMP-9 levels in postmortem homogenates of demyelinated and nondemyelinated cerebral cortical regions from 9MS and 7 control cases and assessed Wisteria floribunda agglutin (WFA)-positive PNs in paraffin sections from 15 MS and 6 controls and PV-positive neurons in sections from 26 MS and 6 controls. Active MMP-9 levels were higher in demyelinated than in nondemyelinated or control cortex (p < 0.05). The area fraction positive for WFA was lower in demyelinated than nondemyelinated MS or control cortex; the latter difference was significant (p < 0.05). Most PV-positive neurons in demyelinated but not intact cortex lackeda PN, and some showed perikaryal phosphorylated neurofilament protein accumulation. Loss of WFA-labeled PNs was not associated with reduced PV-positive neurons numbers. Thus, elevated MMP-9 in cortical plaques is associated with loss of PNs; PV-positive neurons are preserved but show abnormal neurofilament accumulations. Matrix metalloproteinase-mediated degradation of PNs in cortical plaques may, therefore, contribute to neuronal dysfunction and degeneration in MS patients.

Accumulation of cortical hyperphosphorylated neurofilaments as a marker of neurodegeneration in multiple sclerosis

Background: Axonal loss and grey matter neuronal injury are pathological processes that contribute to disease progression in multiple sclerosis (MS). Axon damage has been associated with changes in the phosphorylation state of neurofilaments and the presence of axonal spheroids. Perikaryal accumulation of abnormally phosphorylated neurofilament proteins has been reported in some neurodegenerative diseases. Objectives: The objective of this article is to determine whether abnormally phosphorylated neurofilament accumulates in neuronal perikarya in demyelinated MS cortex. Methods: We used an antibody to hyperphosphorylated neurofilament-H (SMI-34) to assess the level and distribution of this antigen in paraffin sections of cerebral cortex from cases of neuropathologically confirmed MS and controls. We also examined the relationship of neurofilament phosphorylation to cortical demyelination. Results: The number of SMI-34-positive neuronal somata was significantly higher in the MS cortex than the control cortex. As a proportion of the total number of neurons present (i.e. taking account of neuronal loss), the proportion of SMI-34-positive neurons was also significantly higher in the demyelinated and non-demyelinated MS cortex than the control cortex. Conclusions: MS is associated with the widespread accumulation of hyperphosphorylated neurofilament protein in neuronal somata, with the most marked accumulation in regions of cortical demyelination. This aberrant localisation of hyperphosphorylated neurofilament protein may contribute to neuronal dysfunction and degeneration in MS patients.

Reduced axonal motor protein expression in non-lesional grey matter in multiple sclerosis

Background: Multiple sclerosis (MS) is a neurological disease characterised by central nervous system inflammation, demyelination, axonal degeneration and neuronal injury. Preventing neuronal and axon damage is of paramount importance in attempts to prevent disease progression. Intact axonal transport mechanisms are crucial to axonal integrity and evidence suggests these mechanisms are disrupted in MS. Anterograde axonal transport is mediated to a large extent through the kinesin superfamily proteins. Recently, certain kinesin superfamily proteins (KIF5A, KIF1B and KIF21B) were implicated in MS pathology. Objectives: To investigate the expression of KIF5A, KIF21B and KIF1B in MS and control post-mortem grey matter. Methods: Using both quantitative real-time polymerase chain reaction (PCR) and Immunodot-blots assays, we analysed the expression of kinesin superfamily proteins in 27 MS cases and 13 control cases not linked to neurological disease. Results: We have shown significant reductions in KIF5A, KIF21B and KIF1B messenger ribonucleic acid (mRNA) expression and also KIF5A protein expression in MS grey matter, as compared to control grey matter. Conclusion: We have shown significant reductions in mRNA and protein levels of axonal motor proteins in the grey matter of MS cases, which may have important implications for the pathogenesis of neuronal/axonal injury in the disease.

Changes in Expression of the Antioxidant Enzyme SOD3 Occur Upon Differentiation of Human Bone Marrow-Derived Mesenchymal Stem Cells In Vitro

The discovery that mesenchymal stem cells (MSCs) secrete SOD3 may help explain studies in which MSCs have direct antioxidant activities both in vivo and in vitro. SOD3 is an antioxidant enzyme that dismutes toxic free radicals produced during inflammatory processes. Therefore, MSC production and secretion of active and therapeutically significant levels of SOD3 would further support the use of MSCs as a cellular based antioxidant therapy. The aim of this study was therefore to investigate in vitro if MSC differentiation down the adipogenic, chondrogenic, and osteogenic lineages influences the expression of the antioxidant molecule SOD3. Human bone marrow MSCs and their differentiated progeny were cultured under standard conditions and both the SOD3 gene and protein expression examined. Following adipogenesis, cultures demonstrated that both SOD3 protein and gene expression are significantly increased, and conversely, following chondrogenesis SOD3 protein and gene expression is significantly decreased. Following osteogenesis there were no significant changes in SOD3 protein or gene expression. This in vitro study describes the initial characterization of SOD3 expression and secretion by differentiated MSCs. This should help guide further in vivo work establishing the therapeutic and antioxidative potential of MSC and their differentiated progeny.