Chandra Inglis

Neurodegeneration in a Transgenic Mouse Model of Multiple System Atrophy Is Associated with Altered Expression of Oligodendroglial-Derived Neurotrophic Factors

Multiple system atrophy (MSA) is a neurodegenerative disorder characterized by striatonigral degeneration and olivo-pontocerebellar atrophy. Neuronal degeneration is accompanied by primarily oligodendrocytic accumulation of α-synuclein (αsyn) as opposed to the neuronal inclusions more commonly found in other α-synucleinopathies such as Parkinsons disease. It is unclear how αsyn accumulation in oligodendrocytes may lead to the extensive neurodegeneration observed in MSA; we hypothesize that the altered expression of oligodendrocyte-derived neurotrophic factors by αsyn may be involved. In this context, the expression of a number neurotrophic factors reportedly expressed by oligodendrocytes [glial-derived neurotrophic factor (GDNF), brain-derived neurotrophic factor (BDNF), and insulin-like growth factor 1 (IGF-1), as well as basic fibroblast growth factor 2 (bFGF2), reportedly astrocyte derived] were examined in transgenic mouse models expressing human αsyn (hαsyn) under the control of either neuronal (PDGFβ or mThy1) or oligodendrocytic (MBP) promoters. Although protein levels of BDNF and IGF-1 were altered in all the αsyn transgenic mice regardless of promoter type, a specific decrease in GDNF protein expression was observed in the MBP-hαsyn transgenic mice. Intracerebroventricular infusion of GDNF improved behavioral deficits and ameliorated neurodegenerative pathology in the MBP-hαsyn transgenic mice. Consistent with the studies in the MBP-hαsyn transgenic mice, analysis of GDNF expression levels in human MSA samples demonstrated a decrease in the white frontal cortex and to a lesser degree in the cerebellum compared with controls. These results suggest a mechanism in which αsyn expression in oligodendrocytes impacts on the trophic support provided by these cells for neurons, perhaps contributing to neurodegeneration.

Fluoxetine ameliorates behavioral and neuropathological deficits in a transgenic model mouse of α-synucleinopathy

The term α-synucleinopathies refers to a group of age-related neurological disorders including Parkinsons disease (PD), Dementia with Lewy Bodies (DLB) and Multiple System Atrophy (MSA) that display an abnormal accumulation of alpha-synuclein (α-syn). In contrast to the neuronal α-syn accumulation observed in PD and DLB, MSA is characterized by a widespread oligodendrocytic α-syn accumulation. Transgenic mice expressing human α-syn under the oligodendrocyte-specific myelin basic protein promoter (MBP1-hαsyn tg mice) model many of the behavioral and neuropathological alterations observed in MSA. Fluoxetine, a selective serotonin reuptake inhibitor, has been shown to be protective in toxin-induced models of PD, however its effects in an in vivo transgenic model of α-synucleinopathy remain unclear. In this context, this study examined the effect of fluoxetine in the MBP1-hαsyn tg mice, a model of MSA. Fluoxetine administration ameliorated motor deficits in the MBP1-hαsyn tg mice, with a concomitant decrease in neurodegenerative pathology in the basal ganglia, neocortex and hippocampus. Fluoxetine administration also increased levels of the neurotrophic factors, GDNF (glial-derived neurotrophic factor) and BDNF (brain-derived neurotrophic factor) in the MBP1-hαsyn tg mice compared to vehicle-treated tg mice. This fluoxetine-induced increase in GDNF and BDNF protein levels was accompanied by activation of the ERK signaling pathway. The effects of fluoxetine administration on myelin and serotonin markers were also examined. Collectively these results indicate that fluoxetine may represent a novel therapeutic intervention for MSA and other neurodegenerative disorders.

Mitochondrial Inhibitor 3-Nitroproprionic Acid Enhances Oxidative Modification of Alpha-synuclein in a Transgenic Mouse Model of Multiple System Atrophy

Multiple system atrophy (MSA) is a progressive neurodegenerative disease characterized by autonomic failure, parkinsonism, cerebellar ataxia, and oligodendrocytic accumulation of alpha‐synuclein (αsyn). Oxidative stress has been linked to neuronal death in MSA and the mitochondrial toxin 3‐nitropropionic acid (3NP) is known to enhance the motor deficits and neurodegeneration in transgenic mice models of MSA. However, the effect of 3NP administration on αsyn itself has not been studied. In this context, we examined the neuropathological effects of 3NP administration in αsyn transgenic mice expressing human αsyn (hαsyn) under the control of the myelin basic protein (MBP) promoter and the effect of this administration on posttranslational modifications of αsyn, on levels of total αsyn, and on its solubility. We demonstrate that 3NP administration altered levels of nitrated and oxidized αsyn in the MBP‐hαsyn tg while not affecting global levels of phosphorylated or total αsyn. 3NP administration also exaggerated neurological deficits in the MBP‐hαsyn tg mice, resulting in widespread neuronal degeneration and behavioral impairment.

Widespread microRNA dysregulation in multiple system atrophy – disease‐related alteration in miR‐96

MicroRNA (miRNA) are short sequences of RNA that function as post‐transcriptional regulators by binding to target mRNA transcripts resulting in translational repression. A number of recent studies have identified miRNA as being involved in neurodegenerative disorders including Alzheimers disease, Parkinsons disease and Huntingtons disease. However, the role of miRNA in multiple system atrophy (MSA), a progressive neurodegenerative disorder characterized by oligodendroglial accumulation of alpha‐synuclein remains unexamined. In this context, this study examined miRNA profiles in MSA cases compared with controls and in transgenic (tg) models of MSA compared with non‐tg mice. The results demonstrate a widespread dysregulation of miRNA in MSA cases, which is recapitulated in the murine models. The study employed a cross‐disease, cross‐species approach to identify miRNA that were either specifically dysregulated in MSA or were commonly dysregulated in neurodegenerative conditions such as Alzheimers disease, dementia with Lewy bodies, progressive supranuclear palsy and corticobasal degeneration or the tg mouse model equivalents of these disorders. Using this approach we identified a number of miRNA that were commonly dysregulated between disorders and those that were disease‐specific. Moreover, we identified miR‐96 as being up‐regulated in MSA. Consistent with the up‐regulation of miR‐96, mRNA and protein levels of members of the solute carrier protein family SLC1A1 and SLC6A6, miR‐96 target genes, were down‐regulated in MSA cases and a tg model of MSA. These results suggest that miR‐96 dysregulation may play a role in MSA and its target genes may be involved in the pathogenesis of MSA.

Cerebrolysin modulates pronerve growth factor/nerve growth factor ratio and ameliorates the cholinergic deficit in a transgenic model of Alzheimer's disease

Alzheimers disease (AD) is characterized by degeneration of neocortex, limbic system, and basal forebrain, accompanied by accumulation of amyloid‐β and tangle formation. Cerebrolysin (CBL), a peptide mixture with neurotrophic‐like effects, is reported to improve cognition and activities of daily living in patients with AD. Likewise, CBL reduces synaptic and behavioral deficits in transgenic (tg) mice overexpressing the human amyloid precursor protein (hAPP). The neuroprotective effects of CBL may involve multiple mechanisms, including signaling regulation, control of APP metabolism, and expression of neurotrophic factors. We investigate the effects of CBL in the hAPP tg model of AD on levels of neurotrophic factors, including pro‐nerve growth factor (NGF), NGF, brain‐derived neurotrophic factor (BDNF), neurotropin (NT)‐3, NT4, and ciliary neurotrophic factor (CNTF). Immunoblot analysis demonstrated that levels of pro‐NGF were increased in saline‐treated hAPP tg mice. In contrast, CBL‐treated hAPP tg mice showed levels of pro‐NGF comparable to control and increased levels of mature NGF. Consistently with these results, immunohistochemical analysis demonstrated increased NGF immunoreactivity in the hippocampus of CBL‐treated hAPP tg mice. Protein levels of other neurotrophic factors, including BDNF, NT3, NT4, and CNTF, were unchanged. mRNA levels of NGF and other neurotrophins were also unchanged. Analysis of neurotrophin receptors showed preservation of the levels of TrKA and p75NTR immunoreactivity per cell in the nucleus basalis. Cholinergic cells in the nucleus basalis were reduced in the saline‐treated hAPP tg mice, and treatment with CBL reduced these cholinergic deficits. These results suggest that the neurotrophic effects of CBL might involve modulation of the pro‐NGF/NGF balance and a concomitant protection of cholinergic neurons.

Neuronal to oligodendroglial α-synuclein redistribution in a double transgenic model of multiple system atrophy.

Multiple system atrophy is a sporadic, progressive, neurodegenerative disease characterized by an oligodendroglial accumulation of alpha-synuclein (&agr;-syn). The mechanisms underlying the oligodendroglial accumulation of &agr;-syn in the brains of patients with multiple system atrophy have attracted a great deal of interest, given the primarily neuronal role reported for this protein. We examined the interactions between neuronal and oligodendroglial &agr;-syn in the progeny of crosses between parental transgenic (tg) mouse lines that express &agr;-syn either under the oligodendroglial-specific myelin-basic protein promoter (MBP1-h&agr;-syn tg) or under the neuronal platelet-derived growth factor promoter (PDGF-h&agr;-syn tg). Our results demonstrate that progeny from the cross [h&agr;-syn double (dbl) tg mice] displayed a robust redistribution of &agr;-syn accumulation, with a relocalization from a neuronal or a mixed neuronal/oligodendroglial &agr;-syn expression to a more oligodendroglial pattern in both the neocortex and the basal ganglia that closely resembled the parental MBP-h&agr;-syn tg line. The h&agr;-syn dbl tg mice also displayed motor deficits, concomitant with reduced levels of tyrosine hydroxylase and augmented neuropathological alterations in the basal ganglia. These results suggest that the central nervous system milieu in the h&agr;-syn dbl tg mice favors an oligodendroglial accumulation of &agr;-syn. This model represents an important tool to examine the interactions between neuronal and oligodendrocytic &agr;-syn in diseases such as multiple system atrophy.

Beneficial effects of a neurotrophic peptidergic mixture persist for a prolonged period following treatment interruption in a transgenic model of Alzheimer's disease.

Neurodegenerative disorders such as Alzheimers disease (AD) are characterized by the loss of neurotrophic factors, and experimental therapeutical approaches to AD have investigated the efficacy of replacing or augmenting neurotrophic factor activity. Cerebrolysin, a peptide mixture with neurotrophic‐like effects, has been shown to improve cognition in patients with AD and to reduce synaptic and behavioral deficits in transgenic (tg) mice overexpressing the amyloid precursor protein (APP). However, it is unclear how long‐lasting the beneficial effects of Cerebrolysin are and whether or not behavioral and neuropathological alterations will reappear following treatment interruption. The objective of the present study was to investigate the consequences of interrupting Cerebrolysin treatment (washout effect) 3 and 6 months after the completion of a 3‐month treatment period in APP tg mice. We demonstrate that, in APP tg mice, Cerebrolysin‐induced amelioration of memory deficits in the water maze and reduction of neurodegenerative pathology persist for 3 months after treatment interruption; however, these effects dissipate 6 months following treatment termination. Immunohistochemical analysis demonstrated that the decrease in neocortical and hippocampal amyloid plaque load observed in Cerebrolysin‐treated APP tg mice immediately after treatment was no longer apparent at 3 months after treatment interruption, indicating that the beneficial effects of Cerebrolysin at this time point were independent of its effect on amyloid‐β deposition. In conclusion, the results demonstrate that the effects of Cerebrolysin persist for a significant period of time following treatment termination and suggest that this prolonged effect may involve the neurotrophic factor‐like activity of Cerebrolysin.

Alpha-synuclein deficient mice are resistant to toxin-induced multiple system atrophy

Multiple systems atrophy (MSA) is a neurodegenerative disorder characterized by oligodendrocytic accumulations of alpha-synuclein (αsyn). Oxidative stress is a key mechanism proposed to underlie MSA pathology. To address the role of αsyn modifications, over and above general oxidative modifications, this study examined the effects of 3-nitropropionic acid (3NP) administration, a technique used to model MSA, in knock-out mice lacking αsyn (αsynKO). Although susceptible to 3NP-induced oxidative stress, αsynKO mice display reduced neuronal loss and dendritic pathology. The αsynKO mice are resistant to 3NP-induced motor deficits and display attenuated loss of tyrosine hydroxylase and dopamine transporter striatal immunoreactivity. The results suggest that deficits in MSA are not due to general oxidative protein modification but in addition may be related to specific αsyn modifications.

Neurotrophic effects of Cerebrolysin in the Mecp2 308/Y transgenic model of Rett Syndrome

Rett syndrome is a childhood neurodevelopmental disorder caused by mutations in the gene encoding for methyl-CpG-binding protein (MeCP2). Neuropathological studies in patients with Rett syndrome and in MeCP2 mutant models have shown reduced dendritic arborization and abnormal neuronal packing. We have previously shown that Cerebrolysin (CBL), a neurotrophic peptide mixture, ameliorates the synaptic and dendritic pathology in models of aging and neurodegeneration. This study aimed to determine whether CBL was capable of reducing behavioral and neuronal alterations in Mecp2308/Y mutant mice. Two sets of experiments were performed, the first with 4-month-old male Mecp2308/Y mutant mice treated with CBL or vehicle for 3 months (Group A) and the second with 1-month-old mice treated for 6 months (Group B). Behavioral analysis showed improved motor performance with CBL in Group A and a trend toward improvement in Group B. Consistent with behavioral findings, neuropathological analysis of the basal ganglia showed amelioration of dendritic simplification in CBL-treated Mecp2308/Y mutant mice. CBL treatment also ameliorated dendritic pathology and neuronal loss in the hippocampus and neocortex in Mecp2308/Y mutant mice. In conclusion, this study demonstrates that CBL promotes recovery of dendritic and neuronal damage and behavioral improvements in young adult Mecp2308/Y mutant mice and suggests that CBL may have neurotrophic effects in this model. These findings support the possibility that CBL may have beneficial effects in the management of Rett syndrome.

Prion infection promotes extensive accumulation of α-synuclein in aged human α-synuclein transgenic mice

In neurodegenerative disorders of the aging population, misfolded proteins, such as PrPSc, α-synuclein, amyloid β protein and tau, can interact resulting in enhanced aggregation, cross seeding and accelerated disease progression. Previous reports have shown that in Creutzfeldt-Jakob disease and scrapie, α-synuclein accumulates near PrPSc deposits. However, it is unclear if pre-existing human α-synuclein aggregates modified prion disease pathogenesis, or if PrPSc exacerbates the α-synuclein pathology. Here, we inoculated infectious prions into aged α-synuclein transgenic (tg) and non-transgenic littermate control mice by the intracerebral route. Remarkably, inoculation of RML and mNS prions into α-synuclein tg mice resulted in more extensive and abundant intraneuronal and synaptic α-synuclein accumulation. In addition, infectious prions led to the formation of perineuronal α-synuclein deposits with a neuritic plaque-like appearance. Prion pathology was unmodified by the presence of α-synuclein. However, with the mNS prion strain there was a modest but significant acceleration in the time to terminal prion disease in mice having α-synuclein aggregates as compared with non-tg mice. Taken together, these studies support the notion that PrPSc directly or indirectly promotes α-synuclein pathology.