Increased vulnerability of dopaminergic neurons in MPTP-lesioned interleukin-6 deficient mice

To test the hypothesis that neuroinflammation contributes to dopaminergic neuron death in the MPTP-lesioned mouse, we compared nigrostriatal degeneration in interleukin (IL)-6 (+/+) with IL-6 (-/-) mice. In the absence of IL-6, a single injection of MPTP (30 mg/kg) resulted in significantly greater striatal dopamine depletion than that measured in IL-6 (+/+) mice. The observed dopamine depletion was MPTP dose dependent. This loss of striatal dopamine and a significantly greater loss of TH+ cells in the substantia nigra pars compacta in IL-6 (-/-) mice as compared with control IL-6 (+/+) mice, suggest that IL-6 is neuroprotective in the MPTP-lesioned nigrostriatal system. Co-localization experiments identified striatal astrocytes as the source of IL-6 in IL-6 (+/+) mice at 1 and 7 days postinjection of MPTP. The increased sensitivity of dopaminergic neurons to neurotoxicant in the absence of IL-6, is compatible with a neuroprotective activity of IL-6 in the injured nigrostriatal system.     

Prolonged alpha-tocopherol deficiency decreases oxidative stress and unmasks alpha-tocopherol-dependent regulation of mitochondrial function in the brain

Vitamin E is the major lipid-soluble chain-breaking antioxidant in mammals and plays an important role in normal development and physiology. Deficiency (whether dietary or genetic) results in primarily nervous system pathology, including cerebellar neurodegeneration and progressive ataxia (abnormal gait). However, despite the widely acknowledged antioxidant properties of vitamin E, only a few studies have directly correlated levels of reactive oxygen species with vitamin E availability in animal models. We explored the relationship between vitamin E and reactive oxygen species in two mouse models of vitamin E deficiency: dietary deficiency and a genetic model (tocopherol transfer protein, Ttp-/- mice). Both groups of mice developed nearly complete depletion of alpha-tocopherol (the major tocopherol in vitamin E) in most organs, but not in the brain, which was relatively resistant to loss of alpha-tocopherol. F4-neuroprostanes, an index of lipid peroxidation, were unexpectedly lower in brains of deficient mice compared with controls. In vivo oxidation of dihydroethidium by superoxide radical was also significantly lower in brains of deficient animals. Superoxide production by brain mitochondria isolated from vitamin E-deficient and Ttp-/- mice, measured by electron paramagnetic resonance spectroscopy, demonstrated a biphasic dependence on exogenously added alpha-tocopherol. At low concentrations, alpha-tocopherol enhanced superoxide flux from mitochondria, a response that was reversed at higher concentrations. Here we propose a mechanism, supported by molecular modeling, to explain decreased superoxide production during alpha-tocopherol deficiency and speculate that this could be a beneficial response under conditions of alpha-tocopherol deficiency.     

PET imaging a MPTP-induced mouse model of Parkinson's disease using the fluoropropyl-dihydrotetrabenazine analog [18F]-DTBZ (AV-133)

Parkinson's disease (PD) is characterized by the loss of dopamine-producing neurons in the nigrostriatal system. Numerous researchers in the past have attempted to track the progression of dopaminergic depletion in PD. We applied a quantitative non-invasive PET imaging technique to follow this degeneration process in an MPTP-induced mouse model of PD. The VMAT2 ligand (18)F-DTBZ (AV-133) was used as a radioactive tracer in our imaging experiments to monitor the changes of the dopaminergic system. Intraperitoneal administrations of MPTP (a neurotoxin) were delivered to mice at regular intervals to induce lesions consistent with PD. Our results indicate a significant decline in the levels of striatal dopamine and its metabolites (DOPAC and HVA) following MPTP treatment as determined by HPLC method. Images obtained by positron emission tomography revealed uptake of (18)F-DTBZ analog in the mouse striatum. However, reduction in radioligand binding was evident in the striatum of MPTP lesioned animals as compared with the control group. Immunohistochemical analysis further confirmed PET imaging results and indicated the progressive loss of dopaminergic neurons in treated animals compared with the control counterparts. In conclusion, our findings suggest that MPTP induced PD in mouse model is appropriate to follow the degeneration of dopaminergic system and that (18)F-DTBZ analog is a potentially sensitive radiotracer that can used to diagnose changes associated with PD by PET imaging modality.     

Deficiency of inducible nitric oxide synthase protects against MPTP toxicity in vivo

MPTP produces clinical, biochemical, and neuropathologic changes reminiscent of those that occur in idiopathic Parkinson's disease (PD). In the present study we show that MPTP treatment led to activation of microglia in the substantia nigra pars compacta (SNpc), which was associated and colocalized with an increase in inducible nitric oxide synthase (iNOS) expression. In iNOS-deficient mice the increase of iNOS expression but not the activation of microglia was blocked. Dopaminergic SNpc neurons of iNOS-deficient mice were almost completely protected from MPTP toxicity in a chronic paradigm of MPTP toxicity. Because the MPTP-induced decrease in striatal concentrations of dopamine and its metabolites did not differ between iNOS-deficient mice and their wild-type littermates, this protection was not associated with a preservation of nigrostriatal terminals. Our results suggest that iNOS-derived nitric oxide produced in microglia plays an important role in the death of dopaminergic neurons but that other mechanisms contribute to the loss of dopaminergic terminals in MPTP neurotoxicity. We conclude that inhibition of iNOS may be a promising target for the treatment of PD.     

Soluble Epoxide Hydrolase Inhibition Attenuates MPTP-Induced Neurotoxicity in the Nigrostriatal Dopaminergic System: Involvement of α-Synuclein Aggregation and ER Stress

Soluble epoxide hydrolase (sEH) is widely expressed in the mammalian brain and possesses dual enzymatic activities, including C-terminal epoxide hydrolase (C-EH) which degrades epoxyeicosatrienoic acid (EET), a beneficial arachidonic acid metabolite. In the present study, the neuroprotective effect of sEH inhibition on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurodegeneration of nigrostriatal dopaminergic system was investigated using genetic and pharmacological approaches. MPTP (15 mg/kg) was intraperitoneally injected in sEH knockout (KO) mice and C57BL/6J mice as wild-type (WT) mice. Compared with the MPTP-treated WT mice, MPTP-induced reductions in striatal dopamine content and nigral tyrosine hydroxylase level (TH, a biomarker of dopaminergic neurons) were less significant in the treated sEH mice. Furthermore, MPTP-induced HO-1 elevation (a redox-regulated protein), α-synuclein aggregation, and caspase 12 activation (a hallmark of ER stress) were less prominent in sEH KO mice than in WT mice. These data indicate that sEH KO mice are more resistant to MPTP-induced neurotoxicity. The pharmacological effect of N-[1-(1-oxopropyl)-4-piperidinyl]-N0-[4-(trifluoromethoxy)phenyl)-urea (TPPU, an sEH inhibitor) on MPTP-induced neurotoxicity was investigated in WT mice. TPPU (1 mg/kg, i.p.) attenuated MPTP-induced reduction in striatal dopamine content, TH-positive cell numbers, TH, and pro-caspase 9 protein levels (an initiator caspase of apoptosis) in mouse SN. Moreover, TPPU reduced MPTP-induced HO-1 elevation, α-synuclein aggregation and caspase 12 activation, indicating that TPPU is effective in attenuating MPTP-induced oxidative stress, apoptosis, protein aggregation, and ER stress. In conclusion, our study suggests that sEH is a potential target for developing therapies for parkinsonism. Furthermore, sEH inhibitors may be of clinical significance for treating CNS neurodegenerative diseases.     

Overexpression of parkin ameliorates dopaminergic neurodegeneration induced by 1- methyl-4-phenyl-1,2,3,6-tetrahydropyridine in mice

Mutations in the parkin gene are currently thought to be the most common cause of recessive familial Parkinsonism. Parkin functions as an E3 ligase to regulate protein turnover, and its function in mitochondrial quality control has been reported recently. Overexpression of parkin has been found to prevent neuronal degeneration under various conditions both in vivo and in vitro. Here, we generated a transgenic mouse model in which expression of wild type parkin was driven by neuron-specific enolase (NSE) promoter. We reported that both young and old parkin transgenic mice exhibited less reduction of striatal TH protein and number of TH positive neurons in the substantia nigra induced by 1-Methyl-4-Phenyl-1,2,3,6-Tetrahydropyridine (MPTP), compared to wild type littermates. MPTP-induced mitochondrial impairment in the substantia nigra was improved in young parkin transgenic mice. Decreased striatal α-synuclein was demonstrated in old parkin transgenic mice. These results provide reliable evidence from the transgenic mouse model for parkin that overexpression of parkin may attenuate dopaminergic neurodegeneration induced by MPTP through protection of mitochondria and reduction of α-synuclein in the nigrostriatal pathway.     

Estrogen Alters MPTP-Induced Neurotoxicity in Female Mice: Effects on Striatal Dopamine Concentrations and Release

Abstract: The effects of estrogen on MPTP-induced neurotoxicity of the nigrostriatal dopaminergic system were examined in C57Bl and CD-1 mice. Ovariectomized mice with and without estrogen were treated with MPTP or its vehicle. The effects of these treatments on striatal dopamine concentrations and l -DOPA-stimulated dopamine and l -3,4-dihydroxyphenylacetic acid (DOPAC) release in vitro were determined. Dopamine concentrations of C57Bl mice receiving estrogen before MPTP were significantly greater than those of non-estrogen-treated MPTP mice as well as estrogen-treated mice receiving the MPTP vehicle. Dopamine concentrations of the CD-1 mice did not differ with these treatments. l -DOPA-evoked dopamine release values of estrogen-treated C57Bl mice were significantly increased compared with non-estrogen-treated mice. No such differences were observed in the MPTP-treated C57Bl mice. DOPAC release rates were similar to that of dopamine in these C57Bl mice. In the CD-1 mice estrogen also produced a significant increase in l -DOPA-evoked dopamine release; however, this response was unaltered by MPTP treatment. A significant increase in l -DOPA-evoked DOPAC output was obtained only for estrogen-treated CD-1 mice. Both strains show very similar responses to the estrogen treatment, but differential responses of dopamine release to l -DOPA between the C57Bl and CD-1 mice were obtained with regard to the interactive effects of estrogen and MPTP. Our results suggest that in addition to its role as modulator, estrogen may also function as a neuroprotectant against MPTP neurotoxicity of the nigrostriatal dopaminergic system in the C57Bl mouse.     

Involvement of monoamine oxidase inhibition in neuroprotective and neurorestorative effects of Ginkgo biloba extract against MPTP-induced nigrostriatal dopaminergic toxicity in C57 mice.

The present study investigated the neuroprotective and neurorestorative effects of Ginkgo biloba extract (EGb 761) and its two components ginkgolides A (BN52020) and B (BN52021) in mice. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (30 mg/kg/d i.p. for six days) significantly reduced striatal dopamine (DA) levels in C57 mice measured by high performance liquid chromatography with electrochemical detection (HPLC-EC). When C57 mice were pretreated with EGb 761 (20, 50, 100 mg/kg/d i.p.) for 7 days and then treated with the same extract 30 min before MPTP injection for 6 days, the neurotoxic effect of MPTP was antagonized in a dose-dependent fashion. Similar treatment with ginkgolides A and B (5, 10, 50 mg/kg/d i.p.) showed no protective effect. When C57 mice were treated with EGb 761 (50 mg/kg/d i.p.) after MPTP-lesion, the recovery of striatal dopamine (DA) levels was accelerated. However, similar treatment with ginkgolides A or B (10 mg/kg/d i.p.) did not show any effect. EGb 761, but not ginkgolides A and B, nonselectively inhibited mouse brain MAO activity in vitro (IC50 = 36.45 +/- 1.56 microg/ml) tested by an improved fluorimetric assay. The results demonstrate that EGb 761 administered before or after MPTP treatment effectively protects against MPTP-induced nigrostriatal dopaminergic neurotoxicity and that the inhibitory effect of EGb 761 on brain MAO may be involved in its neuroprotective effect.     

Elevation of striatal urate in experimental models of Parkinson's disease: a compensatory mechanism triggered by dopaminergic nigrostriatal degeneration?

Epidemiological studies have indicated an inverse association between high uricemia and incidence of Parkinson's disease (PD). To investigate the link between endogenous urate and neurotoxic changes involving the dopaminergic nigrostriatal system, this study evaluated the modifications in the striatal urate levels in two models of PD. To this end, a partial dopaminergic degeneration was induced by 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) in mice, while a severe dopaminergic degeneration was elicited by unilateral medial forebrain bundle infusion of 6‐hydroxydopamine (6‐OHDA) in rats. Urate levels were measured by in vivo microdialysis at 7 or 14 days from toxin exposure. The results obtained demonstrated higher urate levels in the dopamine‐denervated striatum of 6‐OHDA‐lesioned rats compared with the intact striatum. Moreover, an inverse correlation between urate and dopamine levels was observed in the same area. In contrast, only a trend to significant increase in striatal urate was observed in MPTP‐treated mice. These results demonstrate that a damage to the dopaminergic nigrostriatal system elevates the striatal levels of urate, and suggest that this could be an endogenous compensatory mechanism to attenuate dopaminergic neurodegeneration. This finding may be important in light of the epidemiological and preclinical evidences that indicate a link between urate and development of PD.

     

Reduced MPTP toxicity in noradrenaline transporter knockout mice

The noradrenergic neurons of the locus coeruleus (LC) are damaged in Parkinson's disease (PD). Neurotoxin ablation of the LC noradrenergic neurons has been shown to exacerbate the dopaminergic toxicity of MPTP, suggesting that the noradrenergic system protects dopamine neurons. We utilized mice that exhibit elevated synaptic noradrenaline (NA) by genetically deleting the noradrenaline transporter (NET), a key regulator of the noradrenergic system (NET KO mice). NET KO and wild-type littermates were administered MPTP and striatal dopamine terminal integrity was assessed by HPLC of monoamines, immmunoblotting for dopaminergic markers and tyrosine hydroxylase (TH) immunohistochemistry. MPTP significantly reduced striatal dopamine in wild-type mice, but not in the NET KO mice. To confirm that the protection observed in the NET KO mice was due to the lack of NET, we treated wild-type mice with the specific NET inhibitor, nisoxetine, and then challenged them with MPTP. Nisoxetine conferred protection to the dopaminergic system. These data indicate that NA can modulate MPTP toxicity and suggest that manipulation of the noradrenergic system may have therapeutic value in PD.     

Influences of Chronic Mild Stress Exposure on Motor,Non-Motor Impairments and Neurochemical Variables in Specific Brain Areas of MPTP/Probenecid Induced Neurotoxicity in Mice

Parkinson''s disease (PD) is regarded as a movement disorder mainly affecting the elderly population and occurs due to progressive loss of dopaminergic (DAergic) neurons in nigrostriatal pathway. Patients suffer from non-motor symptoms (NMS) such as depression, anxiety, fatigue and sleep disorders, which are not well focussed in PD research. Depression in PD is a predominant /complex symptom and its pathology lies exterior to the nigrostriatal system. The main aim of this study is to explore the causative or progressive effect of chronic mild stress (CMS), a paradigm developed as an animal model of depression in1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (25 mg/kg. body wt.) with probenecid (250 mg/kg, s.c.) (MPTP/p) induced mice model of PD. After ten i.p. injections (once in 3.5 days for 5 weeks) of MPTP/p or exposure to CMS for 4 weeks, the behavioural (motor and non-motor) impairments, levels and expressions of dopamine (DA), serotonin (5-HT), DAergic markers such as tyrosine hydroxylase (TH), dopamine transporter (DAT), vesicular monoamine transporters—2 (VMAT 2) and α-synuclein in nigrostriatal (striatum (ST) and substantia nigra (SN)) and extra-nigrostriatal (hippocampus, cortex and cerebellum) tissues were analysed. Significantly decreased DA and 5-HT levels, TH, DAT and VMAT 2 expressions and increased motor deficits, anhedonia-like behaviour and α-synuclein expression were found in MPTP/p treated mice. Pre and/or post exposure of CMS to MPTP/p mice further enhanced the MPTP/p induced DA and 5-HT depletion, behaviour abnormalities and protein expressions. Our results could strongly confirm that the exposure of stress after MPTP/p injections worsens the symptoms and neurochemicals status of PD.     

Tauroursodeoxycholic Acid Prevents MPTP-Induced Dopaminergic Cell Death in a Mouse Model of Parkinson’s Disease

Mitochondrial dysfunction and oxidative stress are implicated in the neurodegenerative process in Parkinson??s disease (PD). Moreover, c-Jun N-terminal kinase (JNK) plays an important role in dopaminergic neuronal death in substantia nigra pars compacta. Tauroursodeoxycholic acid (TUDCA) acts as a mitochondrial stabilizer and anti-apoptotic agent in several models of neurodegenerative diseases. Here, we investigated the role of TUDCA in preventing 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced neurodegeneration in a mouse model of PD. We evaluated whether TUDCA modulates MPTP-induced degeneration of dopaminergic neurons in the nigrostriatal axis, and if that can be explained by regulation of JNK phosphorylation, reactive oxygen species (ROS) production, glutathione S-transferase (GST) catalytic activation, and Akt signaling, using C57BL/6 glutathione S-transferase pi (GSTP) null mice. TUDCA efficiently protected against MPTP-induced dopaminergic degeneration. We have previously demonstrated that exacerbated JNK activation in GSTP null mice resulted in increased susceptibility to MPTP neurotoxicity. Interestingly, pre-treatment with TUDCA prevented MPTP-induced JNK phosphorylation in mouse midbrain and striatum. Moreover, the anti-oxidative role of TUDCA was demonstrated in vivo by impairment of ROS production in the presence of MPTP. Finally, results herein suggest that the survival pathway activated by TUDCA involves Akt signaling, including downstream Bad phosphorylation and NF-??B activation. We conclude that TUDCA is neuroprotective in an in vivo model of PD, acting mainly by modulation of JNK activity and cellular redox thresholds, together with activation of the Akt pro-survival pathway. These results open new perspectives for the pharmacological use of TUDCA, as a modulator of neurodegeneration in PD.     

Progranulin Gene Delivery Protects Dopaminergic Neurons in a Mouse Model of Parkinson’s Disease

Parkinson’s disease (PD) is a progressive neurodegenerative disorder characterized by tremor, rigidity and akinesia/bradykinesia resulting from the progressive loss of nigrostriatal dopaminergic neurons. To date, only symptomatic treatment is available for PD patients, with no effective means of slowing or stopping the progression of the disease. Progranulin (PGRN) is a 593 amino acid multifunction protein that is widely distributed throughout the CNS, localized primarily in neurons and microglia. PGRN has been demonstrated to be a potent regulator of neuroinflammation and also acts as an autocrine neurotrophic factor, important for long-term neuronal survival. Thus, enhancing PGRN expression may strengthen the cells resistance to disease. In the present study, we have used the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) model of PD to investigate the possible use of PGRN gene delivery as a therapy for the prevention or treatment of PD. Viral vector delivery of the PGRN gene was an effective means of elevating PGRN expression in nigrostriatal neurons. When PGRN expression was elevated in the SN_C, nigrostriatal neurons were protected from MPTP toxicity in mice, along with a preservation of striatal dopamine content and turnover. Further, protection of nigrostriatal neurons by PGRN gene therapy was accompanied by reductions in markers of MPTP-induced inflammation and apoptosis as well as a complete preservation of locomotor function. We conclude that PGRN gene therapy may have beneficial effects in the treatment of PD.     

The influence and the mechanism of docosahexaenoic acid on a mouse model of Parkinson's disease

This study aimed to investigate the effects of docosahexaenoic acid (DHA) on the oxidative stress that occurs in an experimental mouse model of Parkinson’s disease (PD). An experimental model of PD was created by four intraperitoneal injections of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) (4 × 20 mg/kg, at 12 h intervals). Docosahexaenoic acid was given daily by gavage for 4 weeks (36 mg/kg/day). The motor activity of the mice was evaluated via the pole test, and the dopaminergic lesion was determined by immunohistochemical analysis for tyrosine hydroxylase (TH)-immunopositive cells. The activity of antioxidant enzymes in the brain were determined by spectrophotometric assays and the concentration of thiobarbituric acid-reactive substances (TBARS) were measured as an index of oxidative damage. The number of apoptotic dopaminergic cells significantly increased in MPTP-treated mice compared to controls. Although DHA significantly diminished the number of cell deaths in MPTP-treated mice, it did not improve the decreased motor activity observed in the experimental PD model. Docosahexaenoic acid significantly diminished the amount of cell death in the MPTP + DHA group as compared to the MPTP group. TBARS levels in the brain were significantly increased following MPTP treatment. Glutathione peroxidase (GPx) and catalase (CAT) activities of brain were unaltered in all groups. The activity of brain superoxide dismutase (SOD) was decreased in the MPTP-treated group compared to the control group, but DHA treatment did not have an effect on SOD activity in the MPTP + DHA group. Our current data show that DHA treatment exerts neuroprotective actions on an experimental mouse model of PD. There was a decrease tendency in brain lipid oxidation of MPTP mice but it did not significantly.     

Severe Vitamin E deficiency exacerbates acute hyperoxic lung injury associated with increased oxidative stress and inflammation

Hyperoxia causes acute lung injury along with an increase of oxidative stress and inflammation. It was hypothesized that vitamin E deficiency might exacerbate acute hyperoxic lung injury. This study used alpha-tocopherol transfer protein knockout (alpha-TTP KO) mice fed a vitamin E-deficient diet (KO E(-) mice) as a model of severe vitamin E deficiency. Compared with wild-type (WT) mice, KO E(-) mice showed a significantly lower survival rate during hyperoxia. After 72 h of hyperoxia, KO E(-) mice had more severe histologic lung damage and higher values of the total cell count and the protein content of bronchoalveolar lavage fluid (BALF) than WT mice. IL-6 mRNA expression in lung tissue and the levels of 8-iso-prostaglandin F(2alpha) (8-iso-PGF(2alpha)) in both lungs and BALF were higher in KO E(-) mice than in WT mice. It was concluded that severe vitamin E deficiency exacerbates acute hyperoxic lung injury associated with increased oxidative stress or inflammation.     

Sirtuin 2 (SIRT2) Enhances 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Nigrostriatal Damage via Deacetylating Forkhead Box O3a (Foxo3a) and Activating Bim Protein

Sirtuins are NAD-dependent protein deacetylases that were shown to have beneficial effects against age-related diseases. SIRT2 is a strong deacetylase that is highly expressed in brain. It has been associated with neurodegenerative diseases. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is a dopaminergic neurotoxin that replicates most of the clinical features of Parkinson disease (PD) and produces a reliable and reproducible lesion of the nigrostriatal dopaminergic pathway and neurodegeneration after its systemic administration. Chronic administration of MPTP induces lesion via apoptosis. We show here that SIRT2 deacetylates Foxo3a, increases RNA and protein levels of Bim, and as a result, enhances apoptosis in the MPTP model of PD. We also show that neurodegeneration induced by chronic MPTP regimen is prevented by genetic deletion of SIRT2 in mouse. Deletion of SIRT2 leads to the reduction of apoptosis due to an increase in acetylation of Foxo3a and a decrease in Bim levels. We demonstrate that SIRT2 deacetylates Foxo3a, activates Bim, and induces apoptosis only in 1-methyl-4-phenylpyridinium-treated cells. Therefore, designing SIRT2 inhibitors might be helpful to develop effective treatments for PD.     

Systemically administered neuregulin‐1β1 rescues nigral dopaminergic neurons via the ErbB4 receptor tyrosine kinase in MPTP mouse models of Parkinson's disease

Previously, we demonstrated that systemically injected extracellular domain of neuregulin‐1β1 (Nrg1β1), a nerve growth and differentiation factor, passes the blood‐brain barrier and rescues dopaminergic neurons of substantia nigra in the 6‐hydroxydopamine‐mouse model of Parkinson's disease (PD). Here, we studied the effects of peripherally administered Nrg1β1 in another toxin‐based mouse model of PD. For this purpose, (i) nigrostriatal pathway injury was induced by treatment of adult wild‐type mice with 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP) in acute and subchronic paradigms; and (ii) Nrg1β1 or saline (control) were administered 1 h before each MPTP injection. We found that Nrg1β1 significantly reduced the loss of nigral dopaminergic neurons in both intoxication paradigms (7 days post‐injection). However, Nrg1β1 did not reverse MPTP‐induced decrease in dopamine levels and dopaminergic fibers in the striatum. We also show that MPTP conversion to its toxic metabolite 1‐methyl‐4‐phenylpyridinium as well as levels of dopamine transporter, mediating intracellular uptake of 1‐methyl‐4‐phenylpyridinium, are unaffected by Nrg1β1. Finally, neuroprotective properties of Nrg1β1 on nigral dopaminergic neurons are specifically mediated by ErbB4 as revealed through the study of ErbB4 knockout mice. In conclusion, systemically administered Nrg1β1 protects midbrain dopaminergic neurons against this PD‐related toxic insult. Thus, Nrg1β1 may have a benefit in the treatment of PD patients.

     

Effect of vitamin C deficiency during postnatal development on adult behavior: functional phenotype of Gulo-/- knockout mice

Organisms using oxygen for aerobic respiration require antioxidants to balance the production of reactive oxygen species during metabolic processes. Various species--including humans and other primates--suffer mutations in the GULO gene encoding L-gulono-γ-lactone oxidase; GULO is the rate-limiting enzyme in the biosynthesis of ascorbate, an important cellular antioxidant. Animals lacking the ability to synthesize vitamin C develop scurvy without dietary supplementation. The Gulo-/- knockout (KO) mouse requires oral supplemental vitamin C; without this supplementation the animal dies with a scorbutic condition within several weeks. Vitamin C is known to be most abundant in the brain, where it is believed to play important roles in neuroprotection, neurotransmission and neuromodulation. We therefore hypothesized that ascorbate deficiency in Gulo-/- KO mice might lead to an abnormal behavioral phenotype. We established the amount of ascorbate in the drinking water (220 ppm) necessary for generating a chronic low-ascorbate status in the brain, yet clinically the mice appeared healthy throughout 100 days postpartum at which time all behavioral-phenotyping tests were completed. Compared with Gulo+/+ wild-type littermates, ascorbate-deficient Gulo-/- mice were found to be less active in moving in their environment; when in water, these mice swam more slowly in some tests, consistent with a mild motor deficit. We found no evidence of cognitive, anxiety or sensorimotor-gating problems. Despite being less active, Gulo-/- mice exhibited exaggerated hyperactivity to the dopaminergic agonist methamphetamine. The subnormal movement, combined with hypersensitivity to a dopamine agonist, point to developmental ascorbate deficiency causing long-term striatal dysfunction.     

Protective effect of vitamin E supplements on experimental atherosclerosis is modest and depends on preexisting vitamin E deficiency

Vitamin E has failed to protect humans from cardiovascular disease outcome, yet its role in experimental atherosclerosis remains less clear. A previous study (Proc. Natl. Acad. Sci. USA 97:13830-13834; 2000) showed that vitamin E deficiency caused by disruption of the alpha-tocopherol transfer protein gene (Ttpa) is associated with a modest increase in atherosclerosis in apolipoprotein E gene deficient (Apoe(-/-)) mice. Here we confirm this finding and report that in Apoe(-/-)Ttpa(-/-) mice dietary alpha-tocopherol (alphaT) supplements restored circulating and aortic levels of alphaT, and decreased atherosclerosis in the aortic root to a level comparable to that seen in Apoe(-/-) mice. However, such dietary supplements did not decrease disease in Apoe(-/-) mice, whereas dietary supplements with a synthetic vitamin E analog (BO-653), either alone or in combination with alphaT, decreased atherosclerosis in Apoe(-/-) and in Apoe(-/-)Ttpa(-/-) mice. Differences in atherosclerosis were not associated with changes in the arterial concentrations of F(2)-isoprostanes and cholesterylester hydro(pero)xides, nor were they reflected in the resistance of plasma lipids to ex vivo oxidation. These results show that vitamin E at best has a modest effect on experimental atherosclerosis in hyperlipidemic mice, and only in situations of severe vitamin E deficiency and independent of lipid oxidation in the vessel wall.