Mélanie Bousquet

Beneficial effects of dietary omega-3 polyunsaturated fatty acid on toxin-induced neuronal degeneration in an animal model of Parkinson’s disease

In this study, we examined whether omega‐3 (n‐3) polyunsaturated fatty acids (PUFAs) may exert neuroprotective action in Parkinsons disease, as previously shown in Alzheimers disease. We exposed mice to either a control or a high n‐3 PUFA diet from 2 to 12 months of age and then treated them with the neurotoxin 1‐methyl‐4‐phenyl‐1,2,3,6‐tetrahydropyridine (MPTP;140 mg/kg in 5 days). High n‐3 PUFA dietary consumption completely prevented the MPTP‐induced decrease of tyrosine hy‐droxylase (TH)‐labeled nigral cells (P<0.01 vs. MPTP mice on control diet), Nurrl mRNA (P<0.01 vs. MPTP mice on control diet), and dopamine transporter mRNA levels (P<0.05 vs. MPTP mice on control diet) in the substantia nigra. Although n‐3 PUFA dietary treatment had no effect on striatal dopaminergic terminals, the high n‐3 PUFA diet protected against the MPTP‐induced decrease in dopamine (P<0.05 vs. MPTP mice on control diet) and its metabolite dihydroxyphenylacetic acid (P<0.05 vs. MPTP mice on control diet) in the striatum. Taken together, these data suggest that a high n‐3 PUFA dietary intake exerts neuroprotective actions in an animal model of Parkinsonism. Bous‐quet M., Saint‐Pierre, M., Julien, C., Salem, N. Jr., Cicchetti, F., Calon F. Beneficial effects of dietary omega‐3 polyunsaturated fatty acid on toxin‐induced neuronal degeneration in an animal model of Parkinsons disease. FASEB J. 22, 1213–1225 (2008)

Modulation of brain-derived neurotrophic factor as a potential neuroprotective mechanism of action of omega-3 fatty acids in a parkinsonian animal model.

While we recently reported the beneficial effects of omega-3 polyunsaturated fatty acids (n-3 PUFAs) in a mouse model of Parkinsons disease (PD), the mechanisms of action remain largely unknown. Here, we specifically investigated the contribution of the brain-derived neurotrophic factor (BDNF) to the neuroprotective effect of n-3 PUFA observed in a mouse model of PD generated by a subacute exposure to MPTP using a total of 7 doses of 20mg/kg over 5 days. The ten-month high n-3 PUFA treatment which preceded the MPTP exposure induced an increase of BDNF mRNA expression in the striatum, but not in the motor cortex of animals fed the high n-3 PUFA diet. In contrast, n-3 PUFA treatment increased BDNF protein levels in the motor cortex of MPTP-treated mice, an effect not observed in vehicle-treated mice. The mRNA expression of the high-affinity BDNF receptor tropomyosin-related kinase B (TrkB) was increased in the striatum of MPTP-treated mice fed the high n-3 PUFA diet compared to vehicle and MPTP-treated mice on the control diet and to vehicle mice on the high n-3 PUFA diet. These data suggest that the modulation of BDNF expression contributes, in part, to n-3 PUFA-induced neuroprotection in an animal model of PD.

Differences between subacute and chronic MPTP mice models: investigation of dopaminergic neuronal degeneration and α‐synuclein inclusions

Animal models are invaluable tools to study neurodegenerative disorders but a general consensus on the most accurate rodent model of Parkinson’s disease has not been reached. Here, we examined how different methods of MPTP administration influence the degeneration of the dopaminergic (DA) system. Adult male C57BL/6 mice were treated with the same cumulative dose of MPTP following four distinct procedures: (i) subacute i.p. injections; (ii) 28‐day chronic s.c. infusion; (iii) 28‐day chronic i.p. infusion; and (iv) 14‐day chronic i.p. infusion. Subacute MPTP treatment significantly affected all aspects of the DA system within the nigral and striatal territories. In contrast, the 28‐day chronic s.c. infusion did not significantly alter any components of the DA system. The 28‐ and 14‐day chronic i.p. infusions induced loss of tyrosine hydroxylase (TH)‐positive cells correlated with a decrease in Nurr1 mRNA levels, but no significant decrease in the density of TH striatal fibers. Importantly, however, only the 14‐day chronic MPTP i.p. infusion protocol promoted the formation of neuronal inclusions as noted by the expression of α‐synuclein protein within the cytoplasm of TH nigral neurons. Overall, we found that the 14‐day chronic MPTP i.p. infusion reproduces more accurately the pathological characteristics of early stage Parkinson’s disease.

Defective dentate nucleus GABA receptors in essential tremor

The development of new treatments for essential tremor, the most frequent movement disorder, is limited by a poor understanding of its pathophysiology and the relative paucity of clinicopathological studies. Here, we report a post-mortem decrease in GABA(A) (35% reduction) and GABA(B) (22-31% reduction) receptors in the dentate nucleus of the cerebellum from individuals with essential tremor, compared with controls or individuals with Parkinsons disease, as assessed by receptor-binding autoradiography. Concentrations of GABA(B) receptors in the dentate nucleus were inversely correlated with the duration of essential tremor symptoms (r(2) = 0.44, P < 0.05), suggesting that the loss of GABA(B) receptors follows the progression of the disease. In situ hybridization experiments also revealed a diminution of GABA(B(1a+b)) receptor messenger RNA in essential tremor (↓27%). In contrast, no significant changes of GABA(A) and GABA(B) receptors (protein and messenger RNA), GluN2B receptors, cytochrome oxidase-1 or GABA concentrations were detected in molecular or granular layers of the cerebellar cortex. It is proposed that a decrease in GABA receptors in the dentate nucleus results in disinhibition of cerebellar pacemaker output activity, propagating along the cerebello-thalamo-cortical pathways to generate tremors. Correction of such defective cerebellar GABAergic drive could have a therapeutic effect in essential tremor.

Transgenic conversion of omega-6 into omega-3 fatty acids in a mouse model of Parkinson's disease

We have recently identified a neuroprotective role for omega-3 polyunsaturated fatty acids (n-3 PUFAs) in a toxin-induced mouse model of Parkinsons disease (PD). Combined with epidemiological data, these observations suggest that low n-3 PUFA intake is a modifiable environmental risk factor for PD. In order to strengthen these preclinical findings as prerequisite to clinical trials, we further investigated the neuroprotective role of n-3 PUFAs in Fat-1 mice, a transgenic model expressing an n-3 fatty acid desaturase converting n-6 PUFAs into n-3 PUFAs. Here, we report that the expression of the fat-1 transgene increased cortical n-3:n-6 PUFA ratio (+28%), but to a lesser extent than dietary supplementation (92%). Such a limited endogenous production of n-3 PUFAs in the Fat-1 mouse was insufficient to confer neuroprotection against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine neurotoxicity as assessed by dopamine levels, tyrosine hydroxylase (TH)-positive neurons and fibers, as well as nigral Nurr1 and dopamine transporter (DAT) mRNA expression. Nevertheless, higher cortical docosahexaenoic acid (DHA) concentrations were positively correlated with markers of nigral dopaminergic neurons such as the number of TH-positive cells, in addition to Nurr1 and DAT mRNA levels. These associations are consistent with the protective role of DHA in a mouse model of PD. Taken together, these data suggest that dietary intake of a preformed DHA supplement is more effective in reaching the brain and achieving neuroprotection in an animal model of PD.

Impact of omega-3 fatty acids in Parkinson's disease

Current epidemiological, preclinical and clinical data suggest that omega-3 polyunsaturated fatty acids (n-3 PUFAs) may constitute therapeutic strategy for several disorders of the central nervous system, including Parkinsons disease (PD). PD is a neurodegenerative disorder primarily characterized by motor symptoms but which also includes several other pathological features such as autonomic system failures, mood disorders, and cognitive deficits. Current pharmacological options for the disease are limited to symptom management and their long-term use leads to important side effects. In this review, we discuss the evidence for the effects of n-3 PUFAs in PD both from an epidemiological perspective as well as in light of data gathered on various pathological features of the disease. Effects of n-3 PUFAs on the dopaminergic system, α-synucleinopathy, their possible mechanisms of action as well as their therapeutic potential for PD patients are also reviewed. n-3 PUFAs are inexpensive, readily transferable to the clinical setting and their use could represent a neuroprotective strategy or a disease-modifying option to delay the appearance of symptoms. It could also be beneficial as a symptomatologic treatment or serve as an add-on therapy to current pharmacological approaches. Review of the current literature as well as the undertaking of future clinical trials will shed light on these possibilities.

High-fat diet exacerbates MPTP-induced dopaminergic degeneration in mice.

The identification of modifiable nutritional risk factors is highly relevant to the development of preventive strategies for neurodegenerative disorders including Parkinsons disease (PD). In this study, adult C57BL/6 mice were fed either a control (CD-12%kcal) or a high-fat diet (HFD-60%kcal) for 8 weeks prior to MPTP exposure, a toxin which recreates a number of pathological features of PD. HFD-fed mice significantly gained weight (+41%), developed insulin resistance and a systemic immune response characterized by an increase in circulating leukocytes and plasmatic cytokines/chemokines (interleukin-1α, MCP-1, MIP-1α). As expected, the MPTP treatment produced nigral dopaminergic degeneration as evidenced by the loss of striatal dopamine and the decreased number of nigral tyrosine hydroxylase (TH)- and dopamine transporter-expressing neurons (23% and 25%, respectively). However, exposure to HFD exacerbated the effects of MPTP on striatal TH (23%) and dopamine levels (32%), indicating that diet-induced obesity is associated with a reduced capacity of nigral dopaminergic terminals to cope with MPTP-induced neurotoxicity. Since high-fat consumption is commonplace in our modern society, dietary fat intake may represent an important modifiable risk factor for PD.

Cystamine metabolism and brain transport properties: clinical implications for neurodegenerative diseases.

J. Neurochem. (2010) 114, 1651–1658.

The role of the MYD88-dependent pathway in MPTP-induced brain dopaminergic degeneration

BackgroundMounting evidence supports a significant role of inflammation in Parkinsons disease (PD) pathophysiology, with several inflammatory pathways being suggested as playing a role in the dopaminergic degeneration seen in humans and animal models of the disease. These include tumor necrosis factor, prostaglandins and oxidative-related stress components. However, the role of innate immunity has not been established in PD.MethodsBased on the fact that the myeloid differentiation primary response gene (88) (MyD88) is the most common adaptor protein implicated in toll-like receptor (TLR) signaling, critical in the innate immune response, we undertook a study to investigate the potential contribution of this specific pathway to MPTP-induced brain dopaminergic degeneration using MyD88 knock out mice (MyD88-/-), following our observations that the MyD88-dependent pathway was critical for MPTP dopaminergic toxicity in the enteric nervous system. Post-mortem analyses assessing nigrostriatal dopaminergic degeneration and inflammation were performed using HPLC, western blots, autoradiography and immunofluorescence.ResultsOur results demonstrate that MyD88-/- mice are as vulnerable to MPTP-induced dopamine and DOPAC striatal depletion as wild type mice. Furthermore, MyD88-/- mice show similar striatal dopamine transporter and tyrosine hydroxylase loss, as well as dopaminergic cell loss in the substantia nigra pars compacta in response to MPTP. To evaluate the extent of the inflammatory response created by the MPTP regimen utilized, we further performed bioluminescence imaging using TLR2-luc/gfp transgenic mice and microglial density analysis, which revealed a modest brain microglial response following MPTP. This was accompanied by a significant astrocytic reaction in the striatum, which was of similar magnitude both in wild type and MyD88-/- mice.ConclusionsOur results suggest that subacute MPTP-induced dopaminergic degeneration observed in the central nervous system is MyD88-independent, in contrast to our recent observations that this pathway, in the same cohort of animals, is critical in the loss of dopaminergic neurons in the enteric nervous system.

Cystamine prevents MPTP-induced toxicity in young adult mice via the up-regulation of the brain-derived neurotrophic factor.

Preclinical data suggest that cystamine stands as a promising neuroprotective agent against Huntingtons and Parkinsons diseases. To decipher the mechanisms of action of cystamine, we investigated the effects of various doses of cystamine (10, 50, and 200mg/kg) on the regulation of the brain-derived neurotrophic factor (BDNF), its receptor tropomyosin-receptor-kinase B (TrkB) and on the heat shock protein 70 (Hsp70) brain mRNA expression in relation to the time after administration. We have determined that the lower cystamine dose is the most efficient to promote putative neuroprotective effects. Indeed, an acute administration of 10mg/kg of cystamine increased the expression of BDNF mRNA in the substantia nigra compacta (SNc), although it did not significantly influence TrkB or Hsp70 mRNA. Higher cystamine doses resulted in the absence of activation of any of these markers or led to non-specific effects. We have also substantiated the neuroprotective effect of a 21-day treatment of 10mg/kg/day of cystamine in young adult mice against MPTP-induced loss of tyrosine hydroxylase-striatal fiber density, nigral dopamine cells and nigral Nurr1 mRNA expression. The neuroprotective action of cystamine in the same animals was associated with an up-regulation of BDNF in the SNc. Taken together, these results strengthen the neuroprotective potential of cystamine in the treatment of Parkinsons disease and point towards the up-regulation of BDNF as an important mechanism of action.