High-fat diet exacerbates MPTP-induced do
M. Bousquet a,b, I. St-Amour a,b,c, M. Vandal a,b, P. Juliena Centre de Recherche du CHUL (CHUQ), Axe Neurosciences, Qubec, QC, Canadab Facult de Pharmacie, Universit Laval, Qubec, QC, Canadac Dpartement de Recherche et Dveloppement, Hma-Qubec, Qubec, Canadad Centre de Recherche sur les Maladies Lipidiques, CHUL (CHUQ), Qubec, QC, Canadae ec,
le nsordcal)pathological features of PD. HFD-fedmice signicantly gainedweight (+41%), devel-
plasmatic cytokines/chemokines (interleukin-1, MCP-1, MIP-1). As expected, the MPTP treatment producednigral dopaminergic degeneration as evidenced by
2006). A progressive loss of dopaminergic neurons within the substantia tions such as autonomic system failure, depression and dementia, for
Neurobiology of Disease 45 (2012) 529538
Contents lists available at SciVerse ScienceDirect
j ourna l homepage: www.e lnigra pars compacta (SNpc) accompaniedwith a drastic decrease in stria-tal dopamine (DA) are part of the pathological features discernible in the
which the pathophysiology is still unclear (Chaudhuri and Schapira,2009; Lees et al., 2009). For the vast majority of PD patients, the originof neurodegeneration remains unknown and less than 15% of PD casescan be attributed to specic genetic mutations as identied in -synu-clein (SNCA), LRRK2, PINK1, parkin and DJ1 genes (Meissner et al., 2011).A number of environmental risk factors have been suggested to play akey role in the development of PD but because they are readily modi-able, nutritional factors have received considerable attention over theyears. Several preclinical and epidemiological studies have indeed under-lined the impact of nutrients such as dairy products, numerous vitamins,caffeine and iron on PD pathogenesis despite the fact that some of these
Abbreviations: ARA, arachidonic acid; BDNF, brain-derived neurotrophic factor; CD,control diet; DA, dopamine; DAT, dopamine transporter; DHA, docosahexaenoic acid;DOPAC, 3,4-dihydroxyphenylacetic acid; DPA, docosapentaenoic acid; DTA, docosate-traenoic acid; GDNF, glial cell line-derived neurotrophic factor; GFAP, glial brillaryacidic protein; GM-CSF, granulocyte macrophage colony stimulating factor; HFD,high-fat diet; IFN, interferon; IL, interleukin; LA, linoleic acid; MCP, monocyte chemo-tactic protein; MIP, macrophage inammatory protein; MPTP, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine; n3/n6 PUFA, omega-3/omega-6 polyunsaturatedfatty acid; PD, Parkinson's disease; PDS-95, post-synaptic protein-95; SNpc, substantia
nigra pars compacta; TH, tyrosine hydroxylase; TNF, tum Correspondence to: F. Cicchetti, Centre de Rech
Neurosciences, T2-05, 2705, boulevard Laurier, QuFax: +1 418 654 2753. Correspondence to: F. Calon, CentredeRechercheduC
T2-05, 2705, boulevard Laurier, Qubec, QC, Canada G1V 4GE-mail addresses: Francesca.Cicchetti@crchul.ulaval.c
Frederic.Calon@crchul.ulaval.ca (F. Calon).1 Co-senior authors.
Available online on ScienceDirect (www.scienced
0969-9961/$ see front matter 2011 Elsevier Inc. Alldoi:10.1016/j.nbd.2011.09.009rative disorder affectingge (de Lau and Breteler,
tant motor perturbations such as resting tremors, bradykinesia, akinesiaand muscular rigidity. PD is also characterized by non-motor manifesta-Parkinson's disease (PD) is a neurodegeneover 1% of the population over 60 years of aKeywords:Parkinson's diseaseObesityInsulin resistanceDopamineFlow cytometryCytokinesLeukocytesDopaminergic neuronsNutrition
Introductionnigral 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%), indi-cating that diet-induced obesity is associated with a reduced capacity of nigral dopaminergic terminals to copewith MPTP-induced neurotoxicity. Since high-fat consumption is commonplace in our modern society, dietaryfat intake may represent an important modiable risk factor for PD.
2011 Elsevier Inc. All rights reserved.
brain of PD patients (Calon et al., 2003; Damier et al., 1999; Lees et al.,2009). The dopaminergic neurodegeneration seemingly leads to impor-associations are sEtminan et al., 20we have previouhigh intake of omouse model of P
Increasing evroot of a pletho1996;Willett et a
or necrosis factor.erche du CHUL (CHUQ), Axebec, QC, Canada G1V 4G2.
HUL (CHUQ), AxeNeurosciences,2. Fax: +1 418 654 2761.a (F. Cicchetti),
rights reserved.the loss of striatal dopamine and the decreased number ofAvailable online 21 September 2011
oped insulin resistance and a systemic immune response characterizedby an increase in circulating leukocytes andAccepted 13 September 2011either a control (CD 12%kwhich recreates a number ofDpartement de Psychiatrie & Neurosciences, Facult de Mdecine, Universit Laval, Qubf Institut des nutraceutiques et des aliments fonctionnels (INAF), Universit Laval, Qubec,
a b s t r a c ta r t i c l e i n f o
Article history:Received 26 June 2011Revised 31 August 2011
The identication of modiabgies for neurodegenerative dipaminergic degeneration in miced, F. Cicchetti a,e,,1, F. Calon a,b,f,,1
utritional risk factors is highly relevant to the development of preventive strate-ers including Parkinson's disease (PD). In this study, adult C57BL/6micewere fedor a high-fat diet (HFD 60%kcal) for 8 weeks prior to MPTP exposure, a toxin
sev ie r .com/ locate /ynbd itill being debated (Chen et al., 2007; Costa et al., 2010;05; Powers et al., 2009). In line with the present study,sly reported the neuroprotective effects of a long-termmega-3 polyunsaturated fatty acid (n3 PUFA) in aD (Bousquet et al., 2008; Calon and Cicchetti, 2008).idence suggest that diet-induced weight gain is at thera of health problems (Colditz et al., 1995; Felson,l., 1995, 1999).While obesity andmetabolic disorders,
plex assay detection limit: interleukin (IL)-1 14 pg/ml, IL-1 50 pg/ml, IL-2 16 pg/ml, IL-3 14 pg/mg, IL-4 14 pg/ml,IL-5 12 pg/ml, IL-6 12 pg/ml, IL-10 8 pg/mg, IL-12 28 pg/ml, IL-17 32 pg/ml, interferon (IFN) 32 pg/ml, tumor ne-crosis factor (TNF) 22 pg/ml, macrophage inammatory protein(MIP-1) 12 pg/ml, monocyte chemotactic protein (MCP-1) 12 pg/ml, granulocyte macrophage colony stimulating factor (GM-CSF) 14 pg/ml and RANTES 30 pg/ml) from Quansys Biosciences(Logan, UT) according to the manufacturer's instructions.
Tissue preparation for post-mortem analyses
Fourteen days following the last MPTP injection, animals were sacri-ced under deep anesthesiawith ketamine/xylazine and perfused via in-tracardiac infusion with 1X PBS containing protease inhibitors (Sigma)and phosphatase inhibitors (1 mM tetrasodium pyrophosphate and50 mM sodium uoride). Brains were collected, the frontal cortex wasdissected for fatty acid analyses and the two hemispheres were separat-ed. The left hemisectionwas snap-frozen in 2-methyl-butane and storedat 80 C for cryostat coronal brain sections of 20 m for high perfor-mance liquid chromatography (HPLC) analysis. The right hemisectionwas separated at the level of bregma 1.70 mm, the caudal sectionwas post-xed in 4% paraformaldehyde pH 7.4, while the striatum con-
530 M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538such as diabetes, are well known outcomes of unhealthy high-fat diet(HFD), more recent studies have added neurodegenerative diseases tothe list of possible deleterious consequences of high-fat consumption(Bayer-Carter et al., 2011; Gao et al., 2007; Hiltunen et al., 2011; Julienet al., 2010; Mody et al., 2011). For example, retrospective and prospec-tive epidemiological studies suggest an associationwith ahigh consump-tion of saturated fat from animalmeat and a higher risk of developing PD(Gao et al., 2007). Obesity, a predictable effect of high-fat intake, has alsobeen studied in relation to PD in prospective epidemiological studies.While a signicant weight loss is observed 2 to 4 years prior to diagnosis(Chen et al., 2003), a greater bodymass index (BMI),midlife triceps skin-fold thickness, waist circumference and waist-to-hip ratio have beenlinked to increased risk of developing PD in never smokers (Abbottet al., 2002; Chen et al., 2004; Hu et al., 2006). Other studies, however,have not reported a signicant link between obesity and PD (Logroscinoet al., 2007). With a prevalence increasing with age (Wild et al., 2004),diet-induced obesity often leads to metabolic disorders, including typeII diabetes, and chronic peripheral inammation (Das, 2001). Interest-ingly, a recently published prospective study evaluating the relation-ship between diabetes and the development of PD found an overall41% increased risk (odd ratio) among individuals who have sufferedfrom diabetes for 10 years or more (Xu et al., 2011).
High-fat intake in the general population and resultingmetabolic pe-ripheral perturbations arewidespread. Since high-fat consumption couldbe a modiable risk factor, it is critical to further investigate their effectson the development of neurodegenerative diseases. We evaluated theimpact of a 2-month high intake in calories from fat on insulin resistanceand immune systemic response as well as in the brain of a mousemodelof PD. Our main a priori hypothesis was that a HFD exacerbates the ef-fects of the neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine(MPTP) in mice compared to mice fed a control diet (CD).
Materials and methods
Experimental design, diet and MPTP treatment
Mice were housed in groups of 3 to 4 per cage and were kept understandard conditions throughout the experiments, with free access tofood and water. All procedures were approved by the Laval UniversityAnimal Welfare Committee (#09-098). Forty-nine C57BL/6 male micewere either fed a HFD (60% of calories) or a CD (12% of calories) from2months of age (corresponding to adulthood) until the time of sacrice(see Table 1 for complete description of the diets) (Julien et al., 2010).The MPTP treatment was performed at 4 months of age and consistedof 7 i.p. injections of a MPTPHCl solution (20 mg/kg, free base; Sigma,St. Louis, MO) freshly dissolved in 0.9% saline. MPTP was administeredtwice on therst two days of the experimental protocol at 12-h intervals,and once a day on the three subsequent days, as previously described(Bousquet et al., 2008; Gibrat et al., 2009). Remaining animals received0.9% saline i.p. in replacement of the MPTP injections. To ensure equiva-lent dosage of the neurotoxin to eachmouse and to prevent any lethal in-toxication of obese mice, MPTP doses were calculated for each mousewith respect to the body surface area (BSA) instead of body weight(Cheung et al., 2009). Briey, the BSA is described as: k*m0.667, m beingtheweight (g) of themouse and k (Meeh constant) is determined empir-ically as 9.822 for the C57B/L6 mouse strain (Cheung et al., 2009). Themean weight of the mice on the control diet was 31 g for a calculatedBSA of 97.04 (BSAmean); these mice received 0.62 mg MPTP (on a20 mg/kg basis). The BSA of all mice was determined prior to calculationof MPTP doses (mg) using this formula: BSA0.62/BSAmean.
Insulin sensitivity assessment and plasmatic insulin concentration
Insulin sensitivity was evaluated after 8 weeks of diet. Mice wereinjected with human insulin (1 g/kg) after 6 h of fasting. Blood glucose
wasmonitored (OneTouch UltraMini, LifeScan, Milpitas, CA, USA) at 15,30, 45, 60 and 90 min post-insulin injection. Plasma insulin was mea-sured using an Ultrasensitive Insulin ELISA assay (Mercodia, Uppsala,Sweden) according to the manufacturer's protocol.
Flow cytometry analyses and Q-plex cytokine assay
Blood was collected via the saphenous vein using EDTA-coatedcapillary tubes. Whole blood cell populations were analyzed usingPE conjugated-anti-CD45, AF647 conjugated anti-CD3, AF647conjugated-anti-CD4 and PE conjugated anti-CD8 for T cells, PE-Cy7conjugated anti-B220 for B cells and AF488 conjugated anti-Gr1 forgranulocytes detection (all antibodies are from eBioscience, SanDiego, CA). Briey, 5 l of whole blood cells was stained for 15 minat room temperature in 800 l PBS with 1% fetal bovine serum (Ther-mo Scientic Hyclone, Logan, UT) and immediately analyzed by owcytometry using a CyFlow ML (Partec, Swedesboro, NJ). Serum cyto-kine concentrations (1:2 plasma dilution) were evaluated with anELISA-based fully quantitative Q-PlexMouse Cytokine-Screen (16-
Table 1Diet composition
Protein (% w/w) 20.3 27.4Carbonhydrate (% w/w) 66.0 25.3Fat (% w/w) 5.0 35.1Calories (kcal/g) 3.9 5.3
Ingredients (g/kg)Casein 200.0 200.0DL-methionine 3.0 3.0Corn starch 150.0 125.0Sucrose 500.0 52.5Cellulose, BW200 50.0 50.0Corn oil 30.0 0.0Safower oil 0.0 125.0Soybean oil 10.0 0.0Lard 0.0 135.0Canola oil 10.0 0.0Cholesterol, USP 0.6 3.1
Fatty acid content as determined by gas chromatography (g/kg)n3 PUFAs 2.3 1.5n6 PUFAs 25.5 111.9n6/n3 PUFA ratio 11.1 74.0tained in the rostral section was dissected for Western immunoblotting.
531M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538Lipid extraction and gas chromatography
Approximately 20 mg of frozen frontal cortex tissue from eachmousewas used for fatty acid prole analyses. The frontal cortex was selectedbecause it isminimally affected byMPTP treatment and allowedus to iso-late the effect of the diet on brain fatty acid proles (Bousquet et al., 2008,2011). Weighed brain tissues were homogenized successively with 0.9%NaCl, butylhydroxytoluene-methanol (Sigma, St. Louis, MO) and chloro-form (J.T. Baker, Phillipsburg, NJ) with 22:3n-3 methyl ester as internalstandard (Nu-Chek Prep, Elysian, MN) at a concentration of 500 g/g oftissue. After centrifugation at 2400 g for 7 min, the lower layer was col-lected (Folch et al., 1957). This procedure was repeated and the two ex-tracts were pooled and dried under a stream of N2. Lipid extracts weretransmethylated with methanol:benzene (4:1) and acetyl chloride at98 C for 90 min. After cooling down, 6% K2CO3was added. A 15-min cen-trifugation at 514 g allowed phase separation and the upper layer wascollected in a gas chromatography autosampler vial and capped underN2. Fatty acid methyl ester proles in brain tissue were obtained by cap-illary gas chromatography using a temperature gradient on a HP5890 gaschromatograph (Hewlett Packard, Toronto, Canada) equippedwith aHP-88 capillary column (100 m0.25 mm i.d.0.20 m lm thickness; Agi-lent Technologies) coupled with a ame ionization detector. Heliumwasused as a carrier gas (split ratio 1:80). Fatty acids were identied accord-ing to their retention time, using the following standard mixtures as abasis for comparison: the FAME 37 mix (Supelco Inc., Bellefonte, PA)and the GLC-411 fatty acid mix (Nu-Chek Prep Inc, Elysian, MN), aswell as the following methylated fatty acids C22:5 n6 (Larodan AB,Malm, Sweden) and C22:5 n3 (Supelco Inc., Bellefonte, PA). Amixtureof trans fatty acids containing C18:2 n6 cis/trans (Supelco IncBellefonte, PA), a mixture of cis/trans C18:3 n3 (Supelco Inc Bellefonte,PA), the following Nu-Chek fatty acids: C14:1 trans-9, C16:1 trans-9, andnally isoforms of C18:1 (cis-6, trans-6, cis-11, trans-11: Nu-Chek, andcis-12, cis-13, Supelco Inc.) were also used as a standard mixture.
Visceral fat dissection and adipocyte quantication
Epididymal fat was dissected at sacrice, weighted and immediatelypost-xed in 4% paraformaldehyde pH 7.4 for 24 h. Parafn sections of10 mwere cut using a cryostat. Sections were rst hydrated in ethanoland stained in successive baths of hematoxylin (10 min),water (3 min),70% alcohol and 1% HCl solution and washed with running water. Lith-ium carbonate dips, running water and eosin staining (30 s) were thenperformed prior to alcohol dehydration and coverslipping. Adipocytecircumferences were measured under bright-eld illumination usingStereo Investigator software (MicroBrighteld, Colchester, VT) integrat-edwith an E800Nikonmicroscope (Nikon Canada Inc., Mississauga, ON,Canada). Approximately 80 to 100 cell perimeters per animal werequantied with Neurolucida modeling software (MicroBrighteld).
Paraformaldehyde post-xed sections were processed using stan-dard immunohistochemical procedures as previously described(Bousquet et al., 2008). Briey, sections were incubated overnight at4 C with rabbit anti-tyrosine hydroxylase (TH) (1:5000; Pel-Freez, Rog-ers, AR;) in 0.1% Triton X-100, and 5% normal goat serum in PBS(137 mM NaCl, 2.7 mM KCl, 10 mM sodium phosphate dibasic, 2 mMpotassium phosphate monobasic, pH 7.4). The overnight incubationwas followed by 1 h incubation at room temperature in a PBS solutioncontaining 0.1% Triton X-100, 5% normal goat serum and biotinylatedgoat anti-rabbit IgG (Vector Laboratories, Burlington, ON, Canada;1:1500). An avidinbiotin peroxidase complex (ABC; Vector Laborato-ries, Burlington, ON, Canada), combined with a 3,3-diaminobenzidinetetrahydrochloride (Sigma) immunoreaction, was used to visualize
bound antibodies. Following a reaction of 3,3-diaminobenzidinetetrahydrochloridewith TH, sectionswere counterstainedwith cresyl vi-olet, dehydrated, and coverslipped.
In situ hybridization
The DA transporter (DAT) probe, a 2238-bp fragment, was clonedinto the pBluescript II SK+ plasmid. Linearization was made with Notlenzyme. The antisense probe was synthesized with [35S]UTP and T7RNA polymerase. Brain sections were mounted onto Snowcoat X-traslides (Surgipath, Winnipeg, MB, Canada) and air-dried overnight atroom temperature. Brain sections were prepared for overnight hybrid-ization as previously described (Bousquet et al., 2008; Gibrat et al.,2010). The [35S]UTP-radiolabeled complementary RNA probes wasadded to an hybridization mix (1X Denhart's solution, 10% dextran sul-fate, 50% deionized formamide and 35S coupled 2106 cpm/l probe)and heated at 80 C for 5 min. Each slide was covered with 100 l ofthe hybridization solution and coverslipped. The hybridization was car-ried out overnight on a slidewarmer at 58 C. After hybridization, slideswere rinsed in successive baths of standard salt sodium citrate andRNase A solution before being dehydrated in increasing concentrationsof ethanol. Tissue sections were then exposed to Biomax MR autoradi-ography lms (Kodak, New Haven, CT) for 5 h.
Deffating was performed with four sequential baths of ethanol, twobaths of xylene and three baths of ethanol. Following these steps, slideswere dipped in NTP emulsion (Kodak, New Haven, CT, USA) and pre-pared at 42 C, air-dried for 2 h and stored in the dark for 7 days at 4 C.The emulsion was then developed in D-19 developer (3.5 min) (Kodak,New Haven, CT, USA), rinsed in deionised water and xed (5 min) inRapid Fixer solution (Kodak, New Haven, CT, USA). Slides were rinsedin deionised water for 1 h and then colored. Coloration was performedusing thionine (1 min), followed by water, ethanol dips, an additionalthree ethanol (1 min) and three xylene baths (3 min). Slides were cover-slipped with DPX mounting media.
The loss of dopaminergic neurons was determined by stereologi-cal counts of TH- or DAT-positive cells under bright-eld illumination,as previously described (Bousquet et al., 2008; Gibrat et al., 2010). Toinsure accurate cell count of the area more specically affected by theMPTP administration, corresponding to anterior and medial sections(Jackson-Lewis et al., 1995), every fourth section between antero-posterior levels of2.75 to3.25 was analyzed using the Stereo In-vestigator software (MicroBrighteld) integrated with an E800 Nikonmicroscope (Nikon Canada Inc.). After delineation of the SNpc at lowmagnication (4 objective), a point gridwas overlaid onto each section.Stained cells were countedwith the optical fractionatormethod at highermagnication (20 objective). The counting variables were as follow:distance between counting frames (150 m150 m), counting framesize (100 m) and guard zone thickness (2 m). Cells were countedonly if they did not intersect forbidden lines. The optical fractionatormethod was used to count TH-positive and TH-negative (cresyl violet-positive only) cellular proles (Glaser and Glaser, 2000). Stereologicalcounts were performed blindly by two independent investigators.
High performance liquid chromatography
DA and 3,4-dihydroxyphenylacetic acid (DOPAC) were measuredby HPLC with electrochemical detection, according to a previouslypublished protocol (Bousquet et al., 2011). Extracts of anterior striata(stereotaxic coordinates, AP levels, +1.34 mm to +0.94 mm) werecollected from mouse brain, and 200 l of perchloric acid (0.1 N; Mal-linckrodt Baker, Phillipsburg, NJ) was added to generate a superna-tant. Fifty microliters of supernatant from striatal tissues wasdirectly injected into the HPLC consisting of a Waters 717 plus Auto-
sampler automatic injector, a Waters 1525 Binary Pump equippedwith
CD CDHFD HFDVehicle MPTP
CD CDHFD HFDVehicle MPTP
0 15 30 45 60 900
Time after insulin injection (min)
12 11 11 14
5 5 5 5
24 25 24 25
CD HFD11 11
A B C
D E F G
Fig. 1. HFD induces weight gain and insulin resistance. The high intake in calories from fat (A) led to a signicant weight gain in mice fed the HFD (B). Dissection and weighing of theepididymal fat revealed an increase of this specic area of the visceral white adipose tissue (C). This fat accumulation was visualized and quantied by hematoxylin and eosin stain-ing (D). Photomicrographs of representative animal from vehicle-treated fed the CD (E-upper panel) and the HFD (E-lower panel). The assessment of glucose response following asingle insulin injection showed higher blood glucose levels in obese mice, which persisted 90 min post-injection (F). The AUC quantication corroborated the signicant increase ofblood glucose and conrmed the insulin resistance in mice fed the HFD (G). Insulin levels were increased in HFD-fed mice (H). **=pb0.01; ***=pb0.001 vs CD; ###=pb0.001 vsvehicle on HFD; =pb0.001 vs MPTP-treated on CD. Scale bar in E=100 m. The number of animals per group is indicated in each bar graph.
15 18 15 18 15 18
15 16 15 18
Fig. 2. HFD triggers peripheral immunologic alterations. The two-month dietary treatment induced a signicant increase in blood cells as measured by ow cytometry. Leukocytes(A), granulocytes (B), B and T lymphocytes (C and D) as well as CD4 and CD8 positives cells (E and F) were increased as compared to CD-fed mice. *=pb0.05; **=pb0.01 vs CD.The number of animals per group is indicated in each bar graph.
532 M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538
oxidative stress assessment, carbonylated group within proteinswere derivatized to 2,4-dinitrophenylhydrazone by reaction with2,4-dinitrophenylhydrazine prior to Western immunoblot accordingto the manufacturer's protocol (OxyBlot Protein Oxidation Detection
for post-hoc analyses. Log adjustmentswere used to normalize variances
onocyte chemotactic protein-1 (MCP-1) (B) and the macrophage inammatory protein-1ls in HFD-fed mice. *=pb0.05; **=pb0.01 vs CD. The number of animals per group is in-
533M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538anAtlantis dC18 (3 m)column, aWaters 2465Electrochemical Detector,and a glassy carbon electrode (Waters, Lachine, QC, Canada). The electro-chemical detector was set at 10 nA. The mobile phase consisted of47.8 mM NaH2PO4, 0.9 mM sodium octyl sulfate (Mallinckrodt Baker),0.4 mM EDTA, 2 mM NaCl and 8% MeOH (Mallinckrodt Baker) at pH 2.9and was delivered at 0.8 ml/min. Peaks were identied using the Breezesoftware (Waters). HPLC data were normalized to protein concentra-tions, as determined with a bicinchoninic acid protein assay kit usingBSA as standard (Pierce, Rockford, IL) and according to the manufac-turer's protocol.
Sample preparation and Western immunoblotting
Striatal samples were homogenized in 8 volumes of tris-bufferedsaline (TBS) containing a cocktail of protease inhibitors (Roche, Mis-sissauga, ON, Canada) and phosphatase inhibitors (1 mM tetrasodiumpyrophosphate and 50 mM sodium uoride), sonicated (310 s) andthen centrifuged at 100,000g for 20 min at 4 C. The supernatantwas collected, stored at 80 C and constituted the TBS-soluble in-tracellular and extracellular fraction. The residual pellet was homog-enized in lysis buffer (150 mM NaCl, 10 mM NaH2PO4, 1% (v/v)Triton X-100, 0.5% SDS, and 0.5% sodium deoxycholate) includingthe same protease and phosphatase inhibitors. Following a 20-mincentrifugation (100,000g), supernatants were stored at 80 C togenerate the detergent-soluble fraction which comprises membrane-bound and nuclear proteins (Julien et al., 2010). A bicinchoninic acidprotein assay was utilized to quantify protein concentrations in eachfraction. Twenty micrograms of total protein per sample was added to
17 18 1CD
Fig. 3. HFD induces changes in serum cytokine proles. Interleukin-1 (IL-1) (A), the m(MIP-1) (C) were quantied using a Multiplex ELISA assay and showed increased levedicated in each bar graph.laemmli loading buffer and heated to 95 C for 5 min. Samples werethen subjected to SDS-polyacrylamide (8%) gel electrophoresis. Pro-teins were electroblotted onto 0.45 m Immobilon PVDF membranes(Millipore, Billerica, MA) and blocked in 5% nonfat dry milk and 1%BSA in 1X PBS-tween for 1 h. Membranes were immunoblotted with aprimary antibody rabbit anti-TH (Pel-Freez; 1:5000) to identify dopa-minergic elements, a mouse anti-glial brillary acidic protein (GFAP)(Sigma; 1:10,000) for astrogliosis and a rabbit anti-NFB (Santa CruzBiotechnology, Santa Cruz, CA; 1:1000). For neurotrophic factor assess-ment, a rabbit anti-BDNF (Santa Cruz; 1:1000) and a rabbit anti-GDNF(BioVision San Francisco. CA; 1:1000) were used while a mouse anti-synaptophysin (Chemicon-Millipore; 1:10,000) and a mouse anti-PSD-95 (Neuromab, Davis, CA; 1:5000) were employed to evaluatecomponents of the synapse. Finally, a mouse anti-actin (ABM Inc,Richmond, BC, Canada; 1:10,000) was utilized as a loading control. De-tection with appropriate secondary antibodies, goat anti-rabbit oranti-mouse (Jackson Immunoresearch, West Grove, PA; 1:100,000),followed by the addition of chemiluminescence reagents (KPL, Man-del Scientic, Guelph, ON, Canada), were then performed. Forwhenneeded. Photomicrographswere takenwith aMicrore 1.0 camera(Optronics, Goleta, CA) connected to an E800 Nikon microscope (NikonInc., Qubec, QC, Canada) using the Picture Frame imaging software
Table 2Kit, Millipore, Billerica, MA). Band intensities were quantied using aKODAK Image Station 4000 Digital Imaging System (Molecular Im-aging Software version 4.0.5f7, Eastman Kodak, New Haven, CT).
Statistical analyses and image preparation
Statistical analyses were performed using JMP software version 8.0.2(SAS Institute Inc., Cary, IL) and Prism 4 (GraphPad software, CA). Stu-dent's t-testswere used to analyze food intake,mouseweight, insulin re-sistance test, inammatory cells, cytokines and fatty acid proles. Two-way ANOVAs were performed for all the other experimentations andno signicant interaction between diet and treatment (vehicle orMPTP) were found. Therefore, comparisons were based on one-wayANOVAs andNewmanKeulsmultiple comparison testswere performedPlasmatic levels of cytokines and chemokines 2 months post-HFD
CD HFD pValue
MeanS.E.M. N MeanS.E.M. N
IL-1 117.128.0 12 77.221.6 13 0.2674IL-2 Below detection limitIL-3 Below detection limitIL-4 Below detection limitIL-5 76.719.7 13 84.812.9 14 0.7336IL-6 66.69.2 14 53.398.07 15 0.2907IL-10 Below detection limitIL-12 65.921.7 11 15.810.3 12 0.0559IL-17 Below detection limitIFN 38.27.5 14 46.24.5 15 0.3552TNF 80.514.3 12 Below detection limitGM-CSF 51.212.2 12 57.47.5 14 0.6574RANTES 141.712.1 20 142.49.2 20 0.9674
Values of IL1-, MCP-1 and MIP-1 are presented in Fig. 3.p Value: unpaired Student t-test with Welch's correction.Abbreviations: CD: control diet, GM-CSF: granulocyte macrophage colony stimulatingfactor, HFD: high-fat diet, IFN: interferon, IL: interleukin, TNF: tumor necrosisfactor.
ATotal n-3 PUFAs
n-3:n-6 PUFA ratio
Total n-6 PUFAs
Fig. 4. HFD alters brain fatty acid proles. Frontal cortex fatty acid proles were per-formed by gas chromatography and revealed increased levels in HFD-fed mice inn6 PUFA linoleic acid (LA) (A), docosatetraenoic acid (DTA) (B), docosapentaenoicacid (DPA) (C), arachidonic acid (ARA) (D) as well as in total n6 PUFAs (E). n3PUFA docosahexaenoic acid (DHA) (F) and total n3 PUFAs (G) levels remained sim-ilar between dietary treatments. These cerebral fatty acid changes led to a signicantdecrease in the n3:n6 PUFA ratio (H). *=pb0.05; **=pb0.01; ***=pb0.001 vsCD. The number of animals per group is indicated in each bar graph.
534 M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538(Microbrighteld, Colchester, VT). All images were prepared for illustra-tion with Adobe Photoshop 7.0.
Impact of the HFD on the peripheral system
As a result of the HFD and increased calorie intake (Fig. 1A; Student's ttest; F(groups)1,30=96.71; pb0.001),mice signicantly gainedweight asevidenced by a 41% increase in the HFD group compared to CD-fed mice(Fig. 1B; Student's t test; F(groups)1,47=151.32; pb0.001). Consequentlyto the weight gain, post-mortem dissection of the epididymal fat padrevealed an increased accumulation of white adipose tissue (Fig. 1C;ANOVA; F(groups)3,52=37.68; pb0.001) combined to an increase insize of adipocytes (larger circumference) (Fig. 1DE; ANOVA; F(groups)3,16=49.17; pb0.001). The high intake in fat also triggered insu-lin resistance (Fig. 1F and G; Student's t test; F(groups)1,42=44.48;pb0.001), which was further accompanied by increased levels of plas-matic insulin (Fig. 1H; Student's t test; F(groups)1,20=17.92; pb0.01).No signicant differences between MPTP-treated mice on CD or HFDwere found for insulin quantication 14 days post-MPTP (data notshown).
Prior toMPTP administration, several components relating to system-ic inammation were assessed to evaluate the effects of the HFD on theimmune system. Flow cytometry analyses revealed an increased numberof overall leukocytes (Fig. 2A; Student's t test; F(groups)1,31=10.65;pb0.01). Granulocytes (Fig. 2B; Student's t test; F(groups)1,31=7.69;pb0.01), as well as B and T lymphocytes (Fig. 2CD; Student's t test; F(groups)1,3129=5.45, 7.17; pb0.05), including CD4 (T helper) andCD8 (T cytotoxic) positive cells (Fig. 2EF; Student's t test; F(groups)1,31=7.24, 6.78; pb0.05), were signicantly increased inmice fed the HFD. Two months following the beginning of the diet, 16cytokines were examined using a Multiplex ELISA assay and the high-fat intake led to an increase in IL-1 (Fig. 3A; Student's t test; F(groups)1,33=4.95; pb0.05), MCP-1 (Fig. 3B; Student's t test; F(groups)1,22=7.88; pb0.01) and MIP-1 (Fig. 3C; Student's t test; F(groups)1,22=5.13; pb0.05). IL-1, -2, -3, -4, -5, -6, -10, -12, -17,IFN, TNF, GM-CSF and RANTES were also quantied but remainedsimilar between groups or under the detection limit (Table 2). Plasmasamples were also analyzed 1 h following the last MPTP injection aswell as 5 and 14 days post-MPTP administration. Although no signi-cant differences were observed for the 2 last time points, mice fed theHFD displayed signicantly higher plasma levels of IL-1 than micefed the CD, 1 h post-MPTP (data not shown).
Brain fatty acid proles following high-fat intake
Cerebral fatty acids were evaluated in the frontal cortex. The HFDcontained elevated n6 PUFAs and saturated fat compared to the CDand its consumption rapidly led to insulin resistance in C57BL/6 mice(Lucas et al., 2011; Winzell et al., 2011). As previously shown by ourgroup (Julien et al., 2010), the same HFD formula over a period of9 months induces alterations of brain fatty acid proles, such as a de-crease in the n3:n6 PUFA ratio (Julien et al., 2010). Here, the 2-month dietary treatment induced an increase in levels of total (Fig. 4E;Student's t test; F(groups)1,46=23.24; pb0.001) and individual n6PUFAs, such as linoleic (LA; C18:2 n6, Fig. 4A; Student's t test;F(groups)1,45=21.33; pb0.001), docosatetraenoic (DTA; C22:4 n6,Fig. 4B; Student's t test; F(groups)1,46=32.59; pb0.001), docosapen-taenoic (DPA; C22:5 n6, Fig. 4C; Student's t test; F(groups)1,46=5.11;pb0.05) and arachidonic acids (ARA; C20:4 n6, Fig. 4D; Student'st test; F(groups)1,46=11.19; pb0.01) in the frontal cortex of animalssubjected to the HFD. Levels of docosahexaenoic acid (DHA; C22:6 n3) as well as total n3 PUFAs (Fig. 4FG) remained similar be-
tween mice on either diet. These modications in brain fatty acids
led to an overall 12% decrease in the n3:n6 PUFA ratio (Fig. 4H;Student's t test; F(groups)1,44=115.46; pb0.001).
Impact of HFD on MPTP-induced dopaminergic degeneration
The subacuteMPTP regimen employed here consistently produces asignicant nigral dopaminergic neuronal degeneration of nearly 30%,which is accompanied by a 75% decrease in striatal DA levels (Bousquetet al., 2008; Gibrat et al., 2009). Nigral dopaminergic neuronswere eval-uated using TH- and DAT labeling. As quantied by stereologicalcell counts, MPTP treated-mice depicted a reduction in cell densityof TH- (Fig. 5AE; ANOVA; F(groups)3,37=4.43; pb0.05 in MPTPmice on HFD vs vehicle groups) and DAT-positive cells (Fig. 5FJ;ANOVA; F(groups)3,39=4.38; pb0.05 in MPTP mice on CD and HFD vsvehicle groups). Striatal DA and DOPAC contents, as assessed by HPLC,were decreased in MPTP-treated mice as compared to mice treatedwith saline (Fig. 6AB; ANOVA F(groupes)3,43=23.52; pb0.001). Thetwo-month dietary treatment potentiated the DA depletion as themice fed the HFD were characterized by a 32% lower level of striatalDA after the MPTP insult compared to mice fed the CD (Student t test;F(groups)1,22=4.37; pb0.05 MPTP CD vs MPTP HFD). Interestingly,Western blot quantication of TH protein levels in the striatum, asses-sing dopaminergic terminals, also revealed an exacerbated effect ofthe neurotoxinMPTP inmice fed the HFD (Fig. 6CD). Indeed, TH levelswere decreased by 43% and 58% in MPTP-treated mice on CD and HFD,respectively (ANOVA; F(groups)3,44=52.23; pb0.001 in MPTPmice on
CD and HFD vs vehicle groups; pb0.05 MPTP CD vs MPTP HFD). Two-way ANOVA analyses conrmed the effect of MPTP on dopaminergicmarkers utilized in this study but could not detect the effect of the die-tary treatment.
Underlying mechanisms for the increased vulnerability of striataldopaminergic terminals
In order to identify possible molecular mechanisms associated withthe exacerbation of MPTP-induced striatal dopaminergic depletion inHFDmice,Western blot analyseswere performed for neuroinammatorymolecules, neurotrophic factors, oxidized proteins and synaptic compo-nents (Table 3). These mechanisms were specically selected becauseof their contribution to PD pathophysiology and the probable capacityof HFD to act via these pathways (see Discussion for details). However,no signicant differences were observed for any of these parameters inresponse toHFD orMPTP administration,with the exception of the astro-glial response, where an increase in GFAP protein levels was observed inMPTP-treated mice which was, however, independent of the dietarytreatment (Table 3).
Based on our previouswork demonstrating the benecial effects of an3 PUFA-enriched diet in the MPTP mouse model (Bousquet et al.,2008), we sought to investigate the consequences of a converse
535M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538Fig. 5. MPTP treatment leads to nigral dopaminergic degeneration. The state of the dophydroxylase (TH) (A to E) and in situ hybridization for the dopamine transporter (DAT)positive cells as pointed by the black arrows. Stereological counts of either marker revehicle-treated animals on either diet. *=pb0.05. Scale bar in B applies for C to E=300 m
per group is indicated in each bar graph.ergic system within the SNpc was analyzed using immunohistochemistry for tyrosineo J). The higher magnication of the photomicrograph in the inset (G) illustrates DAT-a decreased in the total number of nigral cells in MPTP-treated mice compared to ve-d scale bar in G applies for H to J=400 m (inset in G=25 m). The number of animals
536 M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538nutritional behavior, the HFD, in a mouse model of parkinsonism. Thecurrent experiment explored both the cerebral consequences followingthe HFD andMPTP treatment as well as the peripheral corollaries of theHFD including metabolic disturbances and the inammatory response.Findings from this study revealed a more notable DA reduction andTH-positive ber degeneration in the striatum of MPTP-treated micefed a HFD for 2 months, despite comparable nigral neuronal cellcount. The high intake in calories from fat caused a weight gain, whichwas accompanied by insulin resistance, increased circulating immunecells and elevated levels of cytokines as well as chemokines. Our datathus suggest that the peripheral consequences of diet-induced obesityare associated with an enhanced vulnerability of dopaminergic termi-nals to MPTP in mice exposed to HFD.
The present observations are in accordance with results from twostudies performed in different animal models of parkinsonism (Choiet al., 2005; Morris et al., 2010). The study conducted by Choi et al. in-cluded two distinct MPTP regimens, 4 subcutaneous (s.c.) injections at2 h interval of a low(5 mg/kg) or a high (15 mg/kg) dose. An exacerbatedeffect of the 8-week high-fat intake was only found in mice exposed tolow doses of MPTP (Choi et al., 2005). HFD was also investigated in the6-hydroxydopamine-lesioned (6-OHDA) rat model of PD (Morris et al.,2010). As observed with s.c. or i.p. administration of MPTP, 6-OHDA-induced DA depletions in the SNpc and striatum were increased in ratsfed the HFD, which correlated with the homeostatic model assessmentof insulin resistance (HOMA-IR) as well as with the adiposity (Morris
Fig. 6. HFD exacerbates the detrimental effects of MPTP in the striatum. MPTP-treated mice das quantied by HPLC and to a greater extent in mice fed the HFD. Western blot analyses of sas compared to MPTP-treated mice fed CD (C and D). *=pb0.05; ***=pb0.001. The numbet al., 2010). Here we observed discrepant outcomes between the nigraland striatal compartments; the dopaminergic terminals of HFD-fedmice were more profoundly affected by the MPTP treatment than thenigral cell bodies, suggesting that terminals are more susceptible tocombined effects of MPTP and HFD. If this nding can be extrapolatedto humans, the prevalent high consumption of fat may increase the vul-nerability of the dopaminergic system to exogenous insult and precipi-tates the onset of the pathology.
High-fat intake, which can lead to excess visceral adiposity, is wellknown to result in metabolic disorders such as insulin and glucose per-turbations, increased systemic inammation, hypertension and dyslipi-demia (Scaglione et al., 2010). Low-grade chronic inammatory state,caused by HFD, is also thought to play a critical role in the pathogenesisof metabolic syndrome. Here, we observed an increase of inammatorycells such as leukocytes as well as cytokines and chemokines, in accor-dance with other studies performed in rodents fed a HFD and also inthe blood of diet-induced obese individuals (Nieman et al., 1999; Strisselet al., 2010;Wu et al., 2007). Interestingly, total leukocyte count stronglycorrelates with BMI in humans (Nieman et al., 1999). Furthermore, thechemokine MCP-1, which plays an important role in recruiting macro-phages to adipose tissue, is also increased in the blood and visceral fatof genetically-induced obese mice (ob/ob) (Sartipy and Loskutoff,2003). Here, an increased in plasmatic IL-1 was observed inMPTP-treated mice fed the HFD 1 h following the last MPTP injec-tion. This increase of IL-1 could have, in part, contributed to generate
isplayed a signicant decrease in striatal DA (A) and in one of its metabolite DOPAC (B)triatal TH levels showed a greater loss of TH proteins in MPTP-treated mice fed the HFDer of animals per group is indicated in each bar graph.
537M. Bousquet et al. / Neurobiology of Disease 45 (2012) 529538a pro-inammatory environment within the brain, thereby increasingthe vulnerability of the dopaminergic terminals. Although the involve-ment of inammation to PD pathogenesis remains unclear, its systemicand cerebral occurrence has been conrmed in several PD animalmodelsas well as in patients (Hunot et al., 1999; Kurkowska-Jastrzebska et al.,1999). For instance, increased levels of several cytokines and chemokinesincluding IL-6, IL-1 and MCP-1 are found in the blood, cerebrospinaluid and/or brain parenchyma samples from PD patients (Reale et al.,2009).While an overall depletion in circulating lymphocytes is observed,an elevated number of activated lymphocytes (CD4+CD25+) has alsobeen found in the blood of PD patients (Bas et al., 2001; Hisanaga et al.,2001). In addition, inltrating lymphocytes have been observed withinthe brain parenchyma of PD patients (Hunot et al., 1999). Taken togeth-er, the intensication of the peripheral inammatory response caused byhigh intake in calories from fat, could in part explain the increased vul-
Table 3Mechanisms underlying the striatal MPTP-induced degeneration exacerbated by theHFD
Markers Vehicle MPTP
CD HFD CD HFD
Neuroinammatory responseGFAP 1660111 1545178 2812148 2673119
NFB 3679171 3567172 3588142 3508208
2080140 2040167 2019198 2235151
Neurotrophic factorspro-BDNF 267.843.7 296.937.7 277.123.5 283.618.3BDNF 15.92.7 17.93.2 14.81.3 18.11.6GDNF 375.935.0 359.728.6 360.720.6 383.925.9
Synaptic proteinsSynaptophysin 4622216 4741233 4367148 4435152PSD-95 4354312 3871337 4083259 4145240
Levels are expressed as meanS.E.M.Abbreviations: BDNF: brain-derived neurotrophic factor, CD: control diet, GDNF: glialcell line-derived neurotrophic factor, GFAP: glial brillary acidic protein, HFD: high-fat diet, NFB: nuclear factor kappa B, PSD-95: post-synaptic density. =pb0.001 Vs Vehicle on CD and HFD.nerability to MPTP of mice fed the HFD compared to MPTP-treatedmice on CD. However, the type of MPTP regimen employed here createsa modest inammatory response, with limited microglial activationpeaks which decrease to control levels 24 h after the last MPTP injection(Drouin-Ouellet et al., in press). Nevertheless, using GFAP immunoblot-ting, we detected a strong astroglial response persisting up to 2 weekspost-MPTP treatment as previously observed (Bousquet et al., 2011)but the dietary intake of fat did not alter GFAP immunoreactivity(Table 3). Therefore, although the HFD clearly induced an inammatoryresponse in the periphery, it remains unclear whether a coinciding neu-roinammation played a role in the amplied vulnerability toMPTP seenhere. It could therefore be postulated that an increase in circulating im-mune cells and cytokine expression could have increased the bloodbrain barrier permeability, thereby generating a temporary inltrationof inammatory cells in MPTP-treated mice fed the HFD (Nerurkar etal., 2011). The increased levels in circulating cytokines and chemokinescould also have directly affected neuronal signaling cascades (Banks,2005; Laamme and Rivest, 1999), thus exacerbating the dopaminergicterminal depletion.
Previous studies have identied several other cerebral effects of aHFD in rodents that may underlie the exacerbated effects of the MPTPtreatment observed here. For example, the effect of low MPTP doseadministered subcutaneously to mice fed a HFD (sacriced 7 dayspost-MPTP) was in part explained via increased nitrogen speciesand phosphorylated neuronal nitric oxide synthase in the striatumand SNpc of mice (Choi et al., 2005). A number of evidence has alsounveiled the effect of PUFAs on neurotrophic factors (Bousquet et al.,2009; Rao et al., 2007). Increased fat intake has been associatedwith de-creased levels of BDNF with impaired hippocampal neurogenesis inadult male rats (Park et al., 2010). Finally, increased protein carbonylswere reported in the hippocampus of 20-month old mice fed a HFDfor 4 months (Bruce-Keller et al., 2010;Morrison et al., 2010). However,as summarized in Table 3, we did not detect changes in striatal neuro-trophic factors or oxidative damage by quantication of protein carbonylsthroughWestern blot assessment. In addition, no differences in pre- andpost-synaptic components were noted as previously reported in an ani-malmodel of Alzheimer's disease fed aHFD for 9 monthswhere an aggra-vation of amyloid- and tau pathologies were observed (Table 3) (Julienet al., 2010).
One the other hand, the increase in n6 PUFAs, especially ARA, result-ing from theHFDmayhave also contributed to the results presented here.Indeed, ARA, via cyclooxygenase and lipoxygenase action, is the precursorof several bioactive eicosanoids such as prostaglandins, leukotrienes andthromboxanes leading to a proinammatory environment (Funk, 2001).Cascades leading to eicosanoid production originating from PUFAs arepresent in neurological disorders including PD (Teismann et al., 2003).In patients, although no overall differences in fatty acid proles werenoted, patients taking levodopa and experiencing motor complicationshad higher levels of cerebral ARA compared to individuals devoid ofthese medication-induced side effects and to age-matched controls(Julien et al., 2006). In agreement with this, dietary n3 PUFAs, whichalso lead to a decrease of brain ARA, is neuroprotective in the sameMPTP model. This supports a mechanistic relationship between cerebralPUFAs and their metabolic products with PD pathogenesis.
The peripheral perturbations caused by a HFD are well established,whereas the outcomes of these unhealthy diets on the brain are less un-derstood. Taken together, the present data suggest that the detrimentalconsequences of high intake in calories from fat translate into a reducedcapacity of the brain to cope with a neurodegenerative stress. Exposureto HFD, and consequently obesity, could confer a greater susceptibilityto environmental toxins and accelerate PD pathogenesis. Further investi-gations are needed to ascertain the direct contribution of systemic im-pairments, notably insulin resistance and increased immune response,to PD and other neurodegenerative diseases and to ultimately determinewhether HFD is a modiable risk factor for PD.
This studywas supported by the Parkinson Society Canada and by theInstitute of Nutrition, Metabolism and Diabetes (INMD) of the CanadianInstitutes of Health Research (CIHR) and the Canada Foundation for Inno-vation (FC and FC). MB and MV were supported by a CIHR scholarshipand IS was supported by an Industrial Innovation PhD Scholarship fromCRSNG/FQRNT.
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High-fat diet exacerbates MPTP-induced dopaminergic degeneration in miceIntroductionMaterials and methodsExperimental design, diet and MPTP treatmentInsulin sensitivity assessment and plasmatic insulin concentrationFlow cytometry analyses and Q-plex cytokine assayTissue preparation for post-mortem analysesLipid extraction and gas chromatographyVisceral fat dissection and adipocyte quantificationImmunohistochemistryIn situ hybridizationStereological quantificationHigh performance liquid chromatographySample preparation and Western immunoblottingStatistical analyses and image preparation
ResultsImpact of the HFD on the peripheral systemBrain fatty acid profiles following high-fat intakeImpact of HFD on MPTP-induced dopaminergic degenerationUnderlying mechanisms for the increased vulnerability of striatal dopaminergic terminals