Pathophysiological Changes in the Enteric Nervous System of Rotenone-Exposed Mice as Early Radiological Markers for Parkinson's Disease.

Parkinson's disease (PD) is known to involve the peripheral nervous system (PNS) and the enteric nervous system (ENS). Functional changes in PNS and ENS appear early in the course of the disease and are responsible for some of the non-motor symptoms observed in PD patients like constipation, that can precede the appearance of motor symptoms by years. Here we analyzed the effect of the pesticide rotenone, a mitochondrial Complex I inhibitor, on the function and neuronal composition of the ENS by measuring intestinal contractility in a tissue bath and by analyzing related protein expression. Our results show that rotenone changes the normal physiological response of the intestine to carbachol, dopamine and electric field stimulation (EFS). Changes in the reaction to EFS seem to be related to the reduction in the cholinergic input but also related to the noradrenergic input, as suggested by the non-adrenergic non-cholinergic (NANC) reaction to the EFS in rotenone-exposed mice. The magnitude and direction of these alterations varies between intestinal regions and exposure times and is associated with an early up-regulation of dopaminergic, cholinergic and adrenergic receptors and an irregular reduction in the amount of enteric neurons in rotenone-exposed mice. The early appearance of these alterations, that start occurring before the substantia nigra is affected in this mouse model, suggests that these alterations could be also observed in patients before the onset of motor symptoms and makes them ideal potential candidates to be used as radiological markers for the detection of Parkinson's disease in its early stages.

Overexpression of Wild-Type Human Alpha-Synuclein Causes Metabolism Abnormalities in Thy1-aSYN Transgenic Mice.

Parkinson's disease is a progressive neurodegenerative disorder characterized by loss of dopaminergic neurons, pathological accumulation of alpha-synuclein and motor symptoms, but also by non-motor symptoms. Metabolic abnormalities including body weight loss have been reported in patients and could precede by several years the emergence of classical motor manifestations. However, our understanding of the pathophysiological mechanisms underlying body weight loss in PD is limited. The present study investigated the links between alpha-synuclein accumulation and energy metabolism in transgenic mice overexpressing Human wild-type (WT) alpha-synuclein under the Thy1 promoter (Thy1-aSYN mice). Results showed that Thy1-aSYN mice gained less body weight throughout life than WT mice, with significant difference observed from 3 months of age. Body composition analysis of 6-month-old transgenic animals showed that body mass loss was due to lower adiposity. Thy1-aSYN mice displayed lower food consumption, increased spontaneous activity, as well as a reduced energy expenditure compared to control mice. While no significant change in glucose or insulin responses were observed, Thy1-aSYN mice had significantly lower plasmatic levels of insulin and leptin than control animals. Moreover, the pathological accumulation of alpha-synuclein in the hypothalamus of 6-month-old Thy1-aSYN mice was associated with a down-regulation of the phosphorylated active form of the signal transducer and activator of transcription 3 (STAT3) and of Rictor (the mTORC2 signaling pathway), known to couple hormonal signals with the maintenance of metabolic and energy homeostasis. Collectively, our results suggest that (i) metabolic alterations are an important phenotype of alpha-synuclein overexpression in mice and that (ii) impaired STAT3 activation and mTORC2 levels in the hypothalamus may underlie the disruption of feeding regulation and energy metabolism in Thy1-aSYN mice.

Is there a role for ghrelin in central dopaminergic systems? Focus on nigrostriatal and mesocorticolimbic pathways.

The gastro-intestinal peptide ghrelin has been assigned many functions. These include appetite regulation, energy metabolism, glucose homeostasis, intestinal motility, anxiety, memory or neuroprotection. In the last decade, this pleiotropic peptide has been proposed as a therapeutic agent in gastroparesis for diabetes and in cachexia for cancer. Ghrelin and its receptor, which is expressed throughout the brain, play an important role in motivation and reward. Ghrelin finely modulates the mesencephalic dopaminergic signaling and is thus currently studied in pathological conditions including dopamine-related disorders. Dopamine regulates motivated behaviors, modulating reward processes, emotions and motor functions to enable the survival of individuals and species. Numerous dopamine-related disorders including Parkinson's disease or eating disorders like anorexia nervosa involve altered ghrelin levels. However, despite the growing interest for ghrelin in these pathological conditions, global integrative studies investigating its role in brain dopaminergic structures are still lacking. In this review, we discuss the role of ghrelin on dopaminergic neurons and its relevance in the search for new therapeutics for Parkinson's disease- and anorexia nervosa-related dopamine deficits.

Involvement of the immune system, endocytosis and EIF2 signaling in both genetically determined and sporadic forms of Parkinson's disease.

The leucine-rich repeat kinase 2 (LRRK2) G2019S mutation is a common genetic cause of Parkinson's disease (PD). Although patients with sporadic PD and individuals with LRRK2-linked PD display the classical PD phenotype, it is not known whether or not the same biological pathways are deregulated in each context. By using transcriptome profiling, we investigated the deregulation of various biological pathways in a total of 47 peripheral blood mononuclear cell (PBMC) samples from patients with sporadic PD, patients heterozygous for the LRRK2 G2019S mutation compared to healthy controls. We found that the deregulation patterns were indeed similar in PBMCs obtained from patients with sporadic PD and from LRRK2 G2019S carriers, with dysfunctions in mitochondrial pathways, cell survival signaling, cancerization, endocytosis signaling and iron metabolism. Analysis of our PBMC data and other publicly available transcriptome datasets (for whole blood samples) showed that deregulation of the immune system, endocytosis and eukaryotic initiation factor 2 (EIF2) signaling are the main features of transcriptome profiles in PD (since they are also present in the transcriptome of dopaminergic neurons from patients). Transcriptome analysis of PBMCs is thus valuable for (i) characterizing the pathophysiological pathways shared by genetic and sporadic forms of PD and (ii) identifying potential biomarkers and therapeutic targets. This minimally invasive approach opens up tremendous perspectives for better diagnosis and therapy of neurodegenerative diseases because it can be applied from the earliest stages of the disease onwards.

Translation initiator EIF4G1 mutations in familial Parkinson disease.

Genome-wide analysis of a multi-incident family with autosomal-dominant parkinsonism has implicated a locus on chromosomal region 3q26-q28. Linkage and disease segregation is explained by a missense mutation c.3614G>A (p.Arg1205His) in eukaryotic translation initiation factor 4-gamma (EIF4G1). Subsequent sequence and genotype analysis identified EIF4G1 c.1505C>T (p.Ala502Val), c.2056G>T (p.Gly686Cys), c.3490A>C (p.Ser1164Arg), c.3589C>T (p.Arg1197Trp) and c.3614G>A (p.Arg1205His) substitutions in affected subjects with familial parkinsonism and idiopathic Lewy body disease but not in control subjects. Despite different countries of origin, persons with EIF4G1 c.1505C>T (p.Ala502Val) or c.3614G>A (p.Arg1205His) mutations appear to share haplotypes consistent with ancestral founders. eIF4G1 p.Ala502Val and p.Arg1205His disrupt eIF4E or eIF3e binding, although the wild-type protein does not, and render mutant cells more vulnerable to reactive oxidative species. EIF4G1 mutations implicate mRNA translation initiation in familial parkinsonism and highlight a convergent pathway for monogenic, toxin and perhaps virally-induced Parkinson disease.

Transcriptional profile of Parkinson blood mononuclear cells with LRRK2 mutation.

To gain insight into systemic molecular events associated with an age-related neurodegenerative disorder, we compared gene expression patterns in peripheral blood mononuclear cells (PBMCs) sampled from elderly, healthy controls and from Parkinson's disease (PD) patients carrying the most frequently found mutation of the LRRK2 gene (G2019S). A transcriptomic approach enabled us to detect differentially expressed genes and revealed perturbations of pathways known to be involved in PD-related neurodegeneration: the ubiquitin-proteasome system, the mitochondrial oxidation system, inflammation, axonal guidance, calcium signalling and apoptosis. Moreover, alterations of the MAP kinase pathway, the actin cytoskeleton, the ephrin receptor system and vesicular transport - all recently associated with the LRRK2 G2019S mutation pathogenesis - were noted. Furthermore, we acquired new evidences of dysregulation in leukocyte extravasation signalling and immune system pathways in PD. These data show that the G2019S mutation affects the entire body and highlight some of the molecular events observed in the brain. This PBMC transcriptomic approach could be used to better understand neurodegeneration in PD and decipher new pathogenetic mechanisms, even at early stages of the disease.

Differing short-term neuroprotective effects of the fibrates fenofibrate and bezafibrate in MPTP and 6-OHDA experimental models of Parkinson's disease.

Earlier study from our group indicated that the peroxisome proliferator-activated receptor-alpha agonist fenofibrate prevents 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced dopaminergic cell loss in C57Bl/6 mice. Our objective was to determine whether or not fibratescan improve motor activity in two experimental models of Parkinson's disease: the MPTP C57Bl/6 mouse and the 6-hydroxydopamine (6-OHDA) Wistar rat. Six groups of mice were set up: sham, sham-fenofibrate, sham-bezafibrate, MPTP, MPTP-fenofibrate and MPTP-bezafibrate. Mice were fed a diet containing 0.2% fenofibrate, 0.2% bezafibrate or no hypolipidaemic agent for 2 weeks. Four groups of rats were set up: sham, sham-fenofibrate, 6-OHDA and 6-OHDA-fenofibrate. Rats were fed a diet containing 0.2% fenofibrate or no hypolipidaemic agent for 4 weeks. In mice, motor activity was quantified using actimetry. Nine parameters were recorded. The results were analyzed with a mixed linear model. In rats, behavioural sensitization was studied with repetitive injections of apomorphine. All the actimetry parameters indicated a decrease of locomotion the day after MPTP injections and eight parameters improved in MPTP mice treated with fenofibrate or bezafibrate. The apomorphine-induced rotation behaviour mildly decreased in 6-OHDA rats treated with fenofibrate, but behavioural sensitization was unchanged. The 6-OHDA and MPTP compounds have different toxicity mechanisms, which could explain why we did not observe the same effect in 6-OHDA rats as in MPTP mice. These data suggest that the protective effect of fibrates can be carried through inhibition of inflammation rather than oxidative stress.

Impact of prenatal stress on neuroendocrine programming.

Since life emerged on the Earth, the development of efficient strategies to cope with sudden and/or permanent changes of the environment has been virtually the unique goal pursued by every organism in order to ensure its survival and thus perpetuate the species. In this view, evolution has selected tightly regulated processes aimed at maintaining stability among internal parameters despite external changes, a process termed homeostasis. Such an internal equilibrium relies quite heavily on three interrelated physiological systems: the nervous, immune, and endocrine systems, which function as a permanently activated watching network, communicating by the mean of specialized molecules: neurotransmitters, cytokines, and hormones or neurohormones. Potential threats to homeostasis might occur as early as during in utero life, potentially leaving a lasting mark on the developing organism. Indeed, environmental factors exert early-life influences on the structural and functional development of individuals, giving rise to changes that can persist throughout life. This organizational phenomenon, encompassing prenatal environmental events, altered fetal growth, and development of long-term pathophysiology, has been named early-life programming. Over the past decade, increased scientific activities have been devoted to deciphering the obvious link between states of maternal stress and the behavioral, cognitive, emotional, and physiological reactivity of the progeny. This growing interest has been driven by the discovery of a tight relationship between prenatal stress and development of short- and long-term health disorders. Among factors susceptible of contributing to such a deleterious programming, nutrients and hormones, especially steroid hormones, are considered as powerful mediators of the fetal organization since they readily cross the placental barrier. In particular, variations in circulating maternal glucocorticoids are known to impact this programming strongly, notably when hormonal surges occur during sensitive periods of development, so-called developmental windows of vulnerability. Stressful events occurring during the perinatal period may impinge on various aspects of the neuroendocrine programming, subsequently amending the offspring's growth, metabolism, sexual maturation, stress responses, and immune system. Such prenatal stress-induced modifications of the phenotypic plasticity of the progeny might ultimately result in the development of long-term diseases, from metabolic syndromes to psychiatric disorders. Yet, we would like to consider the outcome of this neuroendocrine programming from an evolutionary perspective. Early stressful events during gestation might indeed shape internal parameters of the developing organisms in order to adapt the progeny to its everyday environment and thus contribute to an increased reproductive success, or fitness, of the species. Moreover, parental care, adoption, or enriched environments after birth have been shown to reverse negative long-term consequences of a disturbed gestational environment. In this view, considering the higher potential for neonatal plasticity within the brain in human beings as compared to other species, long-term consequences of prenatal stress might not be as inexorable as suggested in animal-based studies published to date.

Prenatal stress has pro-inflammatory consequences on the immune system in adult rats.

The in utero environment is critical for initiating the ontogeny of several physiological systems, including the immune surveillance. Yet, little is known about adverse early experiences on the offspring's immunity and vulnerability to disease. The present work aimed at investigating the impact of restraint prenatal stress (PS) on the development and responsiveness of in vitro and in vivo cellular and humoral immunity of male progeny aged 7 weeks and 6 months. In adult 6-month-old rats, we detected increased circulating CD8(+)-expressing and NK cells in PS rats as compared to controls, associated with higher mRNA expression of IFN-gamma. In addition, in vitro stimulation with phytohemagglutinin-A induced an increase in both the proliferation of T lymphocytes and the secretion of IFN-gamma in PS rats. Interestingly, these alterations were undetectable in younger PS rats (7-week old), except for a slight increase in the mRNA expression of several pro-inflammatory cytokines in peripheral blood mononuclear cells. Moreover, in vivo neutralization of IFN-gamma in young rats had no effects in PS group. In conclusion, we report for the first time long-lasting pro-inflammatory consequences of PS in rats.

Prenatal stress alters Fos protein expression in hippocampus and locus coeruleus stress-related brain structures.

Prenatal stress (PS) durably influences responses of rats from birth throughout life by inducing deficits of the hypothalamo-pituitary-adrenal (HPA) axis feedback. The neuronal mechanisms sustaining such alterations are still unknown. The purpose of the present study was to determine whether in PS and control rats, the exposure to a mild stressor differentially induces Fos protein in hippocampus and locus coeruleus, brain areas involved in the feedback control of the HPA axis. Moreover, Fos protein expression was also evaluated in the hypothalamic paraventricular nucleus (PVN) that reflect the magnitude of the hormonal response to stress. Basal plasma corticosterone levels were not different between the groups, while, PS rats exhibited higher number of Fos-immunoreactive neurons than controls, in the hippocampus and locus coeruleus in basal condition. A higher basal expression of a marker of GABAergic synapses, the vGAT, was also observed in the hypothalamus of PS rats. Fifteen minutes after the end of the exposure to the open arm of the elevated plus-maze (mild stress) a similar increased plasma corticosterone levels was observed in both groups in parallel with an increased number of Fos-immunoreactive neurons in the PVN. Return to basal plasma corticosterone values was delayed only in the PS rats. On the contrary, after stress, no changes in Fos-immunoreactivity were observed in the hippocampus and locus coeruleus of PS rats compared to basal condition. After stress, only PS rats presented an elevation of the number of activated catecholaminergic neurons in the locus coeruleus. In conclusion, these results suggest for the first time that PS alters the neuronal activation of hippocampus and locus coeruleus implicated in the feedback mechanism of the HPA axis. These data give anatomical substrates to sustain the HPA axis hyperactivity classically described in PS rats after stress exposure.