Géraldine Petit

Transfer of human α-synuclein from the olfactory bulb to interconnected brain regions in mice.

Abstractα-Synuclein (α-syn) is a protein prevalent in neural tissue and known to undergo axonal transport. Intracellular α-syn aggregates are a hallmark of Parkinson’s disease (PD). Braak and collaborators have suggested that in people who are destined to eventually develop PD, α-syn aggregate pathology progresses following a stereotypic pattern, starting in the olfactory bulb (OB) and the gut. α-Synuclein aggregates are postulated to spread to interconnected brain regions over several years. Thus, propagation of the pathology via neural pathways can potentially explain how α-syn aggregates spread in PD. We have now studied if α-syn can transfer from the OB to other brain structures through neural connections, by injecting different molecular species of human α-syn (monomers, oligomers, fibrils) into the OB of wild-type mice. We found that non-fibrillar human α-syn is taken up very quickly by OB neurons. Within minutes to hours, it is also found in neurons in structures connected to the OB. Conversely, when we injected bovine serum albumin used as a control protein, we found that it does not diffuse beyond the OB, is rarely taken up by OB cells, and does not transfer to other structures. Taken together, our results show that OB cells readily take up α-syn, and that monomeric and oligomeric, but not fibrillar, forms of α-syn are rapidly transferred to interconnected structures within the timeframe we explored. Our results support the idea that α-syn can transfer along neural pathways and thereby contribute to the progression of the α-syn-related pathology.

Review: The future of cell therapies and brain repair: Parkinson's disease leads the way

During the past 40 years brain tissue grafting techniques have been used both to study fundamental neurobiological questions and to treat neurological diseases. Motor symptoms of Parkinsons disease are largely due to degeneration of midbrain dopamine neurones. Because the nigrostriatal pathology is relatively focused anatomically, Parkinsons disease is considered the ideal candidate for brain repair by neural grafting and dopamine neurone transplantation for it has led the way in the neural transplantation research field. In this mini‐review, we briefly highlight four important areas of development. First, we describe marked functional benefits up to 18 years after transplantation surgery in patients with Parkinsons disease. This is proof‐of‐principle that, using optimal techniques and patient selection, grafted dopamine neurones can work in humans and the duration of the benefit exceeds placebo effects associated with surgery. Second, we describe that eventually protein aggregates containing α‐synuclein, identical to Lewy bodies, develop inside foetal dopamine neurones transplanted to patients with Parkinsons disease. This gives clues about pathogenetic mechanisms operating in Parkinsons disease, and also raises the question whether neural graft function will eventually decline as the result of the disease process. Third, we describe new emerging sources of transplantable dopamine neurones derived from pluripotent stem cells or reprogrammed adult somatic cells. Fourth, we highlight an important European Union‐funded multicentre clinical trial involving transplantation of foetal dopamine neurones in Parkinsons disease. We describe the design of this ongoing trial and how it can impact on the overall future of cell therapy in Parkinsons disease.

Cell transplantation in Parkinson's disease: problems and perspectives.

PURPOSE OF REVIEW We review recent experiments conducted using embryonic tissue and stem cell transplants in experimental models of Parkinsons disease. We also highlight the challenges which remain to be met in order for cell therapy to become clinically effective and safe. RECENT FINDINGS The outcome of previous clinical transplantation trials was variable in terms of motor recovery. We discuss whether transplants can mitigate L-3,4-dihydroxyphenylalanine (L-DOPA)-induced dyskinesias and consider the risk factors which predispose to graft-induced dyskinesias. In addition, we introduce Transeuro, a new European Union-funded multicenter consortium which plans to perform transplantation trials.Stem cells have emerged as an alternative source for the generation of dopaminergic precursors. We briefly outline progress made in the use of human embryonic stem cells and focus predominantly on the emerging field of induced pluripotency. We conclude by introducing the exciting and novel method of direct reprogramming which involves the conversion of fibroblasts to neurons without inducing a pluripotent state. SUMMARY The area of cell transplantation has been revitalized by the identification of parameters which predispose patients to graft-induced dyskinesias and by the emergence of novel methods of generating dopaminergic neurons. Hopefully, the Transeuro clinical trials will give further impetus and act as a stepping stone to future trials employing stem-cell-derived neurons.

Rasagiline ameliorates olfactory deficits in an alpha-synuclein mouse model of Parkinson's disease.

Impaired olfaction is an early pre-motor symptom of Parkinsons disease. The neuropathology underlying olfactory dysfunction in Parkinsons disease is unknown, however α-synuclein accumulation/aggregation and altered neurogenesis might play a role. We characterized olfactory deficits in a transgenic mouse model of Parkinsons disease expressing human wild-type α-synuclein under the control of the mouse α-synuclein promoter. Preliminary clinical observations suggest that rasagiline, a monoamine oxidase-B inhibitor, improves olfaction in Parkinsons disease. We therefore examined whether rasagiline ameliorates olfactory deficits in this Parkinsons disease model and investigated the role of olfactory bulb neurogenesis. α-Synuclein mice were progressively impaired in their ability to detect odors, to discriminate between odors, and exhibited alterations in short-term olfactory memory. Rasagiline treatment rescued odor detection and odor discrimination abilities. However, rasagiline did not affect short-term olfactory memory. Finally, olfactory changes were not coupled to alterations in olfactory bulb neurogenesis. We conclude that rasagiline reverses select olfactory deficits in a transgenic mouse model of Parkinsons disease. The findings correlate with preliminary clinical observations suggesting that rasagiline ameliorates olfactory deficits in Parkinsons disease.

A novel α-synuclein-GFP mouse model displays progressive motor impairment, olfactory dysfunction and accumulation of α-synuclein-GFP.

Compelling evidence suggests that accumulation and aggregation of alpha-synuclein (α-syn) contribute to the pathogenesis of Parkinsons disease (PD). Here, we describe a novel Bacterial Artificial Chromosome (BAC) transgenic model, in which we have expressed wild-type human α-syn fused to green fluorescent protein (GFP), under control of the mouse α-syn promoter. We observed a widespread and high expression of α-syn-GFP in multiple brain regions, including the dopaminergic neurons of the substantia nigra pars compacta (SNpc) and the ventral tegmental area, the olfactory bulb as well as in neocortical neurons. With increasing age, transgenic mice exhibited reductions in amphetamine-induced locomotor activity in the open field, impaired rotarod performance and a reduced striatal dopamine release, as measured by amperometry. In addition, they progressively developed deficits in an odor discrimination test. Western blot analysis revealed that α-syn-GFP and phospho-α-syn levels increased in multiple brain regions, as the mice grew older. Further, we observed, by immunohistochemical staining for phospho-α-syn and in vivo by two-photon microscopy, the formation of α-syn aggregates as the mice aged. The latter illustrates that the model can be used to track α-syn aggregation in vivo. In summary, this novel BAC α-syn-GFP model mimics a unique set of aspects of PD progression combined with the possibility of tracking α-syn aggregation in neocortex of living mice. Therefore, this α-syn-GFP-mouse model can provide a powerful tool that will facilitate the study of α-syn biology and its involvement in PD pathogenesis.

Nonsteroidal Selective Androgen Receptor Modulators and Selective Estrogen Receptor β Agonists Moderate Cognitive Deficits and Amyloid-β Levels in a Mouse Model of Alzheimer's Disease.

Decreases of the sex steroids, testosterone and estrogen, are associated with increased risk of Alzheimers disease. Testosterone and estrogen supplementation improves cognitive deficits in animal models of Alzheimers disease. Sex hormones play a role in the regulation of amyloid-β via induction of the amyloid-β degrading enzymes neprilysin and insulin-degrading enzyme. To mimic the effect of dihydrotestosterone (DHT), we administered a selective androgen receptor agonist, ACP-105, alone and in combination with the selective estrogen receptor β (ERβ) agonist AC-186 to male gonadectomized triple transgenic mice. We assessed long-term spatial memory in the Morris water maze, spontaneous locomotion, and anxiety-like behavior in the open field and in the elevated plus maze. We found that ACP-105 given alone decreases anxiety-like behavior. Furthermore, when ACP-105 is administered in combination with AC-186, they increase the amyloid-β degrading enzymes neprilysin and insulin-degrading enzyme and decrease amyloid-β levels in the brain as well as improve cognition. Interestingly, the androgen receptor level in the brain was increased by chronic treatment with the same combination treatment, ACP-105 and AC-186, not seen with DHT or ACP-105 alone. Based on these results, the beneficial effect of the selective ERβ agonist as a potential therapeutic for Alzheimers disease warrants further investigation.

IGF-1 protects against diabetic features in an in vivo model of Huntington's disease

Huntingtons disease (HD) is the most prevalent polyglutamine expansion disorder. HD is caused by an expansion of CAG triplet in the huntingtin (HTT) gene, associated with striatal and cortical neuronal loss. Central and peripheral metabolic abnormalities and altered insulin-like growth factor-1 (IGF-1) levels have been described in HD. Thus, we hypothesized that restoration of IGF-1-mediated signaling pathways could rescue R6/2 mice from metabolic stress and behavioral changes induced by polyglutamine expansion. We analyzed the in vivo effect of continuous peripheral IGF-1 administration on diabetic parameters, body weight and motor behavior in the hemizygous R6/2 mouse model of HD. We used 9 week-old and age-matched wild-type mice, subjected to continuously infused recombinant IGF-I or vehicle, for 14 days. IGF-1 treatment prevented the age-related decrease in body weight in R6/2 mice. Although blood glucose levels were higher in R6/2 mice, they did not reach a diabetic state. Even though, IGF-1 ameliorated poor glycemic control in HD mice. This seemed to be associated with a decrease in blood insulin levels in R6/2 mice, which was increased following IGF-1 infusion. Similarly, blood IGF-1 levels decreased during aging in both wild-type and R6/2 mice, being significantly improved upon its continuous infusion. Although no significant differences were found in motor function in R6/2-treated mice, IGF-1 treatment highly improved paw clasping scores. In summary, these results suggest that IGF-1 has a protective role against HD-associated impaired glucose tolerance, by enhancing blood insulin levels.

NGF rescues hippocampal cholinergic neuronal markers, restores neurogenesis, and improves the spatial working memory in a mouse model of Huntington's Disease

BACKGROUND Recent studies in Huntingtons disease (HD) mouse models and patients suggest that hippocampal neurons and their cholinergic afferents are involved in the cognitive deficits seen in the disease. Nerve growth factor (NGF) is an essential regulator of cholinergic neuronal survival and neurotransmission. OBJECTIVE We asked whether NGF might be involved in HD and if intra-cerebroventricular infusion of NGF can rescue hippocampal cholinergic neuronal markers, restore neurogenesis, and improve the spatial working memory in R6/1 mouse model of HD. METHODS We quantified NGF protein level by enzyme-linked immunosorbent assay (ELISA), intracerebroventricularly infused NGF, assessed cholinergic neuronal markers by Western blotting and quantitative RT-PCR, evaluated neurogenesis by immunohistochemistry, and studied spatial working memory using radial maze. RESULTS By quantifying NGF protein in the hippocampus of the R6/1 mice at different ages, we found progressive decreases in NGF protein levels. We then increased NGF levels in the R6/1 mice through intra-cerebroventricular infusion. We observed elevations of the cholinergic neurochemical markers vesicular acetylcholine transporter (VAChT) and choline acetyltransferase (ChAT) in the hippocampus and in the septal region, which contain the cell bodies of basal forebrain cholinergic neurons (BFCNs), but not in the striatum that harbors cholinergic interneurons. Finally, we found that NGF infusion also restored hippocampal neurogenesis and improved spatial working memory. CONCLUSIONS Our results suggest that intracerebral injections of NGF might be a valuable therapy against cognitive symptoms in HD and should be further studied in HD animal models and patients.