Martine Saint-Pierre

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)

Neural transplants in patients with Huntington's disease undergo disease-like neuronal degeneration

The clinical evaluation of neural transplantation as a potential treatment for Huntingtons disease (HD) was initiated in an attempt to replace lost neurons and improve patient outcomes. Two of 3 patients with HD reported here, who underwent neural transplantation containing striatal anlagen in the striatum a decade earlier, have demonstrated marginal and transient clinical benefits. Their brains were evaluated immunohistochemically and with electron microscopy for markers of projection neurons and interneurons, inflammatory cells, abnormal huntingtin protein, and host-derived connectivity. Surviving grafts were identified bilaterally in 2 of the subjects and displayed classic striatal projection neurons and interneurons. Genetic markers of HD were not expressed within the graft. Here we report in patients with HD that (i) graft survival is attenuated long-term; (ii) grafts undergo disease-like neuronal degeneration with a preferential loss of projection neurons in comparison to interneurons; (iii) immunologically unrelated cells degenerate more rapidly than the patients neurons, particularly the projection neuron subtype; (iv) graft survival is attenuated in the caudate in comparison to the putamen in HD; (v) glutamatergic cortical neurons project to transplanted striatal neurons; and (vi) microglial inflammatory changes in the grafts specifically target the neuronal components of the grafts. These results, when combined, raise uncertainty about this potential therapeutic approach for the treatment of HD. However, these observations provide new opportunities to investigate the underlying mechanisms involved in HD, as well as to explore additional therapeutic paradigms.

Systemic exposure to paraquat and maneb models early Parkinson's disease in young adult rats.

In recent years, several lines of evidence have shown an increase in Parkinsons disease (PD) prevalence in rural environments where pesticides are widely used. Paraquat (PQ--herbicide) and maneb (MB--fungicide) are among the compounds suspected to induce neuronal degeneration and motor deficits characteristics of PD. Here, we investigated the effects of PQ and MB on dopaminergic (DA) neuron-glia cultures and in vivo in young adult rats. In vitro, PQ led to a loss of DA as compared to non-DA neurons and microglial activation in a dose-dependent manner. Addition of MB had no further effect nor did it lead to microglial activation when used alone. In vivo, 2-month old young adult rats were subjected to intraperitoneal injections of vehicle (n = 4), PQ alone (n = 8), or PQ in combination with MB (n = 8) twice a week for 4 weeks and were sacrificed the day following the last injection. Significant loss of nigral DA neurons was observed in both treatment groups, but a significant decrease in striatal DA fibers was not found. Microglial activation was seen in the nigra of rats subjected to PQ with or without MB. Behavioral analyses demonstrated a mixed pattern of motor impairments, which may have been related to early effects of nigral DA neuronal loss or systemic effects associated with MB exposure in addition to PQ. These results indicate that exposure to PQ with or without MB induces neurodegeneration which might occur via an early inflammatory response in young adult animals.

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.

Mutant Huntingtin Is Present in Neuronal Grafts in Huntington Disease Patients

Huntington disease (HD) is caused by a genetically encoded pathological protein (mutant huntingtin [mHtt]), which is thought to exert its effects in a cell‐autonomous manner. Here, we tested the hypothesis that mHtt is capable of spreading within cerebral tissue by examining genetically unrelated fetal neural allografts within the brains of patients with advancing HD.

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.

Cerebral PET imaging and histological evidence of transglutaminase inhibitor cystamine induced neuroprotection in transgenic R6/2 mouse model of Huntington's disease.

To investigate efficacy of cystamine induced neuroprotection, we conducted PET imaging studies of cerebral glucose metabolism with [(18)F]FDG (2-deoxy-2-[(18)F]fluoro-d-glucose) and striatal dopamine D2 receptor function with [(11)C]raclopride in R6/2 transgenic Huntington mice. In the control mice, exponentially decreasing glucose utilization was observed in the striatum N(str) [SUV]=(41.75+/-11.80)(58,str)*exp(-(0.041+/-0.007)*t [days]); cortex N(cort) [SUV]=24.14+/-3.66)(58,cort)*exp(-(0.043+/-0.007)*t [days]); and cerebellum N(cer) [SUV]=(34.97+/-10.58)(58,cer)*exp(-(0.037+/-0.008)*t [days]) as a function of age starting at 58 days. Given that the underlying degeneration rate in the cystamine treated mice is similar to that observed in control animals, the protection coefficient (beta) calculated from the equation N(t)=N(58)*exp(-(1-beta)*k*t) was 0.133+/-0.035 for the striatum; 0.122+/-0.028 for the cortex and 0.224+/-00.042 for the cerebellum with a dose of 100 mg/kg. The 50 mg/kg cystamine dose provided significant protection only for the striatum and only minor protection was obtained using lower doses. Striatal binding potential of [(11)C]raclopride was 1.059+/-0.030 in the control mice, and enhanced in the cystamine treated animals in a dose dependent manner up to 1.245+/-0.063 using the 100 mg/kg dose. Histological analysis confirmed cystamine induced neuroprotection of striatal and cortical neurons and Nissl staining revealed that formation of cellular inclusions was reversed in a dose dependent manner. Cerebral imaging and histological evidence support the use of cystamine as a neuroprotective agent for Huntingtons disease (HD) pathology.

Cerebrovascular and blood-brain barrier impairments in Huntington's disease: Potential implications for its pathophysiology.

Although the underlying cause of Huntingtons disease (HD) is well established, the actual pathophysiological processes involved remain to be fully elucidated. In other proteinopathies such as Alzheimers and Parkinsons diseases, there is evidence for impairments of the cerebral vasculature as well as the blood–brain barrier (BBB), which have been suggested to contribute to their pathophysiology. We investigated whether similar changes are also present in HD.

Modulation of Dopaminergic and Glutamatergic Brain Function: PET Studies on Parkinsonian Rats

Degeneration of dopaminergic neurons of the substantia nigra pars compacta is a cardinal feature of Parkinsons disease (PD). Although uncertain, the pathology has been suggested to derive from a malfunction of the complex interaction between dopaminergic and metabotropic glutamate receptors (mGluRs). To further address this issue, we investigated the imaging profile and expression of dopamine D2 receptors and mGluRs in a classic parkinsonian rodent model induced by the toxin 6-hydroxydopamine. Methods: Adult male Sprague–Dawley rats (250–300 g) received a stereotaxic injection of 8 μg/2 μL of 6-hydroxydopamine (n = 6) or saline solution (n = 4) in the right medial forebrain bundle. Small-animal PET was performed on all rats 4 wk after the surgical procedure to assess dopamine transporter (DAT) status using 11C-2β-carbomethoxy-3β-(4-fluorophenyl)-tropane (CFT), as well as dopamine D2 receptor and mGluR5 modulation using 11C-raclopride and 2-11C-methyl-6-(2-phenylethynyl)-pyridine (11C-MPEP), respectively. Behavioral studies were also conducted 6 wk after lesioning by d-amphetamine challenge. Immunohistochemistry and Western blotting were carried out at 8 wk after lesioning to confirm dopamine fiber, neuronal loss, and level of striatal mGluR5 expression. Results: PET images showed decreased 11C-CFT binding on the lesioned side, including the structures of the striatum, hippocampus, and cortex, compared with the contralateral intact side. Interestingly, dopamine D2 receptors and mGluR5 upregulation were observed in the right striatum, hippocampus, and cortex, using 11C-raclopride and 11C-MPEP, respectively. A negative correlation was also found between the percentage change in mGluR5 expression and DAT function. Finally, tyrosine hydroxylase immunoreactivity confirmed both dopamine fiber loss (t test, P < 0.01) and neuronal loss (t test, P < 0.01) on the lesioned side. These changes were accompanied by a strongly enhanced mGluR5 expression in the right striatum of the lesioned side analyzed by Western plot. Conclusion: These findings support the existence of compensatory mechanisms in nigrostriatal dopamine degeneration and provide new insights that help further dissect some of the pathways underlying neurodegeneration. In addition, these results reconfirm that PET is a valuable tool for multilevel receptor studies, significantly contributing to the understanding of pathogenic mechanisms and ultimately opening new avenues in the study of neuroprotective approaches toward PD.

Temporal effects of paraquat/maneb on microglial activation and dopamine neuronal loss in older rats

We investigated the effects of combined systemic exposure to the herbicide paraquat (PQ) and the fungicide maneb (MB) in 6‐month‐old rats, an animal model of Parkinsons disease resulting from environmental toxin exposure. Following two doses of PQ (10 mg/kg) and MB (30 mg/kg), 52% of animals developed fatal lung injury. Examination of the remaining animals showed degeneration of dopaminergic (DA) neurons in the substantia nigra pars compacta 6 weeks, but not 4 weeks, following PQ/MB. In contrast, microglial activation was observed at 4 weeks, but had abated by 6 weeks. Compared with our previous findings in younger rats, these results suggest increased susceptibility of older animals to lung and brain toxicity from PQ/MB exposure. Microglial activation preceded, and therefore likely contributed to, DA neurodegeneration. Further, electron microscopy revealed an abnormal appearance of the Golgi apparatus at 4 weeks that was confirmed using double immunostaining for tyrosine hydroxylase and Golgi. This suggests that PQ/MB causes protein processing dysfunction in nigral DA neurons that may be either a direct effect of PQ/MB or the result of microglial activation.