Increased Formation of Reactive Oxygen Species, but No Changes in Glutathione Peroxidase Activity, in Striata of Mice Transgenic for the Huntington's Disease Mutation

The formation of reactive oxygen species (ROS) and the activities of the antioxidant enzymes glutathione peroxidase (GPx) and catalase (CAT) were measured as a function of age in the striatum of mice transgenic for the Huntington's disease (HD) mutation. Striata from R6/1 transgenic male mice were dissected at different ages (11, 19, and 35 weeks). The amount of dichlorofluorescein (DCF), an index of ROS formation, was significantly increased in R6/1 mice at all ages tested, whereas GPx activity remained unchanged when compared with wild-type control animals in all groups evaluated. CAT activity was very low, just above detection in the striata of both control and transgenic mice. Nineteen and 35-week-old R6/1 mice also developed feet clasping behavior, but only 35-week-old animals showed body weight loss. Our findings support an active role of free radicals in the onset and progression of the neurological phenotype of R6/1 mice. We suggest that changes in ROS formation are due to an age-related increased propensity of the striatum of transgenic animals to generate oxygen radicals as a response to the evolving pathological conditions.     

Symptom-related changes of endocannabinoid and palmitoylethanolamide levels in brain areas of R6/2 mice, a transgenic model of Huntington's disease

Previous studies have shown an impairment of the endocannabinoid system in experimental models of Huntington's disease. In transgenic R6/2 mice, created by inserting exon 1 of the human IT15 mutant gene into the mouse, and exhibiting 150 CAG repeats as well as signs of HD, a progressive decline of CB(1) receptor expression and an abnormal sensitivity to CB(1) receptor stimulation have been reported. Here, by using isotope-dilution liquid chromatography-mass spectrometry, we investigated whether the levels of three endogenous neuroprotective substances, the endocannabinoids anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and palmitoylethanolamide (PEA), are altered in different brain areas of transgenic R6/2 versus wild-type (WT) mice at two different disease phases, i.e. in pre-symptomatic (4.5 weeks) or overtly symptomatic (10 weeks) R6/2 mice versus age-matched WT mice (n=4/group). Except for a approximately 25% decrease in 2-AG levels in the cortex, no significant changes in endocannabinoid and PEA levels were observed in pre-symptomatic R6/2 versus WT mice. By contrast, in symptomatic R6/2 mice the levels of all three compounds were significantly (approximately 30-60%) decreased in the striatum, whereas little changes were observed in the hippocampus, and a approximately 28% decrease of 2-AG levels, accompanied by a approximately 50% increase of AEA levels, was found in the cortex. These findings show that endocannabinoid levels change in a disease phase- and region-specific way in the brain of R6/2 mice and indicate that an impaired endocannabinoid system is a hallmark of symptomatic HD, thus suggesting that drugs inhibiting endocannabinoid degradation might be used to treat this disease.     

'Tissue' transglutaminase ablation reduces neuronal death and prolongs survival in a mouse model of Huntington's disease

By crossing Huntington's disease (HD) R6/1 transgenic mice with 'tissue' transglutaminase (TG2) knock-out mice, we have demonstrated that this multifunctional enzyme plays an important role in the neuronal death characterising this disorder in vivo. In fact, a large reduction in cell death is observed in R6/1, TG2(-/-) compared with R6/1 transgenic mice. In addition, we have shown that the formation of neuronal intranuclear inclusions (NII) is potentiated in absence of the 'tissue' transglutaminase. These phenomena are paralleled by a significant improvement both in motor performances and survival of R6/1, TG2(-/-) versus R6/1 mice. Taken together these findings suggest an important role for tissue transglutaminase in the regulation of neuronal cell death occurring in Huntington's disease.     

Mice transgenic for exon 1 of Huntington's disease: properties of cholinergic and dopaminergic pre-synaptic function in the striatum

In Huntington's disease (HD), neuronal loss is most prominent in the striatum leading to emotional, cognitive and progressive motor dysfunction. The R6/2 mice, transgenic for exon 1 of the HD gene, develop a neurological phenotype with similarities to these features of HD. In striatal tissue, electrically evoked release of tritiated acetylcholine (ACh) and dopamine (DA) were compared in wild-type (WT) and R6/2 mice. In R6/2 mice, the evoked release of ACh, its M2 autoreceptor-mediated maximum inhibition and its dopamine D2 heteroreceptor-mediated maximum inhibition was diminished to 51%, 74% and 87% of controls, respectively. Also, the activities of choline acetyltransferase and of synaptosomal high-affinity choline uptake decreased progressively with age in these mice. In the DA release model, however, electrical stimulation elicited equal amounts of [3H]-DA both in WT and R6/2 mice. Moreover, high-affinity DA uptake into striatal slices was similar in WT and R6/2 mice. In order to confirm these findings in vivo, intrastriatal levels of extracellular DA were measured by intracerebral microdialysis in freely moving mice: striatal DA levels were found to be equal in WT and R6/2 mice. In conclusion, in the transgenic R6/2 mice changes occur mainly in striatal cholinergic neurones and their pre-synaptic modulation, but not in the dopaminergic afferent terminals. Whether similar events also contribute to the pathogenesis of HD in humans has to be established.     

Effects of CAG repeat length, HTT protein length and protein context on cerebral metabolism measured using magnetic resonance spectroscopy in transgenic mouse models of Huntington's disease

Huntington's disease is a neurodegenerative illness caused by expansion of CAG repeats at the N-terminal end of the protein huntingtin. We examined longitudinal changes in brain metabolite levels using in vivo magnetic resonance spectroscopy in five different mouse models. There was a large (>50%) exponential decrease in N-acetyl aspartate (NAA) with time in both striatum and cortex in mice with 150 CAG repeats (R6/2 strain). There was a linear decrease restricted to striatum in N171-82Q mice with 82 CAG repeats. Both the exponential and linear decreases of NAA were paralleled in time by decreases in neuronal area measured histologically. Yeast artificial chromosome transgenic mice with 72 CAG repeats, but low expression levels, had less striatal NAA loss than the N171-82Q mice (15% vs. 43%). We evaluated the effect of gene context in mice with an approximate 146 CAG repeat on the hypoxanthine phosphoribosyltransferase gene (HPRT). HPRT mice developed an obese phenotype in contrast to weight loss in the R6/2 and N171-82Q mice. These mice showed a small striatal NAA loss (21%), and a possible increase in brain lipids detectable by magnetic resonance (MR) spectroscopy and decreased brain water T1. Our results indicate profound metabolic defects that are strongly affected by CAG repeat length, as well as gene expression levels and protein context.     

Mitochondrial DNA damage is a hallmark of chemically induced and the R6/2 transgenic model of Huntington's disease

Many forms of neurodegeneration are associated with oxidative stress and mitochondrial dysfunction. Mitochondria are prominent targets of oxidative damage, however, it is not clear whether mitochondrial DNA (mtDNA) damage and/or its lack of repair are primary events in the delayed onset observed in Huntington's disease (HD). We hypothesize that an age-dependent increase in mtDNA damage contributes to mitochondrial dysfunction in HD. Two HD mouse models were studied, the 3-nitropropionic acid (3-NPA) chemically induced model and the HD transgenic mice of the R6/2 strain containing 115-150 CAG repeats in the huntingtin gene. The mitochondrial toxin 3-NPA inhibits complex II of the electron transport system and causes neurodegeneration that resembles HD in the striatum of human and experimental animals. We measured nuclear and mtDNA damage by quantitative PCR (QPCR) in striatum of 5- and 24-month-old untreated and 3-NPA treated C57BL/6 mice. Aging caused an increase in damage in both nuclear and mitochondrial genomes. 3-NPA induced 4-6 more damage in mtDNA than nuclear DNA in 5-month-old mice, and this damage was repaired by 48h in the mtDNA. In 24-month-old mice 3NPA caused equal amounts of nuclear and mitochondrial damage and this damage persistent in both genomes for 48h. QPCR analysis showed a progressive increase in the levels of mtDNA damage in the striatum and cerebral cortex of 7-12-week-old R6/2 mice. Striatum exhibited eight-fold more damage to the mtDNA compared with a nuclear gene. These data suggest that mtDNA damage is an early biomarker for HD-associated neurodegeneration and supports the hypothesis that mtDNA lesions may contribute to the pathogenesis observed in HD.     

Ubiquilin-1 Overexpression Increases the Lifespan and Delays Accumulation of Huntingtin Aggregates in the R6/2 Mouse Model of Huntington's Disease

Huntington''s Disease (HD) is a neurodegenerative disorder that is caused by abnormal expansion of a polyglutamine tract in huntingtin (htt) protein. The expansion leads to increased htt aggregation and toxicity. Factors that aid in the clearance of mutant huntingtin proteins should relieve the toxicity. We previously demonstrated that overexpression of ubiqulin-1, which facilitates protein clearance through the proteasome and autophagy pathways, reduces huntingtin aggregates and toxicity in mammalian cell and invertebrate models of HD. Here we tested whether overexpression of ubiquilin-1 delays or prevents neurodegeneration in R6/2 mice, a well-established model of HD. We generated transgenic mice overexpressing human ubiquilin-1 driven by the neuron-specific Thy1.2 promoter. Immunoblotting and immunohistochemistry revealed robust and widespread overexpression of ubiquilin-1 in the brains of the transgenic mice. Similar analysis of R6/2 animals revealed that ubiquilin is localized in huntingtin aggregates and that ubiquilin levels decrease progressively to 30% during the end-stage of disease. We crossed our ubiquilin-1 transgenic line with R6/2 mice to assess whether restoration of ubiquilin levels would delay HD symptoms and pathology. In the double transgenic progeny, ubiquilin levels were fully restored, and this correlated with a 20% increase in lifespan and a reduction in htt inclusions in the hippocampus and cortex. Furthermore, immunoblots indicated that endoplasmic reticulum stress response that is elevated in the hippocampus of R6/2 animals was attenuated by ubiquilin-1 overexpression. However, ubiquilin-1 overexpression neither altered the load of htt aggregates in the striatum nor improved motor impairments in the mice.     

Brain-derived neurotrophic factor modulates dopaminergic deficits in a transgenic mouse model of Huntington's disease

Dysfunction of dopaminergic neurons may contribute to motor impairment in Huntington's disease. Here, we study the role of brain-derived neurotrophic factor (BDNF) in alterations of the nigrostriatal system associated with transgenics carrying mutant huntingtin. Using huntingtin-BDNF+/- double-mutant mice, we analyzed the effects of reducing the levels of BDNF expression in a model of Huntington's disease (R6/1). When compared with R6/1 mice, these mice exhibit an increased number of aggregates in the substantia nigra pars compacta. In addition, reduction of BDNF expression exacerbates the dopaminergic neuronal dysfunction seen in mutant huntingtin mice, such as the decrease in retrograde labelling of dopaminergic neurons and striatal dopamine content. However, mutant huntingtin mice with normal or lowered BDNF expression show the same decrease in the anterograde transport, number of dopaminergic neurons and nigral volume. In addition, reduced BDNF expression causes decreased dopamine receptor expression in mutant huntingtin mice. Examination of changes in locomotor activity induced by dopamine receptor agonists revealed that, in comparison with R6/1 mice, the double mutant mice exhibit lower activity in response to amphetamine, but not to apomorphine. In conclusion, these findings demonstrate that the decreased BDNF expression observed in Huntington's disease exacerbates dopaminergic neuronal dysfunction, which may participate in the motor disturbances associated with this neurodegenerative disorder.     

Inclusion formation in Huntington's disease R6/2 mouse muscle cultures

Huntington's disease (HD) is an autosomal dominant disorder caused by an expansion in the number of glutamine repeats in the N-terminal region of the huntingtin protein. Nuclear and cytoplasmic aggregates of the N-terminal portion of huntingtin have been found in the brains of HD patients and the brains and non-neuronal tissues of the R6/2 HD transgenic mouse. We have cultured myoblasts and myotubes from transgenic R6/2 mice and littermate controls to investigate the formation of these inclusions in post mitotic cells. Huntingtin immunoreactivity was intense in differentiating, desmin positive myoblasts and myotubes from both control and R6/2 mice suggesting that it may play a role in myotube differentiation. Following differentiation huntingtin and ubiquitin positive aggregates were observed in R6/2 but not control cultures. After 3 weeks in differentiation medium cytoplasmic huntingtin and ubiquitin immunoreactive aggregates were observed in non-myotube cells, while nuclear huntingtin aggregates were seen in a proportion of myotubes after 6 weeks. Growth in the absence of serum resulted in a marked increase in the number of R6/2 myotubes containing nuclear inclusions after 6 weeks demonstrating that environmental factors influenced huntingtin aggregate formation in these cells. Consequently, cultured myotubes from R6/2 mice may be a useful post mitotic cell culture model to study both the biochemical consequences of huntingtin aggregates and the factors that may influence aggregate formation.     

CGS21680 attenuates symptoms of Huntington's disease in a transgenic mouse model

Huntington's disease (HD) is an autosomal dominant neurodegenerative disease caused by a CAG trinucleotide expansion in exon 1 of the Huntingtin (Htt) gene. We show herein that in an HD transgenic mouse model (R6/2), daily administration of CGS21680 (CGS), an A(2A) adenosine receptor (A(2A)-R)-selective agonist, delayed the progressive deterioration of motor performance and prevented a reduction in brain weight. 3D-microMRI analysis revealed that CGS reversed the enlarged ventricle-to-brain ratio of R6/2 mice, with particular improvements in the left and right ventricles. (1)H-MRS showed that CGS significantly reduced the increased choline levels in the striatum. Immunohistochemical analyses further demonstrated that CGS reduced the size of ubiquitin-positive neuronal intranuclear inclusions (NIIs) in the striatum of R6/2 mice and ameliorated mutant Htt aggregation in a striatal progenitor cell line overexpressing mutant Htt with expanded polyQ. Moreover, chronic CGS treatment normalized the elevated blood glucose levels and reduced the overactivation of a major metabolic sensor [5'AMP-activated protein kinase (AMPK)] in the striatum of R6/2 mice. Since AMPK is a master switch for energy metabolism, modulation of energy dysfunction caused by the mutant Htt might contribute to the beneficial effects of CGS. Collectively, CGS is a potential drug candidate for the treatment of HD.     

Tissue transglutaminase contributes to disease progression in the R6/2 Huntington's disease mouse model via aggregate-independent mechanisms

Huntington's disease (HD) is caused by an expansion of CAG repeats within the huntingtin gene and is characterized by intraneuronal mutant huntingtin protein aggregates. In order to determine the role of tissue transglutaminase (tTG) in HD aggregate formation and disease progression, we cross-bred the R6/2 HD mouse model with a tTG knockout mouse line. R6/2 mice that were tTG heterozygous knockouts (R6/2 : tTG+/-) and tTG homozygous knockouts (R6/2 : tTG-/-) showed a very similar increase in aggregate number within the striatum compared with R6/2 mice that were wild-type with respect to tTG (R6/2 : tTG+/+). Interestingly, a significant delay in the onset of motor dysfunction and death occurred in R6/2 : tTG-/- mice compared with both R6/2 : tTG+/+ and R6/2 : tTG+/- mice. As aggregate number was similarly increased in the striatum of both R6/2 : tTG+/- and R6/2 : tTG-/- mice, whereas only R6/2 : tTG-/- mice showed delayed disease progression, these data suggest that the contribution of tTG towards motor dysfunction and death in the R6/2 mouse is independent of its ability to negatively regulate aggregate formation. Moreover, the combined results from this study suggest that the formation of striatal huntingtin aggregates does not directly influence motor dysfunction or death in this HD mouse model.     

Abnormalities of neurotransmitter enzymes in Huntington's chorea

The activities ofl-glutamate decarboxylase (GAD), GABA-transaminase (GABA-T), choline acetyltransferase (CAT), and cysteic and cysteinesulfinic acids decarboxylase (CAD/CSAD) in putamen and frontal cortex in both Huntington's chorea and normal tissues were measured. The greatest difference between Huntington's and normal tissues occurred in putamen, in which the apparent CSAD activity was reduced by 85%, while no difference was observed in frontal cortex. GAD, CAD, and CAT activities were also reduced in putamen by 65%, 63%, and 42%, respectively (P<0.05). Slight reduction in the enzyme activities was also observed in frontal cortex. However, these reductions appeared to be statistically insignificant (P>0.05 in all cases). GABA-T showed little difference in both putamen and frontal cortex in Huntington's chorea and normal tissues. GAD and GABA-T from Huntington's tissues were indistinguishable from those obtained from normal tissues by double diffusion test and by microcomplement fixation test, which is capable of distinguishing proteins with a single amino acid substitution. Furthermore, the similarity of the complement fixation curves for GAD from Huntington's and normal tissues suggests that the decrease in GAD activity is probably due to the reduction in the number of GAD molecules, presumably through the loss of neurons, and not due to the inhibition or inactivation of GAD activity by toxic substances which might be present in Huntington's chorea.     

Dopamine release is severely compromised in the R6/2 mouse model of Huntington's disease

Recently, alterations in dopamine signaling have been implicated in Huntington's disease. In this work, dopamine release and uptake was measured in striatal slices from the R6/2 transgenic mouse model of Huntington's disease using fast-scan cyclic voltammetry at carbon-fiber microelectrodes. Dopamine release in brain slices from 6-week-old R6/2 mice is substantially reduced (53% of wild type), while dopamine uptake is unaffected. In agreement with this, R6/2 mice injected with the dopamine uptake inhibitor cocaine exhibited a blunted motor activity response (54% of wild type). At 10 weeks of age, an even more dramatic motor activity decrease in response to cocaine injection (21% of wild type) was observed. Moreover, the pre-drug activity of 10-week-old R6/2 mice was significantly reduced (by 37%) compared with 6-week-old R6/2 mice. Striatal dopamine release decreased with age, indicating that progressive alterations in dopaminergic pathways may affect motor activity. The inhibition constants of cocaine and methamphetamine (METH) determined in brain slices differed little between genotype or age group, suggesting that the decreased responses to cocaine and METH arise from compromised dopamine release rather than differences in uptake or drug action. Collectively, these data demonstrate (i) a reduction in the ability of dopamine terminals to release dopamine and (ii) the importance of this attenuation of release on the motor symptoms of Huntington's disease.     

Selective deficits in the expression of striatal-enriched mRNAs in Huntington's disease

We have identified and cataloged 54 genes that exhibit predominant expression in the striatum. Our hypothesis is that such mRNA molecules are likely to encode proteins that are preferentially associated with particular physiological processes intrinsic to striatal neurons, and therefore might contribute to the regional specificity of neurodegeneration observed in striatal disorders such as Huntington's disease (HD). Expression of these genes was measured simultaneously in the striatum of HD R6/1 transgenic mice using Affymetrix oligonucleotide arrays. We found a decrease in expression of 81% of striatum-enriched genes in HD transgenic mice. Changes in expression of genes associated with G-protein signaling and calcium homeostasis were highlighted. The most striking decrement was observed for a newly identified subunit of the sodium channel, beta 4, with dramatic decreases in expression beginning at 8 weeks of age. A subset of striatal genes was tested by real-time PCR in caudate samples from human HD patients. Similar alterations in expression were observed in human HD and the R6/1 model for the striatal genes tested. Expression of 15 of the striatum-enriched genes was measured in 6-hydroxydopamine-lesioned rats to determine their dependence on dopamine innervation. No changes in expression were observed for any of these genes. These findings demonstrate that mutant huntingtin protein causes selective deficits in the expression of mRNAs responsible for striatum-specific physiology and these may contribute to the regional specificity of degeneration observed in HD.     

Brain-derived neurotrophic factor over-expression in the forebrain ameliorates Huntington's disease phenotypes in mice

Huntington's disease (HD), a dominantly inherited neurodegenerative disorder characterized by relatively selective degeneration of striatal neurons, is caused by an expanded polyglutamine tract of the huntingtin (htt) protein. The htt mutation reduces levels of brain-derived neurotrophic factor (BDNF) in the striatum, likely by inhibiting cortical BDNF gene expression and anterograde transport of BDNF from cortex to striatum. However, roles of the BDNF reduction in HD pathogenesis have not been established conclusively. We reasoned that increasing striatal BDNF through over-expression would slow progression of the disease if BDNF reduction plays a pivotal role in HD pathogenesis. We employed a Bdnf transgene driven by the promoter for the alpha subunit of Ca²⁺/calmodulin-dependent kinase II to over-express BDNF in the forebrain of R6/1 mice which express a fragment of mutant htt with a 116-glutamine tract. The Bdnf transgene increased BDNF levels and TrkB signaling activity in the striatum, ameliorated motor dysfunction, and reversed brain weight loss in R6/1 mice. Furthermore, it normalized DARPP-32 expression of the 32 kDa dopamine and cAMP-regulated phosphoprotein, increased the number of enkephalin-containing boutons, and reduced formation of neuronal intranuclear inclusions in the striatum of R6/1 mice. These results demonstrate crucial roles of reduced striatal BDNF in HD pathogenesis and suggest potential therapeutic values of BDNF to HD.     

Brain neurotransmitter deficits in mice transgenic for the Huntington's disease mutation

Huntington's disease (HD) is associated with an expansion in the CAG repeat sequence of a gene on chromosome 4, resulting in a neurodegenerative process particularly affecting the striatum and with profound but selective changes in content of various neurotransmitters. Recently, transgenic mice expressing a fragment of the human HD gene containing a large CAG expansion have been generated; these mice exhibit a progressive neurological phenotype that includes motor disturbances, as well as neuronal deficits. To investigate their underlying neurotransmitter pathology, we have determined concentrations of GABA, glutamate, and the monoamine neurotransmitters in several brain regions in these mice and control animals at times before and after the emergence of the behavioural phenotype. In contrast to the findings in HD, striatal GABA was unaffected, although a deficit was observed in the cerebellum, consistent with a dysfunction of Purkinje cells. Losses of the monoamine transmitters were observed, some of which are not seen in HD. Thus, 5-hydroxytryptamine and, to a greater extent, 5-hydroxyindoleacetic acid levels were diminished in all brain regions studied, and noradrenaline was particularly affected in the hippocampus. Dopamine was decreased in the striatum in older animals, parallelling evidence for diminished dopaminergic activity in HD.     

Transgenic mice expressing mutated full-length HD cDNA: a paradigm for locomotor changes and selective neuronal loss in Huntington's disease.

Huntington's disease (HD) is a progressive neurodegenerative disorder characterized clinically by motor and psychiatric disturbances and pathologically by neuronal loss and gliosis (reactive astrocytosis) particularly in the striatum and cerebral cortex. We have recently created HD full-length cDNA transgenic mouse models that may serve as a paradigm for HD. A more detailed characterization of these models is presented here. The transgene encoding normal huntingtin consists of 9417 bp of the huntingtin coding sequences including 16 tandem CAGs coding for polyglutamines as part of exon 1. The transgene is driven by a heterologous cytomegalovirus promoter. Five independent transgenic mouse lines were obtained using this construct. An additional six transgenic lines were obtained using full-length HD constructs that have been modified to include either 48 or 89 CAG repeat expansions. Southern blot and densitometric analyses indicated unique integration sites for the transgene in each of the lines with a copy number ranging from two to 22 copies. Widespread expression of the transgene in brain, heart, spleen, kidney, lung, liver and gonads from each line was determined by Western blot analyses. In the brain, transgene expression was found in cerebral cortex, striatum, hippocampus and cerebellum. Expression of the transgene was as much as five times the endogenous mouse huntingtin level. Phenotypically, only mice expressing 48 or 89 CAG repeats manifested progressive behavioural and motor dysfunction. Early behavioural abnormalities were characterized by trunk curling and clasping of both fore- and hindlimbs when the animals were suspended by their tails. Subsequently, these mice exhibited hyperkinetic movements, including heightened exploratory activities, unidirectional rotational behaviour, backflipping and excessive grooming that lasted for several weeks. Eventually, the animals progressed to a hypokinetic phase consisting of slowed movements and lack of response to sensory stimuli. Urine retention or incontinence was also a prominent feature of the hypokinetic phase. At the end stage of the disease process, HD48(B,D) and HD89(A-C) mice became akinetic just prior to death. Neuropathological examination of mice at various stages indicated that it was only during the hypokinetic phase and thereafter when selective neuronal loss was most apparent. Regions of neurodegeneration and loss included the striatum, cerebral cortex, thalamus and hippocampus. TUNEL staining indicated an apoptotic mode of cell death in these brain regions. Comparative neuronal counts after Nissl staining showed as much as 20% loss of small and medium neurons in the striatum in mice at the hypokinetic and akinetic stages. Reactive astrocytosis accompanied the areas of neurodegeneration and loss. Polyglutamine aggregates in the form of neuronal intranuclear inclusions and diffuse nuclear and perinuclear aggregations were found in a small percentage of neurons, including those in brain regions that are typically spared in HD. This observation suggests that polyglutamine aggregates may not be sufficient to cause neuronal loss in HD. In both behavioural and neuropathological analyses, wild-type and transgenic animals with 16 CAG repeats were indistinguishable from each other and do not exhibit the changes observed for mice carrying the 48 and 89 CAG repeat mutations. Thus, animals expressing the CAG repeat expansions appear to represent clinically analogous models for HD pathogenesis, and may also provide insights into the underlying pathophysiological mechanisms of other triplet repeat disorders.     

Functional striatal hypodopaminergic activity in mice lacking adenosine A(2A) receptors.

Adenosine and caffeine modulate locomotor activity and striatal gene expression, partially through the activation and blockade of striatal A(2A) receptors, respectively. The elucidation of the roles of these receptors benefits from the construction of A(2A) receptor-deficient mice (A(2A)-R(-/-)). These mice presented alterations in locomotor behaviour and striatal expression of genes studied so far, which are unexpected regarding the specific expression of A(2A) receptor by striatopallidal neurones. To clarify the functions of A(2A) receptors in the striatum and to identify the mechanisms leading to these unexpected modifications, we studied the basal expression of immediate early and constitutive genes as well as dopamine and glutamate neurotransmission in the striatum. Basal zif268 and arc mRNAs expression was reduced in mutant mice by 60-80%, not only in the striatum but also widespread in the cerebral cortex and hippocampus. Striatal expression of substance P and enkephalin mRNAs was reduced by about 50% and 30%, respectively, whereas the expression of GAD67 and GAD65 mRNAs was slightly increased and unaltered, respectively. In vivo microdialysis in the striatum revealed a 45% decrease in the extracellular dopamine concentration and three-fold increase in extracellular glutamate concentration. This was associated with an up-regulation of D(1) and D(2) dopamine receptors expression but not with changes in ionotropic glutamate receptors. The levels of tyrosine hydroxylase and of striatal and cortical glial glutamate transporters as well as adenosine A(1) receptors expression were indistinguishable between A(2A)-R(-/-) and wild-type mice. Altogether these results pointed out that the lack of A(2A) receptors leads to a functional hypodopaminergic state and demonstrated that A(2A) receptors are necessary to maintain a basal level in immediate early and constitutive genes expression in the striatum and cerebral cortex, possibly via their control of dopamine pathways.     

Combination therapy with Coenzyme Q10 and creatine produces additive neuroprotective effects in models of Parkinson's and Huntington's Diseases

Coenzyme Q₁₀ (CoQ₁₀) and creatine are promising agents for neuroprotection in neurodegenerative diseases via their effects on improving mitochondrial function and cellular bioenergetics and their properties as antioxidants. We examined whether a combination of CoQ₁₀ with creatine can exert additive neuroprotective effects in a MPTP mouse model of Parkinson's disease, a 3-NP rat model of Huntington's disease (HD) and the R6/2 transgenic mouse model of HD. The combination of the two agents produced additive neuroprotective effects against dopamine depletion in the striatum and loss of tyrosine hydroxylase neurons in the substantia nigra pars compacta (SNpc) following chronic subcutaneous administration of MPTP. The combination treatment resulted in significant reduction in lipid peroxidation and pathologic α-synuclein accumulation in the SNpc neurons of the MPTP-treated mice. We also observed additive neuroprotective effects in reducing striatal lesion volumes produced by chronic subcutaneous administration of 3-NP to rats. The combination treatment showed significant effects on blocking 3-NP-induced impairment of glutathione homeostasis and reducing lipid peroxidation and DNA oxidative damage in the striatum. Lastly, the combination of CoQ₁₀ and creatine produced additive neuroprotective effects on improving motor performance and extending survival in the transgenic R6/2 HD mice. These findings suggest that combination therapy using CoQ₁₀ and creatine may be useful in the treatment of neurodegenerative diseases such as Parkinson's disease and HD.