Evidences for Mutant Huntingtin Inducing Musculoskeletal and Brain Growth Impairments via Disturbing Testosterone Biosynthesis in Male Huntington Disease Animals.

Body weight (BW) loss and reduced body mass index (BMI) are the most common peripheral alterations in Huntington disease (HD) and have been found in HD mutation carriers and HD animal models before the manifestation of neurological symptoms. This suggests that, at least in the early disease stage, these changes could be due to abnormal tissue growth rather than tissue atrophy. Moreover, BW and BMI are reported to be more affected in males than females in HD animal models and patients. Here, we confirmed sex-dependent growth alterations in the BACHD rat model for HD and investigated the associated contributing factors. Our results showed growth abnormalities along with decreased plasma testosterone and insulin-like growth factor 1 (IGF-1) levels only in males. Moreover, we demonstrated correlations between growth parameters, IGF-1, and testosterone. Our analyses further revealed an aberrant transcription of testosterone biosynthesis-related genes in the testes of BACHD rats with undisturbed luteinizing hormone (LH)/cAMP/PKA signaling, which plays a key role in regulating the transcription process of some of these genes. In line with the findings in BACHD rats, analyses in the R6/2 mouse model of HD showed similar results. Our findings support the view that mutant huntingtin may induce abnormal growth in males via the dysregulation of gene transcription in the testis, which in turn can affect testosterone biosynthesis.

Environmental stimulation in Huntington disease patients and animal models.

While Huntington disease (HD) is caused solely by a polyglutamine expansion in the huntingtin gene, environmental factors can influence HD onset and progression. Here, we review studies linking environment and HD in both humans and animal models. In HD patients, we find that: (i) an active lifestyle associates with both a delayed age at onset of HD and a decreased severity of symptoms, (ii) applying physical exercise and behavioral therapies in small cohorts of HD subjects indicate promising effects on the HD symptomatology, (iii) Mediterranean diet correlates with lower motor impairment, and treatments based on omega-3 fatty acids improve motor function , whereas (iv) increased cortisol levels associate with specific HD symptoms. In animal models, in line with the evidence in humans, physical exercise, environmental enrichment and different types of dietary intervention ameliorate or delay several HD phenotypes. In contrast, stress appears to be involved in the HD pathogenesis, and HD mice present increased stress sensitivity. Importantly, studies in animal models have uncovered several molecular factors mediating environmental effects on HD associated neuropathology. However, the influence of the environment on several key HD mechanisms as well as the underlying regulatory factors remain to be explored. Given the role of epigenetic factors and modifications in the interplay between environment and genes, the exploration of their role as mechanisms underlying the environmental action in HD is a promising avenue for both our fundamental understanding of the disease and as a potential for therapy.

Validation of behavioral phenotypes in the BACHD rat model.

Huntington disease (HD) is a neurodegenerative disorder caused by a polyglutamine expansion in the HTT gene. Various HD animal models have been generated to mimic the motor, cognitive and neuropsychiatric disturbances that affect HD patients. Reproducing disease phenotypes within these models is essential to identify reliable readouts for therapy studies. We validated behavioral phenotypes shown earlier by other research groups in the BACHD rat model, using both previously applied and novel tests for motor, cognitive and anxiety-like behaviors. We first confirmed known BACHD rats' phenotypes in rotarod, open field (OF) and elevated plus maze (EPM) tests. We then assessed the reproducibility of key phenotypes in the model using new tests: cliff hanging, passive avoidance (PA), Morris water maze (MWM), light dark box and light spot tests. We confirmed impaired motor coordination in the rotarod test and reduced activity in the OF. In line with earlier results in BACHD rats using different tests, we showed impaired reversal learning in MWM and decreased anxiety-like behavior with the light spot test supporting the validity of BACHD rats as a model of HD. Results in the EPM, light dark box, cliff hanging and PA tests did not confirm earlier findings. This may depend on phenotype inconsistencies or rather be related to differences in environmental variables, test typology, experimental settings, animal age and chosen behavioral parameters.

Intranasal Administration of Mesenchymal Stem Cells Ameliorates the Abnormal Dopamine Transmission System and Inflammatory Reaction in the R6/2 Mouse Model of Huntington Disease.

Intrastriatal administration of mesenchymal stem cells (MSCs) has shown beneficial effects in rodent models of Huntington disease (HD). However, the invasive nature of surgical procedure and its potential to trigger the host immune response may limit its clinical use. Hence, we sought to evaluate the non-invasive intranasal administration (INA) of MSC delivery as an effective alternative route in HD. GFP-expressing MSCs derived from bone marrow were intranasally administered to 4-week-old R6/2 HD transgenic mice. MSCs were detected in the olfactory bulb, midbrain and striatum five days post-delivery. Compared to phosphate-buffered saline (PBS)-treated littermates, MSC-treated R6/2 mice showed an increased survival rate and attenuated circadian activity disruption assessed by locomotor activity. MSCs increased the protein expression of DARPP-32 and tyrosine hydroxylase (TH) and downregulated gene expression of inflammatory modulators in the brain 7.5 weeks after INA. While vehicle treated R6/2 mice displayed decreased Iba1 expression and altered microglial morphology in comparison to the wild type littermates, MSCs restored both, Iba1 level and the thickness of microglial processes in the striatum of R6/2 mice. Our results demonstrate significantly ameliorated phenotypes of R6/2 mice after MSCs administration via INA, suggesting this method as an effective delivering route of cells to the brain for HD therapy.

The BACHD rat model of Huntington disease shows slowed learning in a Go/No-Go-like test of visual discrimination.

Huntington disease is a hereditary neurodegenerative disease, in which patients display a broad range of clinical symptoms. Among these, impaired inhibitory control has been noted. The BACHD rat is a recently developed and established transgenic animal model for Huntington disease, and characterizing the presence of Huntington disease-like behavioural phenotypes in these animals is of importance. Prior studies have indicated that BACHD rats suffer from impaired inhibitory control, although further studies are necessary to fully understand the scope and specific nature of these phenotypes. In the current study, BACHD rats were trained to perform a Go/No-Go-like test of visual discrimination, akin to behavioural tests that have revealed suspected response inhibition impairments in Huntington disease patients. The results indicate that although BACHD rats showed a slow rate of learning to inhibit responses on No-Go trials, once they had learned to handle the basic discrimination, they had an unchanged ability to withhold lever responses during extended periods of time. This suggests that BACHD rats have specific impairments when applying inhibitory control to a new or changed situation. The findings are in line with previous studies of BACHD rats and support the continued use and characterization of this animal model.

Sexual behavior and testis morphology in the BACHD rat model.

BACKGROUND: Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by a mutation in the huntingtin (HTT) gene, which results in brain neurodegeneration and peripheral pathology affecting different organs including testis. Patients with HD suffer from motor and cognitive impairment, and multiple psychiatric symptoms. Among behavioral abnormalities in HD, sexual disturbances have often been reported, but scarcely investigated in animal models. The BACHD rat model of HD carries the human full-length mutated HTT (mHTT) genomic sequence with 97 CAG-CAA repeats and displays HD-like alterations at neuropathological and behavioral level. OBJECTIVE: This study aims to phenotype the BACHD rats' sexual behavior and performance as well as testis morphology because alterations in these aspects have been associated to HD. METHODS: Two rat cohorts at the age of 3 and 7 months were subjected to mating tests to assess different parameters of sexual behavior. Histological analyses for testis morphology were performed in different rat cohorts at 1.5, 7 and 12 months of age whereas immunohistochemical analyses were carried out at 7 and 12 months of age to visualize the presence of mHTT in testicular tissue. Furthermore, western blot analyses were used to assess HTT and mHTT expression levels in striatum and testis at three months of age. RESULTS: At 3 months, BACHD rats showed a decreased time exploring the female anogenital area (AGA), decreased latency to mount, increased number of intromissions and ejaculations and enhanced hit rate. At 7 months, all sexual parameters were comparable between genotypes with the exception that BACHD rats explored the AGA less than wild type rats. Testis analyses did not reveal any morphological alteration at any of the examined ages, but showed presence of mHTT limited to Sertoli cells in transgenic rats at both 7 and 12 months. BACHD rat HTT and mHTT expression levels in testis were lower than striatum at 3 months of age. CONCLUSIONS: The testis phenotype in the BACHD rat model does not mimic the changes observed in human HD testis. The altered sexual behavior in BACHD rats at three months of age could be to a certain extent representative of and share common underlying pathways with some of the sexual disturbances in HD patients. Further investigating the biological causes of the sexual phenotype in BACHD rats may therefore contribute to clarifying the mechanisms at the base of sexual behavior changes in HD.

Environment-dependent striatal gene expression in the BACHD rat model for Huntington disease.

Huntington disease (HD) is an autosomal dominant neurodegenerative disorder caused by a mutation in the huntingtin (HTT) gene which results in progressive neurodegeneration in the striatum, cortex, and eventually most brain areas. Despite being a monogenic disorder, environmental factors influence HD characteristics. Both human and mouse studies suggest that mutant HTT (mHTT) leads to gene expression changes that harbor potential to be modulated by the environment. Yet, the underlying mechanisms integrating environmental cues into the gene regulatory program have remained largely unclear. To better understand gene-environment interactions in the context of mHTT, we employed RNA-seq to examine effects of maternal separation (MS) and environmental enrichment (EE) on striatal gene expression during development of BACHD rats. We integrated our results with striatal consensus modules defined on HTT-CAG length and age-dependent co-expression gene networks to relate the environmental factors with disease progression. While mHTT was the main determinant of expression changes, both MS and EE were capable of modulating these disturbances, resulting in distinctive and in several cases opposing effects of MS and EE on consensus modules. This bivalent response to maternal separation and environmental enrichment may aid in explaining their distinct effects observed on disease phenotypes in animal models of HD and related neurodegenerative disorders.

BACHD rats expressing full-length mutant huntingtin exhibit differences in social behavior compared to wild-type littermates.

BACKGROUND: Huntington disease (HD) is a devastating inherited neurodegenerative disorder characterized by progressive motor, cognitive, and psychiatric symptoms without any cure to slow down or stop the progress of the disease. The BACHD rat model for HD carrying the human full-length mutant huntingtin protein (mHTT) with 97 polyQ repeats has been recently established as a promising model which reproduces several HD-like features. While motor and cognitive functions have been characterized in BACHD rats, little is known about their social phenotype. OBJECTIVE: This study focuses especially on social behavior since evidence for social disturbances exists in human patients. Our objective was to compare social behavior in BACHD and wild-type (WT) rats at different ages, using two different measures of sociability. METHODS: Animals were tested longitudinally at the age of 2, 4 and 8 months in the social interaction test to examine different parameters of sociability. A separate cohort of 7 month old rats was tested in the three chamber social test to measure both sociability and social novelty. Gene expression analyses in 8 months old animals were performed by real time qRT-PCR to evaluate a potential involvement of D1 and D2 dopaminergic receptors and the contribution of Brain-derived neurotrophic factor (BDNF) to the observed behavioral alterations. RESULTS: In the social interaction test, BACHD rats showed age-dependent changes in behaviour when they were-re introduced to their cagemate after a 24 hours-period of individual housing. The time spent on nape attacks increased with aging. Furthermore, a significant higher level of pinning at 2 months of age was shown in the BACHD rats compared to wild-types, followed by a reduction at 4 and 8 months. On the other hand, BACHD rats exhibited a decreased active social behaviour compared to wild-types, reflected by genotype-effects on approaching, following and social nose contact. In the three chamber social test, BACHD rats seemed to show a mild deficit in preference for social novelty, but no changes in social interest. Molecular analyses revealed that BACHD animals exposed to the social interaction test displayed decreased mRNA levels of the total form of BDNF in ventral striatum and unaltered striatal expression of D1 and D2 dopamine receptors. CONCLUSIONS: Taken together, these results indicate deficits in several parameters representative of sociability. Altered BDNF expression in the ventral striatum may contribute to the deficits in sociability in 8 months old BACHD rats. These data support the validity of the BACHD rat model in mimicking features of certain social deficits that could be relevant to symptoms in patients.

Structural and molecular myelination deficits occur prior to neuronal loss in the YAC128 and BACHD models of Huntington disease.

White matter (WM) atrophy is a significant feature of Huntington disease (HD), although its aetiology and early pathological manifestations remain poorly defined. In this study, we aimed to characterize WM-related features in the transgenic YAC128 and BACHD models of HD. Using diffusion tensor magnetic resonance imaging (DT-MRI), we demonstrate that microstructural WM abnormalities occur from an early age in YAC128 mice. Similarly, electron microscopy analysis of myelinated fibres of the corpus callosum indicated that myelin sheaths are thinner in YAC128 mice as early as 1.5 months of age, well before any neuronal loss can be detected. Transcript levels of myelin-related genes in striatal and cortical tissues were significantly lower in YAC128 mice from 2 weeks of age, and these findings were replicated in differentiated primary oligodendrocytes from YAC128 mice, suggesting a possible mechanistic explanation for the observed structural deficits. Concordant with these observations, we demonstrate reduced expression of myelin-related genes at 3 months of age and WM microstructural abnormalities using DT-MRI at 12 months of age in the BACHD rats. These findings indicate that WM deficits in HD are an early phenotype associated with cell-intrinsic effects of mutant huntingtin on myelin-related transcripts in oligodendrocytes, and raise the possibility that WM abnormalities may be an early contributing factor to the pathogenesis of HD.

Despite higher glucocorticoid levels and stress responses in female rats, both sexes exhibit similar stress-induced changes in hippocampal neurogenesis.

Sex differences in stress reactivity may be one of the factors underlying the increased sensitivity for the development of psychopathologies in women. Particularly, an increased hypothalamic-pituitary-adrenal (HPA) axis reactivity in females may exacerbate stress-induced changes in neuronal plasticity and neurogenesis, which in turn may contribute to an increased sensitivity to psychopathology. The main aim of the present study was to examine male-female differences in stress-induced changes in different aspects of hippocampal neurogenesis, i.e. cell proliferation, differentiation and survival. Both sexes were exposed to a wide variety of stressors, where after differences in HPA-axis reactivity and neurogenesis were assessed. To study the role of oestradiol in potential sex differences, ovariectomized females received low or high physiological oestradiol level replacement pellets. The results show that females in general have a higher basal and stress-induced HPA-axis activity than males, with minimal differences between the two female groups. Cell proliferation in the dorsal hippocampus was significantly higher in high oestradiol females compared to low oestradiol females and males, while doublecortin (DCX) expression as a marker of cell differentiation was significantly higher in males compared to females, independent of oestradiol level. Stress exposure did not significantly influence cell proliferation or survival of new cells, but did reduce DCX expression. In conclusion, despite the male-female differences in HPA-axis activity, the effect of repeated stress exposure on hippocampal cell differentiation was not significantly different between sexes.

Chronic partial sleep deprivation reduces brain sensitivity to glutamate N-methyl-D-aspartate receptor-mediated neurotoxicity.

It has been hypothesized that insufficient sleep may compromise neuronal function and contribute to neurodegenerative processes. While sleep loss by itself may not lead to cell death directly, it may affect the sensitivity to a subsequent neurodegenerative insult. Here we examined the effects of chronic sleep restriction (SR) on the vulnerability of the brain to N-methyl-d-aspartate (NMDA)-induced excitotoxicity. Animals were kept awake 20 h per day and were only allowed to rest during the first 4 h of the light phase, i.e. their normal circadian resting phase. After 30 days of SR all rats received a unilateral injection with a neurotoxic dose of NMDA into the nucleus basalis magnocellularis (NBM). Brains were collected for assessment of damage. In the intact non-injected hemisphere, the number of cholinergic cells in the NBM and the density of their projections in the cortex were not affected by SR. In the injected hemisphere, NMDA caused a significant loss of cholinergic NBM cells and cortical fibres in all animals. However, the loss of cholinergic cells was attenuated in the SR group as compared with the controls. These data suggest that, if anything, SR reduces the sensitivity to a subsequent excitotoxic insult. Chronic SR may constitute a mild threat to the brain that does not lead to neurodegeneration by itself but prepares the brain for subsequent neurotoxic challenges. These results do not support the hypothesis that sleep loss increases the sensitivity to neurodegenerative processes.

Maternal separation decreases adult hippocampal cell proliferation and impairs cognitive performance but has little effect on stress sensitivity and anxiety in adult Wistar rats.

Stressful events during childhood are thought to increase the risk for the development of adult psychopathology. A widely used animal model for early life stress is maternal separation (MS), which is thought to affect development and cause alterations in neuroendocrine stress reactivity and emotionality lasting into adulthood. However, results obtained with this paradigm are inconsistent. Here we investigated whether this variation may be related to the type of stressor or the tests used to assess adult stress sensitivity and behavioral performance. Rat pups were exposed to a 3h daily MS protocol during postnatal weeks 1-2. In adulthood, animals were subjected to a wide variety of stressors and tests to obtain a better view on the effects of MS on adult hypothalamic-pituitary-adrenal (HPA) axis regulation, anxiety-like behavior, social interaction and cognition. Also, the influence of MS on adult hippocampal neurogenesis was studied because it might underlie changes in neuroendocrine regulation and behavioral performance. The results show that, independent of the nature of the stressor, MS did not affect the neuroendocrine response. MS did not influence anxiety-like behavior, explorative behavior and social interaction, but did affect cognitive function in an object recognition task. The amount of new born cells in the hippocampal dentate gyrus was significantly decreased in MS animals; yet, cell differentiation and survival were not altered. In conclusion, while interfering with the mother-infant relationship early in life did affect some aspects of adult neuroplasticity and cognitive function, it did not lead to permanent changes in stress sensitivity and emotionality.

Coping with sleep deprivation: shifts in regional brain activity and learning strategy.

STUDY OBJECTIVES: dissociable cognitive strategies are used for place navigation. Spatial strategies rely on the hippocampus, an area important for flexible integration of novel information. Response strategies are more rigid and involve the dorsal striatum. These memory systems can compensate for each other in case of temporal or permanent damage. Sleep deprivation has adverse effects on hippocampal function. However, whether the striatal memory system can compensate for sleep-deprivation-induced hippocampal impairments is unknown. DESIGN: with a symmetrical maze paradigm for mice, we examined the effect of sleep deprivation on learning the location of a food reward (training) and on learning that a previously nonrewarded arm was now rewarded (reversal training). MEASUREMENTS AND RESULTS: five hours of sleep deprivation after each daily training session did not affect performance during training. However, in contrast with controls, sleep-deprived mice avoided a hippocampus-dependent spatial strategy and preferentially used a striatum-dependent response strategy. In line with this, the training-induced increase in phosphorylation of the transcription factor cAMP response-element binding protein (CREB) shifted from hippocampus to dorsal striatum. Importantly, although sleep-deprived mice performed well during training, performance during reversal training was attenuated, most likely due to rigidity of the striatal system they used. CONCLUSIONS: together, these findings suggest that the brain compensates for negative effects of sleep deprivation on the hippocampal memory system by promoting the use of a striatal memory system. However, effects of sleep deprivation can still appear later on because the alternative learning mechanisms and brain regions involved may result in reduced flexibility under conditions requiring adaptation of previously formed memories.

Sleep deprivation impairs spatial working memory and reduces hippocampal AMPA receptor phosphorylation.

Sleep is important for brain function and cognitive performance. Sleep deprivation (SD) may affect subsequent learning capacity and ability to form new memories, particularly in the case of hippocampus-dependent tasks. In the present study we examined whether SD for 6 or 12 h during the normal resting phase prior to learning affects hippocampus-dependent working memory in mice. In addition, we determined effects of SD on hippocampal glutamate alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and their regulatory pathways, which are crucially involved in working memory. After 12 h SD, but not yet after 6 h, spatial working memory in a novel arm recognition task was significantly impaired. This deficit was not likely due to stress as corticosterone levels after SD were not significantly different between groups. In parallel with the change in cognitive function, we found that 12 h SD significantly reduced hippocampal AMPA receptor phosphorylation at the GluR1-S845 site, which is important for incorporation of the receptors into the membrane. SD did not affect protein levels of cyclic-AMP-dependent protein kinase A (PKA) or phosphatase calcineurin (CaN), which regulate GluR1 phosphorylation. However, SD did reduce the expression of the scaffolding molecule A-kinase anchoring protein 150 (AKAP150), which binds and partly controls the actions of PKA and CaN. In conclusion, a relatively short SD during the normal resting phase may affect spatial working memory in mice by reducing hippocampal AMPA receptor function through a change in AKAP150 levels. Together, these findings provide further insight into the possible mechanism of SD-induced hippocampal dysfunction and memory impairment.

Chronically restricted sleep leads to depression-like changes in neurotransmitter receptor sensitivity and neuroendocrine stress reactivity in rats.

STUDY OBJECTIVES: Frequently disrupted and restricted sleep is a common problem for many people in our Western society. In the long run, insufficient sleep may have repercussions for health and may sensitize individuals to psychiatric diseases. In this context, we applied an animal model of chronic sleep restriction to study effects of sleep loss on neurobiological and neuroendocrine systems that have been implied in the pathophysiology of depression, particularly the serotonergic system and the hypothalamic-pituitary-adrenal (HPA) axis. DESIGN: Adult rats were exposed to a schedule of chronic partial sleep deprivation allowing them only 4 h of sleep per day. Sleep restriction was achieved by placing the animals in slowly rotating drums. To examine the regulation and reactivity of the HPA axis, blood samples were collected to measure adrenocorticotropin (ACTH) and corticosterone (CORT) responses. MEASUREMENTS AND RESULTS: While one day of restricted sleep had no significant effect on HPA axis stress reactivity, sleep restriction for a week caused a blunted pituitary ACTH response in a conditioned fear paradigm. Despite this lower ACTH response, adrenal CORT release was normal. The blunted pituitary response may be related to reduced sensitivity of serotonin-1A receptors and/or receptors for corticotropin-releasing hormone (CRH), since sleep restricted rats showed similar reductions in ACTH release to direct pharmacological stimulation with a serotonin-1A agonist or CRH. CONCLUSIONS: Chronic sleep restriction may lead to changes in neurotransmitter receptor systems and neuroendocrine reactivity in a manner similar to that seen in depression. This experimental study thus supports the hypothesis that disrupted and restricted sleep may contribute to the symptomatology of psychiatric disorders.