Search

Huntington’s disease is a fatal neurodegenerative disorder caused by an expanded CAG triplet repeat in the huntingtin (HTT) gene. Previous research focused on neuropathology in the striatum and its association with a typical movement disorder. Direct effects of mutant HTT (mHTT) in the striatum may cause neuropathology, although non-cell autonomous effects have also been suggested. Important non-motor features of HD include psychiatric symptoms and metabolic dysfunction, which may be linked to hypothalamic neuropathology. As hypothalamic neurons project to the ventral striatum, we hypothesized that expression of mHTT in the hypothalamus leads to disrupted neurotransmission in the ventral striatum and causes pathology. The overall aim of this study was to investigate the impact of mHTT expression in the hypothalamus on ventral striatal neuropathology and its contribution to non-HD motor symptoms. We demonstrate that selective expression of mHTT in the hypothalamus leads to the loss of dopamine and cAMP-regulated phosphoprotein (DARPP-32) immunopositive neurons in the ventral striatum in mice. Contrary to the effects of direct expression of mHTT in the hypothalamus, selective overexpression of mHTT in the ventral striatum does not affect body weight. Selective expression of mHTT in the ventral striatum leads to mHTT inclusion formation and loss of DARPP-32 neurons without affecting motor activity or anxiety-like behavior. We show that DARPP-32 neuron loss in the ventral striatum is recapitulated in the R6/2 mouse model of HD. Chemogenetic activation of hypothalamic neurons projecting to the ventral striatum had a blunted response in the R6/2 mice compared to wild-type mice, indicating a disrupted hypothalamus-ventral striatal circuitry. In summary, the expression of mHTT in the hypothalamus may impact the development of ventral striatal pathology in mice. This opens the possibility that non-cell-autonomous effects in the reward circuitry play a role in HD.

Huntington’s disease (HD) is a progressive, multifaceted neurodegenerative disease associated with weight loss and gut problems. Under healthy conditions, tight junction (TJ) proteins maintain the intestinal barrier integrity preventing bacterial translocation from the intestinal lumen to the systemic circulation. Reduction of TJs expression in Parkinson’s disease patients has been linked with increased intestinal permeability—leaky gut syndrome. The intestine contains microbiota, most dominant phyla being Bacteroidetes and Firmicutes; in pathogenic or disease conditions the balance between these bacteria might be disrupted. The present study investigated whether there is evidence for an increased intestinal permeability and dysbiosis in the R6/2 mouse model of HD. Our data demonstrate that decreased body weight and body length in R6/2 mice is accompanied by a significant decrease in colon length and increased gut permeability compared to wild type littermates, without any significant changes in the protein levels of the tight junction proteins (occludin, zonula occludens). Moreover, we found an altered gut microbiota in R6/2 mice with increased relative abundance of Bacteroidetes and decreased of Firmicutes. Our results indicate an increased intestinal permeability and dysbiosis in R6/2 mice and further studies investigating the clinical relevance of these findings are warranted.

Huntington’s disease (HD) is caused by CAG repeat expansion in the huntingtin (HTT) gene. Skeletal muscle wasting alongside central pathology is a well-recognized phenomenon seen in patients with HD and HD mouse models. HD muscle atrophy progresses with disease and affects prognosis and quality of life. Satellite cells, progenitors of mature skeletal muscle fibers, are essential for proliferation, differentiation, and repair of muscle tissue in response to muscle injury or exercise.In this study, we aim to investigate the effect of mutant HTT on the differentiation and regeneration capacity of HD muscle by employing in vitro mononuclear skeletal muscle cell isolation and in vivo acute muscle damage model in R6/2 mice.We found that, similar to R6/2 adult mice, neonatal R6/2 mice also exhibit a significant reduction in myofiber width and morphological changes in gastrocnemius and soleus muscles compared to WT mice. Cardiotoxin (CTX)-induced acute muscle damage in R6/2 and WT mice showed that the Pax7+ satellite cell pool was dampened in R6/2 mice at 4 weeks post-injection, and R6/2 mice exhibited an altered inflammatory profile in response to acute damage.Our results suggest that, in addition to the mutant HTT degenerative effects in mature muscle fibers, expression of mutant HTT in satellite cells might alter developmental and regenerative processes to contribute to the progressive muscle mass loss in HD. Taken together, the results presented here encourage further studies evaluating the underlying mechanisms of satellite cell dysfunction in HD mouse models.

Background Skeletal muscle atrophy is one of the hallmarks of Huntington’s disease (HD), and it correlates with inflammation, mitochondrial dysfunction, and altered energy metabolism. Although improvement in muscle wasting has been shown to slow disease progression and increase life span in animal models, the precise mechanism of overall muscle wasting is not well studied. Aim Using an acute injury model, we aimed to investigate the effects of mutant HTT expression on satellite cell regeneration capacity in the R6/2 mouse model. Methods We used adult and neonatal R6/2 mice and their WT littermates. A chemical injury model was employed using cardiotoxin (CTX) in the tibialis anterior muscle. To assess tissue remodeling, we performed immunohistochemistry using laminin to stain basement membrane and embryonic myosin heavy chain (eMHC) as an indicator of muscle regeneration at 4 weeks and 1 week of post-CTX injection, respectively. Results Body weight and fiber diameter were significantly reduced in both adult and neonatal R6/2 mice compared to WT littermates. At four weeks post-injection, fiber diameter was the same between saline and CTX injected group in WT mice. Yet, fiber diameter was increased in the R6/2 CTX compared to the R6/2 saline group. We found a trend towards increased eMHC positive cells in R6/2 compared to the WT littermates at 1-week post-injection. Conclusion R6/2 skeletal muscle has the ability to regenerate new fibers following an acute injury, and the regeneration process was not profoundly affected by mutant huntingtin expression. We will further investigate HD satellite cell proliferation capacity (i.e., Pax7 positive cells) and inflammatory response (i.e., CD68, CD11b) in response to acute muscle injury.

Background Intracellular calcium (Ca2+) transients regulate all aspects of cell function, including excitability, motility, exocytosis and gene expression. Abnormal Ca2+ signalling has been previously linked with Huntington’s disease (HD) neuropathology, however, how and to what extent it affects muscle tissue is unknown. Ghrelin is the gut-peptide hormone that induces intracellular Ca2+ mobilization by binding to ghrelin receptors in the skeletal muscle. Ghrelin may potentially modify HD muscle phenotype, thus be of relevance for HD treatment. Aim Our main goal is to establish a novel analytical platform to characterize intracellular Ca2+ dyshomeostasis and to assess the effect of ghrelin on Ca2+ dynamics in myofibers. Methods To assess intracellular Ca2+ transients in R6/2 mouse muscle cells and in clinical HD and control myoblasts in vitro, we isolate satellite cells from R6/2 and WT gastrocnemius muscle at postnatal days 7-9 and treat them with ghrelin for 3 days at the proliferation stage. Following 7 days of differentiation, we assess myofiber diameter, and gene expression by mRNA and protein levels of muscle-specific targets in response to ghrelin treatment. Results Compared to WT satellite cells, R6/2 satellite cells exhibit reduced myofiber diameter in vitro. MyoD (a protein which plays a crucial role in muscle differentiation) level is significantly decreased in R6/2 mice. Ghrelin treatment promotes myofiber formation, as ghrelin-treated satellite cells from R6/2 gastrocnemius muscle exhibit increased myofiber diameter and MyoD protein levels compared to the control group. Conclusion Our preliminary data suggest that treatment with ghrelin delays muscle atrophy in R6/2 mice at early stages of HD disease/phenotype. To understand its role in Ca2+ homeostasis, we will analyze intracellular Ca2+ signal patterns and correlate this with the morphological shape descriptors in satellite cells from both R6/2 mice and HD patients.

BackgroundHuntington’s disease (HD) is a neurodegenerative disorder caused by a CAG repeat expansion in the huntingtin (HTT) gene. Metabolic changes are associated with HD progression, and underlying mechanisms are not fully known. As the IKKβ/NF-κB pathway is an essential regulator of metabolism, we investigated the involvement of IKKβ, the upstream activator of NF-κB in hypothalamus-specific HD metabolic changes.MethodsUsing viral vectors, we expressed amyloidogenic N-terminal fragments of mutant HTT (mHTT) fragments in the hypothalamus of mice without IKKβ in the CNS (IKKβ-/-) and control mice (IKKβ+/+). We assessed effects on body weight, metabolic hormones, and hypothalamic neuropathology.ResultsHypothalamic expression of mHTT led to an obese phenotype only in female mice. CNS-specific inactivation of IKKβ prohibited weight gain in females, which was independent of neuroprotection and microglial activation.ConclusionsThe expression of mHTT in the hypothalamus causes metabolic imbalance in a sex-specific fashion, and central inhibition of the IKKβ pathway attenuates the obese phenotype.

Aims: Metabolic dysfunction is involved in modulating the disease process in Huntington disease (HD) but the underlying mechanisms are not known. The aim of this study was to investigate if the metabolic regulators sirtuins are affected in HD. Methods: Quantitative real-time polymerase chain reactions were used to assess levels of SIRT1-3 and downstream targets in post mortem brain tissue from HD patients and control cases as well as after selective hypothalamic expression of mutant huntingtin (HTT) using recombinant adeno-associated viral vectors in mice. Results: We show that mRNA levels of the metabolic regulator SIRT1 are increased in the striatum and the cerebral cortex but not in the less affected cerebellum in post mortem HD brains. Levels of SIRT2 are only increased in the striatum and SIRT3 is not affected in HD. Interestingly, mRNA levels of SIRT1 are selectively increased in the lateral hypothalamic area (LHA) and ventromedial hypothalamus (VMH) in HD. Further analyses of the LHA and VMH confirmed pathological changes in these regions including effects on SIRT1 downstream targets and reduced mRNA levels of orexin (hypocretin), prodynorphin and melanin-concentrating hormone (MCH) in the LHA and of brain-derived neurotrophic factor (BDNF) in the VMH. Analyses after selective hypothalamic expression of mutant HTT suggest that effects on BDNF, orexin, dynorphin and MCH are early and direct, whereas changes in SIRT1 require more widespread expression of mutant HTT. Conclusions: We show that SIRT1 expression is increased in HD-affected brain regions and that metabolic pathways are altered in the HD hypothalamus. (Less)

Background Hypothalamus with its neuroendocrine circuitry is a main regulator of metabolism, emotional control and the reward system. It is also an important region of pathology in clinical Huntington’s disease (HD) with loss of orexin neurons. Given that the hypothalamus is affected already in prodromal HD, pathology in this area may mediate early features of HD such as apathy. We hypothesize that dysfunction of hypothalamic circuitries to the ventral striatum contributes to striatal pathology and the development of altered reward-mediated behavior such as apathy. Aim To investigate the effects of selective mutant HTT expression in the hypothalamus on striatal pathology. Methods Wild-type mice were injected bilaterally with adeno-associated viral (AAV) vectors expressing a mutant (79Q) or a normal (18Q) HTT fragment in the hypothalamus. Stereological quantification of brains processed for DARPP-32, NeuN and cresyl violet was performed in the ventral striatum. Retrograde labelling of the hypothalamic projection neurons to ventral striatum was achieved using a novel vector design. Results Selective hypothalamic expression of a mutant HTT fragment leads to orexin loss and a specific reduction in the number of DARPP-32 and NeuN positive neurons in the ventral striatum. Moreover, the R6/2 model of HD recapitulates these changes with a similar loss of DARPP-32 in ventral striatum. Next, we have shown successful retrograde labelling of hypothalamic projection neurons, which will be sufficient for chemogenetic modulation of hypothalamo-striatal circuitries to investigate the underlying neuronal dysfunction. Conclusions These results suggest that hypothalamic mutant HTT expression can potentially contribute to pathological mechanisms underlying ventral striatum pathology in HD.

There is an unmet need to reliably and non-invasively monitor disease progression in preclinical Huntington’s disease (HD) models. As a marker of axonal damage, neurofilament light chain (NfL) has been suggested a marker for neurodegeneration. NfL concentrations in blood and CSF were recently shown to have prognostic value for clinical HD progression and brain atrophy. We therefore hypothesized that CSF and blood NfL concentrations could be useful preclinical HD markers, reflecting underlying pathology. To test our hypothesis we utilized the R6/2 mouse model of HD and measured NfL concentrations in CSF and serum using the ultrasensitive Single molecule array (Simoa) platform. In addition, we assessed HD mouse disease characteristics. We found robust increases of NfL in CSF and serum in R6/2 mice compared to wild-type littermates. CSF and serum concentrations of NfL were significantly correlated, suggesting similar marker potential of serum NfL. CSF and serum concentrations of NfL correlated with disease severity, as assessed by striatal volume and body weight loss. We here provide evidence that CSF and blood NfL concentrations can be used as accessible and reliable pre-clinical HD markers. This will be of potential use for monitoring HD mouse model disease progression and evaluating preclinical disease-modifying treatment response.

Mutations in components of the molecular motor dynein/dynactin lead to neurodegenerative diseases of the motor system or atypical parkinsonism. These mutations are associated with prominent accumulation of vesicles involved in autophagy and lysosomal pathways, and with protein inclusions. Whether alleviating these defects would affect motor symptoms remain unknown. Here, we show that a mouse model expressing low levels of disease linked-G59S mutant dynactin p150(Glued) develops motor dysfunction >8 months before loss of motor neurons or dopaminergic degeneration is observed. Abnormal accumulation of autophagosomes and protein inclusions were efficiently corrected by lowering dietary protein content, and this was associated with transcriptional upregulations of key players in autophagy. Most importantly this dietary modification partially rescued overall neurological symptoms in these mice after onset. Similar observations were made in another mouse strain carrying a point mutation in the dynein heavy chain gene. Collectively, our data suggest that stimulating the autophagy/lysosomal system through appropriate nutritional intervention has significant beneficial effects on motor symptoms of dynein/dynactin diseases even after symptom onset.

Hypothalamic pathology, metabolic dysfunction and psychiatric symptoms are part of Huntington disease (HD), which is caused by an expanded CAG repeat in the huntingtin (HTT) gene. Inactivation of mutant HTT selectively in the hypothalamus prevents the development of metabolic dysfunction and depressive-like behavior in the BACHD mouse model. The hypothalamic paraventricular nucleus (PVN) is implicated in metabolic and emotional control, therefore we here tested whether inactivation of mutant HTT in the PVN affects metabolic and psychiatric manifestations of HD in BACHD mice. BACHD mice were crossed with mice expressing Cre-recombinase under the Sim1 promoter (Sim1-Cre) to inactivate mutant HTT in Sim1 expressing cells, i.e. the PVN of the hypothalamus. We found that inactivation of mutant HTT in Sim1 cells had a sex-specific effect on both the metabolic and the psychiatric phenotype, as these phenotypes were no longer different in male BACHD/Sim1-Cre mice compared to wild-type littermates. We also found a reduced number of GnRH neurons specifically in the anterior hypothalamus and an increased testes weight in male BACHD mice compared to wild-type littermates. Taken together, expression of mutant HTT in Sim1 cells may play a role for the development of metabolic dysfunction and depressive-like behavior in male BACHD mice.

Expression of mutant huntingtin (htt) protein has been shown to cause metabolic imbalance in animal models of Huntington disease (HD). The pathways involved are not fully understood but dysfunction of both the hypothalamus and brown adipose tissue (BAT) has been implicated. Here we show that targeted expression of mutant HTT in the hypothalamus leads to loss of the A13 dopaminergic cell group located in the zona incerta and reduced mRNA expression of neuropeptide Y1 receptor in the hypothalamus. Furthermore, this is accompanied by downregulation of uncoupling protein 1 expression and PPARγ coactivator-1 alpha in BAT and a rapid body weight gain. Taken together, our data might provide a mechanistic link between expression of mutant HTT, reduced activity of a hypothalamic dopaminergic pathway and dysfunction of BAT and in part explain the development of an obese phenotype in HD mouse models.

Background Huntington’s disease (HD) patients exhibit skeletal muscle wasting that reduces muscle strength and as the disease progresses the muscle degeneration becomes one of the principal components of HD. Muscle pathology in HD correlates with disease duration, as well as CAG repeat length and has been suggested to result from transcriptional dysregulation and mitochondrial abnormalities in muscle fibres. So far, however, no study addressed whether mutant huntingtin (mHTT) expression is the sole cause of abnormalities in the muscle fibres, i.e. alterations of progenitor satellite cell (myoblast) differentiation into the muscle fibres that results in hindered formation and maintenance of skeletal muscle. Aim To determine whether mHTT expression in satellite cells causes and is the principle contributor of severe muscle wasting and motor disturbances in HD. Methods We will characterise the mechanisms and effects of mHTT expression on the proliferation, differentiation capacity and viability of satellite cells in R6/2 and BACHD mouse models of HD. Preliminary results We show that R6/2 and BACHD mouse models exhibit the morphological changes in skeletal muscle. The qualitative histopathological analysis of gastrocnemius muscle tissue revealed chronic muscle degeneration associated with increased endomysial connective tissue, abnormal variation in fibre size in both HD mouse models. Conclusions BACHD and R6/2 mouse models are potentially valuable for understanding HD skeletal muscle pathology, which opens up for identifying disease specific alterations and biomarkers that will aid in assessing the response to future treatment strategies.

The most prominent neuropathology in Huntington’s disease (HD) includes loss of medium spiny projection neurons expressing cAMP regulated phosphoprotein (DARPP-32) in the striatum. Recent studies have indicated that hypothalamic neuropathology with loss of orexin neurons is part of HD. As hypothalamic changes may in fact occur before striatal pathology in HD and ventral striatum receives projections from the hypothalamus, we hypothesised that hypothalamic expression of mutant huntingtin (HTT) may be involved in the development of striatal pathology in HD. Aims: Our aim was therefore to investigate the striatal effects of selective mutant HTT expression in the hypothalamus. Methods Wild-type mice were injected bilaterally with adeno-associated viral vectors expressing a mutant (79Q) or a normal (18Q) HTT fragment in the hypothalamus. Stereological quantification of brains processed for DARPP-32, NeuN and cresyl violet was performed in the striatum at 40–52 weeks post-injection. Results Selective hypothalamic expression of a long mutant HTT fragment (853 aa) leads to orexin loss and a specific reduction in the number of DARPP-32 and NeuN positive neurons with no increase in the number of glial cell profiles in the ventral striatum. Hypothalamic overexpression of shorter fragments (171 aa) with both 79 Q and 18 Q leads to a similar loss of both orexin and striatal neurons. Conclusions These results suggest that hypothalamic overexpression of HTT fragments can lead to loss of medium spiny neurons in the striatum and opens up the possibility that there may be a contribution of dysfunctional hypothalamic neurocircuitries to HD striatal pathology.

Background The homeostatic control of emotions and metabolism is disturbed in Huntington disease (HD). We have recently shown that specific neuropeptide populations in the hypothalamus are affected in HD patients. Transcriptional dysregulation is well known to occur in HD and it has been reported also in the hypothalamus of transgenic HD mice. Less is known about the extent of transcriptional dysregulation in the different hypothalamic nuclei in clinical HD. Aim To investigate whether there are changes in gene expression levels of emotion and metabolism regulating factors in key hypothalamic circuitries in human post mortem tissues from individuals affected with HD. Methods/techniques We have dissected frozen tissue from the paraventricular nucleus, the ventromedial nucleus, the lateral hypothalamus and the supraoptic nucleus of the hypothalamus from 4 HD cases and 4 sex-and age-matched controls. The tissue was then processed for quantitative real time PCR. Results/outcome The RNA integrity value was found to be above 7 for all samples. Our results show reduced mRNA expression levels of orexin (hypocretin) in the lateral hypothalamus as well as of dopamine receptor D2 expression in HD. We have also detected reduced expression of brain-derived neurotrophic factor (BDNF) in the ventromedial hypothalamus in HD. Conclusions These results show significant and specific alterations in gene expression in key hypothalamic nuclei involved in the regulation of emotions and metabolism. Transcriptional alterations in this region may be important for the development of the early non-motor symptoms and signs in HD, and may provide potential targets for therapeutic interventions.