Jenny Sassone

Impaired PGC-1α function in muscle in Huntington's disease

We investigated the role of PPAR gamma coactivator 1alpha (PGC-1alpha) in muscle dysfunction in Huntingtons disease (HD). We observed reduced PGC-1alpha and target genes expression in muscle of HD transgenic mice. We produced chronic energy deprivation in HD mice by administering the catabolic stressor beta-guanidinopropionic acid (GPA), a creatine analogue that reduces ATP levels, activates AMP-activated protein kinase (AMPK), which in turn activates PGC-1alpha. Treatment with GPA resulted in increased expression of AMPK, PGC-1alpha target genes, genes for oxidative phosphorylation, electron transport chain and mitochondrial biogenesis, increased oxidative muscle fibers, numbers of mitochondria and motor performance in wild-type, but not in HD mice. In muscle biopsies from HD patients, there was decreased PGC-1alpha, PGC-1beta and oxidative fibers. Oxygen consumption, PGC-1alpha, NRF1 and response to GPA were significantly reduced in myoblasts from HD patients. Knockdown of mutant huntingtin resulted in increased PGC-1alpha expression in HD myoblast. Lastly, adenoviral-mediated delivery of PGC-1alpha resulted increased expression of PGC-1alpha and markers for oxidative muscle fibers and reversal of blunted response for GPA in HD mice. These findings show that impaired function of PGC-1alpha plays a critical role in muscle dysfunction in HD, and that treatment with agents to enhance PGC-1alpha function could exert therapeutic benefits. Furthermore, muscle may provide a readily accessible tissue in which to monitor therapeutic interventions.

Huntington's disease: The current state of research with peripheral tissues

Huntingtons disease (HD) is a genetically dominant condition caused by expanded CAG repeats. These repeats code for a glutamine tract in the HD gene product huntingtin (htt), which is a protein expressed in almost all tissues. Although most HD symptoms reflect preferential neuronal death in specific brain regions, even before the HD gene was identified numerous reports had described additional abnormalities in the peripheral tissues of HD patients, including weight loss, altered glucose homeostasis, and sub-cellular abnormalities in fibroblasts, lymphocytes and erythrocytes. Several years have elapsed since the HD mutation was discovered, and analyses of peripheral tissues from HD patients have helped to understand the molecular pathogenesis of the disease and revealed that the molecular mechanisms through which mutated htt leads to cell dysfunction are widely shared between central nervous system (CNS) and peripheral tissues. These studies show that in peripheral tissues, mutated htt causes accumulation of intracellular protein aggregates, impairment of energetic metabolism, transcriptional deregulation and hyperactivation of programmed cell-death mechanisms. Here, we review the current knowledge of peripheral tissue alterations in HD patients and in animal models of HD and focus on how this information can be used to identify potential therapeutic possibilities and biomarkers for disease progression.

Ganglioside GM1 induces phosphorylation of mutant huntingtin and restores normal motor behavior in Huntington disease mice

Huntington disease (HD) is a progressive neurodegenerative monogenic disorder caused by expansion of a polyglutamine stretch in the huntingtin (Htt) protein. Mutant huntingtin triggers neural dysfunction and death, mainly in the corpus striatum and cerebral cortex, resulting in pathognomonic motor symptoms, as well as cognitive and psychiatric decline. Currently, there is no effective treatment for HD. We report that intraventricular infusion of ganglioside GM1 induces phosphorylation of mutant huntingtin at specific serine amino acid residues that attenuate huntingtin toxicity, and restores normal motor function in already symptomatic HD mice. Thus, our studies have identified a potential therapy for HD that targets a posttranslational modification of mutant huntingtin with critical effects on disease pathogenesis.

Brain-Derived Neurotrophic Factor in Patients with Huntington's Disease

Reduced Brain-Derived Neurotrophic Factor (BDNF) levels have been described in a number of patho-physiological conditions, most notably, in Huntingtons disease (HD), a progressive neurodegenerative disorder. Since BDNF is also produced in blood, we have undertaken the measurement of its peripheral levels in the attempt to identify a possible link with HD prognosis and/or its progression. Here we evaluated BDNF level in 398 blood samples including 138 controls, 56 preHD, and 204 HD subjects. We found that BDNF protein levels were not reliably different between groups, whether measured in plasma (52 controls, 26 preHD, 105 HD) or serum (39 controls, 5 preHD, 29 HD). Our experience, and a re-analysis of the literature highlighted that intra-group variability and methodological aspects affect this measurement, especially in serum. We also assessed BDNF mRNA levels in blood samples from 47 controls, 25 preHD, and 70 HD subjects, and found no differences among the groups. We concluded that levels of BDNF in human blood were not informative (mRNA levels or plasma protein level) nor reliable (serum protein levels) as HD biomarkers. We also wish to warn the scientific community in interpreting the significance of changes measured in BDNF protein levels in serum from patients suffering from different conditions.

Distinct brain volume changes correlating with clinical stage, disease progression rate, mutation size, and age at onset prediction as early biomarkers of brain atrophy in Huntington's disease.

Searching brain and peripheral biomarkers is a requisite to cure Huntingtons disease (HD). To search for markers indicating the rate of brain neurodegenerative changes in the various disease stages, we quantified changes in brain atrophy in subjects with HD. We analyzed the cross‐sectional and longitudinal rate of brain atrophy, quantitatively measured by fully‐automated multiparametric magnetic resonance imaging, as fractional gray matter (GM, determining brain cortex volume), white matter (WM, measuring the volume of axonal fibers), and corresponding cerebral spinal fluid (CSF, a measure of global brain atrophy), in 94 gene‐positive subjects with presymptomatic to advanced HD, and age‐matched healthy controls. Each of the three brain compartments we studied (WM, GM, and CSF) had a diverse role and their time courses differed in the development of HD. GM volume decreased early in life. Its decrease was associated with decreased serum brain‐derived‐neurotrophic‐factor and started even many years before onset symptoms, then decreased slowly in a nonlinear manner during the various symptomatic HD stages. WM volume loss also began in the presymptomatic stage of HD a few years before manifest symptoms appear, rapidly decreasing near to the zone‐of‐onset. Finally, the CSF volume increase began many years before age at onset. Its volume measured in presymptomatic subjects contributed to improve the CAG‐based model of age at onset prediction. The progressive CSF increase depended on CAG mutation size and continued linearly until the last stages of HD, perhaps representing the best marker of progression rate and severity in HD (R2= 0.25, P < 0.0001).

Early defect of transforming growth factor β1 formation in Huntington's disease.

A defective expression or activity of neurotrophic factors, such as brain‐ and glial‐derived neurotrophic factors, contributes to neuronal damage in Huntington’s disease (HD). Here, we focused on transforming growth factor‐β (TGF‐β1), a pleiotropic cytokine with an established role in mechanisms of neuroprotection. Asymptomatic HD patients showed a reduction in TGF‐β1 levels in the peripheral blood, which was related to trinucleotide mutation length and glucose hypometabolism in the caudate nucleus. Immunohistochemical analysis in post‐mortem brain tissues showed that TGF‐β1 was reduced in cortical neurons of asymptomatic and symptomatic HD patients. Both YAC128 and R6/2 HD mutant mice showed a reduced expression of TGF‐β1 in the cerebral cortex, localized in neurons, but not in astrocytes. We examined the pharmacological regulation of TGF‐β1 formation in asymptomatic R6/2 mice, where blood TGF‐β1 levels were also reduced. In these R6/2 mice, both the mGlu2/3 metabotropic glutamate receptor agonist, LY379268, and riluzole failed to increase TGF‐β1 formation in the cerebral cortex and corpus striatum, suggesting that a defect in the regulation of TGF‐β1 production is associated with HD. Accordingly, reduced TGF‐β1 mRNA and protein levels were found in cultured astrocytes transfected with mutated exon 1 of the human huntingtin gene, and in striatal knock‐in cell lines expressing full‐length huntingtin with an expanded glutamine repeat. Taken together, our data suggest that serum TGF‐β1 levels are potential biomarkers of HD development during the asymptomatic phase of the disease, and raise the possibility that strategies aimed at rescuing TGF‐β1 levels in the brain may influence the progression of HD.

Aripiprazole in the treatment of Huntington’s disease: a case series

Objectives: The aim of the study was to describe the effects of aripiprazole, a new atypical antipsychotic drug that acts as a partial dopamine agonist on motor, behavioral and cognitive functions in patients with genetically confirmed Huntington’s disease (HD). Methods and results: Three HD patients were evaluated for Unified Huntington Disease Rating Scale part I and II and Beck Depression Inventory at baseline, after two months and one-year treatment. Aripiprazole effectively controlled involuntary movements and psychiatric symptoms, with effects on cognitive functions. Conclusions: Our case reports suggest that aripiprazole is well tolerated, remarkably improving some of the motor and behavioral symptoms in patients affected by HD. Randomized, controlled, long-term studies are warranted.

Impaired expression of insulin-like growth factor-1 system in skeletal muscle of amyotrophic lateral sclerosis patients

Adult muscle fibers are a source of growth factors, including insulin‐like growth factor‐1 (IGF‐1). These factors influence neuronal survival, axonal growth, and maintenance of synaptic connections.

Loss of hnRNP K Impairs Synaptic Plasticity in Hippocampal Neurons

Heterogeneous nuclear ribonucleoprotein K (hnRNP K) is an RNA-binding protein implicated in RNA metabolism. Here, we investigated the role of hnRNP K in synapse function. We demonstrated that hnRNP K regulates dendritic spine density and long-term potentiation (LTP) in cultured hippocampal neurons from embryonic rats. LTP requires the extracellular signal-regulated kinase (ERK)1/2-mediated phosphorylation and cytoplasmic accumulation of hnRNP K. Moreover, hnRNP K knockdown prevents ERK cascade activation and GluA1-S845 phosphorylation and surface delivery, which are essential steps for LTP. These findings establish hnRNP K as a new critical regulator of synaptic transmission and plasticity in hippocampal neurons.

Mutant Huntingtin induces activation of the Bcl-2/adenovirus E1B 19-kDa interacting protein (BNip3)

Huntingtons disease (HD) is a neurodegenerative disorder characterized by progressive neuronal death in the basal ganglia and cortex. Although increasing evidence supports a pivotal role of mitochondrial dysfunction in the death of patients’ neurons, the molecular bases for mitochondrial impairment have not been elucidated. We provide the first evidence of an abnormal activation of the Bcl-2/adenovirus E1B 19-kDa interacting protein 3 (BNip3) in cells expressing mutant Huntingtin. In this study, we show an abnormal accumulation and dimerization of BNip3 in the mitochondria extracted from human HD muscle cells, HD model cell cultures and brain tissues from HD model mice. Importantly, we have shown that blocking BNip3 expression and dimerization restores normal mitochondrial potential in human HD muscle cells. Our data shed light on the molecular mechanisms underlying mitochondrial dysfunction in HD and point to BNip3 as a new potential target for neuroprotective therapy in HD.