Sex may influence motor phenotype in a novel rodent model of cerebral palsy.

Cerebral palsy (CP) is the most common cause of childhood motor disability, manifesting most often as spasticity and/or dystonia. Spasticity and dystonia are often co-morbid clinically following severe injury at term gestation. Currently available animal CP models have not demonstrated or differentiated between these two motor phenotypes, limiting their clinical relevance. We sought to develop an animal CP model displaying objectively identifiable spasticity and dystonia. We exposed rat pups at post-natal day 7-8 (equivalent to human 37 post-conceptional weeks) to global hypoxia. Since spasticity and dystonia can be difficult to differentiate from each other in CP, objective electrophysiologic markers of motor phenotypes were assessed. Spasticity was inferred using an electrophysiologic measure of hyperreflexia: soleus Hoffman reflex suppression with 2 Hz tibial nerve stimulation. Dystonia was assessed during voluntary isometric hindlimb withdrawal at different levels of arousal by calculating tibialis anterior and triceps surae electromyographic co-activation as a surrogate of overflow muscle activity. Hypoxia affected spasticity and dystonia measures in a sex-dependent manner. Males had attenuated Hoffman reflex suppression suggestive of spasticity but no change in antagonist muscle co-activation. In contrast, females demonstrated increased co-activation suggestive of dystonia but no change in Hoffman reflex suppression. Therefore, there was an unexpected segregation of electrophysiologically-defined motor phenotypes based on sex with males predominantly demonstrating spasticity and females predominantly demonstrating dystonia. These results require human clinical confirmation but suggest that sex could play a critical role in the motor manifestations of neonatal brain injury.

Native mutant huntingtin in human brain: evidence for prevalence of full-length monomer.

Huntington disease (HD) is caused by polyglutamine expansion in the N terminus of huntingtin (htt). Analysis of human postmortem brain lysates by SDS-PAGE and Western blot reveals htt as full-length and fragmented. Here we used Blue Native PAGE (BNP) and Western blots to study native htt in human postmortem brain. Antisera against htt detected a single band broadly migrating at 575-850 kDa in control brain and at 650-885 kDa in heterozygous and Venezuelan homozygous HD brains. Anti-polyglutamine antisera detected full-length mutant htt in HD brain. There was little htt cleavage even if lysates were pretreated with trypsin, indicating a property of native htt to resist protease cleavage. A soluble mutant htt fragment of about 180 kDa was detected with anti-htt antibody Ab1 (htt-(1-17)) and increased when lysates were treated with denaturants (SDS, 8 M urea, DTT, or trypsin) before BNP. Wild-type htt was more resistant to denaturants. Based on migration of in vitro translated htt fragments, the 180-kDa segment terminated ≈htt 670-880 amino acids. If second dimension SDS-PAGE followed BNP, the 180-kDa mutant htt was absent, and 43-50 kDa htt fragments appeared. Brain lysates from two HD mouse models expressed native full-length htt; a mutant fragment formed if lysates were pretreated with 8 M urea + DTT. Native full-length mutant htt in embryonic HD(140Q/140Q) mouse primary neurons was intact during cell death and when cell lysates were exposed to denaturants before BNP. Thus, native mutant htt occurs in brain and primary neurons as a soluble full-length monomer.

Dysregulation of CalDAG-GEFI and CalDAG-GEFII predicts the severity of motor side-effects induced by anti-parkinsonian therapy.

Voluntary movement difficulties in Parkinson's disease are initially relieved by l-DOPA therapy, but with disease progression, the repeated l-DOPA treatments can produce debilitating motor abnormalities known as l-DOPA-induced dyskinesias. We show here that 2 striatum-enriched regulators of the Ras/Rap/ERK MAP kinase signal transduction cascade, matrix-enriched CalDAG-GEFI and striosome-enriched CalDAG-GEFII (also known as RasGRP), are strongly and inversely dysregulated in proportion to the severity of abnormal movements induced by l-DOPA in a rat model of parkinsonism. In the dopamine-depleted striatum, the l-DOPA treatments produce down-regulation of CalDAG-GEFI and up-regulation of CalDAG-GEFII mRNAs and proteins, and quantification of the mRNA levels shows that these changes are closely correlated with the severity of the dyskinesias. As these CalDAG-GEFs control ERK cascades, which are implicated in l-DOPA-induced dyskinesias, and have differential compartmental expression patterns in the striatum, we suggest that they may be key molecules involved in the expression of the dyskinesias. They thus represent promising new therapeutic targets for limiting the motor complications induced by l-DOPA therapy.

Milestones in huntington disease.

There have been extraordinary advances in our knowledge of the underlying gene, the protein it encodes, various models of disease, and potential targets for effective therapies for Huntington disease. Huntington disease research has increased exponentially in the past 25 years, and we now understand many of the molecular mechanisms underlying the disease. Still, more work needs to be done before we have a full understanding of the pathophysiology of the disease. Clinical research on biomarkers and clinical trials on potential neuroprotective agents are underway. Here we review our progress in these areas over the last 25 years and speculate on what the next 25 years may hold.

Phosphorylation of the homer-binding domain of group I metabotropic glutamate receptors by cyclin-dependent kinase 5.

Phosphorylation of neurotransmitter receptors can modify their activity and regulate neuronal excitability. Cyclin-dependent kinase 5 (cdk5) is a proline-directed serine/threonine kinase involved not only in neuronal development, but also in synaptic function and plasticity. Here we demonstrate that group I metabotropic glutamate receptors (mGluRs), which modulate post-synaptic signaling by coupling to intracellular signal transduction pathways, are phosphorylated by cdk5. In vitro kinase assays reveal that cdk5 phosphorylates mGluR5 within the domain of the receptor that interacts with the scaffolding protein homer. Using a novel phosphospecific mGluR antibody, we show that the homer-binding domain of both mGluR1 and mGluR5 are phosphorylated in vivo, and that inhibition of cdk5 with siRNA decreases the amount of phosphorylated receptor. Furthermore, kinetic binding analysis, by surface plasmon resonance, indicates that phosphorylation of mGluR5 enhances its association with homer. Homer protein complexes in the post-synaptic density, and their disruption by an activity-dependent short homer 1a isoform, have been shown to regulate the trafficking and signaling of the mGluRs and impact many neuroadaptive processes. Phosphorylation of the mGluR homer-binding domain, in contrast to homer 1a induction, provides a novel mechanism for potentially regulating a subset of homer interactions.

Phenotype-genotype discrepancies in the prospective Huntington at-risk observational study.

OBJECTIVE: To examine phenotype-genotype discrepancies (PGDs) wherein genotype-concealed and prospective judgments of the motor onset of Huntington disease (HD) occurred among at-risk adults who had nonexpanded (<37) cytosine-adenine-guanine (CAG) trinucleotide DNA repeats. METHODS: We examined the prospective clinical assessments of investigators who were kept unaware of individual CAG lengths in the Prospective Huntington At-Risk Observational Study (PHAROS) who enrolled and followed undiagnosed adults at risk for HD who chose not to learn their gene status. Subjects (n = 1001) at 43 Huntington Study Group research sites in the US and Canada were evaluated prospectively and systematically between 1999 and 2009. At each site, an investigator was designated to perform comprehensive clinic assessments and another investigator to rate only the motor examination. Phenoconversion from a "premanifest" status to a confidently "manifest" status was based on investigator judgment (diagnostic confidence level) of the extrapyramidal motor features of HD. RESULTS: There were 20 PGDs that over time had less severe motor scores than the 101 phenoconversions with CAG ≥37, but more severe motor scores than nonconversions. Following conversion, subjects with CAG ≥37 expansions worsened more motorically and cognitively than PGD subjects in the < 37 group. PGDs were concentrated among three sites and a few investigators, especially raters who only assessed the motor examination. INTERPRETATION: The ability to detect the clinical onset of HD in a timely and reliable fashion remains the key for developing experimental treatments aimed at postponing the clinical onset of HD. Comprehensive clinical evaluation is a more accurate and reliable basis for determining HD clinical onset than sole reliance on judging the extrapyramidal features of HD.

The Prospective Huntington At-Risk Observational Study (PHAROS): The Emotional Well-Being, Safety and Feasibility of Long-Term Research Participation.

BACKGROUND: There is limited understanding of the feasibility of conducting long-term research among undiagnosed (pre-symptomatic) adults at risk to develop Huntington disease (HD), while protecting their emotional well-being and safety. OBJECTIVE: To assess pre-specified events pertaining to emotional well-being, safety, and feasibility among healthy consenting adults at risk for developing HD who have chosen not to undergo genetic testing. METHODS: PHAROS research participants prospectively reported the occurrence of events pertaining to psychological distress (psychiatric evaluations, depression, suicidality) and feasibility (maintaining confidentiality, study attrition). PHAROS enrolled 1001 participants. RESULTS: Events pertaining to psychological distress were reported by 35% of participants. The most common events included heightened suicide risk (26%), new onset depression (12%), and new mental health evaluation (9%); all occurred significantly more frequently among participants with expanded trinucleotide CAG repeats (≥37). Five deaths occurred, none related to suicide. Forty-one percent of participants reported self-disclosure of their HD at-risk status, and 15% reported that someone else (usually a family member) had done so. Confidentiality of CAG test results was maintained by investigators. The withdrawal rate was largely uniform over the study period and did not differ significantly by gender or CAG status. CONCLUSIONS: The potentially vulnerable research participants in PHAROS showed good emotional tolerability and safety. Individual CAG data were not disclosed, and confidentiality about disclosure of at-risk HD status was well maintained by others (family, friends, etc.). Long-term research participation of adults at risk for HD who choose not to undergo pre-symptomatic DNA testing is well tolerated, safe and feasible.

Discovery of a novel small-molecule targeting selective clearance of mutant huntingtin fragments.

CAG-triplet repeat extension, translated into polyglutamines within the coding frame of otherwise unrelated gene products, causes 9 incurable neurodegenerative disorders, including Huntington's disease. Although an expansion in the CAG repeat length is the autosomal dominant mutation that causes the fully penetrant neurological phenotypes, the repeat length is inversely correlated with the age of onset. The precise molecular mechanism(s) of neurodegeneration remains elusive, but compelling evidence implicates the protein or its proteolytic fragments as the cause for the gain of novel pathological function(s). The authors sought to identify small molecules that target the selective clearance of polypeptides containing pathological polyglutamine extension. In a high-throughput chemical screen, they identified compounds that facilitate the clearance of a small huntingtin fragment with extended polyglutamines fused to green fluorescent protein reporter. Identified hits were validated in dose-response and toxicity tests. Compounds have been further tested in an assay for clearance of a larger huntingtin fragment, containing either pathological or normal polyglutamine repeats. In this assay, the authors identified compounds selectively targeting the clearance of mutant but not normal huntingtin fragments. These compounds were subjected to a functional assay, which yielded a lead compound that rescues cells from induced mutant polyglutamine toxicity.

Discovery of bioactive small-molecule inhibitor of poly adp-ribose polymerase: implications for energy-deficient cells.

Poly (ADP-ribose) polymerase (PARP1) is a nuclear protein that, when overactivated by oxidative stress-induced DNA damage, ADP ribosylates target proteins leading to dramatic cellular ATP depletion. We have discovered a biologically active small-molecule inhibitor of PARP1. The discovered compound inhibited PARP1 enzymatic activity in vitro and prevented ATP loss and cell death in a surrogate model of oxidative stress in vivo. We also investigated a new use for PARP1 inhibitors in energy-deficient cells by using Huntington's disease as a model. Our results showed that insult with the oxidant hydrogen peroxide depleted cellular ATP in mutant cells below the threshold of viability. The protective role of PARP1 inhibitors against oxidative stress has been shown in this model system.

The Complexity of Clinical Huntington's Disease: Developments in Molecular Genetics, Neuropathology and Neuroimaging Biomarkers.

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder characterised by extensive neuronal loss in the striatum and cerebral cortex, and a triad of clinical symptoms affecting motor, cognitive/behavioural and mood functioning. The mutation causing HD is an expansion of a CAG tract in exon 1 of the HTT gene. This chapter provides a multifaceted overview of the clinical complexity of HD. We explore recent directions in molecular genetics including the identification of loci that are genetic modifiers of HD that could potentially reveal therapeutic targets beyond the HTT gene transcript and protein. The variability of clinical symptomatology in HD is considered alongside recent findings of variability in cellular and neurochemical changes in the striatum and cerebral cortex in human brain. We review evidence from structural neuroimaging methods of progressive changes of striatum, cerebral cortex and white matter in pre-symptomatic and symptomatic HD, with a particular focus on the potential identification of neuroimaging biomarkers that could be used to test promising disease-specific and modifying treatments. Finally we provide an overview of completed clinical trials in HD and future therapeutic developments.

Interactions between metabotropic glutamate 5 and adenosine A2A receptors in normal and parkinsonian mice.

Evidence for heteromeric receptor complexes comprising adenosine A2A and metabotropic glutamate 5 (mGlu5) receptors in striatum has raised the possibility of synergistic interactions between striatal A2A and mGlu5 receptors. We investigated the role of striatal A2A receptors in the locomotor stimulant and antiparkinsonian properties of mGlu5 antagonists using complementary pharmacologic and genetic approaches. Locomotion acutely stimulated by the mGlu5 antagonist [2-methyl-6-(phenylethynyl)-pyridine (MPEP)] was absent in mGlu5 knock-out (KO) mice and was potentiated by an A2A antagonist KW-6002 [(E)-1,3-diethyl-8-(3,4-dimethoxystyryl)-7-methylxanthine], both in normal and in dopamine-depleted (reserpinized) mice. Conversely, the MPEP-induced motor response was markedly attenuated in single and double A2A and D2 receptor KO mice. In contrast, motor stimulation by a D1 dopamine agonist was not attenuated in the KO mice. The A2A receptor dependence of MPEP-induced motor stimulation was investigated further using a postnatal forebrain-specific conditional (Cre/loxP system) KO of the A2A receptor. MPEP loses the ability to stimulate locomotion in conditional KO mice, suggesting that this mGlu5 antagonist effect requires the postdevelopmental action of striatal A2A receptors. The potentiation of mGlu5 antagonist-induced motor stimulation by an A2A antagonist and its dependence on both D2 and forebrain A2A receptors highlight the functional interdependence of these receptors. These data also strengthen a rationale for pursuing a combinational drug strategy for enhancing the antiparkinsonian effects of A2A and mGlu5 antagonists.

Risk Factors for Suicidal Ideation in People at Risk for Huntington's Disease.

BACKGROUND: Suicidal ideation (SI) and attempts are increased in Huntington's disease (HD), making risk factor assessment a priority. OBJECTIVE: To determine whether, hopelessness, irritability, aggression, anxiety, CAG expansion status, depression, and motor signs/symptoms were associated with Suicidal Ideation (SI) in those at risk for HD. METHODS: Behavioral and neurological data were collected from subjects in an observational study. Subject characteristics were calculated by CAG status and SI. Logistic regression models were adjusted for demographics. Separate logistic regressions were used to compare SI and non-SI subjects. A combined logistic regression model, including 4 pre-specified predictors, (hopelessness, irritability, aggression, anxiety) was used to assess the relationship of SI to these predictors. RESULTS: 801 subjects were assessed, 40 were classified as having SI, 6.3% of CAG mutation expansion carriers had SI, compared with 4.3% of non- CAG mutation expansion carriers (p = 0.2275). SI subjects had significantly increased depression (p < 0.0001), hopelessness (p < 0.0001), irritability (p < 0.0001), aggression (p = 0.0089), and anxiety (p < 0.0001), and an elevated motor score (p = 0.0098). Impulsivity, assessed in a subgroup of subjects, was also associated with SI (p = 0.0267). Hopelessness and anxiety remained significant in combined model (p < 0.001; p < 0.0198, respectively) even when motor score was included. CONCLUSIONS: Behavioral symptoms were significantly higher in those reporting SI. Hopelessness and anxiety showed a particularly strong association with SI. Risk identification could assist in assessment of suicidality in this group.

LBH589, A Hydroxamic Acid-Derived HDAC Inhibitor, is Neuroprotective in Mouse Models of Huntington's Disease.

BACKGROUND: Modulation of gene transcription by HDAC inhibitors has been shown repeatedly to be neuroprotective in cellular, invertebrate, and rodent models of Huntington's disease (HD). It has been difficult to translate these treatments to the clinic, however, because existing compounds have limited potency or brain bioavailability. OBJECTIVE: In the present study, we assessed the therapeutic potential of LBH589, an orally bioavailable hydroxamic acid-derived nonselective HDAC inhibitor in mouse models of HD. METHOD: The efficacy of LBH589 is tested in two HD mouse models using various biochemical, behavioral and neuropathological outcome measures. RESULTS: We show that LBH589 crosses the blood brain barrier; induces histone hyperacetylation and prevents striatal neuronal shrinkage in R6/2 HD mice. In full-length knock-in HD mice LBH589-treatment improves motor performance and reduces neuronal atrophy. CONCLUSIONS: Our efficacious results of LBH589 in fragment and full-length mouse models of HD suggest that LBH589 is a promising candidate for clinical assessment in HD patients and provides confirmation that non-selective HDAC inhibitors can be viable clinical candidates.

Changes in the expression of the NR2B subunit during aging in macaque monkeys.

Humans, non-human primates and rodents show declines in spatial memory abilities with increased age. Some of these declines in mice are related to changes in the expression of the epsilon2 (epsilon2) (NR2B) subunit of the N-methyl-D-aspartate receptor. The purpose of this study was to determine whether primates show changes during aging in the mRNA expression of the NR2B subunit. In situ hybridization was performed on tissue sections from three different ages of Rhesus monkeys (Macaca mulatta; 6-8, 10-12, and 24-26 years). There was a significant decrease in the mRNA expression of the NR2B subunit overall in the prefrontal cortex and in the caudate nucleus between young and old monkeys. There were no significant changes in NR2B mRNA expression in the hippocampus or the parahippocampal gyrus. The results in the prefrontal cortex, caudate and hippocampus were similar to those seen previously in C57BL/6 mice during aging, which suggests that mice may be useful as a model for primates to further examine the age-related changes in the expression of the NR2B subunit of the NMDA receptor in several important regions of the brain.

Motor dysfunction and gliosis with preserved dopaminergic markers in human alpha-synuclein A30P transgenic mice.

Alpha-synuclein is a major component of Lewy bodies (LBs) in the substantia nigra and cortex in Parkinson's disease (PD) and dementia with Lewy bodies (DLB), and in glial inclusions in multiple systems atrophy (MSA). Mutations in alpha-synuclein have been associated with autosomal dominant forms of PD. We investigated the clinical and neuropathological effects of overexpression of human alpha-synuclein, alpha-synuclein A30P, and alpha-synuclein A53T under the control of the hamster prion protein (PrP) promoter; 5-15x endogenous levels of protein expression were achieved with widespread neuronal, including nigral, transgene expression. High expression of alpha-synuclein A30P in the Tg5093 line was associated with a progressive motor disorder with rigidity, dystonia, gait impairment, and tremor. Histological analysis of this line showed aberrant expression of the protein in cell soma and progressive CNS gliosis, but no discrete Lewy body-like alpha-synuclein inclusions could be identified. Biochemical analysis demonstrated alpha-synuclein fragmentation. Despite strong expression of the transgene in the nigra, there was no specific deterioration of the nigrostriatal dopaminergic system as assessed by quantitation of nigral tyrosine hydroxylase (TH) containing neurons, striatal TH immunoreactivity, dopamine levels, or dopamine receptor number and function. Lower expressing lines had no specific behavioral or histopathological phenotype. Thus, high expression of mutant human alpha-synuclein resulted in a progressive motor and widespread CNS gliotic phenotype independent of dopaminergic dysfunction in the Tg5093 line.

Age-related changes in the protein expression of subunits of the NMDA receptor.

C57Bl/6 mice show decreased expression of the mRNA for the epsilon2 and zeta1 subunits of the N-methyl-D-aspartate (NMDA) receptor in subregions of the cerebral cortex and hippocampus with increased age. The purpose of this study was to determine the effects of aging on the protein expression of the three major subunits of the NMDA receptor. Semi-quantitative Western blot techniques were applied with the use of antibodies that recognize either the epsilon1 (NR2A), epsilon2 (NR2B) or zeta1 (NR1) subunits of the NMDA receptor or a synaptic terminal protein, synaptophysin. In the cerebral cortex of 30-month-old mice, the level of protein expression of both the epsilon2 and zeta1 subunits were decreased significantly from levels found in the 3- and 10-month-old mice and the protein expression of the epsilon1 subunit showed a significant decline between 10 and 30 months of age. In the hippocampus, the epsilon2 subunit exhibited a higher protein expression level in the 10-month-old mice as compared to both the young and old mice and the zeta1 subunit showed a significant drop in expression in the old mice from both 3- and 10-month-olds. Synaptophysin showed significant declines in protein expression with increasing age. These results demonstrated that changes in the protein expression of the major subunits of the NMDA receptor occur during the aging process and, in some cases, were greater than changes seen previously in mRNA expression. These subunit alterations may explain some of the changes that are seen in NMDA receptor functions during aging.

Analysis of cellular, transgenic and human models of Huntington's disease reveals tyrosine hydroxylase alterations and substantia nigra neuropathology.

Huntington's disease (HD) is a progressive, autosomal dominant neurodegenerative disorder that is pathologically characterized by a striatal-specific degeneration. Aberrant dopamine neurotransmission has been proposed as a mechanism underlying the movement disorder of HD. We report that the enzymatic activity of tyrosine hydroxylase (TH), the rate-limiting enzyme for dopamine biosynthesis, is decreased in a transgenic mouse model of HD. In addition, mutant huntingtin was found to disrupt transcription of TH and dopamine beta-hydroxylase (DbetaH) promoter reporter constructs. In situ hybridization revealed extensive loss of TH mRNA and decreased dopaminergic cell size in human HD substantia nigra. TH-immunoreactive protein was reduced in human grade 4 HD substantia nigra by 32% compared to age-matched controls. These findings implicate abnormalities in dopamine neurotransmission in HD and may provide new insights into targets for pharmacotherapy.