Arginine methylation of RNA-binding proteins is impaired in Huntington's disease

Huntington's disease (HD) is a progressive neurodegenerative disorder caused by a CAG repeat expansion in the HD gene, coding for huntingtin protein (HTT). Mechanisms of HD cellular pathogenesis remain undefined and likely involve disruptions in many cellular processes and functions presumably mediated by abnormal protein interactions of mutant HTT. We previously found HTT interaction with several protein arginine methyl-transferase (PRMT) enzymes. Protein arginine methylation mediated by PRMT enzymes is an important post-translational modification with an emerging role in neurodegeneration. We found that normal (but not mutant) HTT can facilitate the activity of PRMTs in vitro and the formation of arginine methylation complexes. These interactions appear to be disrupted in HD neurons. This suggests an additional functional role for HTT/PRMT interactions, not limited to substrate/enzyme relationship, which may result in global changes in arginine protein methylation in HD. Our quantitative analysis of striatal precursor neuron proteome indicated that arginine protein methylation is significantly altered in HD. We identified a cluster highly enriched in RNA-binding proteins with reduced arginine methylation, which is essential to their function in RNA processing and splicing. We found that several of these proteins interact with HTT, and their RNA-binding and localization are affected in HD cells likely due to a compromised arginine methylation and/or abnormal interactions with mutant HTT. These studies reveal a potential new mechanism for disruption of RNA processing in HD, involving a direct interaction of HTT with methyl-transferase enzymes and modulation of their activity and highlighting methylation of arginine as potential new therapeutic target for HD.

Longitudinal imaging highlights preferential basal ganglia circuit atrophy in Huntington's disease

Huntington's disease is caused by a CAG repeat expansion in the Huntingtin gene (HTT), coding for polyglutamine in the Huntingtin protein, with longer CAG repeats causing earlier age of onset. The variable 'Age' × ('CAG'-L), where 'Age' is the current age of the individual, 'CAG' is the repeat length and L is a constant (reflecting an approximation of the threshold), termed the 'CAG Age Product' (CAP) enables the consideration of many individuals with different CAG repeat expansions at the same time for analysis of any variable and graphing using the CAG Age Product score as the X axis. Structural MRI studies have showed that progressive striatal atrophy begins many years prior to the onset of diagnosable motor Huntington's disease, confirmed by longitudinal multicentre studies on three continents, including PREDICT-HD, TRACK-HD and IMAGE-HD. However, previous studies have not clarified the relationship between striatal atrophy, atrophy of other basal ganglia structures, and atrophy of other brain regions. The present study has analysed all three longitudinal datasets together using a single image segmentation algorithm and combining data from a large number of subjects across a range of CAG Age Product score. In addition, we have used a strategy of normalizing regional atrophy to atrophy of the whole brain, in order to determine which regions may undergo preferential degeneration. This made possible the detailed characterization of regional brain atrophy in relation to CAG Age Product score. There is dramatic selective atrophy of regions involved in the basal ganglia circuit-caudate, putamen, nucleus accumbens, globus pallidus and substantia nigra. Most other regions of the brain appear to have slower but steady degeneration. These results support (but certainly do not prove) the hypothesis of circuit-based spread of pathology in Huntington's disease, possibly due to spread of mutant Htt protein, though other connection-based mechanisms are possible. Therapeutic targets related to prion-like spread of pathology or other mechanisms may be suggested. In addition, they have implications for current neurosurgical therapeutic approaches, since delivery of therapeutic agents solely to the caudate and putamen may miss other structures affected early, such as nucleus accumbens and output nuclei of the striatum, the substantia nigra and the globus pallidus.

Improving the representation of stream water sources in surrogate nutrient models with water isotope data

An important part of meeting nutrient reduction goals in the lower Great Lakes basin and assessing the success of different land management strategies is modeling nutrient losses from agricultural land. This study aimed to improve the representation of water source contributions to streamflow in generalized additive models for predicting nutrient fluxes from three headwater agricultural streams in southern Ontario monitored during the Multi-Watershed Nutrient Study (MWNS). The previous development of these models represented baseflow contributions to streamflow using the baseflow proportion derived using an uncalibrated recursive digital filter. Recursive digital filters are commonly used to partition stream discharge into separate components from slower and faster pathways. In this study, we calibrated the recursive digital filter using stream water source information from stable isotopes of oxygen in water. Across sites, optimization of the filter parameters reduced bias in baseflow estimates by as much as 68 %. In most cases, calibrating the filter also improved agreement between filter-derived baseflow and baseflow calculated from isotope and streamflow data: the average Kling-Gupta Efficiencies using default and calibrated parameters were 0.44 and 0.82, respectively. When incorporated into the generalized additive models, the revised baseflow proportion predictor was more often statistically significant, improved model parsimony, and reduced prediction uncertainty. Moreover, this information allowed for a more rigorous interpretation of how different stream water sources influence nutrient losses from the agricultural MWNS watersheds.

Total and dissolved phosphorus losses from agricultural headwater streams during extreme runoff events

Eutrophication continues to be a concerning global water quality issue. Managing and mitigating harmful algal blooms demands clear information on the conditions promoting large phosphorus losses from contributing watersheds. Of particular concern is the amount and form of phosphorus loading to receiving water bodies during extreme runoff events, which are expected to increase in frequency due to climate change. Five years (2015 to 2020) of water quantity and quality data from 11 agricultural watersheds in the lower Great Lakes basin were analyzed and used to model total and dissolved phosphorus losses. This study aimed to assess temporal dynamics in phosphorus concentrations and losses over runoff events covering a wide range of hydrologic conditions and to quantify their relative importance on annual phosphorus losses. Event concentration-discharge relationships for total and dissolved phosphorus were hysteretic and had contrasting dominant patterns across watersheds. The proportion of annual phosphorus losses during events was highly variable between watersheds, accounting for 47-94 %. Extreme events were particularly impactful: as few as three events per year were found to be responsible for nearly half of total phosphorus (20-50 %) and total dissolved phosphorus (14-44 %) losses. Variability in total and dissolved phosphorus losses and concentrations over a wide range of flow conditions suggests that event magnitude is an important control on the relative mobility of particulate and dissolved phosphorus fractions. This study showed that insights into nutrient dynamics and phosphorus budgets in the lower Great Lakes basin and agriculture dominated environments more broadly can be gained by assessing event nutrient losses with respect to flow conditions and patterns in concentration-discharge relationships.

Neuroprotective Effects of σ2R/TMEM97 Receptor Modulators in the Neuronal Model of Huntington's Disease

Huntington's disease (HD) is a genetic neurodegenerative disease caused by an expanded CAG repeat in the Huntingtin (HTT) gene that encodes for an expanded polyglutamine (polyQ) repeat in exon-1 of the human mutant huntingtin (mHTT) protein. The presence of this polyQ repeat results in neuronal degeneration, for which there is no cure or treatment that modifies disease progression. In previous studies, we have shown that small molecules that bind selectively to σ₂R/TMEM97 can have significant neuroprotective effects in models of Alzheimer's disease, traumatic brain injury, and several other neurodegenerative diseases. In the present work, we extend these investigations and show that certain σ₂R/TMEM97-selective ligands decrease mHTT-induced neuronal toxicity. We first synthesized a set of compounds designed to bind to σ₂R/TMEM97 and determined their binding profiles (K_i values) for σ₂R/TMEM97 and other proteins in the central nervous system. Modulators with high affinity and selectivity for σ₂R/TMEM97 were then tested in our HD cell model. Primary cortical neurons were cultured in vitro for 7 days and then co-transfected with either a normal HTT construct (Htt N-586-22Q/GFP) or the mHTT construct Htt-N586-82Q/GFP. Transfected neurons were treated with either σ₂R/TMEM97 or σ₁R modulators for 48 h. After treatment, neurons were fixed and stained with Hoechst, and condensed nuclei were quantified to assess cell death in the transfected neurons. Significantly, σ₂R/TMEM97 modulators reduce the neuronal toxicity induced by mHTT, and their neuroprotective effects are not blocked by NE-100, a selective σ₁R antagonist known to block neuroprotection by σ₁R ligands. These results indicate for the first time that σ₂R/TMEM97 modulators can protect neurons from mHTT-induced neuronal toxicity, suggesting that targeting σ₂R/TMEM97 may lead to a novel therapeutic approach to treat patients with HD.

A biological classification of Huntington's disease: the Integrated Staging System

The current research paradigm for Huntington's disease is based on participants with overt clinical phenotypes and does not address its pathophysiology nor the biomarker changes that can precede by decades the functional decline. We have generated a new research framework to standardise clinical research and enable interventional studies earlier in the disease course. The Huntington's Disease Integrated Staging System (HD-ISS) comprises a biological research definition and evidence-based staging centred on biological, clinical, and functional assessments. We used a formal consensus method that involved representatives from academia, industry, and non-profit organisations. The HD-ISS characterises individuals for research purposes from birth, starting at Stage 0 (ie, individuals with the Huntington's disease genetic mutation without any detectable pathological change) by using a genetic definition of Huntington's disease. Huntington's disease progression is then marked by measurable indicators of underlying pathophysiology (Stage 1), a detectable clinical phenotype (Stage 2), and then decline in function (Stage 3). Individuals can be precisely classified into stages based on thresholds of stage-specific landmark assessments. We also demonstrated the internal validity of this system. The adoption of the HD-ISS could facilitate the design of clinical trials targeting populations before clinical motor diagnosis and enable data standardisation across ongoing and future studies.

Mutant D620N and VPS35 induces motor dysfunction and impairs DAT-mediated dopamine recycling pathway

The D620N mutation in vacuolar protein sorting protein 35 (VPS35) gene has been identified to be linked to late onset familial Parkinson disease (PD). However, the pathophysiological roles of VPS35-D620N in PD remain unclear. Here, we generated the transgenic C. elegans overexpressing either human wild type or PD-linked mutant VPS35-D620N in neurons. C. elegans expressing VPS35-D620N, compared with non-transgenic controls, showed movement disorders and dopaminergic neuron loss. VPS35-D620N worms displayed more swimming induced paralysis but showed no defects in BSR assays, thus indicating the disruption of dopamine (DA) recycling back inside neurons. Moreover, VPS35 formed a protein interaction complex with DA transporter (DAT), RAB5, RAB11, and FAM21. In contrast, the VPS35-D620N mutant destabilized these interactions, thus disrupting DAT transport from early endosomes to recycling endosomes, and decreasing DAT at the cell suffice. These effects together increased DA in synaptic clefts, and led to dopaminergic neuron degeneration and motor dysfunction. Treatment with reserpine significantly decreased the swimming induced paralysis in VPS35-D620N worms, as compared with vehicle treated VPS35-D620N worms. Our studies not only provide novel insight into the mechanisms of VPS35-D620N-induced dopaminergic neuron degeneration and motor dysfunction via disruption of DAT function and the DA signaling pathway, but also indicate a potential strategy to treat VPS35-D620N related PD and other disorders.

Novel predictors related to hysteresis and baseflow improve predictions of watershed nutrient loads: An example from Ontario's lower Great Lakes basin

Eutrophication has re-emerged in the lower Great Lakes basin resulting in critical water quality issues. Models that accurately predict nutrient loading from streams are needed to inform appropriate nutrient management decisions. Generalized additive models (GAMs) that use surrogate data from sensors to predict nutrient loads offer an alternative to commonly applied linear regression and may better handle relationship non-linearities and skewed water quality data. Five years (2015-2020) of water quantity and quality data from 11 agricultural watersheds in southern Ontario were used to develop GAMs to predict total phosphorus (TP) and nitrate (NO₃^-) loads. This study aimed to 1) use GAMs to predict nutrient loads using both common and novel predictors and 2) quantify and examine the variability in seasonal and annual nutrient loads. Along with routine surrogate model predictors (i.e., flow, turbidity, and seasonality), the addition of the baseflow proportion and the hydrograph position of flow observations improved model performance. Conversely, including the antecedent precipitation index minimally affected model performance, regardless of constituent. Seasonal and annual patterns in TP and NO₃^- load predictions mirrored that of the hydrologic regime. This study showed that parsimonious GAMs featuring novel model predictors can be used to predict nutrient loads while accounting for the partitioning of surface and subsurface flow paths and hysteresis between streamflow and water quality parameters that are frequently observed in a wide range of environments.

Interaction of huntingtin with PRMTs and its subsequent arginine methylation affects HTT solubility, phase transition behavior and neuronal toxicity

Huntington's disease (HD) is an incurable neurodegenerative disorder caused by a CAG expansion in the huntingtin gene (HTT). Post-translational modifications of huntingtin protein (HTT), such as phosphorylation, acetylation and ubiquitination, have been implicated in HD pathogenesis. Arginine methylation/dimethylation is an important modification with an emerging role in neurodegeneration; however, arginine methylation of HTT remains largely unexplored. Here we report nearly two dozen novel arginine methylation/dimethylation sites on the endogenous HTT from human and mouse brain and human cells suggested by mass spectrometry with data-dependent acquisition. Targeted quantitative mass spectrometry identified differential arginine methylation at specific sites in HD patient-derived striatal precursor cell lines compared to normal controls. We found that HTT can interact with several type I protein arginine methyltransferases (PRMTs) via its N-terminal domain. Using a combination of in vitro methylation and cell-based experiments, we identified PRMT4 (CARM1) and PRMT6 as major enzymes methylating HTT at specific arginines. Alterations of these methylation sites had a profound effect on biochemical properties of HTT rendering it less soluble in cells and affected its liquid-liquid phase separation and phase transition patterns in vitro. We found that expanded HTT 1-586 fragment can form liquid-like assemblies, which converted into solid-like assemblies when the R200/205 methylation sites were altered. Methyl-null alterations increased HTT toxicity to neuronal cells, while overexpression of PRMT 4 and 6 was beneficial for neuronal survival. Thus, arginine methylation pathways that involve specific HTT-modifying PRMT enzymes and modulate HTT biochemical and toxic properties could provide targets for HD-modifying therapies.

Preventing amyotrophic lateral sclerosis: insights from pre-symptomatic neurodegenerative diseases

Significant progress has been made in understanding the pre-symptomatic phase of amyotrophic lateral sclerosis. While much is still unknown, advances in other neurodegenerative diseases offer valuable insights. Indeed, it is increasingly clear that the well-recognized clinical syndromes of Alzheimer's disease, Parkinson's disease, Huntington's disease, spinal muscular atrophy and frontotemporal dementia are also each preceded by a pre-symptomatic or prodromal period of varying duration, during which the underlying disease process unfolds, with associated compensatory changes and loss of inherent system redundancy. Key insights from these diseases highlight opportunities for discovery in amyotrophic lateral sclerosis. The development of biomarkers reflecting amyloid and tau has led to a shift in defining Alzheimer's disease based on inferred underlying histopathology. Parkinson's disease is unique among neurodegenerative diseases in the number and diversity of non-genetic biomarkers of pre-symptomatic disease, most notably REM sleep behaviour disorder. Huntington's disease benefits from an ability to predict the likely timing of clinically manifest disease based on age and CAG-repeat length alongside reliable neuroimaging markers of atrophy. Spinal muscular atrophy clinical trials have highlighted the transformational value of early therapeutic intervention, and studies in frontotemporal dementia illustrate the differential role of biomarkers based on genotype. Similar advances in amyotrophic lateral sclerosis would transform our understanding of key events in pathogenesis, thereby dramatically accelerating progress towards disease prevention. Deciphering the biology of pre-symptomatic amyotrophic lateral sclerosis relies on a clear conceptual framework for defining the earliest stages of disease. Clinically manifest amyotrophic lateral sclerosis may emerge abruptly, especially among those who harbour genetic mutations associated with rapidly progressive amyotrophic lateral sclerosis. However, the disease may also evolve more gradually, revealing a prodromal period of mild motor impairment preceding phenoconversion to clinically manifest disease. Similarly, cognitive and behavioural impairment, when present, may emerge gradually, evolving through a prodromal period of mild cognitive impairment or mild behavioural impairment before progression to amyotrophic lateral sclerosis. Biomarkers are critically important to studying pre-symptomatic amyotrophic lateral sclerosis and essential to efforts to intervene therapeutically before clinically manifest disease emerges. The use of non-genetic biomarkers, however, presents challenges related to counselling, informed consent, communication of results and limited protections afforded by existing legislation. Experiences from pre-symptomatic genetic testing and counselling, and the legal protections against discrimination based on genetic data, may serve as a guide. Building on what we have learned-more broadly from other pre-symptomatic neurodegenerative diseases and specifically from amyotrophic lateral sclerosis gene mutation carriers-we present a road map to early intervention, and perhaps even disease prevention, for all forms of amyotrophic lateral sclerosis.

Amygdala and anterior cingulate transcriptomes from individuals with bipolar disorder reveal downregulated neuroimmune and synaptic pathways

Recent genetic studies have identified variants associated with bipolar disorder (BD), but it remains unclear how brain gene expression is altered in BD and how genetic risk for BD may contribute to these alterations. Here, we obtained transcriptomes from subgenual anterior cingulate cortex and amygdala samples from post-mortem brains of individuals with BD and neurotypical controls, including 511 total samples from 295 unique donors. We examined differential gene expression between cases and controls and the transcriptional effects of BD-associated genetic variants. We found two coexpressed modules that were associated with transcriptional changes in BD: one enriched for immune and inflammatory genes and the other with genes related to the postsynaptic membrane. Over 50% of BD genome-wide significant loci contained significant expression quantitative trait loci (QTL) (eQTL), and these data converged on several individual genes, including SCN2A and GRIN2A. Thus, these data implicate specific genes and pathways that may contribute to the pathology of BP.

Immortalized striatal precursor neurons from Huntington's disease patient-derived iPS cells as a platform for target identification and screening for experimental therapeutics

We have previously established induced pluripotent stem cell (iPSC) models of Huntington's disease (HD), demonstrating CAG-repeat-expansion-dependent cell biological changes and toxicity. However, the current differentiation protocols are cumbersome and time consuming, making preparation of large quantities of cells for biochemical or screening assays difficult. Here, we report the generation of immortalized striatal precursor neurons (ISPNs) with normal (33) and expanded (180) CAG repeats from HD iPSCs, differentiated to a phenotype resembling medium spiny neurons (MSN), as a proof of principle for a more tractable patient-derived cell model. For immortalization, we used co-expression of the enzymatic component of telomerase hTERT and conditional expression of c-Myc. ISPNs can be propagated as stable adherent cell lines, and rapidly differentiated into highly homogeneous MSN-like cultures within 2 weeks, as demonstrated by immunocytochemical criteria. Differentiated ISPNs recapitulate major HD-related phenotypes of the parental iPSC model, including brain-derived neurotrophic factor (BDNF)-withdrawal-induced cell death that can be rescued by small molecules previously validated in the parental iPSC model. Proteome and RNA-seq analyses demonstrate separation of HD versus control samples by principal component analysis. We identified several networks, pathways, and upstream regulators, also found altered in HD iPSCs, other HD models, and HD patient samples. HD ISPN lines may be useful for studying HD-related cellular pathogenesis, and for use as a platform for HD target identification and screening experimental therapeutics. The described approach for generation of ISPNs from differentiated patient-derived iPSCs could be applied to a larger allelic series of HD cell lines, and to comparable modeling of other genetic disorders.

Huntingtin silencing delays onset and slows progression of Huntington's disease: a biomarker study

Huntington's disease is a dominantly inherited, fatal neurodegenerative disorder caused by a CAG expansion in the huntingtin (HTT) gene, coding for pathological mutant HTT protein (mHTT). Because of its gain-of-function mechanism and monogenic aetiology, strategies to lower HTT are being actively investigated as disease-modifying therapies. Most approaches are currently targeted at the manifest stage, where clinical outcomes are used to evaluate the effectiveness of therapy. However, as almost 50% of striatal volume has been lost at the time of onset of clinical manifest, it would be preferable to begin therapy in the premanifest period. An unmet challenge is how to evaluate therapeutic efficacy before the presence of clinical symptoms as outcome measures. To address this, we aim to develop non-invasive sensitive biomarkers that provide insight into therapeutic efficacy in the premanifest stage of Huntington's disease. In this study, we mapped the temporal trajectories of arteriolar cerebral blood volumes (CBVa) using inflow-based vascular-space-occupancy (iVASO) MRI in the heterozygous zQ175 mice, a full-length mHTT expressing and slowly progressing model with a premanifest period as in human Huntington's disease. Significantly elevated CBVa was evident in premanifest zQ175 mice prior to motor deficits and striatal atrophy, recapitulating altered CBVa in human premanifest Huntington's disease. CRISPR/Cas9-mediated non-allele-specific HTT silencing in striatal neurons restored altered CBVa in premanifest zQ175 mice, delayed onset of striatal atrophy, and slowed the progression of motor phenotype and brain pathology. This study-for the first time-shows that a non-invasive functional MRI measure detects therapeutic efficacy in the premanifest stage and demonstrates long-term benefits of a non-allele-selective HTT silencing treatment introduced in the premanifest Huntington's disease.

Curcumin Reduced H2O2- and G2385R-LRRK2-Induced Neurodegeneration

Mutations in leucine-rich repeat kinase 2 gene (LRRK2) are the most frequent genetic factors contributing to Parkinson's disease (PD). G2385R-LRRK2 increases the risk for PD susceptibility in the Chinese population. However, the pathological role of G2385R-LRRK2 is not clear. In this study, we investigate the roles of G2385R-LRRK2 in neurodegeneration underlying PD pathogenesis using cell biology and pharmacology approaches. We demonstrated that expression of G2385R-LRRK2-induced neurotoxicity in human neuroblastoma SH-SY5Y and mouse primary neurons. G2385R-LRRK2 increased mitochondrial ROS, activates caspase-3/7, and increased PARP cleavage, resulting in neurotoxicity. Treatment with curcumin (an antioxidant) significantly protected against G2385R-LRRK2-induced neurodegeneration by reducing mitochondrial ROS, caspase-3/7 activation, and PARP cleavage. We also found that the cellular environmental stressor, H₂O₂ significantly promotes both WT-LRRK2- and G2385R-LRRK2-induced neurotoxicity by increasing mitochondrial ROS, caspase-3/7 activation, and PARP cleavage, while curcumin attenuated this combined neurotoxicity. These findings not only provide a novel understanding of G2385R roles in neurodegeneration and environment interaction but also provide a pharmacological approach for intervention for G2385R-LRRK2-linked PD.

RNA Toxicity and Perturbation of rRNA Processing in Spinocerebellar Ataxia Type 2

BACKGROUND

Spinocerebellar ataxia type 2 (SCA2) is a neurodegenerative disease caused by expansion of a CAG repeat in Ataxin-2 (ATXN2) gene. The mutant ATXN2 protein with a polyglutamine tract is known to be toxic and contributes to the SCA2 pathogenesis.

OBJECTIVE

Here, we tested the hypothesis that the mutant ATXN2 transcript with an expanded CAG repeat (expATXN2) is also toxic and contributes to SCA2 pathogenesis.

METHODS

The toxic effect of expATXN2 transcripts on SK-N-MC neuroblastoma cells and primary mouse cortical neurons was evaluated by caspase 3/7 activity and nuclear condensation assay, respectively. RNA immunoprecipitation assay was performed to identify RNA binding proteins (RBPs) that bind to expATXN2 RNA. Quantitative PCR was used to examine if ribosomal RNA (rRNA) processing is disrupted in SCA2 and Huntington's disease (HD) human brain tissue.

RESULTS

expATXN2 RNA induces neuronal cell death, and aberrantly interacts with RBPs involved in RNA metabolism. One of the RBPs, transducin β-like protein 3 (TBL3), involved in rRNA processing, binds to both expATXN2 and expanded huntingtin (expHTT) RNA in vitro. rRNA processing is disrupted in both SCA2 and HD human brain tissue.

CONCLUSION

These findings provide the first evidence of a contributory role of expATXN2 transcripts in SCA2 pathogenesis, and further support the role of expHTT transcripts in HD pathogenesis. The disruption of rRNA processing, mediated by aberrant interaction of RBPs with expATXN2 and expHTT transcripts, suggest a point of convergence in the pathogeneses of repeat expansion diseases with potential therapeutic implications. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Ankyrin-G Heterozygous Knockout Mice Display Increased Sensitivity to Social Defeat Stress

The <i>ANK3</i> locus has been repeatedly found to confer an increased risk for bipolar disorder. <i>ANK3</i> codes for Ankyrin-G (Ank-G), a scaffold protein concentrated at axon initial segments, nodes of Ranvier, and dendritic spines, where it organizes voltage-gated sodium and potassium channels and cytoskeletal proteins. Mice with homozygous conditional knockout of Ank-G in the adult forebrain display hyperactivity and reduced anxiety-like behaviors, responsive to mood stabilizers. Their behavior switches to a depression-like phenotype when exposed to chronic social defeat stress (SDS), and then spontaneously reverts to baseline hyperactivity. Ank-G heterozygous conditional knockouts (Ank-G Het cKO) have not previously been characterized. Here, we describe the behavior of Ank-G Het cKO mice compared to littermate controls in the open field, elevated plus maze, and forced swim test, under both unstressed and stressed conditions. We found that Ank-G Het cKO is not significantly different from controls at baseline or after chronic SDS. The chronic stress-induced “depression-like” behavioral phenotype is persistent for at least 28 days and is responsive to fluoxetine. Strikingly, Ank-G Het cKO mice display increased sensitivity to a short duration SDS, which does not affect controls. The heterozygous Ank-G genetic model may provide novel insights into the role of Ank-G in the pathophysiology of stress sensitivity and “depression-like” phenotypes and could be useful for studying Ank-G-related gene-environment interactions.

Mutant-TMEM230-induced neurodegeneration and impaired axonal mitochondrial transport

Parkinson's disease (PD) is a neurodegenerative disease with movement disorders including resting tremor, rigidity, bradykinesia and postural instability. Recent studies have identified a new PD associated gene, TMEM230 (transmembrane protein 230). However, the pathological roles of TMEM230 and its variants are not fully understood. TMEM230 gene encodes two protein isoforms. Isoform2 is the major protein form (~95%) in human. In this study, we overexpress isoform2 TMEM230 variants (WT or PD-linked *184Wext*5 mutant) or knockdown endogenous protein in cultured SH-5Y5Y cells and mouse primary hippocampus neurons to study their pathological roles. We found that overexpression of WT and mutant TMEM230 or knockdown of endogenous TMEM230-induced neurodegeneration and impaired mitochondria transport at the retrograde direction in axons. Mutant TMEM230 caused more severe neurotoxicity and mitochondrial transport impairment than WT-TMEM230 did. Our results demonstrate that maintaining TMEM230 protein levels is critical for neuron survival and axon transport. These findings suggest that mutant-TMEM230-induced mitochondrial transport impairment could be the early event leading to neurite injury and neurodegeneration in PD development.

Impaired response of cerebral oxygen metabolism to visual stimulation in Huntington's disease

Huntington's disease (HD) is a neurodegenerative disease caused by a CAG triplet repeat expansion in the Huntingtin gene. Metabolic and microvascular abnormalities in the brain may contribute to early physiological changes that subserve the functional impairments in HD. This study is intended to investigate potential abnormality in dynamic changes in cerebral blood volume (CBV) and cerebral blood flow (CBF), and cerebral metabolic rate of oxygen (CMRO2) in the brain in response to functional stimulation in premanifest and early manifest HD patients. A recently developed 3-D-TRiple-acquisition-after-Inversion-Preparation magnetic resonance imaging (MRI) approach was used to measure dynamic responses in CBV, CBF, and CMRO2 during visual stimulation in one single MRI scan. Experiments were conducted in 23 HD patients and 16 healthy controls. Decreased occipital cortex CMRO2 responses were observed in premanifest and early manifest HD patients compared to controls (P < 0.001), correlating with the CAG-Age Product scores in these patients (R2 = 0.4, P = 0.001). The results suggest the potential value of this reduced CMRO2 response during visual stimulation as a biomarker for HD and may illuminate the role of metabolic alterations in the pathophysiology of HD.

Pharmacological rescue in patient iPSC and mouse models with a rare DISC1 mutation

We previously identified a causal link between a rare patient mutation in DISC1 (disrupted-in-schizophrenia 1) and synaptic deficits in cortical neurons differentiated from isogenic patient-derived induced pluripotent stem cells (iPSCs). Here we find that transcripts related to phosphodiesterase 4 (PDE4) signaling are significantly elevated in human cortical neurons differentiated from iPSCs with the DISC1 mutation and that inhibition of PDE4 or activation of the cAMP signaling pathway functionally rescues synaptic deficits. We further generated a knock-in mouse line harboring the same patient mutation in the Disc1 gene. Heterozygous Disc1 mutant mice exhibit elevated levels of PDE4s and synaptic abnormalities in the brain, and social and cognitive behavioral deficits. Pharmacological inhibition of the PDE4 signaling pathway rescues these synaptic, social and cognitive behavioral abnormalities. Our study shows that patient-derived isogenic iPSC and humanized mouse disease models are integral and complementary for translational studies with a better understanding of underlying molecular mechanisms.

Mutant G2019S-LRRK2 Induces Abnormalities in Arteriolar Cerebral Blood Volume in Mouse Brains: An MRI Study

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease and the most common movement disorder characterized by motor impairments resulting from midbrain dopamine neuron loss. Abnormalities in small pial arteries and arterioles, which are the primary pathways of local delivery of nutrients and oxygen in brain tissue, have been reported in many neurodegenerative diseases including PD. Mutations in LRRK2 cause genetic PD and contribute to sporadic PD. The most common PD-linked mutation LRRK2 G2019S contributes 20-47% of genetic forms of PD in Caucasian populations. The human LRRK2 G2019S transgenic mouse model displays PD-like movement impairment and was used to identify novel LRRK2 inhibitors, which provides a useful model for studying microvascular abnormalities in PD.

OBJECTIVES

To investigate abnormalities in arteriolar cerebral blood volume (CBVa) in various brain regions using the inflow-based vascular-space occupancy (iVASO) MRI technique in LRRK2 mouse models of PD.

METHODS

Anatomical and iVASO MRI scans were performed in 5 female and 7 male nontransgenic (nTg), 3 female and 4 male wild-type (WT) LRRK2, and 5 female and 7 male G2019S-LRRK2 mice of 9 months of age. CBVa was calculated and compared in the substantia nigra (SN), olfactory cortex, and prefrontal cortex.

RESULTS

Compared to nTg mice, G2019S-LRRK2 mice showed decreased CBVa in the SN, but increased CBVa in the olfactory and prefrontal cortex in both male and female groups, whereas WT-LRRK2 mice showed no change in CBVa in the SN (male and female), the olfactory (female), and prefrontal (female) cortex, but a slight increase in CBVa in the olfactory and prefrontal cortex in the male group only.

CONCLUSIONS

Alterations in the blood volume of small arteries and arterioles (CBVa) were detected in the G2019S-LRRK2 mouse model of PD. The opposite changes in CBVa in the SN and the cortex indicate that PD pathology may have differential effects in different brain regions. Our results suggest the potential value of CBVa as a marker for clinical PD studies.

Huntington disease: new insights into molecular pathogenesis and therapeutic opportunities

Huntington disease (HD) is a neurodegenerative disease caused by CAG repeat expansion in the huntingtin gene (HTT) and involves a complex web of pathogenic mechanisms. Mutant HTT (mHTT) disrupts transcription, interferes with immune and mitochondrial function, and is aberrantly modified post-translationally. Evidence suggests that the mHTT RNA is toxic, and at the DNA level, somatic CAG repeat expansion in vulnerable cells influences the disease course. Genome-wide association studies have identified DNA repair pathways as modifiers of somatic instability and disease course in HD and other repeat expansion diseases. In animal models of HD, nucleocytoplasmic transport is disrupted and its restoration is neuroprotective. Novel cerebrospinal fluid (CSF) and plasma biomarkers are among the earliest detectable changes in individuals with premanifest HD and have the sensitivity to detect therapeutic benefit. Therapeutically, the first human trial of an HTT-lowering antisense oligonucleotide successfully, and safely, reduced the CSF concentration of mHTT in individuals with HD. A larger trial, powered to detect clinical efficacy, is underway, along with trials of other HTT-lowering approaches. In this Review, we discuss new insights into the molecular pathogenesis of HD and future therapeutic strategies, including the modulation of DNA repair and targeting the DNA mutation itself.

Transmembrane Protein 230 Mediates a Poly(ADP-ribose) Polymerase-1-Linked Apoptosis

Mutations in transmembrane protein 230 (TMEM230) gene are suggested to be associated with the autosomal dominant Parkinson’s disease (PD) with typical movement disorders and Lewy body pathology. However, the normal functions and the pathological roles of TMEM230 are not clear. In this study, we used TMEM230 isoform II constructs including wild-type (WT) and four reported PD-linked mutation constructs (Y92C, R141L, 184Wext*5, and 184PGext*5). Ectopic expression of WT and PD-linked mutant TMEM230 variants in cultured cells dramatically induced apoptotic cell death compared with that of vector control cells. Mutant TMEM230 caused cell toxicity at an increased severity than WT TMEM230. Moreover, expression of TMEM230 increased mitochondrial reactive oxygen species (ROS) levels, decreased cellular ATP, activated caspase 3/7, and increased poly(ADP-ribose) polymerase-1 (PARP1) cleavage. Treatment with N-acetylcysteine (NAC; an ROS scavenger) or Z-VAD-FMK (a caspase inhibitor) significantly attenuated TMEM230-induced apoptosis in both cultured cells and primary neurons. Our results indicated that TMEM230 mediated a PARP1-linked apoptotic cell death pathway. These findings not only provide the novel insight into the biological roles of TMEM230 in the PARP1-linked pathway but also provide a TMEM230-induced cell death mechanism underlying PD pathogenesis.

Abnormal Brain Development in Huntington' Disease Is Recapitulated in the zQ175 Knock-In Mouse Model

Emerging cellular and molecular studies are providing compelling evidence that altered brain development contributes to the pathogenesis of Huntington's disease (HD). There has been lacking longitudinal system-level data obtained from in vivo HD models supporting this hypothesis. Our human MRI study in children and adolescents with HD indicates that striatal development differs between the HD and control groups, with initial hypertrophy and more rapid volume decline in HD group. In this study, we aimed to determine whether brain development recapitulates the human HD during the postnatal period. Longitudinal structural MRI scans were conducted in the heterozygous zQ175 HD mice and their littermate controls. We found that male zQ175 HD mice recapitulated the region-specific abnormal volume development in the striatum and globus pallidus, with early hypertrophy and then rapidly decline in the regional volume. In contrast, female zQ175 HD mice did not show significant difference in brain volume development with their littermate controls. This is the first longitudinal study of brain volume development at the system level in HD mice. Our results suggest that altered brain development may contribute to the HD pathogenesis. The potential effect of gene therapies targeting on neurodevelopmental event is worth to consider for HD therapeutic intervention.

TBK1 phosphorylates mutant Huntingtin and suppresses its aggregation and toxicity in Huntington's disease models

Phosphorylation of the N‐terminal domain of the huntingtin (HTT) protein has emerged as an important regulator of its localization, structure, aggregation, clearance and toxicity. However, validation of the effect of bona fide phosphorylation in vivo and assessing the therapeutic potential of targeting phosphorylation for the treatment of Huntington's disease (HD) require the identification of the enzymes that regulate HTT phosphorylation. Herein, we report the discovery and validation of a kinase, TANK‐binding kinase 1 (TBK1), that efficiently phosphorylates full‐length and N‐terminal HTT fragments in vitro (at S13/S16), in cells (at S13) and in vivo. TBK1 expression in HD models (cells, primary neurons, and Caenorhabditis elegans) increases mutant HTT exon 1 phosphorylation and reduces its aggregation and cytotoxicity. We demonstrate that the TBK1‐mediated neuroprotective effects are due to phosphorylation‐dependent inhibition of mutant HTT exon 1 aggregation and an increase in autophagic clearance of mutant HTT. These findings suggest that upregulation and/or activation of TBK1 represents a viable strategy for the treatment of HD by simultaneously lowering mutant HTT levels and blocking its aggregation.

Bioenergetic deficits in Huntington's disease iPSC-derived neural cells and rescue with glycolytic metabolites

Altered cellular metabolism is believed to be an important contributor to pathogenesis of the neurodegenerative disorder Huntington's disease (HD). Research has primarily focused on mitochondrial toxicity, which can cause death of the vulnerable striatal neurons, but other aspects of metabolism have also been implicated. Most previous studies have been carried out using postmortem human brain or non-human cells. Here, we studied bioenergetics in an induced pluripotent stem cell-based model of the disease. We found decreased adenosine triphosphate (ATP) levels in HD cells compared to controls across differentiation stages and protocols. Proteomics data and multiomics network analysis revealed normal or increased levels of mitochondrial messages and proteins, but lowered expression of glycolytic enzymes. Metabolic experiments showed decreased spare glycolytic capacity in HD neurons, while maximal and spare respiratory capacities driven by oxidative phosphorylation were largely unchanged. ATP levels in HD neurons could be rescued with addition of pyruvate or late glycolytic metabolites, but not earlier glycolytic metabolites, suggesting a role for glycolytic deficits as part of the metabolic disturbance in HD neurons. Pyruvate or other related metabolic supplements could have therapeutic benefit in HD.

Physiological and pathological roles of LRRK2 in the nuclear envelope integrity

Mutations in LRRK2 cause autosomal dominant and sporadic Parkinson's disease, but the mechanisms involved in LRRK2 toxicity in PD are yet to be fully understood. We found that LRRK2 translocates to the nucleus by binding to seven in absentia homolog (SIAH-1), and in the nucleus it directly interacts with lamin A/C, independent of its kinase activity. LRRK2 knockdown caused nuclear lamina abnormalities and nuclear disruption. LRRK2 disease mutations mostly abolish the interaction with lamin A/C and, similar to LRRK2 knockdown, cause disorganization of lamin A/C and leakage of nuclear proteins. Dopaminergic neurons of LRRK2 G2019S transgenic and LRRK2 -/- mice display decreased circularity of the nuclear lamina and leakage of the nuclear protein 53BP1 to the cytosol. Dopaminergic nigral and cortical neurons of both LRRK2 G2019S and idiopathic PD patients exhibit abnormalities of the nuclear lamina. Our data indicate that LRRK2 plays an essential role in maintaining nuclear envelope integrity. Disruption of this function by disease mutations suggests a novel phosphorylation-independent loss-of-function mechanism that may synergize with other neurotoxic effects caused by LRRK2 mutations.

Nemo-like kinase reduces mutant huntingtin levels and mitigates Huntington's disease

Nemo-like kinase (NLK), an evolutionarily conserved serine/threonine kinase, is highly expressed in the brain, but its function in the adult brain remains not well understood. In this study, we identify NLK as an interactor of huntingtin protein (HTT). We report that NLK levels are significantly decreased in HD human brain and HD models. Importantly, overexpression of NLK in the striatum attenuates brain atrophy, preserves striatal DARPP32 levels and reduces mutant HTT (mHTT) aggregation in HD mice. In contrast, genetic reduction of NLK exacerbates brain atrophy and loss of DARPP32 in HD mice. Moreover, we demonstrate that NLK lowers mHTT levels in a kinase activity-dependent manner, while having no significant effect on normal HTT protein levels in mouse striatal cells, human cells and HD mouse models. The NLK-mediated lowering of mHTT is associated with enhanced phosphorylation of mHTT. Phosphorylation defective mutation of serine at amino acid 120 (S120) abolishes the mHTT-lowering effect of NLK, suggesting that S120 phosphorylation is an important step in the NLK-mediated lowering of mHTT. A further mechanistic study suggests that NLK promotes mHTT ubiquitination and degradation via the proteasome pathway. Taken together, our results indicate a protective role of NLK in HD and reveal a new molecular target to reduce mHTT levels.

GTP-binding inhibitors increase LRRK2-linked ubiquitination and Lewy body-like inclusions

Parkinson's disease (PD) is one of the most common movement disorders with loss of dopaminergic neurons and the presence of Lewy bodies in certain brain areas. However, it is not clear how Lewy body (inclusion with protein aggregation) formation occurs. Mutations in leucine-rich repeat kinase 2 (LRRK2) can cause a genetic form of PD and contribute to sporadic PD with the typical Lewy body pathology. Here, we used our recently identified LRRK2 GTP-binding inhibitors as pharmacological probes to study the LRRK2-linked ubiquitination and protein aggregation. Pharmacological inhibition of GTP-binding by GTP-binding inhibitors (68 and Fx2149) increased LRRK2-linked ubiquitination predominantly via K27 linkage. Compound 68- or Fx2149 increased G2019S-LRRK2-linked ubiquitinated aggregates, which occurred through the atypical linkage types K27 and K63. Coexpression of K27R and K63R, which prevented ubiquitination via K27 and K63 linkages, reversed the effects of 68 and Fx2149. Moreover, 68 and Fx2149 also promoted G2019S-LRRK2-linked aggresome (Lewy body-like inclusion) formation via K27 and K63 linkages. These findings demonstrate that LRRK2 GTP-binding activity is critical in LRRK2-linked ubiquitination and aggregation formation. These studies provide novel insight into the LRRK2-linked Lewy body-like inclusion formation underlying PD pathogenesis.

G2019S-LRRK2 mutation enhances MPTP-linked Parkinsonism in mice

Parkinson's disease (PD) is a common neurodegenerative disease with a heterogeneous etiology that involves genetic and environmental factors or exogenous. Current LRRK2 PD animal models only partly reproduce the characteristics of the disease with very subtle dopaminergic neuron degeneration. We developed a new model of PD that combines a sub-toxic MPTP insult to the G2019S-LRRK2 mutation. Our newly generated mice, overexpressing mutant G2019S-LRRK2 protein in the brain, displayed a mild, age-dependent progressive motor impairment, but no reduction of lifespan. Cortical neurons from G2019S-LRRK2 mice showed an increased vulnerability to stress insults, compared with neurons overexpressing wild-type WT-LRRK2, or non-transgenic (nTg) neurons. The exposure of LRRK2 transgenic mice to a sub-toxic dose of MPTP resulted in severe motor impairment, selective loss of dopamine neurons and increased astrocyte activation, whereas nTg mice with MPTP exposure showed no deficits. Interestingly, mice overexpressing WT-LRRK2 showed a significant impairment that was milder than for the mutant G2019S-LRRK2 mice. L-DOPA treatments could partially improve the movement impairments but did not protect the dopamine neuron loss. In contrast, treatments with an LRRK2 kinase inhibitor significantly reduced the dopaminergic neuron degeneration in this interaction model. Our studies provide a novel LRRK2 gene-MPTP interaction PD mouse model, and a useful tool for future studies of PD pathogenesis and therapeutic intervention.

Increased Protein Insolubility in Brains From a Subset of Patients With Schizophrenia

OBJECTIVE

The mechanisms leading to schizophrenia are likely to be diverse. However, there may be common pathophysiological pathways for subtypes of the disease. The authors tested the hypothesis that increased protein insolubility and ubiquitination underlie the pathophysiology for a subtype of schizophrenia.

METHODS

Prefrontal cortex and superior temporal gyrus from postmortem brains of individuals with and without schizophrenia were subjected to cold sarkosyl fractionation, separating proteins into soluble and insoluble fractions. Protein insolubility and ubiquitin levels were quantified for each insoluble fraction, with normalization to total homogenate protein. Mass spectrometry analysis was then performed to identify the protein contents of the insoluble fractions. The potential biological relevance of the detected proteins was assessed using Gene Ontology enrichment analysis and Ingenuity Pathway Analysis.

RESULTS

A subset of the schizophrenia brains showed an increase in protein insolubility and ubiquitination in the insoluble fraction. Mass spectrometry of the insoluble fraction revealed that brains with increased insolubility and ubiquitination exhibited a similar peptide expression by principal component analysis. The proteins that were significantly altered in the insoluble fraction were enriched for pathways relating to axon target recognition as well as nervous system development and function.

CONCLUSIONS

This study suggests a pathological process related to protein insolubility for a subset of patients with schizophrenia. Determining the molecular mechanism of this subtype of schizophrenia could lead to a better understanding of the pathways underlying the clinical phenotype in some patients with major mental illness as well as to improved nosology and identification of novel therapeutic targets.

Pridopidine protects neurons from mutant-huntingtin toxicity via the sigma-1 receptor

Huntington's disease (HD) is a neurodegenerative disease caused by a CAG repeat expansion in the Huntingtin gene (HTT), translated into a Huntingtin protein with a polyglutamine expansion. There is preferential loss of medium spiny neurons within the striatum and cortical pyramidal neurons. Pridopidine is a small molecule showing therapeutic potential in HD preclinical and clinical studies. Pridopidine has nanomolar affinity to the sigma-1 receptor (sigma-1R), which is located predominantly at the endoplasmic reticulum (ER) and mitochondrial associated ER membrane, and activates neuroprotective pathways. Here we evaluate the neuroprotective effects of pridopidine against mutant Huntingtin toxicity in mouse and human derived in vitro cell models. We also investigate the involvement of the sigma-1 receptor in the mechanism of pridopidine. Pridopidine protects mutant Huntingtin transfected mouse primary striatal and cortical neurons, with an EC50 in the mid nanomolar range, as well as HD patient-derived induced pluripotent stem cells (iPSCs). This protection by pridopidine is blocked by NE-100, a purported sigma-1 receptor antagonist, and not blocked by ANA-12, a reported TrkB receptor antagonist. 3PPP, a documented sigma-1 receptor agonist, shows similar neuroprotective effects. Genetic knock out of the sigma-1 receptor dramatically decreases protection from pridopidine and 3PPP, but not protection via brain derived neurotrophic factor (BDNF). The neuroprotection afforded by pridopidine in our HD cell models is robust and sigma-1 receptor dependent. These studies support the further development of pridopidine, and other sigma-1 receptor agonists as neuroprotective agents for HD and perhaps for other disorders.

Differential Changes in Functional Connectivity of Striatum-Prefrontal and Striatum-Motor Circuits in Premanifest Huntington's Disease

BACKGROUND

Huntington's disease (HD) is a progressive neurodegenerative disorder. The striatum is one of the first brain regions that show detectable atrophy in HD. Previous studies using functional magnetic resonance imaging (fMRI) at 3 tesla (3 T) revealed reduced functional connectivity between striatum and motor cortex in the prodromal period of HD. Neuroanatomical and neurophysiological studies have suggested segregated corticostriatal pathways with distinct loops involving different cortical regions, which may be investigated using fMRI at an ultra-high field (7 T) with enhanced sensitivity compared to lower fields.

OBJECTIVES

We performed fMRI at 7 T to assess functional connectivity between the striatum and several chosen cortical areas including the motor and prefrontal cortex, in order to better understand brain changes in the striatum-cortical pathways.

METHOD

13 manifest subjects (age 51 ± 13 years, cytosine-adenine-guanine [CAG] repeat 45 ± 5, Unified Huntington's Disease Rating Scale [UHDRS] motor score 32 ± 17), 8 subjects in the close-to-onset premanifest period (age 38 ± 10 years, CAG repeat 44 ± 2, UHDRS motor score 8 ± 2), 11 subjects in the far-from-onset premanifest period (age 38 ± 11 years, CAG repeat 42 ± 2, UHDRS motor score 1 ± 2), and 16 healthy controls (age 44 ± 15 years) were studied. The functional connectivity between the striatum and several cortical areas was measured by resting state fMRI at 7 T and analyzed in all participants.

RESULTS

Compared to controls, functional connectivity between striatum and premotor area, supplementary motor area, inferior frontal as well as middle frontal regions was altered in HD (all p values <0.001). Specifically, decreased striatum-motor connectivity but increased striatum-prefrontal connectivity were found in premanifest HD subjects. Altered functional connectivity correlated consistently with genetic burden, but not with clinical scores.

CONCLUSIONS

Differential changes in functional connectivity of striatum-prefrontal and striatum-motor circuits can be found in early and premanifest HD. This may imply a compensatory mechanism, where additional cortical regions are recruited to subserve functions that have been impaired due to HD pathology. Our results suggest the potential value of functional connectivity as a marker for future clinical trials in HD.

Research Domain Criteria: Strengths, Weaknesses, and Potential Alternatives for Future Psychiatric Research

The Research Domain Criteria (RDoC) paradigm was launched 10 years ago as a superior approach for investigation of mental illness. RDoC conceptualizes normal human behavior, emotion, and cognition as dimensional, with mental illnesses as dimensional extremes. We suggest that RDoC may have value for understanding normal human psychology and some conditions plausibly construed as extremes of normal variation. By contrast, for the most serious of mental illnesses, including dementia, autism, schizophrenia, and bipolar disorder, we argue that RDoC is conceptually flawed. RDoC conflates variation along dimensional axes of normal function with quantitative measurements of disease phenotypes and with the occurrence of diseases in overlapping clusters or spectra. This moves away from the disease model of major mental illness. Further, RDoC imposes a top-down approach to research. We argue that progress in major mental illness research will be more rapid with a bottom-up approach, starting with the discovery of etiological factors, proceeding to investigation of pathogenic pathways, including use of cell and animal models, and leading to a refined nosology and novel, targeted treatments.

Cysteamine Protects Neurons from Mutant Huntingtin Toxicity

BACKGROUND

The potential benefit of cysteamine for Huntington's disease has been demonstrated in HD animal models. Cysteamine and its derivate cystamine were shown to reduce neuropathology and prolong lifespan. Human studies have demonstrated safety, and suggestive results regarding efficacy. Despite all the studies available in vivo, there are only few in vitro studies, and the mechanism of action of cysteamine remains unclear.

OBJECTIVE

The objective of this study is to assess the capacity of cysteamine for neuroprotection against mutant Huntingtin in vitro using cellular models of HD, and to provide initial data regarding mechanism of action.

METHODS

We tested the neuroprotective properties of cysteamine in vitro in our primary neuron and iPSC models of HD.

RESULTS

Cysteamine showed a strong neuroprotective effect (EC50 = 7.1 nM) against mutant Htt-(aa-1-586 82Q) toxicity, in a nuclear condensation cell toxicity assay. Cysteamine also rescued mitochondrial changes induced by mutant Htt. Modulation of the levels of cysteine or glutathione failed to protect neurons, suggesting that cysteamine neuroprotection is not mediated through cysteine metabolism. Taurine and Hypotaurine, which are metabolites of cysteamine can protect neurons against Htt toxicity, but the inhibition of the enzyme converting cysteamine to hypotaurine does not block either protective activity, suggesting independent protective pathways. Cysteamine has been suggested to activate BDNF secretion; however, cysteamine protection was not blocked by BDNF pathway antagonists.

CONCLUSIONS

Cysteamine was strongly neuroprotective with relatively high potency. We demonstrated that the main neuroprotective pathways that have been proposed to be the mechanism of protection by cysteamine can all be blocked and still not prevent the neuroprotective effect. The results suggest the involvement of other yet-to-be-determined neuroprotective pathways.

Altered brain iron content and deposition rate in Huntington's disease as indicated by quantitative susceptibility MRI

Altered brain iron content in the striatum of premanifest and manifest Huntington's disease (HD) has been reported. However, its natural history remains unclear. This study aims to investigate altered brain iron content in premanifest and early HD, and the iron deposition rate in these patients through a longitudinal one-year follow-up test, with quantitative magnetic susceptibility as an iron imaging marker. Twenty-four gene mutation carriers divided into three groups (further-from-onset, closer-to-onset and early HD) and 16 age-matched healthy controls were recruited at baseline, and of these, 14 carriers and 7 controls completed the one-year follow-up. Quantitative magnetic susceptibility and effective transverse relaxation rate ( R 2 ∗ ) were measured at 7.0 Tesla and correlated with atrophy and available clinical and cognitive measurements. Higher susceptibility values indicating higher iron content in the striatum and globus pallidus were only observed in closer-to-onset (N = 6, p < 0.05 in caudate and p < 0.01 in putamen) and early HD (N = 9, p < 0.05 in caudate and globus pallidus and p < 0.01 in putamen). Similar results were found by R 2 ∗ measurement. Such increases directly correlated with HD CAG-age product score and brain atrophy, but not with motor or cognitive scores. More importantly, a significantly higher iron deposition rate (11.9%/years in caudate and 6.1%/years in globus pallidus) was firstly observed in closer-to-onset premanifest HD and early HD as compared to the controls. These results suggest that monitoring brain iron may provide further insights into the pathophysiology of HD disease progression, and may provide a biomarker for clinical trials.

Altered functional connectivity between sub-regions in the thalamus and cortex in schizophrenia patients measured by resting state BOLD fMRI at 7T

The thalamus is a small brain structure that relays neuronal signals between subcortical and cortical regions. Abnormal thalamocortical connectivity in schizophrenia has been reported in previous studies using blood-oxygenation-level-dependent (BOLD) functional MRI (fMRI) performed at 3T. However, anatomically the thalamus is not a single entity, but is subdivided into multiple distinct nuclei with different connections to various cortical regions. We sought to determine the potential benefit of using the enhanced sensitivity of BOLD fMRI at ultra-high magnetic field (7T) in exploring thalamo-cortical connectivity in schizophrenia based on subregions in the thalamus. Seeds placed in thalamic subregions of 14 patients and 14 matched controls were used to calculate whole-brain functional connectivity. Our results demonstrate impaired thalamic connectivity to the prefrontal cortex and the cerebellum, but enhanced thalamic connectivity to the motor/sensory cortex in schizophrenia. This altered functional connectivity significantly correlated with disease duration in the patients. Remarkably, comparable effect sizes observed in previous 3T studies were detected in the current 7T study with a heterogeneous and much smaller cohort, providing evidence that ultra-high field fMRI may be a powerful tool for measuring functional connectivity abnormalities in schizophrenia. Further investigation with a larger cohort is merited to validate the current findings.

G2019S LRRK2 Increases Stress Susceptibility Through Inhibition of DAF-16 Nuclear Translocation in a 14-3-3 Associated-Manner in Caenorhabditis elegans

Mutations in leucine-rich repeat kinase 2 (LRRK2) are common causes of familial Parkinson’s disease (PD). Oxidative stress plays a key role in the pathogenesis of PD. Mutations in LRRK2 have been shown to increase susceptibility to oxidative stress. To explore mechanisms underlying susceptibility to oxidative stress in LRRK2 mutants, we generated stable Caenorhabditis elegans (C. elegans) strains in which human LRRK2 proteins including wild type LRRK2 (WT), G2019S LRRK2 (G2019S), and G2019S-D1994A kinase-dead LRRK2 (KD) were expressed in all neurons. Human 14-3-3 β was injected into LRRK2 transgenic worms to allow co-expression of 14-3-3 β and LRRK2 proteins. We found that G2019S transgenic worms had increased sensitivity to stress (heat and juglone treatment) and impaired stress-induced nuclear translocation of DAF-16. In addition, G2019S inhibited ftt2 (a 14-3-3 gene homolog in C. elegans) knockdown-associated nuclear translocation of DAF-16. Comparably, overexpression of human 14-3-3 β could attenuate G2019S-associated toxicity in response to stress and rescued G2019S-mediated inhibition of sod-3 and dod-3 expression. Taken together, our study provides evidence suggesting that 14-3-3-associated inhibition of DAF-16 nuclear translocation could be a mechanism for G2019S LRRK2-induced oxidative stress and cellular toxicity. Our findings may give a hint that the potential of 14-3-3 proteins as neuroprotective targets in PD patients carrying LRRK2 mutations.

Regional subcortical shape analysis in premanifest Huntington's disease

Huntington's disease (HD) involves preferential and progressive degeneration of striatum and other subcortical regions as well as regional cortical atrophy. It is caused by a CAG repeat expansion in the Huntingtin gene, and the longer the expansion the earlier the age of onset. Atrophy begins prior to manifest clinical signs and symptoms, and brain atrophy in premanifest expansion carriers can be studied. We employed a diffeomorphometric pipeline to contrast subcortical structures' morphological properties in a control group with three disease groups representing different phases of premanifest HD (far, intermediate, and near to onset) as defined by the length of the CAG expansion and the participant's age (CAG-Age-Product). A total of 1,428 magnetic resonance image scans from 694 participants from the PREDICT-HD cohort were used. We found significant region-specific atrophies in all subcortical structures studied, with the estimated abnormality onset time varying from structure to structure. Heterogeneous shape abnormalities of caudate nuclei were present in premanifest HD participants estimated furthest from onset and putaminal shape abnormalities were present in participants intermediate to onset. Thalamic, hippocampal, and amygdalar shape abnormalities were present in participants nearest to onset. We assessed whether the estimated progression of subcortical pathology in premanifest HD tracked specific pathways. This is plausible for changes in basal ganglia circuits but probably not for changes in hippocampus and amygdala. The regional shape analyses conducted in this study provide useful insights into the effects of HD pathology in subcortical structures.

Research Domain Criteria: Cutting Edge Neuroscience or Galen's Humors Revisited?

The Research Domain Criteria (RDoC) scheme has guided the research agenda of the National Institute of Mental Health for the past decade. The essence of RDoC is its dimensional conception of mental illness, with the assumption that psychopathology is a manifestation of extremes along axes of neuropsychological variation. Research, it follows, should emphasize normal neuropsychological function and its associated neurocircuitry. We argue that RDoC, dressed in terms of modern neurobiology, is in fact a return to the humoral theory of Galen, a dimensional approach in which physical and mental health requires a balance of the four basic bodily humors (blood, black bile, yellow bile, and phlegm). The RDoC/Galenic approach may be useful in understanding those conditions best understood as extremes along a continuum, such as personality disorders. However, we contend that for the most severe psychiatric disorders - categorically defined diseases such as schizophrenia, bipolar disorder, and autism - RDoC's Galenic dimensionalism is a retreat from the biomedical approach that seeks to find rational therapeutic targets by identifying etiologic factors and pathogenic pathways. Abandoning this medical model now, in the context of remarkable advances in genetics, neuroimaging, and neuroscience, is a major setback for the advancement of scientific psychiatry.

SCA8 RAN polySer protein preferentially accumulates in white matter regions and is regulated by eIF3F

Spinocerebellar ataxia type 8 (SCA8) is caused by a bidirectionally transcribed CTG·CAG expansion that results in the in vivo accumulation of CUG RNA foci, an ATG-initiated polyGln and a polyAla protein expressed by repeat-associated non-ATG (RAN) translation. Although RAN proteins have been reported in a growing number of diseases, the mechanisms and role of RAN translation in disease are poorly understood. We report a novel toxic SCA8 polySer protein which accumulates in white matter (WM) regions as aggregates that increase with age and disease severity. WM regions with polySer aggregates show demyelination and axonal degeneration in SCA8 human and mouse brains. Additionally, knockdown of the eukaryotic translation initiation factor eIF3F in cells reduces steady-state levels of SCA8 polySer and other RAN proteins. Taken together, these data show polySer and WM abnormalities contribute to SCA8 and identify eIF3F as a novel modulator of RAN protein accumulation.

PPARδ activation by bexarotene promotes neuroprotection by restoring bioenergetic and quality control homeostasis

Neurons must maintain protein and mitochondrial quality control for optimal function, an energetically expensive process. The peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that promote mitochondrial biogenesis and oxidative metabolism. We recently determined that transcriptional dysregulation of PPARδ contributes to Huntington's disease (HD), a progressive neurodegenerative disorder resulting from a CAG-polyglutamine repeat expansion in the huntingtin gene. We documented that the PPARδ agonist KD3010 is an effective therapy for HD in a mouse model. PPARδ forms a heterodimer with the retinoid X receptor (RXR), and RXR agonists are capable of promoting PPARδ activation. One compound with potent RXR agonist activity is the U.S. Food and Drug Administration-approved drug bexarotene. We tested the therapeutic potential of bexarotene in HD and found that bexarotene was neuroprotective in cellular models of HD, including medium spiny-like neurons generated from induced pluripotent stem cells (iPSCs) derived from patients with HD. To evaluate bexarotene as a treatment for HD, we treated the N171-82Q mouse model with the drug and found that bexarotene improved motor function, reduced neurodegeneration, and increased survival. To determine the basis for PPARδ neuroprotection, we evaluated metabolic function and noted markedly impaired oxidative metabolism in HD neurons, which was rescued by bexarotene or KD3010. We examined mitochondrial and protein quality control in cellular models of HD and observed that treatment with a PPARδ agonist promoted cellular quality control. By boosting cellular activities that are dysfunctional in HD, PPARδ activation may have therapeutic applications in HD and potentially other neurodegenerative diseases.

Whole-brain Segmentation and Change-point Analysis of Anatomical Brain MRI-Application in Premanifest Huntington's Disease

Recent advances in MRI offer a variety of useful markers to identify neurodegenerative diseases. In Huntington's disease (HD), regional brain atrophy begins many years prior to the motor onset (during the "premanifest" period), but the spatiotemporal pattern of regional atrophy across the brain has not been fully characterized. Here we demonstrate an online cloud-computing platform, "MRICloud", which provides atlas-based whole-brain segmentation of T1-weighted images at multiple granularity levels, and thereby, enables us to access the regional features of brain anatomy. We then describe a regression model that detects statistically significant inflection points, at which regional brain atrophy starts to be noticeable, i.e. the "change-point", with respect to a disease progression index. We used the CAG-age product (CAP) score to index the disease progression in HD patients. Change-point analysis of the volumetric measurements from the segmentation pipeline, therefore, provides important information of the order and pattern of structural atrophy across the brain. The paper illustrates the use of these techniques on T1-weighted MRI data of premanifest HD subjects from a large multicenter PREDICT-HD study. This design potentially has wide applications in a range of neurodegenerative diseases to investigate the dynamic changes of brain anatomy.

Mapping the order and pattern of brain structural MRI changes using change-point analysis in premanifest Huntington's disease

Huntington's disease (HD) is an autosomal dominant neurodegenerative disorder that progressively affects motor, cognitive, and emotional functions. Structural MRI studies have demonstrated brain atrophy beginning many years prior to clinical onset ("premanifest" period), but the order and pattern of brain structural changes have not been fully characterized. In this study, we investigated brain regional volumes and diffusion tensor imaging (DTI) measurements in premanifest HD, and we aim to determine (1) the extent of MRI changes in a large number of structures across the brain by atlas-based analysis, and (2) the initiation points of structural MRI changes in these brain regions. We adopted a novel multivariate linear regression model to detect the inflection points at which the MRI changes begin (namely, "change-points"), with respect to the CAG-age product (CAP, an indicator of extent of exposure to the effects of CAG repeat expansion). We used approximately 300 T1-weighted and DTI data from premanifest HD and control subjects in the PREDICT-HD study, with atlas-based whole brain segmentation and change-point analysis. The results indicated a distinct topology of structural MRI changes: the change-points of the volumetric measurements suggested a central-to-peripheral pattern of atrophy from the striatum to the deep white matter; and the change points of DTI measurements indicated the earliest changes in mean diffusivity in the deep white matter and posterior white matter. While interpretation needs to be cautious given the cross-sectional nature of the data, these findings suggest a spatial and temporal pattern of spread of structural changes within the HD brain. Hum Brain Mapp 38:5035-5050, 2017. © 2017 Wiley Periodicals, Inc.

Post-translational modifications clustering within proteolytic domains decrease mutant huntingtin toxicity

Huntington's disease (HD) is caused in large part by a polyglutamine expansion within the huntingtin (Htt) protein. Post-translational modifications (PTMs) control and regulate many protein functions and cellular pathways, and PTMs of mutant Htt are likely important modulators of HD pathogenesis. Alterations of selected numbers of PTMs of Htt fragments have been shown to modulate Htt cellular localization and toxicity. In this study, we systematically introduced site-directed alterations in individual phosphorylation and acetylation sites in full-length Htt constructs. The effects of each of these PTM alteration constructs were tested on cell toxicity using our nuclear condensation assay and on mitochondrial viability by measuring mitochondrial potential and size. Using these functional assays in primary neurons, we identified several PTMs whose alteration can block neuronal toxicity and prevent potential loss and swelling of the mitochondria caused by mutant Htt. These PTMs included previously described sites such as serine 116 and newly found sites such as serine 2652 throughout the protein. We found that these functionally relevant sites are clustered in protease-sensitive domains throughout full-length Htt. These findings advance our understanding of the Htt PTM code and its role in HD pathogenesis. Because PTMs are catalyzed by enzymes, the toxicity-modulating Htt PTMs identified here may be promising therapeutic targets for managing HD.

Post-Translational Modifications (PTMs), Identified on Endogenous Huntingtin, Cluster within Proteolytic Domains between HEAT Repeats

Post-translational modifications (PTMs) of proteins regulate various cellular processes. PTMs of polyglutamine-expanded huntingtin (Htt) protein, which causes Huntington's disease (HD), are likely modulators of HD pathogenesis. Previous studies have identified and characterized several PTMs on exogenously expressed Htt fragments, but none of them were designed to systematically characterize PTMs on the endogenous full-length Htt protein. We found that full-length endogenous Htt, which was immunoprecipitated from HD knock-in mouse and human post-mortem brain, is suitable for detection of PTMs by mass spectrometry. Using label-free and mass tag labeling-based approaches, we identified near 40 PTMs, of which half are novel (data are available via ProteomeXchange with identifier PXD005753). Most PTMs were located in clusters within predicted unstructured domains rather than within the predicted α-helical structured HEAT repeats. Using quantitative mass spectrometry, we detected significant differences in the stoichiometry of several PTMs between HD and WT mouse brain. The mass-spectrometry identification and quantitation were verified using phospho-specific antibodies for selected PTMs. To further validate our findings, we introduced individual PTM alterations within full-length Htt and identified several PTMs that can modulate its subcellular localization in striatal cells. These findings will be instrumental in further assembling the Htt PTM framework and highlight several PTMs as potential therapeutic targets for HD.

Analysis of differential gene expression mediated by clozapine in human postmortem brains

Clozapine is the only medication indicated for treating refractory schizophrenia, due to its superior efficacy among all antipsychotic agents, but its mechanism of action is poorly understood. To date, no studies of human postmortem brain have characterized the gene expression response to clozapine. Therefore, we addressed this question by analyzing expression data extracted from published microarray studies involving brains of patients on antipsychotic therapy. We first performed a systematic review and identified four microarray studies of postmortem brains from antipsychotic-treated patients, then extracted the expression data. We then performed generalized linear model analysis on each study separately, and identified the genes differentially expressed in response to clozapine compared to other atypical antipsychotic medications, as well as their associated canonical pathways. We also found a number of genes common to all four studies that we analyzed: GCLM, ZNF652, and GYPC. In addition, pathway analysis highlighted the following processes in all four studies: clathrin-mediated endocytosis, SAPK/JNK signaling, 3-phosphoinositide synthesis, and paxillin signaling. Our analysis yielded the first comprehensive compendium of genes and pathways differentially expressed upon clozapine treatment in the human brain, which may provide insight into the mechanism and unique efficacy of clozapine, as well as the pathophysiology of schizophrenia.