Structural and Functional Neuroimaging of Visual Hallucinations in Lewy Body Disease: A Systematic Literature Review.

Patients with Lewy body disease (LBD) frequently experience visual hallucinations (VH), well-formed images perceived without the presence of real stimuli. The structural and functional brain mechanisms underlying VH in LBD are still unclear. The present review summarises the current literature on the neural correlates of VH in LBD, namely Parkinson's disease (PD), and dementia with Lewy bodies (DLB). Following a systematic literature search, 56 neuroimaging studies of VH in PD and DLB were critically reviewed and evaluated for quality assessment. The main structural neuroimaging results on VH in LBD revealed grey matter loss in frontal areas in patients with dementia, and parietal and occipito-temporal regions in PD without dementia. Parietal and temporal hypometabolism was also reported in hallucinating PD patients. Disrupted functional connectivity was detected especially in the default mode network and fronto-parietal regions. However, evidence on structural and functional connectivity is still limited and requires further investigation. The current literature is in line with integrative models of VH suggesting a role of attention and perception deficits in the development of VH. However, despite the close relationship between VH and cognitive impairment, its associations with brain structure and function have been explored only by a limited number of studies

Progress towards therapies for disease modification in Parkinson's disease

The development of interventions to slow or halt the progression of Parkinson's disease remains a priority for patients and researchers alike. To date, no agents have been shown to have unequivocal evidence of disease-modifying effects in Parkinson's disease. The absence of disease-modifying treatments might relate not only to inadequate approaches for the selection of therapeutic candidates but also to insufficient attention to detail in clinical trial design. Better understanding of Parkinson's disease pathogenesis associated with advances in laboratory models, the use of objective biomarkers of disease progression and target engagement, and a focus on agents known to be safe for human use, alongside the use of precision medicine approaches, should together greatly increase the likelihood for successful identification of disease-modifying treatments for Parkinson's disease

Wilson's disease: update on pathogenesis, biomarkers and treatments

Wilson’s disease is an autosomal–recessive disorder of copper metabolism caused by mutations in ATP7B and associated with neurological, psychiatric, ophthalmological and hepatic manifestations. Decoppering treatments are used to prevent disease progression and reduce symptoms, but neurological outcomes remain mixed. In this article, we review the current understanding of pathogenesis, biomarkers and treatments for Wilson’s disease from the neurological perspective, with a focus on recent advances. The genetic and molecular mechanisms associated with ATP7B dysfunction have been well characterised, but despite extensive efforts to identify genotype–phenotype correlations, the reason why only some patients develop neurological or psychiatric features remains unclear. We discuss pathological processes through which copper accumulation leads to neurodegeneration, such as mitochondrial dysfunction, the role of brain iron metabolism and the broader concept of selective neuronal vulnerability in Wilson’s disease. Delayed diagnoses continue to be a major problem for patients with neurological presentations. We highlight limitations in our current approach to making a diagnosis and novel diagnostic biomarkers, including the potential for newborn screening programmes. We describe recent progress in developing imaging and wet (fluid) biomarkers for neurological involvement, including findings from quantitative MRI and other neuroimaging studies, and the development of a semiquantitative scoring system for assessing radiological severity. Finally, we cover the use of established and novel chelating agents, paradoxical neurological worsening, and progress developing targeted molecular and gene therapy for Wilson’s disease, before discussing future directions for translational research

Neuronal dark matter: the emerging role of microRNAs in neurodegeneration

MicroRNAs (miRNAs) are small, abundant RNA molecules that constitute part of the cell's non-coding RNA “dark matter.” In recent years, the discovery of miRNAs has revolutionised the traditional view of gene expression and our understanding of miRNA biogenesis and function has expanded. Altered expression of miRNAs is increasingly recognized as a feature of many disease states, including neurodegeneration. Here, we review the emerging role for miRNA dysfunction in Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis (ALS) and Huntington's disease pathogenesis. We emphasize the complex nature of gene regulatory networks and the need for systematic studies, with larger sample cohorts than have so far been reported, to reveal the most important miRNA regulators in disease. Finally, miRNA diversity and their potential to target multiple pathways, offers novel clinical applications for miRNAs as biomarkers and therapeutic agents in neurodegenerative diseases

Restriction of mitochondrial calcium overload by mcu inactivation renders a neuroprotective effect in zebrafish models of Parkinson's disease

The loss of dopaminergic neurons (DA) is a pathological hallmark of sporadic and familial forms of Parkinson's disease (PD). We have previously shown that inhibiting mitochondrial calcium uniporter (mcu) using morpholinos can rescue DA neurons in the PTEN-induced putative kinase 1 (pink1)−/− zebrafish model of PD. In this article, we show results from our studies in mcu knockout zebrafish, which was generated using the CRISPR/Cas9 system. Functional assays confirmed impaired mitochondrial calcium influx in mcu−/− zebrafish. We also used in vivo calcium imaging and fluorescent assays in purified mitochondria to investigate mitochondrial calcium dynamics in a pink1−/− zebrafish model of PD. Mitochondrial morphology was evaluated in DA neurons and muscle fibers using immunolabeling and transgenic lines, respectively. We observed diminished mitochondrial area in DA neurons of pink1−/− zebrafish, while deletion of mcu restored mitochondrial area. In contrast, the mitochondrial volume in muscle fibers was not restored after inactivation of mcu in pink1−/− zebrafish. Mitochondrial calcium overload coupled with depolarization of mitochondrial membrane potential leads to mitochondrial dysfunction in the pink1−/− zebrafish model of PD. We used in situ hybridization and immunohistochemical labeling of DA neurons to evaluate the effect of mcu deletion on DA neuronal clusters in the ventral telencephalon of zebrafish brain. We show that DA neurons are rescued after deletion of mcu in pink1−/− and the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) zebrafish model of PD. Thus, inactivation of mcu is protective in both genetic and chemical models of PD. Our data reveal that regulating mcu function could be an effective therapeutic target in PD pathology

Inhibition of the mitochondrial calcium uniporter (MCU) rescues dopaminergic neurons in pink1-/- zebrafish

Mutations in PTEN-induced putative kinase 1 (PINK1) are a cause of early onset Parkinson's disease (PD). Loss of PINK1 function causes dysregulation of mitochondrial calcium homeostasis, resulting in mitochondrial dysfunction and neuronal cell death. We report that both genetic and pharmacological inactivation of the mitochondrial calcium uniporter (MCU), located in the inner mitochondrial membrane, prevents dopaminergic neuronal cell loss in pink1Y431* mutant zebrafish (Danio rerio) via rescue of mitochondrial respiratory chain function. In contrast, genetic inactivation of the voltage dependent anion channel 1 (VDAC1), located in the outer mitochondrial membrane, did not rescue dopaminergic neurons in PINK1 deficient Danio rerio. Subsequent gene expression studies revealed specific upregulation of the mcu regulator micu1 in pink1Y431* mutant zebrafish larvae and inactivation of micu1 also results in rescue of dopaminergic neurons. The functional consequences of PINK1 deficiency and modified MCU activity were confirmed using a dynamic in silico model of Ca2+ triggered mitochondrial activity. Our data suggest modulation of MCU-mediated mitochondrial calcium homeostasis as a possible neuroprotective strategy in PINK1 mutant PD

TIGAR inclusion pathology is specific for Lewy body diseases

BACKGROUND: We previously reported up-regulation of tigarb (the zebrafish orthologue? of human TIGAR, TP53 - Induced Glycolysis and Apoptosis Regulator) in a zebrafish pink1-/- model of Parkinson's disease (PD). Genetic inactivation of tigarb led to the rescue of dopaminergic neurons and mitochondrial function in pink-/- zebrafish. The aim of this study was to determine the relevance of TIGAR for human PD, investigate its disease specificity and identify relevant upstream and downstream mechanisms. MATERIALS AND METHODS: TIGAR Immunohistochemistry using a range of antibodies was undertaken for detailed assessment of TIGAR in formalin-fixed, paraffin-embedded tissue from post mortem brains of PD patients and other neurodegenerative disorders (n = 10 controls, 10 PD cases, 10 dementia with Lewy bodies, 5 motor neurone disease (MND), 3 multiple system atrophy (MSA) and complemented by immunohistochemistry for p53, hexokinase I (HK-I) and hexokinase II (HK-II; n = 4 control, 4 PD, and 4 dementia with Lewy bodies). RESULTS: TIGAR was detected in Lewy bodies and Lewy neurites in the substantia nigra of sporadic PD and Dementia with Lewy bodies (DLB) patients. Staining of adjacent sections confirmed the presence of TIGAR alongside alpha-synuclein in these LB and Neurites. In contrast, TIGAR-positive aggregates were not seen in cortical Lewy bodies. TIGAR protein was also absent in both TDP-43-positive inclusions in MND and glial cytoplasmic inclusions in MSA. Subsequent investigation of the TIGAR-upstream regulator p53 and the downstream targets HK-I and HK-II in PD brains suggested a possible mild increase in HK-I. CONCLUSIONS: TIGAR protein, is present in SN Lewy bodies of both sporadic PD and DLB. The absence of TIGAR protein in the pathological inclusions of MND or MSA suggests disease specificity and further raises the possibility that TIGAR may be involved in PD pathogenesis

N-acetyltransferase 2 (NAT2) gene polymorphisms in Parkinson's disease

BACKGROUND: Parkinson's disease (PD) is a movement disorder caused by the degeneration of dopaminergic neurons in the substantia nigra of the midbrain. The molecular basis of this neural death is unknown, but genetic predisposition and environmental factors may cause the disease. Sequence variations in N-acetyltransferase 2 (NAT2) gene leading to slow acetylation process have been associated with PD, but results are contradictory. METHODS: We analyzed three NAT2 genetic variations, c.481C>T, c.590G>A (p.R197Q) and c.857G>A (p.G286E), which are known to result in a slow acetylator phenotype. Using validated PCR-RFLP assays, we genotyped 243 healthy unrelated Caucasian control subjects and 124 PD patients for these genetic variations. Further, we have undertaken a systematic review of NAT2 studies on PD and we incorporated our results in a meta-analysis consisting of 10 studies, 1,206 PD patients and 1,619 control subjects. RESULTS: Overall, we did not find significant differences in polymorphic acetylation genotypes in PD and control subjects. In the meta-analysis of slow acetylators from 10 studies and representing 604/1206 PD vs. 732/1619 control subjects, a marginally significant odds ratio (OR) of 1.32 (95% CI 1.12–1.54, p < 0.05) was obtained. Re-analysis of the data to exclude the only two studies showing positive association of slow acetylators to PD, resulted in a non-significant OR (1.07, 95% CI 0.9–1.28). Furthermore, meta-analysis of studies for c.590G>A, where both allele and genotype frequencies in PD vs. control subjects were analyzed, did not give significant summary odds ratios as well. CONCLUSION: We found little evidence for differences in polymorphic acetylation genotypes in PD and control subjects. Results of the meta-analyses did not also provide conclusive evidence for an overall association of NAT2 slow acetylator genotypes to PD

Neuroimaging correlates of brain injury in Wilson's disease: a multimodal, whole-brain MRI study

Wilson's disease is an autosomal-recessive disorder of copper metabolism with neurological and hepatic presentations. Chelation therapy is used to 'de-copper' patients but neurological outcomes remain unpredictable. A range of neuroimaging abnormalities have been described and may provide insights into disease mechanisms, in addition to prognostic and monitoring biomarkers. Previous quantitative MRI analyses have focussed on specific sequences or regions of interest, often stratifying chronically-treated patients according to persisting symptoms as opposed to initial presentation. In this cross-sectional study, we performed a combination of unbiased, whole-brain analyses on T1-weighted, fluid-attenuated inversion recovery, diffusion-weighted and susceptibility-weighted imaging data from 40 prospectively-recruited patients with Wilson's disease (age range 16-68). We compared patients with neurological (n = 23) and hepatic (n = 17) presentations to determine the neuroradiological sequelae of the initial brain injury. We also subcategorized patients according to recent neurological status, classifying those with neurological presentations or deterioration in the preceding six months as having 'active' disease. This allowed us to compare patients with active (n = 5) and stable (n = 35) disease and identify imaging correlates for persistent neurological deficits and copper indices in chronically-treated, stable patients. Using a combination of voxel-based morphometry and region-of-interest volumetric analyses, we demonstrate that grey matter volumes are lower in the basal ganglia, thalamus, brainstem, cerebellum, anterior insula and orbitofrontal cortex when comparing patients with neurological and hepatic presentations. In chronically-treated, stable patients, the severity of neurological deficits correlated with grey matter volumes in similar, predominantly subcortical regions. In contrast, the severity of neurological deficits did not correlate with the volume of white matter hyperintensities, calculated using an automated lesion segmentation algorithm. Using tract-based spatial statistics, increasing neurological severity in chronically-treated patients was associated with decreasing axial diffusivity in white matter tracts whereas increasing serum non-caeruloplasmin-bound ('free') copper and active disease were associated with distinct patterns of increasing mean, axial and radial diffusivity. Whole-brain quantitative susceptibility mapping identified increased iron deposition in the putamen, cingulate and medial frontal cortices of patients with neurological presentations relative to those with hepatic presentations and neurological severity was associated with iron deposition in widespread cortical regions in chronically-treated patients. Our data indicate that composite measures of subcortical atrophy provide useful prognostic biomarkers, whereas abnormal mean, axial and radial diffusivity are promising monitoring biomarkers. Finally, deposition of brain iron in response to copper accumulation may directly contribute to neurodegeneration in Wilson's disease