Search

Background: The molecular drivers of early sporadic Parkinson's disease (PD) remain unclear, and the presence of widespread end stage pathology in late disease masks the distinction between primary or causal disease-specific events and late secondary consequences in stressed or dying cells. However, early and mid-stage Parkinson's brains (Braak stages 3 and 4) exhibit alpha-synuclein inclusions and neuronal loss along a regional gradient of severity, from unaffected-mild-moderate-severe. Here, we exploited this spatial pathological gradient to investigate the molecular drivers of sporadic PD., Methods: We combined high precision tissue sampling with unbiased large-scale profiling of protein expression across 9 brain regions in Braak stage 3 and 4 PD brains, and controls, and verified these results using targeted proteomic and functional analyses., Results: We demonstrate that the spatio-temporal pathology gradient in early-mid PD brains is mirrored by a biochemical gradient of a changing proteome. Importantly, we identify two key events that occur early in the disease, prior to the occurrence of alpha-synuclein inclusions and neuronal loss: (i) a metabolic switch in the utilisation of energy substrates and energy production in the brain, and (ii) perturbation of the mitochondrial redox state. These changes may contribute to the regional vulnerability of developing alpha-synuclein pathology. Later in the disease, mitochondrial function is affected more severely, whilst mitochondrial metabolism, fatty acid oxidation, and mitochondrial respiration are affected across all brain regions., Conclusions: Our study provides an in-depth regional profile of the proteome at different stages of PD, and highlights that mitochondrial dysfunction is detectable prior to neuronal loss, and alpha-synuclein fibril deposition, suggesting that mitochondrial dysfunction is one of the key drivers of early disease., (© 2022. The Author(s).)

Parkinson's disease is a multifactorial neurodegenerative disease. The cellular pathology includes dopamine depletion, decrease in mitochondrial complex I enzyme activity, lysosomal glucocerebrosidase enzyme activity and glutathione levels. The SH-SY5Y human neuroblastoma cell line is one of the most widely used cell line models for Parkinson's disease. However, the consensus on its suitability as a model in its proliferative or differentiated state is lacking. In this study, we characterized and compared the biochemical processes most often studied in PD. This in proliferative and differentiated phenotypes of SH-SY5Y cells and several differences were found. Most notably, extracellular dopamine metabolism was significantly higher in differentiated SH-SY5Y. Furthermore, there was a greater variability in glutathione levels in proliferative phenotype (+/- 49%) compared to differentiated (+/- 16%). Finally, enzyme activity assay revealed significant increase in the lysosomal enzyme glucocerebrosidase activity in differentiated phenotype. In contrast, our study has found similarities between the two phenotypes in mitochondrial electron transport chain activity and tyrosine hydroxylase protein expression. The results of this study demonstrate that despite coming from the same cell line, these cells possess some key differences in their biochemistry. This highlights the importance of careful characterization of relevant disease pathways to assess the suitability of cell lines, such as SH-SY5Y cells, for modelling PD or other diseases, i.e. when using the same cell line but different differentiation states., (Copyright © 2021 Elsevier Ltd. All rights reserved.)

Parkinson's disease is a common incurable neurodegenerative disease whose molecular aetiology remains unclear. The identification of Mendelian genes causing rare familial forms of Parkinson's disease has revealed novel proteins and pathways that are likely to be relevant in the pathogenesis of sporadic Parkinson's disease. Recently, mutations in a novel gene, PINK1, encoding a 581 amino acid protein with both mitochondrial targeting and serine/threonine kinase domains, were identified as a cause of autosomal recessive parkinsonism. This provided important evidence for the role of the mitochondrial dysfunction and kinase pathways in neurodegeneration. In this study, we report the first characterization of the PINK1 protein in normal human and sporadic Parkinson's brains, in addition to Parkinson's cases with heterozygous PINK1 mutations. The possible role of the PINK1 protein was also assessed in a number of neurodegenerative diseases characterized by proteinaceous inclusions. For these studies, rabbit polyclonal antibodies were raised against two peptide sequences within the N-terminal hydrophilic loops of PINK1 protein. Using immunohistochemistry and western blotting we were able to demonstrate that PINK1 is a ubiquitous protein expressed throughout the human brain and it is found in all cell types showing a punctate cytoplasmic staining pattern consistent with mitochondrial localization. Fractionation studies of human and rat brain confirm that PINK1 is localized to the mitochondrial membranes. In addition, we show that PINK1 is detected in a proportion of Lewy bodies in cases of sporadic Parkinson's disease and Parkinson's disease associated with heterozygous mutations in the PINK1 gene, which are clinically and pathologically indistinguishable from the sporadic cases. PINK1 was absent in cortical Lewy bodies, in neurofibrillary tangles in Alzheimer's disease, progressive supranuclear palsy and corticobasal degeneration, and in the glial and neuronal alpha-synuclein positive inclusions in multiple system atrophy. These studies provide for the first time in vivo morphological and biochemical evidence to support a mitochondrial localization of PINK1 and underpin the significance of mitochondrial dysfunction in the pathogenesis of nigral cell degeneration in Parkinson's disease.

Reports of parkinsonism in phenylketonuria are exceedingly rare. We report on a patient who had received a delayed diagnosis of phenylketonuria as an infant and subsequently developed levodopa-responsive parkinsonism at the age of 33. Single-photon emission computed tomography (SPECT) using (123)I-FP-CIT ([(123))I]-2 beta-carbomethoxy-3beta-(-4-iodophenyl)-N-(3-fluoropropyl)-nortropane) used to measure dopamine transporter levels on two occasions, 7 and 9 years after the onset of neurological symptoms, were normal. Iodine-123-iodo-lisuride SPECT (IBZM) imaging, however, showed reduced caudate over putamen binding. This combination of imaging findings indicates a possible upregulation of postsynaptic D2 receptors in the context of intact presynaptic dopamine nerve terminal density., ((c) 2004 Movement Disorder Society.)

Two girls and one boy are described, with severe infantile parkinsonism-dystonia. This syndrome is usually caused by endogenous dopamine deficiency but in these patients was associated with elevated dopamine metabolites in CSF and an unusual eye movement disorder: ocular flutter together with saccade initiation failure. Pyramidal tract signs also emerged in the course of the disease in two patients. This combination of symptoms and biochemical findings suggests a unique pathogenic mechanism.

Tyrosine hydroxylase (TH) catalyzes the conversion of L-tyrosine to L-dihydroxyphenylalanine (L-DOPA), the rate-limiting step in the biosynthesis of dopamine. This report describes a missense point mutation in the human TH (hTH) gene in a girl presenting parkinsonian symptoms in early infancy and a very low level of the dopamine metabolite homovanillic acid in the CSF. DNA sequencing revealed a T614-to-C transition in exon 5 (L205P). Both parents and the patient's brother are heterozygous for the mutation. Site-directed mutagenesis and expression in different systems revealed that the recombinant mutant enzyme had a low homospecific activity, i.e. approximately 1.5% of wt-hTH in E. coli and approximately 16% in a cell-free in vitro transcription-translation system. When transiently expressed in human embryonic kidney (A293) cells a very low specific activity (approximately 0.3% of wt-hTH) and immunoreactive hTH (< 2%) was obtained. The expression studies are compatible with the severe clinical phenotype of the L205P homozygous patient carrying this recessively inherited mutation. Treatment with L-DOPA resulted in normalisation of the CSF homovanillic acid concentration and a sustained improvement in parkinsonian symptoms.