Disease Duration Influences Gene Expression in Neuromelanin-Positive Cells From Parkinson’s Disease Patients

Analyses of gene expression in cells affected by neurodegenerative disease can provide important insights into disease mechanisms and relevant stress response pathways. Major symptoms in Parkinson’s disease (PD) are caused by the degeneration of midbrain dopamine (mDA) neurons within the substantia nigra. Here we isolated neuromelanin-positive dopamine neurons by laser capture microdissection from post-mortem human substantia nigra samples recovered at both early and advanced stages of PD. Neuromelanin-positive cells were also isolated from individuals with incidental Lewy body disease (ILBD) and from aged-matched controls. Isolated mDA neurons were subjected to genome-wide gene expression analysis by mRNA sequencing. The analysis identified hundreds of dysregulated genes in PD. Results showed that mostly non-overlapping genes were differentially expressed in ILBD, subjects who were early after diagnosis (less than five years) and those autopsied at more advanced stages of disease (over five years since diagnosis). The identity of differentially expressed genes suggested that more resilient, stably surviving DA neurons were enriched in samples from advanced stages of disease, either as a consequence of positive selection of a less vulnerable long-term surviving mDA neuron subtype or due to up-regulation of neuroprotective gene products.

Vagus Nerve and Stomach Synucleinopathy in Parkinson’s Disease, Incidental Lewy Body Disease, and Normal Elderly Subjects: Evidence Against the “Body-First” Hypothesis

Background: Braak and others have proposed that Lewy-type α-synucleinopathy in Parkinson’s disease (PD) may arise from an exogenous pathogen that passes across the gastric mucosa and then is retrogradely transported up the vagus nerve to the medulla. Objective: We tested this hypothesis by immunohistochemically staining, with a method specific for p-serine 129 α-synuclein (pSyn), stomach and vagus nerve tissue from an autopsy series of 111 normal elderly subjects, 33 with incidental Lewy body disease (ILBD) and 53 with PD. Methods: Vagus nerve samples were taken adjacent to the carotid artery in the neck. Stomach samples were taken from the gastric body, midway along the greater curvature. Formalin-fixed paraffin-embedded sections were immunohistochemically stained for pSyn, shown to be highly specific and sensitive for α-synuclein pathology. Results: Median disease duration for the PD group was 13 years. In the vagus nerve none of the 111 normal subjects had pSyn in the vagus, while 12/26 ILBD (46%) and 32/36 PD (89%) subjects were pSyn-positive. In the stomach none of the 102 normal subjects had pSyn while 5/30 (17%) ILBD and 42/52 (81%) of PD subjects were pSyn-positive. Conclusion: As there was no pSyn in the vagus nerve or stomach of subjects without brain pSyn, these results support initiation of pSyn in the brain. The presence of pSyn in the vagus nerve and stomach of a subset of ILBD cases indicates that synucleinopathy within the peripheral nervous system may occur, within a subset of individuals, at preclinical stages of Lewy body disease.

Seeding Propensity and Characteristics of Pathogenic αSyn Assemblies in Formalin-Fixed Human Tissue from the Enteric Nervous System, Olfactory Bulb, and Brainstem in Cases Staged for Parkinson’s Disease

We investigated α-synuclein’s (αSyn) seeding activity in tissue from the brain and enteric nervous system. Specifically, we assessed the seeding propensity of pathogenic αSyn in formalin-fixed tissue from the gastric cardia and five brain regions of 29 individuals (12 Parkinson’s disease, 8 incidental Lewy body disease, 9 controls) using a protein misfolding cyclic amplification assay. The structural characteristics of the resultant αSyn assemblies were determined by limited proteolysis and transmission electron microscopy. We show that fixed tissue from Parkinson’s disease (PD) and incidental Lewy body disease (ILBD) seeds the aggregation of monomeric αSyn into fibrillar assemblies. Significant variations in the characteristics of fibrillar assemblies derived from different regions even within the same individual were observed. This finding suggests that fixation stabilizes seeds with an otherwise limited seeding propensity, that yield assemblies with different intrinsic structures (i.e., strains). The lag phase preceding fibril assembly for patients ≥80 was significantly shorter than in other age groups, suggesting the existence of increased numbers of seeds or a higher seeding potential of pathogenic αSyn with time. Seeding activity did not diminish in late-stage disease. No statistically significant difference in the seeding efficiency of specific regions was found, nor was there a relationship between seeding efficiency and the load of pathogenic αSyn in a particular region at a given neuropathological stage.

Vagus Nerve and Stomach Synucleinopathy in Parkinson’s Disease, Incidental Lewy Body Disease and Normal Elderly Subjects: Evidence Against the “Body-First” Hypothesis

ABSTRACTBraak and others have proposed that Lewy-type α-synucleinopathy (aSyn) in Parkinson’s disease (PD) may arise from an exogenous pathogen that passes across the gastric mucosa and then is retrogradely transported up the vagus nerve to the medulla. We tested this “body-first” hypothesis by immunohistochemically staining stomach and vagus nerve tissue from an autopsy series of 111 normal elderly subjects (no brain aSyn), 33 with incidental Lewy body disease (ILBD) (brain aSyn without clinical parkinsonism or dementia) and 53 with PD. Median disease duration for the PD group was 13 years. Vagus nerve samples were taken adjacent to the carotid artery in the neck. Stomach samples were taken from the gastric body, midway along the greater curvature. Formalin-fixed paraffin-embedded sections were immunohistochemically stained for α-synuclein phosphorylated at serine-129. In the vagus nerve none of the 111 normal subjects had aSyn in the vagus, while 12/26 ILBD (46%) and 32/36 PD (89%) subjects were aSyn-positive. In the stomach none of the 102 normal subjects had aSyn while 5/30 (17%) ILBD and 42/52 (81%) of PD subjects were aSyn-positive. As there was no aSyn in the vagus nerve or stomach of subjects without brain aSyn, these results support initiation of aSyn in the brain. The presence of aSyn in the vagus nerve and stomach of a subset of ILBD cases indicates that progression of synucleinopathy to the peripheral nervous system may occur at preclinical stages of Lewy body disease.

Insular cortex sub-region-dependent distribution pattern of α-synuclein immunoreactivity in Parkinson’s disease and dementia with Lewy bodies

The insular cortex is a heterogeneous and widely connected brain region. It plays a role in autonomic, cognitive, emotional and somatosensory functions. Its complex and unique cytoarchitecture includes a periallocortical agranular, pro-isocortical dysgranular, and isocortical granular sub-regions. In Parkinson’s disease (PD), the insula shows α-synuclein inclusions in advanced stages of the disease and its atrophy correlates with cognitive deficits. However, little is known regarding its regional neuropathological characteristics and vulnerability in Lewy body diseases. The aim of this study is to assess the distribution pattern of α-synuclein pathology in the insular sub-regions and the selective vulnerability of its different cell types in PD and dementia with Lewy bodies (DLB). Human post-mortem insular tissues from 10 donors with incidental Lewy body disease (iLBD), PD, DLB, and age-matched controls were immunostained for α-synuclein and glial fibrillary acid protein (GFAP). Results showed that a decreasing gradient of α-synuclein pathology was present from agranular to granular sub-regions in iLBD, PD and PD with dementia (PDD) donors. The agranular insula was heavily inflicted, revealing various α-synuclein immunoreactive morphological structures, predominantly Lewy neurites (LNs), and astroglial synucleinopathy. While dysgranular and granular sub-regions showed a decreasing gradient of inclusions and more Lewy bodies (LBs) in deeper layers. In DLB, this gradient was less pronounced and severe pathology was observed in the granular insula compared to PDD and regardless of disease stage. Protoplasmic astrocytes showed α-synuclein inclusions and severe degenerative changes increasing with disease severity. While few von Economo neurons (VENs) in the fronto-insular region revealed inclusions, particularly in PDD patients. Our study reports novel findings on the differential involvement of the insular sub-regions in PD and particular involvement of the agranular sub-region, VENs and astrocytes. Thus, the differential cellular architecture of the insular sub-regions portrays the topographic variation and vulnerability to α-synuclein pathology in Lewy body diseases.