Escherichia coli triggers α-synuclein pathology in the LRRK2 transgenic mouse model of PD

Alpha-synuclein (α-syn) pathology is the hallmark of Parkinson's disease (PD). The leucine-rich repeat kinase 2 (LRRK2) gene is a major-effect risk gene for sporadic PD (sPD). However, what environmental factors may trigger the formation of α-syn pathology in carriers of LRRK2 risk variants are still unknown. Here, we report that a markedly increased abundance of Escherichia coli (E. coli) in the intestinal microbiota was detected in LRRK2 risk variant(R1628P or G2385R) carriers with sPD compared with carriers without sPD. Animal experiments showed that E. coli administration triggered pathological α-syn accumulation in the colon and spread to the brain via the gut-brain axis in Lrrk2 R1628P mice, due to the co-occurrence of Lrrk2 variant-induced inhibition of α-syn autophagic degradation and increased phosphorylation of α-syn caused by curli in E. coli-derived extracellular vesicles. Fecal microbiota transplantation (FMT) effectively ameliorated motor deficits and α-syn pathology in Lrrk2 R1628P mice. Our findings elaborate on the mechanism that E. coli triggers α-syn pathology in Lrrk2 R1628P mice, and highlight a novel gene-environment interaction pattern in LRRK2 risk variants. Even more importantly, the findings reveal the interplay between the specific risk gene and the matched environmental factors triggers the initiation of α-syn pathology in sPD.

Deubiquitinating enzyme YOD1 deubiquitinates and destabilizes α-synuclein

α-synuclein is one of the proteins involved in degenerative neuronal diseases such as Parkinson's disease (PD) or Lewy body dementia (LBD). The pathogenesis is imparted by the abnormal accumulation of α-synuclein resulting in the formation of a Lewy body (LB) and exerting neurotoxicity via an unknown mechanism. Regulation of α-synuclein is achieved by the ubiquitin-proteasome system (UPS), which influences protein homeostasis via inducing proteasome-dependent degradation by attaching a small molecule (ubiquitin) to the substrate. Deubiquitinating enzymes (DUBs) control the UPS by cleaving the peptide or isopeptide bond between ubiquitin and its substrate proteins. In a previous study, we found that YOD1 deubiquitinates and regulates the cellular function of neural precursor cell expressed developmentally down-regulated protein 4 (NEDD4), an E3 ligase that induces α-synuclein degradation. We hypothesized that YOD1 acts as a DUB involved in a modulated pathway of α-synuclein. In the current study, we found that YOD1 directly interacts with α-synuclein and deubiquitinates K6-, K11-, K29-, K33-, and K63-linked polyubiquitin chains on α-synuclein. Furthermore, YOD1 destabilizes α-synuclein protein stability by upregulating NEDD4. Collectively, this suggests the possibility that YOD1 is potentially a new regulator in the NEDD4-α-synuclein pathway.

Granulovacuolar degeneration bodies are independently induced by tau and α-synuclein pathology

BACKGROUND

Granulovacuolar degeneration bodies (GVBs) are intracellular vesicular structures that commonly accompany pathological tau accumulations in neurons of patients with tauopathies. Recently, we developed the first model for GVBs in primary neurons, that requires exogenous tau seeds to elicit tau aggregation. This model allowed the identification of GVBs as proteolytically active lysosomes induced by tau pathology. GVBs selectively accumulate cargo in a dense core, that shows differential and inconsistent immunopositivity for (phosphorylated) tau epitopes. Despite the strong evidence connecting GVBs to tau pathology, these structures have been reported in neurons without apparent pathology in brain tissue of tauopathy patients. Additionally, GVBs and putative GVBs have also been reported in the brain of patients with non-tau proteinopathies. Here, we investigated the connection between pathological protein assemblies and GVBs in more detail.

METHODS

This study combined newly developed primary neuron models for tau and α-synuclein pathology with observations in human brain tissue from tauopathy and Parkinson's disease patients. Immunolabeling and imaging techniques were employed for extensive characterisation of pathological proteins and GVBs. Quantitative data were obtained by high-content automated microscopy as well as single-cell analysis of confocal images.

RESULTS

Employing a novel seed-independent neuronal tau/GVB model, we show that in the context of tauopathy, GVBs are inseparably associated with the presence of cytosolic pathological tau and that intracellular tau aggregation precedes GVB formation, strengthening the causal relationship between pathological accumulation of tau and GVBs. We also report that GVBs are inseparably associated with pathological tau at the single-cell level in the hippocampus of tauopathy patients. Paradoxically, we demonstrate the presence of GVBs in the substantia nigra of Parkinson's disease patients and in a primary neuron model for α-synuclein pathology. GVBs in this newly developed α-synuclein/GVB model are induced in the absence of cytosolic pathological tau accumulations. GVBs in the context of tau or α-synuclein pathology showed similar immunoreactivity for different phosphorylated tau epitopes. The phosphorylated tau immunoreactivity signature of GVBs is therefore independent of the presence of cytosolic tau pathology.

CONCLUSION

Our data identify the emergence of GVBs as a more generalised response to cytosolic protein pathology.

Association of Glial Activation and α-Synuclein Pathology in Parkinson's Disease

The accumulation of pathological α-synuclein (α-syn) in the central nervous system and the progressive loss of dopaminergic neurons in the substantia nigra pars compacta are the neuropathological features of Parkinson's disease (PD). Recently, the findings of prion-like transmission of α-syn pathology have expanded our understanding of the region-specific distribution of α-syn in PD patients. Accumulating evidence suggests that α-syn aggregates are released from neurons and endocytosed by glial cells, which contributes to the clearance of α-syn. However, the activation of glial cells by α-syn species produces pro-inflammatory factors that decrease the uptake of α-syn aggregates by glial cells and promote the transmission of α-syn between neurons, which promotes the spread of α-syn pathology. In this article, we provide an overview of current knowledge on the role of glia and α-syn pathology in PD pathogenesis, highlighting the relationships between glial responses and the spread of α-syn pathology.

Dopaminergic Neurons Differentiated from LRRK2 I1371V-Induced Pluripotent Stem Cells Display a Lower Yield, α-Synuclein Pathology, and Functional Impairment

Being a large multidomain protein, LRRK2 has several confirmed pathological mutant variants for PD, and the incidence of these variants shows ethnicity biases. I1371V, a mutation in the GTPase domain, has been reported in East-Asian populations, but there are no studies reported on dopaminergic (DA) neurons differentiated from this variant. The aim here was to assess the yield, function, and α-synuclein pathology of DA neurons differentiated from LRRK2 I1371V iPSCs. FACS analysis of neural progenitors (NPs) showed a comparable immunopositive population of cells for neural and glial progenitor markers nestin and S100β; however, NPs from I1371V iPSCs showed lower clonogenic and proliferative capacities than healthy control NPs as determined by the neurosphere assay and Ki67 expression. Floor plate cells obtained from I1371V NPs primed with FGF8 showed distinctly lower immunopositivity for FOXA2 and CLIC5 than healthy control FPCs and similar DOC2B expression. On SHH addition, a similar mature neuronal population was obtained from both groups; however, the yield of TH-immunopositive cells was significantly lower in I1371V, with lower expression of mature DA neuronal markers En1, Nurr1, and DAT. Vesicular dopamine release and intracellular Ca²⁺ response with KCl stimulation were lower in I1371V DA neurons, along with a significantly reduced expression of resting vesicle marker VMAT2. A concurrently lower expression of PSD95/Syn-I immunopositive puncta was observed in I1371V differentiated cells. Further, higher phosphorylation of α-synuclein and aggregation of oligomeric α-synuclein in I1371V DA neurons were observed. Our data demonstrated conclusively for the first time that mutations in the I1371V allele of LRRK2 showed developmental deficit from the FPC stage and generated a lower yield/number of TH-immunopositive neurons with impairment in their function and synapse density along with increased α-synuclein pathology.

PARK Genes Link Mitochondrial Dysfunction and Alpha-Synuclein Pathology in Sporadic Parkinson's Disease

Parkinson’s disease (PD) is an age-related neurodegenerative disorder affecting millions of people worldwide. The disease is characterized by the progressive loss of dopaminergic neurons and spread of Lewy pathology (α-synuclein aggregates) in the brain but the pathogenesis remains elusive. PD presents substantial clinical and genetic variability. Although its complex etiology and pathogenesis has hampered the breakthrough in targeting disease modification, recent genetic tools advanced our approaches. As such, mitochondrial dysfunction has been identified as a major pathogenic hub for both familial and sporadic PD. In this review, we summarize the effect of mutations in 11 PARK genes (SNCA, PRKN, PINK1, DJ-1, LRRK2, ATP13A2, PLA2G6, FBXO7, VPS35, CHCHD2, and VPS13C) on mitochondrial function as well as their relevance in the formation of Lewy pathology. Overall, these genes play key roles in mitochondrial homeostatic control (biogenesis and mitophagy) and functions (e.g., energy production and oxidative stress), which may crosstalk with the autophagy pathway, induce proinflammatory immune responses, and increase oxidative stress that facilitate the aggregation of α-synuclein. Thus, rectifying mitochondrial dysregulation represents a promising therapeutic approach for neuroprotection in PD.

Profile of cognitive impairment and underlying pathology in multiple system atrophy

BACKGROUND

The objectives of this study were to elucidate any potential association between α-synuclein pathology and cognitive impairment and to determine the profile of cognitive impairment in multiple system atrophy (MSA) patients. To do this, we analyzed the clinical and pathologic features in autopsy-confirmed MSA patients.

METHODS

We retrospectively reviewed medical records, including neuropsychological test data, in 102 patients with autopsy-confirmed MSA in the Mayo Clinic brain bank. The burden of glial cytoplasmic inclusions and neuronal cytoplasmic inclusions were semiquantitatively scored in the limbic regions and middle frontal gyrus. We also assessed concurrent pathologies potentially causing dementia including Alzheimer's disease, hippocampal sclerosis, and cerebrovascular pathology.

RESULTS

Of 102 patients, 33 (32%) were documented to have cognitive impairment. Those that received objective testing, deficits primarily in processing speed and attention/executive functions were identified, which suggests a frontal-subcortical pattern of dysfunction. Of these 33 patients with cognitive impairment, 8 patients had concurrent pathologies of dementia. MSA patients with cognitive impairment had a greater burden of neuronal cytoplasmic inclusions in the dentate gyrus than patients without cognitive impairment, both including and excluding patients with concurrent pathologies of dementia.

CONCLUSIONS

The cognitive deficits observed in this study were more evident on neuropsychological assessment than with cognitive screens. Based on these findings, we recommend that clinicians consider more in-depth neuropsychological assessments if patients with MSA present with cognitive complaints. Although we did not identify the correlation between cognitive deficits and responsible neuroanatomical regions, a greater burden of neuronal cytoplasmic inclusions in the limbic regions was associated with cognitive impairment in MSA. © 2016 International Parkinson and Movement Disorder Society.

Relationship of neighboring tissue and gliosis to α-synuclein pathology in a fetal transplant for Parkinson's disease

BACKGROUND

Fetal transplantation for Parkinson disease (PD) had been considered a promising therapeutic strategy; however, reports of Lewy bodies (LBs) and Lewy neurites (LNs) in engrafted tissue adds to controversy surrounding this treatment for PD.

METHODS

The brain of a PD patient who had fetal transplantation 14 years before death was evaluated. The graft was studied with routine histologic methods, as well as immunohistochemistry for α-synuclein, neurofilament, synaptophysin and tyrosine hydroxylase (TH), as well as glial fibrillary acidic protein (GFAP) for astrocytes and ionized calcium-binding adaptor molecule 1 (IBA-1) for microglia.

RESULTS

On coronal sections of the brain, the graft extended from the putamen to the amygdala, abutting the anterior hippocampus. Microscopically, the graft consisted of neuron-rich and glia-rich portions. Neuron-rich portions, resembling a neuronal heterotopia, were located in the putamen, whereas the glia-rich portion was more ventral near the amygdala. LBs and LNs were detected in the ventral portion of the graft, especially that part of the graft within the amygdala. Areas with LBs and LNs also had astrogliosis and microgliosis. TH positive neurons were rare and their distribution did not overlap with LBs or LNs.

COMMENTS

LBs and LNs were detected in the transplanted tissue with α-synuclein immunohistochemistry. Unexpected outgrowth of the graft into the amygdala was accompanied by skewed distribution of LBs and gliosis, more abundant in the graft within the amygdala. The distribution of LBs within the graft may suggest the potential role of the local environment as well as gliosis in formation of α-synuclein pathology.