Deregulation of autophagy and vesicle trafficking in Parkinson's disease

ncRNAs and their impact on dopaminergic neurons: Autophagy pathways in Parkinson's disease

Parkinson's Disease (PD) is a complex neurological illness that causes severe motor and non-motor symptoms due to a gradual loss of dopaminergic neurons in the substantia nigra. The aetiology of PD is influenced by a variety of genetic, environmental, and cellular variables. One important aspect of this pathophysiology is autophagy, a crucial cellular homeostasis process that breaks down and recycles cytoplasmic components. Recent advances in genomic technologies have unravelled a significant impact of ncRNAs on the regulation of autophagy pathways, thereby implicating their roles in PD onset and progression. They are members of a family of RNAs that include miRNAs, circRNA and lncRNAs that have been shown to play novel pleiotropic functions in the pathogenesis of PD by modulating the expression of genes linked to autophagic activities and dopaminergic neuron survival. This review aims to integrate the current genetic paradigms with the therapeutic prospect of autophagy-associated ncRNAs in PD. By synthesizing the findings of recent genetic studies, we underscore the importance of ncRNAs in the regulation of autophagy, how they are dysregulated in PD, and how they represent novel dimensions for therapeutic intervention. The therapeutic promise of targeting ncRNAs in PD is discussed, including the barriers that need to be overcome and future directions that must be embraced to funnel these ncRNA molecules for the treatment and management of PD.

Micro-and mesoscale aspects of neurodegeneration in engineered human neural networks carrying the LRRK2 G2019S mutation

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene have been widely linked to Parkinson's disease, where the G2019S variant has been shown to contribute uniquely to both familial and sporadic forms of the disease. LRRK2-related mutations have been extensively studied, yet the wide variety of cellular and network events related to these mutations remain poorly understood. The advancement and availability of tools for neural engineering now enable modeling of selected pathological aspects of neurodegenerative disease in human neural networks in vitro. Our study revealed distinct pathology associated dynamics in engineered human cortical neural networks carrying the LRRK2 G2019S mutation compared to healthy isogenic control neural networks. The neurons carrying the LRRK2 G2019S mutation self-organized into networks with aberrant morphology and mitochondrial dynamics, affecting emerging structure-function relationships both at the micro-and mesoscale. Taken together, the findings of our study points toward an overall heightened metabolic demand in networks carrying the LRRK2 G2019S mutation, as well as a resilience to change in response to perturbation, compared to healthy isogenic controls.

Identification of Key Genes and Immunological Features Associated with Copper Metabolism in Parkinson's Disease by Bioinformatics Analysis

To explore diagnostic genes associated with cuproptosis in Parkinson's disease (PD) and to characterize immune cell infiltration by comprehensive bioinformatics analysis, three PD datasets were downloaded from the GEO database, two of which were merged and preprocessed as the internal training set and the remaining one as the external validation set. Based on the internal training set, differential analysis was performed to obtain differentially expressed genes (DEGs), and weighted gene co-expression network analysis (WGCNA) was conducted to obtain significant module genes. The genes obtained here were intersected to form the intersecting genes. The intersecting genes obtained from DEGs and WGCNA were intersected with cuproptosis-related genes (CRGs) to generate cuproptosis-related disease signature genes, and functional enrichment analysis was performed on Disease Ontology (DO), Gene Ontology (GO), and Kyoto Encyclopedia of Genes and Genomes (KEGG). Subsequently, LASSO analysis of the cuproptosis-related disease signature genes was performed to identify key genes and construct a diagnostic and predictive model. Then, single sample gene set enrichment analysis (ssGSEA) was performed on the internal training set to further analyze the correlation between key genes and immune cells. Lastly, the results were validated using an external validation set. A total of 405 DEGs were obtained by differential analysis, and 6 gene modules were identified by WGCNA analysis. The genes in the most significant modules were intersected with the DEGs to obtain 21 intersecting genes. The functions of the intersecting genes were mainly enriched in neurotransmitter transport, GABA-ergic synapse, synaptic vesicle cycle, serotonergic synapse, phenylalanine metabolism, tyrosine metabolism, tryptophan metabolism, etc. Subsequently, the intersecting genes were intersected with CRGs, and LASSO regression analysis was performed to screen 3 key cuproptosis-related disease signature genes, namely, SLC18A2, SLC6A3, and SV2C. The calibration curve of the nomogram model constructed based on these 3 key genes to predict PD showed good agreement, with a C-index of 0.944 and an area under the ROC (AUC) of 0.944 (0.833-1.000). It was also validated by the external dataset that the model constructed with these 3 key genes had good diagnostic and predictive power for PD. The ssGSEA analysis revealed that neutrophils might be the potential core immune cells and that SLC18A2, SLC6A3, and SV2C were significantly negatively correlated with neutrophils, which was also verified in the validation set. PD diagnosis and prediction model based on CRGs (SLC18A2, SLC6A3, and SV2C) has good diagnostic and predictive performance and could be a useful tool in the diagnosis of PD.

Oxidative Stress and Dopaminergic Metabolism: A Major PD Pathogenic Mechanism and Basis of Potential Antioxidant Therapies

Reactive oxygen species (ROS)-induced oxidative stress triggers the vicious cycle leading to the degeneration of dopaminergic neurons in the nigra pars compacta. ROS produced during the metabolism of dopamine is immediately neutralized by the endogenous antioxidant defense system (EADS) under physiological conditions. Aging decreases the vigilance of EADS and makes the dopaminergic neurons more vulnerable to oxidative stress. As a result, ROS left over by EADS oxidize the dopamine-derived catechols and produces a number of reactive dopamine quinones, which are precursors to endogenous neurotoxins. In addition, ROS causes lipid peroxidation, uncoupling of the electron transport chain, and DNA damage, which lead to mitochondrial dysfunction, lysosomal dysfunction, and synaptic dysfunction. The mutations in genes such as DNAJC6, SYNJ1, SH3GL2, LRRK2, PRKN, and VPS35 caused by ROS have been associated with synaptic dysfunction and the pathogenesis of Parkinson's disease (PD). The available drugs that are used against PD can only delay the progression of the disease, but they produce various side effects. Through their antioxidant activity, flavonoids can substantiate the EADS of dopaminergic neurons and disrupt the vicious cycle incepted by oxidative stress. In this review, we show how the oxidative metabolism of dopamine generates ROS and dopamine-quinones, which then exert unrestrained OS, causing mutations in several genes involved in the proper functioning of mitochondrion, synapse, and lysosome. Besides, we also present some examples of approved drugs used for the treatment of PD, therapies in the clinical trial phase, and an update on the flavonoids that have been tested to boost the EADS of dopaminergic neurons.

Inhibition of the Exocyst Complex Attenuates the LRRK2 Pathological Effects

Pathological mutations in leucine-rich repeat kinase 2 (LRRK2) gene are the major genetic cause of Parkinson's disease (PD). Multiple lines of evidence link LRRK2 to the control of vesicle dynamics through phosphorylation of a subset of RAB proteins. However, the molecular mechanisms underlying these processes are not fully elucidated. We have previously demonstrated that LRRK2 increases the exocyst complex assembly by Sec8 interaction, one of the eight members of the exocyst complex, and that Sec8 over-expression mitigates the LRRK2 pathological effect in PC12 cells. Here, we extend this analysis using LRRK2 drosophila models and show that the LRRK2-dependent exocyst complex assembly increase is downstream of RAB phosphorylation. Moreover, exocyst complex inhibition rescues mutant LRRK2 pathogenic phenotype in cellular and drosophila models. Finally, prolonged exocyst inhibition leads to a significant reduction in the LRRK2 protein level, overall supporting the role of the exocyst complex in the LRRK2 pathway. Taken together, our study suggests that modulation of the exocyst complex may represent a novel therapeutic target for PD.

Longitudinal in vivo metabolic labeling reveals tissue-specific mitochondrial proteome turnover rates and proteins selectively altered by parkin deficiency

Our study utilizes a longitudinal isotopic metabolic labeling approach in vivo in combination with organelle fraction proteomics to address the role of parkin in mitochondrial protein turnover in mice. The use of metabolic labeling provides a method to quantitatively determine the global changes in protein half-lives whilst simultaneously assessing protein expression. Studying two diverse mitochondrial populations, we demonstrated the median half-life of brain striatal synaptic mitochondrial proteins is significantly greater than that of hepatic mitochondrial proteins (25.7 vs. 3.5 days). Furthermore, loss of parkin resulted in an overall, albeit modest, increase in both mitochondrial protein abundance and half-life. Pathway and functional analysis of our proteomics data identified both known and novel pathways affected by loss of parkin that are consistent with its role in both mitochondrial quality control and neurodegeneration. Our study therefore adds to a growing body of evidence suggesting dependence on parkin is low for basal mitophagy in vivo and provides a foundation for the investigation of novel parkin targets.

Tumor necrosis factor α–induced protein 3 mediates inflammation and neuronal autophagy in Parkinson's disease via the NFκB and mTOR pathways

This study aimed to probe the function of tumor necrosis factor α-induced protein 3 (TNFAIP3) in the pathogenesis of Parkinson disease (PD) with its association with autophagy and inflammatory response. TNFAIP3 was reduced in the SN of PD patients (the GSE54282 dataset) and mice and in the MPP⁺-treated SK-N-SH cells. TNFAIP3 inhibited inflammatory response and enhanced autophagy, thereby alleviating PD in mice. NFκB and mTOR pathways were activated in the SN of PD mice and MPP⁺-treated cells. TNFAIP3 blocked the two pathways by preventing the p65 nuclear translocation and stabilizing DEPTOR, an endogenous inhibitor of mTOR. NFκB activator LPS and mTOR activator MHY1485 reversed the effects of TNFAIP3 on mitigation of injury in PD mice and in SK-N-SH cells induced with MPP⁺. Altogether, TNFAIP3 played a neuroprotective role in MPTP-induced mice by restricting NFκB and mTOR pathways.

Comparative and evolutionary analysis of RIP kinases in immune responses

The group of receptor-interacting protein (RIP) kinases has seven members (RIPK1–7), with one homologous kinase domain but distinct non-kinase regions. Although RIPK1–3 have emerged as key modulators of inflammation and cell death, few studies have connected RIPK4–7 to immune responses. The divergence in domain structures and paralogue information in the Ensembl database have raised question about the phylogeny of RIPK1–7. In this study, phylogenetic trees of RIPK1–7 and paralogues constructed using full-length amino acid sequences or Kinase domain demonstrate that RIPK6 and RIPK7 are distinct from RIPK1–5 and paralogues shown in the Ensembl database are inaccurate. Comparative and evolutionary analyses were subsequently performed to gain new clues about the potential functions of RIPK3–7. RIPK3 gene loss in birds and animals that undergo torpor, a common physiological phenomenon in cold environments, implies that RIPK3 may be involved in ischemia-reperfusion injury and/or high metabolic rate. The negligible expression of RIPK4 and RIPK5 in immune cells is likely responsible for the lack of studies on the direct role of these members in immunity; RIPK6 and RIPK7 are conserved among plants, invertebrates and vertebrates, and dominantly expressed in innate immune cells, indicating their roles in innate immunity. Overall, our results provide insights into the multifaceted and conserved biochemical functions of RIP kinases.

Implications of intracellular protein degradation pathways in Parkinson's disease and therapeutics

Parkinson's disease (PD) pathology is the most common motor neurodegenerative disease that occurs due to the progressive degeneration of dopaminergic neurons of the nigrostriatal pathway of the brain. The histopathological hallmark of the disease is fibrillary aggregate called Lewy bodies which majorly contain α-synuclein, suggesting the critical implication of diminished protein degradation mechanisms in disease pathogenesis. This α-synuclein-containing Lewy bodies are evident in both experimental models as well as in postmortem PD brain and are speculated to be pathogenic but still, the lineal association between these aggregates and the complexity of disease pathology is not yet well established and needs further attention. However, it has been reported that α-synuclein aggregates have consorted with the declined proteasome and lysosome activities. Therefore, in this review, we reappraise intracellular protein degradation mechanisms during PD pathology. This article focused on the findings of the last two decades suggesting the implications of protein degradation mechanisms in disease pathogenesis and based on shreds of evidence, some of the approaches are also suggested which may be adopted to find out the novel therapeutic targets for the management of PD patients.

Modeling Parkinson's disease in LRRK2 mice: focus on synaptic dysfunction and the autophagy-lysosomal pathway

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are associated with familial and sporadic forms of Parkinson's disease (PD), for which the LRRK2 locus itself represents a risk factor. Idiopathic and LRRK2-related PD share the main clinical and neuropathological features, thus animals harboring the most common LRRK2 mutations, i.e. G2019S and R1441C/G, have been generated to replicate the parkinsonian phenotype and investigate the underlying pathological mechanisms. Most LRRK2 rodent models, however, fail to show the main neuropathological hallmarks of the disease i.e. the degeneration of dopaminergic neurons in the substantia nigra pars compacta and presence of Lewy bodies or Lewy body-like aggregates of α-synuclein, lacking face validity. Rather, they manifest dysregulation in cellular pathways and functions that confer susceptibility to a variety of parkinsonian toxins/triggers and model the presymptomatic/premotor stages of the disease. Among such susceptibility factors, dysregulation of synaptic activity and proteostasis are evident in LRRK2 mutants. These abnormalities are also manifest in the PD brain and represent key events in the development and progression of the pathology. The present minireview covers recent articles (2018-2021) investigating the role of LRRK2 and LRRK2 mutants in the regulation of synaptic activity and autophagy-lysosomal pathway. These articles confirm a perturbation of synaptic vesicle endocytosis and glutamate release in LRRK2 mutants. Likewise, LRRK2 mutants show a marked impairment of selective forms of autophagy (i.e. mitophagy and chaperone-mediated autophagy) and lysosomal function, with minimal perturbations of nonselective autophagy. Thus, LRRK2 rodents might help understand the contribution of these pathways to PD.

Protein Misfolding and Aggregation: The Relatedness between Parkinson's Disease and Hepatic Endoplasmic Reticulum Storage Disorders

Dysfunction of cellular homeostasis can lead to misfolding of proteins thus acquiring conformations prone to polymerization into pathological aggregates. This process is associated with several disorders, including neurodegenerative diseases, such as Parkinson’s disease (PD), and endoplasmic reticulum storage disorders (ERSDs), like alpha-1-antitrypsin deficiency (AATD) and hereditary hypofibrinogenemia with hepatic storage (HHHS). Given the shared pathophysiological mechanisms involved in such conditions, it is necessary to deepen our understanding of the basic principles of misfolding and aggregation akin to these diseases which, although heterogeneous in symptomatology, present similarities that could lead to potential mutual treatments. Here, we review: (i) the pathological bases leading to misfolding and aggregation of proteins involved in PD, AATD, and HHHS: alpha-synuclein, alpha-1-antitrypsin, and fibrinogen, respectively, (ii) the evidence linking each protein aggregation to the stress mechanisms occurring in the endoplasmic reticulum (ER) of each pathology, (iii) a comparison of the mechanisms related to dysfunction of proteostasis and regulation of homeostasis between the diseases (such as the unfolded protein response and/or autophagy), (iv) and clinical perspectives regarding possible common treatments focused on improving the defensive responses to protein aggregation for diseases as different as PD, and ERSDs.

Autophagy in α-Synucleinopathies-An Overstrained System

Alpha-synucleinopathies comprise progressive neurodegenerative diseases, including Parkinson's disease (PD), dementia with Lewy bodies (DLB), and multiple system atrophy (MSA). They all exhibit the same pathological hallmark, which is the formation of α-synuclein positive deposits in neuronal or glial cells. The aggregation of α-synuclein in the cell body of neurons, giving rise to the so-called Lewy bodies (LBs), is the major characteristic for PD and DLB, whereas the accumulation of α-synuclein in oligodendroglial cells, so-called glial cytoplasmic inclusions (GCIs), is the hallmark for MSA. The mechanisms involved in the intracytoplasmic inclusion formation in neuronal and oligodendroglial cells are not fully understood to date. A possible mechanism could be an impaired autophagic machinery that cannot cope with the high intracellular amount of α-synuclein. In fact, different studies showed that reduced autophagy is involved in α-synuclein aggregation. Furthermore, altered levels of different autophagy markers were reported in PD, DLB, and MSA brains. To date, the trigger point in disease initiation is not entirely clear; that is, whether autophagy dysfunction alone suffices to increase α-synuclein or whether α-synuclein is the pathogenic driver. In the current review, we discuss the involvement of defective autophagy machinery in the formation of α-synuclein aggregates, propagation of α-synuclein, and the resulting neurodegenerative processes in α-synucleinopathies.

Sirtuins and Autophagy in Age-Associated Neurodegenerative Diseases: Lessons from the C. elegans Model

Age-associated neurodegenerative diseases are known to have "impaired protein clearance" as one of the key features causing their onset and progression. Hence, homeostasis is the key to maintaining balance throughout the cellular system as an organism ages. Any imbalance in the protein clearance machinery is responsible for accumulation of unwanted proteins, leading to pathological consequences-manifesting in neurodegeneration and associated debilitating outcomes. Multiple processes are involved in regulating this phenomenon; however, failure to regulate the autophagic machinery is a critical process that hampers the protein clearing pathway, leading to neurodegeneration. Another important and widely known component that plays a role in modulating neurodegeneration is a class of proteins called sirtuins. These are class III histone deacetylases (HDACs) that are known to regulate various vital processes such as longevity, genomic stability, transcription and DNA repair. These enzymes are also known to modulate neurodegeneration in an autophagy-dependent manner. Considering its genetic relevance and ease of studying disease-related endpoints in neurodegeneration, the model system Caenorhabditis elegans has been successfully employed in deciphering various functional outcomes related to critical protein molecules, cell death pathways and their association with ageing. This review summarizes the vital role of sirtuins and autophagy in ageing and neurodegeneration, in particular highlighting the knowledge obtained using the C. elegans model system.

Hydrogen sulphide attenuates neuronal apoptosis of substantia nigra by re-establishing autophagic flux via promoting leptin signalling in a 6-hydroxydopamine rat model of Parkinson's disease

Previous studies reveal that hydrogen sulphide (H₂ S) exerts neuroprotection against neurotoxin-induced Parkinson's disease (PD), but the underlying mechanism remains elusive. The present study was aimed to investigate whether H₂ S inhibits neuronal apoptosis of substantia nigra with the involvement of autophagy via promoting leptin signalling in 6-hydroxydopamine (6-OHDA)-induced PD rats. In this study, neuronal apoptosis was analysed by TUNEL staining, the activity of caspase-3 was measured by Caspase-3 fluorometric assay kit, the expressions of Bax, Bcl-2, Beclin-1, LC3II, P62 and leptin were determined by Western blot analysis, and the numbers of autophagosomes and autolysosomes were assessed by transmission electron microscopy. Results showed that NaHS, a donor of exogenous H₂ S, mitigates 6-OHDA-induced the increases in the numbers of TUNEL-positive cells, the activity of caspase-3 and the expression of Bax, and attenuates 6-OHDA-induced a decrease in the expression of Bcl-2 in substantia nigra of rats. In addition, 6-OHDA enhanced the expressions of Beclin-1, LC3-II and P62, increased the number of autophagosomes, and decreased the number of autolysosomes in the substantia nigra, which were also blocked by administration of NaHS. Furthermore, NaHS reversed 6-OHDA-induced the down-regulation of leptin expression in the substantia nigra, and treatment with leptin-OBR, a blocking antibody of leptin receptor, attenuated the inhibition of NaHS on neuronal apoptosis and the improvement of NaHS on the blocked autophagic flux in substantia nigra of 6-OHDA-treated rats. Taken together, these results demonstrated that H₂ S attenuates neuronal apoptosis of substantia nigra depending on restoring impaired autophagic flux through up-regulating leptin signalling in PD.

Methodological Issues in Randomized Clinical Trials for Prodromal Alzheimer's and Parkinson's Disease

Alzheimer's disease (AD) and Parkinson's disease (PD) are the first and second most common neurodegenerative disorders, respectively. Both are proteinopathies with inexorable courses and no approved disease-modifying therapies. A substantial effort has been made to identify interventions that could slow down the progression of AD and PD; to date, with no success. The advances in biomarker research improved the identification of individuals at risk for these disorders before symptom onset, recognizing the pre-clinical stage, in which there is abnormal protein accumulation but no clinical symptoms of the disease, and the prodromal stage, in which mild symptoms are present but the clinical diagnostic criteria for disease cannot be fulfilled. The ability to detect pre-clinical and prodromal stages of these diseases has encouraged clinical trials for disease-modification at earlier phases, seeking to slow or prevent phenoconversion into clinical disease. Clinical trials at these stages have several challenges, such as the identification of the eligible population, the appropriate choice of biomarkers, the definition of clinical endpoints, the duration of follow-up, and the statistical analysis. This article aims to discuss some of the methodological challenges in the design of trials for pre-clinical and prodromal phases of AD and PD, to critically review the recent studies, and to discuss methodological approaches to mitigate these challenges in trial design.

Synj1 haploinsufficiency causes dopamine neuron vulnerability and alpha-synuclein accumulation in mice

Synaptojanin1 (synj1) is a phosphoinositide phosphatase with dual SAC1 and 5'-phosphatase enzymatic activities in regulating phospholipid signaling. The brain-enriched isoform has been shown to participate in synaptic vesicle (SV) recycling. More recently, recessive human mutations were identified in the two phosphatase domains of SYNJ1, including R258Q, R459P and R839C, which are linked to rare forms of early-onset Parkinsonism. We now demonstrate that Synj1 heterozygous deletion (Synj1+/-), which is associated with an impaired 5'-phosphatase activity, also leads to Parkinson's disease (PD)-like pathologies in mice. We report that male Synj1+/- mice display age-dependent motor function abnormalities as well as alpha-synuclein accumulation, impaired autophagy and dopaminergic terminal degeneration. Synj1+/- mice contain elevated 5'-phosphatase substrate, PI(4,5)P2, particularly in the midbrain neurons. Moreover, pharmacological elevation of membrane PI(4,5)P2 in cultured neurons impairs SV endocytosis, specifically in midbrain neurons, and further exacerbates SV trafficking defects in Synj1+/- midbrain neurons. We demonstrate down-regulation of SYNJ1 transcript in a subset of sporadic PD brains, implicating a potential role of Synj1 deficiency in the decline of dopaminergic function during aging.

lncRNA NEAT1 prompts autophagy and apoptosis in MPTP-induced Parkinson's disease by impairing miR-374c-5p

Long non-coding RNAs (lncRNAs) play biological roles in brain disorder and neurodegenerative diseases. As the functions of lncRNA NEAT1 in Parkinson's disease (PD) remain unknown, in the present study, we aimed to explore the roles and underlying molecular mechanisms of NEAT1 in PD. A PD mouse model induced by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and a cell model of SH-SY5Y induced by N-methyl-4-phenylpyridinium (MPP+) were established. The ratio of tyrosine hydroxylase (TH+) cells was determined by immunofluorescence assay, and the behavioral changes in mice were observed using pole tests and rotarod tests. The cellular viability and apoptosis of SH-SY5Y were detected by MTT assay and flow cytometric analysis, respectively, and the number of autophagosomes was subsequently measured by transmission electron microscopy. High-performance liquid chromatography was performed to detect the content of dopamine, and a dual-luciferase reporter assay was used to clarify the target of NEAT1 simultaneously. The results demonstrated that the level of NEAT1 was upregulated in the MPTP-induced PD mice, dopamine neurons, and the SH-SY5Y cells treated with MPP+, whereas the level of miR-374c-5p was downregulated. NEAT1 level was positively correlated with MPP+ in a concentration-dependent manner. NEAT1 inhibition efficiently facilitated cell proliferation but inhibited apoptosis and autophagy in the MPP+-treated SH-SY5Y cells. Additionally, silencing of NEAT1 increased the TH+ rate of neurons and suppressed autophagy greatly in PD mice. As a possible target of NEAT1, miR-374c-5p could impact on the apoptosis and autophagy of the SH-SY5Y cells. NEAT1 inhibition upregulated the expression of miR-374c-5p, enhanced SH-SY5Y cell viability, and repressed autophagy and apoptosis in MPTP-induced PD mice. These findings indicated a potential therapeutic role of NEAT1 in treating PD.

LRRK2 Modulates the Exocyst Complex Assembly by Interacting with Sec8

Mutations in LRRK2 play a critical role in both familial and sporadic Parkinson's disease (PD). Up to date, the role of LRRK2 in PD onset and progression remains largely unknown. However, experimental evidence highlights a critical role of LRRK2 in the control of vesicle trafficking, likely by Rab phosphorylation, that in turn may regulate different aspects of neuronal physiology. Here we show that LRRK2 interacts with Sec8, one of eight subunits of the exocyst complex. The exocyst complex is an evolutionarily conserved multisubunit protein complex mainly involved in tethering secretory vesicles to the plasma membrane and implicated in the regulation of multiple biological processes modulated by vesicle trafficking. Interestingly, Rabs and exocyst complex belong to the same protein network. Our experimental evidence indicates that LRRK2 kinase activity or the presence of the LRRK2 kinase domain regulate the assembly of exocyst subunits and that the over-expression of Sec8 significantly rescues the LRRK2 G2019S mutant pathological effect. Our findings strongly suggest an interesting molecular mechanism by which LRRK2 could modulate vesicle trafficking and may have important implications to decode the complex role that LRRK2 plays in neuronal physiology.

Several New Putative Bacterial ADP-Ribosyltransferase Toxins Are Revealed from In Silico Data Mining, Including the Novel Toxin Vorin, Encoded by the Fire Blight Pathogen Erwinia amylovora

Mono-ADP-ribosyltransferase (mART) toxins are secreted by several pathogenic bacteria that disrupt vital host cell processes in deadly diseases like cholera and whooping cough. In the last two decades, the discovery of mART toxins has helped uncover the mechanisms of disease employed by pathogens impacting agriculture, aquaculture, and human health. Due to the current abundance of mARTs in bacterial genomes, and an unprecedented availability of genomic sequence data, mART toxins are amenable to discovery using an in silico strategy involving a series of sequence pattern filters and structural predictions. In this work, a bioinformatics approach was used to discover six bacterial mART sequences, one of which was a functional mART toxin encoded by the plant pathogen, Erwinia amylovora, called Vorin. Using a yeast growth-deficiency assay, we show that wild-type Vorin inhibited yeast cell growth, while catalytic variants reversed the growth-defective phenotype. Quantitative mass spectrometry analysis revealed that Vorin may cause eukaryotic host cell death by suppressing the initiation of autophagic processes. The genomic neighbourhood of Vorin indicated that it is a Type-VI-secreted effector, and co-expression experiments showed that Vorin is neutralized by binding of a cognate immunity protein, VorinI. We demonstrate that Vorin may also act as an antibacterial effector, since bacterial expression of Vorin was not achieved in the absence of VorinI. Vorin is the newest member of the mART family; further characterization of the Vorin/VorinI complex may help refine inhibitor design for mART toxins from other deadly pathogens.

Progress in LRRK2-Associated Parkinson's Disease Animal Models

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most frequent cause of familial Parkinson's disease (PD). Several genetic manipulations of the LRRK2 gene have been developed in animal models such as rodents, Drosophila, Caenorhabditis elegans, and zebrafish. These models can help us further understand the biological function and derive potential pathological mechanisms for LRRK2. Here we discuss common phenotypic themes found in LRRK2-associated PD animal models, highlight several issues that should be addressed in future models, and discuss emerging areas to guide their future development.

Degeneration of dopaminergic neurons and impaired intracellular trafficking in Atp13a2 deficient zebrafish

ATP13A2 is the autosomal recessive causative gene for juvenile-onset Parkinson’s disease (PARK9, Parkinson’s disease 9), also known as Kufor-Rakeb syndrome. The disease is characterized by levodopa-responsive Parkinsonism, supranuclear gaze palsy, spasticity, and dementia. Previously, we have reported that Atp13a2 deficient medaka fish showed dopaminergic neurodegeneration and lysosomal dysfunction, indicating that lysosome-autophagy impairment might be one of the key pathogeneses of Parkinson’s disease. Here, we established Atp13a2 deficient zebrafish using CRISPR/Cas9 gene editing. We found that the number of TH + neurons in the posterior tuberculum and the locus coeruleus significantly reduced (dopaminergic neurons, 64 % at 4 months and 37 % at 12 months, p < 0.001 and p < 0.05, respectively; norepinephrine neurons, 52 % at 4 months and 40 % at 12 months, p < 0.001 and p < 0.05, respectively) in Atp13a2 deficient zebrafish, proving the degeneration of dopaminergic neurons. In addition, we found the reduction (60 %, p < 0.05) of cathepsin D protein expression in Atp13a2 deficient zebrafish using immunoblot. Transmission electron microscopy analysis using middle diencephalon samples from Atp13a2 deficient zebrafish showed lysosome-like bodies with vesicle accumulation and fingerprint-like structures, suggesting lysosomal dysfunction. Furthermore, a significant reduction (p < 0.001) in protein expression annotated with vesicle fusion with Golgi apparatus in Atp13a2 deficient zebrafish by liquid-chromatography tandem mass spectrometry suggested intracellular trafficking impairment. Therefore, we concluded that Atp13a2 deficient zebrafish exhibited degeneration of dopaminergic neurons, lysosomal dysfunction and the possibility of intracellular trafficking impairment, which would be the key pathogenic mechanism underlying Parkinson’s disease.

Alpha-Synuclein and LRRK2 in Synaptic Autophagy: Linking Early Dysfunction to Late-Stage Pathology in Parkinson's Disease

The lack of effective disease-modifying strategies is the major unmet clinical need in Parkinson’s disease. Several experimental approaches have attempted to validate cellular targets and processes. Of these, autophagy has received considerable attention in the last 20 years due to its involvement in the clearance of pathologic protein aggregates and maintenance of neuronal homeostasis. However, this strategy mainly addresses a very late stage of the disease, when neuropathology and neurodegeneration have likely “tipped over the edge” and disease modification is extremely difficult. Very recently, autophagy has been demonstrated to modulate synaptic activity, a process distinct from its catabolic function. Abnormalities in synaptic transmission are an early event in neurodegeneration with Leucine-Rich Repeat Kinase 2 (LRRK2) and alpha-synuclein strongly implicated. In this review, we analyzed these processes separately and then discussed the unification of these biomolecular fields with the aim of reconstructing a potential “molecular timeline” of disease onset and progression. We postulate that the elucidation of these pathogenic mechanisms will form a critical basis for the design of novel, effective disease-modifying therapies that could be applied early in the disease process.

Autophagy in Parkinson's Disease

Impaired protein homeostasis and accumulation of damaged or abnormally modified protein are common disease mechanisms in many neurodegenerative disorders, including Parkinson's disease (PD). As one of the major degradation pathways, autophagy plays a pivotal role in maintaining effective turnover of proteins and damaged organelles in cells. Several decades of research efforts led to insights into the potential contribution of impaired autophagy machinery to α-synuclein accumulation and the degeneration of dopaminergic neurons, two major features of PD pathology. In this review, we summarize recent pathological, genetic, and mechanistic findings that link defective autophagy with PD pathogenesis in human patients, animals, and cellular models and discuss current challenges in the field.

Neuronal vulnerability in Parkinson disease: Should the focus be on axons and synaptic terminals?

While current effective therapies are available for the symptomatic control of PD, treatments to halt the progressive neurodegeneration still do not exist. Loss of dopamine neurons in the SNc and dopamine terminals in the striatum drive the motor features of PD. Multiple lines of research point to several pathways which may contribute to dopaminergic neurodegeneration. These pathways include extensive axonal arborization, mitochondrial dysfunction, dopamine's biochemical properties, abnormal protein accumulation of α-synuclein, defective autophagy and lysosomal degradation, and synaptic impairment. Thus, understanding the essential features and mechanisms of dopaminergic neuronal vulnerability is a major scientific challenge and highlights an outstanding need for fostering effective therapies against neurodegeneration in PD. This article, which arose from the Movement Disorders 2018 Conference, discusses and reviews the possible mechanisms underlying neuronal vulnerability and potential therapeutic approaches in PD. © 2019 International Parkinson and Movement Disorder Society.

Levetiracetam treatment ameliorates LRRK2 pathological mutant phenotype

Mutations in leucine-rich repeat kinase 2 (LRRK2) are the most common genetic cause of Parkinson's disease (PD). The LRRK2 physiological and pathological function is still debated. However, different experimental evidence based on LRRK2 cellular localization and LRRK2 protein interactors suggests that LRRK2 may be part and regulate a protein network modulating vesicle dynamics/trafficking. Interestingly, the synaptic vesicle protein SV2A is part of this protein complex. Importantly, SV2A is the binding site of the levetiracetam (LEV), a compound largely used in human therapy for epilepsy treatment. The binding of LEV to SV2A reduces the neuronal firing by the modulation of vesicle trafficking although by an unclear molecular mechanism. In this short communication, we have analysed the interaction between the LRRK2 and SV2A pathways by LEV treatment. Interestingly, LEV significantly counteracts the effect of LRRK2 G2019S pathological mutant expression in three different cellular experimental models. Our data strongly suggest that LEV treatment may have a neuroprotective effect on LRRK2 pathological mutant toxicity and that LEV repositioning could be a viable compound for PD treatment.

Liraglutide promotes autophagy by regulating the AMPK/mTOR pathway in a rat remnant kidney model of chronic renal failure

BACKGROUND

We aimed to determine whether the glucagon-like peptide-1 receptor (GLP-1R) agonist liraglutide (LRG) could ameliorate renal function through promoting autophagy via regulating the AMPK/mTOR pathway in a rat remnant kidney model of chronic renal failure.

METHODS

Rats were divided into four groups (n = 10 per group) as follows: (1) sham, (2) nephrectomy (NPX), (3) LRG control (LRG control), and (4) LRG treatment (LRG). Except for rats in the sham group, all rats underwent 5/6 nephrectomy surgery to establish a remnant kidney model of chronic renal failure. In addition, rats in LRG group received LRG as a subcutaneous injection at a dose of 10 mg/kg (once daily) for 4 consecutive weeks, whereas rats in the LRG control group received treatment similar to that of rats in the LRG group, except saline was used instead of LRG. After 4 weeks of treatment, serum creatinine (Scr), blood urea nitrogen (BUN), and urinary albumin excretion were determined. Immunofluorescence assay, immunoprecipitation assay, and Western blot analysis were performed to evaluate the AMPK/mTOR pathway expression of proteins.

RESULTS

Nephrectomized rats (including rats in the NPX, LRG control, and LRG groups) showed higher levels of the Scr, BUN, and urinary albumin excretion, as well as down-regulation of GLP-1R, LC3-II, and AMPK phosphorylation, and up-regulation of mTOR phosphorylation when compared with rats in the sham group. However, those changes were blocked by liraglutide.

CONCLUSION

Liraglutide may promote autophagy through regulating the AMPK/mTOR pathway to exert renoprotective effects in a rat remnant kidney model of chronic renal failure.

The Missing Heritability of Sporadic Frontotemporal Dementia: New Insights from Rare Variants in Neurodegenerative Candidate Genes

Frontotemporal dementia (FTD) is a common form of dementia among early-onset cases. Several genetic factors for FTD have been revealed, but a large proportion of FTD cases still have an unidentified genetic origin. Recent studies highlighted common pathobiological mechanisms among neurodegenerative diseases. In the present study, we investigated a panel of candidate genes, previously described to be associated with FTD and/or other neurodegenerative diseases by targeted next generation sequencing (NGS). We focused our study on sporadic FTD (sFTD), devoid of disease-causing mutations in GRN, MAPT and C9orf72. Since genetic factors have a substantially higher pathogenetic contribution in early onset patients than in late onset dementia, we selected patients with early onset (<65 years). Our study revealed that, in 50% of patients, rare missense potentially pathogenetic variants in genes previously associated with Alzheimer's disease, Parkinson disease, amyotrophic lateral sclerosis and Lewy body dementia (GBA, ABCA7, PARK7, FUS, SORL1, LRRK2, ALS2), confirming genetic pleiotropy in neurodegeneration. In parallel, a synergic genetic effect on FTD is suggested by the presence of variants in five different genes in one single patient. Further studies employing genome-wide approaches might highlight pathogenic variants in novel genes that explain the still missing heritability of FTD.

Microglial Phagocytosis of Neurons: Diminishing Neuronal Loss in Traumatic, Infectious, Inflammatory, and Autoimmune CNS Disorders

Errors in neuron-microglial interaction are known to lead to microglial phagocytosis of live neurons and excessive neuronal loss, potentially yielding poorer clinical outcomes. Factors that affect neuron-microglial interaction have the potential to influence the error rate. Clinical comorbidities that unfavorably impact neuron-microglial interaction may promote a higher rate of neuronal loss, to the detriment of patient outcome. This paper proposes that many common, clinically modifiable comorbidities have a common thread, in that they all influence neuron-microglial interactions. Comorbidities like traumatic brain injury, infection, stress, neuroinflammation, loss of neuronal metabolic integrity, poor growth factor status, and other factors, all have the potential to alter communication between neurons and microglia. When this occurs, microglial phagocytosis of live neurons can increase. In addition, microglia can shift into a morphological form in which they express major histocompatibility complex II (MHC-II), allowing them to function as antigen presenting cells that present neuronal debris as antigen to invading T cells. This can increase risk for the development of CNS autoimmunity, or can exacerbate existing CNS autoimmunity. The detrimental influence of these comorbidities has the potential to contribute to the mosaic of factors that determine patient outcome in some CNS pathologies that have neuropsychiatric involvement, including TBI and CNS disorders with autoimmune components, where excessive neuronal loss can yield poorer clinical outcomes. Recognition of the impact of these comorbidities may contribute to an understanding of the common clinical observation that many seemingly disparate factors contribute to the overall picture of case management and clinical outcome in these complex disorders. In a clinical setting, knowing how these comorbidities can influence neuron-microglial interaction can help focus surveillance and care on a broader group of potential therapeutic targets. Accordingly, an interest in the mechanisms underlying the influence of these factors on neuron-microglial interactions is appropriate. Neuron-microglial interaction is reviewed, and the various mechanisms by which these potential comorbidities influence neuro-microglial interaction are described.

GSK-3β Inhibitor Alsterpaullone Attenuates MPP+-Induced Cell Damage in a c-Myc-Dependent Manner in SH-SY5Y Cells

Mitochondrial dysfunction plays significant roles in the pathogenesis of Parkinson’s Disease (PD). The inactivation of c-Myc, a down-stream gene of Wnt/β-catenin signaling, may contribute to the mitochondria dysfunction. Inhibition of glycogen synthase kinase 3β (GSK-3β) with Alsterpaullone (Als) can activate the down-stream events of Wnt signaling. Here, we investigated the protective roles of Als against MPP⁺-induced cell apoptosis in SH-SY5Y cells. The data showed that Als effectively rescued c-Myc from the MPP⁺-induced decline via Wnt signaling. Furthermore, Als protected SH-SY5Y cells from the MPP⁺-induced mitochondrial fission and cell apoptosis. However, the protective roles of Als were lost under β-catenin-deficient conditions. These findings indicate that Als, a GSK-3β inhibitor, attenuated the MPP⁺-induced mitochondria-dependent apoptotic via up-regulation of the Wnt signaling.

ATG5 overexpression is neuroprotective and attenuates cytoskeletal and vesicle-trafficking alterations in axotomized motoneurons

Injured neurons should engage endogenous mechanisms of self-protection to limit neurodegeneration. Enhancing efficacy of these mechanisms or correcting dysfunctional pathways may be a successful strategy for inducing neuroprotection. Spinal motoneurons retrogradely degenerate after proximal axotomy due to mechanical detachment (avulsion) of the nerve roots, and this limits recovery of nervous system function in patients after this type of trauma. In a previously reported proteomic analysis, we demonstrated that autophagy is a key endogenous mechanism that may allow motoneuron survival and regeneration after distal axotomy and suture of the nerve. Herein, we show that autophagy flux is dysfunctional or blocked in degenerated motoneurons after root avulsion. We also found that there were abnormalities in anterograde/retrograde motor proteins, key secretory pathway factors, and lysosome function. Further, LAMP1 protein was missorted and underglycosylated as well as the proton pump v-ATPase. In vitro modeling revealed how sequential disruptions in these systems likely lead to neurodegeneration. In vivo, we observed that cytoskeletal alterations, induced by a single injection of nocodazole, were sufficient to promote neurodegeneration of avulsed motoneurons. Besides, only pre-treatment with rapamycin, but not post-treatment, neuroprotected after nerve root avulsion. In agreement, overexpressing ATG5 in injured motoneurons led to neuroprotection and attenuation of cytoskeletal and trafficking-related abnormalities. These discoveries serve as proof of concept for autophagy-target therapy to halting the progression of neurodegenerative processes.