Macroautophagy in sporadic and the genetic form of Parkinson's disease with the A53T α-synuclein mutation

The effect of electroacupuncture at ST25 on Parkinson's disease constipation through regulation of autophagy in the enteric nervous system

The effectiveness and safety of electroacupuncture (EA) for constipation have been confirmed by numerous clinical studies and experiments, and there are also studies on the efficacy of EA for Parkinson's disease (PD) motor symptoms. However, there are few researches on EA for PD constipation. Autophagy is thought to be involved in the mechanistic process of EA in the central nervous system (CNS) intervention in Parkinson's pathology. However, whether it has the same effect on the enteric nervous system (ENS) has not been elucidated. Therefore, we investigated whether EA at Tianshu (ST25) acupoint promotes the clearance of α-Syn and damaged mitochondria aggregated in the ENS in a model of rotenone-induced PD constipation. This study evaluated constipation symptoms by stool characteristics, excretion volume, and water content, and the expression levels of colonic ATG5, LC3II, and Parkin were detected by Western Blot (WB) and Real-Time Quantitative PCR (RT-qPCR). The relationship between the location of α-Syn and Parkin in the colonic ENS was observed by immunofluorescence (IF). The results showed that EA intervention significantly relieved the symptoms of rotenone-induced constipation in PD rats, reversed the rotenone-induced down-regulation of colonic ATG5, LC3II, and Parkin expression, and the positional relationship between colonic α-Syn and Parkin proved to be highly correlated. It is suggested that EA might be helpful in treating PD constipation by modulating Parkin-induced mitochondrial autophagy.

Focus on the Small GTPase Rab1: A Key Player in the Pathogenesis of Parkinson's Disease

Parkinson’s disease (PD) is the second most frequent neurodegenerative disease. It is characterized by the loss of dopaminergic neurons in the substantia nigra and the formation of large aggregates in the survival neurons called Lewy bodies, which mainly contain α-synuclein (α-syn). The cause of cell death is not known but could be due to mitochondrial dysfunction, protein homeostasis failure, and alterations in the secretory/endolysosomal/autophagic pathways. Survival nigral neurons overexpress the small GTPase Rab1. This protein is considered a housekeeping Rab that is necessary to support the secretory pathway, the maintenance of the Golgi complex structure, and the regulation of macroautophagy from yeast to humans. It is also involved in signaling, carcinogenesis, and infection for some pathogens. It has been shown that it is directly linked to the pathogenesis of PD and other neurodegenerative diseases. It has a protective effect against α–σψν toxicity and has recently been shown to be a substrate of LRRK2, which is the most common cause of familial PD and the risk of sporadic disease. In this review, we analyze the key aspects of Rab1 function in dopamine neurons and its implications in PD neurodegeneration/restauration. The results of the current and former research support the notion that this GTPase is a good candidate for therapeutic strategies.

An Emerging Role for Phosphoinositides in the Pathophysiology of Parkinson’s Disease

Recent data support an involvement of defects in homeostasis of phosphoinositides (PIPs) in the pathophysiology of Parkinson’s disease (PD). Genetic mutations have been identified in genes encoding for PIP-regulating and PIP-interacting proteins, that are associated with familial and sporadic PD. Many of these proteins are implicated in vesicular membrane trafficking, mechanisms that were recently highlighted for their close associations with PD. PIPs are phosphorylated forms of the membrane phospholipid, phosphatidylinositol. Their composition in the vesicle’s membrane of origin, as well as membrane of destination, controls vesicular membrane trafficking. We review the converging evidence that points to the involvement of PIPs in PD. The review describes PD- and PIP-associated proteins implicated in clathrin-mediated endocytosis and autophagy, and highlights the involvement of α-synuclein in these mechanisms.

Chaperones and Proteostasis: Role in Parkinson's Disease

Proper folding to attain a defined three-dimensional structure is a prerequisite for the functionality of a protein. Improper folding that eventually leads to formation of protein aggregates is a hallmark of several neurodegenerative disorders. Loss of protein homeostasis triggered by cellular stress conditions is a major contributing factor for the formation of these toxic aggregates. A conserved class of proteins called chaperones and co-chaperones is implicated in maintaining the cellular protein homeostasis. Expanding the body of evidence highlights the role of chaperones as central mediators in the formation, de-aggregation and degradation of the aggregates. Altered expression and function of chaperones is associated with many neurodegenerative diseases including Parkinson’s disease. Several studies indicate that chaperones are at the center of the cause and effect cycle of this disease. An overview of the various chaperones that are associated with homeostasis of Parkinson’s disease-related proteins and their role in pathogenicity will be discussed in this review.

Understanding multifactorial architecture of Parkinson's disease: pathophysiology to management

Parkinson's disease (PD) is the second most common multifactorial neurodegenerative disorder affecting 3% of population during elder age. The loss of substantia nigra, pars compacta (SNpc) neurons and deficiency of striatal dopaminergic neurons produces stables motor deficient. Further, increase alpha-synuclein accumulation, mitochondrial dysfunction, oxidative stress, excitotoxicity, and neuroinflammation plays a crucial role in the pathogenesis of PD. Alpha-synuclein protein encodes for SNCA gene and disturbs the normal physiological neuronal signaling via altering mitochondrial homeostasis. The level of α-synuclein is increased in both normal aging and PD brain to a greater extent and secondly reduced clearance results in accumulation of Lewy bodies (LB). Emerging evidences indicate that mitochondrial dysfunction might be a common cause but pathological insult through protein misfolding, aggregation, and accumulation leads to neuronal apoptosis. The observation supporting that expression of DJ-1, LLRK2, PARKIN, PINK1, and excessive excitotoxicity mediated by dysbalance between GABA and glutamate reduced mitochondrial functioning and increased neurotoxicity. Therefore, the present review summarizes the various pathological mechanisms and also explores the therapeutic strategies which could be useful to ameliorate movement disorder like Parkinsonism.

The Small GTPase RAC1/CED-10 Is Essential in Maintaining Dopaminergic Neuron Function and Survival Against α-Synuclein-Induced Toxicity

Parkinson's disease is associated with intracellular α-synuclein accumulation and ventral midbrain dopaminergic neuronal death in the Substantia Nigra of brain patients. The Rho GTPase pathway, mainly linking surface receptors to the organization of the actin and microtubule cytoskeletons, has been suggested to participate to Parkinson's disease pathogenesis. Nevertheless, its exact contribution remains obscure. To unveil the participation of the Rho GTPase family to the molecular pathogenesis of Parkinson's disease, we first used C elegans to demonstrate the role of the small GTPase RAC1 (ced-10 in the worm) in maintaining dopaminergic function and survival in the presence of alpha-synuclein. In addition, ced-10 mutant worms determined an increase of alpha-synuclein inclusions in comparison to control worms as well as an increase in autophagic vesicles. We then used a human neuroblastoma cells (M17) stably over-expressing alpha-synuclein and found that RAC1 function decreased the amount of amyloidogenic alpha-synuclein. Further, by using dopaminergic neurons derived from patients of familial LRRK2-Parkinson's disease we report that human RAC1 activity is essential in the regulation of dopaminergic cell death, alpha-synuclein accumulation, participates in neurite arborization and modulates autophagy. Thus, we determined for the first time that RAC1/ced-10 participates in Parkinson's disease associated pathogenesis and established RAC1/ced-10 as a new candidate for further investigation of Parkinson's disease associated mechanisms, mainly focused on dopaminergic function and survival against α-synuclein-induced toxicity.

Intercellular transfer of pathogenic α-synuclein by extracellular vesicles is induced by the lipid peroxidation product 4-hydroxynonenal

Parkinson's disease (PD) is characterized by accumulations of toxic α-synuclein aggregates in vulnerable neuronal populations in the brainstem, midbrain, and cerebral cortex. Recent findings suggest that α-synuclein pathology can be propagated transneuronally, but the underlying molecular mechanisms are unknown. Advances in the genetics of rare early-onset familial PD indicate that increased production and/or reduced autophagic clearance of α-synuclein can cause PD. The cause of the most common late-onset PD is unclear, but may involve metabolic compromise and oxidative stress upstream of α-synuclein accumulation. As evidence, the lipid peroxidation product 4-hydroxynonenal (HNE) is elevated in the brain during normal aging and moreso in brain regions afflicted with α-synuclein pathology. Here, we report that HNE increases aggregation of endogenous α-synuclein in primary neurons and triggers the secretion of extracellular vesicles (EVs) containing cytotoxic oligomeric α-synuclein species. EVs released from HNE-treated neurons are internalized by healthy neurons which as a consequence degenerate. Levels of endogenously generated HNE are elevated in cultured cells overexpressing human α-synuclein, and EVs released from those cells are toxic to neurons. The EV-associated α-synuclein is located both inside the vesicles and on their surface, where it plays a role in EV internalization by neurons. On internalization, EVs harboring pathogenic α-synuclein are transported both anterogradely and retrogradely within axons. Focal injection of EVs containing α-synuclein into the striatum of wild-type mice results in spread of synuclein pathology to anatomically connected brain regions. Our findings suggest a scenario for late-onset PD in which lipid peroxidation promotes intracellular accumulation and then extrusion of EVs containing toxic α-synuclein species; the EVs are then internalized by adjacent neurons, so propagating the neurodegenerative process.

Alteration of Upstream Autophagy-Related Proteins (ULK1, ULK2, Beclin1, VPS34 and AMBRA1) in Lewy Body Disease

Autophagy is associated with the pathogenesis of Lewy body disease, including Parkinson's disease (PD) and dementia with Lewy bodies (DLB). It is known that several downstream autophagosomal proteins are incorporated into Lewy bodies (LBs). We performed immunostaining and Western blot analysis using a cellular model of PD and human brain samples to investigate the involvement of upstream autophagosomal proteins (ULK1, ULK2, Beclin1, VPS34 and AMBRA1), which initiate autophagy and form autophagosomes. Time course analysis of cultured cells transfected with flag-α-synuclein and synphilin-1 revealed upregulation of these upstream proteins with accumulation of LB-like inclusions. In human specimens, only mature LBs were positive for upstream autophagosomal proteins. Western blotting of fractionated brain lysates showed that upstream autophagosomal proteins were detected in the soluble and insoluble fraction in DLB, corresponding to the bands of phosphorylated α-synuclein. However, Western blot analysis of total brain lysates in PD and DLB showed that the increase of upstream autophagosomal proteins was only partial. The quantitative, qualitative and locational alteration of upstream autophagosomal proteins in the present study indicates their involvement in the pathogenesis of LB disease. Our data also suggest that misinduction or impairment of upstream autophagy might occur in the disease process of LB disease.

Alpha-Synuclein affects neurite morphology, autophagy, vesicle transport and axonal degeneration in CNS neurons

Many neuropathological and experimental studies suggest that the degeneration of dopaminergic terminals and axons precedes the demise of dopaminergic neurons in the substantia nigra, which finally results in the clinical symptoms of Parkinson disease (PD). The mechanisms underlying this early axonal degeneration are, however, still poorly understood. Here, we examined the effects of overexpression of human wildtype alpha-synuclein (αSyn-WT), a protein associated with PD, and its mutant variants αSyn-A30P and -A53T on neurite morphology and functional parameters in rat primary midbrain neurons (PMN). Moreover, axonal degeneration after overexpression of αSyn-WT and -A30P was analyzed by live imaging in the rat optic nerve in vivo. We found that overexpression of αSyn-WT and of its mutants A30P and A53T impaired neurite outgrowth of PMN and affected neurite branching assessed by Sholl analysis in a variant-dependent manner. Surprisingly, the number of primary neurites per neuron was increased in neurons transfected with αSyn. Axonal vesicle transport was examined by live imaging of PMN co-transfected with EGFP-labeled synaptophysin. Overexpression of all αSyn variants significantly decreased the number of motile vesicles and decelerated vesicle transport compared with control. Macroautophagic flux in PMN was enhanced by αSyn-WT and -A53T but not by αSyn-A30P. Correspondingly, colocalization of αSyn and the autophagy marker LC3 was reduced for αSyn-A30P compared with the other αSyn variants. The number of mitochondria colocalizing with LC3 as a marker for mitophagy did not differ among the groups. In the rat optic nerve, both αSyn-WT and -A30P accelerated kinetics of acute axonal degeneration following crush lesion as analyzed by in vivo live imaging. We conclude that αSyn overexpression impairs neurite outgrowth and augments axonal degeneration, whereas axonal vesicle transport and autophagy are severely altered.

Rifampicin attenuates rotenone-induced inflammation via suppressing NLRP3 inflammasome activation in microglia

A growing body of evidence has supported that environmental factors, such as exposure to heavy metal and pesticides, play an important role in the pathogenesis of Parkinson׳s disease (PD). Rotenone, the active ingredient in various pesticides, has been identified as an inducer of PD. It has been revealed that rotenone induces activation of microglia and generation of pro-inflammatory factors in PD. Our previous studies demonstrated that rifampicin possessed neural protective effect in PD. In this study, we aimed to study the effect of rifampicin on the inflammation induced by rotenone in microglia and the underlying mechanisms. Results demonstrated that rifampicin pretreatment significantly reduced rotenone-induced cytotoxicity and gene expression of IL-1β in BV2 microglia. Moreover, western blot analysis verified that rifampicin pretreatment suppressed NLRP3 inflammasome activation via inhibiting caspase-1 cleavage and protein expression of NLRP3. As it is indicated that reactive oxidative stress (ROS) is one of the activators for NLRP3 inflammasome, we further employed 2',7'-Dichlorodihydrofluorescein diacetate (DCFH-DA) staining and Rhodamine123 staining to detect intracellular ROS and mitochondrial membrane potential (MMP), respectively. Results confirmed that rifampicin obviously reduced intracellular ROS and reversed loss of MMP in BV2 cells treated by rotenone. Taken together, our data indicate that rifampicin pretreatment inhibits maturation of IL-1β and neuroinflammation induced by rotenone via attenuating NLRP3 inflammasome activation. Rifampicin might emerge as a promising candidate for modulating neuroinflammation in PD.

Genetic and chemical activation of TFEB mediates clearance of aggregated α-synuclein

Aggregation of α-synuclein (α-syn) is associated with the development of a number of neurodegenerative diseases, including Parkinson’s disease (PD). The formation of α-syn aggregates results from aberrant accumulation of misfolded α-syn and insufficient or impaired activity of the two main intracellular protein degradation systems, namely the ubiquitin-proteasome system and the autophagy-lysosomal pathway. In this study, we investigated the role of transcription factor EB (TFEB), a master regulator of the autophagy-lysosomal pathway, in preventing the accumulation of α-syn aggregates in human neuroglioma cells. We found that TFEB overexpression reduces the accumulation of aggregated α-syn by inducing autophagic clearance of α-syn. Furthermore, we showed that pharmacological activation of TFEB using 2-hydroxypropyl-β-cyclodextrin promotes autophagic clearance of aggregated α-syn. In summary, our findings demonstrate that TFEB modulates autophagic clearance of α-syn and suggest that pharmacological activation of TFEB is a promising strategy to enhance the degradation of α-syn aggregates.

Genetic perspective on the role of the autophagy-lysosome pathway in Parkinson disease

Parkinson disease (PD), once considered as a prototype of a sporadic disease, is now known to be considerably affected by various genetic factors, which interact with environmental factors and the normal process of aging, leading to PD. Large studies determined that the hereditary component of PD is at least 27%, and in some populations, single genetic factors are responsible for more than 33% of PD patients. Interestingly, many of these genetic factors, such as LRRK2, GBA, SMPD1, SNCA, PARK2, PINK1, PARK7, SCARB2, and others, are involved in the autophagy-lysosome pathway (ALP). Some of these genes encode lysosomal enzymes, whereas others correspond to proteins that are involved in transport to the lysosome, mitophagy, or other autophagic-related functions. Is it possible that all these factors converge into a single pathway that causes PD? In this review, we will discuss these genetic findings and the role of the ALP in the pathogenesis of PD and will try to answer this question. We will suggest a novel hypothesis for the pathogenic mechanism of PD that involves the lysosome and the different autophagy pathways.

Ion mobility-mass spectrometry-based screening for inhibition of α- synuclein aggregation

Aberrant protein folding and formation of amyloid fibrils are associated with numerous debilitating human diseases, for which there are currently no suitable therapeutic treatments. For instance, Parkinson's disease is characterised pathologically by the intraneural accumulation of the amyloid protein α- synuclein. In order to search for new therapeutic agents that are effective in preventing the early conformational changes that precede protein aggregation, it is necessary to devise new analytical screening approaches. Here we demonstrate the use of ion mobility-mass spectrometry for screening of molecules capable of inhibiting the misfolding and aggregation of α-synuclein (specifically, the A53T human mutant). Importantly, this assay allows for the analysis of conformational changes that precede aggregation, and therefore is unique in its ability to identify inhibitors working at the earliest stages of amyloid formation. In addition, we use complementary mass spectrometry methods to probe selected protein-ligand interactions responsible for fibril inhibition.

Proteomics of protein post-translational modifications implicated in neurodegeneration

Mass spectrometry (MS)-based proteomics has developed into a battery of approaches that is exceedingly adept at identifying with high mass accuracy and precision any of the following: oxidative damage to proteins (redox proteomics), phosphorylation (phosphoproteomics), ubiquitination (diglycine remnant proteomics), protein fragmentation (degradomics), and other posttranslational modifications (PTMs). Many studies have linked these PTMs to pathogenic mechanisms of neurodegeneration. To date, identifying PTMs on specific pathology-associated proteins has proven to be a valuable step in the evaluation of functional alteration of proteins and also elucidates biochemical and structural explanations for possible pathophysiological mechanisms of neurodegenerative diseases. This review provides an overview of methods applicable to the identification and quantification of PTMs on proteins and enumerates historic, recent, and potential future research endeavours in the field of proteomics furthering the understanding of PTM roles in the pathogenesis of neurodegeneration.

Dysfunction of two lysosome degradation pathways of α-synuclein in Parkinson's disease: potential therapeutic targets?

Parkinson's disease (PD) is pathologically characterized by the presence of α-synuclein (α-syn)-positive intracytoplasmic inclusions named Lewy bodies in the dopaminergic neurons of the substantia nigra. A series of morbid consequences are caused by pathologically high amounts or mutant forms of α-syn, such as defects of membrane trafficking and lipid metabolism. In this review, we consider evidence that both point mutation and overexpression of α-syn result in aberrant degradation in neurons and microglia, and this is associated with the autophagy-lysosome pathway and endosome-lysosome system, leading directly to pathological intracellular aggregation, abnormal externalization and re-internalization cycling (and, in turn, internalization and re-externalization), and exocytosis. Based on these pathological changes, an increasing number of researchers have focused on these new therapeutic targets, aiming at alleviating the pathological accumulation of α-syn and re-establishing normal degradation.