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

LRRK2 Biology from structure to dysfunction: research progresses, but the themes remain the same

Since the discovery of leucine-rich repeat kinase 2 (LRRK2) as a protein that is likely central to the aetiology of Parkinson’s disease, a considerable amount of work has gone into uncovering its basic cellular function. This effort has led to the implication of LRRK2 in a bewildering range of cell biological processes and pathways, and probable roles in a number of seemingly unrelated medical conditions. In this review we summarise current knowledge of the basic biochemistry and cellular function of LRRK2. Topics covered include the identification of phosphorylation substrates of LRRK2 kinase activity, in particular Rab proteins, and advances in understanding the activation of LRRK2 kinase activity via dimerisation and association with membranes, especially via interaction with Rab29. We also discuss biochemical studies that shed light on the complex LRRK2 GTPase activity, evidence of roles for LRRK2 in a range of cell signalling pathways that are likely cell type specific, and studies linking LRRK2 to the cell biology of organelles. The latter includes the involvement of LRRK2 in autophagy, endocytosis, and processes at the trans-Golgi network, the endoplasmic reticulum and also key microtubule-based cellular structures. We further propose a mechanism linking LRRK2 dimerisation, GTPase function and membrane recruitment with LRRK2 kinase activation by Rab29. Together these data paint a picture of a research field that in many ways is moving forward with great momentum, but in other ways has not changed fundamentally. Many key advances have been made, but very often they seem to lead back to the same places.

Genetic, Structural, and Functional Evidence Link TMEM175 to Synucleinopathies

OBJECTIVE

The TMEM175/GAK/DGKQ locus is the 3rd strongest risk locus in genome-wide association studies of Parkinson disease (PD). We aimed to identify the specific disease-associated variants in this locus, and their potential implications.

METHODS

Full sequencing of TMEM175/GAK/DGKQ followed by genotyping of specific associated variants was performed in PD (n = 1,575) and rapid eye movement sleep behavior disorder (RBD) patients (n = 533) and in controls (n = 1,583). Adjusted regression models and a meta-analysis were performed. Association between variants and glucocerebrosidase (GCase) activity was analyzed in 715 individuals with available data. Homology modeling, molecular dynamics simulations, and lysosomal localization experiments were performed on TMEM175 variants to determine their potential effects on structure and function.

RESULTS

Two coding variants, TMEM175 p.M393T (odds ratio [OR] = 1.37, p = 0.0003) and p.Q65P (OR = 0.72, p = 0.005), were associated with PD, and p.M393T was also associated with RBD (OR = 1.59, p = 0.001). TMEM175 p.M393T was associated with reduced GCase activity. Homology modeling and normal mode analysis demonstrated that TMEM175 p.M393T creates a polar side-chain in the hydrophobic core of the transmembrane, which could destabilize the domain and thus impair either its assembly, maturation, or trafficking. Molecular dynamics simulations demonstrated that the p.Q65P variant may increase stability and ion conductance of the transmembrane protein, and lysosomal localization was not affected by these variants.

INTERPRETATION

Coding variants in TMEM175 are likely to be responsible for the association in the TMEM175/GAK/DGKQ locus, which could be mediated by affecting GCase activity. ANN NEUROL 2020;87:139-153.

The Overcrowded Crossroads: Mitochondria, Alpha-Synuclein, and the Endo-Lysosomal System Interaction in Parkinson's Disease

Parkinson's disease (PD) is the second most common neurodegenerative disorder worldwide, mainly affecting the elderly. The disease progresses gradually, with core motor presentations and a multitude of non-motor manifestations. There are two neuropathological hallmarks of PD, the dopaminergic neuronal loss and the alpha-synuclein-containing Lewy body inclusions in the substantia nigra. While the exact pathomechanisms of PD remain unclear, genetic investigations have revealed evidence of the involvement of mitochondrial function, alpha-synuclein (α-syn) aggregation, and the endo-lysosomal system, in disease pathogenesis. Due to the high energy demand of dopaminergic neurons, mitochondria are of special importance acting as the cellular powerhouse. Mitochondrial dynamic fusion and fission, and autophagy quality control keep the mitochondrial network in a healthy state. Should defects of the organelle occur, a variety of reactions would ensue at the cellular level, including disrupted mitochondrial respiratory network and perturbed calcium homeostasis, possibly resulting in cellular death. Meanwhile, α-syn is a presynaptic protein that helps regulate synaptic vesicle transportation and endocytosis. Its misfolding into oligomeric sheets and fibrillation is toxic to the mitochondria and neurons. Increased cellular oxidative stress leads to α-syn accumulation, causing mitochondrial dysfunction. The proteasome and endo-lysosomal systems function to regulate damage and unwanted waste management within the cell while facilitating the quality control of mitochondria and α-syn. This review will analyze the biological functions and interactions between mitochondria, α-syn, and the endo-lysosomal system in the pathogenesis of PD.

Evidence of Neurobiological Changes in the Presymptomatic PINK1 Knockout Rat

BACKGROUND

Genetic models of Parkinson's disease (PD) coupled with advanced imaging techniques can elucidate neurobiological disease progression, and can help identify early biomarkers before clinical signs emerge. PTEN-induced putative kinase 1 (PINK1) helps protect neurons from mitochondrial dysfunction, and a mutation in the associated gene is a risk factor for recessive familial PD. The PINK1 knockout (KO) rat is a novel model for familial PD that has not been neuroradiologically characterized for alterations in brain structure/function, alongside behavior, prior to 4 months of age.

OBJECTIVE

To identify biomarkers of presymptomatic PD in the PINK1 -/- rat at 3 months using magnetic resonance imaging techniques.

METHODS

At postnatal weeks 12-13; one month earlier than previously reported signs of motor and cognitive dysfunction, this study combined imaging modalities, including assessment of quantitative anisotropy across 171 individual brain areas using an annotated MRI rat brain atlas to identify sites of gray matter alteration between wild-type and PINK1 -/- rats.

RESULTS

The olfactory system, hypothalamus, thalamus, nucleus accumbens, and cerebellum showed differences in anisotropy between experimental groups. Molecular analyses revealed reduced levels of glutathione, ATP, and elevated oxidative stress in the substantia nigra, striatum and deep cerebellar nuclei. Mitochondrial genes encoding proteins in Complex IV, along with mRNA levels associated with mitochondrial function and genes involved in glutathione synthesis were reduced. Differences in brain structure did not align with any cognitive or motor impairment.

CONCLUSIONS

These data reveal early markers, and highlight novel brain regions involved in the pathology of PD in the PINK1 -/- rat before behavioral dysfunction occurs.

mTOR hyperactivity mediates lysosomal dysfunction in Gaucher's disease iPSC-neuronal cells

Bi-allelic GBA1 mutations cause Gaucher's disease (GD), the most common lysosomal storage disorder. Neuronopathic manifestations in GD include neurodegeneration, which can be severe and rapidly progressive. GBA1 mutations are also the most frequent genetic risk factors for Parkinson's disease. Dysfunction of the autophagy-lysosomal pathway represents a key pathogenic event in GBA1-associated neurodegeneration. Using an induced pluripotent stem cell (iPSC) model of GD, we previously demonstrated that lysosomal alterations in GD neurons are linked to dysfunction of the transcription factor EB (TFEB). TFEB controls the coordinated expression of autophagy and lysosomal genes and is negatively regulated by the mammalian target of rapamycin complex 1 (mTORC1). To further investigate the mechanism of autophagy-lysosomal pathway dysfunction in neuronopathic GD, we examined mTORC1 kinase activity in GD iPSC neuronal progenitors and differentiated neurons. We found that mTORC1 is hyperactive in GD cells as evidenced by increased phosphorylation of its downstream protein substrates. We also found that pharmacological inhibition of glucosylceramide synthase enzyme reversed mTORC1 hyperactivation, suggesting that increased mTORC1 activity is mediated by the abnormal accumulation of glycosphingolipids in the mutant cells. Treatment with the mTOR inhibitor Torin1 upregulated lysosomal biogenesis and enhanced autophagic clearance in GD neurons, confirming that lysosomal dysfunction is mediated by mTOR hyperactivation. Further analysis demonstrated that increased TFEB phosphorylation by mTORC1 results in decreased TFEB stability in GD cells. Our study uncovers a new mechanism contributing to autophagy-lysosomal pathway dysfunction in GD, and identifies the mTOR complex as a potential therapeutic target for treatment of GBA1-associated neurodegeneration.

Recent Developments in LRRK2-Targeted Therapy for Parkinson's Disease

Kinase activating missense mutations in leucine-rich repeat kinase 2 (LRRK2) are pathogenically linked to neurodegenerative Parkinson's disease (PD). Over the past decade, substantial effort has been devoted to the development of potent and selective small molecule inhibitors of LRRK2, as well as their preclinical testing across different Parkinson's disease models. This review outlines the genetic and biochemical evidence that pathogenic missense mutations increase LRRK2 kinase activity, which in turn provides the rationale for the development of small molecule inhibitors as potential PD therapeutics. An overview of progress in the development of LRRK2 inhibitors is provided, which in particular indicates that highly selective and potent compounds capable of clinical utility have been developed. We outline evidence from rodent- and human-induced pluripotent stem cell models that support a pathogenic role for LRRK2 kinase activity, and review the substantial experiments aimed at evaluating the safety of LRRK2 inhibitors. We address challenges still to overcome in the translational therapeutic pipeline, including biomarker development and clinical trial strategies, and finally outline the potential utility of LRRK2 inhibitors for other genetic forms of PD and ultimately sporadic PD. Collective evidence supports the ongoing clinical translation of LRRK2 inhibitors as a therapeutic intervention for PD is greatly needed.

Salidroside Protects Dopaminergic Neurons by Enhancing PINK1/Parkin-Mediated Mitophagy

Parkinson's disease (PD) is a common neurodegenerative disease characterized by the degeneration of nigrostriatal dopaminergic (DA) neurons. Our previous studies have suggested that salidroside (Sal) might play neuroprotective effects against PD by preserving mitochondrial Complex I activity. However, the exact mechanism of the neuroprotective effect of Sal remains unclear. Growing evidence indicates that PINK1/Parkin-mediated mitophagy is involved in the development of PD. In this study, we investigated whether Sal exerts a neuroprotective effect by modulating PINK1/Parkin-mediated mitophagy. Results showed that Sal alleviated MPTP-induced motor deficits in pole test. Moreover, Sal diminished MPTP-induced degeneration of nigrostriatal DA neurons as evidenced by upregulated TH-positive neurons in the substantia nigra, increased DAT expression, and high dopamine and metabolite levels in the striatum. Furthermore, in comparison with the MPP⁺/MPTP group, Sal considerably increased the mitophagosome and mitophagy flux. Moreover, in comparison with the MPP⁺/MPTP group, Sal evidently enhanced the mitochondrial expression of PINK1 and Parkin, accompanied by an increase in the colocalization of mitochondria with Parkin. However, transfection of MN9D cells with PINK1 siRNA reversed Sal-induced activated mitophagy and cytoprotective effect. In conclusion, Sal may confer neuroprotective effects by enhancing PINK1/Parkin-mediated mitophagy in MPP⁺/MPTP-induced PD models.

Glucocerebrosidase and its relevance to Parkinson disease

Mutations in GBA1, the gene encoding the lysosomal enzyme glucocerebrosidase, are among the most common known genetic risk factors for the development of Parkinson disease and related synucleinopathies. A great deal is known about GBA1, as mutations in GBA1 are causal for the rare autosomal storage disorder Gaucher disease. Over the past decades, significant progress has been made in understanding the genetics and cell biology of glucocerebrosidase. A least 495 different mutations, found throughout the 11 exons of the gene are reported, including both common and rare variants. Mutations in GBA1 may lead to degradation of the protein, disruptions in lysosomal targeting and diminished performance of the enzyme in the lysosome.

Gaucher disease is phenotypically diverse and has both neuronopathic and non-neuronopathic forms. Both patients with Gaucher disease and heterozygous carriers are at increased risk of developing Parkinson disease and Dementia with Lewy Bodies, although our understanding of the mechanism for this association remains incomplete. There appears to be an inverse relationship between glucocerebrosidase and α-synuclein levels, and even patients with sporadic Parkinson disease have decreased glucocerebrosidase. Glucocerebrosidase may interact with α-synuclein to maintain basic cellular functions, or impaired glucocerebrosidase could contribute to Parkinson pathogenesis by disrupting lysosomal homeostasis, enhancing endoplasmic reticulum stress or contributing to mitochondrial impairment. However, the majority of patients with GBA1 mutations never develop parkinsonism, so clearly other risk factors play a role. Treatments for Gaucher disease have been developed that increase visceral glucocerebrosidase levels and decrease lipid storage, although they have yet to properly address the neurological defects associated with impaired glucocerebrosidase. Mouse and induced pluripotent stem cell derived models have improved our understanding of glucocerebrosidase function and the consequences of its deficiency. These models have been used to test novel therapies including chaperone proteins, histone deacetylase inhibitors, and gene therapy approaches that enhance glucocerebrosidase levels and could prove efficacious in the treatment of forms of parkinsonism. Consequently, this rare monogenic disorder, Gaucher disease, provides unique insights directly applicable to our understanding and treatment of Parkinson disease, a common and complex neurodegenerative disorder.

Mechanism and medical implications of mammalian autophagy

Autophagy is a highly conserved catabolic process induced under various conditions of cellular stress, which prevents cell damage and promotes survival in the event of energy or nutrient shortage and responds to various cytotoxic insults. Thus, autophagy has primarily cytoprotective functions and needs to be tightly regulated to respond correctly to the different stimuli that cells experience, thereby conferring adaptation to the ever-changing environment. It is now apparent that autophagy is deregulated in the context of various human pathologies, including cancer and neurodegeneration, and its modulation has considerable potential as a therapeutic approach.

Biodegradable PLGA nanoparticles restore lysosomal acidity and protect neural PC-12 cells against mitochondrial toxicity

Exposure of mitochondrial parkinsonian neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+) to PC-12 cells results in significant cell death, decreases lysosomal acidity, and inhibits autophagic flux. Biodegradable poly (lactic-co-glycolic acid) (PLGA) nanoparticles (NPs) of ≈100 nm diameter localize to the lysosome, degrade, and subsequently release their acidic components to acidify the local lysosomal environment. The performance of PLGA NPs with different lysosomal pH modulating capabilities is investigated in PC-12 cells under MPP+ induced mitochondrial toxicity. PLGA NPs perform in a compositional dependent manner, where NPs with a higher glycolic acid to lactic acid ratio content degrade faster, and yield greater degrees of lysosomal pH modulation as well as autophagic flux modulation in PC-12 cells under MPP+ insult. These results show that slight compositional changes of the polymeric NP give rise to differing degrees of lysosomal acidification in PC-12 cells and afford improved cellular degradative activity.

Autophagy activation promotes clearance of α-synuclein inclusions in fibril-seeded human neural cells

There is much interest in delineating the mechanisms by which the α-synuclein protein accumulates in brains of individuals with Parkinson's disease (PD). Preclinical studies with rodent and primate models have indicated that fibrillar forms of α-synuclein can initiate the propagation of endogenous α-synuclein pathology. However, the underlying mechanisms by which α-synuclein fibrils seed pathology remain unclear. To investigate this further, we have used exogenous fibrillar α-synuclein to seed endogenous α-synuclein pathology in human neuronal cell lines, including primary human neurons differentiated from induced pluripotent stem cells. Fluorescence microscopy and immunoblot analyses were used to monitor levels of α-synuclein and key autophagy/lysosomal proteins over time in the exogenous α-synuclein fibril-treated neurons. We observed that temporal changes in the accumulation of cytoplasmic α-synuclein inclusions were associated with changes in the key autophagy/lysosomal markers. Of note, chloroquine-mediated blockade of autophagy increased accumulation of α-synuclein inclusions, and rapamycin-induced activation of autophagy, or use of 5'-AMP-activated protein kinase (AMPK) agonists, promoted the clearance of fibril-mediated α-synuclein pathology. These results suggest a key role for autophagy in clearing fibrillar α-synuclein pathologies in human neuronal cells. We propose that our findings may help inform the development of human neural cell models for screening of potential therapeutic compounds for PD or for providing insight into the mechanisms of α-synuclein propagation. Our results further add to existing evidence that AMPK activation may be a therapeutic option for managing PD.

Evaluation of the Common Molecular Basis in Alzheimer's and Parkinson's Diseases

Alzheimer’s disease (AD) and Parkinson’s disease (PD) are the most common neurodegenerative disorders related to aging. Though several risk factors are shared between these two diseases, the exact relationship between them is still unknown. In this paper, we analyzed how these two diseases relate to each other from the genomic, epigenomic, and transcriptomic viewpoints. Using an extensive literature mining, we first accumulated the list of genes from major genome-wide association (GWAS) studies. Based on these GWAS studies, we observed that only one gene (HLA-DRB5) was shared between AD and PD. A subsequent literature search identified a few other genes involved in these two diseases, among which SIRT1 seemed to be the most prominent one. While we listed all the miRNAs that have been previously reported for AD and PD separately, we found only 15 different miRNAs that were reported in both diseases. In order to get better insights, we predicted the gene co-expression network for both AD and PD using network analysis algorithms applied to two GEO datasets. The network analysis revealed six clusters of genes related to AD and four clusters of genes related to PD; however, there was very low functional similarity between these clusters, pointing to insignificant similarity between AD and PD even at the level of affected biological processes. Finally, we postulated the putative epigenetic regulator modules that are common to AD and PD.

Genes associated with Parkinson's disease respond to increasing polychlorinated biphenyl levels in the blood of healthy females

Polychlorinated biphenyls (PCBs) are a class of widespread environmental pollutants, commonly found in human blood, that have been suggested to be linked to the occurrence of sporadic Parkinson's disease (PD). It has been reported that some non-coplanar PCBs accumulate in the brains of female PD patients. To improve our understanding of the association between PCB exposure and PD risk we have applied whole transcriptome gene expression analysis in blood cells from 594 PCB-exposed subjects (369 female, 225 male). Interestingly, we observe that in females, blood levels of non-coplanar PCBs appear to be associated with expression levels of PD-specific genes. However, no such association was detected in males. Among the 131 PD-specific genes affected, 39 have been shown to display similar changes in expression levels in the substantia nigra of deceased PD patients. Especially among the down-regulated genes, transcripts of genes involved in neurotransmitter vesicle-related functions were predominant.

Inhibition of Autophagy Prolongs Recipient Survival Through Promoting CD8+ T Cell Apoptosis in a Rat Liver Transplantation Model

In liver transplantation (LT), although various immunosuppressants have been used in clinical practice, acute rejection remains a common complication that significantly shortens recipient survival. In recent years, manipulating immune tolerance has been regarded as one of the promising solutions to rejection. Autophagy, an evolutionarily conserved protein degradation system, has been reported to be involved in immune rejection and may be a target to establish immune tolerance. However, the role of autophagy in acute rejection reaction after LT has not been elucidated. Here, we showed that the autophagy of CD8⁺ T cells was strongly enhanced in patients with graft rejection and that the autophagy level was positively correlated with the severity of rejection. Similar findings were observed in a rat acute hepatic rejection model. Furthermore, administration of the autophagy inhibitor 3-methyladenine (3-MA) largely decreased the viability and function of CD8⁺ T cells through inhibiting autophagy, which significantly prolonged graft survival in rats. In addition, inhibiting the autophagy of activated CD8⁺ T cells in vitro considerably suppressed mitochondria mediated survival and downregulated T cell function.

Conclusions: We first showed that the inhibition of autophagy significantly prolongs liver allograft survival by promoting the apoptosis of CD8⁺ T cells, which may provide a novel strategy for immune tolerance induction.

Dysfunction of Cellular Proteostasis in Parkinson's Disease

Despite decades of research, current therapeutic interventions for Parkinson’s disease (PD) are insufficient as they fail to modify disease progression by ameliorating the underlying pathology. Cellular proteostasis (protein homeostasis) is an essential factor in maintaining a persistent environment for neuronal activity. Proteostasis is ensured by mechanisms including regulation of protein translation, chaperone-assisted protein folding and protein degradation pathways. It is generally accepted that deficits in proteostasis are linked to various neurodegenerative diseases including PD. While the proteasome fails to degrade large protein aggregates, particularly alpha-synuclein (α-SYN) in PD, drug-induced activation of autophagy can efficiently remove aggregates and prevent degeneration of dopaminergic (DA) neurons. Therefore, maintenance of these mechanisms is essential to preserve all cellular functions relying on a correctly folded proteome. The correlations between endoplasmic reticulum (ER) stress and the unfolded protein response (UPR) that aims to restore proteostasis within the secretory pathway are well-established. However, while mild insults increase the activity of chaperones, prolonged cell stress, or insufficient adaptive response causes cell death. Modulating the activity of molecular chaperones, such as protein disulfide isomerase which assists refolding and contributes to the removal of unfolded proteins, and their associated pathways may offer a new approach for disease-modifying treatment. Here, we summarize some of the key concepts and emerging ideas on the relation of protein aggregation and imbalanced proteostasis with an emphasis on PD as our area of main expertise. Furthermore, we discuss recent insights into the strategies for reducing the toxic effects of protein unfolding in PD by targeting the ER UPR pathway.

Emerging views of mitophagy in immunity and autoimmune diseases

Mitophagy is a vital form of autophagy for selective removal of dysfunctional or redundant mitochondria. Accumulating evidence implicates elimination of dysfunctional mitochondria as a powerful means employed by autophagy to keep the immune system in check. The process of mitophagy may restrict inflammatory cytokine secretion and directly regulate mitochondrial antigen presentation and immune cell homeostasis. In this review, we describe distinctive pathways of mammalian mitophagy and highlight recent advances relevant to its function in immunity. In addition, we further discuss the direct and indirect evidence linking mitophagy to inflammation and autoimmunity underlying the pathogenesis of autoimmune diseases including inflammatory bowel diseases (IBD), systemic lupus erythematosus (SLE) and primary biliary cirrhosis (PBC).Abbreviations: AICD: activation induced cell death; AIM2: absent in melanoma 2; ALPL/HOPS: alkaline phosphatase, biomineralization associated; AMA: anti-mitochondrial antibodies; AMFR: autocrine motility factor receptor; ATG: autophagy-related; BCL2L13: BCL2 like 13; BNIP3: BCL2 interacting protein 3; BNIP3L/NIX: BCL2 interacting protein 3 like; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CARD: caspase recruitment domain containing; CASP1: caspase 1; CD: Crohn disease; CGAS: cyclic GMP-AMP synthase; CXCL1: C-X-C motif chemokine ligand 1; DEN: diethylnitrosamine; DLAT/PDC-E2: dihydrolipoamide S-acetyltransferase; DNM1L/Drp1: dynamin 1 like; ESCRT: endosomal sorting complexes required for transport; FKBP8: FKBP prolyl isomerase 8; FUNDC1: Fun14 domain containing 1; GABARAP: GABA type A receptor-associated protein; HMGB1: high mobility group box 1; HPIV3: human parainfluenza virus type 3; IBD: inflammatory bowel diseases; IEC: intestinal epithelial cell; IFN: interferon; IL1B/IL-1β: interleukin 1 beta; iNK: invariant natural killer; IRGM: immunity related GTPase M; LIR: LC3-interacting region; LPS: lipopolysaccharide; LRRK2: leucine rich repeat kinase 2; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MARCH5: membrane associated ring-CH-type finger 5; MAVS: mitochondrial antiviral signaling protein; MDV: mitochondria-derived vesicle; MFN1: mitofusin 1; MHC: major histocompatibility complex; MIF: macrophage migration inhibitory factor; mtAP: mitochondrial antigen presentation; mtDNA: mitochondrial DNA; MTOR: mechanistic target of rapamycin kinase; mtROS: mitochondrial ROS; MUL1: mitochondrial E3 ubiquitin protein ligase 1; NBR1: NBR1 autophagy cargo receptor; NFKB/NF-ĸB: nuclear factor kappa B subunit; NK: natural killer; NLR: NOD-like receptor; NLRC4: NLR family CARD domain containing 4; NLRP3: NLR family pyrin domain containing 3; OGDH: oxoglutarate dehydrogenase; OMM: outer mitochondrial membrane; OPTN: optineurin; ox: oxidized; PARK7: Parkinsonism associated deglycase; PBC: primary biliary cirrhosis; PEX13: peroxisomal biogenesis factor 13; PHB/PHB1: prohibitin; PHB2: prohibitin 2; PIK3C3/VPS34: phosphatidylinositol 3-kinase catalytic subunit type 3; PINK1: PTEN induced kinase 1; PLEKHM1: pleckstrin homology and RUN domain containing M1; PRKN/PARK2: parkin RBR E3 ubiquitin protein ligase; RAB: member RAS oncogene family; RHEB: Ras homolog: mTORC1 binding; RIPK2: receptor interacting serine/threonine kinase 2; RLR: DDX58/RIG-I like receptor; ROS: reactive oxygen species; SBD: small bile ducts; SLC2A1/GLUT1: solute carrier family 2 member 1; SLE: systemic lupus erythematosus; SMURF1: SMAD specific E3 ubiquitin protein ligase 1; SQSTM1/p62: sequestosome 1; TAX1BP1: Tax1 binding protein 1; TCR: T cell receptor; TFAM: transcription factor A: mitochondrial; Th17: T helper 17; TLR9: toll like receptor 9; TMEM173/STING: transmembrane protein 173; TNF/TNF-α: tumor necrosis factor; Ub: ubiquitin; UC: ulcerative colitis; ULK1: unc-51 like autophagy activating kinase 1; WIPI: WD repeat domain: phosphoinositide interacting; ZFYVE1/DFCP1: zinc finger FYVE-type containing 1.

MicroRNA-124 regulates the expression of p62/p38 and promotes autophagy in the inflammatory pathogenesis of Parkinson's disease

Parkinson's disease (PD) is a neurodegenerative disorder characterized by motor and nonmotor symptoms due to the selective loss of midbrain dopaminergic neurons. The evidence for a chronic inflammatory reaction mediated by microglial cells in the brain is particularly strong in PD. In our previous study, we have shown that brain-specific microRNA-124 (miR-124) is significantly down-regulated in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced mouse model of PD and that it can also inhibit neuroinflammation during the development of PD. However, further investigation is required to understand whether the abnormal expression of miR-124 regulates microglial activation. In this study, we found that the expression of sequestosome 1 (p62) and phospho-p38 mitogen-activated protein kinases (p-p38) showed a significant increase in LPS-treated immortalized murine microglial cell line BV2 cells in an MPTP-induced mouse model of PD. Knockdown of p62 could suppress the secretion of proinflammatory cytokines and p-p38 of microglia. Besides, inhibition of p38 suppressed the secretion of proinflammatory cytokines and promoted autophagy in BV2 cells. Moreover, our study is the first to identify a unique role of miR-124 in mediating the microglial inflammatory response by targeting p62 and p38 in PD. In the microglial culture supernatant transfer model, the knockdown of p62 in BV2 cells prevented apoptosis and death of human neuroblastoma cell lines SH-SY5Y (SH-SY5Y) cells following microglia activation. In addition, the exogenous delivery of miR-124 could suppress p62 and p-p38 expression and could also attenuate the activation of microglia in the substantia nigra par compacta of MPTP-treated mice. Taken together, our data suggest that miR-124 could inhibit neuroinflammation during the development of PD by targeting p62, p38, and autophagy, indicating that miR-124 could be a potential therapeutic target for regulating the inflammatory response in PD.-Yao, L., Zhu, Z., Wu, J., Zhang, Y., Zhang, H., Sun, X., Qian, C., Wang, B., Xie, L., Zhang, S., Lu, G. MicroRNA-124 regulates the expression of p62/p38 and promotes autophagy in the inflammatory pathogenesis of Parkinson's disease.

Dysregulated Lipid Metabolism and Its Role in α-Synucleinopathy in Parkinson's Disease

Parkinson’s disease (PD) is the second most common neurodegenerative disease, the main pathological hallmark of which is the accumulation of α-synuclein (α-syn) and the formation of filamentous aggregates called Lewy bodies in the brainstem, limbic system, and cortical areas. Lipidomics is a newly emerging field which can provide fresh insights and new answers that will enhance our capacity for early diagnosis, tracking disease progression, predicting critical endpoints, and identifying risk in pre-symptomatic persons. In recent years, lipids have been implicated in many aspects of PD pathology. Biophysical and lipidomic studies have demonstrated that α-syn binds preferentially not only to specific lipid families but also to specific molecular species and that these lipid-protein complexes enhance its interaction with synaptic membranes, influence its oligomerization and aggregation, and interfere with the catalytic activity of cytoplasmic lipid enzymes and lysosomal lipases, thereby affecting lipid metabolism. The genetic link between aberrant lipid metabolism and PD is even more direct, with mutations in GBA and SMPD1 enhancing PD risk in humans and loss of GALC function increasing α-syn aggregation and accumulation in experimental murine models. Moreover, a number of lipidomic studies have reported PD-specific lipid alterations in both patient brains and plasma, including alterations in the lipid composition of lipid rafts in the frontal cortex. A further aspect of lipid dysregulation promoting PD pathogenesis is oxidative stress and inflammation, with proinflammatory lipid mediators such as platelet activating factors (PAFs) playing key roles in arbitrating the progressive neurodegeneration seen in PD linked to α-syn intracellular trafficking. Lastly, there are a number of genetic risk factors of PD which are involved in normal lipid metabolism and function. Genes such as PLA2G6 and SCARB2, which are involved in glycerophospholipid and sphingolipid metabolism either directly or indirectly are associated with risk of PD. This review seeks to describe these facets of metabolic lipid dysregulation as they relate to PD pathology and potential pathomechanisms involved in disease progression, while highlighting incongruous findings and gaps in knowledge that necessitate further research.

SMPD1 mutations, activity, and α-synuclein accumulation in Parkinson's disease

BACKGROUND

SMPD1 (acid-sphingomyelinase) variants have been associated with Parkinson's disease in recent studies. The objective of this study was to further investigate the role of SMPD1 mutations in PD.

METHODS

SMPD1 was sequenced in 3 cohorts (Israel Ashkenazi Jewish cohort, Montreal/Montpellier, and New York), including 1592 PD patients and 975 controls. Additional data were available for 10,709 Ashkenazi Jewish controls. Acid-sphingomyelinase activity was measured by a mass spectrometry-based assay in the New York cohort. α-Synuclein levels were measured in vitro following CRISPR/Cas9-mediated knockout and siRNA knockdown of SMPD1 in HeLa and BE(2)-M17 cells. Lysosomal localization of acid-sphingomyelinase with different mutations was studied, and in silico analysis of their effect on acid-sphingomyelinase structure was performed.

RESULTS

SMPD1 mutations were associated with PD in the Ashkenazi Jewish cohort, as 1.4% of PD patients carried the p.L302P or p.fsP330 mutation, compared with 0.37% in 10,709 Ashkenazi Jewish controls (OR, 3.7; 95%CI, 1.6-8.2; P = 0.0025). In the Montreal/Montpellier cohort, the p.A487V variant was nominally associated with PD (1.5% versus 0.14%; P = 0.0065, not significant after correction for multiple comparisons). Among PD patients, reduced acid-sphingomyelinase activity was associated with a 3.5- to 5.8-year earlier onset of PD in the lowest quartile versus the highest quartile of acid-sphingomyelinase activity (P = 0.01-0.001). We further demonstrated that SMPD1 knockout and knockdown resulted in increased α-synuclein levels in HeLa and BE(2)-M17 dopaminergic cells and that the p.L302P and p.fsP330 mutations impair the traffic of acid-sphingomyelinase to the lysosome.

CONCLUSIONS

Our results support an association between SMPD1 variants, acid-sphingomyelinase activity, and PD. Furthermore, they suggest that reduced acid-sphingomyelinase activity may lead to α-synuclein accumulation. © 2019 International Parkinson and Movement Disorder Society.

Autophagy: Supporting cellular and organismal homeostasis by self-eating

Autophagy is a conserved catabolic process that delivers cytoplasmic components and organelles to lysosomes for degradation and recycling. This pathway serves to degrade nonfunctional organelles and aggregate-prone proteins, as well as to produce substrates for energy production and biosynthesis. Autophagy is especially important for the maintenance of stem cells, and for the survival and homeostasis of post-mitotic cells like neurons. Functional autophagy promotes longevity in several model organisms. Autophagy regulates immunity and inflammation at several levels and has both anti- and pro-tumorigenic roles in cancer. This review provides a concise overview of autophagy and its importance in cellular and organismal homeostasis, with emphasis on aging, stem cells, neuronal cells, immunity, inflammation, and cancer.

Trehalose as a promising therapeutic candidate for the treatment of Parkinson's disease

Parkinson's disease (PD) is a progressive movement disorder resulting primarily from loss of nigrostriatal dopaminergic neurons. PD is characterized by the accumulation of protein aggregates, and evidence suggests that aberrant protein deposition in dopaminergic neurons could be related to the dysregulation of the lysosomal autophagy pathway. The therapeutic potential of autophagy modulators has been reported in experimental models of PD. Trehalose is a natural disaccharide that has been considered as a new candidate for the treatment of neurodegenerative diseases. It has a chaperone-like activity, prevents protein misfolding or aggregation, and by promoting autophagy, contributes to the removal of accumulated proteins. In this review, we briefly summarize the role of aberrant autophagy in PD and the underlying mechanisms that lead to the development of this disease. We also discuss reports that used trehalose to counteract the neurotoxicity in PD, focusing particularly on the autophagy promoting, protein stabilization, and anti-neuroinflammatory effects of trehalose.

Extracellular vesicles degradation pathway based autophagy lysosome pathway

As an ancient intracellular degradation pathway, the autophagy lysosome pathway exists in various cells continuously and stably and maintains cellular homeostasis by degrading damaged organelles and misfolded proteins that are prejudicial to cells. Extracellular vesicles (EVs) including microparticles and exosomes, are derived from varieties of mammalian tissue cells such as platelets, endothelial cells, cardiomyocytes. Through large quantity of active substances carried by EVs, EVs exert momentous biological functions. Recent researches have revealed the molecular mechanism of the interaction between extracellular vesicles and autophagy. In this review, we first elaborate that extracellular vesicles are identified and internalized by target cells by means of receptor-ligand. Since extracellular vesicles contain multiple functional molecules, we subsequently describe the process of intracellular autophagy pathway induced by extracellular vesicles, which activates autophagy-related pathways or delivers autophagy-associated molecules. Finally, we introduced the effects of extracellular vesicle-induced autophagy on extracellular vesicles and target cells respectively. In conclusion, this article integrates relevant theoretical knowledge of autophagy caused by extracellular vesicles and provides a new direction for the study of extracellular vesicles in the future.

Inflammatory, regulatory, and autophagy co-expression modules and hub genes underlie the peripheral immune response to human intracerebral hemorrhage

BACKGROUND

Intracerebral hemorrhage (ICH) has a high morbidity and mortality. The peripheral immune system and cross-talk between peripheral blood and brain have been implicated in the ICH immune response. Thus, we delineated the gene networks associated with human ICH in the peripheral blood transcriptome. We also compared the differentially expressed genes in blood following ICH to a prior human study of perihematomal brain tissue.

METHODS

We performed peripheral blood whole-transcriptome analysis of ICH and matched vascular risk factor control subjects (n = 66). Gene co-expression network analysis identified groups of co-expressed genes (modules) associated with ICH and their most interconnected genes (hubs). Mixed-effects regression identified differentially expressed genes in ICH compared to controls.

RESULTS

Of seven ICH-associated modules, six were enriched with cell-specific genes: one neutrophil module, one neutrophil plus monocyte module, one T cell module, one Natural Killer cell module, and two erythroblast modules. The neutrophil/monocyte modules were enriched in inflammatory/immune pathways; the T cell module in T cell receptor signaling genes; and the Natural Killer cell module in genes regulating alternative splicing, epigenetic, and post-translational modifications. One erythroblast module was enriched in autophagy pathways implicated in experimental ICH, and NRF2 signaling implicated in hematoma clearance. Many hub genes or module members, such as IARS, mTOR, S1PR1, LCK, FYN, SKAP1, ITK, AMBRA1, NLRC4, IL6R, IL17RA, GAB2, MXD1, PIK3CD, NUMB, MAPK14, DDX24, EVL, TDP1, ATG3, WDFY3, GSK3B, STAT3, STX3, CSF3R, PIP4K2A, ANXA3, DGAT2, LRP10, FLOT2, ANK1, CR1, SLC4A1, and DYSF, have been implicated in neuroinflammation, cell death, transcriptional regulation, and some as experimental ICH therapeutic targets. Gene-level analysis revealed 1225 genes (FDR p < 0.05, fold-change > |1.2|) have altered expression in ICH in peripheral blood. There was significant overlap of the 1225 genes with dysregulated genes in human perihematomal brain tissue (p = 7 × 10-3). Overlapping genes were enriched for neutrophil-specific genes (p = 6.4 × 10-08) involved in interleukin, neuroinflammation, apoptosis, and PPAR signaling.

CONCLUSIONS

This study delineates key processes underlying ICH pathophysiology, complements experimental ICH findings, and the hub genes significantly expand the list of novel ICH therapeutic targets. The overlap between blood and brain gene responses underscores the importance of examining blood-brain interactions in human ICH.

Modulation of autophagy in human diseases strategies to foster strengths and circumvent weaknesses

Autophagy is central to the maintenance of intracellular homeostasis across species. Accordingly, autophagy disorders are linked to a variety of diseases from the embryonic stage until death, and the role of autophagy as a therapeutic target has been widely recognized. However, autophagy-associated therapy for human diseases is still in its infancy and is supported by limited evidence. In this review, we summarize the landscape of autophagy-associated diseases and current autophagy modulators. Furthermore, we investigate the existing autophagy-associated clinical trials, analyze the obstacles that limit their progress, offer tactics that may allow barriers to be overcome along the way and then discuss the therapeutic potential of autophagy modulators in clinical applications.

Balancing mTOR Signaling and Autophagy in the Treatment of Parkinson's Disease

The mammalian target of rapamycin (mTOR) signaling pathway plays a critical role in regulating cell growth, proliferation, and life span. mTOR signaling is a central regulator of autophagy by modulating multiple aspects of the autophagy process, such as initiation, process, and termination through controlling the activity of the unc51-like kinase 1 (ULK1) complex and vacuolar protein sorting 34 (VPS34) complex, and the intracellular distribution of TFEB/TFE3 and proto-lysosome tubule reformation. Parkinson’s disease (PD) is a serious, common neurodegenerative disease characterized by dopaminergic neuron loss in the substantia nigra pars compacta (SNpc) and the accumulation of Lewy bodies. An increasing amount of evidence indicates that mTOR and autophagy are critical for the pathogenesis of PD. In this review, we will summarize recent advances regarding the roles of mTOR and autophagy in PD pathogenesis and treatment. Further characterizing the dysregulation of mTOR pathway and the clinical translation of mTOR modulators in PD may offer exciting new avenues for future drug development.

Peripheral Acid Sphingomyelinase Activity Is Associated with Biomarkers and Phenotypes of Alcohol Use and Dependence in Patients and Healthy Controls

By catalyzing the hydrolysis of sphingomyelin into ceramide, acid sphingomyelinase (ASM) changes the local composition of the plasma membrane with effects on receptor-mediated signaling. Altered enzyme activities have been noted in common human diseases, including alcohol dependence. However, the underlying mechanisms remain largely unresolved. Blood samples were collected from early-abstinent alcohol-dependent in-patients (n[♂] = 113, n[♀] = 87) and matched healthy controls (n[♂] = 133, n[♀] = 107), and analyzed for routine blood parameters and serum ASM activity. We confirmed increased secretory ASM activities in alcohol-dependent patients compared to healthy control subjects, which decreased slightly during detoxification. ASM activity correlated positively with blood alcohol concentration, withdrawal severity, biomarkers of alcohol dependence (liver enzyme activities of gamma-glutamyl transferase, alanine aminotransferase, aspartate aminotransferase; homocysteine, carbohydrate-deficient transferrin; mean corpuscular volume, and creatine kinase). ASM activity correlated negatively with leukocyte and thrombocyte counts. ASM and gamma-glutamyl transferase were also associated in healthy subjects. Most effects were similar for males and females with different strengths. We describe previously unreported associations between ASM activity and markers of liver damage and myelosuppression. Further research should investigate whether this relationship is causal, or whether these parameters are part of a common pathway in order to gain insights into underlying mechanisms and develop clinical applications.

Mitochondrial quality control and neurodegenerative diseases

Mitochondria homeostasis is sustained by the mitochondrial quality control (MQC) system, which is crucial for cellular health, especially in the maintenance of functional mitochondria. A healthy mitochondria network is essential for life as it regulates cellular metabolism processes, particularly ATP production. Mitochondrial dynamics and mitophagy are two highly integrated processes in MQC system that determines whether damaged mitochondria will be repaired or degraded. Neurons are highly differentiated cells which demand high energy consumption. Therefore, compromised MQC processes and the accumulation of dysfunctional mitochondria may be the main cause of neuronal death and lead to neurodegeneration. Here, we focus on the inseparable relationship of mitochondria dynamics and mitophagy and how their dysfunction may lead to neurodegenerative diseases.

The glycoprotein GPNMB is selectively elevated in the substantia nigra of Parkinson's disease patients and increases after lysosomal stress

GPNMB is a glycoprotein observed upon tissue damage and inflammation and is associated with astrocytes, microglia, and macrophages. Gene variations in GPNMB are linked with Parkinson's disease (PD) risk, and changes in protein levels of GPNMB have been found in lysosomal storage disorders, including Gaucher's disease with glucocerebrosidase (GCase) deficiency. In the current study, GPNMB increases were seen in the substantia nigra (SN) of PD patients compared to age-matched controls. Such PD patients have a decrease in GCase activity and corresponding elevation of glycosphingolipids in the SN (Rocha et al., 2015a). Interestingly, transgenic mice modelling synucleinopathy did not show GPNMB elevations or altered GCase activity levels compared to wild-type mice. However, upon CBE-induced GCase lysosomal dysfunction with elevated glycosphingolipids in wild-type mice, there were similar changes in GPNMB levels in the brain as seen in PD patient brains. These results indicate that GPNMB levels do not depend on alpha-synuclein load per se but relate directly to the lipidopathy changes induced by CBE-mediated GCase inhibition. The experimental modelling of elevating glycolipids resulted in GPNMB elevations with glial activation in several brain regions in mice. This is the first demonstration of region-specific elevations of GPNMB protein in Parkinson's disease. The presence of GPNMB in PD patient substantia nigra, the induction of GPNMB after experimental glycosphingolipid increases, but not with pure alpha-synucleinopathy, point towards the potential for primary lipid-induced degeneration in PD.

New insights into the structure of PINK1 and the mechanism of ubiquitin phosphorylation

Mutations in PINK1 cause early-onset recessive Parkinson's disease. This gene encodes a protein kinase implicated in mitochondrial quality control via ubiquitin phosphorylation and activation of the E3 ubiquitin ligase Parkin. Here, we review and analyze functional features emerging from recent crystallographic, nuclear magnetic resonance (NMR) and mass spectrometry studies of PINK1. We compare the apo and ubiquitin-bound PINK1 structures and reveal an allosteric switch, regulated by autophosphorylation, which modulates substrate recognition. We critically assess the conformational changes taking place in ubiquitin and the Parkin ubiquitin-like domain in relation to its binding to PINK1. Finally, we discuss the implications of these biophysical findings in our understanding of the role of PINK1 in mitochondrial function, and analyze the potential for structure-based drug design.

Characterization of Brain Lysosomal Activities in GBA-Related and Sporadic Parkinson's Disease and Dementia with Lewy Bodies

Mutations in the GBA gene, encoding the lysosomal hydrolase glucocerebrosidase (GCase), are the most common known genetic risk factor for Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). The present study aims to gain more insight into changes in lysosomal activity in different brain regions of sporadic PD and DLB patients, screened for GBA variants. Enzymatic activities of GCase, β-hexosaminidase, and cathepsin D were measured in the frontal cortex, putamen, and substantia nigra (SN) of a cohort of patients with advanced PD and DLB as well as age-matched non-demented controls (n = 15/group) using fluorometric assays. Decreased activity of GCase (− 21%) and of cathepsin D (− 15%) was found in the SN and frontal cortex of patients with PD and DLB compared to controls, respectively. Population stratification was applied based on GBA genotype, showing substantially lower GCase activity (~ − 40%) in GBA variant carriers in all regions. GCase activity was further significantly decreased in the SN of PD and DLB patients without GBA variants in comparison to controls without GBA variants. Our results show decreased GCase activity in brains of PD and DLB patients with and without GBA variants, most pronounced in the SN. The results of our study confirm findings from previous studies, suggesting a role for GCase in GBA-associated as well as sporadic PD and DLB.

Lysosome trafficking and signaling in health and neurodegenerative diseases

Lysosomes, single-membrane organelles defined by a uniquely strong acidic lumenal pH and high content of acid hydrolases, are the shared degradative compartments of the endocytic and autophagic pathways. These pathways, and especially lysosomes, are points of particular vulnerability in many neurodegenerative diseases. Beyond the role of lysosomes in substrate degradation, new findings have ascribed to lysosomes the leading role in sensing and responding to cellular nutrients, growth factors and cellular stress. This review aims to integrate recent concepts of basic lysosome biology and pathobiology as a basis for understanding neurodegenerative disease pathogenesis. Here, we discuss the newly recognized signaling functions of lysosomes and specific aspects of lysosome biology in neurons while re-visiting the classical defining criteria for lysosomes and the importance of preserving strict definitions. Our discussion emphasizes dynein-mediated axonal transport of maturing degradative organelles, with further consideration of their roles in synaptic function. We finally examine how distinctive underlying disturbances of lysosomes in various neurodegenerative diseases result in unique patterns of auto/endolysosomal mistrafficking. The rapidly emerging understanding of lysosomal trafficking and disruptions in lysosome signaling is providing valuable clues to new targets for disease-modifying therapies.

Full sequencing and haplotype analysis of MAPT in Parkinson's disease and rapid eye movement sleep behavior disorder

BACKGROUND

MAPT haplotypes are associated with PD, but their association with rapid eye movement sleep behavior disorder is unclear.

OBJECTIVE

To study the role of MAPT variants in rapid eye movement sleep behavior disorder.

METHODS

Two cohorts were included: (A) PD (n = 600), rapid eye movement sleep behavior disorder (n = 613) patients, and controls (n = 981); (B) dementia with Lewy bodies patients with rapid eye movement sleep behavior disorder (n = 271) and controls (n = 950). MAPT-associated variants and the entire coding sequence of MAPT were analyzed. Age-, sex-, and ethnicity-adjusted analyses were performed to examine the association between MAPT, PD, and rapid eye movement sleep behavior disorder.

RESULTS

MAPT-H2 variants were associated with PD (odds ratios: 0.62-0.65; P = 0.010-0.019), but not with rapid eye movement sleep behavior disorder. In PD, the H1 haplotype odds ratio was 1.60 (95% confidence interval: 1.12-2.28; P = 0.009), and the H2 odds ratio was 0.68 (95% confidence interval: 0.48-0.96; P = 0.03). The H2/H1 haplotypes were not associated with rapid eye movement sleep behavior disorder.

CONCLUSIONS

Our results confirm the protective effect of the MAPT-H2 haplotype in PD, and define its components. Furthermore, our results suggest that MAPT does not play a major role in rapid eye movement sleep behavior disorder, emphasizing different genetic background than in PD in this locus. © 2018 International Parkinson and Movement Disorder Society.

Cellular and Molecular Basis of Neurodegeneration in Parkinson Disease

It has been 200 years since Parkinson disease (PD) was described by Dr. Parkinson in 1817. The disease is the second most common neurodegenerative disease characterized by a progressive loss of dopaminergic neurons in the substantia nigra pars compacta. Although the pathogenesis of PD is still unknown, the research findings from scientists are conducive to understand the pathological mechanisms. It is well accepted that both genetic and environmental factors contribute to the onset of PD. In this review, we summarize the mutations of main seven genes (α-synuclein, LRRK2, PINK1, Parkin, DJ-1, VPS35 and GBA1) linked to PD, discuss the potential mechanisms for the loss of dopaminergic neurons (dopamine metabolism, mitochondrial dysfunction, endoplasmic reticulum stress, impaired autophagy, and deregulation of immunity) in PD, and expect the development direction for treatment of PD.

SIRT3 Protects Rotenone-induced Injury in SH-SY5Y Cells by Promoting Autophagy through the LKB1-AMPK-mTOR Pathway

SIRT3 is a class III histone deacetylase that modulates energy metabolism, genomic stability and stress resistance. It has been implicated as a potential therapeutic target in a variety of neurodegenerative diseases, including Parkinson’s disease (PD). Our previous study demonstrates that SIRT3 had a neuroprotective effect on a rotenone-induced PD cell model, however, the exact mechanism is unknown. In this study, we investigated the underlying mechanism. We established a SIRT3 stable overexpression cell line using lentivirus infection in SH-SY5Y cells. Then, a PD cell model was established using rotenone. Our data demonstrate that overexpression of SIRT3 increased the level of the autophagy markers LC3 II and Beclin 1. After addition of the autophagy inhibitor 3-MA, the protective effect of SIRT3 diminished: the cell viability decreased, while the apoptosis rate increased; α-synuclein accumulation enhanced; ROS production increased; antioxidants levels, including SOD and GSH, decreased; and MMP collapsed. These results reveal that SIRT3 has neuroprotective effects on a PD cell model by up-regulating autophagy. Furthermore, SIRT3 overexpression also promoted LKB1 phosphorylation, followed by activation of AMPK and decreased phosphorylation of mTOR. These results suggest that the LKB1-AMPK-mTOR pathway has a role in induction of autophagy. Together, our findings indicate a novel mechanism by which SIRT3 protects a rotenone-induced PD cell model through the regulation of autophagy, which, in part, is mediated by activation of the LKB1-AMPK-mTOR pathway.

Neuronal Cell Death

Neuronal cell death occurs extensively during development and pathology, where it is especially important because of the limited capacity of adult neurons to proliferate or be replaced. The concept of cell death used to be simple as there were just two or three types, so we just had to work out which type was involved in our particular pathology and then block it. However, we now know that there are at least a dozen ways for neurons to die, that blocking a particular mechanism of cell death may not prevent the cell from dying, and that non-neuronal cells also contribute to neuronal death. We review here the mechanisms of neuronal death by intrinsic and extrinsic apoptosis, oncosis, necroptosis, parthanatos, ferroptosis, sarmoptosis, autophagic cell death, autosis, autolysis, paraptosis, pyroptosis, phagoptosis, and mitochondrial permeability transition. We next explore the mechanisms of neuronal death during development, and those induced by axotomy, aberrant cell-cycle reentry, glutamate (excitoxicity and oxytosis), loss of connected neurons, aggregated proteins and the unfolded protein response, oxidants, inflammation, and microglia. We then reassess which forms of cell death occur in stroke and Alzheimer's disease, two of the most important pathologies involving neuronal cell death. We also discuss why it has been so difficult to pinpoint the type of neuronal death involved, if and why the mechanism of neuronal death matters, the molecular overlap and interplay between death subroutines, and the therapeutic implications of these multiple overlapping forms of neuronal death.

Parkinson disease related ATP13A2 evolved early in animal evolution

Several human P5-type transport ATPases are implicated in neurological disorders, but little is known about their physiological function and properties. Here, we investigated the relationship between the five mammalian P5 isoforms ATP13A1-5 in a comparative study. We demonstrated that ATP13A1-4 isoforms undergo autophosphorylation, which is a hallmark P-type ATPase property that is required for substrate transport. A phylogenetic analysis of P5 sequences revealed that ATP13A1 represents clade P5A, which is highly conserved between fungi and animals with one member in each investigated species. The ATP13A2-5 isoforms belong to clade P5B and diversified from one isoform in fungi and primitive animals to a maximum of four in mammals by successive gene duplication events in vertebrate evolution. We revealed that ATP13A1 localizes in the endoplasmic reticulum (ER) and experimentally demonstrate that ATP13A1 likely contains 12 transmembrane helices. Conversely, ATP13A2-5 isoforms reside in overlapping compartments of the endosomal system and likely contain 10 transmembrane helices, similar to what was demonstrated earlier for ATP13A2. ATP13A1 complemented a deletion of the yeast P5A ATPase SPF1, while none of ATP13A2-5 could complement either the loss of SPF1 or that of the single P5B ATPase YPK9 in yeast. Thus, ATP13A1 carries out a basic ER function similar to its yeast counterpart Spf1p that plays a role in ER related processes like protein folding and processing. ATP13A2-5 isoforms diversified in mammals and are expressed in the endosomal system where they may have evolved novel complementary or partially redundant functions. While most P5-type ATPases are widely expressed, some P5B-type ATPases (ATP13A4 and ATP13A5) display a more limited tissue distribution in the brain and epithelial glandular cells, where they may exert specialized functions. At least some P5B isoforms are of vital importance for the nervous system, since ATP13A2 and ATP13A4 are linked to respectively Parkinson disease and autism spectrum disorders.

Mitochondrial function and autophagy: integrating proteotoxic, redox, and metabolic stress in Parkinson's disease

Parkinson's disease (PD) is a movement disorder with widespread neurodegeneration in the brain. Significant oxidative, reductive, metabolic, and proteotoxic alterations have been observed in PD postmortem brains. The alterations of mitochondrial function resulting in decreased bioenergetic health is important and needs to be further examined to help develop biomarkers for PD severity and prognosis. It is now becoming clear that multiple hits on metabolic and signaling pathways are likely to exacerbate PD pathogenesis. Indeed, data obtained from genetic and genome association studies have implicated interactive contributions of genes controlling protein quality control and metabolism. For example, loss of key proteins that are responsible for clearance of dysfunctional mitochondria through a process called mitophagy has been found to cause PD, and a significant proportion of genes associated with PD encode proteins involved in the autophagy-lysosomal pathway. In this review, we highlight the evidence for the targeting of mitochondria by proteotoxic, redox and metabolic stress, and the role autophagic surveillance in maintenance of mitochondrial quality. Furthermore, we summarize the role of α-synuclein, leucine-rich repeat kinase 2, and tau in modulating mitochondrial function and autophagy. Among the stressors that can overwhelm the mitochondrial quality control mechanisms, we will discuss 4-hydroxynonenal and nitric oxide. The impact of autophagy is context depend and as such can have both beneficial and detrimental effects. Furthermore, we highlight the potential of targeting mitochondria and autophagic function as an integrated therapeutic strategy and the emerging contribution of the microbiome to PD susceptibility.

Mechanisms of α-Synuclein Induced Synaptopathy in Parkinson's Disease

Parkinson's disease (PD) is characterized by intracellular inclusions of aggregated and misfolded α-Synuclein (α-Syn), and the loss of dopaminergic (DA) neurons in the brain. The resulting motor abnormalities mark the progression of PD, while non-motor symptoms can already be identified during early, prodromal stages of disease. Recent studies provide evidence that during this early prodromal phase, synaptic and axonal abnormalities occur before the degenerative loss of neuronal cell bodies. These early phenotypes can be attributed to synaptic accumulation of toxic α-Syn. Under physiological conditions, α-Syn functions in its native conformation as a soluble monomer. However, PD patient brains are characterized by intracellular inclusions of insoluble fibrils. Yet, oligomers and protofibrils of α-Syn have been identified to be the most toxic species, with their accumulation at presynaptic terminals affecting several steps of neurotransmitter release. First, high levels of α-Syn alter the size of synaptic vesicle pools and impair their trafficking. Second, α-Syn overexpression can either misregulate or redistribute proteins of the presynaptic SNARE complex. This leads to deficient tethering, docking, priming and fusion of synaptic vesicles at the active zone (AZ). Third, α-Syn inclusions are found within the presynaptic AZ, accompanied by a decrease in AZ protein levels. Furthermore, α-Syn overexpression reduces the endocytic retrieval of synaptic vesicle membranes during vesicle recycling. These presynaptic alterations mediated by accumulation of α-Syn, together impair neurotransmitter exocytosis and neuronal communication. Although α-Syn is expressed throughout the brain and enriched at presynaptic terminals, DA neurons are the most vulnerable in PD, likely because α-Syn directly regulates dopamine levels. Indeed, evidence suggests that α-Syn is a negative modulator of dopamine by inhibiting enzymes responsible for its synthesis. In addition, α-Syn is able to interact with and reduce the activity of VMAT2 and DAT. The resulting dysregulation of dopamine levels directly contributes to the formation of toxic α-Syn oligomers. Together these data suggest a vicious cycle of accumulating α-Syn and deregulated dopamine that triggers synaptic dysfunction and impaired neuronal communication, ultimately causing synaptopathy and progressive neurodegeneration in Parkinson's disease.

Association study of genetic variation in the autophagy lysosome pathway genes and risk of eight kinds of cancers

The autophagy lysosome pathway is essential to maintain cell viability and homeostasis in response to many stressful environments, which is reported to play a vital role in cancer development and therapy. However, the association of genetic alterations of this pathway with risk of cancer remains unclear. Based on genome-wide association study data of eight kinds of cancers, we used an adaptive rank truncated product approach to perform a pathway-level and gene-level analysis, and used a logistic model to calculate SNP-level associations to examine whether an altered autophagy lysosome pathway contributes to cancer susceptibility. Among eight kinds of cancers, four of them showed significant statistics in the pathway-level analysis, including breast cancer (p = 0.00705), gastric cancer (p = 0.00880), lung cancer (p = 0.000100) and renal cell carcinoma (p = 0.00190). We also found that some autophagy lysosome genes had signals of association with cancer risk. Our results demonstrated that inherited genetic variants in the overall autophagy lysosome pathway and certain associated genes might contribute to cancer susceptibility, which warrant further evaluation in other independent datasets.

Glucocerebrosidase and Parkinson Disease: Molecular, Clinical, and Therapeutic Implications

Parkinson disease (PD) is a complex neurodegenerative disease characterised by multiple motor and non-motor symptoms. In the last 20 years, more than 20 genes have been identified as causes of parkinsonism. Following the observation of higher risk of PD in patients affected by Gaucher disease, a lysosomal disorder caused by mutations in the glucocerebrosidase (GBA) gene, it was discovered that mutations in this gene constitute the single largest risk factor for development of idiopathic PD. Patients with PD and GBA mutations are clinically indistinguishable from patients with idiopathic PD, although some characteristics emerge depending on the specific mutation, such as slightly earlier onset. The molecular mechanisms which lead to this increased PD risk in GBA mutation carriers are multiple and not yet fully elucidated, they include alpha-synuclein aggregation, lysosomal-autophagy dysfunction and endoplasmic reticulum stress. Moreover, dysfunction of glucocerebrosidase has also been demonstrated in non-GBA PD, suggesting its interaction with other pathogenic mechanisms. Therefore, GBA enzyme function represents an interesting pharmacological target for PD. Cell and animal models suggest that increasing GBA enzyme activity can reduce alpha-synuclein levels. Clinical trials of ambroxol, a glucocerebrosidase chaperone, are currently ongoing in PD and PD dementia, as is a trial of substrate reduction therapy. The aim of this review is to summarise the main features of GBA-PD and discuss the implications of glucocerebrosidase modulation on PD pathogenesis.

The lysosomal enzyme alpha-Galactosidase A is deficient in Parkinson's disease brain in association with the pathologic accumulation of alpha-synuclein

The aberrant accumulation of alpha-synuclein (α-syn) is believed to contribute to the onset and pathogenesis of Parkinson's disease (PD). The autophagy-lysosome pathway (ALP) is responsible for the high capacity clearance of α-syn. ALP dysfunction is documented in PD and pre-clinical evidence suggests that inhibiting the ALP promotes the pathological accumulation of α-syn. We previously identified the pathological accumulation of α-syn in the brains of mice deficient for the soluble lysosomal enzyme alpha-Galactosidase A (α-Gal A), a member of the glycosphingolipid metabolism pathway. In the present study, we quantified α-Gal A activity and levels of its glycosphingolipid metabolites in postmortem temporal cortex specimens from control individuals and in PD individuals staged with respect to α-syn containing Lewy body pathology. In late-state PD temporal cortex we observed significant decreases in α-Gal A activity and the 46kDa "active" species of α-Gal A as determined respectively by fluorometric activity assay and western blot analysis. These decreases in α-Gal A activity/levels correlated significantly with increased α-syn phosphorylated at serine 129 (p129S-α-syn) that was maximal in late-stage PD temporal cortex. Mass spectrometric analysis of 29 different isoforms of globotriaosylceramide (Gb3), a substrate of α-Gal A indicated no significant differences with respect to different stages of PD temporal cortex. However, significant correlations were observed between increased levels of several Gb3 isoforms and with decreased α-Gal A activity and/or increased p129S-α-syn. Deacylated Gb3 (globotriaosylsphingosine or lyso-Gb3) was also analyzed in PD brain tissue but was below the limit of detection of 20pmol/g. Analysis of other lysosomal enzymes revealed a significant decrease in activity for the lysosomal aspartic acid protease cathepsin D but not for glucocerebrosidase (GCase) or cathepsin B in late-stage PD temporal cortex. However, a significant correlation was observed between decreasing GCase activity and increasing p129S-α-syn. Together our findings indicate α-Gal A deficiency in late-stage PD brain that correlates significantly with the pathological accumulation of α-syn, and further suggest the potential for α-Gal A and its glycosphingolipid substrates as putative biomarkers for PD.

Reduced LRRK2 in association with retromer dysfunction in post-mortem brain tissue from LRRK2 mutation carriers

Missense mutations in leucine-rich repeat kinase 2 (LRRK2) are pathogenic for familial Parkinson's disease. However, it is unknown whether levels of LRRK2 protein in the brain are altered in patients with LRRK2-associated Parkinson's disease. Because LRRK2 mutations are relatively rare, accounting for approximately 1% of all Parkinson's disease, we accessioned cases from five international brain banks to investigate levels of the LRRK2 protein, and other genetically associated Parkinson's disease proteins. Brain tissue was obtained from 17 LRRK2 mutation carriers (12 with the G2019S mutation and five with the I2020T mutation) and assayed by immunoblot. Compared to matched controls and idiopathic Parkinson's disease cases, we found levels of LRRK2 protein were reduced in the LRRK2 mutation cases. We also measured a decrease in two other proteins genetically implicated in Parkinson's disease, the core retromer component, vacuolar protein sorting associated protein 35 (VPS35), and the lysosomal hydrolase, glucocerebrosidase (GBA). Moreover, the classical retromer cargo protein, cation-independent mannose-6-phosphate receptor (MPR300, encoded by IGF2R), was also reduced in the LRRK2 mutation cohort and protein levels of the receptor were correlated to levels of LRRK2. These results provide new data on LRRK2 protein expression in brain tissue from LRRK2 mutation carriers and support a relationship between LRRK2 and retromer dysfunction in LRRK2-associated Parkinson's disease brain.

Sleep disorders and Parkinson disease; lessons from genetics

Parkinson disease is a common, age-related neurodegenerative disorder, projected to afflict millions of individuals in the near future. Understanding its etiology and identifying clinical, genetic or biological markers for Parkinson disease onset and progression is therefore of major importance. Various sleep-related disorders are the most common group of non-motor symptoms in advanced Parkinson disease, but they can also occur during its prodromal phase. However, with the exception of REM sleep behavior disorder, it is unclear whether they are part of the early pathological process of Parkinson disease, or if they develop as Parkinson disease advances because of treatments and neurodegeneration progression. The advancements in genetic studies in the past two decades have generated a wealth of information, and recent genetic studies offer new insight on the association of sleep-related disorders with Parkinson disease. More specifically, comparing genetic data between Parkinson disease and sleep-related disorders can clarify their association, which may assist in determining whether they can serve as clinical markers for Parkinson disease risk or progression. In this review, we discuss the current knowledge on the genetics of sleep-related disorders in Parkinson disease context, and the potential implications on research, diagnosis, counseling and treatment.