Abstract
Parkinson’s disease (PD) is a chronic progressive neurodegenerative disease, which is characterized by severe loss of dopaminergic neurons and formation of Lewy bodies, which are rich in aggregated alpha-synuclein (α-syn). Two decades of intensive research have compiled a massive body of evidence that aggregation of α-syn is a critical process in PD and other synucleinopathies. The dissemination of Lewy body pathology throughout the central nervous system strongly suggests a cell-to-cell transmission of α-syn. Although in vitro and in vivo evidence has convincingly demonstrated that aggregation-prone α-syn can spread from cell to cell, the exact mechanisms and the role for the disease pathology remain elusive. Except for cases of direct contact, the transmission of α-syn from cell to cell requires that α-syn is released to the extracellular space and taken up by recipient cells. Furthermore, internalized α-syn needs to gain access to the cytoplasm and/or target organelles of the recipient cell. Here, we review the current state of knowledge about release and uptake of α-syn and discuss the key questions that remain unanswered.
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Introduction
Parkinson’s disease (PD) is the second most common neurodegenerative disease, affecting up to 0.3% of the entire world population (de Lau and Breteler 2006). It is a chronic progressive disease, which leads to a high degree of disability and a compromise in the quality of life. PD is characterized by a devastating loss of neurons in affected areas, foremost dopaminergic neurons in the substantia nigra pars reticulata (Gibb 1991; Gibb and Lees 1991). Pathologically, PD is characterized by the accumulation of large intracellular inclusions termed ‘Lewy bodies’ and ‘Lewy neurites’ (Lewy 1912). Since the discovery that the small protein alpha-synuclein (α-syn) is the main constituent of Lewy bodies 20 years ago (Spillantini et al. 1997), a lot of attention and research has been focused on the aggregation of α-syn. A seminal study by Braak and colleagues elegantly demonstrated that Lewy body pathology spreads throughout the central nervous system (CNS) following a uniform pattern along anatomically interconnected areas (Braak et al. 2003). This and follow-up studies gave rise to a hypothesis that aggregation of α-syn, or α-syn itself, can spread from cell to cell by uptake and release of aggregation-prone α-syn, further promoting seeded aggregation of endogenous α-syn in a template fashion. Despite a compelling body of evidence that α-syn is transmitted from cell to cell both in vitro and in vivo, many questions remain open and hinder the development of therapeutic strategies that could prevent the spread of the disease throughout the CNS.
Aggregation of α-syn
α-syn is a small, well-conserved protein that is expressed in many tissues and cell types (Shibayama-Imazu et al. 1993; Iwai et al. 1995; Lavedan 1998; Villar-Pique et al. 2016). Increased levels of α-syn are associated with synucleinopathies, as exemplified by patients with α-syn gene duplication and triplication, the latter presenting with early-onset PD (Singleton et al. 2003; Chartier-Harlin et al. 2004; Ibanez et al. 2004). Inside the cell, α-syn localizes mainly to the cytoplasm; however, it has also been reported to be located in the nucleus, attached to mitochondria or at the endoplasmic reticulum, while in the CNS, it is located at the pre-synaptic termini (McLean et al. 2000b; Goers et al. 2003; Li et al. 2007; Devi et al. 2008; Guardia-Laguarta et al. 2014). Although the physiological function of α-syn is still unclear, its strong conservation, ubiquitous expression and high abundance (up to 1% of the total protein in CNS) indicates its importance for the cell. In aqueous solutions, α-syn is suggested to have an intrinsically disordered structure, adopting many possible conformations, whereas in association to membranes it acquires a helical conformation (Weinreb et al. 1996; Davidson et al. 1998; McLean et al. 2000a; Chandra et al. 2003). Which form of α-syn represents the physiologic form inside mammalian cells is still a matter of debate. Some studies argued that the predominant form of α-syn in the cell is a disordered monomer (Fauvet et al. 2012; Burre et al. 2013); others provide evidence for membrane-associated α-syn homotetramers to be the physiologically relevant form (Bartels et al. 2011; Dettmer et al. 2013). Despite the discussion on the physiological form of α-syn, it is clear that aggregated α-syn is central to the pathology of synucleinopathies. This became obvious after the discovery that α-syn is the main component of Lewy bodies and Lewy neurites (Spillantini et al. 1997). The investigation of these and further types of α-syn-positive inclusions (e.g., glial cytoplasmic inclusions) has provided helpful insights into α-syn pathology in the human brain and suggested that α-syn aggregation is a key early process in inclusion formation (Kuusisto et al. 2003; Saito et al. 2003) and synaptic dysfunction (Kramer and Schulz-Schaeffer 2007). Furthermore, the observation of glial α-syn immunoreactivities hinted at the possibility that α-syn is transferred between different cell types and that this process may play a role in the degradation of pathologic α-syn (Braak et al. 2007; Kovacs et al. 2014; Rohan et al. 2016; Loria et al. 2017).
In intracellular inclusions, α-syn is found as large, beta-sheet-enriched fibrils (Spillantini et al. 1998). Recently, it has been demonstrated that different strains of aggregated α-syn fibrils exist, which exhibit specific effects on cells, have different seeding properties and can induce distinct synucleinopathies in vivo (Bousset et al. 2013; Peelaerts et al. 2015; Pieri et al. 2016). α-syn fibrils are formed in a multistep-process, involving numerous intermediate states including protofibrils, large oligomers and small oligomers (Hoyer et al. 2002; Caughey and Lansbury 2003; Munishkina et al. 2003). These intermediate species are termed “on-(fibrillary)-pathway” and are metastable, spontaneously forming large fibrils upon incubation (Cappai et al. 2005). In addition, α-syn can also associate to “off-pathway” oligomers, which do not turn into large fibrillar assemblies (Ehrnhoefer et al. 2008). On- and off-pathway oligomers are toxic to cells, can compromise membrane integrity and seed the aggregation of endogenous α-syn (Danzer et al. 2007, 2009; Winner et al. 2011). The exact molecular events that result in the initial aggregation of α-syn remain largely disputed and many mechanisms have been proposed: a dose-dependent effect of α-syn expression, saturation of membranes with α-syn, stabilization of intermediate species by the environment, impact by bacterial and eukaryotic amyloid proteins, truncation and other post-translational modifications, as well as prion-like, template-driven aggregation. All of these can result in the formation of aggregation-prone α-syn, leading to self-aggravating pathology.
Once a cell contains aberrant α-syn, there are three possibilities for handling it: degradation, deposition in a specialized compartment (inclusion), or release into the extracellular space. Both deposition inside the cell and release into the extracellular space are tightly related to failure of proper degradation. Degradation of α-syn can occur both via autophagic clearance and by proteasomal degradation (Cuervo et al. 2004; Rideout et al. 2004; Emmanouilidou et al. 2010b; Dargemont and Ossareh-Nazari 2012). Moreover, it has been demonstrated that depending on the conformation of α-syn, it can be targeted to the proteasome or to the lysosome (Shin et al. 2005). Both endogenous (cytoplasmic) and internalized α-syn aggregates can be targeted to the lysosome, the former via autophagy and the later via the endosome (Lee et al. 2004, 2008a). Failure of autophagic clearance can result in the secretion via non-classical exocytosis and drastically promote release of aggregated α-syn (Alvarez-Erviti et al. 2011).
Release into the extracellular space (Fig. 1)
α-syn lacks a classical secretory signal and was initially believed to be an exclusively intracellular protein. However, measurable quantities of α-syn have been detected in CSF, plasma and cell culture supernatant (El-Agnaf et al. 2006; Mollenhauer et al. 2008). The possibility of neuron-to-neuron transmission of misfolded α-syn in PD was highlighted by the appearance of aggregated α-syn in naïve transplanted embryonic stem cells in PD brains (Kordower et al. 2008; Li et al. 2008). Recombinant α-syn oligomers can be taken up by neurons in culture and trigger cell death (Danzer et al. 2007, 2009). Furthermore, Desplats et al. (2009) demonstrated that α-syn can be directly transmitted from neuronal cells overexpressing α-syn to transplanted embryonic stem cells both in tissue culture and in transgenic animals, supporting the idea that a prion-like mechanism could be responsible for the host-to-graft transfer of PD pathology (Brundin et al. 2008). In cell culture, α-syn is released by cell lines overexpressing α-syn and both by wild-type and α-syn-overexpressing primary neurons (El-Agnaf et al. 2003; Lee et al. 2005; Sung et al. 2005). Interestingly, the amount of released α-syn appears to correlate with the levels of intracellular α-syn (Reyes et al. 2015). The first important question, therefore, is whether α-syn is released passively or actively from the cell. Passive release can occur by two different ways: diffusion through the cell membrane and release through compromised cell membranes. Only monomeric but not oligomeric and aggregated α-syn can pass the cell membrane by diffusion (Ahn et al. 2006; Lee et al. 2008a). Diffusion of monomeric α-syn can occur in both directions and relies on a so-far unidentified membrane translocator, since α-syn cannot simply pass the lipid bilayer or escape from vesicles (Lee et al. 2005, 2008a). Remarkably, exogenously applied α-syn monomers can enter and exit the cell by diffusion, while α-syn synthesized by the cell in the cytoplasm remains trapped inside the cell (Lee et al. 2008a). This suggests that rapid formation of physiological multimers (e.g., tetramers) or posttranslational modifications prevent nascent α-syn from passively exiting the cell. There is little evidence that α-syn is released through compromised cell membranes and cell death. An in vivo study by Ulusoy and colleagues suggested that transmission of α-syn in a rat model does not result from neuronal death or injury and even requires healthy functioning neurons (Ulusoy et al. 2015). Importantly, it is possible that considerably less α-syn is available outside the cell in vivo, and therefore cell death may contribute more to the extracellular pool. However, evidence that α-syn is released passively in vivo is largely missing. Although much progress has been made in the establishment of extracellular α-syn as a biomarker, a systematic increase in PD and other synucleinopathies remains a matter of debate (El-Agnaf et al. 2003; Llorens et al. 2016; Shahnawaz et al. 2017). Different species of α-syn can be found in blood, CSF and saliva not only of PD patients but also of healthy controls with no indications of manifest or prodromal neurological disease (El-Agnaf et al. 2003; Llorens et al. 2016; Simonsen et al. 2016). Thus, it remains to be clarified if neuron death contributes to α-syn release in vivo and if this α-syn has diagnostic value, as well as relevance for the spread of disease.
If α-syn is released actively by the cell, several important questions arise: What is the mechanism of α-syn secretion? How is α-syn secretion regulated? What is the function of α-syn secretion in cells? The answers to these questions are closely associated with the question which species of α-syn are secreted. Several active mechanisms have been demonstrated for the release of monomeric, oligomeric and aggregated α-syn: ER-Golgi-dependent exocytosis and non-classical exocytosis, as well as in association with vesicles (Lee et al. 2005; Emmanouilidou et al. 2010a; Jang et al. 2010; Alvarez-Erviti et al. 2011; Danzer et al. 2011). Both monomeric and aggregated α-syn can be secreted through non-classical exocytosis by neurons in cells culture (Lee et al. 2005). Monomeric, oligomeric and aggregated α-syn can also be found in exosomes from cells overexpressing α-syn (Emmanouilidou et al. 2010a; Alvarez-Erviti et al. 2011; Danzer et al. 2012; Bliederhaeuser et al. 2016). Interestingly, secretion of α-syn is increased by stress, α-syn aggregation, lysosomal dysfunction, inhibition of the proteasome and mitochondrial dysfunction (Lee et al. 2005; Jang et al. 2010). Thus, α-syn secretion is actively regulated by conditions that promote α-syn aggregation. The function of α-syn release is likely also specific for different species of α-syn. For example, the secretion of α-syn monomers and small oligomers can aim to prevent the recruitment of endogenous α-syn by an aggregation seed or could have a purely physiologic function, like enhancement of vesicle recycling (Chandra et al. 2005). In contrast, secretion of aggregated α-syn can protect neurons from its toxicity and aim at the uptake and degradation by other cell types like professional phagocytes and astrocytes, or the degradation by extracellular enzymes. Indeed, microglia degrade efficiently extracellular α-syn (Lee et al. 2008b) and several extracellular proteases (Calpain 1, neurosin) can degrade extracellular α-syn and are active in brains from PD and DLB patients (Ogawa et al. 2000). Importantly, low-molecular weight α-syn released from cells does not necessarily have to be aggregation-prone per se but can be rendered so by extracellular processing like truncation. By contrast, aggregated α-syn released from neighboring cells probably resists proteolytic degradation outside the cell and is internalized by recipient cells.
As evident from the above-mentioned studies, release of α-syn seems to be dependent on the conformation of α-syn. This notion is further supported by the observation that familial PD mutations increase the secretion of α-syn in vitro (Lazaro et al. 2014). Thus, if the proteins responsible for the specific recognition and secretion of aberrant α-syn are identified, novel approaches to prevent disease spread may emerge. Unfortunately, it has been difficult to study the secretion of different conformations of α-syn since it is impossible to let the cell produce only one species of α-syn. This technical hurdle has prevented the efficient identification of the mechanism responsible for the specific secretion of pathologic but not physiologic α-syn.
Uptake from the extracellular space (Fig. 1)
The uptake of α-syn from the extracellular space has been intensively studied in recent years. Uptake of pathologic α-syn results in toxicity and seeding of aggregation of endogenous α-syn and is possibly a critical step necessary for the cell-to-cell transmission of α-syn pathology.
As with release, uptake of extracellular α-syn can occur passively (by diffusion), or actively, i.e., by endocytosis. Diffusion of monomeric but not oligomeric and aggregated α-syn through the plasma membrane has been observed, as discussed in the previous section but it has not been investigated whether it contributes to the transmission of pathology. Otherwise, extracellular α-syn is taken up by different types of endocytosis. Two main types of endocytosis can be distinguished: pinocytosis (often referred to simply as endocytosis) and phagocytosis. These two main types utilize different protein machineries and are responsible for the engulfment of different types of extracellular material: large particles are engulfed by phagocytosis, while macromolecules, small molecules and extracellular fluid are internalized by pinocytosis. While pinocytosis occurs constitutively in virtually all mammalian cells, phagocytosis is carried out mainly by professional phagocytes like macrophages and microglia. Thus, the uptake mechanism and fate of extracellular α-syn vary depending on the species of α-syn and on the type of recipient cell.
Pinocytosis is constitutive and accounts for the internalization of extracellular material, which is trapped in endocytic pits. Solutes and small molecules are internalized this way by clathrin-, caveolae- or actin-dependent processes. In addition, larger molecules can be efficiently internalized by pinocytosis through binding to a specific receptor, a process that is termed ‘receptor-mediated endocytosis’ and is clathrin-mediated. Uptake of α-syn by pinocytosis has been demonstrated in many studies with different cell types: differentiated SH-SY5Y, COS-7 and primary neurons. Hansen et al. observed that exogenously applied α-syn is internalized in a dynamin-dependent process also in vivo (Hansen et al. 2011). Interestingly, blocking the internalization of endocytic vesicles by dynamin inhibition resulted in an accumulation of α-syn oligomers and aggregates on the cell membrane (Lee et al. 2008a, b). The same was observed when proteins on the outer side of the cell membrane were trimmed by treatment with an unspecific protease (Lee et al. 2008a, b). This strongly suggests that aggregated α-syn is taken up by receptor-mediated endocytosis. Indeed, α3-subunit of Na+/K + -ATPase has been reported to be a cell surface partner of α-syn assemblies (Shrivastava et al. 2015). Furthermore, Mao et al. recently identified LAG3 as a receptor that binds specifically α-syn pre-formed fibrils (PFFs), initiating α-syn transmission and toxicity (Mao et al. 2016). Interestingly, α-syn PFFs also bound to neurexin 1a (Mao et al. 2016), which was also found by Shrivastava et al. to be a cell surface binding partner for α-syn fibrils (Shrivastava et al. 2015). Mao and colleagues screened a large panel of transmembrane proteins for their affinity to bind α-syn PFFs and found three receptors, of which LAG3 showed the highest specificity for α-syn PFFs. Not only did LAG3 exhibit high affinity for aggregated and not for monomeric α-syn but it also did not bind tau and amyloid beta aggregates. In addition, ablation of LAG3 in neurons disrupted transmission of α-syn pathology and alleviated dopaminergic cell loss and disease phenotype in an animal model (Mao et al. 2016). The identification of receptors for aggregated α-syn on neurons opens interesting possibilities; however, much remains to be elucidated. For example, it should be investigated whether LAG3 is also responsible for the internalization of α-syn oligomers, whether it binds aggregates produced from the cells and whether it binds different strains of α-syn fibrils. Interestingly, Lee et al. demonstrated that different types of brain cells take up exogenous synuclein with different kinetics (Lee et al. 2008b). In particular, microglia were much more efficient than neurons and astrocytes, both in uptake and degradation of extracellular α-syn. This findings suggest that either the same uptake pathways are differentially regulated in different cell types or that different cell types are equipped with distinct receptors for extracellular α-syn. Liu and colleagues identified ciliary neurotrophic factor receptor as a mediator of neurotoxicity induced by α-syn (Liu et al. 2010) but independent of α-syn endocytosis; in another study, inhibition of TLR2 partially ablated uptake of neuron-released α-syn by microglia (Kim et al. 2013). Therefore, it remains to be elucidated which exact receptors are involved in the uptake not only of different species of α-syn but also by different brain cells. The picture is further complicated by the fact that α-syn produced in mammalian cells may be modified such that its interaction with receptors and uptake is totally different compared with recombinant α-syn. This hypothesis is suggested by two independent observations: first, Lee and colleagues noticed that while monomeric recombinant α-syn can freely move into and out of the cell through the cell membrane, cell-produced monomeric α-syn remains trapped inside the cell (Lee et al. 2008a). Second, Delenclos and colleagues demonstrated that α-syn oligomers purified from a neuroglioma H4 cell line stably overexpressing α-syn are attached to the outer side of the cell membrane, although it has been shown numerous times that recombinant α-syn oligomers are readily internalized by different cell types (Delenclos et al. 2017). Thus, the solid body of knowledge about the uptake of different recombinant α-syn species cannot be simply translated to cell-produced α-syn without extensive testing.
The studies discussed above have all investigated the uptake of α-syn, which is not enclosed in vesicles. However, we and others have previously shown that a portion of α-syn is secreted in association to exosomes, small membrane-enclosed vesicles (Emmanouilidou et al. 2010a; Danzer et al. 2012). Although a relatively small amount of extracellular α-syn is associated with exosomes, their potential as a biomarker of PD, as well as their role in the pathogenesis of PD, are gaining increasing attention (Tofaris 2017). Using a well-established luciferase complementation system, it has been shown that both neurons and microglia take up α-syn oligomers much more efficiently in association with exosomes (Danzer et al. 2012; Bliederhaeuser et al. 2016). Interestingly, inhibition of phagocytosis or micropinocytosis of exosome-associated α-syn oligomers by cytochalasin D was not found in neuroglioma H4 cells (Delenclos et al. 2017), while we have previously found that microglia and monocytes efficiently take up exosomes via actin- and PI3K-dependent pathways, strongly indicative of phagocytosis (Bliederhaeuser et al. 2016). Virtually all types of uptake have so far been described for exosomes; however, there is still no consensus in the literature which uptake mechanism is responsible for exosome internalization and it seems that the uptake mode is dependent not only on the recipient cell type but also on the cell type the released the exosomes, as well as on the cargo (Feng et al. 2010; Mulcahy et al. 2014). Thus, uptake of exosome-associated α-syn likely occurs through different mechanisms in neurons and professional phagocytes. It remains to be investigated whether uptake by different mechanisms results in different intracellular trafficking and effects on cells.
A further prerequisite for the prion-like spread of misfolded α-syn is that the transmitted α-syn gains access to the cytoplasm of the recipient cell, where the pool of the endogenous protein is localized. Elegant studies by Freeman et al. and Flavin et al. demonstrated that aggregated α-syn can evade degradation after uptake from the extracellular space and can escape into the cytoplasm from endosomal–lysosomal compartments (Freeman et al. 2013; Flavin et al. 2017). Following rupture of lysosomes, α-syn aggregates can induce mitochondrial dysfunction, inflammatory activation and oxidative stress. Therefore, it is also possible that α-syn that escapes the lysosome can directly seed the aggregation of cytoplasmic α-syn.
Conclusions
In recent years, much progress has been made in our understanding of the molecular processes that underlie the transmission of α-syn pathology from cell to cell. New knowledge is available regarding mechanisms that increase the secretion of α-syn, extracellular modifications of α-syn, receptors involved in the uptake and the involvement of vesicles. The contribution of different cell types and the differences between different α-syn species have also gained appreciation. Although our knowledge has improved significantly, there are still numerous technical difficulties that need to be overcome and questions that need to be answered, before we understand cell-to-cell transmission of α-syn well enough to tailor efficient therapies for PD and other synucleinopathies.
References
Ahn KJ, Paik SR, Chung KC, Kim J (2006) Amino acid sequence motifs and mechanistic features of the membrane translocation of alpha-synuclein. J Neurochem 97:265–279
Alvarez-Erviti L, Seow Y, Schapira AH, Gardiner C, Sargent IL, Wood MJ, Cooper JM (2011) Lysosomal dysfunction increases exosome-mediated alpha-synuclein release and transmission. Neurobiol Dis 42:360–367
Bartels T, Choi JG, Selkoe DJ (2011) Alpha-synuclein occurs physiologically as a helically folded tetramer that resists aggregation. Nature 477:107–110
Bliederhaeuser C, Grozdanov V, Speidel A, Zondler L, Ruf WP, Bayer H, Kiechle M, Feiler MS, Freischmidt A, Brenner D, Witting A, Hengerer B, Fandrich M, Ludolph AC, Weishaupt JH, Gillardon F, Danzer KM (2016) Age-dependent defects of alpha-synuclein oligomer uptake in microglia and monocytes. Acta Neuropathol 131:379–391
Bousset L, Pieri L, Ruiz-Arlandis G, Gath J, Jensen PH, Habenstein B, Madiona K, Olieric V, Bockmann A, Meier BH, Melki R (2013) Structural and functional characterization of two alpha-synuclein strains. Nat Commun 4:2575
Braak H, Del Tredici K, Rub U, de Vos RA, Jansen Steur EN, Braak E (2003) Staging of brain pathology related to sporadic Parkinson’s disease. Neurobiol Aging 24:197–211
Braak H, Sastre M, Del Tredici K (2007) Development of alpha-synuclein immunoreactive astrocytes in the forebrain parallels stages of intraneuronal pathology in sporadic Parkinson’s disease. Acta Neuropathol 114:231–241
Brundin P, Li JY, Holton JL, Lindvall O, Revesz T (2008) Research in motion: the enigma of Parkinson’s disease pathology spread. Nat Rev Neurosci 9:741–745
Burre J, Vivona S, Diao J, Sharma M, Brunger AT, Sudhof TC (2013) Properties of native brain alpha-synuclein. Nature 498:E4–E6 discussion E6-7
Cappai R, Leck SL, Tew DJ, Williamson NA, Smith DP, Galatis D, Sharples RA, Curtain CC, Ali FE, Cherny RA, Culvenor JG, Bottomley SP, Masters CL, Barnham KJ, Hill AF (2005) Dopamine promotes alpha-synuclein aggregation into SDS-resistant soluble oligomers via a distinct folding pathway. FASEB J 19:1377–1379
Caughey B, Lansbury PT (2003) Protofibrils, pores, fibrils, and neurodegeneration: separating the responsible protein aggregates from the innocent bystanders. Annu Rev Neurosci 26:267–298
Chandra S, Chen X, Rizo J, Jahn R, Sudhof TC (2003) A broken alpha -helix in folded alpha -Synuclein. J Biol Chem 278:15313–15318
Chandra S, Gallardo G, Fernandez-Chacon R, Schluter OM, Sudhof TC (2005) Alpha-synuclein cooperates with CSPalpha in preventing neurodegeneration. Cell 123:383–396
Chartier-Harlin MC, Kachergus J, Roumier C, Mouroux V, Douay X, Lincoln S, Levecque C, Larvor L, Andrieux J, Hulihan M, Waucquier N, Defebvre L, Amouyel P, Farrer M, Destee A (2004) Alpha-synuclein locus duplication as a cause of familial Parkinson’s disease. Lancet 364:1167–1169
Cuervo AM, Stefanis L, Fredenburg R, Lansbury PT, Sulzer D (2004) Impaired degradation of mutant alpha-synuclein by chaperone-mediated autophagy. Science 305:1292–1295
Danzer KM, Haasen D, Karow AR, Moussaud S, Habeck M, Giese A, Kretzschmar H, Hengerer B, Kostka M (2007) Different species of alpha-synuclein oligomers induce calcium influx and seeding. J Neurosci 27:9220–9232
Danzer KM, Kranich LR, Ruf WP, Cagsal-Getkin O, Winslow AR, Zhu L, Vanderburg CR, McLean PJ (2012) Exosomal cell-to-cell transmission of alpha synuclein oligomers. Mol Neurodegener 7:42
Danzer KM, Krebs SK, Wolff M, Birk G, Hengerer B (2009) Seeding induced by alpha-synuclein oligomers provides evidence for spreading of alpha-synuclein pathology. J Neurochem 111:192–203
Danzer KM, Ruf WP, Putcha P, Joyner D, Hashimoto T, Glabe C, Hyman BT, McLean PJ (2011) Heat-shock protein 70 modulates toxic extracellular alpha-synuclein oligomers and rescues trans-synaptic toxicity. FASEB J 25:326–336
Dargemont C, Ossareh-Nazari B (2012) Cdc48/p97, a key actor in the interplay between autophagy and ubiquitin/proteasome catabolic pathways. Biochim Biophys Acta 1823:138–144
Davidson WS, Jonas A, Clayton DF, George JM (1998) Stabilization of alpha-synuclein secondary structure upon binding to synthetic membranes. J Biol Chem 273:9443–9449
de Lau LM, Breteler MM (2006) Epidemiology of Parkinson’s disease. Lancet Neurol 5:525–535
Delenclos M, Trendafilova T, Mahesh D, Baine AM, Moussaud S, Yan IK, Patel T, McLean PJ (2017) Investigation of endocytic pathways for the internalization of exosome-associated oligomeric alpha-synuclein. Front Neurosci 11:172
Desplats P, Lee HJ, Bae EJ, Patrick C, Rockenstein E, Crews L, Spencer B, Masliah E, Lee SJ (2009) Inclusion formation and neuronal cell death through neuron-to-neuron transmission of alpha-synuclein. Proc Natl Acad Sci U S A 106:13010–13015
Dettmer U, Newman AJ, Luth ES, Bartels T, Selkoe D (2013) In vivo cross-linking reveals principally oligomeric forms of alpha-synuclein and beta-synuclein in neurons and non-neural cells. J Biol Chem 288:6371–6385
Devi L, Raghavendran V, Prabhu BM, Avadhani NG, Anandatheerthavarada HK (2008) Mitochondrial import and accumulation of alpha-synuclein impair complex I in human dopaminergic neuronal cultures and Parkinson disease brain. J Biol Chem 283:9089–9100
Ehrnhoefer DE, Bieschke J, Boeddrich A, Herbst M, Masino L, Lurz R, Engemann S, Pastore A, Wanker EE (2008) EGCG redirects amyloidogenic polypeptides into unstructured, off-pathway oligomers. Nat Struct Mol Biol 15:558–566
El-Agnaf OM, Salem SA, Paleologou KE, Cooper LJ, Fullwood NJ, Gibson MJ, Curran MD, Court JA, Mann DM, Ikeda S, Cookson MR, Hardy J, Allsop D (2003) Alpha-synuclein implicated in Parkinson’s disease is present in extracellular biological fluids, including human plasma. FASEB J 17:1945–1947
El-Agnaf OM, Salem SA, Paleologou KE, Curran MD, Gibson MJ, Court JA, Schlossmacher MG, Allsop D (2006) Detection of oligomeric forms of alpha-synuclein protein in human plasma as a potential biomarker for Parkinson’s disease. FASEB J 20:419–425
Emmanouilidou E, Melachroinou K, Roumeliotis T, Garbis SD, Ntzouni M, Margaritis LH, Stefanis L, Vekrellis K (2010a) Cell-produced alpha-synuclein is secreted in a calcium-dependent manner by exosomes and impacts neuronal survival. J Neurosci 30:6838–6851
Emmanouilidou E, Stefanis L, Vekrellis K (2010b) Cell-produced alpha-synuclein oligomers are targeted to, and impair, the 26S proteasome. Neurobiol Aging 31:953–968
Fauvet B, Mbefo MK, Fares MB, Desobry C, Michael S, Ardah MT, Tsika E, Coune P, Prudent M, Lion N, Eliezer D, Moore DJ, Schneider B, Aebischer P, El-Agnaf OM, Masliah E, Lashuel HA (2012) Alpha-synuclein in central nervous system and from erythrocytes, mammalian cells, and Escherichia coli exists predominantly as disordered monomer. J Biol Chem 287:15345–15364
Feng D, Zhao WL, Ye YY, Bai XC, Liu RQ, Chang LF, Zhou Q, Sui SF (2010) Cellular internalization of exosomes occurs through phagocytosis. Traffic 11:675–687
Flavin WP, Bousset L, Green ZC, Chu Y, Skarpathiotis S, Chaney MJ, Kordower JH, Melki R, Campbell EM (2017) Endocytic vesicle rupture is a conserved mechanism of cellular invasion by amyloid proteins. Acta Neuropathol 134:629–653
Freeman D, Cedillos R, Choyke S, Lukic Z, McGuire K, Marvin S, Burrage AM, Sudholt S, Rana A, O’Connor C, Wiethoff CM, Campbell EM (2013) Alpha-synuclein induces lysosomal rupture and cathepsin dependent reactive oxygen species following endocytosis. PLoS ONE 8:e62143
Gibb WR (1991) Neuropathology of the substantia nigra. Eur Neurol 31(Suppl 1):48–59
Gibb WR, Lees AJ (1991) Anatomy, pigmentation, ventral and dorsal subpopulations of the substantia nigra, and differential cell death in Parkinson’s disease. J Neurol Neurosurg Psychiatry 54:388–396
Goers J, Manning-Bog AB, McCormack AL, Millett IS, Doniach S, Di Monte DA, Uversky VN, Fink AL (2003) Nuclear localization of alpha-synuclein and its interaction with histones. Biochemistry 42:8465–8471
Guardia-Laguarta C, Area-Gomez E, Rub C, Liu Y, Magrane J, Becker D, Voos W, Schon EA, Przedborski S (2014) Alpha-synuclein is localized to mitochondria-associated ER membranes. J Neurosci 34:249–259
Hansen C, Angot E, Bergstrom AL, Steiner JA, Pieri L, Paul G, Outeiro TF, Melki R, Kallunki P, Fog K, Li JY, Brundin P (2011) Alpha-synuclein propagates from mouse brain to grafted dopaminergic neurons and seeds aggregation in cultured human cells. J Clin Invest 121:715–725
Hoyer W, Antony T, Cherny D, Heim G, Jovin TM, Subramaniam V (2002) Dependence of alpha-synuclein aggregate morphology on solution conditions. J Mol Biol 322:383–393
Ibanez P, Bonnet AM, Debarges B, Lohmann E, Tison F, Pollak P, Agid Y, Durr A, Brice A (2004) Causal relation between alpha-synuclein gene duplication and familial Parkinson’s disease. Lancet 364:1169–1171
Iwai A, Masliah E, Yoshimoto M, Ge N, Flanagan L, de Silva HA, Kittel A, Saitoh T (1995) The precursor protein of non-a beta component of Alzheimer’s disease amyloid is a presynaptic protein of the central nervous system. Neuron 14:467–475
Jang A, Lee HJ, Suk JE, Jung JW, Kim KP, Lee SJ (2010) Non-classical exocytosis of alpha-synuclein is sensitive to folding states and promoted under stress conditions. J Neurochem 113:1263–1274
Kim C, Ho DH, Suk JE, You S, Michael S, Kang J, Joong Lee S, Masliah E, Hwang D, Lee HJ, Lee SJ (2013) Neuron-released oligomeric alpha-synuclein is an endogenous agonist of TLR2 for paracrine activation of microglia. Nat Commun 4:1562
Kordower JH, Chu Y, Hauser RA, Freeman TB, Olanow CW (2008) Lewy body-like pathology in long-term embryonic nigral transplants in Parkinson’s disease. Nat Med 14:504–506
Kovacs GG, Breydo L, Green R, Kis V, Puska G, Lorincz P, Perju-Dumbrava L, Giera R, Pirker W, Lutz M, Lachmann I, Budka H, Uversky VN, Molnar K, Laszlo L (2014) Intracellular processing of disease-associated alpha-synuclein in the human brain suggests prion-like cell-to-cell spread. Neurobiol Dis 69:76–92
Kramer ML, Schulz-Schaeffer WJ (2007) Presynaptic alpha-synuclein aggregates, not Lewy bodies, cause neurodegeneration in dementia with Lewy bodies. J Neurosci 27:1405–1410
Kuusisto E, Parkkinen L, Alafuzoff I (2003) Morphogenesis of Lewy bodies: dissimilar incorporation of alpha-synuclein, ubiquitin, and p62. J Neuropathol Exp Neurol 62:1241–1253
Lavedan C (1998) The synuclein family. Genome Res 8:871–880
Lazaro DF, Rodrigues EF, Langohr R, Shahpasandzadeh H, Ribeiro T, Guerreiro P, Gerhardt E, Krohnert K, Klucken J, Pereira MD, Popova B, Kruse N, Mollenhauer B, Rizzoli SO, Braus GH, Danzer KM, Outeiro TF (2014) Systematic comparison of the effects of alpha-synuclein mutations on its oligomerization and aggregation. PLoS Genet 10:e1004741
Lee HJ, Khoshaghideh F, Patel S, Lee SJ (2004) Clearance of alpha-synuclein oligomeric intermediates via the lysosomal degradation pathway. J Neurosci 24:1888–1896
Lee HJ, Patel S, Lee SJ (2005) Intravesicular localization and exocytosis of alpha-synuclein and its aggregates. J Neurosci 25:6016–6024
Lee HJ, Suk JE, Bae EJ, Lee JH, Paik SR, Lee SJ (2008a) Assembly-dependent endocytosis and clearance of extracellular alpha-synuclein. Int J Biochem Cell Biol 40:1835–1849
Lee HJ, Suk JE, Bae EJ, Lee SJ (2008b) Clearance and deposition of extracellular alpha-synuclein aggregates in microglia. Biochem Biophys Res Commun 372:423–428
Lewy FH (1912) Paralysis agitans. I. Pathologische Anatomie. In: Lewandowsky M (ed) Handbuch der Neurologie, vol 3. Springer, Berlin, pp 920–958
Li JY, Englund E, Holton JL, Soulet D, Hagell P, Lees AJ, Lashley T, Quinn NP, Rehncrona S, Bjorklund A, Widner H, Revesz T, Lindvall O, Brundin P (2008) Lewy bodies in grafted neurons in subjects with Parkinson’s disease suggest host-to-graft disease propagation. Nat Med 14:501–503
Li WW, Yang R, Guo JC, Ren HM, Zha XL, Cheng JS, Cai DF (2007) Localization of alpha-synuclein to mitochondria within midbrain of mice. Neuroreport 18:1543–1546
Liu J, Shi M, Hong Z, Zhang J, Bradner J, Quinn T, Beyer RP, McGeer PL, Chen S (2010) Identification of ciliary neurotrophic factor receptor alpha as a mediator of neurotoxicity induced by alpha-synuclein. Proteomics 10:2138–2150
Llorens F, Schmitz M, Varges D, Kruse N, Gotzmann N, Gmitterova K, Mollenhauer B, Zerr I (2016) Cerebrospinal alpha-synuclein in alpha-synuclein aggregation disorders: tau/alpha-synuclein ratio as potential biomarker for dementia with Lewy bodies. J Neurol 263:2271–2277
Loria F, Vargas JY, Bousset L, Syan S, Salles A, Melki R, Zurzolo C (2017) Alpha-synuclein transfer between neurons and astrocytes indicates that astrocytes play a role in degradation rather than in spreading. Acta Neuropathol 134:789–808
Mao X, Ou MT, Karuppagounder SS, Kam TI, Yin X, Xiong Y, Ge P, Umanah GE, Brahmachari S, Shin JH, Kang HC, Zhang J, Xu J, Chen R, Park H, Andrabi SA, Kang SU, Goncalves RA, Liang Y, Zhang S, Qi C, Lam S, Keiler JA, Tyson J, Kim D, Panicker N, Yun SP, Workman CJ, Vignali DA, Dawson VL, Ko HS, Dawson TM (2016) Pathological alpha-synuclein transmission initiated by binding lymphocyte-activation gene 3. Science 353, aah3374
McLean PJ, Kawamata H, Ribich S, Hyman BT (2000a) Membrane association and protein conformation of alpha-synuclein in intact neurons. Effect of Parkinson’s disease-linked mutations. J Biol Chem 275:8812–8816
McLean PJ, Ribich S, Hyman BT (2000b) Subcellular localization of alpha-synuclein in primary neuronal cultures: effect of missense mutations. J Neural Transm 58(Suppl):53–63
Mollenhauer B, Cullen V, Kahn I, Krastins B, Outeiro TF, Pepivani I, Ng J, Schulz-Schaeffer W, Kretzschmar HA, McLean PJ, Trenkwalder C, Sarracino DA, Vonsattel JP, Locascio JJ, El-Agnaf OM, Schlossmacher MG (2008) Direct quantification of CSF alpha-synuclein by ELISA and first cross-sectional study in patients with neurodegeneration. Exp Neurol 213:315–325
Mulcahy LA, Pink RC, Carter DR (2014) Routes and mechanisms of extracellular vesicle uptake. J Extracell Vesicles 3
Munishkina LA, Phelan C, Uversky VN, Fink AL (2003) Conformational behavior and aggregation of alpha-synuclein in organic solvents: modeling the effects of membranes. Biochemistry 42:2720–2730
Ogawa K, Yamada T, Tsujioka Y, Taguchi J, Takahashi M, Tsuboi Y, Fujino Y, Nakajima M, Yamamoto T, Akatsu H, Mitsui S, Yamaguchi N (2000) Localization of a novel type trypsin-like serine protease, neurosin, in brain tissues of Alzheimer’s disease and Parkinson’s disease. Psychiatry Clin Neurosci 54:419–426
Peelaerts W, Bousset L, Van der Perren A, Moskalyuk A, Pulizzi R, Giugliano M, Van den Haute C, Melki R, Baekelandt V (2015) Alpha-synuclein strains cause distinct synucleinopathies after local and systemic administration. Nature 522:340–344
Pieri L, Madiona K, Melki R (2016) Structural and functional properties of prefibrillar α-synuclein oligomers. Sci Rep 6:24526
Reyes JF, Olsson TT, Lamberts JT, Devine MJ, Kunath T, Brundin P (2015) A cell culture model for monitoring alpha-synuclein cell-to-cell transfer. Neurobiol Dis 77:266–275
Rideout HJ, Dietrich P, Wang Q, Dauer WT, Stefanis L (2004) Alpha-synuclein is required for the fibrillar nature of ubiquitinated inclusions induced by proteasomal inhibition in primary neurons. J Biol Chem 279:46915–46920
Rohan Z, Milenkovic I, Lutz MI, Matej R, Kovacs GG (2016) Shared and distinct patterns of oligodendroglial response in alpha-synucleinopathies and tauopathies. J Neuropathol Exp Neurol 75:1100–1109
Saito Y, Kawashima A, Ruberu NN, Fujiwara H, Koyama S, Sawabe M, Arai T, Nagura H, Yamanouchi H, Hasegawa M, Iwatsubo T, Murayama S (2003) Accumulation of phosphorylated alpha-synuclein in aging human brain. J Neuropathol Exp Neurol 62:644–654
Shahnawaz M, Tokuda T, Waragai M, Mendez N, Ishii R, Trenkwalder C, Mollenhauer B, Soto C (2017) Development of a biochemical diagnosis of Parkinson disease by detection of alpha-synuclein misfolded aggregates in cerebrospinal fluid. JAMA Neurol 74:163–172
Shibayama-Imazu T, Okahashi I, Omata K, Nakajo S, Ochiai H, Nakai Y, Hama T, Nakamura Y, Nakaya K (1993) Cell and tissue distribution and developmental change of neuron specific 14 kDa protein (phosphoneuroprotein 14). Brain Res 622:17–25
Shin Y, Klucken J, Patterson C, Hyman BT, McLean PJ (2005) The co-chaperone carboxyl terminus of Hsp70-interacting protein (CHIP) mediates alpha-synuclein degradation decisions between proteasomal and lysosomal pathways. J Biol Chem 280:23727–23734
Shrivastava AN, Redeker V, Fritz N, Pieri L, Almeida LG, Spolidoro M, Liebmann T, Bousset L, Renner M, Lena C, Aperia A, Melki R, Triller A (2015) Alpha-synuclein assemblies sequester neuronal alpha3-Na+/K+-ATPase and impair Na+ gradient. EMBO J 34:2408–2423
Simonsen AH, Kuiperij B, El-Agnaf OM, Engelborghs S, Herukka SK, Parnetti L, Rektorova I, Vanmechelen E, Kapaki E, Verbeek M, Mollenhauer B (2016) The utility of alpha-synuclein as biofluid marker in neurodegenerative diseases: a systematic review of the literature. Biomark Med 10:19–34
Singleton AB, Farrer M, Johnson J, Singleton A, Hague S, Kachergus J, Hulihan M, Peuralinna T, Dutra A, Nussbaum R, Lincoln S, Crawley A, Hanson M, Maraganore D, Adler C, Cookson MR, Muenter M, Baptista M, Miller D, Blancato J, Hardy J, Gwinn-Hardy K (2003) Alpha-synuclein locus triplication causes Parkinson’s disease. Science 302:841
Spillantini MG, Crowther RA, Jakes R, Hasegawa M, Goedert M (1998) Alpha-synuclein in filamentous inclusions of Lewy bodies from Parkinson’s disease and dementia with lewy bodies. Proc Natl Acad Sci U S A 95:6469–6473
Spillantini MG, Schmidt ML, Lee VM, Trojanowski JQ, Jakes R, Goedert M (1997) Alpha-synuclein in Lewy bodies. Nature 388:839–840
Sung JY, Park SM, Lee CH, Um JW, Lee HJ, Kim J, Oh YJ, Lee ST, Paik SR, Chung KC (2005) Proteolytic cleavage of extracellular secreted {alpha}-synuclein via matrix metalloproteinases. J Biol Chem 280:25216–25224
Tofaris GK (2017) A critical assessment of exosomes in the pathogenesis and stratification of Parkinson’s disease. J Parkinsons Dis 7:569–576
Ulusoy A, Musgrove RE, Rusconi R, Klinkenberg M, Helwig M, Schneider A, Di Monte DA (2015) Neuron-to-neuron alpha-synuclein propagation in vivo is independent of neuronal injury. Acta Neuropathol Commun 3:13
Villar-Pique A, Lopes da Fonseca T, Outeiro TF (2016) Structure, function and toxicity of alpha-synuclein: the Bermuda triangle in synucleinopathies. J Neurochem 139(Suppl 1):240–255
Weinreb PH, Zhen W, Poon AW, Conway KA, Lansbury PT Jr (1996) NACP, a protein implicated in Alzheimer’s disease and learning, is natively unfolded. Biochemistry 35:13709–13715
Winner B, Jappelli R, Maji SK, Desplats PA, Boyer L, Aigner S, Hetzer C, Loher T, Vilar M, Campioni S, Tzitzilonis C, Soragni A, Jessberger S, Mira H, Consiglio A, Pham E, Masliah E, Gage FH, Riek R (2011) In vivo demonstration that alpha-synuclein oligomers are toxic. Proc Natl Acad Sci U S A 108:4194–4199
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Grozdanov, V., Danzer, K.M. Release and uptake of pathologic alpha-synuclein. Cell Tissue Res 373, 175–182 (2018). https://doi.org/10.1007/s00441-017-2775-9
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DOI: https://doi.org/10.1007/s00441-017-2775-9