α-Synucleinopathy associated with G51D SNCA mutation: a link between Parkinson’s disease and multiple system atrophy?

132

115

Ubiquitination regulates, via different modes of modifications, a variety of biological processes, and aberrations in the process have been implicated in the pathogenesis of several neurodegenerative diseases. However, our ability to dissect the pathophysiological relevance of the ubiquitination code has been hampered due to the lack of methods that allow site-specific introduction of ubiquitin (Ub) chains to a specific substrate. Here, we describe chemical and semisynthetic strategies for site-specific incorporation of K48-linked di-or tetra-Ub chains onto the side chain of Lys12 of α-Synuclein (α-Syn). These advances provided unique opportunities to elucidate the role of ubiquitination and Ub chain length in regulating α-Syn stability, aggregation, phosphorylation, and clearance. In addition, we investigated the cross-talk between phosphorylation and ubiquitination, the two most common α-Syn pathological modifications identified within Lewy bodies and Parkinson disease. Our results suggest that α-Syn functions under complex regulatory mechanisms involving cross-talk among different posttranslational modifications. eukaryotes is the covalent attachment of ubiquitin (Ub) to proteins. This reversible modification, which regulates a variety of biological processes, such as protein degradation, trafficking, and DNA damage response (1, 2), involves the attachment of the C terminus of Ub mainly to the side chain of a Lys residue in a protein substrate via an isopeptide linkage. The process is catalyzed by three enzymes that act in concert: the Ub-activating enzyme (E1), the Ub-conjugating enzyme (E2), and the Ub ligase (E3). The reaction is repeated, and a second Ub is attached to an internal Lys in the previously conjugated ubiquitin. Several repeats result in the synthesis of a poly-Ub chain that can be of varying lengths and internal linkages. The presence of seven Lys residues as possible anchoring sites within Ub in addition to the N-terminal amine results in a highly complex landscape of diverse Ub bioconjugates, which accounts for the diversity of the Ub signaling (3).Research in the Ub field, which aims at understanding the ubiquitination system at the molecular level, has been hampered by the difficulties of controlling ubiquitination in the cell and challenges associated with the preparation of specific Ub conjugates in vitro. These limitations have inspired the development of novel synthetic strategies to facilitate site-specific ubiquitination of proteins (4, 5). Recent advancements in the field have enabled the synthesis of relatively large amounts of highly complex Ub conjugates of defined covalent structure and provided novel insights into the structural, biochemical, and functional consequences of protein ubiquitination, along with unique opportunities to elucidate the molecular basis of Ub signaling. For example, monoubiquitinated α-Synuclein (α-Syn) and histone H2B bearing native isopeptide bonds were prepared and used to shed light on the role of monoubiquitination in regulating α-Syn aggregation a...

Section: Resultsmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Synthetic polyubiquitinated α-Synuclein reveals important insights into the roles of the ubiquitin chain in regulating its pathophysiology

Haj‐Yahya

Fauvet

Herman-Bachinsky

et al. 2013

132

115

“…other neurodegenerative disorders (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18). α-Synuclein is largely cytosolic, but readily binds to membranes, and associates with synaptic vesicles in the presynaptic terminal (22,23).…”

Section: α-Synuclein Multimerizes On Phospholipid Surfaces In An Antimentioning

confidence: 99%

“…Point mutations in α-synuclein (A30P, E46K, H50Q, G51D, and A53T) as well as α-synuclein gene duplications and triplications produce early-onset Parkinson's disease (PD) (4)(5)(6)(7)(8)(9)(10). Moreover, α-synuclein is a major component of intracellular protein aggregates called Lewy bodies, which are pathological hallmarks of neurodegenerative disorders such as PD, Lewy body dementia, and multiple system atrophy (11)(12)(13)(14).…”

mentioning

confidence: 99%

α-Synuclein assembles into higher-order multimers upon membrane binding to promote SNARE complex formation

Burré¹,

Sharma²,

Südhof

2014

410

452

Physiologically, α-synuclein chaperones soluble NSF attachment protein receptor (SNARE) complex assembly and may also perform other functions; pathologically, in contrast, α-synuclein misfolds into neurotoxic aggregates that mediate neurodegeneration and propagate between neurons. In neurons, α-synuclein exists in an equilibrium between cytosolic and membrane-bound states. Cytosolic α-synuclein appears to be natively unfolded, whereas membrane-bound α-synuclein adopts an α-helical conformation. Although the majority of studies showed that cytosolic α-synuclein is monomeric, it is unknown whether membrane-bound α-synuclein is also monomeric, and whether chaperoning of SNARE complex assembly by α-synuclein involves its cytosolic or membrane-bound state. Here, we show using chemical cross-linking and fluorescence resonance energy transfer (FRET) that α-synuclein multimerizes into large homomeric complexes upon membrane binding. The FRET experiments indicated that the multimers of membrane-bound α-synuclein exhibit defined intermolecular contacts, suggesting an ordered array. Moreover, we demonstrate that α-synuclein promotes SNARE complex assembly at the presynaptic plasma membrane in its multimeric membrane-bound state, but not in its monomeric cytosolic state. Our data delineate a folding pathway for α-synuclein that ranges from a monomeric, natively unfolded form in cytosol to a physiologically functional, multimeric form upon membrane binding, and show that only the latter but not the former acts as a SNARE complex chaperone at the presynaptic terminal, and may protect against neurodegeneration.Parkinson's disease | synapse | SNARE proteins | membrane fusion α -Synuclein is an abundant presynaptic protein that physiologically acts to promote soluble NSF attachment protein receptor (SNARE) complex assembly in vitro and in vivo (1-3). Point mutations in α-synuclein (A30P, E46K, H50Q, G51D, and A53T) as well as α-synuclein gene duplications and triplications produce early-onset Parkinson's disease (PD) (4-10). Moreover, α-synuclein is a major component of intracellular protein aggregates called Lewy bodies, which are pathological hallmarks of neurodegenerative disorders such as PD, Lewy body dementia, and multiple system atrophy (11-14). Strikingly, neurotoxic α-synuclein aggregates propagate between neurons during neurodegeneration, suggesting that such α-synuclein aggregates are not only intrinsically neurotoxic but also nucleate additional fibrillization (15-18).α-Synuclein is highly concentrated in presynaptic terminals where α-synuclein exists in an equilibrium between a soluble and a membrane-bound state, and is associated with synaptic vesicles (19)(20)(21)(22). The labile association of α-synuclein with membranes (23, 24) suggests that binding of α-synuclein to synaptic vesicles, and its dissociation from these vesicles, may regulate its physiological function. Membrane-bound α-synuclein assumes an α-helical conformation (25-32), whereas cytosolic α-synuclein is natively unfolded and monomeric (refs. 25, 2...

“…In Parkinson disease (PD), a causative role for αS has been established via the discovery of mutations in the αS gene SNCA resulting in autosomal-dominant PD (4)(5)(6)(7)(8)(9)(10)(11). Although αS inclusions (e.g., Lewy bodies) are the hallmark pathology of PD, how they contribute to disease pathogenesis remains controversial (1,3,4,12).…”

mentioning

confidence: 99%

Intramuscular injection of α-synuclein induces CNS α-synuclein pathology and a rapid-onset motor phenotype in transgenic mice

Sacino¹,

Brooks²,

Thomas³

et al. 2014

289

343

It has been hypothesized that α-synuclein (αS) misfolding may begin in peripheral nerves and spread to the central nervous system (CNS), leading to Parkinson disease and related disorders. Although recent data suggest that αS pathology can spread within the mouse brain, there is no direct evidence for spread of disease from a peripheral site. In the present study, we show that hind limb intramuscular (IM) injection of αS can induce pathology in the CNS in the human Ala53Thr (M83) and wild-type (M20) αS transgenic (Tg) mouse models. Within 2-3 mo after IM injection in αS homozygous M83 Tg mice and 3-4 mo for hemizygous M83 Tg mice, these animals developed a rapid, synchronized, and predictable induction of widespread CNS αS inclusion pathology, accompanied by astrogliosis, microgliosis, and debilitating motor impairments. In M20 Tg mice, starting at 4 mo after IM injection, we observed αS inclusion pathology in the spinal cord, but motor function remained intact. Transection of the sciatic nerve in the M83 Tg mice significantly delayed the appearance of CNS pathology and motor symptoms, demonstrating the involvement of retrograde transport in inducing αS CNS inclusion pathology. Outside of scrapie-mediated prion disease, to our knowledge, this findiing is the first evidence that an entire neurodegenerative proteinopathy associated with a robust, lethal motor phenotype can be initiated by peripheral inoculation with a pathogenic protein. Furthermore, this facile, synchronized rapid-onset model of α-synucleinopathy will be highly valuable in testing disease-modifying therapies and dissecting the mechanism(s) that drive αS-induced neurodegeneration.amyloid | Parkinson disease S ynucleinopathies are a group of diseases defined by the presence of amyloidogenic α-synuclein (αS) inclusions that can occur in neurons and glia of the central nervous system (CNS) (1-4). In Parkinson disease (PD), a causative role for αS has been established via the discovery of mutations in the αS gene SNCA resulting in autosomal-dominant PD (4-11). Although αS inclusions (e.g., Lewy bodies) are the hallmark pathology of PD, how they contribute to disease pathogenesis remains controversial (1,3,4,12).Postmortem studies have suggested that αS pathology may spread following neuroanatomical tracts (13-15) and between cells (16-18). αS pathology has also been found in the peripheral nervous system (PNS): for example, in the enteric and pelvic plexus (19,20). And it has been suggested that αS pathology might originate in the nerves of the PNS and spread to the CNS (14). Experimentally, it has been reported that intracerebral injections of preformed amyloidogenic αS fibrils in nontransgenic (nTg) and αS transgenic (Tg) mice induce the formation of intracellular αS inclusions that appear to progress from the site of injection (21-26). Collectively, these studies support the notion that αS inclusion pathology may propagate via a prion-like conformational self-templating mechanism (27, 28). A caveat of the direct intracerebral injection of αS is tha...