Medeiros Audrey T.

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Audrey T.

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  • Article
    α-Synuclein dimers impair vesicle fission during clathrin-mediated synaptic vesicle recycling
    (Frontiers Media, 2017-12-11) Medeiros, Audrey T. ; Soll, Lindsey G. ; Tessari, Isabella ; Bubacco, Luigi ; Morgan, Jennifer R.
    α-Synuclein is a presynaptic protein that regulates synaptic vesicle (SV) trafficking. In Parkinson’s disease (PD) and several other neurodegenerative disorders, aberrant oligomerization and aggregation of α-synuclein lead to synaptic dysfunction and neurotoxicity. Despite evidence that α-synuclein oligomers are generated within neurons under physiological conditions, and that altering the balance of monomers and oligomers contributes to disease pathogenesis, how each molecular species of α-synuclein impacts SV trafficking is currently unknown. To address this, we have taken advantage of lamprey giant reticulospinal (RS) synapses, which are accessible to acute perturbations via axonal microinjection of recombinant proteins. We previously reported that acute introduction of monomeric α-synuclein inhibited SV recycling, including effects on the clathrin pathway. Here, we report the effects of α-synuclein dimers at synapses. Similar to monomeric α-synuclein, both recombinant α-synuclein dimers that were evaluated bound to small liposomes containing anionic lipids in vitro, but with reduced efficacy. When introduced to synapses, the α-synuclein dimers also induced SV recycling defects, which included a build up of clathrin-coated pits (CCPs) with constricted necks that were still attached to the plasma membrane, a phenotype indicative of a vesicle fission defect. Interestingly, both α-synuclein dimers induced longer necks on CCPs as well as complex, branching membrane tubules, which were distinct from the CCPs induced by a dynamin inhibitor, Dynasore. In contrast, monomeric α-synuclein induced a buildup of free clathrin-coated vesicles (CCVs), indicating an inhibition of clathrin-mediated endocytosis at a later stage during the clathrin uncoating process. Taken together, these data further support the conclusion that excess α-synuclein impairs SV recycling. The data additionally reveal that monomeric and dimeric α-synuclein produce distinct effects on clathrin-mediated endocytosis, predicting different molecular mechanisms. Understanding what these mechanisms are could help to further elucidate the normal functions of this protein, as well as the mechanisms underlying PD pathologies.
  • Article
    α-Synuclein-112 impairs synaptic vesicle recycling consistent with its enhanced membrane binding properties
    (Frontiers Media, 2020-05-29) Soll, Lindsey G. ; Eisen, Julia N. ; Vargas, Karina J. ; Medeiros, Audrey T. ; Hammar, Katherine M. ; Morgan, Jennifer R.
    Synucleinopathies are neurological disorders associated with α-synuclein overexpression and aggregation. While it is well-established that overexpression of wild type α-synuclein (α-syn-140) leads to cellular toxicity and neurodegeneration, much less is known about other naturally occurring α-synuclein splice isoforms. In this study we provide the first detailed examination of the synaptic effects caused by one of these splice isoforms, α-synuclein-112 (α-syn-112). α-Syn-112 is produced by an in-frame excision of exon 5, resulting in deletion of amino acids 103–130 in the C-terminal region. α-Syn-112 is upregulated in the substantia nigra, frontal cortex, and cerebellum of parkinsonian brains and higher expression levels are correlated with susceptibility to Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and multiple systems atrophy (MSA). We report here that α-syn-112 binds strongly to anionic phospholipids when presented in highly curved liposomes, similar to α-syn-140. However, α-syn-112 bound significantly stronger to all phospholipids tested, including the phosphoinositides. α-Syn-112 also dimerized and trimerized on isolated synaptic membranes, while α-syn-140 remained largely monomeric. When introduced acutely to lamprey synapses, α-syn-112 robustly inhibited synaptic vesicle recycling. Interestingly, α-syn-112 produced effects on the plasma membrane and clathrin-mediated synaptic vesicle endocytosis that were phenotypically intermediate between those caused by monomeric and dimeric α-syn-140. These findings indicate that α-syn-112 exhibits enhanced phospholipid binding and oligomerization in vitro and consequently interferes with synaptic vesicle recycling in vivo in ways that are consistent with its biochemical properties. This study provides additional evidence suggesting that impaired vesicle endocytosis is a cellular target of excess α-synuclein and advances our understanding of potential mechanisms underlying disease pathogenesis in the synucleinopathies.
  • Article
    Hsc70 ameliorates the vesicle recycling defects caused by excess alpha-synuclein at synapses
    (Society for Neuroscience, 2020-01-15) Banks, Susan M. L. ; Medeiros, Audrey T. ; McQuillan, Molly ; Busch, David J. ; Ibarraran-Viniegra, Ana Sofia ; Sousa, Rui ; Lafer, Eileen M. ; Morgan, Jennifer R.
    α-Synuclein overexpression and aggregation are linked to Parkinson’s disease (PD), dementia with Lewy bodies (DLB), and several other neurodegenerative disorders. In addition to effects in the cell body, α-synuclein accumulation occurs at presynapses where the protein is normally localized. While it is generally agreed that excess α-synuclein impairs synaptic vesicle trafficking, the underlying mechanisms are unknown. We show here that acute introduction of excess human α-synuclein at a classic vertebrate synapse, the lamprey reticulospinal (RS) synapse, selectively impaired the uncoating of clathrin-coated vesicles (CCVs) during synaptic vesicle recycling, leading to an increase in endocytic intermediates and a severe depletion of synaptic vesicles. Furthermore, human α-synuclein and lamprey γ-synuclein both interact in vitro with Hsc70, the chaperone protein that uncoats CCVs at synapses. After introducing excess α-synuclein, Hsc70 availability was reduced at stimulated synapses, suggesting Hsc70 sequestration as a possible mechanism underlying the synaptic vesicle trafficking defects. In support of this hypothesis, increasing the levels of exogenous Hsc70 along with α-synuclein ameliorated the CCV uncoating and vesicle recycling defects. These experiments identify a reduction in Hsc70 availability at synapses, and consequently its function, as the mechanism by which α-synuclein induces synaptic vesicle recycling defects. To our knowledge, this is the first report of a viable chaperone-based strategy for reversing the synaptic vesicle trafficking defects associated with excess α-synuclein, which may be of value for improving synaptic function in PD and other synuclein-linked diseases.
  • Article
    Effects of excess brain-derived human alpha-synuclein on synaptic vesicle trafficking
    (Frontiers Media, 2021-02-04) Román-Vendrell, Cristina ; Medeiros, Audrey T. ; Sanderson, John B. ; Jiang, Haiyang ; Bartels, Tim ; Morgan, Jennifer R.
    α-Synuclein is a presynaptic protein that regulates synaptic vesicle trafficking under physiological conditions. However, in several neurodegenerative diseases, including Parkinson’s disease, dementia with Lewy bodies, and multiple system atrophy, α-synuclein accumulates throughout the neuron, including at synapses, leading to altered synaptic function, neurotoxicity, and motor, cognitive, and autonomic dysfunction. Neurons typically contain both monomeric and multimeric forms of α-synuclein, and it is generally accepted that disrupting the balance between them promotes aggregation and neurotoxicity. However, it remains unclear how distinct molecular species of α-synuclein affect synapses where α-synuclein is normally expressed. Using the lamprey reticulospinal synapse model, we previously showed that acute introduction of excess recombinant monomeric or dimeric α-synuclein impaired distinct stages of clathrin-mediated synaptic vesicle endocytosis, leading to a loss of synaptic vesicles. Here, we expand this knowledge by investigating the effects of native, physiological α-synuclein isolated from the brain of a neuropathologically normal human subject, which comprised predominantly helically folded multimeric α-synuclein with a minor component of monomeric α-synuclein. After acute introduction of excess brain-derived human α-synuclein, there was a moderate reduction in the synaptic vesicle cluster and an increase in the number of large, atypical vesicles called “cisternae.” In addition, brain-derived α-synuclein increased synaptic vesicle and cisternae sizes and induced atypical fusion/fission events at the active zone. In contrast to monomeric or dimeric α-synuclein, the brain-derived multimeric α-synuclein did not appear to alter clathrin-mediated synaptic vesicle endocytosis. Taken together, these data suggest that excess brain-derived human α-synuclein impairs intracellular vesicle trafficking and further corroborate the idea that different molecular species of α-synuclein produce distinct trafficking defects at synapses. These findings provide insights into the mechanisms by which excess α-synuclein contributes to synaptic deficits and disease phenotypes.
  • Article
    Impacts of increased α-synuclein on clathrin-mediated endocytosis at synapses : implications for neurodegenerative diseases
    (Wolters Kluwer, 2018-04-27) Medeiros, Audrey T. ; Bubacco, Luigi ; Morgan, Jennifer R.
    Parkinson's disease (PD) is a neurodegenerative disease that impacts the lives of millions of people worldwide. A pathological hallmark of PD, as well as dementia with Lewy bodies (DLB) and several Alzheimer's disease variants, is the appearance of intracellular inclusions called Lewy bodies, which contain high levels of aggregated α-synuclein. α-Synuclein is a presynaptic protein that normally associates with synaptic vesicle membranes and regulates synaptic vesicle trafficking under physiological conditions (Calo et al., 2016). However, in familial PD, multiplication and several point mutations in the α-synuclein gene (SNCA) ultimately lead to toxic aggregation of the α-synuclein protein and subsequent degeneration of dopaminergic neurons in the substantia nigra, although other brain areas are also affected (Schulz-Schaeffer, 2010).
  • Article
    Chaperone proteins as ameliorators of alpha-synuclein-induced synaptic pathologies: Insights into Parkinson's disease
    (Medknow Publications, 2020-11-27) Banks, Susan M. L. ; Medeiros, Audrey T. ; Sousa, Rui ; Lafer, Eileen M. ; Morgan, Jennifer R.
    α-Synuclein accumulation causes synaptic vesicle trafficking defects and may underlie neurodegenerative disorders: Neurodegenerative disorders, such as Parkinson’s disease (PD) and other synucleinopathies, impact the lives of millions of patients and their caregivers. Synucleinopathies include PD, dementia with Lewy Bodies (DLB), multiple system atrophy, and several Alzheimer’s Disease variants. They are clinically characterized by intracellular inclusions called Lewy Bodies, which are rich in atypical aggregates of the protein α-synuclein. While dopaminergic neurons in the substantia nigra are particularly susceptible to α-synuclein-induced aggregation and neurodegeneration, glutamatergic neurons in other brain regions (e.g. cortex) are also frequently affected in PD and other synucleinopathies (Schulz-Schaeffer 2010). Several point mutations in the α-synuclein gene (SNCA), as well as duplication/triplication of SNCA, are linked to familial Parkinson’s disease. In animal models, these genetic alterations lead to overexpression and aberrant accumulation of α-synuclein within neurons, and eventually to neurodegeneration. Interestingly, in both animal models and human patients, α-synuclein aggregation often occurs at neuronal synapses and within axons prior to the appearance of larger aggregates (i.e. Lewy bodies) and other signs of neurodegeneration (Schulz-Schaeffer 2010; Volpicelli-Daley et al., 2011). The level of synaptic aggregation of α-synuclein is highly correlated with greater cognitive deficits in PD and DLB patients (Schulz-Schaeffer 2010). Thus, it is essential to understand how excess α-synuclein impacts synapses, as this may represent an early stage in the neurodegenerative disease progression and thus a viable target for therapeutic intervention, particularly with respect to cognitive impairment.
  • Article
    Hsc70 rescues the synaptic vesicle trafficking defects caused by α-synuclein dimers
    (Caltech Library, 2023-03-01) Brady, Emily B ; McQuillan, Molly ; Medeiros, Audrey T ; Bubacco, Luigi ; Sousa, Rui ; Lafer, Eileen M ; Morgan, Jennifer R
    Aberrant buildup of α-synuclein is associated with Parkinson's disease (PD) and other neurodegenerative disorders. At synapses, α-synuclein accumulation leads to severe synaptic vesicle trafficking defects. We previously demonstrated that different molecular species of α-synuclein produce distinct effects on synaptic vesicle recycling, and that the synaptic phenotypes caused by monomeric α-synuclein were ameliorated by Hsc70. Here, we tested whether Hsc70 could also correct synaptic deficits induced by α-synuclein dimers. Indeed, co-injection of Hsc70 with α-synuclein dimers completely reversed the synaptic deficits, resulting in synapses with normal appearance. This work lends additional support for pursuing chaperone-based strategies to treat PD and other synucleinopathies.