No abstract

No abstract

Parkinson disease (PD) is a neurodegenerative disorder particularly characterized by the loss of dopaminergic neurons in the substantia nigra. Pesticide exposure has been associated with PD occurrence, and we previously reported that the fungicide benomyl interferes with several cellular processes potentially relevant to PD pathogenesis. Here we propose that benomyl, via its bioactivated thiocarbamate sulfoxide metabolite, inhibits aldehyde dehydrogenase (ALDH), leading to accumulation of the reactive dopamine metabolite 3,4-dihydroxyphenylacetaldehyde (DOPAL), preferential degeneration of dopaminergic neurons, and development of PD. This hypothesis is supported by multiple lines of evidence. (i) We previously showed in mice the metabolism of benomyl to S-methyl N-butylthiocarbamate sulfoxide, which inhibits ALDH at nanomolar levels. We report here that benomyl exposure in primary mesencephalic neurons (ii) inhibits ALDH and (iii) alters dopamine homeostasis. It induces selective dopaminergic neuronal damage (iv) in vitro in primary mesencephalic cultures and (v) in vivo in a zebrafish system. (vi) In vitro cell loss was attenuated by reducing DOPAL formation. (vii) In our epidemiology study, higher exposure to benomyl was associated with increased PD risk. This ALDH model for PD etiology may help explain the selective vulnerability of dopaminergic neurons in PD and provide a potential mechanism through which environmental toxicants contribute to PD pathogenesis.

α-synuclein (aSyn) expression is implicated in neurodegenerative processes, including Parkinson’s disease (PD) and dementia with Lewy bodies (DLB). In animal models of these diseases, axon pathology often precedes cell death, raising the question of whether aSyn has compartment-specific toxic effects that could require early and/or independent therapeutic intervention. The relevance of axonal pathology to degeneration can only be addressed through longitudinal, in vivo monitoring of different neuronal compartments. With current imaging methods, dopaminergic neurons do not readily lend themselves to such a task in any vertebrate system. We therefore expressed human wild-type aSyn in zebrafish peripheral sensory neurons, which project elaborate superficial axons that can be continuously imaged in vivo. Axonal outgrowth was normal in these neurons but, by 2 days post-fertilization (dpf), many aSyn-expressing axons became dystrophic, with focal varicosities or diffuse beading. Approximately 20% of aSyn-expressing cells died by 3 dpf. Time-lapse imaging revealed that focal axonal swelling, but not overt fragmentation, usually preceded cell death. Co-expressing aSyn with a mitochondrial reporter revealed deficits in mitochondrial transport and morphology even when axons appeared overtly normal. The axon-protective protein Wallerian degeneration slow (WldS) delayed axon degeneration but not cell death caused by aSyn. By contrast, the transcriptional coactivator PGC-1α, which has roles in the regulation of mitochondrial biogenesis and reactive-oxygen-species detoxification, abrogated aSyn toxicity in both the axon and the cell body. The rapid onset of axonal pathology in this system, and the relatively moderate degree of cell death, provide a new model for the study of aSyn toxicity and protection. Moreover, the accessibility of peripheral sensory axons will allow effects of aSyn to be studied in different neuronal compartments and might have utility in screening for novel disease-modifying compounds.

Background:Exposure to the commonly used dithiocarbamate (DTC) pesticides is associated with an increased risk of developing Parkinson disease (PD), although the mechanisms by which they exert their toxicity are not completely understood.Objective:We studied the mechanisms of ziram’s (a DTC fungicide) neurotoxicity in vivo.Methods:Zebrafish (ZF) embryos were utilized to determine ziram’s effects on behavior, neuronal toxicity, and the role of synuclein in its toxicity.Results:Nanomolar-range concentrations of ziram caused selective loss of dopaminergic (DA) neurons and impaired swimming behavior. Because ziram increases α-synuclein (α-syn) concentrations in rat primary neuronal cultures, we investigated the effect of ziram on ZF γ-synuclein 1 (γ1). ZF express 3 synuclein isoforms, and ZF γ1 appears to be the closest functional homologue to α-syn. We found that recombinant ZF γ1 formed fibrils in vitro, and overexpression of ZF γ1 in ZF embryos led to the formation of neuronal aggregates and neurotoxicity in a manner similar to that of α-syn. Importantly, knockdown of ZF γ1 with morpholinos and disruption of oligomers with the molecular tweezer CLR01 prevented ziram’s DA toxicity.Conclusions:These data show that ziram is selectively toxic to DA neurons in vivo, and this toxicity is synuclein-dependent. These findings have important implications for understanding the mechanisms by which pesticides may cause PD.Citation:Lulla A, Barnhill L, Bitan G, Ivanova MI, Nguyen B, O’Donnell K, Stahl MC, Yamashiro C, Klärner FG, Schrader T, Sagasti A, Bronstein JM. 2016. Neurotoxicity of the Parkinson disease-associated pesticide ziram is synuclein-dependent in zebrafish embryos. Environ Health Perspect 124:1766–1775; http://dx.doi.org/10.1289/EHP141

Identifying mechanisms responsible for early cell fate specifications and formation of the three germ layers is a fundamental issue in developmental and evolutionary biology. The canonical Notch signaling pathway stimulated by Delta-and Jagged-like ligands is functionally conserved among the metazoa (2, 29) and is required for early cell fate specifications or the formation of germ layers in Caenorhabditis elegans (12, 41) and sea urchins (1, 43-45, 52) and for endoderm patterning in zebrafish (3, 21). Drosophila melanogaster (5, 6) and C. elegans (28) need maternal contributions of certain Notch pathway components for early development, while sea urchins (25) and zebrafish (11, 35, 53) apparently do not.

RKE-1 cells induced to overexpress activated Notch1 (RKE-ER-N ic

Protein O-fucosyltransferase 1 (Pofut1) transfers fucose to serine or threonine on proteins, including Notch receptors, that contain EGF repeats with a particular consensus sequence. Here we demonstrate that agrin is O-fucosylated in a Pofut1-dependent manner, and that this glycosylation can regulate agrin function. Fucosylation of recombinant C45 agrin, both active (neural, z8) and inactive (muscle, z0) splice forms, was eliminated when agrin was overexpressed in Pofut1-deficient cells or by mutation of a consensus site for Pofut1 fucosylation (serine 1726 in the EGF4 domain). Loss of Ofucosylation caused a gain of function for muscle agrin such that it stimulated AChR clustering and MuSK phosphorylation in cultured myotubes at levels normally only found with the neural splice form. Deletion of Pofut1 in cultured primary myotubes and in adult skeletal muscle increased AChR aggregation. In addition, Pofut1 gene and protein expression and Pofut1 activity of the EGF4 domain of agrin were modulated during neuromuscular development. These data are consistent with a role for Pofut1 in AChR aggregation during synaptogenesis via the regulation of the synaptogenic activity of muscle agrin. Keywords glycosylation; agrin; synapse; neuromuscular junction; fucose; Notch An essential step in the formation of all types of synapses is the concentration of neurotransmitter receptors in the postsynaptic membrane such that they are localized in a manner that allows efficient and robust neurotransmission by the presynaptic nerve terminal. Nowhere is this more dramatically in evidence than at the mammalian neuromuscular junction, Publisher's Disclaimer: This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. NIH Public Access NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author Manuscriptwhere postsynaptic concentration of the nicotinic acetylcholine receptors (AChRs) approaches a thousand-fold relative to AChR protein expression in the extrasynaptic membrane (Sanes and Lichtman, 2001). While this concentration of AChRs is brought about by multiple cellular and molecular mechanisms, the lateral migration of extrasynaptic AChRs during development to the postsynaptic membrane requires the stimulation of signal transduction pathways in skeletal myofibers by agrin, a motor nerve-derived synaptogenic factor (Kummer et al., 2006).Agrin is a highly glycosylated extracellular matrix protein that is essential for the formation of the mammalian neuromuscular junction (Martin, 2003b;Sanes et al., 1998b). Studies using recombinant forms of agrin have shown that high affinity AChR aggregating activity is contained wi...