Dopamine neuron degeneration induced by MPP+ is independent of CED-4 pathway in Caenorhabditis elegans

Abstract

Dear Editor,Parkinson's disease (PD) is a common neurodegenerative disease characterized by progressive loss of dopamine neurons in the substantia nigra, and manifests the cardinal clinical symptoms of resting tremors, rigidity, bradykinesia, hyperkinesias and abnormal posture. In the 1980s a synthetic heroin contaminant, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), was discovered as a cause of parkinsonism in a group of drug addicts. Since then, mechanisms involved in 1-methyl-4-phenylpyridinium (MPP + )-induced neurotoxicity have been extensively studied in various animal models and cell cultures. MPTP is highly lipophilic and can easily cross the blood-brain barrier and cell membrane. MPTP is metabolized in glial cells by monoamine oxidase type B to its active ionic metabolite MPP + , which is then selectively taken up by dopamine neurons via dopamine transporter (DAT). Hitherto, it has not been clearly defined whether the cell death induced by MPP + is apoptotic and/or necrotic. Contradictory results have been obtained from the treatment with different doses of MPP + in different culture systems [1][2][3][4]. This study, therefore, aims at determining the cell death mechanisms underlying MPP + -induced dopamine neuron degeneration in vivo in a living animal model of Caenorhabditis elegans.C. elegans hermaphrodite contains eight dopamine neurons: four symmetrically arranged cephalic cells (CEPs, two dorsal and two ventral), two bilateral anterior deirids (ADEs) in the head, and two bilateral posterior deirids (PDEs) near the vulva. The processes of dopamine neurons run through the body and tail. Since C. elegans is transparent, using the green fluorescent protein (GFP) attached to the DAT gene promoter (Pdat-1::GFP) we can visualize the bodies and processes of dopamine neurons to study dopamine neuron degeneration in vivo. A number of mutant alleles related to apoptotic cell death and necrotic cell death genes are available in C. elegans, which afford us an opportunity to investigate the relationship between MPP + -induced dopamine neuron degeneration and cell death pathways in vivo using the living animal model.In order to investigate MPP + -induced neurotoxicity in dopamine neurons of C. elegans in vivo, we synchronized Pdat-1::GFP reporter strain BZ555 at L1 stage and incubated the worms in various concentrations of MPP + (from 0.25 to 1.0 mM) and observed the GFP-labeled dopamine neurons 24, 48, and 72 h after MPP + treatment. Dramatic changes of GFP fluorescence in dopamine neurons were detected in MPP + -treated worms, but not in vehicle-treated worms. By 24 h after MPP + treatment, the GFP signal of CEP and ADE dendrites was significantly reduced or lost with retention of GFP in cell soma ( Figure 1A-i, ii, iii). In addition, blebbing along the CEP and ADE processes and swelling in the dopamine cell bodies were observed in some worms ( Figure 1A-ii). By 48 h, GFP was completely lost in a part of dopamine neurons. By 72 h after incubation with 0.5 mM MPP + , we found that a few of the worms surv...

Neuroprotective efficacy of aminopropyl carbazoles in a mouse model of Parkinson disease

“…To investigate the neuroprotective efficacy of P7C3A20, P7C3, and Dimebon from MPP + toxicity in C. elegans, we monitored dopaminergic cell death in a transgenic strain of worms in which dopaminergic neurons fluoresce green by virtue of GFP expression driven by the dopaminergic neuron-specific promoter dat-1 (15). As shown in Fig.…”

Behavioral Phenotyping and Pathological Indicators of Parkinson's Disease in C. elegans Models

“…The eight dopaminergic neurons of C. elegans have been fluorescently tagged with GFP using the DAT-1 promoter in neuronal transgenic strains BZ555 ([dat-1p::GFP]), BY200 [dat-1p::GFP, pRF4(rol-6(su1006)], and TG2435 ([dat-1p::GFP + rol-6(su1006)]) (Nass et al, 2002; Pu and Le, 2008; Masoudi et al, 2014; Cooper et al, 2015). Studying these cells in a genetic background of overexpressed α-synuclein or after treatment with the environmental toxin 6-OHDA has revealed that DA neurons degenerate with age and identified alleles that confer 6-OHDA resistance (Nass et al, 2005; Hamamichi et al, 2008).…”

“…In addition to transgenic C. elegans models involving the overexpression or mutation of PD-linked genes to study the genetic causes of PD, environmental agents have also been used to study PD-related neuronal degeneration and cell death (Nass et al, 2002; Pu and Le, 2008; Ali and Rajini, 2012; Zhou et al, 2013). Previous studies have modeled the motor aspects of PD using in vivo exposure to toxins that cause an overload of ROS and disrupt the electron transport chain in mitochondria leading to neuronal abnormalities and eventually cell death (Varcin et al, 2012; Dias et al, 2013; Hwang, 2013; Chege and Mccoll, 2014).…”

Astragalus Polysaccharide Suppresses 6‐Hydroxydopamine‐Induced Neurotoxicity in Caenorhabditis elegans

“…As shown in Figure 4, unexpectedly, 6-OHDA exposure did not influence the transcript levels of ced-4 , ced-3 , ced-9, and egl-1 in BZ555 nematodes, suggesting that these gene expressions may be not involved in 6-OHDA-mediated neuronal apoptosis in C. elegans . Interestingly, another neurotoxin 1-methyl-4-phenylpyridnium ion (MPP + ) that can trigger parkinsonism also destroys C. elegans dopaminergic neurons independent of ced-4 pathway [38]. However, a recent study has shown that 6-OHDA activates the mitochondrial apoptosis pathway including the release of cytochrome c to cytosol and the activation of caspase-3 in rat adrenal phaeochromocytoma PC12 cells [39], indicating that other mechanisms may contribute to 6-OHDA-induced neuronal apoptosis.…”