- Research article
- Open Access
- Open Peer Review
Paeonolum protects against MPP+-induced neurotoxicity in zebrafish and PC12 cells
- Xi-Lin Lu†1, 2, 3,
- Yue-Hao Lin†4,
- Qi Wu1, 2, 3,
- Feng-Juan Su1, 2, 3,
- Cheng-Hui Ye5,
- Lei Shi6,
- Bai-Xuan He1, 2, 3,
- Fei-Wen Huang1, 2, 3,
- Zhong Pei1, 2, 3Email author and
- Xiao-Li Yao1, 2, 3Email author
© Lu et al.; licensee BioMed Central. 2015
- Received: 3 December 2014
- Accepted: 22 April 2015
- Published: 29 April 2015
Parkinson’s disease (PD) is the second most common neurodegenerative disease, affecting 2% of the population aged over 65 years old. Mitochondrial defects and oxidative stress actively participate in degeneration of dopaminergic (DA) neurons in PD. Paeonolum, a main component isolated from Moutan cortex, has potent antioxidant ability. Here, we have examined the effects of paeonolum against MPP+-induced neurotoxicity in zebrafish and PC12 cells.
The overall viability and neurodegeneration of DA neurons was assessed in ETvmat2:green fluorescent protein (GFP) transgenic zebrafish, in which most monoaminergic neurons are labeled by GFP. Damage to PC12 cells was measured using a cell viability assay and assessment of nuclear morphology. Intracellular reactive oxygen species (ROS) and the level of total GSH were assessed. The mitochondrial cell death pathway including mitochondrial membrane potential, cytochrome C release and caspase-3 activity were also examined in PC12 cells.
Paeonolum protected against MPP+-induced DA neurodegeneration and locomotor dysfunction in zebrafish in a concentration-dependent manner. Similar neuroprotection was replicated in the PC12 cellular model of MPP+ toxicity. Paeonolum attenuated MPP+-induced intracellular ROS accumulation and restored the level of total GSH in PC12 cells. Furthermore, paeonolum significantly inhibited the mitochondrial cell death pathway induced by MPP+.
Collectively, the present study demonstrates that paeonolum protects zebrafish and PC12 cells against MPP+-induced neurotoxicity.
- Total GSH
Parkinson’s disease (PD) is the second most prevalent neurodegenerative disease, affecting 2% of the population aged over 65 years. Clinically, PD patients mainly present with impairments in movement including: rigidity, resting tremor and postural instability [1,2]. Current treatments only reduce symptoms, but do not stop the progression of PD. Therefore, there is an urgent need to find more appropriate treatments that can prevent the PD progression.
Although the pathogenesis of PD remains largely unknown, both oxidative stress and mitochondrial dysfunction play pivotal roles in the pathogenesis of PD. For example, a defect in respiratory chain complex I activity in mitochondria has been observed in dopaminergic (DA) neurons in PD patients [3-7]. It is generally believed that both genetic susceptibility and environmental factors contribute to the etiology of PD. However, the majority of PD cases are sporadic, indicating a critical role for environmental factors in the pathogenesis of PD. 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) is an environmental toxin and can selectively damage DA neurons in the substantia nigra (SN) which in turn leads to clinical symptoms similar to those of PD in humans [8,9]. Thus, MPTP and its metabolite MPP+ have been widely used to model PD in mammals [1,2,9,10].
Recently, model organisms such as zebrafish, are becoming powerful tools to study human diseases. Many of the basic physiological processes, metabolic signaling pathways and neurotransmitters in humans are conserved in such models [11,12]. Because model organisms are easy to grow and cost-effective to maintain, their use as a high-throughput strategy to identify new drug targets for human diseases is increasing. Recently, a zebrafish model of MPP+ toxicity has been established that can recapitulate many key features of PD including the specific degeneration of DA neurons and impairment of movement . This model has been increasingly used as an in vivo tool for screening neuroprotective agents for PD.
MPP+-mediated neurotoxicity is believed to be mediated by inhibition of complex I activity and excessive formation of reactive oxygen species (ROS) [1,2,14]. Many antioxidants and agents that can protect the mitochondria have been reported to reduce MPTP-induced neurotoxicity and some have shown promising results in clinical trials with PD patients [2,15].
In recent years, natural antioxidants have become attractive targets for drug development in neurodegenerative diseases because of their demonstrated neuroprotective effects in animal models and low levels of toxicity. Paeonolum is a main component isolated from Moutan cortex. Paeonolum has been used as an anti-inflammatory drug for thousands of years in China. In addition to anti-inflammatory actions, paeonolum has many other pharmacological properties including antiproliferative and antioxidative actions. Most importantly, paeonolum can easily cross the blood–brain barrier (BBB) which makes it an attractive compound for central nervous system (CNS) drug development . The present study was conducted to investigate the neuroprotective potential of paeonolum against MPP+-induced neurotoxicity in zebrafish and PC12 cells.
The isolation of paeonolum
The root bark of Paeonia suffruticosa belongs to Ranunculaceae. Paeonolum was isolated and purified by the State Key Laboratory of Quality Research in Chinese Medicine, Institute of Chinese Medical Sciences, University of Macau, China, according to a published method . The purity of the compound was >98%. Paeonolum was dissolved in dimethyl sulfoxide (DMSO) and stored at −20°C until use. The solution form of paeonolum was then diluted by PBS to the concentration needed. All reagents were purchased from Sigma (Sigma, Shanghai, China) unless otherwise stated.
Zebrafish MPP+ model and paeonolum treatment
The ETvmat2:green fluorescent protein (GFP) transgenic zebrafish was identified from a large-scale enhancer trap screen using a Tol2 vector containing a 249-bp zebrafish gata2 minimal promoter linked to a GFP reporter gene [18,19]. The fish line was maintained in a recirculating aquaculture system at 28.5°C. The MPP+ (Sigma-Aldrich) was dissolved in distilled water to 40 mM and was used at a final concentration of 100–1000 μM for the treatment. Embryos were obtained from the ETvmat2:GFP transgenic fish. At 22–24 hours post-fertilization (hpf), GFP-positive embryos were collected and dechorionated. Ten embryos were then transferred into a six-well plate containing 4 ml Holtfreter’s buffer with 0.003% phenylthiourea (Sigma-Aldrich) and MPP+. The MPP+-containing buffer was changed once after 2 days and at 5 days post-fertilization (dpf), the larval zebrafish were examined under a fluorescence microscope.
Testing of the locomotor activity
An automated computer tracking system was used to determine the locomotor activity of zebrafish larvae (Viewpoint Life Sciences Inc.). At 4 dpf, larval zebrafish were transferred to 96-well microplates and acclimated at 28°C overnight for 24 h. The 96-well microplates were then put into the zebrafish tracking box (Viewpoint Life Sciences Inc.) and activity of the zebrafish monitored using an automated video-tracking system (Viewpoint video-tracking system and software). The speed corresponding to the total length traveled by the larvae was divided by time and then analyzed (Viewpoint software). The results represent the mean swim speed of 10 larvae and are expressed in mm/s.
Briefly, zebrafish (5 dpf) with or without compounds were anaesthetized by treatment with 0.4% tricaine and mounted onto glass slide. Overall morphology of the zebrafish was visualized at 4× magnification under an OLYMPUS IX71 inverted microscope.
Cell culture and cell viability assay
PC12 (rat pheochromocytoma) cells were cultured in RPMI-1640 (Invitrogen, USA) supplemented with 10% heat-inactivated horse serum (Invitrogen, USA) and 5% heat-inactivated fetal calf serum (Invitrogen, USA) in an humidified incubator (Thermo electron corporation, USA) with 5% CO2 at 37°C. PC12 Cells were differentiated on collagen-coated plates by treating with 100 ng/ml nerve growth factor for 9 days and then washed with RPMI-1640 medium containing 1% fetal bovine serum, 24 h before experiments. Cellular viability was assessed using the MTT kit (MTT Cell Growth Kit, Chemicon, USA) according to the manufacturers instructions. Briefly, PC12 cells were diluted to 1 × 105 cells/mL and plated at 100 μL per well in a 96-well microplate, then treated with various concentrations of paeonolum and/or MPP+ (250 μM) for 24 h. 10 μL of the MTT labeling reagent (0.5 mg/mL) was added into each well at 24 h after MPP+ treatment and cells were further incubated with MTT in an humidified incubator at 37°C with 5% CO2 and 95% air (v/v) at 90% humidity for 4 h to allow formation of purple formazan crystal. Four hours later, 100 μL of solubilization reagent was added to each well. Finally, the absorbance of the solubilized purple formazan crystals was measured using a microplate spectrophotometer at an absorbance wavelength of 570 nm. In order to examine MPP+-induced nuclear morphology, PC12 cells were stained with the fluorescent dye, DAPI (2.5 μg/ml, Sigma, USA). PC12 cells (1 × 105 cells/ml) were treated with MPP+ alone or in the presence of paeonolum for 24 h at 37°C and changes in nuclear morphology of the cells were assessed by microscopic observation. Briefly, PC12 cells were fixed in 4% polylysine on ice for 15 min and were then washed twice with PBS. The cells were then incubated with DAPI in PBS for 20 min at room temperature. Nuclear morphology of cells stained with DAPI was visualized under a fluorescence microscope (Olympus DP70, Japan) and quantification was performed by a person who was blinded to the experimental treatment. Condensed, shrunken, fragmented or irregular nuclei were considered signs of cell death. To quantitatively analyze changes in nuclear morphology, the percentage of cells with abnormal nuclei was calculated. All cells from 10 random microscopic fields at 40× magnification were counted and more than 500 cells in total were observed for each treatment group. The ratio of dead cells to total number of cells was then compared among the different treatment groups. The results were obtained from four independent experiments performed in triplicate.
Measurement of intracellular reactive oxygen species
Intracellular ROS were measured by using the fluorescent probe 2,7-dichlorofluorescein diacetate (DCF-DA). The dye DCF-DA is oxidized to fluorescent 2,7-dichlorofluorescin (DCF) by intracellular hydrogen peroxide or low-molecular-weight peroxides. PC12 cells (1 × 105 cells/ml) were seeded in 96-well plates and incubated with MPP+ alone or in the presence of paeonolum for 24 h. Cells were incubated with 10 μM DCF-DA at 37°C for 30 min and then washed twice with PBS. Quantitative measurements of fluorescence readings were determined at 485/538 nm (excitation/emission) using a SpectraMax GEMINI EM fluorescent plate reader (Molecular Devices, USA) from cells in 96-well plates. The results were obtained from three independent experiments performed in triplicate.
Measurement of mitochondrial membrane potential
Mitochondrial membrane potential was measured using the fluorescence dye rhodamine 123 (Invitrogen). Cells were exposed to 10 μM rhodamine 123 for 25 min and then washed twice with HBSS before the fluorescence was determined with a SpectraMax GEMINI EM fluorescent plate reader (Molecular Devices, USA) at 511/534 nm. The results were obtained from three independent experiments performed in triplicate.
Measurement of total glutathione level
The level of total glutathione (reduced form GSH + oxidized form GSSG) was determined using glutathione reductase. PC12 cells were treated with MPP+ alone or in the presence of paeonolum for 24 h at 37°C, centrifuged at 412 × g for 10 min in a microplate centrifuge, the media removed and cells were washed twice with PBS. Cells were dissolved with 2% 5-sulfosalicylic acid (100 μl) and incubated in 100 μl of the reaction mixture containing 22 mM sodium EDTA, 600 μM NADPH, 12 mM DTNB and 105 mM NaH2PO4, pH 7.5 at 37°C. Glutathione reductase (20 μl of 100 U/ml) was added, and the mixture incubated for an additional 10 min. Absorbance was measured at 412 nm using a microplate spectrophotometer. A standard curve was obtained from absorbance of the diluted commercial GSH that was incubated in the mixture as in samples. The results were obtained from three independent experiments performed in triplicate.
Measurement of caspase-3 activity
Caspase-3 activity was determined by using the caspase-3 activity assay kit (Life Science, USA). Briefly, after treatment, cells were harvested and washed with cold PBS. Each cell sample was resuspended in cell lysis buffer (100 mM HEPES, pH 7.4, 10% sucrose, 0.1% CHAPS, 1 mM EDTA, 10 mM dithiothreitol, 1 mM PMSF, 10 mg/ml pepstain, and 10 mg/ml leupeptin) and left on ice for 40 min. The lysed cells were then centrifuged to pellet the cellular debris. The supernatant containing 50 mg protein was incubated with 5 μM fluorogenic substrate peptide Z-DEVD-ER110 in 100 μl of lysis buffer. The intensity of fluorescence of Z-DEVD-ER110 substrate was measured in a fluorescence microplate reader using excitation at 496 nm and emission detection at 520 nm.
Immunoblot analysis for cytochrome c
After treatment, cells were collected and washed with PBS, then resuspended in ice-cold homogenizing buffer (250 mM sucrose, 1 mM dithiothreitol, 1 mM phenylmethylsulfonylfluoride, 1 mg/mL aprotinin and 1 mg/mL leupeptin). Cells were homogenized with a glass Dounce homogenizer. The homogenate was centrifuged at 1000 rpm for 10 min. Then the resulting supernatant was centrifuged at 10,000 rpm (4°C, first for 10 min, and then for 1 h), to produce cytosol. 50 mg of each protein sample was subjected to SDS-polyacrylamide gel electrophoresis on a 12% gel. Then the protein was transferred onto a nitrocellulose membrane and immunoblotted with cytochrome c antibody as previously described . Finally samples were incubated with goat anti-mouse IgG-horseradish peroxidase. The densitometric analysis of protein bands was performed using the image J analysis system.
Data are presented as mean ± SEM. One-way ANOVA was performed followed by a Tukey post-hoc test to compare the significance between the individual groups. P-values less than 0.05 were considered significant.
All experimental procedures were approved by the Institutional Animal Ethical Committee of Sun Yat-sen University and were conducted according to the Guide for the Care and Use of Laboratory Animal of the National Institute of Health (Publication No. 80–23, revised 1996).
Paeonolum attenuated MPP+-induced neurotoxicity in zebrafish
Paeonolum reduced MPP+-induced PC12 cell damage in a concentration-dependent manner
Paeonolum reduced MPP+-induced intracellular ROS
Paeonolum attenuated MPP+-induced reduction in mitochondrial membrane potential
To examine whether paeonolum had a protective effect in mitochondria, we detected the mitochondrial membrane potential using rhodamine 123. Treatment of PC12 cells with 250 μM MPP+ for 24 h produced a significant loss in mitochondrial membrane potential compared with normal controls. The relative fluorescence values of rhodamine 123 in MPP+-treated cells were 55.43 ± 9.63% in the vehicle alone group, 57.83 ± 11.25%, 65.23 ± 10.21%, 59.37 ± 10.36%, 65.23 ± 10.21%, 77.08 ± 10.87% and 83.18 ± 11.27% in treatment groups with paeonolum used at 10, 25, 50, 100 or 150 μM, respectively. Compared with vehicle treatment, paeonolum (50–150 μM) significantly attenuated the MPP+-induced reduction of mitochondrial membrane potential in a concentration-dependent manner.
Paeonolum restored MPP+-induced depletion of total GSH level
Paeonolum against MPP+-induced neurotoxicity involves the intrinsic mitochondrial pathway
In the present study, we have examined the protective effects of paeonolum against MPP+- induced toxicity in a transgenic zebrafish line (ETvmat2:GFP) and PC12 cells. Zebrafish are an excellent model for studying PD because their nervous system shares many similarities with humans . In zebrafish, PT neurons in the posterior tuberculum of the ventral diencephalon are equivalent to the nigrostriatal system in humans. In addition, the pathways involved in processing, packaging and transport of DA are also conserved between zebrafish and humans. Similar to mammals, DA neurons in zebrafish take up MPP+, mainly through the high-affinity DA transporter. The accumulation of MPP+ inside neurons in turn inactivates the mitochondrial complex I of the respiratory chain and induces cell death. In the transgenic zebrafish ETvmat2:GFP line, most monoaminergic neurons, are labeled by GFP allowing clear observation of MPP+-induced DA neurodegeneration in living animals. Consistent with previous observations, we found that MPP+ induced a large loss of PT neurons, indicating selective damage to DA neurons in a concentration-dependent manner. Furthermore, MPP+ also reduced locomotor activity in the zebrafish. Interestingly, the reduction of locomotor activity was closely associated with a loss of PT neurons in MPP+ -treated zebrafish. Given that locomotor activity in zebrafish can be easily monitored and measured on a large scale, using an automated computer tracking system, this model may be good for high throughput screening of drugs to treat PD.
To explore whether the findings in zebrafish can be translated into a future clinical approach, we investigated the mechanisms underlying the neuroprotection of paeonolum in PC12 cells. PC12 cells were used to established a MPP+-induced cellular model of PD because PC12 cells exhibit similar characteristics to DA neurons and have some of the physiological properties of DA neurons [23,24]. We found that incubation of PC12 cells with MPP+ at 250 μM for 24 h induced up to 50–60% of PC12 cell death which is in agreement with previous studies [10,25]. Similar to the findings in our zebrafish model using MPP+, paeonolum reduced MPP+-induced PC12 toxicity in a concentration-dependent manner, indicating that zebrafish can serve as a valuable model for translational research in the field of PD.
Substantial clinical and experimental evidence has demonstrated the critical role of mitochondrial dysfunction in the pathogenesis of PD [2,6]. Mitochondria are the major source of ROS production. MPP+ is a mitochondrial toxin and specifically inhibits mitochondrial complex I, which further promotes the opening of the mitochondrial permeability pore and causes the collapse of the mitochondrial membrane potential, causing excessive generation of ROS [1,14,26]. Excessive ROS production can damage the respiratory chain and further stimulate ROS, forming a vicious cycle resulting in cell death. Consistent with this idea, MPP+ significantly reduced the mitochondrial membrane potential in PC12 cells, whereas pretreatment with paeonolum attenuated the degree of MPP+-induced loss of mitochondrial membrane potential, suggesting that paeonolum may have a direct protective action on mitochondria. It is generally believed that the neurotoxic effects of MPP+ are mediated by oxidative stress. Although the antioxidant activity of paeonolum has been demonstrated in different systems, it is not clear whether antioxidant activity of paeonolum is also contributed to its neuroprotective effect in our model of MPP+ toxicity. We found that paeonolum attenuated MPP + −induced ROS production in a concentration-dependent manner. In addition, paeonolum also rescued the reduction of the activity of the intracellular antioxidant GSH. Given that paeonolum did not have any direct effect on GSH activity on its own, this beneficial effect may have been indirectly related to its action as a general antioxidant.
Pathologically, PD is caused by a selective loss of DA neurons in the SN. Increasing evidence from human studies on postmortem brains from PD patients, suggests that apoptotic cell death is most likely contribute to the neuronal loss observed in PD. Similarly, MPP+ induces apoptosis in both animals and cell cultures via affecting the mitochondrial pathway. As an inhibitor of mitochondrial complex I, MPP+ triggers opening of the mitochondrial permeability transition pore, induces release of apoptotic proteins such as cytochrome c into the cytoplasm and initiates caspase-3 activation, finally resulting in biochemical and morphological alterations suggestive of apoptosis. We found that paeonolum significantly suppressed MPP+-induced the loss of mitochondrial membrane potential, cytochrome c release and caspase-3 activity, suggesting that paeonolum is able to attenuate MPP+-induced toxicity through inhibition of the mitochondrial cell death cascade.
Here, we have demonstrated the neuroprotective action of paeonolum against MPP+ toxicity in zebrafish and PC12 cells. Paeonolum exerts its protective action through reducing overproduction of ROS, attenuating loss of mitochondrial membrane potential and restoring GSH levels in MPP+-treated PC12 cells. The low toxicity, antioxidant properties and ease to cross the BBB warrant further investigation of this compound.
This study was supported by grants from the National Key Clinical Department, National Key Discipline, Guangdong Key Laboratory For Diagnosis and Treatment of Major Neurological Diseases, the National Natural Science Foundation of China (No. 81371255, 81100936), Doctoral Program of Higher Education of China (No. 20110171110058), Guangdong Technological grant (No. 2010B050700024, 2011B050400031, 2012B031800107), Guangdong Department of Science & Technology Translational Medicine Center grant (No. 2011A080300002) and the Natural Science Foundation of Guangdong Province (No. S2011010004860).
The authors would like to offer special thanks to the North Center of National Zebrafish Resources of China for their technological support with the zebrafish.
- Dauer W, Przedborski S. Parkinson's disease: mechanisms and models. Neuron. 2003;39:889–909.View ArticlePubMedGoogle Scholar
- Henchcliffe C, Beal MF. Mitochondrial biology and oxidative stress in Parkinson disease. pathogenesis. Nat Clin Pract Neurol. 2008;4:600–9.View ArticlePubMedGoogle Scholar
- Banerjee R, Starkov AA, Beal MF, Thomas B. Mitochondrial dysfunction in the limelight of Parkinson's disease pathogenesis. Biochim Biophys Acta. 2009;1792:651–63.View ArticlePubMedGoogle Scholar
- Ebadi M, Sharma SK. Peroxynitrite and mitochondrial dysfunction in the pathogenesis of Parkinson's disease Antioxid. Redox Signal. 2003;5:319–35.View ArticleGoogle Scholar
- Mandemakers W, Morais VA, De Strooper B. A cell biological perspective on mitochondrial dysfunction in Parkinson disease and other neurodegenerative diseases. J Cell Sci. 2007;120:1707–16.View ArticlePubMedGoogle Scholar
- Schapira AH, Cooper JM, Dexter D, Clark JB, Jenner P, Marsden CD. Mitochondrial complex I deficiency in Parkinson's disease. J Neurochem. 1990;54:823–7.View ArticlePubMedGoogle Scholar
- Schapira AH, Gu M, Taanman JW, Tabrizi SJ, Seaton T, Cleeter M, et al. Mitochondria in the etiology and pathogenesis of Parkinson's disease. Ann Neurol. 1998;44:S89–98.View ArticlePubMedGoogle Scholar
- Langston JW, Ballard P, Tetrud JW, Irwin I. Chronic parkinsonism in humans due to a product of meperidine-analog synthesis. Science. 1983;219:979–80.View ArticlePubMedGoogle Scholar
- Tetrud JW, Langston JW. MPTP-induced parkinsonism as a model for Parkinson's disease. Acta Neurol Scand Suppl. 1989;126:35–40.View ArticlePubMedGoogle Scholar
- Marongiu ME, Piccardi MP, Bernardi F, Corsini GU, Del Zompo M. Evaluation of the toxicity of the dopaminergic neurotoxins MPTP and MPP+ in PC12 pheochromocytoma cells: binding and biological studies. Neurosci Lett. 1988;94:349–54.View ArticlePubMedGoogle Scholar
- Link CD. Transgenic invertebrate models of age-associated neurodegenerative diseases. Mech Ageing Dev. 2001;122:1639–49.View ArticlePubMedGoogle Scholar
- Nass R, Blakely RD. The Caenorhabditis elegans dopaminergic system: opportunities for insights into dopamine transport and neurodegeneration. Annu Rev Pharmacol Toxicol. 2003;43:521–44.View ArticlePubMedGoogle Scholar
- Wen L, Wei W, Gu W, Huang P, Ren X, Zhang Z, et al. Visualization of monoaminergic neurons and neurotoxicity of MPTP in live transgenic zebrafish. Dev Biol. 2008;314:4–92.View ArticleGoogle Scholar
- Cassarino DS. The parkinsonian neurotoxin MPP+ opens the mitochondrial permeability transition pore and releases cytochrome c in isolated mitochondria via an oxidative mechanism. Biochim Biophys Acta. 1999;1453:49–62.View ArticlePubMedGoogle Scholar
- Abdel-Salam OM. Drugs used to treat Parkinson's disease, present status and future directions. CNS Neurol Disord Drug Targets. 2008;7:321–42.View ArticlePubMedGoogle Scholar
- Li HWS, Yang Q, Xin Y, Cao W, Zang B, Wang JB, et al. LC tissue distribution study of paeonol in rats after oral administration. Chromatographia. 2011;73:495–500.View ArticleGoogle Scholar
- Hsieh CL, Cheng CY, Tsai TH, Lin IH, Liu CH, Chiang SY, et al. Paeonol reduced cerebral infarction involving the superoxide anion and microglia activation in ischemia-reperfusion injured rats. J Ethnopharmacol. 2006;106:208–15.View ArticlePubMedGoogle Scholar
- Kawakami K, Takeda H, Kawakami N, Kobayashi M, Matsuda N, Mishina M. A transposon-mediated gene trap approach identifies developmentally regulated genes in zebrafish. Dev Cell. 2004;7:133–44.View ArticlePubMedGoogle Scholar
- Meng A, Tang H, Ong BA, Farrell MJ, Lin S. Promoter analysis in living zebrafish embryos identifies a cis-acting motif required for neuronal expression of GATA-2. Proc Natl Acad Sci U S A. 1997;94:6267–72.View ArticlePubMedPubMed CentralGoogle Scholar
- Luo X, Budihardjo I, Zou H, Slaughter C, Wang X. Bid, a Bcl2 interacting protein, mediates cytochrome c release from mitochondria in response to activation of cell surface death receptors. Cell. 1998;94:481–90.View ArticlePubMedGoogle Scholar
- Lopez-Schier H, Hudspeth AJ. A two-step mechanism underlies the planar polarization of regenerating sensory hair cells. Proc Natl Acad Sci U S A. 2006;103:18615–20.View ArticlePubMedPubMed CentralGoogle Scholar
- Bruni G, Lakhani P, Kokel D. Discovering novel neuroactive drugs through high-throughput behavior-based chemical screening in the zebrafish. Front Pharmacol. 2014;5:153.View ArticlePubMedPubMed CentralGoogle Scholar
- Presse F, Cardona B, Borsu L, Nahon JL. Lithium increases melanin-concentrating hormone mRNA stability and inhibits tyrosine hydroxylase gene expression in PC12 cells. Brain Res Mol Brain Res. 1997;52:270–83.View ArticlePubMedGoogle Scholar
- Zachor DA, Moore JF, Brezausek C, Theibert A, Percy AK. Cocaine inhibits NGF-induced PC12 cells differentiation through D(1)-type dopamine receptors. Brain Res. 2000;869:85–97.View ArticlePubMedGoogle Scholar
- Lee CS. Modulation of 1-methyl-4-phenylpyridinium-induced mitochondrial dysfunction and cell death in PC12 cells by K(ATP) channel block. J Neural Transm. 2007;114:297–305.View ArticlePubMedGoogle Scholar
- Nicotra A, Parvez S. Apoptotic molecules and MPTP-induced cell death. Neurotoxicol Teratol. 2002;24:599–605.View ArticlePubMedGoogle Scholar
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