Arylpiperazine-mediated activation of Akt protects SH-SY5Y neuroblastoma cells from 6-hydroxydopamine-induced apoptotic and autophagic death

Schwann cells differentiated from skin-derived precursors provide neuroprotection via autophagy inhibition in a cellular model of Parkinson's disease

Autophagy has been shown to play an important role in Parkinson’s disease. We hypothesized that skin-derived precursor cells exhibit neuroprotective effects in Parkinson’s disease through affecting autophagy. In this study, 6-hydroxydopamine-damaged SH-SY5Y cells were pretreated with a culture medium containing skin-derived precursors differentiated into Schwann cells (SKP-SCs). The results showed that the SKP-SC culture medium remarkably enhanced the activity of SH-SY5Y cells damaged by 6-hydroxydopamine, reduced excessive autophagy, increased tyrosine hydroxylase expression, reduced α-synuclein expression, reduced the autophagosome number, and activated the PI3K/AKT/mTOR pathway. Autophagy activator rapamycin inhibited the effects of SKP-SCs, and autophagy inhibitor 3-methyladenine had the opposite effect. These findings confirm that SKP-SCs modulate the PI3K/AKT/mTOR pathway to inhibit autophagy, thereby exhibiting a neuroprotective effect in a cellular model of Parkinson’s disease. This study was approved by the Animal Ethics Committee of Laboratory Animal Center of Nantong University (approval No. S20181009-205) on October 9, 2018.

Arsenic induces autophagy-dependent apoptosis via Akt inactivation and AMPK activation signaling pathways leading to neuronal cell death

Inorganic arsenic (As³⁺), a well-known worldwide industrial and environmental pollutant, has been linked to neurodegenerative disorders (NDs). Autophagy plays an important role in controlling neuronal cell survival/death. However, limited information is available regarding the toxicological mechanism at the interplay between autophagy and As³⁺-induced neurotoxicity. The present study found that As³⁺ exposure induced a concomitant activation of apoptosis and autophagy in Neuro-2a cells, which was accompanied with the increase of phosphatidylserine exposure on outer membrane leaflets and apoptotic cell population, and the activation of caspase-3, -7, and PARP as well as the elevation of protein expressions of LC3-II, Atg-5, and Beclin-1, and the accumulation of autophagosome. Pretreatment of cells with autophagy inhibitor 3-MA, but not that of Z-VAD-FMK (a pan-caspase inhibitor), effectively prevented the As³⁺-induced autophagic and apoptotic responses, indicating that As³⁺-triggered autophagy was contributing to neuronal cell apoptosis. Furthermore, As³⁺ exposure evoked the dephosphorylation of Akt. Pretreatment with SC79, an Akt activator, could significantly attenuated As³⁺-induced Akt inactivation as well as autophagic and apoptotic events. Expectedly, inhibition of Akt signaling with LY294002 obviously enhanced As³⁺-triggered autophagy and apoptosis. Exposure to As³⁺ also dramatically increased the phosphorylation level of AMPKα. Pretreatment of AMPK inhibitor (Compound C) could markedly abrogate the As³⁺-induced phosphorylated AMPKα expression, and autophagy and apoptosis activation. Taken together, these results indicated that As³⁺ exerted its cytotoxicity in neuronal cells via the Akt inactivation/AMPK activation downstream-regulated autophagy-dependent apoptosis pathways, which ultimately lead to cell death. Our findings suggest that the regulation of Akt/AMPK signals may be a promising intervention to against As³⁺-induced neurotoxicity and NDs.

Alpha-lipoic acid alleviated 6-OHDA-induced cell damage by inhibiting AMPK/mTOR mediated autophagy

Oxidative stress and autophagy are involved in the pathogenesis of Parkinson's disease. The relationship between oxidative stress and autophagy is a hot spot of scientific research. Alpha-lipoic acid (ALA) is a natural antioxidant. ALA has been reported to reduce oxidative stress and apoptosis in PD models, but its role in autophagy regulation of PD has been reported very little. In this study, we investigated the protective effects of ALA on 6-OHDA induced neurotoxicity, and explored the potential mechanisms associated with the crosstalk between oxidative stress and autophagy. Our results showed that 6-OHDA induced accumulation of ROS in SH-SY5Y cells, accompanied by excessive autophagy and apoptosis. ALA protected against 6-OHDA induced neuronal death through inhibition of oxidative stress and autophagy. Furthermore, we found that ALA inhibited AMPK phosphorylation while activated mTOR phosphorylation thereby blocking AMPK/mTOR signaling pathway involved autophagy. In conclusion, ALA alleviated 6-OHDA induced cell injury possibly by inhibiting autophagy mediated by AMPK/mTOR pathway.

Neuroprotective effects of genistein on SH-SY5Y cells overexpressing A53T mutant α-synuclein

Genistein, a potent antioxidant compound, protects dopaminergic neurons in a mouse model of Parkinson's disease. However, the mechanism underlying this action remains unknown. This study investigated human SH-SY5Y cells overexpressing the A53T mutant of α-synuclein. Four groups of cells were assayed: a control group (without any treatment), a genistein group (incubated with 20 μM genistein), a rotenone group (treated with 50 μM rotenone), and a rotenone + genistein group (incubated with 20 μM genistein and then treated with 50 μM rotenone). A lactate dehydrogenase release test confirmed the protective effect of genistein, and genistein remarkably reversed mitochondrial oxidative injury caused by rotenone. Western blot assays showed that BCL-2 and Beclin 1 levels were markedly higher in the genistein group than in the rotenone group. Terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling revealed that genistein inhibited rotenone-induced apoptosis in SH-SY5Y cells. Compared with the control group, the expression of NFE2L2 and HMOX1 was significantly increased in the genistein + rotenone group. However, after treatment with estrogen receptor and NFE2L2 channel blockers (ICI-182780 and ML385, respectively), genistein could not elevate NFE2L2 and HMOX1 expression. ICI-182780 effectively prevented genistein-mediated phosphorylation of NFE2L2 and remarkably suppressed phosphorylation of AKT, a protein downstream of the estrogen receptor. These findings confirm that genistein has neuroprotective effects in a cell model of Parkinson's disease. Genistein can reduce oxidative stress damage and cell apoptosis by activating estrogen receptors and NFE2L2 channels.

Identification of NQO1 and ferrochelatase as interaction partners for neuroprotective N-{[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-arylamides

Affinity chromatography was used to identify potential cellular targets that are responsible for neuroprotective activity of N-{[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-arylamides. Active and inactive representatives of N-{[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-arylamides bearing an extended linker were synthesized and immobilized on an agarose-based matrix. This was followed by the identification of specifically bound proteins isolated out of the whole rat brain extract. Inducible flavoprotein NAD(P)H:quinone oxidoreductase (NQO1) was identified as candidates for cellular targets.

Mesencephalic astrocyte-derived neurotrophic factor alleviated 6-OHDA-induced cell damage via ROS-AMPK/mTOR mediated autophagic inhibition

Autophagy and apoptosis are commonly involved in the dopaminergic neuron damage in the pathogenesis of Parkinson's disease. Recently, the autophagy pathway is thought to be critical to the process of PD. Therefore, the regulation of autophagy may be a potential strategy for PD treatment. Mesencephalic astrocyte-derived neurotrophic factor (MANF) has been reported to have neuroprotective effects through anti-apoptosis, anti-oxidative, and anti-inflammatory mechanisms in PD. In this study, we investigated the role of autophagy system in MANF-mediated neuroprotection against 6-hydroxydopamine (6-OHDA)-induced neurotoxicity. Our results showed that MANF protected SH-SY5Y cells against 6-OHDA-induced cell viability decrease and apoptosis by inhibiting autophagy. Mitochondrion damage and energetic dysfunction triggered by reactive oxidative stress (ROS) accumulation were also alleviated by MANF treatment. Furthermore, MANF downregulated phosphorylation of AMP-activated protein kinase (AMPK), a cellular energy sensor and regulator, but upregulated phosphorylation of Mammalian target of rapamycin (mTOR) under energy depletion conditions, indicating AMPK/mTOR signaling pathway is involved in the autophagic inhibition of MANF. These results suggest that autophagic inhibition provides protective mechanism of MANF in 6-OHDA-induced SH-SY5Y cell death and this inhibition is associated with AMPK/mTOR pathway.

Tris (1, 3-dichloro-2-propyl) phosphate induces apoptosis and autophagy in SH-SY5Y cells: Involvement of ROS-mediated AMPK/mTOR/ULK1 pathways

Tris (1, 3-dichloro-2-propyl) phosphate (TDCIPP), an extensively used organophosphorus flame retardant, is frequently detected in the environment and biota. Recent studies have shown that TDCIPP has neurotoxic effects. We hypothesized that the neurotoxicity might occur via the induction of the apoptosis and autophagy pathways. In the present study, we investigated TDCIPP-induced apoptotic death and autophagy in SH-SY5Y cells. Treatment with TDCIPP induced increased reactive oxygen species (ROS) generation and cell apoptosis, as well as autophagy. The autophagy inhibitor 3-methyladenine (3-MA) markedly decreased the expression of the autophagy marker beclin-1, microtubule-associated protein light chain 3-II (LC3II), p62/sequestosome 1 (SQSTM1) degradation, and promoted apoptosis. Conversely, the autophagy inducer rapamycin (Rapa) alleviated TDCIPP-induced apoptosis and markedly increased the expression of the autophagy markers. Pretreatment with N-acetyl cysteine (NAC) eliminated the increased ROS generation, resulting in increased cell viability. For further examination of the signaling pathways involved in TDCIPP-induced autophagy, compound C, a pharmacological inhibitor of adenosine monophosphate activated protein kinase (AMPK) was used. Western blotting showed that compound C markedly reduced the expression of phospho-AMPK (p-AMPK) and phospho-Unc-51-like kinase 1 (p-ULK1), increased phospho-mammalian target of rapamycin (p-mTOR) expression, and decreased beclin-1 and LC3II expression. These results suggested that the AMPK/mTOR/ULK1 signaling pathway was involved in TDCIPP-induced autophagy. The antioxidant NAC antagonized TDCIPP-induced activation of AMPK and autophagy. Taken together, our findings provide the first evidence that TDCIPP promotes apoptosis and autophagy simultaneously and that this process involves the ROS-mediated AMPK/mTOR/ULK1 pathways. Lastly, the induction of autophagy is a protective mechanism against TDCIPP-induced apoptosis.

Meclizine-induced enhanced glycolysis is neuroprotective in Parkinson disease cell models

Meclizine is a well-tolerated drug routinely used as an anti-histamine agent in the management of disequilibrium. Recently, meclizine has been assessed for its neuroprotective properties in ischemic stroke and Huntington disease models. We found that meclizine protected against 6-hydroxydopamine-induced apoptosis and cell death in both SH-SY5Y cells and rat primary cortical cultures. Meclizine increases the level of 6-phosphofructo-2-kinase/fructose-2,6-biphosphatase 3 (PFKFB3), which activates phosphofructokinase, a rate-determining enzyme of glycolysis. This protection is therefore mediated by meclizine’s ability to enhance glycolysis and increase mitochondrial hyperpolarization. Meclizine represents an interesting candidate for further investigation to re-purpose for its potential to be neuroprotective in Parkinson disease.

Neuroprotective arylpiperazine dopaminergic/serotonergic ligands suppress experimental autoimmune encephalomyelitis in rats

Arylpiperazine-based dopaminergic/serotonergic ligands exert neuroprotective activity. We examined the effect of arylpiperazine D2 /5-HT1A ligands, N-{4-[2-(4-phenyl-piperazin-1-yl)-ethyl}-phenyl]-picolinamide (6a) and N-{3-[2-(4-phenyl-piperazin-1-yl)-ethyl]-phenyl}-picolinamide (6b), in experimental autoimmune encephalomyelitis (EAE), a model of neuroinflammation. Both compounds (10 mg/kg i.p.) reduced EAE clinical signs in spinal cord homogenate-immunized Dark Agouti rats. Compound 6b was more efficient in delaying the disease onset and reducing the maximal clinical score, which correlated with its higher affinity for D2 and 5-HT1A receptors. The protection was retained if treatment was limited to the effector (from day 8 onwards), but not the induction phase (day 0-7) of EAE. Compound 6b reduced CNS immune infiltration and expression of mRNA encoding the proinflammatory cytokines tumor necrosis factor, IL-6, IL-1, and GM-CSF, TH 1 cytokine IFN-γ, TH 17 cytokine IL-17, as well as the signature transcription factors of TH 1 (T-bet) and TH 17 (RORγt) cells. Arylpiperazine treatment reduced apoptosis and increased the activation of anti-apoptotic mediators Akt and p70S6 kinase in the CNS of EAE animals. The in vitro treatment with 6b protected oligodendrocyte cell line OLN-93 and neuronal cell line PC12 from mitogen-activated normal T cells or myelin basic protein-activated encephalitogenic T cells. In conclusion, arylpiperazine dopaminergic/serotonergic ligands suppress EAE through a direct neuroprotective action and decrease in CNS inflammation. Arylpiperazine dopaminergic/serotonergic ligands reduce neurological symptoms of acute autoimmune encephalomyelitis in rats without affecting the activation of autoreactive immune response, through mechanisms involving a decrease in CNS immune infiltration, as well as direct protection of CNS from immune-mediated damage. These data indicate potential usefulness of arylpiperazine-based compounds in the treatment of neuroinflammatory disorders such as multiple sclerosis.

Neurotoxin mechanisms and processes relevant to Parkinson's disease: an update

The molecular mechanism responsible for degenerative process in the nigrostriatal dopaminergic system in Parkinson's disease (PD) remains unknown. One major advance in this field has been the discovery of several genes associated to familial PD, including alpha synuclein, parkin, LRRK2, etc., thereby providing important insight toward basic research approaches. There is an consensus in neurodegenerative research that mitochon dria dysfunction, protein degradation dysfunction, aggregation of alpha synuclein to neurotoxic oligomers, oxidative and endoplasmic reticulum stress, and neuroinflammation are involved in degeneration of the neuromelanin-containing dopaminergic neurons that are lost in the disease. An update of the mechanisms relating to neurotoxins that are used to produce preclinical models of Parkinson´s disease is presented. 6-Hydroxydopamine, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine, and rotenone have been the most wisely used neurotoxins to delve into mechanisms involved in the loss of dopaminergic neurons containing neuromelanin. Neurotoxins generated from dopamine oxidation during neuromelanin formation are likewise reviewed, as this pathway replicates neurotoxin-induced cellular oxidative stress, inactivation of key proteins related to mitochondria and protein degradation dysfunction, and formation of neurotoxic aggregates of alpha synuclein. This survey of neurotoxin modeling-highlighting newer technologies and implicating a variety of processes and pathways related to mechanisms attending PD-is focused on research studies from 2012 to 2014.

The Parkinsonian mimetic, 6-OHDA, impairs axonal transport in dopaminergic axons

6-hydroxydopamine (6-OHDA) is one of the most commonly used toxins for modeling degeneration of dopaminergic (DA) neurons in Parkinson's disease. 6-OHDA also causes axonal degeneration, a process that appears to precede the death of DA neurons. To understand the processes involved in 6-OHDA-mediated axonal degeneration, a microdevice designed to isolate axons fluidically from cell bodies was used in conjunction with green fluorescent protein (GFP)-labeled DA neurons. Results showed that 6-OHDA quickly induced mitochondrial transport dysfunction in both DA and non-DA axons. This appeared to be a general effect on transport function since 6-OHDA also disrupted transport of synaptophysin-tagged vesicles. The effects of 6-OHDA on mitochondrial transport were blocked by the addition of the SOD1-mimetic, Mn(III)tetrakis(4-benzoic acid)porphyrin chloride (MnTBAP), as well as the anti-oxidant N-acetyl-cysteine (NAC) suggesting that free radical species played a role in this process. Temporally, microtubule disruption and autophagy occurred after transport dysfunction yet before DA cell death following 6-OHDA treatment. The results from the study suggest that ROS-mediated transport dysfunction occurs early and plays a significant role in inducing axonal degeneration in response to 6-OHDA treatment.

SA4503, a sigma-1 receptor agonist, suppresses motor neuron damage in in vitro and in vivo amyotrophic lateral sclerosis models

Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease. Recently, it has been reported that a mutation in the sigma-1 receptor causes juvenile ALS. Therefore, the function of the sigma-1 receptor may be important in the pathology of ALS. In the present study, we investigated the effect of SA4503, a sigma-1 receptor agonist, against in in vitro and in vivo ALS models. We first investigated whether SA4503, a sigma-1 receptor agonist, prevented superoxide dismutase 1 (SOD1(G93A))- and serum free-induced cell death of mice motor neuron cells (NSC34) in in vitro model of an ALS. At concentrations of 1-10μM, SA4503 reduced SOD1(G93A)-induced cell death in a concentration-dependent manner, and BD1047, a sigma-1 receptor antagonist, inhibited the protective effect of SA4503. Next, we investigated whether SA4503 affected the phosphorylation levels of Akt (Ser 473) and extracellular signal-regulated kinase (ERK) 1/2 and the expression of the sigma-1 receptor. SA4503 promoted the phosphorylation of Akt (Ser 473) and ERK1/2 in a time-dependent manner, but SA4503 did not affect the expression of the sigma-1 receptor. These results suggest that the protective effect of SA4503 might be involved in promoting the phosphorylation of Akt and ERK1/2. We then investigated whether SA4503 suppressed the progression of ALS in an SOD1(G93A) ALS mouse model. SA4503 did not affect the onset time of ALS. However, it significantly extended the survival time in the SOD1(G93A) mice compared with a vehicle-treated group. These findings indicate that SA4503 is effective in suppressing motor neuron degeneration and symptom progression in ALS.

How Parkinsonian toxins dysregulate the autophagy machinery

Since their discovery, Parkinsonian toxins (6-hydroxydopamine, MPP+, paraquat, and rotenone) have been widely employed as in vivo and in vitro chemical models of Parkinson's disease (PD). Alterations in mitochondrial homeostasis, protein quality control pathways, and more recently, autophagy/mitophagy have been implicated in neurotoxin models of PD. Here, we highlight the molecular mechanisms by which different PD toxins dysregulate autophagy/mitophagy and how alterations of these pathways play beneficial or detrimental roles in dopamine neurons. The convergent and divergent effects of PD toxins on mitochondrial function and autophagy/mitophagy are also discussed in this review. Furthermore, we propose new diagnostic tools and discuss how pharmacological modulators of autophagy/mitophagy can be developed as disease-modifying treatments for PD. Finally, we discuss the critical need to identify endogenous and synthetic forms of PD toxins and develop efficient health preventive programs to mitigate the risk of developing PD.

P90RSK and Nrf2 Activation via MEK1/2-ERK1/2 Pathways Mediated by Notoginsenoside R2 to Prevent 6-Hydroxydopamine-Induced Apoptotic Death in SH-SY5Y Cells

6-Hydroxydopamine (6-OHDA) is known to contribute to neuronal death in Parkinson's disease. In this study, we found that the preincubation of SH-SY5Y cells for 24 h with 20  μ M notoginsenoside R2 (NGR2), which is a newly isolated notoginsenoside from Panax notoginseng, showed neuroprotective effects against 6-OHDA-induced oxidative stress and apoptosis. NGR2 incubation successively resulted in the activation of P90RSK, inactivation of BAD, and inhibition of 6-OHDA-induced mitochondrial membrane depolarization, thus preventing the mitochondrial apoptosis pathway. NGR2 incubation also led to the activation of Nrf2 and subsequent activity enhancement of phase II detoxifying enzymes, thus suppressing 6-OHDA-induced oxidative stress, and these effects could be removed by Nrf2 siRNA. We also found that the upstream activators of P90RSK and Nrf2 were the MEK1/2-ERK1/2 pathways but not the JNK, P38, or PI3K/Akt pathways. Interestingly, NGR2 incubation could also activate MEK1/2 and ERK1/2. Most importantly, NGR2-mediated P90RSK and Nrf2 activation, respective downstream target activation, and neuroprotection were reversed by the genetic silencing of MEK1/2 and ERK1/2 by using siRNA and PD98059 application. These results suggested that the neuroprotection elicited by NGR2 against 6-OHDA-induced neurotoxicity was associated with NGR2-mediated P90RSK and Nrf2 activation through MEK1/2-ERK1/2 pathways.