Autophagy-dependent and -independent involvement of AMP-activated protein kinase in 6-hydroxydopamine toxicity to SH-SY5Y neuroblastoma cells

Trehalose Attenuates In Vitro Neurotoxicity of 6-Hydroxydopamine by Reducing Oxidative Stress and Activation of MAPK/AMPK Signaling Pathways

The effects of trehalose, an autophagy-inducing disaccharide with neuroprotective properties, on the neurotoxicity of parkinsonian mimetics 6-hydroxydopamine (6-OHDA) and 1-methyl-4-phenylpiridinium (MPP+) are poorly understood. In our study, trehalose suppressed 6-OHDA-induced caspase-3/PARP1 cleavage (detected by immunoblotting), apoptotic DNA fragmentation/phosphatidylserine externalization, oxidative stress, mitochondrial depolarization (flow cytometry), and mitochondrial damage (electron microscopy) in SH-SY5Y neuroblastoma cells. The protection was not mediated by autophagy, autophagic receptor p62, or antioxidant enzymes superoxide dismutase and catalase. Trehalose suppressed 6-OHDA-induced activation of c-Jun N-terminal kinase (JNK), p38 mitogen-activated protein kinase (MAPK), and AMP-activated protein kinase (AMPK), as revealed by immunoblotting. Pharmacological/genetic inhibition of JNK, p38 MAPK, or AMPK mimicked the trehalose-mediated cytoprotection. Trehalose did not affect the extracellular signal-regulated kinase (ERK) and mechanistic target of rapamycin complex 1 (mTORC1)/4EBP1 pathways, while it reduced the prosurvival mTORC2/AKT signaling. Finally, trehalose enhanced oxidative stress, mitochondrial damage, and apoptosis without decreasing JNK, p38 MAPK, AMPK, or AKT activation in SH-SY5Y cells exposed to MPP+. In conclusion, trehalose protects SH-SY5Y cells from 6-OHDA-induced oxidative stress, mitochondrial damage, and apoptosis through autophagy/p62-independent inhibition of JNK, p38 MAPK, and AMPK. The opposite effects of trehalose on the neurotoxicity of 6-OHDA and MPP+ suggest caution in its potential development as a neuroprotective agent.

A2AR antagonists triggered the AMPK/m-TOR autophagic pathway to reverse the calcium-dependent cell damage in 6-OHDA induced model of PD

Calcium dyshomeostasis, oxidative stress, autophagy and apoptosis are the pathogenesis of selective dopaminergic neuronal loss in Parkinson's disease (PD). Earlier, we reported that A2A R modulates IP3-dependent intracellular Ca2+ signalling via PKA. Moreover, A2A R antagonist has been reported to reduce oxidative stress and apoptosis in PD models, however intracellular Ca2+ ([Ca2+]i) dependent autophagy regulation in the 6-OHDA model of PD has not been explored. In the present study, we investigated the A2A R antagonists mediated neuroprotective effects in 6-OHDA-induced primary midbrain neuronal (PMN) cells and unilateral lesioned rat model of PD. 6-OHDA-induced oxidative stress (ROS and superoxide) and [Ca2+]i was measured using Fluo4AM, DCFDA and DHE dye respectively. Furthermore, autophagy was assessed by Western blot of p-m-TOR/mTOR, p-AMPK/AMPK, LC3I/II, Beclin and β-actin. Apoptosis was measured by Annexin V-APC-PI detection and Western blot of Bcl2, Bax, caspase3 and β-actin. Dopamine levels were measured by Dopamine ELISA kit and Western blot of tyrosine hydroxylase. Our results suggest that 6-OHDA-induced PMN cell death occurred due to the interruption of [Ca2+]i homeostasis, accompanied by activation of autophagy and apoptosis. A2A R antagonists prevented 6-OHDA-induced neuronal cell death by decreasing [Ca2+]i overload and oxidative stress. In addition, we found that A2A R antagonists upregulated mTOR phosphorylation and downregulated AMPK phosphorylation thereby reducing autophagy and apoptosis both in 6-OHDA induced PMN cells and 6-OHDA unilateral lesioned rat model. In conclusion, A2A R antagonists alleviated 6-OHDA toxicity by modulating [Ca2+]i signalling to inhibit autophagy mediated by the AMPK/mTOR pathway.

Melatonin Ameliorates Ovarian Hyperstimulation Syndrome (OHSS) through SESN2 Regulated Antiapoptosis

Background

Ovarian hyperstimulation syndrome (OHSS) is one of the most severe complications after ovarian stimulation during assisted reproductive technology (ART). However, its pathogenesis still remains unclear. Melatonin is an important antioxidant factor in female reproduction and Sestrin-2 (SESN2) is reported to be involved in cellular response to different stress conditions. Whether or not melatonin and SESN2 are involved in OHSS is still a question to us clinicians.

Methods and Results

We collected the granulosa cells of OHSS patients and focused on the role of SESN2 in OHSS. We also studied the role and mechanism of melatonin plays in OHSS patients. We found that the expression of SESN2 was increased in the granulosa cells of OHSS patients (n = 24) than those in controls (n = 15). Incubation with angiotensin II (1 μM, 2 μM) in HUVECs and H2O2 (0.1 mM, 0.2 mM) in KGNs increased the generation of ROS concurrent with the increased expression of SESN2, while melatonin treatment partly restored SESN2 levels. The mechanism study demonstrated that SESN2 was deeply involved in the regulation of AMPK and mTOR, whereas melatonin partially restored angiotensin II or H2O2 induced the activation of AMPK phosphorylation and the inhibition of mTOR, 4EBP1 and S6K1 phosphorylation, all of which could trigger cell apoptosis.

Conclusions

These findings indicated that melatonin attenuated ROS-induced apoptosis through SESN2-AMPK-mTOR in OHSS. Thus, melatonin is likely to be a potential and important therapeutic agent for treating and preventing OHSS.

6-Hydroxydopamine Induces Neurodegeneration in Terminally Differentiated SH-SY5Y Neuroblastoma Cells via Enrichment of the Nucleosomal Degradation Pathway: a Global Proteomics Approach

The SH-SY5Y human neuroblastoma cells have been used for decades as a cell-based model of dopaminergic neurons to explore the underlying science of cellular and molecular mechanisms of neurodegeneration in Parkinson’s disease (PD). However, data revealing the protein expression changes in 6-OHDA induced cytotoxicity in differentiated SH-SY5Y cells remain void. Therefore, we investigated the differentially regulated proteins expressed in terminally differentiated SH-SY5Y cells (differ-SH-SY5Y neural cells) exposed to 6-hydroxydopamine (6-OHDA) using the LC–MS/MS technology and construed the data using the online bioinformatics databases such as PANTHER, STRING, and KEGG. Our studies demonstrated that the neuronal development in differ-SH-SY5Y neural cells was indicated by the overexpression of proteins responsible for neurite formations such as calnexin (CANX) and calreticulin (CALR) besides significant downregulation of ribosomal proteins. The enrichment of the KEGG ribosome pathway was detected with significant downregulation (p < 0.05) of all the 21 ribosomal proteins in differ-SH-SY5Y neural cells compared with undifferentiated cells. Whereas in the PD model, the pathological changes induced by 6-OHDA were indicated by the presence of unfolded and misfolded proteins, which triggered the response of 10 kDa heat shock proteins (HSP), namely HSPE1 and HSPA9. Moreover, the 6-OHDA-induced neurodegeneration in differ-SH-SY5Y neural cells also upregulated the voltage-dependent anion-selective channel protein 1 (VDAC1) protein and enriched the KEGG systemic lupus erythematosus (SLE) pathway that was regulated by 17 histone proteins (p < 0.05) in differ-SH-SY5Y neural cells. These results suggest that the nucleosomal degradation pathway may have regulated the 6-OHDA induced neurodegeneration in PD cell-based model, which is reflected by increased apoptosis and histone release in differ-SH-SY5Y neural cells.

The Cross-Links of Endoplasmic Reticulum Stress, Autophagy, and Neurodegeneration in Parkinson's Disease

Parkinson’s disease (PD) is the most common neurodegenerative movement disorder, and it is characterized by the selective loss of dopaminergic (DA) neurons in the substantia nigra pars compacta (SNpc), as well as the presence of intracellular inclusions with α-synuclein as the main component in surviving DA neurons. Emerging evidence suggests that the imbalance of proteostasis is a key pathogenic factor for PD. Endoplasmic reticulum (ER) stress-induced unfolded protein response (UPR) and autophagy, two major pathways for maintaining proteostasis, play important roles in PD pathology and are considered as attractive therapeutic targets for PD treatment. However, although ER stress/UPR and autophagy appear to be independent cellular processes, they are closely related to each other. In this review, we focused on the roles and molecular cross-links between ER stress/UPR and autophagy in PD pathology. We systematically reviewed and summarized the most recent advances in regulation of ER stress/UPR and autophagy, and their cross-linking mechanisms. We also reviewed and discussed the mechanisms of the coexisting ER stress/UPR activation and dysregulated autophagy in the lesion regions of PD patients, and the underlying roles and molecular crosslinks between ER stress/UPR activation and the dysregulated autophagy in DA neurodegeneration induced by PD-associated genetic factors and PD-related neurotoxins. Finally, we indicate that the combined regulation of ER stress/UPR and autophagy would be a more effective treatment for PD rather than regulating one of these conditions alone.

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.

The antidiabetic drug troglitazone protects against PrP (106‑126)‑induced neurotoxicity via the PPARγ‑autophagy pathway in neuronal cells

Prion diseases, which involve the alteration of cellular prion protein into a misfolded isoform, disrupt the central nervous systems of humans and animals alike. Prior research has suggested that peroxisome proliferator-activator receptor (PPAR)γ and autophagy provide some protection against neurodegeneration. PPARs are critical to lipid metabolism regulation and autophagy is one of the main cellular mechanisms by which cell function and homeostasis is maintained. The present study examined the effect of troglitazone, a PPARγ agonist, on autophagy flux in a prion peptide (PrP) (106–126)-mediated neurodegeneration model. Western blot analysis confirmed that treatment with troglitazone increased LC3-II and p62 protein expression, whereas an excessive increase in autophagosomes was verified by transmission electron microscopy. Troglitazone weakened PrP (106–126)-mediated neurotoxicity via PPARγ activation and autophagy flux inhibition. A PPARγ antagonist blocked PPARγ activation as well as the neuroprotective effects induced by troglitazone treatment, indicating that PPARγ deactivation impaired troglitazone-mediated protective effects. In conclusion, the present study demonstrated that troglitazone protected primary neuronal cells against PrP (106–126)-induced neuronal cell death by inhibiting autophagic flux and activating PPARγ signals. These results suggested that troglitazone may be a useful therapeutic agent for the treatment of neurodegenerative disorders and prion diseases.

AdipoRon Treatment Induces a Dose-Dependent Response in Adult Hippocampal Neurogenesis

AdipoRon, an adiponectin receptor agonist, elicits similar antidiabetic, anti-atherogenic, and anti-inflammatory effects on mouse models as adiponectin does. Since AdipoRon can cross the blood-brain barrier, its chronic effects on regulating hippocampal function are yet to be examined. This study investigated whether AdipoRon treatment promotes hippocampal neurogenesis and spatial recognition memory in a dose-dependent manner. Adolescent male C57BL/6J mice received continuous treatment of either 20 mg/kg (low dose) or 50 mg/kg (high dose) AdipoRon or vehicle intraperitoneally for 14 days, followed by the open field test to examine anxiety and locomotor activity, and the Y maze test to examine hippocampal-dependent spatial recognition memory. Immunopositive cell markers of neural progenitor cells, immature neurons, and newborn cells in the hippocampal dentate gyrus were quantified. Immunosorbent assays were used to measure the serum levels of factors that can regulate hippocampal neurogenesis, including adiponectin, brain-derived neurotrophic factor (BDNF), and corticosterone. Our results showed that 20 mg/kg AdipoRon treatment significantly promoted hippocampal cell proliferation and increased serum levels of adiponectin and BDNF, though there were no effects on spatial recognition memory and locomotor activity. On the contrary, 50 mg/kg AdipoRon treatment impaired spatial recognition memory, suppressed cell proliferation, neuronal differentiation, and cell survival associated with reduced serum levels of BDNF and adiponectin. The results suggest that a low-dose AdipoRon treatment promotes hippocampal cell proliferation, while a high-dose AdipoRon treatment is detrimental to the hippocampus function.

Regulation of AKT/AMPK signaling, autophagy and mitigation of apoptosis in Rutin-pretreated SH-SY5Y cells exposed to MPP. Metab Brain Dis 2021;36:315-326. [PMID: 33146846 DOI: 10.1007/s11011-020-00641-z]

Accumulating evidence suggest that apoptosis, autophagy and dysregulation of signaling pathways are common mechanisms involved in Parkinson's disease (PD) pathogenesis, and thus development of therapeutic agents targeting these mechanisms may be useful for the treatment of this disease. Although rutin (a bioflavonoid) is reported to have pharmacological benefits such as antioxidant, anti-inflammatory and antitumor activities, there are very few reports on the activity of this compound in 1-methyl-4-phenylpyridinium (MPP⁺)-induced PD models. Accordingly, we investigated the effects of rutin on apoptosis, autophagy and cell signaling markers (AKT/AMPK) in SH-SY5Y cells exposed to MPP⁺. Results show reduced changes in nuclear morphology and mitigation of caspase 3/7 and 9 activities in rutin pre-treated cells exposed to MPP⁺. Likewise, rutin regulated cell signaling pathways (AKT/AMPK) and significantly decreased protein expression levels of cleaved PARP, cytochrome c, LC3-II and p62. Also, rutin significantly increased protein expression levels of full-length caspase 3 in SH-SY5Y cells treated with MPP⁺. Transmission electron microscope (TEM) images demonstrated a reduction in autophagosomes in rutin-pretreated SH-SY5Y cells exposed to MPP⁺. These results provide experimental support for rutin's neuroprotective activity against MPP⁺-induced toxicity in SH-SY5Y cells, which is as a promising therapeutic agent for clinical trials in humans.

Inhibition of the antioxidant enzyme PRDX1 activity promotes MPP+-induced death in differentiated SH-SY5Y cells and may impair its colocalization with eEF1A2

AIM

eEF1A2 is highly expressed in postmitotic cells and has been reported to interact with the antioxidant enzyme peroxiredoxin 1 (PRDX1). PRDX1 is involved in motor neuron differentiation. Here, we studied the relationship between eEF1A2 and PRDX1 during dopaminergic neuron differentiation, and examined their possible association in an oxidative stress model of Parkinson's disease (PD).

MAIN METHODS

Expression of eEF1A2 and PRDX1 in SH-SY5Y cells at various durations of retinoic acid (RA) induction was detected using qRT-PCR, Western blotting and immunofluorescence. Neurons of 10-day differentiation were treated with the PRDX1 inhibitor H7, MPP⁺ and H7 plus MPP⁺. The cell viability, the amounts of apoptotic nuclei, DHE signals, and the expression of p53, p-Akt and p-mTOR were determined. The colocalization of eEF1A2 and PRDX1 was visualized using confocal microscopy.

KEY FINDINGS

eEF1A2 gradually increased after RA-induced differentiation of SH-SY5Y cells, while PRDX1 protein gradually decreased. MPP⁺ treatment increased eEF1A2 in both undifferentiated and differentiated neurons; however, PRDX1 appeared to elevate only in mature neurons. The inhibition of the PRDX1 activity with H7 promoted MPP⁺-induced cell death, as evidenced by decreased cell viability, increased apoptotic nuclei, increased the DHE signal, and increased p53. However, H7 induced the activation of the prosurvival Akt and mTOR in MPP⁺-treated cells. Besides, a colocalization of eEF1A2 and PRDX1 was evidenced in MPP⁺-treated neurons. This colocalization was possibly prevented by inhibiting the PRDX1 activity, resulting in aggravated neuronal death.

SIGNIFICANCE

Our results suggest that the possible association between eEF1A2 and PRDX1 may be a promising target for modifying neuronal death in PD.

Molecular mechanisms of apoptosis and autophagy elicited by combined treatment with oridonin and cetuximab in laryngeal squamous cell carcinoma

Combined oridonin (ORI), a natural and safe kaurene diterpenoid isolated from Rabdosia rubescens, and cetuximab (Cet), an anti-EGFR monoclonal antibody, have been reported to exert synergistic anti-tumor effects against laryngeal squamous cell carcinoma (LSCC) both in vitro and in vivo by our group. In the present study, we further found that ORI/Cet treatment not only resulted in apoptosis but also induced autophagy. AMPK/mTOR signaling pathway was found to be involved in the activation of autophagy in ORI/Cet-treated LSCC cells, which is independent of p53 status. Additionally, chromatin immunoprecipitation (ChIP) assay showed that ORI/Cet significantly increased the binding NF-κB family member p65 with the promotor of BECN 1, and p65-mediated up-regulation of BECN 1 caused by ORI/Cet is coupled to increased autophagy. On the other hand, we demonstrated that either Beclin 1 SiRNA or autophagy inhibitors could increase ORI/Cet induced-apoptosis, indicating that autophagy induced by combination of the two agents plays a cytoprotective role. Interestingly, 48 h after the combined treatment, autophagy began to decrease but apoptosis was significantly elevated. Our findings suggest that autophagy might be strongly associated with the antitumor efficacy of ORI/Cet, which may be beneficial to the clinical application of ORI/Cet in LSCC treatment.

TMP21 regulates autophagy by modulating ROS production and mTOR activation

Autophagy is a catabolic cellular response to stress that has been liked to various human diseases. However, the precise involvement of autophagy in health and disease remains unclear. To explore the molecular mechanisms of autophagy, we investigated the effect of TMP21. We found that the down-regulation of TMP21 induced autophagy in SH-SY5Y cells. In addition, the enhanced autophagy observed upon TMP21 depletion was almost completely blocked in ATG5 knockout (KO) or ATG7-KO HeLa cells. Silencing of TMP21 in SH-SY5Y cells also increased the production of cellular reactive oxygen species (ROS). Accordingly, treatment with the ROS scavenger NAC suppressed autophagy activation as well as ROS production in TMP21-depleted cells. In addition, the inhibition of mTOR by treatment with Torin1 was mitigated in TMP21 overexpressing cells compared with that in control cells. Taken together, these results indicated that TMP21 could regulate autophagy by modulating ROS production and mTOR activation.

α-Arbutin Protects Against Parkinson's Disease-Associated Mitochondrial Dysfunction In Vitro and In Vivo

Parkinson's disease (PD), the most common neurodegenerative movement disorder, is characterized by the progressive loss of dopaminergic neurons in substantia nigra. The underlying mechanisms of PD pathogenesis have not been fully illustrated and currently PD remains incurable. Accumulating evidences suggest that mitochondrial dysfunction plays pivotal role in the dopaminergic neuronal death. Therefore, discovery of novel and safe agent for rescuing mitochondrial dysfunction would benefit PD treatment. Here we demonstrated for the first time that α-Arbutin (Arb), a natural polyphenol extracted from Ericaceae species, displayed significant protective effect on the rotenone (Rot)-induced mitochondrial dysfunction and apoptosis of human neuroblastoma cell (SH-SY5Y). We further found that the neuroprotective effect of Arb was associated with ameliorating oxidative stress, stabilizing of mitochondrial membrane potential, and enhancing adenosine triphosphate production. To investigate the underlying mechanism, we checked the AMP-activated protein kinase and autophagy pathway and we found that both were involved in the neuroprotection of Arb. Moreover, we explored the protective effect of Arb in drosophila PD model and found that Arb rescued parkin deficiency-induced motor function disability and mitochondrial abnormality of drosophila. Taken together, our study demonstrated that Arb got excellent neuroprotective effect on PD models both in vitro and in vivo and Arb might serve as a potent therapeutic agent for the treatment of PD.

MeHg-induced autophagy via JNK/Vps34 complex pathway promotes autophagosome accumulation and neuronal cell death

Methylmercury (MeHg), an environmental toxin, may specifically cause neurological disorders. Recent studies have reported that autophagy can be induced by metals and be involved in metal cytotoxicity. However, the role of autophagy in MeHg-induced neurotoxicity remains unknown. Here, we demonstrate that MeHg induces mTOR-independent autophagy through JNK/Vps34 complex pathway, which further promotes autophagosome accumulation and neuronal cell death. In addition to cell death, MeHg increased LC3-II expression in a concentration- and time-dependent manner in neuronal cells; furthermore, western blot analysis of LC3-II expression under baf A1-treated condition indicates that MeHg activates autophagy induction. However, we found lysosomal degradative function was impaired by MeHg. Under this condition, MeHg-activated autophagy induction would elicit autophagosome accumulation and cell death. Consistent with this inference, the autophagy inhibitor decreased the MeHg-induced autophagosome accumulation and neuronal cells death, whereas the autophagy inducers further augmented MeHg cytotoxicity. Then, the mechanism of autophagy induction is investigated. We show that MeHg-induced autophagy is mTOR-independent. Vacuolar protein sorting 34 (Vps34) complex is critical for mTOR-independent autophagy. MeHg induced the interaction between Beclin1 and Vps34 to form Vps34 complex. Importantly, knockdown of Vps34 inhibited autophagy induction by MeHg. Furthermore, we found that JNK, but not p38 or ERK, promoted the formation of Vps34 complex and autophagy induction. Finally, inhibition of JNK or downregulation of Vps34 decreased autophagosome accumulation and alleviated MeHg-induced neuronal cell death. The present study implies that inhibiting JNK/Vps34 complex autophagy induction pathway may be a novel therapeutic approach for the treatment of MeHg-induced neurotoxicity.

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.

Apelin-36 exerts the cytoprotective effect against MPP+-induced cytotoxicity in SH-SY5Y cells through PI3K/Akt/mTOR autophagy pathway

AIMS

Parkinson's disease (PD) is a common neurodegenerative disease typically associated with the accumulation of α-synuclein. Autophagy impairment is thought to be involved in the dopaminergic neurodegeneration in PD. We investigate the effect of Apelin-36 on the activated phosphatidylinositol 3-kinase (PI3K)/protein kinase B(Akt)/the mammalian target of rapamycin (mTOR) autophagy pathway in 1-methyl-4-phenylpyridinium (MPP⁺)-treated SH-SY5Y cells, which is involved in the cytoprotective effect of Apelin-36.

MAIN METHODS

SH-SY5Y cells were treated with 1-Methyl-4-phenylpyridine (MPP⁺) with or without Apelin-36. The cell viability, apoptotic ratio, the form of autophagic vacuoles, the expression of tyrosine hydroxylase (TH), α-synuclein, phosphorylation of PI3K, AKT, mTOR, microtubule-associated protein 1 Light Chain 3 II/I (LC3II/I) and p62 were detected to investigate the neuroprotective effect of Apelin-36.

KEY FINDINGS

The results indicate that Apelin-36 significantly improved the cell viability and decreased the apoptosis in MPP⁺-treated SH-SY5Y cells. The decreased expression of tyrosine hydroxylase (TH) induced by MPP⁺ was significantly increased by Apelin36 pretreatment. Moreover, Apelin36 significantly increased the autophagic vacuoles. The ratio of LC3II/I was significantly increased by Apelin36, as well as the decreased p62 expression. In addition, the activated PI3K/AKT/mTOR pathway induced by MPP⁺ was significantly inhibited by Apelin36. Additionally, Apelin36 significantly decreased the α-synuclein expression. Furthermore, the cytoprotective effect of Apelin-36 was weakened by pretreatment with Insulin-like Growth Factor-1 (IGF-1), an activator of PI3K/Akt, and MHY1485, an mTOR activator.

SIGNIFICANCE

Our results demonstrated that Apelin-36 protects against MPP⁺-induced cytotoxicity through PI3K/Akt/mTOR autophagy pathway in PD model in vitro, which provides a new theoretical basis for the treatment of PD.

Axin-2 knockdown promote mitochondrial biogenesis and dopaminergic neurogenesis by regulating Wnt/β-catenin signaling in rat model of Parkinson's disease

Wnts and the components of Wnt/β-catenin signaling are widely expressed in midbrain and required to control the fate specification of dopaminergic (DAergic) neurons, a neuronal population that specifically degenerate in Parkinson's disease (PD). Accumulating evidence suggest that mitochondrial dysfunction plays a key role in pathogenesis of PD. Axin-2, a negative regulator of Wnt/β-catenin signaling affects mitochondrial biogenesis and death/birth of new DAergic neurons is not fully explored. We investigated the functional role of Axin-2/Wnt/β-catenin signaling in mitochondrial biogenesis and DAergic neurogenesis in 6-hydroxydopamine (6-OHDA) induced rat model of PD-like phenotypes. We demonstrate that single unilateral injection of 6-OHDA into the medial forebrain bundle (MFB) potentially dysregulates Wnt/β-catenin signaling in substantia nigra pars compacta (SNpc). We used shRNA lentiviruses to genetically knockdown Axin-2 to up-regulate Wnt/β-catenin signaling in SNpc in parkinsonian rats. Genetic knockdown of Axin-2 up-regulates Wnt/β-catenin signaling by destabilizing the β-catenin degradation complex in SNpc in parkinsonian rats. Axin-2 shRNA mediated activation of Wnt/β-catenin signaling improved behavioural functions and protected the nigral DAergic neurons by increasing mitochondrial functionality in parkinsonian rats. Axin-2 shRNA treatment reduced apoptotic signaling, autophagy and ROS generation and improved mitochondrial membrane potential which promotes mitochondrial biogenesis in SNpc in parkinsonian rats. Interestingly, Axin-2 shRNA-mediated up-regulation of Wnt/β-catenin signaling enhanced net DAergic neurogenesis by regulating proneural genes (Nurr-1, Pitx-3, Ngn-2, and NeuroD1) and mitochondrial biogenesis in SNpc in parkinsonian rats. Therefore, our data suggest that pharmacological/genetic manipulation of Wnt signaling that enhances the endogenous regenerative capacity of DAergic neurons may have implication for regenerative approaches in PD.

Inhibition of Autophagy by Captopril Attenuates Prion Peptide-Mediated Neuronal Apoptosis via AMPK Activation

Accumulation of prion protein (PrPc) into a protease-resistant form (PrPsc) in the brains of humans and animals affects the central nervous system. PrPsc occurs only in mammals with transmissible prion diseases. Prion protein refers to either the infectious pathogen itself or the main component of the pathogen. Recent studies suggest that autophagy is one of the major functions that keep cells alive and which has a protective effect against neurodegeneration. In this study, we investigated whether the anti-hypertensive drug, captopril, could attenuate prion peptide PrP (106-126)-induced calcium alteration-mediated neurotoxicity. Treatment with captopril increased both LC3-II (microtubule-associated protein 1A/1B-light chain 3-II) and p62 protein levels, indicating autophagy flux inhibition. Electron microscopy confirmed the occurrence of autophagic flux inhibition in neuronal cells treated with captopril. Captopril attenuated PrP (106-126)-induced neuronal cell death via AMPK activation and autophagy inhibition. Compound C suppressed AMPK activation as well as the neuroprotective effects of captopril. Thus, these data showed that an anti-hypertensive drug has a protective effect against prion-mediated neuronal cell death via autophagy inhibition and AMPK activation, and also suggest that anti-hypertensive drugs may be effective therapeutic agents against neurodegenerative disorders, including prion diseases.

6-Hydroxydopamine induces secretion of PARK7/DJ-1 via autophagy-based unconventional secretory pathway

PARK7/DJ-1 is a Parkinson disease- and cancer-associated protein that functions as a multifunctional protein involved in gene transcription regulation and anti-oxidative defense. Although PARK7 lacks the secretory signal sequence, it is secreted and plays important physiological and pathophysiological roles. Whereas secretory proteins that lack the endoplasmic reticulum-targeting signal sequence are secreted from cells by way of what is called the unconventional secretion mechanism, the specific processes responsible for causing PARK7 to be secreted across the plasma membrane have remained unclear. In the present study, we found that PARK7 secretion was increased by treatment with 6-OHDA via the unconventional secretory pathway in human neuroblastoma SH-SY5Y cells and MEF cells. We also found that 6-OHDA-induced PARK7 secretion was suppressed in Atg5-, Atg9-, or Atg16l1-deficient MEF cells or ATG16L1 knockdown SH-SY5Y cells, indicating that the autophagy-based unconventional secretory pathway is involved in PARK7 secretion. We moreover observed that 6-OHDA-derived electrophilic quinone induced oxidative stress as indicated by a decrease in glutathione levels, and that this was suppressed by pretreatment with antioxidant NAC. We further found that NAC treatment suppressed autophagy and PARK7 secretion. We also observed that 6-OHDA-induced autophagy was associated with activation of AMPK and ULK1 via a pathway which was independent of MTOR. Collectively these results suggest that electrophilic 6-OHDA quinone enhances oxidative stress, and that this is followed by AMPK-ULK1 pathway activation and induction of secretory autophagy to produce unconventional secretion of PARK7.

Abbreviations: 6-OHDA: 6-hydroxydopamine; AMPK: AMP-activated protein kinase; ATG: autophagy related; CAV1: caveolin 1; ER: endoplasmic reticulum; FN1: fibronectin 1; GSH: glutathione; IDE: insulin degrading enzyme; IL: interleukin; LDH: lactate dehydrogenase; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MEF: mouse embryonic fibroblast; MTOR: mechanistic target of rapamycin kinase; NAC: N-acetyl-L-cysteine; PARK7/DJ-1: Parkinsonism associated deglycase; PD: Parkinson disease; RPS6KB1/p70S6K: ribosomal protein S6 kinase B1; RPN1: ribophorin I; ROS: reactive oxygen species; ULK1: unc-51 like autophagy activating kinase 1; WT: wild-type

Metformin treatment prevents amyloid plaque deposition and memory impairment in APP/PS1 mice

Alzheimer'sdisease(AD) is characterized by deposition of amyloid-β (Aβ)plaques, neurofibrillary tangles, andneuronal loss, accompaniedbyneuroinflammation. Neuroinflammatoryprocesses are thought to contribute toAD pathophysiology. Metformin has been reported to have anti-inflammatory efficacy. However, whether metformin is responsible for the anti-neuroinflammationand neuroprotection on APPswe/PS1ΔE9 (APP/PS1) mice remains unclear. Here we showed that metformin attenuated spatial memory deficit, neuron loss in the hippocampus and enhanced neurogenesis in APP/PS1 mice. In addition, metformin administration decreased amyloid-β (Aβ)plaque load and chronic inflammation (activated microglia and astrocytes as well as pro-inflammatory mediators) in the hippocampus and cortex. Further study demonstrated that treatment with metformin enhanced cerebral AMPK activation. Meanwhile, metformin notably suppressed the activation of P65 NF-κB, mTOR and S6K, reduced Bace1 protein expression. Our data suggest that metformin can exert functional recovery of memory deficits and neuroprotective effect on APP/PS1 mice via triggering neurogenesis and anti-inflammation mediated by regulating AMPK/mTOR/S6K/Bace1 and AMPK/P65 NF-κB signaling pathways in the hippocampus, which may contribute to improvement in neurological deficits.

Overexpression of miR‑185 inhibits autophagy and apoptosis of dopaminergic neurons by regulating the AMPK/mTOR signaling pathway in Parkinson's disease

Parkinson's disease (PD) is an age-associated neurodegenerative disorder characterized by the death of dopaminergic neurons in the substantia nigra pars compacta. Activation of 5′-adenosine monophosphate-activated protein kinase (AMPK) has been suggested to be associated with PD pathogenesis. The aim of the present study was to investigate the effects of the aberrant expression of microRNA-185 (miR-185) in PD. A 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced in vitro model of PD was generated using the human SH-SY5Y dopaminergic neuroblastoma cell line, in order to examine the potential molecular mechanisms underlying the roles of miR-185 in PD. miR-185 expression was assessed in MPTP-treated SH-SY5Y cells using reverse transcription-quantitative polymerase chain reaction (RT-qPCR). In addition, MPTP-treated SH-SY5Y cells were transfected with a miR-185 mimic or scramble miRNA, and flow cytometry was used to evaluate the level of cellular apoptosis. The expression of autophagy markers, including Beclin 1, microtubule-associated protein light chain 3 (LC3) I and LC3II, as well as key molecules involved in the AMPK/mechanistic target of rapamycin (mTOR) signaling pathway, such as phosphorylated (p)-AMPK and p-mTOR, was examined using RT-qPCR and western blot analyses. In addition, SH-SY5Y cells were treated with the AMPK inhibitor, Compound C, and its effects on cellular apoptosis were assessed. The results demonstrated that miR-185 was significantly downregulated in SH-SY5Y cells treated with MPTP at concentrations of >100 µM when compared with untreated controls. Following transfection with a miR-185 mimic, miR-185 expression in SH-SY5Y cells was significantly increased when compared with blank control cells. Notably, miR-185 overexpression was revealed to significantly reduce the MPTP-induced increase in cellular apoptosis. In addition, the expression levels of Beclin 1, LC3I/II, p-AMPK and p-mTOR were significantly upregulated in MPTP-treated SH-SY5Y cells; whereas miR-185 overexpression significantly downregulated the expression of these factors. Furthermore, miR-185 overexpression significantly suppressed apoptosis of SH-SY5Y cells treated with MPTP plus Compound C when compared with the Compound C group. In conclusion, the results of the present study suggest that overexpression of miR-185 may inhibit autophagy and apoptosis of dopaminergic cells in PD potentially via regulation of the AMPK/mTOR signaling pathway. Therefore, AMPK/mTOR-mediated autophagy and apoptotic signaling pathways may be potential novel therapeutic targets for the development of alternative strategies for the treatment of patients with PD.

The involvement of autophagy and cytoskeletal regulation in TDCIPP-induced SH-SY5Y cell differentiation

Exposure and toxicity to organophosphate-based flame retardants are an increasing health concern. Neurons appear to be particularly vulnerable to the effects of these chemicals. For example, in vitro studies have shown that tris(1,3-dichloro-2-propyl) phosphate (TDCIPP) induces apoptosis and autophagy in neural cells. In the present study, we investigated the cell biological mechanisms of TDCIPP-induced neurotoxicity using undifferentiated human SH-SY5Y neuroblastoma cells as a model. Interestingly, TDCIPP treatment promoted differentiation in SH-SY5Y cells, which displayed various alterations including neurite elongation, an expansion of the numbers of neurite-bearing cells, and an increase in expression of cytoskeletal components normally enriched in neurons. Furthermore, the upregulation of microtubule-associated protein light chain 3, the degradation of p62/sequestosome 1, and the formation of autophagosomes occurred in treated cells, suggesting that TDCIPP exposure induces autophagy. However, pretreatment with the autophagy inhibitor 3-methyladenine suppressed TDCIPP-induced autophagy and reduced expression of the aforementioned cytoskeletal components. This correlated with a reduction in neurite outgrowth and numbers of neurite-bearing cells. Taken together, these results indicate that autophagy might promote TDCIPP-induced SH-SY5Y cell differentiation, which leads to an increase in expression of cytoskeletal components and neurite outgrowth. This study offers key insights into the mechanisms of neurotoxicity associated with this commonly used organophosphate.

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.

Tris (1,3-dichloro-2-propyl) phosphate-induced apoptotic signaling pathways in SH-SY5Y neuroblastoma cells

Tris (1, 3-dichloro-2-propyl) phosphate (TDCIPP, also known as TDCPP), an extensively used flame retardant, is frequently detected in the environment and biota. Recent studies have shown that TDCIPP has neurotoxic effects. In this study, we determined the mechanisms of TDCIPP-induced neurotoxicity in human neuroblastoma (SH-SY5Y) cells. By using morphological examination, flow cytometry, and mitochondrial membrane potential (ΔYm) measurement, we confirmed that exposure to TDCIPP caused apoptosis accompanied by the activation of apoptosis-related genes (e.g. Bax and Bcl-2) and caspase 3 protein in SH-SY5Y cells. Increased reactive oxygen species (ROS) formation and intracellular calcium ions ([Ca²⁺]_i) were also observed in TDCIPP-treated SH-SY5Y cells. Exposure to TDCIPP led to the activation of protein markers of endoplasmic reticulum (ER) stress, including eukaryotic translation initiation factor 2a subunit (p-EIF2a), activation transcription factor (ATF4), glucose-regulated protein (GRP78), and the proapoptotic factor C/EBP homologous protein (CHOP). To determine the role of the ER in apoptosis, phenyl butyric acid (PBA), an ER stress inhibitor, was applied. Treatment with PBA effectively attenuated TDCIPP-induced ER stress and protected against apoptotic death in SH-SY5Y cells by inhibition of Bax expression and promotion of Bcl-2 expression. Furthermore, we found that pretreatment of the cells with the ROS scavenger N-acetyl cysteine (NAC) inhibited the ER stress response and prevented apoptosis. The combination of PBA and NAC pretreatment could further prevent TDCIPP induced ER-stress and apoptotic death compared with PBA or NAC pretreatment alone. Thus, in the present study, we demonstrated that TDCIPP induces cytotoxicity through a ROS-dependent mechanism involving ER stress and activation of mitochondrial apoptotic pathways in SH-SY5Y cells.

N-Acetylcysteine in Combination with IGF-1 Enhances Neuroprotection against Proteasome Dysfunction-Induced Neurotoxicity in SH-SY5Y Cells

Ubiquitin proteasome system (UPS) dysfunction has been implicated in the development of many neuronal disorders, including Parkinson's disease (PD). Previous studies focused on individual neuroprotective agents and their respective abilities to prevent neurotoxicity following a variety of toxic insults. However, the effects of the antioxidant N-acetylcysteine (NAC) on proteasome impairment-induced apoptosis have not been well characterized in human neuronal cells. The aim of this study was to determine whether cotreatment of NAC and insulin-like growth factor-1 (IGF-1) efficiently protected against proteasome inhibitor-induced cytotoxicity in SH-SY5Y cells. Our results demonstrate that the proteasome inhibitor, MG132, initiates poly(ADP-ribose) polymerase (PARP) cleavage, caspase 3 activation, and nuclear condensation and fragmentation. In addition, MG132 treatment leads to endoplasmic reticulum (ER) stress and autophagy-mediated cell death. All of these events can be attenuated without obvious reduction of MG132 induced protein ubiquitination by first treating the cells with NAC and IGF-1 separately or simultaneously prior to exposure to MG132. Moreover, our data demonstrated that the combination of the two proved to be significantly more effective for neuronal protection. Therefore, we conclude that the simultaneous use of growth/neurotrophic factors and a free radical scavenger may increase overall protection against UPS dysfunction-mediated cytotoxicity and neurodegeneration.

Mild mitochondrial metabolic deficits by α-ketoglutarate dehydrogenase inhibition cause prominent changes in intracellular autophagic signaling: Potential role in the pathobiology of Alzheimer's disease

Brain activities of the mitochondrial enzyme α-ketoglutarate dehydrogenase complex (KGDHC) are reduced in Alzheimer's disease and other age-related neurodegenerative disorders. The goal of the present study was to test the consequences of mild impairment of KGDHC on the structure, protein signaling and dynamics (mitophagy, fusion, fission, biogenesis) of the mitochondria. Inhibition of KGDHC reduced its in situ activity by 23-53% in human neuroblastoma SH-SY5Y cells, but neither altered the mitochondrial membrane potential nor the ATP levels at any tested time-points. The attenuated KGDHC activity increased translocation of dynamin-related protein-1 (Drp1) and microtubule-associated protein 1A/1B-light chain 3 (LC3) from the cytosol to the mitochondria, and promoted mitochondrial cytochrome c release. Inhibition of KGDHC also increased the negative surface charges (anionic phospholipids as assessed by Annexin V binding) on the mitochondria. Morphological assessments of the mitochondria revealed increased fission and mitophagy. Taken together, our results suggest the existence of the regulation of the mitochondrial dynamism including fission and fusion by the mitochondrial KGDHC activity via the involvement of the cytosolic and mitochondrial protein signaling molecules. A better understanding of the link among mild impairment of metabolism, induction of mitophagy/autophagy and altered protein signaling will help to identify new mechanisms of neurodegeneration and reveal potential new therapeutic approaches.

Adoptive Autophagy Activation: a Much-Needed Remedy Against Chemical Induced Neurotoxicity/Developmental Neurotoxicity

The profound significance of autophagy as a cell survival mechanism under conditions of metabolic stress is a well-proven fact. Nearly a decade-long research in this area has led scientists to unearth various roles played by autophagy other than just being an auto cell death mechanism. It is implicated as a vital cell survival pathway for clearance of all the aberrant cellular materials in case of cellular injury, metastasis, disease states, cellular stress, neurodegeneration and so on. In this review, we emphasise the critical role of autophagy in the environmental stressors-induced neurotoxicity and its therapeutic implications for the same. We also attempt to shed some light on the possible protective role of autophagy in developmental neurotoxicity (DNT) which is a rapidly growing health issue of the human population at large and hence a point of rising concern amongst researchers. The intimate association between DNT and neurodegenerative disorders strongly indicates towards adopting autophagy activation as a much-needed remedy for DNT.

Comparative mRNA Expression of eEF1A Isoforms and a PI3K/Akt/mTOR Pathway in a Cellular Model of Parkinson's Disease

The PI3K/Akt/mTOR pathway is one of dysregulated pathways in Parkinson's disease (PD). Previous studies in nonneuronal cells showed that Akt regulation can be increased by eukaryotic protein elongation factor 1 alpha 2 (eEF1A2). eEF1A2 is proposed to contribute protection against apoptotic death, likely through activation of the PI3K/Akt pathway. Whether eEF1A2 plays a role in the prevention of cell death in PD has not been investigated. Recently, gene profiling on dopaminergic neurons from postmortem PD patients showed both upregulation and downregulation of some PI3K and mTOR genes. In this paper, the expression of all gene members of the PI3K/Akt/mTOR pathway in relation to those of the eEF1A isoforms in a cellular model of PD was investigated at the mRNA level. The results showed a similar trend of upregulation of genes of the eEF1A isoforms (eEF1A1 and eEF1A2) and of the PI3K (classes I–III)/Akt (Akt1, Akt2, and Akt3)/mTOR (mTORC1 and mTORC2) pathway in both nondifferentiated and differentiated SH-SY5Y dopaminergic cells treated with 1-methyl-4-phenylpyridinium (MPP⁺). Upregulation of eEF1A2, Akt1, and mTORC1 was consistent with the relative increase of eEF1A2, Akt, phospho-Akt, and mTORC1 proteins. The possible role of eEF1A isoforms in the regulation of the PI3K/Akt/mTOR pathway in PD is discussed.

Mitochondria: A Therapeutic Target for Parkinson's Disease?

Parkinson’s disease (PD) is one of the most common neurodegenerative disorders. The exact causes of neuronal damage are unknown, but mounting evidence indicates that mitochondrial-mediated pathways contribute to the underlying mechanisms of dopaminergic neuronal cell death both in PD patients and in PD animal models. Mitochondria are organized in a highly dynamic tubular network that is continuously reshaped by opposing processes of fusion and fission. Defects in either fusion or fission, leading to mitochondrial fragmentation, limit mitochondrial motility, decrease energy production and increase oxidative stress, thereby promoting cell dysfunction and death. Thus, the regulation of mitochondrial dynamics processes, such as fusion, fission and mitophagy, represents important mechanisms controlling neuronal cell fate. In this review, we summarize some of the recent evidence supporting that impairment of mitochondrial dynamics, mitophagy and mitochondrial import occurs in cellular and animal PD models and disruption of these processes is a contributing mechanism to cell death in dopaminergic neurons. We also summarize mitochondria-targeting therapeutics in models of PD, proposing that modulation of mitochondrial impairment might be beneficial for drug development toward treatment of PD.

Beclin-1-independent autophagy positively regulates internal ribosomal entry site-dependent translation of hypoxia-inducible factor 1α under nutrient deprivation

Hypoxia has been shown to induce hypoxia-inducible factor-1alpha (HIF-1α) expression to support many cellular changes required for tumor growth and metastasis. In addition to hypoxia, nutrient deprivation is another stress condition widely existing in solid tumors due to the poor blood supply. Our data showed that nutrient deprivation induces a significant HIF-1α protein expression and potentiates the HIF-1α responses of hypoxia and CoCl₂. This effect is not because of enhancement of HIF-1α stability or transcription. Rather we found it is through the cap-independent but internal ribosome entry site (IRES)-dependent translation. Notably inhibition of autophagy by si-ATG5, 3-methyladenine and chloroquine, but not si-Beclin-1, significantly reverses nutrient deprivation-induced HIF-1α responses. Furthermore, it is interesting to note the contribution of IRES activation for hypoxia-induced HIF-1α expression, however, different from nutrient starvation, si-Beclin 1 but not si-ATG5 can inhibit hypoxia-induced HIF-1α IRES activation and protein expression. Taken together, we for the first time highlight a link from alternative autophagy to cap-independent protein translation of HIF-1α under two unique stress conditions. We demonstrate Beclin 1-independent autophagy is involved to positively regulate nutrient deprivation induced-HIF-1α IRES activity and protein expression, while ATG5-independent autophagy is involved in the HIF-1 IRES activation caused by hypoxia.

Inhibition of glycogen synthase kinase-3β enhances cognitive recovery after stroke: the role of TAK1

Memory deficits are common among stroke survivors. Identifying neuroprotective agents that can prevent memory impairment or improve memory recovery is a vital area of research. Glycogen synthase kinase-3β (GSK-3β) is involved in several essential intracellular signaling pathways. Unlike many other kinases, GSK-3β is active only when dephosphorylated and activation promotes inflammation and apoptosis. In contrast, increased phosphorylation leads to reduced GSK-3β (pGSK-3β) activity. GSK-3β inhibition has beneficial effects on memory in other disease models. GSK-3β regulates both the 5'AMP-activated kinase (AMPK) and transforming growth factor-β-activated kinase (TAK1) pathways. In this work, we examined the effect of GSK-3β inhibition, both independently, in conjunction with a TAK inhibitor, and in AMPK-α2 deficient mice, after stroke to investigate mechanistic interactions between these pathways. GSK-3β inhibition was neuroprotective and ameliorated stroke-induced cognitive impairments. This was independent of AMPK signaling as the protective effects of GSK-3β inhibition were seen in AMPK deficient mice. However, GSK-3β inhibition provided no additive protection in mice treated with a TAK inhibitor suggesting that TAK1 is an upstream regulator of GSK-3β. Targeting GSK-3β could be a novel therapeutic strategy for post-stroke cognitive deficits.

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 neuroprotective role of metformin in advanced glycation end product treated human neural stem cells is AMPK-dependent

Diabetic neuronal damage results from hyperglycemia followed by increased formation of advanced glycosylation end products (AGEs), which leads to neurodegeneration, although the molecular mechanisms are still not well understood. Metformin, one of the most widely used anti-diabetic drugs, exerts its effects in part by activation of AMP-activated protein kinase (AMPK). AMPK is a critical evolutionarily conserved enzyme expressed in the liver, skeletal muscle and brain, and promotes cellular energy homeostasis and biogenesis by regulating several metabolic processes. While the mechanisms of AMPK as a metabolic regulator are well established, the neuronal role for AMPK is still unknown. In the present study, human neural stem cells (hNSCs) exposed to AGEs had significantly reduced cell viability, which correlated with decreased AMPK and mitochondria associated gene/protein (PGC1α, NRF-1 and Tfam) expressions, as well as increased activation of caspase 3 and 9 activities. Metformin prevented AGEs induced cytochrome c release from mitochondria into cytosol in the hNSCs. Co-treatment with metformin significantly abrogated the AGE-mediated effects in hNSCs. Metformin also significantly rescued hNSCs from AGE-mediated mitochondrial deficiency (lower ATP, D-loop level, mitochondrial mass, maximal respiratory function, COX activity, and mitochondrial membrane potential). Furthermore, co-treatment of hNSCs with metformin significantly blocked AGE-mediated reductions in the expression levels of several neuroprotective genes (PPARγ, Bcl-2 and CREB). These findings extend our understanding of the molecular mechanisms of both AGE-induced neuronal toxicity, and AMPK-dependent neuroprotection by metformin. This study further suggests that AMPK may be a potential therapeutic target for treating diabetic neurodegeneration.

Ghrelin augments the expressions and secretions of proinflammatory adipokines, VEGF120 and MCP-1, in differentiated 3T3-L1 adipocytes

Ghrelin is a physiological-active peptide with growth hormone-releasing activity, orexigenic activity, etc. In addition, the recent study has also suggested that ghrelin possesses the pathophysiological abilities related with type 2 diabetes. However, the ghrelin-direct-effects implicated in type 2 diabetes on peripheral tissues have been still unclear, whereas its actions on the central nervous system (CNS) appear to induce the development of diabetes. Thus, to assess its peripheral effects correlated with diabetes, we investigated the regulatory mechanisms about adipokines, which play a central role in inducing peripheral insulin resistance, secreted from mature 3T3-L1 adipocytes stimulated with ghrelin in vitro . The stimulation with 50 nmol/L ghrelin for 24 h resulted in the significant 1.9-fold increase on vascular endothelial growth factor-120 (VEGF(120)) releases (p < 0.01) and the 1.7-fold on monocyte chemoattractant protein-1 (MCP-1) (p < 0.01) from 3T3-L1 adipocytes, respectively, while ghrelin failed to enhance tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), IL-6, IL-10 and adiponectin secretions. In addition, Akt phosphorylation on Ser473 and c-Jun NH2 -terminal protein kinase (JNK) phosphorylation on Thr183/Tyr185 were markedly enhanced 1.4-fold (p < 0.01) and 1.6-fold (p < 0.01) in the ghrelin-stimulated adipocytes, respectively. Furthermore, the treatment with LY294002 (50 μmol/L) and Wortmannin (10nmol/L), inhibitors of phosphatidylinositol 3-kinase (PI3K), significantly decreased the amplified VEGF(120) secretion by 29% (p < 0.01) and 28% (p < 0.01) relative to the cells stimulated by ghrelin alone, respectively, whereas these inhibitors had no effects on increased MCP-1 release. On the other hand, JNK inhibitor SP600125 (10 μmol/L) clearly reduced the increased MCP-1, but not VEGF(120), release by 35% relative to the only ghrelin-stimulated cells (p < 0.01). In conclusion, ghrelin can enhance the secretions of proinflammatory adipokines, VEGF(120) and MCP-1, but fails to affect IL-10 and adiponectin which are considered to be anti-inflammatory adipokines. Moreover, this augmented VEGF(120) release is invited through the activation of PI3K pathways and the MCP-1 is through JNK pathways. Consequently, our results strongly suggest that ghrelin can induce the development of diabetes via its direct-action in peripheral tissues as well as via in CNS.

Sulforaphane-induced autophagy flux prevents prion protein-mediated neurotoxicity through AMPK pathway

Prion diseases are neurodegenerative and infectious disorders that involve accumulation of misfolded scrapie prion protein, and which are characterized by spongiform degeneration. Autophagy, a major homeostatic process responsible for the degradation of cytoplasmic components, has garnered attention as the potential target for neurodegenerative diseases such as prion disease. We focused on protective effects of sulforaphane found in cruciferous vegetables on prion-mediated neurotoxicity and the mechanism of sulforaphane related to autophagy. In human neuroblastoma cells, sulforaphane protected prion protein (PrP) (106-126)-mediated neurotoxicity and increased autophagy flux marker microtubule-associated protein 1 light chain 3-II protein levels, following a decrease of p62 protein level. Pharmacological and genetical inhibition of autophagy by 3MA, wortmannin and knockdown of autophagy-related 5 (ATG5) led to block the effect of sulforaphane against PrP (106-126)-induced neurotoxicity. Furthermore we demonstrated that both sulforaphane-induced autophagy and protective effect of sulforaphane against PrP (106-126)-induced neurotoxicity are dependent on the AMP-activated protein kinase (AMPK) signaling. The present results indicated that sulforaphane of cruciferous vegetables enhanced autophagy flux led to the protection effects against prion-mediated neurotoxicity, which was regulated by AMPK signaling pathways in human neuron cells. Our data also suggest that sulforaphane has a potential value as a therapeutic tool in neurodegenerative disease including prion diseases.

Novel curcumin analogue IHCH exhibits potent anti‑proliferative effects by inducing autophagy in A549 lung cancer cells

Curcumin is a natural polyphenolic compound that exhibits strong antioxidant and anticancer activities; however, low bioavailability has restricted its application in chemotherapeutic trials. The present study aimed to investigate the anticancer effect of the novel curcumin derivative 2E,6E‑2‑(1H‑indol‑3‑yl) methylene)‑6‑(4‑hydroxy‑3‑methoxy benzylidene)‑cyclohexanone (IHCH) on A549 lung cancer cells. Cells were treated with IHCH at different concentrations (1‑40 µM) for different time periods (1‑36 h). Microscopic analysis revealed that IHCH inhibited A549 cell growth and induced the formation of characteristic autophagolysosomes in a dose‑ and time‑dependent manner. Furthermore, the inhibitory rate of IHCH (40 µM) on A549 cell viability was 77.34% after 36 h of treatment. Acridine orange staining revealed an increase in autophagic vacuoles in the IHCH‑treated A549 cells. Monodansylcadaverine staining was used to analyze autophagy rate. Immunocytochemistry revealed an increase in light chain (LC) 3 protein expression in the IHCH‑treated cells and western blot analysis detected the conversion of LC3‑I to LC3‑II, as well as the recruitment of LC3 to autophagosomes in the cytoplasmatic compartment, suggesting the occurrence of autophagy. These findings show that IHCH induced autophagy in A549 cells, which is a novel cell death mechanism induced by curcumin derivatives.

The protective role of AMP-activated protein kinase in alpha-synuclein neurotoxicity in vitro

In the present study, we investigated the role of the main intracellular energy sensor, AMP-activated protein kinase (AMPK), in the in vitro neurotoxicity of α-synuclein (ASYN), one of the key culprits in the pathogenesis of Parkinson's disease. The loss of viability in retinoic acid-differentiated SH-SY5Y human neuroblastoma cells inducibly overexpressing wild-type ASYN was associated with the reduced activation of AMPK and its activator LKB1, as well as AMPK target Raptor. ASYN-overexpressing rat primary neurons also displayed lower activity of LKB1/AMPK/Raptor pathway. Restoration of AMPK activity by metformin or AICAR reduced the in vitro neurotoxicity of ASYN overexpression, acting independently of the prosurvival kinase Akt or the induction of autophagic response. The conditioned medium from ASYN-overexpressing cells, containing secreted ASYN, as well as dopamine-modified or nitrated recombinant ASYN oligomers, all inhibited AMPK activation in differentiated SH-SY5Y cells and reduced their viability, but not in the presence of metformin or AICAR. The RNA interference-mediated knockdown of AMPK increased the sensitivity of SH-SY5Y cells to the harmful effects of secreted ASYN. AMPK-dependent protection from extracellular ASYN was also observed in rat neuron-like pheochromocytoma cell line PC12. These data demonstrate the protective role of AMPK against the toxicity of both intracellular and extracellular ASYN, suggesting that modulation of AMPK activity may be a promising therapeutic strategy in Parkinson's disease.

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.

The mTOR signaling pathway in pediatric neuroblastoma

Neuroblastoma (NB) is the most common extracranial malignant solid tumors of childhood, and the majority of these high-risk tumors is resistant to nearly all the treatments and has a significantly worse outcome. The mammalian target of rapamycin (mTOR) plays a critical role in oncogenesis and cancer progression of many tumors. This review will describe the function of mTOR, its genetic regulation in pediatric neuroblastoma, and its value as a target for inhibition by anticancer agents for patients with NB.