Identification of novel Nrf2-activating neuroprotective agents: Elucidation of structural congeners of (-)-galiellalactone and congener-based novel Nrf2 activators.

Herein, (-)-galiellalactone 1 congeners responsible for the nuclear factor erythroid 2-related factor 2 (Nrf2)-activating neuroprotective effects were elucidated. Additionally, novel congener-based Nrf2 activators were identified using a drug repositioning strategy. (-)-Galiellalactone, which comprises a tricyclic lactone skeleton, significantly activates antioxidant response element (ARE)-mediated transcription in neuroblastoma SH-SY5Y cells. Interestingly, two cyclohexene-truncated [3.3] bicyclic lactone analogs, which possess an exocyclic α-methylene-γ-butyrolactone moiety, exhibited higher Nrf2/ARE transcriptional activities than the parent (-)-galiellalactone. We confirmed that the cyclohexene moiety embedding the [3.3] bicyclic lactone congener does not play the essential role of (-)-galiellalactone for Nrf2/ARE activation. Nrf2/ARE activation by novel analogs resulted in the upregulation of downstream antioxidative and phase II detoxifying enzymes, heme oxygenase-1, and NAD(P)H quinone oxidoreductase 1, which are closely related to the cytoprotective effects on neurodegenerative diseases. (-)-Galiellalactone and its [3.3] bicyclic variants 3l and 3p increased the expression of antioxidant genes and exhibited neuroprotective effects against 6-hydroxydopamine-mediated neurotoxicity in the neuroblastoma SH-SY5Y cell line.

Ursolic acid enhances autophagic clearance and ameliorates motor and non-motor symptoms in Parkinson's disease mice model.

Protein aggregation and the abnormal accumulation of aggregates are considered as common mechanisms of neurodegeneration such as Parkinson's disease (PD). Ursolic acid (UA), a natural pentacyclic triterpenoid compound, has shown a protective activity in several experimental models of brain dysfunction through inhibiting oxidative stress and inflammatory responses and suppressing apoptotic signaling in the brain. In this study, we investigated whether UA promoted autophagic clearance of protein aggregates and attenuated the pathology and characteristic symptoms in PD mouse model. Mice were injected with rotenone (1 mg · kg-1 · d-1, i.p.) five times per week for 1 or 2 weeks. We showed that rotenone injection induced significant motor deficit and prodromal non-motor symptoms accompanied by a significant dopaminergic neuronal loss and the deposition of aggregated proteins such as p62 and ubiquitin in the substantia nigra and striatum. Co-injection of UA (10 mg · kg-1 · d-1, i.p.) ameliorated all the rotenone-induced pathological alterations. In differentiated human neuroblastoma SH-SY5Y cells, two-step treatment with a proteasome inhibitor MG132 (0.25, 2.5 µM) induced marked accumulation of ubiquitin and p62 with clear and larger aggresome formation, while UA (5 µM) significantly attenuated the MG132-induced protein accumulation. Furthermore, we demonstrated that UA (5 µM) significantly increased autophagic clearance by promoting autophagic flux in primary neuronal cells and SH-SY5Y cells; UA affected autophagy regulation by increasing the phosphorylation of JNK, which triggered the dissociation of Bcl-2 from Beclin 1. These results suggest that UA could be a promising therapeutic candidate for reducing PD progression from the prodromal stage by regulating abnormal protein accumulation in the brain.

Differentiated HT22 cells as a novel model for in vitro screening of serotonin reuptake inhibitors.

The mouse hippocampal neuronal cell line HT22 is frequently used as an in vitro model to investigate the role of hippocampal cholinergic neurons in cognitive functions. HT22 cells are derived from hippocampal neuronal HT4 cells. However, whether these cells exhibit the serotonergic neuronal phenotype observed in mature hippocampal neurons has not been determined yet. In this present study, we examined whether the differentiation of HT22 cells enhances the serotonergic neuronal phenotype, and if so, whether it can be used for antidepressant screening. Our results show that differentiation of HT22 cells promoted neurite outgrowth and upregulation of N-methyl-D-aspartate receptor and choline acetyltransferase, which is similar to that observed in primary cultured hippocampal neurons. Furthermore, proteins required for serotonergic neurotransmission, such as tryptophan hydroxylase 2, serotonin (5-hydroxytryptamine, 5-HT)1a receptor, and serotonin transporter (SERT), were significantly upregulated in differentiated HT22 cells. The transcription factor Pet-1 was upregulated during HT22 differentiation and was responsible for the regulation of the serotonergic neuronal phenotype. Differentiation also enhanced the functional serotonergic properties of HT22 cells, as evidenced by increase in intracellular 5-HT levels, serotonin transporter SERT glycosylation, and 5-HT reuptake activity. The sensitivity of 5-HT reuptake inhibition by venlafaxine in differentiated HT22 cells (IC50, 27.21 nM) was comparable to that in HEK293 cells overexpressing serotonin transporter SERT (IC50, 30.65 nM). These findings suggest that the differentiation of HT22 cells enhances their functional serotonergic properties, and these cells could be a potential in vitro system for assessing the efficacy of antidepressant 5-HT reuptake inhibitors.

Ciliogenesis is Not Directly Regulated by LRRK2 Kinase Activity in Neurons.

Mutations in the Leucine-rich repeat kinase 2 (LRRK2) gene are the most prevalent cause of familial Parkinson's disease (PD). The increase in LRRK2 kinase activity observed in the pathogenic G2019S mutation is important for PD development. Several studies have reported that increased LRRK2 kinase activity and treatment with LRRK2 kinase inhibitors decreased and increased ciliogenesis, respectively, in mouse embryonic fibroblasts (MEFs) and retinal pigment epithelium (RPE) cells. In contrast, treatment of SH-SY5Y dopaminergic neuronal cells with PD-causing chemicals increased ciliogenesis. Because these reports were somewhat contradictory, we tested the effect of LRRK2 kinase activity on ciliogenesis in neurons. In SH-SY5Y cells, LRRK2 inhibitor treatment slightly increased ciliogenesis, but serum starvation showed no increase. In rat primary neurons, LRRK2 inhibitor treatment repeatedly showed no significant change. Little difference was observed between primary cortical neurons prepared from wild-type (WT) and G2019S+/- mice. However, a significant increase in ciliogenesis was observed in G2019S+/- compared to WT human fibroblasts, and this pattern was maintained in neural stem cells (NSCs) differentiated from the induced pluripotent stem cells (iPSCs) prepared from the same WT/G2019S fibroblast pair. NSCs differentiated from G2019S and its gene-corrected WT counterpart iPSCs were also used to test ciliogenesis in an isogenic background. The results showed no significant difference between WT and G2019S regardless of kinase inhibitor treatment and B27-deprivation-mimicking serum starvation. These results suggest that LRRK2 kinase activity may be not a direct regulator of ciliogenesis and ciliogenesis varies depending upon the cell type or genetic background.

Peroxisome proliferator-activated receptor gamma: a novel therapeutic target for cognitive impairment and mood disorders that functions via the regulation of adult neurogenesis.

The proliferation, differentiation, and migration of neural precursor cells occur not only during embryonic development but also within distinct regions of the adult brain through the process of adult neurogenesis. As neurogenesis can potentially regulate brain cognition and neuronal plasticity, the factors that enhance neurogenesis can be attractive therapeutic targets for improving cognitive function and regulating neurodegenerative and neuropsychiatric disorders, including affective and mood disorders. Peroxisome proliferator-activated receptors (PPARs) are a class of ligand-activated transcription factors belonging to the nuclear receptor superfamily. PPARγ is a target for insulin sensitizers and plays an essential role in regulating various metabolic processes, including adipogenesis and glucose homeostasis. Interestingly, evidence demonstrates the role of PPARγ activation in regulating neurogenesis. The pharmacological activation of PPARγ using specific ligands increases the proliferation and differentiation of neural stem cells in specific brain regions, including the hippocampus, and prevents neurodegeneration and improves cognition and anxiety/depression-like behaviors in animal models. We summarize here recent reports on the role of PPARγ in adult neurogenesis, as well as the mechanisms involved, and suggest that PPARγ can serve as a potential therapeutic target for neurological and/or neurodegenerative diseases.

Recent advances in the pathology of prodromal non-motor symptoms olfactory deficit and depression in Parkinson's disease: clues to early diagnosis and effective treatment.

Parkinson's disease (PD) is a progressive neurodegenerative disease characterized by movement dysfunction due to selective degeneration of dopaminergic neurons in the substantia nigra pars compacta. Non-motor symptoms of PD (e.g., sensory dysfunction, sleep disturbance, constipation, neuropsychiatric symptoms) precede motor symptoms, appear at all stages, and impact the quality of life, but they frequently go unrecognized and remain untreated. Even when identified, traditional dopamine replacement therapies have little effect. We discuss here the pathology of two PD-associated non-motor symptoms: olfactory dysfunction and depression. Olfactory dysfunction is one of the earliest non-motor symptoms in PD and predates the onset of motor symptoms. It is accompanied by early deposition of Lewy pathology and neurotransmitter alterations. Because of the correlation between olfactory dysfunction and an increased risk of progression to PD, olfactory testing can potentially be a specific diagnostic marker of PD in the prodromal stage. Depression is a prevalent PD-associated symptom and is often associated with reduced quality of life. Although the pathophysiology of depression in PD is unclear, studies suggest a causal relationship with abnormal neurotransmission and abnormal adult neurogenesis. Here, we summarize recent progress in the pathology of the non-motor symptoms of PD, aiming to provide better guidance for its effective management.

Amitriptyline interferes with autophagy-mediated clearance of protein aggregates via inhibiting autophagosome maturation in neuronal cells.

Amitriptyline is a tricyclic antidepressant commonly prescribed for major depressive disorders, as well as depressive symptoms associated with various neurological disorders. A possible correlation between the use of tricyclic antidepressants and the occurrence of Parkinson's disease has been reported, but its underlying mechanism remains unknown. The accumulation of misfolded protein aggregates has been suggested to cause cellular toxicity and has been implicated in the common pathogenesis of neurodegenerative diseases. Here, we examined the effect of amitriptyline on protein clearance and its relevant mechanisms in neuronal cells. Amitriptyline exacerbated the accumulation of abnormal aggregates in both in vitro neuronal cells and in vivo mice brain by interfering with the (1) formation of aggresome-like aggregates and (2) autophagy-mediated clearance of aggregates. Amitriptyline upregulated LC3B-II, but LC3B-II levels did not increase further in the presence of NH4Cl, which suggests that amitriptyline inhibited autophagic flux rather than autophagy induction. Amitriptyline interfered with the fusion of autophagosome and lysosome through the activation of PI3K/Akt/mTOR pathway and Beclin 1 acetylation, and regulated lysosome positioning by increasing the interaction between proteins Arl8, SKIP, and kinesin. To the best of our knowledge, we are the first to demonstrate that amitriptyline interferes with autophagic flux by regulating the autophagosome maturation during autophagy in neuronal cells. The present study could provide neurobiological clue for the possible correlation between the amitriptyline use and the risk of developing neurodegenerative diseases.

Electroacupuncture for chemotherapy-induced anorexia through humoral appetite regulation: A preliminary experimental study.

Chemotherapy-induced anorexia (CIA), which may lead to severe nutrition-associated problems, is a common complication associated with anti-cancer therapies. In the present study, the anti-anorexigenic effect of electroacupuncture (EA) was explored through assessing a change in appetite-associated peptides and c-Fos expression in a rat model of cisplatin-induced anorexia. In order to identify the most effective acupuncture point, 20 male Wistar rats (divided into five groups including the normal saline control, cisplatin only control and three groups according to the acupoints stimulated) were subjected to EA for 10 min at CV12, ST36 or PC6 daily for 4 days. Subsequently, the rats received intraperitoneal injections of cisplatin (6 mg/kg) to induce CIA. Food intake and reduction in body weight gain as the anorexia-associated outcomes were assessed daily for up to 3 days after cisplatin injection, and CV12 was eventually chosen as the most effective acupoint to test the anti-anorexigenic effect of EA. Furthermore, food intake, body weight and the concentrations of appetite-associated peptides, including ghrelin, cholecystokinin (CCK) and 5-hydroxytryptamine (5-HT), in addition to c-Fos expression, were comparatively assessed between the CV12 EA group (n=6; rats treated with EA at CV12 daily for 4 days) and a control group (n=6; rats without treatment). The results indicated that the CV12 EA group exhibited a better outcome regarding food intake and body weight compared with the controls. Although there was no statistically significant difference observed, the secretion of serum ghrelin and CCK was increased in the CV12 EA group compared with that in the control group. The plasma level of 5-HT after cisplatin injection in the CV12 EA group was lower compared with that in the control, although no statistical significance was reached. Although not statistically significant, the expression of c-Fos protein in the nucleus tractus solitarius (NTS) was reduced in the CV12 EA rats. In addition, the hypothalamic mRNA levels of brain-derived neurotrophic factor (BDNF) were significantly increased in the CV12 EA group. In the hypothalamus, the expression of neuropeptide Y mRNA slightly increased in the cisplatin + CV12 EA group compared with the cisplatin only control group. In conclusion, the anti-anorexigenic effect of EA on CIA may be associated with an increase in the secretion of ghrelin and CCK and a decrease in the secretion of 5-HT into the serum, a reduction of c-Fos expression in the NTS and an increase in BDNF mRNA expression in the hypothalamus.

Abnormal hippocampal neurogenesis in Parkinson's disease: relevance to a new therapeutic target for depression with Parkinson's disease.

Parkinson's disease (PD) is a common progressive neurodegenerative disorder characterized by motor dysfunction, including bradykinesia, tremor, rigidity, and postural instability. Recent clinical findings recognize PD as a complex disease with diverse neuropsychiatric complications. Depression is the most frequent non-motor psychiatric symptom experienced in PD, and it is associated with poor quality of life. While the pathophysiology of PD-associated depression is not directly related to neurodegenerative processes in the substantia nigra, underlying mechanisms remain unclear and there are few symptomatic treatments. Altered adult hippocampal neurogenesis is considered crucial for the development and treatment of depression. In genetic animal models and human postmortem studies of PD, severely impaired adult neurogenesis has been observed, with patients showing hippocampal atrophy and disrupted hippocampal neurogenesis. Because adult newborn neurons appear to exert various functions, which relate to non-motor symptoms observed in PD, there might be a close correlation between malformation of newborn neurons in the adult hippocampus and depressive symptoms. Here, we discuss current concepts regarding impaired hippocampal neurogenesis and non-motor symptoms of PD, and review PD-associated pathophysiological factors regulating neurogenesis, including inflammatory signaling and autophagy. We present a novel framework for targeting adult hippocampal neurogenesis, which could provide a promising treatment for PD-associated depression.

LRRK2 G2019S Induces Anxiety/Depression-like Behavior before the Onset of Motor Dysfunction with 5-HT1A Receptor Upregulation in Mice.

Mutations in the leucine-rich repeat kinase 2 (LRRK2) gene are the most common genetic cause of Parkinson's disease (PD). The neuropathology of LRRK2 mutation-related PD, including increased dopaminergic neurodegeneration and Lewy bodies, is indistinguishable from that of idiopathic PD. The subtle nonmotor phenotypes of LRRK2 mutation-related PD have not been fully evaluated. In the present study, we examined anxiety/depression-like behaviors and accompanying neurochemical changes in differently aged transgenic (Tg) mice expressing human mutant LRRK2 G2019S. Through multiple behavioral tests, including light-dark test, elevated plus maze, sucrose preference test, forced swimming test, and tail-suspension test, we found that anxiety/depression-like behavior appeared in middle-aged (43-52 weeks) Tg mice before the onset of PD-like motor dysfunction. These behavioral tests were performed using both male and female mice, and there were no sex-related differences in behavioral changes in the middle-aged Tg mice. Along with behavioral changes, serotonin levels also significantly declined in the hippocampus of Tg mice. Additionally, increases in the expression of the 5-HT1A receptor (5-HT1AR) grew more significant with aging and were detected in the hippocampus, amygdala, and dorsal raphe nucleus. In vitro study using the serotonergic RN46A and hippocampal HT22 cells showed that 5-HT1AR upregulation was related to enhanced expression of LRRK2 G2019S and was attenuated by the LRRK2 inhibitor LRRK2-IN-1. Wild-type LRRK2 had no significant effect on 5-HT1AR transcription. The present study provides the first in vivo and in vitro evidence demonstrating abnormal regulation of 5-HT1AR along with the manifestation of anxiety/depression-like, nonmotor symptom in PD related to LRRK2.SIGNIFICANCE STATEMENT Parkinson's disease (PD), the second most common neurodegenerative disorder, is clinically characterized by motor dysfunctions. In most cases, various nonmotor symptoms present several years before the onset of the classical motor features of PD and severely affect the quality of life of patients. Here, we demonstrate the causative role of leucine-rich repeat kinase 2 (LRRK2), a common PD-linked mutation, in the development of anxiety/depression-like behaviors. We found that age-dependent 5-HT1A receptor upregulation in the hippocampus, amygdala, and dorsal raphe nucleus is accompanied by the expression of the LRRK2 mutant phenotype. Our findings demonstrating a potential mechanism for nonmotor psychiatric symptoms produced by LRRK2 mutation suggest that directly targeting the 5-HT1A receptor can improve the therapeutic efficacy of drugs for PD-associated depression.

Alpha-Synuclein Suppresses Retinoic Acid-Induced Neuronal Differentiation by Targeting the Glycogen Synthase Kinase-3ß/ß-Catenin Signaling Pathway.

Alpha-synuclein (α-SYN) is expressed during neuronal development and is mainly involved in the modulation of synaptic transmission. Missense mutations and amplifications of this gene have been associated with the pathogenesis of Parkinson's disease. Here, we evaluate whether α-SYN plays a detrimental role in the phenotypic and morphological regulation of neurons. We also identify the underlying mechanisms of this process in all-trans-retinoic acid (RA)-induced differentiated SH-SY5Y cells, which represents dopaminergic (DAergic) phenotype. Our results indicate that overexpression of wild-type or mutant A53T α-SYN attenuated the RA-induced upregulation of tyrosine hydroxylase and dopamine transporter as well as neurite outgrowth in SH-SY5Y cells. In addition, GSK-3ß inactivation and downstream ß-catenin stabilization were associated with RA-induced differentiation, which was attenuated by α-SYN. Moreover, protein phosphatase 2A was positively regulated by α-SYN and was implicated in the α-SYN-mediated interference with RA signaling. The results obtained from SH-SY5Y cells were verified in primary cultures of mesencephalic DAergic neurons from A53T α-SYN transgenic mice, which represent high levels of α-SYN and protein phosphatase 2A in the midbrain. The number and length of neurites in tyrosine hydroxylase-positive as well as Tau-positive cells from A53T α-SYN transgenic mice were significantly lower than those in littermate controls. The current results provide novel insight into the role of α-SYN in the regulation of neuronal differentiation, including DAergic neurons. Identifying the signaling pathway involved in the α-SYN-mediated dysregulation of neuronal differentiation could lead to a better understanding of the developmental processes underlying α-SYN-related pathologies and facilitate the discovery of specifically targeted therapeutics.

LRRK2 interferes with aggresome formation for autophagic clearance.

Autosomal-dominant mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) account for the most common monogenic form of Parkinson's disease (PD). A link between autophagy dysregulation and LRRK2 has consistently been reported, but it remains poorly defined which step is targeted by LRRK2. Here, we sought to examine the effect of LRRK2 on the sequestration and degradation of aggregated protein complexes for autophagic clearance. Because two major intracellular protein degradation systems, the ubiquitin proteasome system and the autophagy, are functionally coupled, proteasome inhibition is suggested to activate autophagy. So, we induced protein quality control-associated autophagy using the proteasome inhibitor MG132 in differentiated SH-SY5Y cells and mice expressing G2019S mutant LRRK2 to uncover how the autophagy pathway is affected by LRRK2. We found that LRRK2 disrupted aggresome formation for autophagic clearance of accumulated protein aggregates. Specifically, we observed the following in differentiated SH-SY5Y cells with overexpressed wild-type and G2019S LRRK2: 1) large, clear, perinuclear aggresomes were not detected under MG132, instead, much smaller aggregates were broadly distributed in the cytosol; 2) enhanced accumulation of LC3-II and p62/ubiquitin-positive protein inclusions were noted; and 3) protein aggregates were not cleared even after a recovery period, which exacerbated the MG132-induced cytotoxicity. Notably, higher protein accumulation was detected in the brains of G2019S transgenic mice than in the brains of littermate control mice under proteasome inhibition. Our present findings provide insight into the precise mechanisms that underlie autophagy dysregulation in the brains of patients with PD with LRRK2 mutations.

Hypoxia-inducible factor-1α upregulates tyrosine hydroxylase and dopamine transporter by nuclear receptor ERRγ in SH-SY5Y cells.

Hypoxia-inducible factor-1α (HIF-1α) is a transcription factor relevant to the development of many mammalian organs including the brain. However, the molecular mechanisms by which signaling events mediate neuronal differentiation have not been fully elucidated. In the present study, we show for the first time that the orphan nuclear receptor estrogen-related receptor γ (ERRγ) is upregulated by HIF-1α and plays essential roles in HIF-1α-induced upregulation of dopaminergic marker molecules such as tyrosine hydroxylase and dopamine transporter. We found that deferoxamine upregulated HIF-1α and enhanced the dopaminergic phenotype and neurite outgrowth of SH-SY5Y cells. Deferoxamine activated transcription and protein expression of ERRγ, and deferoxamine-induced upregulation of tyrosine hydroxylase and dopamine transporter was attenuated by using the ERRγ inverse agonist or silencing ERRγ. Altogether, these results suggest that HIF-1α can positively regulate the dopaminergic phenotype through ERRγ. This study could provide new perspectives for understanding the mechanisms underlying the promotion of dopaminergic neuronal differentiation by hypoxia.

Preconditioning stimulus of proteasome inhibitor enhances aggresome formation and autophagy in differentiated SH-SY5Y cells.

The abnormal accumulation of protein aggregates is a dominant pathological feature common in neurodegenerative diseases. Autophagy contributes to the processing of aggregated proteins resistant to proteasomal degradation. Autophagic degradation is multi-step process, and especially aggresome formation is a specific and active cellular process for appropriate autophagy-mediated protein homeostasis mechanism. Here, we showed that preconditioning of cells with a non-toxic low dose of MG132 induced autophagy, using an in vitro experimental model that closely represents the characteristics of the autophagy pathway under proteasome inhibition. Clear and large aggresome-like protein accumulation was observed in the perinuclear region of differentiated SH-SY5Y cells with preconditioning stimulus. This results in up-regulation of autophagosome formation and turnover and degradation of intracellular ubiquitinated and p62-bound protein aggregates. Pretreatment with low dose of MG132 attenuated proteinopathy-related cytotoxicity. Together, our experimental model could provide a proper in vitro system for studying the autophagy-related pathophysiology of neurodegeneration, especially therapeutic targeting of intracellular aggresome-like aggregates formation.

SIRT2 interferes with autophagy-mediated degradation of protein aggregates in neuronal cells under proteasome inhibition.

Abnormal protein aggregates have been suggested as a common pathogenesis of many neurodegenerative diseases. Two well-known protein degradation pathways are responsible for protein homeostasis by balancing protein biosynthesis and degradative processes: the ubiquitin-proteasome system (UPS) and autophagy-lysosomal system. UPS serves as the primary route for degradation of short-lived proteins, but large-size protein aggregates cannot be degraded by UPS. Autophagy is a unique cellular process that facilitates degradation of bulky protein aggregates by lysosome. Recent studies have demonstrated that autophagy plays a crucial role in the pathogenesis of neurodegenerative diseases characterized by abnormal protein accumulation, suggesting that regulation of autophagy may be a valuable therapeutic strategy for the treatment of various neurodegenerative diseases. Sirtuin-2 (SIRT2) is a class III histone deacetylase that is expressed abundantly in aging brain tissue. Here, we report that SIRT2 increases protein accumulation in murine cholinergic SN56 cells and human neuroblastoma SH-SY5Y cells under proteasome inhibition. Overexpression of SIRT2 inhibits lysosome-mediated autophagic turnover by interfering with aggresome formation and also makes cells more vulnerable to accumulated protein-mediated cytotoxicity by MG132 and amyloid beta. Moreover, MG132-induced accumulation of ubiquitinated proteins and p62 as well as cytotoxicity are attenuated in siRNA-mediated SIRT2-silencing cells. Taken together, these results suggest that regulation of SIRT2 could be a good therapeutic target for a range of neurodegenerative diseases by regulating autophagic flux.

Licochalcone E activates Nrf2/antioxidant response element signaling pathway in both neuronal and microglial cells: therapeutic relevance to neurodegenerative disease.

Oxidative stress and neuroinflammation are hallmarks of neurodegenerative diseases, which do not play independently but work synergistically through complex interactions exacerbating neurodegeneration. Therefore, the mechanism that is directly implicated in controlling oxidative stress and inflammatory response could be an attractive strategy to prevent the onset and/or delay the progression of neurodegenerative diseases. The transcription factor nuclear factor-E2-related factor-2 (Nrf2) is the guardian of redox homeostasis by regulating a battery of antioxidant and phase II detoxification genes, which are relevant to defense mechanism against oxidative stress and inflammatory responses. In this study, we show that a recently identified Glycyrrhiza-inflata-derived chalcone, licochalcone E (Lico-E), attenuates lipopolysaccharide-induced inflammatory responses in microglial BV2 cells and protects dopaminergic SH-SY5Y cells from 6-hydroxydopamine cytotoxicity. Lico-E activates Nrf2-antioxidant response element (ARE) system and up-regulates downstream NAD(P)H:quinone oxidoreductase 1 (NQO1) and heme oxygenase-1 (HO-1). Anti-inflammatory and cytoprotective effects of Lico-E are attenuated in siRNA-mediated Nrf2-silencing cells as well as in the presence with specific inhibitor of HO-1 or NQO1, respectively. Lico-E also has neuroprotective effect against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-induced nigrostriatal dopaminergic neurodegeneration in mice, with up-regulation of HO-1 and NQO1 in the substantia nigra of the brain. This study demonstrates that Lico-E is a potential activator of the Nrf2/ARE-dependent pathway and is therapeutically relevant not only to oxidative-stress-related neurodegeneration but also inflammatory responses of microglial cells both in vitro and in vivo.

Aroclor1254 interferes with estrogen receptor-mediated neuroprotection against beta-amyloid toxicity in cholinergic SN56 cells.

Because estrogen plays important neurotrophic and neuroprotective roles in the brain by activating estrogen receptors (ERs), disruption of normal estrogen signaling can leave neurons vulnerable to a variety of insults, including ß-amyloid peptide (Aß). Aroclor1254 (A1254) belongs to the endocrine-disrupting chemical (EDC) polychlorinated biphenyls and has anti-estrogenic properties. In the present study, we evaluated the effect of A1254 on the protective activity of estrogen against Aß toxicity in differentiated cholinergic SN56 cells. Aged Aß25-35 causes apoptotic cell death in differentiated SN56 cells, and the cytotoxic evidences are effectively rescued by estrogen. We found that A1254 abolishes the neuroprotective activity of estrogen against Aß toxicity, and attenuates the suppressive effect of estrogen on Aß-induced tau phosphorylation and JNK activation. The effects of A1254 on the neuroprotective effects of estrogen in Aß toxicity are very similar to the effects of the estrogen receptor antagonist ICI182,780. Thus, exposure to EDCs that have anti-estrogenic activity might interfere with normal estrogen-activated neuroprotective signaling events and leave neurons more vulnerable to dangerous stimuli. Our present results provide new understanding of the mechanisms contributing to the harmful effects of EDCs on the function and viability of neurons, and the possible relevance of EDCs in the pathogenesis of neurodegenerative diseases such as Alzheimer's disease.

Involvement of induction and mitochondrial targeting of orphan nuclear receptor Nur77 in 6-OHDA-induced SH-SY5Y cell death.

The orphan nuclear receptor Nur77 is a member of the nuclear receptor superfamily. Nur77 is known to regulate survival and death in response to extracellular stimuli, but it is unclear whether Nur77 is regulated by oxidative stress and contributes to the cytotoxicity in neurodegenerative diseases. Here we showed that (1) Nur77 was up-regulated, phosphorylated, and translocated from the nucleus into the cytosol and mitochondria by H(2)O(2) treatment in HEK293 cells, as well as in 6-hydroxy dopamine (6-OHDA)-treated dopaminergic SH-SY5Y cells, (2) oxidative stress-mediated cell death was exacerbated in Nur77-overexpressed cells and abolished by dominant-negative-Nur77 transfection, and (3) blockade of nuclear export attenuated 6-OHDA-induced SH-SY5Y cell death. Together, our results show that the nuclear export and targeting to mitochondria of Nur77 and resultant activation of apoptotic death may participate in the pathogenesis of Parkinson's disease.

Proteome response to ochratoxin A-induced apoptotic cell death in mouse hippocampal HT22 cells.

Mycotoxins are commonly encountered natural products, and are capable of poisoning animals or humans that inhale mold particles from mycotoxin-contaminated foods. Ochratoxin A (OTA) is produced by Aspergillu ochracus and Penicillium verrucosum, and is often found in cereals and agricultural products. Although previous studies have focused on the potent nephrotoxicity and renal carcinogenicity of OTA, more recent studies suggest that it accumulates in the brain and causes oxidative stress and DNA damage in various brain regions and neuronal populations. In the present study, we undertook to investigate the potential harm caused by environmental exposure to OTA in terms of its effects on neuronal cell viability and proteome profiles. OTA was found to significantly reduce the viabilities of human neuroblastoma SH-SY5Y and mouse hippocampal HT22 cells, as assessed by lactic dehydrogenase release into culture media. Generation of reactive oxygen species was detected in OTA-treated SH-SY5Y and HT22 cells, however, caspase activation and increase in p53 phosphorylation were only detected in HT22 cells, and the expressions of several proteins were found to be significantly altered after treating HT22 cells with OTA. Valosin containing protein, prolyl 4-hydroxylase, Atp5b protein, nucleophosmin 1, eukaryotic translation elongation factor 1 delta isoform, ornithine aminotransferase, prohibitin, and peroxiredoxin 6, which have been suggested to be implicated in the pathogenesis of neurodegenerative disorders, were up-regulated. Our findings suggest that coordinated regulations of molecular networks are involved in the OTA-induced cytotoxicity and that proteome response can be an indicative for neurodegeneration.