Differential effects of overexpression of wild-type and mutant human alpha-synuclein on MPP+-induced neurotoxicity in PC12 cells

Focused Ultrasound-Induced Blood–Brain Barrier Opening Enhanced α-Synuclein Expression in Mice for Modeling Parkinson’s Disease

Parkinson’s disease (PD) is characterized by α-synuclein (αSNCA) aggregation in dopaminergic neurons. Gradual accumulation of αSNCA aggregates in substantia nigra (SN) diminishes the normal functioning of soluble αSNCA, leading to a loss of dopamine (DA) neurons. In this study, we developed focused ultrasound-targeted microbubble destruction (UTMD)-mediated PD model that could generate the disease phenotype via αSNCA CNS gene delivery. The formation of neuronal aggregates was analyzed with immunostaining. To evaluate the DA cell loss, we used tyrosine hydroxylase immunostaining and HPLC analysis on DA and its two metabolites, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). This loss of DA was associated with a dose-dependent impairment in motor function, as assessed by the rotarod motor assessment. We demonstrate that UTMD-induced SNCA expression initiates αSNCA aggregation and results in a 50% loss of DA in SN. UTMD-related dose-dependent neuronal loss was identified, and it correlates with the degree of impairment of motor function. In comparison to chemical neurotoxin 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated and conventional intracerebral (IC)-injected animal models of PD, the UTMD-mediated αSNCA-based mouse model offers the advantage of mimicking the rapid development of the PD phenotype. The PD models that we created using UTMD also prove valuable in assessing specific aspects of PD pathogenesis and can serve as a useful PD model for the development of new therapeutic strategies.

Exendin-4 Reversed the PC12 Cell Damage Induced by circRNA CDR1as/miR-671/GSK3β Signaling Pathway

The purpose of this paper is to study the effect of circRNA cerebellar degeneration-related protein 1 antisense RNA(CDR1as)/miR-671/GSK3β signaling pathway on PC12 cell injury and the mechanism of Exendin-4 (Ex-4) in PC12 cell injury protection. Quantitative reverse-transcription polymerase chain reaction (qRT-PCR) was used to detect the expression levels of circular RNA CDR1as and miR-671 in PC12 cells. By overexpressing or knocking out CDR1as, miR-671, and GSK3β, the role of CDR1as, miR-671, and GSK3β in PC12 cell injury was analyzed. The binding of CDR1as to miR-671 and GSK3β to miR-671 was verified by dual luciferase reporter assay. PC12 cells were treated with 1-methyl-4 phenyl-pyridine ion (MPP⁺) to construct a PC12 cell damage model. PC12 cell transfection experiments were used to confirm the role of CDR1as/miR-671/GSK3β signal axis in PC12 cell damage, and the role of Ex-4 in the association of circRNA CDR1as/miR-671/GSK3β signaling axis and PC12 cell damage. PC12 cell damage was detected by 3-(4,5-dimethyl thiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) and cellular lactate dehydrogenase (LDH) release. Ex-4 reversed the phosphorylation levels of PI3K, AKT, and GSK-3β in MPP⁺-treated PC12 cells, and reduced MPP⁺-induced PC12 cell damage. CircRNA CDR1as upregulated the expression of GSK3β by sponge miR-671. Ex-4 downregulated CDR1as expression and upregulated miR-671 expression in MPP⁺-induced PC12 cell. Silencing of CDR1as reduced MPP⁺-induced PC12 cell damage. CDR1as transfection downregulated the expression of miR-671 in PC12 cells, promoted the expression and phosphorylated of GSK3β, and induced PC12 cell damage. GSK3β silencing reversed CDR1as-induced PC12 cell damage. CDR1as promoted the phosphorylation level of GSK3β in PC12 cells to cause cell damage; Ex-4 reversed the phosphorylation of GSK3β caused by CDR1as in PC12 cells and reduced the PC12 cell damage caused by CDR1as. Ex-4 reverses the damage of PC12 cells induced by CDR1as/miR-671/GSK3β signaling pathway.

Ucf-101 protects in vivoandin vitro models of PD against 6-hydroxydopamine toxicity by alleviating endoplasmic reticulum stress via the Wnt/β-catenin pathway

The accumulation of α-syn which induce endoplasmic reticulum stress (ERS) and mediate various signaling pathways involved in DA neuronal degeneration, and the apoptosis of dopamine (DA) neurons are pathological markers of Parkinson's disease (PD). High-temperature requirement protein A2 (HtrA2) is synthesized in the endoplasmic reticulum, and the expression level of HtrA2 can be upregulated by drugs or by unfolded proteins. Ucf-101 is a specific inhibitor of HtrA2, and studies have shown that Ucf-101 reduced apoptosis in PC12 cells. Our study showed that PC12 cells treated with 60 μM 6-OHDA for 24 h had significantly decreased cell viability compared to that of controls. A low concentration (2.5 μM) of Ucf-101 decreased the apoptosis rate of the PD cell model, but a high concentration (≥10 μM) increased the apoptosis rate, compared to that of controls. 6-OHDA upregulated the expression of HtrA2, α-syn, CHOP, Grp78 and active caspase-3 and reduced the levels of TH and XIAP. Ucf-101 reduced the level of ERS and apoptosis bothin vivoandin vitro. The ratio of p-GSK3β (Tyr216 to Ser9) increased in PD rats. However, Ucf-101 down-regulated the activation of GSK3β and activated the Wnt/β-catenin pathway that was caused by 6-OHDA. Ucf-101 activated the Wnt/β-catenin pathway and significantly attenuated 6-OHDA-induced neurotoxicity, which was related to the inhibition of ERS and the reduction of the apoptosis rate of PC12 cells and DA neurons in the midbrain of PD rats. Ucf-101 has certain neuroprotective effects.

Motor learning and metaplasticity in striatal neurons: relevance for Parkinson's disease

Nigro-striatal dopamine transmission is central to a wide range of neuronal functions, including skill learning, which is disrupted in several pathologies such as Parkinson's disease. The synaptic plasticity mechanisms, by which initial motor learning is stored for long time periods in striatal neurons, to then be gradually optimized upon subsequent training, remain unexplored. Addressing this issue is crucial to identify the synaptic and molecular mechanisms involved in striatal-dependent learning impairment in Parkinson's disease. In this study, we took advantage of interindividual differences between outbred rodents in reaching plateau performance in the rotarod incremental motor learning protocol, to study striatal synaptic plasticity ex vivo. We then assessed how this process is modulated by dopamine receptors and the dopamine active transporter, and whether it is impaired by overexpression of human α-synuclein in the mesencephalon; the latter is a progressive animal model of Parkinson's disease. We found that the initial acquisition of motor learning induced a dopamine active transporter and D1 receptors mediated long-term potentiation, under a protocol of long-term depression in striatal medium spiny neurons. This effect disappeared in animals reaching performance plateau. Overexpression of human α-synuclein reduced striatal dopamine active transporter levels, impaired motor learning, and prevented the learning-induced long-term potentiation, before the appearance of dopamine neuronal loss. Our findings provide evidence of a reorganization of cellular plasticity within the dorsolateral striatum that is mediated by dopamine receptors and dopamine active transporter during the acquisition of a skill. This newly identified mechanism of cellular memory is a form of metaplasticity that is disrupted in the early stage of synucleinopathies, such as Parkinson's disease, and that might be relevant for other striatal pathologies, such as drug abuse.

Biological Effects of Tetrahydroxystilbene Glucoside: An Active Component of a Rhizome Extracted from Polygonum multiflorum

Polygonum multiflorum Thunb. (PM), a traditional Chinese medicinal herb, has been widely used in the Orient as a tonic and antiaging agent. 2,3,5,4'-Tetrahydroxystilbene-2-O-β-D-glucoside (TSG, C20H22O9, FW = 406.38928) is one of the active components extracted from PM. TSG is an antioxidant agent, which exhibits remarkable antioxidative activities in vivo and in vitro. The antioxidant effect of TSG is achieved by its radical-scavenging effects. TSG can inhibit apoptosis and protect neuronal cells against injury through multifunctional cytoprotective pathways. TSG performs prophylactic and therapeutic activities against Alzheimer's disease, Parkinson's disease, and cerebral ischemia/reperfusion injury. It is also antiatherosclerotic and anti-inflammatory. However, the mechanisms underlying these pharmacological activities are unclear. This study aimed at reviewing experimental studies and describing the effectiveness and possible mechanisms of TSG.

α-Synuclein-Dependent Calcium Entry Underlies Differential Sensitivity of Cultured SN and VTA Dopaminergic Neurons to a Parkinsonian Neurotoxin

Parkinson's disease (PD) is a debilitating neurodegenerative disease characterized by a loss of dopaminergic neurons in the substantia nigra (SN). Although mitochondrial dysfunction and dysregulated α-synuclein (aSyn) expression are postulated to play a role in PD pathogenesis, it is still debated why neurons of the SN are targeted while neighboring dopaminergic neurons of the ventral tegmental area (VTA) are spared. Using electrochemical and imaging approaches, we investigated metabolic changes in cultured primary mouse midbrain dopaminergic neurons exposed to a parkinsonian neurotoxin, 1-methyl-4-phenylpyridinium (MPP+). We demonstrate that the higher level of neurotoxicity in SN than VTA neurons was due to SN neuron-specific toxin-induced increase in cytosolic dopamine (DA) and Ca2+, followed by an elevation of mitochondrial Ca2+, activation of nitric oxide synthase (NOS), and mitochondrial oxidation. The increase in cytosolic Ca2+ was not caused by MPP+-induced oxidative stress, but rather depended on the activity of both L-type calcium channels and aSyn expression, suggesting that these two established pathogenic factors in PD act in concert.

Tetrahydroxystilbene glucoside inhibits α-synuclein aggregation and apoptosis in A53T α-synuclein-transfected cells exposed to MPP+

Increasing evidence has solidified the involvement of α-synuclein (α-Syn) and neurotoxins in the pathogenesis of Parkinson’s disease (PD), suggesting a combination of genetic and environmental influences. 2,3,5,4′-Tetrahydroxystilbene-2-O-β-D-glucoside (TSG) is one of the main active components extracted from Polygonum multiflorum. The purpose of the present study was to investigate the effects of TSG on α-Syn aggregation, mitochondrial dysfunction, oxidative stress, and apoptosis in vitro. A53T mutant α-synuclein-transfected cells (A53T AS cells) plus MPP+ exposure were used as a complex cell model of PD. The expression of proteins was determined by Western blot assay. Flow cytometry was utilized to measure mitochondrial membrane potential and apoptosis. The results showed that MPP+ exposure for 24 h induced more severe damage in A53T AS cells than in vector control cells. Pretreatment of TSG for 24 h significantly increased the cell viability; decreased lactate dehydrogenase leakage; inhibited α-Syn over-expression and aggregation; elevated mitochondrial membrane potential; decreased reactive oxygen species, Bax/Bcl-2 ratio, and caspase-3 activity; and inhibited apoptosis in A53T AS cells exposed to MPP+. These results suggest that TSG may be an attractive candidate for PD therapy.

Taurine inhibits 2,5-hexanedione-induced oxidative stress and mitochondria-dependent apoptosis in PC12 cells

2,5-hexanedione (HD) is the ultimate neurotoxic metabolite of hexane, causing the progression of nerve diseases in human. It was reported that HD induced apoptosis and oxidative stress. Taurine has been shown to be a potent antioxidant. In the present study, we investigated the protection of taurine against HD-induced apoptosis in PC12 cells and the underlying mechanism. Our results showed the decreased viability and increased apoptosis in HD-exposed PC12 cells. HD also induced the disturbance of Bax and Bcl-2 expression, the loss of MMP, the release of mitochondrial cytochrome c and caspase-3 activation in PC12 cells. Moreover, HD resulted in an increase in reactive oxygen species (ROS) level and a decline in the activities of superoxidedismutase and catalase in PC12 cells. However, taurine pretreatment ameliorated the increased apoptosis and the alterations in key regulators of mitochondria-dependent pathway in PC12 exposed to HD. The increased ROS level and the decreased activities of the antioxidant enzymes in HD group were attenuated by taurine. These results indicate that pretreatment of taurine may, at least partly, prevent HD-induced apoptosis via inhibiting mitochondria-dependent pathway. It is also suggested that the potential of taurine against HD-induced apoptosis may benefit from its anti-oxidative property.

Impairment of mitochondria dynamics by human A53T α-synuclein and rescue by NAP (davunetide) in a cell model for Parkinson's disease

The formation of oligomers and aggregates of overexpressed or mutant α-synuclein play a role in the degeneration of dopaminergic neurons in Parkinson's disease by causing dysfunction of mitochondria, reflected in their disturbed mobility and production of ROS. The mode of action and mechanisms underlying this mitochondrial impairment is still unclear. We have induced stable expression of wild-type, A30P or A53T α-synuclein in neuronally differentiated SH-SY5Y neuroblastoma cells and studied anterograde and retrograde mitochondrial trafficking in this cell model for Parkinson's disease. In contrast to wild-type and A30P, A53T α-synuclein significantly inhibited mitochondrial trafficking, at first retrogradely and in a later stage anterogradely. Accordingly, A53T α-synuclein also caused the highest increase in ROS production in the dysmobilized mitochondria in comparison to wild-type or A30P α-synuclein. Treatment with NAP, the eight amino acid peptide identified as the active component of activity-dependent neuroprotective protein (ADNP), completely annihilated the adverse effects of A53T on mitochondrial dynamics. Our results reveal that A53T α-synuclein (oligomers or aggregates) leads to the inhibition of mitochondrial trafficking, which can be rescued by NAP, suggesting the involvement of microtubule disruption in the pathophysiology of Parkinson's disease.

Role of TGFβ signaling in the pathogenesis of Alzheimer's disease

Aging is the main risk factor for Alzheimer’s disease (AD); being associated with conspicuous changes on microglia activation. Aged microglia exhibit an increased expression of cytokines, exacerbated reactivity to various stimuli, oxidative stress, and reduced phagocytosis of β-amyloid (Aβ). Whereas normal inflammation is protective, it becomes dysregulated in the presence of a persistent stimulus, or in the context of an inflammatory environment, as observed in aging. Thus, neuroinflammation can be a self-perpetuating deleterious response, becoming a source of additional injury to host cells in neurodegenerative diseases. In aged individuals, although transforming growth factor β (TGFβ) is upregulated, its canonical Smad3 signaling is greatly reduced and neuroinflammation persists. This age-related Smad3 impairment reduces protective activation while facilitating cytotoxic activation of microglia through several cellular mechanisms, potentiating microglia-mediated neurodegeneration. Here, we critically discuss the role of TGFβ-Smad signaling on the cytotoxic activation of microglia and its relevance in the pathogenesis of AD. Other protective functions, such as phagocytosis, although observed in aged animals, are not further induced by inflammatory stimuli and TGFβ1. Analysis in silico revealed that increased expression of receptor scavenger receptor (SR)-A, involved in Aβ uptake and cell activation, by microglia exposed to TGFβ, through a Smad3-dependent mechanism could be mediated by transcriptional co-factors Smad2/3 over the MSR1 gene. We discuss that changes of TGFβ-mediated regulation could at least partially mediate age-associated microglia changes, and, together with other changes on inflammatory response, could result in the reduction of protective activation and the potentiation of cytotoxicity of microglia, resulting in the promotion of neurodegenerative diseases.

Role of aldehyde dehydrogenase 2 in 1-methy-4-phenylpyridinium ion-induced aldehyde stress and cytotoxicity in PC12 cells

Aldehyde stress contributes to molecular mechanisms of cell death and the pathogenesis of Parkinson's disease (PD). The neurotoxin 1-Methy-4-Phenylpyridinium Ion (MPP(+)) is commonly used to model PD. Aldehyde dehydrogenase 2 (ALDH2) is an important enzyme detoxifying aldehydes. The aim of this study is to evaluate whether MPP(+)-induced neurotoxicity is involved in aldehyde stress by modulation of ALDH2. Our results demonstrated that treatment of PC12 cells with MPP(+) leads to aldehyde stress by increasing in loads of malondialdehyde and 4-hydroxynonenal, which indicated that MPP(+)-induced aldehyde stress contributes to its cytotoxicity in PC12 cells. We also showed that MPP(+) up-regulates the expression and activity of ALDH2 in PC12 cells and that inhibition of ALDH2 by its specific inhibitor daidzin prevents MPP(+)-induced decrease in cell viability and increases in apoptosis, oxidative stress and aldehyde stress in PC12 cells. These findings suggest that aldehyde stress contributes to MPP(+)-induced toxicity in PC12 cells by upregulation of ALDH2. This study provides a novel insight into the role of ALDH2 in the neurotoxicity of MPP(+).

Trifluoperazine rescues human dopaminergic cells from wild-type α-synuclein-induced toxicity

Parkinson's disease (PD) is the most frequent neurodegenerative movement disorder. Presently, there is no causal therapy available to slow down or halt disease progression. The presynaptic protein alpha-synuclein aggregates to form intraneuronal Lewy bodies in PD. It is generally believed that intermediates on the way from monomers to the large aggregates would mediate neurotoxicity, but the precise species and mechanism responsible for neuronal death are controversially debated. To study alpha-synuclein-mediated toxicity, we developed a new model in which moderate overexpression of wild-type alpha-synuclein led to gradual death of human postmitotic dopaminergic neurons. In accordance with findings in postmortem PD brains, small oligomeric species occurred and the autophagic flux was impaired in our model. The phenothiazine neuroleptic trifluoperazine, an activator of macroautophagy, selectively reduced one particular alpha-synuclein species and rescued cells. Inversely, blocking of autophagy led to an accumulation of this oligomeric species and increased cell death. These data show that activation of autophagy is a promising approach to protect against alpha-synuclein pathology and likely acts by targeting one specific alpha-synuclein species.

Crosstalk between the proteasome system and autophagy in the clearance of α-synuclein

AIM

A growing body of evidence suggests that α-synuclein accumulation may play an important role in the pathogenesis of Parkinson's disease. The aim of this study was to investigate the roles of the proteasome and autophagy pathways in the clearance of wild-type and mutant α-synuclein in PC12 cells.

METHODS

PC12 cells overexpressing either wild-type or A30P mutant α-synuclein were treated with the proteasome inhibitor epoxomicin, the macroautophagy inhibitor 3-MA and the macroautophagy activator rapamycin alone or in combination. The cell viability was assessed using MTT assay. Immunofluorescence and Western blot analysis were used to detect the level of α-synuclein, LAMP-2A, E1 activase, and E2 ligase in the cells. Chymotrypsin-like proteasomal activity was measured using a commercial kit.

RESULTS

When the proteasome and macroautophagy in the wild-type and mutant cells were inhibited with epoxomicin and 3-MA, respectively, the cell viability was significantly decreased, and the α-synuclein level was increased. Both epoxomicin and 3-MA activated the chaperone-mediated autophagy (CMA) by increasing the level of the CMA-limiting enzyme LAMP-2A. Furthermore, 3-MA or epoxomicin significantly decreased chymotrypsin-like proteasomal activity. 3-MA or epoxomicin did not change E1 activase expression in either mutant or wild-type cells, but increased E2 ligase expression, especially when used together. Macroautophagy inducer rapamycin increased the cell viability and reduced epoxomicin-induced α-synuclein accumulation. Interestingly, CMA was also activated by rapamycin.

CONCLUSION

Our results demonstrate the existence of complex crosstalk between different forms of autophagy and between autophagy and the proteasome pathway in the clearance of α-synuclein in PC12 cells.

Protection against neurotoxicity by an autophagic mechanism

The objective of the present study was to investigate the effects of 3-n-butylphthalide (NBP) on a 1-methyl-4-phenylpyridinium (MPP⁺)-induced cellular model of Parkinson's disease (PD) and to illustrate the potential mechanism of autophagy in this process. For this purpose, rat PC12 pheochromocytoma cells were treated with MPP⁺ (1 mM) for 24 h following pretreatment with NBP (0.1 mM). Cell metabolic viability was determined by the MTT assay and cell ultrastructure was examined by transmission electron microscopy. The intracellular distribution and expression of α-synuclein and microtubule-associated protein light chain 3 (LC3) were detected by immunocytochemistry and Western blotting. Our results demonstrated that: 1) NBP prevented MPP⁺-induced cytotoxicity in PC12 cells by promoting metabolic viability. 2) NBP induced the accumulation of autophagosomes in MPP⁺-treated PC12 cells. 3) Further study of the molecular mechanism demonstrated that NBP enhanced the colocalization of α-synuclein and LC3 and up-regulated the protein level of LC3-II. These results demonstrate that NBP protects PC12 cells against MPP⁺-induced neurotoxicity by activating autophagy-mediated α-synuclein degradation, implying that it may be a potential effective therapeutic agent for the treatment of PD.

HDAC6 regulates aggresome-autophagy degradation pathway of α-synuclein in response to MPP+-induced stress

Increasing evidence suggests that the ubiquitin-binding histone deacetylase-6 (HDAC6) plays an important role in the clearance of misfolded proteins by autophagy. In this study, we treated PC-12 cells over-expressing human mutant (A53T) α-synuclein (α-syn) and SH-SY5Y cells with MPP(+). It was found that HDAC6 expression significantly increased and mainly colocalized with α-syn in the perinuclear region to form aggresome-like bodies. HDAC6 deficiency blocked the formation of aggresome-like bodies and interfered with the autophagy in response to MPP(+)-induced stress. Moreover, misfolded α-syn accumulated into the nuclei, resulting in its reduced clearance, and finally, the number of apoptotic cells significantly increased. Taken together, HDAC6 participated in the degradation of MPP(+)-induced misfolded α-syn aggregates by regulating the aggresome-autophagy pathway. Understanding the mechanism may disclose potential therapeutic targets for synucleinopathies such as Parkinson's disease.

Prosurvival effect of human wild-type alpha-synuclein on MPTP-induced toxicity to central but not peripheral catecholaminergic neurons isolated from transgenic mice

In the present work we report the generation of a new line of alpha-synuclein (alpha-SYN) transgenic mice in which the human wild-type alpha-SYN cDNA is expressed under the control of a tyrosine hydroxylase (TH) promoter. We provide evidence that the ectopic protein is found in TH expressing neurons of both central and peripheral nervous systems. The transgene is expressed very early in development coinciding with the activity of the TH promoter and in the adult brain the human protein distributes normally to the nerve endings and cell bodies of dopaminergic nigral neurons without any evidence of abnormal aggregation. Our results indicate that expression of human wild-type alpha-SYN does not affect normal development or maintenance of TH immunoreactive nigral neurons, striatal dopamine content, or locomotor activity. Systemic administration of the parkinsonian neurotoxin 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) induces a loss of TH immunoreactive nigral neurons and terminals and of dopamine levels to the same degree in both transgenic and non-transgenic adult mice. Intoxication also results in a similar loss of cardiac noradrenaline in both genotypes. Surprisingly, cultured transgenic ventral mesencephalic fetal dopaminergic neurons exhibit complete resistance to cell death induced by 1-methyl-4-phenylpyridinium ion (MPP(+)) intoxication, without changes in dopamine transporter (DAT) surface levels. Interestingly, this protection is not observed in other populations of catecholaminergic neurons such as peripheral sympathetic neurons, despite their high sensitivity to MPP(+)in vitro.

Hydrogen sulfide inhibits MPP(+)-induced apoptosis in PC12 cells

AIMS

Hydrogen sulfide (H2S) is a well-known cytotoxic gas. Recently it has been shown to protect neurons against oxidative stress caused by glutamate, hypochlorous acid (HOCl), and beta-amyloid. The aim of the present study is to explore the cytoprotection of H2S against 1-methyl-4-phenylpyridinium ion (MPP(+))-induced apoptosis and the molecular mechanisms underlying in PC12 cells, a rat cell line derived from pheochromocytoma cells.

MAIN METHODS

Cell viability was determined by the conventional 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide reduction assay. Apoptosis was assessed by Hoechst 33258 nuclear staining and flow cytometric (FCM) analysis after propidium iodide staining. The mitochondrial membrane potential (MMP) was measured by rhodamine 123 (Rh123) probe and reactive oxygen species (ROS) were measured by dihydrorhodamine probe using FCM analysis.

KEY FINDINGS

MPP(+) reduced the cell viability and induced apoptosis of PC12 cells along with dissipation of MMP as well as overproduction of ROS. Sodium hydrosulfide (NaHS), a H2S donor, protected PC12 cells against MPP(+)-induced cytotoxicity and apoptosis not only by reducing the loss of MMP, but also by attenuating an increase in intracellular ROS.

SIGNIFICANCE

H2S significantly protected PC12 cells against cytotoxicity and apoptosis induced by MPP(+), which was associated with the inhibition by H(2)S of MPP(+)-induced dissipation of MMP and overproduction of ROS. These findings can significantly advance therapeutic approaches to the neurodegenerative diseases which are associated with oxidative stress, such as Parkinson's disease.

MPP+ impairs autophagic clearance of alpha-synuclein by impairing the activity of dynein

Increasing evidence suggests that dynein has an important role in the clearance of misfolded proteins by autophagy. Here we show that treatment of cells with 1-methyl-4-phenylpyridinium (MPP) cause alpha-synuclein overexpression and aggregation, leading to the accumulation of autophagic vacuoles and the recruitment of LC3-II to these vacuoles in the cytoplasm. After MPP treatment, dynein expression decreased and was mainly aggregated at the periphery of cytoplasm and lost its colocalization with alpha-synuclein and lamp1, indicating that dynein lost its function in the aggresome formation and failed to return autophagosome and lysosomes to the center of the cell for degradation. We consider that dynein plays an important role in the autophagic clearance of aggregate-prone proteins.

Role of autophagy and proteasome degradation pathways in apoptosis of PC12 cells overexpressing human alpha-synuclein

Parkinson's disease is a common neurodegenerative disease in the elderly. Its causes and mechanisms are not clearly understood. To explore the specific role of autophagy and the ubiquitin-proteasome pathway in apoptosis, a specific proteasome inhibitor and macroautophagy inhibitor and stimulator were selected to investigate pheochromocytoma (PC12) cell lines transfected with human mutant (A30P) and wild-type (WT) alpha-synuclein. The apoptosis ratio was assessed by flow cytometry. LC3, heat shock protein 70 (hsp70) and caspase-3 expression in cell culture were determined by Western blot. The hallmarks of apoptosis and autophagy were assessed with transmission electron microscopy. Compared to the control group or the rapamycin (autophagy stimulator) group, the apoptosis ratio in A30P and WT cells was significantly higher after treatment with inhibitors of the proteasome and macroautophagy. The results of Western blots for caspase-3 expression were similar to those of flow cytometry; hsp70 protein was significantly higher in the proteasome inhibitor group than in control, but in the autophagy inhibitor and stimulator groups, hsp70 was similar to control. These findings show that inhibition of the proteasome and autophagy promotes apoptosis, and the macroautophagy stimulator rapamycin reduces the apoptosis ratio. And inhibiting or stimulating autophagy has less impact on hsp70 than the proteasome pathway.

Synphilin-1A inhibits seven in absentia homolog (SIAH) and modulates alpha-synuclein monoubiquitylation and inclusion formation

Parkinson disease (PD) is characterized by the presence of ubiquitylated inclusions and the death of dopaminergic neurons. Seven in absentia homolog (SIAH) is a ubiquitin-ligase that ubiquitylates alpha-synuclein and synphilin-1 and is present in Lewy bodies of PD patients. Understanding the mechanisms that regulate the ubiquitylation of PD-related proteins might shed light on the events involved in the formation of Lewy bodies and death of neurons. We show in this study that the recently described synphilin-1 isoform, synphilin-1A, interacts in vitro and in vivo with the ubiquitin-protein isopeptide ligase SIAH and regulates its activity toward alpha-synuclein and synphilin-1. SIAH promotes limited ubiquitylation of synphilin-1A that does not lead to its degradation by the proteasome. SIAH also increases the formation of synphilin-1A inclusions in the presence of proteasome inhibitors, supporting the participation of ubiquitylated synphilin-1A in the formation of Lewy body-like inclusions. Synphilin-1A/SIAH inclusions recruit PD-related proteins, such as alpha-synuclein, synphilin-1, Parkin, PINK1, and UCH-L1. We found that synphilin-1A robustly increases the steady-state levels of SIAH by decreasing its auto-ubiquitylation and degradation. In addition, synphilin-1A blocks the ubiquitylation and degradation of the SIAH substrates synphilin-1 and deleted in colon cancer protein. Furthermore, synphilin-1A strongly decreases the monoubiquitylation of alpha-synuclein by SIAH and the formation of alpha-synuclein inclusions, supporting a role for monoubiquitylation in alpha-synuclein inclusion formation. Our results suggest a novel function for synphilin-1A as a regulator of SIAH activity and formation of Lewy body-like inclusions.

Trafficking of dopamine transporters in psychostimulant actions

Brain dopamine (DA) plays a pivotal role in drug addiction. Since the plasma membrane DA transporter (DAT) is critical for terminating DA neurotransmission, it is important to understand how DATs are regulated and this regulation impacts drug addiction. The number of cell surface DATs is controlled by constitutive and regulated endocytic trafficking. Psychostimulants impact this trafficking. Amphetamines, DAT substrates, cause rapid up-regulation and slower down-regulation of DAT whereas cocaine, a DAT inhibitor, increases surface DATs. Recent reports have begun to elucidate the molecular mechanisms of these psychostimulant effects and link changes in DAT trafficking to psychostimulant-induced reward/reinforcement in animal models.

alpha-Synuclein enhances secretion and toxicity of amyloid beta peptides in PC12 cells

alpha-Synuclein is the fundamental component of Lewy bodies which occur in the brain of 60% of sporadic and familial Alzheimer's disease patients. Moreover, a proteolytic fragment of alpha-synuclein, the so-called non-amyloid component of Alzheimer's disease amyloid, was found to be an integral part of Alzheimer's dementia related plaques. However, the role of alpha-synuclein in pathomechanism of Alzheimer's disease remains elusive. In particular, the relationship between alpha-synuclein and amyloid beta is unknown. In the present study we showed the involvement of alpha-synuclein in amyloid beta secretion and in the mechanism of amyloid beta evoked mitochondria dysfunction and cell death. Rat pheochromocytoma PC12 cells transfected with amyloid beta precursor protein bearing Swedish double mutation (APPsw) and control PC12 cells transfected with empty vector were used in this study. alpha-Synuclein (10microM) was found to increase by twofold amyloid beta secretion from control and APPsw PC12 cells. Moreover, alpha-synuclein decreased the viability of PC12 cells by about 50% and potentiated amyloid beta toxicity leading to mitochondrial dysfunction and caspase-dependent programmed cell death. Inhibitor of caspase-3 (Z-DEVD-FMK, 100microM), and a mitochondrial permeability transition pore blocker, cyclosporine A (2microM) protected PC12 cells against alpha-synuclein or amyloid beta evoked cell death. In contrast Z-DEVD-FMK and cyclosporine A were ineffective in APPsw cells containing elevated amount of amyloid beta treated with alpha-synuclein. It was found that the inhibition of neuronal and inducible nitric oxide synthase reversed the toxic effect of alpha-synuclein in control but not in APPsw cells. Our results indicate that alpha-synuclein enhances the release and toxicity of amyloid beta leading to nitric oxide mediated irreversible mitochondria dysfunction and caspase-dependent programmed cell death.