TMEM67 is required for the gating function of the transition zone that controls entry of membrane-associated proteins ARL13B and INPP5E into primary cilia.

Primary cilia transduce signals via transmembrane and membrane-associated proteins localized to the ciliary membrane in vertebrate cells. In humans, transmembrane protein 67 (TMEM67), a component of the multiprotein complex functioning as a gatekeeper at the transition zone (TZ) of primary cilia, is mutated in patients suffering from cilia-related pleiotropic diseases, collectively referred to as ciliopathies. The requirement of TMEM67 for the gating function of the TZ that delivers membrane proteins into the ciliary compartment has not been determined. In this study, we established hTERT-RPE1 cells with knockout (KO) of TMEM67 and examined whether cilium formation and TZ gating are affected by its ablation. TMEM67-KO cells displayed impaired ciliogenesis, elongated cilia, perturbed ciliary localization of membrane-associated proteins ARL13B and INPP5E but normal recruitment of TZ proteins CEP290, RPGRIP1L and NPHP5. The exogenous expression of ciliopathy-associated TMEM67 mutants restored ciliary localization of ARL13B and INPP5E but failed to attenuate aberrant cilium elongation in TMEM67-KO cells. Furthermore, we found that TMEM67 localization is not confined to the TZ but extends into the cilium. Our findings indicate that TMEM67 is required not only for ciliogenesis and cilium length regulation but also for the gating function of the TZ independently of RPGRIP1L/CEP290/NPHP5 recruitment to this region. They further suggest that aberrant cilium elongation underlies the pathogenesis of TMEM67-linked ciliopathies.

TULP3 is required for localization of membrane-associated proteins ARL13B and INPP5E to primary cilia.

The primary cilia are known as biosensors that transduce signals through the ciliary membrane proteins in vertebrate cells. The ciliary membrane contains transmembrane proteins and membrane-associated proteins. Tubby-like protein 3 (TULP3), a member of the tubby family, has been shown to interact with the intraflagellar transport-A complex (IFT-A) and to be involved in the ciliary localization of transmembrane proteins, although its role in the ciliary entry of membrane-associated proteins has remained unclear. Here, to determine whether TULP3 is required for the localization of ciliary membrane-associated proteins, we generated and analyzed TULP3-knockout (KO) hTERT RPE-1 (RPE1) cells. Immunofluorescence analysis demonstrated that ciliary formation was downregulated in TULP3-KO cells and that membrane-associated proteins, ADP-ribosylation factor-like 13B (ARL13B) and inositol polyphosphate-5-phosphatase E (INPP5E), failed to localize to primary cilia in TULP3-KO cells. These defects in the localization of ARL13B and INPP5E in TULP3-KO cells were rescued by the exogenous expression of wild-type TULP3, but not that of mutant TULP3 lacking the ability to bind IFT-A. In addition, the expression of TUB protein, another member of the tubby family whose endogenous expression is absent in RPE1 cells, also rescued the defective ciliary localization of ARL13B and INPP5E in TULP3-KO cells, suggesting that there is functional redundancy between TULP3 and TUB. Our findings indicate that TULP3 participates in ciliogenesis, and targets membrane-associated proteins to primary cilia via binding to IFT-A.

Long-Term Systemic Exposure to Rotenone Induces Central and Peripheral Pathology of Parkinson's Disease in Mice.

Parkinson's disease (PD) is a progressive neurodegenerative disease with motor and non-motor symptoms that precede the onset of motor symptoms. Rotenone is often used to induce PD-like pathology in the central nervous system (CNS) and enteric nervous system (ENS). However, there is little or no information on the temporal changes in other neural tissues and the spread of pathology throughout the entire body organs. Here, we recorded the serial immunohistochemical changes in neurons and glial cells of the striatum, substantia nigra (SN), olfactory bulb (OB), thoracic cord (ThC) and ascending colon (AC) induced by 1-, 3- and 6-week administration of rotenone (50 mg/kg/day) infused subcutaneously in C57BL mice using an osmotic pump. Rotenone exposure for 3 or 6 weeks caused neurodegeneration in the striatum, whereas neuronal damage was seen in the SN and OB only after 6 weeks. Moreover, rotenone induced neurodegeneration in the myenteric plexus of AC but not in ThC. Rotenone also activated glial cells before any apparent neurodegeneration in the CNS but not in the ENS. Our results demonstrated that subcutaneous administration of rotenone can cause progressive neurodegeneration in the OB and AC, in addition to the nigrostriatal pathway, and temporal differential glial activation, and that these changes do not spread retrogradely from OB or ENS to nigrostriatal pathway. The results suggested that the different vulnerability of neurons to the neurotoxic effects of rotenone administrated subcutaneously are due to glial activation in these neural tissues.

Visualization of astrocytic primary cilia in the mouse brain by immunofluorescent analysis using the cilia marker Arl13b.

In vertebrates, almost all somatic cells extend a single immotile cilium, referred to as a primary cilium. Increasing evidence suggests that primary cilia serve as cellular antennae in many types of tissues by sensing chemical or mechanical stimuli in the milieu surrounding the cells. In rodents an antibody to adenylyl cyclase 3 (AC3) has been widely used to label the primary cilia of neurons in vivo by immunostaining, whereas the lack of markers for the primary cilia of astrocytes has made it difficult to observe astrocytic primary cilia in vivo. Here, we obtained a visualization of astrocytic primary cilia in the mouse brain. In the somatosensory cortex, a large portion of neurons and astrocytes at postnatal day 10 (P10), and of neurons at P56 had AC3-positive primary cilia, whereas only approx. one-half of the astrocytes in the P56 mice carried primary cilia weakly positive for AC3. In contrast, the majority of astrocytes had ADP-ribosylation factor-like protein 13B (Arl13b)-positive primary cilia in the somatosensory cortex and other brain regions of P56 mice. The lengths of astrocytic primary cilia positive for Arl13b varied among the brain regions. Our data indicate that Arl13b is a noteworthy marker of astrocytic primary cilia in the brain.

Targeting 5-HT(1A) receptors in astrocytes to protect dopaminergic neurons in Parkinsonian models.

Astrocytes are abundant neuron-supporting glial cells that harbor a powerful arsenal of neuroprotective antioxidative molecules and neurotrophic factors. Here we examined whether enrichment with healthy striatal astrocytes can provide neuroprotection against progressive dopaminergic neurodegeneration. Serotonin 1A (5-HT1A) agonist 8-OH-DPAT induced astrocyte proliferation and increased metallothionein-1/-2 (MT-1/-2), antioxidative molecules, in cultured astrocytes and the striatum of mice. Primary cultured mesencephalic dopamine neurons were protected against oxidative stress by preincubation with conditioned media from 8-OH-DPAT-treated astrocytes. These protective effects were canceled by 5-HT1A antagonist or MT-1/-2-specific antibody. Furthermore, reduction of nigrostriatal dopaminergic neurons in 6-hydroxydopamine-lesioned parkinsonian model mice was significantly abrogated by repeated injections of 8-OH-DPAT. Treatment with 8-OH-DPAT markedly increased the expression of MT in striatal astrocytes in the hemi-parkinsonian mice. Our study provides a promising therapeutic strategy of neuroprotection against oxidative stress and progressive dopaminergic neurodegeneration by demonstrating the efficacy of targeting 5-HT1A receptors in astrocytes.

Cyclooxygenase-independent neuroprotective effects of aspirin against dopamine quinone-induced neurotoxicity.

Prostaglandin H synthase exerts not only cyclooxygenase activity but also peroxidase activity. The latter activity of the enzyme is thought to couple with oxidation of dopamine to dopamine quinone. Therefore, it has been proposed that cyclooxygenase inhibitors could suppress dopamine quinone formation. In the present study, we examined effects of various cyclooxygenase inhibitors against excess methyl L-3,4-dihydroxyphenylalanine (L-DOPA)-induced quinoprotein (protein-bound quinone) formation and neurotoxicity using dopaminergic CATH.a cells. The treatment with aspirin inhibited excess methyl L-DOPA-induced quinoprotein formation and cell death. However, acetaminophen did not show protective effects, and indomethacin and meloxicam rather aggravated these methyl L-DOPA-induced changes. Aspirin and indomethacin did not affect the level of glutathione that exerts quenching dopamine quinone in dopaminergic cells. In contrast with inhibiting effects of higher dose in the previous reports, relatively lower dose of aspirin that affected methyl L-DOPA-induced quinoprotein formation and cell death failed to prevent cyclooxygenase-induced dopamine chrome generation in cell-free system. Furthermore, aspirin but not acetaminophen or meloxicam showed direct dopamine quinone-scavenging effects in dopamine-semiquinone generating systems. The present results suggest that cyclooxygenase shows little contribution to dopamine oxidation in dopaminergic cells and that protective effects of aspirin against methyl L-DOPA-induced dopamine quinone neurotoxicity are based on its cyclooxygenase-independent property.

Length impairments of the axon initial segment in rodent models of attention-deficit hyperactivity disorder and autism spectrum disorder.

The axon initial segment (AIS) is a structural neuronal compartment of the proximal axon that plays key roles in sodium channel clustering, action potential initiation, and signal propagation of neuronal outputs. Mutations in constitutive genes of the AIS, such as ANK3, have been identified in patients with neurodevelopmental disorders. Nevertheless, morphological changes in the AIS in neurodevelopmental disorders have not been characterized. In this study, we investigated the length of the AIS in rodent models of attention-deficit hyperactivity disorder (ADHD) and autism spectrum disorder (ASD). We observed abnormalities in AIS length in both animal models. In ADHD model rodents, we observed shorter AIS length in layer 2/3 (L2/3) neurons of the medial prefrontal cortex (mPFC) and primary somatosensory barrel field (S1BF). Further, we observed shorter AIS length in S1BF L5 neurons. In ASD model mice, we observed shorter AIS length in L2/3 and L5 neurons of the S1BF. These results suggest that impairments in AIS length are common phenomena in neurodevelopmental disorders such as ADHD and ASD and may be conserved across species. Our findings provide novel insight into the potential contribution of the AIS to the pathophysiology and pathogenesis of neurodevelopmental disorders.

Astrocyte-derived metallothionein protects dopaminergic neurons from dopamine quinone toxicity.

Our previous studies demonstrated the involvement of quinone formation in dopaminergic neuron dysfunction in the L-DOPA-treated parkinsonian model and in methamphetamine (METH) neurotoxicity. We further reported that the cysteine-rich metal-binding metallothionein (MT) family of proteins protects dopaminergic neurons against dopamine (DA) quinone neurotoxicity by its quinone-quenching property. The aim of this study was to examine MT induction in astrocytes in response to excess DA and the potential neuroprotective effects of astrocyte-derived MTs against DA quinone toxicity. DA exposure significantly upregulated MT-1/-2 in cultured striatal astrocytes, but not in mesencephalic neurons. This DA-induced MT upregulation in astrocytes was blocked by treatment with a DA-transporter (DAT) inhibitor, but not by DA-receptor antagonists. Expression of nuclear factor erythroid 2-related factor (Nrf2) and its binding activity to antioxidant response element of MT-1 gene were significantly increased in the astrocytes after DA exposure. Nuclear translocation of Nrf2 was suppressed by the DAT inhibitor. Quinone formation and reduction of mesencephalic DA neurons after DA exposure were ameliorated by preincubation with conditioned media from DA-treated astrocytes. These protective effects were abrogated by MT-1/-2-specific antibody. Adding exogenous MT-1 to glial conditioned media also showed similar neuroprotective effects. Furthermore, MT-1/-2 expression was markedly elevated specifically in reactive astrocytes in the striatum of L-DOPA-treated hemi-parkinsonian mice or METH-injected mice. These results suggested that excess DA taken up by astrocytes via DAT upregulates MT-1/-2 expression specifically in astrocytes, and that MTs or related molecules secreted specifically by astrocytes protect dopaminergic neurons from damage through quinone quenching and/or scavenging of free radicals.

Neuroprotective effects of zonisamide target astrocyte.

OBJECTIVE: Recent double-blind, controlled trials in Japan showed that the antiepileptic agent zonisamide (ZNS) improves the cardinal symptoms of Parkinson's disease. Glutathione (GSH) exerts antioxidative activity through quenching reactive oxygen species and dopamine quinone. GSH depletion within dopaminergic neurons impairs mitochondrial complex I activity, followed by age-dependent nigrostriatal neurodegeneration. This study examined changes in GSH and GSH synthesis-related molecules, and the neuroprotective effects of ZNS on dopaminergic neurodegeneration using 6-hydroxydopamine-injected hemiparkinsonian mice brain and cultured neurons or astrocytes. METHODS AND RESULTS: ZNS increased both the cell number and GSH levels in astroglial C6 cells, but not in dopaminergic neuronal CATH.a cells. Repeated injections of ZNS (30mg/kg intraperitoneally) for 14 days also significantly increased GSH levels and S100beta-positive astrocytes in mouse basal ganglia. Repeated ZNS injections (30mg/kg) for 7 days in the hemiparkinsonian mice increased the expression of cystine/glutamate exchange transporter xCT in activated astrocytes, which supply cysteine to neurons for GSH synthesis. Treatment of these mice with ZNS also increased GSH levels and completely suppressed striatal levodopa-induced quinone formation. Reduction of nigrostriatal dopamine neurons in the lesioned side of hemiparkinsonian mice was significantly abrogated by repeated injections of ZNS with or without adjunctive levodopa starting 3 weeks after 6-hydroxydopamine lesioning. INTERPRETATION: These results provide new pharmacological evidence for the effects of ZNS. ZNS markedly increased GSH levels by enhancing the astroglial cystine transport system and/or astroglial proliferation via S100beta production or secretion. ZNS acts as a neuroprotectant against oxidative stress and progressive dopaminergic neurodegeneration.

Factors that influence primary cilium length.

Almost all mammalian cells carry one primary cilium that functions as a biosensor for chemical and mechanical stimuli. Genetic damages that compromise cilia formation or function cause a spectrum of disorders referred to as ciliapathies. Recent studies have demonstrated that some pharmacological agents and extracellular environmental changes can alter primary cilium length. Renal injury is a well-known example of an environmental insult that triggers cilia length modification. Lithium treatment causes primary cilia to extend in several cell types including neuronal cells;this phenomenon is likely independent of glycogen synthase kinase-3ß inhibition. In renal epithelial cell lines, deflection of the primary cilia by fluid shear shortens them by reducing the intracellular cyclic AMP level, leading to a subsequent decrease in mechanosensitivity to fluid shear. Primary cilium length is also influenced by the dynamics of actin filaments and microtubules through the levels of soluble tubulin in the cytosol available for primary cilia extension. Thus, mammalian cells can adapt to the extracellular environment by modulating the primary cilium length, and this feedback system utilizing primary cilia might exist throughout the mammalian body. Further investigation is required concerning the precise molecular mechanisms underlying the control of primary cilium length in response to environmental factors.

Pericentrin, a centrosomal protein related to microcephalic primordial dwarfism, is required for olfactory cilia assembly in mice.

The Drosophila pericentrin-like protein has been shown to be essential for the formation of the sensory cilia of chemosensory and mechanosensory neurons by mutant analysis in flies, while the in vivo function of pericentrin, a well-studied mammalian centrosomal protein related to microcephalic primordial dwarfism, has been unclear. To determine whether pericentrin is required for ciliogenesis in mammals, we generated and analyzed mice with a hypomorphic mutation of Pcnt encoding the mouse pericentrin. Immunofluorescence analysis demonstrated that olfactory cilia of chemosensory neurons in the nasal olfactory epithelium were malformed in the homozygous mutant mice. On the other hand, the assembly of motile and primary cilia of non-neuronal epithelial cells and the formation of sperm flagella were not affected in the Pcnt-mutant mice. The defective assembly of olfactory cilia in the mutant was apparent from birth. The mutant animals displayed reduced olfactory performance in agreement with the compromised assembly of olfactory cilia. Our findings suggest that pericentrin is essential for the assembly of chemosensory cilia of olfactory receptor neurons, but it is not globally required for cilia formation in mammals.

SCYL1 arginine methylation by PRMT1 is essential for neurite outgrowth via Golgi morphogenesis.

Arginine methylation is a common posttranslational modification that modulates protein function. SCY1-like pseudokinase 1 (SCYL1) is crucial for neuronal functions and interacts with γ2-COP to form coat protein complex I (COPI) vesicles that regulate Golgi morphology. However, the molecular mechanism by which SCYL1 is regulated remains unclear. Here, we report that the γ2-COP-binding site of SCYL1 is arginine-methylated by protein arginine methyltransferase 1 (PRMT1) and that SCYL1 arginine methylation is important for the interaction of SCYL1 with γ2-COP. PRMT1 was colocalized with SCYL1 in the Golgi fraction. Inhibition of PRMT1 suppressed axon outgrowth and dendrite complexity via abnormal Golgi morphology. Knockdown of SCYL1 by small interfering RNA (siRNA) inhibited axon outgrowth, and the inhibitory effect was rescued by siRNA-resistant SCYL1, but not SCYL1 mutant, in which the arginine methylation site was replaced. Thus, PRMT1 regulates Golgi morphogenesis via SCYL1 arginine methylation. We propose that SCYL1 arginine methylation by PRMT1 contributes to axon and dendrite morphogenesis in neurons.

Lithium treatment elongates primary cilia in the mouse brain and in cultured cells.

The molecular mechanisms underlying the therapeutic effects of lithium, a first-line antimanic mood stabilizer, have not yet been fully elucidated. Treatment of the algae Chlamydomonas reinhardtii with lithium has been shown to induce elongation of their flagella, which are analogous structures to vertebrate cilia. In the mouse brain, adenylyl cyclase 3 (AC3) and certain neuropeptide receptors colocalize to the primary cilium of neuronal cells, suggesting a chemosensory function for the primary cilium in the nervous system. Here we show that lithium treatment elongates primary cilia in the mouse brain and in cultured cells. Brain sections from mice chronically fed with Li(2)CO(3) were subjected to immunofluorescence study. Primary cilia carrying both AC3 and the receptor for melanin-concentrating hormone (MCH) were elongated in the dorsal striatum and nucleus accumbens of lithium-fed mice, as compared to those of control animals. Moreover, lithium-treated NIH3T3 cells and cultured striatal neurons exhibited elongation of the primary cilia. The present results provide initial evidence that a psychotropic agent can affect ciliary length in the central nervous system, and furthermore suggest that lithium exerts its therapeutic effects via the upregulation of cilia-mediated MCH sensing. These findings thus contribute novel insights into the pathophysiology of bipolar mood disorder and other psychiatric diseases.

Reduction of nuclear peroxisome proliferator-activated receptor gamma expression in methamphetamine-induced neurotoxicity and neuroprotective effects of ibuprofen.

We examined changes in nuclear peroxisome proliferator-activated receptor gamma (PPAR gamma) in the striatum in methamphetamine (METH)-induced dopaminergic neurotoxicity, and also examined effects of treatment with drugs possessing PPAR gamma agonistic properties. The marked reduction of nuclear PPAR gamma-expressed cells was seen in the striatum 3 days after METH injections (4 mg/kg x 4, i.p. with 2-h interval). The reduction of dopamine transporter (DAT)-positive signals and PPAR gamma expression, and accumulation of activated microglial cells were significantly and dose-dependently attenuated by four injections of a nonsteroidal anti-inflammatory drug and a PPAR gamma ligand, ibuprofen (10 or 20 mg/kg x 4, s.c.) given 30 min prior to each METH injection, but not by either a low or high dose of aspirin. Either treatment of ibuprofen or aspirin, that showed no effects on METH-induced hyperthermia, significantly blocked the METH-induced striatal cyclooxygenase (COX) expression. Furthermore, the treatment of an intrinsic PPAR gamma ligand 15d-PG J2 also attenuated METH injections-induced reduction of striatal DAT. Therefore, the present study suggests the involvement of reduction of PPAR gamma expression in METH-induced neurotoxicity. Taken together with the previous report showing protective effects of other PPAR gamma ligand, these results imply that the protective effects of ibuprofen against METH-induced neurotoxicity may be based, in part, on its anti-inflammatory PPAR gamma agonistic properties, but not on its COX-inhibiting property or hypothermic effect.

Association studies and gene expression analyses of the DISC1-interacting molecules, pericentrin 2 (PCNT2) and DISC1-binding zinc finger protein (DBZ), with schizophrenia and with bipolar disorder.

Disrupted-in-Schizophrenia 1 (DISC1) and its molecular cascade have been implicated in the pathophysiology of major psychoses. Previously, we identified pericentrin 2 (PCNT2) and DISC1-binding zinc finger protein (DBZ) as binding partners of DISC1; further, we observed elevated expression of PCNT2 in the postmortem brains and in the lymphocytes of bipolar disorder patients, compared to controls. Here, we examined the association of PCNT2 with schizophrenia in a case-control study of Japanese cohorts. We also examined the association of DBZ with schizophrenia and with bipolar disorder, and compared the mRNA levels of DBZ in the postmortem brains of schizophrenia, bipolar and control samples. DNA from 180 schizophrenia patients 201 controls were used for the association study of PCNT2 and DBZ with schizophrenia. Association of DBZ with bipolar disorder was examined in DNA from 238 bipolar patients and 240 age- and gender-matched controls. We observed significant allelic and genotypic associations of the PCNT2 SNPs, rs2249057, rs2268524, and rs2073380 (Ser/Arg) with schizophrenia; the association of rs2249057 (P = 0.002) withstand multiple testing correction. Several two SNP- and three SNP-haplotypes showed significant associations; the associations of haplotypes involving rs2249057 withstand multiple testing correction. No associations were observed for DBZ with schizophrenia or with bipolar disorder; further, there was no significant difference between the DBZ mRNA levels of control, schizophrenia and bipolar postmortem brains. We suggest a possible role of PCNT2 in the pathogenesis of schizophrenia. Abnormalities of PCNT2, the centrosomal protein essential for microtubule organization, may be suggested to lead to neurodevelopmental abnormalities.

DISC1-kendrin interaction is involved in centrosomal microtubule network formation.

Disrupted-In-Schizophrenia 1 (DISC1) was identified as a novel gene disrupted by a (1;11)(q42.1;q14.3) translocation segregating with schizophrenia, bipolar disorder and other major mental illnesses in a Scottish family. We previously identified 446-533 amino acids of DISC1 as the kendrin-binding region by means of a directed yeast two-hybrid interaction assay and showed that the DISC1-kendrin interaction is indispensable for the centrosomal localization of DISC1. In this study, to confirm the DISC1-kendrin interaction, we examined the interaction between deletion mutants of DISC1 and kendrin. Then, we demonstrated that the carboxy-terminus of DISC1 is indispensable for the interaction with kendrin. Furthermore, the immunocytochemistry revealed that the carboxy-terminus of DISC1 is also required for the centrosomal targeting of DISC1. Overexpression of the DISC1-binding region of kendrin or the DISC1 deletion mutant lacking the kendrin-binding region impairs the microtubule organization. These findings suggest that the DISC1-kendrin interaction plays a key role in the microtubule dynamics.

Preventing effects of a novel anti-parkinsonian agent zonisamide on dopamine quinone formation.

The neurotoxicity of dopamine (DA) quinones as dopaminergic neuron-specific oxidative stress is considered to play a role in the pathogenesis and/or progression of Parkinson's disease (PD), since DA quinones conjugate with several key PD pathogenic molecules (e.g., tyrosine hydroxylase, alpha-synuclein and parkin) to form protein-bound quinone (quinoprotein) and consequently inhibit their functions. Zonisamide (ZNS) is used as an anti-epileptic agent but also improved the cardinal symptoms of PD in recent clinical trials in Japan. To evaluate the effects of ZNS on excess cytosolic free DA-induced quinone toxicity, we examined changes in DA quinone-related indices after ZNS treatment both in in vitro cell-free system and in cultured cells. Co-incubation of DA and ZNS in a cell-free system caused conversion of DA to stable melanin via formation of DA-semiquinone radicals and DA chrome. Long-term (5 days) treatment with ZNS decreased quinoprotein and increased DA/DOPA chromes in dopaminergic CATH.a cells. ZNS significantly inhibited quinoprotein formation induced by treatment with tetrahydrobiopterin and ketanserin that elevate cytosolic free DA in the cells. Our results suggest that the novel anti-parkinsonian agent ZNS possesses preventing effects against DA quinone formation induced by excess amount of cytosolic DA outside the synaptic vesicles.

Dopamine induces supernumerary centrosomes and subsequent cell death through Cdk2 up-regulation in dopaminergic neuronal cells.

Aggregation of proteins in the centrosome is implicated in the pathophysiology of Parkinson's disease. However, the relevance of the centrosome in neurodegeneration is still obscure. Centrosome duplication is initiated by the cyclin E/cyclin-dependent kinase 2 (Cdk2) complex. The present study determined changes in cyclin E or Cdk2 expression and in the centrosomal structure in dopaminergic neuronal CATH.a cells exposed to 50, 100 and 150 micromolar dopamine (DA) for 24 h. DA induced significant increase in Cdk2 protein and cyclin E protein, but not cyclin e mRNA. In DA-treated cells, the intense cyclin E- and Cdk2-immunofluorescence signals were co-localized around large and supernumerary centrosomes, and these two parameters of centrosome amplification were significantly increased compared with the control. Simultaneous co-treatment with DA and a Cdk2 inhibitor blocked centrosome amplification and enhanced cell viability. Our results demonstrated that DA could lead to cyclin E accumulation and Cdk2 up-regulation triggering supernumerary centrosomes and apoptotic cell death.

Protective effects of metallothionein against dopamine quinone-induced dopaminergic neurotoxicity.

Dopamine (DA) quinone as DA neuron-specific oxidative stress conjugates with cysteine residues in functional proteins to form quinoproteins. Here, we examined the effects of cysteine-rich metal-binding proteins, metallothionein (MT)-1 and -2, on DA quinone-induced neurotoxicity. MT quenched DA semiquinones in vitro. In dopaminergic cells, DA exposure increased quinoproteins and decreased cell viability; these were ameliorated by pretreatment with MT-inducer zinc. Repeated L-DOPA administration markedly elevated striatal quinoprotein levels and reduced the DA nerve terminals specifically on the lesioned side in MT-knockout parkinsonian mice, but not in wild-type mice. Our results suggested that intrinsic MT protects against L-DOPA-induced DA quinone neurotoxicity in parkinsonian mice by its quinone-quenching property.

Methamphetamine-induced dopaminergic neurotoxicity is regulated by quinone-formation-related molecules.

Recently, the neurotoxicity of dopamine (DA) quinone formation by auto-oxidation of DA has focused on dopaminergic neuron-specific oxidative stress. In the present study, we examined DA quinone formation in methamphetamine (METH)-induced dopaminergic neuronal cell death using METH-treated dopaminergic cultured CATH.a cells and METH-injected mouse brain. In CATH.a cells, METH treatment dose-dependently increased the levels of quinoprotein (protein-bound quinone) and the expression of quinone reductase in parallel with neurotoxicity. A similar increase in quinoprotein levels was seen in the striatum of METH (4 mg/kg X4, i.p., 2 h interval)-injected BALB/c mice, coinciding with reduction of DA transporters. Furthermore, pretreatment of CATH.a cells with quinone reductase inducer, butylated hydroxyanisole, significantly and dose-dependently blocked METH-induced elevation of quinoprotein, and ameliorated METH-induced cell death. We also showed the protective effect of tyrosinase, which rapidly oxidizes DA and DA quinone to form stable melanin, against METH-induced dopaminergic neurotoxicity in vitro and in vivo using tyrosinase null mice. Our results indicate that DA quinone formation plays an important role, as a dopaminergic neuron-specific neurotoxic factor, in METH-induced neurotoxicity, which is regulated by quinone formation-related molecules.