• We are sorry, but NCBI web applications do not support your browser and may not function properly. More information
Logo of fasebjClick here to go to the full-featured web site.Click here to learn how to submit an article to The FASEB Journal.Never miss an issue. Click here to subscribe to The FASEB Journal s full content.Click here for the latest news from The FASEB Journal.Find out what s being published every day. Click here to subscribe to RSS feeds.Click here to visit The FASEB Journal's full-featured site.
FASEB J. Sep 2009; 23(9): 2820–2830.
PMCID: PMC2796901

α-Synuclein contributes to GSK-3β-catalyzed Tau phosphorylation in Parkinson’s disease models

Abstract

We have shown in the parkinsonism-inducing neurotoxin MPP+/MPTP model that α-Synuclein (α-Syn), a presynaptic protein causal in Parkinson’s disease (PD), contributes to hyperphosphorylation of Tau (p-Tau), a protein normally linked to tauopathies, such as Alzheimer’s disease (AD). Here, we investigated the kinase involved and show that the Tau-specific kinase, glycogen synthase kinase 3β (GSK-3β), is robustly activated in various MPP+/MPTP models of Parkinsonism (SH-SY5Y cotransfected cells, mesencephalic neurons, transgenic mice overexpressing α-Syn, and postmortem striatum of PD patients). The activation of GSK-3β was absolutely dependent on the presence of α-Syn, as indexed by the absence of p-GSK-3β in cells lacking α-Syn and in α-Syn KO mice. MPP+ treatment induced translocation and accumulation of p-GSK-3β in nuclei of SH-SY5Y cells and mesencephalic neurons. Through coimmunoprecipitation (co-IP), we found that α-Syn, pSer396/404-Tau, and p-GSK-3β exist as a heterotrimeric complex in SH-SY5Y cells. GSK-3β inhibitors (lithium and TDZD-8) protected against MPP+-induced events in SH-SY5Y cells, preventing cell death and p-GSK-3β formation, by reversing increases in α-Syn accumulation and p-Tau formation. These data unveil a previously unappreciated role of α-Syn in the induction of p-GSK-3β, and demonstrate the importance of this kinase in the genesis and maintenance of neurodegenerative changes associated with PD.—Duka, T., Duka, V., Joyce, J. N., Sidhu, A. α-Synuclein contributes to GSK-3β-catalyzed Tau phosphorylation in Parkinson’s disease models.

Keywords: synucleopathies, tauopathies, neurodegeneration, Alzheimer’s disease

The microtubule (MT)-associated protein, Tau (1) and the presynaptic MT-binding protein, α-Synuclein (α-Syn) (2) have been classically linked to Alzheimer’s disease (AD) or Parkinson’s disease, respectively. Yet, there is increasing clinical evidence of a strong association between tauopathies and synucleopathies, where abnormalities in both Tau and α-Syn have been described. Thus, α-Syn-positive structures in different brain regions have been found in sporadic and familial AD patients (2,3,4,5,6), while Lewy bodies (LBs) are found in the amygdala of some sporadic and familial cases of AD and Down’s syndrome (7,8,9,10). Tau-immunoreactive LBs are detected in the medulla of 80% of individuals with sporadic PD or dementia with LBs, where Tau is often localized at the periphery of LBs (11, 12). Further evidence of an association of Tau pathology in synucleinopathies relies on the observation of p-Tau inclusions in transgenic mice overexpressing the A30P α-Syn mutation (3), as well as in synaptic-enriched fractions in 12-mo-old A53T transgenic mice (14). Moreover, it has long been hypothesized that α-Syn and p-Tau may be closely linked and that some toxic interaction must exist between these two proteins (15,16,17), but the mechanisms whereby such interactions may occur remain unknown. We have analyzed the linkage between α-Syn and p-Tau in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of PD, in which α-Syn was able to direct the hyperphosphorylation of Tau at specific sites: Ser-262 and Ser-396/404, but not Ser-202 (18). The requirement for α-Syn in this process was mandatory, and in α-Syn−/− mice or cells, the neurotoxin failed to increase p-Tau.

GSK-3β phosphorylates a majority of sites on Tau, which results in paired helical filaments (PHFs), as shown in cell culture (19) and rodent (20, 21) models of AD. Transgenic mice that overexpress GSK-3β also develop pretangle structures in the hippocampus and experience increased neuronal death, gliosis, and spatial learning deficits in the Morris water maze (22). It has been shown (23) that filaments resembling PHFs assemble when Sf9 cells overexpress hereditary frontotemporal dementia with parkinsonism-17 (FTDP-17) Tau (a form of Tau that includes three major mutations: G272V, P301L, and R406W). The amount of these polymers is decreased in lithium (Li)-treated cells, which suggests that phosphorylation of FTDP-17 Tau by GSK-3β induces a conformational change favoring the formation of fibrillar polymers (23). Moreover, a growing body of evidence suggests that GSK-3β is an important modulator of apoptosis and an increase in GSK-3β activity precedes the induction of apoptosis (24, 25). GSK-3β sits at the convergence of several signaling pathways that are critical for neuronal viability and proper function, and several apoptotic stimuli, including Aβ peptide, ischemia, and neurotoxins, such as MPTP and 6-hydroxydopamine, appear to be involved in pathways that activate GSK-3β (26,27,28).

To further explore the participation of GSK-3β and its active isoform p-GSK-3β, which is phosphorylated at Tyr-216, in the α-Syn-mediated induction of p-Tau, the current studies were undertaken. Here, we show that α-Syn triggers key events in diverse models of PD, causing recruitment of p-GSK-3β, enabling the hyperphosphorylation of Tau, providing for novel sites of intervention in the treatment and management of this disease.

MATERIALS AND METHODS

Postmortem human tissue

Postmortem brain striata were provided by the Sun Health Research Institute Brain Donor Program (Sun City, AZ, USA). The 10 age-matched control samples and 18 PD case samples were chosen to minimize differences in age, postmortem interval (<8 h), and sex. Diagnosis of PD followed standard clinical criteria and included a positive response to antiparkinsonian medication (e.g., l-dopa). Control cases were neuropathologically normal by histological examination and did not meet criteria for AD, PD, dementia with Lewy bodies, progressive supranuclear palsy, or other diagnostic category. Details on diagnosis, tissue collection, storage, and preparation of tissues were previously described (29).

Animals

α-Syn-knockout (α-Syn-KO) mice. All studies used male C57BL6 and homozygous α-Syn−/− (B6;129X- SncaTMLRossl) mice aged 8–12 wk. Mice were originally obtained in breeding pairs from Jackson Laboratories (Bar Harbor, ME, USA) to generate a stable breeding colony, as described previously (30).

Human α-Syn (hα-Syn)-overexpressor Tg mice. Male transgenic mice that overexpress α-Syn under the platelet-derived growth factor β (PDGFβ) promoter (31) and wild-type C57BL6 mice aged 8 mo were used for all experimental procedures.

Subchronic MPTP administration

Male homozygous α-Syn-KO and wild-type littermate control mice (8/group) received subcutaneous injections of vehicle (saline, 1 ml/kg) or MPTP (20 mg/kg) once daily for five consecutive days. Three days following the last injection, animals were decapitated; brains were quickly removed, frozen over dry ice, and stored at −80°C until analysis (18). Transgenic mice overexpressing PDGF-hα-Syn (8/group) were subchronically injected with MPTP, 4 injections with 20 mg/kg s.c., or saline as a vehicle, 2×/d at 8 h apart (32).

Cell culture and transfections

SH-SY5Y cells were cultured in DMEM F-12 supplemented with 10% fetal bovine serum, 5% glutamine, and 5% antibiotic/antimycotic. Cells were maintained at 37°C, 5% CO2. Human α-Syn and human dopamine transporter (hDAT) cDNAs were subcloned into pcDNA3.1, as described previously (33). SH-SY5Y human neuroblastoma cells stably transfected with α-Syn or mock transfected with vector alone (pcDNA3.1) were generated as described previously (34). Stably transfected cells were transiently cotransfected at 80% confluence with either hDAT or vector DNAs by FuGENE 6 transfection reagent (Roche Molecular Biochemicals, Indianapolis, IN, USA), as described by the manufacturer, and grown for a further 48 h after transfection to allow for expression of the hDAT transgene.

Primary mesencephalic neuronal cultures

Primary neuronal cultures from the ventral mesencephalon and prefrontal cortex of gestational 17- to 18-d-old rat embryos were prepared and maintained in a chemically defined, serum-free medium, permitting the maturation of neurons, while minimizing glial cell proliferation, according to previously described protocols (33). Experiments were performed on 8- to 10-d-old cultures.

Cell treatment

Primary cultures were treated in the serum-free medium, whereas SH-SY5Y cells were grown and treated in DMEM/F12 + 10% FBS, 2 mM l-glutamine, 100 U/ml penicillin, and 100 μg/ml streptomycin, at 37°C and 5% CO2. MPP+ (1-methyl-4-phenylpyridinium) iodide, prepared at 5 to 50 μM concentrations, was added directly to the medium in the 6-well dishes. Cells were exposed to MPP+ for 24–48 h or treated with an equal volume of vehicle (0.1% DMSO). For lithium (LiCl) and 4-benzyl-2-methyl-1,2,4-thiadiazolidine-3,5-dione (TDZD-8) treatments, SH-SY5Y cells cotransfected with α-Syn and DAT were serum-starved overnight, exposed to LiCl (0.1–10.0 mM) or TDZD-8 (0.04–1 μM) for 16 h in the continued presence of MPP+ (50 μM), and harvested 48 h after the initial addition of MPP+.

Determination of cell viability

Following the above cell treatment protocol, the level of cellular 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) was quantified, as described previously (35) Briefly, cells in 12-well plates were rinsed with phosphate buffered saline (PBS), and MTT (0.5 mg/ml) was added to each well. The microplate was incubated at 37°C for an additional 3 h. At the end of the incubation period, the medium with MTT was removed, and 1 ml pure ethanol (EtOH) was added to each well. The plate was shaken on the microplate shaker to dissolve the blue MTT-formazan. Absorbances were read at 564 nm. Cell viability was expressed as a percentage of the control culture.

Western blot analysis

Western blot analysis was performed as described previously (18). Samples were analyzed by Western blots with 12% SDS-PAGE. Primary antibodies used were TAU-5 (phosphorylation-independent antibody; 1:1000; Chemicon, Temecula, CA, USA), PHF-1 (pSer396/404; 1/500; provided by P. Davies, Albert Einstein College of Medicine, Bronx, NY, USA), CP13 (pSer202; 1:500; provided by P. Davies), and pSer262 (1/1,000; Biosource); α-Syn (mouse mAb; 1:1000; BD Transduction Laboratories, Franklin Lakes, NJ, USA); DAT (1:1000, Chemicon); GSK-3β (mouse mAb; 1:500; BD Transduction Laboratories); pY216-GSK-3β (mouse mAb; 1:500; BD Transduction Laboratories). Equal protein loading was confirmed with anti-β-actin antibody (sc-1616; 1:500; Santa Cruz Biotechnology, Santa Cruz, CA, USA). Protein bands were scanned by Epson Perfection 4870 Photo Scanner (Epson America, Long Beach, CA, USA) and quantitatively analyzed by Scion Image (Scion Corp., Frederick, MD, USA).

Immunoprecipitation

Cells were lysed in lysis buffer (10 mM Tris, pH 7.4; 150 mM NaCl; 1 mM EDTA; 1 mM EGTA; and 0.5% Nonidet P-40) supplemented with protease and phosphatase inhibitor cocktail. Solubilized proteins (300 μg) were precleared for 3 h at 4°C with protein A/G Plus-agarose immunoprecipitation reagent (Santa Cruz Biotechnology). After immunoprecipitation overnight at 4°C with α-Syn polyclonal Abs (1:100; Chemicon), or p-GSK-3β (Tyr216) (1:100; Santa Cruz Biotechnology), or nonimmune sera, immune complexes were recovered with protein A-Sepharose beads added for 5 h at 4°C. After 3 washes with lysis buffer, samples were boiled for 10 min and analyzed by Western blots.

Nuclear and cytoplasmic fractionation

Monolayers in 6-well dishes were trypsinized, and the cell suspension was washed with 3 vol of ice-cold phosphate-buffered saline by repeated centrifugation (500 g, 2 min, 4°C.) The cell pellet was gently resuspended in 300 μl/well of harvest buffer (250 mM sucrose; 50 mM Tris-Cl, pH 7.5; 5 mM MgCl2; and 0.5% (v/v) Nonidet P-40 supplemented with Complete, EDTA-free protease inhibitor mixture). After 5 min on ice, the nuclei were pelleted (1000 g, 5 min, 4°C). The supernatant (cytoplasmic fraction) was collected and cleared by centrifugation (16,000 g, 15 min, 4°C). The nuclear pellets were resuspended in nuclear extraction buffer (10 mM HEPES, pH 7.9; 10 mM KCl; and 1 mM EDTA) and pelleted again at 1000 g for 15 min. Both the cytoplasmic and nuclear protein extracts were sonicated for 10 s on ice. Complete separation of the cytosolic and nuclear fraction was verified by immunoblotting each fraction for tubulin (anti-β-tubulin III rabbit Ab; 1:1000; Sigma), a cytosolic protein, and histone (anti-histone H1 monoclonal Ab; 1:1000; Upstate Biotechnology, Inc., Lake Placid, NY, USA), a nuclear protein.

Statistical analysis

Results were expressed as means ± sd and statistically analyzed by the t test between two groups and analysis of variance among multiple groups. Statistical significance was accepted at the P < 0.05 level.

RESULTS

MPP+ induces α-Syn-dependent Tau phosphorylation through activation of GSK-3β

To test whether GSK-3β activity was altered after MPP+ treatment, we assessed GSK-3β activation by measuring the level of phosphorylated Tyr-216. SH-SY5Y neuroblastoma cells stably transfected with α-Syn (SHα-Syn) and transiently transfected with hDAT DNA (SHα-Syn/hDAT; ref. 34), were treated with 50 μM MPP+ for up to 48 h. It was essential to cotransfect cells with hDAT, since in the absence of the transporter MPP+ cannot enter cells, resulting in only very low toxicity (34). Vehicle-treated cells were used as controls for each time point of treatment. Cells were lysed, and p-GSK-3β was detected by Western blots using the pY216 antibody (Fig. 1A). There was a time-dependent elevation in the levels of p-GSK-3β formed on treatment of cells with MPP+, and after 48 h, a maximal increase of 166.16 ± 6.36% (P<0.05, n=5) was observed, relative to vehicle-treated cells. Total GSK-3β levels were unchanged by these treatments.

Figure 1.
MPP+ induces GSK-3β activation (A), overexpression of α-Syn (B), increases in p-Tau (C), and reductions in cell viability (D) in SHα-Syn/hDAT cells. SH-SY5Y neuroblastoma cells were stably transfected with α-Syn ...

MPP+ also induced a time-dependent increase in the accumulation of α-Syn (Fig. 1B), consistent with our previous findings in both transfected cells and in vivo (18, 34), and at 48 h, there was a maximal increase of 183.09 ± 11.24% in α-Syn levels (P<0.05, n=5).

To determine whether such increases in p-GSK-3β resulted in Tau hyperphosphorylation at known AD-linked substrate sites of this kinase, SH-SY5Y cells were incubated in the presence or absence of 50 μM MPP+ for 0–48 h, and cell lysates were immunoblotted with the phospho-dependent antibodies of Tau (Fig. 1C). MPP+ treatment for 24 h induced a robust and early increase in p-Tau at the pSer262 epitope (184.77±8.33; P<0.05, n=5), which decreased 32 h after MPP+ exposure (122.81±12.83; P<0.05, n=5) compared to vehicle-treated cells at the respective time points. After 40–48 h MPP+ treatment, the immunoreactivity in pSer262 remained elevated as compared to control cells. A significant (P<0.05) time-dependent increase (114.59±8.9, 123.54±10.03, 153.38±5.45, and 188.58±11.24% vs. vehicle-treated cells at 24, 32, 40, and 48 h after MPP+ exposure, respectively; n=5) in pSer396/404 levels was also seen in SHα-Syn/hDAT cells (Fig. 1C). We also probed for pSer202 but observed only small changes that were not significant, as compared to those seen with the pSer396/404 and pSer262 antibodies. These time-dependent changes in p-Tau on MPP+ exposure suggests that Tau is sequentially hyperphosphorylated in a time-dependent manner, first at Ser-262 and then at the Ser-396/404 epitope.

We next measured cell cytotoxicity in SH-SY5Y or SHα-Syn/hDAT cells treated with 50 μM of MPP+ for different times (24–48 h) by MTT assays (Fig. 1D). In cells expressing hDAT but no α-Syn (SH-SY5Y), treatment with MPP+ induced only a modest decrease in the number of viable cells, reaching a maximum after 48 h MPP+ treatment (71.89±3.33% viability vs. control levels; P<0.05, n=5). However, the cytotoxicity of MPP+ was more potent in the additional presence of α-Syn, and after 48 h MPP+ exposure, there was increased cell death in SHα-Syn cells (55.51±7.3% viability vs. control; P<0.05, n=5). These data are consistent with our earlier findings (18, 34) that the presence of α-Syn enhances MPP+ toxicity.

GSK-3β blockade by lithium or TDZD-8 reverses MPP+-induced increases in p-Tau formation, α-Syn accumulation, and cell viability in SHα-Syn/hDAT cells

To further assess the involvement of p-GSK-3β in MPP+ cytotoxicity, SHα-Syn/hDAT cells were treated with 50 μM MPP+ for 48 h in the absence or presence of increasing amounts of LiCl, an inhibitor of GSK-3β (Fig. 2A). LiCl prevented the MPP+-mediated increase in p-GSK-3β levels in a dose-dependent manner, with an IC50 of 1 mM; 10 mM of LiCl completely blocked the formation of p-GSK-3β (149.49±13.71, 122.04±5.09, and 101.16±12.71% at 0.1, 1.0, and 10.0 mM, respectively; P<0.05, n=5). LiCl also significantly reduced, but did not completely prevent, the observed increase in α-Syn levels caused by MPP+ (Fig. 2B) in a dose-dependent manner, indicating that at least part of the mechanism leading to α-Syn accumulation is independent of p-GSK-3β activation. LiCl completely reversed the MPP+-induced increase of pSer262 and pSer396/404 (Fig. 2C) in a dose dependent manner, indicating that GSK-3β is involved in MPP+-induced hyperphosphorylation of Tau. Interestingly, the IC50 of p-GSK-3β in preventing Tau phosphorylation at Ser-262 by LiCl was ~0.1 mM, while that for Ser-396/404-Tau was ~3 mM. In agreement with these findings, LiCl also diminished cell death induced by MPP+ in a dose-dependent manner (68.22±3.8, 77.54±3.49, and 85.59±9.94% at 0.1, 1.0, and 10.0 mM, respectively; P<0.05, n=5) (Fig. 2D).

Figure 2.
Effect of lithium chloride on MPP+-treated cells. SHα-Syn cells cotransfected with hDAT were treated with 50 μM MPP+ for 48 h in the absence or presence of indicated concentrations of LiCl. A–C) Western blots were ...

Although lithium is an inhibitor of GSK-3β, it may also cross-react with other kinases; we therefore used an additional highly selective, non-ATP competitive inhibitor of p-GSK-3β inhibitor, TDZD-8 (34). TDZD-8 blocked the activation of p-GSK-3β at much lower levels than that seen for LiCl, and at 0.04 μM, phosphorylation of GSK-3β was blocked (Fig. 3A). TDZD-8 also reduced accumulation of α-Syn at lower concentrations than LiCl, and at 1 μM, the increase in α-Syn by MPP+ was completely reversed (Fig. 3B). Similarly, TDZD-8 blocked the hyperphosphorylation of Tau, with greater inhibition of pSer396/404 immunoreactivity (by 52%) observed at 1 μM than with LiCl at the same concentration (Fig. 3C). TDZD-8 blockade of GSK-3β phosphorylation also resulted in increased cell survival (73.33±6.84, 80.11±4.57, and 74.93.59±6.91% of control at 0.04, 0.2, and 1.0 μM, respectively; P<0.05, n=5) (Fig. 3D). Together, these data further support a role for GSK-3β in mediating MPP+ cytotoxicity in this cellular model of PD.

Figure 3.
Effect of TDZD-8 on MPP+-treated cells. SHα-Syn cells cotransfected with hDAT were treated with 50 μM MPP+ for 48 h in the absence or presence of the indicated concentrations of TDZD-8. A–C) Western blots were conducted ...

GSK-3β is activated in MPP+-treated mesencephalic neurons, Tg mice subchronically treated with MPTP, and postmortem striatum of PD patients

To investigate the actions of MPP+ on p-GSK-3β in neurons, primary mesencephalic neurons were isolated from E18 rat embryos (18). MPP+ significantly increased p-GSK-3β levels (Fig. 4A) in a dose-dependent manner in these neurons (151.11±16.6, 185.54±12.6, and 232.1±18.8% vs. vehicle-treated neurons, at 0.5, 5, and 50 μM MPP+, respectively; P<0.05, n=3).

Figure 4.
Increased p-GSK-3β activatory phosphorylation in mesencephalic neurons (A), α-Syn-KO mice (B), and Tg mice overexpressing human α-Syn (C) after MPP+/MPTP applications, and in postmortem striata from clinically diagnosed ...

We then proceeded to investigate the contribution of α-Syn to MPTP-induced GSK-3β Tyr-216 phosphorylation, using α-Syn-KO mice. Administration of MPTP to WT mice increased striatal levels of p-GSK-3β (131.7±14.6% vs. saline-injected mice; P<0.05, n=4) (Fig. 4B). By contrast, administration of MPTP to α-Syn-KO mice failed to affect any changes in p-GSK-3β levels, which was not significantly different from α-Syn-KO mice treated with saline. A similar increase in striatal p-GSK-3β was also evident in Tg mice overexpressing α-Syn subchronically treated with MPTP (178.7±23.5% vs. saline-injected mice; P<0.05, n=4) (Fig. 4C). It should be noted that the increase in α-Syn-overexpressing Tg mice was >2-fold higher than that seen in WT type mice, suggesting that increased α-Syn levels lead to increased p-GSK-3β activation. Moreover, even in the Tg mice treated with saline alone, significantly higher levels (126.5±12.4% vs. saline-injected WT mice; P<0.05, n=4) of p-GSK-3β were seen, due to the overexpression of α-Syn in these mice. These combined data show that α-Syn is essential for activation of GSK-3β, since in its absence in α-Syn KO mice, MPTP failed to increase p-GSK-3β, while on its overexpression in Tg mice, MPTP caused robust increases in p-GSK-3β. It should be noted that the absence or presence of α-Syn did not change total GSK-3β levels (Fig. 4B, C), suggesting that α-Syn did not alter GSK-3β via a direct effect on total protein.

We next ascertained the clinical relevance of our findings by examining human postmortem striata from patients diagnosed with PD. When expressed relative to total GSK-3β, a significant increase (141.7±7.2%; P<0.05, n=18) was seen for the PD group, relative to age-matched controls (n=10) (Fig. 4C). These data mimic our in vitro and in vivo findings, providing evidence for increased p-GSK-3β levels in the pathophysiology of PD in humans.

MPP+ treatment induced translocation and accumulation of p-GSK-3β and α-Syn in the nucleus

Another emerging topic in the study of the regulation of GSK-3β and α-Syn concerns their subcellular localization, and toxic stimuli increase nuclear levels of GSK-3β (37) and α-Syn (38). We used cytoplasmic/nuclear subfractionation to analyze the nuclear translocation of p-GSK-3β in SHα-Syn/hDAT cells and mesencephalic neurons treated with different concentrations of MPP+. MPP+ induced a dose-dependent decrease in the cytosolic levels of p-GSK-3β, which was simultaneously accompanied by increased accumulation of p-GSK-3β in the nucleus of SHα-Syn/hDAT cells (Fig. 5A). Loss of cytosolic levels with increased nuclear levels of p-GSK-3β were seen in cells treated with 50μM MPP+ for 48 h (50.8±5.99 and 240.45±9.21% vs. vehicle-treated cells, respectively; n=4, P<0.05).

Figure 5.
MPP+-induced nuclear accumulation of GSK-3β. A, B) Top panels: representative Western blots of Hα-Syn/hDAT cells (A) and mesencephalic neurons (B) after application of MPP+ for 48 h. Cellular fractionation was confirmed ...

MPP+ treatment of mesencephalic neurons for 48 h first led to an increase in p-GSK-3β levels in the cytosol, followed by a decrease in cytosolic GSK-3β at higher concentrations of MPP+. By contrast, in all instances, the nuclear levels of p-GSK-3β were increased at all doses of MPP+, and at 50 μM of the neurotoxin (405.08±29.39% of p-GSK-3β vs. vehicle-treated neurons; P<0.05, n=3) (Fig. 5B).

When we similarly examined p-GSK-3β levels in cytosol and nucleus of human striata isolated from PD patients, increases in p-GSK-3β levels were seen in the cytosol (132.6±18.5%; P<0.05, n=18) compared to cytosolic extracts from striata of age-matched, non-PD controls (n=10) (Fig. 5C). Moreover, increased translocation of p-GSK-3β into the striatal nucleus of PD patients was also seen (161.6±29.6%; P<0.05, n=18) relative to control subjects (n=10).

When α-Syn levels in the nuclei and cytoplasm were examined, significantly elevated levels of α-Syn were also seen in the nucleus of transfected cells (Fig. 5A) and in mesencephalic neurons (Fig. 5B) on treatment with MPP+ in a dose-dependent manner. In addition, α-Syn levels in the nucleus were also increased in PD patients (Fig. 5C). It should be noted that the nuclei in PD striata are likely to be of glial and postsynaptic striatal origin. Nonetheless, on the basis of our findings of increased p-GSK-3β and α-Syn in the nuclei of the cellular models, it is likely that increases in nuclei presence of these proteins is an intrinsic part of PD.

Increased interaction between α-Syn, p-GSK-3β, and pSer396/404-Tau stimulated by MPP+

We next treated SH-SY5Y or SHα-Syn cells transiently transfected with hDAT DNA with 50 μM MPP+ for 24 and 48 h. Coimmunoprecipitations (co-IPs) were conducted on cell lysates with antibodies against α-Syn (Fig. 6A), p-GSK-3β (Fig. 6B), or pSer396/404-Tau (Fig. 6C). In α-Syn-precipitated samples, both p-GSK-3β and pSer396/404-Tau were detected in the immunopellets; in response to MPP+, there was an increase of ~86 and 80% in p-GSK-3β and pSer396/404-Tau immunoreactivities after 48 h of treatment, respectively (Fig. 6A). In these immunopellets, α-Syn was detected at similar levels, indicating that there were no differences in the amount of protein present in the pellets (Fig. 6A). In p-GSK-3β-immunoprecipitated extracts, α-Syn and pSer396/404-Tau were also detected in the immunopellets (Fig. 6B), with an increase in levels of α-Syn (~52%) and pSer396/404-Tau (~30%) after 50 μM MPP+ treatment for 48 h; p-GSK-3β levels in these pellets were also unchanged, attesting to the presence of equal amounts of protein. Finally, in co-IPs using the pSer396/404 antibody, increased levels of α-Syn (~110%) and p-GSK-3β (~98%) were detected in the immunopellets (Fig. 6C), without changes in pSer396/404-Tau levels. Together, these results indicate that on MPP+ treatment, a heterotrimeric protein complex consisting of α-Syn, p-GSK-3β, and pSer396/404-Tau is actively formed within SHα-Syn/hDAT cells.

Figure 6.
Co-IP studies indicated a complex of p-GSK-3β, α-Syn, and pSer396/404-Tau after MPP+ treatment. A–C) Time course of immunoprecipitation (IP) with α-Syn (A), p-GSK-3β (B), and Tau at Ser-396/404 (C) antibodies ...

DISCUSSION

Our recent studies have shown that the PD-linked neurotoxin MPTP contributes to the hyperphosphorylation of Tau in a manner strictly dependent on the presence of both DAT and α-Syn (18, 34). Because Tau is hyperphosphorylated by MPTP in an α-Syn-dependent manner at the p-GSK-3β-favored sites during MPTP neurotoxicity, Ser-396/404 and Ser-262, we studied here the direct involvement of p-GSK-3β in several diverse models of PD and in postmortem human striata. p-GSK-3β is known to have a critical role in neuronal apoptosis and pathogenesis of AD (24, 39,40,41,42), but its involvement, if any, in PD neurodegeneration is ill defined. PD mimetics such as 6-OHDA, rotenone, and MPP+/MPTP induce neuronal apoptosis in a GSK-3β-dependent manner in SH-SY5Y cells, PC12 cells, cerebellar granule neurons, and dopaminergic neurons (26,27,28), but it was unclear whether such responses were due to an innate consequence of oxidative stress, and the participation of α-Syn in these events was unknown. Moreover, the kinase has not been previously known to be activated in in vivo models of PD. Our work here for the first time demonstrates that in several in vitro and in vivo experimental models of PD, GSK-3β is activated in the presence of α-Syn by phosphorylation of the kinase at Tyr216, which then leads to Tau hyperphosphorylation at Ser-262 and Ser-396/404. Notably, we had similar findings in human postmortem PD striata, indicating that GSK-3β activation is of high clinical relevance.

Phosphorylation of GSK-3β at Ser-9 inhibits its activity, while activation occurs through dephosphorylation at Ser-9 and concomitant phosphorylation at Tyr216, which can result from autophosphorylation and from intracellular signaling mechanisms (43,44,45); p-GSK-3β is commonly denoted to represent the active form of the kinase phosphorylated at Tyr216. Our studies indicate that the oxidative stress associated with MPTP/MPP+-induced inhibition of complex I of the mitochondrial respiratory chain is not the mode by which GSK-3β is activated. Indeed, in SH-SY5Y cells lacking α-Syn and in α-Syn-KO mice, both of which express DAT but not α-Syn, and thus take up the neurotoxin, increases in p-GSK-3β levels were not observed, despite the presence of oxidative stress. These findings suggest that oxidative stress and production of free radicals, per se, through MPTP/MPP+-inhibition of complex I is insufficient to directly cause activation of p-GSK-3β. That p-GSK-3β is involved in the genesis of PD-like neurodegeneration and cell death was further demonstrated with lithium, as well as TDZD-8, a highly selective and potent GSK-3β inhibitor. Application of these inhibitors to cells reversed cell death induced by MPP+, while simultaneously reducing hyperphosphorylation of Tau at Ser-262 and Ser-396/404, along with reduced levels of accumulated α-Syn.

The most interesting aspect of our studies was the finding that α-Syn is absolutely necessary for activation of GSK-3β. Thus, in SH-SY5Y cells lacking α-Syn, or in α-Syn−/− mice, we were unable to see increases in p-GSK-3β levels or changes in Tau hyperphosphorylated at Ser-262 or Ser-396/404, despite treatment with MPP+/MPTP. Moreover, in α-Syn overexpressing Tg mice, the mere overexpression of α-Syn was sufficient to see a robust increase in p-GSK-3β levels, even in the absence of MPTP. This finding is of high clinical significance in partly understanding the genesis of PD, where gene duplication and triplication of α-Syn is linked to sporadic PD (46,47). Thus, in the event of gene duplication or triplication, increases in α-Syn levels could trigger the spontaneous formation of p-GSK-3β. Indeed, in postmortem striata from PD patients, which are known to contain high levels of α-Syn (48), a large and significant increase in p-GSK-3β levels was seen in our studies. Even in the absence of gene duplication and triplication, α-Syn is believed to accumulate in nigral neurons through inefficient clearance of this protein via the proteosomal degradative pathway (49), suggesting that under these circumstances also, p-GSK-3β levels could sharply increase.

The precise mechanism by which α-Syn contributes to the activation of GSK-3β remains to be established. Activation of GSK-3β via its phosphorylation at Tyr216 occurs through autophosphorylation (43) and several proapoptotic stimuli (50), as well as certain phospholipids, sulfatide, and heparin (51). Recent studies have suggested that chaperone proteins, such as hsp90, may be essential in autophosphorylation, since molecular chaperones are involved in protein folding (52). Thus, binding to chaperone proteins may change the protein folding structure of GSK-3β in a manner that permits easier autophosphorylative access to the Tyr216 site. α-Syn bears structural similarity to the 14-3–3 chaperone protein, a protein also known to interact with GSK-3β (53), and a chaperone-like function has been previously suggested for α-Syn (54). Therefore, it is possible that α-Syn acts to form protein complexes with GSK-3β, and in a manner reminiscent of hsp90, aiding the autophosphorylation of GSK-3β at Tyr216. Once activated, p-GSK-3β then proceeds to cause the hyperphosphorylation of Tau. Indeed, from our co-IP assays, physical interaction between α-Syn and GSK-3β was shown to occur, and these proteins were also able to form heterotrimeric complexes with Tau.

It is likely that α-Syn also has a major role in facilitating hyperphosphorylation of Tau. Both α-Syn and Tau bind to microtubules (1, 2, 55), are colocalized in cells and neurons (1), and can form heterodimeric complexes with one another (18). Similar to 14-3-3, which simultaneously binds to and bridges Tau and GSK-3β, stimulating GSK3-β-catalyzed Tau hyperphosphorylation (53), α-Syn may also have a similar bridging role in facilitating Tau hyperphosphorylation by p-GSK-3β. In this context, it should be noted that while both p-Tau and p-GSK-3β form complexes with one other in the absence of α-Syn, such interactions were significantly and robustly increased (by ~60–130%) in the presence of α-Syn and MPP+, as indexed by our reciprocal co-IP assays.

In addition to hyperphosphorylation of Tau, p-GSK-3β has the capacity to phosphorylate nuclear transcription factors such as Jun, Myc, HSF-1, and cAMP response element-binding protein (38) within the nucleus. In our experiments, there were increased levels of p-GSK-3β in the nucleus, probably representing translocation of nascently formed p-GSK-3β. By phosphorylating nuclear transcription factors, it is easy to envision how p-GSK-3β in the nucleus can trigger a series of events, which results in a proapoptotic response by the cell. Thus, blockade of the activity of this enzyme may represent a novel target in the treatment of Parkinson’s disease. In this context, it should be noted that p-GSK-3β inhibitors are in clinical trials in the treatment of AD (56, 57) and in AD Tg mouse models, chronic treatment with lithium shows promise in reducing Tau tangles (58).

The importance of GSK-3β inhibitors as potential PD therapeutics is further validated by their capacity to interfere with two of the major degenerative processes associated with PD: tau hyperphosphorylation and α-Syn-induced toxicity due to increased accumulation of this protein. In the present study, we utilized LiCl and TDZD-8 to inhibit the kinase in SH-SY5Y-cotransfected cells expressing α-Syn and hDAT. Both inhibitors blocked GSK-3β activation in a dose-dependent manner, with concomitant decreases in hyperphopsphorylation of tau, α-Syn accumulation, and cell death.

That elevated levels of p-GSK-3β are also seen in human PD brains, with high levels seen in the nucleus, suggests that this kinase is involved in the pathogenic progress of the human disease. This finding is also underscored by a recent report in which two functional single nucleotide polymorphisms have been reported in PD brains, resulting in increased phosphorylation of Tau and interaction of GSK-3β with Tau (59). Given the common neurochemical features of degenerative diseases, such as hyperphosphorylated Tau and α-Syn accumulation, GSK-3β inhibitors may well emerge as a new class of wide-spectrum drugs useful in preventing neurodegenerative diseases such as tauopathies and synucleopathies.

Acknowledgments

We are grateful to Dr. P. Davies (Albert Einstein College of Medicine, Bronx, NY, USA) for providing the antibodies PHF-1 and CP13 against Tau phosphorylated at Ser-396/404 and Ser-202. We thank Dr. John L. Goudreau (Department of Pharmacology and Toxicology, Michigan State University, East Lansing, MI, USA) for providing the striata from MPTP-treated α-Syn-knockout mice. We also thank Dr. Milan Rusnak for isolation of mesencephalic primary neurons. This work was supported in part by grants from the National Institute of Aging, R01AG028108, and National Institutes of Neurological Disorders and Stroke, R01NS45326, to A.S.

References

  • Hanger D P, Anderton B H, Noble W. Tau phosphorylation: the therapeutic challenge for neurodegenerative disease. Trends Mol Med. 2009;15:112–119, 2009. [PubMed]
  • Wersinger C, Sidhu A. Disruption of the interaction of alpha-synuclein with microtubules enhances cell surface recruitment of the dopamine transporter. Biochemistry. 2005;44:13612–13624. [PubMed]
  • Hamilton R L. Lewy bodies in Alzheimer’s disease: a neuropathological review of 145 cases using alpha-synuclein immunohistochemistry. Brain Pathol. 2000;10:378–384. [PubMed]
  • Kotzbauer P T, Trojanowski J Q, Lee V M. Lewy body pathology in Alzheimer’s disease. J Mol Neurosci. 2001;17:225–232. [PubMed]
  • Arai Y, Yamazaki M, Mori O, Muramatsu H, Asano G, Katayama Y. Alpha-synuclein-positive structures in cases with sporadic Alzheimer’s disease: morphology and its relationship to tau aggregation. Brain Res. 2001;888:287–296. [PubMed]
  • Hishikawa N, Hashizume Y, Ujihira N, Okada Y, Yoshida M, Sobue G. Alpha-synuclein-positive structures in association with diffuse neurofibrillary tangles with calcification. Neuropathol Appl Neurobiol. 2003;29:280–287. [PubMed]
  • Popescu A, Lippa C F, Lee V M, Trojanowski J Q. Lewy bodies in the amygdala: increase of alpha-synuclein aggregates in neurodegenerative diseases with tau-based inclusions. Arch Neurol. 2004;61:1915–1919. [PubMed]
  • Trembath Y, Rosenberg C, Ervin J F, Schmechel D E, Gaskell P, Pericak-Vance M, Vance J, Hulette C M. Lewy body pathology is a frequent co-pathology in familial Alzheimer’s disease. Acta Neuropathol. 2003;105:484–488. [PubMed]
  • Lippa S M, Lippa C F, Mori H. α-Synuclein aggregation in pathological aging and Alzheimer’s disease: the impact of beta-amyloid plaque level. Am J Alzheimers Dis Other Demen. 2005;20:315–318. [PubMed]
  • Lippa C F, Schmidt M L, Lee V M, Trojanowski J Q. Antibodies to alpha-synuclein detect Lewy bodies in many Down’s syndrome brains with Alzheimer’s disease. Ann Neurol. 1999;45:353–357. [PubMed]
  • Arima K, Hirai S, Sunohara N, Aoto K, Izumiyama Y, Uéda K, Ikeda K, Kawai M. Cellular co-localization of phosphorylated tau- and NACP/alpha-synuclein-epitopes in lewy bodies in sporadic Parkinson’s disease and in dementia with Lewy bodies. Brain Res. 1999;843:53–61. [PubMed]
  • Ishizawa T, Mattila P, Davies P, Wang D, Dickson D W. Colocalization of tau and alpha-synuclein epitopes in Lewy bodies. J Neuropathol Exp Neurol. 2003;4:389–397. [PubMed]
  • Frasier M, Walzer M, McCarthy L, Magnuson D, Lee J M, Haas C, Kahle P, Wolozin B. Tau phosphorylation increases in symptomatic mice overexpressing A30P alpha-synuclein. Exp Neurol. 2005;192:274–287. [PubMed]
  • Muntané G, Dalfó E, Martinez A, Ferrer I. Phosphorylation of tau and alpha-synuclein in synaptic-enriched fractions of the frontal cortex in Alzheimer’s disease, and in Parkinson’s disease and related alpha-synucleinopathies. Neuroscience. 2008;152:913–923. [PubMed]
  • Geddes J W. α-Synuclein: a potent inducer of tau pathology. Exp Neurol. 2005;192:244–250. [PubMed]
  • Frasier M, Wolozin B. Following the leader: fibrillization of alpha-synuclein and tau. Exp Neurol. 2004;187:235–239. [PubMed]
  • Dickson D W. Tau and synuclein and their role in neuropathology. Brain Pathol. 1999;9:657–661. [PubMed]
  • Duka T, Rusnak M, Drolet R E, Duka V, Wersinger C, Goudreau J L, Sidhu A. Alpha-synuclein induces hyperphosphorylation of Tau in the MPTP model of parkinsonism. FASEB J. 2006;20:2302–2312. [PubMed]
  • Lovestone S, Reynolds C H, Latimer D, Davis D R, Anderton B H, Gallo J M, Hanger D, Mulot S, Marquardt B, Stabel S, Woodgett J R, Miller C J. Alzheimer’s disease-like phosphorylation of the microtubule-associated protein tau by glycogen synthase kinase-3 in transfected mammalian cells. Curr Biol. 1994;4:1077–1086. [PubMed]
  • Hong M, Chen D C, Klein P S, Lee V M. Lithium reduces tau phosphorylation by inhibition of glycogen synthase kinase-3. J Biol Chem. 1997;272:25326–25332. [PubMed]
  • Muñoz-Montaño J R, Moreno F J, Avila J, Diaz-Nido J. Lithium inhibits Alzheimer’s disease-like tau protein phosphorylation in neurons. FEBS Lett. 1997;411:183–188. [PubMed]
  • Hernández F, Borrell J, Guaza C, Avila J, Lucas J J. Spatial learning deficit in transgenic mice that conditionally over-express GSK-3beta in the brain but do not form tau filaments. J Neurochem. 2002;83:1529–1533. [PubMed]
  • Gómez-Ramos A, Abad X, López Fanarraga M, Bhat R, Zabala J C, Avila J. Expression of an altered form of tau in Sf9 insect cells results in the assembly of polymers resembling Alzheimer’s paired helical filaments. Brain Res. 2004;1007:57–64. [PubMed]
  • Pap M, Cooper G M. Role of glycogen synthase kinase-3 in the phosphatidylinositol 3-kinase/Akt cell survival pathway. J Biol Chem. 1998;273:19929–19932. [PubMed]
  • Bijur G N, De Sarno P, Jope R S. Glycogen synthase kinase-3beta facilitates staurosporine- and heat shock-induced apoptosis. Protection by lithium. J Biol Chem. 2000;275:7583–7590. [PubMed]
  • Chen G, Bower K A, Ma C, Fang S, Thiele C J, Luo J. Glycogen synthase kinase 3beta (GSK3beta) mediates 6-hydroxydopamine-induced neuronal death. FASEB J. 2004;18:1162–1164. [PubMed]
  • Kozikowski A P, Gaisina I N, Petukhov P A, Sridhar J, King L T, Blond S Y, Duka T, Rusnak M, Sidhu A. Highly potent and specific GSK-3β inhibitors that block tau phosphorylation and decrease α-synuclein protein expression in a cellular model of Parkinson’s disease. Chem Med Chem. 2006;1:256–266. [PubMed]
  • Wang W, Yang Y, Ying C, Li W, Ruan H, Zhu X, You Y, Han Y, Chen R, Wang Y, Li M. Inhibition of glycogen synthase kinase-3β protects dopaminergic neurons from MPTP toxicity. Neuropharmacology. 2007;52:1678–1684. [PubMed]
  • Joyce J N, Ryoo H L, Beach T B, Caviness J N, Stacy M, Gurevich E V, Reiser M, Adler C H. Loss of response to levodopa in Parkinson’s disease and co-occurrence with dementia: role of D3 and not D2 receptors. Brain Res. 2002;955:138–152. [PubMed]
  • Drolet R E, Behrouz B, Lookingland K J, Goudreau J L. Mice lacking alpha-synuclein have an attenuated loss of striatal dopamine following prolonged chronic MPTP administration. Neurotoxicology. 2004;25:761–769. [PubMed]
  • Masliah E, Rockenstein E, Veinbergs I, Mallory M, Hashimoto M, Takeda A, Sagara Y, Sisk A, Mucke L. Dopaminergic loss and inclusion body formation in alpha-synuclein mice: implications for neurodegenerative disorders. Science. 2000;287:1265–1269. [PubMed]
  • Joyce J N, Presgraves S, Renish L, Borwege S, Osredkar T, Hagner D, Replogle M, PazSoldan M, Millan M J. Neuroprotective effects of the novel D3/D2 receptor agonist and antiparkinson agent, S32504, in vitro against 1-methyl-4-phenylpyridinium (MPP+) and in vivo against 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP): a comparison to ropinirole. Exp Neurol. 2003;184:393–407. [PubMed]
  • Wersinger C, Prou D, Vernier P, Sidhu A. Modulation of dopamine transporter function by alpha-synuclein is altered by impairment of cell adhesion and by induction of oxidative stress. FASEB J. 2003;17:2151–2153. [PubMed]
  • Duka T, Sidhu A. The neurotoxin, MPP+, induces hyperphosphorylation of Tau, in the presence of alpha-Synuclein, in SH-SY5Y neuroblastoma cells. Neurotox Res. 2006;10:1–10. [PubMed]
  • Loo D T, Rillema J R. Measurement of cell death. Methods Cell Biol. 1998;57:251–264. [PubMed]
  • Kim S D, Yang S I, Kim H C, Shin C Y, Ko K H. Inhibition of GSK-3β mediates expression of MMP-9 through ERK1/2 activation and translocation of NF-κB in rat primary astrocyte. Brain Res. 2007;1186:12–20. [PubMed]
  • Bijur G N, Jope R S. Proapoptotic stimuli induce nuclear accumulation of glycogen synthase kinase-3 β J Biol Chem. 2001;276:37436–37442. [PMC free article] [PubMed]
  • Goers J, Manning-Bog A B, McCormack A L, Miller I S, Doniach S, Di Monte D A, Uversky V N, Fink A L. Nuclear localization of α-synuclein and its interaction with histones. Biochemistry. 2003;42:8465–8471. [PubMed]
  • Hetman M, Cavanaugh J E, Kimelman D, Xia Z. Role of glycogen synthase kinase-3β in neuronal apoptosis induced by trophic withdrawal. J Neurosci. 2000;20:2567–2574. [PubMed]
  • Frame S, Cohen P. GSK3 takes centre stage more than 20 years after its discovery. Biochem J. 2001;359:1–16. [PMC free article] [PubMed]
  • Li B, Ryder J, Su Y, Moore S A, Jr, Liu F, Solenberg P, Brune K, Fox N, Ni B, Liu R, Zhou Y. Overexpression of GSK3βS9A resulted in tau hyperphosphorylation and morphology reminiscent of pretangle-like neurons in the brain of PDGSK3β transgenic mice. Transgenic Res. 2004;13:385–396. [PubMed]
  • Luna-Muñoz J, García-Sierra F, Falcón V, Menéndez I, Chávez-Macías L, Mena R. Regional conformational change involving phosphorylation of tau protein at the Thr231, precedes the structural change detected by Alz-50 antibody in Alzheimer’s disease. J Alzheimers Dis. 8:29–41. [PubMed]
  • Cole A R, Knebel A, Morrice N A, Robertson L A, Irving A J, Connolly C N, Sutherland C. GSK-3 phosphorylation of the Alzheimer epitope within collapsin response mediator proteins regulates axon elongation in primary neurons. J Biol Chem. 2004;279:50176–50180. [PMC free article] [PubMed]
  • Cohen P, Frame S. The renaissance of GSK3. Nat Rev Mol Cell Biol. 2001;2:769–776. [PubMed]
  • Bhat R V, Shanley J, Correll M P, Fieles W E, Keith R A, Scott C W, Lee C M. Regulation and localization of tyrosine216 phosphorylation of glycogen synthase kinase-3β in cellular and animal models of neuronal degeneration. Proc Natl Acad Sci U S A. 2000;97:11074–11079. [PMC free article] [PubMed]
  • Ibáñez P, Bonnet A M, Débarges B, Lohmann E, Tison F, Pollak P, Agid Y, Dürr A, Brice A. Causal relation between alpha-synuclein gene duplication and familial Parkinson’s disease. Lancet. 2004;364:1169–1171. [PubMed]
  • Singleton A B, Farrer M, Johnson J, Singleton A, Hague S, Kachergus J, Hulihan M, Peuralinna T, Dutra A, Nussbaum R, Lincoln S, Crawley A, Hanson M, Maraganore D, Adler C, Cookson M R, Muenter M, Baptista M, Miller D, Blancato J, Hardy J, Gwinn-Hardy K. α-Synuclein locus triplication causes Parkinson’s disease. Science. 2003;302:841. [PubMed]
  • Kirik D, Rosenblad C, Burger C, Lundberg C, Johansen T E, Muzyczka N, Mandel R J, Björklund A. Parkinson-like neurodegeneration induced by targeted overexpression of α-synuclein in the nigrostriatal system. J Neurosci. 2002;22:2780–2791. [PubMed]
  • Bedford L, Hay D, Paine S, Rezvani N, Mee M, Lowe J, Mayer R J. Is malfunction of the ubiquitin proteasome system the primary cause of alpha-synucleinopathies and other chronic human neurodegenerative disease? Biochim Biophys Acta. 2008;1782:683–690. [PubMed]
  • Habas A, Kharebava G, Szatmari E, Hetman M. NMDA neuroprotection against a phosphatidylinositol-3 kinase inhibitor, LY294002 by NR2B-mediated suppression of glycogen synthase kinase-3β-induced apoptosis. J Neurochem. 2006;96:335–348. [PubMed]
  • Kawakami F, Yamaguchi A, Suzuki K, Yamamoto T, Ohtsuki K. Biochemical characterization of phospholipids, sulfatide and heparin as potent stimulators for autophosphorylation of GSK-3β and the GSK-3β-mediated phosphorylation of myelin basic protein in vitro. J Biochem. 2007;143:359–367. [PubMed]
  • Lochhead P A, Kinstrie R, Sibbet G, Rawjee T, Morrice N, Cleghon V. A chaperone-dependent GSK3beta transitional intermediate mediates activation-loop autophosphorylation. Mol Cell. 24:627–633. [PubMed]
  • Agarwal-Mawal A, Qureshi H Y, Cafferty P W, Yuan Z, Han D, Lin R, Paudel H K. 14–3-3 connects glycogen synthase kinase-3 beta to tau within a brain microtubule-associated tau phosphorylation complex. J Biol Chem. 2003;278:12722–12728. [PubMed]
  • Ostrerova N, Petrucelli L, Farrer M, Mehta N, Choi P, Hardy J, Wolozin B. α-Synuclein shares physical and functional homology with 14-3-3 proteins. J Neurosci. 19:5782–57891. [PubMed]
  • Jeannotte A M, Sidhu A. Regulation of the norepinephrine transporter by α-synuclein-mediated interactions with microtubules. Eur J Neurosci. 2007;26:1509–1520. [PubMed]
  • Vadivelan S, Sinha B N, Tajne S, Jagarlapudi S A. Fragment and knowledge-based design of selective GSK-3β inhibitors using virtual screening models. [Online] Eur J Med Chem. 2008 doi:10.1016/j.ejmech.2008.08.012. [PubMed]
  • Martinez A, Perez D I. GSK-3 inhibitors: a ray of hope for the treatment of Alzheimer’s disease? J Alzheimers Dis. 2008;15:181–191. [PubMed]
  • Caccamo A, Oddo S, Tran L X, LaFerla F M. Lithium reduces tau phosphorylation but not A beta or working memory deficits in a transgenic model with both plaques and tangles. Am J Pathol. 2007;170:1669–1675. [PMC free article] [PubMed]
  • Kwok J B, Hallupp M, Loy C T, Chan D K, Woo J, Mellick G D, Buchanan D D, Silburn P A, Halliday G M, Schofield P R. GSK3B polymorphisms alter transcription and splicing in Parkinson’s disease. Ann Neurol. 2005;58:829–839. [PubMed]

Articles from The FASEB Journal are provided here courtesy of The Federation of American Societies for Experimental Biology
PubReader format: click here to try

Formats:

Related citations in PubMed

See reviews...See all...

Cited by other articles in PMC

See all...

Links