Inhibiting Tau Hyperphosphorylation Research Articles

PL - 028 Aerobic exercise inhibits tau hyperphosphorylation through activation of the PI3K/Akt pathway in the hippocampus of APP/PS1 mice

Objective Many studies suggest that regular physical exercise can reduce the risk of Alzheimer’s disease and slow its onset and progression. However, the exact mechanism is still unclear. Clinically, Alzheimer’s disease is characterized by the presence of extracellular amyloid plaques and intraneuronal neurofibrillary tangles, which are associated with amyloid-β and tau hyperphosphorylation respectively. The PI3K/Akt signaling pathway regulates tau phosphorylation and plays a pivotal role in the development of pathology in Alzheimer’s disease. Here we investigated the effects of aerobic exercise on tau phosphorylation and examined whether these effects were mediated by the PI3K/Akt pathway in the hippocampus of APP/PS1 transgenic mice.
 Methods 40 male APP/PS1 transgenic mice were randomly divided into four groups: sedentary group (T-SE; n=10), exercise group (T-EX; n=10), sedentary with GNE-317 treatment group (T-SEG; n=10) and exercise with GNE-317 treatment group (T-EXG; n=10). GNE-317 is a potent and selective PI3K/Akt pathway inhibitor that can cross the blood-brain barrier and show effective suppression of Akt phosphorylation in the mice brain. The mice in the T-EX and T-EXG groups were given exercise training on a treadmill for 5 days/week for 8 weeks with 0% grade, and progressively ran from 30 min/day at 12 m/min, up to 60 min/day at 15 m/min. The mice in the T-SE and T-SEG groups were placed individually on another treadmill at 0 m/min for the same duration. 48 hours after the last exercise bout, all mice were intraperitoneally injected an anesthetic for inducing anesthesia, and the hippocampus were rapidly extracted. The protein and phosphorylation levels of tau, PI3K, Akt and GSK3β were assayed by Western blot and immunohistochemistry. The cognitive function were tested by morris water maze.
 Results We found out that 8 weeks of aerobic exercise reduced tau phosphorylation at multiple sites including Ser202, Thr231 and Ser396, and increased phosphorylation of Akt at Thr308 and Ser473 and of GSK3β at Ser9. Furthermore, in the morris water maze test, the exercise group showed a reduced escape time and distance compared with those of the sedentary group, suggesting that aerobic exercise improved learning and cognitive ability. While the above-mentioned results were attenuated in the PI3K/Akt inhibitor GNE-317 treatment groups.
 Conclusions Our study demonstrated that aerobic exercise could inhibit tau hyperphosphorylation and improve cognitive funtion through activation of the PI3K/Akt pathway in the hippocampus of APP/PS1 mice.

Cornel Iridoid Glycoside Inhibits Tau Hyperphosphorylation via Regulating Cross-Talk Between GSK-3β and PP2A Signaling.

Neurofibrillary pathology contributes to neuronal dysfunction and correlates with the clinical progression of Alzheimer’s disease (AD). Tau phosphorylation is mainly regulated by a balance of glycogen synthase kinase-3β (GSK-3β) and protein phosphatase 2A (PP2A) activities. Cornel iridoid glycoside (CIG) is a main component extracted from Cornus officinalis. The purpose of this study was to investigate the effects of CIG on GSK-3β and PP2A, thus to explore the mechanisms of CIG to inhibit tau hyperphosphorylation. The rat model of tau hyperphosphorylation was established by intraventricular injection of wortmannin and GF-109203X (GFX) to activate GSK-3β. The results showed that intragastrical administration of CIG inhibited tau hyperphosphorylation in the brain of rats induced by wortmannin/GFX. The results in vivo and in vitro exhibited that CIG inhibited tau hyperphosphorylation and GSK-3β over-activation. In the mechanism of action, CIG’s attenuating GSK-3β activity was found to be dependent on PI3K/AKT signaling pathway. PP2A catalytic C subunit (PP2Ac) siRNA abrogated the effect of CIG on PI3K/AKT/GSK-3β. Additionally and crucially, we also found that CIG inhibited the demethylation of PP2Ac at Leu309 in vivo and in vitro. It enhanced PP2A activity, decreased tau hyperphosphorylation, and protected cell morphology in okadaic acid (OA)-induced cell model in vitro. PP2Ac siRNA abated the inhibitory effect of CIG on tau hyperphosphorylation. Moreover, CIG inhibited protein phosphatase methylesterase-1 (PME-1) and demethylation of PP2Ac, enhanced PP2A activity, and decreased tau hyperphosphorylation in PME-1-transfectd cells. Taken together, CIG inhibited GSK-3β activity via promoting P13K/AKT and PP2A signaling pathways. In addition, CIG also elevated PP2A activity via inhibiting PME-1-induced PP2Ac demethylation to inhibit GSK-3β activity, thus regulated the cross-talk between GSK-3β and PP2A signaling and consequently inhibited tau hyperphosphorylation. These results suggest that CIG may be a promising agent for AD therapy.

Effects of celastrol on Tau hyperphosphorylation and expression of HSF-1 and HSP70 in SH-SY5Y neuroblastoma cells induced by amyloid-β peptides.

To observe the effects of celastrol on Tau hyperphosphorylation induced by amyloid-β peptides (Aβ) in SH-SY5Y neuroblastoma cells, the changes of Tau hyperphosphorylation and the expression of heat shock protein 90 (HSP90), HSP70, and heat shock factor 1(HSF-1) in SH-SY5Y cells treated with Aβ1-42 and celastrol were measured. Tau hyperphosphorylation and HSP90 expression induced by Aβ1-42 was also measured by Western blotting after HSP70 or HSF-1 knockdown by siRNA. The interaction between HSP70 and Tau or HSP70 and carboxyl terminus of HSP70 interacting protein (CHIP) was measured by co-immunoprecipitation. Compared with the control group, the expressions of HSP70 and HSF-1 were markedly decreased after the induction of Aβ1-42 , whereas the expressions of HSP90, Tau phospho S199/202, and Tau phospho S396 were markedly increased. Meanwhile, both celastrol treatment and knockdown of HSP70 or HSF-1 in SH-SY5Y cells significantly inhibited the Tau hyperphosphorylation and HSP90 expression induced by Aβ1-42 . Moreover, celastrol treatment had no effects on Aβ1-42 -induced decreased expression of HSP70 and HSF-1, Tau ubiquitination, and the interaction of HSP70/Tau and HSP70/CHIP. These results suggest that celastrol- inhibited Tau hyperphosphorylation may not be dependent on the cause of HSF-1/HSP70/CHIP-mediated ubiquitination of Tau.

Upregulation of TREM2 Ameliorates Neuroinflammatory Responses and Improves Cognitive Deficits Triggered by Surgical Trauma in Appswe/PS1dE9 Mice

Background/Aims: TREM2 plays a crucial role in modulating microglial function through interaction with DAP12, the adapter for TREM2. Emerging evidence has demonstrated that TREM2 could suppress neuroinflammatory responses by repression of microglia-mediated cytokine production. This study investigated the potential role of TREM2 in surgery-induced cognitive deficits and neuroinflammatory responses in wild-type (WT) and APPswe/PS1dE9 mice. Methods: Adult APPswe/PS1dE9 transgenic male mice (a classic transgenic model of Alzheimer’s disease, 3 months old) and their age-matched WT mice received intracerebral lentiviral particles encoding the mouse TREM2 gene and then were subjected to partial hepatectomy at 1 month after the lentiviral particle injection. The behavioral changes were evaluated with an open-field test and Morris water maze test on postoperative days 3, 7, and 14. Hippocampal TREM2, DAP12, and interleukin (IL)-1β were measured at each time point. Ionized calcium-binding adapter molecule 1 (Iba-1), microglial M2 phenotype marker Arg1, synaptophysin, tau hyperphosphorylation (T396), and glycogen synthase kinase-3β (GSK-3β) were also examined in the hippocampus. Results: Surgical trauma induced an exacerbated cognitive impairment and enhanced hippocampal IL-1β expression in the transgenic mice on postoperative days 3 and 7. A corresponding decline in the levels of TREM2 was also found on postoperative days 3, 7, and 14. Overexpression of TREM2 downregulated the levels of IL-1β, ameliorated T396 expression, inhibited the activity of GSK-3β, and improved sickness behavior. Increased Arg1 expression and a high level of synaptophysin were also observed in the transgenic mice following TREM2 overexpression. Conclusion: The downregulation of TREM2 exacerbated surgery-induced cognitive deficits and exaggerated neuroinflammatory responses in this rodent model. Overexpression of TREM2 potentially attenuated these effects by decreasing the associated production of proinflammatory cytokines, inhibiting tau hyperphosphorylation, and enhancing synaptophysin expression.

Cornel iridoid glycoside protected synaptic function by inhibiting tau hyperphosphorylation

Cornel iridoid glycoside protected synaptic function by inhibiting tau hyperphosphorylation

α-Lipoic acid improves abnormal behavior by mitigation of oxidative stress, inflammation, ferroptosis, and tauopathy in P301S Tau transgenic mice

Alzheimer's disease (AD) is the most common neurodegenerative disease and is characterized by neurofibrillary tangles (NFTs) composed of Tau protein. α-Lipoic acid (LA) has been found to stabilize the cognitive function of AD patients, and animal study findings have confirmed its anti-amyloidogenic properties. However, the underlying mechanisms remain unclear, especially with respect to the ability of LA to control Tau pathology and neuronal damage. Here, we found that LA supplementation effectively inhibited the hyperphosphorylation of Tau at several AD-related sites, accompanied by reduced cognitive decline in P301S Tau transgenic mice. Furthermore, we found that LA not only inhibited the activity of calpain1, which has been associated with tauopathy development and neurodegeneration via modulating the activity of several kinases, but also significantly decreased the calcium content of brain tissue in LA-treated mice. Next, we screened for various modes of neural cell death in the brain tissue of LA-treated mice. We found that caspase-dependent apoptosis was potently inhibited, whereas autophagy did not show significant changes after LA supplementation. Interestingly, Tau-induced iron overload, lipid peroxidation, and inflammation, which are involved in ferroptosis, were significantly blocked by LA administration. These results provide compelling evidence that LA plays a role in inhibiting Tau hyperphosphorylation and neuronal loss, including ferroptosis, through several pathways, suggesting that LA may be a potential therapy for tauopathies.

LX2343 alleviates cognitive impairments in AD model rats by inhibiting oxidative stress-induced neuronal apoptosis and tauopathy.

Alzheimer's disease (AD) is a progressive neurodegenerative disease leading to the irreversible loss of brain neurons and cognitive abilities, and the vicious interplay between oxidative stress (OS) and tauopathy is believed to be one of the major players in AD development. Here, we demonstrated the capability of the small molecule N-(1,3-benzodioxol-5-yl)-2-[5-chloro-2-methoxy(phenylsulfonyl)anilino]acetamide (LX2343) to ameliorate the cognitive dysfunction of AD model rats by inhibiting OS-induced neuronal apoptosis and tauopathy. Streptozotocin (STZ) was used to induce OS in neuronal cells in vitro and in AD model rats that were made by intracerebroventricular injection of STZ (3 mg/kg, bilaterally), and Morris water maze test was used to evaluate the cognitive dysfunction in ICV-STZ rats. Treatment with LX2343 (5-20 μmol/L) significantly attenuated STZ-induced apoptosis in SH-SY5Y cells and mouse primary cortical neurons by alleviating OS and inhibiting the JNK/p38 and pro-apoptotic pathways. LX2343 was able to restore the integrity of mitochondrial function and morphology, increase ATP biosynthesis, and reduce ROS accumulation in the neuronal cells. In addition, LX2343 was found to be a non-ATP competitive GSK-3β inhibitor with IC50 of 1.84±0.07 μmol/L, and it potently inhibited tau hyperphosphorylation in the neuronal cells. In ICV-STZ rats, administration of LX2343 (7, 21 mg·kg-1·d-1, ip, for 5 weeks) efficiently improved their cognitive deficits. LX2343 ameliorates the cognitive dysfunction in the AD model rats by suppressing OS-induced neuronal apoptosis and tauopathy, thus highlighting the potential of LX2343 for the treatment of AD.

Intranasal BMP9 Ameliorates Alzheimer Disease-Like Pathology and Cognitive Deficits in APP/PS1 Transgenic Mice.

Alzheimer’s disease (AD) is the most common type of dementia and has no effective therapies. Previous studies showed that bone morphogenetic protein 9 (BMP9), an important factor in the differentiation and phenotype maintenance of cholinergic neurons, ameliorated the cholinergic defects resulting from amyloid deposition. These findings suggest that BMP9 has potential as a therapeutic agent for AD. However, the effects of BMP9 on cognitive function in AD and its underlying mechanisms remain elusive. In the present study, BMP9 was delivered intranasally to 7-month-old APP/PS1 mice for 4 weeks. Our data showed that intranasal BMP9 administration significantly improved the spatial and associative learning and memory of APP/PS1 mice. We also found that intranasal BMP9 administration significantly reduced the amyloid β (Aβ) plaques overall, inhibited tau hyperphosphorylation, and suppressed neuroinflammation in the transgenic mouse brain. Furthermore, intranasal BMP9 administration significantly promoted the expression of low-density lipoprotein receptor-related protein 1 (LRP1), an important membrane receptor involved in the clearance of amyloid β via the blood-brain barrier (BBB), and elevated the phosphorylation levels of glycogen synthase kinase-3β (Ser9), which is considered the main kinase involved in tau hyperphosphorylation. Our results suggest that BMP9 may be a promising candidate for treating AD by targeting multiple key pathways in the disease pathogenesis.

Beneficial effects of cornel iridoid glycoside on behavioral impairment and senescence status in SAMP8 mice at different ages

The aim of the present study was to investigate the effects of cornel iridoid glycoside (CIG) on behavioral changes and senescent status in senescence-accelerated mouse-prone 8 (SAMP8) mice at different ages (6, 10, and 14 months old). The learning and memory ability, the motor function and the aging conditions of SAMP8 mice were evaluated after CIG treatment in this study. Results showed that intragastrical administration of CIG (100 and 200mg/kg) for two months obviously improved the impaired cognitive ability of SAMP8 mice at the age of 6 months and 10 months, respectively. The treatment with CIG significantly increased the motor function of SAMP8 mice at 10 months and 14 months of age, respectively. CIG also evidently decreased the high grading score of senescence and increased the low surviving rate of SAMP8 mice at the age of 14 months. In addition, CIG treatment inhibited tau hyperphosphorylation in the hippocampus and striatum of SAMP8 mice at different ages. Together, these results indicate that CIG represent a potentially useful treatment for ameliorating the impaired cognitive ability, the motor dysfunction, aging conditions and hyperphosphorylation of tau in aging and age-related neurodegenerative diseases, such as Alzheimer’s disease.

The combination of 1α,25dihydroxyvitaminD3 with resveratrol improves neuronal degeneration by regulating endoplasmic reticulum stress, insulin signaling and inhibiting tau hyperphosphorylation in SH-SY5Y cells

Endoplasmic reticulum (ER) stress is a critical factor involved in the pathogenesis of Alzheimer's disease (AD). Vitamin D and resveratrol are two nutritional factors that have reported neuroprotective effects, and findings from cellular models suggest that resveratrol could potentiate vitamin D's effects. We aimed to determine the effects of vitamin D & resveratrol on ER stress mediated neurodegeneration and whether synergistic effects existed. Tunicamycin and Aβ25–35 was utilized to induce ER stress in SH-SY5Y cells, cells were then incubated with vitamin D and resveratrol. The combination of vitamin D & resveratrol completely reversed tunicamycin and Aβ25–35 induced cytotoxicity in SH-SY5Y cells, as well as elevation in ER stress markers (i.e.GRP78, p-eIF2α and CHOP), insulin signaling disruption (i.e. elevation in p-IRS-1serine307 and reduction in p-Akt serine473) and tau phosphorylation (i.e. reduction in p-GSK3β serine9, and elevation in p-Tau serine396 &404). Further studies are required to clarify whether the observed synergistic effects in the present study would also existed in vivo, this will lay scientific foundation whether the combination of vitamin D with resveratrol might be an effective maneuver in the treatment of AD in human subjects.

Morroniside-Induced PP2A Activation Antagonizes Tau Hyperphosphorylation in a Cellular Model of Neurodegeneration.

An accumulation of hyperphosphorylated tau in the brain is a hallmark of Alzheimer's disease (AD). Deficits in protein phosphatase 2A (PP2A) are associated with tau hyperphosphorylation in AD. To investigate the effects of morroniside (MOR), isolated from Cornus officinalis, on tau hyperphosphorylation and its underlying mechanisms related to PP2A. SK-N-SH cells were pretreated with 50-200 μM MOR for 24 h followed by 20 nM okadaic acid (OA) for 6 h. PP2Ac siRNA was transfected into HEK293 cells to determine the direct interaction of MOR with PP2A. Western blotting was used to measure the expression of proteins and enzymes. PP2A activity was measured by molybdenum blue spectrophotometry. Pretreatment with MOR improved the cellular morphological damage and inhibited tau hyperphosphorylation in SK-N-SH cells induced by OA, a PP2A inhibitor. Moreover, MOR increased PP2A activity, concurrent with a decrease in the expression of demethylated PP2A at Leu309 and phosphorylated PP2A at Tyr307. MOR decreased protein phosphatase methylesterase 1 (PME-1) expression and the ratio of PME-1/leucine carboxyl methyltransferase 1 (LCMT-1). Furthermore, MOR treatment decreased the phosphorylation of Src at Tyr416, which regulates the phosphorylation of PP2A. MOR had no effect on PP2Ac expression and tau hyperphosphorylation in PP2Ac siRNA-transfected cells. MOR attenuated OA-induced tau hyperphosphorylation via PP2A activation, and its mechanism might be related to the regulation of PP2Ac post-translational modification and upstream enzymes such as Src and PME-1.

Indirubin-3'-monoxime suppresses amyloid-beta-induced apoptosis by inhibiting tau hyperphosphorylation.

Indirubin-3'-monoxime is an effective inhibitor of cyclin-dependent protein kinases, and may play an obligate role in neuronal apoptosis in Alzheimer's disease. Here, we found that indirubin-3'-monoxime improved the morphology and increased the survival rate of SH-SY5Y cells exposed to amyloid-beta 25-35 (Aβ25-35), and also suppressed apoptosis by reducing tau phosphorylation at Ser199 and Thr205. Furthermore, indirubin-3'-monoxime inhibited phosphorylation of glycogen synthase kinase-3β (GSK-3β). Our results suggest that indirubin-3'-monoxime reduced Aβ25-35-induced apoptosis by suppressing tau hyperphosphorylation via a GSK-3β-mediated mechanism. Indirubin-3'-monoxime is a promising drug candidate for Alzheimer's disease.

Xanthoceraside attenuates tau hyperphosphorylation and cognitive deficits in intracerebroventricular-streptozotocin injected rats

Xanthoceraside, a novel triterpenoid saponin extracted from the fruit husks of Xanthoceras sorbifolia Bunge, reverses cognitive deficits in intracerebroventricular injection of Aβ25-35 or Aβ1-42 mice. However, whether xanthoceraside has a positive effect on hyperphosphorylated tau protein remains unclear. We investigated the effects of xanthoceraside on behavioural impairments induced by intracerebroventricular injection of streptozotocin (STZ) in rats and its potential mechanisms. The rats were administered with xanthoceraside (0.06, 0.12 or 0.24 mg/kg) or vehicle once daily after STZ intracerebroventricular injections. The Y-maze test and novel object recognition test were performed 21 and 22 days after the second STZ injection, respectively. The levels of hyperphosphorylated tau, phosphatidylinositol-3-kinase (PI3K)/serine/threonine protein kinase B (Akt), glycogen synthase kinase-3β (GSK-3β), protein phosphatase 1 (PP-1) and protein phosphatase 2A (PP-2A) were also tested by Western blot. Xanthoceraside treatment significantly attenuated learning and memory impairments and reduced the level of STZ-induced hyperphosphorylated tau protein. Xanthoceraside also enhanced PP-2A and PP-1 expressions, increased PI3K (p85) and Akt (Ser473) phosphorylation and decreased GSK-3β (tyr216) phosphorylation. Xanthoceraside has protective effect against learning and memory impairments and inhibits tau hyperphosphorylation in the hippocampus, possibly through the inhibition of the PI3K/Akt-dependent GSK-3β signalling pathway and an enhancement of phosphatases activity.

Mild hypothermia inhibits Tau hyperphosphorylation induced by severe traumatic brain injuries

Objective To investigate the effect of mild hypothermia on Tau hyperphosphorylation induced by severe traumatic brain injury (sTBI).Methods The in vitro injury model of SK-N-SH cells was established by the cell fluid percussion device.The phosphorylation of Tau at Thr231 or Ser396 was examined by western blot or fluorescent staining at 1 h,6 h,or 12 h after injury.The in vivo injury model of SD rats was established by the rat fluid percussion device (2.4 atm).Mild hypothermia (33℃,4 h)was performed immediately after the injury.The phosphorylation of Tau at Thr231 or Ser396 was examined by western blot or fluorescent staining at 6 h,24 h,or 72 h after injury.Results The phosphorylation of Tau at Thr231 and Ser396 in vitro was increased from 1 h and reached to the highest level at 6 h after the injury.The western blot showed that the phosphorylation of Tau at Thr231 and Ser396 in vivo was elevated from 6 h,reached to the highest level at 24 h,and still stay at a markedly higher level at 72 h after the injury.The immunohistochemistry also showed an obvious stain enhancement in CA1 and the cortex of injured brains.Mild hypothermia could significantly reverse the hyperphosphorylation of Tau at Thr231 and Ser396 induced by sTBI.Conclusion Application of mild hypothermia could significantly restore sTBI-mediated Tau hyperphosphorylation,which underlies a possible strategy for TBI related Alzheimer's Disease. Key words: Mild hypothermia; Severe traumatic brain injury; Tau; Phosphorylation

Attenuation of low dose methylmercury and glutamate induced‐cytotoxicity and tau phosphorylation by an N‐methyl‐D‐aspartate antagonist in human neuroblastoma (SHSY5Y) cells

Methylmercury (MeHg), a known neurotoxin, has been reported to alter glutamate homeostasis in the neuronal environment resulting in excitotoxicity. This study was conducted to investigate whether, and if so, under what conditions, that low dose MeHg would enhance the toxicity of glutamate and to what extent that blockade of NMDA receptors would alter MeHg and glutamate's toxicity in cultured neuroblastoma cells. Neuroblastoma cells (SH-SY5Y) were used in a cell culture model to study effects of MeHg, glutamate (glu), a calcium chelator (BAPTA-AM), and a noncompetitive NMDA antagonist, MK-801 on cell growth, cell survival, and phosphorylation of tau protein, as a measure of cellular events associated with tauopathies. Exposure of cells to a combination of MeHg (50 nM) and glutamate (1 mM) resulted in both a greater decrease in cell viability as well as a greater induction in tau phosphorylation, as compared to exposures with MeHg and glutamate alone. MK-801, an NMDA receptor antagonist, and the intracellular calcium chelator, BAPTA-AM, both significantly inhibited tau hyperphosphorylation and protected cells from the effects of combination exposures to glutamate and MeHg. These results may indicate that exposure to even nontoxic levels of MeHg may prime neuronal cells to be more susceptible to neuronal injury from excitotoxicants such as glutamate and thus may increase the likelihood of neurological disease states. In conclusion, low-dose MeHg-induced toxicity may be related to an increase in the cellular response to glutamate and that NMDA receptor antagonists may provide a potential treatment for MeHg-associated neurological diseases.

Effects of traditional Chinese medicine Fuzhisan on PP1 expression in the hippocampus of SAMP8 mice

Ethnopharmacological relevance Fuzhisan (FZS) is a traditional Chinese medicine clinically used in treating dementia for more than 15 years in China. The drug exerts its therapeutic effects via a multi-target mechanism. Previous studies showed that FZS attenuated the damage caused by amyloid beta protein and could inhibit tau hyperphosphorylation as well. Here protein phosphatase 1 (PP1) is to be investigated as a new mechanism underlying therapeutic effects of FZS. Materials and methods Hippocampal PP1 immunostaining as well as the protein level determined by Western-blot were carried out in SAMP8 mice. Results Lower PP1 expression was observed in SAMP8 compared to its age-matched control SAMR1 mice. Fuzhisan, treating for consecutive 30 days, increased the number of PP1-postive cells through CA1-CA3 subfields in SAMP8. It also unregulated overall hippocampal PP1 levels of SAMP8. The effects enhanced as the dose of FZS rose from 1.2 g/kg/d to 4.8 g/kg/d. Conclusions PP1 could be a potential novel target of FZS. FZS may be beneficial for the treatment of dementia or even senile cognitive decline via PP1.

Effects of Memantine on Cerebrospinal Fluid Biomarkers of Neurofibrillary Pathology

Previous studies showed that memantine inhibits tau hyperphosphorylation in vitro. In this study, phosphorylated tau (P-tau) and total tau (T-tau) were measured before and after 6 month treatment with memantine in 12 subjects ranging from normal cognition with subjective memory complaints, through mild cognitive impairment to mild Alzheimer's disease. Thirteen non-treated individuals served as controls. Treatment was associated with a reduction of P-tau in subjects with normal cognition. No treatment effects were seen among impaired individuals, suggesting that longer treatment time may be necessary to achieve biomarker effect in this group.

Calcitonin gene-related peptide enhances CREB phosphorylation and attenuates tau protein phosphorylation in rat brain during focal cerebral ischemia/reperfusion

Calcitonin gene-related peptide (CGRP) is a potent vasodilator and immune cell modulator. Exogenous CGRP could increase the cerebral blood flow significantly and protect the ischemic neurons, but its mechanism is not entirely clear. The effect of CGRP on the expressions of CREB and tau in the ipsilateral parietal cortex were detected in focal cerebral ischemia/reperfusion model. The expression of CREB mRNA decreased in ischemia/reperfusion group (I/R group) compared with that of the sham operation group, and it got highest in CGRP group. CREB expression was lesser in I/R group than sham group, but it became more in CGRP group than I/R group. Phospho-CREB became more in I/R group, and it got most in CGRP group in the cortex. No significant difference was observed on Tau mRNA expression in all the groups. The level of tau hyperphosphorylation at Ser199/202 site and total tau in rat parietal cortex were significantly higher in I/R group than sham group. CGRP significantly inhibited tau hyperphosphorylation and the level of total tau also significantly reduced in CGRP group than that in I/R group. CGRP can upregulate the expression of CREB and phospho-CREB and attenuate the level of tau hyperphosphorylation in the ischemic neurons of the parietal cortex during focal cerebral ischemia/reperfusion. Phosphorylating CREB and inhibiting tau phosphorylation are probably involved in the mechanism of protective effect of CGRP to ischemic neurons.

Isoflavones Prevent Endoplasmic Reticulum Stress-Mediated Neuronal Degeneration by Inhibiting Tau Hyperphosphorylation in SH-SY5Y Cells

Several studies have demonstrated a protective effect of estrogen against the risk of developing neurodegenerative diseases; however, the molecular mechanisms involved have not been fully addressed. Isoflavones have been proposed as potential alternatives to estrogen replacement therapy. Therefore, in the present study, we investigated effects of isoflavones on cell death and tau phosphorylation in SH-SY5Y human neuroblastoma cells. Cells were treated with tunicamycin (TM) to induce endoplasmic reticulum (ER) stress-mediated toxicity, which is involved in development of neurodegenerative diseases. Treatment of cells with either 17beta-estradiol or isoflavones (either genistein or daidzein) significantly protected cells against cell death. The protective effect against cell death was blocked by a specific estrogen receptor blocker, ICI 182,780, suggesting that isoflavones protect against cell death via estrogen receptor-dependent pathways. Isoflavones also suppressed ER stress as determined by decreased expressions of the immunoglobulin binding protein (BiP) mRNA, spliced X-box binding protein-1 (Xbp-1) mRNAs, and C/EBP homologous protein (CHOP). TM activated glycogen synthase kinase 3beta (GSK3beta), a kinase involved in tau phosphorylation; in contrast, isoflavones inactivated GSK3beta and decreased tau hyperphosphorylation. In conclusion, our results clearly demonstrate that isoflavones prevent ER stress-mediated neurotoxicity by inhibiting tau hyperphosphorylation in SH-SY5Y cells.

Role of Dickkopf-1, an Antagonist of the Wnt/β-Catenin Signaling Pathway, in Estrogen-Induced Neuroprotection and Attenuation of Tau Phosphorylation

17beta-Estradiol (E2) has been implicated to be neuroprotective in a variety of neurodegenerative disorders, although the mechanism remains poorly understood. The current study sheds light on this issue by demonstrating that low physiological levels of E2 protects the hippocampus CA1 against global cerebral ischemia by preventing elevation of dickkopf-1 (Dkk1), an antagonist of the Wnt/beta-catenin signaling pathway, which is a principal mediator of neurodegeneration in cerebral ischemia and Alzheimer's disease. E2 inhibition of Dkk1 elevation correlated with a reduction of phospho-beta-catenin and elevation of nuclear beta-catenin levels, as well as enhancement of Wnt-3, suggesting E2 activation of the Wnt/beta-catenin signaling pathway. In agreement, the beta-catenin downstream prosurvival factor, survivin, was induced by E2 at 24 and 48 h after cerebral ischemia, an effect observed only in surviving neurons because degenerating neurons lacked survivin expression. E2 suppression of Dkk1 elevation was found to be caused by attenuation of upstream c-Jun N-terminal protein kinase (JNK)/c-Jun signaling, as E2 attenuation of JNK/c-Jun activation and a JNK inhibitor significantly blocked Dkk1 induction. Tau hyperphosphorylation has been implicated to have a prodeath role in Alzheimer's disease and cerebral ischemia, and E2 attenuates tau hyperphosphorylation. Our study demonstrates that tau hyperphosphorylation is strongly induced after global cerebral ischemia, and that E2 inhibits tau hyperphosphorylation by suppressing activation of the JNK/c-Jun/Dkk1 signaling pathway. Finally, exogenous Dkk1 replacement via intracerebroventricular administration completely reversed E2-induced neuroprotection, nuclear beta-catenin induction, and phospho-tau attenuation, further suggesting that E2 inhibition of Dkk1 is a critical mechanism underlying its neuroprotective and phospho-tau regulatory effects after cerebral ischemia.