PTEN, a negative regulator of PI3 kinase signalling, alters tau phosphorylation in cells by mechanisms independent of GSK-3

Targeting of PP2 A/GSK3β/PTEN Axis in Alzheimer Disease: The Mooting Evidence, Divine, and Devil

Alzheimer disease (AD) is a progressive neurodegenerative disease of the brain due to extracellular accumulation of Aβ. In addition, intracellular accumulation of hyperphosphorlyated tau protein which form neurofibrillary tangle (NFT) is associated with progressive neuronal injury and the development of AD. Aβ and NFTs interact together to induce inflammation and oxidative stress which further induce neurodegeneration in AD. The exact relationship between Aβ and tau, the two proteins that accumulate within these lesions, has proven elusive. A growing body of work supports the notion that Aβ may directly or indirectly interact with tau to accelerate NFTs formation. Aβ can adversely affect distinct molecular and cellular pathways, thereby facilitating tau phosphorylation, aggregation, mislocalization, and accumulation. Aβ may drive tau pathology by activating specific kinases, providing a straightforward mechanism by which Aβ may enhance tau hyperphosphorylation and NFT formation. Many cellular signaling pathways such as protein phosphatase 2A (PP2A), glycogen synthase kinase 3β (GSK3β), and phosphatase and tensin homologue (PTEN) are intricate in AD neuropathology. PP2A which involved in the dephosphorylation of tau protein is deregulated in AD, and correlated with cognitive impairment. PTEN is a critical regulator of neuronal growth, survival, and development, improving synaptic plasticity and axonal regeneration. Nevertheless, mutated PTEN is associated with the development of cognitive impairment by inhibiting the expression and the activity of PP2A. Furthermore, dysregulation of GSK3β affects Aβ, tau protein phosphorylation, synaptic plasticity and other signaling pathways involved in the pathogenesis of AD. Therefore, there is a close interaction among GSK3β, PTEN, and PP2A. GSK3β exaggerates AD neuropathology by inhibiting PP2A and activates the expression of PTEN. These findings specified a related interaction among GSK3β, PTEN, and PP2A, and modulation of the single component of this axis may not produce an effective effect against AD neuropathology. Modulation of this axis by metformin and statins can reduce AD neuropathology. Therefore, this review aims to discuss the role of GSK3β/PTEN/PP2A axis in AD neuropathology and how targeting of this axis by metformin and statins can produce effective therapeutic strategy in the management of AD. In conclusion, inhibition of GSK3β and PTEN and activation of PP2A may be more suitable than modulation of single signaling pathway. Metformin and statins by activating PP2A and inhibiting of GSK3β and PTEN attenuate the development and progression of AD.

Bioinformatic analysis of hippocampal histopathology in Alzheimer's disease and the therapeutic effects of active components of traditional Chinese medicine

Background and aim

Pathological changes in the central nervous system (CNS) begin before the clinical symptoms of Alzheimer's Disease (AD) manifest, with the hippocampus being one of the first affected structures. Current treatments fail to alter AD progression. Traditional Chinese medicine (TCM) has shown potential in improving AD pathology through multi-target mechanisms. This study investigates pathological changes in AD hippocampal tissue and explores TCM active components that may alleviate these changes.

Methods

GSE5281 and GSE173955 datasets were downloaded from GEO and normalized to identify differentially expressed genes (DEGs). Key functional modules and hub genes were analyzed using Cytoscape and R. Active TCM components were identified from literature and the Pharmacopoeia of the People's Republic of China. Enrichment analyses were performed on target genes overlapping with DEGs.

Result

From the datasets, 76 upregulated and 363 downregulated genes were identified. Hub genes included SLAMF, CD34, ELN (upregulated) and ATP5F1B, VDAC1, VDAC2, HSPA8, ATP5F1C, PDHA1, UBB, SNCA, YWHAZ, PGK1 (downregulated). Literature review identified 33 active components from 23 herbal medicines. Target gene enrichment and analysis were performed for six components: dihydroartemisinin, berberine, naringenin, calycosin, echinacoside, and icariside II.

Conclusion

Mitochondrial to synaptic vesicle dysfunction pathways were enriched in downregulated genes. Despite downregulation, UBB and SNCA proteins accumulate in AD brains. TCM studies suggest curcumin and echinacoside may improve hippocampal pathology and cognitive impairment in AD. Further investigation into their mechanisms is needed.

How Can Insulin Resistance Cause Alzheimer's Disease?

Alzheimer's disease (AD) is a neurodegenerative disorder associated with cognitive decline. Despite worldwide efforts to find a cure, no proper treatment has been developed yet, and the only effective countermeasure is to prevent the disease progression by early diagnosis. The reason why new drug candidates fail to show therapeutic effects in clinical studies may be due to misunderstanding the cause of AD. Regarding the cause of AD, the most widely known is the amyloid cascade hypothesis, in which the deposition of amyloid beta and hyperphosphorylated tau is the cause. However, many new hypotheses were suggested. Among them, based on preclinical and clinical evidence supporting a connection between AD and diabetes, insulin resistance has been pointed out as an important factor in the development of AD. Therefore, by reviewing the pathophysiological background of brain metabolic insufficiency and insulin insufficiency leading to AD pathology, we will discuss how can insulin resistance cause AD.

The Role of ERK1/2 Pathway in the Pathophysiology of Alzheimer's Disease: An Overview and Update on New Developments

Alzheimer's disease (AD) is the most common neurodegenerative disorder worldwide. Several findings suggest that correcting the dysregulated signaling pathways may offer a potential therapeutic approach in this disease. Extracellular signal-regulated kinase 1/2 (ERK1/2), a member of the mitogen-activated protein kinase family, plays a major role in regulation of cell proliferation, autophagy process, and protein synthesis. The available literature suggests dysregulated ERK1/2 in AD patients with potential implications in the multifaceted underlying pathologies of AD, including amyloid-β plaque formation, tau phosphorylation, and neuroinflammation. In this regard, in the current review, we aim to summarize the reports on the potential roles of ERK1/2 in AD pathophysiology.

Tau Protein as Therapeutic Target for Cancer? Focus on Glioblastoma

Despite being extensively studied for several decades, the microtubule-associated protein Tau has not finished revealing its secrets. For long, Tau has been known for its ability to promote microtubule assembly. A less known feature of Tau is its capability to bind to cancer-related protein kinases, suggesting a possible role of Tau in modulating microtubule-independent cellular pathways that are associated with oncogenesis. With the intention of finding new therapeutic targets for cancer, it appears essential to examine the interaction of Tau with these kinases and their consequences. This review aims at collecting the literature data supporting the relationship between Tau and cancer with a particular focus on glioblastoma tumors in which the pathological significance of Tau remains largely unexplored. We will first treat this subject from a mechanistic point of view showing the pivotal role of Tau in oncogenic processes. Then, we will discuss the involvement of Tau in dysregulating critical pathways in glioblastoma. Finally, we will outline promising strategies to target Tau protein for the therapy of glioblastoma.

The role and therapeutic implication of protein tyrosine phosphatases in Alzheimer's disease

Protein tyrosine phosphatases (PTPs) are important regulator of neuronal signal transduction and a growing number of PTPs have been implicated in Alzheimer's disease (AD). In the brains of patients with AD, there are a variety of abnormally phosphorylated proteins, which are closely related to the abnormal expression and activity of PTPs. β-Amyloid plaques (Aβ) and hyperphosphorylated tau protein are two pathological hallmarks of AD, and their accumulation ultimately leads to neurodegeneration. Studies have shown that protein phosphorylation signaling pathways mediates intracellular accumulation of Aβ and tau during AD development and are involved in synaptic plasticity and other stress responses. Here, we summarized the roles of PTPs related to the pathogenesis of AD and analyzed their therapeutic potential in AD.

Dysfunctional proteins in neuropsychiatric disorders: From neurodegeneration to autism spectrum disorders

Despite fundamental differences in disease course and outcomes, neurodevelopmental (autism spectrum disorders - ASD) and neurodegenerative disorders (Alzheimer's disease - AD and Parkinson's disease - PD) present surprising, common traits in their molecular pathomechanisms. Uncontrolled oligomerization and aggregation of amyloid β (Aβ), microtubule-associated protein (MAP) tau, or α-synuclein (α-syn) contribute to synaptic impairment and the ensuing neuronal death in both AD and PD. Likewise, the pathogenesis of ASD may be attributed, at least in part, to synaptic dysfunction; attention has also been recently paid to irregularities in the metabolism and function of the Aβ precursor protein (APP), tau, or α-syn. Commonly affected elements include signaling pathways that regulate cellular metabolism and survival such as insulin/insulin-like growth factor (IGF) - PI3 kinase - Akt - mammalian target of rapamycin (mTOR), and a number of key synaptic proteins critically involved in neuronal communication. Understanding how these shared pathomechanism elements operate in different conditions may help identify common targets and therapeutic approaches.

Dual-specificity phosphatases in mental and neurological disorders

The dual-specificity phosphatase (DUSP) family includes a heterogeneous group of protein phosphatases that dephosphorylate both phospho-tyrosine and phospho-serine/phospho-threonine residues within a single substrate. These protein phosphatases have many substrates and modulate diverse neural functions, such as neurogenesis, differentiation, and apoptosis. DUSP genes have furthermore been associated with mental disorders such as depression and neurological disorders such as Alzheimer's disease. Herein, we review the current literature on the DUSP family of genes concerning mental and neurological disorders. This review i) outlines the structure and general functions of DUSP genes, and ii) overviews the literature on DUSP genes concerning mental and neurological disorders, including model systems, while furthermore providing perspectives for future research.

Gamma radiation improves AD pathogenesis in APP/PS1 mouse model by potentiating insulin sensitivity

Alzheimer's disease (AD) is the largest unmet medical complication. The devastation caused by the disease can be assumed from the disease symptoms like speech impairment, loss of self-awareness, acute memory loss etc. The individuals suffering from AD completely depend on caregivers and have to bear the high cost of treatment which increases the socio-economic burden on the society. Recent studies have shown that radiation exposure can have therapeutic effects when given in suitable amount for a specific time period. Therefore, we investigated the role of gamma irradiation in AD pathogenesis. The effect of radiation on amelioration of disease progression was studied in AD transgenic mice model (APP/PS1). Our in-vivo studies using APP/PS1 mice demonstrated that a single dose of 4.0 Gy gamma irradiation improves AD associated behavioral impairment. Radiation exposure also increased the level of anti-oxidant enzymes and reduced the astrocyte activation in the brain of APP/PS1 mice. A significant reduction was observed in AD associated proteins (APP, pTau, BACE) and neurofibrillary tangle formations (NFTs). Exposure to a single dose of 4 Gy gamma radiation also increased glucose metabolic functionality in AD transgenic mouse model. The kinases involved in insulin signaling such as GSK, ERK and JNK were also found to be modulated. However, an increased level of GSK3β (ser 9) was observed, which could be responsible for downregulating ERK and JNK phosphorylation. This resulted in a decrease in neurofibrillary tangle formations and amyloid deposition. The reduced hyperphosphorylation of Tau can be attributed to the increased level of GSK3β (ser 9) downregulating ERK and JNK phosphorylation. Thus, a single dose of 4 Gy gamma irradiation was found to have therapeutic benefits in treating AD via potentiating insulin signaling in APP/PS1 transgenic mice.

Microtubule-associated protein tau (MAPT) promotes bicalutamide resistance and is associated with survival in prostate cancer

INTRODUCTION

Microtubule-associated protein tau (MAPT), facilitates tubulin assembly and microtubule stabilization. Several studies have shown that overexpression of MAPT is linked to poor prognosis and is involved in taxane resistance in cancer. This study aimed to assess the expression and function of MAPT in prostate cancer (CaP).

METHODS

The expression of MAPT was determined using immunohistochemistry in CaP. We analyzed the interaction between MAPT, Phosphatase and Tensin Homolog (PTEN), and androgen receptor and investigated the role of MAPT in bicalutamide resistance.

RESULTS

Immunohistochemistry in 155 CaP cases showed that 15% of them were positive for MAPT. High MAPT expression was significantly orrelated with high Gleason score and high T stage. Kaplan-Meier analysis showed that the high MAPT expression was significantly associated with poor prostate-specific antigen recurrence survival after radical prostatectomy. There was an inverse correlation between MAPT and PTEN. In the CaP cell lines, knockout of PTEN increased the expression of MAPT, whereas knockdown of MAPT suppressed the expression of androgen receptor and increased the sensitivity to bicalutamide. Furthermore, immunohistochemical staining of MAPT showed that high MAPT expression was significantly associated with poor overall survival in 74 CaP patients who were treated with androgen deprivation therapy.

CONCLUSION

These results suggest that MAPT may be a promising predictive biomarker for survival and play an essential role in bicalutamide resistance in CaP.

Aberrant expression of the microtubule-associated protein tau is an independent prognostic feature in prostate cancer

Background

Microtubule-associated protein Tau (MAPT) overexpression has been linked to poor prognosis and decreased response to taxane-based therapies in several cancer types, but its relevance in prostate cancer is unknown.

Methods

In this study, MAPT expression was analyzed by immunohistochemistry on a tissue microarray containing 17,747 prostate cancers.

Results

MAPT was absent in normal prostate epithelial cells but detectable in 1004 (8.2%) of 12,313 interpretable cancers. Its expression was associated with advanced tumor stage, high Gleason grade, positive lymph nodes, and early biochemical recurrence (p < 0.0001 each). For example, MAPT was found in 3.6% of 2072 Gleason ≤3 + 3 cancers but in 14.4% of 704 Gleason ≥4 + 4 cancers. High-level MAPT staining was also linked to TMPRSS2:ERG fusions (p < 0.0001). MAPT staining was seen in 15.2 and 16% of cancers with TMPRSS2:ERG fusion detected by immunohistochemistry and fluorescence in-situ hybridization, but in only 3.5 and 3.9% of cancers without ERG staining or ERG rearrangements. Moreover, an association was found between MAPT expression and PTEN deletions, with 19% MAPT positivity in 948 PTEN deleted cancers but only 7% MAPT positivity in 3895 tumors with normal PTEN copy numbers (p < 0.0001). Multivariate analysis revealed that the prognostic value of MAPT was independent from established parameters. Conventional large section analyses showed intratumoral MAPT heterogeneity in all three analyzed cancers.

Conclusions

The results of our study identify MAPT, as a moderate prognostic marker in prostate cancer, whose clinical impact, however, may be limited due to the rarity and heterogeneity of its expression.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5390-1) contains supplementary material, which is available to authorized users.

MicroRNAs as diagnostic and therapeutic tools for Alzheimer's disease: advances and limitations

Alzheimer’s disease (AD) is the most common age-related, progressive neurodegenerative disease. It is characterized by memory loss and cognitive decline and responsible for most cases of dementia in the elderly. Late-onset or sporadic AD accounts for > 95% of cases, with age at onset > 65 years. Currently there are no drugs or other therapeutic agents available to prevent or delay the progression of AD. The cellular and molecular changes occurring in the brains of individuals with AD include accumulation of β-amyloid peptide and hyperphosphorylated tau protein, decrease of acetylcholine neurotransmitter, inflammation, and oxidative stress. Aggregation of β-amyloid peptide in extracellular plaques and the hyperphosphorylated tau protein in intracellular neurofibrillary tangles are characteristic of AD. A major challenge is identifying molecular biomarkers of the early-stage AD in patients as most studies have been performed with blood or brain tissue samples (postmortem) at late-stage AD. Subjects with mild cognitive impairment almost always have the neuropathologic features of AD with about 50% of mild cognitive impairment patients progressing to AD. They could provide important information about AD pathomechanism and potentially also highlight minimally or noninvasive, easy-to-access biomarkers. MicroRNAs are dysregulated in AD, and may facilitate the early detection of the disease and potentially the continual monitoring of disease progression and allow therapeutic interventions to be evaluated. Four recent reviews have been published of microRNAs in AD, each of which identified areas of weakness or limitations in the reported studies. Importantly, studies in the last three years have shown considerable progress in overcoming some of these limitations and identifying specific microRNAs as biomarkers for AD and mild cognitive impairment. Further large-scale human studies are warranted with less disparity in the study populations, and using an appropriate method to validate the findings.

Effect of tibolone pretreatment on kinases and phosphatases that regulate the expression and phosphorylation of Tau in the hippocampus of rats exposed to ozone

Oxidative stress (OS) is a key process in the development of many neurodegenerative diseases, memory disorders, and other pathological processes related to aging. Tibolone (TIB), a synthetic hormone used as a treatment for menopausal symptoms, decreases lipoperoxidation levels, prevents memory impairment and learning disability caused by ozone (O3) exposure. However, it is not clear if TIB could prevent the increase in phosphorylation induced by oxidative stress of the microtubule-associated protein Tau. In this study, the effects of TIB at different times of administration on the phosphorylation of Tau, the activation of glycogen synthase kinase-3β (GSK3β), and the inactivation of Akt and phosphatases PP2A and PTEN induced by O3 exposure were assessed in adult male Wistar rats. Rats were divided into 10 groups: control group (ozone-free air plus vehicle [C]), control + TIB group (ozone-free air plus TIB 1 mg/kg [C + TIB]); 7, 15, 30, and 60 days of ozone exposure groups [O3] and 7, 15, 30, and 60 days of TIB 1 mg/kg before ozone exposure groups [O3 + TIB]. The effects of O3 exposure and TIB administration were assessed by western blot analysis of total and phosphorylated Tau, GSK3β, Akt, PP2A, and PTEN proteins and oxidative stress marker nitrotyrosine, and superoxide dismutase activity and lipid peroxidation of malondialdehyde by two different spectrophotometric methods (Marklund and TBARS, respectively). We observed that O3 exposure increases Tau phosphorylation, which is correlated with decreased PP2A and PTEN protein levels, diminished Akt protein levels, and increased GSK3β protein levels in the hippocampus of adult male rats. The effects of O3 exposure were prevented by the long-term treatment (over 15 days) with TIB. Malondialdehyde and nitrotyrosine levels increased from 15 to 60 days of exposure to O3 in comparison to C group, and superoxide dismutase activity decreased. Furthermore, TIB administration limited the changes induced by O3 exposure. Our results suggest a beneficial use of hormone replacement therapy with TIB to prevent neurodegeneration caused by O3 exposure in rats.

PTEN Inhibition in Human Disease Therapy

The tumor suppressor PTEN is a major homeostatic regulator, by virtue of its lipid phosphatase activity against phosphatidylinositol 3,4,5-trisphosphate [PI(3,4,5)P3], which downregulates the PI3K/AKT/mTOR prosurvival signaling, as well as by its protein phosphatase activity towards specific protein targets. PTEN catalytic activity is crucial to control cell growth under physiologic and pathologic situations, and it impacts not only in preventing tumor cell survival and proliferation, but also in restraining several cellular regeneration processes, such as those associated with nerve injury recovery, cardiac ischemia, or wound healing. In these conditions, inhibition of PTEN catalysis is being explored as a potentially beneficial therapeutic intervention. Here, an overview of human diseases and conditions in which PTEN inhibition could be beneficial is presented, together with an update on the current status of specific small molecule inhibitors of PTEN enzymatic activity, their use in experimental models, and their limitations as research or therapeutic drugs.

Pharmacological inhibition of PTEN attenuates cognitive deficits caused by neonatal repeated exposures to isoflurane via inhibition of NR2B-mediated tau phosphorylation in rats

Evidence has shown that children exposed to repeated anesthesia in early childhood display long-term cognitive disabilities. However, the underlying mechanisms remain largely unclear. Our previous study has indicated the involvement of phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in isoflurane-induced decrease of self-renewal capacity in hippocampal neural precursor cells. Additionally, it is demonstrated by others that PTEN inhibition could protect against cognitive impairment via reduction of tau phosphorylation in the alzheimer's disease model. Therefore, in the present in vivo study, we aimed to examine the effects of PTEN inhibition on the cognitive dysfunction and tau hyperphosphorylation caused by neonatal repeated exposures to isoflurane. Our results showed that the neonatal repeated exposures to isoflurane resulted in the activation of PTEN in the hippocampus. The treatment of PTEN inhibitor BPV (pic) restored PSD-95 synthesis, and attenuated tau phosphorylation as well as the cognitive dysfunction caused by the repeated isoflurane exposures. In addition, BPV (pic) treatment reversed the activation of NR2B-containing NMDARs induced by repeated isoflurane exposures, while in turn, the antagonism of NR2B subunit with ifenprodil alleviated tau phosphorylation, indicating a possible role of NR2B as the downstream of PTEN in mediating tau phosphorylation in the neonatal rats repeatedly exposed to isoflurane. In conclusion, our results reveal a novel role of PTEN in mediating tau phosphorylation and cognitive deficits caused by neonatal repeated exposures to isoflurane, implying that targeting on PTEN may be a potential therapeutic approach for the anesthetic-related cognitive decline in the developing brain.

Active β-catenin is regulated by the PTEN/PI3 kinase pathway: a role for protein phosphatase PP2A

Dysregulation of Wnt/β-catenin signaling has been associated with the development and progression of many cancers. The stability and subcellular localization of β-catenin, a dual functional protein that plays a role in intracellular adhesion and in regulating gene expression, is tightly regulated. However, little is known about the transcriptionally active form of β-catenin, Active Beta Catenin (ABC), that is unphosphorylated at serine 37 (Ser37) and threonine 41 (Thr41). Elucidating the mechanism by which β-catenin is activated to generate ABC is vital to the development of therapeutic strategies to block β-catenin signaling for cancer treatment. Using melanoma, breast and prostate cancer cell lines, we show that while cellular β-catenin levels are regulated by the Wnt pathway, cellular ABC levels are mainly regulated by the PI3K pathway and are dependent on the phosphatase activity of the protein phosphatase PP2A. Furthermore, we demonstrate that although the PI3K/PTEN pathway does not regulate total β-catenin protein levels within the cell, it plays a role in regulating the subcellular localization of β-catenin. Our results support a novel functional interaction/cross-talk between the PTEN/PI3K and Wnt pathways in the regulation of the subcellular/nuclear levels of ABC, which is crucially important for the protein's activity as a transcription factor and its biological effects in health and disease.

FcγRIIb-SHIP2 axis links Aβ to tau pathology by disrupting phosphoinositide metabolism in Alzheimer's disease model

Amyloid-β (Aβ)-containing extracellular plaques and hyperphosphorylated tau-loaded intracellular neurofibrillary tangles are neuropathological hallmarks of Alzheimer's disease (AD). Although Aβ exerts neuropathogenic activity through tau, the mechanistic link between Aβ and tau pathology remains unknown. Here, we showed that the FcγRIIb-SHIP2 axis is critical in Aβ_1-42-induced tau pathology. Fcgr2b knockout or antagonistic FcγRIIb antibody inhibited Aβ_1-42-induced tau hyperphosphorylation and rescued memory impairments in AD mouse models. FcγRIIb phosphorylation at Tyr273 was found in AD brains, in neuronal cells exposed to Aβ_1-42, and recruited SHIP2 to form a protein complex. Consequently, treatment with Aβ_1-42 increased PtdIns(3,4)P₂ levels from PtdIns(3,4,5)P₃ to mediate tau hyperphosphorylation. Further, we found that targeting SHIP2 expression by lentiviral siRNA in 3xTg-AD mice or pharmacological inhibition of SHIP2 potently rescued tau hyperphosphorylation and memory impairments. Thus, we concluded that the FcγRIIb-SHIP2 axis links Aβ neurotoxicity to tau pathology by dysregulating PtdIns(3,4)P₂ metabolism, providing insight into therapeutic potential against AD.

The rise and fall of insulin signaling in Alzheimer's disease

The prevalence of both diabetes and Alzheimer's disease (AD) are reaching epidemic proportions worldwide. Alarmingly, diabetes is also a risk factor for Alzheimer's disease. The AD brain is characterised by the accumulation of peptides called Aβ as plaques in the neuropil and hyperphosphorylated tau protein in the form of neurofibrillary tangles within neurons. How diabetes confers risk is unknown but a simple linear relationship has been proposed whereby the hyperinsulinemia associated with type 2 diabetes leads to decreased insulin signaling in the brain, with downregulation of the PI3K/AKT signalling pathway and its inhibition of the major tau kinase, glycogen synthase kinase 3β. The earliest studies of post mortem AD brain tissue largely confirmed this cascade of events but subsequent studies have generally found either an upregulation of AKT activity, or that the relationship between insulin signaling and AD is independent of glycogen synthase kinase 3β altogether. Given the lack of success of beta-amyloid-reducing therapies in clinical trials, there is intense interest in finding alternative or adjunctive therapeutic targets for AD. Insulin signaling is a neuroprotective pathway and represents an attractive therapeutic option. However, this incredibly complex signaling pathway is not fully understood in the human brain and particularly in the context of AD. Here, we review the ups and downs of the research efforts aimed at understanding how diabetes modifies AD risk.

Effects of PTEN inhibition on the regulation of Tau phosphorylation in rat cortical neuronal injury after oxygen and glucose deprivation

OBJECTIVE

This report investigated the involvement of the PTEN pathway in the regulation of Tau phosphorylation using an oxygen and glucose deprivation (OGD) model with rat cortical neurons.

METHODS

Primary cortical neurons were used to establish the oxygen and glucose deprivation (OGD) model in vitro. These were randomly divided into control, OGD, bpV+OGD, As+OGD, Se+OGD and Mock treatment groups. The neuron viability was assessed by MTT, the cell apoptosis was detected using TUNEL staining. The expression of Phospho-PTEN/PTEN, Phospho-Tau/Tau, Phospho-Akt/Akt and Phospho-GSK-3β/GSK-3β were detected by Western blotting.

RESULTS

OGD induced Tau phosphorylation through PTEN and glycogen synthase kinase-3β (GSK-3β) activation, together with a decrease in AKT activity. Pre-treatment with bpv, a potent PTEN inhibitor, and PTEN antisense nucleotides decreased PTEN and GSK-3β activity and caused alterations in Tau phosphorylation. Neuronal apoptosis was also reduced.

CONCLUSIONS

The PTEN/Akt/GSK-3β/Tau pathway is involved in the regulation of neuronal injury, providing a novel route for protecting neurons following neonatal HI.

MicroRNA-146a suppresses ROCK1 allowing hyperphosphorylation of tau in Alzheimer's disease

MicroRNA-146a is upregulated in the brains of patients with Alzheimer’s disease (AD). Here, we show that the rho-associated, coiled-coil containing protein kinase 1 (ROCK1) is a target of microRNA-146a in neural cells. Knockdown of ROCK1 mimicked the effects of microRNA-146a overexpression and induced abnormal tau phosphorylation, which was associated with inhibition of phosphorylation of the phosphatase and tensin homolog (PTEN). The ROCK1/PTEN pathway has been implicated in the neuronal hyperphosphorylation of tau that occurs in AD. To determine the function of ROCK1 in AD, brain tissue from 17 donors with low, intermediate or high probability of AD pathology were obtained and analyzed. Data showed that ROCK1 protein levels were reduced and ROCK1 colocalised with hyperphosphorylated tau in early neurofibrillary tangles. Intra-hippocampal delivery of a microRNA-146a specific inhibitor (antagomir) into 5xFAD mice showed enhanced hippocampal levels of ROCK1 protein and repressed tau hyperphosphorylation, partly restoring memory function in the 5xFAD mice. Our in vitro and in vivo results confirm that dysregulation of microRNA-146a biogenesis contributes to tau hyperphosphorylation and AD pathogenesis, and inhibition of this microRNA could be a viable novel in vivo therapy for AD.

Selective clearance of aberrant tau proteins and rescue of neurotoxicity by transcription factor EB

Accumulating evidence implicates impairment of the autophagy-lysosome pathway in Alzheimer's disease (AD). Recently discovered, transcription factor EB (TFEB) is a molecule shown to play central roles in cellular degradative processes. Here we investigate the role of TFEB in AD mouse models. In this study, we demonstrate that TFEB effectively reduces neurofibrillary tangle pathology and rescues behavioral and synaptic deficits and neurodegeneration in the rTg4510 mouse model of tauopathy with no detectable adverse effects when expressed in wild-type mice. TFEB specifically targets hyperphosphorylated and misfolded Tau species present in both soluble and aggregated fractions while leaving normal Tau intact. We provide in vitro evidence that this effect requires lysosomal activity and we identify phosphatase and tensin homolog (PTEN) as a direct target of TFEB that is required for TFEB-dependent aberrant Tau clearance. The specificity and efficacy of TFEB in mediating the clearance of toxic Tau species makes it an attractive therapeutic target for treating diseases of tauopathy including AD.

Subcellular targeting and dynamic regulation of PTEN: implications for neuronal cells and neurological disorders

PTEN is a lipid and protein phosphatase that regulates a diverse range of cellular mechanisms. PTEN is mainly present in the cytosol and transiently associates with the plasma membrane to dephosphorylate PI(3,4,5)P3, thereby antagonizing the PI3-Kinase signaling pathway. Recently, PTEN has been shown to associate also with organelles such as the endoplasmic reticulum (ER), the mitochondria, or the nucleus, and to be secreted outside of the cell. In addition, PTEN dynamically localizes to specialized sub-cellular compartments such as the neuronal growth cone or dendritic spines. The diverse localizations of PTEN imply a tight temporal and spatial regulation, orchestrated by mechanisms such as posttranslational modifications, formation of distinct protein–protein interactions, or the activation/recruitment of PTEN downstream of external cues. The regulation of PTEN function is thus not only important at the enzymatic activity level, but is also associated to its spatial distribution. In this review we will summarize (i) recent findings that highlight mechanisms controlling PTEN movement and sub-cellular localization, and (ii) current understanding of how PTEN localization is achieved by mechanisms controlling posttranslational modification, by association with binding partners and by PTEN structural or activity requirements. Finally, we will discuss the possible roles of compartmentalized PTEN in developing and mature neurons in health and disease.

A network view on Parkinson's disease

Network-based systems biology tools including Pathway Studio 9.0 were used to identify Parkinson's disease (PD) critical molecular players, drug targets, and underlying biological processes. Utilizing several microarray gene expression datasets, biomolecular networks such as direct interaction, shortest path, and microRNA regulatory networks were constructed and analyzed for the disease conditions. Network topology analysis of node connectivity and centrality revealed in combination with the guilt-by-association rule 17 novel genes of PD-potential interest. Seven new microRNAs (miR-132, miR-133a1, miR-181-1, miR-182, miR-218-1, miR-29a, and miR-330) related to Parkinson's disease were identified, along with more microRNA targeted genes of interest like RIMS3, SEMA6D and SYNJ1. David and IPA enrichment analysis of KEGG and canonical pathways provided valuable mechanistic information emphasizing among others the role of chemokine signaling, adherence junction, and regulation of actin cytoskeleton pathways. Several routes for possible disease initiation and neuro protection mechanisms triggered via the extra-cellular ligands such as CX3CL1, SEMA6D and IL12B were thus uncovered, and a dual regulatory system of integrated transcription factors and microRNAs mechanisms was detected.

Autism as early neurodevelopmental disorder: evidence for an sAPPα-mediated anabolic pathway

Autism is a neurodevelopmental disorder marked by social skills and communication deficits and interfering repetitive behavior. Intellectual disability often accompanies autism. In addition to behavioral deficits, autism is characterized by neuropathology and brain overgrowth. Increased intracranial volume often accompanies this brain growth. We have found that the Alzheimer's disease (AD) associated amyloid-β precursor protein (APP), especially its neuroprotective processing product, secreted APP α, is elevated in persons with autism. This has led to the "anabolic hypothesis" of autism etiology, in which neuronal overgrowth in the brain results in interneuronal misconnections that may underlie multiple autism symptoms. We review the contribution of research in brain volume and of APP to the anabolic hypothesis, and relate APP to other proteins and pathways that have already been directly associated with autism, such as fragile X mental retardation protein, Ras small GTPase/extracellular signal-regulated kinase, and phosphoinositide 3 kinase/protein kinase B/mammalian target of rapamycin. We also present additional evidence of magnetic resonance imaging intracranial measurements in favor of the anabolic hypothesis. Finally, since it appears that APP's involvement in autism is part of a multi-partner network, we extend this concept into the inherently interactive realm of epigenetics. We speculate that the underlying molecular abnormalities that influence APP's contribution to autism are epigenetic markers overlaid onto potentially vulnerable gene sequences due to environmental influence.

Tau protein phosphatases in Alzheimer's disease: the leading role of PP2A

Tau phosphorylation is regulated by a balance between tau kinase and phosphatase activities. Disruption of this equilibrium was suggested to be at the origin of abnormal tau phosphorylation and thereby that might contributes to tau aggregation. Thus, understanding the regulation modes of tau dephosphorylation is of high interest in determining the possible causes at the origin of the formation of tau aggregates and to elaborate protection strategies to cope with these lesions in AD. Among the possible and relatively specific interventions that reverse tau phosphorylation is the stimulation of certain tau phosphatases. Here, we reviewed tau protein phosphatases, their physiological roles and regulation, their involvement in tau phosphorylation and the relevance to AD. We also reviewed the most common compounds acting on each tau phosphatase including PP2A.

Unveiling clusters of RNA transcript pairs associated with markers of Alzheimer's disease progression

Background

One primary goal of transcriptomic studies is identifying gene expression patterns correlating with disease progression. This is usually achieved by considering transcripts that independently pass an arbitrary threshold (e.g. p<0.05). In diseases involving severe perturbations of multiple molecular systems, such as Alzheimer’s disease (AD), this univariate approach often results in a large list of seemingly unrelated transcripts. We utilised a powerful multivariate clustering approach to identify clusters of RNA biomarkers strongly associated with markers of AD progression. We discuss the value of considering pairs of transcripts which, in contrast to individual transcripts, helps avoid natural human transcriptome variation that can overshadow disease-related changes.

Methodology/Principal Findings

We re-analysed a dataset of hippocampal transcript levels in nine controls and 22 patients with varying degrees of AD. A large-scale clustering approach determined groups of transcript probe sets that correlate strongly with measures of AD progression, including both clinical and neuropathological measures and quantifiers of the characteristic transcriptome shift from control to severe AD. This enabled identification of restricted groups of highly correlated probe sets from an initial list of 1,372 previously published by our group. We repeated this analysis on an expanded dataset that included all pair-wise combinations of the 1,372 probe sets. As clustering of this massive dataset is unfeasible using standard computational tools, we adapted and re-implemented a clustering algorithm that uses external memory algorithmic approach. This identified various pairs that strongly correlated with markers of AD progression and highlighted important biological pathways potentially involved in AD pathogenesis.

Conclusions/Significance

Our analyses demonstrate that, although there exists a relatively large molecular signature of AD progression, only a small number of transcripts recurrently cluster with different markers of AD progression. Furthermore, considering the relationship between two transcripts can highlight important biological relationships that are missed when considering either transcript in isolation.

Mitochondrial dysfunction in Pten haplo-insufficient mice with social deficits and repetitive behavior: interplay between Pten and p53

Etiology of aberrant social behavior consistently points to a strong polygenetic component involved in fundamental developmental pathways, with the potential of being enhanced by defects in bioenergetics. To this end, the occurrence of social deficits and mitochondrial outcomes were evaluated in conditional Pten (Phosphatase and tensin homolog) haplo-insufficient mice, in which only one allele was selectively knocked-out in neural tissues. Pten mutations have been linked to Alzheimer's disease and syndromic autism spectrum disorders, among others. By 4–6 weeks of age, Pten insufficiency resulted in the increase of several mitochondrial Complex activities (II–III, IV and V) not accompanied by increases in mitochondrial mass, consistent with an activation of the PI3K/Akt pathway, of which Pten is a negative modulator. At 8–13 weeks of age, Pten haplo-insufficient mice did not show significant behavioral abnormalities or changes in mitochondrial outcomes, but by 20–29 weeks, they displayed aberrant social behavior (social avoidance, failure to recognize familiar mouse, and repetitive self-grooming), macrocephaly, increased oxidative stress, decreased cytochrome c oxidase (CCO) activity (50%) and increased mtDNA deletions in cerebellum and hippocampus. Mitochondrial dysfunction was the result of a downregulation of p53-signaling pathway evaluated by lower protein expression of p21 (65% of controls) and the CCO chaperone SCO2 (47% of controls), two p53-downstream targets. This mechanism was confirmed in Pten-deficient striatal neurons and, HCT 116 cells with different p53 gene dosage. These results suggest a unique pathogenic mechanism of the Pten-p53 axis in mice with aberrant social behavior: loss of Pten (via p53) impairs mitochondrial function elicited by an early defective assembly of CCO and later enhanced by the accumulation of mtDNA deletions. Consistent with our results, (i) SCO2 deficiency and/or CCO activity defects have been reported in patients with learning disabilities including autism and (ii) mutated proteins in ASD have been found associated with p53-signaling pathways.

PTEN, a widely known negative regulator of insulin/PI3K signaling, positively regulates neuronal insulin resistance

Lipid and protein tyrosine phosphatase, phosphatase and tension homologue (PTEN), is a widely known negative regulator of insulin/phosphoinositide 3-kinase signaling. Down-regulation of PTEN is thus widely documented to ameliorate insulin resistance in peripheral tissues such as skeletal muscle and adipose. However, not much is known about its exact role in neuronal insulin signaling and insulin resistance. Moreover, alterations of PTEN in neuronal systems have led to discovery of several unexpected outcomes, including in the neurodegenerative disorder Alzheimer's disease (AD), which is increasingly being recognized as a brain-specific form of diabetes. In addition, contrary to expectations, its neuron-specific deletion in mice resulted in development of diet-sensitive obesity. The present study shows that PTEN, paradoxically, positively regulates neuronal insulin signaling and glucose uptake. Its down-regulation exacerbates neuronal insulin resistance. The positive role of PTEN in neuronal insulin signaling is likely due to its protein phosphatase actions, which prevents the activation of focal adhesion kinase (FAK) and extracellular signal-regulated kinase (ERK), the kinases critically involved in neuronal energy impairment and neurodegeneration. Results suggest that PTEN acting through FAK, the direct protein substrate of PTEN, prevents ERK activation. Our findings provide an explanation for unexpected outcomes reported earlier with PTEN alterations in neuronal systems and also suggest a novel molecular pathway linking neuronal insulin resistance and AD, the two pathophysiological states demonstrated to be closely linked.

PTEN: A molecular target for neurodegenerative disorders

PTEN (phosphatase and tensin homologue deleted in chromosome 10) was first identified as a candidate tumour suppressor gene located on chromosome 10q23. It is considered as one of the most frequently mutated genes in human malignancies. Emerging evidence shows that the biological function of PTEN extends beyond its tumour suppressor activity. In the central nervous system PTEN is a crucial regulator of neuronal development, neuronal survival, axonal regeneration and synaptic plasticity. Furthermore, PTEN has been linked to the pathogenesis of neurodegenerative disorders such as Alzheimer’s disease, Parkinson’s disease and amyotrophic lateral sclerosis. Recently increased attention has been focused on PTEN as a potential target for the treatment of brain injury and neurodegeneration. In this review we discuss the essential functions of PTEN in the central nervous system and its involvement in neurodegeneration.

Human recombinant Cripto-1 increases doubling time and reduces proliferation of HeLa cells independent of pro-proliferation pathways

Human oncofetal protein Cripto-1 (CR-1) is overexpressed in many types of cancers. CR-1 binds to cell surface Glypican-1 to activate Erk1/2 MAPK and Akt pathways leading to cell proliferation. However, we show that treatment with recombinant CR-1 reduces proliferation of HeLa cells by increasing the doubling time without triggering cell death or cell cycle arrest. Using a comparative study with U-87 MG cells, we show that the pro-proliferative pathway of CR-1 is not effective in HeLa cells due to lower expression of Glypican-1. Further we show that treatment with recombinant CR-1 increases PTEN in HeLa cells leading to downregulation of PI3K/Akt pathway. The anti-proliferative effect gets potentiated when the pro-proliferative pathway is blocked.

Autism, Alzheimer disease, and fragile X: APP, FMRP, and mGluR5 are molecular links

The present review highlights an association between autism, Alzheimer disease (AD), and fragile X syndrome (FXS). We propose a conceptual framework involving the amyloid-β peptide (Aβ), Aβ precursor protein (APP), and fragile X mental retardation protein (FMRP) based on experimental evidence. The anabolic (growth-promoting) effect of the secreted α form of the amyloid-β precursor protein (sAPPα) may contribute to the state of brain overgrowth implicated in autism and FXS. Our previous report demonstrated that higher plasma sAPPα levels associate with more severe symptoms of autism, including aggression. This molecular effect could contribute to intellectual disability due to repression of cell-cell adhesion, promotion of dense, long, thin dendritic spines, and the potential for disorganized brain structure as a result of disrupted neurogenesis and migration. At the molecular level, APP and FMRP are linked via the metabotropic glutamate receptor 5 (mGluR5). Specifically, mGluR5 activation releases FMRP repression of APP mRNA translation and stimulates sAPP secretion. The relatively lower sAPPα level in AD may contribute to AD symptoms that significantly contrast with those of FXS and autism. Low sAPPα and production of insoluble Aβ would favor a degenerative process, with the brain atrophy seen in AD. Treatment with mGluR antagonists may help repress APP mRNA translation and reduce secretion of sAPP in FXS and perhaps autism.

Tau, prions and Aβ: the triad of neurodegeneration

This article highlights the features that connect prion diseases with other cerebral amyloidoses and how these relate to neurodegeneration, with focus on tau phosphorylation. It also discusses similarities between prion disease and Alzheimer's disease: mechanisms of amyloid formation, neurotoxicity, pathways involved in triggering tau phosphorylation, links to cell cycle pathways and neuronal apoptosis. We review previous evidence of prion diseases triggering hyperphosphorylation of tau, and complement these findings with cases from our collection of genetic, sporadic and transmitted forms of prion diseases. This includes the novel finding that tau phosphorylation consistently occurs in sporadic CJD, in the absence of amyloid plaques.

Progesterone regulates the phosphorylation of protein phosphatases in the brain

Previous studies have shown that progesterone modulates the activity of different kinases and the phosphorylation of Tau in the brain. These actions of progesterone may be involved in the hormonal regulation of neuronal differentiation, neuronal function, and neuroprotection. However, the action of progesterone on protein phosphatases in the nervous system has not been explored previously. In this study we have assessed the effect of the administration of progesterone to adult ovariectomized rats on protein phosphatase 2A (PP2A) and phosphatase and tensin homolog deleted on chromosome 10 (PTEN) in the hypothalamus, the hippocampus, and the cerebellum. Total levels of PP2A, the state of methylation of PP2A, and total levels of PTEN were unaffected by the hormone in the three brain regions studied. In contrast, progesterone significantly increased the levels of PP2A phosphorylated in tyrosine 307 in the hippocampus and the cerebellum and significantly decreased the levels of PTEN phosphorylated in serine 380 in the hypothalamus and in the hippocampus compared with control values. Estradiol priming blocked the effect of progesterone on PP2A phosphorylation in the hippocampus and on PTEN phosphorylation in the hypothalamus and the hippocampus. In contrast, the action of progesterone on PP2A phosphorylation in the cerebellum was not modified by estradiol priming. These findings suggest that the regulation of the phosphorylation of PP2A and PTEN may be involved in the effects of progesterone on the phosphorylation of Tau and on the activity of phophoinositide-3 kinase and mitogen-activated protein kinase in the brain.

Genetic determinants at the interface of cancer and neurodegenerative disease

It has been hypothesized that oncogenesis and neurodegeneration may share common mechanistic foundations. Recent evidence now reveals a number of genes in which alteration leads to either carcinogenesis or neurodegeneration, depending on cellular context. Pathways that have emerged as having critical roles in both cancer and neurodegenerative disease include those involving genes such as PARK2, ATM, PTEN, PTPRD, and mTOR. A number of mechanisms have been implicated, and commonly affected cellular processes include cell cycle regulation, DNA repair, and response to oxidative stress. For example, we have recently shown that the E3 ubiquitin ligase PARK2 is mutated or deleted in many different human malignancies and helps drive loss on chromosome 6q25.2-27, a genomic region frequently deleted in cancers. Mutation in PARK2 is also the most common cause of juvenile Parkinson's disease. Mutations in PARK2 result in an upregulation of its substrate cyclin E, resulting in dysregulated entry into the cell cycle. In neurons, this process results in cell death, but in cycling cells, the result is a growth advantage. Thus, depending on whether the cell affected is a dividing cell or a post-mitotic neuron, responses to these alterations may differ, ultimately leading to varying disease phenotypes. Here, we review the substantial data implicating specific genes in both cancer and neurodegenerative disease.

Pro-survival role for Parkinson's associated gene DJ-1 revealed in trophically impaired dopaminergic neurons

A mouse genetic study reveals a novel cell-survival role for the Parkinson's disease-associated gene DJ-1 in dopaminergic neurons that have reduced support from endogenous survival factors.

The mechanisms underlying the selective death of substantia nigra (SN) neurons in Parkinson disease (PD) remain elusive. While inactivation of DJ-1, an oxidative stress suppressor, causes PD, animal models lacking DJ-1 show no overt dopaminergic (DA) neuron degeneration in the SN. Here, we show that aging mice lacking DJ-1 and the GDNF-receptor Ret in the DA system display an accelerated loss of SN cell bodies, but not axons, compared to mice that only lack Ret signaling. The survival requirement for DJ-1 is specific for the GIRK2-positive subpopulation in the SN which projects exclusively to the striatum and is more vulnerable in PD. Using Drosophila genetics, we show that constitutively active Ret and associated Ras/ERK, but not PI3K/Akt, signaling components interact genetically with DJ-1. Double loss-of-function experiments indicate that DJ-1 interacts with ERK signaling to control eye and wing development. Our study uncovers a conserved interaction between DJ-1 and Ret-mediated signaling and a novel cell survival role for DJ-1 in the mouse. A better understanding of the molecular connections between trophic signaling, cellular stress and aging could uncover new targets for drug development in PD.

The major pathological event in Parkinson disease is the loss of dopaminergic neurons in a midbrain structure, the substantia nigra. The study of familial Parkinson disease has uncovered several disease-associated genes, including DJ-1. Subsequent studies have suggested that the DJ-1 protein is a suppressor of oxidative stress that might modify signaling pathways that regulate cell survival. However, because animal models lacking DJ-1 function do not show dopaminergic neurodegeneration, the function(s) of DJ-1 in vivo remain unclear. Using mouse genetics, we found that DJ-1 is required for survival of neurons of the substantia nigra only in aging conditions and only in neurons that are partially impaired in receiving trophic signals. Aging mice that lack DJ-1 and Ret, a receptor for a neuronal survival factor, lose more dopaminergic neurons in the substantia nigra as compared with aging mice that lack only Ret. Using the fruit fly Drosophila, we determined that DJ-1 interacts with constitutively active Ret and with its associated downstream signaling pathways. Therefore, understanding the molecular connections between trophic signaling, cellular stress and aging could facilitate the identification of new targets for drug development in Parkinson Disease.

CLA reduces breast cancer cell growth and invasion through ERalpha and PI3K/Akt pathways

We previously reported that conjugated linoleic acid (CLA), a naturally occurring fatty acid, inhibits the growth of ERalpha(+) MCF-7 and ERalpha(-) MDA-MB-231 human breast cancer cells by negative modulation of the ERK/MAPK pathway and apoptosis induction. Here we show that in these cell lines CLA also down-regulates the PI3K/Akt cascade. In MCF-7 cells CLA also triggers ERalpha/PP2A complex formation reducing the phosphorylation state and transcriptional activity of Eralpha whereas in MDA-MB-231 cells CLA does not induce PP2A activation. Moreover, CLA induces the expression of proteins involved in cell adhesion and inhibits cell migration and MMP-2 activity. These findings suggest that CLA may induce the down-regulation of ERalpha signalling and the reduction of cell invasion through the modulation of balancing between phosphatases and kinases.

Accumulation of tumor-suppressor PTEN in Alzheimer neurofibrillary tangles

The phosphatase and tensin homologue deleted on chromosome 10 (PTEN) negatively regulates intracellular levels of PIP3 and antagonizes the PI3K signaling pathway important for cell survival. The present study determined whether altered distribution of PTEN occurs in Alzheimer's disease (AD) brains. We investigated a possible role for PTEN in postmortem brain tissues from elderly controls and patients with AD using immunoblotting and microscopic analyses. Intense immunolabeling was found in the large neurons such as pyramidal cells. In normal neurons, PTEN was located in the nucleus, the cytoplasm of cell bodies and the proximal portion of apical dendrites. Reduced expression and redistribution of PTEN was seen in the remaining neurons in AD. In addition, PTEN was redistributed in damaged neurons from the nucleus and cytoplasm to neuritic pathology such as intracellular neurofibrillary tangles (NFTs), neuropil threads and dystrophic neurites within senile plaques in AD hippocampus, subiculum, entorhinal cortex and angular gyrus. Furthermore, double immunofluorescence staining showed dual labeling of intracellular NFTs for PTEN and tau, labeling of some axons for PTEN and phosphorylated neurofilament, and weak labeling of a few reactive astrocytes around senile plaques for PTEN and GFAP. Double labeling of NFTs was observed in a subset of tangle-bearing neurons either for PTEN and GSK3beta or for PTEN and MEK. Thus our results suggest that PTEN delocalized from the nucleus to the cytoplasm and to intracellular NFTs may cause a deregulation of PI3K pathway in the cytoplasm and may induce the nuclear dysfunction of PTEN in AD degenerating neurons.

Progesterone as a regulator of phosphorylation in the central nervous system

Progesterone exerts a variety of actions in the central nervous system under physiological and pathological conditions. As in other tissues, progesterone acts in the brain through classical progesterone receptors and through alternative mechanisms. Here, we review the role of progesterone as a regulator of kinases and phosphatases, such as extracellular-signal regulated kinases, phosphoinositide 3-kinase, Akt, glycogen synthase kinase 3, protein phosphatase 2A and phosphatase and tensin homolog deleted on chromosome 10. In addition, we analyzed the effects of progesterone on the phosphorylation of Tau, a protein that is involved in microtubule stabilization in neurons.

Neurite outgrowth is enhanced by laminin-mediated down-regulation of the low affinity neurotrophin receptor, p75NTR

Laminin (LN), an extracellular matrix component, is a key factor in promoting axonal regeneration, coordinately regulating growth in conjunction with trophic signals provided by the neurotrophins, including nerve growth factor (NGF). This study investigated potential interactions between the LN and NGF-mediated signaling pathways in PC12 cells and primary neurons. Neurite outgrowth stimulated by NGF was enhanced on a LN substrate. Western blot analysis of pertinent signal transduction components revealed both enhanced phosphorylation of early signaling intermediates upon co-stimulation, and a LN-induced down-regulation of p75NTR which could be prevented by the addition of integrin inhibitory arginine-glycine-aspartate (RGD) peptides. This p75NTR down-regulation was associated with a LN-mediated up-regulation of PTEN and resulted in a decrease in Rho activity. Studies using over-expression or siRNA-mediated knock-down of PTEN demonstrate a consistent inverse relationship with p75NTR, and the over-expression of p75NTR impaired neurite outgrowth on a LN substrate, as well as resulting in sustained activation of Rho which is inhibitory to neurite outgrowth. p75NTR is documented for its role in the transduction of inhibitory myelin-derived signals, and our results point to extracellular matrix regulation of p75NTR as a potential mechanism to ameliorate inhibitory signaling leading to optimized neurite outgrowth.

A comparative study of beta-amyloid peptides Abeta1-42 and Abeta25-35 toxicity in organotypic hippocampal slice cultures

Accumulation of the neurotoxic amyloid beta-peptide (Abeta) in the brain is a hallmark of Alzheimer's disease (AD). Several synthetic Abeta peptides have been used to study the mechanisms of toxicity. Here, we sought to establish comparability between two commonly used Abeta peptides Abeta1-42 and Abeta25-35 on an in vitro model of Abeta toxicity. For this purpose we used organotypic slice cultures of rat hippocampus and observed that both Abeta peptides caused similar toxic effects regarding to propidium iodide uptake and caspase-3 activation. In addition, we also did not observe any effect of both peptides on Akt and PTEN phosphorylation; otherwise the phosphorylation of GSK-3beta was increased. Although further studies are necessary for understanding mechanisms underlying Abeta peptide toxicity, our results provide strong evidence that Abeta1-42 and the Abeta25-35 peptides induce neural injury in a similar pattern and that Abeta25-35 is a convenient tool for the investigation of neurotoxic mechanisms involved in AD.

Microtubule-associated protein tau in development, degeneration and protection of neurons

As a principal neuronal microtubule-associated protein, tau has been recognized to play major roles in promoting microtubule assembly and stabilizing the microtubules and to maintain the normal morphology of the neurons. Recent studies suggest that tau, upon alternative mRNA splicing and multiple posttranslational modifications, may participate in the regulations of intracellular signal transduction, development and viability of the neurons. Furthermore, tau gene mutations, aberrant mRNA splicing and abnormal posttranslational modifications, such as hyperphosphorylation, have also been found in a number of neurodegenerative disorders, collectively known as tauopathies. Therefore, changes in expression of the tau gene, alternative splicing of its mRNA and its posttranslational modification can modulate the normal architecture and functions of neurons as well as in a situation of tauopathies, such as Alzheimer's disease. The primary aim of this review is to summarize the latest developments and perspectives in our understanding about the roles of tau, especially hyperphosphorylation, in the development, degeneration and protection of neurons.

Neuroinflammation: implications for the pathogenesis and molecular diagnosis of Alzheimer's disease

During the past few years, an increasing set of evidence has supported the major role of deregulation of the interaction patterns between glial cells and neurons in the pathway toward neuronal degeneration. Neurons and glial cells, together with brain vessels, constitute an integrated system for brain function. Inflammation is a process related with the onset of several neurodegenerative disorders, including Alzheimer's disease (AD). Several hypotheses have been postulated to explain the pathogenesis of AD, but none provides insight into the early events that trigger metabolic and cellular alterations in neuronal degeneration. The amyloid hypothesis was sustained on the basis that Abeta-peptide deposition into senile plaques is responsible for neurodegeneration. However, recent findings point to Abeta oligomers as responsible for synaptic impairment in neuronal degeneration. Amyloid is only one among many other major factors affecting the quality of neuronal cells. Another explanation derives from the tau hypothesis, supported by the observations that tau hyperphosphorylations constitute a common feature of most of the altered signaling pathways in degenerating neurons. Altered tau patterns have been detected in the cerebrospinal fluids of AD patients, and a close correlation was observed between the levels of hyperphosphorylated tau isoforms and the degree of cognitive impairment. On the other hand, the anomalous effects of cytokines and trophic factors share in common the activation of tau hyperphosphorylation patterns. In this context, a neuroimmunological approach to AD becomes relevant. When glial cells that normally provide neurotrophic factors essential for neurogenesis are activated by a set of stressing events, they overproduce cytokines and NGF, thus triggering altered signaling patterns in the etiopathogenesis of AD. A solid set of discoveries has strengthened the idea that altered patterns in the glia-neuron interactions constitute early molecular events within the cascade of cellular signals that lead to neurodegeneration in AD. A direct correlation has been established between the Abeta-induced neurodegeneration and cytokine production and its subsequent release. In effect, neuroinflammation is responsible for an abnormal secretion of proinflammatory cytokines that trigger signaling pathways that activate brain tau hyperphosphorylation in residues that are not modified under normal physiological conditions. Other cytokines such as IL-3 and TNF-alpha seem to display neuroprotective activities. Elucidation of the events that control the transitions from neuroprotection to neurodegeneration should be a critical point toward elucidation of AD pathogenesis.

Hyperphosphorylation of tau and neurofilaments and activation of CDK5 and ERK1/2 in PTEN-deficient cerebella

Inherited mutations to the tumor suppressor PTEN sporadically lead to cerebellar gangliocytoma characterized by migration defects. This has been modeled by CNS-specific PTEN ablation in mice, but the underlying mechanism cannot be explained by the known role of PTEN in Akt/PKB inactivation. Here we show that the loss of PTEN in mouse cerebellar neurons causes neurodegeneration by hyperphosphorylation of tau and neurofilaments, and activation of Cdk5 and pERK1/2, suggesting that dysregulation of the PTEN/pAkt pathway can mediate neurodegeneration.