Correlation between synaptogenesis and the PTEN phosphatase expression in dendrites during postnatal brain development

PTEN Activity Defines an Axis for Plasticity at Cortico-Amygdala Synapses and Influences Social Behavior

Phosphatase and tensin homolog on chromosome 10 (PTEN) is a tumor suppressor and autism-associated gene that exerts an important influence over neuronal structure and function during development. In addition, it participates in synaptic plasticity processes in adulthood. As an attempt to assess synaptic and developmental mechanisms by which PTEN can modulate cognitive function, we studied the consequences of 2 different genetic manipulations in mice: presence of additional genomic copies of the Pten gene (Ptentg) and knock-in of a truncated Pten gene lacking its PDZ motif (Pten-ΔPDZ), which is required for interaction with synaptic proteins. Ptentg mice exhibit substantial microcephaly, structural hypoconnectivity, enhanced synaptic depression at cortico-amygdala synapses, reduced anxiety, and intensified social interactions. In contrast, Pten-ΔPDZ mice have a much more restricted phenotype, with normal synaptic connectivity, but impaired synaptic depression at cortico-amygdala synapses and virtually abolished social interactions. These results suggest that synaptic actions of PTEN in the amygdala contribute to specific behavioral traits, such as sociability. Also, PTEN appears to function as a bidirectional rheostat in the amygdala: reduction in PTEN activity at synapses is associated with less sociability, whereas enhanced PTEN activity accompanies hypersocial behavior.

One Step Histological Detection and Staining of the PTEN Tumor Suppressor Protein by a Single Strand DNA

Antibodies are the most used technological tool in histochemistry. However, even with monoclonal antibodies, their standardization is difficult due to variation of biological systems as well as to variability due to the affinity and amplification of the signal arising from secondary peroxidase detection systems. In this article we combined two synthetic molecules to facilitate the standardization of a detection protocol of protein markers in histological sections. The first molecule was an aptamer, a 50-base single-stranded DNA fragment, which recognizes a PTEN tumor suppressor. The second molecule used was also another single stranded 18-base aptamer DNA fragment, which forms a quadruplex structure guanine box. This G-quadruplex recognizes and attaches a molecule of hemin, increasing the catalytic capacity for the hydrogen peroxide. Our results show how the correct structural design of DNA combining an aptamer together with the peroxidase-like DNAzyme allows to detect proteins in histological sections. This tool offers the standardization of the detection of prognostic markers in cancer, in quality and quantity, due to its synthetic nature and its 1:1 antigen:enzyme ratio. This is the first time that reproducible results have been presented in histological sections staining a cancer marker using a single-stranded DNA molecule with dual function.

PTEN in Autism and Neurodevelopmental Disorders

Phosphatase and tensin homolog (PTEN) is a classical tumor suppressor that antagonizes phosphatidylinositol 3-phosphate kinase (PI3K)/AKT signaling. Although there is a strong association of PTEN germline mutations with cancer syndromes, they have also been described in a subset of patients with autism spectrum disorders with macrocephaly characterized by impairments in social interactions and communication, repetitive behavior and, occasionally, epilepsy. To investigate PTEN's role during neurodevelopment and its implication for autism, several conditional Pten knockout mouse models have been generated. These models are valuable tools to understand PTEN's spatiotemporal roles during neurodevelopment. In this review, we will highlight the anatomical and phenotypic results from animal studies and link them to cellular and molecular findings.

Intermittent fasting uncovers and rescues cognitive phenotypes in PTEN neuronal haploinsufficient mice

Phosphatase and tensin homolog (PTEN) is an important protein with key modulatory functions in cell growth and survival. PTEN is crucial during embryogenesis and plays a key role in the central nervous system (CNS), where it directly modulates neuronal development and synaptic plasticity. Loss of PTEN signaling function is associated with cognitive deficits and synaptic plasticity impairment. Accordingly, Pten mutations have a strong link with autism spectrum disorder. In this study, neuronal Pten haploinsufficient male mice were subjected to a long-term environmental intervention – intermittent fasting (IF) – and then evaluated for alterations in exploratory, anxiety and learning and memory behaviors. Although no significant effects on spatial memory were observed, mutant mice showed impaired contextual fear memory in the passive avoidance test – an outcome that was effectively rescued by IF. In this study, we demonstrated that IF modulation, in addition to its rescue of the memory deficit, was also required to uncover behavioral phenotypes otherwise hidden in this neuronal Pten haploinsufficiency model.

Dendritic spine anomalies and PTEN alterations in a mouse model of VPA-induced autism spectrum disorder

Mounting evidence suggests that the etiology of autism spectrum disorders (ASDs) is profoundly influenced by exposure to environmental factors, although the precise molecular and cellular links remain ill-defined. In this study, we examined how exposure to valproic acid (VPA) during pregnancy is associated with an increased incidence of ASD. A mouse model was established by injecting VPA at embryonic day 13, and its behavioral phenotypes including impaired social interaction, increased repetitive behaviors and decreased nociception were observed at postnatal days 21-42. VPA-treated mice showed dysregulation of synaptic structure in cortical neurons, including a reduced proportion of filopodium-type and stubby spines and increased proportions of thin and mushroom-type spines, along with a decreased spine head size. We also found that VPA-treatment led to decreased expression of phosphate and tensin homolog (PTEN) and increased levels of p-AKT protein in the hippocampus and cortex. Our data suggest that there is a correlation between VPA exposure and dysregulation of PTEN with ASD-like behavioral and neuroanatomical changes, and this may be a potential mechanism of VPA-induced ASD.

Reframing autism as a behavioral syndrome and not a specific mental disorder: Implications of genetic and phenotypic heterogeneity

Clinical and molecular genetics have advanced current knowledge on genetic disorders associated with autism. A review of diverse genetic disorders associated with autism is presented and for the first time discussed extensively with regard to possible common underlying mechanisms leading to a similar cognitive-behavioral phenotype of autism. The possible role of interactions between genetic and environmental factors, including epigenetic mechanisms, is in particular examined. Finally, the pertinence of distinguishing non-syndromic autism (isolated autism) from syndromic autism (autism associated with genetic disorders) will be reconsidered. Given the high genetic and etiological heterogeneity of autism, autism can be viewed as a behavioral syndrome related to known genetic disorders (syndromic autism) or currently unknown disorders (apparent non-syndromic autism), rather than a specific categorical mental disorder. It highlights the need to study autism phenotype and developmental trajectory through a multidimensional, non-categorical approach with multivariate analyses within autism spectrum disorder but also across mental disorders, and to conduct systematically clinical genetic examination searching for genetic disorders in all individuals (children but also adults) with autism.

A Subset of Autism-Associated Genes Regulate the Structural Stability of Neurons

Autism spectrum disorder (ASD) comprises a range of neurological conditions that affect individuals’ ability to communicate and interact with others. People with ASD often exhibit marked qualitative difficulties in social interaction, communication, and behavior. Alterations in neurite arborization and dendritic spine morphology, including size, shape, and number, are hallmarks of almost all neurological conditions, including ASD. As experimental evidence emerges in recent years, it becomes clear that although there is broad heterogeneity of identified autism risk genes, many of them converge into similar cellular pathways, including those regulating neurite outgrowth, synapse formation and spine stability, and synaptic plasticity. These mechanisms together regulate the structural stability of neurons and are vulnerable targets in ASD. In this review, we discuss the current understanding of those autism risk genes that affect the structural connectivity of neurons. We sub-categorize them into (1) cytoskeletal regulators, e.g., motors and small RhoGTPase regulators; (2) adhesion molecules, e.g., cadherins, NCAM, and neurexin superfamily; (3) cell surface receptors, e.g., glutamatergic receptors and receptor tyrosine kinases; (4) signaling molecules, e.g., protein kinases and phosphatases; and (5) synaptic proteins, e.g., vesicle and scaffolding proteins. Although the roles of some of these genes in maintaining neuronal structural stability are well studied, how mutations contribute to the autism phenotype is still largely unknown. Investigating whether and how the neuronal structure and function are affected when these genes are mutated will provide insights toward developing effective interventions aimed at improving the lives of people with autism and their families.

The associations between Parkinson's disease and cancer: the plot thickens

Epidemiological studies support a general inverse association between the risk of cancer development and Parkinson’s disease (PD). In recent years however, increasing amount of eclectic evidence points to a positive association between PD and cancers through different temporal analyses and ethnic groups. This positive association has been supported by several common genetic mutations in SNCA, PARK2, PARK8, ATM, p53, PTEN, and MC1R resulting in cellular changes such as mitochondrial dysfunction, aberrant protein aggregation, and cell cycle dysregulation. Here, we review the epidemiological and biological advances of the past decade in the association between PD and cancers to offer insight on the recent and sometimes contradictory findings.

Balancing Proliferation and Connectivity in PTEN-associated Autism Spectrum Disorder

Germline mutations in PTEN, which encodes a widely expressed phosphatase, was mapped to 10q23 and identified as the susceptibility gene for Cowden syndrome, characterized by macrocephaly and high risks of breast, thyroid, and other cancers. The phenotypic spectrum of PTEN mutations expanded to include autism with macrocephaly only 10 years ago. Neurological studies of patients with PTEN-associated autism spectrum disorder (ASD) show increases in cortical white matter and a distinctive cognitive profile, including delayed language development with poor working memory and processing speed. Once a germline PTEN mutation is found, and a diagnosis of phosphatase and tensin homolog (PTEN) hamartoma tumor syndrome made, the clinical outlook broadens to include higher lifetime risks for multiple cancers, beginning in childhood with thyroid cancer. First described as a tumor suppressor, PTEN is a major negative regulator of the phosphatidylinositol 3-kinase/protein kinase B/mammalian target of rapamycin (mTOR) signaling pathway-controlling growth, protein synthesis, and proliferation. This canonical function combines with less well-understood mechanisms to influence synaptic plasticity and neuronal cytoarchitecture. Several excellent mouse models of Pten loss or dysfunction link these neural functions to autism-like behavioral abnormalities, such as altered sociability, repetitive behaviors, and phenotypes like anxiety that are often associated with ASD in humans. These models also show the promise of mTOR inhibitors as therapeutic agents capable of reversing phenotypes ranging from overgrowth to low social behavior. Based on these findings, therapeutic options for patients with PTEN hamartoma tumor syndrome and ASD are coming into view, even as new discoveries in PTEN biology add complexity to our understanding of this master regulator.

Pten haploinsufficient mice show broad brain overgrowth but selective impairments in autism-relevant behavioral tests

Accelerated head and brain growth (macrocephaly) during development is a replicated biological finding in a subset of individuals with autism spectrum disorder (ASD). However, the relationship between brain overgrowth and the behavioral and cognitive symptoms of ASD is poorly understood. The PI3K-Akt-mTOR pathway regulates cellular growth; several genes encoding negative regulators of this pathway are ASD risk factors, including PTEN. Mutations in PTEN have been reported in individuals with ASD and macrocephaly. We report that brain overgrowth is widespread in Pten germline haploinsufficient (Pten(+/-)) mice, reflecting Pten mRNA expression in the developing brain. We then ask if broad brain overgrowth translates into general or specific effects on the development of behavior and cognition by testing Pten(+/-) mice using assays relevant to ASD and comorbidities. Deficits in social behavior were observed in both sexes. Males also showed abnormalities related to repetitive behavior and mood/anxiety. Females exhibited circadian activity and emotional learning phenotypes. Widespread brain overgrowth together with selective behavioral impairments in Pten(+/-) mice raises the possibility that most brain areas and constituent cell types adapt to an altered trajectory of growth with minimal impact on the behaviors tested in our battery; however, select areas/cell types relevant to social behavior are more vulnerable or less adaptable, thus resulting in social deficits. Probing dopaminergic neurons as a candidate vulnerable cell type, we found social behavioral impairments in mice with Pten conditionally inactivated in dopaminergic neurons that are consistent with the possibility that desynchronized growth in key cell types may contribute to ASD endophenotypes.

PTEN inactivation by germline/somatic c.950_953delTACT mutation in patients with Lhermitte-Duclos disease manifesting progressive phenotypes

Lhermitte-Duclos disease (LDD), a neurological manifestation of Cowden syndrome (CS), is a rare and benign cerebellar disorder, featured by dysplastic cerebellar ganglion cells which replace granular and Purkinje cells. Phosphatase and Tensin Homolog (PTEN) is confirmed as the susceptibility gene for CS which represents the most complex features and is not easily recognizable. We reported two index patients with LDD diagnosed either in an isolated form or coexist with CS. These two patients displayed progressive though comparable phenotypes and were found to carry an identical PTEN c.950_953delTACT mutation in either germline or somatic sources of DNA, respectively. Negative or moderate expression levels of PTEN were validated by immunohistochemistry in the corresponding patients' affected tissues. This study has revealed a novel pathogenicity locus to LDD/CS as a candidate for early molecular diagnosis. In addition, the differential PTEN mutation status with corresponding LDD phenotypes suggests a potential correlation between germline or somatic mutation and coexisting LDD/CS or isolated LDD, respectively. Furthermore, our data could lend some reference to the underlying molecular mechanism of LDD pathogenesis in the future.

In MMTV-Her-2/neu transgenic mammary tumors the absence of caveolin-1-/- alters PTEN and NHERF1 but not β-catenin expression

In a recent study, we have shown that in mammary tumors from mice lacking the Cav-1 gene, there are alterations in specific heat shock proteins as well as in tumor development. With this in mind, we have now investigated other proteins in the same mammary mouse tumor model (Her-2/neu expressing mammary tumors from Cav-1 wild type and Cav-1 null mice), to further comprehend the complex tumor-stroma mechanisms involved in regulating stress responses during tumor development. In this tumor model the cancer cells always lacked of Cav-1, so the KO influenced the Cav-1 in the stroma. By immunohistochemistry, we have found a striking co-expression of β-catenin and Her-2/neu in the tumor cells. The absence of Cav-1 in the tumor stroma had no effect on expression or localization of β-catenin and Her-2/neu. Both proteins appeared co-localized at the cell surface during tumor development and progression. Since Her-2/neu activation induces MTA1, we next evaluated MTA1 in the mouse tumors. Although this protein was found in numerous nuclei, the absence of Cav-1 did not alter its expression level. In contrast, significantly more PTEN protein was noted in the tumors lacking Cav-1 in the stroma, with the protein localized mainly in the nuclei. P-Akt levels were relatively low in tumors from both Cav-1 WT and Cav-1 KO mice. There was also an increase in nuclear NHERF1 expression levels in the tumors arising from Cav-1 KO mice. The data obtained in the MMTV-neu model are consistent with a role for Cav-1 in adjacent breast cancer stromal cells in modulating the expression and localization of important proteins implicated in tumor cell behavior.

Preventive effects of AdR-siPTEN through the regulation of NMDA receptor NR2B subunit in trigeminal ganglia of migraine rats

OBJECTIVE

Migraine is a refractory disease that is due to neuronal hyperexcitability, and has high incidence, mortality, and disability rates. The N-methyl-D-aspartate receptor 2B (NR2B) subunit has been found to play an important role in the pathogenesis of migraine. There is evidence suggesting that a tumor suppressor phosphatase and tensin homolog (PTEN) can confer a neuroprotective effect on cerebral ischemic injury by regulating NR2B levels. However, the role of PTEN in migraines is still unclear. This study aimed to define whether PTEN is involved in the pathogenesis of migraine through modulating NR2B, nitric oxide synthase (NOS), and nitric oxide (NO) in the trigeminal ganglia of rats with glyceryl trinitrate-induced migraine.

METHODS

Adenovirus-expressing siPTEN or RFP was independently injected into the Sp5 (spinal trigeminal nucleus) of rats suffering from migraines. Seven days later, tactile sensory testing was performed to detect the tactile threshold. Immunofluorescence assay, western blot assay, RT-PCR, and biochemical examination were done to measure PTEN, NR2B, NOS, and NO levels in the trigeminal ganglia of migraine rats.

RESULTS

NR2B, NOS, and NO levels significantly (P<0.05) decreased in the trigeminal ganglia of migraine-affected rats pretreated with adenovirus-expressing siPTEN.

CONCLUSION

These results suggest that PTEN in trigeminal ganglia is implicated in the pathogenesis of migraine, and PTEN may be a novel and promising candidate for future treatment and/or prevention of migraine via regulating NR2B and decreasing NO production in trigeminal ganglia.

PTEN plasticity: how the taming of a lethal gene can go too far

PTEN loss drives many cancers and recent genetic studies reveal that often PTEN is antagonised at the protein level without alteration of DNA or RNA expression. This scenario can already cause malignancy, because PTEN is haploinsufficient. We here review normally occurring mechanisms of PTEN protein regulation and discuss three processes where PTEN plasticity is needed: ischaemia, development, and wound healing. These situations demand transient PTEN suppression, whereas cancer exploits them for continuous proliferation and survival advantages. Therefore, increased understanding of PTEN plasticity may help us better interpret tumour development and ultimately lead to drug targets for PTEN supporting cancer therapy.

Downregulation of Hsp27 (HSPB1) in MCF-7 human breast cancer cells induces upregulation of PTEN

Hsp27 (HSPB1) is usually overexpressed in breast cancers affecting the disease outcome and the sensitivity of tumors to chemotherapy and radiotherapy. Hsp27 interacts with other proteins such as β-catenin, histone deacetylase HDAC6, transcription factor STAT2 and procaspase-3. Phosphatase and tensin homologue (PTEN) is a tumor suppressor gene that is deleted in many human tumors. The PI3K/Akt signaling pathway is negatively regulated by PTEN. Hsp27 is described as a key component of the Akt signaling cascade: Akt, BAD, Forkhead transcription factors, Hsp27, mitogen-activated protein kinase kinase-3 and -6. Here, we have examined whether the downregulation of Hsp27 by siHsp27 affects the PTEN levels in the MCF-7 human breast cancer cell line. PTEN was detected with two different antibodies using western blots and immunocytochemistry. p-Akt was also evaluated by western blot. In addition, Hsp27 and PTEN were immunoprecipitated to know whether these proteins interact. Intracellular colocalization studies were carried out by confocal microscopy. A significant reduction in the Hsp27 levels was noted in the siHsp27 transfected cells. These Hsp27 downregulated cells showed a significant increased expression of PTEN. The MW 76 and 55 kDa PTEN forms were upregulated as revealed by two different antibodies. The phosphatase activity of PTEN seems to be active because p-Akt levels were reduced. Hsp27 immunoprecipitation was bringing PTEN and vice versa, these two proteins seem to interact at cytoplasmic level by FRET. Downregulation of Hsp27 stabilized PTEN protein levels. Chaperone-assisted E3 ligase C terminus of Hsc70-interacting protein (CHIP) levels were not significantly influenced by Hsp27 downregulation. In conclusion, we report a novel function of Hsp27 modulating the PTEN levels in human breast cancer cells suggesting an interaction between these two molecules.

Regulation of axonal growth and neuromuscular junction formation by neuronal phosphatase and tensin homologue signaling

Axonal growth and synaptogenesis are sequential events of neuronal development. Phosphatase and tensin homologue (PTEN) is expressed in motor neurons, and its disruption leads to continued axonal extension, even upon muscle contact, leading to synaptogenic suppression. Thus PTEN is involved in target-mediated cessation of axonal growth and subsequent synaptic differentiation.

During the development of the vertebrate neuromuscular junction (NMJ), motor axon tips stop growing after contacting muscle and transform into presynaptic terminals that secrete the neurotransmitter acetylcholine and activate postsynaptic ACh receptors (AChRs) to trigger muscle contraction. The neuron-intrinsic signaling that retards axonal growth to facilitate stable nerve–muscle interaction and synaptogenesis is poorly understood. In this paper, we report a novel function of presynaptic signaling by phosphatase and tensin homologue (PTEN) in mediating a growth-to-synaptogenesis transition in neurons. In Xenopus nerve–muscle cocultures, axonal growth speed was halved after contact with muscle, when compared with before contact, but when cultures were exposed to the PTEN blocker bisperoxo (1,10-phenanthroline) oxovanadate, axons touching muscle grew ∼50% faster than their counterparts in control cultures. Suppression of neuronal PTEN expression using morpholinos or the forced expression of catalytically inactive PTEN in neurons also resulted in faster than normal axonal advance after contact with muscle cells. Significantly, interference with PTEN by each of these methods also led to reduced AChR clustering at innervation sites in muscle, indicating that disruption of neuronal PTEN signaling inhibited NMJ assembly. We thus propose that PTEN-dependent slowing of axonal growth enables the establishment of stable nerve–muscle contacts that develop into NMJs.

Interference with the PTEN-MAST2 interaction by a viral protein leads to cellular relocalization of PTEN

PTEN (phosphatase and tensin homolog deleted on chromosome 10) and MAST2 (microtubule-associated serine and threonine kinase 2) interact with each other through the PDZ domain of MAST2 (MAST2-PDZ) and the carboxyl-terminal (C-terminal) PDZ domain-binding site (PDZ-BS) of PTEN. These two proteins function as negative regulators of cell survival pathways, and silencing of either one promotes neuronal survival. In human neuroblastoma cells infected with rabies virus (RABV), the C-terminal PDZ domain of the viral glycoprotein (G protein) can target MAST2-PDZ, and RABV infection triggers neuronal survival in a PDZ-BS-dependent fashion. These findings suggest that the PTEN-MAST2 complex inhibits neuronal survival and that viral G protein disrupts this complex through competition with PTEN for binding to MAST2-PDZ. We showed that the C-terminal sequences of PTEN and the viral G protein bound to MAST2-PDZ with similar affinities. Nuclear magnetic resonance structures of these complexes exhibited similar large interaction surfaces, providing a structural basis for their binding specificities. Additionally, the viral G protein promoted the nuclear exclusion of PTEN in infected neuroblastoma cells in a PDZ-BS-dependent manner without altering total PTEN abundance. These findings suggest that formation of the PTEN-MAST2 complex is specifically affected by the viral G protein and emphasize how disruption of a critical protein-protein interaction regulates intracellular PTEN trafficking. In turn, the data show how the viral protein might be used to decipher the underlying molecular mechanisms and to clarify how the subcellular localization of PTEN regulates neuronal survival.

Role of phosphoinositides at the neuronal synapse

Synaptic transmission is amongst the most sophisticated and tightly controlled biological phenomena in higher eukaryotes. In the past few decades, tremendous progress has been made in our understanding of the molecular mechanisms underlying multiple facets of neurotransmission, both pre- and postsynaptically. Brought under the spotlight by pioneer studies in the areas of secretion and signal transduction, phosphoinositides and their metabolizing enzymes have been increasingly recognized as key protagonists in fundamental aspects of neurotransmission. Not surprisingly, dysregulation of phosphoinositide metabolism has also been implicated in synaptic malfunction associated with a variety of brain disorders. In the present chapter, we summarize current knowledge on the role of phosphoinositides at the neuronal synapse and highlight some of the outstanding questions in this research field.

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.

Different conformations of phosphatase and tensin homolog, deleted on chromosome 10 (PTEN) protein within the nucleus and cytoplasm of neurons

PTEN is a critical gene involved in the regulation of many cellular processes. The product of this gene has dual phosphatase activity and is able to dephosphorylate the 5′ end of the phosphatidylinositol (3,4,5)-trisphosphate. Within the cellular nucleus, this protein has been associated with regulation of the expression of many genes, although the mechanism of this regulation remains unclear. In this paper, two specific oligonucleotide aptamers were developed and selected, using the SELEX procedure, according to their ability to detect the PTEN protein in different subcellular compartments of neurons. While one aptamer was able to detect PTEN in the nucleus, the other recognized PTEN in the cytoplasm. The recognition pattern of PTEN by both aptamers was confirmed using antibodies in western blots of the proteins purified from mouse cerebellar homogenates and subcellular fractions. Additionally, we demonstrated that the two aptamers recognized different epitopes of the target peptide. The results presented here could not be fully explained by the canonical phosphatase structure of PTEN, suggesting the existence of different conformations of phosphatase in the nucleus and the cytoplasm.

ProNGF induces PTEN via p75NTR to suppress Trk-mediated survival signaling in brain neurons

Proneurotrophins and mature neurotrophins activate different signaling pathways with distinct effects on their target cells: proneurotrophins can induce apoptotic signaling via p75(NTR), whereas mature neurotrophins activate Trk receptors to influence survival and differentiation. Here, we demonstrate that the PTEN (phosphatase and tensin homolog deleted on chromosome 10) phosphatase represents a novel switch between the survival and apoptotic signaling pathways in rat CNS neurons. Simultaneous activation of p75(NTR) by proNGF and TrkB signaling by BDNF elicited apoptosis despite TrkB phosphorylation. Apoptosis induced by p75(NTR) required suppression of TrkB-induced phosphoinositide-3 kinase signaling, mediated by induction of PTEN, for apoptosis to proceed. Inhibition of PTEN restored the ability of BDNF to phosphorylate Akt and protect cultured basal forebrain neurons from proNGF-induced death. In vivo, inhibition or knockdown of PTEN after pilocarpine-induced seizures protected CNS neurons from p75(NTR)-mediated death, demonstrating that PTEN is a crucial factor mediating the balance between p75(NTR)-induced apoptotic signaling and Trk-mediated survival signaling in brain neurons.

Role of phosphatase and tensin homolog in the development of the mammalian auditory system

Phosphatase and tensin homolog (PTEN) is a tumor suppressor gene that controls neural stem cell renewal and differentiation and is a potential target for regeneration in the optic nerve. Here we show that it has a critical pattern of expression in the mammalian developing auditory system. PTEN was expressed in the cochlear-vestibular ganglion at embryonic day 10.5 and then progressively in hair cells as they differentiated from the base to the apex of the cochlea. By postnatal day 7, PTEN was downregulated in hair cells and subsequently in the neurons. This very specific, transient expression pattern suggests that PTEN plays a crucial role in the differentiation of the sensory neurons and hair cells and that it is a potential therapeutic target for hearing regeneration.

PTEN is recruited to the postsynaptic terminal for NMDA receptor-dependent long-term depression

Phosphatase and tensin homolog deleted on chromosome ten (PTEN) is an important regulator of phosphatidylinositol-(3,4,5,)-trisphosphate signalling, which controls cell growth and differentiation. However, PTEN is also highly expressed in the adult brain, in which it can be found in dendritic spines in hippocampus and other brain regions. Here, we have investigated specific functions of PTEN in the regulation of synaptic function in excitatory hippocampal synapses. We found that NMDA receptor activation triggers a PDZ-dependent association between PTEN and the synaptic scaffolding molecule PSD-95. This association is accompanied by PTEN localization at the postsynaptic density and anchoring within the spine. On the other hand, enhancement of PTEN lipid phosphatase activity is able to drive depression of AMPA receptor-mediated synaptic responses. This activity is specifically required for NMDA receptor-dependent long-term depression (LTD), but not for LTP or metabotropic glutamate receptor-dependent LTD. Therefore, these results reveal PTEN as a regulated signalling molecule at the synapse, which is recruited to the postsynaptic membrane upon NMDA receptor activation, and is required for the modulation of synaptic activity during plasticity.

PTEN attenuates PIP3/Akt signaling in the cochlea of the aging CBA/J mouse

We have previously reported the activation of cell death pathways in the sensory cells of the aging cochlea. Here we investigate age-associated changes in survival mechanisms focusing on phosphatidylinositol 3,4,5-trisphosphate (PIP(3))/Akt signaling. The animal model is the CBA/J mouse of 18 months of age prior to the onset of major functional loss (ABR thresholds, 26+/-8 dB SPL) which is compared to young animals of 3 months of age (ABR thresholds, 19+/-7 dB SPL). Immunostaining on cochlear cryosections revealed a wide-spread distribution of PIP(3) in the cochlea which was markedly attenuated in old animals in inner and outer hair cells, Deiters cells and pillar cells. Protein levels of the lipid phosphatase PTEN which regulates PIP(3) increased in those cells with aging while its mRNA did not, suggesting an age-related reduction of PTEN degradation. Furthermore, staining intensity of phosphorylated PTEN (ser380) and its nuclear localization increased. Consistent with a reduction of PIP(3), the phosphorylation of the downstream target Akt at threonine 308 significantly decreased in outer hair cells. The results suggest a decline of the survival capacity of aging outer hair cells due to a decrease in PIP(3)/Akt signaling caused by an increase of PTEN.

Phosphatase PTEN in neuronal injury and brain disorders

The phosphatase and tensin homologue PTEN was originally identified as a tumor suppressor. In the CNS, mutation or inactivation of PTEN is best known for playing a tumorigenic role in the molecular pathogenesis of glioblastoma. However, recent studies show that PTEN is associated with several brain diseases other than cancer, suggesting a broader role of PTEN in CNS pathophysiology. Here, we review the evidence for the crucial involvement of PTEN in neuronal injury as well as in neurological and psychiatric disorders, and discuss the potential of PTEN as a molecular target for the development of a novel CNS therapeutic strategy.

The PTEN phosphatase is essential for long-term depression of hippocampal synapses

Activity-induced long-term potentiation (LTP) and long-term depression (LTD) of synaptic transmission are two types of enduring changes in neuronal connections that are believed to underlie learning and memory functions. Here we show that CA1 synapses in hippocampal slices from PTEN-deficient mice exhibit LTP, but are resistant to LTD. PTEN reduces phosphatidylinositol-3-kinase (PI3-K) activity, and pharmacological inhibition of PI3-K restores LTD in PTEN-deficient mice, suggesting that inhibition of PI3-K by PTEN is necessary for LTD induction. These findings demonstrate a pivotal role for PTEN in LTD, and suggest that alterations in PTEN could have an impact on learning and memory processes.

Implication of PTEN in production of reactive oxygen species and neuronal death in in vitro models of stroke and Parkinson's disease

Oxidative stress plays crucial role in the pathogenesis of neurodegenerative diseases. However, the precise mechanism for an increased production of reactive oxygen species (ROS) under pathological conditions is not yet fully understood. We have recently demonstrated an implication of phosphatase and tensin homologue deleted on chromosome 10 (PTEN), a tumor suppressor, in ROS generation and neuronal apoptosis induced by staurosporine. These findings raised further interest whether PTEN functions as a common mediator of oxidative stress in neurodegenerative processes. To address this issue, neural cells were exposed to oxygen-glucose deprivation (OGD) and to the neurotoxin 1-methyl-4-phenylpyridinium iodide (MPP(+)), which mimic cerebral ischemia and Parkinson's disease, respectively. OGD for 4 h followed by 16 h of reoxygenation or incubation with MPP(+) (250 microM) for 48 h induced 33% and 45% neuronal death in rat hippocampal and in human dopaminergic SH-SY5Y neurons, respectively, accompanied by a gradual increase in the intracellular level of ROS. The increase in ROS by OGD and by MPP(+) did not cause oxidative inactivation of PTEN and thus, PTEN remains constitutively active. In support, the protein level of PTEN was not reduced in both cell cultures after challenging with OGD or MPP(+). Importantly, the elevated intracellular ROS levels and the neuronal death caused by OGD or by MPP(+) toxicity were significantly inhibited when PTEN was downregulated by a specific antisense oligonucleotide or by siRNA. Because SOD2 protein level is not altered either by knockdown of PTEN nor by an inhibition of the PI3K/Akt signalling, we suggest that SOD2 do not contribute to the pathomechanism of oxidative stress induced by PTEN or by inhibiting the related Akt signalling. The present study highlights PTEN as a crucial and common mediator of ROS generation and neuronal death and suggests that PTEN could become a potential therapeutic target for interfering with neurodegeneration.

Pten regulates neuronal arborization and social interaction in mice

CNS deletion of Pten in the mouse has revealed its roles in controlling cell size and number, thus providing compelling etiology for macrocephaly and Lhermitte-Duclos disease. PTEN mutations in individuals with autism spectrum disorders (ASD) have also been reported, although a causal link between PTEN and ASD remains unclear. In the present study, we deleted Pten in limited differentiated neuronal populations in the cerebral cortex and hippocampus of mice. Resulting mutant mice showed abnormal social interaction and exaggerated responses to sensory stimuli. We observed macrocephaly and neuronal hypertrophy, including hypertrophic and ectopic dendrites and axonal tracts with increased synapses. This abnormal morphology was associated with activation of the Akt/mTor/S6k pathway and inactivation of Gsk3beta. Thus, our data suggest that abnormal activation of the PI3K/AKT pathway in specific neuronal populations can underlie macrocephaly and behavioral abnormalities reminiscent of certain features of human ASD.

Anp32e/Cpd1 regulates protein phosphatase 2A activity at synapses during synaptogenesis

Anp32e/Cpd1, a member of the acidic nuclear phosphoprotein (Anp)32 family, is characterized by the presence of an amino terminal domain containing four leucine-rich repeats and a carboxyl-terminal low-compositional complexity acidic region. In previous studies performed to understand the biological role of Anp32e/Cpd1, we showed a predominant presence of Anp32e/Cpd1 in the nucleus. However, when Anp32e/Cpd1 is in the cytoplasm, it co-localizes spatially with protein phosphatase 2A (PP2A) near cell membranes, far from the synapses. In the present work, we show that Anp32e/Cpd1 is also present as a membrane-bound 74/76-kDa protein with a widespread distribution in the brain. We reveal that the expression, synthesis and half-life of this high-molecular-weight form of Anp32e/Cpd1 are spatially and temporally correlated with the cerebellar synaptogenesis period. We demonstrate that synaptic Anp32e/Cpd1 co-localizes, interacts and inhibits PP2A activity, and that phosphorylation of Anp32/Cpd1 is required for the Anp32e-PP2A interaction. Also, subcellular localization was shown with electronic microscopy. Finally, we examine Anp32e/Cpd1 and PP2A distribution in two ataxic mutant models, weaver and staggerer, and show that their co-localization in Purkinje cell dendrites depends on parallel fibre/Purkinje cell contacts. Based on these observations, we propose that Anp32e/Cpd1 mediates synaptogenesis process by modulating PP2A activity.

PTEN: A crucial mediator of mitochondria-dependent apoptosis

The highly frequent mutation of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) in various cancers has attracted much attention to study its role in tumorigenesis. As an important tumor suppressor, the pro-apoptotic function of PTEN has been linked to its capacity antagonizing the PI3K/Akt signaling pathway. However, less data are available concerning its role in neurodegeneration in which apoptotic processes are also involved. In the present study, we attempted to study the role and the underlying mechanism of PTEN in neuronal apoptosis. Using primary rat hippocampal cultures, staurosporine (STS, 100 nM) induced a time-dependent apoptosis, accompanied by a marked production of reactive oxygen species (ROS), release of cytochrome c and activation of caspase 9 and 3. However, the expression of PTEN, and the levels of phospho-PTEN and phospho-Akt were not changed at all time points tested (0.5-24 h) after STS stimulation, suggesting that the protein level as well as the phosphorylation status of PTEN were not related to the procession of apoptosis. Interestingly, immunostaining revealed a punctate intracellular distribution of PTEN from 2 to 8 h after adding STS. Double labeling and Western blotting of mitochondrial fraction demonstrated a mitochondrial location and accumulation of PTEN, respectively, after challenging with STS. Furthermore, we provide evidence for the first time that PTEN was associated with Bax in the absence and the presence of STS. Of note, the STS-induced marked increase in the cellular ROS level, release of cytochrome c and activation of caspase 3 were inhibited in cultured hippocampal cells when PTEN was knocked down by a specific antisense. Moreover, knockdown of PTEN significantly protected hippocampal cells from apoptotic damage. These findings demonstrated that PTEN is a crucial mediator of mitochondria-dependent apoptosis, and thus could become a molecular target for interfering with neurodegenerative diseases.