Browsing by Author "Varela-Nallar, Lorena"

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    Andrographolide promotes hippocampal neurogenesis and spatial memory in the APPswe/PS1ΔE9 mouse model of Alzheimer's disease
    (2021) Arredondo, Sebastian B.; Reyes, Daniel T.; Herrera-Soto, Andrea; Mardones, Muriel D.; Inestrosa, Nibaldo C.; Varela-Nallar, Lorena
    In Alzheimer ' s disease (AD) there is a reduction in hippocampal neurogenesis that has been associated to cognitive deficits. Previously we showed that Andrographolide (ANDRO), the main bioactive component of Andrographis paniculate, induces proliferation in the hippocampus of the APPswe/PSEN1 Delta E9 (APP/PS1) mouse model of AD as assessed by staining with the mitotic marker Ki67. Here, we further characterized the effect of ANDRO on hippocampal neurogenesis in APP/PS1 mice and evaluated the contribution of this process to the cognitive effect of ANDRO. Treatment of 8-month-old APP/PS1 mice with ANDRO for 4 weeks increased proliferation in the dentate gyrus as evaluated by BrdU incorporation. Although ANDRO had no effect on neuronal differentiation of newborn cells, it strongly increased neural progenitors, neuroblasts and newborn immature neurons, cell populations that were decreased in APP/PS1 mice compared to age-matched wild-type mice. ANDRO had no effect on migration or in total dendritic length, arborization and orientation of immature neurons, suggesting no effects on early morphological development of newborn neurons. Finally, ANDRO treatment improved the performance of APP/PS1 mice in the object location memory task. This effect was not completely prevented by co-treatment with the anti-mitotic drug TMZ, suggesting that other effects of ANDRO in addition to the increase in neurogenesis might underlie the observed cognitive improvement. Altogether, our data indicate that in APP/PS1 mice ANDRO stimulates neurogenesis in the hippocampus by inducing proliferation of neural precursor cells and improves spatial memory performance.
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    Frizzled-1 is involved in the neuroprotective effect of Wnt3a against aβ oligomers
    (2008) Chacon, Marcelo A.; Varela-Nallar, Lorena; Inestrosa, Nibaldo C.
    The activation of the canonical Writ signaling pathway protects hippocampal neurons against the toxicity of Alzheimer's amyloid-beta-peptide (A beta), however, the role played by the Writ receptors Frizzleds, has not been studied. We report here that Frizzled-1 mediates the activation of the canonical Wnt/beta-catenin pathway by Wnt3a in PC 12 cells. In addition, the protective effect of Wnt3a against the toxicity of A beta oligomers was modulated by Frizzled-1 expression levels in both PC 12 cells and hippocampal neurons. Over-expression of Frizzled-1 significantly increased cell survival induced by Wnt3a and diminished caspase-3 activation, while knocking-clown Frizzled-1 expression by antisense oligonucleotides decreased the Wnt3a protection. Over-expression of wild-type beta-catenin, but not a transcriptionally inactive mutated version, prevented the toxicity of A suggesting that the transcription of Writ target genes may be involved in these events. This was confirmed by co-transfecting both Frizzled-1 and the inactive form of beta-catenin, which does not elicited protection levels similar to those showed with endogenous beta-catenin. Our results indicate that Wnt3a protects from A beta-oligomers toxicity by activating the canonical Wnt signaling pathway through the Frizzled-1 receptor, suggesting a therapeutic potential for this signaling pathway in the treatment of Alzheimer's disease.
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    Frizzled-1 receptor regulates adult hippocampal neurogenesis
    (2016) Inestrosa Cantín, Nibaldo; Mardones, Muriel D.; Andaur, Gabriela A.; Varas-Godoy, Manuel; Henriquez, Jenny F.; Salech, Felipe; Behrens, María I.; Couve, Andrés; Varela-Nallar, Lorena
    Abstract Background In the adult hippocampus new neurons are continuously generated from neural stem cells (NSCs) present at the subgranular zone of the dentate gyrus. This process is controlled by Wnt signaling, which plays a complex role in regulating multiple steps of neurogenesis including maintenance, proliferation and differentiation of progenitor cells and the development of newborn neurons. Differential effects of Wnt signaling during progression of neurogenesis could be mediated by cell-type specific expression of Wnt receptors. Here we studied the potential role of Frizzled-1 (FZD1) receptor in adult hippocampal neurogenesis. Results In the adult dentate gyrus, we determined that FZD1 is highly expressed in NSCs, neural progenitors and immature neurons. Accordingly, FZD1 is expressed in cultured adult hippocampal progenitors isolated from mouse brain. To evaluate the role of this receptor in vivo we targeted FZD1 in newborn cells using retroviral-mediated RNA interference. FZD1 knockdown resulted in a marked decrease in the differentiation of newborn cells into neurons and increased the generation of astrocytes, suggesting a regulatory role for the receptor in cell fate commitment. In addition, FZD1 knockdown induced an extended migration of adult-born neurons within the granule cell layer. However, no differences were observed in total dendritic length and dendritic arbor complexity between control and FZD1-deficient newborn neurons. Conclusions Our results show that FZD1 regulates specific stages of adult hippocampal neurogenesis, being required for neuronal differentiation and positioning of newborn neurons into the granule cell layer, but not for morphological development of adult-born granule neurons.Abstract Background In the adult hippocampus new neurons are continuously generated from neural stem cells (NSCs) present at the subgranular zone of the dentate gyrus. This process is controlled by Wnt signaling, which plays a complex role in regulating multiple steps of neurogenesis including maintenance, proliferation and differentiation of progenitor cells and the development of newborn neurons. Differential effects of Wnt signaling during progression of neurogenesis could be mediated by cell-type specific expression of Wnt receptors. Here we studied the potential role of Frizzled-1 (FZD1) receptor in adult hippocampal neurogenesis. Results In the adult dentate gyrus, we determined that FZD1 is highly expressed in NSCs, neural progenitors and immature neurons. Accordingly, FZD1 is expressed in cultured adult hippocampal progenitors isolated from mouse brain. To evaluate the role of this receptor in vivo we targeted FZD1 in newborn cells using retroviral-mediated RNA interference. FZD1 knockdown resulted in a marked decrease in the differentiation of newborn cells into neurons and increased the generation of astrocytes, suggesting a regulatory role for the receptor in cell fate commitment. In addition, FZD1 knockdown induced an extended migration of adult-born neurons within the granule cell layer. However, no differences were observed in total dendritic length and dendritic arbor complexity between control and FZD1-deficient newborn neurons. Conclusions Our results show that FZD1 regulates specific stages of adult hippocampal neurogenesis, being required for neuronal differentiation and positioning of newborn neurons into the granule cell layer, but not for morphological development of adult-born granule neurons.
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    H3K9 Methyltransferases Suv39h1 and Suv39h2 Control the Differentiation of Neural Progenitor Cells in the Adult Hippocampus
    (2022) Guerra, Miguel V.; Caceres, Matias I.; Herrera-Soto, Andrea; Arredondo, Sebastian B.; Varas-Godoy, Manuel; van Zundert, Brigitte; Varela-Nallar, Lorena
    In the dentate gyrus of the adult hippocampus new neurons are generated from neural precursor cells through different stages including proliferation and differentiation of neural progenitor cells and maturation of newborn neurons. These stages are controlled by the expression of specific transcription factors and epigenetic mechanisms, which together orchestrate the progression of the neurogenic process. However, little is known about the involvement of histone posttranslational modifications, a crucial epigenetic mechanism in embryonic neurogenesis that regulates fate commitment and neuronal differentiation. During embryonic development, the repressive modification trimethylation of histone H3 on lysine 9 (H3K9me3) contributes to the cellular identity of different cell-types. However, the role of this modification and its H3K9 methyltransferases has not been elucidated in adult hippocampal neurogenesis. We determined that during the stages of neurogenesis in the adult mouse dentate gyrus and in cultured adult hippocampal progenitors (AHPs), there was a dynamic change in the expression and distribution of H3K9me3, being enriched at early stages of the neurogenic process. A similar pattern was observed in the hippocampus for the dimethylation of histone H3 on lysine 9 (H3K9me2), another repressive modification. Among H3K9 methyltransferases, the enzymes Suv39h1 and Suv39h2 exhibited high levels of expression at early stages of neurogenesis and their expression decreased upon differentiation. Pharmacological inhibition of these enzymes by chaetocin in AHPs reduced H3K9me3 and concomitantly decreased neuronal differentiation while increasing proliferation. Moreover, Suv39h1 and Suv39h2 knockdown in newborn cells of the adult mouse dentate gyrus by retrovirus-mediated RNA interference impaired neuronal differentiation of progenitor cells. Our results indicate that H3K9me3 and H3K9 methyltransferases Suv39h1 and Suv39h2 are critically involved in the regulation of adult hippocampal neurogenesis by controlling the differentiation of neural progenitor cells.
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    PSD95 regulates morphological development of adult-born granule neurons in the mouse hippocampus
    (2019) Mardones, Muriel D.; Jorquera, Patricia, V; Herrera-Soto, Andrea; Ampuero, Estibaliz; Bustos, Fernando J.; van Zundert, Brigitte; Varela-Nallar, Lorena
    In the adult hippocampus new neurons are generated in the dentate gyrus from neural progenitor cells. Adult-born neurons integrate into the hippocampal circuitry and contribute to hippocampal function. PSD95 is a major postsynaptic scaffold protein that is crucial for morphological maturation and synaptic development of hippocampal neurons. Here we study the function of PSD95 in adult hippocampal neurogenesis by downregulating PSD95 expression in newborn cells using retroviral-mediated RNA interference. Retroviruses coding for a control shRNA or an shRNA targeting PSD95 (shPSD95) were stereotaxically injected into the dorsal dentate gyms of 2-month-old C57BL/6 mice. PSD95 knockdown did not affect neuronal differentiation of newborn cells into neurons, or migration of newborn neurons into the granule cell layer. Morphological analysis revealed that newborn neurons expressing shPSD95 showed increased dendritic length and increased number of high-order dendrites. Concomitantly, dendrites from shPSD95-expressing newborn granule neurons showed a reduction in the density of dendritic spines. These results suggest that PSD95 is required for proper dendritic and spine maturation of adult-born neurons, but not for early stages of neurogenesis in the hippocampus.
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    Reduced repressive epigenetic marks, increased DNA damage and Alzheimer's disease hallmarks in the brain of humans and mice exposed to particulate urban air pollution
    (2020) Calderon-Garciduenas, Lilian; Herrera-Soto, Andrea; Jury, Nur; Maher, Barbara A.; Gonzalez-Maciel, Angelica; Reynoso-Robles, Rafael; Ruiz-Rudolph, Pablo; van Zundert, Brigitte; Varela-Nallar, Lorena
    Exposure to air pollutants is associated with an increased risk of developing Alzheimer's disease (AD). AD pathological hallmarks and cognitive deficits are documented in children and young adults in polluted cities (e.g. Metropolitan Mexico City, MMC). Iron-rich combustion- and friction-derived nanoparticles (CFDNPs) that are abundantly present in airborne particulate matter pollution have been detected in abundance in the brains of young urbanites. Epigenetic gene regulation has emerged as a candidate mechanism linking exposure to air pollution and brain diseases. A global decrease of the repressive histone post-translational modifications (HPTMs) H3K9me2 and H3K9me3 (H3K9me2/me3) has been described both in AD patients and animal models. Here, we evaluated nuclear levels of H3K9me2/me3 and the DNA double-strand-break marker gamma-H2AX by immunostaining in post-mortem prefrontal white matter samples from 23 young adults (age 29 +/- 6 years) who resided in MMC (n = 13) versus low-pollution areas (n = 10). Lower H3K9me2/me3 and higher gamma-H2A.X staining were present in MMC urbanites, who also displayed the presence of hyperphosphorylated tau and amyloid-beta (A beta) plaques. Transmission electron microscopy revealed abundant CFDNPs in neuronal, glial and endothelial nuclei in MMC residents' frontal samples. In addition, mice exposed to particulate air pollution (for 7 months) in urban Santiago (Chile) displayed similar brain impacts; reduced H3K9me2/me3 and increased gamma-H2A.X staining, together with increased levels of AD-related tau phosphorylation. Together, these findings suggest that particulate air pollution, including metal-rich CFDNPs, impairs brain chromatin silencing and reduces DNA integrity, increasing the risk of developing AD in young individuals exposed to high levels of particulate air pollution.
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    SIRT1 Regulates Dendritic Development in Hippocampal Neurons
    (2012) Codocedo, Juan F.; Allard, Claudio; Godoy, Juan A.; Varela-Nallar, Lorena; Inestrosa, Nibaldo C.
    Dendritic arborization is required for proper neuronal connectivity. SIRT1, a NAD+ dependent histone deacetylase, has been associated to ageing and longevity, which in neurons is linked to neuronal differentiation and neuroprotection. In the present study, the role of SIRT1 in dendritic development was evaluated in cultured hippocampal neurons which were transfected at 3 days in vitro with a construct coding for SIRT1 or for the dominant negative SIRT1H363Y, which lacks the catalytic activity. Neurons overexpressing SIRT1 showed an increased dendritic arborization, while neurons overexpressing SIRT1H363Y showed a reduction in dendritic arbor complexity. The effect of SIRT1 was mimicked by treatment with resveratrol, a well known activator of SIRT1, which has no effect in neurons overexpressing SIRT1H363Y indicating that the effect of resveratrol was specifically mediated by SIRT1. Moreover, hippocampal neurons overexpressing SIRT1 were resistant to dendritic dystrophy induced by A beta aggregates, an effect that was dependent on the deacetylase activity of SIRT1. Our findings indicate that SIRT1 plays a role in the development and maintenance of dendritic branching in hippocampal neurons, and suggest that these effects are mediated by the ROCK signaling pathway.
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    Tetrahydrohyperforin Increases Adult Hippocampal Neurogenesis in Wild-Type and APPswe/PS1 ΔE9 Mice
    (2013) Abbott, Ana C.; Toledo, Carla Calderon; Aranguiz, Florencia C.; Inestrosa, Nibaldo C.; Varela-Nallar, Lorena
    Tetrahydrohyperforin (IDN5706), a semi-synthetic derivative of hyperforin, has shown neuroprotective properties preventing the impairment of synaptic plasticity and cognitive decline in an in vivo model of Alzheimer's disease (AD). Considering the reported role of adult neurogenesis in the plasticity of the hippocampal network, we investigated whether IDN5706 affects adult neurogenesis and hippocampal function. In hippocampal progenitors cultured from adult rats, IDN5706 increased proliferation. Moreover, treatment with IDN5706 for 4 weeks increased cell proliferation in the subgranular zone (SGZ) of the hippocampus in 2 month-old wild-type mice in vivo. As determined by double labeling with BrdU and neuronal markers, IDN5706 treatment increased the number of immature neurons and newborn mature neurons in the adult dentate gyrus. In addition, IDN5706 treatment improved long-term memory in a hippocampal-dependent spatial memory task. Finally, IDN5706 treatment increased cell proliferation and neural commitment in the SGZ of the double transgenic APPswe/PS1 Delta E9 mouse model of AD. These results indicate that IDN5706 increases adult hippocampal neurogenesis and may have therapeutic value in neurological disorders in which adult neurogenesis is impaired.
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    The functional links between prion protein and copper
    (2006) Varela-Nallar, Lorena; Inestrosa Cantín, Nibaldo
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    Wnt5a promotes hippocampal postsynaptic development and GluN2B-induced expression via the eIF2α HRI kinase
    (2021) Ramos-Fernandez, Eva; Arrazola, Macarena S.; Oliva, Carolina A.; Arredondo, Sebastian B.; Varela-Nallar, Lorena; Inestrosa, Nibaldo C.
    Wnt signaling plays a key role in neurodevelopment and neuronal maturation. Specifically, Wnt5a stimulates postsynaptic assemblies, increases glutamatergic neurotransmission and, through calcium signaling, generates nitric oxide (NO). Trying to unveil the molecular pathway triggering these postsynaptic effects, we found that Wnt5a treatment induces a time-dependent increases in the length of the postsynaptic density (PSD), elicits novel synaptic contacts and facilitates F-actin flow both in in vitro and ex vivo models. These effects were partially abolished by the inhibition of the Heme-regulated eukaryotic initiation factor 2 alpha (HRI) kinase, a kinase which phosphorylates the initiation translational factor eIF2 alpha. When phosphorylated, eIF2 alpha normally avoids the translation of proteins not needed during stress conditions, in order to avoid unnecessary energetic expenses. However, phosphorylated eIF2 alpha promotes the translation of some proteins with more than one open reading frame in its 5 ' untranslated region. One of these proteins targeted by Wnt-HRI-eIF2 alpha mediated translation is the GluN2B subunit of the NMDA receptor. The identified increase in GluN2B expression correlated with increased NMDA receptor function. Considering that NMDA receptors are crucial for excitatory synaptic transmission, the molecular pathway described here contributes to the understanding of the fast and plastic translational mechanisms activated during learning and memory processes.