Browsing by Author "Bustos, Fernando J."

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    Epigenetic silencing of the osteoblast-lineage gene program during hippocampal maturation
    (2021) Aguilar, Rodrigo; Bustos, Fernando J.; Nardocci, Gino; van Zundert, Brigitte; Montecino, Martin
    Accumulating evidence indicates that epigenetic control of gene expression plays a significant role during cell lineage commitment and subsequent cell fate maintenance. Here, we assess epigenetic mechanisms operating in the rat brain that mediate silencing of genes that are expressed during early and late stages of osteogenesis. We report that repression of the osteoblast master regulator Sp7 in embryonic (E18) hippocampus is mainly mediated through the Polycomb complex PRC2 and its enzymatic product H3K27me3. During early postnatal (P10), juvenile (P30), and adult (P90) hippocampal stages, the repressive H3K27me3 mark is progressively replaced by nucleosome enrichment and increased CpG DNA methylation at the Sp7 gene promoter. In contrast, silencing of the late bone phenotypic Bglap gene in the hippocampus is PRC2-independent and accompanied by strong CpG methylation from E18 through postnatal and adult stages. Forced ectopic expression of the primary master regulator of osteogenesis Runx2 in embryonic hippocampal neurons activates the expression of its downstream target Sp7 gene. Moreover, transcriptomic analyses show that several genes associated with the mesenchymal-osteogenic lineages are transcriptionally activated in these hippocampal cells that express Runx2 and Sp7. This effect is accompanied by a loss in neuronal properties, including a significant reduction in secondary processes at the dendritic arbor and reduced expression of critical postsynaptic genes like PSD95. Together, our results reveal a developmental progression in epigenetic control mechanisms that repress the expression of the osteogenic program in hippocampal neurons at embryonic, postnatal, and adult stages.
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    Excessive release of inorganic polyphosphate by ALS/FTD astrocytes causes non-cell-autonomous toxicity to motoneurons
    (2022) Arredondo, Cristian; Cefaliello, Carolina; Dyrda, Agnieszka; Jury, Nur; Martinez, Pablo; Diaz, Ivan; Amaro, Armando; Tran, Helene; Morales, Danna; Pertusa, Maria; Stoica, Lorelei; Fritz, Elsa; Corvalan, Daniela; Abarzua, Sebastian; Mendez-Ruette, Maxs; Fernandez, Paola; Rojas, Fabiola; Kumar, Meenakshi Sundaram; Aguilar, Rodrigo; Almeida, Sandra; Weiss, Alexandra; Bustos, Fernando J.; Gonzalez-Nilo, Fernando; Otero, Carolina; Tevy, Maria Florencia; Bosco, Daryl A.; Saez, Juan C.; Kahne, Thilo; Gao, Fen-Biao; Berry, James D.; Nicholson, Katharine; Sena-Esteves, Miguel; Madrid, Rodolfo; Varela, Diego; Montecino, Martin; Brown, Robert H.; van Zundert, Brigitte
    Non-cell-autonomous mechanisms contribute to neurodegenerative diseases such as amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD), in which astrocytes release unidentified factors that are toxic to motoneurons (MNs). We report here that mouse and patient iPSC-derived astrocytes with diverse ALS/FTD-linked mutations (SOD1, TARDBP, and C9ORF72) display elevated levels of intracellular inorganic polyphosphate (polyP), a ubiquitous, negatively charged biopolymer. PolyP levels are also increased in astrocyte-conditioned media (ACM) from ALS/FTD astrocytes. ACM-mediated MN death is prevented by degrading or neutralizing polyP in ALS/FTD astrocytes or ACM. Studies further reveal that postmortem familial and sporadic ALS spinal cord sections display enriched polyP staining signals and that ALS cerebrospinal fluid (CSF) exhibits increased polyP concentrations. Our in vitro results establish excessive astrocyte-derived polyP as a critical factor in non-cell-autonomous MN degeneration and a potential therapeutic target for ALS/ FTD. The CSF data indicate that polyP might serve as a new biomarker for ALS/FTD.
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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.