Center for Geroscience

Santiago, Chile

Center for Geroscience

Santiago, Chile
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Obacz J.,University of Rennes 1 | Avril T.,University of Rennes 1 | Le Reste P.-J.,University of Rennes 1 | Le Reste P.-J.,University Hospital Pontchaillou | And 8 more authors.
Science Signaling | Year: 2017

Cellular stress induced by the accumulation of misfolded proteins at the endoplasmic reticulum (ER) is a central feature of secretory cells and is observed in many tissues in various diseases, including cancer, diabetes, obesity, and neurodegenerative disorders. Cellular adaptation to ER stress is achieved by the activation of the unfolded protein response (UPR), an integrated signal transduction pathway that transmits information about the protein folding status at the ER to the cytosol and nucleus to restore proteostasis. In the past decade, ER stress has emerged as a major pathway in remodeling gene expression programs that either prevent transformation or provide selective advantage in cancer cells. Controlled by the formation of a dynamic scaffold onto which many regulatory components assemble, UPR signaling is a highly regulated process that leads to an integrated reprogramming of the cell. In this Review, we provide an overview of the regulatory mechanisms underlying UPR signaling and how this pathway modulates cancer progression, particularly the aggressiveness and chemotherapeutic resistance exhibited by glioblastoma, a form of brain cancer. We also discuss the emerging cross-talk between the UPR and related metabolic processes to ensure maintenance of proteostasis, and we highlight possible therapeutic opportunities for targeting the pathway with small molecules. © 2017 The Authors, some rights reserved.

Villarroel-Campos D.,University of Chile | Villarroel-Campos D.,Center for Geroscience | Henriquez D.R.,University of Chile | Bodaleo F.J.,University of Chile | And 7 more authors.
Journal of Neuroscience | Year: 2016

Rab35 is a key protein for cargo loading in the recycling endosome. In neuronal immortalized cells, Rab35 promotes neurite differentiation. Here we describe that Rab35 favors axon elongation in rat primary neurons in an activity-dependent manner. In addition, we show that the p53-related protein kinase (PRPK) negatively regulates axonal elongation by reducing Rab35 protein levels through the ubiquitin-proteasome degradation pathway. PRPK-induced Rab35 degradation is regulated by its interaction with microtubuleassociated protein 1B (MAP1B), a microtubule stabilizing binding protein essential for axon elongation. Consistently, axon defects found in MAP1B knock-out neurons were reversed by Rab35 overexpression or PRPK inactivation suggesting an epistatic relationship among these proteins. These results define a novel mechanism to support axonal elongation, by which MAP1B prevents PRPK-induced Rab35 degradation. Such a mechanism allows Rab35-mediated axonal elongation and connects the regulation of actin dynamics withmembrane trafficking. In addition, our study reveals for the first time that the ubiquitin-proteasome degradation pathway regulates a Rab GTPase. © 2016 the authors.

Gupta A.,National University of Ireland | Hossain M.M.,National University of Ireland | Read D.E.,National University of Ireland | Hetz C.,University of Chile | And 3 more authors.
Scientific Reports | Year: 2015

The endoplasmic reticulum (ER) responds to changes in intracellular homeostasis through activation of the unfolded protein response (UPR). UPR can facilitate the restoration of cellular homeostasis, via the concerted activation of three ER stress sensors, namely IRE1, PERK and ATF6. Global approaches in several cellular contexts have revealed that UPR regulates the expression of many miRNAs that play an important role in the regulation of life and death decisions during UPR. Here we show that expression of miR-424(322)-503 cluster is downregulated during UPR. IRE1 inhibitor (4 Î 1/48C) and deficiency of XBP1 had no effect on downregulation of miR-424(322)-503 during UPR. Treatment of cells with CCT030312, a selective activator of EIF2AK3/PERK signalling, leads to the downregulation of miR-424(322)-503 expression. The repression of miR-424(322)-503 cluster during conditions of ER stress is compromised in PERK-deficient MEFs. miR-424 regulates the expression of ATF6 via a miR-424 binding site in its 3′ UTR and attenuates the ATF6 transcriptional activity during UPR. Further miR-424 had no effect on IRE1-XBP1 axis but enhanced the regulated IRE1-dependent decay (RIDD). Our results suggest that miR-424 constitutes an obligatory fine-tuning mechanism where PERK-mediated downregulation of miR-424(322)-503 cluster regulates optimal activation of IRE1 and ATF6 during conditions of ER stress.

Medinas D.B.,University of Chile | Medinas D.B.,Center for Geroscience | Gonzalez J.V.,University of Chile | Gonzalez J.V.,Center for Geroscience | And 6 more authors.
Frontiers in Molecular Neuroscience | Year: 2017

Amyotrophic lateral sclerosis (ALS) is a fatal neurodegenerative disease characterized by the progressive loss of motoneurons and paralysis. The mechanisms underlying neuronal degeneration in ALS are starting to be elucidated, highlighting disturbances in motoneuron proteostasis. Endoplasmic reticulum (ER) stress has emerged as an early pathogenic event underlying motoneuron vulnerability and denervation in ALS. Maintenance of ER proteostasis is controlled by a dynamic signaling network known as the unfolded protein response (UPR). Inositol-requiring enzyme 1 (IRE1) is an ER-located kinase and endoribonuclease that operates as a major ER stress transducer, mediating the establishment of adaptive and pro-apoptotic programs. Here we discuss current evidence supporting the role of ER stress in motoneuron demise in ALS and build the rational to target IRE1 to ameliorate neurodegeneration. © 2017 Medinas, González, Falcon and Hetz.

Villarroel-Campos D.,University of Chile | Villarroel-Campos D.,Center for Geroscience | Bronfman F.C.,University of Santiago de Chile | Gonzalez-Billault C.,University of Chile | Gonzalez-Billault C.,Center for Geroscience
Cytoskeleton | Year: 2016

Neurons are highly polarized cells that contain specialized subcellular domains involved in information transmission in the nervous system. Specifically, the somatodendritic compartment receives neuronal inputs while the axons convey information through the synapse. The establishment of asymmetric domains requires a specific delivery of components, including organelles, proteins, and membrane. The Rab family of small GTPases plays an essential role in membrane trafficking. Signaling cascades triggered by extrinsic and intrinsic factors tightly regulate Rab functions in cells, with Rab protein activation depending on GDP/GTP binding to establish a binary mode of action. This review summarizes the contributions of several Rab family members involved in trans-Golgi, early/late endosomes, and recycling endosomes during neurite development and axonal outgrowth. The regulation of some Rabs by guanine exchanging factors and GTPase activating proteins will also be addressed. Finally, discussion will be provided on how specific effector-mediated Rab activation modifies several molecules essential to neuronal differentiation. © 2016 Wiley Periodicals, Inc. © 2016 Wiley Periodicals, Inc.

Mardones P.,University of Chile | Mardones P.,Center for Geroscience | Rubinsztein D.C.,University of Cambridge | Hetz C.,University of Chile | And 2 more authors.
Science Signaling | Year: 2016

Although vertebrates cannot synthesize the natural disaccharide trehalose, exogenous administration of trehalose to mammalian cells may be beneficial for protein misfolding disorders. In this issue, DeBosch et al. show that trehalose may also be useful in treating nonalcoholic fatty liver disease and identify inhibition of cellular glucose import through SLC2A (also known as GLUT) transporters as a mechanism by which trehalose stimulates autophagy through the adenosine monophosphate- activated protein kinase (AMPK). © 2016 by the American Association for the Advancement of Science.

Bodaleo F.J.,University of Chile | Bodaleo F.J.,Center for Geroscience | Gonzalez-Billault C.,University of Chile | Gonzalez-Billault C.,Center for Geroscience | Gonzalez-Billault C.,The Buck Institute for Research on Aging
Frontiers in Molecular Neuroscience | Year: 2016

The capacity of the nervous system to generate neuronal networks relies on the establishment and maintenance of synaptic contacts. Synapses are composed of functionally different presynaptic and postsynaptic compartments. An appropriate synaptic architecture is required to provide the structural basis that supports synaptic transmission, a process involving changes in cytoskeletal dynamics. Actin microfilaments are the main cytoskeletal components present at both presynaptic and postsynaptic terminals in glutamatergic synapses. However, in the last few years it has been demonstrated that microtubules (MTs) transiently invade dendritic spines, promoting their maturation. Nevertheless, the presence and functions of MTs at the presynaptic site are still a matter of debate. Early electron microscopy (EM) studies revealed that MTs are present in the presynaptic terminals of the central nervous system (CNS) where they interact with synaptic vesicles (SVs) and reach the active zone. These observations have been reproduced by several EM protocols; however, there is empirical heterogeneity in detecting presynaptic MTs, since they appear to be both labile and unstable. Moreover, increasing evidence derived from studies in the fruit fly neuromuscular junction proposes different roles for MTs in regulating presynaptic function in physiological and pathological conditions. In this review, we summarize the main findings that support the presence and roles of MTs at presynaptic terminals, integrating descriptive and biochemical analyses, and studies performed in invertebrate genetic models. © 2016 Bodaleo and Gonzalez-Billault.

Court F.A.,Major University | Court F.A.,Center for Geroscience | Court F.A.,University of Santiago de Chile | Alvarez J.,University of Santiago de Chile
Advances in Experimental Medicine and Biology | Year: 2016

Here we propose a model of a peripheral axon with a great deal of autonomy from its cell body-the autonomous axon-but with a substantial dependence on its ensheathing Schwann cell (SC), the axon-SC unit. We review evidence in several fields and show that (i) axons can extend sprouts and grow without the concurrence of the cell body, but regulated by SCs; (ii) axons synthesize their proteins assisted by SCs that supply them with ribosomes and, probably, with mRNAs by way of exosomes; (iii) the molecular organization of the axoplasm, i.e., its phenotype, is regulated by the SC, as illustrated by the axonal microtubular content, which is down-regulated by the SC; and (iv) the axon has a program for self-destruction that is boosted by the SC. The main novelty of this model axon-SC unit is that it breaks with the notion that all proteins of the nerve cell are specified by its own nucleus. The notion of a collaborative specification of the axoplasm by more than one nucleus, which we present here, opens a new dimension in the understanding of the nervous system in health and disease and is also a frame of reference to understand other tissues or cell associations. © Springer International Publishing Switzerland 2016.

Uribe-Arias A.,University of Antioquia | Posada-Duque R.A.,University of Antioquia | Gonzalez-Billault C.,University of Chile | Gonzalez-Billault C.,Center for Geroscience | And 3 more authors.
Journal of Neurochemistry | Year: 2016

Cyclin-dependent kinase 5 (CDK5) plays important roles in synaptic function. Its unregulated over-activation has been, however, associated with neurodegeneration in Alzheimer's disease. Our previous studies revealed that CDK5 silencing ameliorates tauopathy and spatial memory impairment in the 3xTgAD mouse model. However, how CDK5 targeting affects synaptic adhesion proteins, such as those involved in the cadherin/catenin system, during learning and memory processes is not completely understood. In this study, we detected reduced expression of p120 catenin (p120 ctn), N-cadherin, and β-catenin in the brain of human Alzheimer's disease patients, in addition to a reduced PSD95 and GluN2B protein levels in a 3xTgAD mouse model. Such decrease in synaptic proteins was recovered by CDK5 silencing in mice leading to a better learning and memory performance. Additionally, CDK5 inhibition or knockout increased p120 ctn levels. Moreover, in a glutamate-induced excitotoxicity model, CDK5 silencing-induced neuroprotection depended on p120 ctn. Together, those findings suggest that p120 ctn plays an important role in the neuronal dysfunction of Alzheimer's disease models and contributes to CDK5 silencing-induced neuroprotection and improvement of memory function. (Figure presented.) p120ctn is part of the synaptic adhesion molecular complex N-cadh/p120ctn/B-ctn/PSD95, and it has a pivotal role in cell adhesion stabilization and dendritic spine modulation. Our data show that synaptic adhesion complex is affected in AD human brains and in AD models. This complex is recovered by the silencing of CDK5, preventing memory dysfunction in an AD mice model and contributing to the neuroprotection in a depend-mode of p120ctn. © 2016 International Society for Neurochemistry

PubMed | University of Chile and Center for Geroscience
Type: | Journal: Scientific reports | Year: 2016

Microtubule-associated protein 1B (MAP1B) is expressed predominantly during the early stages of development of the nervous system, where it regulates processes such as axonal guidance and elongation. Nevertheless, MAP1B expression in the brain persists in adult stages, where it participates in the regulation of the structure and physiology of dendritic spines in glutamatergic synapses. Moreover, MAP1B expression is also found in presynaptic synaptosomal preparations. In this work, we describe a presynaptic phenotype in mature neurons derived from MAP1B knockout (MAP1B KO) mice. Mature neurons express MAP1B, and its deficiency does not alter the expression levels of a subgroup of other synaptic proteins. MAP1B KO neurons display a decrease in the density of presynaptic and postsynaptic terminals, which involves a reduction in the density of synaptic contacts, and an increased proportion of orphan presynaptic terminals. Accordingly, MAP1B KO neurons present altered synaptic vesicle fusion events, as shown by FM4-64 release assay, and a decrease in the density of both synaptic vesicles and dense core vesicles at presynaptic terminals. Finally, an increased proportion of excitatory immature symmetrical synaptic contacts in MAP1B KO neurons was detected. Altogether these results suggest a novel role for MAP1B in presynaptic structure and physiology regulation in vitro.

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