Raquel Sanchez-Varo


Permanent Professor at Human Physiology, Human Histology, Anatomical Pathology, and Physics and Sport Education Department. Faculty of Medicine
University of Malaga




Bachelor in Biology (University of Seville, 2002)
Bachelor in Biochemistry (University of Seville, 2004)
PhD University of Malaga (2011)


Histology, Cell Biology, Neuroscience


Scopus Publications

Scopus Publications

  • Enhancement of neurogenesis and cognition through intranasal co-delivery of galanin receptor 2 (GALR2) and neuropeptide Y receptor 1 (NPY1R) agonists: a potential pharmacological strategy for cognitive dysfunctions
    Raquel Sánchez-Varo, Alexander López-Salas, Rasiel Beltran-Casanueva, Estela Díaz-Sánchez, Jose Erik Alvarez-Contino, Miguel Angel Barbancho-Fernández, Pedro Serrano-Castro, Kjell Fuxe, Dasiel O. Borroto-Escuela, Natalia García-Casares,et al.

    Springer Science and Business Media LLC
    Abstract Background Spatial memory deficits and reduced neuronal survival contribute to cognitive decline seen in the aging process. Current treatments are limited, emphasizing the need for innovative therapeutic strategies. This research explored the combined effects of intranasally co-administered galanin receptor 2 (GALR2) and neuropeptide Y1 receptor (NPY1R) agonists, recognized for their neural benefits, on spatial memory, neuronal survival, and differentiation in adult rats. After intranasal co-delivery of the GALR2 agonist M1145 and a NPY1R agonist to adult rats, spatial memory was tested with the object-in-place task 3 weeks later. We examined neuronal survival and differentiation by assessing BrdU-IR profiles and doublecortin (DCX) labeled cells, respectively. We also used the GALR2 antagonist M871 to confirm GALR2's crucial role in promoting cell growth. Results Co-administration improved spatial memory and increased the survival rate of mature neurons. The positive effect of GALR2 in cell proliferation was confirmed by the nullifying effects of its antagonist. The treatment boosted DCX-labeled newborn neurons and altered dendritic morphology, increasing cells with mature dendrites. Conclusions Our results show that intranasal co-delivery of GALR2 and NPY1R agonists improves spatial memory, boosts neuronal survival, and influences neuronal differentiation in adult rats. The significant role of GALR2 is emphasized, suggesting new potential therapeutic strategies for cognitive decline.

  • Adipose tissue as a therapeutic target for vascular damage in Alzheimer's disease
    Miriam Bettinetti‐Luque, Laura Trujillo‐Estrada, Eduardo Garcia‐Fuentes, Juana Andreo‐Lopez, Raquel Sanchez‐Varo, Lourdes Garrido‐Sánchez, Ángela Gómez‐Mediavilla, Manuela G. López, Melissa Garcia‐Caballero, Antonia Gutierrez,et al.

    Adipose tissue has recently been recognized as an important endocrine organ that plays a crucial role in energy metabolism and in the immune response in many metabolic tissues. With this regard, emerging evidence indicates that an important crosstalk exists between the adipose tissue and the brain. However, the contribution of adipose tissue to the development of age‐related diseases, including Alzheimer's disease, remains poorly defined. New studies suggest that the adipose tissue modulates brain function through a range of endogenous biologically active factors known as adipokines, which can cross the blood–brain barrier to reach the target areas in the brain or to regulate the function of the blood–brain barrier. In this review, we discuss the effects of several adipokines on the physiology of the blood–brain barrier, their contribution to the development of Alzheimer's disease and their therapeutic potential.

  • Microbiome Alterations and Alzheimer’s Disease: Modeling Strategies with Transgenic Mice
    Juan Antonio López-Villodres, Alejandro Escamilla, Silvia Mercado-Sáenz, Carmen Alba-Tercedor, Luis Manuel Rodriguez-Perez, Isabel Arranz-Salas, Raquel Sanchez-Varo, and Diego Bermúdez

    In the last decade, the role of the microbiota–gut–brain axis has been gaining momentum in the context of many neurodegenerative and metabolic disorders, including Alzheimer’s disease (AD) and diabetes, respectively. Notably, a balanced gut microbiota contributes to the epithelial intestinal barrier maintenance, modulates the host immune system, and releases neurotransmitters and/or neuroprotective short-chain fatty acids. However, dysbiosis may provoke immune dysregulation, impacting neuroinflammation through peripheral–central immune communication. Moreover, lipopolysaccharide or detrimental microbial end-products can cross the blood–brain barrier and induce or at least potentiate the neuropathological progression of AD. Thus, after repeated failure to find a cure for this dementia, a necessary paradigmatic shift towards considering AD as a systemic disorder has occurred. Here, we present an overview of the use of germ-free and/or transgenic animal models as valid tools to unravel the connection between dysbiosis, metabolic diseases, and AD, and to investigate novel therapeutical targets. Given the high impact of dietary habits, not only on the microbiota but also on other well-established AD risk factors such as diabetes or obesity, consistent changes of lifestyle along with microbiome-based therapies should be considered as complementary approaches.

  • Correction to: Galectin-3, a novel endogenous TREM2 ligand, detrimentally regulates inflammatory response in Alzheimer’s disease (Acta Neuropathologica, (2019), 138, 2, (251-273), 10.1007/s00401-019-02013-z)
    Antonio Boza-Serrano, Rocío Ruiz, Raquel Sanchez-Varo, Juan García-Revilla, Yiyi Yang, Itzia Jimenez-Ferrer, Agnes Paulus, Malin Wennström, Anna Vilalta, David Allendorf,et al.

    Springer Science and Business Media LLC

  • Animal and Cellular Models of Alzheimer’s Disease: Progress, Promise, and Future Approaches
    Laura Trujillo-Estrada, Elisabeth Sanchez-Mejias, Raquel Sanchez-Varo, Juan Antonio Garcia-Leon, Cristina Nuñez-Diaz, Jose Carlos Davila, Javier Vitorica, Frank M. LaFerla, Ines Moreno-Gonzalez, Antonia Gutierrez,et al.

    SAGE Publications
    Alzheimer’s disease (AD) is an incurable neurodegenerative disease affecting over 45 million people worldwide. Transgenic mouse models have made remarkable contributions toward clarifying the pathophysiological mechanisms behind the clinical manifestations of AD. However, the limited ability of these in vivo models to accurately replicate the biology of the human disease have precluded the translation of promising preclinical therapies to the clinic. In this review, we highlight several major pathogenic mechanisms of AD that were discovered using transgenic mouse models. Moreover, we discuss the shortcomings of current animal models and the need to develop reliable models for the sporadic form of the disease, which accounts for the majority of AD cases, as well as human cellular models to improve success in translating results into human treatments.

  • Transgenic Mouse Models of Alzheimer’s Disease: An Integrative Analysis
    Raquel Sanchez-Varo, Marina Mejias-Ortega, Juan Jose Fernandez-Valenzuela, Cristina Nuñez-Diaz, Laura Caceres-Palomo, Laura Vegas-Gomez, Elisabeth Sanchez-Mejias, Laura Trujillo-Estrada, Juan Antonio Garcia-Leon, Ines Moreno-Gonzalez,et al.

    Alzheimer’s disease (AD) constitutes the most prominent form of dementia among elderly individuals worldwide. Disease modeling using murine transgenic mice was first initiated thanks to the discovery of heritable mutations in amyloid precursor protein (APP) and presenilins (PS) genes. However, due to the repeated failure of translational applications from animal models to human patients, along with the recent advances in genetic susceptibility and our current understanding on disease biology, these models have evolved over time in an attempt to better reproduce the complexity of this devastating disease and improve their applicability. In this review, we provide a comprehensive overview about the major pathological elements of human AD (plaques, tauopathy, synaptic damage, neuronal death, neuroinflammation and glial dysfunction), discussing the knowledge that available mouse models have provided about the mechanisms underlying human disease. Moreover, we highlight the pros and cons of current models, and the revolution offered by the concomitant use of transgenic mice and omics technologies that may lead to a more rapid improvement of the present modeling battery.

  • Plaque-Associated Oligomeric Amyloid-Beta Drives Early Synaptotoxicity in APP/PS1 Mice Hippocampus: Ultrastructural Pathology Analysis
    Raquel Sanchez-Varo, Elisabeth Sanchez-Mejias, Juan Jose Fernandez-Valenzuela, Vanessa De Castro, Marina Mejias-Ortega, Angela Gomez-Arboledas, Sebastian Jimenez, Maria Virtudes Sanchez-Mico, Laura Trujillo-Estrada, Ines Moreno-Gonzalez,et al.

    Frontiers Media SA
    Alzheimer’s disease (AD) is a devastating neurodegenerative disorder characterized by initial memory impairments that progress to dementia. In this sense, synaptic dysfunction and loss have been established as the pathological features that best correlate with the typical early cognitive decline in this disease. At the histopathological level, post mortem AD brains typically exhibit intraneuronal neurofibrillary tangles (NFTs) along with the accumulation of amyloid-beta (Abeta) peptides in the form of extracellular deposits. Specifically, the oligomeric soluble forms of Abeta are considered the most synaptotoxic species. In addition, neuritic plaques are Abeta deposits surrounded by activated microglia and astroglia cells together with abnormal swellings of neuronal processes named dystrophic neurites. These periplaque aberrant neurites are mostly presynaptic elements and represent the first pathological indicator of synaptic dysfunction. In terms of losing synaptic proteins, the hippocampus is one of the brain regions most affected in AD patients. In this work, we report an early decline in spatial memory, along with hippocampal synaptic changes, in an amyloidogenic APP/PS1 transgenic model. Quantitative electron microscopy revealed a spatial synaptotoxic pattern around neuritic plaques with significant loss of periplaque synaptic terminals, showing rising synapse loss close to the border, especially in larger plaques. Moreover, dystrophic presynapses were filled with autophagic vesicles in detriment of the presynaptic vesicular density, probably interfering with synaptic function at very early synaptopathological disease stages. Electron immunogold labeling showed that the periphery of amyloid plaques, and the associated dystrophic neurites, was enriched in Abeta oligomers supporting an extracellular location of the synaptotoxins. Finally, the incubation of primary neurons with soluble fractions derived from 6-month-old APP/PS1 hippocampus induced significant loss of synaptic proteins, but not neuronal death. Indeed, this preclinical transgenic model could serve to investigate therapies targeted at initial stages of synaptic dysfunction relevant to the prodromal and early AD.

  • Amyloid-β impairs the phagocytosis of dystrophic synapses by astrocytes in Alzheimer's disease
    Maria V. Sanchez‐Mico, Sebastian Jimenez, Angela Gomez‐Arboledas, Clara Muñoz‐Castro, Carmen Romero‐Molina, Victoria Navarro, Elisabeth Sanchez‐Mejias, Cristina Nuñez‐Diaz, Raquel Sanchez‐Varo, Elena Galea,et al.

    Reactive astrocytes and dystrophic neurites, most aberrant presynaptic elements, are found surrounding amyloid‐β plaques in Alzheimer's disease (AD). We have previously shown that reactive astrocytes enwrap, phagocytose, and degrade dystrophic synapses in the hippocampus of APP mice and AD patients, but affecting less than 7% of dystrophic neurites, suggesting reduced phagocytic capacity of astrocytes in AD. Here, we aimed to gain insight into the underlying mechanisms by analyzing the capacity of primary astrocyte cultures to phagocytose and degrade isolated synapses (synaptoneurosomes, SNs) from APP (containing dystrophic synapses and amyloid‐β peptides), Tau (containing AT8‐ and AT100‐positive phosphorylated Tau) and WT (controls) mice. We found highly reduced phagocytic and degradative capacity of SNs‐APP, but not AT8/AT100‐positive SNs‐Tau, as compared with SNs‐WT. The reduced astrocyte phagocytic capacity was verified in hippocampus from 12‐month‐old APP mice, since only 1.60 ± 3.81% of peri‐plaque astrocytes presented phagocytic structures. This low phagocytic capacity did not depend on microglia‐mediated astrocyte reactivity, because removal of microglia from the primary astrocyte cultures abrogated the expression of microglia‐dependent genes in astrocytes, but did not affect the phagocytic impairment induced by oligomeric amyloid‐β alone. Taken together, our data suggest that amyloid‐β, but not hyperphosphorylated Tau, directly impairs the capacity of astrocytes to clear the pathological accumulation of oligomeric amyloid‐β, as well as of peri‐plaque dystrophic synapses containing amyloid‐β, perhaps by reducing the expression of phagocytosis receptors such as Mertk and Megf10, thus increasing neuronal damage in AD. Therefore, the potentiation or recovery of astrocytic phagocytosis may be a novel therapeutic avenue in AD.

  • Enhancing microtubule stabilization rescues cognitive deficits and ameliorates pathological phenotype in an amyloidogenic Alzheimer’s disease model
    Juan Jose Fernandez-Valenzuela, Raquel Sanchez-Varo, Clara Muñoz-Castro, Vanessa De Castro, Elisabeth Sanchez-Mejias, Victoria Navarro, Sebastian Jimenez, Cristina Nuñez-Diaz, Angela Gomez-Arboledas, Ines Moreno-Gonzalez,et al.

    Springer Science and Business Media LLC
    AbstractIn Alzheimer’s disease (AD), and other tauopathies, microtubule destabilization compromises axonal and synaptic integrity contributing to neurodegeneration. These diseases are characterized by the intracellular accumulation of hyperphosphorylated tau leading to neurofibrillary pathology. AD brains also accumulate amyloid-beta (Aβ) deposits. However, the effect of microtubule stabilizing agents on Aβ pathology has not been assessed so far. Here we have evaluated the impact of the brain-penetrant microtubule-stabilizing agent Epothilone D (EpoD) in an amyloidogenic model of AD. Three-month-old APP/PS1 mice, before the pathology onset, were weekly injected with EpoD for 3 months. Treated mice showed significant decrease in the phospho-tau levels and, more interesting, in the intracellular and extracellular hippocampal Aβ accumulation, including the soluble oligomeric forms. Moreover, a significant cognitive improvement and amelioration of the synaptic and neuritic pathology was found. Remarkably, EpoD exerted a neuroprotective effect on SOM-interneurons, a highly AD-vulnerable GABAergic subpopulation. Therefore, our results suggested that EpoD improved microtubule dynamics and axonal transport in an AD-like context, reducing tau and Aβ levels and promoting neuronal and cognitive protection. These results underline the existence of a crosstalk between cytoskeleton pathology and the two major AD protein lesions. Therefore, microtubule stabilizers could be considered therapeutic agents to slow the progression of both tau and Aβ pathology.

  • Human pluripotent stem cell-derived neural cells as a relevant platform for drug screening in alzheimer’s disease
    Juan Antonio Garcia-Leon, Laura Caceres-Palomo, Elisabeth Sanchez-Mejias, Marina Mejias-Ortega, Cristina Nuñez-Diaz, Juan Jose Fernandez-Valenzuela, Raquel Sanchez-Varo, Jose Carlos Davila, Javier Vitorica, and Antonia Gutierrez

    Extracellular amyloid-beta deposition and intraneuronal Tau-laden neurofibrillary tangles are prime features of Alzheimer’s disease (AD). The pathology of AD is very complex and still not fully understood, since different neural cell types are involved in the disease. Although neuronal function is clearly deteriorated in AD patients, recently, an increasing number of evidences have pointed towards glial cell dysfunction as one of the main causative phenomena implicated in AD pathogenesis. The complex disease pathology together with the lack of reliable disease models have precluded the development of effective therapies able to counteract disease progression. The discovery and implementation of human pluripotent stem cell technology represents an important opportunity in this field, as this system allows the generation of patient-derived cells to be used for disease modeling and therapeutic target identification and as a platform to be employed in drug discovery programs. In this review, we discuss the current studies using human pluripotent stem cells focused on AD, providing convincing evidences that this system is an excellent opportunity to advance in the comprehension of AD pathology, which will be translated to the development of the still missing effective therapies.

  • Editorial: Risk Factors for Alzheimer's Disease
    Ines Moreno-Gonzalez, Rodrigo Morales, David Baglietto-Vargas, and Raquel Sanchez-Varo

    Frontiers Media SA
    Departamento Biologia Celular, Genetica y Fisiologia, Facultad de Ciencias, Instituto de Investigacion Biomedica de Malaga-IBIMA, Universidad de Malaga, Málaga, Spain, Networking Research Center on Neurodegenerative Diseases (CIBERNED), Madrid, Spain, Department of Neurology, The University of Texas Health Science Center at Houston, Houston, TX, United States, Centro Integrativo de Biología y Química Aplicada (CIBQA), Universidad Bernardo O’Higgins, Santiago,

  • Distinct disease-sensitive GABAergic neurons in the perirhinal cortex of Alzheimer's mice and patients
    Elisabeth Sanchez‐Mejias, Cristina Nuñez‐Diaz, Raquel Sanchez‐Varo, Angela Gomez‐Arboledas, Juan Antonio Garcia‐Leon, Juan Jose Fernandez‐Valenzuela, Marina Mejias‐Ortega, Laura Trujillo‐Estrada, David Baglietto‐Vargas, Ines Moreno‐Gonzalez,et al.

    Neuronal loss is the best neuropathological substrate that correlates with cortical atrophy and dementia in Alzheimer's disease (AD). Defective GABAergic neuronal functions may lead to cortical network hyperactivity and aberrant neuronal oscillations and in consequence, generate a detrimental alteration in memory processes. In this study, using immunohistochemical and stereological approaches, we report that the two major and non‐overlapping groups of inhibitory interneurons (SOM‐cells and PV‐cells) displayed distinct vulnerability in the perirhinal cortex of APP/PS1 mice and AD patients. SOM‐positive neurons were notably sensitive and exhibited a dramatic decrease in the perirhinal cortex of 6‐month‐old transgenic mice (57% and 61% in areas 36 and 35, respectively) and, most importantly, in AD patients (91% in Braak V–VI cases). In addition, this interneuron degenerative process seems to occur in parallel, and closely related, with the progression of the amyloid pathology. However, the population expressing PV was unaffected in APP/PS1 mice while in AD brains suffered a pronounced and significant loss (69%). As a key component of cortico‐hippocampal networks, the perirhinal cortex plays an important role in memory processes, especially in familiarity‐based memory recognition. Therefore, disrupted functional connectivity of this cortical region, as a result of the early SOM and PV neurodegeneration, might contribute to the altered brain rhythms and cognitive failures observed in the initial clinical phase of AD patients. Finally, these findings highlight the failure of amyloidogenic AD models to fully recapitulate the selective neuronal degeneration occurring in humans.

  • Galectin-3, a novel endogenous TREM2 ligand, detrimentally regulates inflammatory response in Alzheimer’s disease
    Antonio Boza-Serrano, Rocío Ruiz, Raquel Sanchez-Varo, Juan García-Revilla, Yiyi Yang, Itzia Jimenez-Ferrer, Agnes Paulus, Malin Wennström, Anna Vilalta, David Allendorf,et al.

    Springer Science and Business Media LLC
    AbstractAlzheimer’s disease (AD) is a progressive neurodegenerative disease in which the formation of extracellular aggregates of amyloid beta (Aβ) peptide, fibrillary tangles of intraneuronal tau and microglial activation are major pathological hallmarks. One of the key molecules involved in microglial activation is galectin-3 (gal3), and we demonstrate here for the first time a key role of gal3 in AD pathology. Gal3 was highly upregulated in the brains of AD patients and 5xFAD (familial Alzheimer’s disease) mice and found specifically expressed in microglia associated with Aβ plaques. Single-nucleotide polymorphisms in the LGALS3 gene, which encodes gal3, were associated with an increased risk of AD. Gal3 deletion in 5xFAD mice attenuated microglia-associated immune responses, particularly those associated with TLR and TREM2/DAP12 signaling. In vitro data revealed that gal3 was required to fully activate microglia in response to fibrillar Aβ. Gal3 deletion decreased the Aβ burden in 5xFAD mice and improved cognitive behavior. Interestingly, a single intrahippocampal injection of gal3 along with Aβ monomers in WT mice was sufficient to induce the formation of long-lasting (2 months) insoluble Aβ aggregates, which were absent when gal3 was lacking. High-resolution microscopy (stochastic optical reconstruction microscopy) demonstrated close colocalization of gal3 and TREM2 in microglial processes, and a direct interaction was shown by a fluorescence anisotropy assay involving the gal3 carbohydrate recognition domain. Furthermore, gal3 was shown to stimulate TREM2–DAP12 signaling in a reporter cell line. Overall, our data support the view that gal3 inhibition may be a potential pharmacological approach to counteract AD.

  • Distinct microglial responses in two transgenic murine models of TAU pathology
    Carmen Romero-Molina, Victoria Navarro, Raquel Sanchez-Varo, Sebastian Jimenez, Juan J. Fernandez-Valenzuela, Maria V. Sanchez-Mico, Clara Muñoz-Castro, Antonia Gutierrez, Javier Vitorica, and Marisa Vizuete

    Frontiers Media SA
    Microglial cells are crucial players in the pathological process of neurodegenerative diseases, such as Alzheimer’s disease (AD). Microglial response in AD has been principally studied in relation to amyloid-beta pathology but, comparatively, little is known about inflammatory processes associated to tau pathology. In the hippocampus of AD patients, where tau pathology is more prominent than amyloid-beta pathology, a microglial degenerative process has been reported. In this work, we have directly compared the microglial response in two different transgenic tau mouse models: ThyTau22 and P301S. Surprisingly, these two models showed important differences in the microglial profile and tau pathology. Where ThyTau22 hippocampus manifested mild microglial activation, P301S mice exhibited a strong microglial response in parallel with high phospho-tau accumulation. This differential phospho-tau expression could account for the different microglial response in these two tau strains. However, soluble (S1) fractions from ThyTau22 hippocampus presented relatively high content of soluble phospho-tau (AT8-positive) and were highly toxic for microglial cells in vitro, whereas the correspondent S1 fractions from P301S mice displayed low soluble phospho-tau levels and were not toxic for microglial cells. Therefore, not only the expression levels but the aggregation of phospho-tau should differ between both models. In fact, most of tau forms in the P301S mice were aggregated and, in consequence, forming insoluble tau species. We conclude that different factors as tau mutations, accumulation, phosphorylation, and/or aggregation could account for the distinct microglial responses observed in these two tau models. For this reason, deciphering the molecular nature of toxic tau species for microglial cells might be a promising therapeutic approach in order to restore the deficient immunological protection observed in AD hippocampus.

  • Microglia in Alzheimer's disease: Activated, dysfunctional or degenerative
    Victoria Navarro, Elisabeth Sanchez-Mejias, Sebastian Jimenez, Clara Muñoz-Castro, Raquel Sanchez-Varo, Jose C. Davila, Marisa Vizuete, Antonia Gutierrez, and Javier Vitorica

    Frontiers Media SA
    Microglial activation has been considered a crucial player in the pathological process of multiple human neurodegenerative diseases. In some of these pathologies, such as Amyotrophic Lateral Sclerosis or Multiple Sclerosis, the immune system and microglial cells (as part of the cerebral immunity) play a central role. In other degenerative processes, such as Alzheimer’s disease (AD), the role of microglia is far to be elucidated. In this “mini-review” article, we briefly highlight our recent data comparing the microglial response between amyloidogenic transgenic models, such as APP/PS1 and AD patients. Since the AD pathology could display regional heterogeneity, we focus our work at the hippocampal formation. In APP based models a prominent microglial response is triggered around amyloid-beta (Aβ) plaques. These strongly activated microglial cells could drive the AD pathology and, in consequence, could be implicated in the neurodegenerative process observed in models. On the contrary, the microglial response in human samples is, at least, partial or attenuated. This patent difference could simply reflect the lower and probably slower Aβ production observed in human hippocampal samples, in comparison with models, or could reflect the consequence of a chronic long-standing microglial activation. Beside this differential response, we also observed microglial degeneration in Braak V–VI individuals that, indeed, could compromise their normal role of surveying the brain environment and respond to the damage. This microglial degeneration, particularly relevant at the dentate gyrus, might be mediated by the accumulation of toxic soluble phospho-tau species. The consequences of this probably deficient immunological protection, observed in AD patients, are unknown.

  • Phagocytic clearance of presynaptic dystrophies by reactive astrocytes in Alzheimer's disease
    Angela Gomez-Arboledas, Jose C. Davila, Elisabeth Sanchez-Mejias, Victoria Navarro, Cristina Nuñez-Diaz, Raquel Sanchez-Varo, Maria Virtudes Sanchez-Mico, Laura Trujillo-Estrada, Juan Jose Fernandez-Valenzuela, Marisa Vizuete,et al.

    Reactive astrogliosis, a complex process characterized by cell hypertrophy and upregulation of components of intermediate filaments, is a common feature in brains of Alzheimer's patients. Reactive astrocytes are found in close association with neuritic plaques; however, the precise role of these glial cells in disease pathogenesis is unknown. In this study, using immunohistochemical techniques and light and electron microscopy, we report that plaque‐associated reactive astrocytes enwrap, engulf and may digest presynaptic dystrophies in the hippocampus of amyloid precursor protein/presenilin‐1 (APP/PS1) mice. Microglia, the brain phagocytic population, was apparently not engaged in this clearance. Phagocytic reactive astrocytes were present in 35% and 67% of amyloid plaques at 6 and 12 months of age, respectively. The proportion of engulfed dystrophic neurites was low, around 7% of total dystrophies around plaques at both ages. This fact, along with the accumulation of dystrophic neurites during disease course, suggests that the efficiency of the astrocyte phagocytic process might be limited or impaired. Reactive astrocytes surrounding and engulfing dystrophic neurites were also detected in the hippocampus of Alzheimer's patients by confocal and ultrastructural analysis. We posit that the phagocytic activity of reactive astrocytes might contribute to clear dysfunctional synapses or synaptic debris, thereby restoring impaired neural circuits and reducing the inflammatory impact of damaged neuronal parts and/or limiting the amyloid pathology. Therefore, potentiation of the phagocytic properties of reactive astrocytes may represent a potential therapy in Alzheimer's disease.

  • Dual roles of Aβ in proliferative processes in an amyloidogenic model of Alzheimer's disease
    David Baglietto-Vargas, Elisabeth Sánchez-Mejias, Victoria Navarro, Sebastián Jimenez, Laura Trujillo-Estrada, Angela Gómez-Arboledas, Maria Sánchez-Mico, Raquel Sánchez-Varo, Marisa Vizuete, José Carlos Dávila,et al.

    Springer Science and Business Media LLC
    AbstractAlzheimer’s disease is a major neurodegenerative disorder that leads to severe cognitive deficits in the elderly population. Over the past two decades, multiple studies have focused on elucidating the causative factors underlying memory defects in Alzheimer’s patients. In this regard, new evidence linking Alzheimer’s disease-related pathology and neuronal stem cells suggests that hippocampal neurogenesis impairment is an important factor underlying these cognitive deficits. However, because of conflicting results, the impact of Aβ pathology on neurogenesis/gliogenesis remains unclear. Here, we investigated the effect of Aβ on neuronal and glial proliferation by using an APP/PS1 transgenic model and in vitro assays. Specifically, we showed that neurogenesis is affected early in the APP/PS1 hippocampus, as evidenced by a significant decrease in the proliferative activity due to a reduced number of both radial glia-like neural stem cells (type-1 cells) and intermediate progenitor cells (type-2 cells). Moreover, we demonstrated that soluble Aβ from APP/PS1 mice impairs neuronal cell proliferation using neurosphere cultures. On the other hand, we showed that oligomeric Aβ stimulates microglial proliferation, whereas no effect was observed on astrocytes. These findings indicate that Aβ has a differential effect on hippocampal proliferative cells by inhibiting neuronal proliferation and triggering the formation of microglial cells.

  • Glutaminase and MMP-9 downregulation in cortex and hippocampus of LPA<sup>1</sup> receptor null mice correlate with altered dendritic spine plasticity
    Ana Peñalver, José A. Campos-Sandoval, Eduardo Blanco, Carolina Cardona, Laura Castilla, Mercedes Martín-Rufián, Guillermo Estivill-Torrús, Raquel Sánchez-Varo, Francisco J. Alonso, Mercedes Pérez-Hernández,et al.

    Frontiers Media SA
    Lysophosphatidic acid (LPA) is an extracellular lipid mediator that regulates nervous system development and functions acting through G protein-coupled receptors (GPCRs). Here we explore the crosstalk between LPA1 receptor and glutamatergic transmission by examining expression of glutaminase (GA) isoforms in different brain areas isolated from wild-type (WT) and KOLPA1 mice. Silencing of LPA1 receptor induced a severe down-regulation of Gls-encoded long glutaminase protein variant (KGA) (glutaminase gene encoding the kidney-type isoforms, GLS) protein expression in several brain regions, particularly in brain cortex and hippocampus. Immunohistochemical assessment of protein levels for the second type of glutaminase (GA) isoform, glutaminase gene encoding the liver-type isoforms (GLS2), did not detect substantial differences with regard to WT animals. The regional mRNA levels of GLS were determined by real time RT-PCR and did not show significant variations, except for prefrontal and motor cortex values which clearly diminished in KO mice. Total GA activity was also significantly reduced in prefrontal and motor cortex, but remained essentially unchanged in the hippocampus and rest of brain regions examined, suggesting activation of genetic compensatory mechanisms and/or post-translational modifications to compensate for KGA protein deficit. Remarkably, Golgi staining of hippocampal regions showed an altered morphology of glutamatergic pyramidal cells dendritic spines towards a less mature filopodia-like phenotype, as compared with WT littermates. This structural change correlated with a strong decrease of active matrix-metalloproteinase (MMP) 9 in cerebral cortex and hippocampus of KOLPA1 mice. Taken together, these results demonstrate that LPA signaling through LPA1 influence expression of the main isoenzyme of glutamate biosynthesis with strong repercussions on dendritic spines maturation, which may partially explain the cognitive and learning defects previously reported for this colony of KOLPA1 mice.

  • Soluble phospho-tau from Alzheimer’s disease hippocampus drives microglial degeneration
    Elisabeth Sanchez-Mejias, Victoria Navarro, Sebastian Jimenez, Maria Sanchez-Mico, Raquel Sanchez-Varo, Cristina Nuñez-Diaz, Laura Trujillo-Estrada, Jose Carlos Davila, Marisa Vizuete, Antonia Gutierrez,et al.

    Springer Science and Business Media LLC

  • Early neuronal loss and axonal/presynaptic damage is associated with accelerated amyloid-β accumulation in AβPP/PS1 Alzheimer's disease mice subiculum
    Laura Trujillo-Estrada, José Carlos Dávila, Elisabeth Sánchez-Mejias, Raquel Sánchez-Varo, Angela Gomez-Arboledas, Marisa Vizuete, Javier Vitorica, and Antonia Gutiérrez

    IOS Press
    The progressive cognitive decline leading to dementia in Alzheimer's disease (AD) patients is the consequence of a severe loss of synapses and neurons affecting particular cell subpopulations in selected brain areas, with the subiculum being one of the earliest regions displaying severe atrophy and pathology. The lack of significant neuronal loss in most AD models is, in fact, the major shortcoming for the preclinical evaluation of drugs that could have greater potential in patients to alleviate or prevent this disease. In this study, using immunohistochemical and stereological approaches, we have analyzed the histopathological events in the subiculum of AβPP751SwedLondon/PS1M146L mice, a transgenic model that displays neuronal vulnerability at early ages in hippocampus and entorhinal cortex. Our results indicate that the subiculum is the earliest affected region in the hippocampus, showing a selective early loss of both principal neurons (28%) and SOM-positive interneurons (69%). In addition, our data demonstrate the existence of an early axonal and synaptic pathology, which may represent the beginning of the synaptic disruption and loss. These neurodegenerative processes occur in parallel, and closely related, with the onset and accelerated progression of the extracellular amyloid-β deposition, thus suggesting plaques as major contributors of neuronal/axonal damage. Data reported here indicate that this AD model displays a selective AD-like neurodegenerative phenotype in highly vulnerable regions, including the subiculum, and therefore can be a very useful model for testing the therapeutic ability of potential compounds to protect neurons and ameliorate disease symptoms.

  • Defective lysosomal proteolysis and axonal transport are early pathogenic events that worsen with age leading to increased APP metabolism and synaptic Abeta in transgenic APP/PS1 hippocampus
    Manuel Torres, Sebastian Jimenez, Raquel Sanchez-Varo, Victoria Navarro, Laura Trujillo-Estrada, Elisabeth Sanchez-Mejias, Irene Carmona, Jose Carlos Davila, Marisa Vizuete, Antonia Gutierrez,et al.

    Springer Science and Business Media LLC
    Abstract Background Axonal pathology might constitute one of the earliest manifestations of Alzheimer disease. Axonal dystrophies were observed in Alzheimer’s patients and transgenic models at early ages. These axonal dystrophies could reflect the disruption of axonal transport and the accumulation of multiple vesicles at local points. It has been also proposed that dystrophies might interfere with normal intracellular proteolysis. In this work, we have investigated the progression of the hippocampal pathology and the possible implication in Abeta production in young (6 months) and aged (18 months) PS1(M146L)/APP(751sl) transgenic mice. Results Our data demonstrated the existence of a progressive, age-dependent, formation of axonal dystrophies, mainly located in contact with congophilic Abeta deposition, which exhibited tau and neurofilament hyperphosphorylation. This progressive pathology was paralleled with decreased expression of the motor proteins kinesin and dynein. Furthermore, we also observed an early decrease in the activity of cathepsins B and D, progressing to a deep inhibition of these lysosomal proteases at late ages. This lysosomal impairment could be responsible for the accumulation of LC3-II and ubiquitinated proteins within axonal dystrophies. We have also investigated the repercussion of these deficiencies on the APP metabolism. Our data demonstrated the existence of an increase in the amyloidogenic pathway, which was reflected by the accumulation of hAPPfl, C99 fragment, intracellular Abeta in parallel with an increase in BACE and gamma-secretase activities. In vitro experiments, using APPswe transfected N2a cells, demonstrated that any imbalance on the proteolytic systems reproduced the in vivo alterations in APP metabolism. Finally, our data also demonstrated that Abeta peptides were preferentially accumulated in isolated synaptosomes. Conclusion A progressive age-dependent cytoskeletal pathology along with a reduction of lysosomal and, in minor extent, proteasomal activity could be directly implicated in the progressive accumulation of APP derived fragments (and Abeta peptides) in parallel with the increase of BACE-1 and gamma-secretase activities. This retard in the APP metabolism seemed to be directly implicated in the synaptic Abeta accumulation and, in consequence, in the pathology progression between synaptically connected regions.

  • Abnormal accumulation of autophagic vesicles correlates with axonal and synaptic pathology in young Alzheimer's mice hippocampus
    Raquel Sanchez-Varo, Laura Trujillo-Estrada, Elisabeth Sanchez-Mejias, Manuel Torres, David Baglietto-Vargas, Ines Moreno-Gonzalez, Vanessa De Castro, Sebastian Jimenez, Diego Ruano, Marisa Vizuete,et al.

    Springer Science and Business Media LLC

  • Age-dependent accumulation of soluble amyloid β (Aβ) oligomers reverses the neuroprotective effect of soluble amyloid precursor protein-α (sAPPα) by modulating phosphatidylinositol 3-kinase (PI3K)/Akt-GSK- 3β pathway in Alzheimer mouse model
    Sebastian Jimenez, Manuel Torres, Marisa Vizuete, Raquel Sanchez-Varo, Elisabeth Sanchez-Mejias, Laura Trujillo-Estrada, Irene Carmona-Cuenca, Cristina Caballero, Diego Ruano, Antonia Gutierrez,et al.

    Elsevier BV
    Neurotrophins, activating the PI3K/Akt signaling pathway, control neuronal survival and plasticity. Alterations in NGF, BDNF, IGF-1, or insulin signaling are implicated in the pathogenesis of Alzheimer disease. We have previously characterized a bigenic PS1×APP transgenic mouse displaying early hippocampal Aβ deposition (3 to 4 months) but late (17 to 18 months) neurodegeneration of pyramidal cells, paralleled to the accumulation of soluble Aβ oligomers. We hypothesized that PI3K/Akt/GSK-3β signaling pathway could be involved in this apparent age-dependent neuroprotective/neurodegenerative status. In fact, our data demonstrated that, as compared with age-matched nontransgenic controls, the Ser-9 phosphorylation of GSK-3β was increased in the 6-month PS1×APP hippocampus, whereas in aged PS1×APP animals (18 months), GSK-3β phosphorylation levels displayed a marked decrease. Using N2a and primary neuronal cell cultures, we demonstrated that soluble amyloid precursor protein-α (sAPPα), the predominant APP-derived fragment in young PS1×APP mice, acting through IGF-1 and/or insulin receptors, activated the PI3K/Akt pathway, phosphorylated the GSK-3β activity, and in consequence, exerted a neuroprotective action. On the contrary, several oligomeric Aβ forms, present in the soluble fractions of aged PS1×APP mice, inhibited the induced phosphorylation of Akt/GSK-3β and decreased the neuronal survival. Furthermore, synthetic Aβ oligomers blocked the effect mediated by different neurotrophins (NGF, BDNF, insulin, and IGF-1) and sAPPα, displaying high selectivity for NGF. In conclusion, the age-dependent appearance of APP-derived soluble factors modulated the PI3K/Akt/GSK-3β signaling pathway through the major neurotrophin receptors. sAPPα stimulated and Aβ oligomers blocked the prosurvival signaling. Our data might provide insights into the selective vulnerability of specific neuronal groups in Alzheimer disease.

  • Calretinin interneurons are early targets of extracellular amyloid-β pathology in PS1/AβPP Alzheimer mice hippocampus
    David Baglietto-Vargas, Ines Moreno-Gonzalez, Raquel Sanchez-Varo, Sebastian Jimenez, Laura Trujillo-Estrada, Elisabeth Sanchez-Mejias, Manuel Torres, Manuel Romero-Acebal, Diego Ruano, Marisa Vizuete,et al.

    IOS Press
    Specific neuronal networks are preferentially affected in the early stages of Alzheimer's disease (AD). The distinct subpopulations of hippocampal inhibitory GABAergic system have been shown to display differential vulnerability to neurodegeneration in AD. We have previously reported a substantial loss of SOM/NPY interneurons, whereas those expressing parvalbumin were unaltered, in the hippocampus of 6 month-old PS1/AbetaPP transgenic mice. In the present study, we now investigated the pathological changes of hippocampal calretinin (CR) interneurons in this PS1/AbetaPP model from 2 to 12 months of age. The total number of CR-immunoreactive inhibitory cells was determined by stereology in CA1 and CA2/3 subfields. Our findings show a substantial decrease (35%-45%) of CR-positive interneurons in both hippocampal subfields of PS1/AbetaPP mice at very early age (4 months) compared to age-matched control mice. This decrease was accompanied by a reduced CR mRNA content as determined by quantitative RT-PCR. However, the number of another hippocampal CR-positive population (belonging to Cajal-Retzius cells) was not affected. The selective early loss of CR-interneurons was parallel to the appearance of extracellular Abeta deposits, preferentially in CR-axonal fields, and the formation of dystrophic neurites. This specific GABAergic subpopulation plays a crucial role in the generation of synchronous rhythmic activity in hippocampus by controlling other interneurons. Therefore, early alterations of hippocampal inhibitory functionality in AD, caused by select CR-cells neurodegeneration, could result in cognitive impairments seen in initial stages of the disease.