Microglia-secreted TNF-α affects differentiation efficiency and viability of pluripotent stem cell-derived human dopaminergic precursors.

Disease is a neurodegenerative disorder characterised by the progressive loss of dopaminergic cells of the substantia nigra pars compacta. Even though successful transplantation of dopamine-producing cells into the striatum exhibits favourable effects in animal models and clinical trials; transplanted cell survival is low. Since every transplant elicits an inflammatory response which can affect cell survival and differentiation, we aimed to study in vivo and in vitro the impact of the pro-inflammatory environment on human dopaminergic precursors. We first observed that transplanted human dopaminergic precursors into the striatum of immunosuppressed rats elicited an early and sustained activation of astroglial and microglial cells after 15 days' post-transplant. This long-lasting response was associated with Tumour necrosis factor alpha expression in microglial cells. In vitro, conditioned media from activated BV2 microglial cells increased cell death, decreased Tyrosine hydroxylase-positive cells and induced morphological alterations on human neural stem cells-derived dopaminergic precursors at two differentiation stages: 19 days and 28 days. Those effects were ameliorated by inhibition of Tumour necrosis factor alpha, a cytokine which was previously detected in vivo and in conditioned media from activated BV-2 cells. Our results suggest that a pro-inflammatory environment is sustained after transplantation under immunosuppression, providing a window of opportunity to modify this response to increase transplant survival and differentiation. In addition, our data show that the microglia-derived pro-inflammatory microenvironment has a negative impact on survival and differentiation of dopaminergic precursors. Finally, Tumour necrosis factor alpha plays a key role in these effects, suggesting that this cytokine could be an interesting target to increase the efficacy of human dopaminergic precursors transplantation in Parkinson's Disease.

A metabotropic glutamate receptor 3 (mGlu3R) isoform playing neurodegenerative roles in astrocytes is prematurely up-regulated in an Alzheimer's model.

Subtype 3 metabotropic glutamate receptor (mGlu3R) displays a broad range of neuroprotective effects. We previously demonstrated that mGlu3R activation in astrocytes protects hippocampal neurons from Aß neurotoxicity through stimulation of both neurotrophin release and Aß uptake. Alternative-spliced variants of mGlu3R were found in human brains. The most prevalent variant, mGlu3Δ4, lacks exon 4 encoding the transmembrane domain and can inhibit ligand binding to mGlu3R. To date, neither its role in neurodegenerative disorders nor its endogenous expression in CNS cells has been addressed. The present paper describes for the first time an association between altered hippocampal expression of mGlu3Δ4 and Alzheimer's disease (AD) in the preclinical murine model PDAPP-J20, as well as a deleterious effect of mGlu3Δ4 in astrocytes. As assessed by western blot, hippocampal mGlu3R levels progressively decreased with age in PDAPP-J20 mice. On the contrary, mGlu3Δ4 levels were drastically increased with aging in nontransgenic mice, but prematurely over-expressed in 5-month-old PDAPP-J20-derived hippocampi, prior to massive senile plaque deposition. Also, we found that mGlu3Δ4 co-precipitated with mGlu3R mainly in 5-month-old PDAPP-J20 mice. We further showed by western blot that primary cultured astrocytes and neurons expressed mGlu3Δ4, whose levels were reduced by Aß, thereby discouraging a causal effect of Aß on mGlu3Δ4 induction. However, heterologous expression of mGlu3Δ4 in astrocytes induced cell death, inhibited mGlu3R expression, and prevented mGlu3R-dependent Aß glial uptake. Indeed, mGlu3Δ4 promoted neurodegeneration in neuron-glia co-cultures. These results provide evidence of an inhibitory role of mGlu3Δ4 in mGlu3R-mediated glial neuroprotective pathways, which may lie behind AD onset.

Inflammation and Insulin Resistance as Risk Factors and Potential Therapeutic Targets for Alzheimer's Disease.

Overnutrition and modern diets containing high proportions of saturated fat are among the major factors contributing to a low-grade state of inflammation, hyperglycemia and dyslipidemia. In the last decades, the global rise of type 2 diabetes and obesity prevalence has elicited a great interest in understanding how changes in metabolic function lead to an increased risk for premature brain aging and the development of neurodegenerative disorders such as Alzheimer's disease (AD). Cognitive impairment and decreased neurogenic capacity could be a consequence of metabolic disturbances. In these scenarios, the interplay between inflammation and insulin resistance could represent a potential therapeutic target to prevent or ameliorate neurodegeneration and cognitive impairment. The present review aims to provide an update on the impact of metabolic stress pathways on AD with a focus on inflammation and insulin resistance as risk factors and therapeutic targets.

Microglial autophagy is impaired by prolonged exposure to ß-amyloid peptides: evidence from experimental models and Alzheimer's disease patients.

Alzheimer's disease (AD) is a progressive neurodegenerative disorder characterized by the presence of misfolded proteins, amyloid-ß (Aß) aggregates, and neuroinflammation in the brain. Microglial cells are key players in the context of AD, being capable of releasing cytokines in response to Aß and degrading aggregated proteins by mechanisms involving the ubiquitin-proteasome system and autophagy. Here, we present in vivo and in vitro evidence showing that microglial autophagy is affected during AD progression. PDAPPJ20 mice-murine model of AD-exhibited an accumulation of the autophagy receptor p62 and ubiquitin+ aggregates in Iba1+ microglial cells close to amyloid deposits in the hippocampus. Moreover, cultured microglial BV-2 cells showed an enhanced autophagic flux during a 2-h exposure to fibrillar Aß, which was decreased if the exposure was prolonged to 24 h, a condition analogous to the chronic exposure to Aß in the human pathology. The autophagic impairment was also associated with lysosomal damage, depicted by membrane permeabilization as shown by the presence of the acid hydrolase cathepsin-D in cytoplasm and altered LysoTracker staining. These results are compatible with microglial exhaustion caused by pro-inflammatory conditions and persistent exposure to aggregated Aß peptides. In addition, we found LC3-positive autophagic vesicles accumulated in phagocytic CD68+ microglia in human AD brain samples, suggesting defective autophagy in microglia of AD brain. Our results indicate that the capacity of microglia to degrade Aß and potentially other proteins through autophagy may be negatively affected as the disease progresses. Preserving autophagy in microglia thus emerges as a promising approach for treating AD. Graphical abstract.

Periodic dietary restriction ameliorates amyloid pathology and cognitive impairment in PDAPP-J20 mice: Potential implication of glial autophagy.

Dietary restriction promotes cell regeneration and stress resistance in multiple models of human diseases. One of the conditions that could potentially benefit from this strategy is Alzheimer's disease, a chronic, progressive and prevalent neurodegenerative disease. Although there are no effective pharmacological treatments for this pathology, lifestyle interventions could play therapeutic roles. Our objectives were 1) to evaluate the effects of dietary restriction on cognition, hippocampal amyloid deposition, adult neurogenesis and glial reactivity and autophagy in a mouse model of familial Alzheimer's disease, and 2) to analyze the role of glial cells mediating the effects of nutrient restriction in an in vitro model. Therefore, we established a periodic dietary restriction protocol in adult female PDAPP-J20 transgenic mice for 6 weeks. We found that dietary restriction, not involving overall caloric restriction, attenuated cognitive deficits, amyloid pathology and microglial reactivity in transgenic mice when compared with ad libitum-fed transgenic animals. Also, transgenic mice showed an increase in the astroglial positive signal for LC3, an autophagy-associated protein. In parallel, hippocampal adult neurogenesis was decreased in transgenic mice whereas dietary-restricted transgenic mice showed a neurogenic status similar to controls. In vitro experiments showed that nutrient restriction decreased astroglial and, indirectly, microglial NFκB activation in response to amyloid ß peptides. Furthermore, nutrient restriction was able to preserve astroglial autophagic flux and to decrease intracellular amyloid after exposure to amyloid ß peptides. Our results suggest neuroprotective effects of nutrient restriction in Alzheimer's disease, with modulation of glial activation and autophagy being potentially involved pathways.

Early Exposure to a High-Fat Diet Impacts on Hippocampal Plasticity: Implication of Microglia-Derived Exosome-like Extracellular Vesicles.

Adolescence is a transitional period from childhood to adulthood characterized by puberty and brain maturation involving behavioral changes and environmental vulnerability. Diet is one of the factors affecting brain health, potentially leading to long-lasting effects. Hence, we studied the impact of early exposure (P21-60) to a high-fat diet (HFD) on mouse hippocampus, analyzing inflammation, adult neurogenesis, dendritic spine plasticity, and spatial memory. Glycemia and seric pro-inflammatory IL1ß were higher in HFD mice without differences on body weight. In the HFD hippocampus, neuroinflammation was evidenced by Iba1+ cells reactivity together with a higher expression of TNFα and IL1ß while the neurogenic capability in the dentate gyrus was strongly reduced. We found a predominance of immature Dil-labeled dendritic spines from CA1 neurons along with diminished levels of the scaffold protein Shank2, suggesting a defective connectivity. Moreover, the HFD group exhibited spatial memory alterations. To elucidate whether microglia could be mediating HFD-associated neuronal changes, the lipotoxic context was emulated by incubating primary microglia with palmitate, a saturated fatty acid present in HFD. Palmitate induced a pro-inflammatory profile as shown by secreted cytokine levels. The isolated exosome fraction from palmitate-stimulated microglia induced an immature dendritic spine phenotype in primary GFP+ hippocampal neurons, in line with the in vivo findings. These results provide novel data concerning microglia to neuron communication and highlight that fat excess during a short and early period of life could negatively impact on cognition and synaptic plasticity in a neuroinflammatory context, where microglia-derived exosomes could be implicated. Graphical Abstract ᅟ.

Juvenile exposure to a high fat diet promotes behavioral and limbic alterations in the absence of obesity.

The incidence of metabolic disorders including obesity, type 2 diabetes and metabolic syndrome have seriously increased in the last decades. These diseases - with growing impact in modern societies - constitute major risk factors for neurodegenerative disorders such as Alzheimer's disease (AD), sharing insulin resistance, inflammation and associated cognitive impairment. However, cerebral cellular and molecular pathways involved are not yet clearly understood. Thus, our aim was to study the impact of a non-severe high fat diet (HFD) that resembles western-like alimentary habits, particularly involving juvenile stages where the brain physiology and connectivity are in plain maturation. To this end, one-month-old C57BL/6J male mice were given either a control diet or HFD during 4 months. Exposure to HFD produced metabolic alterations along with changes in behavioral and central parameters, in the absence of obesity. Two-month-old HFD mice showed increased glycemia and plasmatic IL1ß but these values normalized at the end of the HFD protocol at 5 months of age, probably representing an acute response that is compensated at later stages. After four months of HFD exposure, mice presented dyslipidemia, increased Lipoprotein-associated phospholipase A2 (Lp-PLA2) activity, hepatic insulin resistance and inflammation. Alterations in the behavioral profile of the HFD group were shown by the impediment in nest building behavior, deficiencies in short and mid-term spatial memories, anxious and depressive- like behavior. Regarding the latter disruptions in emotional processing, we found an increased neural activity in the amygdala, shown by a greater number of c-Fos+ nuclei. We found that hippocampal adult neurogenesis was decreased in HFD mice, showing diminished cell proliferation measured as Ki67+ cells and neuronal differentiation in SGZ by doublecortin labeling. These phenomena were accompanied by a neuroinflammatory and insulin-resistant state in the hippocampus, depicted by a reactive phenotype in Iba1+ microglia cells (increased in number and soma size) and an impaired response to insulin given by decreased phosphorylated Akt levels and increased levels of inhibitory phosphorylation of IRS1. Our data portray a set of alterations in behavioral and neural parameters as a consequence of an early-life exposure to a quite moderate high fat diet, many of which can resemble AD-related features. These results highly emphasize the need to study how metabolic and neurodegenerative disorders are interrelated in deep, thus allowing the finding of successful preventive and therapeutic approaches.

Glial alterations from early to late stages in a model of Alzheimer's disease: Evidence of autophagy involvement in Aß internalization.

Alzheimer's disease (AD) is a progressive neurodegenerative disease without effective therapy. Brain amyloid deposits are classical histopathological hallmarks that generate an inflammatory reaction affecting neuronal and glial function. The identification of early cell responses and of brain areas involved could help to design new successful treatments. Hence, we studied early alterations of hippocampal glia and their progression during the neuropathology in PDAPP-J20 transgenic mice, AD model, at 3, 9, and 15 months (m) of age. At 3 m, before deposits formation, microglial Iba1+ cells from transgenic mice already exhibited signs of activation and larger soma size in the hilus, alterations appearing later on stratum radiatum. Iba1 immunohistochemistry revealed increased cell density and immunoreactive area in PDAPP mice from 9 m onward selectively in the hilus, in coincidence with prominent amyloid Congo red + deposition. At pre-plaque stages, GFAP+ astroglia showed density alterations while, at an advanced age, the presence of deposits was associated with important glial volume changes and apparently being intimately involved in amyloid degradation. Astrocytes around plaques were strongly labeled for LC3 until 15 m in Tg mice, suggestive of increased autophagic flux. Moreover, ß-Amyloid fibrils internalization by astrocytes in in vitro conditions was dependent on autophagy. Co-localization of Iba1 with ubiquitin or p62 was exclusively found in microglia contacting deposits from 9 m onward, suggesting torpid autophagy. Our work characterizes glial changes at early stages of the disease in PDAPP-J20 mice, focusing on the hilus as an especially susceptible hippocampal subfield, and provides evidence that glial autophagy could play a role in amyloid processing at advanced stages.

[Hippocampal and cognitive alterations precede amyloid deposition in a mouse model for Alzheimer's disease]. / Alteraciones hipocampales y cambios cognitivos preceden al depósito de placas amiloides en un modelo murino de la enfermedad de Alzheimer.

Although there is strong evidence about neuronal and glial disturbances at advanced stages of Alzheimer's disease, less attention has been directed to early, preamyloid changes that could contribute to the progression of the disease. We evaluated neuronal and glial morphological changes and behavioral disturbances in PDAPP-J20 transgenic (Tg) mice, carrying mutated human APP gene (amyloid precursor protein), at 5 months of age, before brain amyloid deposition occurs. Using NeuN immunohistochemistry we found decreased numbers of pyramidal and granular neurons in the hippocampus associated with a reduction of hippocampal volume in Tg mice compared with controls. Neurogenesis was impaired, evidenced by means of DCX immunohistochemistry in the dentate gyrus. In the CA3 region we found a decreased density of synaptophysin, suggesting synaptic disturbance, but no changes were found in CA1 synaptic spine density. Using confocal microscopy we observed decreased number and cell complexity of GFAP+ astrocytes, indicating potential glial atrophy. Cognitive impairment (novel location recognition test) and increased anxiety (open field) were detected in Tg mice, associated with more c-Fos+ nuclei in the amygdala, possibly indicating a role for emotionality in early stages of the disease. The study of early alterations in the course of amyloid pathology could contribute to the development of diagnostic and preventive strategies.

Alteraciones hipocampales y cambios cognitivos preceden al deposito de placas amiloides en un modelo murino de la enfermedad de Alzheimer

Existen múltiples evidencias de alteraciones neuronales y gliales en etapas avanzadas de la enfemedad de Alzheimer con abundantes depósitos cerebrales de beta amiloide, aunque hay pocos datos de cambios tempranos que podrían contribuir al desarrollo de la enfermedad. Evaluamos alteraciones morfológicas neuronales y gliales, y cambios cognitivos y emocionales tempranos en ratones transgénicos PDAPP-J20 (Tg), portadores del gen humano de APP (amyloid precursor protein) mutado, a los 5 meses de edad, aún sin depósitos amiloides en el hipocampo y con niveles bajos de péptidos amiloides cerebrales. Mediante inmunohistoquímica para NeuN, los Tg presentaron menor número de neuronas piramidales y granulares en el hipocampo, junto con un menor volumen de la estructura, en comparación con los controles no transgénicos. La neurogénesis se encontró afectada, evidenciada por reducido número de neuronas DCX+ en el giro dentado. En la región CA3, hubo una menor densidad de sinaptofisina sugiriendo alteraciones sinápticas entre neuronas granulares y piramidales, sin cambios en la densidad de espinas dendríticas en CA1. Utilizando microscopía confocal, observamos una disminución del número de astrocitos GFAP+ con una reducción de la complejidad celular, sugiriendo atrofia glial. Se detectó un déficit cognitivo (reconocimiento de localización novedosa de un objeto) y un aumento de la ansiedad (campo abierto) en los Tg, con aumento en los núcleos c-Fos+ en amígdala, evidenciando el papel de la emocionalidad en los inicios de la enfermedad. El estudio de las alteraciones iniciales en la enfermedad amiloide podría contribuir al desarrollo de métodos de diagnóstico temprano y de terapéutica preventiva.

Although there is strong evidence about neuronal and glial disturbances at advanced stages of Alzheimer’s disease, less attention has been directed to early, pre-amyloid changes that could contribute to the progression of the disease. We evaluated neuronal and glial morphological changes and behavioral disturbances in PDAPP-J20 transgenic (Tg) mice, carrying mutated human APP gene (amyloid precursor protein), at 5 months of age, before brain amyloid deposition occurs. Using NeuN immunohistochemistry we found decreased numbers of pyramidal and granular neurons in the hippocampus associated with a reduction of hippocampal volume in Tg mice compared with controls. Neurogenesis was impaired, evidenced by means of DCX immunohistochemistry in the dentate gyrus. In the CA3 region we found a decreased density of synaptophysin, suggesting synaptic disturbance, but no changes were found in CA1 synaptic spine density. Using confocal microscopy we observed decreased number and cell complexity of GFAP+ astrocytes, indicating potential glial atrophy. Cognitive impairment (novel location recognition test) and increased anxiety (open field) were detected in Tg mice, associated with more c-Fos+ nuclei in the amygdala, possibly indicating a role for emotionality in early stages of the disease. The study of early alterations in the course of amyloid pathology could contribute to the development of diagnostic and preventive strategies.

Alteraciones hipocampales y cambios cognitivos preceden al deposito de placas amiloides en un modelo murino de la enfermedad de Alzheimer

Existen múltiples evidencias de alteraciones neuronales y gliales en etapas avanzadas de la enfemedad de Alzheimer con abundantes depósitos cerebrales de beta amiloide, aunque hay pocos datos de cambios tempranos que podrían contribuir al desarrollo de la enfermedad. Evaluamos alteraciones morfológicas neuronales y gliales, y cambios cognitivos y emocionales tempranos en ratones transgénicos PDAPP-J20 (Tg), portadores del gen humano de APP (amyloid precursor protein) mutado, a los 5 meses de edad, aún sin depósitos amiloides en el hipocampo y con niveles bajos de péptidos amiloides cerebrales. Mediante inmunohistoquímica para NeuN, los Tg presentaron menor número de neuronas piramidales y granulares en el hipocampo, junto con un menor volumen de la estructura, en comparación con los controles no transgénicos. La neurogénesis se encontró afectada, evidenciada por reducido número de neuronas DCX+ en el giro dentado. En la región CA3, hubo una menor densidad de sinaptofisina sugiriendo alteraciones sinápticas entre neuronas granulares y piramidales, sin cambios en la densidad de espinas dendríticas en CA1. Utilizando microscopía confocal, observamos una disminución del número de astrocitos GFAP+ con una reducción de la complejidad celular, sugiriendo atrofia glial. Se detectó un déficit cognitivo (reconocimiento de localización novedosa de un objeto) y un aumento de la ansiedad (campo abierto) en los Tg, con aumento en los núcleos c-Fos+ en amígdala, evidenciando el papel de la emocionalidad en los inicios de la enfermedad. El estudio de las alteraciones iniciales en la enfermedad amiloide podría contribuir al desarrollo de métodos de diagnóstico temprano y de terapéutica preventiva.(AU)

Although there is strong evidence about neuronal and glial disturbances at advanced stages of Alzheimer’s disease, less attention has been directed to early, pre-amyloid changes that could contribute to the progression of the disease. We evaluated neuronal and glial morphological changes and behavioral disturbances in PDAPP-J20 transgenic (Tg) mice, carrying mutated human APP gene (amyloid precursor protein), at 5 months of age, before brain amyloid deposition occurs. Using NeuN immunohistochemistry we found decreased numbers of pyramidal and granular neurons in the hippocampus associated with a reduction of hippocampal volume in Tg mice compared with controls. Neurogenesis was impaired, evidenced by means of DCX immunohistochemistry in the dentate gyrus. In the CA3 region we found a decreased density of synaptophysin, suggesting synaptic disturbance, but no changes were found in CA1 synaptic spine density. Using confocal microscopy we observed decreased number and cell complexity of GFAP+ astrocytes, indicating potential glial atrophy. Cognitive impairment (novel location recognition test) and increased anxiety (open field) were detected in Tg mice, associated with more c-Fos+ nuclei in the amygdala, possibly indicating a role for emotionality in early stages of the disease. The study of early alterations in the course of amyloid pathology could contribute to the development of diagnostic and preventive strategies.(AU)

Deregulation of mitochondria-shaping proteins Opa-1 and Drp-1 in manganese-induced apoptosis.

Mitochondria are dynamic organelles that undergo fusion and fission processes. These events are regulated by mitochondria-shaping proteins. Changes in the expression and/or localization of these proteins lead to a mitochondrial dynamics impairment and may promote apoptosis. Increasing evidence correlates the mitochondrial dynamics disruption with the occurrence of neurodegenerative diseases. Therefore, we focused on this topic in Manganese (Mn)-induced Parkinsonism, a disorder associated with Mn accumulation preferentially in the basal ganglia where mitochondria from astrocytes represent an early target. Using MitoTracker Red staining we observed increased mitochondrial network fission in Mn-exposed rat astrocytoma C6 cells. Moreover, Mn induced a marked decrease in fusion protein Opa-1 levels as well as a dramatic increase in the expression of fission protein Drp-1. Additionally, Mn provoked a significant release of high MW Opa-1 isoforms from the mitochondria to the cytosol as well as an increased Drp-1 translocation to the mitochondria. Both Mdivi-1, a pharmacological Drp-1 inhibitor, and rat Drp-1 siRNA reduced the number of apoptotic nuclei, preserved the mitochondrial network integrity and prevented cell death. CsA, an MPTP opening inhibitor, prevented mitochondrial Δψm disruption, Opa-1 processing and Drp-1 translocation to the mitochondria therefore protecting Mn-exposed cells from mitochondrial disruption and apoptosis. The histological analysis and Hoechst 33258 staining of brain sections of Mn-injected rats in the striatum showed a decrease in cellular mass paralleled with an increase in the occurrence of apoptotic nuclei. Opa-1 and Drp-1 expression levels were also changed by Mn-treatment. Our results demonstrate for the first time that abnormal mitochondrial dynamics is implicated in both in vitro and in vivo Mn toxicity. In addition we show that the imbalance in fusion/fission equilibrium might be involved in Mn-induced apoptosis. This knowledge may provide new therapeutic tools for the treatment of Manganism and other neurodegenerative diseases.

Astroglial mGlu3 receptors promote alpha-secretase-mediated amyloid precursor protein cleavage.

Amyloid precursor protein (APP) shedding yields the Alzheimer's disease (AD)-related peptide amyloid ß (Aß) through ß- and γ-secretase cleavage. Alternatively, α-secretase cleavage generates a soluble and neuroprotective fragment (sAPPα) while precludes the production of Aß. Although metabotropic glutamate (mGlu) receptors were associated with induction of sAPPα production in astrocytes, there was no further evidence regarding the specific subtype receptor or the mechanisms involved in this action. In the present study, we used the dual mGlu2/3 receptor agonist LY379268, which in pure astrocyte cultures selectively activates mGlu3 receptor subtype since mGlu2 receptor subtype is not expressed by these cells. We showed that LY379268 incremented sAPPα release from cultured astrocytes by inducing α-secretases expression, whereas it decreased ß-secretase levels. LY379268-induced increase of PPAR-γ levels could be involved in the effect of the agonist on sAPPα release. Using the PDAPP-J20 murine model of AD we described a strong reduction in mGlu2/3 receptor expression in the hippocampus of 5- and 14-month-old transgenic mice compared to control littermates. Moreover, mGlu3 receptor expression is also decreased specifically in hippocampal astrocytes of these transgenic animals as a function of age. Therefore, diminished levels of hippocampal mGlu3 receptors might have implications in the development of the disease in these transgenic mice considering the anti-amyloidogenic action of mGlu3 receptors in astrocytes.

Neuronal and glial alterations, increased anxiety, and cognitive impairment before hippocampal amyloid deposition in PDAPP mice, model of Alzheimer's disease.

In the context of Alzheimer's disease (AD), hippocampal alterations have been well described in advanced stages of the pathology, when amyloid deposition, inflammation and glial activation occur, but less attention has been directed to studying early brain and behavioral changes. Using an animal model of AD, the transgenic PDAPP-J20 mouse at 5 months of age, when no amyloid plaques are present and low cerebral levels of amyloid peptides are detectable, we found structural, morphological, and cellular alterations in the hippocampus. Young transgenic mice showed a reduced hippocampal volume with less number of pyramidal and granular neurons, which additionally exhibited cell atrophy. The neurogenic capability in this zone, measured as DCX+ cells, was strongly diminished and associated to alterations in cell maturity. A decrease in presynaptic synaptophysin optical density was detected in mossy fibers reaching CA3 subfield but not in Golgi stained- CA1 dendritic spine density. Employing confocal microscopy and accurate stereological tools we also found a reduction in the number of GFAP+ cells, along with decreased astrocyte complexity, suggesting a potential detriment of neural support. According with untimely neuroglial alterations, young PDAPP mice failed in the novel location recognition test, that depends on hippocampal function. Moreover, multivariate statistical analysis of the behavioral outcome in the open-field test evidenced an elevated anxiety score in Tg mice compared with age-matched control mice. In line with this, the transgenic group showed a higher number of c-Fos+ nuclei in central and basolateral amygdala, a result that supports the early involvement of the emotionality factor in AD pathology. Applying an integrative approach, this work focuses on early structural, morphological and functional changes and provides new and compelling evidence of behavioral alterations that precede manifest AD.

Alteraciones hipocampales y cambios cognitivos preceden al depósito de placas amiloides en un modelo murino de la enfermedad de Alzheimer. / [Hippocampal and cognitive alterations precede amyloid deposition in a mouse model for Alzheimers disease].

Although there is strong evidence about neuronal and glial disturbances at advanced stages of Alzheimers disease, less attention has been directed to early, preamyloid changes that could contribute to the progression of the disease. We evaluated neuronal and glial morphological changes and behavioral disturbances in PDAPP-J20 transgenic (Tg) mice, carrying mutated human APP gene (amyloid precursor protein), at 5 months of age, before brain amyloid deposition occurs. Using NeuN immunohistochemistry we found decreased numbers of pyramidal and granular neurons in the hippocampus associated with a reduction of hippocampal volume in Tg mice compared with controls. Neurogenesis was impaired, evidenced by means of DCX immunohistochemistry in the dentate gyrus. In the CA3 region we found a decreased density of synaptophysin, suggesting synaptic disturbance, but no changes were found in CA1 synaptic spine density. Using confocal microscopy we observed decreased number and cell complexity of GFAP+ astrocytes, indicating potential glial atrophy. Cognitive impairment (novel location recognition test) and increased anxiety (open field) were detected in Tg mice, associated with more c-Fos+ nuclei in the amygdala, possibly indicating a role for emotionality in early stages of the disease. The study of early alterations in the course of amyloid pathology could contribute to the development of diagnostic and preventive strategies.

Estradiol increases dendritic length and spine density in CA1 neurons of the hippocampus of spontaneously hypertensive rats: a Golgi impregnation study.

Increased neuronal vulnerability has been described in the brain of spontaneously hypertensive rats (SHR), models of primary hypertension. Previous data indicate that estradiol treatment corrects several dysfunctions of the hippocampus and hypothalamus of SHR. Considering this evidence we analyzed the dendritic arborization and spine density of the CA1 subfield in SHR and Wistar-Kyoto (WKY) normotensive rats with and without estradiol treatment. Five month old male SHR and WKY rats received single estradiol or cholesterol pellets (sham treatment) for 2 weeks. A substantial rise of circulating estradiol (>25 fold) and testicular atrophy was present in all estradiol-receiving rats. In both SHR and WKY rats, estradiol decreased blood pressure by ~20 mm Hg; however, a moderate hypertension persisted in SHR (164 mm Hg). Using a modified Golgi impregnation technique, apical and basal dendrites of the CA1 subfield were subjected to Sholl analysis. Spine density was also statistically analyzed. Apical dendritic length was significantly lower in SHR compared to WKY rats (p<0.01), whereas estradiol treatment increased dendritic length in the SHR group only (SHR vs SHR+estradiol; p<0.01). Apical dendritic length plotted against the shell distances 20-100, 120-200 and 220-300 µm, revealed that changes were more pronounced in the range 120-200 µm between SHR vs. WKY rats (p<0.05) and SHR vs. SHR+estradiol (p<0.05). Instead, basal dendrites were not significantly modified by hypertension or steroid treatment. Spine density of apical dendrites was lower in SHR than WKY (p<0.05) and was up-regulated in the SHR+estradiol group compared to the SHR group (p<0.001). Similar changes were obtained for basal dendritic spines. These data suggest that changes of neuronal processes in SHR are plastic events restorable by estradiol treatment. In conjunction with previous results, the present data reveal new targets of estradiol neuroprotection in the brain of hypertensive rats.

Environmental enrichment prevents astroglial pathological changes in the hippocampus of APP transgenic mice, model of Alzheimer's disease.

Alzheimer's disease (AD) is a neurodegenerative disease that affects neurons and glial cells and leads to dementia. Growing evidence shows that glial changes may precede neuronal alterations and behavioral impairment in the progression of the disease. The modulation of these changes could be addressed as a potential therapeutic strategy. Environmental enrichment has been classically associated to effects on neuronal morphology and function but less attention has been paid to the modulation of glia. We thus characterized astroglial changes in the hippocampus of adult PDAPP-J20 transgenic mice, a model of AD, exposed for 3 months to an enriched environment, from 5 to 8 months of age. Using confocal microscopy, three-dimensional reconstruction and Sholl analysis, we evaluated the morphology of two distinct populations of astrocytes: those associated to amyloid ß plaques and those that were not. We found that plaque-associated astrocytes in PDAPP-J20 mice had an increased volume and process ramification than control astrocytes. Non-plaque-associated astrocytes showed a decrease in volume and an increase in the ramification of GFAP+ processes as compared with control astrocytes. Environmental enrichment prevented these alterations and promoted a cellular morphology similar to that found in control mice. Morphological changes in non-plaque-associated astrocytes were found also at 5 months of age, before amyloid ß deposition in the hippocampus. These results suggest that glial alterations have an early onset in AD pathogenesis and that the exposure to an enriched environment is an appropriate strategy to reverse them. Cellular and molecular pathways involved in this regulation could constitute potential novel therapeutic targets.

Short-term environmental enrichment enhances adult neurogenesis, vascular network and dendritic complexity in the hippocampus of type 1 diabetic mice.

BACKGROUND: Several brain disturbances have been described in association to type 1 diabetes in humans. In animal models, hippocampal pathological changes were reported together with cognitive deficits. The exposure to a variety of environmental stimuli during a certain period of time is able to prevent brain alterations and to improve learning and memory in conditions like stress, aging and neurodegenerative processes. METHODOLOGY/PRINCIPAL FINDINGS: We explored the modulation of hippocampal alterations in streptozotocin-induced type 1 diabetic mice by environmental enrichment. In diabetic mice housed in standard conditions we found a reduction of adult neurogenesis in the dentate gyrus, decreased dendritic complexity in CA1 neurons and a smaller vascular fractional area in the dentate gyrus, compared with control animals in the same housing condition. A short exposure -10 days- to an enriched environment was able to enhance proliferation, survival and dendritic arborization of newborn neurons, to recover dendritic tree length and spine density of pyramidal CA1 neurons and to increase the vascular network of the dentate gyrus in diabetic animals. CONCLUSIONS/SIGNIFICANCE: The environmental complexity seems to constitute a strong stimulator competent to rescue the diabetic brain from neurodegenerative progression.

Hippocampal neurovascular and hypothalamic-pituitary-adrenal axis alterations in spontaneously type 2 diabetic GK rats.

Metabolic and vascular consequences of diabetes mellitus induce several CNS complications. The dentate gyrus of the hippocampus, a well-recognized target for diabetic alterations, is a neurogenic area associated with memory and learning processes. Here, we explored the hippocampal neurogenesis and its microenvironment (astrocytes, vascularisation and glucocorticoid influence) in a spontaneous model of type 2 diabetes, the Goto-Kakizaki rat. The number of proliferative Ki67(+) cells and young doublecortin(+) neurons was 2-fold higher in the hippocampus from diabetic rats than in normoglycemic control Wistar at 4 months of age. However, there was no difference in cell survival, studied 3 weeks after bromodeoxyuridine administration. Labeling of endothelial cells against von Willebrand factor, demonstrated a 50% decrease in the granular cell layer fractional area covered by blood vessels and a diminished capillary branching in diabetic rats. Finally, Goto-Kakizaki rats exhibited decreased glucocorticoid receptor immunolabeling in CA1, associated with higher corticosteronemia. In conclusion, diabetic rats showed increased cell proliferation and neuronal differentiation without concomitant survival modification. A high proliferation rate, potentially reflecting a compensatory mechanism for neuronal suffering, also exists in various pathological situations. However, endothelial alteration induced by chronic hyperglycemia, hyperleptinemia and insulin resistance and associated with deleterious glucocorticoid effects might impair effective neurogenesis in diabetic Goto-Kakizaki rats.

Neuronal plasticity and antidepressants in the diabetic brain.

The hippocampus, a limbic structure linked to higher brain functions, appears vulnerable in diabetic subjects that have a higher risk of stroke, dementia, and cognitive decline. The dentate gyrus (DG) of the hippocampus is one of the limited neurogenic brain areas during adulthood; neurons born in the DG are involved in some types of learning and memory processes. We found a decrease in the ability for proliferation and neuronal differentiation of newborn cells, measured by bromodeoxyuridine incorporation in the DG, from streptozotocin-induced diabetic mice. The hilar region, formed by mature neurons presenting higher sensitivity to brain damage, showed a reduced neuronal density in diabetic mice with respect to vehicle-treated mice. Interestingly, in a spontaneous model of type 1 diabetes, we corroborated a decrease in the rate of neurogenesis in the nonobese diabetic mice compared to control strains, and this reduction was also found during the prediabetic stage. The antidepressant fluoxetine administered over a period of 10 days to diabetic mice was effective in preventing changes in proliferation and differentiation of new neurons. Confocal microscope studies, including using neuronal and glial markers, suggested that differentiation toward a neuronal phenotype was decreased in diabetic animals and was reversed by the antidepressant treatment. In addition, the loss of hilar neurons was avoided by fluoxetine treatment. Several reports have demonstrated that high susceptibility to stress and elevated corticosterone levels are detrimental to neurogenesis and contribute to neuronal loss. These features are common in some types of depression, diabetes, and aging processes, suggesting they participate in the reported hippocampal abnormalities present in these conditions.