Alberto Pérez-Mediavilla

Phenylbutyrate ameliorates cognitive deficit and reduces tau pathology in an Alzheimer's disease mouse model.

Chromatin modification through histone acetylation is a molecular pathway involved in the regulation of transcription underlying memory storage. Sodium 4-phenylbutyrate (4-PBA) is a well-known histone deacetylase inhibitor, which increases gene transcription of a number of genes, and also exerts neuroprotective effects. In this study, we report that administration of 4-PBA reversed spatial learning and memory deficits in an established mouse model of Alzheimers disease (AD) without altering β-amyloid burden. We also observed that the phosphorylated form of tau was decreased in the AD mouse brain after 4-PBA treatment, an effect probably due to an increase in the inactive form of the glycogen synthase kinase 3β (GSK3β). Interestingly, we found a dramatic decrease in brain histone acetylation in the transgenic mice that may reflect an indirect transcriptional repression underlying memory impairment. The administration of 4-PBA restored brain histone acetylation levels and, as a most likely consequence, activated the transcription of synaptic plasticity markers such as the GluR1 subunit of the AMPA receptor, PSD95, and microtubule-associated protein-2. The results suggest that 4-PBA, a drug already approved for clinical use, may provide a novel approach for the treatment of AD.

Rosiglitazone rescues memory impairment in Alzheimer's transgenic mice: mechanisms involving a reduced amyloid and tau pathology.

Clinical studies suggest that agonists at peroxisome proliferator-activated receptor gamma (PPARγ) may exert beneficial effects in patients with mild-to-moderate Alzheimers disease (AD), but the mechanism for the potential therapeutic interest of this class of drugs has not yet been elucidated. Here, in mice overexpressing mutant human amyloid precursor protein, we found that chronic treatment with rosiglitazone, a high-affinity agonist at PPARγ, facilitated β-amyloid peptide (Aβ) clearance. Rosiglitazone not only reduced Aβ burden in the brain but, importantly, almost completely removed the abundant amyloid plaques observed in the hippocampus and entorhinal cortex of 13-month-old transgenic mice. In the hippocampus, neuropil threads containing phosphorylated tau, probably corresponding to dystrophic neurites, were also decreased by the drug. Rosiglitazone switched on the activated microglial phenotype, promoting its phagocytic ability, reducing the expression of proinflammatory markers and inducing factors for alternative differentiation. The decreased amyloid pathology may account for the reduction of p-tau-containing neuropil threads and for the rescue of impaired recognition and spatial memory in the transgenic mice. This study provides further insights into the mechanisms for the beneficial effect of rosiglitazone in AD patients.

Rosiglitazone reverses memory decline and hippocampal glucocorticoid receptor down-regulation in an Alzheimer's disease mouse model.

Clinical trials with rosiglitazone, a potent agonist at peroxisome proliferator-activated receptor gamma (PPARgamma) suggest an improvement of cognitive function in Alzheimers disease (AD) patients. The mechanisms mediating this potential beneficial effect remain to be fully elucidated. In mice overexpressing mutant human amyloid precursor protein (hAPP), a model of AD, we found that memory impairment in the object recognition test was prevented and also reversed by chronic rosiglitazone treatment. Given the possible involvement of glucocorticoid receptors (GR) in the actions of PPARgamma-ligands, we studied the effect of chronic rosiglitazone treatment on GR levels in the hippocampus of hAPP mice. An early down-regulation of GR, not related to elevated plasma corticosterone levels, was found in different hippocampal subfields of the transgenic mice and this decrease was prevented by rosiglitazone. In parallel with behavioural studies, rosiglitazone also normalized GR levels in older animals. This effect may contribute to explain the attenuation of memory decline by PPARgamma activation in an AD mouse model.

Early Changes in Hippocampal Eph Receptors Precede the Onset of Memory Decline in Mouse Models of Alzheimer's Disease

Synapse loss occurs early in Alzheimers disease (AD) and is considered the best pathological correlate of cognitive decline. Ephrins and Eph receptors are involved in regulation of excitatory neurotransmission and play a role in cytoskeleton remodeling. We asked whether alterations in Eph receptors could underlie cognitive impairment in an AD mouse model overexpressing human amyloid-beta protein precursor (hA beta PP) with familial mutations (hA beta PP swe-ind mice). We found that EphA4 and EphB2 receptors were reduced in the hippocampus before the development of impaired object recognition and spatial memory. Similar results were obtained in another line of transgenic A beta PP mice, Tg2576. A reduction in Eph receptor levels was also found in postmortem hippocampal tissue from patients with incipient AD. At the time of onset of memory decline inhA beta PP swe-ind mice, no change in surface expression of AMPA or NMDA receptor subunits was apparent, but we found changes in Eph-receptor downstream signaling, in particular a decrease in membrane-associated phosho-cofilin levels that may cause cytoskeletal changes and disrupted synaptic activity. Consistent with this finding, Eph receptor activation in cell culture increased phosho-cofilin levels. The results suggest that alterations in Eph receptors may play a role in synaptic dysfunction in the hippocampus leading to cognitive impairment in a model of AD.

Suppression of angiogenesis and tumor growth by adenoviral-mediated gene transfer of pigment epithelium-derived factor.

Pigment epithelium-derived factor (PEDF) was identified from retinal pigment epithelial cells and has been shown to display neurotrophic effects. In addition it has been found to induce a potent inhibition of angiogenesis. In this study we have explored whether overexpression of PEDF by a gene transfer approach can block tumor angiogenesis and reduce tumor growth. We found that cells infected with an adenovirus encoding PEDF under the control of the CMV promoter (AdPEDF) secreted PEDF protein into the medium that exhibited strong inhibitory effects on migration and tube formation of endothelial cells cultured in the presence of vascular endothelial growth factor. Moreover, the systemic administration of AdPEDF was able to inhibit angiogenesis in Matrigel assay in vivo, and treatment with this adenovirus of established hepatocellular carcinoma tumor in nude mice resulted in strong suppression of tumor growth. This anti-tumor effect could also be seen in a mouse lung carcinoma model by systemic administration of vector. In that model, treatment of tumor by intratumoral injection of AdPEDF also caused significant inhibition of tumor growth. The anti-tumor effect was related to a decrease in density of microvessels in tumors after treatment with AdPEDF. These data suggest that the antiangiogenic properties of PEDF can be exploited to inhibit the establishment of tumor neovasculature and reduce tumor growth.

Overexpression of wild-type human APP in mice causes cognitive deficits and pathological features unrelated to Aβ levels

Transgenic mice expressing mutant human amyloid precursor protein (APP) develop an age-dependent amyloid pathology and memory deficits, but no overt neuronal loss. Here, in mice overexpressing wild-type human APP (hAPP(wt)) we found an early memory impairment, particularly in the water maze and to a lesser extent in the object recognition task, but beta-amyloid peptide (Abeta(42)) was barely detectable in the hippocampus. In these mice, hAPP processing was basically non-amyloidogenic, with high levels of APP carboxy-terminal fragments, C83 and APP intracellular domain. A tau pathology with an early increase in the levels of phosphorylated tau in the hippocampus, a likely consequence of enhanced ERK1/2 activation, was also observed. Furthermore, these mice presented a loss of synapse-associated proteins: PSD95, AMPA and NMDA receptor subunits and phosphorylated CaMKII. Importantly, signs of neurodegeneration were found in the hippocampal CA1 subfield and in the entorhinal cortex that were associated to a marked loss of MAP2 immunoreactivity. Conversely, in mice expressing mutant hAPP, high levels of Abeta(42) were found in the hippocampus, but no signs of neurodegeneration were apparent. The results support the notion of Abeta-independent pathogenic pathways in Alzheimers disease.

Enhanced Expression of the Voltage-Dependent Anion Channel 1 (VDAC1) in Alzheimer's Disease Transgenic Mice: An Insight into the Pathogenic Effects of Amyloid-β

The mitochondrial voltage-dependent anion channel 1 (VDAC1) is involved in the release of apoptotic proteins with possible relevance in Alzheimers disease (AD) neuropathology. Through proteomic analysis followed by Western blotting and immunohistochemical techniques, we have found that VDAC1 is overexpressed in the hippocampus from amyloidogenic AD transgenic mice models. VDAC1 was also overexpressed in postmortem brain tissue from AD patients at an advanced stage of the disease. Interestingly, amyloid-β (Aβ) soluble oligomers were able to induce upregulation of VDAC1 in a human neuroblastoma cell line, further supporting a correlation between Aβ levels and VDAC1 expression. In hippocampal extracts from transgenic mice, a significant increase was observed in the levels of VDAC1 phosphorylated at an epitope that is susceptible to phosphorylation by glycogen synthase kinase-3β, whose activity was also increased. The levels of hexokinase I (HXKI), which interacts with VDAC1 and affects its function, were decreased in mitochondrial samples from AD models. Since phospho-VDAC and reduced HXKI levels favors a VDAC1 conformational state more prone to the release proapoptotic factors, regulation of the function of this channel may be a promising therapeutic approach to combat AD.

Accelerated aging of the GABAergic septohippocampal pathway and decreased hippocampal rhythms in a mouse model of Alzheimer's disease

Patients with Alzheimers disease (AD) display altered functioning of cortical networks, including altered patterns of synchronous activity and a serious deficit in cholinergic septohippocampal (SH) innervation. However, the mechanisms underlying these alterations and the implication of the GABAergic SH component in AD are largely unknown. In addition, the GABAergic septohippocampal pathway (SHP) is believed to regulate synchronous hippocampal activity by controlling the activity of interneurons. Here we show, using well‐characterized pathway tracing experiments, that innervation of the GABAergic SHP decreases during normal aging. Furthermore, in an AD mouse model (hAPPSw,Ind; J20 mice), the GABAergic SHP shows a dramatic and early onset of this decrease in 8‐mo‐old mice. This decline is not caused by neuronal loss, but by the reduced number and complexity of GABAergic SH axon terminals. Finally, we demonstrate that hippocampal θ and γ rhythm power spectra are markedly diminished in 8‐mo‐old behaving mice expressing mutated hAPP. In addition to the well‐known loss of cholinergic input to the hippocampus in AD, these data suggest that the altered patterns of synchronous activity seen in patients with AD could be caused by the loss of GABAergic SH axons, which modulate hippocampal network activities.—Rubio, S. E., Vega‐Flores, G., Martínez, A., Bosch, C., Pérez‐Mediavilla, A., del Río, J., Gruart, A., Delgado‐García, J. M., Soriano, E., Pascual, M. Accelerated aging of the GABAergic septohippocampal pathway and decreased hippocampal rhythms in a mouse model of Alzheimers disease. FASEB J. 26, 4458–4467 (2012). www.fasebj.org

Chronic mild stress in mice promotes cognitive impairment and CDK5-dependent tau hyperphosphorylation.

This study was undertaken to know whether cognition deficits produced by chronic mild stress (CMS) were associated with pathological markers of Alzheimers disease (AD). The results show that the impairment in the Morris water maze test induced by CMS correlated with an increase in CDK5-dependent phospho-tau levels and with an increase in APP processing. Mice exposed to CMS may then constitute a non-transgenic model for sporadic forms of AD.

GPR40 activation leads to CREB and ERK phosphorylation in primary cultures of neurons from the mouse CNS and in human neuroblastoma cells

GPR40, the free fatty acid receptor 1, is expressed strongly in the primate pancreas and brain. While the role of pancreatic GPR40 in glucose homeostasis has been extensively studied, the absence of this G‐protein‐coupled receptor from the brain of rodents has hampered studies into its role in the central nervous system. However, we found intense GPR40 mRNA expression by in situ hybridization in mouse hippocampal and motor cortex neurons. Furthermore, in a neuroblastoma cell GPR40 was activated by docosahexaenoic acid and selective agonists, yet not by palmitic acid. Significantly, the activation of GPR40 provoked the phosphorylation of the cAMP response element‐binding protein, CREB. The receptor was also functional in primary cultures of murine neurons, in which its activation by a selective agonist produced the phosphorylation of CREB and of extracellular signal‐regulated kinases, ERK1/2. These results suggest that mice represent a suitable model for elucidating the role of GPR40 in brain function.