Ana Ricobaraza

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.

Phenylbutyrate rescues dendritic spine loss associated with memory deficits in a mouse model of Alzheimer disease

Alzheimers disease (AD) and ageing are associated with impaired learning and memory, and recent findings point toward modulating chromatin remodeling through histone acetylation as a promising therapeutic strategy. Here we report that systemic administration of the HDAC inhibitor 4‐phenylbutyrate (PBA) reinstated fear learning in the Tg2576 mouse model of AD. Tg2576 mice develop age‐dependent amyloid pathology and cognitive decline that closely mimics disease progression in humans. Memory reinstatement by PBA was observed independently of the disease stage: both in 6‐month‐old Tg2576 mice, at the onset of the first symptoms, but also in aged, 12‐ to 16‐month‐old mice, when amyloid plaque deposition and major synaptic loss has occurred. Reversal of learning deficits was associated to a PBA‐induced clearance of intraneuronal Aβ accumulation, which was accompanied by mitigation of endoplasmic reticulum (ER) stress, and to restoration of dendritic spine densities of hippocampal CA1 pyramidal neurons to control levels. Furthermore, the expression of plasticity‐related proteins such as the NMDA receptor subunit NR2B and the synaptic scaffold SAP102 was significantly increased by PBA. Our data suggest that the beneficial effects of PBA in memory are mediated both via its chemical chaperone‐like activity and via the transcriptional activation of a cluster of proteins required for the induction of synaptic plasticity and structural remodeling.

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.

Sildenafil restores cognitive function without affecting β-amyloid burden in a mouse model of Alzheimer's disease.

BACKGROUND AND PURPOSE Inhibitors of phosphodiesterase 5 (PDE5) affect signalling pathways by elevating cGMP, which is a second messenger involved in processes of neuroplasticity. In the present study, the effects of the PDE5 inhibitor, sildenafil, on the pathological features of Alzheimers disease and on memory‐related behaviour were investigated.

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.

Sildenafil protects against 3-nitropropionic acid neurotoxicity through the modulation of calpain, CREB, and BDNF.

In this study we tested whether phosphodiesterase 5 (PDE5) inhibitors, sildenafil and vardenafil, would afford protection against 3-nitropropionic acid (3NP), which produces striatal lesions that closely mimic some of the neuropathological features of Huntingtons Disease (HD). The neurotoxin was given over 5 days by constant systemic infusion using osmotic minipumps. Animals treated with PDE5 inhibitors (sildenafil or vardenafil) showed improved neurologic scores, reduced the loss of striatal DARPP-32 protein levels and lesion volumes, and decreased calpain activation produced by 3NP. This protective effect was independent of changes in 3NP-induced succinate dehydrogenase inhibition. Furthermore, striatal p-CREB levels along with the expression of BDNF were significantly increased in sildenafil-treated rats. In summary, PDE5 inhibitors protected against 3NP-induced striatal degeneration by reducing calpain activation and by promoting survival pathways. These data encourage further evaluation of PDE5 inhibitors in transgenic mouse models of HD.

Phenylbutyrate is a Multifaceted Drug that Exerts Neuroprotective Effects and Reverses the Alzheimer´s Disease-like Phenotype of a Commonly Used Mouse Model

4-Phenylbutyrate (PBA) is a histone deacetylase (HDAC) inhibitor whose efficacy in the Tg2576 mouse model of Alzheimer´s disease (AD) is correlated with decreased tau phosphorylation, clearance of intraneuronal Aβ and restoration of dendritic spine density in hippocampal CA1 pyramidal neurons. PBA is also a chemical chaperone that facilitates cell proteostasis. To determine the relative contributions of HDAC inhibition and chaperone-like activity in the anti-AD effects of PBA, we compared the effect of PBA with that of sodium butyrate (NaBu), an HDAC inhibitor with no chaperone activity. In neuronal cultures from Tg2576 mice, we observed a correlation between histone 3 acetylation and decreased p-tau levels. Moreover, we observed a decrease in the processing of the amyloid precursor protein (APP) in Tg2576 neurons treated with PBA, but not with NaBu. In Tg2576 mice administered PBA or NaBu for 3 weeks, only PBA normalized the pathological AD markers, implicating, at least in part, other mechanism as the chaperone-like activity in the reversal of the AD-like phenotype of Tg2576 mice. Furthermore, treatment with PBA but not NaBu prevented the neuronal loss in the hippocampus of hAPPWT-overexpressing mice, as was particularly evident in the CA1 layer. In addition to its activity as a HDAC inhibitor, the chaperone activity of PBA appears to at least partially, mediate its reversal of the AD phenotype in Tg2576 mice and its neuroprotective effect in a model of hippocampal neuronal loss.

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.

Chronic mild stress accelerates the onset and progression of the Alzheimer's disease phenotype in Tg2576 mice.

The etiology of the more common (sporadic) forms of Alzheimers disease (AD) remains unknown, although age is the most important risk factor. Nevertheless, interactions between environmental risk factors and genetic background may also influence the onset and progression of sporadic AD. Chronic stress, associated with altered memory and other neurological processes, is thought to influence the pathogenesis of AD. Hence, we evaluated the effect of unpredictable and consecutive chronic mild stressors on the onset of an AD-related pathology in the Tg2576 mouse line that overexpresses the human amyloid-β protein precursor with the Swedish mutation (hAβPP(Swe)). Two months after exposure to chronic mild stress, 4 month-old animals that normally display no pathological features of AD, not only expressed pathological markers but also experienced cognitive dysfunction in the Morris water maze test. These findings suggest that chronic mild stress accelerates the onset of cognitive impairment and produces an increase in hippocampal amyloid-β and phospho-tau levels on a background of AD susceptibility.