Reversal of Object Recognition Memory Deficit in Perirhinal Cortex-Lesioned Rats and Primates and in Rodent Models of Aging and Alzheimer's Diseases.

The integrity of the perirhinal cortex (PRh) is essential for object recognition memory (ORM) function, and damage to this brain area in animals and humans induces irreversible ORM deficits. Here, we show that activation of area V2, a brain area interconnected with brain circuits of ventral stream and medial temporal lobe that sustain ORM, by expression of regulator of G-protein signaling 14 of 414 amino acids (RGS14414) restored ORM in memory-deficient PRh-lesioned rats and nonhuman primates. Furthermore, this treatment was sufficient for full recovery of ORM in rodent models of aging and Alzheimer's disease, conditions thought to affect multiple brain areas. Thus, RGS14414-mediated activation of area V2 has therapeutic relevance in the recovery of recognition memory, a type of memory that is primarily affected in patients or individuals with symptoms of memory dysfunction. These findings suggest that area V2 modulates the processing of memory-related information through activation of interconnected brain circuits formed by the participation of distinct brain areas.

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 (PPARgamma) may exert beneficial effects in patients with mild-to-moderate Alzheimer's 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 PPARgamma, facilitated beta-amyloid peptide (Abeta) clearance. Rosiglitazone not only reduced Abeta 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.

Early changes in hippocampal Eph receptors precede the onset of memory decline in mouse models of Alzheimer's disease.

Synapse loss occurs early in Alzheimer's 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.

Overexpression of wild-type human APP in mice causes cognitive deficits and pathological features unrelated to Abeta 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 Alzheimer's disease.

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 Alzheimer's 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.

Synthesis and biological properties of beta-turned Abeta(31-35) constrained analogues.

A series of constrained pentapeptide analogues of the fragment Abeta(31-35) has been prepared using solid phase synthesis protocols. The results of conformational studies and surface plasmon resonance (SPR) experiments seem to indicate that the affinity of these constrained analogues for immobilized Abeta(25-35) peptide could be related to their ability to adopt a Leu34N-Ile31O beta-turn-like folded conformation.