Manuel Torres

Inflammatory Response in the Hippocampus of PS1M146L/APP751SL Mouse Model of Alzheimer's Disease: Age-Dependent Switch in the Microglial Phenotype from Alternative to Classic

Although the microglial activation is concomitant to the Alzheimers disease, its precise role (neuroprotection vs neurodegeneration) has not yet been resolved. Here, we show the existence of an age-dependent phenotypic change of microglial activation in the hippocampus of PS1xAPP model, from an alternative activation state with Aβ phagocytic capabilities (at 6 months) to a classic cytotoxic phenotype (expressing TNF-α and related factors) at 18 months of age. This switch was coincident with high levels of soluble Aβ oligomers and a significant pyramidal neurodegeneration. In vitro assays, using astromicroglial cultures, demonstrated that oligomeric Aβ42 and soluble extracts from 18-month-old PS1xAPP hippocampus produced a potent TNF-α induction whereas monomeric Aβ42 and soluble extract from 6- or 18-month-old control and 6-month-old PS1xAPP hippocampi produced no stimulation. This stimulatory effect was avoided by immunodepletion using 6E10 or A11. In conclusion, our results show evidence of a switch in the activated microglia phenotype from alternative, at the beginning of Aβ pathology, to a classical at advanced stage of the disease in this model. This change was induced, at least in part, by the age-dependent accumulation of extracellular soluble Aβ oligomers. Finally, these cytotoxic activated microglial cells could participate in the neuronal lost observed in AD.

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

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.

Abnormal accumulation of autophagic vesicles correlates with axonal and synaptic pathology in young Alzheimer’s mice hippocampus

Dystrophic neurites associated with amyloid plaques precede neuronal death and manifest early in Alzheimer’s disease (AD). In this work we have characterized the plaque-associated neuritic pathology in the hippocampus of young (4- to 6-month-old) PS1M146L/APP751SL mice model, as the initial degenerative process underlying functional disturbance prior to neuronal loss. Neuritic plaques accounted for almost all fibrillar deposits and an axonal origin of the dystrophies was demonstrated. The early induction of autophagy pathology was evidenced by increased protein levels of the autophagosome marker LC3 that was localized in the axonal dystrophies, and by electron microscopic identification of numerous autophagic vesicles filling and causing the axonal swellings. Early neuritic cytoskeletal defects determined by the presence of phosphorylated tau (AT8-positive) and actin–cofilin rods along with decreased levels of kinesin-1 and dynein motor proteins could be responsible for this extensive vesicle accumulation within dystrophic neurites. Although microsomal Aβ oligomers were identified, the presence of A11-immunopositive Aβ plaques also suggested a direct role of plaque-associated Aβ oligomers in defective axonal transport and disease progression. Most importantly, presynaptic terminals morphologically disrupted by abnormal autophagic vesicle buildup were identified ultrastructurally and further supported by synaptosome isolation. Finally, these early abnormalities in axonal and presynaptic structures might represent the morphological substrate of hippocampal dysfunction preceding synaptic and neuronal loss and could significantly contribute to AD pathology in the preclinical stages.

Calretinin Interneurons are Early Targets of Extracellular Amyloid-β Pathology in PS1/AβPP Alzheimer Mice Hippocampus

Specific neuronal networks are preferentially affected in the early stages of Alzheimers 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.

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

BackgroundAxonal 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.ResultsOur 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.ConclusionA 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.

Age‐related increase in the immunoproteasome content in rat hippocampus: molecular and functional aspects

Alterations in the proteasome activity in the CNS have been described during aging. However, a detailed study of all proteasome subunits is actually lacking. We have analyzed, in vivo, the age‐related modifications in the molecular composition of hippocampal proteasomes. We found that the immunoproteasome/proteasome ratio was increased in aged hippocampus. The processing of the low‐molecular‐mass protein (LMP)7/β5i subunit, practically absent in young hippocampus, was increased in aged animals. Among the potential factors underlying these modifications we evaluated the neuroinflammation and the transcription factor Zif268. Lipopolysaccharide (LPS)‐induced neuroinflammation in young rats, up‐regulated the expression of immunoproteasome subunits and increased the processing of the LMP7/β5i protein. Moreover, the hydrophobicity of cellular peptides, analyzed by liquid chromatography, increased in both, young LPS‐injected animals and aged rats, suggesting that immunoproteasomes including the LMP7/β5i subunit could, at least in part, account for this modification. Also, the mRNA expression of the transcription factor Zif268, which down‐regulates the immunoproteasome subunit LMP7/β5i by binding to sequences within the promoter regions, was decreased in both, aged hippocampus and young LPS‐injected animals. Finally, we found that spatial memory training in young animals, a situation in which the expression of Zif268 is increased, modified the mRNA expression of the constitutive and catalytic subunits in an opposite manner. Based on present data, we propose that the age‐related increases in the content of hippocampal immunoproteasome is mostly because of neuroinflammatory processes associated to aging.

Membrane lipid modifications and therapeutic effects mediated by hydroxydocosahexaenoic acid on Alzheimer's disease.

Alzheimers disease (AD) is a neurodegenerative pathology with relevant unmet therapeutic needs. Both natural aging and AD have been associated with a significant decline in the omega-3 polyunsaturated fatty acid docosahexaenoic acid (DHA), and accordingly, administration of DHA has been proposed as a possible treatment for this pathology. However, recent clinical trials in mild-to-moderately affected patients have been inconclusive regarding the real efficacy of DHA in halting this disease. Here, we show that the novel hydroxyl-derivative of DHA (2-hydroxydocosahexaenoic acid - OHDHA) has a strong therapeutic potential to treat AD. We demonstrate that OHDHA administration increases DHA levels in the brain of a transgenic mouse model of AD (5xFAD), as well as those of phosphatidylethanolamine (PE) species that carry long polyunsaturated fatty acids (PUFAs). In 5xFAD mice, administration of OHDHA induced lipid modifications that were paralleled with a reduction in amyloid-β (Αβ) accumulation and full recovery of cognitive scores. OHDHA administration also reduced Aβ levels in cellular models of AD, in association with alterations in the subcellular distribution of secretases and reduced Aβ-induced tau protein phosphorylation as well. Furthermore, OHDHA enhanced the survival of neuron-like differentiated cells exposed to different insults, such as oligomeric Aβ and NMDA-mediated neurotoxicity. These results were supported by model membrane studies in which incorporation of OHDHA into lipid-raft-like vesicles was shown to reduce the binding affinity of oligomeric and fibrillar Aβ to membranes. Finally, the OHDHA concentrations used here did not produce relevant toxicity in zebrafish embryos in vivo. In conclusion, we demonstrate the pleitropic effects of OHDHA that might prove beneficial to treat AD, which suggests that an upstream event, probably the modulation of the membrane lipid composition and structure, influences cellular homeostasis reversing the neurodegenerative process. This Article is Part of a Special Issue Entitled: Membrane Structure and Function: Relevance in the Cells Physiology, Pathology and Therapy.

Cognitive recovery and restoration of cell proliferation in the dentate gyrus in the 5XFAD transgenic mice model of Alzheimer's disease following 2-hydroxy-DHA treatment

Alzheimer’s disease (AD) is the most common neurodegenerative disorder in the elderly. In the last years, abnormalities of lipid metabolism and in particular of docosahexaenoic acid (DHA) have been recently linked with the development of the disease. According to the recent studies showing how hydroxylation of fatty acids enhances their biological activity, here we show that chronic treatment with a hydroxylated derivative of DHA, the 2-hydroxy-DHA (2OHDHA) in the 5XFAD transgenic mice model of AD improves performance in the radial arm maze test and restores cell proliferation in the dentate gyrus, with no changes in the presence of beta amyloid (Aβ) plaques. These results suggest that 2OHDHA induced restoration of cell proliferation can be regarded as a major component in memory recovery that is independent of Aβ load thus, setting the starting point for the development of a new drug for the treatment of AD.

Activity-Dependent Neuroprotective Protein (ADNP) Expression in the Amyloid Precursor Protein/Presenilin 1 Mouse Model of Alzheimer's Disease

A major determinant in the pathogenesis of Alzheimer’s disease (AD) is the deposition of β-amyloid (Aβ) peptides in specific areas of the central nervous system. Therefore, animal models of Alzheimer amyloidosis are excellent tools to identify candidates to facilitate drug screening and to understand the molecular pathology of AD. Activity-dependent neuroprotective protein (ADNP) plays an essential role in brain development, and NAP (NAPVSIPQ, generic name: davunetide)—a peptide derived from ADNP—is currently in clinical development for the treatment of neurodegenerative disorders. However, the link between ADNP expression and AD remains unexplored. To test whether ADNP is affected by the onset of AD and progression, we employed the PS1xAPP mouse model (PS1M146Lu2009×u2009APP751SL transgenic mice) to analyze the mRNA expression of ADNP in the hippocampus and cerebellum in early and advanced stages of disease. Results showed that ADNP expression in 6-month-old PS1xAPP mice hippocampus was higher than in wild-type (WT) mice. ADNP was originally identified as a vasoactive intestinal peptide (VIP)-responsive gene taking part in the VIP-mediated neurotrophic pathway. Interestingly, the expression of VIP was not affected in the same experimental setting, suggesting that ADNP expression is a VIP-independent marker associated with AD. Moreover, in the cerebellum, a brain area not affected by Aβ deposition, ADNP mRNA expression in 6-month-old PS1xAPP and WT were not different. A similar extent of hippocampal ADNP expression was observed in 18-month-old WT and PS1xAPP mice, in contrast to the differential expression level at 6xa0months of age. However, hippocampal ADNP expression in both WT and PS1xAPP was increased with aging similar to VIP mRNA expression. Our findings support the hypothesis that ADNP expression is related to early or mild AD progression by a VIP-independent mechanism.

Extracellular Amyloid-β and Cytotoxic Glial Activation Induce Significant Entorhinal Neuron Loss in Young PS1M146L/APP751SL Mice

Here we demonstrated that extracellular, not intracellular, amyloid-beta (Abeta) and the associated cytotoxic glial neuroinflammatory response are major contributors to early neuronal loss in a PS1xAPP model. A significant loss of principal (27%) and SOM/NPY (56-46%) neurons was found in the entorhinal cortex at 6 months of age. Loss of principal cells occurred selectively in deep layers (primarily layer V) whereas SOM/NPY cell loss was evenly distributed along the cortical column. Neither layer V pyramidal neurons nor SOM/NPY interneurons displayed intracellular Abeta immunoreactivity, even after formic acid retrieval; thus, extracellular factors should be preferentially implicated in this selective neurodegeneration. Amyloid deposits were mainly concentrated in deep layers at 4-6 months, and of relevance was the existence of a potentially cytotoxic inflammatory response (TNFalpha, TRAIL, and iNOS mRNAs were upregulated). Moreover, non-plaque associated activated microglial cells and reactive astrocytes expressed TNFalpha and iNOS, respectively. At this age, in the hippocampus of same animals, extracellular Abeta induced a non-cytotoxic glial activation. The opposite glial activation, at the same chronological age, in entorhinal cortex and hippocampus strongly support different mechanisms of disease progression in these two regions highly affected by Abeta pathology.