P2X7-deficiency improves plasticity and cognitive abilities in a mouse model of Tauopathy.

Alzheimer's disease is the most common form of dementia characterized by intracellular aggregates of hyperphosphorylated Tau protein and extracellular accumulation of amyloid ß (Aß) peptides. We previously demonstrated that the purinergic receptor P2X7 (P2X7) plays a major role in Aß-mediated neurodegeneration but the relationship between P2X7 and Tau remained overlooked. Such a link was supported by cortical upregulation of P2X7 in patients with various type of frontotemporal lobar degeneration, including mutation in the Tau-coding gene, MAPT, as well as in the brain of a Tauopathy mouse model (THY-Tau22). Subsequent phenotype analysis of P2X7-deficient Tau mice revealed the instrumental impact of this purinergic receptor. Indeed, while P2X7-deficiency had a moderate effect on Tau pathology itself, we observed a significant reduction of microglia activation and of Tau-related inflammatory mediators, particularly CCL4. Importantly, P2X7 deletion ultimately rescued synaptic plasticity and memory impairments of Tau mice. Altogether, the present data support a contributory role of P2X7 dysregulation on processes governing Tau-induced brain anomalies. Due to the convergent role of P2X7 blockade in both Aß and Tau background, P2X7 inhibitors might prove to be ideal candidate drugs to curb the devastating cognitive decline in Alzheimer's disease and Tauopathies.

Effects of Chronic Masitinib Treatment in APPswe/PSEN1dE9 Transgenic Mice Modeling Alzheimer's Disease.

BACKGROUND: Masitinib is a selective tyrosine kinase inhibitor that modulates mast cells activity. A previous phase II study reported a cognitive effect of masitinib in patients with Alzheimer's disease. OBJECTIVE: We aimed to shed light on the mode of action of masitinib in Alzheimer's disease. METHODS/RESULTS: We demonstrated here that chronic oral treatment of APPswe/PSEN1dE9 transgenic mice modeling Alzheimer's disease restored normal spatial learning performance while having no impacts on amyloid-ß loads nor on neuroinflammation. However, masitinib promoted a recovery of synaptic markers. Complete genetic depletion of mast cells in APPswe/PSEN1dE9 mice similarly rescued synaptic impairments. CONCLUSION: These results underline that masitinib therapeutic efficacy might primarily be associated with a synapto-protective action in relation with mast cells inhibition.

Mechanisms Associated with Type 2 Diabetes as a Risk Factor for Alzheimer-Related Pathology.

Current evidence suggests dementia and pathology in Alzheimer's Disease (AD) are both dependent and independent of amyloid processing and can be induced by multiple 'hits' on vital neuronal functions. Type 2 diabetes (T2D) poses the most important risk factor for developing AD after ageing and dysfunctional IR/PI3K/Akt signalling is a major contributor in both diseases. We developed a model of T2D, coupling subdiabetogenic doses of streptozotocin (STZ) with a human junk food (HJF) diet to more closely mimic the human condition. Over 35 weeks, this induced classic signs of T2D (hyperglycemia and insulin dysfunction) and a modest, but stable deficit in spatial recognition memory, with very little long-term modification of proteins in or associated with IR/PI3K/Akt signalling in CA1 of the hippocampus. Intracerebroventricular infusion of soluble amyloid beta 42 (Aß42) to mimic the early preclinical rise in Aß alone induced a more severe, but short-lasting deficits in memory and deregulation of proteins. Infusion of Aß on the T2D phenotype exacerbated and prolonged the memory deficits over approximately 4 months, and induced more severe aberrant regulation of proteins associated with autophagy, inflammation and glucose uptake from the periphery. A mild form of environmental enrichment transiently rescued memory deficits and could reverse the regulation of some, but not all protein changes. Together, these data identify mechanisms by which T2D could create a modest dysfunctional neuronal milieu via multiple and parallel inputs that permits the development of pathological events identified in AD and memory deficits when Aß levels are transiently effective in the brain.

New role of P2X7 receptor in an Alzheimer's disease mouse model.

Extracellular aggregates of amyloid ß (Aß) peptides, which are characteristic of Alzheimer's disease (AD), act as an essential trigger for glial cell activation and the release of ATP, leading to the stimulation of purinergic receptors, especially the P2X7 receptor (P2X7R). However, the involvement of P2X7R in the development of AD is still ill-defined regarding the dual properties of this receptor. Particularly, P2X7R activates the NLRP3 inflammasome leading to the release of the pro-inflammatory cytokine, IL-1ß; however, P2X7R also induces cleavage of the amyloid precursor protein generating Aß peptides or the neuroprotective fragment sAPPα. We thus explored in detail the functions of P2X7R in AD transgenic mice. Here, we show that P2X7R deficiency reduced Aß lesions, rescued cognitive deficits and improved synaptic plasticity in AD mice. However, the lack of P2X7R did not significantly affect the release of IL-1ß or the levels of non-amyloidogenic fragment, sAPPα, in AD mice. Instead, our results show that P2X7R plays a critical role in Aß peptide-mediated release of chemokines, particularly CCL3, which is associated with pathogenic CD8+ T cell recruitment. In conclusion, our study highlights a novel detrimental function of P2X7R in chemokine release and supports the notion that P2X7R may be a promising therapeutic target for AD.

Evidence for altered dendritic spine compartmentalization in Alzheimer's disease and functional effects in a mouse model.

Alzheimer's disease (AD) is associated with a progressive loss of synapses and neurons. Studies in animal models indicate that morphological alterations of dendritic spines precede synapse loss, increasing the proportion of large and short ("stubby") spines. Whether similar alterations occur in human patients, and what their functional consequences could be, is not known. We analyzed biopsies from AD patients and APP x presenilin 1 knock-in mice that were previously shown to present a loss of pyramidal neurons in the CA1 area of the hippocampus. We observed that the proportion of stubby spines and the width of spine necks are inversely correlated with synapse density in frontal cortical biopsies from non-AD and AD patients. In mice, the reduction in the density of synapses in the stratum radiatum was preceded by an alteration of spine morphology, with a reduction of their length and an enlargement of their neck. Serial sectioning examined with electron microscopy allowed us to precisely measure spine parameters. Mathematical modeling indicated that the shortening and widening of the necks should alter the electrical compartmentalization of the spines, leading to reduced postsynaptic potentials in spine heads, but not in soma. Accordingly, there was no alteration in basal synaptic transmission, but long-term potentiation and spatial memory were impaired. These results indicate that an alteration of spine morphology could be involved in the early cognitive deficits associated with AD.

Camelid single-domain antibodies: A versatile tool for in vivo imaging of extracellular and intracellular brain targets.

Detection of intracerebral targets with imaging probes is challenging due to the non-permissive nature of blood-brain barrier (BBB). The present work describes two novel single-domain antibodies (VHHs or nanobodies) that specifically recognize extracellular amyloid deposits and intracellular tau neurofibrillary tangles, the two core lesions of Alzheimer's disease (AD). Following intravenous administration in transgenic mouse models of AD, in vivo real-time two-photon microscopy showed gradual extravasation of the VHHs across the BBB, diffusion in the parenchyma and labeling of amyloid deposits and neurofibrillary tangles. Our results demonstrate that VHHs can be used as specific BBB-permeable probes for both extracellular and intracellular brain targets and suggest new avenues for therapeutic and diagnostic applications in neurology.

Acute amnestic encephalopathy in amyloid-ß oligomer-injected mice is due to their widespread diffusion in vivo.

Amyloid-ß (Aß) oligomers are the suspected culprit as initiators of Alzheimer's disease (AD). However, their diffusion in the brain remains unknown. Here, we studied Aß oligomers' dissemination and evaluated their in vivo toxicity. Wild-type mice were injected with 50 pmol of synthetic Aß oligomers (of different size) in the hippocampus. Oligomers diffused largely in the brain as soon as 1 hour and up to 7 days after injection. A transient encephalopathy with memory impairment was induced by this unique injection. The immunoreactivity of the postsynaptic marker PSD95 was diffusely decreased. Similar results (both on memory and PSD95 immunoreactivity) were obtained with delipidated and high molecular weight oligomers (>50 kDa) but not with smaller assemblies. Tau hyperphosphorylation was observed in the oligomer-injected brains. Finally, fos immunostaining was increased in Aß-derived diffusible ligands-injected mice, suggesting neuronal hyperactivity. Rapid and widespread diffusion of Aß oligomers was demonstrated in vivo and associated with decreased synaptic markers and memory deficits which gives new insight to the pathogenicity of Aß.

Curcumin-conjugated nanoliposomes with high affinity for Aß deposits: possible applications to Alzheimer disease.

Accumulation of amyloid peptide (Aß) in senile plaques is a hallmark lesion of Alzheimer disease (AD). The design of molecules able to target the amyloid pathology in tissue is receiving increasing attention, both for diagnostic and for therapeutic purposes. Curcumin is a fluorescent molecule with high affinity for the Aß peptide but its low solubility limits its clinical use. Curcumin-conjugated nanoliposomes, with curcumin exposed at the surface, were designed. They appeared to be monodisperse and stable. They were non-toxic in vitro, down-regulated the secretion of amyloid peptide and partially prevented Aß-induced toxicity. They strongly labeled Aß deposits in post-mortem brain tissue of AD patients and APPxPS1 mice. Injection in the hippocampus and in the neocortex of these mice showed that curcumin-conjugated nanoliposomes were able to specifically stain the Aß deposits in vivo. Curcumin-conjugated nanoliposomes could find application in the diagnosis and targeted drug delivery in AD. FROM THE CLINICAL EDITOR: In this preclinical study, curcumin-conjugated nanoliposomes were investigated as possible diagnostics and targeted drug delivery system in Alzheimer's disease, demonstrating strong labeling of Aß deposits both in human tissue and in mice, and in vitro downregulation of amyloid peptide secretion and prevention of Aß-induced toxicity.

Critical role of cPLA2 in Aß oligomer-induced neurodegeneration and memory deficit.

Soluble beta-amyloid (Aß) oligomers are considered to putatively play a critical role in the early synapse loss and cognitive impairment observed in Alzheimer's disease. We previously demonstrated that Aß oligomers activate cytosolic phospholipase A(2) (cPLA(2)), which specifically releases arachidonic acid from membrane phospholipids. We here observed that cPLA(2) gene inactivation prevented the alterations of cognitive abilities and the reduction of hippocampal synaptic markers levels noticed upon a single intracerebroventricular injection of Aß oligomers in wild type mice. We further demonstrated that the Aß oligomer-induced sphingomyelinase activation was suppressed and that phosphorylation of Akt/protein kinase B (PKB) was preserved in neuronal cells isolated from cPLA(2)(-/-) mice. Interestingly, expression of the Aß precursor protein (APP) was reduced in hippocampus homogenates and neuronal cells from cPLA(2)(-/-) mice, but the relationship with the resistance of these mice to the Aß oligomer toxicity requires further investigation. These results therefore show that cPLA(2) plays a key role in the Aß oligomer-associated neurodegeneration, and as such represents a potential therapeutic target for the treatment of Alzheimer's disease.