Modelling the amyloid cascade hypothesis and prion-like propagation of Tau-pathology in vivo, as tools for therapeutic target identification and validation

Alzheimer’s disease (AD) is the most predominant form of dementia. The amyloid cascade hypothesis remains the predominant hypothesis for the pathogenetic process and main framework for disease modifying treatments. Within the amyloid cascade hypothesis, Aβ-induced Tau-pathology is considered a key initiating event of the disease process, yet remains mechanistically unresolved. In AD, the progression of Tau-pathology occurs in a very characteristic way, which strongly correlates with the progression of the AD symptoms, therefore it is used for disease staging. Recently, prion-like propagation of Tau-pathology has been proposed as a compelling mechanism underlying this stereotypic progression along functional neuronal networks. Understanding and interfering with Aβ-induced Tau-alterations and with the subsequent propagation of Tau-pathology represent important goals for therapeutic design to interfere with AD development and progression. This thesis focuses on the generation of animal models which robustly recapitulate the amyloid cascade hypothesis, the amyloid-induced Tau-pathology and the prion-like propagation of Tau-pathology, and on the analysis of the molecular mechanisms and the functional repercussions of these processes in vivo.(BIFA - Sciences biomédicales et pharmaceutiques) -- UCL, 201

Models of β-amyloid induced Tau-pathology: the long and "folded" road to understand the mechanism

The amyloid cascade hypothesis has been the prevailing hypothesis in Alzheimer's Disease research, although the final and most wanted proof i.e. fully successful anti-amyloid clinical trials in patients, is still lacking. This may require a better in depth understanding of the cascade. Particularly, the exact toxic forms of Aβ and Tau, the molecular link between them and their respective contributions to the disease process need to be identified in detail. Although the lack of final proof has raised substantial criticism on the hypothesis per se, accumulating experimental evidence in in vitro models, in vivo models and from biomarkers analysis in patients supports the amyloid cascade and particularly Aβ-induced Tau-pathology, which is the focus of this review. We here discuss available models that recapitulate Aβ-induced Tau-pathology and review some potential underlying mechanisms. The availability and diversity of these models that mimic the amyloid cascade partially or more complete, provide tools to study remaining questions, which are crucial for development of therapeutic strategies for Alzheimer's Disease

Impaired recognition memory and emotional reactivity associated with loss of cortical integrity in rats after chronic exposure to aluminum

Although the neurotoxic effects of aluminum (Al) have been extensively investigated, with a particular emphasis on the contribution of this metal to several neurodegenerative conditions such as Alzheimer’s disease, there are few studies on behavioral impairments associated with Al exposure. This lack of data is even more provocative since recent researches have shown that Al induces significant cerebrovascular alterations in cortical architectures. We have investigated possible behavioral impairments of spatial recognition memory and emotional reactivity on rats that were chronically exposed to Al. Concurently, we have studied cytoarchitectural integrity of isocortex, hippocampus and entorhinal cortex, and striatopallidal structures on brain sections stained with the Bielchowsky silver stain method. Our results indicated spatial recognition memory deficits that were significantly represented on spontaneous alternation task performances, but less obvious on Morris water maze task performances of experimental animals, suggesting differences in the sensitivity of these two spatial memory paradigms. We also observed emotional reactivity patterns of modifications on male and female rats exposed to Al. This sexsegregated difference was not completely surprising since estrogens could have neuroprotective effects on adult female rats exposed to Al, although this specific hormonal modulation remains to be tested. These behavioral modifications were associated with massive cellular depletion in frontal isocortex, hippocampus and entorhinal cortex, but relatively spared striatopallidal structures. We concluded that Al primarily induces the structural alteration and functional isolation of the hippocampus, correlated with behavioral deficits on hippocampal-dependent tasks

Role of the membranair GxxxG motifs in the oligomerization and toxicity of the beta-amyloid peptide

Alzheimer’s disease is a neurodegenerative disease that causes progressive loss of cognitive functions, leading the patient to dementia. Two types of lesions appear in the brain: neurofibrillary tangles and senile plaques. These are composed mainly of β-amyloid peptide (Aβ) that derives from a precursor, the Amyloid Precursor Protein (APP). Aβ exists under different forms: monomeric, oligomeric or fibrillar. Recent datas indicate that the oligomeric form of Aβ induces neurodegeneration and a loss of neuronal functions. The aim of the project is to study the mechanisms involved in Aβ oligomers’ formation and their toxic properties. APP possesses particular motifs in its membrane-anchored Aβ sequence: GxxxG and GxxxG-like motifs. These motifs are involved in the dimerization of membrane helices. Detailed analysis of this region and our recent work indicate that these two patterns (GxxxG and GxxxA) would control the formation of oligomeric Aβ in membranes. We are actually studying the mechanisms underlying the formation of these oligomers by a site-directed mutagenesis approach. Expression of those mutants in CHO cells revealed that some of them displayed dramatic changes in the Aβ oligomerization profile. We are also analyzing their localization in the cell and their toxic properties in vitro and in vivo by injecting mice brains with AAVs

In vivo imaging of neuronal circuit's dynamics in the mouse tauopathy model

OBJECTIVES In Alzheimer's brains, neurofibrilary tangles (NFTs) and tau pathology spread in stereotypical manner. Recent studies demonstrated that similar spreading pattern could be reproduced in animal models by injecting tau fibrils in specific brain areas where they serve as seeds for aggregation of endogenous tau. It is not fully clear what are the effects of tau pathology spreading on neuronal activity and functioning. In present study we address this question using two-photon in vivo imaging in tau seeding mouse model. METHODS We are able to induce NFTs formation by injecting recombinant tau fibrils in cortex of P301S transgenic mice. To study neuronal activity and neuronal circuit's dynamics we have established an approach which combines two-photon calcium imaging through cranial window with imaging in awake, head-fixed mice. In that way, we follow same neuronal populations over prolonged periods of time. Furthermore, by applying FSB, a dye which labels NFTs, we can directly visualize NFTs formation and spreading in vivo. RESULTS Our results suggest that formation of NFTs takes place in first two weeks after tau fibrils injection in cortex of P301S mice. NFTs could be detected throughout all cortical layers. Using in vivo two-photon calcium imaging we can reliably record activity from layer 2/3 neurons for more than 2 months after seeding. CONCLUSIONS In conclusion, our method enables in vivo investigation of tau pathology effects on neuronal functioning. Identifying and preventing early tau pathology induced changes in neuronal functioning could be potential therapy strategy for Alzheimer's disease and other tauopathies

Activation of cholesterol turnover as a pharmacological approach to increase neuronal activity in Alzheimer's disease

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In vitro hepatic differentiation of human bone marrow mesenchymal stem cells under differential exposure to liver-specific factors.

Recent findings demonstrated that stem cells could be harvested from a patient and used to repair his or her own damaged liver. Additionally, stem cells may be manipulated in vitro to induce hepatic differentiation. The current study aims to determine the differentiation efficacy of various liver-specific factors (hepatocyte growth factor, Insulin-Transferrin-Selenium, dexamethasone, and nicotinamide) used for stem cell differentiation into hepatocyte-like cells. Human mesenchymal stem cells were exposed to different media containing these compounds added individually or in various combinations. Hepatic differentiation was assessed via quantitative reverse transcription-polymerase chain reaction and immunocytochemical staining for stemness or liver-specific genes and proteins, including albumin, cytokeratins 18 and 19, HepPar-1, alpha-fetoprotein, and nestin. In addition, functional tests for glycogen storage, urea production, glucose, and albumin synthesis were also performed. The expression profiles of albumin, alpha-fetoprotein, and cytokeratin 19 demonstrated that when hepatocyte growth factor, nicotinamide, or dexamethasone were added individually, incomplete hepatocyte differentiation was achieved; the obtained cell populations contained progenitors that expressed both hepatic (albumin) and biliary (cytokeratin 19) markers, as well as alpha-fetoprotein. Hepatocyte growth factor and nicotinamide were the factors with the most hepatogenic potential. When all factors were added to the culture, cells exhibited features that closely resembled human adult hepatocytes as determined by their gene expression patterns (albumin, HepPar-1, and alpha-fetoprotein, but not cytokeratin 19) and functional testing. These cells with hepatic function may become important tools for liver transplant procedures, liver development studies, and pharmacologic research