Céline Morissette

Targeting soluble Aβ peptide with Tramiprosate for the treatment of brain amyloidosis

Amyloid beta-peptide (Abeta) is a major constituent of senile plaques in Alzheimers disease (AD). Neurotoxicity results from the conformational transition of Abeta from random-coil to beta-sheet and its oligomerization. Among a series of ionic compounds able to interact with soluble Abeta, Tramiprosate (3-amino-1-propanesulfonic acid; 3APS; Alzhemedtrade mark) was found to maintain Abeta in a non-fibrillar form, to decrease Abeta(42)-induced cell death in neuronal cell cultures, and to inhibit amyloid deposition. Tramiprosate crosses the murine blood-brain barrier (BBB) to exert its activity. Treatment of TgCRND8 mice with Tramiprosate resulted in significant reduction (approximately 30%) in the brain amyloid plaque load and a significant decrease in the cerebral levels of soluble and insoluble Abeta(40) and Abeta(42) (approximately 20-30%). A dose-dependent reduction (up to 60%) of plasma Abeta levels was also observed, suggesting that Tramiprosate influences the central pool of Abeta, changing either its efflux or its metabolism in the brain. We propose that Tramiprosate, which targets soluble Abeta, represents a new and promising therapeutic class of drugs for the treatment of AD.

Mouse syngenic in vitro blood-brain barrier model: a new tool to examine inflammatory events in cerebral endothelium

Although cerebral endothelium disturbance is commonly observed in central nervous system (CNS) inflammatory pathologies, neither the cause of this phenomenon nor the effective participation of blood–brain barrier (BBB) in such diseases are well established. Observations were mostly made in vivo using mouse models of chronic inflammation. This paper presents a new mouse in vitro model suitable for the study of underlying mechanistic events touching BBB functions during CNS inflammatory disturbances. This model consists of a coculture with both primary cell types isolated from mice. Mouse brain capillary endothelial cell (MBCEC)s coming from brain capillaries are in culture with their in vivo partners and form differentiated monolayers that retain endothelial markers and numerous phenotypic properties of in vivo cerebral endothelium, such as: (1) peripheral distribution of tight junction proteins (occludin, claudin-5, claudin-3 and JAM-1); (2) high trans-endothelium electrical resistance value; (3) attenuated paracellular flux of sucrose and inulin; (4) P-gp expression; (5) no MECA-32 expression. Furthermore, this endothelium expresses cell adhesion molecules described in vivo and shows intracellular cell adhesion molecule-1 and vascular cell adhesion molecule-1 upregulation under lipopolysaccharide-treatment. Therefore, this well-differentiated model using autologous cells appears as a suitable support to reconstitute pathological in vitro BBB model.

Inflammation occurs early during the Aβ deposition process in TgCRND8 mice

Alzheimers disease (AD) is characterized by a progressive cognitive decline leading to dementia and involves the deposition of amyloid-beta (Abeta) peptides into senile plaques. Other neuropathological features that accompany progression of the disease include a decrease in synaptic density, neurofibrillary tangles, dystrophic neurites, inflammation, and neuronal cell loss. In this study, we report the early kinetics of brain amyloid deposition and its associated inflammation in an early onset transgenic mouse model of AD (TgCRND8) harboring the human amyloid precursor protein gene with the Indiana and Swedish mutations. Both diffuse and compact plaques were detected as early as 9-10 weeks of age. Abeta-immunoreactive (Abeta-IR) plaques (4G8-positive) appeared first in the neocortex and amygdala, then in the hippocampal formation, and lastly in the thalamus. Compact plaques (ThioS-positive) with an amyloid core were observed as early as diffuse plaques were detected, but in lower numbers. Amyloid deposition increased progressively with age. The formation of plaques was concurrent with the appearance of activated microglial cells and shortly followed by the clustering of activated astrocytes around plaques at 13-14 weeks of age. This TgCRND8 mouse model allows for a rapid, time-dependent study of the relationship between the fibrillogenic process and the inflammatory response during the brain amyloidogenic process.

The cAMP-specific phosphodiesterase 4B mediates Aβ-induced microglial activation

Microglial activation is a key player in the degenerative process that accompanies the deposition of amyloid-beta (Abeta) peptide into senile plaques in Alzheimers disease (AD) patients. The goal of this study is to identify novel genes involved in microglial activation in response to Abeta peptide. Prompted by the fact that soluble Abeta(1-42) (sAbeta(1-42))-stimulated primary rat microglia produce more tumor necrosis factor-alpha (TNF-alpha) than fibrillar Abeta(1-42) (fAbeta(1-42))-stimulated microglia, we examined gene expression in these cells following stimulation using cDNA arrays. This analysis confirms the upregulation caused by both sAbeta(1-42) and fAbeta(1-42) of pro-inflammatory molecules such as TNF-alpha, interleukin-1beta and macrophage inflammatory protein-1alpha. In addition, other transcripts not previously described in the context of Abeta-induced microglial activation were identified. The modulation of some of these genes within microglial cells seems to be specific to sAbeta(1-42) as compared to fAbeta(1-42) suggesting that different forms of Abeta may activate distinct pathways during the progression of AD. Importantly, we demonstrate that Pde4B, a cAMP-specific phosphodiesterase, is upregulated by Abeta and results in an increased production of TNF-alpha. Inhibition of Pde4B reduces by up to 70% the release of TNF-alpha from sAbeta-stimulated microglial cells, implicating cAMP as an important mediator of Abeta-induced microglial activation.

Genetic and physical mapping of the mouse host resistance locus Lgn1

lDepartment of Biochemistry, McGill University, Montreal, Canada, H3G-1Y6 2Department of Genetics, Faculty of Veterinary Medicine, University of Liege, 4000 Liege, Belgium 3Genetique Medicale, Hopital Salnte-Justine, Montreal, Quebec, Canada, H3T-1C5 4Center for the Study of Host Resistance, Montreal General Hospital, Montreal, Canada, H3G 1A4 5Department of Microbiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu, 807 Japan

Proteoglycans and Amyloidogenic Proteins in Peripheral Amyloidosis

Amyloidogenic proteins have the characteristic of adopting a β-sheet conformation and assembling into fibrils. Although similar in fibrillar appearance, each type of peripheral amyloid deposits differs in the nature of the amyloidogenic protein forming fibrils. Other elements, known as the common structural elements of the amyloid deposits, also contribute to amyloidogenic process in vivo. Among these elements, heparan sulfate proteoglycans (HSPGs) have been shown to bind to different types of amyloidogenic proteins and to promote the formation of β-sheet secondary structure. Once fibrils are formed, HSPGs protect the fibrils from proteolytic degradation, which lead to the accumulation of the deposits in the targeted organs. Understanding the regulation of protein folding by proteoglycans can lead to the development of low molecular weight compounds, which bind to the amyloidogenic proteins prior to their organization as fibrils. Such binding would interfere with the natural association of amyloidogenic protein with HSPGs and maintain the amyloid protein in a non-fibrillar structure (either random coil or a mix of α-helix and β-sheet structure). It would also favor their clearance, and thereby inhibit or completely block the formation of amyloid deposits. Since HSPGs interact with several types of amyloidogenic proteins, such an approach may be beneficial for the treatment of systemic and localized types of amyloidosis.

Differences in the amyloid-β-induced inflammatory response in microglia from C57BL/6 and A/J strains of mice

The microglial inflammatory response to Abeta(1-42) stimulation with or without IFN-gamma priming was investigated in low and high responder strains of mice, A/J and C57BL/6, respectively. A/J microglia showed moderate morphological changes upon stimulation with IFN-gamma alone or with Abeta(1-42). Conversely, C57BL/6 microglia showed major changes in their cellular morphology, which were accompanied by a decrease in NO release and a marked increase in TNF-alpha production. These results indicate that the magnitude of the microglial inflammatory response to Abeta is strongly influenced by genetic factors. Individual differences in the regulation of the microglial response may be a key player in the rate of development of the neuropathology of AD.