Thierry Oster

Ciliary Neurotrophic Factor Cell-Based Delivery Prevents Synaptic Impairment and Improves Memory in Mouse Models of Alzheimer's Disease

The development of novel therapeutic strategies for Alzheimers disease (AD) represents one of the biggest unmet medical needs today. Application of neurotrophic factors able to modulate neuronal survival and synaptic connectivity is a promising therapeutic approach for AD. We aimed to determine whether the loco-regional delivery of ciliary neurotrophic factor (CNTF) could prevent amyloid-β (Aβ) oligomer-induced synaptic damages and associated cognitive impairments that typify AD. To ensure long-term administration of CNTF in the brain, we used recombinant cells secreting CNTF encapsulated in alginate polymers. The implantation of these bioreactors in the brain of Aβ oligomer-infused mice led to a continuous secretion of recombinant CNTF and was associated with the robust improvement of cognitive performances. Most importantly, CNTF led to full recovery of cognitive functions associated with the stabilization of synaptic protein levels in the Tg2576 AD mouse model. In vitro as well as in vivo, CNTF activated a Janus kinase/signal transducer and activator of transcription-mediated survival pathway that prevented synaptic and neuronal degeneration. These preclinical studies suggest that CNTF and/or CNTF receptor-associated pathways may have AD-modifying activity through protection against progressive Aβ-related memory deficits. Our data also encourage additional exploration of ex vivo gene transfer for the prevention and/or treatment of AD.

Docosahexaenoic acid and synaptic protection in Alzheimer's disease mice

Alzheimers disease (AD) is a major public health concern due to longer life expectancy in the Western countries. Amyloid-beta (Abeta) oligomers are considered the proximate effectors in the early stages of AD. AD-related cognitive impairment, synaptic loss and neurodegeneration result from interactions of Abeta oligomers with the synaptic membrane and subsequent activation of pro-apoptotic signalling pathways. Therefore, membrane structure and lipid status appear determinant in Abeta-induced toxicity. Numerous epidemiological studies have highlighted the beneficial influence of docosahexaenoic acid (DHA, C22:6 n-3) on the preservation of synaptic function and memory capacities in aged individuals or upon Abeta exposure, whereas its deficiency is presented as a risk factor for AD. An elevated number of studies have been reporting the beneficial effects of dietary DHA supplementation on cognition and synaptic integrity in various AD models. In this review, we describe the important potential of DHA to preserve neuronal and brain functions and classified its numerous molecular and cellular effects from impact on membrane lipid content and organisation to activation of signalling pathways sustaining synaptic function and neuronal survival. DHA appears as one of the most valuable diet ingredients whose neuroprotective properties could be crucial for designing nutrition-based strategies able to prevent AD as well as other lipid- and age-related diseases whose prevalence is progressing in elderly populations.

The essential role of lipids in Alzheimer's disease.

In the absence of efficient diagnostic and therapeutic tools, Alzheimers disease (AD) is a major public health concern due to longer life expectancy in the Western countries. Although the precise cause of AD is still unknown, soluble beta-amyloid (Abeta) oligomers are considered the proximate effectors of the synaptic injury and neuronal death occurring in the early stages of AD. Abeta oligomers may directly interact with the synaptic membrane, leading to impairment of synaptic functions and subsequent signalling pathways triggering neurodegeneration. Therefore, membrane structure and lipid status should be considered determinant factors in Abeta-oligomer-induced synaptic and cell injuries, and therefore AD progression. Numerous epidemiological studies have highlighted close relationships between AD incidence and dietary patterns. Among the nutritional factors involved, lipids significantly influence AD pathogenesis. It is likely that maintenance of adequate membrane lipid content could prevent the production of Abeta peptide as well as its deleterious effects upon its interaction with synaptic membrane, thereby protecting neurons from Abeta-induced neurodegeneration. As major constituents of neuronal lipids, n-3 polyunsaturated fatty acids are of particular interest in the prevention of AD valuable diet ingredients whose neuroprotective properties could be essential for designing preventive nutrition-based strategies. In this review, we discuss the functional relevance of neuronal membrane features with respect to susceptibility to Abeta oligomers and AD pathogenesis, as well as the prospective capacities of lipids to prevent or to delay the disease.

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

Soluble beta-amyloid (Aβ) oligomers are considered to putatively play a critical role in the early synapse loss and cognitive impairment observed in Alzheimers disease. We previously demonstrated that Aβ 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 Aβ oligomers in wild type mice. We further demonstrated that the Aβ 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 Aβ 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 Aβ oligomer toxicity requires further investigation. These results therefore show that cPLA(2) plays a key role in the Aβ oligomer-associated neurodegeneration, and as such represents a potential therapeutic target for the treatment of Alzheimers disease.

Membrane raft domains and remodeling in aging brain.

Lipids are the fundamental structural components of biological membranes. For a long time considered as simple barriers segregating aqueous compartments, membranes are now viewed as dynamic interfaces providing a molecular environment favorable to the activity of membrane-associated proteins. Interestingly, variations in membrane lipid composition, whether quantitative or qualitative, play a crucial role in regulation of membrane protein functionalities. Indeed, a variety of alterations in brain lipid composition have been associated with the processes of normal and pathological aging. Although not establishing a direct cause-and-effect relationship between these complex modifications in cerebral membranes and the process of cognitive decline, evidence shows that alterations in membrane lipid composition affect important physicochemical properties notably impacting the lateral organization of membranes, and thus microdomains. It has been suggested that preservation of microdomain functionality may represent an effective strategy for preventing or decelerating neuronal dysfunction and cerebral vulnerability, processes that are both aggravated by aging. The working hypothesis developed in this review proposes that preservation of membrane organization, for example, through nutritional supplementation of docosahexaenoic acid, could prevent disturbances in and preserve effective cerebral function.

Increased Susceptibility of Dyslipidemic LSR +/− Mice to Amyloid Stress is Associated with Changes in Cortical Cholesterol Levels

Alzheimers disease (AD) is a neurodegenerative disease that has been linked to changes in cholesterol metabolism. Neuronal cholesterol content significantly influences the pro-apoptotic effect of amyloid-β peptide42 (Aβ42), which plays a key role in AD development. We previously reported that aged mice with reduced expression of the lipolysis stimulated lipoprotein receptor (LSR+/-), demonstrate membrane cholesterol accumulation and decreased intracellular lipid droplets in several brain regions, suggesting a potential role of LSR in brain cholesterol distribution. We questioned if these changes rendered the LSR+/- mouse more susceptible to Aβ42-induced cognitive and biochemical changes. Results revealed that intracerebroventricular injection of oligomeric Aβ42 in male 15-month old LSR+/+ and LSR+/- mice led to impairment in learning and long-term memory and decreased cortical cholesterol content of both groups; these effects were significantly amplified in the Aβ42-injected LSR+/- group. Total latency of the Morris test was significantly and negatively correlated with cortical cholesterol content of the LSR+/- mice, but not of controls. Significantly lower cortical PSD95 and SNAP-25 levels were detected in Aβ42-injected LSR+/- mice as compared to Aβ42-injected LSR+/+ mice. In addition, 24S-hydroxy cholesterol metabolite levels were significantly higher in the cortex of LSR+/- mice. Taken together, these results suggest that changes in cortex cholesterol regulation as a result of the LSR+/- genotype were linked to increased susceptibility to amyloid stress, and we would therefore propose the aged LSR+/- mouse as a new model for understanding the link between modified cholesterol regulation as a risk factor for AD.

Enzymatic production of bioactive docosahexaenoic acid phenolic ester

Docosahexaenoic acid (DHA) is increasingly considered for its health benefits. However, its use as functional food ingredient is still limited by its instability. In this work, we developed an efficient and solvent-free bioprocess for the synthesis of a phenolic ester of DHA. A fed-batch process catalyzed by Candida antarctica lipase B was optimised, leading to the production of 440 g/L vanillyl ester (DHA-VE). Structural characterisation of the purified product indicated acylation of the primary OH group of vanillyl alcohol. DHA-VE exhibited a high radical scavenging activity in acellular systems. In vivo experiments showed increased DHA levels in erythrocytes and brain tissues of mice fed DHA-VE-supplemented diet. Moreover, in vitro neuroprotective properties of DHA-VE were demonstrated in rat primary neurons exposed to amyloid-β oligomers. In conclusion, DHA-VE synergized the main beneficial effects of two common natural biomolecules and therefore appears a promising functional ingredient for food applications.

Lactational exposure of mice to low levels of non-dioxin-like polychlorinated biphenyls increases susceptibility to neuronal stress at a mature age.

Lactational exposure to low levels of the sum of the six indicator polychlorinated biphenyls (Σ6 NDL-PCBs, 10ng/kg/day) is known to lead to persistent anxious behavior in young and adult offspring mice at postnatal days 40 and 160, respectively. At more advanced life stages, we evaluated the effects on the mouse brain of neuronal stress induced by the synaptotoxic amyloid-beta (Aβ) peptide. Perinatal exposure of lactating mice to Σ6 NDL-PCBs did not affect short-term memory performances of their offspring male mice aged 14 months as compared to control PCB-naive mice. However, following intracerebroventricular injection of soluble Aβ oligomers, significant impairments in long-term memory were detected in the mice that had been lactationally treated with Σ6 NDL-PCBs. In addition, immunoblot analyses of the synaptosomal fraction of hippocampal tissues from treated mice revealed a lower expression of the synaptic proteins synaptophysin and PSD-95. Though preliminary, our findings suggest for the first time that early exposure to low levels of NDL-PCBs induce late neuronal vulnerability to amyloid stress. Additional experiments are needed to confirm whether early environmental influences are involved in the etiology of brain aging and cognitive decline.

Inhibitory Action of Benzo[α]pyrene on Hepatic Lipoprotein Receptors In Vitro and on Liver Lipid Homeostasis in Mice

Background Dyslipidemia associated with obesity often manifests as increased plasma LDL and triglyceride-rich lipoprotein levels suggesting changes in hepatic lipoprotein receptor status. Persistent organic pollutants have been recently postulated to contribute to the obesity etiology by increasing adipogenesis, but little information is available on their potential effect on hepatic lipoprotein metabolism. Objective The objective of this study was to investigate the effect of the common environmental pollutant, benzo[α]pyrene (B[α]P) on two lipoprotein receptors, the LDL-receptor and the lipolysis-stimulated lipoprotein receptor (LSR) as well as the ATP-binding cassette transporter A1 (ABCA1) using cell and animal models. Results LSR, LDL-receptor as well as ABCA1 protein levels were significantly decreased by 26–48% in Hepa1-6 cells incubated (<2 h) in the presence of B[α]P (≤1 µM). Real-time PCR analysis and lactacystin studies revealed that this effect was due primarily to increased proteasome, and not lysosomal-mediated degradation rather than decreased transcription. Furthermore, ligand blots revealed that lipoproteins exposed to 1 or 5 µM B[α]P displayed markedly decreased (42–86%) binding to LSR or LDL-receptor. B[α]P-treated (0.5 mg/kg/48 h, i.p. 15 days) C57BL/6J mice displayed higher weight gain, associated with significant increases in plasma cholesterol, triglycerides, and liver cholesterol content, and decreased hepatic LDL-receptor and ABCA1 levels. Furthermore, correlational analysis revealed that B[α]P abolished the positive association observed in control mice between the LSR and LDL-receptor. Interestingly, levels of other proteins involved in liver cholesterol metabolism, ATP-binding cassette transporter G1 and scavenger receptor-BI, were decreased, while those of acyl-CoA:cholesterol acyltransferase 1 and 2 were increased in B[α]P-treated mice. Conclusions B[α]P demonstrates inhibitory action on LSR and LDL-R, as well as ABCA1, which we propose leads to modified lipid status in B[α]P-treated mice, thus providing new insight into mechanisms underlying the involvement of pollutants in the disruption of lipid homeostasis, potentially contributing to dyslipidemia associated with obesity.

Maintenance of membrane organization in the aging mouse brain as the determining factor for preventing receptor dysfunction and for improving response to anti-Alzheimer treatments

Although a major risk factor for Alzheimers disease (AD), the aging parameter is not systematically considered in preclinical validation of anti-AD drugs. To explore how aging affects neuronal reactivity to anti-AD agents, the ciliary neurotrophic factor (CNTF)-associated pathway was chosen as a model. Comparison of the neuroprotective properties of CNTF in 6- and 18-month old mice revealed that CNTF resistance in the older animals is associated with the exclusion of the CNTF-receptor subunits from rafts and their subsequent dispersion to non-raft cortical membrane domains. This age-dependent membrane remodeling prevented both the formation of active CNTF-receptor complexes and the activation of prosurvival STAT3 and ERK1/2 pathways, demonstrating that age-altered membranes impaired the reactivity of potential therapeutic targets. CNTF-receptor distribution and CNTF signaling responses were improved in older mice receiving dietary docosahexaenoic acid, with CNTF-receptor functionality being similar to those of younger mice, pointing toward dietary intervention as a promising adjuvant strategy to maintain functional neuronal membranes, thus allowing the associated receptors to respond appropriately to anti-AD agents.