Marie-Claire Lanhers

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.

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.

The antitumor effects of an arsthinol–cyclodextrin complex in a heterotopic mouse model of glioma

In this paper, we examined arsthinol-cyclodextrin complexes, which display an anticancer activity. The association constants were 17,502±522 M(-1) for hydroxypropyl-β-cyclodextrin and 12,038±10,168 M(-1) for randomized methylated β-cyclodextrin. (1)H NMR experiments in solution also confirmed the formation of these complexes and demonstrated an insertion of the arsthinol (STB) with its dithiarsolane extremity into the wide rim of the hydroxypropyl-β-cyclodextrin cavity. Complexed arsthinol was more effective than arsenic trioxide (As2O3) and melarsoprol on the U87 MG cell line. Importantly, in the in vivo study, we observed significant antitumor activity against heterotopic xenografts after i.p. administration and did not see any signs of toxicity. This remains to be verified using an orthotopic model.

Lactoferrin and its hydrolysate bind directly to the oleate‐activated form of the lipolysis stimulated lipoprotein receptor

The hepatic removal of triglyceride‐rich chylomicrons during the postprandial phase represents an important step towards determining the bioavailability of dietary lipids amongst the peripheral tissues. Indeed, elevated postprandial lipemia is often associated with obesity and increased risk of coronary heart disease. The milk protein, lactoferrin, has been shown to inhibit hepatic chylomicron remnant removal by the liver, resulting in increased postprandial lipemia. Despite numerous studies on potential targets for lactoferrin, the molecular mechanisms underlying the effect of lactoferrin remain unclear. We recently demonstrated that the lipolysis stimulated lipoprotein receptor (LSR) contributes to the removal of triglyceride‐rich lipoproteins during the postprandial phase. Here, we report that while lactoferrin does not have any significant effect on LSR protein levels in mouse Hepa1–6 cells, this protein colocalizes with LSR in cells but only in the presence of oleate, which is needed to obtain LSR in its active form as lipoprotein receptor. Ligand blotting using purified LSR revealed that lactoferrin binds directly to the receptor in the presence of oleate and prevents the binding of triglyceride‐rich lipoproteins. Both C‐ and N‐lobes of lactoferrin as well as a mixture of peptides derived from its hydrolysis retained the ability to bind LSR in its active form. We propose then that the elevated postprandial lipemia observed upon lactoferrin treatment in vivo is mediated in part by its direct interaction with free fatty acid activated LSR, thus preventing clearance of chylomicrons and their remnants through the LSR pathway.

Improved Neuroprotection Provided by Drug Combination in Neurons Exposed to Cell-Derived Soluble Amyloid-β Peptide

Oligomeric amyloid-β (Aβ) peptide contributes to impaired synaptic connections and neurodegenerative processes, and as such, represents a primary therapeutic target for Alzheimers disease (AD)-modifying approaches. However, the lack of efficacy of drugs that inhibit production of Aβ demonstrates the need for a better characterization of its toxic effects, both on synaptic and neuronal function. Here, we used conditioned medium obtained from recombinant HEK-AβPP cells expressing the human amyloid-β protein precursor (Aβ-CM), to investigate Aβ-induced neurotoxic and synaptotoxic effects. Characterization of Aβ-CM revealed that it contained picomolar amounts of cell-secreted Aβ in its soluble form. Incubation of primary cortical neurons with Aβ-CM led to significant decreases in synaptic protein levels as compared to controls. This effect was no longer observed in neurons incubated with conditioned medium obtained from HEK-AβPP cells grown in presence of the γ-secretase inhibitor, Semagacestat or LY450139 (LY-CM). However, neurotoxic and pro-apoptotic effects of Aβ-CM were only partially prevented using LY-CM, which could be explained by other deleterious compounds related to chronic oxidative stress that were released by HEK-AβPP cells. Indeed, full neuroprotection was observed in cells exposed to LY-CM by additional treatment with the antioxidant resveratrol, or with the pluripotent n-3 polyunsaturated fatty acid docosahexaenoic acid. Inhibition of Aβ production appeared necessary but insufficient to prevent neurodegenerative effects associated with AD due to other neurotoxic compounds that could exert additional deleterious effects on neuronal function and survival. Therefore, association of various types of protective agents needs to be considered when developing strategies for AD treatment.