Membrane Partitioning: ��Classical�� and ��Nonclassical�� Hydrophobic Effects

The free energy of transfer of nonpolar solutes from water to lipid bilayers is often dominated by a large negative enthalpy rather than the large positive entropy expected from the hydrophobic effect. This common observation has led to the idea that membrane partitioning is driven by the "nonclassical" hydrophobic effect. We examined this phenomenon by characterizing the partitioning of the well-studied peptide melittin using isothermal titration calorimetry (ITC) and circular dichroism (CD). We studied the temperature dependence of the entropic (-TΔS) and enthalpic (ΔH) components of free energy (ΔG) of partitioning of melittin into lipid membranes made of various mixtures of zwitterionic and anionic lipids. We found significant variations of the entropic and enthalpic components with temperature, lipid composition and vesicle size but only small changes in ΔG (entropy-enthalpy compensation). The heat capacity associated with partitioning had a large negative value of about -0.5 kcal mol(-1) K(-1). This hallmark of the hydrophobic effect was found to be independent of lipid composition. The measured heat capacity values were used to calculate the hydrophobic-effect free energy ΔG (hΦ), which we found to dominate melittin partitioning regardless of lipid composition. In the case of anionic membranes, additional free energy comes from coulombic attraction, which is characterized by a small effective peptide charge due to the lack of additivity of hydrophobic and electrostatic interactions in membrane interfaces [Ladokhin and White J Mol Biol 309:543-552, 2001]. Our results suggest that there is no need for a special effect-the nonclassical hydrophobic effect-to describe partitioning into lipid bilayers.     

Refolding of recombinant human interferon ��-2a from Escherichia coli by urea gradient size exclusion chromatography

Protein refolding is still a puzzle in the production of recombinant proteins expressed as inclusion bodies (IBs) in Escherichia coli. Gradient size exclusion chromatography (SEC) is a recently developed method for refolding of recombinant proteins in IBs. In this study, we used a decreasing urea gradient SEC for the refolding of recombinant human interferon ??-2a (rhIFN??-2a) which was overexpressed as IBs in E. coli. In chromatographic process, the denatured rhIFN??-2a would pass along the 8.0?C3.0 M urea gradient and refold gradually. Several operating conditions, such as final concentration of urea along the column, gradient length, the ratio of reduced to oxidized glutathione and flow rate were investigated, respectively. Under the optimum conditions, 1.2 × 10⁸ IU/mg of specific activity and 82% mass recovery were obtained from the loaded 10 ml of 1.75 mg/ml denatured protein, and rhIFN??-2a was also purified during this process with the purity of higher than 92%. Compared with dilution method, urea gradient SEC was more efficient for the rhIFN??-2a refolding in terms of specific activity and mass recovery.     

Cell Adhesion, the Backbone of the Synapse: ��Vertebrate�� and ��Invertebrate�� Perspectives

Synapses are asymmetric intercellular junctions that mediate neuronal communication. The number, type, and connectivity patterns of synapses determine the formation, maintenance, and function of neural circuitries. The complexity and specificity of synaptogenesis relies upon modulation of adhesive properties, which regulate contact initiation, synapse formation, maturation, and functional plasticity. Disruption of adhesion may result in structural and functional imbalance that may lead to neurodevelopmental diseases, such as autism, or neurodegeneration, such as Alzheimer''s disease. Therefore, understanding the roles of different adhesion protein families in synapse formation is crucial for unraveling the biology of neuronal circuit formation, as well as the pathogenesis of some brain disorders. The present review summarizes some of the knowledge that has been acquired in vertebrate and invertebrate genetic model organisms.Synapses are asymmetric, intercellular junctions that are the basic structural units of neuronal transmission. The correct development of synaptic specializations and the establishment of appropriate connectivity patterns are crucial for the assembly of functional neuronal circuits. Improper synapse formation and function may cause neurodevelopmental disorders, such as mental retardation (MsR) and autism spectrum disorders (ASD) (McAllister 2007; Sudhof 2008), and likely play a role in neurodegenerative disorders, such as Alzheimer''s disease (AD) (Haass and Selkoe 2007).At chemical synapses (reviewed in Sudhof 2004; Zhai and Bellen 2004; Waites et al. 2005; McAllister 2007; Jin and Garner 2008), the presynaptic compartment contains synaptic vesicles (SV), organized in functionally distinct subcellular pools. A subset of SVs docks to the presynaptic membrane around protein-dense release sites, named active zones (AZ). Upon the arrival of an action potential at the terminal, the docked and “primed” SVs fuse with the plasma membrane and release neurotransmitter molecules into the synaptic cleft. Depending on the type of synapse (i.e., excitatory vs. inhibitory synapses), neurotransmitters ultimately activate an appropriate set of postsynaptic receptors that are accurately apposed to the AZ.Synapse formation occurs in several steps (Fig. 1) (reviewed in Eaton and Davis 2003; Goda and Davis 2003; Waites et al. 2005; Garner et al. 2006; Gerrow and El-Husseini 2006; McAllister 2007). Spatiotemporal signals guide axons through heterogeneous cellular environments to contact appropriate postsynaptic targets. At their destination, axonal growth cones initiate synaptogenesis through adhesive interactions with target cells. In the mammalian central nervous system (CNS), immature postsynaptic dendritic spines initially protrude as thin, actin-rich filopodia on the surface of dendrites. Similarly, at the Drosophila neuromuscular junction (NMJ), myopodia develop from the muscles (Ritzenthaler et al. 2000). The stabilization of intercellular contacts and their elaboration into mature, functional synapses involves cytoskeletal arrangements and recruitment of pre- and postsynaptic components to contact sites in spines and boutons. Conversely, retraction of contacts results in synaptic elimination. Both stabilization and retraction sculpt a functional neuronal circuitry.Open in a separate windowFigure 1.(A–C) Different stages of synapse formation. (A) Target selection, (B) Synapse assembly, (C) Synapse maturation and stabilization. (D–F) The role of cell adhesion molecules in synapse formation is exemplified by the paradigm of N-cadherin and catenins in regulation of the morphology and strength of dendritic spine heads. (D) At an early stage the dendritic spines are elongated from motile structures “seeking” their synaptic partners. (E) The contacts between the presynaptic and postsynaptic compartments are stabilized by recruitment of additional cell adhesion molecules. Adhesional interactions activate downstream pathways that remodel the cytoskeleton and organize pre- and postsynaptic apparatuses. (F) Cell adhesion complexes, stabilized by increased synaptic activity, promote the expansion of the dendritic spine head and the maturation/ stabilization of the synapse. Retraction and expansion is dependent on synaptic plasticity.In addition to the plastic nature of synapse formation, the vast heterogeneity of synapses (in terms of target selection, morphology, and type of neurotransmitter released) greatly enhances the complexity of synaptogenesis (reviewed in Craig and Boudin 2001; Craig et al. 2006; Gerrow and El-Husseini 2006). The complexity and specificity of synaptogenesis relies upon the modulation of adhesion between the pre- and postsynaptic components (reviewed in Craig et al. 2006; Gerrow and El-Husseini 2006; Piechotta et al. 2006; Dalva et al. 2007; Shapiro et al. 2007; Yamada and Nelson 2007; Gottmann 2008). Cell adhesive interactions enable cell–cell recognition via extracellular domains and also mediate intracellular signaling cascades that affect synapse morphology and organize scaffolding complexes. Thus, cell adhesion molecules (CAMs) coordinate multiple synaptogenic steps.However, in vitro and in vivo studies of vertebrate CAMs are often at odds with each other. Indeed, there are no examples of mutants for synaptic CAMs that exhibit prominent defects in synapse formation. This apparent “resilience” of synapses is probably caused by functional redundancy or compensatory effects among different CAMs (Piechotta et al. 2006). Hence, studies using simpler organisms less riddled by redundancy, such as Caenorhabditis elegans and Drosophila, have aided in our understanding of the role that these molecules play in organizing synapses.In this survey, we discuss the roles of the best characterized CAM families of proteins involved in synaptogenesis. Our focus is to highlight the complex principles that govern the molecular basis of synapse formation and function from a comparative perspective. We will present results from cell culture studies as well as in vivo analyses in vertebrate systems and refer to invertebrate studies, mainly performed in Drosophila and C. elegans, when they have provided important insights into the role of particular CAM protein families. However, we do not discuss secreted factors, for which we refer the reader to numerous excellent reviews (as for example Washbourne et al. 2004; Salinas 2005; Piechotta et al. 2006; Shapiro et al. 2006; Dalva 2007; Yamada and Nelson 2007; Biederer and Stagi 2008; Salinas and Zou 2008).     

Apolipoprotein M expression increases the size of nascent pre�� HDL formed by ATP binding cassette transporter A1

Apolipoprotein M (apoM) is a novel apolipoprotein that is reportedly necessary for preβ HDL formation; however, its detailed function remains unknown. We investigated the biogenesis and properties of apoM and its effects on the initial steps of nascent preβ HDL assembly by ABCA1 in HEK293 cells. Transiently transfected apoM was localized primarily in the endomembrane compartment. Pulse-chase analyses demonstrated that apoM is inefficiently secreted, relative to human serum albumin, and that ∼50% remains membrane-associated after extraction with sodium carbonate, pH 11.5. To investigate the role of apoM in nascent preβ HDL formation, ABCA1-expressing or control cells, transfected with empty vector, apoM, or C-terminal epitope-tagged apoM (apoM-C-FLAG), were incubated with ¹²⁵I-apoA-I for 24 h. Conditioned media were harvested and fractionated by fast-protein liquid chromatography (FPLC) to monitor HDL particle size. Preβ HDL particles were formed effectively in the absence of apoM expression; however, increased apoM expression stimulated the formation of larger-sized nascent preβ HDLs. Immunoprecipitation with anti-apoA-I antibody followed by apoM Western blot analysis revealed that little secreted apoM was physically associated with preβ HDL. Our results suggest that apoM is an atypical secretory protein that is not necessary for ABCA1-dependent preβ HDL formation but does stimulate the formation of larger-sized preβ HDL. We propose that apoM may function catalytically at an intracellular site to transfer lipid onto preβ HDL during or after their formation by ABCA1.     

Does size matter?

For 40 years, the debate has raged. Do mammalian cells monitor cell size when deciding whether to divide? More recent models suggest an indirect solution, but the field is far from reaching a final verdict.     

De la m��ditation bouddhiste �� la th��rapie cognitive fond��e sur la pleine conscience

For the general public, Buddhist meditation has been a very fashionable subject for several years. It is presented either as a spiritual way to personal fulfilment or as a quick and effective relaxation technique. Otherwise, we have to keep in mind that Buddhist meditation is a lifestyle, born 2,500 years ago, integrated into a complex philosophic, religious, spiritual, and cultural system of thoughts. Moreover, it directly inspired the third cognitive wave of the cognitive and behavioural therapy, from which Mindfulness-Based Cognitive therapy (MBCT) was derived. The MBCT program is intended to prevent relapse/recurrence in major depression and has been the object of clinical trials with the aim of evaluating it using a scientific basis, but other indications are developed.     

Traitement des pathologies psychiatriques et stimulation magn��tique transcranienne r��p��t��e (rTMS): o�� en est-on ?

Objective

Over the past 15 years, the therapeutic effects of repetitive transcranial magnetic stimulation (rTMS) have been well studied in psychiatric disorders. We propose to conduct a qualitative review of the literature to allow a focus on the value of this technique, including its main indications.

Results

This technique, by the induction of a change in cortical excitability, can provide symptomatic improvement in various psychiatric disorders. We first focused on its effectiveness in mood disorders (mainly in uni or bipolar depressive episodes), then in schizophrenia (auditory hallucinations and negative symptoms), and lately in other psychiatric disorders. We are also considering how to implement this technique in clinical practice and future development.

Conclusion

Results reported in literature suggest that rTMS might fit into the strategies of caremainly for unipolar depression and auditory hallucinations. Recommendations should be published in this regard during 2011. Optimization of this technique and the extension to other psychiatric indications are still under study.     

Integrins ��2��1 and ��11��1 regulate the survival of mesenchymal stem cells on collagen I

Although mesenchymal stem cells (MSCs) are the natural source for bone regeneration, the exact mechanisms governing MSC crosstalk with collagen I have not yet been uncovered. Cell adhesion to collagen I is mostly mediated by three integrin receptors – α1β1, α2β1 and α11β1. Using human MSC (hMSC), we show that α11 subunit exhibited the highest basal expression levels but on osteogenic stimulation, both α2 and α11 integrins were significantly upregulated. To elucidate the possible roles of collagen-binding integrins, we applied short hairpin RNA (shRNA)-mediated knockdown in hMSC and found that α2 or α11 deficiency, but not α1, results in a tremendous reduction of hMSC numbers owing to mitochondrial leakage accompanied by Bcl-2-associated X protein upregulation. In order to clarify the signaling conveyed by the collagen-binding integrins in hMSC, we analyzed the activation of focal adhesion kinase, extracellular signal-regulated protein kinase and serine/threonine protein kinase B (PKB/Akt) kinases and detected significantly reduced Akt phosphorylation only in α2- and α11-shRNA hMSC. Finally, experiments with hMSC from osteoporotic patients revealed a significant downregulation of α2 integrin concomitant with an augmented mitochondrial permeability. In conclusion, our study describes for the first time that disturbance of α2β1- or α11β1-mediated interactions to collagen I results in the cell death of MSCs and urges for further investigations examining the impact of MSCs in bone conditions with abnormal collagen I.     

��-Secretase Inhibitor Potency Is Decreased by Aberrant ��-Cleavage Location of the ��Swedish Mutant�� Amyloid Precursor Protein

The amyloid-β (Aβ) peptide, widely known as the causative molecule of Alzheimer disease (AD), is generated by the sequential cleavage of amyloid precursor protein (APP) by the aspartyl proteases BACE1/β-secretase and presenilin/γ-secretase. Inhibition of BACE1, therefore, is a promising strategy for preventing the progression of AD. However, β-secretase inhibitors (BSIs) exhibit unexpectedly low potency in cells expressing “Swedish mutant” APP (APPswe) and in the transgenic mouse Tg2576, an AD model overexpressing APPswe. The Swedish mutation dramatically accelerates β-cleavage of APP and hence the generation of Aβ; this acceleration has been assumed to underlie the poor inhibitory activity of BSI against APPswe processing. Here, we studied the mechanism by which the Swedish mutation causes this BSI potency decrease. Surprisingly, decreased BSI potency was not observed in an in vitro assay using purified BACE1 and substrates, indicating that the accelerated β-cleavage resulting from the Swedish mutation is not its underlying cause. By focusing on differences between the cell-based and in vitro assays, we have demonstrated here that the potency decrease is caused by the aberrant subcellular localization of APPswe processing and not by accelerated β-cleavage or the accumulation of the C-terminal fragment of β-cleaved APP. Because most patients with sporadic AD express wild type APP, our findings suggest that the wild type mouse is superior to the Tg2576 mouse as a model for determining the effective dose of BSI for AD patients. This work provides novel insights into the potency decrease of BSI and valuable suggestions for its development as a disease-modifying agent.     

Evolutionary Contributions to Solving the ��Matrilineal Puzzle��

Matriliny has long been debated by anthropologists positing either its primitive or its puzzling nature. More recently, evolutionary anthropologists have attempted to recast matriliny as an adaptive solution to modern social and ecological environments, tying together much of what was known to be associated with matriliny. This paper briefly reviews the major anthropological currents in studies of matriliny and discusses the contribution of evolutionary anthropology to this body of literature. It discusses the utility of an evolutionary framework in the context of the first independent test of Holden et al.'s 2003 model of matriliny as daughter-biased investment. It finds that historical daughter-biased transmission of land among the Mosuo is consistent with the model, whereas current income transmission is not. In both cases, resources had equivalent impacts on male and female reproduction, a result which predicts daughter-biased resource transmission given any nonzero level of paternity uncertainty. However, whereas land was transmitted traditionally to daughters, income today is invested in both sexes. Possible reasons for this discrepancy are discussed.     

Travaux pr��paratoires �� la r��daction du chapitre V de la CIM-11

The 10th version of the International Classification of Disease (ICD-10) of the World Health Organisation (WHO) is currently in a revision phase. This article recommends a possible method of updating of the group ??Schizophrenia, schizotypal and delusional disorders,?? which attempts to reconcile the three demands made by the WHO for the new ICD-11: updating of classification practices, ease of use and destigmatisation of the terminology.