Mouse Delta Opioid Receptors are Located on Presynaptic Afferents to Hippocampal Pyramidal Cells

Delta opioid receptors participate in the control of chronic pain and emotional responses. Recent data have also identified their implication in drug-context associations pointing to a modulatory role on hippocampal activity. We used fluorescent knock-in mice that express a functional delta opioid receptor fused at its carboxy terminus with the green fluorescent protein in place of the native receptor to investigate the receptor neuroanatomical distribution in this structure. Fine mapping of the pyramidal layer was performed in hippocampal acute brain slices and organotypic cultures using fluorescence confocal imaging, co-localization with pre- and postsynaptic markers and correlative light-electron microscopy. The different approaches concurred to identify delta opioid receptors on presynaptic afferents to glutamatergic principal cells. In the latter, only scarce receptors were detected that were confined within the Golgi or vesicular intracellular compartments with no receptor present at the cell surface. In the mouse hippocampus, expression of functional delta opioid receptors is therefore mostly associated with interneurons emphasizing a presynaptic modulatory effect on the pyramidal cell firing rate.     

Inhibition of NAMPT pathway by FK866 activates the function of p53 in HEK293T cells

Inactivation of p53 protein by endogenous and exogenous carcinogens is involved in the pathogenesis of different human malignancies. In cancer associated with SV-40 DNA tumor virus, p53 is considered to be non-functional mainly due to its interaction with the large T-antigen. Using the 293T cell line (HEK293 cells transformed with large T antigen) as a model, we provide evidence that p53 is one of the critical downstream targets involved in FK866-mediated killing of 293T cells. A reduced rate of apoptosis and an increased number of cells in S-phase was accompanied after knockdown of p53 in these cells. Inhibition of NAMPT by FK866, or inhibition of SIRT by nicotinamide decreased proliferation and triggered death of 293T cells involving the p53 acetylation pathway. Additionally, knockdown of p53 attenuated the effect of FK866 on cell proliferation, apoptosis, and cell cycle arrest. The data presented here shed light on two important facts: (1) that p53 in 293T cells is active in the presence of FK866, an inhibitor of NAMPT pathway; (2) the apoptosis induced by FK866 in 293T cells is associated with increased acetylation of p53 at Lys382, which is required for the functional activity of p53.     

Functional and structural characterization of α-(1->2) branching sucrase derived from DSR-E glucansucrase

ΔN₁₂₃-glucan-binding domain-catalytic domain 2 (ΔN₁₂₃-GBD-CD2) is a truncated form of the bifunctional glucansucrase DSR-E from Leuconostoc mesenteroides NRRL B-1299. It was constructed by rational truncation of GBD-CD2, which harbors the second catalytic domain of DSR-E. Like GBD-CD2, this variant displays α-(1→2) branching activity when incubated with sucrose as glucosyl donor and (oligo-)dextran as acceptor, transferring glucosyl residues to the acceptor via a ping-pong bi-bi mechanism. This allows the formation of prebiotic molecules containing controlled amounts of α-(1→2) linkages. The crystal structure of the apo α-(1→2) branching sucrase ΔN₁₂₃-GBD-CD2 was solved at 1.90 Å resolution. The protein adopts the unusual U-shape fold organized in five distinct domains, also found in GTF180-ΔN and GTF-SI glucansucrases of glycoside hydrolase family 70. Residues forming subsite −1, involved in binding the glucosyl residue of sucrose and catalysis, are strictly conserved in both GTF180-ΔN and ΔN₁₂₃-GBD-CD2. Subsite +1 analysis revealed three residues (Ala-2249, Gly-2250, and Phe-2214) that are specific to ΔN₁₂₃-GBD-CD2. Mutation of these residues to the corresponding residues found in GTF180-ΔN showed that Ala-2249 and Gly-2250 are not directly involved in substrate binding and regiospecificity. In contrast, mutant F2214N had lost its ability to branch dextran, although it was still active on sucrose alone. Furthermore, three loops belonging to domains A and B at the upper part of the catalytic gorge are also specific to ΔN₁₂₃-GBD-CD2. These distinguishing features are also proposed to be involved in the correct positioning of dextran acceptor molecules allowing the formation of α-(1→2) branches.     

Modulation of neuronal pentraxin 1 expression in rat pancreatic β-cells submitted to chronic glucotoxic stress

Insulin secretory granules are β-cell vesicles dedicated to insulin processing, storage, and release. The secretion of insulin secretory granule content in response to an acute increase of glucose concentration is a highly regulated process allowing normal glycemic homeostasis. Type 2 diabetes is a metabolic disease characterized by chronic hyperglycemia. The consequent prolonged glucose exposure is known to exert deleterious effects on the function of various organs, notably impairment of insulin secretion by pancreatic β-cells and induction of apoptosis. It has also been described as modifying gene and protein expression in β-cells. Therefore, we hypothesized that a modulation of insulin secretory granule protein expression induced by chronic hyperglycemia may partially explain β-cell dysfunction. To identify the potential early molecular mechanisms underlying β-cell dysfunction during chronic hyperglycemia, we performed SILAC and mass spectrometry experiments to monitor changes in the insulin secretory granule proteome from INS-1E rat insulinoma β-cells cultivated either with 11 or 30 mm of glucose for 24 h. Fourteen proteins were found to be differentially expressed between these two conditions, and several of these proteins were not described before to be present in β-cells. Among them, neuronal pentraxin 1 was only described in neurons so far. Here we investigated its expression and intracellular localization in INS-1E cells. Furthermore, its overexpression in glucotoxic conditions was confirmed at the mRNA and protein levels. According to its role in hypoxia-ischemia-induced apoptosis described in neurons, this suggests that neuronal pentraxin 1 might be a new β-cell mediator in the AKT/GSK3 apoptotic pathway. In conclusion, the modification of specific β-cell pathways such as apoptosis and oxidative stress may partially explain the impairment of insulin secretion and β-cell failure, observed after prolonged exposure to high glucose concentrations.     

Acanthaster planci outbreak: decline in coral health, coral size structure modification and consequences for obligate decapod assemblages

Although benthic motile invertebrate communities encompass the vast majority of coral reef diversity, their response to habitat modification has been poorly studied. A variety of benthic species, particularly decapods, provide benefits to their coral host enabling them to cope with environmental stressors, and as a result benefit the overall diversity of coral-associated species. However, little is known about how invertebrate assemblages associated with corals will be affected by global perturbations, (either directly or indirectly via their coral host) or their consequences for ecosystem resilience. Analysis of a ten year dataset reveals that the greatest perturbation at Moorea over this time was an outbreak of the corallivorous sea star Acanthaster planci from 2006 to 2009 impacting habitat health, availability and size structure of Pocillopora spp. populations and highlights a positive relationship between coral head size and survival. We then present the results of a mensurative study in 2009 conducted at the end of the perturbation (A. planci outbreak) describing how coral-decapod communities change with percent coral mortality for a selected coral species, Pocillopora eydouxi. The loss of coral tissue as a consequence of A. planci consumption led to an increase in rarefied total species diversity, but caused drastic modifications in community composition driven by a shift from coral obligate to non-obligate decapod species. Our study highlights that larger corals left with live tissue in 2009, formed a restricted habitat where coral obligate decapods, including mutualists, could subsist. We conclude that the size structure of Pocillopora populations at the time of an A. planci outbreak may greatly condition the magnitude of coral mortality as well as the persistence of local populations of obligate decapods.     

Identification of ILK as a new partner of the ADAM12 disintegrin and metalloprotease in cell adhesion and survival

Based on its shedding and binding activities, the disintegrin and metalloprotease 12 (ADAM12) has been implicated in cell signaling. Here we investigate the intracellular protein interaction network of the transmembrane ADAM12L variant using an integrative approach. We identify the integrin-linked kinase (ILK) as a new partner for ADAM12L cellular functions. We demonstrate that ADAM12L coimmunoprecipitates with ILK in cells and that its cytoplasmic tail is required for this interaction. In human cultured hepatic stellate cells (HSCs), which express high levels of endogenous ADAM12L and ILK, the two proteins are redistributed to focal adhesions upon stimulation of a β1 integrin-dependent pathway. We show that down-regulation of ADAM12L in HSCs leads to cytoskeletal disorganization and loss of adhesion. Conversely, up-regulation of ADAM12L induces the Akt Ser-473 phosphorylation-dependent survival pathway via stimulation of β1 integrins and activation of phosphoinositide 3-kinase (PI3K). Depletion of ILK inhibits this effect, which is independent of ADAM12L proteolytic activity and involves its cytoplasmic domain. We further demonstrate that overexpression of ADAM12L promotes kinase activity from ILK immunoprecipitates. Our data suggest a new role for ADAM12L in mediating the functional association of ILK with β1 integrin to regulate cell adhesion/survival through a PI3K/Akt signaling pathway.     

Bipartite graphs as models of population structures in evolutionary multiplayer games

By combining evolutionary game theory and graph theory, "games on graphs" study the evolutionary dynamics of frequency-dependent selection in population structures modeled as geographical or social networks. Networks are usually represented by means of unipartite graphs, and social interactions by two-person games such as the famous prisoner's dilemma. Unipartite graphs have also been used for modeling interactions going beyond pairwise interactions. In this paper, we argue that bipartite graphs are a better alternative to unipartite graphs for describing population structures in evolutionary multiplayer games. To illustrate this point, we make use of bipartite graphs to investigate, by means of computer simulations, the evolution of cooperation under the conventional and the distributed N-person prisoner's dilemma. We show that several implicit assumptions arising from the standard approach based on unipartite graphs (such as the definition of replacement neighborhoods, the intertwining of individual and group diversity, and the large overlap of interaction neighborhoods) can have a large impact on the resulting evolutionary dynamics. Our work provides a clear example of the importance of construction procedures in games on graphs, of the suitability of bigraphs and hypergraphs for computational modeling, and of the importance of concepts from social network analysis such as centrality, centralization and bipartite clustering for the understanding of dynamical processes occurring on networked population structures.     

Dendritic cell vaccination in acute myeloid leukemia

The prognosis of patients with acute myeloid leukemia (AML) remains dismal, with a 5-year overall survival rate of only 5.2% for the continuously growing subgroup of AML patients older than 65 years. These patients are generally not considered eligible for intensive chemotherapy and/or allogeneic hematopoietic stem cell transplantation because of high treatment-related morbidity and mortality, emphasizing the need for novel, less toxic, treatment alternatives. It is within this context that immunotherapy has gained attention in recent years. In this review, we focus on the use of dendritic cell (DC) vaccines for immunotherapy of AML. DC are central orchestrators of the immune system, bridging innate and adaptive immunity and critical to the induction of anti-leukemic immunity. We discuss the rationale and basic principles of DC-based therapy for AML and review the clinical experience that has been obtained so far with this form of immunotherapy for patients with AML.