White matter maturation reshapes structural connectivity in the late developing human brain.

From toddler to late teenager, the macroscopic pattern of axonal projections in the human brain remains largely unchanged while undergoing dramatic functional modifications that lead to network refinement. These functional modifications are mediated by increasing myelination and changes in axonal diameter and synaptic density, as well as changes in neurochemical mediators. Here we explore the contribution of white matter maturation to the development of connectivity between ages 2 and 18 y using high b-value diffusion MRI tractography and connectivity analysis. We measured changes in connection efficacy as the inverse of the average diffusivity along a fiber tract. We observed significant refinement in specific metrics of network topology, including a significant increase in node strength and efficiency along with a decrease in clustering. Major structural modules and hubs were in place by 2 y of age, and they continued to strengthen their profile during subsequent development. Recording resting-state functional MRI from a subset of subjects, we confirmed a positive correlation between structural and functional connectivity, and in addition observed that this relationship strengthened with age. Continuously increasing integration and decreasing segregation of structural connectivity with age suggests that network refinement mediated by white matter maturation promotes increased global efficiency. In addition, the strengthening of the correlation between structural and functional connectivity with age suggests that white matter connectivity in combination with other factors, such as differential modulation of axonal diameter and myelin thickness, that are partially captured by inverse average diffusivity, play an increasingly important role in creating brain-wide coherence and synchrony.

Repeated Interaction and the Revelation of the Monitor's Type: A Principal-Monitor-Agent Problem

This paper studies a dynamic principal-monitor-agent relation where a strategic principal delegates the task of monitoring the effort of a strategic agent to a third party. The latter we call the monitor, whose type is initially unknown. Through repeated interaction the agent might learn his type. We show that this process damages the principal's payoffs. Compensation is assumed exogenous, limiting to a great extent the provision of incentives. We go around this difficulty by introducing costly replacement strategies, i.e. the principal replaces the monitor, thus disrupting the agent's learning. We found that even when replacement costs are null, if the revealed monitor is strictly preferred by both parties, there is a loss in efficiency due to the impossibility of bene…tting from it. Nonetheless, these strategies can partially recover the principal's losses. Additionally, we establish upper and lower bounds on the payoffs that the principal and the agent can achieve. Finally we characterize the equilibrium strategies under public and private monitoring (with communication) for different cost and impatience levels.

Protein-protein interaction investigated by steered molecular dynamics: the TCR-pMHC complex.

We present a novel steered molecular dynamics scheme to induce the dissociation of large protein-protein complexes. We apply this scheme to study the interaction of a T cell receptor (TCR) with a major histocompatibility complex (MHC) presenting a peptide (p). Two TCR-pMHC complexes are considered, which only differ by the mutation of a single amino acid on the peptide; one is a strong agonist that produces T cell activation in vivo, while the other is an antagonist. We investigate the interaction mechanism from a large number of unbinding trajectories by analyzing van der Waals and electrostatic interactions and by computing energy changes in proteins and solvent. In addition, dissociation potentials of mean force are calculated with the Jarzynski identity, using an averaging method developed for our steering scheme. We analyze the convergence of the Jarzynski exponential average, which is hampered by the large amount of dissipative work involved and the complexity of the system. The resulting dissociation free energies largely underestimate experimental values, but the simulations are able to clearly differentiate between wild-type and mutated TCR-pMHC and give insights into the dissociation mechanism.

Structural and functional interaction sites between Na,K-ATPase and FXYD proteins.

Several members of the FXYD protein family are tissue-specific regulators of Na,K-ATPase that produce distinct effects on its apparent K(+) and Na(+) affinity. Little is known about the interaction sites between the Na,K-ATPase alpha subunit and FXYD proteins that mediate the efficient association and/or the functional effects of FXYD proteins. In this study, we have analyzed the role of the transmembrane segment TM9 of the Na,K-ATPase alpha subunit in the structural and functional interaction with FXYD2, FXYD4, and FXYD7. Mutational analysis combined with expression in Xenopus oocytes reveals that Phe(956), Glu(960), Leu(964), and Phe(967) in TM9 of the Na,K-ATPase alpha subunit represent one face interacting with the three FXYD proteins. Leu(964) and Phe(967) contribute to the efficient association of FXYD proteins with the Na,K-ATPase alpha subunit, whereas Phe(956) and Glu(960) are essential for the transmission of the functional effect of FXYD proteins on the apparent K(+) affinity of Na,K-ATPase. The relative contribution of Phe(956) and Glu(960) to the K(+) effect differs for different FXYD proteins, probably reflecting the intrinsic differences of FXYD proteins on the apparent K(+) affinity of Na,K-ATPase. In contrast to the effect on the apparent K(+) affinity, Phe(956) and Glu(960) are not involved in the effect of FXYD2 and FXYD4 on the apparent Na(+) affinity of Na,K-ATPase. The mutational analysis is in good agreement with a docking model of the Na,K-ATPase/FXYD7 complex, which also predicts the importance of Phe(956), Glu(960), Leu(964), and Phe(967) in subunit interaction. In conclusion, by using mutational analysis and modeling, we show that TM9 of the Na,K-ATPase alpha subunit exposes one face of the helix that interacts with FXYD proteins and contributes to the stable interaction with FXYD proteins, as well as mediating the effect of FXYD proteins on the apparent K(+) affinity of Na,K-ATPase.

Estimating the risk of developing type 2 diabetes: a comparison of several risk scores: the Cohorte Lausannoise study.

To compare in the Swiss population the results of several scores estimating the risk of developing type 2 diabetes. This was a single-center, cross-sectional study conducted between 2003 and 2006 in Lausanne, Switzerland. Overall, 3,251 women and 2,937 men, aged 35-75 years, were assessed, of which 5,760 (93%) were free from diabetes and included in the current study. The risk of developing type 2 diabetes was assessed using seven different risk scores, including clinical data with or without biological data. Participants were considered to be eligible for primary prevention according to the thresholds provided for each score. The results were then extrapolated to the Swiss population of the same sex and age. The risk of developing type 2 diabetes increased with age in all scores. The prevalence of participants at high risk ranged between 1.6 and 24.9% in men and between 1.1 and 15.7% in women. Extrapolated to the Swiss population of similar age, the overall number of participants at risk, and thus susceptible to intervention, ranged between 46,708 and 636,841. In addition, scores that included the same clinical variables led to a significantly different prevalence of participants at risk (4.2% [95% CI 3.4-5.0] vs. 12.8% [11.5-14.1] in men and 2.9% [2.4-3.6] vs. 6.0% [5.2-6.9] in women). CONCLUSIONS; The prevalence of participants at risk for developing type 2 diabetes varies considerably according to the scoring system used. To adequately prevent type 2 diabetes, risk-scoring systems must be validated for each population considered.

Three-dimensional models of 14α-sterol demethylase (Cyp51A) from Aspergillus lentulus and Aspergillus fumigatus: an insight into differences in voriconazole interaction.

Aspergillus lentulus, an Aspergillus fumigatus sibling species, is increasingly reported in corticosteroid-treated patients. Its clinical significance is unknown, but the fact that A. lentulus shows reduced antifungal susceptibility, mainly to voriconazole, is of serious concern. Heterologous expression of cyp51A from A. fumigatus and A. lentulus was performed in Saccharomyces cerevisiae to assess differences in the interaction of Cyp51A with the azole drugs. The absence of endogenous ERG11 was efficiently complemented in S. cerevisiae by the expression of either Aspergillus cyp51A allele. There was a marked difference between azole minimum inhibitory concentration (MIC) values of the clones expressing each Aspergillus spp. cyp51A. Saccharomyces cerevisiae clones expressing A. lentulus alleles showed higher MICs to all of the azoles tested, supporting the hypothesis that the intrinsic azole resistance of A. lentulus could be associated with Cyp51A. Homology models of A. fumigatus and A. lentulus Cyp51A protein based on the crystal structure of Cyp51p from Mycobacterium tuberculosis in complex with fluconazole were almost identical owing to their mutual high sequence identity. Molecular dynamics (MD) was applied to both three-dimensional protein models to refine the homology modelling and to explore possible differences in the Cyp51A-voriconazole interaction. After 20ns of MD modelling, some critical differences were observed in the putative closed form adopted by the protein upon voriconazole binding. A closer study of the A. fumigatus and A. lentulus voriconazole putative binding site in Cyp51A suggested that some major differences in the protein's BC loop could differentially affect the lock-up of voriconazole, which in turn could correlate with their different azole susceptibility profiles.

LILRB2 interaction with HLA class I correlates with control of HIV-1 infection.

Natural progression of HIV-1 infection depends on genetic variation in the human major histocompatibility complex (MHC) class I locus, and the CD8+ T cell response is thought to be a primary mechanism of this effect. However, polymorphism within the MHC may also alter innate immune activity against human immunodeficiency virus type 1 (HIV-1) by changing interactions of human leukocyte antigen (HLA) class I molecules with leukocyte immunoglobulin-like receptors (LILR), a group of immunoregulatory receptors mainly expressed on myelomonocytic cells including dendritic cells (DCs). We used previously characterized HLA allotype-specific binding capacities of LILRB1 and LILRB2 as well as data from a large cohort of HIV-1-infected individuals (N = 5126) to test whether LILR-HLA class I interactions influence viral load in HIV-1 infection. Our analyses in persons of European descent, the largest ethnic group examined, show that the effect of HLA-B alleles on HIV-1 control correlates with the binding strength between corresponding HLA-B allotypes and LILRB2 (p = 10(-2)). Moreover, overall binding strength of LILRB2 to classical HLA class I allotypes, defined by the HLA-A/B/C genotypes in each patient, positively associates with viral replication in the absence of therapy in patients of both European (p = 10(-11)-10(-9)) and African (p = 10(-5)-10(-3)) descent. This effect appears to be driven by variations in LILRB2 binding affinities to HLA-B and is independent of individual class I allelic effects that are not related to the LILRB2 function. Correspondingly, in vitro experiments suggest that strong LILRB2-HLA binding negatively affects antigen-presenting properties of DCs. Thus, we propose an impact of LILRB2 on HIV-1 disease outcomes through altered regulation of DCs by LILRB2-HLA engagement.

Humoral Immune Response Kinetics in Philander opossum and Didelphis marsupialis Infected and Immunized by Trypanosoma cruzi Employing an Immunofluorescence Antibody Test

Philander opossum and Didelphis marsupialis considered the most ancient mammals and an evolutionary success, maintain parasitism by Trypanosoma cruzi without developing any apparent disease or important tissue lesion. In order to elucidate this well-balanced interaction, we decided to compare the humoral immune response kinetics of the two didelphids naturally and experimentally infected with T. cruzi and immunized by different schedules of parasite antigens, employing an indirect fluorescence antibody test (IFAT). Both didelphids responded with high serological titers to different immunization routes, while the earliest response occurred with the intradermic route. Serological titers of naturally infected P. opossum showed a significant individual variation, while those of D. marsupialis remained stable during the entire follow-up period. The serological titers of the experimentally infected animals varied according to the inoculated strain. Our data suggest that (1) IFAT was sensitive for follow-up of P. opossum in natural and experimental T. cruzi infections; (2) both P. opossum and D. marsupialis are able to mount an efficient humoral immune response as compared to placental mammals; (3) experimentally infected P. opossum and D. marsupialis present distinct patterns of infection, depending on the subpopulation of T. cruzi, (4) the differences observed in the humoral immune responses between P. opossum and D. marsupialis, probably, reflect distinct strategies selected by these animals during their coevolution with T. cruzi.

Pharmacokinetic interaction between methotrexate and chloral hydrate.

We report the case of a drug interaction between methotrexate (MTX) and chloral hydrate (CH) observed in a child treated for acute leukemia. Significantly slower MTX clearance and increased MTX exposure occurred on the first three courses of a high-dose chemotherapy when co-administered with CH despite normal renal function, adequate hydration, and alkalinization. Mean MTX area under the curve associated with CH administration was 1,134 µmol hours/L, compared to 608 µmol hours/L after discontinuation of CH. This interaction possibly resulted from a competition between anionic CH metabolites and MTX for renal tubular excretion.

An infrared reflection-absorption spectroscopic (IRRAS) study of the interaction of lipid A and lipopolysaccharide Re with endotoxin-binding proteins.

Lipopolysaccharides (LPS, endotoxins) are main constituents of the outer membranes of Gram-negative bacteria, with the 'endotoxic principle' lipid A anchoring LPS into the membrane. When LPS is removed from the bacteria by the action of the immune system or simply by cell dividing, it may interact strongly with immunocompetent cells such as mononuclear cells. This interaction may lead, depending on the LPS concentration, to beneficial (at low) or pathophysiological (at high concentrations) reactions, the latter frequently causing the septic shock syndrome. There is a variety of endogenous LPS-binding proteins. To this class belong lactoferrin (LF) and hemoglobin (Hb), which have been shown to suppress and enhance the LPS-induced cytokine secretion in mononuclear cells, respectively. To elucidate the interaction mechanisms of endotoxins with these proteins, we have investigated in an infrared reflection-absorption spectroscopy (IRRAS) study the interaction of LPS or lipid A monolayers at the air/water interface with LF and Hb proteins, injected into the aqueous subphase. The data are clearly indicative of completely different interaction mechanisms of the endotoxins with the proteins, with the LF acting only at the LPS backbone, whereas Hb incorporates into the lipid monolayer. These data allow an understanding of the different reactivities in the biomedicinal systems.

Involvement of CD73, equilibrative nucleoside transporters and inosine in rhythm and conduction disturbances mediated by adenosine A1 and A2A receptors in the developing heart.

We previously established that exogenous adenosine (ADO) induces transient arrhythmias in the developing heart via the adenosine A1 receptor (A1AR) and downstream activation of NADPH oxidase/ERK and PLC/PKC pathways. Here, we investigated the mechanisms by which accumulation of endogenous ADO and its derived compound inosine (INO) in the interstitial compartment induce rhythm and conduction troubles. The validated model of the spontaneously beating heart obtained from 4-day-old chick embryos was used. Quantitative RT-PCR showed that enzymes involved in ADO and INO metabolism (CD39, CD73 and eADA) as well as equilibrative (ENT1, -3, -4) and concentrative (CNT3) nucleoside transporters were differentially expressed in atria, ventricle and outflow tract. Inactivation of ENTs by dipyridamole, 1) increased myocardial ADO level, 2) provoked atrial arrhythmias and atrio-ventricular blocks (AVB) in 70% of the hearts, 3) prolonged P wave and QT interval without altering contractility, and 4) increased ERK2 phosphorylation. Blockade of CD73-mediated phosphohydrolysis of AMP to ADO, MEK/ERK pathway inhibition or A1AR inhibition prevented these arrhythmias. Exposure to exogenous INO also caused atrial ectopy associated with AVB and ERK2 phosphorylation which were prevented by A1AR or A2AAR antagonists exclusively or by MEK/ERK inhibitor. Inhibition of ADA-mediated conversion of ADO to INO increased myocardial ADO and decreased INO as expected, but slightly augmented heart rate variability without provoking AVB. Thus, during cardiogenesis, disturbances of nucleosides metabolism and transport, can lead to interstitial accumulation of ADO and INO and provoke arrhythmias in an autocrine/paracrine manner through A1AR and A2AAR stimulation and ERK2 activation.

Trypanosoma cruzi-cardiomyocytes: new contributions regarding a better understanding of this interaction

The present paper summarizes new approaches regarding the progress done to the understanding of the interaction of Trypanosoma cruzi-cardiomyocytes. Mannose receptors localized at the surface of heart muscle cell are involved in binding and uptake of the parasite. One of the most striking events in the parasite-heart muscle cells interaction is the disruption of the actin cytoskeleton. We have investigated the regulation of the actin mRNA during the cytopathology induced in myocardial cells by the parasite. T. cruzi invasion increases calcium resting levels in cardiomyocytes. We have previously shown that Ca2+ ATPase of the sarcoplasmic reticulum (SERCA) is involved in the invasion of T. cruzi in cardiomyocytes. Treating the cells with thapsigargin, a drug that binds to all SERCA ATPases and causes depletion of intracellular calcium stores, we found a 75% inhibition in the T. cruzi-cardiomyocytes invasion.