The authors consider processes on social networks that can potentially involve three factors: homophily, or the formation of social ties due to matching individual traits; social contagion, also known as social influence; and the causal effect of an individual’s covariates on his or her behavior or other measurable responses. The authors show that generically, all of these are confounded with each other. Distinguishing them from one another requires strong assumptions on the parametrization of the social process or on the adequacy of the covariates used (or both). In particular the authors demonstrate, with simple examples, that asymmetries in regression coefficients cannot identify causal effects and that very simple models of imitation (a form of social contagion) can produce substantial correlations between an individual’s enduring traits and his or her choices, even when there is no intrinsic affinity between them. The authors also suggest some possible constructive responses to these results.
contagion; social influence; homophily; causal inference; network confounding; neutral models
This study sought to determine whether the quality of enzyme preparations can be determined from their melting curves, which may easily be obtained using a fluorescent probe and a standard RT-PCR machine. Thermal melt data on 31 recombinant enzymes from Plasmodium parasites were acquired by incrementally heating them to 90 °C and measuring unfolding with a fluorescent dye; activity assays specific to each enzyme were also performed. Four of the enzymes were denatured to varying degrees with heat and SDS prior to the thermal melt and activity assays. In general, melting curve quality correlated with enzyme activity; enzymes with high-quality curves were found almost uniformly to be active, while those with lower-quality curves were more varied in their catalytic performance. Inspection of melting curves of bovine xanthine oxidase and Entamoeba histolytica cysteine protease 1 allowed active stocks to be distinguished from inactive stocks, implying that a relationship between melting curve quality and activity persists over a wide range of experimental conditions and species. Our data suggest that melting curves can help to distinguish properly folded proteins from denatured ones and therefore may be useful in selecting stocks for further study and in optimizing purification procedures for specific proteins.
thermal melting; malaria; protein denaturation
In obesity, phenotypic switches occur in macrophage populations such that the predominantly M2-polarised anti-inflammatory state seen in lean individuals changes to a predominantly M1-polarised pro-inflammatory state in those who are obese. However, the mechanisms by which these phenotypic shifts occur have not yet been fully elucidated.
The effects of oxLDL (1-40 μg/ml; 24 h) on several parameters relevant to the Unfolded Protein Response (UPR)-mediated lipotoxic effects of oxLDL (disruption of ER Ca2+ handling; activation of the UPR transcription factor XBP-1; upregulation of the UPR target genes BiP and CHOP; apoptosis; cell viability) were investigated in human primary monocyte-derived macrophages, and also in monocyte-macrophages derived from the THP-1 monocytic cell line. A consistent pattern was observed: M2-polarised macrophages were more sensitive to the lipotoxic effects of oxLDL than either non-polarised macrophages or non-differentiated monocytic cells. Specifically, M2-polarised macrophages were the only cell type to undergo significantly increased apoptosis (Primary cells: 1.23 ± 0.01 basal; THP-1-derived: 1.97 ± 0.12 basal; P < 0.05 in both cases) and decreased cell viability (Primary cells: 0.79 ± 0.04 basal; THP-1-derived: 0.67 ± 0.02 basal; P < 0.05 in both cases) when exposed to oxLDL levels similar to those seen in overweight individuals (ie. 1 μg/ml).
We propose that the enhanced susceptibility of M2-polarised macrophages to lipotoxicity seen in the present in vitro study could, over time, contribute to the phenotypic shift seen in obese individuals in vivo. This is because a higher degree of oxLDL-induced lipotoxic cell death within M2 macrophages could contribute to a decrease in numbers of M2 cells, and thus a relative increase in proportion of non-M2 cells, within macrophage populations. Given the pro-inflammatory characteristics of a predominantly M1-polarised state, the data presented here may constitute a useful contribution to our understanding of the origin of the pro-inflammatory nature of obesity, and of the pathogenesis of obesity-associated inflammatory disorders such as Type 2 Diabetes and atherosclerosis.
alternative M2 monocyte/macrophage polarisation; UPR; oxLDL; lipotoxicity
Radiochromic plastic and gel materials have recently emerged which can yield 3D dose information over clinical volumes in high resolution. These dosimeters can provide a much more comprehensive verification of complex radiation therapy treatments than can be achieved by conventional planar and point dosimeters. To achieve full clinical potential, these dosimeters require a fast and accurate read-out technology. Broad-beam optical-computed tomography (optical-CT) systems have shown promise, but can be sensitive to stray light artifacts originating in the imaging chain. In this work we present and evaluate a method to correct for stray light artifacts by deconvolving a measured, spatially invariant, point spread function (PSF). The correction was developed for the DLOS (Duke large field-of-view optical-CT scanner) in conjunction with radiochromic PRESAGE® dosimeters. The PSF was constructed from a series of acquisitions of projection images of various sized apertures placed in the optical imaging chain. Images were acquired with a range of exposure times, and for a range of aperture sizes (0.2–11 mm). The PSF is investigated under a variety of conditions, and found to be robust and spatially invariant, key factors enabling the viability of the deconvolution approach. The spatial invariance and robustness of the PSF are facilitated by telecentric imaging, which produces a collimated light beam and removes stray light originating upstream of the imaging lens. The telecentric capability of the DLOS therefore represents a significant advantage, both in keeping stray light levels to a minimum and enabling viability of an accurate PSF deconvolution method to correct for the residual. The performance of the correction method was evaluated on projection images containing known optical-density variations, and also on known 3D dose distributions. The method is shown to accurately account for stray light on small field dosimetry with corrections up to 3% in magnitude shown here although corrections of >10% have been observed in extreme cases. The dominant source of stray light was found to be within the imaging lens. Correcting for stray light extended the dynamic range of the system from ~30 to ~60 dB. The correction should be used when measurements need to be accurate within 3%.
The recent emergence of radiochromic dosimeters with low inherent light-scattering presents the possibility of fast 3D dosimetry using broad-beam optical computed tomography (optical-CT). Current broad beam scanners typically employ either a single or a planar array of light-emitting diodes (LED) for the light source. The spectrum of light from LED sources is polychromatic and this, in combination with the non-uniform spectral absorption of the dosimeter, can introduce spectral artifacts arising from preferential absorption of photons at the peak absorption wavelengths in the dosimeter. Spectral artifacts can lead to large errors in the reconstructed attenuation coefficients, and hence dose measurement. This work presents an analytic method for correcting for spectral artifacts which can be applied if the spectral characteristics of the light source, absorbing dosimeter, and imaging detector are known or can be measured. The method is implemented here for a PRESAGE® dosimeter scanned with the DLOS telecentric scanner (Duke Large field-of-view Optical-CT Scanner). Emission and absorption profiles were measured with a commercial spectrometer and spectrophotometer, respectively. Simulations are presented that show spectral changes can introduce errors of 8% for moderately attenuating samples where spectral artifacts are less pronounced. The correction is evaluated by application to a 16 cm diameter PRESAGE® cylindrical dosimeter irradiated along the axis with two partially overlapping 6 × 6 cm fields of different doses. The resulting stepped dose distribution facilitates evaluation of the correction as each step had different spectral contributions. The spectral artifact correction was found to accurately correct the reconstructed coefficients to within ~1.5%, improved from ~7.5%, for normalized dose distributions. In conclusion, for situations where spectral artifacts cannot be removed by physical filters, the method shown here is an effective correction. Physical filters may be less viable if they introduce strong sensitivity to Schlieren bands in the dosimeters.
Optical-computed tomography (CT) and optical-emission computed tomography (ECT) are recent techniques with potential for high-resolution multi-faceted 3D imaging of the structure and function in unsectioned tissue samples up to 1–4 cc. Quantitative imaging of 3D fluorophore distribution (e.g. GFP) using optical-ECT is challenging due to attenuation present within the sample. Uncorrected reconstructed images appear hotter near the edges than at the center. A similar effect is seen in SPECT/PET imaging, although an important difference is attenuation occurs for both emission and excitation photons. This work presents a way to implement not only the emission attenuation correction utilized in SPECT, but also excitation attenuation correction and source strength modeling which are unique to optical-ECT. The performance of the correction methods was investigated by the use of a cylindrical gelatin phantom whose central region was filled with a known distribution of attenuation and fluorophores. Uncorrected and corrected reconstructions were compared to a sectioned slice of the phantom imaged using a fluorescent dissecting microscope. Significant attenuation artifacts were observed in uncorrected images and appeared up to 80% less intense in the central regions due to attenuation and an assumed uniform light source. The corrected reconstruction showed agreement throughout the verification image with only slight variations (~5%). Final experiments demonstrate the correction in tissue as applied to a tumor with constitutive RFP.
Rheumatoid arthritis (RA) is a debilitating, chronic, persistent inflammatory disease that is characterised by painful and swollen joints. The aetiology of RA is unknown, however whereas past research has concentrated on the role of immune or inflammatory infiltrating cells in inflammation, it is becoming clear that stromal cells play a critical part in regulating the quality and duration of an inflammatory response. In this review we assess the role of fibroblasts within the inflamed synovium in modulating immune responses; in particular we examine the role of stromal cells in the switch from resolving to persistent inflammation as is found in the rheumatoid synovium.
Rheumatoid arthritis; Cytokines; Chemokines; Synovitis; Inflammation
Synovial fibroblasts share a number of phenotype markers with fibroblasts derived from bone marrow. In this study we investigated the role of matched fibroblasts obtained from 3 different sources (bone marrow, synovium, and skin) to test the hypothesis that synovial fibroblasts share similarities with bone marrow–derived fibroblasts in terms of their ability to support survival of T cells and neutrophils.
Matched synovial, bone marrow, and skin fibroblasts were established from 8 different patients with rheumatoid arthritis who were undergoing knee or hip surgery. Resting or activated fibroblasts were cocultured with either CD4 T cells or neutrophils, and the degree of leukocyte survival, apoptosis, and proliferation were measured.
Fibroblasts derived from all 3 sites supported increased survival of CD4 T cells, mediated principally by interferon-β. However, synovial and bone marrow fibroblasts shared an enhanced site-specific ability to maintain CD4 T cell survival in the absence of proliferation, an effect that was independent of fibroblast activation or proliferation but required direct T cell–fibroblast cell contact. In contrast, fibroblast-mediated neutrophil survival was less efficient, being independent of the site of origin of the fibroblast but dependent on prior fibroblast activation, and mediated solely by soluble factors, principally granulocyte–macrophage colony-stimulating factor.
These results suggest an important functional role for fibroblasts in the differential accumulation of leukocyte subsets in a variety of tissue microenvironments. The findings also provide a potential explanation for site-specific differences in the pattern of T cell and neutrophil accumulation observed in chronic inflammatory diseases.
High expression of galectin 3 at sites of joint destruction in rheumatoid arthritis (RA) suggests that galectin 3 plays a role in RA pathogenesis. Previous studies have demonstrated the effects of galectins on immune cells, such as lymphocytes and macrophages. This study was undertaken to investigate the hypothesis that galectin 3 induces proinflammatory effects in RA by modulating the pattern of cytokine and chemokine production in synovial fibroblasts.
Matched samples of RA synovial and skin fibroblasts were pretreated with galectin 3 or tumor necrosis factor α (TNFα), and the levels of a panel of cytokines, chemokines, and matrix metalloproteinases (MMPs) were determined using enzyme-linked immunosorbent assays and multiplex assays. Specific inhibitors were used to dissect signaling pathways, which were confirmed by Western blotting and NF-κB activation assay.
Galectin 3 induced secretion of interleukin-6 (IL-6), granulocyte–macrophage colony-stimulating factor, CXCL8, and MMP-3 in both synovial and skin fibroblasts. By contrast, galectin 3–induced secretion of TNFα, CCL2, CCL3, and CCL5 was significantly greater in synovial fibroblasts than in skin fibroblasts. TNFα blockade ruled out autocrine TNFα-stimulated induction of chemokines. The MAPKs p38, JNK, and ERK were necessary for IL-6 production, but phosphatidylinositol 3-kinase (PI 3-kinase) was required for selective CCL5 induction. NF-κB activation was required for production of both IL-6 and CCL5.
Our findings indicate that galectin 3 promotes proinflammatory cytokine secretion by tissue fibroblasts. However, galectin 3 induces the production of mononuclear cell–recruiting chemokines uniquely from synovial fibroblasts, but not matched skin fibroblasts, via a PI 3-kinase signaling pathway. These data provide further evidence of the role of synovial fibroblasts in regulating the pattern and persistence of the inflammatory infiltrate in RA and suggest a new and important functional consequence of the observed high expression of galectin 3 in the rheumatoid synovium.
Achieving accurate small field dosimetry is challenging. This study investigates the utility of a radiochromic plastic PRESAGE® read with optical-CT for the acquisition of radiosurgery field commissioning data from a Novalis Tx system with a high-definition multileaf collimator (HDMLC). Total scatter factors (Sc, p), beam profiles, and penumbrae were measured for five different radiosurgery fields (5, 10, 20, 30 and 40 mm) using a commercially available optical-CT scanner (OCTOPUS, MGS Research). The percent depth dose (PDD), beam profile and penumbra of the 10 mm field were also measured using a higher resolution in-house prototype CCD-based scanner. Gafchromic EBT® film was used for independent verification. Measurements of Sc, p made with PRESAGE® and film agreed with mini-ion chamber commissioning data to within 4% for every field (range 0.2–3.6% for PRESAGE®, and 1.6–3.6% for EBT). PDD, beam profile and penumbra measurements made with the two PRESAGE®/optical-CT systems and film showed good agreement with the high-resolution diode commissioning measurements with a competitive resolution (0.5 mm pixels). The in-house prototype optical-CT scanner allowed much finer resolution compared with previous applications of PRESAGE®. The advantages of the PRESAGE® system for small field dosimetry include 3D measurements, negligible volume averaging, directional insensitivity, an absence of beam perturbations, energy and dose rate independence.
To investigate the dosimetric properties of a new Presage formulation which exhibits a reversible color change on exposure to radiation. PresageREU offers the intriguing possibility of the first re-useable 3D dosimetry material.
Method and Materials
Small volumes of PresageREU in 1×1×5cm optical cuvettes were irradiated and re-irradiated under a variety of conditions and times to investigate a range of properties including re-usability, dose-rate dependence, dose sensitivity, temporal response, energy sensitivity, and temperature dependence.
The radiation induced change in optical density (OD) was found to be linear with dose after initial and subsequent irradiations. After the first irradiation OD was observed to clear in ~2 weeks when stored at room temperature. 3 subsequent irradiations of the same cuvettes showed a very similar strong OD response, although there was a significant increase between this response and that achieve at initial irradiation.
The PresageREU formulation shows strong potential as the first re-useable 3D dosimetry material. When dosimeters are stored at room temperature (~22°C) clearing can occur in 2–3 weeks.
Several millions of kilometres of pipes and cables are buried beneath our streets in the UK. As they are not visible and easily accessible, the monitoring of their integrity as well as the quality of their contents is a challenge. Any information of these properties aids the utility owners in their planning and management of their maintenance regime. Traditionally, expensive and very localised sensors are used to provide irregular measurements of these properties. In order to have a complete picture of the utility network, cheaper sensors need to be investigated which would allow large numbers of small sensors to be incorporated into (or near to) the pipe leading to so-called smart pipes. This paper focuses on a novel trial where a short section of a prototype smart pipe was buried using mainly off-the-shelf sensors and communication elements. The challenges of such a burial are presented together with the limitations of the sensor system. Results from the sensors were obtained during and after burial indicating that off-the-shelf sensors can be used in a smart pipes system although further refinements are necessary in order to miniaturise these sensors. The key challenges identified were the powering of these sensors and the communication of the data to the operator using a range of different methods.
smart pipes; intelligent water distribution networks; MEMS; smart technology; structural monitoring
Th17 cells have been implicated in the pathogenesis of rheumatoid arthritis (RA). The aim of this study was to systematically analyse the phenotype, cytokine profile and frequency of interleukin-17 (IL-17) producing CD4-positive T cells in mononuclear cells isolated from peripheral blood, synovial fluid and synovial tissue of RA patients with established disease, and to correlate cell frequencies with disease activity.
Flow cytometry was used to analyse the phenotype and cytokine production of mononuclear cells isolated from peripheral blood (PBMC) (n = 44), synovial fluid (SFMC) (n = 14) and synovium (SVMC) (n = 10) of RA patients and PBMC of healthy controls (n = 13).
The frequency of IL-17-producing CD4 T cells was elevated in RA SFMC compared with RA PBMC (P = 0.04). However, the frequency of this population in RA SVMC was comparable to that in paired RA PBMC. The percentage of IL-17-producing CD4 T cells coexpressing tumor necrosis factor alpha (TNFα) was significantly increased in SFMC (P = 0.0068). The frequency of IFNγ-producing CD4 T cells was also significantly higher in SFMC than paired PBMC (P = 0.042). The majority of IL-17-producing CD4 T cells coexpressed IFNγ. IL-17-producing CD4 T cells in RA PBMC and SFMC exhibited very little IL-22 or IL-23R coexpression.
These findings demonstrate a modest enrichment of IL-17-producing CD4 T cells in RA SFMC compared to PBMC. Th17 cells in SFMC produce more TNFα than their PBMC counterparts, but are not a significant source of IL-22 and do not express IL-23R. However, the percentage of CD4 T cells which produce IL-17 in the rheumatoid joint is low, suggesting that other cells may be alternative sources of IL-17 within the joints of RA patients.
In the last decade, thermal melt/thermal shift assays have become a common tool for identifying ligands and other factors that stabilize specific proteins. Increased stability is indicated by an increase in the protein's melting temperature (Tm). In optimizing the assays for subsequent screening of compound libraries, it is important to minimize the variability of Tm measurements so as to maximize the assay's ability to detect potential ligands. Here we present an investigation of Tm variability in recombinant proteins from Plasmodium parasites. Ligands of Plasmodium proteins are particularly interesting as potential starting points for drugs for malaria, and new drugs are urgently needed. A single standard buffer (100 mM HEPES, pH 7.5, 150 mM NaCl) permitted estimation of Tm for 58 of 61 Plasmodium proteins tested. However, with several proteins, Tm could not be measured with a consistency suitable for high-throughput screening unless alternative protein-specific buffers were employed. We conclude that buffer optimization to minimize variability in Tm measurements increases the success of thermal melt screens involving proteins for which a standard buffer is suboptimal.
thermal shift assays; protein unfolding; protein stabilization; superoxide dismutase
Increasing availability and extent of biological ocean time series (from both in situ and satellite data) have helped reveal significant phenological variability of marine plankton. The extent to which the range of this variability is modified as a result of climate change is of obvious importance. Here we summarize recent research results on phenology of both phytoplankton and zooplankton. We suggest directions to better quantify and monitor future plankton phenology shifts, including (i) examining the main mode of expected future changes (ecological shifts in timing and spatial distribution to accommodate fixed environmental niches vs. evolutionary adaptation of timing controls to maintain fixed biogeography and seasonality), (ii) broader understanding of phenology at the species and community level (e.g. for zooplankton beyond Calanus and for phytoplankton beyond chlorophyll), (iii) improving and diversifying statistical metrics for indexing timing and trophic synchrony and (iv) improved consideration of spatio-temporal scales and the Lagrangian nature of plankton assemblages to separate time from space changes.
plankton; phenology; life history; climate change
Treatment of γ,δ-unsaturated ketones with hydrogen peroxide and acid provides a rapid entry into the medicinally important 1,2,4-trioxane structure. Alkene substitution that stabilizes carbocationic intermediates proved to be important for the success of this transformation.
Endogenous fluorophores provide a simple, but elegant means to investigate the relationship between agonist-evoked Ca2+ signals and the activation of mitochondrial metabolism. In this article, we discuss the methods and strategies to measure cellular pyridine nucleotide and flavoprotein fluorescence alone or in combination with Ca2+-sensitive indicators. These methods were developed using primary cultured hepatocytes and neurons, which contain relatively high levels of endogenous fluorophores and robust metabolic responses. Nevertheless, these methods are amendable to a wide variety of primary cell types and cell lines that maintain active mitochondrial metabolism.
Mitochondria; calcium; inositol 1,4,5-trisphosphate; pyridine nucleotides; flavoproteins; membrane potential; digital fluorescence imaging; confocal microscopy
In genetic studies of rare complex diseases it is common to ascertain familial data from population based registries through all incident cases diagnosed during a pre-defined enrollment period. Such an ascertainment procedure is typically taken into account in the statistical analysis of the familial data by constructing either a retrospective or prospective likelihood expression, which conditions on the ascertainment event. Both of these approaches lead to a substantial loss of valuable data.
Methodology and Findings
Here we consider instead the possibilities provided by a Bayesian approach to risk analysis, which also incorporates the ascertainment procedure and reference information concerning the genetic composition of the target population to the considered statistical model. Furthermore, the proposed Bayesian hierarchical survival model does not require the considered genotype or haplotype effects be expressed as functions of corresponding allelic effects. Our modeling strategy is illustrated by a risk analysis of type 1 diabetes mellitus (T1D) in the Finnish population-based on the HLA-A, HLA-B and DRB1 human leucocyte antigen (HLA) information available for both ascertained sibships and a large number of unrelated individuals from the Finnish bone marrow donor registry. The heterozygous genotype DR3/DR4 at the DRB1 locus was associated with the lowest predictive probability of T1D free survival to the age of 15, the estimate being 0.936 (0.926; 0.945 95% credible interval) compared to the average population T1D free survival probability of 0.995.
The proposed statistical method can be modified to other population-based family data ascertained from a disease registry provided that the ascertainment process is well documented, and that external information concerning the sizes of birth cohorts and a suitable reference sample are available. We confirm the earlier findings from the same data concerning the HLA-DR3/4 related risks for T1D, and also provide here estimated predictive probabilities of disease free survival as a function of age.
Technologies based on DNA microarrays have the potential to provide detailed information on genomic aberrations in tumor cells. In practice a major obstacle for quantitative detection of aberrations is the heterogeneity of clinical tumor tissue. Since tumor tissue invariably contains genetically normal stromal cells, this may lead to a failure to detect aberrations in the tumor cells.
Using SNP array data from 44 non-small cell lung cancer samples we have developed a bioinformatic algorithm that accurately models the fractions of normal and tumor cells in clinical tumor samples. The proportion of normal cells in combination with SNP array data can be used to detect and quantify copy number neutral loss-of-heterozygosity (CNNLOH) in the tumor cells both in crude tumor tissue and in samples enriched for tumor cells by laser capture microdissection.
Genome-wide quantitative analysis of CNNLOH using the CNNLOH Quantifier method can help to identify recurrent aberrations contributing to tumor development in clinical tumor samples. In addition, SNP-array based analysis of CNNLOH may become important for detection of aberrations that can be used for diagnostic and prognostic purposes.
Excess levels of circulating amino acids (AAs) play a causal role in specific human pathologies, including obesity and type 2 diabetes. Moreover, obesity and diabetes are contributing factors in the development of cancer, with recent studies suggesting this link is in part mediated by AA activation of mammalian Target Of Rapamycin (mTOR) Complex1. AAs appear to mediate this response through class 3 PI3K, or hVps34, rather than through the canonical class 1 PI3K pathway used by growth factors and hormones. Here we show that AAs induce a rise in intracellular Ca2+ ([Ca2+]i), which triggers mTOR Complex1 and hVps34 activation. We demonstrate that the rise in [Ca2+]i increases the direct binding of Ca2+/CaM to an evolutionarily conserved motif in hVps34 that is required for lipid kinase activity and increased mTOR Complex1 signaling. These findings have important implications regarding the basic signaling mechanisms linking metabolic disorders with cancer progression.
Various approaches have been described for metal-on-metal hip resurfacing. We compared the posterolateral and direct lateral approaches for complications, pain, function, and implant survival in the short and medium term for two surgeons in a consecutive series of 790 patients (909 hips; July 1997 to July 2004) followed until July 2007. The direct lateral approach group included 135 resurfacing procedures and the posterolateral group included 774 procedures. There was no difference between the two groups for age or gender. The minimum followup for the anterolateral group was 2 years (mean, 5.1 years; range, 2.0–9.4 years) and for the posterolateral group 2 years (mean, 5.5 years; range, 2.0–9.6 years). There were no differences between the two approaches for complications, additional surgery, implant survival, or Oxford hip scores. The 8-year survival rate was 97.9% (95% confidence interval, 89.9–100) for the direct lateral approach and 97.2% (95% confidence interval, 93.9–99.3) for the posterolateral approach. This study indicates both approaches offer excellent pain reduction and return to function after Birmingham hip resurfacing with no difference in survival or in the incidence of complications. An 8-year survival rate of 97% can be achieved using either the posterolateral approach or the direct lateral approach.
Level of Evidence: Level III, therapeutic study. See the Guidelines for authors for a complete description of levels of evidence.
We propose a method for improving the quality of signal from DNA microarrays by using several scans at varying scanner sen-sitivities. A Bayesian latent intensity model is introduced for the analysis of such data. The method improves the accuracy at which expressions can be measured in all ranges and extends the dynamic range of measured gene expression at the high end. Our method is generic and can be applied to data from any organism, for imaging with any scanner that allows varying the laser power, and for extraction with any image analysis software. Results from a self-self hybridization data set illustrate an improved precision in the estimation of the expression of genes compared to what can be achieved by applying standard methods and using only a single scan.
Diet-induced obesity and its serious consequences such as diabetes, cardiovascular disease, and cancer are rapidly becoming a major global health threat. Therefore, understanding the cellular and molecular mechanisms by which dietary fat causes obesity and diabetes is of paramount importance in order to identify preventive and therapeutic strategies. Increased dietary fat intake results in high plasma levels of triglyceride-rich lipoproteins (TGRL). Tissue uptake of TGRL has been shown to promote glucose intolerance. We generated mice with an adipocyte-specific inactivation of the multifunctional receptor LDL receptor–related protein–1 (LRP1) to determine its role in mediating the effects of TGRL on diet-induced obesity and diabetes. Knockout mice displayed delayed postprandial lipid clearance, reduced body weight, smaller fat stores, lipid-depleted brown adipocytes, improved glucose tolerance, and elevated energy expenditure due to enhanced muscle thermogenesis. We further demonstrated that inactivation of adipocyte LRP1 resulted in resistance to dietary fat–induced obesity and glucose intolerance. These findings identify LRP1 as a critical regulator of adipocyte energy homeostasis, where functional disruption leads to reduced lipid transport, increased insulin sensitivity, and muscular energy expenditure.
Uptake of Ca2+ by mitochondria serves as a regulator of a number of important cellular functions, including energy metabolism, cytoplasmic Ca2+ signals, and apoptosis. Recent findings reveal that the process of Ca2+ uptake by the mitochondrial uniporter is itself regulated by Ca2+ in a temporally complex manner.
Malaria parasites, Plasmodia, spend most of their asexual life cycle within red blood cells, where they proliferate and mature. The erythrocyte cytoplasm has very low [Ca2+] (<100 nM), which is very different from the extracellular environment encountered by most eukaryotic cells. The absence of extracellular Ca2+ is usually incompatible with normal cell functions and survival. In the present work, we have tested the possibility that Plasmodia overcome the limitation posed by the erythrocyte intracellular environment through the maintenance of a high [Ca2+] within the parasitophorous vacuole (PV), the compartment formed during invasion and within which the parasites grow and divide. Thus, Plasmodia were allowed to invade erythrocytes in the presence of Ca2+ indicator dyes. This allowed selective loading of the Ca2+ probes within the PV. The [Ca2+] within this compartment was found to be ∼40 μM, i.e., high enough to be compatible with a normal loading of the Plasmodia intracellular Ca2+ stores, a prerequisite for the use of a Ca2+-based signaling mechanism. We also show that reduction of extracellular [Ca2+] results in a slow depletion of the [Ca2+] within the PV. A transient drop of [Ca2+] in the PV for a period as short as 2 h affects the maturation process of the parasites within the erythrocytes, with a major reduction 48 h later in the percentage of schizonts, the form that re-invades the red blood cells.
parasitophorous vacuole; signal transduction; Plasmodium; calcium indicators; melatonin