Background: Adipose tissue is a primary in vivo site of inflammation in obesity. Excess visceral adipose tissue (VAT), when compared to subcutaneous adipose tissue (SAT), imparts an increased risk of ...obesity-related comorbidities and mortality, and exhibits differences in inflammation. Defining depot-specific differences in inflammatory function may reveal underlying mechanisms of adipose-tissue-based inflammation. Methods: Stromovascular cell fractions (SVFs) from VAT and SAT from obese humans undergoing bariatric surgery were studied in an in vitro culture system with transcriptional profiling, flow cytometric phenotyping, enzyme-linked immunosorbent assay and intracellular cytokine staining. Results: Transcriptional profiling of SVF revealed differences in inflammatory transcript levels in VAT relative to SAT, including elevated interferon- (IFN-) transcript levels. VAT demonstrated a broad leukocytosis relative to SAT that included macrophages, T cells and natural killer (NK) cells. IFN- induced a proinflammatory cytokine expression pattern in SVF and adipose tissue macrophages (ATM). NK cells, which constitutively expressed IFN-, were present at higher frequency in VAT relative to SAT. Both T and NK cells from SVF expressed IFN- on activation, which was associated with tumor necrosis factor- expression in macrophages. Conclusion: These data suggest involvement of NK cells and IFN- in regulating ATM phenotype and function in human obesity and a potential mechanism for the adverse physiologic effects of VAT.
Key message
Herbivorous mammals, from small voles to large ungulates, strip and eat the bark of young plantation trees. They do this most frequently at times when sources of protein food that can ...support their reproduction and lactation are in short supply. Furthermore, they preferentially attack—often repeatedly—trees that have experienced some form of environmental stress, leaving neighbouring trees untouched. Such stressed trees carry higher levels of amino acids in their phloem. These facts, coupled with the similarly timed and selective harvesting of bark phloem by some Australia marsupials and Northern Hemisphere woodpeckers indicate that it is the trees’ protein-enriched phloem that the bark strippers are seeking.
More and more studies are demonstrating that populations of animals ‐ from herbivores to top predators, vertebrates and invertebrates ‐ are limited by their food, and that the availability of this ...food is dictated by the weather. Satellite monitoring is revealing how cyclic and quasi‐cyclic climatic patterns, like the El Niño Southern Oscillation and the North Atlantic Oscillation, are driving and synchronising these weather‐driven changes in the supplies of food. Changes in the amount of food available operate to limit the abundance of populations largely through their influence on the survival of the very young: the Achilles heel of all populations.
Any individual organism struggles to use whatever resources it can get from a mostly inhospitable environment to maximise the proliferation of its genes. Each level of a food chain is thus dependent upon, and pressing hard against the limits set by the one below. The resulting intra‐ and inter‐specific interactions produce a multitude of complex outcomes, that significantly influence the dynamics of populations, but do not determine their ultimate size. There is no density‐dependent regulation of abundance. Intra‐specific competition does not determine the size of populations, it only decides which few individuals gain access to the limited food. Nor do predators regulate their prey. They, too, are limited by their food, and the abundance and quality of food is dictated by the weather.
Aims
Hypoxia has been implicated as a cause of adipose tissue inflammation in obesity, although the inflammatory response of human adipose tissue to hypoxia is not well understood. The goal of this ...study was to define in vitro inflammatory responses of human adipose tissue to hypoxia and identify molecular mechanisms of hypoxia-induced inflammation.
Methods
The inflammatory milieu and responses of visceral (VAT) and subcutaneous (SAT) adipose tissue explants and purified stromovascular cells (SVFs) from obese and lean humans were studied in an in vitro hypoxic culture system using quantitative real-time PCR, ELISA, western blotting, immunofluorescence microscopy, flow cytometry and immunohistochemistry.
Results
Human adipose tissue in obesity demonstrates an increased leucocyte infiltrate that is greater in VAT than SAT and involves macrophages, T cells and natural killer (NK) cells. Hypoxic culture regulates inflammatory cytokine secretion and transcription of metabolic stress response genes in human adipose tissue SVF. Adipocyte diameter is increased and adipose tissue capillary density is decreased in obese participants. Inhibition of c-Jun terminal kinase (JNK) or p38 significantly attenuates hypoxia-induced SVF inflammatory responses. Hypoxia induces phosphorylation of p38 in adipose tissue.
Conclusions
Human adipose tissue in obesity is characterised by a depot-specific inflammatory cell infiltrate that involves not only macrophages, but also T cells and NK cells. Hypoxia induces inflammatory cytokine secretion by human adipose tissue SVF, the primary source of which is adipose tissue macrophages. These data implicate p38 in the regulation of hypoxia-induced inflammation and suggest that alterations in adipocyte diameter and adipose tissue capillary density may be potential underlying causes of adipose tissue hypoxia.
The cluster size dependence of superconductivity in the conventional two-dimensional Hubbard model, commonly believed to describe high-temperature superconductors, is systematically studied using the ...dynamical cluster approximation and quantum Monte Carlo simulations as a cluster solver. Because of the nonlocality of the d-wave superconducting order parameter, the results on small clusters show large size and geometry effects. In large enough clusters, the results are independent of the cluster size and display a finite temperature instability to d-wave superconductivity.
Aims. In this work we examine how environment influences the merger fraction, from the low density field environment to higher density groups and clusters. We also study how the properties of a group ...or cluster, as well as the position of a galaxy in the group or cluster, influences the merger fraction. Methods. We identified galaxy groups and clusters in the North Ecliptic Pole using a friends-of-friends algorithm and the local density. Once identified, we determined the central galaxies, group radii, velocity dispersions, and group masses of these groups and clusters. Merging systems were identified with a neural network as well as visually. With these identifications and properties of groups and clusters and merging galaxy identifications, we examined how the merger fraction changes as the local density changes for all galaxies as well as how the merger fraction changes as the properties of the groups or clusters change. Results. We find that the merger fraction increases as local density increases and decreases as the velocity dispersion increases, as is often found in the literature. A decrease in merger fraction as the group mass increases is also found. We also find that groups with larger radii have higher merger fractions. The number of galaxies in a group does not influence the merger fraction. Conclusions. The decrease in merger fraction as group mass increases is a result of the link between group mass and velocity dispersion. Hence, this decrease in merger fraction with increasing mass is a result of the decrease of merger fraction with velocity dispersion. The increasing relation between group radii and merger fraction may be a result of larger groups having smaller velocity dispersion at a larger distance from the centre or larger groups hosting smaller, infalling groups with more mergers. However, we do not find evidence of smaller groups having higher merger fractions.
Outbreaks of cambium‐feeding beetles follow droughts, becoming most severe in overmature trees and those growing on stressful sites or planted beyond their natural range. Outbreaks develop from small ...endemic populations confined to a few senescing or damaged trees and expand into neighbouring trees that become newly stressed as a drought intensifies, eventually coalescing as a full‐blown outbreak. The beetles' larvae normally face a severe nutritional challenge feeding on the slow outflow of dilute nutrients in the phloem of damaged or senescing trees. This is reflected in their slow rate of growth. But when drought stresses trees, they senesce more quickly, releasing a faster flow of more concentrated nutrients that enhances the survival of the insects. The increased survival and faster rate of growth of larvae feeding in this enriched phloem can generate an outbreak. Both the dieback of the trees and the outbreaks of these insects are generated by drought. This hypothesis presents a parsimonious explanation for outbreaks of cambium‐feeding insects. Apart from providing a focus for future research, it has the added benefit that it replaces non‐explanatory descriptions of these outbreaks with a testable biological explanation based on known plant and insect physiology.
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