Capillaries within compartments: microvascular interpretation of dynamic positron emission tomography data

Measurement of exchange of substances between blood and tissue has been a long-lasting challenge to physiologists, and considerable theoretical and experimental accomplishments were achieved before the development of the positron emission tomography (PET). Today, when modeling data from modern PET scanners, little use is made of earlier microvascular research in the compartmental models, which have become the standard model by which the vast majority of dynamic PET data are analysed. However, modern PET scanners provide data with a sufficient temporal resolution and good counting statistics to allow estimation of parameters in models with more physiological realism. We explore the standard compartmental model and find that incorporation of blood flow leads to paradoxes, such as kinetic rate constants being time-dependent, and tracers being cleared from a capillary faster than they can be supplied by blood flow. The inability of the standard model to incorporate blood flow consequently raises a need for models that include more physiology, and we develop microvascular models which remove the inconsistencies. The microvascular models can be regarded as a revision of the input function. Whereas the standard model uses the organ inlet concentration as the concentration throughout the vascular compartment, we consider models that make use of spatial averaging of the concentrations in the capillary volume, which is what the PET scanner actually registers. The microvascular models are developed for both single- and multi-capillary systems and include effects of non-exchanging vessels. They are suitable for analysing dynamic PET data from any capillary bed using either intravascular or diffusible tracers, in terms of physiological parameters which include regional blood flow.     

Pasteurella pneumotropica in rabbits from a "Pasteurella-free" production colony

Pasteurella pneumotropica was isolated from the nasopharyngeal area of two of five rabbits obtained from a "Pasteurella-free" production colony. No evidence of disease was observed in these rabbits during clinical and necropsy examinations.     

Brite/beige fat and UCP1 — is it thermogenesis?

The presence of two distinct types of adipose tissue, which have opposing functions, has been known for decades. White adipose tissue (WAT) is the main tissue of energy storage, while brown adipose tissue (BAT) dissipates energy as heat and is required for non-shivering thermoregulation. In the last few years, a third type of adipocyte was identified, termed the brite (“brown and white”) or beige adipocyte. Their physiological control and role, however, are not fully clarified. Brite/beige adipocytes have a positive impact on systemic metabolism that is generally explained by the thermogenesis of brite/beige adipocytes; although thermogenesis has not been directly measured but is mostly inferred by gene expression data of typical thermogenic genes such as uncoupling protein 1 (UCP1). Here we critically review functional evidence for the thermogenic potential of brite/beige adipocytes, leading to the conclusion that direct measurements of brite/beige adipocyte bioenergetics, beyond gene regulation, are pivotal to quantify their thermogenic potential. In particular, we exemplified that the massive induction of UCP1 mRNA during the browning of isolated subcutaneous adipocytes in vitro is not reflected in significant alterations of cellular bioenergetics. Herein, we demonstrate that increases in mitochondrial respiration in response to beta-adrenergic stimulus can be independent of UCP1. Using HEK293 cells expressing UCP1, we show how to directly assess UCP1 function by adequate activation in intact cells. Finally, we provide a guide on the interpretation of UCP1 activity and the pitfalls by solely using respiration measurements. The functional analysis of beige adipocyte bioenergetics will assist to delineate the impact of browning on thermogenesis, possibly elucidating additional physiological roles and its contribution to systemic metabolism, highlighting possible avenues for future research. This article is part of a Special Issue entitled: 18th European Bioenergetic Conference.     

Exploring the activity of tobacco etch virus protease in detergent solutions

Tobacco etch virus (TEV) protease is generally used to remove affinity tags from target proteins. It has been reported that some detergents inhibit the activity of this protease, and therefore should be avoided when removing affinity tags from membrane proteins. The aim of this study was to explore and evaluate this further. Hence, affinity tag removal with TEV protease was tested from three membrane proteins (a Pgp synthase and two CorA homologs) in the presence of 16 different detergents commonly used in membrane protein purification and crystallization. We observed that in the presence of the same detergent (Triton X-100), TEV protease could remove the affinity tag completely from one protein (CorA) but not from another protein (Pgp synthase). There was also a large variation in yield of cleaved membrane protein in different detergents, which probably depends on features of the protein-detergent complex. These observations show that, contrary to an earlier report, detergents do not inhibit the enzymatic activity of the TEV protease.     

The Environmental Foodprint of Obesity

Emissions of greenhouse gases (GHG) are linked to global warming and adverse climate changes. Meeting the needs of the increasing number of people on the planet presents a challenge for reducing total GHG burden. A further challenge may be the size of the average person on the planet and the increasing number of people with excess body weight. We used data on GHG emissions from various sources and estimated that obesity is associated with ~20% greater GHG emissions compared with the normal‐weight state. On a global scale, obesity contributes to an extra GHG emissions of ~49 megatons per year of CO₂ equivalent (CO₂eq) from oxidative metabolism due to greater metabolic demands, ~361 megatons per year of CO₂eq from food production processes due to increased food intake, and ~290 megatons per year of CO₂eq from automobile and air transportation due to greater body weight. Therefore, the total impact of obesity may be extra emissions of ~700 megatons per year of CO₂eq, which is about 1.6% of worldwide GHG emissions. Inasmuch as obesity is an important contributor to global GHG burden, strategies to reduce its prevalence should prioritize efforts to reduce GHG emissions. Accordingly, reducing obesity may have considerable benefits for both public health and the environment.     

Phylogenetic relationships among superfamilies of Hymenoptera

The first comprehensive analysis of higher‐level phylogeny of the order Hymenoptera is presented. The analysis includes representatives of all extant superfamilies, scored for 392 morphological characters, and sequence data for four loci (18S, 28S, COI and EF‐1α). Including three outgroup taxa, 111 terminals were analyzed. Relationships within symphytans (sawflies) and Apocrita are mostly resolved. Well supported relationships include: Xyeloidea is monophyletic, Cephoidea is the sister group of Siricoidea + [Xiphydrioidea + (Orussoidea + Apocrita)]; Anaxyelidae is included in the Siricoidea, and together they are the sister group of Xiphydrioidea + (Orussoidea + Apocrita); Orussoidea is the sister group of Apocrita, Apocrita is monophyletic; Evanioidea is monophyletic; Aculeata is the sister group of Evanioidea; Proctotrupomorpha is monophyletic; Ichneumonoidea is the sister group of Proctotrupomorpha; Platygastroidea is sister group to Cynipoidea, and together they are sister group to the remaining Proctotrupomorpha; Proctotrupoidea s. str. is monophyletic; Mymarommatoidea is the sister group of Chalcidoidea; Mymarommatoidea + Chalcidoidea + Diaprioidea is monophyletic. Weakly supported relationships include: Stephanoidea is the sister group of the remaining Apocrita; Diaprioidea is monophyletic; Ceraphronoidea is the sister group of Megalyroidea, which together form the sister group of [Trigonaloidea (Aculeata + Evanioidea)]. Aside from paraphyly of Vespoidea within Aculeata, all currently recognized superfamilies are supported as monophyletic. The diapriid subfamily Ismarinae is raised to family status, Ismaridae stat. nov. © The Will Henning Society 2011.     

Soluble signalling factors derived from differentiated cartilage tissue affect chondrogenic differentiation of rat adult marrow stromal cells.

BACKGROUND: Chondral defects show lack of proper regeneration whereas osteochondral lesions display limited regeneration capacity. Latter is probably due to immigration of chondroprogenitor cells from the subchondral bone. Known chondroprogenitor cells for cartilage tissues are multi-potent adult marrow stromal or mesenchymal stem cells (MSCs). In vitro chondrogenic differentiation of these precursor cells usually require cues from growth and signalling factors provided in vivo by surrounding tissues and cells. We hypothesise that signalling factors secreted by differentiated cartilage tissue can initiate and maintain chondrogenic differentiation status of MSCs. METHODS: To study such paracrine communication between allogenic rat articular cartilage and rat MSCs embedded in alginate beads a novel coculture system without addition of external growth factors has been established. RESULTS: Impact of cartilage on differentiating MSCs was observed at two different time points. Firstly, sustained expression of Sox9 was observed at an early stage which indicated induction of chondrogenic differentiation. Secondly, late stage repression of collagen X indicated pre-hypertrophic arrest of differentiation. In the culture supernatant we have identified vascular endothelial growth factor alpha (VEGF-164 alpha), matrix metalloproteinase (MMP) -13 and tissue inhibitors of MMPs (TIMP-1 and TIMP-2) which could be traced back either to the cartilage explant or to the MSCs under the influence of cartilage. CONCLUSION: The identified factors might be involved in regulation of collagen X gene and protein expression and therefore, may have an impact on the control and regulation of MSCs differentiation.