Impaired glucose homeostasis in mice lacking the alpha1b-adrenergic receptor subtype

To assess the role of the alpha1b-adrenergic receptor (AR) in glucose homeostasis, we investigated glucose metabolism in knockout mice deficient of this receptor subtype (alpha1b-AR-/-). Mutant mice had normal blood glucose and insulin levels, but elevated leptin concentrations in the fed state. During the transition to fasting, glucose and insulin blood concentrations remained markedly elevated for at least 6 h and returned to control levels after 24 h whereas leptin levels remained high at all times. Hyperinsulinemia in the post-absorptive phase was normalized by atropine or methylatropine indicating an elevated parasympathetic activity on the pancreatic beta cells, which was associated with increased levels of hypothalamic NPY mRNA. Euglycemic clamps at both low and high insulin infusion rates revealed whole body insulin resistance with reduced muscle glycogen synthesis and impaired suppression of endogenous glucose production at the low insulin infusion rate. The liver glycogen stores were 2-fold higher in the fed state in the alpha1b-AR-/- compared with control mice, but were mobilized at the same rate during the fed to fast transition or following glucagon injections. Finally, high fat feeding for one month increased glucose intolerance and body weight in the alpha1b-AR-/-, but not in control mice. Altogether, our results indicate that in the absence of the alpha1b-AR the expression of hypotalamic NPY and the parasympathetic nervous activity are both increased resulting in hyperinsulinemia and insulin resistance as well as favoring obesity and glucose intolerance development during high fat feeding.     

Sex ratio evolution through group selection using diffusion approximation

We consider a haploid, hermaphrodite population subdivided into an infinite number of demes of finite size N. Assuming recurrent mutation, random union of gametes, partial dispersal, genetic drift, and incorporating group competition, a diffusion approximation is used to describe the evolution of sex ratio, corresponding to sex allocation to male versus female functions. The stationary distribution is deduced. In presence of group selection, a female-biased sex ratio in the whole population is found to be optimal in the sense that an allele coding for this sex ratio is always more frequent at equilibrium when segregating with another allele coding for a different sex ratio than for the same sex ratio. Numerical studies are presented to check the validity and accuracy of this prediction.Research supported in part by grants from NSERC of Canada and FCAR of Quebec. This work is part of the first authors Ph.D. thesis at the Université de Montréal under the supervision of the second author.Send offprint requests to: Sabin Lessard     

Cerebral malaria, a key role for endothelial cells?

Five to six hundred millions of people, throughout the world, suffer from malaria and more than one million die each year as a consequence, in about 20% of the cases, of cerebral malaria, an important complication of Plasmodium falciparum infection (Holding & Snow, 2001). Despite many studies, the physiopathology of these cerebral occurrences is not understood, especially concerning the intricacy and respective roles of the various mechanisms identified: sequestration of parasitized red cells in microvessels, cytokine secretion, changes in the T lymphocyte repertoire, host genetic factors driving sensitivity pathogenic factors from Plasmodium (Mazier et al., 2000).     

Controlled sulfatation of natural anionic bacterial polysaccharides can yield agents with specific regenerating activity in vivo

The regenerating activities of chemically modified anionic bacterial polysaccharides by O-sulfonation were investigated using a in vivo model of rat injured muscle regeneration. Glucuronan (GA), a linear homopolysaccharide of -->4)-beta-D-GlcpA-(1--> residues partially acetylated at the C-3 and/or the C-2 position, and glucoglucuronan (GGA), a linear heteropolysaccharide of -->3)-beta-D-GlcpA-(1-->4)-beta-D-Glcp-(1--> residues were sulfated. SO3-DMF sulfatation complex provided polysaccharides with different sulfur contents, however, a depolymerization occurred because we did not use large excess of pyridine to obtain pure modified polysaccharides. A regenerating activity on injured extensor digitorum longus (EDL) muscles on rats was obtained with these two sulfated anionic polymers. The position of sulfate groups on glucoglucuronan (primary or secondary alcohol) seems to have no influence on the biological activity by opposition to the degree of sulfatation both for the glucuronans and the glucoglucuronans. The yield of acetate groups in the glucuronan polymer modulated the specific activity.     

Increase in selenium requirements with physical activity loads in well-trained athletes is not linear

Selenium requirements in athletes are supposed to be increased with energy expenditure (EE) to preserve selenium status and an optimal antioxidant balance. The question of whether selenium intakes are related to EE and whether plasma selenium status induces up-regulation in erythrocyte endogenous antioxidant defense and decreases plasma oxidative damage markers in athletes was addressed. 118 well-trained athletes completed 7 d food and activities records in a cross-sectional study. Blood was sampled on day 8. Among the athletes, 23% of the males and 66% of the females had selenium intakes below two-third of the French RDA. Plasma selenium concentrations in most of less trained athletes were lower than the postulated concentration to be required to maximize erythrocyte GSH-Px activity. Athletes with the highest daily EE had the highest selenium intakes, percentage of vegetal protein intakes and plasma selenium concentrations. Only 2.6% of the athletes exhibited low plasma selenium concentrations (< 0.75 micromol/l). The relation between plasma selenium and EE was polynomial (r = 0.50; P < 0.005). Erythrocyte GSH-Px activity in athletes was not linked to selenium status. Selenium requirements are increased in athletes without being linearly related to EE.     

Serial pronuclear transfer increases the developmental potential of in vitro-matured oocytes in mouse cloning

In vitro-matured germinal vesicle oocytes are an interesting source of cytoplast recipients in both animal and human nuclear transfer (NT) experiments. We investigated two technical aspects that might improve the developmental potential of nuclear transfer mouse embryos constructed from in vitro-matured germinal vesicle oocytes. In a first step, the effect of two maturation media on the embryonic development of NT embryos originating from in vitro-matured oocytes was compared. Supplementation of the oocyte maturation medium with serum and gonadotrophins improved the developmental rate of NT embryos constructed from in vitro-matured oocytes, but it was still inferior to that obtained with in vivo-matured metaphase II (MII) oocytes. Second, we investigated the effect of serial pronuclear transfer from NT zygotes originating from both in vitro- and in vivo-matured oocytes to in vivo-fertilized zygotic cytoplasts. Blastocyst quality was evaluated by counting nuclei from trophectoderm and inner cell mass cells using a differential staining. Sequential pronuclear transfer significantly improved the blastocyst formation rate of NT embryos originating from in vitro-matured oocytes up to the rate obtained with in vivo-matured MII oocytes. We conclude that the developmental potential of NT embryos constructed from in vitro-matured oocytes can be optimized by serial pronuclear transfer to in vivo-produced zygotic cytoplasts.     

Active caspase-8 translocates into the nucleus of apoptotic cells to inactivate poly(ADP-ribose) polymerase-2

Caspase-8 is the prototypic initiator of the death domain receptor pathway of apoptosis. Here, we report that caspase-8 not only triggers and amplifies the apoptotic process at cytoplasmic sites but can also act as an executioner at nuclear levels. In a murine model of acute ischemia, caspase-8 is relocated into the nucleus of apoptotic neurons, where it cleaves PARP-2, a member of the poly(ADP-ribose) polymerase family involved in DNA repair. As indicated by site-directed mutagenesis, PARP-2 cleavage occurs preferentially at the LQMD sequence mapped between the DNA binding and the catalytic domains of the protein. This is close to the cleavage sequence found in Bid, the cytoplasmic target of caspase-8. Activity assays confirm that cleavage of PARP-2 results in inactivation of its poly(ADP-ribosylation) property, proportional to the efficiency of the cleavage. Our findings add to the complexity of proteolytic caspase networks by demonstrating that caspase-8 is in turn an initiator, amplifier, and effector caspase.     

Affinity-dependent alterations of mouse B cell development by noninherited maternal antigen

We have examined the passage of maternal cells into the fetus during the gestation and postpartum in mice. Using enhanced green fluorescent protein (EGFP)-transgenic females, we showed that maternal cells frequently gain access to the fetus, mostly in syngeneic pregnancies, but also in allogeneic and outbred crosses. EGFP-transgenic cells, including B, T, and natural killer cells, can persist until adulthood, primarily in bone marrow and thymus. We then asked whether maternal cells, bearing antigens not inherited by the fetus, influence the development of fetal and neonatal B lymphocytes. We have used the B cell receptor 3-83 mu/delta transgenic mouse model, whose B cells recognize the major histocompatibility complex class I molecules H-2Kk and H-2Kb, with a high or moderate affinity, respectively. The fate of transgenic B cells in animals exposed to noninherited H-2Kk or H-2Kb maternal antigens (NIMA) during gestation and lactation was compared with those of nonexposed controls. In H-2Kk-exposed fetuses, NIMA-specific transgenic B cells are partially deleted during late gestation. Nondeleted cells have downmodulated their B cell receptor. In contrast, in NIMA H-2Kb-exposed neonates, transgenic B cells present an activated phenotype, including proliferation, upregulation of surface CD69, and preferential localization in the T cell zone of splenic follicles. This state of activation is still clearly detectable up to 3 wk of age. Thus, we show that fetal and neonatal B cell development is affected by maternal cells bearing antigens noninherited by the fetus and that this phenomenon is highly dependent on the affinity of the B cell receptor for the NIMA.