Effects of Murine Norovirus Infection on a Mouse Model of Diet-Induced Obesity and Insulin Resistance

Murine norovirus (MNV) is prevalent in SPF mouse facilities in the United States, and we currently lack sufficient data to determine whether it should be eliminated. It is generally accepted that the virus does not cause clinical symptoms in immunocompetent mice. However, we previously reported that MNV infection alters the phenotype of a mouse model of bacteria-induced inflammatory bowel disease in part through its effects on dendritic cells. The tropism of MNV toward macrophages and dendritic cells makes MNV a potential intercurrent variable in murine models of macrophage-driven inflammatory diseases, such as obesity, insulin resistance, and atherosclerosis. Therefore, we determined whether MNV infection altered obesity and insulin resistance phenotypes in C57BL/6 mice, a widely used model of diet-induced obesity. We found that MNV did not alter weight gain, food intake, and glucose metabolism in this model, but it did induce subtle changes in lymphoid tissue. Further studies using other models of metabolic diseases are needed to provide additional information on the potential role this ‘subclinical’ virus might have on disease progression in mouse models of inflammatory diseases.Abbreviations: HFD, high-fat diet; IPGTT, intraperitoneal glucose tolerance test; IPITT, intraperitoneal insulin tolerance test; MLN, mesenteric lymph node; MNV, murine norovirusMurine norovirus (MNV) is endemic in many SPF mouse colonies across North America,⁵ creating considerable potential for this virus to interfere with mouse models of human diseases. In addition, the presence of MNV in some mouse colonies and not in others may help explain phenotypic variability in mouse models across institutions. This virus is related to the human Norwalk virus that causes gastrointestinal inflammation in humans. Although MNV does not cause any overt illness in immunocompetent mice, significant inflammation and mortality can be induced in mice with abnormal innate immunity.⁷ Previously, we investigated the influence of MNV on the development of bacteria-induced inflammatory bowel disease in FVB.129P2-PAbcb1atm1Bor (Mdr1a^−/−) mice.⁸ We found that infection with MNV accelerated the progression of inflammatory bowel disease in this mouse model when mice were coinfected with Helicobacter bilis. In addition, infection with MNV alone altered the immune response, probably through changes in dendritic cells.⁸ These findings suggest that MNV may induce subtle changes in immune responses even in immunocompetent mice, given that MNV is known to preferentially infect macrophages and dendritic cells.²²Obesity has been defined as a disease of chronic inflammation, and in recent years, the prominent role that macrophages play in this process has been recognized.^9,10,21,24 Obesity is a risk factor for various chronic diseases that share inflammation as a critical component of the disease process, such as metabolic syndrome, diabetes, and atherosclerosis.³ Because MNV has tropism for macrophages, we wished to determine whether MNV infection influences the development of obesity and insulin resistance in a widely used animal model of diet-induced obesity. C57BL/6 mice are the most frequently used ‘wild-type’ strain and are prone to develop insulin resistance as obesity develops during high-fat feeding.¹ We hypothesized that MNV may accelerate inflammation by stimulating macrophage accumulation in adipose tissue, resulting in a more severe obesity or insulin resistance phenotype when mice are fed a high-fat diet.     

Genotype-by-environment interactions influencing the emergence of rpoS mutations in Escherichia coli populations

Polymorphisms in rpoS are common in Escherichia coli. rpoS status influences a trade-off between nutrition and stress resistance and hence fitness across different environments. To analyze the selective pressures acting on rpoS, measurement of glucose transport rates in rpoS+ and rpoS bacteria was used to estimate the role of F(nc), the fitness gain due to improved nutrient uptake, in the emergence of rpoS mutations in nutrient-limited chemostat cultures. Chemostats with set atmospheres, temperatures, pH's, antibiotics, and levels of osmotic stress were followed. F(nc) was reduced under anaerobiosis, high osmolarity, and with chloramphenicol, consistent with a reduced rate of rpoS enrichment in these conditions. F(nc) remained high, however, with alkaline pH and low temperature but rpoS sweeps were diminished. Under these conditions, F(sp), the fitness reduction due to lowered stress protection, became significant. We also estimated whether the fitness need for the gene was related to its regulation. No consistent pattern emerged between the level of RpoS and the loss of rpoS function in particular environments. This dissection allows an unprecedented view of the genotype-by-environment interactions controlling a mutational sweep and shows that both F(nc) and F(sp) are influenced by individual stresses and that additional factors contribute to selection pressure in some environments.     

Self-reported sugar-sweetened beverage intake among college students

Objective: To characterize sugar‐sweetened beverage intake of college students. Research Methods and Procedures: Undergraduates in an urban southern community campus were surveyed anonymously about sugared beverage consumption (soda, fruit drinks, energy drinks, sports drinks, sweet ice tea) in the past month. Results: Two hundred sixty‐five undergraduates responded (66% women, 46% minority, 100% of volunteers solicited). Most students (95%) reported sugared beverage intake in the past month, and 65% reported daily intake. Men were more likely than women to report daily intake (74% vs. 61%, p = 0.035). Soda was the most common sugar‐sweetened beverage. Black undergraduates reported higher sugared beverage intake than whites (p = 0.02), with 91% of blacks reporting sugar‐sweetened fruit drink intake in the past month and 50% reporting daily consumption. Mean estimated caloric intake from combined types of sugar‐sweetened beverages was significantly higher among black students than whites, 796 ± 941 vs. 397 ± 396 kcal/d (p = 0.0003); the primary source of sugar‐sweetened beverage calories among blacks was sugared fruit drinks (556 ± 918 kcal/d). Younger undergraduates reported significantly higher intake than older students (p = 0.025). Discussion: Self‐reported sugar‐sweetened beverage consumption among undergraduates is substantial and likely contributes considerable non‐nutritive calories, which may contribute to weight gain. Black undergraduates may be particularly vulnerable due to higher sugared beverage intake. Obesity prevention interventions targeting reductions in sugar‐sweetened beverages in this population merit consideration.     

Distribution of endothelin receptor subtypes ETA and ETB in the rat kidney.

The endothelin (ET) receptor system is markedly involved in the regulation of renal function under both physiological and pathophysiological conditions. The present study determined the detailed cellular localization of both ET receptor subtypes, ET(A) and ET(B), in the vascular and tubular system of the rat kidney by immunofluorescence microscopy. In the vascular system we observed both ET(A) and ET(B) receptors in the media of interlobular arteries and afferent and efferent arterioles. In interlobar and arcuate arteries, only ET(A) receptors were present on vascular smooth muscle cells. ET(B) receptor immunoreactivity was sparse on endothelial cells of renal arteries, whereas there was strong labeling of peritubular and glomerular capillaries as well as vasa recta endothelium. ET(A) receptors were evident on glomerular mesangial cells and pericytes of descending vasa recta bundles. In the renal tubular system, ET(B) receptors were located in epithelial cells of proximal tubules and inner medullary collecting ducts, whereas ET(A) receptors were found in distal tubules and cortical collecting ducts. Distribution of ET(A) and ET(B) receptors in the vascular and tubular system of the rat kidney reported in the present study supports the concept that both ET receptor subtypes cooperate in mediating renal cortical vasoconstriction but exert differential and partially antagonistic effects on renal medullary function.     

Optimising the foliar uptake of zinc oxide nanoparticles: Do leaf surface properties and particle coating affect absorption?

Foliar absorption of zinc (Zn) is limited by several barriers, the first of which is the leaf cuticle. In this study, we investigated the absorption of Zn from Zn oxide nanoparticles (ZnO-NPs) in wheat (Triticum aestivum cv Gladius) and sunflower (Helianthus annuus cv Hyoleic 41) to determine the importance of NP surface coating for Zn absorption. Fourier transform infrared (FTIR) spectroscopy showed a higher polysaccharide content in the wheat cuticle than sunflower, indicated by a more pronounced glycosidic bond at 1020 cm⁻¹, but wax and cutin content were similar. Scanning electron microscopy (SEM) revealed that t richome density was twice as high in wheat (3600 ± 900 cm⁻²) as in sunflower (1600 cm⁻²) and stomatal density four times higher in sunflower (6400 ± 800 cm⁻² in wheat and 22 900 cm⁻² in sunflower). Suspensions of ZnO-NPs with coatings of different hydrophobicity were applied to leaves to compare Zn absorption using X-ray fluorescence microscopy (XFM) and inductively coupled plasma mass spectroscopy (ICP-MS). Absorption of Zn was similar between wheat and sunflower when Zn was applied at 1000 mg Zn l⁻¹, but much less Zn was absorbed from all ZnO products than from soluble Zn fertiliser. Particle coating did not affect Zn absorption, but it may facilitate particle adhesion to leaves, providing a longer-term source of resupply of Zn ions to the leaves. Differences in leaf surface characteristics did not affect Zn absorption, indicating that the cuticle is the main pathway of absorption under these conditions.     

Polar bear stress hormone cortisol fluctuates with the North Atlantic Oscillation climate index

Polar bears are heavily dependent on sea ice for hunting sufficient prey to meet their energetic needs. When the bears are left fasting, it may cause a rise in the levels of the stress hormone cortisol. Cortisol is the major corticosteroid hormone in most mammals, including polar bears. Production and regulation of this stress hormone are vital for the body as it is part of a myriad of processes, including in relation to metabolism, growth, development, reproduction, and immune function. In the present study, we examined the correlation between East Greenland polar bear hair cortisol concentration (HCC), a matrix that reflects longer-term hormone levels, and the fluctuations of the North Atlantic Oscillation (NAO) index, a large-scale climate phenomenon applied as a proxy for sea ice extent in the Greenland Sea along the coast of East Greenland. In doing so, a significant positive correlation (r = 0.88; p = 0.0004) was found between polar bear hair cortisol and the NAO, explaining 77 % of the variation in HCC observed between years over the period 1989–2009. This result indicates that interannual fluctuations in climate and ice cover have a substantial influence on longer-term cortisol levels in East Greenland polar bears. Further research into the implications and consequences inherent in this correlation are recommended, preferably across multiple polar bear populations.     

Characterization of residues in the cytoplasmic domain of the LDL receptor required for exit from the endoplasmic reticulum

Newly synthesized low density lipoprotein receptors (LDLRs) exit the endoplasmic reticulum (ER) as the first step in the secretory pathway. In this study we have generated truncating deletions and substitutions within the 50 amino acid cytoplasmic domain of the LDLR in order to identify residues required for the exit from the ER. Western blot analysis was used to determine the relative amounts of the 120 kDa precursor form of the LDLR located in the ER and the 160 kDa mature form that has exited the ER. These studies have shown that the exit of an LDLR lacking the cytoplasmic domain, is markedly reduced. Moreover, the longer the cytoplasmic domain, the more efficient is the exit from the ER. At least 30 residues were required for the LDLR to efficiently exit the ER. Mutations in the two di-acidic motifs ExE₈₁₄ and/or ExD₈₃₇ had only a small effect on the exit from the ER. The requirement for a certain length of the cytoplasmic domain for efficient exit from the ER, could reflect the distance needed to interact with the COPII complex of the ER membrane or the requirement for the LDLR to undergo dimerization.     

The cytoplasmic domain is not involved in directing Class 5 mutant LDL receptors to lysosomal degradation

The low density lipoprotein receptor (LDLR) binds and internalizes low density lipoprotein (LDL). At the mildly acidic pH of the sorting endosomes, LDL is released from the receptor and the receptor recycles back to the cell membrane. Mutations in the LDLR gene may disrupt the normal function of the LDLR in different ways. Class 5 mutations result in receptors that are able to bind and internalize LDL, but they fail to release LDL in the sorting endosomes and fail to recycle. Instead they are rerouted to the lysosomes for degradation. However, the underlying mechanism remains to be determined. To study the role of the cytoplasmic domain of the LDLR for rerouting Class 5 mutants to the lysosomes, we have performed studies to determine whether Class 5 mutants caused by mutations E387K or V408M are degraded when the cytoplasmic domain has been altered or deleted. As determined by confocal laser-scanning microscopy, these mutant LDLR were inserted into the cell membrane and were able to internalize LDL. As determined by Western blot analysis, Class 5 mutants without a cytoplasmic domain still were degraded after binding LDL. Thus, the cytoplasmic domain does not play a role in rerouting Class 5 mutant LDLR to the lysosomes. Rather, one may speculate that sterical hindrance may prevent Class 5 mutants with bound LDL from entering the narrow recycling tubules of the sorting endosome.     

Dramatic shifts in Hawaiian monk seal distribution predicted from divergent regional trends

Total estimated abundance of Hawaiian monk seals was just 1,161 individuals in 2008 and this number is decreasing. Most monk seals reside in the remote Northwestern Hawaiian Islands (NWHI) where the decline is approximately 4%/yr, whereas relatively fewer seals currently occupy the main Hawaiian Islands (MHI). It is widely accepted that the MHI population is increasing, although there are no formal estimates of total abundance, population growth rate or vital rates. This lack of information has hampered efforts to anticipate future scenarios and plan conservation measures. We present the first estimates of MHI monk seal survival and age‐specific reproductive rates. Using these rates, a conservative estimate of current MHI abundance and a previously published stochastic simulation model, we estimate the MHI population growth rate and projected abundance trend. Analogous estimates for the NWHI are derived from a much richer data set. Estimated survival from weaning to age 1 yr is 77% in the MHI, much higher than recent NWHI estimates ranging from 42% to 57%. Moreover, MHI females begin reproducing at a younger age and attain higher birth rates than observed in the NWHI. The estimated MHI intrinsic rate of population growth is 1.07 compared to a 0.89–0.96 range in the NWHI. Assuming an initial abundance of 152 animals in the MHI, projections indicate that if current demographic trends continue, abundance in the NWHI and MHI will equalize in approximately 15 yr. These results underscore the imperative to mitigate the NWHI decline while devoting conservation efforts to foster population growth in the MHI, where documented threats including fishery interactions, direct killing, and disease could rapidly undo the current fragile positive trend.