Effects of structural habitat on drift distance and benthic settlement of the caddisfly,Ceratopsyche sparna

We conducted two experiments in flow-through, artificial streams to examine how habitat structure affected drift and benthic resettlement of larval hydropsychid caddisflies (Ceratopsyche sparna). In the first experiment, we quantified drift distance and the number of times larvae re-entered the drift in 9.0 × 0.51-m channels with contiguous patches (ea. 2.5-m long) of biofilm-covered gravel, biofilm-covered cobbles (– Cladophora), and Cladophora-covered cobbles (+ Cladophora). In the second experiment, we tracked nocturnal movements of larvae after benthic settlement in 2.8 × 0.1-m channels, each containing one of the three habitat types. In experiment 1, drift distance was (1) greatest in gravel and lowest in cobbles + Cladophora, (2) inversely related to hydraulic roughness of habitats, (3) independent of body size, and (4) similar for live and dead larvae. Average drift distance was relatively short (<2.5 m), regardless of habitat type. Number of drift re-entries also varied among habitats, being greatest in gravel and lowest in cobbles + Cladophora. No larvae re-entered the drift after settling in Cladophora patches. Results from experiment 2 revealed that drift propensities were higher for larvae in biofilm-covered gravel and cobbles than in cobbles + Cladophora. Larvae remaining in substrate patches (i.e. not drifting) laid fewer draglines in biofilm-covered stones than in Cladophora patches. Extent of benthic movement (i.e., crawling) by non-drifting larvae did not differ significantly among habitats. However, distance moved did differ with flow direction, being 4× greater downstream than upstream. These results highlight how local substrate and hydraulic conditions interact to affect small-scale movements of caddisfly larvae.     

Effects of acetaminophen and ibuprofen on renal function in anesthetized normal and sodium-depleted dogs

In certain conditions, renal prostaglandins (PGs) are importantdeterminants of kidney function. Under these "renal PG-dependent states," pharmacological inhibition of vasodilatory PG may result inexcessive renal vasoconstriction and adversely affect kidney function.The purposes of this study were to determine whether acetaminophen(Acet), a weak PG-synthesis inhibitor, influences kidney function inthe renal PG-dependent state of anesthesia and sodium depletion.Comparisons were made with ibuprofen (Ibu). Measurements ofPGE₂ excretion were used to assessrenal PG synthesis. Acet (15 mg/kg) and Ibu (10 mg/kg) both decreasedrenal blood flow and glomerular filtration rate by ~20-30% innormal, anesthetized, sodium-replete dogs. Although Acet producedsimilar changes in renal blood flow and glomerular filtration rate inthe low-sodium dogs, Ibu caused a significantly greater renalvasoconstriction (64 ± 10%) in these animals. Both Acet and Ibuinhibited urinary PGE₂ excretionin sodium-replete and low-sodium dogs. Ibu tended to have a greater andmore prolonged effect than did Acet. These results suggest that Acetalters PGE₂ excretion and kidneyfunction under renal PG-dependent conditions; the effects, however, are less severe than those seen with Ibu.     

N-acetylcysteine and taurine prevent hyperglycemia-induced insulin resistance in vivo: possible role of oxidative stress

Exposure to high concentrations of glucose and insulin results in insulin resistance of metabolic target tissues, a characteristic feature of type 2 diabetes. High glucose has also been associated with oxidative stress, and increased levels of reactive oxygen species have been proposed to cause insulin resistance. To determine whether oxidative stress contributes to insulin resistance induced by hyperglycemia in vivo, nondiabetic rats were infused with glucose for 6 h to maintain a circulating glucose concentration of 15 mM with and without coinfusion of the antioxidant N-acetylcysteine (NAC), followed by a 2-h hyperinsulinemic-euglycemic clamp. High glucose (HG) induced a significant decrease in insulin-stimulated glucose uptake [tracer-determined disappearance rate (Rd), control 41.2 +/- 1.7 vs. HG 32.4 +/- 1.9 mg. kg-1. min-1, P < 0.05], which was prevented by NAC (HG + NAC 45.9 +/- 3.5 mg. kg-1. min-1). Similar results were obtained with the antioxidant taurine. Neither NAC nor taurine alone altered Rd. HG caused a significant (5-fold) increase in soleus muscle protein carbonyl content, a marker of oxidative stress that was blocked by NAC, as well as elevated levels of malondialdehyde and 4-hydroxynonenal, markers of lipid peroxidation, which were reduced by taurine. In contrast to findings after long-term hyperglycemia, there was no membrane translocation of novel isoforms of protein kinase C in skeletal muscle after 6 h. These data support the concept that oxidative stress contributes to the pathogenesis of hyperglycemia-induced insulin resistance.     

Hemodynamics influences vascular peroxynitrite formation: Implication for low-density lipoprotein apo-B-100 nitration

Hemodynamics, specifically, fluid shear stress, modulates the focal nature of atherogenesis. Superoxide anion (O2(-.)) reacts with nitric oxide (.NO) at a rapid diffusion-limited rate to form peroxynitrite (O2(-.) + .NO-->ONOO(-)). Immunohistostaining of human coronary arterial bifurcations or curvatures, where OSS develops, revealed the presence of nitrotyrosine staining, a fingerprint of peroxynitrite; whereas in straight segments, where PSS occurs, nitrotyrosine was absent. We examined vascular nitrative stress in models of oscillatory (OSS) and pulsatile shear stress (PSS). Bovine aortic endothelial cells (BAEC) were exposed to fluid shear stress that simulates arterial blood flow: (1) PSS at a mean shear stress (tau(ave)) of 23 dyn cm(-2) and a temporal gradient (partial differential(tau)/partial differential(t)) at 71 dyn cm(-2) s(-1), and (2) OSS at tau(ave) = 0.02 dyn cm(- 2) and partial differential(tau)/partial differential(t) = +/- 3.0 dyn cm(-2) s(-1) at a frequency of 1 Hz. OSS significantly up-regulated one of the NADPH oxidase subunits (NOx4) expression accompanied with an increase in O2(-.) production. In contrast, PSS up-regulated eNOS expression accompanied with .NO production (total NO(2)(-) and NO(3)(-)). To demonstrate that O2(-.) and .NO are implicated in ONOO(-) formation, we added low-density lipoprotein cholesterol (LDL) to the medium in which BAEC were exposed to the above flow conditions. The medium was analyzed for LDL apo-B-100 nitrotyrosine by liquid chromatography electrospray ionization tandem mass spectrometry (LC/ESI/MS/MS). OSS induced higher levels of 3-nitrotyrosine, dityrosine, and o-hydroxyphenylalanine compared with PSS. In the presence of ONOO(-), specific apo-B-100 tyrosine residues underwent nitration in the alpha and beta helices: alpha-1 (Tyr(144)), alpha-2 (Tyr(2524)), beta-2 (Tyr(3295)), alpha-3 (Tyr(4116)), and beta-2 (Tyr(4211)). Hence, the characteristics of shear stress in the arterial bifurcations influenced the relative production of O2(-.) and .NO with an implication for ONOO(-) formation as evidenced by LDL protein nitration.     

Two putative BIN2 substrates are nuclear components of brassinosteroid signaling

GSK3 is a highly conserved kinase that negatively regulates many cellular processes by phosphorylating a variety of protein substrates. BIN2 is a GSK3-like kinase in Arabidopsis that functions as a negative regulator of brassinosteroid (BR) signaling. It was proposed that BR signals, perceived by a membrane BR receptor complex that contains the leucine (Leu)-rich repeat receptor-like kinase BRI1, inactivate BIN2 to relieve its inhibitory effect on unknown downstream BR-signaling components. Using a yeast (Saccharomyces cerevisiae) two-hybrid approach, we discovered a potential BIN2 substrate that is identical to a recently identified BR-signaling protein, BES1. BES1 and its closest homolog, BZR1, which was also uncovered as a potential BR-signaling protein, display specific interactions with BIN2 in yeast. Both BES1 and BZR1 contain many copies of a conserved GSK3 phosphorylation site and can be phosphorylated by BIN2 in vitro via a novel GSK3 phosphorylation mechanism that is independent of a priming phosphorylation or a scaffold protein. Five independent bes1 alleles containing the same proline-233-Leu mutation were identified as semidominant suppressors of two different bri1 mutations. Over-expression of the wild-type BZR1 gene partially complemented bin2/+ mutants and resulted in a BRI1 overexpression phenotype in a BIN2(+) background, whereas overexpression of a mutated BZR1 gene containing the corresponding proline-234-Leu mutation rescued a weak bri1 mutation and led to a bes1-like phenotype. Confocal microscopic analysis indicated that both BES1 and BZR1 proteins were mainly localized in the nucleus. We propose that BES1/BZR1 are two nuclear components of BR signaling that are negatively regulated by BIN2 through a phosphorylation-initiated process.     

Sensitivity Analysis of an ENteric Immunity SImulator (ENISI)-Based Model of Immune Responses to Helicobacter pylori Infection

Agent-based models (ABM) are widely used to study immune systems, providing a procedural and interactive view of the underlying system. The interaction of components and the behavior of individual objects is described procedurally as a function of the internal states and the local interactions, which are often stochastic in nature. Such models typically have complex structures and consist of a large number of modeling parameters. Determining the key modeling parameters which govern the outcomes of the system is very challenging. Sensitivity analysis plays a vital role in quantifying the impact of modeling parameters in massively interacting systems, including large complex ABM. The high computational cost of executing simulations impedes running experiments with exhaustive parameter settings. Existing techniques of analyzing such a complex system typically focus on local sensitivity analysis, i.e. one parameter at a time, or a close “neighborhood” of particular parameter settings. However, such methods are not adequate to measure the uncertainty and sensitivity of parameters accurately because they overlook the global impacts of parameters on the system. In this article, we develop novel experimental design and analysis techniques to perform both global and local sensitivity analysis of large-scale ABMs. The proposed method can efficiently identify the most significant parameters and quantify their contributions to outcomes of the system. We demonstrate the proposed methodology for ENteric Immune SImulator (ENISI), a large-scale ABM environment, using a computational model of immune responses to Helicobacter pylori colonization of the gastric mucosa.     

Lipid-induced pancreatic β-cell dysfunction: focus on in vivo studies

The phenomenon of lipid-induced pancreatic β-cell dysfunction ("lipotoxicity") has been very well documented in numerous in vitro experimental systems and has become widely accepted. In vivo demonstration of β-cell lipotoxicity, on the other hand, has not been consistently demonstrated, and there remains a lack of consensus regarding the in vivo effects of chronically elevated free fatty acids (FFA) on β-cell function. Much of the disagreement relates to how insulin secretion is quantified in vivo and in particular whether insulin secretion is assessed in relation to whole body insulin sensitivity, which is clearly reduced by elevated FFA. By correcting for changes in in vivo insulin sensitivity, we and others have shown that prolonged elevation of FFA impairs β-cell secretory function. Prediabetic animal models and humans with a positive family history of type 2 diabetes are more susceptible to this impairment, whereas those with severe impairment of β-cell function (such as individuals with type 2 diabetes) demonstrate no additional impairment of β-cell function when FFA are experimentally raised. Glucolipotoxicity (i.e., the combined β-cell toxicity of elevated glucose and FFA) has been amply demonstrated in vitro and in some animal studies but not in humans, perhaps because there are limitations in experimentally raising plasma glucose to sufficiently high levels for prolonged periods of time. We and others have shown that therapies directed toward diminishing oxidative stress and ER stress have the potential to reduce lipid-induced β-cell dysfunction in animals and humans. In conclusion, lipid-induced pancreatic β-cell dysfunction is likely to be one contributor to the complex array of genetic and metabolic insults that result in the relentless decline in pancreatic β-cell function in those destined to develop type 2 diabetes, and mechanisms involved in this lipotoxicity are promising therapeutic targets.     

Systematic Reverse Engineering of Network Topologies: A Case Study of Resettable Bistable Cellular Responses

A focused theme in systems biology is to uncover design principles of biological networks, that is, how specific network structures yield specific systems properties. For this purpose, we have previously developed a reverse engineering procedure to identify network topologies with high likelihood in generating desired systems properties. Our method searches the continuous parameter space of an assembly of network topologies, without enumerating individual network topologies separately as traditionally done in other reverse engineering procedures. Here we tested this CPSS (continuous parameter space search) method on a previously studied problem: the resettable bistability of an Rb-E2F gene network in regulating the quiescence-to-proliferation transition of mammalian cells. From a simplified Rb-E2F gene network, we identified network topologies responsible for generating resettable bistability. The CPSS-identified topologies are consistent with those reported in the previous study based on individual topology search (ITS), demonstrating the effectiveness of the CPSS approach. Since the CPSS and ITS searches are based on different mathematical formulations and different algorithms, the consistency of the results also helps cross-validate both approaches. A unique advantage of the CPSS approach lies in its applicability to biological networks with large numbers of nodes. To aid the application of the CPSS approach to the study of other biological systems, we have developed a computer package that is available in Information S1.     

The Women's Health Initiative: The food environment, neighborhood socioeconomic status, BMI, and blood pressure

Using data (n = 60,775 women) from the Women's Health Initiative Clinical Trial (WHI CT)—a national study of postmenopausal women aged 50–79 years—we analyzed cross‐sectional associations between the availability of different types of food outlets in the 1.5 miles surrounding a woman's residence, census tract neighborhood socioeconomic status (NSES), BMI, and blood pressure (BP). We simultaneously modeled NSES and food outlets using linear and logistic regression models, adjusting for multiple sociodemographic factors, population density and random effects at the tract and metropolitan statistical area (MSA) level. We found significant associations between NSES, availability of food outlets and individual‐level measurements of BMI and BP. As grocery store/supermarket availability increased from the 10th to the 90th percentile of its distribution, controlling for confounders, BMI was lower by 0.30 kg/m². Conversely, as fast‐food outlet availability increased from the 10th to the 90th percentile, BMI was higher by 0.28 kg/m². When NSES increased from the 10th to the 90th percentile of its distribution, BMI was lower by 1.26 kg/m². As NSES increased from the 10th to the 90th percentile, systolic and diastolic BP were lower by 1.11 mm Hg and 0.40 mm Hg, respectively. As grocery store/supermarket outlet availability increased from the 10th and 90th percentiles, diastolic BP was lower by 0.31 mm Hg. In this national sample of postmenopausal women, we found important independent associations between the food and socioeconomic environments and BMI and BP. These findings suggest that changes in the neighborhood environment may contribute to efforts to control obesity and hypertension.