Endocytosis of apolipoprotein A-V by members of the low density lipoprotein receptor and the VPS10p domain receptor families

Apolipoprotein A-V (apoA-V) is present in low amounts in plasma and has been found to modulate triacylglycerol levels in humans and in animal models. ApoA-V displays affinity for members of the low density lipoprotein receptor (LDL-R) gene family, known as the classical lipoprotein receptors, including LRP1 and SorLA/LR11. In addition to LDL-A binding repeats, the mosaic receptor SorLA/LR11 also possesses a Vps10p domain. Here we show that apoA-V also binds to sortilin, a receptor from the Vsp10p domain gene family that lacks LDL-A repeats. Binding of apoA-V to sortilin was competed by neurotensin, a ligand that binds specifically to the Vps10p domain. To investigate the biological fate of receptor-bound apoA-V, binding experiments were conducted with cultured human embryonic kidney cells transfected with either SorLA/LR11 or sortilin. Compared with nontransfected cells, apoA-V binding to SorLA/LR11- and sortilin-expressing cells was markedly enhanced. Internalization experiments, live imaging studies, and fluorescence resonance energy transfer analyses demonstrated that labeled apoA-V was rapidly internalized, co-localized with receptors in early endosomes, and followed the receptors through endosomes to the trans-Golgi network. The observed decrease of fluorescence signal intensity as a function of time during live imaging experiments suggested ligand uncoupling in endosomes with subsequent delivery to lysosomes for degradation. This interpretation was supported by experiments with (125)I-labeled apoA-V, demonstrating clear differences in degradation between transfected and nontransfected cells. We conclude that apoA-V binds to receptors possessing LDL-A repeats and Vsp10p domains and that apoA-V is internalized into cells via these receptors. This could be a mechanism by which apoA-V modulates lipoprotein metabolism in vivo.     

Up-regulation of nicotinic receptors by nicotine varies with receptor subtype

Recent evidence suggests that in addition to alpha4beta2 and alpha3-containing nicotinic receptors, alpha6-containing receptors are present in midbrain dopaminergic neurons and involved in the nicotine reward pathway. Using heterologous expression, we found that alpha6beta2, like alpha3beta2 and alpha4beta2 receptors, formed high affinity epibatidine binding complexes that are pentameric, trafficked to the cell surface, and produced acetylcholine-evoked currents. Chronic nicotine exposure up-regulated alpha6beta2 receptors with differences in up-regulation time course and concentration dependence compared with alpha4beta2 receptors, the predominant high affinity nicotine binding site in brain. The alpha6beta2 receptor up-regulation required higher nicotine concentrations than for alpha4beta2 but lower than for alpha3beta2 receptors. The alpha6beta2 up-regulation occurred 10-fold faster than for alpha4beta2 and slightly faster than for alpha3beta2. Our data suggest that nicotinic receptor up-regulation is subtype-specific such that alpha6-containing receptors up-regulate in response to transient, high nicotine exposures, whereas sustained, low nicotine exposures up-regulate alpha4beta2 receptors.     

Using haplotypes to monitor the migration of fall armyworm (Lepidoptera: Noctuidae) corn-strain populations from Texas and Florida

Fall armyworm, Spodoptera frugiperda (J. E. Smith) (Lepidoptera: Noctuidae), infestations in most of North America north of Mexico arise from annual migrations of populations that overwinter in southern Texas and Florida. A comparison of the cytochrome oxidase I haplotype profiles within the fall armyworm corn-strain, the subgroup that preferentially infests corn (Zea mays L.) and sorghum (Sorghum vulgare Pers.), identified significant differences in the proportions of certain haplotypes between the Texas and Florida populations. These proportional differences were preserved as the populations migrated, providing a molecular metric by which the source of a migrant population could be identified. The migratory pattern derived from this method for several southeastern states was shown to be consistent with predictions based on analysis of historical agricultural and fall armyworm infestation data. These results demonstrate the utility of haplotype proportions to monitor fall armyworm migration, and they also introduce a potential method to predict the severity of cotton crop infestations in the short term.     

Effect of electrical stimulation of the LES on LES pressure in a canine model

Gastric electrical stimulation modulates lower esophageal sphincter pressure (LESP). High-frequency neural stimulation (NES) can induce gut smooth muscle contractions. To determine whether lower esophageal sphincter (LES) electrical stimulation (ES) can affect LESP, bipolar electrodes were implanted in the LES of four dogs. Esophageal manometry during sham or ES was performed randomly on separate days. Four stimuli were used: 1) low-frequency: 350-ms pulses at 6 cycles/min; 2) high-frequency-1: 1-ms pulses at 50 Hz; 3) high-frequency-2: 1-ms pulses at 20 Hz; and 4) NES: 20-ms bipolar pulses at 50 Hz. Recordings were obtained postprandially. Tests consisted of three 20-min periods: baseline, stimulation/sham, and poststimulation. The effect of NES was tested under anesthesia and following IV administration of l-NAME and atropine. Area under the curve (AUC) and LESP were compared among the three periods, by ANOVA and t-test, P < 0.05. Data are shown as means +/- SD. We found that low-frequency stimulation caused a sustained increase in LESP: 32.1 +/- 12.9 (prestimulation) vs. 43.2 +/- 18.0 (stimulation) vs. 50.1 +/- 23.8 (poststimulation), P < 0.05. AUC significantly increased during and after stimulation. There were no significant changes with other types of ES. With NES, LESP initially rose and then decreased below baseline (LES relaxation). During NES, N(G)-nitro-l-arginine methyl ester increased both resting LESP and the initial rise in LESP and markedly diminished the relaxation. Atropine lowered resting LESP and abolished the initial rise in LESP. In conclusion, low frequency ES of the LES increases LESP in conscious dogs. NES has dual effect on LESP: an initial stimulation, cholinergically mediated, followed by relaxation mediated by nitric oxide.     

Structure-activity studies of AtPep1, a plant peptide signal involved in the innate immune response

AtPep1, a 23-amino acid peptide recently isolated from Arabidopsis leaves, induces the expression of the genes encoding defense proteins against pathogens. We investigated the structure-activity relationship of AtPep1 with its receptor, a 170 kDa leucine-rich repeat receptor kinase (AtPEPR1) by utilizing a suspension cell assay (the alkalinization assay). Binding of AtPep1 to AtPEPR1 on the cell surface is accompanied by an increase in the pH of Arabidopsis suspension cell media by 1 pH unit in 15 min with a half-maximal response of 0.25 nM. Sequential removal of N-terminal amino acids had little effect on activity until the peptide was reduced to 15 amino acids [AtPep1(9-23)], which decreased the activity by less than one order of magnitude. Activity was completely abolished when nine C-terminal amino acids remained. Removal of the C-terminal asparagine from AtPep1(9-23), resulted in a decrease in activity (12 max approximately 100 nM). AtPep1(9-23) was used for alanine-substitution analysis and revealed two important residues for activity, a serine, [A(15)]AtPep1(9-23) (12 max approximately 10nM), and a glycine, [A(17)]AtPep1(9-23) (12 max approximately 1000 nM). Neither [A(17)]AtPep1(9-23) nor the C-terminal truncated AtPep1, AtPep1(9-22), were able to compete with AtPep1(9-23) in the alkalinization assay. The importance of the glycine residue for binding to the AtPep receptor was also confirmed by competition assays using radiolabeled AtPep1. d-Alanine or 2-methylalanine substituted at the glycine position displayed only a slight decrease in activity whereas l- and d-proline substitution caused a loss of activity. Homologs of AtPep1 identified in Arabidopsis and other species revealed a strict conservation of the glycine residue.     

Isolation of a novel chromium(III) binding protein from bovine liver tissue after chromium(VI) exposure

In the ongoing investigation into the biological importance and toxicity issues surrounding the bioinorganic chemistry of chromium, the accepted literature procedure for the isolation of the biological form of chromium, low molecular weight chromium binding protein (LMWCr) or chromodulin, was investigated for its specificity. When chromium(VI) is added to bovine liver homogenate, results presented here indicate at least four chromium(III) binding peptides and proteins are produced and that the process is non-specific for the isolation of LMWCr. A novel trivalent chromium containing protein (1) has been isolated to purity and initial characterization is reported here. Chromium(III) identification was determined by optical spectroscopy and diphenylcarbazide testing. This chromium binding protein has a molecular weight of 15.6kDa, which was determined from both gel-electrophoresis and mass spectrometry. The protein is comprised primarily of Asx, Glx, His, Gly/Thr, Ala, and Lys in a 1.00:2.51:0.37:2.09:0.39:1.17 ratio and is anionic at pH 7.4. In addition, the protein binds approximately 2.5 chromium(III) ions per molecule.     

N-Terminal 112 amino acid residues are not required for the sialyltransferase activity of Photobacterium damsela α2,6-sialyltransferase

Photobacterium damsela α2,6-sialyltransferase was cloned as N- and C- His-tagged fusion proteins with different lengths (16–497 aa or 113–497 aa). Expression and activity assays indicated that the N-terminal 112 amino acid residues of the protein were not required for its α2,6-sialyltransferase activity. Among four truncated forms tested, N-His-tagged Δ15Pd2,6ST(N) containing 16–497 amino acid residues had the highest expression level. Similar to the Δ15Pd2,6ST(N), the shorter Δ112Pd2,6ST(N) was active in a wide pH range of 7.5–10.0. A divalent metal ion was not required for the sialyltransferase activity, and the addition of EDTA and dithiothreitol did not affect the activity significantly. Mingchi Sun and Yanhong Li contributed equally to this work.     

Mechanical characterization of electrospun polycaprolactone (PCL): a potential scaffold for tissue engineering

This paper investigates the mechanical behavior of electrospun polycaprolactone (PCL) under tensile loading. PCL in bulk form degrades slowly and is biocompatible, two properties that make it a viable option for tissue engineering applications in biomedicine. Of particular interest is the use of electrospun PCL tubes as scaffolds for tissue engineered blood vessel implants. Stress relaxation and tensile tests have been conducted with specimens at room temperature (21 degrees C) and 37 degrees C. Additionally, to probe the effects of moisture on mechanical behavior, specimens were tested either dry (in air) or submerged in water. In general, the electrospun PCL was found to exhibit rate dependence, as well as some dependence on the test temperature and on whether the sample was wet or dry. Two different models were investigated to describe the experimentally observed material behavior. The models used were Fung's theory of quasilinear viscoelasticity (QLV) and the eight-chain model developed for rubber elastomers by Arruda and Boyce (1993, "A Three-Dimensional Constitutive Model for the Large Stretch Behavior of Rubber Elastic Materials," J. Mech. Phys. Solids, 41(2), pp. 389-412). The implementation and fitting results, as well as the advantages and disadvantages of each model, are presented. In general, it was found that the QLV theory provided a better fit.     

Intersexual Conflict and Group Size in <Emphasis Type="Italic">Alouatta palliata</Emphasis>: A 23-year Evaluation

Models of optimal primate group size suggest that group formation and growth arise to benefit individual fitness, but that size is limited by costs. The ecological constraints hypothesis posits that group formation and growth is driven by protection from predation or the advantages of group foraging, while an upper limit on group size is constrained by travel costs and intragroup competition for food or other critical resources. Socioecological models also predict that individual reproductive success, hypothesized to decrease with increasing group size, also places an upper limit on the number of individuals in a group. Our analysis of 23 yr of group composition data on mantled howlers (Alouatta palliata) from a single Panamanian study site on Barro Colorado Island not only corroborates the socioecological model but also shows that female reproductive success increased, whereas that of males decreased, with the less female-biased sex ratios in larger groups. We suggest that the conflict of interest between the sexes over adult sex ratio, particularly the male proportion in a group, in combination with ecological factors, is an important determinant of group size and composition.