Apolipoprotein A-I charge and conformation regulate the clearance of reconstituted high density lipoprotein in vivo

While low apolipoprotein A-I (apoA-I) levels are primarily associated with increased high density lipoprotein (HDL) fractional catabolic rate (FCR), the factors that regulate the clearance of HDL from the plasma are unclear. In this study, the effect of lipid composition of reconstituted HDL particles (LpA-I) on their rate of clearance from rabbit plasma has been investigated. Sonicated LpA-I containing 1 to 2 molecules of purified human apoA-I and 5 to 120 molecules of palmitoyl-oleoyl phosphatidylcholine (POPC) exhibit similar charge and plasma FCR to that for lipid free apoA-I, 2.8 pools/day. Inclusion of 1 molecule of apoA-II to an LpA-I complex increases the FCR to 3.5 pools/day, a value similar to that observed for exchanged-labeled HDL3. In contrast, addition of 40 molecules of triglyceride, diglyceride, or cholesteryl ester to a sonicated LpA-I containing 120 moles of POPC and 2 molecules of apoA-I increases the negative charge of the particle and reduces the FCR to 1.8 pools/day. Discoidal LpA-I are the most positively charged lipoprotein particles and also have the fastest clearance rates, 4.5 pools/day. Immunochemical characterization of the different LpA-I particles shows that the exposure of an epitope at residues 98 to 121 of the apoA-I molecule is associated with an increased negative particle charge and a slower clearance from the plasma.We conclude that the charge and conformation of apoA-I are sensitive to the lipid composition of LpA-I and play a central role in regulating the clearance of these lipoproteins from plasma. conformation regulate the clearance of reconstituted high density lipoprotein in vivo.     

Phylogeny and biogeography of the Malagasy and Australasian rainbowfishes (Teleostei: Melanotaenioidei): Gondwanan vicariance and evolution in freshwater

Phylogenetic relationships of the Malagasy and Australasian rainbowfishes are investigated using 4394 characters derived from five mitochondrial genes (12S, 16S, tRNA-Valine, ND5, and COI), three nuclear genes (28S, histone H3, and TMO-4c4), and 102 morphological transformations. This study represents the first phylogenetic analysis of the endemic Malagasy family Bedotiidae and includes a nearly complete taxonomic review of all nominal species, as well as numerous undescribed species. Simultaneous analysis of the molecular and morphological datasets results in two equally most parsimonious trees. Results indicate that Bedotiidae (Bedotia+Rheocles) and Bedotia are monophyletic, whereas Rheocles is paraphyletic with the inclusion of two recently described species from northeastern Madagascar, R. vatosoa, and R. derhami. Rheocles vatosoa and R. derhami are sister taxa, and this clade is recovered as the sister group to Bedotia. The remaining species of Rheocles are not sexually dimorphic and comprise a clade that is recovered as the sister group to Bedotia+(R. derhami+R. vatosoa), all of which are sexually dichromatic, and sexually dimorphic for pigmentation and fin development. Three geographically distinct clades are recovered within Bedotia, one comprising species with distributions ranging from mid- to southeastern Madagascar, another including species restricted to eastern drainages north of the Masoala Peninsula, and a third comprising taxa with distributions extending from the Masoala Peninsula south to the Ivoloina River. The Australian/New Guinean melanotaeniids are monophyletic and are recovered as the sister group to Bedotiidae. The Australasian Telmatherinidae and Pseudomugilidae comprise a clade that is recovered as the sister group to the Melanotaeniidae-Bedotiidae clade. This sister-group relationship between Malagasy bedotiids and a clade restricted to Australia-New Guinea, and the absence of a close relationship between bedotiids and African or Mascarene atheriniforms, is congruent with the break-up of Gondwana, not a scenario reliant on Cenozoic trans-oceanic dispersal. Finally, results of the phylogenetic analysis indicate that Atheriniformes is polyphyletic and further corroborate recent morphological hypotheses, which have recovered Bedotiidae in a derived position within Atherinoidei.     

The amino acid sequences of the carboxyl termini of human and mouse hepatic lipase influence cell surface association

Human hepatic lipase (hHL) mainly exists cell surface bound, whereas mouse HL (mHL) circulates in the blood stream. Studies have suggested that the carboxyl terminus of HL mediates cell surface binding. We prepared recombinant hHL, mHL, and chimeric proteins (hHLmt and mHLht) in which the carboxyl terminal 70 amino acids of hHL were exchanged with the corresponding sequence from mHL. The hHL, mHL, and hHLmt proteins were catalytically active using triolein and tributyrin as substrates. In transfected cells, the majority of hHLs bound to the cell surface, with only 4% of total extracellular hHL released into heparin-free media, whereas under the same conditions, 61% of total extracellular mHLs were released. Like mHL, hHLmt showed decreased cell surface binding, with 68% of total extracellular hHLmt released. To determine the precise amino acid residues involved in cell surface binding, we prepared a truncated hHL mutant (hHL471) by deleting the carboxyl terminal five residues (KRKIR). The hHL471 also retained hydrolytic activity with triolein and tributyrin, and showed decreased cell surface binding, with 40% of total extracellular protein released into the heparin-free media.These data suggest that the determinants of cell surface binding exist within the carboxyl terminal 70 amino acids of hHL, of which the last five residues play an important role.     

HDL regulates the displacement of hepatic lipase from cell surface proteoglycans and the hydrolysis of VLDL triacylglycerol

We have previously shown that hepatic lipase (HL) is inactive when bound to purified heparan sulfate proteoglycans and can be liberated by HDL and apolipoprotein A-I (apoA-I), but not by LDL or VLDL. In this study, we show that HDL is also able to displace HL directly from the surface of the hepatoma cell line, HepG2, and Chinese hamster ovary cells stably overexpressing human HL. ApoA-I is more efficient at displacing cell surface HL than is HDL, and different HDL classes vary in their ability to displace HL from the cell surface. HDL2s have a greater capacity to remove HL from the cell surface and intracellular compartments, as compared with the smaller HDL particles. The different HDL subclasses also uniquely affect the activity of the enzyme. HDL2 stimulates HL-mediated hydrolysis of VLDL-triacylglycerol, while HDL3 is inhibitory. Inhibition of VLDL hydrolysis appears to result from a decreased interlipoprotein shuttling of HL between VLDL and the smaller, more dense HDL particles. This study suggests that high HDL2 levels are positively related to efficient triacylglycerol hydrolysis by their ability to enhance the liberation of HL into the plasma compartment and by a direct stimulation of VLDL-triacylglycerol hydrolysis.     

Temperature as a control over ecosystem CO<Subscript>2</Subscript> fluxes in a high-elevation,subalpine forest

We evaluated the hypothesis that CO(2) uptake by a subalpine, coniferous forest is limited by cool temperature during the growing season. Using the eddy covariance approach we conducted observations of net ecosystem CO(2) exchange (NEE) across two growing seasons. When pooled for the entire growing season during both years, light-saturated net ecosystem CO(2) exchange (NEE(sat)) exhibited a temperature optimum within the range 7-12 degrees C. Ecosystem respiration rate ( R(e)), calculated as the y-intercept of the NEE versus photosynthetic photon flux density (PPFD) relationship, increased with increasing temperature, causing a 15% reduction in net CO(2) uptake capacity for this ecosystem as temperatures increased from typical early season temperatures of 7 degrees C to typical mid-season temperatures of 18 degrees C. The ecosystem quantum yield and the ecosystem PPFD compensation point, which are measures of light-utilization efficiency, were highest during the cool temperatures of the early season, and decreased later in the season at higher temperatures. Branch-level measurements revealed that net photosynthesis in all three of the dominant conifer tree species exhibited a temperature optimum near 10 degrees C early in the season and 15 degrees C later in the season. Using path analysis, we statistically isolated temperature as a seasonal variable, and identified the dynamic role that temperature exhibits in controlling ecosystem fluxes early and late in the season. During the spring, an increase in temperature has a positive effect on NEE, because daytime temperatures progress from near freezing to near the photosynthetic temperature optimum, and R(e )values remain low. During the middle of the summer an increase in temperature has a negative effect on NEE, because inhibition of net photosynthesis and increases in R(e). When taken together, the results demonstrate that in this high-elevation forest ecosystem CO(2) uptake is not limited by cool-temperature constraints on photosynthetic processes during the growing-season, as suggested by some previous ecophysiological studies at the branch and needle levels. Rather, it is warm temperatures in the mid-summer, and their effect on ecosystem respiration, that cause the greatest reduction in the potential for forest carbon sequestration.     

Effects of environmental salinity and 17alpha-methyltestosterone on growth and oxygen consumption in the tilapia, Oreochromis mossambicus

Effects of environmental salinity and 17α-methyltestosterone (MT) on growth and oxygen consumption were examined in the tilapia, Oreochromis mossambicus. Yolk-sac fry were collected from brood stock in fresh water (FW). After yolk-sac absorption, they were assigned randomly to one of four groups: FW, MT treatment in FW, seawater (SW) and MT treatment in SW. All treatment groups were fed to satiation three times daily. The fish reared in SW (both control and MT-treated groups) grew significantly larger than either group in FW from day 43 throughout the experiment (195 days). The fish fed with MT added to their feed grew significantly larger than their respective controls from day 85 in FW and in SW until the end of the experiment. The routine metabolic rate (RMR) was determined monthly from month 2 (day 62) to month 5 (day 155). A significant negative correlation was seen between RMR and body mass in all treatment groups. Among fish of the same age, the SW-reared tilapia had significantly lower RMRs than the FW-reared fish. The MT-treated fish in SW showed significantly lower RMRs than the SW control group at months 3–5, whereas MT treatment in FW significantly increased the RMR at month 3. Comparison of regression lines between RMR and body mass indicates that MT treatment in FW caused a significant increase in oxygen consumption at a given mass of the fish, whereas MT treatment was without effect on RMR in SW-reared fish. These results clearly indicate that SW-rearing and MT treatment accelerate growth of tilapia, and that RMR decreases as fish size increased. It is also likely that the increased RMR and growth in MT-treated tilapia in FW may be due to the metabolic actions of MT, although the reason for the absence of MT treatment in SW is unclear.     

Group 2 Innate Lymphoid Cell Proportions Are Diminished in Young Helminth Infected Children and Restored by Curative Anti-helminthic Treatment

BackgroundGroup 2 Innate lymphoid cells (ILC2s) are innate cells that produce the TH2 cytokines IL-5 and IL-13. The importance of these cells has recently been demonstrated in experimental models of parasitic diseases but there is a paucity of data on ILC2s in the context of human parasitic infections and in particular of the blood dwelling parasite Schistosoma haematobium.ConclusionThis study demonstrates that ILC2s are diminished in young helminth infected children and restored by removal of the parasites by treatment, indicating a previously undescribed association between a human parasitic infection and ILC2s and suggesting a role of ILC2s before the establishment of protective acquired immunity in human schistosomiasis.     

Spatial and temporal localization of SPIRRIG and WAVE/SCAR reveal roles for these proteins in actin-mediated root hair development

Root hairs are single-cell protrusions that enable roots to optimize nutrient and water acquisition. These structures attain their tubular shapes by confining growth to the cell apex, a process called tip growth. The actin cytoskeleton and endomembrane systems are essential for tip growth; however, little is known about how these cellular components coordinate their activities during this process. Here, we show that SPIRRIG (SPI), a beige and Chediak Higashi domain-containing protein involved in membrane trafficking, and BRK1 and SCAR2, subunits of the WAVE/SCAR (W/SC) actin nucleating promoting complex, display polarized localizations in Arabidopsis thaliana root hairs during distinct developmental stages. SPI accumulates at the root hair apex via post-Golgi compartments and positively regulates tip growth by maintaining tip-focused vesicle secretion and filamentous-actin integrity. BRK1 and SCAR2 on the other hand, mark the root hair initiation domain to specify the position of root hair emergence. Consistent with the localization data, tip growth was reduced in spi and the position of root hair emergence was disrupted in brk1 and scar1234. BRK1 depletion coincided with SPI accumulation as root hairs transitioned from initiation to tip growth. Taken together, our work uncovers a role for SPI in facilitating actin-dependent root hair development in Arabidopsis through pathways that might intersect with W/SC.