Regulation of phospholipid scramblase activity during apoptosis and cell activation by protein kinase Cdelta

Phospholipid scramblase induces nonspecific bidirectional movement of phospholipids across the membrane during cell activation and has been proposed to mediate the appearance of phosphatidylserine (PS) in the plasma membrane outer leaflet during apoptosis, a cell surface change that is critical for apoptotic cell removal. We report here that protein kinase C (PKC) delta plays an important role in activated transbilayer movement of phospholipids and surface PS exposure by directly enhancing the activity of phospholipid scramblase. Specific inhibition of PKCdelta by rottlerin prevented both apoptosis- and activation-induced scramblase activity. PKCdelta was either selectively cleaved and activated in a caspase 3-dependent manner (during apoptosis) or translocated to the plasma membrane (in stimulated cells) and could directly phosphorylate scramblase immunoprecipitated from Jurkat cells. Furthermore, reconstitution of PKCdelta and scramblase, but not scramblase or PKCdelta alone in Chinese hamster ovary cells demonstrated enhanced scramblase activity.     

Seasonal and microhabitat influences on diatom assemblages and their representation in sediment traps and surface sediments from adjacent High Arctic lakes: Cape Bounty,Melville Island,Nunavut

The spatial (i.e. microhabitat) and temporal (i.e. seasonal) characteristics of diatom assemblages in adjacent High Arctic lakes were studied intensively June–August 2004. These baseline data are used to improve understanding of modern diatom community dynamics, as well to inform paleoenvironmental reconstructions. Diatoms were collected approximately weekly through the melt season from each principal benthic substrate (moss/macrophyte, rock scrapes, littoral sediment), plankton, and sediment traps, and were compared to the uppermost 0.5 cm of a surface core obtained from the deepest part of the lake where sediment cores are routinely collected. Water samples were collected concurrently with diatom samples to investigate species–environment relationships. The lakes share approximately half of their common taxa, the most abundant overall in both lakes being small Cyclotella species. Results of detrended correspondence analysis (DCA) indicate that the largest gradient in species turnover existed between benthic and planktonic communities in both lakes, and that sediment trap and the surface core top samples most closely resemble the planktonic assemblage, with an additional contribution from the lotic environment. Our results indicate clear micro-spatial controls on species assemblages and a degree of disconnection between the benthos and deep lake sediments that manifests as an under-representation of benthic taxa in deep lake surface sediments. These findings are particularly relevant in the context of interpreting the paleoenvironmental record and assessing ecosystem sensitivity to continued climate change.     

The mechanism of internalization of platelet-activating factor in activated human neutrophils. Enhanced transbilayer movement across the plasma membrane.

Recent studies suggest that cellular internalization of platelet-activating factor (PAF), a potent ether phospholipid mediator of inflammation, is modulated by, as yet undefined cellular mechanisms. Using an albumin extraction method, the internalization of PAF and several PAF analogues was studied in the resting and stimulated human neutrophil. Our data demonstrate that internalization of these analogues is largely dependent on the state of cellular activation and that the process is not specific for certain unique structural features of the PAF molecule including the 1-position ether linkage, 2-position acetyl substitution, or choline polar head group. Furthermore, the internalization process was shown not to be dependent on the PAF receptor, metabolism of the molecule, or the process of endocytosis. Data are presented to suggest that the route of internalization of PAF is enhanced transbilayer movement (flipping) across the plasma membrane occurring as a result of changes in membrane physical properties accompanying cellular activation. It is proposed that in addition to enhanced internalization of PAF, modulation of PAF biosynthesis and net release from the stimulated neutrophil may be consequences of enhanced transbilayer movement of PAF across the activated plasma membrane.     

Biomarker assessment of organic matter sources and degradation in Canadian High Arctic littoral sediments

This paper presents an uncomplicated approach to improve estimates of groundwater nutrient load to a marine embayment. A two-dimensional chemical profile of shallow groundwater was analysed in a sandy beach in three seasons (early summer, late summer and mid winter) and an adjusted estimate of groundwater nutrient discharge was derived that accounts for a complex biogeochemical environment and non-conservative behaviour of nutrients in the pre-discharge beach groundwater. The study was conducted at Cockburn Sound, Western Australia, where there has been significant groundwater contamination and associated marine ecological degradation. Losses in nitrogen and increases in phosphorus were observed along the discharge pathway beyond that expected from mixing with marine water, and the changes were attributed to chemically and biologically mediated reactions. A slow groundwater velocity (0.14–0.18 m day^?1), high organic carbon (TOC = 0.35–4.9 mmol l^?1, DOC = 0.28–4.6 mmol l^?1) and low to sub-oxic conditions (DO = 0.4–24% saturation) were deemed suitable for chemically and biologically mediated reactions to occur and subsequently alter regional estimates of groundwater nutrient concentration. Accounting for this environment, groundwater loads were calculated that were 1–2 orders of magnitude less than previous regional-based estimates: 0.4–13 kg NO _x ^?  day^?1, 0.2–24 kg NH₄ ⁺ day^?1 and 0.004–0.8 kg FRP day^?1. This paper applies knowledge of recent research and presents scope to marine managers or modellers to account for groundwater inputs to the marine environment.     

Hydrological controls on the diatom assemblage of a seasonal arctic river: Boothia Peninsula,Nunavut, Canada

This study characterizes the melt season diatom assemblage of a middle arctic river with respect to hydrological conditions. In addition, the potential to identify species that show a strong affinity for the lotic environment provides an opportunity to interpret stratigraphic changes in these species in the lake sedimentary record in terms of past hydrological change. Understanding long-term hydrological variability is critical for assessing both current and future environmental change. Significantly higher relative abundances of Achnanthes minutissimaKützing, Fragilaria capucina var. vaucheriae (Kützing) Lange-Bertalot, Diatoma tenuisAgardh, Cymbella arctica(Lagerstedt) Schmidt, C. minutaHilse ex. Rabenhorst, C. silesiaca Bleisch and Encyonema fogedii Krammer in the lotic environment throughout the 2001 growing season compared to the lacustrine sedimentary record suggest that these species characterize the Lord Lindsay River diatom assemblage. Comparison of seasonal abundances of these taxa to hydrological parameters including discharge, electrical conductivity, and water temperature reveal key information about the character of this community. The fact that the river diatom assemblage changes very little throughout the sampling period, despite major changes in hydrological conditions, suggests a degree of resilience and inherent structure in the community. However, a decrease in diatom biomass in response to rapid and dramatic changes in hydrological conditions following a major rainfall event suggests that a threshold tolerance may exist, with potentially important implications for interpreting stratigraphic changes in the paleoenvironmental record.     

Does artificial light pollution impair problem‐solving success in peafowl?

Behavioral innovations allow animals to adjust their behavior to solve novel problems. While innovative behavior can be important for animals living in new environments, anthropogenic pollution may limit their ability to adapt by impairing cognition or motivation. In particular, exposure to light pollution at night can cause sleep deprivation and may, therefore, hinder innovative behavior. To test this hypothesis, we examined experimentally whether exposure to acute light pollution impacts problem‐solving success in peafowl (Pavo cristatus). After peafowl were exposed to artificial light pollution for one night, they were presented with a problem‐solving task in which they could extract food by piercing the lid of an unfamiliar food bowl. Their problem‐solving success was unrelated to short‐term light pollution exposure. Other factors, including persistence, sex of the bird, and moon illumination, influenced their success in solving the task. The results suggest that short‐term exposure to light pollution does not limit behavioral innovation, but long‐term studies are necessary to further probe this question.     

A model for the extracellular release of PAF: the influence of plasma membrane phospholipid asymmetry.

Recent studies suggesting that cellular activation leads to enhanced transbilayer movement of phospholipids and loss of plasma membrane phospholipid asymmetry lead us to hypothesize that such events may govern the release of PAF, a potent, but variably release, lipid mediator synthesized by numerous inflammatory cells. To model these membrane events, we studied the transbilayer movement of PAF across the human erythrocyte and erythrocyte ghost plasma membrane, membranes with documented phospholipid asymmetry which can be deliberately manipulated. Utilizing albumin to extract outer leaflet PAF, transbilayer movement of PAF was shown to be significantly enhanced in erythrocytes and ghosts altered to lose membrane asymmetry when compared to movement in those with native membrane asymmetry. Verification of membrane changes was demonstrated using merocyanine 540 (MC540), a dye which preferentially stains loosely packed or hydrophobic membranes, and acceleration of the modified Russell's viper venom clotting assay by externalized anionic phospholipids. Utilizing the erythrocyte ghost loaded with PAF in either the outer or the inner leaflet, enhanced transbilayer movement to the opposite leaflet was seen to accompany loss of membrane asymmetry. Studies utilizing ghosts loaded with albumin intracellularly demonstrated that 'acceptor' molecules binding PAF further influence the disposition of PAF across the plasma membrane. Taken together, these findings suggest that the net release of PAF from activated inflammatory cells will depend on localization of PAF to the plasma membrane, transbilayer movement, which is facilitated by alteration of membrane phospholipid asymmetry, and removal from the membrane by extracellular and intracellular 'acceptor' molecules.     

Polyamine regulation of plasma membrane phospholipid flip-flop during apoptosis.

During apoptosis, phosphatidylserine (PS) is moved from the plasma membrane inner leaflet to the outer leaflet where it triggers recognition and phagocytosis of the apoptotic cell. Although the mechanisms of PS appearance during apoptosis are not well understood, it is thought that declining activity of the aminophospholipid translocase and calcium-mediated, nonspecific flip-flop of phospholipids play a role. As previous studies in the erythrocyte ghost have shown that polyamines can alter flip-flop of phospholipids, we asked whether alterations in cellular polyamines in intact cells undergoing apoptosis would affect PS appearance, either by altering aminophospholipid translocase activity or phospholipid flip-flop. Cells of the human leukemic cell line, HL-60, were incubated with or without the ornithine decarboxylase inhibitor, difluoromethylornithine (DFMO), and induced to undergo apoptosis by ultraviolet irradiation. Whereas DFMO treatment resulted in profound depletion of putrescine and spermidine (but not spermine), it had no effect on caspase activity, DNA fragmentation, or plasma membrane vesiculation, typical characteristics of apoptosis. Notably, DFMO treatment prior to ultraviolet irradiation did not alter the decline in PS inward movement by the aminophospholipid translocase as measured by the uptake of 6-[(7-nitrobenz-2-oxa-1,3-diazol-4-yl)aminocaproyl] (NBD)-labeled PS detected in the flow cytometer. Conversely, the appearance of endogenous PS in the plasma membrane outer leaflet detected with fluorescein isothiocyanate-labeled annexin V and enhanced phospholipid flip-flop detected by the uptake of 1-palmitoyl-1-[6-[(7-nitro-2-1, 3-benzoxadiazol-4-yl)aminocaproyl]-sn-glycero-3-phosphocholine (NBD-PC) seen during apoptosis were significantly inhibited by prior DFMO treatment. Importantly, replenishment of spermidine, by treatment with exogenous putrescine to bypass the metabolic blockade by DFMO, restored both enhanced phospholipid flip-flop and appearance of PS during apoptosis. Such restoration was seen even in the presence of cycloheximide but was not seen when polyamines were added externally just prior to assay. Taken together, these data show that intracellular polyamines can modulate PS appearance resulting from nonspecific flip-flop of phospholipids across the plasma membrane during apoptosis.