A block in endoplasmic reticulum-to-Golgi trafficking inhibits phospholipid synthesis and induces neutral lipid accumulation

Seeking to better understand how membrane trafficking is coordinated with phospholipid synthesis in yeast, we investigated lipid synthesis in several Sec(-) temperature-sensitive mutants, including sec13-1. Upon shift of sec13-1 cells to the restrictive temperature of 37 degrees C, phospholipid synthesis decreased dramatically relative to the wild type control, whereas synthesis of neutral lipids, especially triacylglycerol (TAG), increased. When examined by fluorescence microscopy, the number of lipid droplets appeared to increase and formed aggregates in sec13-1 cells shifted to 37 degrees C. Electron microscopy confirmed the increase in lipid droplet number and revealed that many were associated with the vacuole. Analysis of lipid metabolism in strains lacking TAG synthase genes demonstrated that the activities of the products of these genes contribute to accumulation of TAG in sec13-1 cells after the shift to 37 degrees C. Furthermore, the permissive temperature for growth of the sec13-1 strain lacking TAG synthase genes was 3 degrees C lower than sec13-1 on several different growth media, indicating that the synthesis of TAG has physiological significance under conditions of secretory stress. Together these results suggest that following a block in membrane trafficking, yeast cells channel lipid metabolism from phospholipid synthesis into synthesis of TAG and other neutral lipids to form lipid droplets. We conclude that this metabolic switch provides a degree of protection to cells during secretory stress.

The lysophospholipid acyltransferase antagonist CI-976 inhibits a late step in COPII vesicle budding

The mechanism of coat protein (COP)II vesicle fission from the endoplasmic reticulum (ER) remains unclear. Lysophospholipid acyltransferases (LPATs) catalyze the conversion of various lysophospholipids to phospholipids, a process that can promote spontaneous changes in membrane curvature. Here, we show that 2,2-methyl-N-(2,4,6,-trimethoxyphenyl)dodecanamide (CI-976), a potent LPAT inhibitor, reversibly inhibited export from the ER in vivo and the formation of COPII vesicles in vitro. Moreover, CI-976 caused the rapid and reversible accumulation of cargo at ER exit sites (ERESs) containing the COPII coat components Sec23/24 and Sec13/31 and a marked enhancement of Sar1p-mediated tubule formation from ERESs, suggesting that CI-976 inhibits the fission of assembled COPII budding elements. These results identify a small molecule inhibitor of a very late step in COPII vesicle formation, consistent with fission inhibition, and demonstrate that this step is likely facilitated by an ER-associated LPAT.

Adipocyte differentiation-related protein reduces the lipid droplet association of adipose triglyceride lipase and slows triacylglycerol turnover

Although neutral lipid storage droplets are ubiquitous in eukaryotic cells, very little is known about how their synthesis and turnover are controlled. Adipocyte differentiation-related protein (ADRP; also known as adipophilin) is found on the surface of lipid droplets in most mammalian cell types. To learn how ADRP affects lipid storage, we stably expressed the protein in human embryonic kidney 293 (HEK 293) cells, which express little endogenous ADRP. As expected, ADRP was targeted to the surface of lipid droplets and caused an increase in triacylglycerol (TAG) mass under both basal and oleate-supplemented conditions. At least part of the increased mass resulted from a 50% decrease in the rate of TAG hydrolysis in ADRP-expressing cells. Furthermore, ADRP expression increased the fraction of total cellular TAG that was stored in lipid droplets. ADRP expression induced a striking decrease in the association of adipose triglyceride lipase (ATGL) and mannose-6-phosphate receptor tail-interacting protein of 47 kDa with lipid droplets and also decreased the lipid droplet association of several other unknown proteins. Transient expression of ADRP in two other cell lines also reduced the lipid droplet association of catalytically inactive ATGL. We conclude that the reduced lipid droplet association of ATGL and/or other lipases may explain the decrease in TAG turnover observed in ADRP-expressing HEK 293 cells.

Quantitative phase microscopy with asynchronous digital holography

We demonstrate a new method of measuring quantitative phase in imaging of biological materials. This method, asynchronous digital holography, employs knowledge of a moving fringe created by acousto-optic modulators to execute phase-shifting interferometry using two near-simultaneous interferograms. The method can be used to obtain quantitative phase images of dynamic biological samples on millisecond time scales. We present results on a standard sample, and on live cell samples.

Measurement properties of the CHAMPS physical activity questionnaire in a sample of older Australians

BACKGROUND

The effective evaluation of physical activity interventions for older adults requires measurement instruments with acceptable psychometric properties that are sufficiently sensitive to detect changes in this population.

AIM

To assess the measurement properties (reliability and validity) of the Community Healthy Activities Model Program for Seniors (CHAMPS) questionnaire in a sample of older Australians.

METHODS

CHAMPS data were collected from 167 older adults (mean age 79.1 S.D. 6.3 years) and validated with tests of physical ability and the SF-12 measures of physical and mental health. Responses from a sub-sample of 43 older adults were used to assess 1-week test-retest reliability.

RESULTS

Approximately 25% of participants needed assistance to complete the CHAMPS questionnaire. There were low but significant correlations between the CHAMPS scores and the physical performance measures (rho=0.14-0.32) and the physical health scale of the SF-12 (rho=0.12-0.24). Reliability coefficients were highest for moderate-intensity (ICC=0.81-0.88) and lowest for vigorous-intensity physical activity (ICC=0.34-0.45). Agreement between test-retest estimates of sufficient physical activity for health benefits (> or =150min and > or =5 sessions per week) was high (percent agreement=88% and Cohen's kappa=0.68).

CONCLUSION

These findings suggest that the CHAMPS questionnaire has acceptable measurement properties, and is therefore suitable for use among older Australian adults, as long as adequate assistance is provided during administration.

ATGL has a key role in lipid droplet/adiposome degradation in mammalian cells

Lipid droplets (LDs), also called adiposomes, are found in many eukaryotic cells, and are highly upregulated in lipid-storage cells, such as adipocytes. The mechanism by which adiposomes and their component neutral lipids are degraded is an important health issue with the rapidly spreading epidemic of obesity. Recently, a novel triglyceride lipase (adipose triglyceride lipase (ATGL)) that catalyses the initial step in triglyceride hydrolysis in adipocyte LDs was identified. Here, we show that ATGL also functions in non-adipocyte cells, and has an important role in LD degradation in these cells. Overexpression of wild-type ATGL causes a marked decrease in LD size, whereas a catalytically inactive mutant retains the ability to localize to LDs, but is unable to decrease their size. Depletion of ATGL by RNA interference leads to a significant increase in the size of LDs. These results show that ATGL has an important role in LD/adiposome turnover in mammalian cells.

Antibiotic susceptibilities of Yersinia enterocolitica recovered from children over a 12-year period☆

Antibiotic susceptibility testing by the microdilution technique was performed on 184 Yersinia enterocolitica isolates recovered from children with gastroenteritis in the Detroit area during a 12-year period. The majority of isolates were resistant to ampicillin, ticarcillin and cefazolin. The most active agents were cefotaxime, ceftriaxone, cefepime, gentamicin, tobramycin, sulphamethoxazole/trimethoprim, imipenem and ciprofloxacin. Cefotaxime and ceftriaxone were effective in the treatment of bacteraemia in 12 patients.

Sitting time and socio-economic differences in overweight and obesity

OBJECTIVES

To examine (1) the inter-relationships between socio-economic status (SES), physical activity, three different domains of sitting time (weekday, weekend day and leisure-time sitting), and being overweight or obese (body mass index>/=25 kg/m(2)); and (2) the potential mediation effects of sitting time in the relationship between socio-economic factors and being overweight or obese in working Australian adults.

DESIGN

Observational epidemiological study.

SUBJECTS

One thousand forty eight working adults. Using a multistage sampling design on neighbourhood SES, participants were from high and low SES neighbourhoods of an Australian capital city.

MEASUREMENTS

Neighbourhood SES was assessed using census data; individual SES was based on self-reported educational attainment and household income. There were three sitting time variables: sitting time on weekdays, weekend days and in leisure time. Overweight and obesity were determined using self-reported body weight and height.

RESULTS

Gender, age, neighbourhood SES, education, working hours and physical activity were independently associated with weekday, weekend day and leisure-related sitting time. With the exception of education and working hours, these variables were also independently associated with being overweight or obese. Leisure-time sitting was found to be a mediator in the relationships between gender, education and being overweight or obese.

CONCLUSION

Strategies to promote less sitting in leisure time are required to combat overweight and obesity in Australian adults, especially among those from low SES neighbourhoods, and among those with high levels of education and income who work long hours.

A comparative study of secretory immunoglobulin A and immunoglobulin G in host defense in an in vitro pneumonia model

BACKGROUND

An exaggerated inflammatory response to infections including nosocomial pneumonia may be detrimental to the host and contribute to morbidity and mortality. Both secretory immunoglobulin A (SIgA) and IgG contribute to the immune defense of respiratory surfaces. However, their relative ability to protect against invasive infections and the resultant host inflammatory response are unknown and were the basis for this study.

METHODS

Calu-3 cell (a respiratory epithelial cell line) monolayers were established in a Transwell system (Costar Corp., Cambridge, MA). Escherichia coli and either polyclonal SIgA or IgG were inoculated into the apical chamber and neutrophils (polymorphonuclear neutrophils) were added to the basal chamber. PMN cytotoxic potential was indexed by %CD11b expression, superoxide anion (O(2)-) production, and % elastase release. Bacterial translocation into the basal chamber was quantitated after log transformation. Calu-3 monolayer integrity was indexed by permeability to dextran fluorescein isothiocyanate.

RESULTS

The addition of E coli to Calu-3/polymorphonuclear cocultures led to increases in O(2)- generation, elastase release, and CD11b expression. These effects were diminished by the addition of SIgA but not IgG. A similar effect was noted with Calu-3 barrier function.

CONCLUSIONS

SIgA may function to protect against microbial invasion of respiratory surfaces and protect against tissue injury from an exaggerated inflammatory response.

Weight gained in two years by a population of mid-aged women: how much is too much?

OBJECTIVE

To establish the prevalence of weight change in mid-aged women over a 2-year period, and to assess the relationship between weight change and physical and mental well-being (SF36) in order to begin debate about the need for quantified standards of weight gain.

DESIGN

Prospective study of weight change and well-being over a 2-year period among mid-aged women participating in a large national survey.

SUBJECTS

Seven thousand two hundred and seventy women without surgical menopause aged between 45 and 50 years (termed mid-aged), enrolled in the Australian Longitudinal Study on Women's Health.

MEASUREMENTS

Weight change (self-reported weight at two time points) and physical and mental well-being (SF-36) explored using linear regression, while adjusting for potential confounders.

RESULTS

Only half the women maintained their weight within 2.25 kg, and one-third gained more than this amount in a 2-year period. While weight gain (> or = 2.25 kg) was negatively associated with physical well-being, both weight loss and weight gain were associated with poorer mental well-being.

CONCLUSION

This is the first prospective study using a large, population-based cohort to demonstrate that small changes in weight are associated with changes in well-being in mid-aged Australian women. It provides further evidence of the need for public health messages to specify the actual amount that constitutes weight gain, but further research is needed to establish these standards for the entire population.

Immunoglobulin a modulates inflammatory responses in an in vitro model of pneumonia

BACKGROUND

Preservation of mucosal immunity has been shown to affect the risk and outcome of pneumonia in severely injured patients. Secretory immunoglobulin A (SIgA) is the principle humoral defense of mucosal surfaces in the body and has several antiinflammatory properties. Polymorphonuclear neutrophils (PMN) function to kill invading microorganisms, but their exaggerated inflammatory responses may cause tissue injury to the host. The purpose of this study was to compare the ability of different immunoglobulin (Ig) isotypes to modulate PMN cytotoxic potential cocultured with respiratory epithelial cells challenged with bacteria.

METHODS

Calu-3 cell monolayers were established on membranes (0.1-microm pore) in a two-chamber culture system. Escherichia coli (EC) incubated with either polyclonal SIgA or IgG was inoculated into the apical chamber and PMNs (10/mL) added to the basal chamber. PMN cytotoxic potential was indexed by % CD11b expression, superoxide anion (O2) production, and elastase release. Dextran flux was used to index Calu-3 monolayer permeability.

RESULTS

Addition of EC to PMN-Calu-3 cell coculture increased % CD11b expression, O2 production, and elastase release. IgG had no effect on PMN activation after EC challenge. SIgA abrogated PMN activation and the increase in Calu-3 cell monolayer permeability noted with EC or EC + IgG treatment groups.

CONCLUSION

PMN cytotoxic potential was decreased by the presence of SIgA but not IgG in an in vitro model to simulate pneumonia in vivo. SIgA may not only function to protect against microbial invasion of mucosal surfaces, but may also protect against tissue injury from an exaggerated inflammatory response.

Promoting physical activity to older adults: A preliminary evaluation of three general practice-based strategies

The aim of this study was to explore the feasibility of an exercise scientist (ES) working in general practice to promote physical activity (PA) to 55 to 70 year old adults. Participants were randomised into one of three groups: either brief verbal and written advice from a general practitioner (GP) (G1, N=9): or individualised counselling and follow-up telephone calls from an ES, either with (G3, N=8) or without a pedometer (G2, N=11). PA levels were assessed at week 1, after the 12-wk intervention and again at 24 weeks. After the 12-wk intervention, the average increase in PA was 116 (SD=237) min/wk: N=28, p<0.001. Although there were no statistically significant between-group differences, the average increases in PA among G2 and G3 participants were 195 (SD=207) and 138 (SD=315) min/wk respectively, compared with no change (0.36, SD=157) in G1. After 24 weeks, average PA levels remained 56 (SD=129) min/wk higher than in week 1. The small numbers of participants in this feasibility study limit the power to detect significant differences between groups, but it would appear that individualised counselling and follow-up contact from an ES, with or without a pedometer, can result in substantial changes in PA levels. A larger study is now planned to confirm these findings.

A unique lysophospholipid acyltransferase (LPAT) antagonist, CI-976, affects secretory and endocytic membrane trafficking pathways

Previous studies have shown that inhibition of a Golgi-complex-associated lysophospholipid acyltransferase (LPAT) activity by the drug CI-976 stimulates Golgi tubule formation and subsequent redistribution of resident Golgi proteins to the endoplasmic reticulum (ER). Here, we show that CI-976 stimulates tubule formation from all subcompartments of the Golgi complex, and often these tubules formed independently, i.e. individual tubules usually did not contain markers from different subcompartments. Whereas the cis, medial and trans Golgi membranes redistributed to the ER, the trans Golgi network (TGN) collapsed back to a compact juxtanuclear position similar to that seen with brefeldin A (BFA) treatment. Also similar to BFA, CI-976 induced the formation of endosome tubules, but unlike BFA, these tubules did not fuse with TGN tubules. Finally, CI-976 produced an apparently irreversible block in the endocytic recycling pathway of transferrin (Tf) and Tf receptors (TfRs) but had no direct effect on Tf uptake from the cell surface. Tf and TfRs accumulated in centrally located, Rab11-positive vesicles indicating that CI-976 inhibits export of cargo from the central endocytic recycling compartment. These results, together with previous studies, demonstrate that CI-976 inhibits multiple membrane trafficking steps, including ones found in the endocytic and secretory pathways, and imply a wider role for lysophospholipid acyltransferases in membrane trafficking.

Intestinal Epithelial Cells Modulate PMN Activation and Apoptosis Following Bacterial and Hypoxic Challenges

BACKGROUND

The post-ischemic gut may serve to prime and activate neutrophils which may lead to the subsequent development of the systemic inflammatory response syndrome (SIRS) and multiple organ failure. However, the initiating event which may trigger this immunoinflammatory cascade from the gut is unknown. Recent studies have indicated that intestinal epithelial cells (IEC) play an integral role in generating and transmitting signals between luminal bacteria and the host cells in the underlying gut tissues. The purpose of this study was to investigate the ability of IEC to modulate PMN responses to bacteria and/or hypoxia/reoxygenation (H/R) challenges in vitro.

METHODS

Caco2 cell monolayers were established in a two-chamber cell culture system. Neutrophils from normal human volunteers were placed in the basal chamber and the cell co-culture exposed to either apical bacteria (E. coli) and/or H/R challenge. PMN apoptosis, and percentage of CD11b expression, superoxide anion production, and elastase release were subsequently quantitated.

RESULTS

Coculture of PMNs with Caco2 cells led to a significant reduction in neutrophil apoptosis in both normoxic and H/R conditions. CD11b expression was increased in PMNs exposed to bacteria but the greatest expression was noted with PMN cocultured with Caco2 cells and H/R. Superoxide anion production was increased in all groups following either H/R or bacterial challenge and H/R. Elastase release was highest in neutrophils following H/R and exposure to E. coli.

CONCLUSION

IEC modulate PMN response to bacteria and H/R insults. This results in the production of activated neutrophils with an exaggerated lifespan which may promote remote organ failure. Attempts to modulate this response may be useful in preventing multiple organ failure following severe traumatic shock.

The Pivotal Role of Tumor Necrosis Factor-?? in Signaling Apoptosis in Intestinal Epithelial Cells under Shock Conditions

BACKGROUND

Apoptosis is essential for the regulation of cell number and function of intestinal epithelial cells but may contribute to intestinal barrier failure after shock and other low-flow conditions to the gut.

METHODS

Caco2 intestinal cell monolayers were challenged with recombinant tumor necrosis factor (TNF). In a second group of experiments, Caco2 cells were exposed to bacteria and/or hypoxia followed by reoxygenation. Apoptosis was detected using annexin-V propidium-iodide staining. Cell culture supernatants were also obtained in the second group of experiments and TNF levels quantitated. Monolayer integrity was assessed by measurement of paracellular permeability and transepithelial electrical resistance.

RESULTS

Apical but not basal recombinant TNF increased Caco2 apoptosis. Exposure to either bacteria alone or hypoxia/reoxygenation alone did not increase apoptosis; however, the combined insults significantly increased apoptosis. The increased apoptosis occurred in a delayed fashion in both groups. TNF was released in a polar fashion, and the greatest levels were noted after exposure to both bacteria and hypoxia-reoxygenation. There was also an increase in paracellular permeability in this group; however, no change in transepithelial electrical resistance was noted. The effects on apoptosis and permeability were abrogated by anti-TNF antibodies.

CONCLUSION

Intestinal epithelial cell apoptosis contributes to barrier failure after shock conditions and is related to augmented TNF release.

Evaluation of four commercially available extended-spectrum beta-lactamase phenotypic confirmation tests

Extended-spectrum beta-lactamase (ESBL) production in members of the Enterobacteriaceae can confer resistance to extended-spectrum cephalosporins, aztreonam, and penicillin. As such, the accurate detection of ESBL producers is essential for the appropriate selection of antibiotic therapy. Twenty previously characterized isolates and 49 clinical isolates suspected of ESBL production were tested by four ESBL phenotypic confirmatory methods for accuracy and ease of use. The four ESBL phenotypic confirmation tests included Dried MicroScan ESBL plus ESBL Confirmation panels (Dade Behring, Inc., West Sacramento, Calif.), Etest ESBL (AB BIODISK, Piscataway, N.J.), Vitek GNS-120 (bioMerieux, Inc., Hazelwood, Mo.), and BD BBL Sensi-Disk ESBL Confirmatory Test disks (BD Biosciences, Sparks, Md.). Results were compared to frozen microdilution panels prepared according to NCCLS specifications, and discrepant isolates were sent for molecular testing. The test sensitivities for the ESBL phenotypic confirmatory test methods used in this study were as follows: MicroScan ESBL plus ESBL confirmation panel, 100%; VITEK 1 GNS-120, 99%; Etest ESBL, 97%; and BD BBL Sensi-Disk ESBL Confirmatory Test disks, 96%. The test specificities were as follows: BD BBL Sensi-Disk ESBL Confirmatory Test disks, 100%; MicroScan ESBL plus ESBL confirmation panel and VITEK 1 GNS-120, 98%; and Etest ESBL, 94%. All methods were easy to perform; however, the Etest method required more expertise to interpret the results. All tests offer a feasible solution for confirming ESBL production in the clinical laboratory.

Use of Acyltransferase Inhibitors to Block Vesicular Traffic Between the ER and Golgi Complex

This article describes the use of acyltransferase inhibitors as probes for studying the potential role of lysophospholipid acyltransferases (LPAT) in intracellular membrane trafficking in the secretory and endocytic pathways. The small molecule inhibitors that are described here were originally found as acyl-CoA:cholesterol acyltransferase (ACAT) inhibitors. One of these, CI-976 (2,2-methyl-N-(2,4,6,-trimethoxyphenyl)dodecanamide), was also found to be a potent LPAT inhibitor. CI-976 is a small, hydrophobic, membrane-permeant compound and both in vivo and in vitro studies have shown that it, but not other ACAT inhibitors, has a profound effect on multiple membrane trafficking pathways in eukaryotic cells including: (1) inhibition of COPII vesicle budding from the endoplasmic reticulum (ER), (2) inhibition of transferrin and transferrin receptor export from the endocytic recycling compartment, and (3) stimulation of tubule-mediated retrograde trafficking of Golgi membranes to the ER. Here we describe the use of CI-976 and other ACAT inhibitors for studies with both cultured mammalian cells and in vitro reconstitution assays, with a particular emphasis on COPII vesicle budding from the ER. All of these studies strongly suggest that CI-976-sensitive LPATs play a role in coated vesicle fission, and therefore, CI-976 is a valuable addition to the arsenal of small molecule inhibitors that can be used to study secretory and endocytic membrane trafficking pathways.

Immunoglobulin A protease is a virulence factor for gram-negative pneumonia

BACKGROUND

Secretory immunoglobulin A (SIgA) is the principal immunologic defense of respiratory and other mucosal surfaces in the body. SIgA is relatively stable in mucosal secretions. However, cleavage of SIgA by bacterial proteases might render it immunologically inactive and thus contribute to the development of pneumonia as well as other infections. Bacterial species and infection sites might be important in the expression of bacterial protease activity and serve as the impetus to this study.

METHODS

Bacterial isolates from respiratory and nonrespiratory sites were incubated with SIgA in vitro. SIgA degradation was determined by size exclusion ultrafiltration and gel electrophoresis.

RESULTS

IgA protease activity was evident in gram-negative but not gram-positive respiratory isolates. Gram-negative isolates from nonrespiratory sources did not exhibit IgA protease activity.

CONCLUSIONS

Expression of IgA protease activity might be important in the development and subsequent outcome of gram-negative pneumonia in the patient in the surgical intensive care unit.