Actin coating and compression of fused secretory vesicles are essential for surfactant secretion - a role for Rho, formins and myosin II

Secretion of vesicular contents by exocytosis is a fundamental cellular process. Increasing evidence suggests that post-fusion events play an important role in determining the composition and quantity of the secretory output. In particular, regulation of fusion pore dilation and closure is considered a key regulator of the post-fusion phase. However, depending on the nature of the cargo, additional mechanisms might be essential to facilitate effective release. We have recently described that in alveolar type II (ATII) cells, lamellar bodies (LBs), which are secretory vesicles that store lung surfactant, are coated with actin following fusion with the plasma membrane. Surfactant, a lipoprotein complex, does not readily diffuse out of fused LBs following opening and dilation of the fusion pore. Using fluorescence microscopy, atomic force microscopy and biochemical assays, we present evidence that actin coating and subsequent contraction of the actin coat is essential to facilitate surfactant secretion. Latrunculin B prevents actin coating of fused LBs and inhibits surfactant secretion almost completely. Simultaneous imaging of the vesicle membrane and the actin coat revealed that contraction of the actin coat compresses the vesicle following fusion. This leads to active extrusion of vesicle contents. Initial actin coating of fused vesicles is dependent on activation of Rho and formin-dependent actin nucleation. Actin coat contraction is facilitated by myosin II. In summary, our data suggest that fusion pore opening and dilation itself is not sufficient for release of bulky vesicle cargos and that active extrusion mechanisms are required

Effects of sample handling and storage on quantitative lipid analysis in human serum

There is sparse information about specific storage and handling protocols that minimize analytical error and variability in samples evaluated by targeted metabolomics. Variance components that affect quantitative lipid analysis in a set of human serum samples were determined. The effects of freeze-thaw, extraction state, storage temperature, and freeze-thaw prior to density-based lipoprotein fractionation were quantified. The quantification of high abundance metabolites, representing the biologically relevant lipid species in humans, was highly repeatable (with coefficients of variation as low as 0.01 and 0.02) and largely unaffected by 1–3 freeze-thaw cycles (with 0–8% of metabolites affected in each lipid class). Extraction state had effects on total lipid class amounts, including decreased diacylglycerol and increased phosphatidylethanolamine in thawed compared with frozen samples. The effects of storage temperature over 1 week were minimal, with 0–4% of metabolites affected by storage at 4°C, −20°C, or −80°C in most lipid classes, and 19% of metabolites in diacylglycerol affected by storage at −20°C. Freezing prior to lipoprotein fractionation by density ultracentrifugation decreased HDL free cholesterol by 37% and VLDL free fatty acid by 36%, and increased LDL cholesterol ester by 35% compared with fresh samples. These findings suggest that density-based fractionation should preferably be undertaken in fresh serum samples because up to 37% variability in HDL and LDL cholesterol could result from a single freeze-thaw cycle. Conversely, quantitative lipid analysis within unfractionated serum is minimally affected even with repeated freeze-thaw cycles

Spontaneous remodeling of HDL particles at acidic pH enhances their capacity to induce cholesterol efflux from human macrophage foam cells

Peer reviewe

Less but better: cardioprotective lipid profile of patients with GCK-MODY despite lower HDL cholesterol level

Patients with diabetes caused by single-gene mutations generally exhibit an altered course of diabetes. Those with mutations of the glucokinase gene (GCK-MODY) show good metabolic control and low risk of cardiovascular complications despite paradoxically lowered high-density lipoprotein (HDL) cholesterol levels. In order to investigate the matter, we analyzed the composition of low-density lipoprotein (LDL) and HDL subpopulations in such individuals. The LipoPrint(©) system (Quantimetrix, USA) based on non-denaturing, linear polyacrylamide gel electrophoresis was used to separate and measure LDL and HDL subclasses in fresh-frozen serum samples from patients with mutations of glucokinase or HNF1A, type 1 diabetes (T1DM) and healthy controls. Fresh serum samples from a total of 37 monogenic diabetes patients (21 from GCK-MODY and 16 from HNF1A-MODY), 22 T1DM patients and 15 healthy individuals were measured in this study. Concentrations of the small, highly atherogenic LDL subpopulation were similar among the compared groups. Large HDL percentage was significantly higher in GCK-MODY than in control (p = 0.0003), T1DM (p = 0.0006) and HNF1A-MODY groups (p = 0.0246). Patients with GCK-MODY were characterized by significantly lower intermediate HDL levels than controls (p = 0.0003) and T1DM (p = 0.0005). Small, potentially atherogenic HDL content differed significantly with the GCK-MODY group showing concentrations of that subfraction from control (p = 0.0096), T1DM (p = 0.0193) and HNF1A-MODY (p = 0.0057) groups. Within-group heterogeneity suggested the existence of potential gene–gene or gene–environment interactions. GCK-MODY is characterized by a strongly protective profile of HDL cholesterol subpopulations. A degree of heterogeneity within the groups suggests the existence of interactions with other genetic or clinical factors

Family Literacy across Three Generations of Undergraduate Students in Africa and the United States: Relation of Family Literacy Experiences on the Grade Point Averages of Undergraduate Students at the University of Botswana, University of Pretoria in South Africa, and Vanderbilt University in the United States

Supervised by John J. Rieser.The aim of this study was to describe literacy across three generations of undergraduate students (the students, their parents, and their grandparents) in Southern African (at the University of Pretoria and at the University of Botswana) and in the United States (Vanderbilt University). And, in addition to the main aim, there was an investigation of possible causal relationships that connect the literacy experiences that the undergraduates reported having experienced in the home before the age of five years. The results show strikingly different patterns of family literacy across the three generations: none of the University of Botswana students’ grandparents could read, fewer than half could read at the University of Pretoria, and all could read at Vanderbilt; fewer than half of the University of Botswana parents could read, more than 70% of the University of Pretoria parents could read; all of the Vanderbilt parents could read, and all of the undergraduate students could read. Series of analyses of variance and t-tests were conducted to investigate influences over the college students’ grade point averages, probing the effects of family literacy, reading opportunities in the home, and experiences with story and picture books as young children. Again, the significant findings varied across students from the three universities. For University of Botswana students, there was only one statistically significant relationship, namely, their access to picture books when they were young children. For University of Pretoria students, there were many statistically significant relationships that connected mother and grandfather literacy as well as numbers of adult books and children’s books to university GPA. And as for Vanderbilt students, there was little variability in the data, since all students reported to have literate parents and grandparents, many adult books in the home, and many children’s books in the home.Thesis completed in partial fulfillment of the requirements of the Honors Program in Psychological SciencesPeabody College of EducationVanderbilt UniversityDepartment of Pyschology and Human Developmen