Separation and analysis of subcellular organelles in a human promyelocytic leukemia cell line, HL-60: application to the study of myeloid lysosomal enzyme synthesis and processing

We describe a system for analysis of the intracellular pathways in the biosynthesis and packaging of functionally important proteins in human myeloid cells. The human promyelocytic cell line HL-60 was used since peripheral blood neutrophils are terminally differentiated and do not actively synthesize protein. Cells were disrupted by nitrogen cavitation and subcellular organelles in postnuclear supernatant separated on a discontinuous gradient of Percoll modified to resolve organelles important in protein synthesis. This Percoll gradient separated azurophilic granules from less dense organelles and partially separated the less dense organelles from one another. Approximate densities of organelles identified by electron microscopy and by biochemical markers are azurophilic granules, 1.102 g/mL; endoplasmic reticulum, 1.039 g/mL; Golgi apparatus, 1.032 g/mL; and plasma membrane, 1.027 g/mL. We validated the utility of this method of subcellular fractionation by examining intracellular transport of myeloperoxidase, a myeloid lysosomal enzyme present in azurophilic granules. The subunits of mature myeloperoxidase (molecular weight [mol wt] = 59,000 and 13,500) cosediment with biochemical markers for lysosomes, whereas the large-mol wt (89,000) precursor forms cosediments with biochemical markers of less dense organelles. Within the limits of assay sensitivity, the 89,000-mol wt precursor is enzymatically inactive and has no spectral evidence for a heme group, suggesting that precursors of myeloperoxidase may undergo proteolytic maturation in a prelysosomal compartment with concomitant incorporation of a heme group and acquisition of enzymatic activity. This system of analysis should be suitable for the identification, subcellular localization, and maturational analysis of other myeloid lysosomal enzymes as well as functionally important membrane proteins.     

Fodrin and band 4.1 in a plasma membrane-associated fraction of human neutrophils

Erythrocytes possess a well-characterized submembranous filamentous network which interacts with transmembrane glycoproteins and is composed primarily of spectrin, ankyrin, band 4.1, and short actin filaments. An analogous structure was recently described in platelets. Human polymorphonuclear leukocytes (PMNs) were examined for the presence and plasma membrane association of similar proteins. Isolated PMNs, free of contamination with erythrocytes or platelets, were disrupted by nitrogen cavitation and separated into subcellular organelles on a discontinuous Percoll gradient. Detergent lysates of plasma membrane vesicles, but not azurophilic or specific granules, contained insoluble actin filaments and associated proteins. Immunoblots of detergent-insoluble plasma membrane fractions contained proteins recognized by antibodies to brain fodrin and erythrocyte band 4.1, whereas blots probed with antibodies to erythrocyte spectrin and ankyrin were negative. Fodrin and band 4.1 were not detected in granule fractions, but some fodrin was present in the cytosol. The association of proteins related to fodrin and band 4.1 with the plasma membrane suggests that PMNs contain a submembranous skeleton structurally analogous to that of erythrocytes and platelets. The specific function of these proteins and their structural organization in human PMNs await further study.     

Differential effects of trabecular meshwork stiffness on outflow facility in normal human and porcine eyes

Purpose. The study was designed to determine trabecular meshwork (TM) stiffness and its relationship to outflow facility (C) in perfused normal human and porcine eyes. Methods. Human and porcine eyes were perfused at pressures of 10, 20, 30, and 40 mm Hg to determine C and how outflow resistance (R = 1/C) varied with the pressure. Following perfusions, TM tissue segments were dissected and stretched uniaxially to determine the circumferential bulk Young's modulus (E). The statistical significance of difference between different groups was evaluated using a two-tailed Student's t-test or Mann-Whitney U test. Results. A larger E correlated with a higher C measured at 10 and 20 mm Hg (P < 0.05), and a similar trend was observed at 30 and 40 mm Hg in human eyes (n = 7). Additionally, a higher C correlated to a lower variance of R, and a stiffer TM correlated to a lower variance of R in human eyes (P < 0.05). For porcine TM, E was inversely correlated to a cross-sectional area (P < 0.003, n = 11), and its value (24.9 and 1.5 kPa; geometric mean and geometric SE) was lower than E of human TM (515 ± 136 kPa; mean ± SE) (P < 0.01). C and variance of R were not significantly different between the species. Conclusions. A higher circumferential stiffness of the TM correlated with a higher outflow facility and less IOP elevation-induced variation in outflow resistance in normal human eyes, but not in porcine eyes. For future studies, these correlations need to be evaluated in glaucomatous eyes to better understand normal and abnormal TM functions.     

Effects of the 1997–1998 El Ni?o Episode on Community Rates of Diarrhea

Objectives. To improve our understanding of climate variability and diarrheal disease at the community level and inform predictions for future climate change scenarios, we examined whether the El Niño climate pattern is associated with increased rates of diarrhea among Peruvian children.Methods. We analyzed daily surveillance data for 367 children aged 0 to 12 years from 2 cohorts in a peri-urban shantytown in Lima, Peru, 1995 through 1998. We stratified diarrheal incidence by 6-month age categories, season, and El Niño, and modeled between-subject heterogeneity with random effects Poisson models.Results. Spring diarrheal incidence increased by 55% during El Niño compared with before El Niño. This increase was most acute among children older than 60 months, for whom the risk of a diarrheal episode during the El Niño spring was nearly 100% greater (relative risk = 1.96; 95% confidence interval = 1.24, 3.09).Conclusions. El Niño–associated climate variability affects community rates of diarrhea, particularly during the cooler seasons and among older children. Public health officials should develop preventive strategies for future El Niño episodes to mitigate the increased risk of diarrheal disease in vulnerable communities.The effect of weather on disease transmission is well recognized for many infectious diseases that exhibit seasonal patterns,1 including diarrhea,2,3 respiratory infections,4 malaria,5 and dengue.6 There is growing concern that severe weather changes resulting from El Niño episodes and global climate change directly affect human health.7 Diarrheal illnesses are among the highest disease burdens in children younger than 5 years of age worldwide8 and are predicted to increase with climate change. However, specific estimates for the magnitude of this increase in the community setting remain uncertain, in part because epidemiological data on the relationship between community rates of diarrhea and extreme weather variability are scarce.9 Although the relationship between specific weather variables and infectious disease has been examined extensively with retrospective, hospital-based data,10–14 data from prospective population-based cohort studies are limited. Determining the effects of El Niño on rates of diarrhea with a cohort study would greatly improve our understanding of climate variability and diarrheal disease at the community level and inform predictions for other extreme weather episodes or future climate change scenarios.15The El Niño southern oscillation (ENSO) is a main driver of global interannual weather variation. Occurring every 3 to 7 years, the ENSO phenomenon leads to extreme worldwide weather events, such as heavy flooding and drought.16 The ENSO provides health researchers with an opportunity to model effects of local climate anomalies on infectious disease dynamics,17 and it has been linked to changes in rates of cholera,18–21 diarrhea,11,22,23 malaria,10 dengue,24 hantavirus,25 viral pneumonia,26 and Rift Valley fever.27The 1997–1998 El Niño episode altered weather conditions around the world—particularly severely along the Peruvian coastline. This El Niño episode has been described as the strongest yet recorded.28 Previously, we found that the number of pediatric hospital admissions for diarrheal diseases in Lima, Peru, increased substantially during this episode, especially during the winter months.11 A separate study found similar results for adults.22 In this study, we sought to examine the effects of the 1997–1998 El Niño episode on rates of childhood diarrhea and several parasitic agents in a peri-urban Peruvian community with cohort studies conducted between June 1995 and August 1998.