Apolipoprotein A-I Helsinki promotes intracellular acyl-CoA cholesterol acyltransferase (ACAT) protein accumulation

Reverse cholesterol transport is a process of high antiatherogenic relevance in which apolipoprotein AI (apoA-I) plays an important role. The interaction of apoA-I with peripheral cells produces through mechanisms that are still poorly understood the mobilization of intracellular cholesterol depots toward plasma membrane. In macrophages, these mechanisms seem to be related to the modulation of the activity of acyl-CoA cholesterol acyltransferase (ACAT), the enzyme responsible for the intracellular cholesterol ester biosynthesis that is stored in lipid droplets. The activation of ACAT and the accumulation of lipid droplets play a key role in the transformation of macrophages into foam cells, leading to the formation of atheroma or atherosclerotic plaque. ApoA-I Helsinki (or ?K107) is a natural apoA-I variant with a lysine deletion in the central protein region, carriers of which have increased atherosclerosis risk. We herein show that treatment of cultured RAW macrophages or CHOK1 cells with ?K107, but not with wild-type apoA-I or a variant containing a similar deletion at the C-terminal region (?K226), lead to a marked increase (more than 10 times) in the intracellular ACAT1 protein level as detected by western blot analysis. However, we could only detect a slight increase in cholesteryl ester produced by ?K107 mainly when Chol loading was supplied by low-density lipoprotein (LDL). Although a similar choline-phospholipid efflux is evoked by these apoA-I variants, the change in phosphatidylcholine/sphyngomyelin distribution produced by wild-type apoA-I is not observed with either ?K107 or ?K226.     

PIK3R1 Mutations Cause Syndromic Insulin Resistance with Lipoatrophy

Short stature, hyperextensibility of joints and/or inguinal hernia, ocular depression, Rieger anomaly, and teething delay (SHORT) syndrome is a developmental disorder with an unknown genetic cause and hallmarks that include insulin resistance and lack of subcutaneous fat. We ascertained two unrelated individuals with SHORT syndrome, hypothesized that the observed phenotype was most likely due to de novo mutations in the same gene, and performed whole-exome sequencing in the two probands and their unaffected parents. We then confirmed our initial observations in four other subjects with SHORT syndrome from three families, as well as 14 unrelated subjects presenting with syndromic insulin resistance and/or generalized lipoatrophy associated with dysmorphic features and growth retardation. Overall, we identified in nine affected individuals from eight families de novo or inherited PIK3R1 mutations, including a mutational hotspot (c.1945C>T [p.Arg649Trp]) present in four families. PIK3R1 encodes the p85α, p55α, and p50α regulatory subunits of class IA phosphatidylinositol 3 kinases (PI3Ks), which are known to play a key role in insulin signaling. Functional data from fibroblasts derived from individuals with PIK3R1 mutations showed severe insulin resistance for both proximal and distal PI3K-dependent signaling. Our findings extend the genetic causes of severe insulin-resistance syndromes and provide important information with respect to the function of PIK3R1 in normal development and its role in human diseases, including growth delay, Rieger anomaly and other ocular affections, insulin resistance, diabetes, paucity of fat, and ovarian cysts.     

The Arabidopsis oligopeptidases TOP1 and TOP2 are salicylic acid targets that modulate SA‐mediated signaling and the immune response

Salicylic acid (SA) is a small phenolic molecule with hormonal properties, and is an essential component of the immune response. SA exerts its functions by interacting with protein targets; however, the specific cellular components modulated by SA and critical for immune signal transduction are largely unknown. To uncover cellular activities targeted by SA, we probed Arabidopsis protein microarrays with a functional analog of SA. We demonstrate that thimet oligopeptidases (TOPs) constitute a class of SA‐binding enzymes. Biochemical evidence demonstrated that SA interacts with TOPs and inhibits their peptidase activities to various degrees both in vitro and in plant extracts. Functional characterization of mutants with altered TOP expression indicated that TOP1 and TOP2 mediate SA‐dependent signaling and are necessary for the immune response to avirulent pathogens. Our results support a model whereby TOP1 and TOP2 act in separate pathways to modulate SA‐mediated cellular processes.     

Intra-Seasonal Flexibility in Avian Metabolic Performance Highlights the Uncoupling of Basal Metabolic Rate and Thermogenic Capacity

Stochastic winter weather events are predicted to increase in occurrence and amplitude at northern latitudes and organisms are expected to cope through phenotypic flexibility. Small avian species wintering in these environments show acclimatization where basal metabolic rate (BMR) and maximal thermogenic capacity (M_SUM) are typically elevated. However, little is known on intra-seasonal variation in metabolic performance and on how population trends truly reflect individual flexibility. Here we report intra-seasonal variation in metabolic parameters measured at the population and individual levels in black-capped chickadees ( Poecile atricapillus ). Results confirmed that population patterns indeed reflect flexibility at the individual level. They showed the expected increase in BMR (6%) and M_SUM (34%) in winter relative to summer but also, and most importantly, that these parameters changed differently through time. BMR began its seasonal increase in November, while M_SUM had already achieved more than 20% of its inter-seasonal increase by October, and declined to its starting level by March, while M_SUM remained high. Although both parameters co-vary on a yearly scale, this mismatch in the timing of variation in winter BMR and M_SUM likely reflects different constraints acting on different physiological components and therefore suggests a lack of functional link between these parameters.     

The role of proline residues in the folding kinetics of the bovine pancreatic trypsin inhibitor derivative RCAM(14–38)

The role of proline residues in the folding of the trypsin inhibitor derivative RCAM(14–38) has been studied by testing for slow-folding species of the unfolded protein, which could result from the introduction of wrong proline isomers after unfolding. The unfolded protein at 25 °C contains chiefly fast-folding (U_F) molecules: they refold with a time constant of 40 milliseconds at pH 6.8 in 1.9 m-guanidinium chloride. At least one minor slow-folding (U_s) species has been found, using fluorescence to monitor refolding. The reaction in which this U_s species is formed after unfolding shows the properties expected for the cis: Irans isomerization of a proline residue. When refolding is monitored by tyrosine absorbance, two minor slow reactions are found. The faster reaction is in the same time range (15 s at 25 °C) as that studied by fluorescence, and the slower reaction is quite slow (200 s at 25 °C). It is not known whether the slower reaction results from a second U_s species. There are four trans proline residues in bovine pancreatic trypsin inhibitor: the proportion of slow-folding molecules (not more than 25% at 25 °C) is smaller than expected if every proline residue can produce a U_s species and if the cis to trans ratio of each residue after unfolding is at least 0.1:0.9.Criteria based on folding kinetics are given for classifying the types of folding reaction shown by unfolded molecules containing a single wrong proline isomer. Levitt (1980) has classified three types of proline residues according to the energy difference (small, intermediate or large) between the native protein and the predicted minimum energy structure containing a wrong proline isomer. He suggests that these three types of proline residues can be recognized by the types of folding reactions they produce. Only type II (intermediate) folding reactions have thus far been characterized by the criteria introduced here. We point out that the type of folding reaction depends also on the folding conditions, and a possible explanation for this effect is given.     

Effects of age, gender and time on receptor expression and anti-Aspergillus functions of human phagocytes

Phagocytes play a central role in immune defense. Their dysfunction predisposes to infections. This study determined the expression level of nine receptors involved in Aspergillus immune response as well as the values of phagocytosis and production of radical oxygen species after Aspergillus stimulation, in a healthy adult population.The expression values of the CD11b, CD11c, CD14, CD18, CD35, CD181, CD182, CD282 and CD284 receptors on peripheral human monocytes and granulocytes was established. A heterogenous expression of the CD282 on granulocytes was observed as CD181, CD182 and CD284 on monocytes. Similarly, we observed considerable variation in the expression of these receptors over time. Only CD282 on granulocytes varied with sex. No variation with age was observed. Adherence of Aspergillus conidia to phagocytes was dependent of individual, sex, age and time. A better characterization of these innate immunity parameters is necessary to develop in the future an immunologic surveillance strategy for transplant recipients.     

Early steps in microbial colonization processes at deep-sea hydrothermal vents

A pluri-disciplinary in situ colonization experiment was performed to study early stages of colonization in deep-sea vent Alvinella spp. worm habitats. Four colonization devices were deployed onto Alvinella spp. colonies of different chimneys of the East-Pacific Rise (EPR 13 degrees N), for two different periods: a short (less than a week) and a longer one (3 weeks). Video imagery and monitoring of the thermal and physico-chemical conditions were performed during the colonization experiments. Numerous microorganisms bearing specialized adhesion-appendages and/or high amounts of polymeric extracellular matrix were observed on devices, which may efficiently contribute to the colonization of new surfaces. The microbial cohorts preceding and accompanying Alvinella spp. settlement were identified. In all cases, Archaea could not be detected and the microbial mats were essentially composed of e-Proteobacteria. Within this group, one phylotype (AlviH2) was found to dominate the libraries of three colonization devices. Dominance of e-Proteobacteria in the libraries may reflect the wide physiological variety encountered within this group or an adaptability of these microorganisms towards their changing environment. Bacteria affiliated to the Cytophaga-Flavobacterium-Bacteroides group or to the e-Proteobacteria, that grow either chemo-organoheterotrophically by fermentation or chemolithoautotrophically with H2 as an electron donor and S degrees /S2O32- or NO3- as a terminal electron acceptor, were isolated from one of the microbial mat formed in 20 days.