Immunological functions of leptin and adiponectin

Recent years have seen several advances in our understanding of the functions of adipose tissue regarding not only the energy storage, but also the regulation of complex metabolic and endocrine functions. In this context, leptin and adiponectin, the two most abundant adipocyte products, represent one of the best example of adipocytokines involved in the control of energy expenditure, lipid and carbohydrate metabolism as well as in the regulation of immune responses. Leptin and adiponectin secretion is counter-regulated in vivo, in relation to degree of adiposity, since plasma leptin concentrations are significantly elevated in obese subjects in proportion to body mass index while adiponectin secretion decreases in relation to the amount of adipose tissue. In this review we focus on the main biological activities of leptin and adiponectin on the lipid and carbohydrate metabolism and on their contribute in regulation of innate and adaptive immune responses.     

Calcium Dependence of Synaptic Vesicle Recycling Before and After Synaptogenesis

Abstract: Using an immunocytochemical assay to monitor synaptic vesicle exocytosis/endocytosis independently of neurotransmitter release, we have investigated some aspects of vesicle recycling in hippocampal neurons at different developmental stages. A calcium- and depolarization-dependent exocytotic/endocytotic recycling of synaptic vesicles was found to take place in neurons already before the formation of synaptic contacts. The analysis of synaptic vesicle recycling at different calcium concentrations revealed the presence of two release components: the first one activated by low calcium concentrations and sustaining vesicle recycling before synaptogenesis, and a second one activated by high calcium concentrations, which is specifically turned on after the establishment of synaptic contacts. These data suggest that formation of synapses correlates with the activation of a putative low-affinity calcium sensor, which allows synaptic vesicle exocytosis to be triggered and turned off over extremely short time scales, in response to large increases in the level of intracellular calcium.     

Protein Kinase Activity of in vitro Cultured Plant Cells in Relation to Growth and Starch Metabolism

Taking tetcyclacis, a norbornenodiazentine derivative, as an example, the influence of a growth retardant on the shoot growth of sunflower, soybean, and maize seedlings grown and treated in hydroculture was investigated. In detail, the reduction in the length of various shoot sections {epicotyl, 1st internode, leaf blade) caused by the retardant was studied. At low concentrations of the retardant (\lt10^-6 M) the shortening effects are substantially attributable to an influence on cell elongation, whereas cell division is inhibited as the concentration increases (τ10^-6 M). A comparison of the effects of tetcyclacis in cell suspension cultures of appropriate plant species showed that also in this system concentrations τ 10^-6 M inhibited cell division growth, i. e. there is comparability of plant/ cell culture regarding the retardant effect on cell division. In contrast to the intact plants, however, cell elongation appears to be of only subordinate importance for the growth of cell cultures, as it has been shown using parsley cell suspension cultures.It is discussed to what extent influencing the gibberellin or sterol biosynthesis by means of tetcyclacis provides an explanation for the concentration-dependent effect on the cell division and cell elongation processes.     

Neurite Fasciculation Mediated by Complexes of Axonin-1 and Ng Cell Adhesion Molecule

Neural cell adhesion molecules composed of immunoglobulin and fibronectin type III-like domains have been implicated in cell adhesion, neurite outgrowth, and fasciculation. Axonin-1 and Ng cell adhesion molecule (NgCAM), two molecules with predominantly axonal expression exhibit homophilic interactions across the extracellular space (axonin- 1/axonin-1 and NgCAM/NgCAM) and a heterophilic interaction (axonin-1–NgCAM) that occurs exclusively in the plane of the same membrane (cis-interaction). Using domain deletion mutants we localized the NgCAM homophilic binding in the Ig domains 1-4 whereas heterophilic binding to axonin-1 was localized in the Ig domains 2-4 and the third FnIII domain. The NgCAM–NgCAM interaction could be established simultaneously with the axonin-1–NgCAM interaction. In contrast, the axonin-1–NgCAM interaction excluded axonin-1/axonin-1 binding. These results and the examination of the coclustering of axonin-1 and NgCAM at cell contacts, suggest that intercellular contact is mediated by a symmetric axonin-1₂/NgCAM₂ tetramer, in which homophilic NgCAM binding across the extracellular space occurs simultaneously with a cis-heterophilic interaction of axonin-1 and NgCAM. The enhanced neurite fasciculation after overexpression of NgCAM by adenoviral vectors indicates that NgCAM is the limiting component for the formation of the axonin-1₂/NgCAM₂ complexes and, thus, neurite fasciculation in DRG neurons.     

Effect of puromycin on cartilage proteoglycan structure and capacity to bind hyaluronic acid

Rat chondrosarcoma chondrocytes were cultured in the presence of puromycin to induce premature termination of core protein precursor. The structure and function of intracellular and extracellular proteoglycans were assessed by molecular sieve chromatography and polyacrylamide gel electrophoresis. [³H]Serine incorporation was maximally inhibited by 3 × 10^?4m puromycin but unaffected by 10 ^?5m puromycin. Proteoglycans synthesized in the presence of puromycin exhibited increased monomer size due to increased chondroitin sulfate chain size, typical of proteoglycans synthesized in the presence of protein synthesis inhibitors, but no loss in ability to bind to hyaluronic acid; and no loss in core protein size was observed after treatment with chondroitinase. These data suggest that chondrocytes select only completed or nearly completed core protein molecules to process into proteoglycans.     

Impact of antigen presentation on TCR modulation and cytokine release: implications for detection and sorting of antigen-specific CD8+ T cells using HLA-A2 wild-type or HLA-A2 mutant tetrameric complexes

Soluble MHC class I molecules loaded with antigenic peptides are available either to detect and to enumerate or, alternatively, to sort and expand MHC class I-restricted and peptide-reactive T cells. A defined number of MHC class I/peptide complexes can now be implemented to measure T cell responses induced upon Ag-specific stimulation, including CD3/CD8/zeta-chain down-regulation, pattern, and quantity of cytokine secretion. As a paradigm, we analyzed the reactivity of a Melan-A/MART-1-specific and HLA-A2-restricted CD8(+) T cell clone to either soluble or solid-phase presented peptides, including the naturally processed and presented Melan-A/MART-1 peptide AAGIGILTV or the peptide analog ELAGIGILTV presented either by the HLA-A2 wild-type (wt) or mutant (alanineright arrowvaline aa 245) MHC class I molecule, which reduces engagement of the CD8 molecule with the HLA-A2 heavy chain. Soluble MHC class I complexes were used as either monomeric or tetrameric complexes. Soluble monomeric MHC class I complexes, loaded with the Melan-A/MART-1 peptide, resulted in CD3/CD8 and TCR zeta-chain down-regulation, but did not induce measurable cytokine release. In general, differences pertaining to CD3/CD8/zeta-chain regulation and cytokine release, including IL-2, IFN-gamma, and GM-CSF, were associated with 1) the format of Ag presentation (monomeric vs tetrameric MHC class I complexes), 2) wt vs mutant HLA-A2 molecules, and 3) the target Ag (wt vs analog peptide). These differences are to be considered if T cells are exposed to recombinant MHC class I Ags loaded with peptides implemented for detection, activation, or sorting of Ag-specific T cells.     

Biofilm induced tolerance towards antimicrobial peptides

Increased tolerance to antimicrobial agents is thought to be an important feature of microbes growing in biofilms. We address the question of how biofilm organization affects antibiotic susceptibility. We established Escherichia coli biofilms with differential structural organization due to the presence of IncF plasmids expressing altered forms of the transfer pili in two different biofilm model systems. The mature biofilms were subsequently treated with two antibiotics with different molecular targets, the peptide antibiotic colistin and the fluoroquinolone ciprofloxacin. The dynamics of microbial killing were monitored by viable count determination, and confocal laser microscopy. Strains forming structurally organized biofilms show an increased bacterial survival when challenged with colistin, compared to strains forming unstructured biofilms. The increased survival is due to genetically regulated tolerant subpopulation formation and not caused by a general biofilm property. No significant difference in survival was detected when the strains were challenged with ciprofloxacin. Our data show that biofilm formation confers increased colistin tolerance to cells within the biofilm structure, but the protection is conditional being dependent on the structural organization of the biofilm, and the induction of specific tolerance mechanisms.