Possible Role of Interleukin-1β in Type 2 Diabetes Onset and Implications for Anti-inflammatory Therapy Strategies

Increasing evidence of a role of chronic inflammation in type 2 diabetes progression has led to the development of therapies targeting the immune system. We develop a model of interleukin-1β dynamics in order to explain principles of disease onset. The parameters in the model are derived from in vitro experiments and patient data. In the framework of this model, an IL-1β switch is sufficient and necessary to account for type 2 diabetes onset. The model suggests that treatments targeting glucose bear the potential of stopping progression from pre-diabetes to overt type 2 diabetes. However, once in overt type 2 diabetes, these treatments have to be complemented by adjuvant anti-inflammatory therapies in order to stop or decelerate disease progression. Moreover, the model suggests that while glucose-lowering therapy needs to be continued all the way, dose and duration of the anti-inflammatory therapy needs to be specifically controlled. The model proposes a framework for the discussion of clinical trial outcomes.     

Phosphatidylinositol 3'-kinase activity is critical for initiating the oxidative burst and bacterial destruction during CEACAM3-mediated phagocytosis

Carcinoembryonic antigen-related cell adhesion molecule 3 (CEACAM3) is an immunoglobulin-related receptor expressed on human granulocytes. CEACAM3 functions as a single chain phagocytotic receptor recognizing gram-negative bacteria such as Neisseria gonorrhoeae, which possess CEACAM-binding adhesins on their surface. The cytoplasmic domain of CEACAM3 contains an immunoreceptor tyrosine-based activation motif (ITAM)-like sequence that is phosphorylated upon receptor engagement. Here we show that the SH2 domains of the regulatory subunit of phosphatidylinositol 3'-kinase (PI3K) bind to tyrosine residue 230 of CEACAM3 in a phosphorylation-dependent manner. PI3K is rapidly recruited and directly associates with CEACAM3 upon bacterial binding as shown by FRET analysis. Although PI3K activity is not required for efficient uptake of the bacteria by CEACAM3-transfected cells or primary human granulocytes, it is critical for the stimulated production of reactive oxygen species by infected phagocytes and the intracellular degradation of CEACAM-binding bacteria. Together, our results highlight the ability of CEACAM3 to coordinate signaling events that not only mediate bacterial uptake, but also trigger the killing of internalized pathogens.     

Conjugated linoleic acids mediate insulin release through islet G protein-coupled receptor FFA1/GPR40

Among dietary components, conjugated linoleic acids (CLAs) have attracted considerable attention as weight loss supplements in the Western world because they reduce fat stores and increase muscle mass. However, a number of adverse effects are also ascribed to the intake of CLAs such as aggravation of insulin resistance and the risk of developing diabetes. However, the mechanisms accounting for the effects of CLAs on glucose homeostasis are incompletely understood. Herein we provide evidence that CLAs specifically activate the cell surface receptor FFA1, an emerging therapeutic target to treat type 2 diabetes. Using different recombinant cellular systems engineered to stably express FFA1 and a set of diverse functional assays including the novel, label-free non-invasive dynamic mass redistribution technology (Corning® Epic® biosensor), both CLA isomers cis-9, trans-11-CLA and trans-10, cis-12-CLA were found to activate FFA1 in vitro at concentrations sufficient to also account for FFA1 activation in vivo. Each CLA isomer markedly increased glucose-stimulated insulin secretion in insulin-producing INS-1E cells that endogenously express FFA1 and in primary pancreatic β-cells of wild type but not FFA1^−/− knock-out mice. Our findings establish a clear mechanistic link between CLAs and insulin production and identify the cell surface receptor FFA1 as a molecular target for CLAs, explaining their acute stimulatory effects on insulin secretion in vivo. CLAs are also revealed as insulinotropic components in widely used nutraceuticals, a finding with significant implication for development of FFA1 modulators to treat type 2 diabetes.     

The unique plant RhoGAPs are dimeric and contain a CRIB motif required for affinity and specificity towards cognate small G proteins

Plant Rho proteins (ROPs) are inactivated by specific GTPase activating proteins, called RopGAPs. Many of these comprise the exclusive combination of a classic, catalytic Arg-containing RhoGAP domain, and a Cdc42/ Rac interactive binding (CRIB) motif which in animal and fungi has been identified in effectors for Cdc42 and Rac1, but never in any GAP protein. Both elements are required for an efficient RopGAP activity. Here, we analyzed the effect of the CRIB motif on the complex formation and the binding reaction with plant and human Rho proteins by using kinetic and equilibrium methods. We show that RopGAP2 from Arabidopsis thaliana dimerizes via its GAP domain and forms a 2:2 complex with ROP. The CRIB effector motif mediates high affinity and specificity in binding. The catalytic Arg in the context of the CRIB motif is inhibitory for binding. The unusually slow association and dissociation reactions suggest a major conformational change whereby the CRIB motif functions as a lid for binding and/or release of ROP. We propose a two-site interaction model where ROP binds to the CRIB motif as described for the human CRIB effectors and to the catalytic GAP domain as described for animal RhoGAPs.     

Complete genome sequence of the hemotrophic Mycoplasma suis strain KI3806

Mycoplasma suis, a member of the hemotrophic mycoplasma (HM) group, parasitize erythrocytes of pigs. Increasing evidence suggests that M. suis is also a zoonotic agent. Highly pathogenic strains of M. suis (e.g., M. suis KI3806) have been demonstrated to invade erythrocytes. This complete sequenced and manually annotated genome of M. suis KI3806 is the first available from this species and from the HM group. The DNA was isolated from blood samples of experimentally infected pigs due to the lack of an in vitro cultivation system. The small circular chromosome of 709,270 bp, encoding an unexpectedly high number of hypothetical proteins and limited transport and metabolic capacities, could reflect the unique lifestyle of HM on the surface of erythrocytes.     

TNF receptor-1 is required for the formation of splenic compartments during adult, but not embryonic life

Lymphotoxin β-receptor (LTβR) and TNF receptor-1 (TNFR1) are important for the development of secondary lymphoid organs during embryonic life. The significance of LTβR and TNFR1 for the formation of lymphoid tissue during adult life is not well understood. Immunohistochemistry, morphometry, flow cytometry, and laser microdissection were used to compare wild-type, LTβR(-/-), TNFR1(-/-) spleens with splenic tissue that has been newly formed 8 wk after avascular implantation into adult mice. During ontogeny, LTβR is sufficient to induce formation of the marginal zone, similar-sized T and B cell zones, and a mixed T/B cell zone that completely surrounded the T cell zone. Strikingly, in adult mice, the formation of splenic compartments required both LTβR and TNFR1 expression, demonstrating that the molecular requirements for lymphoid tissue formation are different during embryonic and adult life. Thus, interfering with the TNFR1 pathway offers the possibility to selectively block the formation of ectopic lymphoid tissue and at the same time to spare secondary lymphoid organs such as spleen and lymph nodes. This opens a new perspective for the treatment of autoimmune and inflammatory diseases.     

Function and Localization Dynamics of Bifunctional Penicillin-Binding Proteins in Caulobacter crescentus

The peptidoglycan cell wall of bacteria is a complex macromolecule composed of glycan strands that are cross-linked by short peptide bridges. Its biosynthesis involves a conserved group of enzymes, the bifunctional penicillin-binding proteins (bPBPs), which contain both a transglycosylase and a transpeptidase domain, thus being able to elongate the glycan strands and, at the same time, generate the peptide cross-links. The stalked model bacterium Caulobacter crescentus possesses five bPBP paralogs, named Pbp1A, PbpC, PbpX, PbpY, and PbpZ, whose function is still incompletely understood. In this study, we show that any of these proteins except for PbpZ is sufficient for growth and normal morphogenesis when expressed at native or elevated levels, whereas inactivation of all five paralogs is lethal. Growth analyses indicate a central role of PbpX in the resistance of C. crescentus against the noncanonical amino acid d-alanine. Moreover, we show that PbpX and PbpY localize to the cell division site. Their recruitment to the divisome is dependent on the essential cell division protein FtsN and likely involves interactions with FtsL and the putative peptidoglycan hydrolase DipM. The same interaction pattern is observed for Pbp1A and PbpC, although these proteins do not accumulate at midcell. Our findings demonstrate that the bPBPs of C. crescentus are, to a large extent, redundant and have retained the ability to interact with the peptidoglycan biosynthetic machineries responsible for cell elongation, cytokinesis, and stalk growth. Nevertheless, they may preferentially act in specific peptidoglycan biosynthetic complexes, thereby facilitating the independent regulation of distinct growth processes.