Lipid rafts and membrane traffic

Membrane rafts are regions of increased lipid acyl chain order that differ in their lipid and protein composition from the surrounding membrane. By providing an additional level of compartmentalization they have been proposed to serve many functions in cellular signal transduction and trafficking. We will review their potential involvement in different forms of membrane traffic, explicitly excluding signalling, and discuss select aspects of the raft hypothesis in its current form.     

Microstructure,mineral and mechanical properties of teleost intermuscular bones

There is an increasing interest in understanding teleost bone biomechanics in several scientific communities, for instance as interesting biomaterials with specific structure-function relationships. Intermuscular bones of teleost fish have previously been described to play a role in the mechanical force transmission between muscle and bone, but their biomechanical properties are not yet fully described. Here, we have investigated intermuscular bones (IBs) of the North Atlantic Herring with regard to their structure and micro-architecture, mineral-related properties, and micro-mechanical tensile properties. A total of 115 IBs from 18 fish were investigated. One cohort of IBs, containing 20 bones from 2 smaller fish and 23 bones of 3 larger fish, was used for mechanical testing, wide-angle X-ray scattering, and scanning electron microscopy. Another cohort, containing 36 bones from 7 smaller fish and 36 bones from 6 larger fish, was used for microCT. Results show some astonishing properties of the IBs: (i) IBs present higher ductility, lower Young's modulus but similar strength and TMD (Tissue Mineral Density) compared to mammalian bone, and (ii) IBs from small fish were 49% higher in Young’s modulus than fish bones from larger fish while their TMD was not statistically different and crystal length was 8% higher in large fish bones. Our results revealed that teleost IB presents a hybrid nature of soft and hard tissue that differs from other bone types, which might be associated with their evolution from mineralized tendons. This study provides new data regarding teleost fish bone biomechanical and micro-structural properties.     

ABCC8 genetic variants and risk of diabetes mellitus

Diabetes mellitus (DM) is a major health problem worldwide and it will rapidly increase. This disease is characterized by hyperglycemia caused by defects in insulin secretion, insulin action or both. DM has three types: T1DM, T2M and gestational DM (GDM), of them T2DM is more frequent. Multiple genes and their interactions are involved in insulin secretion pathway. Sulfonylurea receptor encoded by ABCC8 gene, together with inward-rectifier potassium ion channel (Kir6.2) regulates insulin secretion by ATP-sensitive K⁺ (KATP) channel located in the plasma membranes. Disruption of these molecules by different mutations is responsible for risk of DM. Several single nucleotide polymorphisms (SNPs) of ABCC8 gene and their interaction are involved in pathogenicity of DM. This review summarizes the current evidence of contribution of ABC8 genetic variants to the development of DM.     

Fetal Liver Stromal Cells Support Blast Growth in Transient Abnormal Myelopoiesis in Down Syndrome Through GM‐CSF

Transient abnormal myelopoiesis (TAM) in neonates with Down syndrome, which spontaneously resolves within several weeks or months after birth, may represent a very special form of leukemia arising in the fetal liver (FL). To explore the role of the fetal hematopoietic microenvironment in the pathogenesis of TAM, we examined the in vitro influences of stromal cells of human FL and fetal bone marrow (FBM) on the growth of TAM blasts. Both FL and FBM stromal cells expressed mesenchymal cell antigens (vimentin, α‐smooth muscle actin, CD146, and nestin), being consistent with perivascular cells/mesenchymal stem cells that support hematopoietic stem cells. In addition, a small fraction of the FL stromal cells expressed an epithelial marker, cytokeratin 8, indicating that they could be cells in epithelial‐mesenchymal transition (EMT). In the coculture system, stromal cells of the FL, but not FBM, potently supported the growth of TAM blast progenitors, mainly through humoral factors. High concentrations of hematopoietic growth factors were detected in culture supernatants of the FL stromal cells and a neutralizing antibody against granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) almost completely inhibited the growth‐supportive activity of the culture supernatants. These results indicate that FL stromal cells with unique characteristics of EMT cells provide a pivotal hematopoietic microenvironment for TAM blasts and that GM‐CSF produced by FL stromal cells may play an important role in the pathogenesis of TAM. J. Cell. Biochem. 115: 1176–1186, 2014. © 2014 The Authors. Journal of Cellular Biochemistry published by Wiley Periodicals, Inc.     

Surface raw electromyography has a moderate discriminatory capacity for differentiating between healthy individuals and those with TMD: A diagnostic study

The use of surface electromyography (sEMG) to identify subjects with chronic temporomandibular disorders (TMD) is controversial. The main objective of this study is to determine the diagnostic accuracy of EMG to differentiate between healthy subjects and those with TMD.This study evaluated 53 individuals with TMD who were referred to the university service and who fulfilled the eligibility criteria during the period of the study. Thirty-eight dental students were also recruited satisfying same eligibility criteria but without TMD. The inclusion criteria were to be fully dentate, have normal occlusion, and be righthanded. The exclusion criteria were periodontal pathology, caries or damaged dental tissues, orthodontic therapy, maxillofacial disease, botulinum A toxin therapy, and psychological disorders.The means of the masseter muscles, right (RM) and left (LM), and temporalis muscles, right (RT) and left (LT), and intraindividual indexes during resting and during clenching were calculated. Raw sEMG activity was used to determine the cutoff points and calculate the diagnostic accuracy of sEMG. The diagnostic accuracy of these variables for a diagnosis of TMD was evaluated by using the Receiver Operating Characteristic (ROC) curve and the area under it (AUC). A new transformed diagnostic variable was obtained by using the Generalized Additive Models (GAM). Optimal cutoff points were obtained where the sensitivity and specificity were similar and by the Youden index. The highest estimated AUC was 0.660 (95% CI 0.605–0.871) corresponding to the rLT variable during rest. When rLT and rACTIVITY (differences divided by sums of temporalis versus masseter muscles) were considered as a linear combination, the AUC increased to 0.742 (95% CI; 0.783–0.934).In conclusion, the raw sEMG evaluation of rest provided moderate sensitivity and specificity to discriminate between healthy individuals and those with TMD. The use of the indexes (mainly assessing the dominance of temporalis over masseter muscles during rest) is strongly recommended to increase the discriminatory capacity of raw sEMG evaluation.     

Characterization of the interaction of diacylglycerol acyltransferase-2 with the endoplasmic reticulum and lipid droplets

Acyl CoA:diacylglycerol acyltransferase-2 (DGAT2) is an integral membrane protein that catalyzes the synthesis of triacylglycerol (TG). DGAT2 is present in the endoplasmic reticulum (ER) and also localizes to lipid droplets when cells are stimulated with oleate. Previous studies have shown that DGAT2 can interact with membranes and lipid droplets independently of its two transmembrane domains, suggesting the presence of an additional membrane binding domain. In order to identify additional membrane binding regions, we confirmed that DGAT2 has only two transmembrane domains and demonstrated that the loop connecting them is present in the ER lumen. Increasing the length of this short loop from 5 to 27 amino acids impaired the ability of DGAT2 to localize to lipid droplets. Using a mutagenesis approach, we were able to identify a stretch of amino acids that appears to have a role in binding DGAT2 to the ER membrane. Our results confirm that murine DGAT2 has only two transmembrane domains but also can interact with membranes via a previously unidentified helical domain containing its active site.     

cDNA cloning, recombinant expression and bioactivity of Père David's deer BAFF

B cell activating factor (BAFF), a member of the TNF family, is a critical cytokine for the survival, proliferation, maturation, and differentiation of B cells. In the present study, Père David's deer BAFF (miBAFF) was amplified from Elaphurus davidianus using RT-PCR. This is the first BAFF cloned from a member of Cervidae family. The open reading frame (ORF) of the miBAFF cDNA consists of 843 bases that encode a 280-amino acid protein bearing typical TNF homology domain. Sequence alignment shows that miBAFF shares 39.3%-97% sequence homology with the BAFF sequences of other mammals. Comparative protein modeling predicted that the 3D structure of the soluble mature portion of miBAFF (misBAFF) is very similar to that of human BAFF (hsBAFF). Recombinant misBAFF fused to a SUMO-tag was efficiently expressed in Escherichia coli BL21 (DE3) cells. The protein molecular weight of ~36 KDa was determined using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and Western blotting. In vitro, purified misBAFF was shown to promote the survival and proliferation of Père David's deer peripheral blood lymphocytes and mouse B cells. These results indicate that miBAFF plays an important role in the survival/proliferation of mouse B cells and, shows highly conserved evolutionarily, leading to functional cross-reactivity that exists between mouse and Père David's deer BAFF.     

Carbohydrate transporting membrane proteins of the rumen bacterium, Butyrivibrio proteoclasticus

The research was aimed at finding which membrane proteins of the rumen bacterium Butyrivibrio proteoclasticus are involved in the uptake of carbohydrates resulting from extracellular enzymatic degradation of hemicellulose and fructan. The proteomic analysis of cells grown with fructose or xylan as the sole substrate identified 13 membrane proteins predicted to function as carbohydrate transporters. One protein detected was the membrane component of a fructose-specific phosphoenolpyruvate:sugar phosphotransferase system believed to be involved in the fructose uptake following extracellular fructan breakdown. The other 12 proteins were all ABC transport system substrate-binding proteins, nine of which belong to functional category COG1653 that includes proteins predicted to transport oligosaccharides. Four of the SBPs were significantly upregulated in xylan grown cells, and three of these were found in polysaccharide utilisation loci where they are clustered with other genes involved in hemicellulose breakdown and metabolism. It is possible that the carbon source available regulates a wider network of genes. The information on the mechanisms used by rumen bacteria to take up carbohydrates from their environment may improve our understanding of the ruminant digestion and facilitate strategies for improved pasture and stored feed utilisation.     

Positional dependence of non-native polar mutations on folding of CFTR helical hairpins

Mutations of the cystic fibrosis transmembrane conductance regulator (CFTR) cause CF disease by altering the biosynthesis, maturation, folding and ion conductance of this protein. Our laboratory has focused on expression and structural analysis of the CFTR transmembrane (TM) domains using two-TM segments (i.e., helix-loop-helix constructs) which we term ‘helical hairpins’; these represent the minimal model of tertiary contacts between two helices in a membrane. Previous studies on a library of TM3/4 hairpins of the first CFTR TM domain suggested that introduction of non-native polar residues into TM4 can compromise CFTR function through side chain-side chain H-bonding interactions with native Q207 in TM3 [Choi, M. Y., Cardarelli, L., Therien, A. G., and Deber, C. M. Non-native interhelical hydrogen bonds in the cystic fibrosis transmembrane conductance regulator domain modulated by polar mutations, Biochemistry 43 (2004) 8077-8083]. In the present work, we combine gel shift assays with a series of NMR experiments for comparative structural characterization of the wild type TM3/4 hairpin and its mutants V232D, I231D, Q207N/V232E. Over 95% of the backbone resonances of a ¹⁵N,¹³C-labelled V232D-TM3/4 construct in the membrane-mimetic environment of perfluorooctanoate (PFO) micelles were successfully assigned, and the presence and boundaries of helical segments within TM3 and TM4 were defined under these conditions. Comparative analysis of ¹⁵N and ¹H chemical shift variations among HSQC spectra of WT-, V232D-, I231D- and Q207N/V232E-TM3/4 indicated that hairpin conformations vary with the position of a polar mutation (i.e., V232D and I231D vs. WT), but remain similar when hairpins with identically-positioned polar partners are compared (i.e., V232D vs. Q207N-V232E). The overall findings suggest that a polar mutation in a TM helix can potentially distort native interfacial packing determinants in membrane proteins such as CFTR, with consequences that may lead to disease.