Nonlinear viscoelasticty plays an essential role in the functional behavior of spinal ligaments

Despite the significant role ligament viscoelasticity plays in functional spinal biomechanics, relatively few studies have been performed to develop constitutive models that explicitly characterize this complex behavior. Unfortunately, the application and interpretation of these previous models are limited due to the use of simplified (quasi-linear) viscoelastic formulations or characterization techniques that have been shown to affect the predictive accuracy of the fitted coefficients. In order to surmount these previous limitations, the current study presents the application of a novel fitting technique (applied to stress relaxation experiments) and nonlinear viscoelastic constitutive formulation to human cervical spine anterior longitudinal ligament (ALL), posterior longitudinal ligament (PLL) and ligamentum flavum (LF). The fitted coefficients were validated by quantifying the ability of the constitutive equation to predict an independent cyclic data set across multiple physiologic strain amplitudes and frequencies. The resulting validated constitutive formulation indicated that the strain-dependent viscoelastic behavior of the longitudinal ligaments (ALL and PLL) was dominated by both the short-term (t=0.1s) and the steady-state (as t→∞) behavior. Conversely, the LF exhibited consistent relaxation behavior across the investigated temporal spectrum. From these data, it can be hypothesized that the unique strain-dependent temporal behavior of these spinal ligaments may be a functional adaptation that minimizes muscular expenditure during quasi-static postures while maximizing structural stability of the spine during transient loading events.     

Effects of Coxiella burnetii on MAPKinases phosphorylation

Q fever is a disease caused by Coxiella burnetii, an obligate intracellular bacterium. Acute Q fever is characterized by efficient immune response, whereas chronic Q fever is characterized by dysregulated immune response as demonstrated by the lack of granulomas, the failure of C. burnetii to induce lymphoproliferation, and interferon-γ production. The mitogen-activated protein kinase (MAPK) signaling pathway plays crucial roles in innate immune responses and control of bacterial infections. However, its role in Q fever has not been addressed. First, we investigated the activation of MAPKs p38, c-jun N-terminal kinase (JNK) and extracellular signal-regulated kinase (ERK) 1/2 in murine macrophages stimulated with C. burnetii. Coxiella burnetii NM phase I (virulent) and NM phase II (avirulent) induced the activation of JNK and ERK1/2. Avirulent C. burnetii activate p38, whereas C. burnetii did not induce the phosphorylation of p38. Second, the level of p38 activation was studied in Q fever patients. We found that p38 was activated in monocyte-derived macrophages from healthy donors and patients with acute Q fever in response to a potent agonist such as lipopolysaccharide. Interestingly, p38 was not activated in patients with active chronic Q fever and was activated in patients with cured chronic Q fever. These results suggest that the determination of p38 activation may serve as a tool for measuring Q fever activity.     

Multilocus enzyme electrophoresis analysis of Trypanosoma cruzi isolates from a geographically restricted endemic area for Chagas' disease in Argentina

A set of 65 Trypanosoma cruzi stocks from dogs, opossums, insect vectors and humans was isolated in a geographically restricted endemic area for Chagas' disease in Argentina and was analysed by multilocus enzyme electrophoresis for 15 loci. The results show that at least five multilocus genotypes (clonets) circulate in the study area, one belonging to T. cruzi IIe, one to T. cruzi IId and three clonets belonging to T. cruzi I; and they confirm the presence of these lineages in the country. The three clonets attributed to T. cruzi I were identical to each other for all loci except for Sod-2, where three different patterns were identified. These patterns suggest the presence of two homozygous genotypes and one heterozygous genotype. Our results also suggest association of clonet IIe with dogs, clonet IId with humans and the three T. cruzi I clonets with Didelphis albiventris. On the other hand, there was no significant association between Triatoma infestans and any particular clonet circulating in the area. These findings are consistent with the hypothesis of natural selection, from mixed populations of T. cruzi in vectors, toward more restricted populations in mammals. The epidemiological implications of the possible selection of different clonets by different mammal hosts and the significance of two homozygous genotypes and one heterozygous genotype for the Sod-2 locus are discussed.     

BMP2 initiates chondrogenic lineage development of adult human mesenchymal stem cells in high-density culture

Human bone marrow-derived mesenchymal stem cells (MSCs) have been shown to differentiate into distinct mesenchymal tissues including bone and cartilage. The capacity of MSCs to replicate undifferentiated and to mature into cartilaginous tissues suggests these cells as an attractive cell source for cartilage tissue engineering. Here we show that the stimulation of human bone marrow-derived MSCs with recombinant bone morphogenetic protein-2 (BMP2) results in chondrogenic lineage development under serum-free conditions. Histological staining of proteoglycan with Alcian blue and immunohistochemical staining of cartilage-specific type II collagen revealed the deposition of typical cartilage extracellular matrix components. Semi-quantitative real-time gene expression analysis of characteristic chondrocytic matrix genes, such as cartilage link protein, cartilage oligomeric matrix protein, aggrecan, and types I, II, and IX collagen, confirmed the induction of the chondrocytic phenotype in high-density culture upon stimulation with BMP2 and transforming growth factor-beta3 (TGFbeta3). Histologic staining of mineralized extracellular matrix with von Kossa, immunostaining of type X collagen (typical for hypertrophic chondrocytes), and gene expression analysis of osteocalcin and adipocyte-specific fatty acid binding protein (aP2) further documented that BMP2 induced chondrogenic lineage development and not osteogenesis and/or adipogenesis in human MSCs. These results suggest BMP2 as a promising candidate for tissue engineering approaches regenerating articular cartilage on the basis of mesenchymal progenitors from bone marrow.     

The 1.15A crystal structure of the Staphylococcus aureus methionyl-aminopeptidase and complexes with triazole based inhibitors

Methionyl aminopeptidases (MetAPs) represent a unique class of protease that are responsible for removing the N-terminal methionine residue from proteins and peptides. There are two major classes of MetAPs (type I and type II) described and each class can be subdivided into two subclasses. Eukaryotes contain both the type I and type II MetAPs, whereas prokaryotes possess only the type I enzyme. Due to the physiological importance of these enzymes there is considerable interest in inhibitors to be used as antiangiogenic and antimicrobial agents. Here, we describe the 1.15A crystal structure of the Staphylococcus aureus MetAP-I as an apo-enzyme and its complexes with various 1,2,4-triazole-based derivatives at high-resolution. The protein has a typical "pita-bread" fold as observed for the other MetAP structures. The inhibitors bind in the active site with the N1 and N2 atoms of the triazole moiety complexing two divalent ions. The 1,2,4-triazols represent a novel class of potent non-peptidic inhibitors for the MetAP-Is.     

The prodomain of a secreted hydrophobic mini-protein facilitates its export from the endoplasmic reticulum by hitchhiking on sorting receptors

Misfolded secretory proteins are retained in the endoplasmic reticulum (ER) by quality control mechanisms targeted to exposed hydrophobic surfaces. Paradoxically, certain conotoxins expose extensive hydrophobic surfaces upon folding to their bioactive structures. How then can such secreted mini-proteins traverse the secretory pathway? Here we show that secretion of the hydrophobic conotoxin-TxVI is strongly dependent on its propeptide domain, which enhances TxVI export from the ER. The propeptide domain interacts with sorting receptors from the sortilin Vps10p domain family. The sortilin-TxVI interaction occurs in the ER, and sortilin facilitates export of TxVI from the ER to the Golgi. Thus, the prodomain in a secreted hydrophobic protein acts as a tag that can facilitate its ER export by a hitchhiking mechanism.     

Ca2+ -dependent interaction of S100A1 with the sarcoplasmic reticulum Ca2+ -ATPase2a and phospholamban in the human heart

The Ca(2+)-binding S100A1 protein displays a specific and high expression level in the human myocardium and is considered to be an important regulator of heart contractility. Diminished protein levels detected in dilated cardiomyopathy possibly contribute to impaired Ca(2+) handling and contractility in heart failure. To elucidate the S100A1 signaling pathway in the human heart, we searched for S100A1 target proteins by applying S100A1-specific affinity chromatography and immunoprecipitation techniques. We detected the formation of a Ca(2+)-dependent complex of S100A1 with SERCA2a and PLB in the human myocardium. Using confocal laser scanning microscopy, we showed that all three proteins co-localize at the level of the SR in primary mouse cardiomyocytes and confirmed these results by immunoelectron microscopy in human biopsies. Our results support a regulatory role of S100A1 in the contraction-relaxation cycle in the human heart.     

PLTP secreted by HepG2 cells resembles the high-activity PLTP form in human plasma

Plasma phospholipid transfer protein (PLTP) is an important regulator of plasma HDL levels and HDL particle distribution. PLTP is present in plasma in two forms, one with high and the other with low phospholipid transfer activity. We have used the human hepatoma cell line, HepG2, as a model to study PLTP secreted from hepatic cells. PLTP activity was secreted by the cells into serum-free culture medium as a function of time. However, modification of a previously established ELISA assay to include a denaturing sample pretreatment with the anionic detergent sodium dodecyl sulphate was required for the detection of the secreted PLTP protein. The HepG2 PLTP could be enriched by Heparin-Sepharose affinity chromatography and eluted in size-exclusion chromatography at a position corresponding to the size of 160 kDa. PLTP coeluted with apolipoprotein E (apoE) but not with apoB-100 or apoA-I. A portion of PLTP was retained by an anti-apoE immunoaffinity column together with apoE, suggesting an interaction between these two proteins. Furthermore, antibodies against apoE but not those against apoB-100 or apoA-I were capable of inhibiting PLTP activity. These results show that the HepG2-derived PLTP resembles in several aspects the high-activity form of PLTP found in human plasma.     

Suppression of arbuscular mycorrhizal colonization and nodulation in split-root systems of alfalfa after pre-inoculation and treatment with Nod factors

Roots of legumes establish symbiosis with arbuscular mycorrhizal fungi (AMF) and nodule-inducing rhizobia. The existing nodules systemically suppress subsequent nodule formation in other parts of the root, a phenomenon termed autoregulation. Similarly, mycorrhizal roots reduce further AMF colonization on other parts of the root system. In this work, split- root systems of alfalfa (Medicago sativa) were used to study the autoregulation of symbiosis with Sinorhizobium meliloti and the mycorrhizal fungus Glomus mosseae. It is shown that nodulation systemically influences AMF root colonization and vice versa. Nodules on one half of the split-root system suppressed subsequent AMF colonization on the other half. Conversely, root systems pre-colonized on one side by AMF exhibited reduced nodule formation on the other side. An inhibition effect was also observed with Nod factors (lipo-chito-oligosaccharides). NodSm-IV(C16:2, S) purified from S. meliloti systemically suppressed both nodule formation and AMF colonization. The application of Nod factors, however, did not influence the allocation of (14)C within the split-root system, excluding competition for carbohydrates as the regulatory mechanism. These results indicate a systemic regulatory mechanism in the rhizobial and the arbuscular mycorrhizal association, which is similar in both symbioses.     

Effects on adenylate cyclase activities of unsaturated fatty acid incorporation into rat liver plasma membrane phospholipids specific modulation by linoleate

The adenylate cyclase activities of the rat liver plasma membrane were measured simultaneously with the incorporation of acyl chains into the membrane phospholipids using oleyl CoA, linoleyl CoA or arachidonyl CoA thioester. The basal, fluoride — and glucagon — stimulated adenylate cyclase activities were increased by the incorporation of linoleate into the plasma membrane phospholipids. Oleyl CoA did not alter the adenylate cyclase activities whereas arachidonyl CoA, at high concentration, decreased the adenylate cyclase activities. These data indicate a specific effect of phospholipid molecular species containing linoleate.