An efficient organocatalytic cascade reaction has been developed involving a Michael-hemiaminalization relay for the asymmetric synthesis of spiropiperidinone derivatives : bearing adjacent quaternary and tertiary chiral centers via LUMO or HOMO activation. Importantly, this methodology demonstrates that applying distinct activation modes to different substrates in the same reaction can diverge diastereoselectivity. To our knowledge, this is also one of the few published cases of primary amine catalytic [3 + 3] cycloaddition reactions involving alpha-branched beta-ketoamides.
Graphene hydrogel has shown greatly potentials in bone tissue engineering recently, but it is relatively weak in the practical use. Here we report a facile method to synthesize high strength composite graphene hydrogel. Graphene oxide (GO), hydroxyapatite (HA) nanoparticles (NPs) and chitosan (CS) self-assemble into a 3-dimensional hydrogel with the assistance of crosslinking agent genipin (GNP) for CS and reducing agent sodium ascorbate (NaVC) for GO simultaneously. The dense and oriented microstructure of the resulted composite gel endows it with high mechanical strength, high fixing capacity of HA and high porosity. These properties together with the good biocompatibility make the ternary composite gel a promising material for bone tissue engineering. Such a simultaneous crosslinking and reduction strategy can also be applied to produce a variety of 3D graphene-polymer based nanocomposites for biomaterials, energy storage materials and adsorbent materials. (C) 2016 Elsevier Ltd. All rights reserved.
Wnt/beta-catenin signal is required in bone formation and remodling, but little is known about whether Wnt/beta-catenin signal could promote osteogenic differentiation of rat bone marrow mesenchymal stem cells (BMSCs) after uniaxial mechanical stretch. In this study, rat BMSCs were identified by flow cytometry and used for mechanical stretch. A custom-made uniaxial dynamic stretch apparatus was applied for rat BMSCs stretch. There were 2 groups in the study: the mechanical stretch group and the nonstretch control group. Cell morphology, alkaline phosphatase (ALP) activity, mRNA levels (Wnt3a, Lrp5, beta-catenin, as well as Runx2 were evaluated using quantitative real-time reverse transcription-polymerase chain reaction) and protein levels (beta-catenin and Runx2 were examined using western blot) were observed in both groups. The authors finally found that not only the cell proliferation, ALP activity, but also mRNA expression of Wnt3a, Lrp5, beta-catenin, and Runx2 in BMSCs were markedly elevated by mechanical stretch than the controls. Protein levels of beta-catenin and Runx2 were significantly higher than that of control as well. Activation of mechanical stretch was partially reversed by DKK-1, a classical inhibitor of Wnt/beta-catenin signal. These results demonstrate that uniaxial mechanical stretch could stimulate osteogenic differentiation and proliferation of BMSCs by activating the Wnt/beta-catenin signaling.
Introduction: Mutations in the proteinase bone morphogenetic protein-1 (BMP1) were recently identified in patients with osteogenesis imperfecta, which can be associated with type 1 dentinogenesis imperfecta. BMP1 is co-expressed in various tissues and has overlapping activities with the closely related proteinase mammalian tolloid-like 1 (TLL1). In this study we investigated whether removing the overlapping activities of BMP1 and TLL1 affects the mineralization of tooth root dentin. Methods: Floxed alleles of the BMP1 and TLL1 genes were excised via ubiquitously expressed Cre induced by tamoxifen treatment beginning at 3 days of age (harvested at 3 weeks of age) or beginning at 4 weeks of age (harvested at 8 weeks of age). Multiple techniques, including x-ray analysis, double-labeling with calcein and alizarin red stains for measurement of dentin formation rate, and histologic and immunostaining assays, were used to analyze the dentin phenotype. Results: BMP1/TLL1 double knockout mice displayed short and thin root dentin, defects in dentin mineralization, and delayed tooth eruption. Molecular mechanism studies revealed accumulation of collagens in dentin and a sharp reduction in non-collagenous proteins such as dentin matrix protein 1 and dentin sialophosphoprotein. Furthermore, we found a strong reduction in tartrate-resistant acid phosphatase, which is likely caused by defects in bone cells. Conclusions: BMP1/TLL1 appear to play crucial roles in maintaining extracellular matrix homeostasis essential to root formation and dentin mineralization.