Calcium plays a fundamental role as second messenger in intracellular signaling and bone serves as the body's calcium reserve to tightly maintain blood calcium levels. Calcium in ingested meal is the main supply and inadequate calcium intake causes osteoporosis and bone fracture. Here, we describe a novel mechanism of how ingested calcium is deposited on bone. Meal ingestion elicits secretion of the gut hormone gastric inhibitory polypeptide (GIP) from endocrine K cells in the duodenum. Bone histomorphometrical analyses revealed that bone formation parameters in the mice lacking GIP receptor (GIPR(-/-)) were significantly lower than those of wild-type (GIPR(+/+)) mice, and that the number of osteoclasts, especially multinuclear osteoclasts, was significantly increased in GIPR(-/-) mice, indicating that GIPR(-/-) mice have high-turnover osteoporosis. In vitro examination showed the percentage of osteoblastic cells undergoing apoptosis to be significantly decreased in the presence of GIP. Because GIPR(-/-) mice exhibited an increased plasma calcium concentration after meal ingestion, GIP directly links calcium contained in meal to calcium deposition on bone.

No abstract

DNA nanotechnology-based nanosystems and macrosystems have attracted much attention in the biomedical research field. The nature of DNA endows these systems with biodegradable, biocompatible, and immunomodulatory properties. Here, we present an injectable hydrogel system that consists only of chemically synthesized short DNA strands, water, and salts. Several preparations of polypod-like structured DNA, or polypodna, were designed, including tri-, tetra-, penta- and hexapodna, as the building blocks of self-gelling DNA hydrogel. Under physiological conditions, properly designed polypodna preparations formed a hydrogel. The analysis of the modulus data of the hydrogel consisting of two sets of hexapodna preparations showed that this injectable hydrogel was reorganized at a time scale of 0.25s. Then, DNA hydrogel containing unmethylated cytosine-phosphate-guanine (CpG) dinucleotides was used to stimulate innate immunity through Toll-like receptor 9, the receptor for CpG DNA. Gel formation significantly increased the activity of immunostimulatory CpG DNA, retarded the clearance after intradermal injection into mice, and increased the immune responses to ovalbumin (OVA) incorporated into the hydrogel as a model antigen. OVA/CpG DNA hydrogel induced much less local or systemic adverse reactions than OVA injected with complete Freund's adjuvant or alum. GpC DNA hydrogel containing no CpG sequences was less effective, indicating the importance of immunomodulation by CpG DNA hydrogel. Thus, we have created an efficient system for sustained delivery of antigens or other bioactive compounds.

Viscoelastic, dielectric, and rheo-optical behavior was examined for miscible blends of high-M cis-polyisoprene (PI) and poly(p-tert-butylstyrene) (PtBS). The slow dielectric relaxation of the blends was exclusively attributed to the global motion of the PI chains having the type-A dipoles. The PI and PtBS chains behaved as the fast and slow (low- and high-friction) components and were well entangled with each other. The dynamics of these chains changed significantly with temperature T. At high T, the blend exhibited two-step entanglement plateau of the storage modulus G′(ω), and the plateaus at high and low angular frequencies (ω) were attributed, with the aid of the dielectric data, to the entanglement among all component chains and that between the PtBS chains, respectively. The entanglement length a characterizing the high-ω plateau was well described by a simple mixing rule based on the number fraction n of the Kuhn segments of the components, a = n PI a PI bulk + n PtBS a PtBS bulk. This result was consistent with the current molecular picture relating the entanglement density to the packing length p (≅a/20). The complex moduli G* of the blends in the high-ω plateau zone were well described by a simple blending law combined with this mixing rule of a, which was consistent with the rheo-optical data. At low T, the blend exhibited the Rouse-like power-law behavior of storage and loss moduli, G′ = G′′∝ ω1/2, in the range of ω where the high-ω plateau was supposed to emerge. This lack of the high-ω plateau was attributed to retardation of the Rouse equilibration of the PI chain over the entanglement length a due to the hindrance from the slow PtBS chains: The PI and PtBS chains appeared to be equilibrated cooperatively/simultaneously at a rate essentially determined by PtBS. The Rouse equilibration time, evaluated from the G* data of the blend, was just moderately shorter than the dielectrically determined relaxation time of PI. Thus, the high-ω plateau zone was too narrow to be resolved experimentally, and the PI chains relaxed almost immediately after their Rouse equilibration (retarded by PtBS). This PI relaxation activated the constraint release (CR) relaxation of PtBS to dilate the entanglement mesh for PtBS. A simple model considering the Rouse equilibration and CR/dilation processes described the G* data of the blend surprisingly well, lending support to the molecular picture of the cooperative/simultaneous Rouse equilibration of the PI and PtBS chains. The model calculation was consistent with the rheo-optical data, which lent further support to this molecular picture.