[Regulation of osteoblasts and chondrocytes by Wnt signaling.]

Wnt plays important roles in regulation of differentiation of osteoblast and chondrocyte and their function. Wnt family members ingeniously utilize canonical Wnt signaling pathway through ß-catenin and non-canonical Wnt signaling pathway independent of ß-catenin, consequently regulating development, formation and homeostasis of bone and cartilage. Recent studies revealed that canonical Wnt signal activates transcriptional regulator, TAZ, in addition to transcription factors, LEF and TCF. Canonical Wnt signal crosstalks with BMP signal by stimulating complex formation of LEF1, TAZ and Runx2. Although molecular mechanism of non-canonical Wnt signal is getting clearer, the precise role of non-canonical Wnt signal in bone and cartilage seems still elusive.

Self-Strengthening of Cross-Linked Elastomers via the Use of Dynamic Covalent Macrocyclic Mechanophores.

The creation of polymeric materials that self-strengthen in response to a mechanical force is an important objective in the field of polymer chemistry. Here, the mechanochemical strengthening of cross-linked elastomers using macrocyclic mechanophores that contain a dynamic covalent disulfide bond is reported. Cross-linked poly(hexyl methacrylate) (CPHMA) polymers with macrocyclic mechanophores inserted at the cross-linking points were synthesized via free radical polymerization. Tensile and swelling tests showed that the addition of the macrocyclic mechanophores to the CPHMA polymers successfully impart them with self-strengthening functionality following compression, without the need for any additives such as monomers and modifiers, or any other stimuli.

Photoinduced Regulation of the Heat Resistance in Polymer Networks with Diarylethene-Conjugated Reversible Covalent Cross-Links.

A cross-linker with a diarylethene-conjugated Diels-Alder adduct (DAE/DA) was synthesized and applied in a radical polymerization system to afford polymer networks whose dynamic nature can be changed reversibly by photoirradiation. Free-radical polymerization of hexyl methacrylate and the DAE/DA-based cross-linker furnished an insoluble and transparent poly(hexyl methacrylate) network with DAE/DA moieties at their cross-linking points, which undergo de-cross-linking via a thermally induced retro-DA reaction upon heating. The photoregulation of such a thermal de-cross-linking reaction in DAE/DA-based polymer networks was demonstrated by swelling experiments and tensile tests, revealing drastic changes in the heat resistance and mechanical properties upon exposure to UV-vis irradiation.

Modification of amine-cured epoxy resins by boronic acids based on their reactivity with intrinsic diethanolamine units.

Amine-cured epoxy polymers were modified after curing, exploiting the reactivity of their intrinsic diethanolamine (DEA) units toward boronic acids. The condensation of DEA units with various boronic acids resulted in changes in the thermal, mechanical, and optical properties of the original amine-cured epoxy polymers.

The photoregulation of a mechanochemical polymer scission.

Control over mechanochemical polymer scission by another external stimulus may offer an avenue to further advance the fields of polymer chemistry, mechanochemistry, and materials science. Herein, we demonstrate that light can regulate the mechanochemical behavior of a diarylethene-conjugated Diels-Alder adduct (DAE/DA) that reversibly isomerizes from a weaker open form to a stronger closed form under photoirradiation. Pulsed ultrasonication experiments, spectroscopic analyses, and density functional theory calculations support the successful photoregulation of the reactivity of this DAE/DA mechanophore, which is incorporated at the mid-chain of a polymer, and indicate that higher force and energy are required to cleave the closed form of the DAE/DA mechanophore relative to the open form. The present photoregulation concept provides an attractive approach toward the generation of new mechanofunctional polymers.

Interaction of LEF1 with TAZ is necessary for the osteoblastogenic activity of Wnt3a.

Canonical Wnt signalling plays an important role in osteoblast differentiation and bone formation. However, the molecular mechanisms by which canonical Wnt signalling exerts its osteoblastogenic effect remain elusive. Here, we investigated the relationship between lymphoid enhancer-binding factor 1 (LEF1) and transcriptional co-activator with PDZ-binding motif (TAZ), both of which are transcriptional regulators that mediate canonical Wnt signalling during osteoblast differentiation. Reporter assay and co-immunoprecipitation experiments revealed functional and physical interaction between LEF1 and TAZ. Overexpression of dominant-negative forms of either LEF1 or TAZ markedly inhibited Wnt3a-dependent osteoblast differentiation. Moreover, we found that LEF1 and TAZ formed a transcriptional complex with runt-related transcription factor 2 (Runx2) and that inhibition of LEF1 or TAZ by their dominant-negative forms dramatically suppressed the osteoblastogenic activity of Ruxn2. Additionally, Wnt3a enhanced osteoblast differentiation induced by bone morphogenetic protein 2 (BMP2), which stimulates osteoblast differentiation by regulating Runx2. Collectively, these findings suggest that interaction between LEF1 and TAZ is crucial for the osteoblastogenic activity of Wnt3a and that LEF1 and TAZ contribute to the cooperative effect of Wnt3a and BMP2 on osteoblast differentiation through association with Runx2.