Low-level laser irradiation promotes the differentiation of bone marrow stromal cells into osteoblasts through the APN/Wnt/ß-catenin pathway.

OBJECTIVE: The relationship between adiponectin (APN) pathway and Wnt pathway was explored through BMSCs, and the effect of low-level laser irradiation (LLLI) on bone marrow stromal cells (BMSCs) and its mechanism were further studied. MATERIALS AND METHODS: 3-week-old Sprague-Dawley (SD) rats were selected, and mesenchymal stem cells were separately cultured and purified. 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay was used to analyze cell proliferation. After osteogenic and adipogenic induction, cultures were conducted, respectively, cells were stained with alizarin red and oil red O. Reverse transcription-polymerase chain reaction (RT-PCR) was used to detect the expressions of osteogenesis-related genes, runt-related transcription factor 2 (RUNX2), and osteocalcin (OC) and those of adipogenesis-related genes, peroxisome proliferator-activated receptor-gamma (PPARγ) and CCAAT/enhancer-binding protein alpha (c/EBPα). Western blotting was used to detect the expressions of ß-catenin in the cytoplasm and nucleus. The lentiviral expression vector of adiponectin receptors (APN-R) was constructed, and the expression of APN receptor genes was silenced. The expressions of ß-catenin in APN receptors and the nucleus within cells were detected. RESULTS: LLLI promoted the bone formation by inducing the differentiation direction of mesenchymal stem cells, increasing the number of osteoblasts in the bone marrow and inhibiting the reduction of the number of adipocytes. LLLI regulates the Wnt pathway, promotes the entry of ß-catenin into the nucleus, activates the osteogenic effect of the Wnt pathway so as to promote the bone formation of osteoblasts and inhibit bone resorption of osteoclasts. LLLI promotes the entry of ß-catenin into the nucleus and the osteogenic differentiation of BMSCs through the APN pathway. CONCLUSIONS: In summary, LLLI can promote osteogenesis and inhibit adipocytes formation, thus attenuating bone resorption of osteoclasts. The mechanism of LLLI is that it promotes the entry of ß-catenin into the nucleus and regulates the Wnt pathway and the differentiation direction of mesenchymal stem cells through the APN signal pathway, thus promoting bone formation.

Optogenetic protein clustering and signaling activation in mammalian cells.

We report an optogenetic method based on Arabidopsis thaliana cryptochrome 2 for rapid and reversible protein oligomerization in response to blue light. We demonstrated its utility by photoactivating the ß-catenin pathway, achieving a transcriptional response higher than that obtained with the natural ligand Wnt3a. We also demonstrated the modularity of this approach by photoactivating RhoA with high spatiotemporal resolution, thereby suggesting a previously unknown mode of activation for this Rho GTPase.

Low-dose radiation stimulates Wnt/ß-catenin signaling, neural stem cell proliferation and neurogenesis of the mouse hippocampus in vitro and in vivo.

Neurogenesis in the hippocampus is actively involved in neural circuit plasticity and learning function of mammals, but it may decrease dramatically with aging and aging-related neurodegenerative disorder Alzheimer's disease. Accumulating studies have indicated that Wnt/ß-catenin signaling is critical in control of proliferation and differentiation fate of neural stem cells or progenitors in the hippocampus. In this study, the biological effects of low-dose radiation in stimulating Wnt/ß-catenin signaling, neural stem cell proliferation and neurogenesis of hippocampus were interestingly identified by in vitro cell culture and in vivo animal studies. First, low-dose radiation (0.3Gy) induced significant increasing of Wnt1, Wnt3a, Wnt5a, and ß-catenin expression in both neural stem cells and in situ hippocampus by immunohistochemical and PCR detection. Secondly, low-dose radiation enhanced the neurogenesis of hippocampus indicated by increasing proliferation and neuronal differentiation of neural stem cells, going up of nestin-expressing cells and BrdU-incorporation in hippocampus. Thirdly, it promoted cell survival and reduced apoptotic death of neuronal stem cells by flowcytometry analysis. Finally, Morris water-maze test showed behavioral improvement of animal learning in low-dose radiation group. Accordingly, detrimental influence on Wnt/ß-catenin signaling or neurogenesis was confirmed in high-dose radiation (3.0Gy) group. Taken together, this study has revealed certain beneficial effects of low-dose radiation to stimulate neural stem cell proliferation, the neurogenesis of hippocampus and animal learning most possibly by triggering Wnt/ß-catenin signaling cascades, suggesting its translational application role in devising new therapy for aging-related neurodegenerative disorders particularly Alzheimer's disease.

Beta-catenin is a mediator of the response of fibroblasts to irradiation.

Radiation causes soft tissue complications that include fibrosis and deficient wound healing. beta-Catenin, a key component in the canonical Wnt-signaling pathway, is activated in fibrotic processes and wound repair and, as such, could play a role in mediating cellular responses to irradiation. beta-Catenin can form a transcriptionally active complex with members of the Tcf family. A reporter mouse model, in addition to human cell cultures, was used to demonstrate that ionizing radiation activates beta-catenin-mediated, Tcf-dependent transcription both in vitro and in vivo. Furthermore, radiation activates beta-catenin via a Wnt-mediated mechanism, as in the presence of dickkopf-1, an inhibitor of Wnt receptor activation, beta-catenin levels did not increase after irradiation. Fibroblast cell cultures were derived from mice expressing either null or stabilized beta-catenin alleles. Cells expressing stabilized beta-catenin alleles had a higher proliferation rate and formed more colony-forming units than wild-type or null cells after irradiation. Wound healing was studied in these same mice after irradiation. There was a positive correlation between the tensile strength of the wound, the expression levels of type 1 collagen in the skin, and beta-catenin levels. Mice treated with lithium showed increased beta-catenin levels and increased wound strength. beta-Catenin mediates the effects of ionizing radiation in fibroblasts, and its modulation has the potential to decrease the severity of radiation-induced soft tissue complications.