This study aimed to investigate the characteristics of composite scaffolds in combination of fibroin and carboxymethyl cellulose (CMC) in bone tissue engineering. Fibroin is a useful biomaterial and is a major component of silk yarns composed of fibrous proteins. Improving for binding efficiency in bone formation after implanted scaffold, CMC was added to fibroin. CMC could improve injectable characters in bone substitutes by adding in scaffold material, fibroin. The porous shapes, porosity, surface wettability, water absorption, and thermal properties of the CMC added fibroin scaffold were better than fibroin only scaffold. For tissue engineering of bone marrow mesenchymal stem cells (BMSCs), BMSCs isolated from mice were seeded onto the scaffold, and the cell proliferation rate was measured. alkaline phosphatase activity in BMSCs was higher in the scaffold containing CMC than that in the scaffold containing fibroin alone. The expression levels of osteocyte marker genes and proteins were increased in the CMC scaffold. The biocompatibility and hydrophilicity of CMC scaffolds play important roles in the growth and proliferation of osteocytes. Furthermore, the CMC scaffold design proposed in this study could play an important role in facilitating cartilage, ossification, and nerve differentiation of BMSCs.

We recently found that in human osteoblasts Homer1 complexes to CaSR and mediates AKT initiation via mTORC2 leading to beneficial effects in osteoblasts including -catenin stabilization and mTORC1 activation (doi: 10.1074/jbc.RA118.006587). Herein we further investigated the relationship between Homer1 and CaSR and demonstrate a link between the protein levels of CaSR and Homer1 in human osteoblasts in primary culture. Thus, when siRNA was used to suppress the CaSR, we observed upregulated Homer1 levels and when siRNA was used to suppress Homer1 we observed downregulated CaSR protein levels using immunofluorescence staining of cultured osteoblasts as well as western blot analyses of cell protein extracts. This finding was confirmed in vivo as the bone cells from osteoblast specific CaSR(-/-) mice showed increased Homer1 expression compared to wild-type. Furthermore, when the commonly used osteosarcoma cell lines MG63 and SAOS-2 were compared to primary osteoblasts, higher levels of Homer1 protein were associated with increased protein levels of the CaSR as well as mTOR and Rictor. CaSR and Homer1 protein were both expressed in osteocytes embedded in the long bones of wild-type mice, and immunofluorescent studies of these cells revealed that Homer1 protein sub-cellular localization was markedly altered in the osteocytes of CaSR(-/-) mice compared to wt. The study identifies additional roles for Homer1 in the control of the protein level and subcellular localization of CaSR in cells of the osteoblast lineage, in addition to its established role of mTORC2 activation downstream of the receptor.

Steroid hormone production by adrenal cortex, gonads and placenta (so called glandular steroidogenesis) is responsible for the endocrine control of the body’s homeostasis and organized by a feedback regulatory mechanism based on the hypothalamus-pituitary-steroidogenic gland axis. On the other hand, recently discovered extraglandular steroidogenesis occurring locally in different tissues is rather linked to paracrine or autocrine signaling and it is independent of the control by the hypothalamus and pituitary. Bone cells, such as bone-forming osteoblast, osteoblast-derived osteocytes and bone-resorbing osteoclasts respond to steroid hormones produced by both glandular and extraglandular steroidogenesis. Recently, new techniques to identify steroid hormones as well as synthetic steroids and steroidogenesis inhibitors have been introduced, which greatly empowered steroid hormone research. Based on recent literature and new advances in the field, here we review the local role of steroid hormones in regulating bone homeostasis and skeletal lesion formation. The novel idea of extraglandular steroidogenesis occurring within the skeletal system raises the possibility of the development of new therapies for the treatment of bone diseases.