Regulation of endochondral ossification by transcription factors

Effects of perchlorate and exogenous T4 exposures on development, metamorphosis and endochondral ossification in Bufo gargarizans larvae

Several endocrine-disrupting chemicals (EDCs) have been proven to interfere with the physiological function of thyroid hormone (TH), which affected growth and development. However, few studies have investigated the effects of EDCs on TH axis with consequence for skeletal development in amphibians. This study thus examined the potential role of perchlorate and T4 in growth, development and endochondral ossification during metamorphosis of Bufo gargarizans. Our studies showed that NaClO₄ treatment caused weight gain and delayed the developmental stage in B. gargarizans tadpoles, while T4 decreased body size and survival rate, accelerated metamorphic duration and increased the risk of early death. Histological sections suggested that NaClO₄ and T4 treatments caused damages to thyroid tissue, such as decreased thyroid gland size, follicle size, colloid area, the height of follicular epithelial cells and the number of follicles. In addition, the double skeletal staining and RT-qPCR showed that NaClO₄ and T4 treatments inhibited the endochondral ossification by regulating TH synthesis (TRs, Dios) and endochondral ossification-related genes (MMPs, Runxs, VEGFs and VEGFRs) expression levels, which might affect terrestrial locomotion and terrestrial life. Altogether, these thyroid injury and gene expression changes as caused by NaClO₄ and T4 may have an influence on development and endochondral ossification during the metamorphosis of amphibians.

Localization of Bmi1 in osteoblast-lineage cells during endochondral ossification

Encoded by B cell-specific moloney murine leukemia virus integration site 1, Bmi1 is part of the polycomb group of proteins localized in stem and undifferentiated cells. It regulates the expression of various differentiation genes. However, the regulatory mechanism of skeletal development by Bmi1 remains poorly understood. In this study, we aimed to observe Bmi1 distribution during endochondral ossification processes in rat bone development and fracture healing. Immunoreactivity of Bmi1 was detected in the mesenchymal cell aggregation area at embryonic day (E) 14 and in cells around the center of cartilage primordium at E 16. Subsequently, the calcified bone matrix was formed around the cartilage primordium, and osteoblasts expressing Runt-related transcription factor 2 (Runx2) and Osterix (Osx) showed immunopositivity for Bmi1. At 4 days after bone fracture, the connective tissue around the fractured bone contained Bmi1-positive cells. At 42 days after fracture, osteoblasts along the surface of the new bone revealed Bmi1-, Runx2- and Osx-positive reactions, but the Bmi1 immunoreactivity in osteocytes was less than the Runx2 and Osx immunoreactivities. In conclusion, Bmi1 is localized in the osteoblast-lineage cells in their early differentiation stages, and it might regulate their differentiation during endochondral ossification.

Atelocollagen promotes chondrogenic differentiation of human adipose-derived mesenchymal stem cells

Effective engineering approaches for cartilage regeneration involve a combination of cells and biomaterial scaffolds. Multipotent mesenchymal stem cells (MSCs) are important sources for cartilage regeneration. Atelocollagen provides a suitable substrate for MSC attachment and enhancing chondrogenic differentiation. Here, we assessed the chondrogenic potential of adipose tissue derived human MSCs (hMSCs) mixed with atelocollagen gel. We observed cell attachment, viability, and microstructures by electron microscopy over 21 days. The levels of Sox9, type II collagen, aggrecan, type I collagen, Runx2, type X collagen, ALP, Osterix, and MMP13 were measured by RT-qPCR. Cartilage matrix-related proteins were assessed by enzyme-linked immunosorbent assay (ELISA), histology, and immunohistochemistry. hMSCs of all groups exhibited well-maintained cell survival, distribution and morphology. Abundant type II collagen fibers developed on day 21; while Sox9, type II collagen, and aggrecan expression increased over time in the atelocollagen group. However, type I collagen, RUNX2, type X collagen (CoL10A1), Osterix, and ALP were not expressed. These results corroborated the protein expression detected by ELISA. Further, histological analysis revealed lacunae-like structures, while staining demonstrated glycosaminoglycan accumulation. Cumulatively, these results indicate that atelocollagen scaffolds improve hMSC chondrogenic differentiation and are a potential approach for cartilage regeneration.