Pax6 Expressed in Osteocytes Inhibits Canonical Wnt Signaling

The transcription factor Pax6, which belongs to the paired box-containing gene family, regulates developmental processes, especially in the eyes, central nervous tissues and craniofacial structures. However, the role of Pax6 in bone has never been studied exclusively. Here we report that Pax6 is expressed at both the mRNA and protein level in the calvaria and long bones of adult mice as well as osteocyte-like MLOY4 cells and suppresses the canonical Wnt signaling pathway. Moreover, the expression levels of Pax6 were much higher in the calvaria than the long bones, and Pax6 was also expressed at E16 to E18 in both the calvaria and long bones. Knockdown of Pax6 in MLOY4 cells did not affect cell proliferation or survival; however, the expression of Sost, an osteocyte marker gene, was significantly decreased. In addition, the overexpression of Pax6 suppressed the canonical Wnt signaling pathway by enhancing the expression of Sost. Furthermore, we also demonstrated that Pax6 binds to the Sost promoter and that stimulation of Sost transcription by Pax6 was dependent on a specific Pax6-binding sequence within the promoter. In conclusion, the results of the present study suggest that Pax6 is expressed in bone and may play an important role in osteocyte differentiation by controlling canonical Wnt signaling.ope

The Transcription Factor Protein Sox11 Enhances Early Osteoblast Differentiation by Facilitating Proliferation and the Survival of Mesenchymal and Osteoblast Progenitors

Sox11 deletion mice are known to exhibit developmental defects of craniofacial skeletal malformations, asplenia, and hypoplasia of the lung, stomach, and pancreas. Despite the importance of Sox11 in the developing skeleton, the role of Sox11 in osteogenesis has not been studied yet. In this study, we identified that Sox11 is an important transcription factor for regulating the proliferation and survival of osteoblast precursor cells as well as the self-renewal potency of mesenchymal progenitor cells via up-regulation of Tead2. Furthermore, Sox11 also plays an important role in the segregation of functional osteoblast lineage progenitors from osteochondrogenic progenitors. Facilitation of osteoblast differentiation from mesenchymal cells was achieved by enhanced expression of the osteoblast lineage specific transcription factors Runx2 and Osterix. Morpholino-targeted disruption of Sox11 in zebrafish impaired organogenesis, including the bones, which were under mineralized. These results indicated that Sox11 plays a crucial role in the proliferation and survival of mesenchymal and osteoblast precursors by Tead2, and osteogenic differentiation by regulating Runx2 and Osterix.ope

miR-182 is a negative regulator of osteoblast proliferation, differentiation, and skeletogenesis through targeting FoxO1

Uncontrolled oxidative stress impairs bone formation and induces age-related bone loss in humans. The FoxO family is widely accepted to play an important role in protecting diverse cells from reactive oxygen species (ROS). Activation of FoxO1, the main FoxO in bone, stimulates proliferation and differentiation as well as inhibits apoptosis of osteoblast lineage cells. Despite the important role of FoxO1, little is known about how FoxO1 expression in bone is regulated. Meanwhile, several recent studies reported that microRNAs (miRNAs) could play a role in osteoblast differentiation and bone formation by targeting various transcriptional factors. Here, we identified one additional crucial miRNA, miR-182, which regulates osteoblastogenesis by repressing FoxO1 and thereby negatively affecting osteogenesis. Overexpression of miR-182 in osteoblast lineage cells increased cell apoptosis and inhibited osteoblast differentiation, whereas in vivo overexpression of miR-182 in zebrafish impaired bone formation. From in silico analysis and validation experiments, FoxO1 was identified as the target of miR-182, and restoration of FoxO1 expression in miR-182-overexpressing osteoblasts rescued them from the inhibitory effects of miR-182. These results indicate that miR-182 functions as a FoxO1 inhibitor to antagonize osteoblast proliferation and differentiation, with a subsequent negative effect on osteogenesis. To treat bone aging, an antisense approach targeting miR-182 could be of therapeutic value.ope