Abstract
Wnt signaling pathways are a highly conserved pathway, which plays an important role from the embryonic development to bone formation. The effect of Wnt pathway on osteogenesis relies on their cellular environment and the expression of target genes. However, the molecular mechanism of that remains unclear. On the basis of the preliminary results, we observed the contrary effect of canonical Wnt signaling on osteogenic differentiation of periodontal ligament stem cells (PDLSCs) in the different culture environment. Furthermore, we found that the expression level of miR-17 was also varied with the change in the culture environment. Therefore, we hypothesized that miR-17 and canonical Wnt signaling may have potential interactions, particularly the inner regulation relationship in different microenvironments. In this paper, we observed that canonical Wnt signaling promoted osteogenesis of PDLSCs in the fully culture medium, while inhibited it in the osteogenic differentiation medium. Interestingly, alteration in the expression level of endogenous miR-17 could partially reverse the different effect of canonical Wnt signaling. Furthermore, the role of miR-17 was because of its target gene TCF3 (transcription factor 3), a key transcription factor of canonical Wnt pathway. Overexpression of TCF3 attenuated the effect of miR-17 on modulating canonical Wnt signaling. Finally, we elucidated that TCF3 enhanced osteogenesis both in vitro and in vivo. In brief, the different level of miR-17 was the main cause of the different effect of canonical Wnt signaling, and TCF3 was the crucial node of miR-17–canonial Wnt signaling regulation loop. This understanding of microRNAs regulating signaling pathways in different microenvironments may pave the way for fine-tuning the process of osteogenesis in bone-related disorders.
Highlights
Among the several pathways, the effect of Wnt signaling was the most controversial.[3,4] It has been reported that canonical Wnt pathway promotes the osteogenesis of murine MSCs and osteoprogenitor cells through the upregulation of osteoblast-related genes.[5,6] On the other side, de Boer et al.[7] showed that activation of canonical Wnt signaling suppressed dexamethasone-induced osteogenesis in hMSCs
Our results suggest that miR-17 modulates the contrary effect of canonical Wnt signaling on osteogenesis in different microenvironments mainly through targeting TCF3 directly, which has been proven to act as a positive regulator of osteogenesis
The expression levels of osteoblast-related genes were measured, including Runx[2], which is a critical transcription factor for osteogenic differentiation because it provides a permanent directional signal for lineage determination; alkaline phosphatase (ALP) is an important index for osteogenic differentiation that is not controlled by Runx2/Cbfa[1], osteocalcin and osteopontin, mature osteoblast markers
Summary
The effect of Wnt signaling was the most controversial.[3,4] It has been reported that canonical Wnt pathway promotes the osteogenesis of murine MSCs and osteoprogenitor cells through the upregulation of osteoblast-related genes.[5,6] On the other side, de Boer et al.[7] showed that activation of canonical Wnt signaling suppressed dexamethasone-induced osteogenesis in hMSCs. Recent evidences have shown that osteogenic differentiation is regulated by post-transcriptional mechanisms, most significantly by microRNAs (miRNAs).[16,17,18] Stem cells that develop into osteoblasts have already been shown to be controlled by various miRNAs. For instance, miR-204/211 targets Runx[2] and inhibits osteoblastic differentiation of bonemarrow-derived MSCs.[19] miR-335 negatively regulates Runx[2] to inhibit the osteoblastic differentiation of hMSCs isolated from the bone marrow, adipose tissue and articular cartilage.[20] miR-20a can promote the osteogenesis of hMSCs via BMP signaling.[21] Previously, we demonstrated that miR-17 acted as a negative regulator of osteogenesis in the normal microenvironment. Our results suggest that miR-17 modulates the contrary effect of canonical Wnt signaling on osteogenesis in different microenvironments mainly through targeting TCF3 directly, which has been proven to act as a positive regulator of osteogenesis
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