Abstract
Metastasis suppressor 1 (MTSS1) plays an inhibitory role in tumorigenesis and metastasis of a variety of cancers. To date, the function of MTSS1 in the differentiation of marrow stromal progenitor cells remains to be explored. In the current study, we investigated whether and how MTSS1 has a role in osteoblast differentiation and bone homeostasis. Our data showed that MTSS1 mRNA was upregulated during osteoblast differentiation and downregulated in the osteoblastic lineage cells of ovariectomized and aged mice. Functional studies revealed that MTSS1 promoted the osteogenic differentiation from marrow stromal progenitor cells. Mechanistic explorations uncovered that the inactivation of Src and afterward activation of canonical Wnt signaling were involved in osteoblast differentiation induced by MTSS1. The enhanced osteogenic differentiation induced by MTSS1 overexpression was attenuated when Src was simultaneously overexpressed, and conversely, the inhibition of osteogenic differentiation by MTSS1 siRNA was rescued when the Src inhibitor was supplemented to the culture. Finally, the in vivo transfection of MTSS1 siRNA to the marrow of mice significantly reduced the trabecular bone mass, along with the reduction of trabecular osteoblasts, the accumulation of marrow adipocytes, and the increase of phospho-Src-positive cells on the trabeculae. No change in the number of osteoclasts was observed. This study has unraveled that MTSS1 contributes to osteoblast differentiation and bone homeostasis through regulating Src-Wnt/β-catenin signaling. It also suggests the potential of MTSS1 as a new target for the treatment of osteoporosis.
Highlights
Bone marrow mesenchymal stem cells (BMSCs) have the potential to differentiate toward multiple cell types including osteoblasts, adipocytes, chondrocytes and myoblasts
This study has for the first time unraveled that Metastasis suppressor 1 (MTSS1) contributes to osteoblast differentiation and bone homeostasis through regulating Src-Wnt/β-catenin signaling
We further investigated the physiological role of MTSS1 in the differentiation of BMSCs in mice. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) analysis demonstrated that the in vivo transfection of MTSS1 small interfering RNAs (siRNAs) is effective in knocking down the endogenous expression of MTSS1 in the BMSCs of the tibiae (Fig. 7A, B)
Summary
Bone marrow mesenchymal stem cells (BMSCs) have the potential to differentiate toward multiple cell types including osteoblasts, adipocytes, chondrocytes and myoblasts. The capabilities of BMSCs to differentiate toward osteoblastic and adipogenic lineages are similar and a reciprocal and competitive relationship usually exists between osteogenesis and adipogenesis [1, 2]. The modulation of osteogenic and adipogenic commitment of BMSCs is finely orchestrated by a variety of transcription factors and signaling pathways including runt related transcription factor-2 (Runx2), osterix, bone morphogenetic proteins (BMPs), and. The transcription factors, i.e., peroxisome proliferator activated receptor γ (PPARγ) and CCAAT/enhancer binding proteins (C/EBPs) are the major positive regulators of adipocyte differentiation [8, 9].
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