Laminin regulates the osteogenic differentiation of dental follicle cells via integrin-α2/-β1 and the activation of the FAK/ERK signaling pathway

Dental follicle cells (DFCs) are ideal for studies concerning the differentiation of dental precursor cells into alveolar osteoblasts and cementoblasts. Previous investigations have suggested that the extracellular matrix (ECM) protein laminin and the ECM receptor integrin-α2/-β1 play regulatory roles during the osteogenic differentiation of DFCs. Our present data indicate that laminin impairs alkaline phosphatase (ALP) activity following osteogenic induction while inducing integrin-α2/-β1 expression, osteogenic differentiation marker elevation, and DFC biomineralization. Integrin-α2/-β1 facilitates the laminin-dependent expression of osteogenic differentiation markers and the laminin-dependent inhibition of ALP activity. Moreover, these laminin-dependent effects on the osteogenic differentiation of DFCs can be reversed by the inhibition of the FAK/ERK signaling pathway. Thus, laminin regulates the inhibition of early osteogenic differentiation markers and the induction of late osteogenic differentiation markers via integrin-α2/-β1 and the activation of the FAK/ERK signaling pathway.     

BMP9经Smad信号通路调控iSCAP成骨/成牙本质分化

目的：研究BMP9是否能够激活 iSCAP细胞中的Smad信号通路,以及Smad信号通路在BMP9诱导iSCAP细胞成骨/成牙本质向分化过程中的作用。方法：首先,采用Western印迹实验检测Ad-BMP9转染iSCAP后Smad1/5/8蛋白的磷酸化水平。随后,利用dnALK1重组腺病毒和BMP9条件培养基作用于iSCAP,Western印迹实验检测Smad1/5/8蛋白磷酸化水平;采用碱性磷酸酶（ALP）活性检测和染色方法分析早期成骨/成牙本质指标变化,茜素红染色法检测钙盐沉积程度;RT-PCR成骨/成牙本质相关基因Runx2、OCN、OPN和DMP1表达的影响。结果：BMP9可上调iSCAP中Smad1/5/8的磷酸化水平;dnALK1抑制BMP9条件培养基作用后,可抑制Smad1/5/8的磷酸化,iSCAP细胞中早期成骨/成牙本质标志物ALP活性和晚期成骨/成牙本质标志钙盐结节减少,重要成骨转录因子Runx2基因表达减少,成骨/成牙本质相关基因OCN、OPN、DMP1的表达也受到了抑制。结论：Smad信号通路在BMP9诱导iSCAP成骨/成牙本质过程中存在并起着重要作用。     

Formation of bone-like tissue by dental follicle cells co-cultured with dental papilla cells

During tooth root formation, dental follicle cells (DFCs) differentiate into osteoblasts/cementoblasts when they are in contact with pre-existing dentin. Since some factors of dentin matrix were also produced by dental papilla cells (DPCs) and could induce DFCs differentiation, we hypothesized that DPCs can directly promote DFCs differentiation and that differentiation could occur in a co-culture model. To test this hypothesis, we investigated the characteristics of DFCs that are influenced by DPCs in an in vitro co-culture and in vivo heterotopic transplant model. One week into the co-culture, there were significant increases in the mRNA level of bone morphogenetic protein 2 (BMP2), osteoprotegerin (OPG), bone sialoprotein (BSP) and osteocalcin (OCN), and a decrease of the receptor activator of nuclear factor κB ligand (RANKL). Additionally, the number of BMP2-, OPG-, BSP- and OCN-positive DFCs increased whereas RANKL-positive DFCs decreased. Three weeks after co-culture, DFCs produced calcified nodules, accompanied with increased sub-cellular organelles for protein synthesis and secretion. In the heterotopic transplant model, the adult male rats were used as hosts, DFCs were transplanted into the omentum. In vivo 5-week growth of DFCs in the presence of DPCs led to the formation of bone-like tissues, positive for BSP, OCN and BMP2. In contrast, DFCs alone led to fibrous-like tissues. These results indicated that in the absence of pre-existing dentin, DPCs can stimulate osteogenesis and inhibit osteoclastogenesis in DFCs and suggested a novel strategy to promote DFCs differentiation.     

Overexpression of HDAC1 induces cellular senescence by Sp1/PP2A/pRb pathway

The differentiation of stem cells can be directed by the grade of stiffness of the developed tissue cells. For example a rigid extracellular matrix supports the osteogenic differentiation in bone marrow derived mesenchymal stem cells (MSCs). However, less is known about the relation of extracellular matrix stiffness and cell differentiation of ectomesenchymal dental precursor cells. Our study examined for the first time the influence of the surface stiffness on the proliferation and osteogenic differentiation of human dental follicle cells (DFCs). Cell proliferation of DFCs was only slightly decreased on cell culture surfaces with a bone-like stiffness. The osteogenic differentiation in DFCs could only be initiated with a dexamethasone based differentiation medium after using varying stiffness. Here, the softest surface improved the induction of osteogenic differentiation in comparison to that with the highest stiffness. In conclusion, different to bone marrow derived MSCs, soft ECMs have a superior capacity to support the osteogenic differentiation of DFCs.     

MiR-137 knockdown promotes the osteogenic differentiation of human adipose-derived stem cells via the LSD1/BMP2/SMAD4 signaling network

MicroRNAs are a group of endogenous regulators that participate in several cellular physiological processes. However, the role of miR-137 in the osteogenic differentiation of human adipose-derived stem cells (hASCs) has not been reported. This study verified a general downward trend in miR-137 expression during the osteogenic differentiation of hASCs. MiR-137 knockdown promoted the osteogenesis of hASCs in vitro and in vivo. Mechanistically, inhibition of miR-137 activated the bone morphogenetic protein 2 (BMP2)-mothers against the decapentaplegic homolog 4 (SMAD4) pathway, whereas repressed lysine-specific histone demethylase 1 (LSD1), which was confirmed as a negative regulator of osteogenesis in our previous studies. Furthermore, LSD1 knockdown enhanced the expression of BMP2 and SMAD4, suggesting the coordination of LSD1 in the osteogenic regulation of miR-137. This study indicated that miR-137 negatively regulated the osteogenic differentiation of hASCs via the LSD1/BMP2/SMAD4 signaling network, revealing a new potential therapeutic target of hASC-based bone tissue engineering.