Abstract
SummaryMature osteoblasts are the cells responsible for bone formation and are derived from precursor osteoblasts. However, the mechanisms that control this differentiation are poorly understood. In fact, unlike the majority of organs in the body, which are composed of “soft” tissue from which cells can easily be isolated and studied, the “hard” mineralized tissue of bone has made it difficult to study the function of bone cells. Here, we established an in vitro model that mimics this differentiation under physiological conditions. We obtained mature osteoblasts and characterized them on the basis of the following parameters: the strong expression of osteoblastic markers, such as Runx2 and Col-I; the achievement of specific dimensions (the cell volume increases 26-fold compared to the osteoblast precursors); and the production of an abundant extracellular matrix also called osteoid. We demonstrated that the differentiation of osteoblast precursors into mature osteoblasts requires the continuous activation of Bone Morphogenetic Protein (BMP) receptors, which we established with the immobilization of a BMP-2mimetic peptide on a synthetic matrix mimicking in vivo microenvironment. Importantly, we demonstrated that the organization of the F-actin network and acetylated microtubules of the cells were modified during the differentiation process. We showed that the perturbation of the F-actin cytoskeleton organization abolished the differentiation process. In addition, we demonstrated that expression of the Runx2 gene is required for this differentiation. These findings demonstrate the retro-regulation of cytoplasmic and genic components due to the continuous induction of BMP-2 and also provide more detailed insights into the correct signaling of BMPs for cell differentiation in bone tissue.
Highlights
Unlike the majority of organs in the body, which are composed of ‘‘soft’’ tissue from which cells can be isolated and studied, the ‘‘hard’’ mineralized tissue of bone has made it difficult to study the function of bone cells
We demonstrated that the differentiation of osteoblast precursors into mature osteoblasts requires the continuous activation of Bone Morphogenetic Protein (BMP) receptors, which we established with the immobilization of a BMP-2mimetic peptide on a synthetic matrix mimicking in vivo microenvironment
A synthetic extracellular matrix (ECM)-BMP-2 analogs in two-dimensional (2D) culture systems controlling cell fate was created and their effects have been evaluated on the behavior of a mouse osteoblastic precursor cell line (MC3T3-E1)
Summary
Unlike the majority of organs in the body, which are composed of ‘‘soft’’ tissue from which cells can be isolated and studied, the ‘‘hard’’ mineralized tissue of bone has made it difficult to study the function of bone cells. The extracellular matrix (ECM) is composed of proteins that promote cell adhesion, and growth factors such as BMPs that promote cell differentiation (Chen et al, 2004; Wagner et al, 2010). These various proteins exhibit different distributions (Marie, 2009). Diseases in different tissues are caused by malfunctions in the BMP signaling pathways (Ramirez and Rifkin, 2009; Maciel et al, 2010; Mazzaferro et al, 2010; Sethi and Kang, 2011)
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