The influence of an in vitro generated bone-like extracellular matrix on osteoblastic gene expression of marrow stromal cells

The function and development of cells rely heavily on the signaling interactions with the surrounding extracellular matrix (ECM). Therefore, a tissue engineering scaffold should mimic native ECM to recreate the in vivo environment. Previously, we have shown that an in vitro generated ECM secreted by cultured cells enhances the mineralized matrix deposition of marrow stromal cells (MSCs). In this study, MSC expression of 45 bone-related genes using real-time reverse transcriptase polymerase chain reaction (RT-PCR) was determined. Upregulation of osteoblastic markers such as collagen type I, matrix extracellular phosphoglycoprotein with ASARM motif, parathyroid hormone receptor, and osteocalcin, indicated that the MSCs on plain titanium scaffolds differentiated down the osteoblastic lineage and deposited a mineralized matrix on day 12. Significant mineralized matrix deposition was observed as early as day 4 on ECM-containing scaffolds and was associated with the enhancement in expression of a subset of osteoblast-specific genes that included a 2-fold increase in osteopontin expression at day 1 and a 6.5-fold increase in osteocalcin expression at day 4 as well as downregulation of chondrogenic gene markers. These results were attributed to the cellular interactions with growth factors and matrix molecules that are likely present in the in vitro generated ECM since the genes for insulin-like growth factor 1, insulin-like growth factor 2, vascular endothelial growth factor, dentin matrix protein, collagen type IV, cartilage oligomeric protein, and matrix metalloproteinase 13 were significantly upregulated during ECM construct generation. Overall, the data demonstrate that modulation of MSC differentiation occurs at the transcriptional level and gene expression of bone-related proteins is differentially regulated by the ECM. This study presents enormous implications for tissue engineering strategies, as it demonstrates that modification of a biomaterial with an in vitro generated ECM containing cell-generated bioactive signaling molecules can effectively direct gene expression and differentiation of seeded progenitor cell populations.