Enhanced derivation of osteogenic cells from murine embryonic stem cells after treatment with HepG2-conditioned medium and modulation of the embryoid body formation period: application to skeletal tissue engineering.

Despite the considerable progress made in directing embryonic stem cell (ESC) differentiation to therapeutically useful lineages, several issues remain to be resolved before ESCs can be used for cell therapy: 1) increasing the efficiency of specific lineage generation, and 2) developing time- and cost-effective culture systems for controlling ESC differentiation. Our study aimed to develop efficient methods to enhance mesodermal differentiation and thereby upregulate osteogenic differentiation of ESCs. Specifically, murine ESCs (mESCs) were cultured in the presence of 50% conditioned medium (CM) from the human hepatocarcinoma cell line HepG2, which resulted in enhanced mesoderm formation during embryoid body (EB) formation in the CM-treated mESCs (CM-mESCs). By varying the length of EB culture time, we achieved the selective control and stimulation of osteogenic differentiation and suppression of cardiogenic differentiation. Hence, reducing the EB culture of the CM-mESCs to 1 day resulted in 5-10-fold enhancement of osteogenic differentiation, as determined by bone nodule formation, higher alkaline phosphatase activity, the presence of well-organized osteoblast-cadherin in the bone nodules, and increased cbfa-1/runx2 gene expression. In contrast, increasing the EB culture of the CM-mESCs to 5 days resulted in three- to four-fold enhanced cardiogenic differentiation. These findings for development of highly efficient culture systems and protocols for mESC differentiation into osteogenic lineage that are time- and cost-effective can be used in skeletal tissue engineering applications.