[Effects of osteoblasts and inductor on proliferation and osteodifferentiation of marrow stromal stem cells]

To find a new culture system to induce proliferation and osteodifferentiation of marrow stromal cells (MSCs) in vitro for bone tissue engineering.

There were four groups in this experiment to study effects of Passage 3 osteoblasts derived from the rat cranium and the osteogenic inductor (1 nmol/L dexamethasone, 10 mmol/L beta-glycero-phosphate, 50 microg/ml retinoic acid) on growth of MSCs isolated from the rat femur and the tibia. MSCs were cultured in the DMEM medium (the control group) and in the osteoinductive culture medium (the inductor group); furthermore, MSCs were co-cultured with the osteoblasts in the DMEM medium (the osteoblast group) and in the osteoinductive culture medium (the combined treatment group). The cells in the four groups were counted every 2 days for 8 days and alkaline phosphatase (ALP) activity of MSCs at 10 days of cultivation was measured. The MRNA expression of osteocalcin (OC) of MSCs at 2 weeks was assayed with the reverse transcript polymerase chain reaction (RT-PCR).

There were more cells in the osteoblast group than in the control group (31.73 +/- 3.31 x 10(4) VS. 24.33 +/- 3.04 x 10(4), P < 0. 05), but there were fewer cells in the inductor group (16.23 +/- 2.44 x 10(4), P < 0.05). There was no significant difference in the cell number between the combined treatment group (21.54 +/- 2.29 x 10(4)) and the control group (P > 0.05). The ALP activity was higher in the combined treatment group (2.01 +/- 0.56 U) than in the control group (1.27 +/- 0.43 U), in the inductor group (1.27 +/- 0.43 U), and in the osteoblast group (0.77 +/- 0.19 U). The osteocalcin mRNA was expressed in the three treatment groups but was not expressed in the control group. The significantly higher level of the osteocalcin mRNA was expressed in the inductor group (0.783 +/- 0.094) and in the combined treatment group (0.814 +/- 0.071) than in the osteoblast group (0.302 +/- 0.026) (P < 0.05).

The combined use of the osteoblast and the inductor can induce marrow stromal cells. Their combined use does not affect the normal proliferation but can obviously promote the osteodifferentiation of marrow stromal cells. This combined use can become a new culture system of the seed cells for bone tissue engineering.