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調控間葉前驅細胞之分化過程：由軟骨化途徑中轉為骨質新生化調控間葉前驅細胞之分化過程：由軟骨化途徑中轉為骨質新生化 • 間葉前驅細胞具有分化成許多不同種類細胞的能力。在動物胚胎軀幹發育的過程中，先有軟骨的形成，接著再出現硬骨。然而到底硬骨是由間葉前驅細胞分化而來的，還是由軟骨細胞轉變而成仍然無法釐清。根據過去研究，間葉前驅細胞在腎上腺皮質酮(dexamethasone)跟轉形成長因子(TGF-β1)的存在之下會分化成類軟骨細胞。然而，如果間葉前驅細胞走向軟骨分化的路徑時，是否可以再次被引導往骨質分化的路徑。在本篇的研究中，我們利用正在進行軟骨分化的間葉前驅細胞作基礎，來探討是否微環境的改變會引導間葉前驅細胞從軟骨化轉變成骨質分化。從這個實驗中可以釐清，是否當間葉前驅細胞在軟骨化過程中，會被限制住在軟骨的分化路徑，或是仍然具有往其他路徑分化的能力。在本篇實驗中，先利用腎上腺皮質酮(dexamethasone)跟轉形成長因子(TGF-β1)處理間葉前驅細胞7天，使得間葉前驅細胞走向軟骨分化，再利用骨細胞成長因子或硬骨生成培養基處理7天。發現經過這個處理過程的間葉前驅細胞，表現出比未處理的間葉前驅細胞，高出3至6倍鹼性磷酸脢活性。同時，另一個重要的間葉前驅細胞軟骨化表現蛋白第二型膠原蛋白，只有在腎上腺皮質酮跟轉形成長因子持續處理的組別中表現，而在其他處理的組別都沒有表現。另一個重要的骨質分化的標記，核心結合因子(cbfa1)也只在有骨細胞成長因子處理跟硬骨生成培養基處理的組別中表現出來。軟骨細胞經過骨細胞成長因子處理跟硬骨生成培養基處理兩個星期之後，比未處理的組別表現出較高的第一型膠原蛋白，及較低的第二型膠原蛋白。根據這些結果，可發現間葉前驅細胞被誘導往軟骨分化後，可以再次被引導往骨質新生的分化路徑。而且，成熟的軟骨細胞在經骨細胞成長因子處理或硬骨生成培養基培養下，仍然可以被引導走向硬骨分化。
Switching of Mesenchymal Progenitor Cell (MPC) Differentiation from Chondrogenesis to Osteogenesis • Mesenchymal progenitor cells (MPCs) are multipotential cells which can differentiate into many types of cells. In animal embryonic skeleton development, cartilage develops first, and bone formation follows. Whether the bone formation is derived directly from MPCs or chondrocytes is still unclear. According to previous study, MPCs differentiate into chondrocyte-like cells in the presence of dexamethasone (DEX) and transforming growth factor-β1 (TGF-β1). However, if MPCs are on the way to chondrogenic lineage, could they be re-directed to osteogenesis. In this study, it was intended to use MPCs in the chondrogenic pathway as a model to investigate whether the changes in microenvironment will switch MPC differentiation from chondrogenesis to osteogenesis. This experimental model may reveal whether MPCs in Chondrogenic pathway are limited in differentiating potential or retain ability to differentiate into other lineages.In our experimental model, mesenchymal progenitor cells (MPCs) pre-treated with dexamethasone and TGF-β1 for 7 days, to induce chondrogenic differentiation, and then treated with osteogenic growth factor or osteogenic medium for another 7 days. It was found that the activity of alkaline phosphatase (ALP), the osteogenic marker, of treated MPCs was greatly up-regulated for 3 to 6 folds. Meanwhile, the expression of type II collagen, the important marker for chondrogenesis of MPCs, was found in cells treated only with DEX/ TGF-β1 but not cells treated with osteogenic factor or control group. On the other hand, the expression of another important osteogenic marker core-bonding factor a1 (Cbfa1) was also shown in MPCs on the way to chondrogenesis and then treated with osteogenic growth factors and osteogenic medium. Furthermore, chondrocytes treated with osteogenic growth factors and osteogenic medium for 2 weeks also expressed higher type I collagen and lower type II collagen than the control cells.According to the above results, it appears that after MPCs have been induced to initiate chondrogenic differentiation, their differentiation fate might continue toward chondrogenesis, or be switched to osteogenic differentiation depending on the factors presented in their microenvironment. Furthermore, in the presence of these osteogenic growth factor or medium, chondrocytes might also be induced to differentiate towards osteogenic pathway.
