Department of Bone and Cartilage Biology, Osaka University Graduate School of Medicine, Suita, Osaka, Japan.
J Clin Invest. 2011 Feb;121(2):640-57. doi: 10.1172/JCI44605.
Repair of cartilage injury with hyaline cartilage continues to be a challenging clinical problem. Because of the limited number of chondrocytes in vivo, coupled with in vitro de-differentiation of chondrocytes into fibrochondrocytes, which secrete type I collagen and have an altered matrix architecture and mechanical function, there is a need for a novel cell source that produces hyaline cartilage. The generation of induced pluripotent stem (iPS) cells has provided a tool for reprogramming dermal fibroblasts to an undifferentiated state by ectopic expression of reprogramming factors. Here, we show that retroviral expression of two reprogramming factors (c-Myc and Klf4) and one chondrogenic factor (SOX9) induces polygonal chondrogenic cells directly from adult dermal fibroblast cultures. Induced cells expressed marker genes for chondrocytes but not fibroblasts, i.e., the promoters of type I collagen genes were extensively methylated. Although some induced cell lines formed tumors when subcutaneously injected into nude mice, other induced cell lines generated stable homogenous hyaline cartilage–like tissue. Further, the doxycycline-inducible induction system demonstrated that induced cells are able to respond to chondrogenic medium by expressing endogenous Sox9 and maintain chondrogenic potential after substantial reduction of transgene expression. Thus, this approach could lead to the preparation of hyaline cartilage directly from skin, without generating iPS cells.
软骨损伤的修复一直是一个具有挑战性的临床问题。由于体内软骨细胞数量有限，再加上软骨细胞在体外向成纤维软骨细胞去分化，后者分泌 I 型胶原，基质结构和力学功能发生改变，因此需要一种新的细胞来源来产生透明软骨。诱导多能干细胞（iPS）的产生为通过异位表达重编程因子将真皮成纤维细胞重编程为未分化状态提供了一种工具。在这里，我们表明，逆转录病毒表达两种重编程因子（c-Myc 和 Klf4）和一种软骨生成因子（SOX9）可直接从成年真皮成纤维细胞培养物中诱导出多角形软骨细胞。诱导细胞表达软骨细胞而不是成纤维细胞的标记基因，即 I 型胶原基因的启动子被广泛甲基化。尽管一些诱导细胞系在皮下注射到裸鼠中形成肿瘤，但其他诱导细胞系产生了稳定的均质透明软骨样组织。此外，强力霉素诱导的诱导系统表明，诱导细胞能够通过表达内源性 Sox9 对软骨形成培养基作出反应，并在转基因表达大量减少后保持软骨形成潜能。因此，这种方法可以直接从皮肤中制备透明软骨，而无需生成 iPS 细胞。
