Tekari Adel, Luginbuehl Reto, Hofstetter Willy, Egli Rainer J
Group for Bone Biology & Orthopaedic Research, Department Clinical Research, University of Bern, Bern, Switzerland; Graduate School for Cellular and Biomedical Sciences, University of Bern, Bern, Switzerland.
RMS Foundation, Bettlach, Switzerland.
PLoS One. 2015 Mar 16;10(3):e0120857. doi: 10.1371/journal.pone.0120857. eCollection 2015.
Cartilage is a tissue with limited self-healing potential. Hence, cartilage defects require surgical attention to prevent or postpone the development of osteoarthritis. For cell-based cartilage repair strategies, in particular autologous chondrocyte implantation, articular chondrocytes are isolated from cartilage and expanded in vitro to increase the number of cells required for therapy. During expansion, the cells lose the competence to autonomously form a cartilage-like tissue, that is in the absence of exogenously added chondrogenic growth factors, such as TGF-βs. We hypothesized that signaling elicited by autocrine and/or paracrine TGF-β is essential for the formation of cartilage-like tissue and that alterations within the TGF-β signaling pathway during expansion interfere with this process. Primary bovine articular chondrocytes were harvested and expanded in monolayer culture up to passage six and the formation of cartilage tissue was investigated in high density pellet cultures grown for three weeks. Chondrocytes expanded for up to three passages maintained the potential for autonomous cartilage-like tissue formation. After three passages, however, exogenous TGF-β1 was required to induce the formation of cartilage-like tissue. When TGF-β signaling was blocked by inhibiting the TGF-β receptor 1 kinase, the autonomous formation of cartilage-like tissue was abrogated. At the initiation of pellet culture, chondrocytes from passage three and later showed levels of transcripts coding for TGF-β receptors 1 and 2 and TGF-β2 to be three-, five- and five-fold decreased, respectively, as compared to primary chondrocytes. In conclusion, the autonomous formation of cartilage-like tissue by expanded chondrocytes is dependent on signaling induced by autocrine and/or paracrine TGF-β. We propose that a decrease in the expression of the chondrogenic growth factor TGF-β2 and of the TGF-β receptors in expanded chondrocytes accounts for a decrease in the activity of the TGF-β signaling pathway and hence for the loss of the potential for autonomous cartilage-like tissue formation.
软骨是一种自我修复潜力有限的组织。因此,软骨缺损需要手术治疗以预防或延缓骨关节炎的发展。对于基于细胞的软骨修复策略,尤其是自体软骨细胞植入,关节软骨细胞从软骨中分离出来并在体外扩增,以增加治疗所需的细胞数量。在扩增过程中,细胞失去了自主形成软骨样组织的能力,即在没有外源性添加的软骨生成生长因子(如转化生长因子-βs)的情况下。我们假设自分泌和/或旁分泌转化生长因子-β引发的信号传导对于软骨样组织的形成至关重要,并且扩增过程中转化生长因子-β信号通路内的改变会干扰这一过程。收获原代牛关节软骨细胞并在单层培养中扩增至第六代,然后在高密度微团培养中培养三周,研究软骨组织的形成。扩增至三代的软骨细胞保持了自主形成软骨样组织的潜力。然而,三代之后,需要外源性转化生长因子-β1来诱导软骨样组织的形成。当通过抑制转化生长因子-β受体1激酶来阻断转化生长因子-β信号传导时,软骨样组织的自主形成被消除。在微团培养开始时,与原代软骨细胞相比,三代及之后的软骨细胞中编码转化生长因子-β受体1和2以及转化生长因子-β2的转录本水平分别下降了三倍、五倍和五倍。总之,扩增后的软骨细胞自主形成软骨样组织依赖于自分泌和/或旁分泌转化生长因子-β诱导的信号传导。我们认为,扩增后的软骨细胞中软骨生成生长因子转化生长因子-β2以及转化生长因子-β受体表达的降低导致了转化生长因子-β信号通路活性的下降,从而导致自主形成软骨样组织的潜力丧失。