Johnson Kristen A, van Etten Deborah, Nanda Nisha, Graham Robert M, Terkeltaub Robert A
Veterans Affairs Medical Center, University of California San Diego, La Jolla, California 92161, USA.
J Biol Chem. 2003 May 23;278(21):18824-32. doi: 10.1074/jbc.M301055200. Epub 2003 Feb 26.
Altered chondrocyte differentiation, including development of chondrocyte hypertrophy, mediates osteoarthritis and pathologic articular cartilage matrix calcification. Similar changes in endochondral chondrocyte differentiation are essential for physiologic growth plate mineralization. In both articular and growth plate cartilages, chondrocyte hypertrophy is associated with up-regulated expression of certain protein-crosslinking enzymes (transglutaminases (TGs)) including the unique dual-functioning TG and GTPase TG2. Here, we tested if TG2 directly mediates the development of chondrocyte hypertrophic differentiation. To do so, we employed normal bovine chondrocytes and mouse knee chondrocytes from recently described TG2 knockout mice, which are phenotypically normal. We treated chondrocytes with the osteoarthritis mediator IL-1 beta, with the all-trans form of retinoic acid (ATRA), which promotes endochondral chondrocyte hypertrophy and pathologic calcification, and with C-type natriuretic peptide, an essential factor in endochondral development. IL-1 beta and ATRA induced TG transamidation activity and calcification in wild-type but not in TG2 (-/-) mouse knee chondrocytes. In addition, ATRA induced multiple features of hypertrophic differentiation (including type X collagen, alkaline phosphatase, and MMP-13), and these effects required TG2. Significantly, TG2 (-/-) chondrocytes lost the capacity for ATRA-induced expression of Cbfa1, a transcription factor necessary for ATRA-induced chondrocyte hypertrophy. Finally, C-type natriuretic peptide, which did not modulate TG activity, comparably promoted Cbfa1 expression and hypertrophy (without associated calcification) in TG2 (+/+) and TG2 (-/-) chondrocytes. Thus, distinct TG2-independent and TG2-dependent mechanisms promote Cbfa1 expression, articular chondrocyte hypertrophy, and calcification. TG2 is a potential site for intervention in pathologic calcification promoted by IL-1 beta and ATRA.
软骨细胞分化改变，包括软骨细胞肥大的发展，介导骨关节炎和病理性关节软骨基质钙化。软骨内软骨细胞分化的类似变化对于生理性生长板矿化至关重要。在关节软骨和生长板软骨中，软骨细胞肥大均与某些蛋白质交联酶（转谷氨酰胺酶（TGs））表达上调有关，包括独特的双功能TG和GTP酶TG2。在此，我们测试了TG2是否直接介导软骨细胞肥大分化的发展。为此，我们使用了来自最近描述的TG2基因敲除小鼠的正常牛软骨细胞和小鼠膝关节软骨细胞，这些小鼠表型正常。我们用骨关节炎介质白细胞介素-1β、促进软骨内软骨细胞肥大和病理性钙化的全反式视黄酸（ATRA）以及软骨内发育的关键因子C型利钠肽处理软骨细胞。白细胞介素-1β和ATRA在野生型小鼠膝关节软骨细胞中诱导TG转酰胺活性和钙化，但在TG2（-/-）小鼠膝关节软骨细胞中未诱导。此外，ATRA诱导肥大分化的多个特征（包括X型胶原、碱性磷酸酶和基质金属蛋白酶-13），而这些效应需要TG2。重要的是，TG2（-/-）软骨细胞失去了ATRA诱导Cbfa1表达的能力，Cbfa1是ATRA诱导软骨细胞肥大所必需的转录因子。最后，不调节TG活性的C型利钠肽在TG2（+/+）和TG2（-/-）软骨细胞中同等程度地促进Cbfa1表达和肥大（无相关钙化）。因此，不同的TG2非依赖性和TG2依赖性机制促进Cbfa1表达、关节软骨细胞肥大和钙化。TG2是干预由白细胞介素-1β和ATRA促进的病理性钙化的潜在靶点。
