Zhou Guangdi, Jiang Xuchao, Zhang Hai, Lu Yinzhong, Liu Anjun, Ma Xianhua, Yang Guan, Yang Rui, Shen Hongxing, Zheng Jianming, Hu Yiping, Yang Xiao, Zhang Weiping J, Xie Zhifang
Department of Pathophysiology, Second Military Medical University, Shanghai 200433, China Department of Pathophysiology, Second Military Medical University, Shanghai 200433, China.
Department of Pathophysiology, Second Military Medical University, Shanghai 200433, China.
Development. 2015 Jan 15;142(2):385-93. doi: 10.1242/dev.108530.
The terminal differentiation of hypertrophic chondrocytes is a tightly regulated process that plays a pivotal role in endochondral ossification. As a negative regulator, Sox9 is essentially downregulated in terminally differentiated hypertrophic chondrocytes. However, the underlying mechanism of Sox9 silencing is undefined. Here we show that the zinc finger protein Zbtb20 regulates the terminal differentiation of hypertrophic chondrocytes by repressing Sox9. In the developing skeleton of the mouse, Zbtb20 protein is highly expressed by hypertrophic chondrocytes from late embryonic stages. To determine its physiological role in endochondral ossification, we have generated chondrocyte-specific Zbtb20 knockout mice and demonstrate that disruption of Zbtb20 in chondrocytes results in delayed endochondral ossification and postnatal growth retardation. Zbtb20 deficiency caused a delay in cartilage vascularization and an expansion of the hypertrophic zone owing to reduced expression of Vegfa in the hypertrophic zone. Interestingly, Sox9, a direct suppressor of Vegfa expression, was ectopically upregulated at both mRNA and protein levels in the late Zbtb20-deficient hypertrophic zone. Furthermore, knockdown of Sox9 greatly increased Vegfa expression in Zbtb20-deficient hypertrophic chondrocytes. Our findings point to Zbtb20 as a crucial regulator governing the terminal differentiation of hypertrophic chondrocytes at least partially through repression of Sox9.
肥大软骨细胞的终末分化是一个受到严格调控的过程，在软骨内成骨中起关键作用。作为一种负调节因子，Sox9在终末分化的肥大软骨细胞中基本下调。然而，Sox9沉默的潜在机制尚不清楚。在这里，我们表明锌指蛋白Zbtb20通过抑制Sox9来调节肥大软骨细胞的终末分化。在小鼠发育中的骨骼中，从胚胎后期开始，肥大软骨细胞高度表达Zbtb20蛋白。为了确定其在软骨内成骨中的生理作用，我们构建了软骨细胞特异性Zbtb20基因敲除小鼠，并证明软骨细胞中Zbtb20的破坏导致软骨内成骨延迟和出生后生长迟缓。Zbtb20缺乏导致软骨血管化延迟和肥大区扩大，这是由于肥大区Vegfa表达降低所致。有趣的是，在晚期Zbtb20缺乏的肥大区，作为Vegfa表达直接抑制因子的Sox9在mRNA和蛋白质水平均异位上调。此外，敲低Sox9可显著增加Zbtb20缺乏的肥大软骨细胞中Vegfa的表达。我们的研究结果表明，Zbtb20是至少部分通过抑制Sox9来调控肥大软骨细胞终末分化的关键调节因子。
