Objective

Chondrocyte hypertrophic differentiation, a key process in endochondral ossification, is also a feature of osteoarthritis leading to cartilage destruction. Here we investigated the role of the adaptor protein Src homology and Collagen A (ShcA) in chondrocyte differentiation and osteoarthritis.

Methods

Mice ablated for ShcA in osteochondroprogenitor cells were generated by crossing mice carrying the Twist2-Cre transgene with ShcA^flox/flox mice. Their phenotype (n = 5 to 14 mice per group) was characterized using histology, immuno-histology and western-blot. To identify the signaling mechanisms involved, in vitro experiments were conducted on wild type and ShcA deficient chondrocytes (isolated from n = 4 to 7 littermates) and the chondroprogenitor cell line ATDC5 (n = 4 independent experiments) using western-blot, cell fractionation and confocal microscopy.

Results

Deletion of ShcA decreases the hypertrophic zone of the growth plate (median between group difference −11.37% [95% confidence interval −17.34 to −8.654]), alters the endochondral ossification process, and leads to dwarfism (3 months old male mice nose-to-anus length −1.48 cm [-1.860 to −1.190]). ShcA promotes ERK1/2 activation, nuclear translocation of RunX2, the master transcription factor for chondrocyte hypertrophy, while maintaining the Runx2 inhibitor, YAP1, in its cytosolic inactive form. This leads to hypertrophic commitment and expression of markers of hypertrophy, such as Collagen X. In addition, loss of ShcA protects from age-related osteoarthritis development in mice (2 years old mice OARSI score −6.67 [-14.25 to −4.000]).

Conclusion

This study reveals ShcA as a new player in the control of chondrocyte hypertrophic differentiation and its deletion slows down osteoarthritis development.

中文翻译：

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ShcA 通过 RunX2 核易位和 YAP1 失活促进小鼠软骨细胞肥大和骨关节炎

客观的

软骨细胞肥大分化是软骨内骨化的关键过程，也是导致软骨破坏的骨关节炎的特征。在这里，我们研究了衔接蛋白 Src 同源性和胶原 A (ShcA) 在软骨细胞分化和骨关节炎中的作用。

方法

通过将携带 Twist2-Cre 转基因的小鼠与 ShcA flox/flox 小鼠杂交产生在骨软骨祖细胞中因 ShcA^消融的小鼠。 使用组织学、免疫组织学和蛋白质印迹来表征它们的表型（每组n = 5 至 14 只小鼠）。为了确定所涉及的信号传导机制，使用蛋白质 印迹 、细胞分级分离和共聚焦显微镜。

结果

删除 ShcA 会降低生长板的肥大区（组间差异的中位数为 -11.37% [95% 置信区间 -17.34 至 -8.654]），改变软骨内骨化过程，并导致侏儒症（3 个月大的雄性小鼠鼻-至肛门长度 -1.48 厘米 [-1.860 至 -1.190]）。ShcA 促进 ERK1/2 的激活、RunX2 的核转位，RunX2 是软骨细胞肥大的主要转录因子，同时保持 Runx2 抑制剂 YAP1 的细胞溶质无活性形式。这导致肥大承诺和肥大标志物的表达，例如胶原蛋白 X。此外，ShcA 的缺失可防止小鼠发生与年龄相关的骨关节炎（2 岁小鼠 OARSI 评分 -6.67 [-14.25 至 -4.000]）。

结论

这项研究揭示了 ShcA 作为控制软骨细胞肥大分化的新参与者，其缺失减缓了骨关节炎的发展。