Akt1 in Murine Chondrocytes Controls Cartilage Calcification During Endochondral Ossification Under Physiologic and Pathologic Conditions
Akt1 in Murine Chondrocytes Controls Cartilage Calcification During Endochondral Ossification Under Physiologic and Pathologic Conditions
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DOI：
10.1002/art.27296
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发表时间：
2010-03-01
影响因子：
--
通讯作者：
Kawaguchi, Hiroshi
中科院分区：
文献类型：
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作者：
Fukai, Atsushi;Kawamura, Naohiro;Kawaguchi, Hiroshi
Objective.研究磷酸肌醇依赖的丝氨酸/苏氨酸蛋白激酶Akt 1在软骨细胞内软骨骨化过程中的作用。在放射学和组织学分析中比较了纯合子Akt 1缺陷（Akt 1（-/-））小鼠及其野生型同窝小鼠的skeleton表型。通过手术诱导小鼠膝关节不稳定来建立实验性骨关节炎（OA）模型。为了进行功能分析，我们使用了新生小鼠的原代肋软骨和关节软骨细胞以及逆转录病毒过表达组成型活性Akt 1或Akt 1的小干扰RNA（siRNA）的小鼠软骨形成ATDC 5细胞。在Akt亚型（Akt 1、Akt 2和Akt 3）中，Akt 1在软骨细胞中表达最高，Akt 1（-/-）软骨细胞中Akt蛋白的总水平降低，表明Akt 1的主导作用。Akt 1（-/-）小鼠表现出侏儒症与正常的增殖和肥大区，但抑制软骨钙化的生长板相比，野生型同窝出生。在手术诱导的OA小鼠中，Akt 1（-/-）关节中的钙化骨赘形成，但软骨降解没有被阻止。在Akt 1（-/-）软骨细胞或过表达Akt 1 siRNA的ATDC 5细胞培养物中，钙化被显著抑制，在过表达组成型活性Akt 1的ATDC 5细胞中，钙化被增强。Akt 1功能的获得或丧失均不影响增殖和肥大分化。Akt 1缺陷或siRNA可增强ANK和核苷酸焦磷酸酶/磷酸二酯酶1（nucleotide pyrophosphatase/phosphodiesterase 1，nucleotide pyrophosphatase 1）的表达，而组成性激活的Akt 1可抑制其表达。我们的研究结果表明，软骨细胞中的Akt 1通过抑制骨骼生长中软骨内骨化和OA中骨赘形成过程中的焦磷酸盐来控制软骨钙化。
Objective. To examine the role of the phosphoinositide-dependent serine/threonine protein kinase Akt1 in chondrocytes during endochondral ossification.Methods. Skeletal phenotypes of homozygous Akt1-deficient (Akt1(-/-)) mice and their wild-type littermates were compared in radiologic and histologic analyses. An experimental osteoarthritis (OA) model was created by surgically inducing instability in the knee joints of mice. For functional analyses, we used primary costal and articular chondrocytes from neonatal mice and mouse chondrogenic ATDC5 cells with retroviral overexpression of constitutively active Akt1 or small interfering RNA (siRNA) for Akt1.Results. Among the Akt isoforms (Akt1, Akt2, and Akt3), Akt1 was the most highly expressed in chondrocytes, and the total level of Akt protein was decreased in Akt1(-/-) chondrocytes, indicating a dominant role of Akt1. Akt1(-/-) mice exhibited dwarfism with normal proliferative and hypertrophic zones but suppressed cartilage calcification in the growth plate compared with their wild-type littermates. In mice with surgically induced OA, calcified osteophyte formation, but not cartilage degradation, was prevented in the Akt1(-/-) joints. Calcification was significantly suppressed in cultures of Akt1(-/-) chondrocytes or ATDC5 cells overexpressing siRNA for Akt1 and was enhanced in ATDC5 cells overexpressing constitutively active Akt1. Neither proliferation nor hypertrophic differentiation was affected by the gain or loss of function of Akt1. The expression of ANK and nucleotide pyrophosphatase/phosphodiesterase 1, which accumulate pyrophosphate, a crucial calcification inhibitor, was enhanced by Akt1 deficiency or siRNA for Akt1 and was suppressed by constitutively active Akt1.Conclusion. Our findings indicate that Akt1 in chondrocytes controls cartilage calcification by inhibiting pyrophosphate during endochondral ossification in skeletal growth and during osteophyte formation in OA.