Endocrine Unit, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts, USA.
Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, USA.
JCI Insight. 2019 Mar 7;4(5). doi: 10.1172/jci.insight.97903.
During endochondral bone formation, chondrocyte hypertrophy represents a crucial turning point from chondrocyte differentiation to bone formation. Both parathyroid hormone-related protein (PTHrP) and histone deacetylase 4 (HDAC4) inhibit chondrocyte hypertrophy. Using multiple mouse genetics models, we demonstrate in vivo that HDAC4 is required for the effects of PTHrP on chondrocyte differentiation. We further show in vivo that PTHrP leads to reduced HDAC4 phosphorylation at the 14-3-3-binding sites and subsequent HDAC4 nuclear translocation. The Hdac4-KO mouse shares a similar but milder phenotype with the Pthrp-KO mouse, indicating the possible existence of other mediators of PTHrP action. We identify HDAC5 as an additional mediator of PTHrP signaling. While the Hdac5-KO mouse has no growth plate phenotype at birth, the KO of Hdac5 in addition to the KO of Hdac4 is required to block fully PTHrP action on chondrocyte differentiation at birth in vivo. Finally, we show that PTHrP suppresses myocyte enhancer factor 2 (Mef2) action that allows runt-related transcription factor 2 (Runx2) mRNA expression needed for chondrocyte hypertrophy. Our results demonstrate that PTHrP inhibits chondrocyte hypertrophy and subsequent bone formation in vivo by allowing HDAC4 and HDAC5 to block the Mef2/Runx2 signaling cascade. These results explain the phenotypes of several genetic abnormalities in humans.
在软骨内骨形成过程中，软骨细胞肥大代表着从软骨细胞分化到骨形成的关键转折点。甲状旁腺激素相关蛋白（PTHrP）和组蛋白去乙酰化酶 4（HDAC4）都抑制软骨细胞肥大。我们利用多种小鼠遗传学模型，在体内证明了 HDAC4 是 PTHrP 对软骨细胞分化产生作用所必需的。我们进一步在体内表明，PTHrP 导致结合 14-3-3 的 HDAC4 磷酸化减少，随后 HDAC4 核转位。Hdac4-KO 小鼠与 Pthrp-KO 小鼠具有相似但较轻的表型，表明 PTHrP 作用可能存在其他介导物。我们鉴定出 HDAC5 是 PTHrP 信号的另一个介导物。虽然 Hdac5-KO 小鼠在出生时没有生长板表型，但在体内阻断 PTHrP 对软骨细胞分化的作用完全需要 Hdac4 和 Hdac5 的 KO。最后，我们表明 PTHrP 抑制肌细胞增强因子 2（Mef2）的作用，从而允许 runt 相关转录因子 2（Runx2）mRNA 的表达，这是软骨细胞肥大所必需的。我们的结果表明，PTHrP 通过允许 HDAC4 和 HDAC5 阻断 Mef2/Runx2 信号级联来抑制体内软骨细胞肥大和随后的骨形成。这些结果解释了人类几种遗传异常的表型。
