Nakatani Teruyo, Chen Tiffany, Partridge Nicola C
Department of Basic Science and Craniofacial Biology, New York University College of Dentistry, New York, NY 10010, USA.
Department of Basic Science and Craniofacial Biology, New York University College of Dentistry, New York, NY 10010, USA.
Bone. 2016 Sep;90:142-51. doi: 10.1016/j.bone.2016.06.010. Epub 2016 Jun 16.
Histone deacetylase 4 (Hdac4) regulates chondrocyte hypertrophy. Hdac4(-/-) mice are runted in size and do not survive to weaning. This phenotype is primarily due to the acceleration of onset of chondrocyte hypertrophy and, as a consequence, inappropriate endochondral mineralization. Previously, we reported that Hdac4 is a repressor of matrix metalloproteinase-13 (Mmp13) transcription, and the absence of Hdac4 leads to increased expression of MMP-13 both in vitro (osteoblastic cells) and in vivo (hypertrophic chondrocytes and trabecular osteoblasts). MMP-13 is thought to be involved in endochondral ossification and bone remodeling. To identify whether the phenotype of Hdac4(-/-) mice is due to up-regulation of MMP-13, we generated Hdac4/Mmp13 double knockout mice and determined the ability of deletion of MMP-13 to rescue the Hdac4(-/-) mouse phenotype. Mmp13(-/-) mice have normal body size. Hdac4(-/-)/Mmp13(-/-) double knockout mice are significantly heavier and larger than Hdac4(-/-) mice, they survive longer, and they recover the thickness of their growth plate zones. In Hdac4(-/-)/Mmp13(-/-) double knockout mice, alkaline phosphatase (ALP) expression and TRAP-positive osteoclasts were restored (together with an increase in Mmp9 expression) but osteocalcin (OCN) was not. Micro-CT analysis of the tibiae revealed that Hdac4(-/-) mice have significantly decreased cortical bone area compared with the wild type mice. In addition, the bone architectural parameter, bone porosity, was significantly decreased in Hdac4(-/-) mice. Hdac4(-/-)/Mmp13(-/-) double knockout mice recover these cortical parameters. Likewise, Hdac4(-/-) mice exhibit significantly increased Tb.Th and bone mineral density (BMD) while the Hdac4(-/-)/Mmp13(-/-) mice significantly recovered these parameters toward normal for this age. Taken together, our findings indicate that the phenotype seen in the Hdac4(-/-) mice is partially derived from elevation in MMP-13 and may be due to a bone remodeling disorder caused by overexpression of this enzyme.
组蛋白去乙酰化酶4（Hdac4）调节软骨细胞肥大。Hdac4基因敲除（Hdac4(-/-)）小鼠体型矮小，无法存活至断奶。这种表型主要是由于软骨细胞肥大的起始加速，结果导致软骨内矿化异常。此前，我们报道Hdac4是基质金属蛋白酶-13（Mmp13）转录的抑制因子，Hdac4缺失导致MMP-13在体外（成骨细胞）和体内（肥大软骨细胞和小梁成骨细胞）的表达均增加。MMP-13被认为参与软骨内骨化和骨重塑。为了确定Hdac4(-/-)小鼠的表型是否归因于MMP-13的上调，我们构建了Hdac4/Mmp13双基因敲除小鼠，并确定敲除MMP-13能否挽救Hdac4(-/-)小鼠的表型。Mmp13基因敲除（Mmp13(-/-)）小鼠体型正常。Hdac4(-/-)/Mmp13(-/-)双基因敲除小鼠比Hdac4(-/-)小鼠明显更重、更大，存活时间更长，其生长板区域厚度恢复。在Hdac4(-/-)/Mmp13(-/-)双基因敲除小鼠中，碱性磷酸酶（ALP）表达和抗酒石酸酸性磷酸酶（TRAP）阳性破骨细胞恢复（同时Mmp9表达增加），但骨钙素（OCN）未恢复。胫骨的显微计算机断层扫描（Micro-CT）分析显示，与野生型小鼠相比，Hdac4(-/-)小鼠的皮质骨面积显著减少。此外，Hdac4(-/-)小鼠的骨结构参数骨孔隙率显著降低。Hdac4(-/-)/Mmp13(-/-)双基因敲除小鼠恢复了这些皮质参数。同样，Hdac4(-/-)小鼠的骨小梁厚度（Tb.Th）和骨密度（BMD）显著增加，而Hdac4(-/-)/Mmp13(-/-)小鼠的这些参数在该年龄时显著恢复至正常水平。综上所述，我们的研究结果表明，Hdac4(-/-)小鼠中观察到的表型部分源于MMP-13的升高，可能是由于该酶的过表达导致的骨重塑紊乱。
