Georg August University of Göttingen, Göttingen, Germany.
Arthritis Rheumatol. 2014 Apr;66(4):831-40. doi: 10.1002/art.38325.
During development of the vertebrate skeleton, chondrocytes form a cartilage template that is gradually replaced by bone. Hormones of the Hedgehog (HH) family have been implicated in the ossification process, but their exact relationship to normal or pathogenic bone formation is unclear. This study was undertaken to establish a genetic tool that allows the discrete inactivation of genes in spinal chondrocytes, and to investigate in vivo how chondrocyte-specific ablation of the inhibitory HH receptor Patched 1 (Ptch1) affects skeleton integrity.
A Cre-deleter mouse strain, mb1-Cre, for selective gene recombination in spinal chondrocytes was identified by in situ hybridization and histologic analysis. The mb1-Cre(+/-) animals were crossed with mice that harbor a loxP-flanked Ptch1 gene (Ptch1(flox/flox) ) to abrogate the inhibition of the HH signaling pathway in chondrocytes. The skeletal integrity of F1 mice was characterized by high-resolution flat-panel-based volume computed tomography and histologic staining procedures.
During the first weeks after birth, all mb1-Cre(+/-) /Ptch1(flox/flox) mice developed progressive spinal fusion with malformation of the vertebrae. This phenotype was caused by aberrant chondrocyte proliferation in the intervertebral discs that blocked endochondral ossification. Importantly, the disease pattern occurred in an inflammation-independent manner.
Our findings indicate that chronic activation of the HH signal pathway in spinal chondrocytes can trigger an ankylosing spine morphology without immune cell contributions. Hence, the destruction of cartilage and loss of axial joint integrity can result from chondrocyte-intrinsic defects of monogenic origin.
在脊椎动物骨骼发育过程中，软骨细胞形成软骨模板，该模板逐渐被骨骼取代。Hedgehog（HH）家族的激素已被牵涉到成骨过程中，但它们与正常或病理性骨形成的确切关系尚不清楚。本研究旨在建立一种遗传工具，允许在脊椎软骨细胞中离散地灭活基因，并研究体内抑制性 HH 受体 Patched 1（Ptch1）的软骨细胞特异性缺失如何影响骨骼完整性。
通过原位杂交和组织学分析，鉴定了一种用于脊髓软骨细胞选择性基因重组的 Cre 缺失鼠品系 mb1-Cre。mb1-Cre(+/-) 动物与携带loxP 侧翼 Ptch1 基因（Ptch1(flox/flox)）的小鼠交配，以消除软骨细胞中 HH 信号通路的抑制。通过高分辨率基于平板的体积计算机断层扫描和组织学染色程序来表征 F1 小鼠的骨骼完整性。
在出生后的头几周内，所有 mb1-Cre(+/-) /Ptch1(flox/flox) 小鼠均出现进行性脊柱融合，并伴有椎体畸形。这种表型是由椎间盘内异常的软骨细胞增殖引起的，该增殖阻止了软骨内成骨。重要的是，这种疾病模式是在非炎症依赖性方式下发生的。
我们的研究结果表明，脊髓软骨细胞中 HH 信号通路的慢性激活可引发强直性脊柱炎形态，而无需免疫细胞的参与。因此，软骨和轴向关节完整性的破坏可能是由单基因来源的软骨细胞内在缺陷引起的。
