Morphological and biochemical re-evaluation of the process of cavitation in the rat knee joint: cellular and cell strata alterations in the interzone
Morphological and biochemical re-evaluation of the process of cavitation in the rat knee joint: cellular and cell strata alterations in the interzone
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DOI：
10.1046/j.1469-7580.2000.19740659.x
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发表时间：
2000-11-01
影响因子：
2.4
通讯作者：
Kida, MY
中科院分区：
文献类型：
--
作者：
Ito, MM;Kida, MY
为了探讨细胞凋亡对滑膜关节空化的作用机制，阐明空化过程中细胞形态的变化，我们采用光镜、电镜、TUNEL方法和DNA片段电泳研究了大鼠膝关节的发育过程。尽管空化发生在由2个外层和一个称为中间带的中间层组成的带间，但在任何胚胎阶段，在带间都没有观察到细胞死亡的形态学或生化迹象，特别是细胞凋亡。区间可见明显的影响细胞分化的显微和超微结构变化，即间质细胞逐渐伸长，细胞质空泡化和固缩，在中间区伸长的细胞在某些层平行排列。部分细胞进一步变平为梭形细胞，层数减少到2层。其余的细胞被二次整合到外层，成为成软骨细胞。胶原原纤维在外层呈网状排列，明显不同于中间区细长细胞平行于长轴排列的方向。此外，胶原原纤维的密度在外层高于中间区。在空化过程中，蜡质切片（E16.5）中间区的细长细胞与环氧树脂切片（E18.5）的纺锤形细胞之间出现了初始分离。排列在腔内的梭形细胞，即骨骺和半月板的表面，最终变成软骨细胞。蛋白聚糖和胶原原纤维的减少以及细胞外基质中透明质酸的合成现在被普遍认为是基于“凝聚力丧失”概念的空化机制的一部分。区间的显微和超微结构变化似乎反映了层间胶原原纤维的排列和密度以及细胞外基质发育状况的差异。此外，这些改变似乎不太可能抑制推定的关节线上透明质酸的合成，因为这种合成发生在质膜上。因此纺锤体细胞之间的分离应该代表了发育程序化空化的机制。细胞外基质的重组可能是参与空化过程的带间细胞变形所必需的。
To assess the contribution of apoptosis to the mechanism of synovial joint cavitation, and to clarify morphological cellular changes during cavitation, we investigated the development of the rat knee joint by light and electron microscopy, TUNEL methods, and electrophoresis of DNA fragments. Although cavitation occurred within the interzone, which consists of 2 outer and a middle layer termed the intermediate zone, no morphological or biochemical signs of cell death, in particular apoptosis, were seen in the interzone at any embryonic stage. Microscopic and ultrastructural alterations affecting cell differentiation were clearly observed in the interzone, i.e. mesenchymal cells gradually showed elongation, cytoplasmic vacuolation and pyknosis in the intermediate zone where the elongated cells were arranged in parallel in some strata. Some of these cells were further flattened into spindle cells and the number of strata decreased to 2. The rest of the cells were incorporated secondarily into the outer layers, becoming chondroblasts. Collagen fibrils were arranged in a network structure in the outer layers, which obviously differed from the directional pattern parallel to the long axis of elongated cells in the intermediate zone. In addition, the density of collagen fibrils was higher in the outer layers than in the intermediate zone. During cavitation, the initial separation was detected between the elongated cells in the intermediate zone in paraffin sections at E16.5 and the spindle cells in epoxy sections at E18.5. The spindle cells lining the cavity, namely, the surfaces of the epiphysis and meniscus, finally became chondrocytes. The diminution of proteoglycans and collagen fibrils and the synthesis of hyaluronan in the extracellular matrix are now generally believed to be parts of the mechanism for cavitation based on the concept of 'loss of cohesion'. The microscopic and ultrastructural alterations in the interzone seemed to reflect differences in the arrangement and density of collagen fibrils and the developmental condition of the extracellular matrix between layers. Also it did not seem likely that these alterations inhibit the synthesis of hyaluronan at the presumptive joint line because this synthesis takes place at the plasma membrane. Separation between spindle cells should therefore represent the mechanism for developmentally programmed cavitation. Reorganization of the extracellular matrix is probably necessary for the cellular metamorphoses in the interzone involved in the process of cavitation.