Ciliated cell observation by SEM on the surface of human incudo-malleolar-joint articular cartilage: are they a new chondrocyte phenotype?

Abstract

Background: Scanning electron microscopy (SEM) study of the human incus bone is scanty whilst, to our knowledge, no information regarding human incudo-malleolar joint articular-cartilage morphology has previously been provided.

Aims/objectives: Our aim was to shed some light on this morphological issue and to propose some theoretical perspectives on its functional role.

Material and methods: The human incudo-malleolar joint was documented with field emission SEM on samples recovered during ear surgery procedures after patients’ informed consent.

Results: Normal articular cartilage chondrocytes, flattened cells with prominent nucleus and short microvilli were observed. Interestingly, cells provided with long cilia were identified. Type A cilia are arranged in a pyramidal formation with extra-long cilia stemming from the cluster, projecting upwards in an antenna-like formation ending with a dilated structure that as a whole, resembles the stereocilia with kinocilium. Types B, C and D cilia resemble those of the genital and respiratory tracts.

Conclusions and significance: It is therefore possible to hypothesize that the observed ciliated cells may be a new chondrocyte phenotype with sensory function. Motile cilia confer the ability to distinguish variations in synovial fluid chemical composition and, in addition, they perhaps may also play some role in the mechanism of sound transmission.

Chinese abstract

背景：扫描电子显微镜（SEM）对人砧骨的研究很少。而据我们所知, 此前还没有关于连接砧骨-踝部的关节软骨形态的信息。

目的：我们的目的是澄清这一形态学问题, 并对其功能作用提出一些理论性观点。

材料与方法：经患者知情同意, 对耳外科手术过程中获得的标本进行场发射扫描电镜观察, 记录人砧骨-踝部关节。

结果：观察到正常的关节软骨细胞、细胞核明显得扁平细胞以及短微绒毛。有趣的是, 鉴定出有长纤毛的细胞。A型纤毛呈金字塔状排列, 超长纤毛由簇体生长, 向上呈天线状排列, 末端为扩张结构, 整体上与带扭结的立体纤毛相似。B、C和D型纤毛与生殖器和呼吸道纤毛相似。

结论和意义：因此可以推测, 观察到的纤毛细胞可能是一种新的具有感觉功能的软骨细胞表型。活动纤毛具有辨别滑液化学成分变化的能力, 此外, 它们也可能在声音传播机制方面起一定作用。

Keywords:

• articular cartilage
• chondrocyte
• cilia
• incudo-malleolar joint
• incus
• scanning electron microscopy

Acknowledgements

Data availability: (1) Our data are represented by the images obtained through the microscopes supplied by our laboratory; (2) the images are kept in the computers of the electronic microscopy laboratory; (3) the original images can be viewed only upon a motivated request sent by e-mail to the corresponding author.

Additional information

Funding

This work is supported by the MIUR Grant.