Int J Med Sci 2013; 10(13):1805-1816. doi:10.7150/ijms.6530 This issue
1. Department of Orthopaedics, Xijing Hospital, Fourth Military Medical University, Xi'an, China;
2. National Science Library, Chinese Academy of Sciences, Beijing, People's Republic of China;
3. Department of Orthopaedics and Traumatology, University of Hong Kong, Pokfulam, Hong Kong, SAR China
† These authors contribute equally to this work.
Objective: As a main cellular component within the disc, nucleus pulposus (NP) cells play important roles in disc physiology. However, little is known on the biologic hallmarks of human NP cells. Therefore, the present study aimed to address the features of human NP cells.
Methods: Human NP samples were collected from normal cadavers, patients with scoliosis and disc degeneration as normal, disease control and degenerative NP, respectively. The NP samples were studied using transmission electron microscopy and TUNEL assay. Pre-digested NP samples were studied using flow cytometry with PI/Annexin V staining.
Results: Both control and degenerative human NP consisted of mainly viable cells with a variety of morphology. Both necrosis and apoptosis were noted in human NP as forms of cell death with increased apoptosis in degenerative NP, which was further confirmed by the TUNEL assay. Phagocytic NP cells had the hallmarks of both stationary macrophages with lysosomes and NP cells with the endoplasmic reticulum. Annulus fibrosus cells have similar morphologic characteristics with NP cells in terms of cell nest, phagocytosis and intracellular organs. Moreover, NP cells with long processes existed in degenerative and scoliotic NP rather than normal NP. When cultured in glucose-free medium, NP cells developed long and thin processes.
Conclusion: Human degenerative NP consists of primarily viable cells. We present direct and in vivo evidence that both human annulus fibrosus and NP cells have phagocytic potential. Moreover, NP cells with long processes exist in both scoliotic and degenerative NP with lack of glucose as one of the possible underlying mechanisms.
Keywords: annulus fibrosus, nucleus pulposus, disc degeneration, apoptosis, flow cytometry, electronic microscopy, TUENL assay, human, cell culture.