Expression of Leptin and Its Functional Receptor on Disc Cells: Contribution to Cell Proliferation

Study Design. Human herniated disc tissues and rat nucleus pulposus (NP) cells were used following approval by the authors' institutional Human Ethics Review Committee and Animal Care and Use Committee. Objective. To determine the expression of leptin and its functional receptor in herniated disc tissues, and to elucidate whether leptin can stimulate rat NP cells to proliferate in vitro. Summary of Background Data. There is evidence showing that chondrocytes express leptin and functional leptin receptor, and leptin stimulates chondrocyte proliferation in vitro and may play a role in the pathogenesis of osteoarthritis by contributing to osteophyte formation. Intervertebral disc degeneration, similar to osteoarthritis, is also a complicated process in which increased cell proliferation is involved. However, little attention has been paid to the causes of the increased cell proliferation during disc degeneration. Methods. Forty-five herniated discs were harvested and immunostained to determine the distribution and type of leptin/functional leptin receptor-expressing cells. The proliferating activity of rat NP cells stimulated with leptin was also evaluated by using 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay and by immunostaining for proliferation cell nuclear antigen (PCNA). Results. Immunohistochemical results from 45 herniated discs showed that leptin/functional leptin receptor-positive cells are commonly seen in cell clusters and proliferating fibrocartilaginous areas, and that the percentage of leptin/functional leptin receptor-positive cells correlates with the age of the patients. Leptin administration led to increased proliferation of rat NP cells in a dose-dependent manner, as shown by MTT assay and by counting the percentage of PCNA-positive cells. Conclusion. Our results suggested that disc cells can express leptin and its functional receptor, that leptin can stimulate proliferation of disc cells in vitro, and therefore that leptin may play a role in the process of intervertebral disc degeneration by contributing to the formation of cell cluster and proliferating fibrocartilaginous tissue.

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