Analysis of Cathepsin K in human periodontal ligament cells

Objectives: Periodontal ligament (PDL) plays crucial roles in maintaining the homeostasis of tooth and periodontium. In order to clarify the character of PDL at molecular level, we constructed human PDL full length cDNA library and analyzed gene expression of PDL tissues comprehensively. In this library, we found high expression of Cathepsin K (CTSK). Although CTSK is a well-known cysteine protease, no information of CTSK in PDL has been published. Thus, we further investigated the CTSK expression and function in PDL cells in this study. Methods: We analyzed an expression profile of active genes in the human PDL obtained by collecting sequences with a full length cDNA library. Human PDL cells were cultured with β-glycerophosphate and ascorbic acid for cytodifferentiation, and then mRNA expression was analyzed by real-time PCR. The expression of CTSK in various human tissues was analyzed by real-time PCR. In addition, the expression of CTSK in unstimulated and cytokine-stimulated human PDL cells was also analyzed. Results: Twenty-six high expression genes were identified in the expression profile of human PDL. Out of those, we selected 8 genes whose expression and function in PDL tissues haven't been reported. Among the 8 genes, CTSK, Ferritin and FLJ25143 were highly upregulated during the cytodifferentiation process of human PDL cells. Interestingly the expression of CTSK in PDL tissues was much higher than other human tissues. Real-time PCR analysis revealed that CTSK expression in human PDL cells was upregulated by IL-1 α and IFN- γ, and downregulated by FGF-2, BMP-2 and IGF-1. Conclusion: This is the first report of CTSK expression in human PDL. CTSK might be involved in collagen metabolism in PDL tissues for homeostasis, repair and regeneration of periodontium. This study was supported by Grant-in-Aids from Japan Society for the Promotion of Science (No.21792119 and 20390529).