Abstract
An osteoclast is a large multinucleated cell that is formed by mononuclear preosteoclast fusion. Dendritic cell-specific transmembrane protein (DC-STAMP) is one of the key regulators of osteoclast cell-cell fusion. When tea extract was added to RAW264.7 cells stimulated by nuclear factor kappa-B ligand (RANKL), the mRNA expression of DC-STAMP was enhanced while that of tartrate-resistant acid phosphatase (TRAP), an osteoclast differentiation marker, was suppressed. These observations indicated that increased DC-STAMP mRNA in RAW264.7 cells by tea extract occurred independently of the RANKL-mediated signaling pathway in osteoclastogenesis. Real-time PCR analysis indicated that epigallocatechin gallate (EGCg) might be one of the stimulating factors. Moreover, the increase in DC-STAMP mRNA induced by tea extract tended to be higher than that induced by a reconstituted mixture of the four major tea catechins. On the other hand, the increase in DC-STAMP mRNA was also observed in RANKL-unstimulated macrophage-like RAW264.7 cells. These results suggest that tea extract modulates the expression of DC-STAMP mRNA not only in osteoclastic cells but also in the other cell types.
