Introduction: CD44 is a transmembrane glycoprotein with various biological functions. Histologic studies have shown that CD44 is strongly expressed in odontoblasts at the appositional stage of tooth development. We investigated whether CD44 is involved in the mineralization of dental pulp cells. Methods: Ten human third molars with incomplete root formation were collected and processed for immunohistochemistry of CD44. Dental pulp cells isolated from another 5 human third molars were assayed for their viability, alkaline phosphatase activity, and alizarin red staining in vitro after silencing stably their expression of CD44 by using the short hairpin RNA technique. The CD44 knockdown cells were cultured on a collagen sponge and transplanted subcutaneously into the dorsal surfaces of immunocompromised mice. After 6 weeks, the subcutaneous tissues were processed for alizarin red staining and immunohistochemistry of human specific antigen. The dental pulp cells transduced with control short hairpin RNA were used as the control in all assays. Results: CD44 is expressed in odontogenic cells with active mineral deposition during tooth development. Odontoblasts in the root ends of immature teeth express a stronger CD44 signal compared with those in the crown portion. When CD44 expression was stably suppressed in dental pulp cells, their mineralization activities were substantially decreased in both in vitro and in vivo assays. Conclusions: CD44 may play a crucial role in the initial mineralization of tooth-associated structures. However, further studies are required to clarify the underlying mechanisms.
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