Cell surface accumulation of intracellular leucine proline-enriched proteoglycan 1 enhances odontogenic potential of human dental pulp stem cells

Primary dental pulp cells can be differentiated into odontoblasts, which are responsible for dentin formation and mineralization. Successful differentiation has been verified using a few markers. However, odontoblast-specific cell surface markers have not been fully studied yet. Previously, we have constructed monoclonal antibodies to identify cell surface molecules of odontoblasts by decoy immunization. Mass spectrometry confirmed that one of these antibodies, the anti-OD40 antibody, recognized LEucine PRoline-Enriched Proteoglycan 1 (LEPRE1) as a specific antigen. Among three alternative splicing isoforms of LEPRE1, this new antibody showed the most stable antigenic affinity for LEPRE1a, a canonical transcript. Anti-OD40 antibody could strongly bind to the cell surface as odontogenic differentiation progressed. Intracellular and cell surface accumulation of this protein completely disappeared during dentin maturation and mineralization. Overexpression and knock-down experiments showed that intracellular LEPRE1/OD40 should not accumulate too much and that it should move from ER to the cell surface for efficient odontogenic differentiation. Indeed, when LEPRE1/OD40 already located on the cell surface was blocked with antibody, odontogenic differentiation of human dental pulp cells was inhibited. In addition to its role in differentiation, our new antibody which only recognizes LEPRE1a isoform specifically will be useful in studying differentiated functions between LEPRE1a and other isoforms found in osteogenesis imperfecta and dentinogenesis imperfecta.