Cellular Aging promotes CEMP1 Expression in STRO-1 positive PDL cells

We investigated the effects of cellular aging on the expression of cementum and mineralization-specific proteins in human periodontal ligament (PDL) cells, since this is not well studied. Previously, we showed that STRO-1- and cementum protein 1 (CEMP1) - positive PDL cells behave like cementoblasts, since they can be directed toward cementogenesis. However, the mineralization characteristics of these cells during aging have not been examined. Thus, we examined mineralization and expression of the mineralization-related proteins, CEMP1, collagen I (COL I) and osteopontin (OPN) in STRO-1 positive selected and unselected human PDL cells, control human cementoblastoma cells, and human mesenchymal stem cells (hMSC). Early (young) and late (aged) passage cells were compared. Aged STRO-1 positive cells exhibited the highest level of mineralization as assessed by Alizarin red staining and energy dispersive x-ray spectroscopy. Aged STRO-1 positive PDL cells also exhibited high levels of CEMP1, OPN, and COL I expression at two weeks compared to all other cells. At earlier time points, osteogenic induction significantly enhanced CEMP1 expression in aged STRO-1 positive and parental PDL cells. In contrast, STRO-1 negative cells exhibited high CEMP1 expression only in young cells. High CEMP1 expression was also present in young cells derived from cementoblastoma cells and hMSC. Expression of OPN and COL I varied for STRO-1 negative PDL, cementoblastoma, and hMSC cells. In summary, cellular aging significantly promotes mineralization and expression of CEMP1, OPN, and COL I in STRO-1 positive PDL cells. These findings may impact periodontal tissue function and regeneration in the context of aging tissues.