Aging affects the phenotypic characteristics of human periodontal ligament cells and the cellular response to hormonal stimulation in vitro

Background and Objective: Aging modulates the proliferative activity and organic matrix production of cells in vivo and in vitro. Here, we explore how aging affects the phenotypic characteristics of human periodontal ligament cells and their response to hormonal stimulation. Material and Methods: Fifth passage periodontal ligament cells from subjects aged 12-14 (group 1), 41-55 (group 2) and 61-70 years (group 3) were characterized for the expression of mesenchymal marker genes and proteins by real-time PCR and flow cytometry. Confluent cultures were exposed to 10-12 m parathyroid hormone(1-34) [PTH(1-34)] intermittently for three cycles. At harvest, cell number, alkaline phosphatase activity and osteocalcin production were determined by cell count, biochemical assay and ELISA. Results: The characterization of the cells revealed a decreased expression of osteoblast-specific marker genes along with a lower percentage of cells presenting the respective proteins with age. An intermittent exposure of the cultures to 10-12 m PTH(1-34) induced an increase of the cell number as opposed to a significant decrease of alkaline phosphatase activity and osteocalcin production. The cellular response to PTH(1-34) was strongest in group 1. Basal osteoprotegerin levels were highest in the cultures from the oldest donors and inhibited by intermittent PTH(1-34) in all groups. Conclusion: Our data indicate that periodontal ligament cells from older subjects display a less differentiated phenotype and a reduced response to intermittent PTH, suggesting a compromised ability to maintain tissue homeostasis and a limited possibility to support periodontal repair processes with age. The high basal osteoprotegerin expression in older subjects might serve as a compensatory mechanism.