Role of Mechanical Stress and Extracellular Matrixes in Periodontal Ligament Fibroblasts

Objectives: Periodontal ligament (PDL) is a fibrillary connective tissue that acts as a cushion to a mechanical stress (MS) such as occlusal pressure between alveolar bone and the cementum of the dental root. It is also considered that MS is indispensable to maintain the cellular function of PDL. However, its cellular mechanism is still unclear. DNA microarray analysis revealed that extracellular matrixes (ECM) such as osteopontin (OPN) and osteonectin were extremely reduced in PDL fibroblasts under primary cell culture condition against PDL tissues. In this study, we attempted to elucidate the role of MS and ECM in maintenance of the cellular function in PDL fibroblasts.
Methods: PDL fibroblasts were isolated from human premolar teeth of patients extracted for orthodontic treatment. PDL fibroblasts were cultured on 24 well culture dishes for gravity loading or on silicon chamber of STREX for cell stretching with type I collagen (ColI). MS was applied to the culture dishes and the silicon chambers by centrifuge and STREX apparatus, respectively. The expression of PDL marker genes, PLAP-1 and periostin was determined by RT-PCR. In addition, the cell condition in culture was analyzed on silicon chamber with or without OPN expression.
Results: ID1 (Inhibitor of DNA binding 1) was induced by both MS, however, PLAP-1 and periostin were not increased. Furthermore, PLAP-1 was induced in OPN expression cells by stretching although this induction was diminished by OPN overexpression. Moreover, OPN expression enhanced cell attachment on the ColI coated silicon chamber against cell stretching stress.
Conclusions: MS might play an important role in maintenance of the cellular function of PDL fibroblast with ECM.