Influence of Mechanical Compression on Stem Cell Property in Human PDL Cells

Abstract

Periodontal ligament (PDL) is a mechanical responsive tissue that subject to mastication and orthodontic force. PDL contains heterogenous cell population including residual stem cells, that play roles in maintaining PDL homeostasis. Evidences suggested that mechanical stimuli could modulate stem cell fate, however, the role of mechanical stimulation in stem cells properties of PDL stem cells is still unclear. Objective: To investigate the stem property alteration in human PDL cells under the influence of compressive force. Material and Methods: PDL stem cells were isolated from healthy periodontal tissue obtained from third molar extracted teeth. The characteristics of PDL stem cells were confirmed by the expression of CD73, CD90 and CD105 as well as the ability to differentiate into osteoblast-like cells. The 3rd - 5th passage of human PDL cells were used in the study. Cells were subjected to varied magnitude of static compressive force for 24 hours (control, 0.5g/cm', 1.0g/cm', 1.5g/cm* and 2.0g/cm*). MTT assay, CFU-F assay, flow cytometry for immunophenotyping (STRO-1, CD73, CD90, CD105) and qPCR for gene expression were used to determine the stem property. The expression of periostin, a forced-responsive matricellular protein, was also examined. Result: A biphasic dose response of periostin expression was observed. Periostin was expressed maximum at 1.0g/cm compression then declined. Nanos, Oct, stemness regulatory gene, and osx, osteogenic differentiation marker, were expressed in consistent pattern with periostin expression. A correlation coefficient analysis also showed strong relationship between periostin and Nanog expression. CFU-F assay was used to represent the self renewal capacity. The results showed that CFU-F increased at 1.0g/cm? and decreased at 0.5g/cm'. All cell surface markers were expressed in all samples but no difference was found between groups. Conclusion: The results showed compressive force could effects stem cell fate in differential manner. The changes in periostin expression was associated with the self-renewal capacity changes. Increased periostin due to compressive force might play a role in stem properties in PDL, since periostin function involved Wnt signaling and PIK/Akt signaling via integrin that regulate stemness in many stem cell systems.