Molecular Variation of Mandibular Periosteum

Abstract

This study investigated the molecular features of pig mandibular periosteum related to the characteristic posterior‐apposition and anterior‐resorption of the ramus during growth. Periosteal tissue (for direct RNA extraction) and cells (for culturing) were obtained from growing pig anterior and posterior mandibular‐ramal surfaces. Cells were cultured in osteogenic media and loaded by cyclic tension (magnitude 0, 5%, 10%), followed by RNA extraction. The expression of molecules involved in osteogenic differentiation (osteocalcin, OCN; runt‐related transcription factor 2, RUNX2) and bone formation/resorption regulation (osteoprotegerin, OPG; receptor‐activator for nuclear factor κ‐b ligand, RANKL) was quantified by real time RT‐PCR. We found that both tissue and unloaded cell samples had stronger OPG expression at the posterior location (p<0.05), while RANKL, RUNX2 and OCN expression was similar between locations. Coinciding with bone apposition, the posterior cells had lower RANKL/OPG ratio than the anterior. With tensile strain, the expression of RANKL, RUNX2 and OCN tended to be upregulated in anterior cells but downregulated in posterior cells. These results indicate that regional difference of mandibular periosteal apposition/resorption may be related to the variation of RANKL/OPG expression and reaction to mechanical strain. Funded by American Association of Orthodontists Foundation.