Hyper-Occlusal Loading Affects to the Expression of Collagen Modifying Enzymes

Type I collagen, a major component of periodontal ligament (PDL), is post-translationaly modified by series of enzymes during biosynthesis. Among the collagen modifying enzymes, lysyl hydroxylases (LHs) alter the collagen crosslink pathways that are important for the tissue specific mechanical properties. Objectives: The purpose of this study was to investigate the effect of hyper occlusal loading on the post-translational modifications of type I collagen on PDL Methods: Primary hPDL cells were obtained from extracted human teeth by enzymatic digestion. The hPDL cells were subjected to compressive force for 12 or 24 hours. A real-time PCR was performed for gene expression analysis with following primers; Cbfa1/Runx2, SPP1 (OPN), Type I collagen alpha 2 chain (Col1a2), LH1-3 and GAPDH. Four weeks old male SD rats were subjected to hyper occlusal loading. Briefly, a piece of metal was adhered onto the occlusal surface of right maxillary molar. After three days, paraffin embedded histology section was prepared and immunohistochemistry was carried out to detect the anti-LH2 positive cells. Results: Gene expression of OPN was upregulated upon loading while Cbfa1/Runx2 and Col1a2 didn't change. Among the collagen modifying enzymes analyzed, only LH2 gene expression was responded upon loading. The LH2 has been proposed to alter the crosslink pathway to the stable and irreversible form. The increases of LH2 positive cells were confirmed on the hyper occlusal loaded PDL tissue. The LH2 positive cells were preferentially observed at the bone side of PDL. Conclusions: Mechanical loading enhance the expression of LH2 in vitro and in vivo, indicating the stabilization of PDL tissue. These results are suggesting that the PDL tissue homeostasis is at least partially regulated by the post-translational modifications of collagen.