Long non-coding RNAs modulate the osteogenic differentiation of healthy and inflamed periodontal ligament cells

Abstract

Periodontitis is a bacteria‐induced, host‐mediated inflammatory disease that results in the progressive destruction of tooth-supporting tissues and bone. The periodontal ligament (PDL), a thin layer of connective tissue between the cementum and alveolar bone, contributes significantly to the development, function, and regeneration of the periodontium. PDL progenitor cells (PDL cells) have multipotent differentiation potential and are considered to be an appropriate cell source for periodontal regeneration in the treatment of periodontitis. PDL cells have reduced osteogenic potential in periodontitis patients compared with periodontally healthy individuals. Currently, the primary goal of periodontal therapy is to stop disease progression and achieve a stable periodontal condition. However, whether the regenerative potential of the treated stable periodontium can be fully recovered following periodontal therapy is unknown. Therefore, it is crucial to enhance the osteogenic potential of PDL cells and ultimately promote bone formation in periodontitis patients. Long non-coding RNAs (lncRNAs) are critical regulators of diverse biological processes and diseases, including the osteogenic differentiation of PDL cells. In this study, the characteristics and osteogenic potentials of healthy, inflammatory, and treated stable PDL cells were elucidated and the regulatory roles of lncRNAs in the osteogenic differentiation of these cells were explored. PDL cells from periodontally healthy individuals (H-PDL cells), patients with inflammatory periodontitis (I-PDL cells), and patients with treated stable periodontitis (S-PDL cells) were successfully isolated and cultured. It was found that the S-PDL cells had a higher proliferation rate and osteogenic potential than the I-PDL cells but lower than those of the H-PDL cells. Clinically, it is established that patients with treated stable periodontitis, especially the susceptible ones, remain at a high risk of recurrent periodontitis. Therefore, in this study, the proliferation rates and osteogenic differentiation potentials of H-PDL, I-PDL, and S-PDL cells were further assessed upon bacterial lipopolysaccharide (LPS) stimulation to impose inflammatory challenge. LPS significantly impaired the osteogenic potentials of the I-PDL and S-PDL cells, but not of the H-PDL cells. Orthodontic tooth movement is a unique mechanical loading-induced bone remodeling and regeneration process, in which PDL cells play a critical role due to their mechanosensitivity. Tensile loading significantly enhanced the osteogenic differentiation of the H-PDL and S-PDL cells, but not of the I-PDL cells. Next, RNA sequencing was performed to characterize the lncRNA expression profiles of PDL cells subjected to tensile loading. Further testing was conducted to determine whether MIR22HG, an lncRNA significantly upregulated in H-PDL cells following tensile loading, could positively account for tension-induced osteogenesis in PDL cells. According to the results, MIR22HG may promote the osteogenic differentiation of PDL cells via the PI3K/AKT pathway. This study provides new evidence regarding the characteristics and osteogenic potentials of inflammatory and treated stable periodontium and advances the current understanding of the regulatory roles of lncRNAs in the osteogenesis of PDL cells. The findings may contribute to the further development of novel therapeutic strategies for bone regeneration as well as safe and efficient orthodontic tooth movement in periodontitis patients.