Periodontal ligament-associated protein-1 engages in teeth overeruption and periodontal fiber disorder following occlusal hypofunction.

Abstract

Teeth overeruption is a problem of clinical significance, but the underlying mechanism how changes in external occlusal force convert to the periodontium remodeling signals has been a largely under explored domain. And recently, periodontal ligament-associated protein-1 (PLAP-1)/asporin was found to play a pivotal role in maintaining periodontal homeostasis. The aim of this study was to explore the function of PLAP-1 in the periodontally hypofunctional tissue turnover. After extracting left maxillary molars in mice, the left and right mandibular molars were distributed into hypofunction group (HG) and control group (CG), respectively. Mice were sacrificed for radiographic, histological, and molecular biological analyses after 1, 4 and 12 weeks. In vitro, dynamic compression was applied using Flexcell FX-5000 Compression System to simulate intermittent occlusal force. The expression of PLAP1 in loaded and unloaded human periodontal ligament cells (hPDLCs) was compared, and its molecular biological effects were further explored by small interfering RNA (siRNA) targeting PLAP1. In vivo, fiber disorder in periodontal ligament (PDL), bone apposition at furcation regions, and bone resorption in alveolar bone were illustrated in the HG compared with the CG. In addition, PLAP-1 positive area decreased significantly in PDL following occlusal unloading. In vitro, the loss of compressive loading relatively downregulated PLAP1 expression, which was essential to promote collagen I but inhibit osterix and osteocalcin expression in hPDLCs. PLAP-1 presumably plays a pivotal role in occlusal force-regulated periodontal homeostasis by facilitating collagen fiber synthesis in hPDLCs and suppressing excessive osteoblast differentiation, further preventing teeth from overeruption. Further evidence in PLAP-1 conditional knockout mice is needed.