Lipopolysaccharide Downregulates the Osteo-/Odontogenic Differentiation of Stem Cells From Apical Papilla by Inducing Autophagy

Introduction: The dentinogenesis potential of stem cells during dentin-pulp tissue regeneration may be compromised by microorganism components. Here we aimed to investigate the cell viability and osteo-/odontogenic differentiation of stem cells from apical papilla (SCAP) exposed to bacterial lipopolysaccharide (LPS) and to evaluate the molecular mechanism in vitro. Methods: CCK8 assay was used to assess the SCAP proliferation rate on exposure to different concentrations of LPS in medium. Dentin matrix protein-1 (DMP-1), runt-related transcription factor-2 (Runx-2), and alkaline phosphatase (ALP) expression and mineralized nodule formation were detected by Western blotting and alizarin red S staining to evaluate SCAP osteo-/odontogenic differentiation. Autophagosomes in SCAP and the autophagy-related markers Beclin 1, autophagy-related gene 5 (Atg5), and microtubule-associated proteins light chain 3 (LC3) were detected by transmission electron microscopy and Western blotting, respectively. Effects of the autophagy inhibitor 3-methyladenine on LPS-treated SCAP osteo-/odontogenic differentiation were also examined. Results: SCAP cell viability was decreased by 5 mg/mL LPS treatment on day 3. LPS (5 mg/mL) inhibited SCAP osteo-/odontogenic differentiation and decreased DMP-1, Runx-2, and ALP expression. Moreover, LC3, Atg5, and Beclin 1 expression and autophagosome number were elevated. Conversely, autophagy inhibition rescued the number of mineralized nodules and DMP-1, Runx-2, and ALP expression in the LPS-treated SCAP. Conclusions: Our findings indicated that autophagy was involved in the suppression of SCAP osteo-/odontogenic differentiation in an LPS-induced inflammatory environment. This study discloses autophagy modulation as a potential new strategy to improve SCAP osteo-/odontogenic differentiation in an inflammatory environment.