Upregulation of Adipogenic Lineage Differentiation and Markers in Inflamed-Dental Pulp

Introduction: Vital pulp therapy (VPT) and pulp regeneration or revascularization are current endodontic treatments that aim to either repair or regenerate dental pulp affected by caries, trauma, or iatrogenic exposure. Teeth undergoing these procedures are usually in a state of inflammation ranging from reversible pulpitis to pulpal necrosis. This inflammatory microenvironment provides a unique challenge to the dental stem cells used in VPT or pulp revascularization. Leptin, an inflammation-related protein, and its receptor (Lep-R) have been shown to be upregulated in dental pulp stem cells (DPSCs) exposed to hypoxic conditions in vitro, simulating inflammation. This study investigates the difference in leptin expression and adipogenic differentiation potential between ex vivo dental pulp diagnosed as normal and irreversible pulpitis. Methods: In vitro (simulated stressor model): DPSCs were isolated from seven virgin, human extracted third molars with normal pulp. Half of the DPSCs were exposed to hypoxic (5% oxygen) conditions and the remaining half were cultured in normoxic (21% oxygen) conditions. DPSCs were evaluated for lipid accumulation using oil red O stain and light microscopy. Ex vivo (disease model): Dental pulp was procured from six, virgin, human extracted premolars with normal pulp and six, non-restorable carious, human extracted premolars and molars with irreversible pulpitis. Pulp tissue was analyzed for adipogenic lineage proteins using a BioPlex Luminex Assay (BioRad, CA, USA). Results: In vitro (simulated stressor model): DPSCs exposed to hypoxic conditions have a higher concentration of cells with lipid accumulation. Ex vivo (disease model): Leptin and Lep-R are significantly (p0.05) up-regulated in the irreversibly inflamed pulp compared to healthy pulp. Conclusions: This study demonstrates that the stress of hypoxia and caries-driven irreversible pulpitis drive differentiation of DPSCs towards an adipogenic lineage with increased leptin production. In the future, leptin may be employed as a therapeutic molecule in bioengineering models to facilitate regenerative endodontics.