Engineering a Novel Stem Cells from Apical Papilla-Macrophages Organoid for Regenerative Endodontics

A 3-dimensional (3D) tissue construct with a heterogeneous cell population is critical to understand the interactions between immune cells and stem cells from the apical papilla (SCAPs) in the periapical region for developing treatment strategies in regenerative endodontics. This study aimed to develop and characterize a 3D tissue construct with a binary cell system for studying the interactions between SCAPs and macrophages in the presence of lipopolysaccharide (proinflammatory) and interleukin 4 (anti-inflammatory) environments.

SCAPs and macrophages were seeded in the 3D-printed dumbbell-shaped molds to generate tissue constructs with a binary cell population. Two experimental (lipopolysaccharide and interleukin 4) and control (non-stimulation) conditions were applied to the tissue constructs to determine the characteristics of the tissue construct, the volume of viable cells, and their morphology using confocal laser scanning microscopy from a 0- to 7-day period. Experiments were conducted in triplicate, and data were analyzed with trend analysis and 2-way analysis of variance at a significance of P < .05.

The tissue constructs revealed distinct SCAP-macrophage interaction in pro/anti-inflammatory environments. SCAPs displayed characteristic self-organization as a cap-shaped structure in the tissue construct. The growth of cells and cell-to-cell and cell-to-matrix interactions resulted in 70% and 30% decreased dimension of the tissue graft on the SCAP side and macrophage side, respectively, at day 7 (P < .0001). The tissue environments influenced SCAP-macrophage interactions, resulting in an altered viable cell volume (P < .05), morphology, and structural organization.

This study developed and characterized an apical papilla organoid in a 3D collagen-based tissue construct for studying SCAP-macrophage crosstalk in tissue regeneration as well as repair.