Revisiting Stromal Cell Markers in Dental Pulp and Apical Papilla Cells

STRO-1 remains a widely used odontogenic mesenchymal stromal cell (MSC) marker, yet its ambiguous expression, non-specific tissue distribution, and unsolved structural features continue to raise questions. This study aimed to systematically characterize STRO-1 expression in human dental pulp stromal cells (hDPSCs), stromal cells from the apical papilla (SCAPs), and their native tissues, alongside CXCR4 as a biologically relevant reference marker associated with dental pulp injury and repair.

STRO-1 and CXCR4 expression were characterized in hDPSCs and SCAPs by flow cytometry and immunofluorescence, including assessment of surface and intracellular localization and changes during in-vitro expansion. STRO-1 expression was further evaluated under osteogenic differentiation and lipopolysaccharide stimulation. Tissue distribution of both markers was examined in healthy dental pulp and apical papilla, ex-vivo pulp healing model, and a clinical specimen following regenerative endodontic treatment (RET). CXCR4-enriched and CXCR4-depleted populations were assessed for colony formation, migration, and adipogenic differentiation.

In-vitro, STRO-1 showed negligible surface expression and predominantly intracellular localization, whereas CXCR4 demonstrated more accessible and quantifiable expression in expanded cells. In healthy tissues, both markers were mainly detected in perivascular regions. Following ex-vivo pulp healing, their distribution extended beyond these regions. In the RET specimen, STRO-1 and CXCR4 were expressed in vascularized pulp-like tissue and odontoblast-like cells adjacent to reparative dentin.

STRO-1 has important limitations for identifying and isolating expanded dental stromal cells because of its restricted surface availability and predominantly intracellular localization. CXCR4 may serve as a complementary marker for investigating stromal cell heterogeneity and injury-responsive populations.