Interaction Between Osteopontin and Macrophages in the Inflammatory Pulp Microenvironment

Objectives: To investigate the expression of osteopontin (OPN) in human inflamed dental pulp tissue and its co-localization relationship with macrophages, shedding light on the potential diagnostic utility of OPN in dental pulp inflammation and its association with macrophage phenotypes.
Methods: Bioinformatics analysis and clinical samples verification were employed to confirm OPN as a diagnostic marker distinguishing between inflamed and normal dental pulp tissues and to explore its relationship with immune cells. Multiplex immunohistochemistry was utilized to detect the expression and spatial distribution of OPN alongside macrophage markers in inflamed dental pulp tissues. Conditioned media were collected from human dental pulp cells induced by lipopolysaccharide or not, and then co-cultured with THP-1 derived macrophages, allowing for the assessment of relevant polarization markers.
Results: OPN emerged as a promising candidate for distinguishing inflamed dental pulp from normal pulp, with qRT-PCR revealing a significant upregulation of the OPN gene in inflamed dental pulp tissues. Multiplex immunohistochemistry demonstrated co-localization of OPN with macrophage markers CD68, M1 marker CD80, and M2 marker CD163 within inflamed dental pulp tissues. Conditioned medium from lipopolysaccharide-stimulated human dental pulp stem cells was found to enhance OPN expression in macrophages. OPN+ macrophages exhibited an M2b phenotype with elevated CD86, IL6, TNFα, IL10, and CCL1 expression, while CCL17 and MerTK remained unchanged.
Conclusions: It is reported for the first time that OPN is an immune-related diagnostic marker for pulpitis, and the inflammatory pulp microenvironment can promote the expression of OPN in macrophages. OPN⁺ macrophages in the inflamed pulp are associated with M2b phenotypes. These insights offer potential for improved diagnosis and targeted therapy.