Maqui berry cystatin inhibits cathepsin k activity and stimulates osteogenic differentiation of human dental pulp cells

OBJECTIVES: Cystatins, endogenous inhibitors of cysteine proteases, regulate extracellular matrix degradation. Their plant-derived homologs (phytocystatins) include MaquiCPI-3, a recombinant protein obtained from Aristotelia chilensis (maqui berry). This study aimed to investigate the inhibitory effect of MaquiCPI-3 on human cathepsin K (CTSK) activity and its cytotoxicity and impact on the proliferation, migration, and osteogenic differentiation of human dental pulp cells (hDPCs). METHODOLOGY: The inhibitory activity of MaquiCPI-3 against CTSK was measured using a spectrofluorometer with the fluorogenic substrate Z-Phe-Arg-AMC. The hDPCs from third molars were characterized by flow cytometry for mesenchymal (CD90, CD73, CD105) and hematopoietic (CD34, CD45) markers. The hDPCs, either exposed to MaquiCPI-3 or left untreated (control), were assessed for viability (MTT assay), proliferation (bromodeoxyuridine incorporation), chemotaxis (Transwell assay), mineralized nodule formation (Alizarin Red S staining), alkaline phosphatase activity (thymolphthalein release), and expression of mineralization-related genes (qPCR). Data were analyzed using one- or two-way ANOVA with appropriate post hoc tests or nonparametric alternatives (α=0.05). RESULTS: MaquiCPI-3 potently inhibited CTSK (Ki=1.72 nM, Ki,app=2.08 nM), showed no cytotoxicity, and significantly enhanced ALP activity, mineralized nodule formation, and expression of BMP-2 and osteocalcin, stimulating no hDPC proliferation or migration when compared with the control. CONCLUSIONS: MaquiCPI-3 increased no cell proliferation or migration, its ability to inhibit CTSK activity and induce an osteogenic phenotype shows promising potential therapeutic strategies aimed at repairing and regenerating pulp and periapical tissues and controlling bone resorption.