Investigation of the effects of human bone marrow-derived mesenchymal stem cells and vitamin K2 on osteosarcoma cells by targeting WNT/β-catenin pathway

Osteosarcoma (OS), which is histologically characterized by the presence of malignant osteoid, is the most common primary bone tumor in children and adolescents. OS, which has an aggressive and metastatic structure, usually metastasizes to the lung and causes the fatal course of the disease. Although bone marrow-derived mesenchymal stem cells (MSC) are known to play an important role in the microenvironment, their effect on osteosarcoma cell survival is controversial. Communication in the tumor microenvironment is provided by the activation/inhibition of different pathways via secreted cytokines, chemokines and extracellular vesicles. In addition, investigating the relationship between vitamin K2 in the microenvironment and bone metabolism is important in elucidating the possible roles of vitamin K2 in the modulation of osteogenesis. In our study, the apoptotic effects of healthy bone marrow MSCs and vitamin K2 on Saos-2 cells were investigated in co-culture experiments in vitro without cell-cell contact (membrane/insert). Apoptotic properties of Saos-2 cells were analyzed by flow cytometry. Alkaline phosphatase (ALP) enzyme activity was measured spectrophotometrically to evaluate the ability of Saos-2 cells to induce osteoblastic maturation. The cytokines (IL-6 and TGF-β1) released into the supernatant after culture were determined by the Elisa method. Expression studies of β-catenin protein in Saos-2 cells were determined immunocytochemically. According to our co-culture results, it was determined that the number of apoptotic cells increased in the interaction of Saos-2 cells with MSCs, but there was no statistically significant difference. Although a decrease was detected in ALP enzyme activity measurements obtained from culture supernatants, the results were not statistically significant. According to Elisa results obtained from culture supernatants, a decrease in the amount of secreted IL-6 and TGF-β1 cytokines was detected, but no statistically significant difference was found. It was determined that the expression of β-catenin, stained by immunohistochemically, in Saos-2 cells was significantly decreased in the cell nuclei of the co-culture groups. In the light of these findings, it was determined that MSCs and vitamin K2 were effective in the osteosarcoma microenvironment via the Wnt signaling pathway. It was concluded that vitamin K2 can reduce tumorigenicity, but it should be supported by in vivo and in vitro pre-clinical studies with different doses and durations for therapeutic use.