Mandibular invasion in Oral Squamous Cell Carcinoma is associated with osteoclast count and expression of its regulating proteins

Abstract

Abstract Background Oral squamous cell carcinoma (OSCC) frequently invades the jaw. The exact mechanism of bone invasion remains unclear. This study investigates the role of osteoclasts and RANKL/OPG/RANK in the development of bone invasion in OSCC. Methods OSCC-patients treated with resection were included and divided in three groups; Non-invasion (NI-group), erosion (E-group) and bone invasion (I-group). Tissue-sections were stained with Cathepsin K (for counting osteoclasts), RANKL, OPG and RANK. Staining intensity was scored in tumor-front, tumor-center, tumor-backside and normal mucosa. Immunohistochemistry and qPCR for RANKL/OPG/RANK was performed in five head-and-neck SCC organoids to correlate protein and mRNA-expression levels. Results The mean number of osteoclasts in Cathepsin K stained sections in the NI-group was 3.09 (1.12-5.05; 95%CI), in the E-group 6.15 (4.04–8.25; 95%CI) and in the I-group 10.58 (5.81–15.34; 95%CI). Compared to normal mucosa, the expression in all tumor regions was higher for RANKL, in most tumor regions for OPG and not higher for RANK. RANKL-expression in tumor-front was higher than expression in tumor-backside (I-group). RANK-expression in the tumor-front and the tumor-center was higher than expression in tumor-backside in all groups. qPCR showed a 20-43x higher RANKL-mRNA expression in 3/5 tumor organoid samples compared to a normal squamous cell organoid line and no higher mRNA-expression of OPG and RANK. There was no correlation between protein and mRNA expression in the HNSCC organoids. Conclusion The number of osteoclasts and their regulating proteins RANKL/OPG/RANK differ between OSCC patients with and without bone invasion. Bone invasive OSCCs have more osteoclasts and express more RANKL in tumor-front, which suggest that OSCC’s induce bone invasion by stimulating osteoclast activation by regulating the production of RANKL/OPG/RANK proteins.