Role of Cathepsin K in Bone Invasion of Pituitary Adenomas: A Dual Mechanism Involving Cell Proliferation and Osteoclastogenesis

Purpose: This study aimed to investigate the regulation and underlying mechanism of Cathepsin K (CTSK) in bone-invasive pituitary adenomas (BIPAs). Experimental Design: A total of 1437 patients with pituitary adenomas were included and followed up. RNA sequencing, immunohistochemistry, and RT-PCR were used to analyze to detect CTSK expression. The effects of CTSK on cellular proliferation, bone matrix degradation, and osteoclast differentiation were determined by gain/loss of function experiments in vitro and in vivo. The exploration of signaling pathways was determined by molecular biology experiments. Results: Here, we reported a significant fraction (~10%) of pituitary adenoma patients developed bone invasion, which was correlated with tumor recurrence. Patients with BIPAs had shorter recurrence-free survival. CTSK expression was increased in BIPA patients and was strongly associated with a worse prognosis. Increased CTSK expression enhanced pituitary adenoma cell proliferation through the activation of the mammalian target of rapamycin (mTOR) signaling pathway and promoted bone invasion by increasing osteoclast differentiation both in vitro and in vivo. Treatment with the CTSK inhibitor odanacatib effectively inhibited pituitary adenoma cell proliferation and bone invasion in these models. Additionally, CTSK facilitated osteoclast differentiation by promoting RANKL expression in MC3T3-E1 cells via interaction with TLR4. Conclusion: CTSK has the potential to become a novel predictive biomarker and therapeutic target for BIPAs.