Hyung-Mun Yun, Kyung-Ran Park
Hepatocellular carcinoma (HCC) is frequently complicated by bone metastasis, leading to severe skeletal-related events. While alpha-fetoprotein (AFP) is the gold-standard biomarker for HCC diagnosis, its functional role as a systemic or paracrine mediator in the bone metastatic microenvironment remains largely unexplored. In the present study, we investigated whether HCC-secreted AFP impairs bone formation by disrupting autophagic flux, the glycogen synthase kinase 3β (GSK3β)/β-catenin signaling pathway, and Runt-related transcription factor 2 (Runx2) stability in osteoblasts. Our results showed that AFP dose-dependently inhibited osteoblast differentiation and mineralization. Mechanistically, AFP impaired autophagic flux, resulting in reduced phosphorylated GSK3β (p-GSK3β) and β-catenin levels, which were accompanied by decreased Runx2 protein expression. Pharmacological activation of autophagy with rapamycin effectively reversed these AFP-induced changes, restoring GSK3β/β-catenin signaling and Runx2 expression. Furthermore, using an ex vivo mouse calvarial defect model, we found that HepG2-derived AFP markedly impaired new bone regeneration and reduced the numbers of osteoblasts and osteocytes. Importantly, these effects were significantly attenuated by AFP silencing in HepG2 cells. Collectively, our findings identify HCC-derived AFP as a potential mediator of bone impairment rather than solely a diagnostic biomarker. Targeting AFP-mediated impairment of autophagic flux may represent a promising therapeutic strategy for mitigating skeletal complications and restoring bone homeostasis in patients with bone-metastatic HCC.