Insulin Growth Factor Binding Protein-6 and the Liver

The insulin-like growth factor (IGF) axis orchestrates hepatic development, regeneration, and metabolism, yet the roles of individual IGF-binding proteins (IGFBPs) remain incompletely defined. IGFBP-6, a high-affinity, IGF-II-preferring binding protein, has emerged as a context-dependent modulator of IGF bioavailability and cell signaling with additional IGF-independent actions. This review synthesizes current evidence on IGFBP-6 in liver biology and disease. We first outline hepatic expression, regulation, and post-translational processing of IGFBP-6 across development, homeostasis, and injury, and summarize its effects on canonical IGF-II/IGF1R signaling and downstream phosphatidylinositol 3-kinase-protein kinase B (PI3K-AKT) and rat sarcoma-mitogen-activated protein kinase (RAS-MAPK) pathways. We then evaluate experimental and clinical data linking IGFBP-6 to steatotic liver disease, inflammation, and fibrogenesis, including putative roles in hepatocyte stress responses, stellate cell activation, and extracellular matrix remodeling. Finally, we examine IGFBP-6 in primary liver cancers-hepatocellular carcinoma and cholangiocarcinoma-highlighting evidence for tumor-suppressive versus pro-migratory activities, potential crosstalk with hypoxia, Wnt/β-catenin and TGF-β signaling, and interactions with the tumor immune microenvironment. Across conditions, we assess the translational potential of IGFBP-6 as a circulating or tissue biomarker, its utility for patient stratification, and prospects for therapeutic targeting-either by modulating IGF-II sequestration or exploiting IGF-independent mechanisms. We conclude by identifying key knowledge gaps, methodological limitations, and priorities for future studies, including standardized measurement, cell-type-resolved profiling, and in vivo perturbation in clinically relevant models. Collectively, the review positions IGFBP-6 as a nuanced regulator of liver pathophysiology and a promising, yet underexplored, lever for diagnosis and therapy.