TGF-β serves as a critical signaling determinant of liver progenitor cell activation and function.

When massive hepatic necrosis-associated (MHN-associated) acute liver failure (ALF) occurs following severe damage, liver progenitor cells (LPCs) exit quiescence and enter differentiation programs during which they acquire hepatocyte-like functions. How LPCs maintain quiescence under physiological conditions and orchestrate activation following MHN remains largely unknown. We elucidate an essential role of TGF-β in regulating LPC quiescence and activation. Spatial transcriptomics and single-cell sequencing revealed that LPCs receive multiple signals, particularly TGF-β, HGF, and EGF, from surrounding hepatic stellate cells and macrophages in patients and zebrafish with MHN-induced ALF. Physiologically, TGF-β inhibits LPC proliferation by blocking G1-to-S phase transition, an effect reversed by Smad7 overexpression in a murine injury model. We observed extensive LPC proliferation in patients with ALF despite strong TGF-β/phosphorylated SMAD signaling. Immunostaining revealed concurrent activation of HGF/MET, EGF/EGFR, and downstream STAT3/ERK pathways in LPCs. In vitro, HGF or EGF overcame TGF-β-mediated growth arrest and promoted LPC proliferation. Beyond acting as a mitogen, HGF additionally induced hepatocyte gene programs (e.g., Hnf4a, Hnf1a) in LPCs. Strikingly, TGF-β signaling was required for HGF-dependent hepatocyte gene induction, indicating a dual role in restraining LPC proliferation and promoting functional maturation. These findings position TGF-β as a context-dependent determinant of LPC activation and lineage specification during ALF.