Fig. 3

Mechanisms behind low levels of hepcidin in liver disease. BMPR, bone morphogenetic protein receptor; C/EBP alpha, CCAAT enhancer binding protein alpha; HAMP, hepcidin antimicrobial peptide; HCV, hepatitis C virus; HFE, hemochromatosis protein; HH, hemochromatosis; HJV, hemojuvelin; IL-6, interleukin 6; InR, insulin receptor; STAT3, signal transducer and activator of transcription 3; TFR2, transferrin receptor 2; TLR4, toll-like receptor 4. Different pathogenic factors are responsible for low values of hepcidin. In HH mechanisms behind low levels of hepcidin are already known and they include defective signalling though HJV, HFE, TFR2 or through direct inhibition of HAMP gene. Alcohol inhibits hepcidin expression through its actions on C/EBP, but also indirectly through TLR4 pathway. It is believed that TLR4 mediates this action of alcohol through nonparenchymal liver cells, but the paracrine signal responsible for this effect is unknown. HCV also suppresses hepcidin expression through oxidative stress, which inhibits C/EBP and STAT3 actions on HAMP. Cholestasis, on the other hand, suppresses hepcidin expression by inhibiting IL-6/STAT3 pathway. In AILD mechanisms behind low levels of hepcidin are unknown. In hepatic insulin resistance defective insulin signaling is linked with defective hepcidin expression, partially through STAT3 pathway