Osteoprotegerin is More Than a Possible Serum Marker in Liver Fibrosis: A Study into Its Function in Human and Murine Liver

Osteoprotegerin (OPG) serum levels are associated with liver fibrogenesis and have been proposed as a biomarker for diagnosis. However, the source and role of OPG in liver fibrosis are unknown, as is the question whether OPG expression responds to treatment. Therefore, we aimed to elucidate the regulation of OPG production and its biological activity in human and mouse livers. OPG levels were significantly higher in lysates of human cirrhotic and mouse fibrotic livers compared to healthy livers. Hepatic OPG expression localized in cirrhotic collagenous bands in and around myofibroblasts. Single cell sequencing of murine liver cells showed hepatic stellate cells (HSC) to be the main producers of OPG in healthy livers. Using mouse precision-cut liver slices, we found OPG production induced by transforming growth factor β1 (TGFβ1) stimulation. Moreover, OPG itself stimulated expression of genes associated with fibrogenesis in liver slices through TGFβ1, suggesting profibrotic activity of OPG. Resolution of fibrosis in mice was associated with significantly lower OPG levels in livers as compared to their fibrotic counterparts.OPG stimulates fibrogenesis through TGFβ1 and is closely associated with the degree of fibrogenesis. It may therefore be a novel drug target for liver fibrosis or be used as a biomarker for treatment success of novel antifibrotics.