Mechanisms of hepatic fibrogenesis

Substantial improvements in the treatment of chronic liver disease have accelerated interest in uncovering the mechanisms underlying hepatic fibrosis and its resolution. Activation of resident hepatic stellate cells into proliferative, contractile, and fibrogenic cells in liver injury remains a dominant theme driving the field. However, several new areas of rapid progress in the past 5-10 years also have taken root, including: (1) identification of different fibrogenic populations apart from resident stellate cells, for example, portal fibroblasts, fibrocytes, and bone-marrow-derived cells, as well as cells derived from epithelial mesenchymal transition; (2) emergence of stellate cells as finely regulated determinants of hepatic inflammation and immunity; (3) elucidation of multiple pathways controlling gene expression during stellate cell activation including transcriptional, post-transcriptional, and epigenetic mechanisms; (4) recognition of disease-specific pathways of fibrogenesis; (5) re-emergence of hepatic macrophages as determinants of matrix degradation in fibrosis resolution and the importance of matrix cross-linking and scar maturation in determining reversibility; and (6) hints that hepatic stellate cells may contribute to hepatic stem cell behavior, cancer, and regeneration. Clinical and translational implications of these advances have become clear, and have begun to impact significantly on the management and outlook of patients with chronic liver disease.