Galectin-3 modulates phagocytosis-induced stellate cell activation and liver fibrosis in vivo

Jiang JX, Chen X, Hsu DK, Baghy K, Serizawa N, Scott F, Takada Y, Takada Y, Fukada H, Chen J, Devaraj S, Adamson R, Liu F, Torok NJ. Galectin-3 modulates phagocytosis-induced stellate cell activation and liver fibrosis in vivo. Am J Physiol Gastrointest Liver Physiol 302: G439-G446, 2012. First published December 8, 2011; doi: 10.1152/ajpgi.00257.2011.-Hepatic stellate cells (HSC), the key fibrogenic cells of the liver, transdifferentiate into myofibroblasts upon phagocytosis of apoptotic hepatocytes. Galectin-3, a beta-galactoside-binding lectin, is a regulator of the phagocytic process. In this study, our aim was to study the mechanism by which extracellular galectin-3 modulates HSC phagocytosis and activation. The role of galectin-3 in engulfment was evaluated by phagocytosis and integrin binding assays in primary HSC. Galectin-3 expression was studied by real-time PCR and enzyme-linked immunosorbent assay, and in vivo studies were done in wild-type and galectin-3(-/-) mice. We found that HSC from galectin-3(-/-) mice displayed decreased phagocytic activity, expression of transforming growth factor-beta 1, and procollagen alpha 1(I). Recombinant galectin-3 reversed this defect, suggesting that extracellular galectin-3 is required for HSC activation. Galectin-3 facilitated the alpha v beta 3 heterodimer-dependent binding, indicating that galectin-3 modulates HSC phagocytosis via cross-linking this integrin and enhancing the tethering of apoptotic cells. Blocking integrin alpha v beta 3 resulted in decreased phagocytosis. Galectin-3 expression and release were induced in active HSC engulfing apoptotic cells, and this was mediated by the nuclear factor-kappa B signaling. The upregulation of galectin-3 in active HSC was further confirmed in vivo in bile duct-ligated (BDL) rats. Galectin-3(-/-) mice displayed significantly decreased fibrosis, with reduced expression of alpha-smooth muscle actin and procollagen alpha 1(I) following BDL. In summary, extracellular galectin-3 plays a key role in liver fibrosis by mediating HSC phagocytosis, activation, and subsequent autocrine and paracrine signaling by a feedforward mechanism.