32, 35 Quantitative analysis revealed a progressive accumulation of A6+/EpCam−-positive cell clusters with a hepatocyte-like morphology, which LGK974 were located in close proximity to oval cells only in the Metfl/fl control livers, but not in c-Metfl/fl; Mx1-Cre+/− or c-Metfl/fl; Alb-Cre+/− livers (Fig. 4A,B; and data not shown). Significantly, only A6+ hepatocyte-like cells expressed hepatocyte nuclear factor 4-alpha (HNF-4α) transcription factor, a well-known marker of hepatocytic differentiation,36 whereas ductular oval cells were HNF-4α negative (Fig. 4C). These data demonstrate that loss of c-Met impaired the ability of oval cells to differentiate into hepatocytic lineage. Next, we examined the changes in

RNA Synthesis inhibitor distribution of oval cells migrating inside the parenchyma. For this, we divided the hepatic lobule into three zones—periportal (0-97 μm), middle (97-194 μm), and central (194-290 μm)—and measured the distance between the portal tract

and migrating oval cells visualized by A6 staining. In control livers, oval cells formed small ducts expanding toward the central zone (Fig. 5). The average distance between the portal veins and endpoint of A6-positive small branching ducts with poorly defined lumen increased from 92.6 μm at 1 week to 132.7 μm at 4 weeks. In contrast, in c-Met-deficient livers, A6-positive cells lined larger ducts with round lumen, click here which were confined to portal tracts and did not spread into parenchyma (the average distance from portal tracts was 78.2 and 79.0 μm at 1 and 4 weeks, respectively) (Fig. 5A-C). Thus, the absence of c-Met altered the pattern of ductular reaction and impaired its distribution in the parenchyma. Next, we assessed whether the absence of c-Met signaling altered the stem cell/oval cell microenvironment. Consistent with the protective role of HGF/c-Met against fibrosis,37 both c-Met mutant models developed a more extensive periportal fibrosis, as judged by the quantification

of Sirius red staining, which was more pronounced in c-Metfl/fl; Mx1-Cre+/− livers (Fig. 6A,B). By 4 weeks after the initiation of the DDC diet, the Sirius red–positive areas were significantly larger, both in c-Metfl/fl; Mx1-Cre+/− and in c-Metfl/fl; Alb-Cre+/− livers, as compared to the respective DDC-treated control mice (Fig. 6C). Monitoring liver fibrosis, using second harmonic generation confocal imaging, confirmed the presence of a much more dense and altered collagen matrix structure in c-Met-deficient mice maintained on the DDC diet (Fig. 6A). In contrast with straight and well-organized collagen fibers in DDC-treated control livers, mutant livers displayed irregular, wavy, and significantly less aligned collagen fibers or bundles. This was paralleled by a diminished macrophage mobilization, as measured by IHC and FACS analysis using Kupffer-cell–specific F4/80 antibody (Fig. 6A, D, E).