g., activated (myo)-fibroblasts (such as HSC/MF), which are also able to ingest apoptotic selleck chemical cells, although at a much slower rate than macrophages (26). This will consequently lead to a prolonged exposure of the organism to apoptotic cells and leakage of toxic cell contents, causing persistence of inflammation, autoimmune reactions (25), and fibrogenic activation of HSC/MF by apoptotic bodies (6). It is temping to speculate that this scenario may be responsible for the failure of resolution in advanced CCl4-induced liver fibrosis when macrophages were depleted during the recovery phase (12). However, in this study the persistence of apoptotic cells upon macrophage depletion was not measured.

Our findings indicate that clearance of proliferating bile ductular structures is a dynamic process that is characteristic of and central to the reversal of secondary biliary (BDL-induced) fibrosis, with apoptosis of cholangiocytes, by far exceeding that of nonbiliary cells. This is particularly evident at the peak of reversal, where dramatic increase in cholangiocyte apoptosis coincides with a maximum of MMP activity and pronounced histological signs of septal fragmentation and architectural remodeling (Figs. 1, ,3,3, and and5).5). Interestingly, although we were not able to detect an increase in net MMP activity in the early peak of cholangiocyte apoptosis (3 days after RY, Fig. 3), this was nonetheless followed by a significant decrease in total collagen content (Fig. 1C) and MMP-3 induction at the mRNA level (Fig. 5C).

It is likely that analysis of crude liver homogenates, where MMPs and their inhibitors are mixed together, does not allow the detection of local increase in MMP activity at the cellular level because of the persistent surplus of MMP inhibitors such as TIMP-1 (Fig. 2B). We cannot exclude that the proposed MMP-dependent macrophage mechanism might also be operative at that early time point at the local microenvironment level, where MMPs and metalloproteinase inhibitors are spatially separated. Proliferating (activated) cholangiocytes are a prominent source of several key profibrogenic cytokines that activate ECM-producing HSC/MF in a paracrine manner (30, 44), recapitulating early developmental programs of ductal plate formation. They also express integrin ��v��6, which contributes to fibrogenesis by binding and activating the profibrogenic cytokine TGF-��1 (37, 46).

Of note, those profibrogenic transcripts, which are abruptly downregulated immediately following RY-anastomosis, are predominantly expressed by activated bile ductular cells, which undergo rapid deactivation/apoptosis after RY-anastomosis. Thus prior in situ hybridization and immunohistochemistry studies demonstrated prominent cholangiocyte expression of CTGF (44), procollagen-��2(IV) (29), TGF-��2 Batimastat (30), and integrin-��6 (37, 46)(Fig. 2A; Supplemental Fig. S1).