Figure 3. Impaired fibrolysis precludes fibrosis reversal in old mice. (A) CCl4 was injected three times a week for two weeks to young and old mice (n=6/group). Livers were harvested 48h or 96h after the last injection. (B) Sirius red stained liver sections in CCl4-treated young and old mice (magnification 80x). Collagen fibers were evaluated as percentage of stained area in the section (n=6/group). Scale bare 100µm. (C) Activated stellate cells were identified by alphaSMA immunohistochemistry staining in young and old mice 48 and 96 hours after the last CCl4 injection (magnification 80x) (n=6/group). Scale bare 100µm. (D) Hepatic gene expression of Mmp13 and Cxcl9 (Mean ± SEM) (n=6/group). (E) Collagenase activity was measured in controls and CCl4-treated groups (Mean ± SEM) (n=6/group). Results are expressed in units/ml. One unit of collagenase activity is defined as the cleavage of 1 mg of collagen per minute. Statistical analysis was performed by two-way ANOVA for repeated measures (boxes) followed by Bonferroni’s post-hoc correction. *P<0.05; **P<0.01 for differences between age groups.