Abstract
Liver depleted of hepatic stellate cells (HSCs) is resistant to ischemia/reperfusion-, concanavalin A-, and acetaminophen-induced acute injury. Whether HSCs regulate carbon tetrachloride (CCl(4) )-induced acute liver injury is not known. CCl(4) treatment damages pericentral hepatocytes that express CCl(4) -metabolizing Cyp2E1 and activates HSCs. We investigated whether HSC-depletion in mice transgenic for thymidine kinase under the glial fibrillary acidic protein promoter (GFAP-TK-Tg) confers resistance to injury and inflammation due to CCl(4) rechallenge. GFAP-TK-Tg or wild type (WT) mice were administered 0.16 ml/kg CCl(4) (3× at 3 days intervals), then 40 μg/g/day ganciclovir for 10 days. The treatment depletes ~70%-75% HSCs from GFAP-TK-Tg but not WT mice while the liver recovers from earlier CCl(4) -induced injury. Mice were then administered CCl(4) , and liver injury and inflammation were determined at 24 h. HSC-depleted and HSC-sufficient mice showed similar CCl(4) -induced hepatocyte necrosis and oxidative stress. However, increase in F4/80(+) macrophages, but not CD68(+) cells, was greater in CCl(4) rechallenged HSC-depleted compared to HSC-sufficient mice. Expression of tumor necrosis factor-α (TNF-α), CCL2, and CXCL1 increased similarly, whereas increase in interleukin-6 (IL6), IL1β, and IL10 expression was higher in CCl(4) rechallenged HSC-depleted compared to HSC-sufficient mice. CCl(4) rechallenge of HSC-sufficient mice rapidly activated HSCs causing significant fibrosis with increased expression of Col1a1, transforming growth factor β1 (TGFβ1), tissue inhibitors of metalloproteinases 1 (TIMP1); increase in TIPM1 was much lower and metalloproteinases 13 (MMP13) greater in CCl(4) rechallenged HSC-depleted mice. Interestingly, hepatic recruitment of both profibrogenic (Ly6C(hi) ) and antifibrogenic restorative (Ly6C(lo) ) macrophages, and neutrophils was significantly greater in CCl(4) rechallenged HSC-depleted mice. These data suggest that CCl(4) directly damages hepatocytes but HSCs regulate inflammation. Rapid fibrogenesis in CCl(4) rechallenged HSC-sufficient mice recovered from earlier injury indicates that even transiently activated HSCs that had reverted to the quiescent phenotype remain primed to become reactivated.