Differential recruitment of monocyte-derived macrophages in control and stellate cell-depleted mice during recurrent carbon tetrachloride-induced acute liver injury

Liver depleted of hepatic stellate cells (HSCs) is resistant to ischemia/reperfusion-, concanavalin A-, and acetaminophen-induced acute injury. Whether HSCs regulate carbon tetrachloride (CCl4)-induced acute liver injury is not known. CCl(4 )treatment damages pericentral hepatocytes that express CCl4-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 CCl4 (3x at 3 days intervals), then 40 mu g/g/day ganciclovir for 10 days. The treatment depletes similar to 70%-75% HSCs from GFAP-TK-Tg but not WT mice while the liver recovers from earlier CCl4 -induced injury. Mice were then administered CCl4, and liver injury and inflammation were determined at 24 h. HSC-depleted and HSC-sufficient mice showed similar CCl4-induced hepatocyte necrosis and oxidative stress. However, increase in F4/80(+) macrophages, but not CD68(+) cells, was greater in CCl4 rechallenged HSC-depleted compared to HSC-sufficient mice. Expression of tumor necrosis factor-alpha (TNF-alpha), CCL2, and CXCL1 increased similarly, whereas increase in interleukin-6 (IL6), IL1 beta, and IL10 expression was higher in CCl4 rechallenged HSC-depleted compared to HSC-sufficient mice. CCl4 rechallenge of HSC-sufficient mice rapidly activated HSCs causing significant fibrosis with increased expression of Col1a1, transforming growth factor beta 1 (TGF beta 1), 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 CCl4 rechallenged HSC-depleted mice. These data suggest that CCl4 directly damages hepatocytes but HSCs regulate inflammation. Rapid fibrogenesis in CCl4 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.