Signal Transductions Mechanism And Regulating Effect Of Kuffer Cell On Apoptosis Of Hepatic Stellate Cell In Resolution Of Hepatic Fibrosis

Hepatic fibrosis represent the consequences of a sustained wound healing response to chronic liver injury,characterized by excessive deposition of extracellular matrix (ECM) proteins.A wealth of evidence now indicated that this process was irreversible. Key to this is the discovery that reversion of fibrosis is accompanied by clearance of activated hepatic stellate cell(HSC) by apoptosis.Therefore,modulation of apoptosis of activated HSC could be an important complementary pathway in preventing hepatic fibrosis.Recent studies demonstrated that the double-edged sword of kupffer cell(KC) activity in hepatic fibrosis progression versus recovery.During fibrosis progression,it is believed that KC is likely to promote activation of HSC.In contrast,during recovery of hepatic fibrosis KC could also provoke apoptosis of HSC by the expression of TNF-related apoptosis-inducing ligand(known as TRAIL) and other apoptotic stimul. In this study,using widely studied models induced by parenchymal injury from carbon tetrachlodde(CCl₄) treatment to investigate the mechanisms and regulative effect of TRAIL secreted from KC on apoptosis of HSC in recovery from hepatic fibrosis and the effects of leflunomide(Lef) on this signal pathway.The main contents are divided into three sections,as follows:1.Determin distinct phases(progression phase and recovery phase) of hepatic fibrosis In this section,following dynamic observation the change of pathologic histology, the levels of HA,LN,â…£-C and PCâ…¢in serum and Hyp in liver,we definited that the model of progression and recovery of hepatic fibrosis was rats with CCl₄ 12 week and 4 week spontaneous recovery after injecting CCl₄ 12 week.By dual staining with TUNEL andα-SMA,spontaneous apoptosis was observed in activation HSC.During recovery from fibrosis,with the number of HSC reduced,the proportion of HSC apoptosis decreased,suggesting that HSC cell numbers are controlled by apoptosis.It is well known that interstitial collagenase activity decreases during fibrotie liver injury,and this decrease occurs through the activity of TIMPs. Specially,the reduction in TIMPs levels is associated with an increase in eollagenase activity.Moreover,activated HSC may be an important source of these TIMPs in injured liver.We,therefore,quantified expression of rat interstitial collagens(MMP-13) in parallel with collagenase inhibitors TIMP-1 during recovery from hepatic fibrosis.In this study,an increase in procollagen-1,MMP13 and TIMP-1 mRNA expression was observed in rat liver homogenates of fibrosis model(treatment CCl₄12 w).After 8 wk spontaneous recovery,procollagen-1 and TIMP-1 mRNA expression significantly decreased.In contrast,MMP-13 mRNA expression remained at levels comparable to fibrosis model(treatment CCl₄12 w) and does not diminish in parallel with TIMP-1 throughout 4 wk recovery.Our date indicated that apoptosis of HSC not only eliminates the major source of collagen,but also the major source of TIMP-1,the inhibitor of matrix degradation.That leads to increased activity of MMP-13 interstitial collagenase, which is the primary mechanism of fibrosis resolution.2.Investigation TRAIL-elicited signal transductions pathway in HSC during recovery from hepatic fibrosis.Tumor necrosis factor related apoptosis-inducing ligand(TRAIL) was identified on the basis of sequence homology to other members of the TNF family.Currently,five TRAIL receptors belonging to the TNF-a receptor superfamily have been identified. Two of them,TRAIL-R1/DR4 and TRAIL-R2/DR5 contain death domains,signal apoptosis by using the adapter protein FADD,and induce apoptosis via a caspase-dependent process,whereas TRAIL-R3/DcR1 and TRAIL-R4/DcR2 act as putative decoy receptors and do not transmit the death signal.Furthermore, TRAIL-R1/DR4 and TRAIL-R2/DR5 were seldom expressed in surface of human hepatocytes.Accordingly,selective removal only activated and not quiescent HSC via TRAIL-induced apoptotic signaling would be a deal therapeutic approach to attenuate liver fibrosis.Western-blot andα-SMA and TRAIL-R2/DR5 iimmunofluorescence dual tained results shown that,compared with control,activated HSC expressed TRAIL-R1/DR4 and TRAIL-R2/DR5.Moreover,in the coculture system of KC and HSC of distinct period,apoptosis of HSC was mediated by KC through TRAIL and activated HSC may be more susceptible to apoptotic stimuli than their quiescent counterparts.Exogenous oligomerization TRAIL interfered with HSC shown that,during recovery from hepatic fibrosis,TRAIL through chondrosome channel to induced apoptosis of activated HSC.3.Investigation effect of Lef on TRAIL-elicited signal transductions pathway during recovery from hepatic fibrosisActivation and proliferation of hepatic stellate cells are central in the development and progression of hepatic fibrosis,whereas their removal by apoptosis may contribute to the termination of this response.In this study,A771726(0.01,0.1å’Œ1μmol/L), leflunomide's metabolite,significantly increased apoptosis of HSC during recovery from hepatic fibrosis.Further research demonstrated that,A771726 could induce apoptosis of HSC in recovery,and the mechanism is by downregulation of c-FLIP and RIP,activation of apoptosis death receptor pathway,upregulation of Bid and amplification of the mitochondrial pathway.Collectively,priming apoptosis were novel insight into the mechanisms by which Lef may exert in hepatic fibrosis. metalloproteinase;cytokine;apoptosis;tumor necrosis factor-related apoptosis-inducing ligand;tumor necrosis factor-related apoptosis-inducing ligand receptor;leflunomide; A771726...