Cathepsin B inactivation attenuates hepatic apoptosis and fibrosis during cholestasis

Hepatocyte apoptosis and liver fibrosis are key teamres of cholestatic liver injury. Emerging data implicate a lysosolnal, cathepsin B-dependent pathway of apoptosis in bepatocytes. In this pathway, catbepsin B is released from lysosomes and tuggers mitochondrial dyshmction l%wever, the contribution of this pathway to hver injury and the relationship ot apoptosis to fibrosis remains unclear. Our Aim was to ascertain if inactivation of cathepsin B attenuates hvcr injury and fibrogenesis dunng extrahepatic cholestasis METHODS: Wild type (catB *s ~), cathepsin B-deticient (knockout) (catB~); and R 3032 (a catbepsin B inhibitor) treated catB */* mice undement bile duct ligation, Liver injury was examined by quantitating hepatocyte apopmsis with the TUNEL assay and determining serum ALT values, mRNA expression iur markers of stellate cell activation, a4MA, and fibrogenic actiwty, TGF-b and collagen I, was quantitated using real time PCR technolo~'. Liver fibrosis was assessed by digital image analysis ot Sirras red stained sections RESULTS: TUNEL positive hepamcytes and serum Allvalues were significandy reduced in cattY: and R 3032-treated catB +j+ 3-day BDL mice vs, catB +~ BDL mice, Consistent with these observations, mitochondrial cytochn)me c release, a marker for the mitochondrial pathway of apoptosis, was reduced in catB e and in R 3032-treated catB++ compared to catB ++ BDL mice, Stellate cell activation, as assessed by a-SMA was 14.0-fold greater in catB j+ vs catB v and 3-fold greater than in R 3032treated cazB +j+ BDL mice. Collagen al(I) was 102-told greater in catB ~+ vs. catB / BDL mice and 76-told greater in catB ~ ~ vs R 3032-treated ca~B +~ BDL mice. Serum bile acid and bilimbin values were mrtually identical in nil three experimental groups indicating that the above diliFrences could not be ascribed to difterences in cholestasis. Finally, in 2 week BDL mice, Sirius red staining for hepatic collagen deposition was significantly reduced in catB ~ mice compared to wdd type animals In CONCLUSION these findings not only support a prminnent tom tor the lysosomal pathway of apoptosis in cholestatic liver injury, but also link hepatocyte apoptosis to liver fibrogenesis These observations suggest cathepsin B inactivation or inhibition may be a therapeutic antifibrogenic strategy in cholestatic liver diseases.