Enhanced liver fibrosis in ASMase−/− mice after CCl4 administration was ameliorated after CtsB inhibition. A–D, serum alanine transaminase (ALT) levels (A), CtsB activity (B), CtsD and α-SMA protein expression (C), and hydroxyproline levels in liver homogenate (D). E, α-SMA immunostaining of liver section at ×40 magnification. Data are mean ± S.E. (error bars), n = 6 animals/group. *, p ≤ 0.05 versus vehicle-treated mice; #, p ≤ 0.05 versus CCl4 ASMase−/−-treated mice.