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1 Department of Medicine,
Activated, but
not quiescent, hepatic stellate cells (lipocytes) have a high level of
collagen type I and smooth muscle actin (SMA) gene expression.
Therefore, stellate cell activation is a critical step in hepatic
fibrosis. The mechanisms leading to stellate cell activation in vivo
are unknown. The characteristic hepatic oxidative stress cascade
induced in rats by CCl4 markedly stimulated stellate cell entry into S phase, nuclear factor (NF)-
B activity, and c-myb expression. These
changes were prevented by pentoxifylline, which also decreased
CCl4-induced hepatic injury. As
expected, cAMP-mediated phosphorylation of
CREB-Ser133 was induced in vivo in
stellate cells by pentoxifylline but not by its metabolite 5, an
N-1 carboxypropyl derivative, which
lacks phosphodiesterase inhibitory activity. Stellate cell nuclear
extracts from CCl4-treated, but
not from control, animals formed a complex with the critical promoter E
box of the
-SMA gene, which was disrupted by
c-myb antibodies and competed with by
c-myb cognate DNA. Treatment with
pentoxifylline or metabolite 5 prevented the molecular abnormalities
characteristic of stellate cell activation induced by
CCl4. These results suggest that
induction of c-myb plays an important
role in the in vivo activation of stellate cells. Pentoxifylline blocks
stellate cell activation in vivo independently of its inhibitory
effects on phosphodiesterases by interfering with the oxidative stress
cascade and the activation of NF-
B and
c-myb.
CREB phosphorylation; liver fibrogenesis; c-myb expression
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