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From the Thomas E. Starzl Transplantation
Institute*
and the Departments of
Pathology
and
Surgery,
Division of Transplantation,
University of Pittsburgh Medical Center, Pittsburgh; and the Graduate
School of Public Health,§
University of
Pittsburgh, Pittsburgh, Pennsylvania
Early chronic liver allograft rejection (CR) is characterized by distinctive cytological changes in biliary epithelial cells (BECs) that resemble cellular senescence, in vitro, and precede bile duct loss. If patients suffering from early CR are treated aggressively, the clinical and histopathological manifestations of CR can be completely reversed and bile duct loss can be prevented. We first tested whether the senescence-related p21WAF1/Cip1 protein is increased in BECs during early CR, and whether treatment reversed the expression. The percentage of p21+ BECs and the number of p21+ BECs per portal tract is significantly increased in early CR (26 ± 17% and 3.6 ± 3.1) compared to BECs in normal liver allograft biopsies or those with nonspecific changes (1 ± 1% and 0.1 ± 0.3; P < 0.0001 and P < 0.02), chronic hepatitis C (2 ± 3% and 0.7 ± 1; P < 0.0001 and P < 0.04) or obstructive cholangiopathy (7 ± 7% and 0.7 ± 0.6; P < 0.006 and P = 0.04). Successful treatment of early CR is associated with a decrease in the percentage of p21+ BECs and the number of p21+ BECs per portal tract. In vitro, nuclear p21WAF1/Cip1 expression is increased in large and multinucleated BECs, and is induced by transforming growth factor (TGF)-ß. TGF-ß1 also increases expression of TGF-ß receptor II, causes phosphorylation of SMAD-2 and nuclear translocation of p21WAF1/Cip1, which inhibits BEC growth. Because conversion from cyclosporine to tacrolimus is an effective treatment for early CR, we next tested whether these two immunosuppressive drugs directly influenced BEC growth in vitro. The results show that cyclosporine, but not tacrolimus, stimulates BEC TGF-ß1 production, which in turn, causes BEC mito-inhibition and up-regulation of nuclear p21WAF1/Cip1. In conclusion, expression of the senescence-related p21WAF1/Cip1 protein is increased in BECs during early CR and decreases with successful recovery. Replicative senescence accounts for the characteristic BEC cytological alterations used for the diagnosis of early CR and lack of a proliferative response to injury. The ability of cyclosporine to inhibit the growth of damaged BECs likely accounts for the relative duct sparing properties of tacrolimus.
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