[Role of rapamycin in cholangiocytes regeneration after liver transplantation]

To investigate the role of IL-6/STAT3 pathway in the proliferation of cholangiocytes after liver transplantation and determine whether or not rapamycin (RPM) depresses the regeneration of cholangiocytes by blocking the activation of STAT3.

Rats were randomized into OLT-1 h and OLT-12 h groups (supplied livers preserved for 1 or 12 h), anti-sIL-6R group (rats of the OLT-12 h group injected intravenously with 16.7 µg/kg anti-rat sIL-6R antibody at 1 hour pre-operation and daily post-operation), RPM group (rats of the OLT-12 h group injected intraperitoneally with 0.05 mg/kg RPM for 3 days pre-operation and daily post-operation) and sham group (transverse laparotomy and closure without liver manipulation). At 1, 3, 7, 14 d post-operation, the IL-6 concentration in liver homogenate and cholangiocytes proliferation were detected by ELISA (enzyme linked immunosorbent assay) and histochemistry respectively. The expressions of IL-6 mRNA, phosphorylated-STAT3 and cyclin D1 protein in cholangiocytes were determined by real-time RT-PCR (reverse transcription-polymerase chain reaction) or Western blot. The DNA binding activity of STAT3 was determined by electrophoretic mobility shift assay. The serum concentrations of ALP (alkaline phosphatase) and GGT (γ-glutamyltransferase) were also measured.

The minimal expressions of IL-6, p-STAT3, cyclin D1 and DNA binding activity of STAT3 were detected in OLT-1h group. And a slight increase of IOD (integral optical density) ratio (38 ± 10 and 22 ± 7) indicated a mild cholangiocytes proliferation. The concentrations of GGT were (69 ± 6) U/L, (34 ± 4) U/L and ALP (86 ± 9) U/L, (45 ± 3) U/L. The expression of IL-6 in liver homogenate were (273 ± 20) ng/g, (159 ± 18) ng/g and 0.40 ± 0.04, 0.23 ± 0.04 in cholangiocytes. The expressions of P-STAT3 were 0.420 ± 0.023 and 0.230 ± 0.040 in cholangiocytes and cyclin D1 0.580 ± 0.023 and 0.420 ± 0.015 respectively. Cholangiocytes responded to extended cold preservation with severe bile duct injures and marked increases in IL-6 secretion, p-STAT3 and cyclin D1 protein expression and DNA binding activity of STAT3, followed by compensatory cholangiocytes regeneration. Meanwhile biochemical index and morphology indicated that bile duct injury recovered at 14 d post-operation. The IOD ratios were 38 ± 10 and 22 ± 7 respectively. The expressions of IL-6 were (659 ± 28) and (446 ± 23) ng/g in liver homogenate and 0.73 ± 0.06 and 0.54 ± 0.04 in cholangiocytes. The expression of P-STAT3 were 0.72 ± 0.04 and 0.58 ± 0.06 in cholangiocytes and cyclin D1 0.88 ± 0.04 and 0.74 ± 0.07 respectively. However, anti-sIL-6R inhibited the cholangiocytes proliferation and reduced the expressions of IL-6, STAT3 and cyclin D1. The DNA binding activity of STAT3 with cellular injury and the increases of serum ALP or GGT were also abrogated by the administration of anti-sIL-6R. With similar results, the RPM treatment had insignificant effects on the expression of IL-6.

The IL-6/STAT3 pathway initiates the cholangiocytes regeneration after liver transplantation so as to accelerate the biliary recovery. However RPM represses the cholangiocytes regeneration by inhibiting the STAT3 activation. It may have a negative effect on the healing and recovery of bile ducts in grafts with extended cold preservation.