Roles of TNF-α in ductular metaplasia of hepatocytes

有证据表明，成熟肝细胞可以在体内和体外转分化为胆管细胞，尽管其机制尚不清楚。我们研究了库普弗细胞产生的细胞因子是否会影响三维培养系统中肝细胞的表型。本文报道肿瘤坏死因子α（TNF-α）是一种强烈诱导肝细胞胆管分化的细胞因子。将大鼠肝细胞的球状聚集体包埋在I型胶原凝胶基质中，并在各种细胞因子的存在下培养。其中TNF-α抑制白蛋白表达，而增加细胞角蛋白19（CK 19）和生精免疫球蛋白超家族（SgIGSF）的表达。在TNF-α存在下2至3周后，肝细胞球状体转化为由CK 19阳性细胞组成的广泛分支的管状结构。这些细胞对分泌素的反应是分泌增加，并表达功能性胆管标记物。TNF-α诱导Jun N-末端激酶（JNK）和c-Jun磷酸化，JNK抑制剂可抑制形态发生。当这些导管细胞通过胶原酶消化从凝胶中回收并在Matrigel上培养时，它们逐渐恢复肝细胞表型。我们的研究结果表明，TNF-α通过JNK-c-Jun途径促进肝细胞的小管分化，并且这种转分化至少部分可逆。

There have been several lines of evidence showing that mature hepatocytes can transdifferentiate into bile ductular cells both in vivo and in vitro, although the mechanism is unclear. We examined whether cytokines produced by Kupffer cells affected the phenotype of hepatocytes in a three-dimensional culture system. Here, we report that tumor necrosis factor α (TNF-α) is a cytokine which strongly induces bile ductular differentiation of hepatocytes. Spheroidal aggregates of rat hepatocytes were embedded within a type I collagen gel matrix and cultured in the presence of various cytokines. Among those tested, TNF-α inhibited albumin expression, while enhanced the expression of cytokeratin 19 (CK19) and spermatogenic immunoglobulin superfamily (SgIGSF). After 2 to 3 weeks in the presence of TNF-α, hepatocytic spheroids were transformed into extensively branching tubular structures composed of CK19-positive cells. These cells responded to secretin with an increased secretion and expressed functional bile duct markers. TNF-α induced phosphorylation of Jun N-terminal kinase (JNK) and c-Jun, and the morphogenesis was inhibited by a JNK inhibitor. When these ductular cells were retrieved from gels by collagenase digestion and cultured on Matrigel, they gradually recovered hepatocytic phenotype. Our results suggest that TNF-α promote ductular differentiation of hepatocytes via the JNK-c-Jun pathway and that the transdifferentiation is at least partly reversible.