Godoy Patricio, Hengstler Jan G, Ilkavets Iryna, Meyer Christoph, Bachmann Anastasia, Müller Alexandra, Tuschl Gregor, Mueller Stefan O, Dooley Steven
Molecular Alcohol Research in Gastroenterology, Department of Medicine II, Faculty of Medicine at Mannheim, University of Heidelberg, Germany.
Hepatology. 2009 Jun;49(6):2031-43. doi: 10.1002/hep.22880.
Hepatocytes in culture are a valuable tool to investigate mechanisms involved in the response of the liver to cytokines. However, it is well established that hepatocytes cultured on monolayers of dried stiff collagen dedifferentiate, losing specialized liver functions. In this study, we show that hepatocyte dedifferentiation is a reversible consequence of a specific signaling network constellation triggered by the extracellular matrix. A dried stiff collagen activates focal adhesion kinase (FAK) via Src, leading to activation of the Akt and extracellular signal-regulated kinase (ERK) 1/2 pathways. Akt causes resistance to transforming growth factor beta (TGF-beta)-induced apoptosis by antagonizing p38, whereas ERK1/2 signaling opens the route to epithelial-mesenchymal transition (EMT). Apoptosis resistance is reversible by inhibiting Akt or Src, and EMT can be abrogated by blocking the ERK1/2 pathway. In contrast to stiff collagen, a softer collagen gel does not activate FAK, keeping the hepatocytes in a state where they remain sensitive to TGF-beta-induced apoptosis and do not undergo EMT. In this culture system, inhibition of p38 as well as overexpression of constitutively active Akt causes apoptosis resistance, whereas constitutively active Ras induces EMT. Finally, we show that matrix-induced EMT is reversible by replating cells from dried stiff to soft gel collagen. Our results demonstrate that hepatocyte dedifferentiation in vitro is an active process driven by FAK-mediated Akt and ERK1/2 signaling. This leads to similar functional and morphological alterations as observed for regenerating hepatocytes in vivo and is reversible when Akt and/or ERK1/2 signaling pathways are antagonized.
Hepatocytes can exist in a differentiated and a dedifferentiated state that are reversible and can be switched by manipulating the responsible key factors of the signaling network.
培养的肝细胞是研究肝脏对细胞因子反应所涉及机制的宝贵工具。然而，众所周知，在干燥坚硬的胶原蛋白单层上培养的肝细胞会去分化，丧失专门的肝脏功能。在本研究中，我们表明肝细胞去分化是由细胞外基质触发的特定信号网络组合的可逆结果。干燥坚硬的胶原蛋白通过Src激活粘着斑激酶（FAK），导致Akt和细胞外信号调节激酶（ERK）1/2通路的激活。Akt通过拮抗p38导致对转化生长因子β（TGF-β）诱导的细胞凋亡产生抗性，而ERK1/2信号传导开启了上皮-间质转化（EMT）的途径。通过抑制Akt或Src可使细胞凋亡抗性逆转，并且通过阻断ERK1/2通路可消除EMT。与坚硬的胶原蛋白相反，较软的胶原蛋白凝胶不会激活FAK，使肝细胞保持对TGF-β诱导的细胞凋亡敏感且不会发生EMT的状态。在这种培养系统中，抑制p38以及组成型活性Akt的过表达会导致细胞凋亡抗性，而组成型活性Ras会诱导EMT。最后，我们表明通过将细胞从干燥坚硬的胶原蛋白重新接种到柔软的凝胶胶原蛋白上，基质诱导的EMT是可逆的。我们的结果表明，体外肝细胞去分化是由FAK介导的Akt和ERK1/2信号传导驱动的一个活跃过程。这导致了与体内再生肝细胞中观察到的类似的功能和形态改变，并且当Akt和/或ERK1/2信号通路被拮抗时是可逆的。
肝细胞可以存在于分化和去分化状态，这两种状态是可逆的，并且可以通过操纵信号网络的相关关键因素来切换。
