Distinct dedifferentiation processes affect caveolin-1 expression in hepatocytes
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RESEARCH
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Distinct dedifferentiation processes affect caveolin-1 expression in hepatocytes Christoph Meyer1, Johanna Dzieran1, Yan Liu1,2, Felizitas Schindler1, Stefan Munker1, Alexandra Müller1, Cédric Coulouarn3 and Steven Dooley1*
Abstract Background: Dedifferentiation and loss of hepatocyte polarity during primary culture of hepatocytes are major drawbacks for metabolic analyses. As a prominent profibrotic cytokine and potent inducer of epithelial mesenchymal transition (EMT), TGF-β contributes to these processes in liver epithelial cells. Yet, a distinction between culture dependent and TGF-β driven hepatocyte dedifferentiation has not been shown to date. Results: Here, we show that in both settings, mesenchymal markers are induced. However, upregulation of Snai1 and downregulation of E-Cadherin are restricted to TGF-β effects, neglecting a full EMT of culture dependent hepatocyte dedifferentiation. Mechanistically, the latter is mediated via FAK/Src/ERK/AKT pathways leading to the induction of the oncogene caveolin-1 (Cav1). Cav1 was recently proposed as a new EMT marker, but our results demonstrate Cav1 is not up-regulated in TGF-β mediated hepatocyte EMT, thus limiting validity of its use for this purpose. Importantly, marking differences on Cav1 expression exist in HCC cell lines. Whereas well differentiated HCC cell lines exhibit low and inducible Cav1 protein levels - by TGF-β in a FAK/Src dependent manner, poorly differentiated cell lines display high Cav1 expression levels which are not further modulated by TGF-β. Conclusions: This study draws a detailed distinction between intrinsic and TGF-β mediated hepatocyte dedifferentiation and elucidates cellular pathways involved. Additionally, by evaluating the regulation of the oncogene Cav1, we provide evidence to argue against Cav1 as a reliable EMT marker.
Background Primary cultures of human or rodent hepatocytes are of particular value for investigating drug metabolism and toxicity. However, basic functional hepatocyte features such as bile canaliculi formation, bile secretion, polarity and metabolic activities (including detoxification by Cyp and other drug-metabolizing enzymes) are rapidly lost during culture on a collagen layer (monolayer or 2D culture). To overcome these limitations, alternative hepatocyte culture systems have been developed, including co-culture systems, bioreactors and 3D systems, where hepatocytes are embedded in a soft collagen matrix [1,2]. However, hepatocyte culture on a single stiff collagen surface possesses interesting features for researchers. Indeed, monolayer culture of primary hepatocytes offers * Correspondence: [email protected] 1 Department of Medicine II, Section Molecular Hepatology, Medical Faculty Mannheim, Heidelberg University, Mannheim, Germany Full list of author information is available at the end of the article
an astonishing view on cell plasticity, and allows delineation of pathways regulating hepatocyte polarity and homeostasis [3]. Even though hepatocyte dedifferenti
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