As the genes encoding enzymes adjacent in the network are not regulated in this way, the only conclusive explanation is that the re-formation of phospholipids that depend on sphingosine kinase, such as sphingomyelin and the various ceramides, is enhanced by TGFβ. It has been found that Vanin (Vnn1), besides the enzymatic function as pantetheinases, plays a role in inflammation, Inhibitors,research,lifescience,medical oxidative stress, cell migration, and numerous diseases [33]. Vanin is strongly up-regulated in the control culture and the effect is attenuated by TGFβ. 2.13. Endogenous TGFβ Production It has been noted that hepatocytes in monolayer culture start to produce TGFβ [10].

Indeed, the RNA encoding TGFβ1 increases threefold in Inhibitors,research,lifescience,medical the control experiment, see Figure 8B. Thus, even in the control TGFβ is not completely absent. Interestingly, in TGFβ treated group, there is an even larger increase in endogenous TGFβ production, which additionally

accelerates the effects sensitive to TGFβ. Furthermore, the expression of the main TGFβ receptor Tgfbr1, while constantly low in the control experiment, increases dramatically in TGFβ treated hepatocytes. Thus, in TGFβ Inhibitors,research,lifescience,medical treated hepatocytes, an amplified effect of TGFβ is observed. The other TGFβ form, TGFβ2, the alternative receptor Tgfbr2, and the associated protein Tgfbrap1 are relatively constant throughout both culture conditions. 3. Discussion As the metabolism of primary hepatocytes changes during culture even without the addition of TGFβ, the question arises as for which conclusions can be drawn from TGFβ treated cultures for hepatocytes in vivo. It must be assumed that changes induced by TGFβ are

independent from the changes induced by culture stress, Inhibitors,research,lifescience,medical at least regarding metabolic liver functions. Endogenous production of TGFβ in the control culture is taken into account in Section 2.13. Consequently, the main problem is to distinguish whether the TGFβ treatment just leads to an acceleration of processes that would Inhibitors,research,lifescience,medical have occurred later in the control or whether there is a specific regulation that would not have occurred. To GPX6 account for this, the findings in the results section have been related to studies of metabolic functions in hepatocytes and also other cell types. Although fetal calf serum is provided for 3 hours directly after extraction from mouse liver to medical facilitate the survival from extraction stress, in the presented course of the experiment a serum-free medium is used [4]. Apparently, this condition differs from the in vivo state where the hepatocyte is confronted with a constantly changing metabolic load. It is commonly accepted that each metabolic challenge of hepatocytes in vivo stimulates a response of transcription, while a lack of new responses leads to a gradual loss of enzymatic capacity by protein degradation [34].