PH triggers activation of the immediate early genes (i.e., genes that are rapidly, but transiently, activated) within approximately the first 4 hours,1 and

thereby hepatocytes reenter the cell-division cycle. Immediate early genes encode proteins that regulate later phases in G1 and play an important role in cell growth in the regenerating liver.1, 2 The process of liver www.selleckchem.com/products/azd9291.html regeneration after hepatectomy is coordinated by both pro- and antiproliferative factors. Transforming growth factor-beta1 (TGF-β1) is a potent inhibitor of mitogen-stimulated DNA synthesis in cultured hepatocytes.3 Therefore, it has been thought that TGF-β1 is a potent candidate to limit or stop liver regeneration after PH hepatectomy.4 Because TGF-β is synthesized and secreted as a latent complex, the important step in regulating its biological activity is the conversion of the latent www.selleckchem.com/autophagy.html form into the active one. However, the contribution of TGF-β to the liver’s regenerative response after PH hepatectomy is still poorly understood. TGF-β1 messenger RNA

(mRNA) induction occurs within 4 hours, and levels of TGF-β1 remain elevated until 72 hours after PH hepatectomy.5, 6 In sharp contrast, in the model of complete lack of TGF-β signaling using hepatocyte-specific TGF-β type II receptor knockout

mice, the lack of TGF-β signaling does not result in prolonged hepatocyte proliferation; rather, only transiently up-regulated proliferation of hepatocytes is shown in the later phase after hepatectomy, with a peak at ∼36 hours.7 These Wilson disease protein differences raise an open question about whether locally activated TGF-β1 is indeed essential for the inhibition of hepatocyte proliferation in vivo. Furthermore, the time course of locally activated TGF-β1 and its activation mechanism after PH hepatectomy still remain largely unknown. The matricellular protein, thrombospondin-1 (TSP-1), was first shown as a component of the α-granule in platelets and can act as a major activator of latent TGF-β1.8, 9 TSP-1 is induced in response to tissue damage or stress and plays a role as a transient component of extracellular matrix during tissue repair.8, 10, 11 However, the roles of TSP-1 and of TSP-1/TGF-β1 interdependence during liver regeneration have not yet been addressed. We hypothesize that the initiation of local TGF-β activation occurs much earlier after PH hepatectomy, and TSP-1 plays a critical role in this process. Here, using a TSP-1-deficient mouse model, we investigated whether TSP-1 would be a suitable molecular target for accelerating liver regeneration after PH.