Nevertheless, the liver finally regenerated, albeit with a strong delay (Wang et al,2009)

Nevertheless, the liver finally regenerated, albeit with a strong delay (Wang et al,2009). == Transforming growth factor (TGF-) == The three types of TGF- SB-423557 that exist in mammals (TGF-13) exert their functions through activation of heteromeric receptor complexes consisting of type I and type II transmembrane receptors (Moustakas & Heldin,2009). signalling targets in liver regeneration. This review summarizes the results obtained by functional studies that have resolved the functions and mechanisms of action of growth factors and cytokines in liver regeneration after acute injury to this organ. Keywords:apoptosis, growth factor, hepatectomy, liver regeneration, proliferation == INTRODUCTION == The liver plays a central role in the regulation of whole body metabolism as well as in compound detoxification. Due to these essential functions, injuries to this organ need to be rapidly and efficiently repaired. Various types of insults induce liver damage, such as cell loss caused by viruses, autoimmune diseases and toxins, including alcohol or commonly used anti-inflammatory, anti-convulsant or chemotherapeutic drugs as well as resection of liver tissue in patients with primary or metastatic liver tumours. Interestingly, the liver has a unique ability to fully regenerate and thus differs significantly Mouse monoclonal to CD4.CD4 is a co-receptor involved in immune response (co-receptor activity in binding to MHC class II molecules) and HIV infection (CD4 is primary receptor for HIV-1 surface glycoprotein gp120). CD4 regulates T-cell activation, T/B-cell adhesion, T-cell diferentiation, T-cell selection and signal transduction from other SB-423557 organs, which heal with a scar (Fausto et al,2006; Michalopoulos,2007). However, the regenerative capacity is insufficient after chronic injury as observed in chronic viral hepatitis or after long-term alcohol abuse, for example. These conditions often cause liver cirrhosis, which is characterized by the replacement of functional epithelial tissue by non-functional connective tissue. In the worst case, liver failure can occur. Although an enormous part of the global populace is affected by these conditions, therapeutic options are still unsatisfactory and are mainly supportive. Therefore, the development of specific therapies to enhance the regenerative capacity of the SB-423557 liver is essential for the improvement of human health. This requires a thorough understanding of the mechanisms underlying liver regeneration and the identification of factors orchestrating this process. A particularly useful model to study liver regeneration in mice and rats is usually partial hepatectomy (PH), in which the large and median lobes of the liver, which comprise approximately two-thirds of the organ, are surgically removed (Fig 1B). As a consequence, the normally quiescent and highly differentiated liver cells (Fig 1A) proliferate (Fig 1C and D) and the original liver mass is usually restored within a few days (approximately 10 days in rodents) by growth of the remaining liver tissue. Most importantly, normal liver regeneration is not accompanied by massive inflammation or necrosis and thus does not induce a fibrotic response. Hepatocytes are the first to enter the cell cycle and undergo one to two rounds of cell division within 23 days. They initially receive signals to exit from G0and to initiate the expression of a set of genes required for regeneration. Subsequently, hepatocytes progress through the cell cycle and undergo mitosis. This is followed by the proliferation of hepatic stellate cells, Kupffer cells and biliary epithelial cells. Furthermore, proliferation of endothelial cells and sprouting angiogenesis occur to re-establish the liver vasculature (Michalopoulos,2007). == Physique 1. The different cell types of the liver and liver regeneration after partial hepatectomy (PH). == The activation, proliferation, migration, differentiation and survival of cells in the regenerating liver are controlled by a large number SB-423557 of growth factors and cytokines that are expressed at the site of injury or reach the liver via the circulatory system. However, the functions of endogenous growth factors in the regenerative process of the liver have been only partially elucidated and their proposed functions are frequently based on descriptive expression studies and/or results from cell culture assays. The development of genetically altered mice that overexpress or have functional loss of growth factors, cytokines or their receptors and their use for liver regeneration studies has provided exciting and often unexpected results. In this review, we summarize thein vivofunctions of cytokines and growth factors in liver regeneration reported so far. Because there are numerous reviews on liver fibrosis, we focus on the normal regeneration process, which is seen after PH. == Glossary == == Complement component 5a == A protein fragment released from complement component 5, which can act as a pro-inflammatory cytokine. The function is usually mediated by the C5a receptor, a member of the G-protein coupled receptor family. == Hepatic stellate cells == Specialized pericytes that line the walls of liver sinusoids. == Hepatocytes == The liver parenchymal cellsspecialized epithelial cells, which carry out most of the functions of the liver, including metabolism and detoxification. == Kupffer cells == Phagocytic cells of the liver that are considered as resident macrophages of this organ. == Lipopolysaccharide (LPS) == A major component of the cell wall of SB-423557 Gram-negative bacteria; LPSs are endotoxins and important antigens. == MyD88.