Liver regeneration (LR) is a process during which the liver recovers its mass and function after damage due to various causes such as partial hepatectomy (PH). It involves a sequence of well-orchestrated changes in physiological and biochemical activities, especially in the gene expression profile in a variety of liver cells. In order to produce reliable gene expression of target genes in eight kinds of rat hepatic cells during LR, the determination of internal control housekeeping genes (HKGs) is required. Eight kinds of hepatic cells were first isolated from liver tissue with high purity and activity. Then quantitative real-time reverse transcription (RT)-PCR was applied to detect expression changes of six commonly used HKGs (18SrRNA, B2M, ACTB, UBC, GAPDH, and HK1) in eight types of hepatic cells isolated from regenerating liver at 0, 2, 6, 12, 24, 30, 36, 72, 120, and 168 h after PH. The amplification of the HKGs was statistically analyzed by using geNorm algorithm. Using this method, 18SrRNA-UBC, ACTB-HK1, ACTB-GADPH, B2M-ACTB, 18SrRNA-UBC, B2M-UBC, B2M-ACTB, and B2M-UBC were found to be the two most stable reference genes for rat regenerating hepatocytes, hepatic stellate cells, Kupffer cells, biliary epithelial cells, sinusoidal endothelial cells, pit cells, dendritic cells, and oval cells, respectively, regardless of the stages of LR. In conclusion, this study has laid a good foundation for investigating gene expression of target genes in different types of hepatic cells during LR.

Liver regeneration after partial hepatectomy is a process with various types of cells involved. The role of Kupffer cells (KCs) in liver regeneration is still controversial. In this study we isolated KCs from regenerating liver and conducted cell-specific microarray analysis. The results demonstrated that the controversial role of KCs in liver regeneration could be explained with the expression patterns of TGF-α, IL-6, TNF, and possibly IL-18 during liver regeneration. IL-18 may play an important role in negative regulation of liver regeneration. The functional profiles of gene expression in KCs also indicated that KC signaling might play a negative role in cell proliferation: signaling genes were down regulated before cell division. Immune response genes in KCs were also down regulated during liver regeneration, demonstrating similar expression profiles to that of hepatocytes. The expression patterns of key genes in these functional categories were consistent with the temporal functional profiles.

Rat liver regeneration after partial hepatectomy (PH) is a good model to study the regulation of cell proliferation. We isolated hepatocytes from regenerating liver at different time points after PH and used microarray Rat Genome 230 2.0 chip to analyze the functional profiles of all up- or down-regulated genes manually and with automatic gene ontological tools. We found that the transcript expressions of PH and sham operation group were apparently different. For PH group, in the priming phase (2-12  h), signaling, transcription, response to stimulus genes predominated in up-regulated genes; in the proliferation phase (24-72 h), cell proliferation genes predominated; in the termination phase (120-168  h), differentiation and translation genes predominated; while metabolism genes predominated in the down-regulated genes at all time points (2-168  h). These functional profiles are consistent with the cellular and molecular phenomenon observed during liver regeneration, and can be closely connected with the biological process. Moreover, the results indicated that not only the quantity of specific genes but also the number of the genes in the specific functional category was regulated during liver regeneration, which means the number of similar genes in a specific functional category matters as well as the regulation of the genes. The changes of the number of the regulated cell proliferation genes and metabolism genes during liver regeneration were similar to the expression patterns of some cell division genes and metabolism genes.

Kazal-type serine protease inhibitor is one of the most important and widely distributed protease inhibitor families. Pancreatic secretory trypsin inhibitor (PSTI), also known as serine protease inhibitor Kazal type I(SPINK1), binds rapidly to trypsin, inhibits its activity and is likely to protect the pancreas from prematurely activated trypsinogen. Therefore, it is an important factor in the onset of pancreatitis. Recent studies found that PSTI/SPINK1 is also involved in self-regulation of acinar cell phagocytosis, proliferation and growth of a variety of cell lines. In addition, it takes part in the response to inflammatory factor or injury and is highly related to adult type II citrullinemia.

Rapidly proliferating tissue may require enhanced DNA repair capacity in order to avoid fixation of promutagenic DNA lesions to mutations. Partial hepatectomy (PH) triggers cell proliferation during liver regeneration (LR). However, little is known on how DNA repair genes change and how they are regulated at the transcriptional level during LR. In the present study, the Rat Genome 230 2.0 array was used to detect the expression profiles of DNA repair genes during LR, and differential expression of selected genes was confirmed by real-time RT-PCR. 69 DNA repair genes were found to be associated with LR, more than half of which distributed in a cluster characterized by a gradual increase at 24-72h and then returning to normal. The expression of base excision repair-and transcription-coupled repair-related genes was enhanced in the early and intermediate phases of LR, whereas the expression of genes related to HR, NHEJ and DNA cross-link repair, as well as DNA polymerases and related accessory factors, and editing or processing nucleases, were mainly enhanced in the intermediate phase. The expression changes of genes in DNA damage response were complicated throughout the whole LR. Our data also suggest that the expression of most DNA repair genes may be regulated by the cell cycle during LR.Key words: partial hepatectomy, rat genome array, DNA repair genes, liver regeneration. The liver has an outstanding capacity for regeneration (Taub, 2004). The process of hepatic cells initiating the cell cycle and proliferating rapidly, in order to compensate for lost liver tissues after rat partial hepatectomy (PH), is called liver regeneration (LR) (Lai et al., 2005;Suzuki and Tsukamoto, 2004). Injured liver cells and cell remnants caused by PH are harmful to the organism, while injured areas therefrom are susceptible to infection by antigens and xenobiotics, all possibly leading to inflammatory and immune responses (Shao et al., 2007;Zhang et al., 2006). Furthermore, carbohydrate, lipid, and protein and amino acid metabolisms are highly active, thereby providing nutrients or energy, especially for active DNA replication in LR (Fausto et al., 2006). As a result, a wider variety of endogenous damage produced by inflammation, normal metabolic byproducts (i.e. ROS) or replication errors, may constantly occur in LR.It is common knowledge that DNA repair processes counteract genetic damage and maintain genome integrity (Wood et al., 2001). Many researchers have discovered that inherited mutations affecting DNA repair genes are strongly associated with high cancer risks (Jass, 2006). Decreased DNA repair capacity may be an important factor predisposing to the development of preneoplastic lesions, neoplastic nodules and malignant tumors (Vielhauer et al., 2001). It is generally believed that rapidly proliferating tissue undergoing DNA synthesis may require enhanced DNA repair capacity, so as to avoid fixation of promutagenic DNA lesions to mutations (Kaufmann et al., 1991;Riis et al., 2002). While hepatic cell proliferation...