| Background:Hepatic fibrosis(HF) is a wound-healing response to a variety of chronic stimuli.All types of liver cells and a variety of soluble factors are involved in the hepatic fibrosis progression and its mechanism is highly complex. The activation of hepatic stellate cell(HSC) is a key event in hepatic fibrosis. Activated HSC expresses alpha-smooth muscle actin(α-SMA) and produces increased amounts of extracellular matrix(ECM)components such as CollagenⅠ. Hepatic fibrosis is the result of the disequilibrium between synthesis and degradation of ECM components. The accumulation of the ECM is the main pathologic feature of hepatic fibrosis. In recent years, studies have shown that liver fibrosis and early liver cirrhosis are reversible.Phosphatase and tensin homolog deleted on chromosome ten(PTEN), the first tumor-suppressing gene, exhibited double phosphatase activity of both protein phosphatase and lipid phosphatase. In the previous studies, PTEN is involved in the development of tumor. Recent reports have implicated PTEN in liver fibrosis progression.Our group has devoted to the pathogenesis of hepatic fibrosis and has found that PTEN negatively regulates hepatic fibrosis in small animals. Then is PTEN involved in hepatic fibrosis progression in beagles? It has not been reported. Therefore, in this study we observe the expression of CollagenⅠ, α-SMA and PTEN in hepatic fibrosis induced by TAA in beagles.Objective:To observe the expression of PTEN in TAA-induced hepatic fibrosis and to explore whether PTEN is involved in hepatic fibrosis in beagles.Methods:Twelve healthy male beagles, eight-month-old, weighing(10 ± 1) kg, were randomly divided into control group(n=6) and TAA model group(n=6). Control beagles received only normal saline. In TAA model group beagles were given subcutaneous injection of TAA(12 mg/kg, two times per week lasting for twelve weeks). The same part of the liver tissue were obtained through 1.5% pentobarbital sodium anesthesia at twelve weeks. Liver sections were fixed in 10% neutral formalin and were embeded.Haematoxylin and eosin staining(H&E staining) and Masson’s trichrome staining were used to determine histopathology changes and fibrillar collagen. The expression ofα-SMA, CollagenⅠand PTEN was detected by immunohistochemical staining in liver tissues.Results:(1) The HE staining and Masson’s trichrome staining showed that hepatic cord structure was clear and cytoplasm was full in control group. Hepatic cells arranged radially around the central vein in control group. While in TAA model group hepatic cord structure disappeared, hepatic cells swelled, and fatty degeneration and necrosis were visible, accompanying a large number of inflammatory cells infiltration. The connective tissue proliferated leading to the destruction of normal structure in hepatic lobule.(2) Image analysis of Masson’s trichrome staining showed that the expression of collagen fibers was significantly increased in TAA model group compared to control group and the difference was statistically significant(1.23% ± 0.21% vs 6.47% ± 1.32%,P <0.01).(3) The results of the immunohistochernistry staining are as follows: ① In normal liver, α-SMA was occasionally detected in blood vessels wall, and the expression level was low. While in TAA model group, α-SMA expression was increased in the central vein, the fiber septa, portal area and hepatic sinusoid. It was brownish yellow. ② In normal liver, theexpression of CollagenⅠ was few in the central vein, blood vessels wall and bile duct in portal area, and in liver sinusoidal. The expression of CollagenⅠ was enhanced obviously in portal area, fiber septa and hepatic sinusoid in TAA model group.③Immunohistochemical examination of PTEN showed widespread staining of PTEN protein in the cytoplasm, and, to a lesser extent, in the nuclei; in TAA model group, PTEN relatively decreased in the portal area, the fibrous septa and around the bile duct.(4) Image analysis of immunohistochemical staining showed that the expression of CollagenⅠ and α-SMA in hepatic tissue of TAA model group were significantly increased compared with control group and the difference was statistically significant(CollagenⅠ: 2.11 ± 0.51 vs 0.12 ± 0.03, P <0.01; α-SMA : 2.35 ± 0.65 vs 0.32 ± 0.13,P <0.01), whereas the expression of PTEN was significantly decreased and the difference was statistically significant(5.16 ± 0.73 vs 0.30 ± 0.07, P <0.01).(5) We found a significant positive correlation between α-SMA and CollagenⅠexpression(r=0.79, P<0.01); there was also significant negative correlation between PTEN and α-SMA expression(r =-0.96, P<0.01).Conclusion:The expression of PTEN was down-regulated in hepatic fibrosis induced by TAA in beagles. PTEN may be involved in the development of hepatic fibrosis in large animals. |
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