| BackgroundLiver fibrosis is a key link of various chronic liver diseases developing to liver cirrhosis, but its mechanism of the development and progress is not very clear. In recent years it has been reported that mast cells play a direct or indirect role in the process of other tissue fibrosis, but the concrete mechanism was complex and not definitive. It is speculated that mast cells secret stimulating factors such as tryptase, which can activate protease activated receptor-2 (PAR-2) on the membrane of target cells to stimulate its synthesis of I type collagen. For mast cells take part in liver fibrosis, it is conferred that activation of PAR-2 has an important effect on liver fibrosis, which has not yet been proved.ObjectiveTo investigate the expression of PAR-2 in the rat model of liver fibrosis and its relationship with liver fibrosis. Methods and Materials1. Liver fibrosis was induced by subcutaneous injection of CCl4 twice per week for 12 weeks and rats were sacrificed at 2, 4, 8, 12 weeks.2. Liver tissues were stained by routine HE stain and Masson collagen stain to assess the degree of rat liver fibrosis. 3. Mast cells were displayed by toluidine blue stain and counted.4. The content of liver hydroxyproline was measured by the method of base hydrolyzate.5. The mRNA expression and the protein expression of PAR-2 in liver were detected by RT-PCR and immunohistochemistry at each time point, respectively.Results1. Live fibrosis aggravated gradually with the extension of model making. There was less than 1% of fibrosis areas in normal liver tissue, but there were about 5%, 11%, 16% , 25% at 2, 4, 8, 12 weeks in model groups respectively.2. In normal rat liver there was a few mast cells (2.533±0.952) distributing along the hepatic portal area, in the model groups the number of mast cells increased by degree (2weeks vs. control group, 9.080±0.540 vs. 2.533±0.952, P<0.05 ; 4weeks vs. 2weeks, 15.667±2.906 vs. 9.080±0.540, P<0.05; 8weeks vs. 4weeks, 32.040±3.278 vs. 15.667±2.906, P<0.05), and they distributed densely around the hepatic portal area and the central veins. In early phase mast cells distributed mostly in the hepatic portal area and along the fibrous gap in late phase. The cell bodies became larger and granules were released after 8 weeks.3. The content of liver hydroxyproline increased progressively from 0 weeks to 12 weeks post-injection.4. In normal liver PAR-2 mRNA was hardly detected, at 2 weeks there was a little expression of PAR-2 mRNA (PAR-2/β-actin 2weeks vs. control group, 0.148±0.013 vs. 0, P<0.05 ) , at 4 weeks its expression increased(PAR-2/β-actin 4weeks vs. 2weeks, 0.351±0.021 vs. 0.148±0.013, P<0.05)and it maintained at a high level after 8 weeks(PAR-2/β-actin 8weeks vs. 4weeks, 0.803±0.016 vs. 0.351±0.021, P<0.05).5. There was little expression of PAR-2 protein in normal liver, at 2 weeks expression of PAR-2 protein increased a little(positive signal greyscale 2 weeks vs. control group, 162.464±1.280 vs. 156.035±0.514, P<0.05), at 4 weeks its expression increased (positive signal greyscale 4weeks vs. 2weeks, 174.751±1.257 vs. 162.464±1.280, P<0.05)and it maintained at a high level after 8 weeks(positive signal greyscale 8weeks vs. 4weeks, 185.654±2.102 vs. 174.751±1.257, P<0.05).PAR-2 expressed mainly in HSC, vascular endothelial cell, fibroblast in the portal areas and etc.Conclusions1. Mast cells take part in the process of liver fibrosis.2. PAR-2 mRNA expression and the protein expression of PAR-2 were consistent with the increase of the mast cells and the content of liver hydroxyproline, which suggests that the activation of PAR-2 is associated with liver fibrosis.
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