Early alteration in TGF-β mRNA expression in irradiated rat liver

Abstract

Purpose: Radiation of the liver results in hepatic fibrosis as a late complication. TGF-β has been implicated in the pathogenesis of fibrosis. The purpose of this study was to determine if there is early alteration in TGF-β expression before hepatic fibrosis is evident. Methods and Materials: Male Sprague-Dawley rats weighing 150–175 g were used. A partial volume of liver as large as a 2 cm × 1 cm rectangle was given a single dose of 25 Gy gamma radiation. Animals were sequentially sacrificed from day 0 to day 28. Appearance of hepatic fibrosis was tested by trichrome stain. Levels of mRNA expression of TGF-β1 and TGF-β3 were measured by Northern blot hybridization. Change in the level of mRNA expression was analyzed by densitometry. The expression of TGF-βs was also analyzed in tissue with immunohistochemical staining. Results: In trichrome-stained liver tissues obtained through 28 days after irradiation, there was no evidence of hepatic fibrosis. The expression of mRNAs of TGF-β1 and TGF-β3 showed different features; The level of TGF-β1 mRNA showed a gradual increase to the peak level of 3.6-fold at day 28, the last analyzed time. In contrast, TGF-β3 mRNA showed an early peak of 4.8-fold at day 7 followed by a decrease to the lowest level of 1.6-fold at the last analyzed time. The expression of TGF-βs was also analyzed in tissue with immunohistochemical staining. At day 28 after radiation, increased positive staining for TGF-β1 was observed around the central vein. Positive staining appeared mainly in nonhepatocytic cells. For TGF-β3, the same pattern of positive staining was observed at day 7. Conclusion: The results of this study suggest that the alteration in mRNA expression of TGF-β1 and TGF-β3 occurs very early after radiation. The contrasting difference in the mRNA expression pattern of TGF-β1 and TGF-β3 suggests that interaction of the TGF-βs may be involved in fibrogenesis of irradiated liver, with TGF-β1 as a positive regulator and TGF-β3 as a negative regulator.