Objective To examine the collagen fiber mRNA expression in rat lung tissue exposed to silica dust impacted by 3-methyladenine (3-MA).

Methods Eighty healthy male rats were developed silicosis and randomly divided into a silicosis control group and a 3-MA group. The 3-MA group received intraperitoneal injection of 1.5 mg/(kg·d) 3-MA every other day for 28 days. Rats were executed at different time points to observe pathologic changes of rat lung tissue by HE staining and to measure the mRNA levels of hydroxyproline, collagen type Ⅰ fiber, and collagen type Ⅲ fiber.

Results By HE staining, the degree of lung fibrosis in the 3-MA group was lighter than that of the control group in every selected time point. The lung tissue samples showed different fibrosis degrees along with prolonged dust exposure. The hydroxyproline levels in the 3-MA group at 7 d (0.39±0.02), 14 d (0.43±0.01), 28 d (0.36±0.02), 60 d (0.34±0.04) and 90 d (0.49±0.03) were lower than those in the control group at corresponding time points (0.41±0.03, 0.48±0.01, 0.49±0.02, 0.60±03.02, 0.73±0.03) (P < 0.05), and the difference among different time points was statistically significant (F=55.99, P < 0.05). The collagen type Ⅰ fiber mRNA level of the 3-MA group at 7 d (1.11±0.30) was higher than that of the control group (0.83±0.13), and except of 28 d, the levels at other time points (14 d: 0.70±0.23, 60 d: 0.92±0.08, 90 d: 1.38±0.37) were lower than those of the control group (14 d: 1.06±0.16, 60 d: 1.10±0.25, 90 d: 2.06±0.66) (P < 0.05), the statistical differences among different time points in same group were identified (H=23.36, P < 0.05). The collagen type Ⅲ fiber mRNA level of the 3-MA group was (0.77±0.19) at 7 d, declined at 14 d (0.44±0.26), 28 d (0.35±0.09), and 60 d (0.31±0.06), and rose again at 90 d (1.44±0.31), showing significant differences among time points in same group (H=28.77, P < 0.05); moreover, the collagen typeⅢfiber mRNA levels of the 3-MA group were lower than those of the control group at each time point (7 d: 0.83±0.13, 14 d: 1.06±0.16, 28 d: 0.98±0.11, 60 d: 1.10±0.25, 90 d: 2.06±0.67) (P < 0.05).

Conclusion After the intervention of 3-MA, the collagen fiber mRNA expression levels are different compared with the control group at the same time point or the same group at different time points. It can be concluded that 3-MA may affect the development of silicosis fibrosis in rats.