Dynamic Variation of RAS on Silicotic Fibrosis Pathogenesis in Rats

The dynamic variation of renin-angiotensin system (RAS) in silicosis remains unclear. Seventy Wistar rats were divided into 7 groups including control group, silicosis groups (inhaling SiO2 for 2, 4, 8, 16 and 24 weeks, respectively) and Captopril (Cap) group. Rat lung primary fibroblasts were divided into control group, SiO2-stimulated group (0, 0.5, 1, 3, 6, 12, 24 and 48 h) and Cap group. The silicotic nodules were formed and collagens were deposited gradually in silicosis group observed by haematoxylin and eosin (HE) staining and Van Gieson (VG) staining. Cap relieved the lung fibrosis and collagen deposition. Immunohistochemistry indicated the positive expression of alpha-smooth muscle actin (alpha-SMA) was increased gradually in silicotic rat lung tissue. Western blotting revealed the expression of collagen type I (Col I) and alpha-SMA was up-regulated in silicotic rat lung tissue and fibroblasts stimulated by SiO2. Cap decreased the expression of Col I and alpha-SMA in silicotic rat lung tissue and fibroblasts stimulated by SiO2. Western blotting also demonstrated the expression of angiotensin-converting enzyme (ACE) and angiotensin II type 1 receptor (AT1) was increased, and the expression of ACE2 and Mas was decreased gradually in silicotic rat lung tissue and fibroblasts stimulated by SiO2. ELISA showed the serum levels of ACE and angiotensin II (Ang II) were also increased and ACE2 and Ang (1-7) were decreased in the silicosis group. Treatment with Cap decreased the expression levels of ACE, Ang II and AT1, and increased the expression levels of ACE2, Ang (1-7) and Mas. These findings suggested that an imbalance between ACE-Ang II-AT1 axis and ACE2-Ang (1-7)-Mas axis may participate in the development of silicosis.