Objective: To study the transformation characteristics of tight junction of microvessel endothelial cells in bleomycin (BLM) induced pulmonary fibrosis (PF), and the effects of vascular endothelial growth factor (VEGF) on mononuclear chemotaxis protein-1 (MCP-1) mRNA expression in pulmonary microvessel endothelial cells (EC).
Methods: Forty healthy rats were equally divided into a control and an experimental group in random. In the experimental group, PF were induced by BLM application. In each group, 10 rats were instilled by lanthanum sal at 3, 7, 14 and 28 d after BLM application, and lung samples were made and observed by transmission electron microscopy. The pulmonary microvessel EC of the other 10 rats in each group were preserved by tissue culture methods at the same time, and the cells were transfected with sense VEGF cDNA, and then MCP-1 mRNA expression was detected by reverse transcriptase-polymerase chain reaction (RT-PCR) technique.
Results: Blood vessel endothelial cells of the control group were intact. The basement membrane was shown as a continuous line. Granules of lanthanum sal did not cross the tight junction of endothelial cells. The width of the junction gap in rats of the experimental group treated at different times was increased and lanthanum particles of high density were seen in the gap junction, particularly on day 3, and were distributed in the area of subendothelium. The MCP-1 mRNA expression in VEGF transfected microvessel EC was significantly higher than that of the control group (1.21 +/- 0.22 vs 0.36 +/- 0.06, P < 0.05).
Conclusion: In BLM induced PF, the opening of the tight junction of EC, and the high expression of MCP-1 induce inflammatory cell infiltration and cytokine over-secretion, which in turn enhances proliferation of fibroblasts, one of the important factors underlying lung fibrosis.