Abstract: BACKGROUND: Pulmonary pericytes are located at the concavity where pulmonary vessels are interconnected, which is closely related to the formation and stability of pulmonary vascularization. However, there are few studies on how pulmonary pericytes affect the activity of pulmonary vascular endothelial cells in the pathogenesis of broncho-pulmonary dysplasia.
OBJECTIVE: To analyze the relationship between the quantity of subgroups of pulmonary pericytes and endothelial cells in different stages of broncho-pulmonary dysplasia and to explore the effects of PDGFR-β+NG2+α-SMA+ pericytes on the early tube-forming activity of pulmonary vascular endothelial cells.
METHODS: (1) Animal experiment: Twelve newborn C57BL/6 mice were randomly divided into normoxia and hyperoxia groups within 24 hours of birth, with six mice in each group. Mice in the hyperoxia group were exposed to an 85% O2 environment to build the mouse models of broncho-pulmonary dysplasia, while those in the normoxia group were fed in the same room air. The lung tissues of the mice in the two groups were taken at 7 and 14 days after birth. The pathological changes of the lung tissues were observed by hematoxylin-eosin staining. Three subgroups of pulmonary pericytes were measured by flow cytometry: PDGFR-β+NG2+α-SMA-, PDGFR-β+NG2+α-SMA+, and PDGFR-β+NG2-α-SMA+ cells. (2) Cellular experiment: Passage 3 PDGFR-β+NG2+α-SMA+ pericytes were co-cultured with mouse pulmonary vascular endothelial cells (experimental group) at a ratio of 1:4. Mouse pulmonary vascular endothelial cells cultured alone were used as controls. The tube-forming difference between two groups was analyzed after 15 hours of co-culture.
RESULT AND CONCLUSION: (1) Animal experiment: Hematoxylin-eosin staining revealed that on day 7, the lung tissue of mice in the normoxia group had regular structure, obvious alveolar structure, and uniform size, while the number of alveoli in the lung tissue of mice in the hyperoxia group was less and the morphology of alveoli was irregular. On day 14, the alveoli of mice in the normoxia group gradually developed and matured, the alveolar structure gradually became regular and uniform in size, and the alveolar density gradually increased. The lung tissue structure of mice in the hyperoxia group was relatively disordered and the alveolar formation was delayed with the size gradually increasing and the alveolar structure being simplified. Flow cytometry results indicated that the number of PDGFR-β+NG2-α-SMA+ and PDGFR-β+NG2+α-SMA+ pericytes was increased in the hypoxia group compared with the normoxia group (P < 0.01), while the number of PDGFR-β+NG2+α-SMA- pericytes and pulmonary vascular endothelial cells was decreased (P < 0.01, P < 0.04). (2) Cellular experiment: In the control group, the pulmonary vascular endothelial cells arranged in cords and extended around, and lumen-like structures formed in some areas. In the experimental group, PDGFR-β+NG2+α-SMA+ pericytes and their pseudopodia were not observed, the irregular grid structure of pulmonary vascular endothelial cells was significantly less than that of the control group, and the endothelial cells mainly clustered in clumps. To conclude, α-SMA+ pericyte subgroups are predominant in mice with broncho-pulmonary dysplasia. PDGFR-β+NG2+α-SMA+ pericytes can directly inhibit the tube-forming activity of pulmonary vascular endothelial cells, which may be involved in the process of abnormal vascularization in broncho-pulmonary dysplasia.

Key words: pulmonary pericyte, pulmonary vascular endothelial cell, lung development, tube formation, broncho-pulmonary dysplasia, animal experiment