Abstract: BACKGROUND: Studies have shown that exosomes can improve hypoxic pulmonary hypertension. There are significant differences in the function of exosomes from different sources and different environments. The effect of hypoxic preconditioning with umbilical cord mesenchymal stem cell-derived exosomes on the proliferation of rat pulmonary artery smooth muscle cells is unclear.  
OBJECTIVE: To explore the effects of umbilical cord mesenchymal stem cell-derived exosomes pretreated with hypoxia on the hypoxia-induced proliferation of rat pulmonary artery smooth muscle cells.
METHODS: Primary human umbilical cord mesenchymal stem cells were isolated and cultured by tissue adhesion method, and the exosomes of human umbilical cord mesenchymal stem cells were extracted by ultrafiltration. Rat pulmonary artery smooth muscle cells were isolated by tissue digestion. The inhibition rate of cell proliferation after the intervention of exosomes with different concentrations was measured by cell counting kit-8 assay to determine the appropriate mass concentration and intervention time for the action of exosomes. Passage 3 pulmonary artery smooth muscle cells were divided into normoxic control group, hypoxic control group, hypoxic+normoxic exosome group and hypoxic+hypoxic exosome group. 5-Ethynyl-2'-deoxyuridine method was used to detect the proliferation of cells in each group. The expression level of nuclear proliferation antigen protein was detected by western blot assay.  
RESULTS AND CONCLUSION: (1) Compared with the normoxic control group, the proliferation of pulmonary artery smooth muscle cells in the hypoxic control group was significantly increased. Compared with the hypoxic control group, the cell proliferation ability of the hypoxic+normoxic exosome group decreased, and the proliferation ability of the hypoxic+hypoxic exosome group decreased more significantly. (2) Compared with the normoxic control group, the expression level of nuclear proliferation antigen protein was increased in the hypoxic control group. Compared with the hypoxic control group, the expression level of nuclear proliferation antigen protein was slightly reduced in the hypoxic+normoxic exosome group. The expression level of nuclear proliferation antigen protein was significantly diminished in the hypoxic+hypoxic exosome group. (3) The results showed that the exosomes derived from human umbilical cord mesenchymal stem cells pretreated with hypoxia had the ability to inhibit the proliferation of pulmonary artery smooth muscle cells.

Key words: hypoxic preconditioning, pulmonary artery smooth muscle cell, human umbilical cord mesenchymal stem cell, cell proliferation, exosome