[Human umbilical mesenchymal stem cells-derived exosomes modulate the proliferation, apoptosis and migration of human retinal pigment epithelial cells in hypoxia]

Objective: To study the effects of human umbilical mesenchymal stem cells (HUMSCs) exosomes on the proliferation and apoptotic as well as migration of human retinal pigment epithelial cells (HRPE) in hypoxia, and explore its mechanism. Method: Direct adherent culture was adopted to cultivate umbilical cord mesenchymal stem cells and amplified to the fourth generation. Markers on the cell surface were identified by flow cytometry. Culture medium was collect without serum from the 4th generation umbilical cord mesenchymal stem cells. Exosomes were separated and extracted, then the ultrastructure was observed under electron microscope and examined expression of CD63 and CD9 protein by Western blot method with isolated and extracted exosomes. HRPE was cultivated in vitro culture, proliferation was detected at the time point of 0, 1, 2, 3, 4, 5 d with MTT assay under hypoxic condition. Meanwhile, the cell migration was quantified by Wound-Healing Assay under hypoxic condition at 0, 24, 48 and 72 h respectively combined with apoptosis test. The HRPE cells in the growth period were divided into 5 groups: the control group, the hypoxia group and the pretreated exosomes group (100, 200, 300 μg/ml). In all groups, apoptosis was observed by Annexin V/PI dual-dye flow cytometry after 48 h's incubation. Proliferation was observed by MTT assay and the migration was observed with Wound-Healing Assay. Results: Flow cytometry detection of the surface marker of HUMSCs in the 4th generation showed strong positive expression of CD105, CD73, CD90. It was suggested that HUMSCs with isolated culture had MSC specific phenotype with duction of lipids and osteoblasts in vitro. The separated exosomes were observed with spherical membranous structures in different sizes by scanning electron microscopy, and Western blot detected positive expression of CD63 and CD9. In vitro culture of HRPE detected by MTT assay for cell proliferation at the time of hypoxic 0, 1, 2, 3, 4, 5 d, the results showed that, comparing with time point 0 d, other groups had statistically significant OD values. In the first 2 days, the proliferation ability of RPE cells gradually increased as the time of hypoxia prolonged(1.862±0.135, 2.278±0.244). After 3 d, the proliferation ability of RPE cells gradually decreased(1.419±0.124, 1.599±0.156). Wound-Healing Assay results showed that the migration distance gradually increased as[(29.883±4.504), (36.200±1.928) μm] the time of hypoxia increased from 0 to 72 h. The cells were fully covering at the point of 72 h [(1.223±0.194), (0.430±0.299) μm]. Apoptosis test results showed that the number of apoptotic cells was different(3.628%±1.348%, 20.123%±1.183%) with the extension of hypoxia Oxygen before 2 d from 0 to 72 h. At the time of d3, there were more apoptotic cells(42.290%±3.217%). There is a significant difference from pre-2d.RPE cells were divided into 5 groups: the control group, the hypoxia group and the pretreated exosomes group (100, 200, 300 μg/ml).After 48 h hypoxia incubation, MTT assay results showed that, compared with the control group (1.870±0.499), the number of cell proliferation was significantly increased (t=-3.116, P<0.05), while compared with the hypoxia group(2.616±0.307), the proliferation number of exosomes was significantly reduced [(2.041±0.115), (1.931±0.205), (1.929±0.025); t=-4.920, -4.540, -5.286, P<0.01], and there was no significant difference between groups with different doses of the exosomes (F=1.181,P>0.05). Annexin V/PI dual-dye flow cytometry was used to observe the apoptosis results. Compared with the control group 1.180%±0.689%, the number of apoptosis in hypoxia group was significantly increased (19.273%±1.194%, t=-32.141, P<0.01), while compared with the hypoxia group, the number of apoptosis in the exosomes was significantly decreased (12.318%±1.087%, 11.878%±1.348%, 11.090%±1.716%; t=-10.547, -10.057, 9.589, P<0.01). There was no significant difference between the groups with different doses of exosomes (F=1.173, P>0.05). Wound-Healing Assay results showed that, compared with the control group(68.047±2.851) μm, the migration distance of the hypoxia group was significantly increased [(13.470±2.255)μm, t=36.778, P<0.01] while compared with the hypoxia group, the migration distance of the exosomes was reduced (33.110±1.774, 24.650±1.175, 26.440±1.674; t=11.766, 10.770, 11.311, P<0.01), and there was no significant difference between the groups of the exosomes (F=1.179, P>0.05). Conclusion: Human umbilical cord mesenchymal stem cells can effectively inhibit the apoptosis and migration of HRPE cells in hypoxia. It provides a theoretical basis for the research and treatment of RPE related diseases. (Chin J Ophthalmol, 2019, 55: 933-941).