To investigate the effect of small extracellular vesicles (sEVs) derived from mesenchymal stem cells (MSCs) in mouse model of retinal light injury and the possible mechanism.

Human umbilical cord derived MSCs were identified by flow cytometry.Supernatants of passage 3-5 MSCs were collected.sEVs were harvested by ultracentrifugation and were identified by transmission electron microscopy.Sixty-five healthy female SPF-grade BALB/c mice aged 8-10 weeks were randomly divided into normal group (17 mice), phosphate buffered saline (PBS) group (24 mice) and sEVs group (24 mice). Mice in PBS and sEVs groups were intravitreally injected with 2 μl of PBS and sEVs, respectively, and were exposed to 930 lx blue light for 6 hours.No intervention was administered to the normal group.Three days after lighting, mice retinal structure was observed by hematoxylin-eosin staining.Apoptotic retinal cells were detected by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling (TUNEL). Retinal function was tested by electroretinogram.Differentially expressed mRNAs between PBS group and sEVs group were assayed by mRNA transcriptome sequencing and were analyzed through KEGG cluster analysis.The differential mRNAs were verified via real-time quantitative PCR.The study protocol was approved by the Animal Ethics Committee of Tianjin Medical University Eye Hospital (No.TJYY20201221035).

MSCs were positive for CD90 and CD105, negative for CD34 and CD45.The extracted MSC-sEVs showed a bilayer membrane vesicle with a diameter of 80-140 nm.Hematoxylin-eosin staining showed the arrangement of photoreceptor nuclei was disordered in outer nuclear layer in PBS group.The disorder of photoreceptor nuclei arrangement of sEVs group was slighter than that of PBS group.The apoptotic cell number of sEVs group was (14.60±4.04)/visual field, which was lower than (24.00±8.52)/visual field of PBS group, with a statistically significant difference (t=2.37, P<0.05). The a-wave amplitude of sEVs group was (64.38±16.70)μV, which was higher than (16.78±6.37) μV of PBS group, showing a statistically significant difference (P<0.05). The b-wave amplitudes of PBS and sEVs groups were (132.40±39.41) μV and (154.86±34.08) μV, respectively, which were lower than (338.38±27.41) μV of normal group, and the differences were statistically significant (both at P<0.05). A total of 110 differentially expressed mRNAs were detected.There were 109 downregulated mRNAs in sEVs group.Differentially expressed mRNAs were mainly inflammation- and immune-related pathways.PCR showed that the expression level of C-C motif chemokine ligand 2, C-C motif chemokine receptor 2, leukotriene B4, leukocyte Ig-like receptor A6 and interleukin-1β in sEVs group were significantly decreased in comparison with PBS group (all at P<0.05).

MSC-sEVs can ameliorate blue light-induced retinal structural and functional damage.The protective effect may be achieved through inhibiting inflammatory response.

Retina; Light/injury; Mesenchymal stem cells; Small extracellular vesicle