ABSTRACT
Objective:Observing the effect of exosomes derived from hypoxic Bone marrow mesenchymal stem cells (BMSCs) on the function of chondrocytes, and exploring the role and mechanism of exosomal miR-196b-5p. Evaluating the application prospects of hypoxic BMSCs exosomes and miR-196b-5p for cartilage regeneration.Methods:Chondrocytes were cultured in the supernatant of BMSCs cultured under normoxia or hypoxia, respectively. The proliferation of chondrocytes was detected by CCK-8 assay and the expressions of Collagen type 2 (Col2), Col1, Aggrecan and SOX9 were detected by qPCR to evaluate the effect of hypoxic BMSCs paracrine on chondrocyte functions. Obtaining normoxic and hypoxic exosomes through ultracentrifugation, and testing their effects on the proliferation and anabolic-related genes of chondrocytes through CCK-8 assay and qPCR. Verifying the expression of miR-196b-5p in hypoxic exosomes based on exosomal miRNA array. Knocking out miR-196b-5p in hypoxic BMSCs, and detecting the effect of hypoxic exosomal miR-196b-5p on the functions of chondrocytes by loss-of-function assay. Predicting the downstream of miR-196b-5p through bioinformatics tools, and exploring the mechanism of hypoxic exosomal miR-196b-5p by gain-of-function assays. Hypoxic exosomes and miR-196b-5p-knockout hypoxic exosomes were loaded on silk fibroin hydrogel and subcutaneously into nude mice. After 4 weeks of culture, histological staining of saffron O, Masson and biochemical content of sGAG and collagen were performed to assess the application prospect of hypoxic exosomes and hypoxic exosomal miR-196b-5p on cartilage regeneration. Results:The results of CCK-8 assay and qPCR indicated that the supernatant of hypoxic BMSCs significantly promoted the proliferation of chondrocytes 1.20±0.07 and the expression of cartilage-related markers (Col2 2.95±0.17, Aggrecan 2.45±0.27, SOX9 2.92±0.29) compared to normoxic BMSCs (0.94±0.04, 1.89±0.09, 1.67±0.21, 1.76±0.16), the differences were statistically significant ( P<0.05). The result of CCK-8 assay showed that hypoxic exosomes (1.28±0.04) promoted the proliferation of chondrocytes compared to normoxic exosomes 1.05±0.06, the differences were statistically significant ( P<0.05). CCK-8 assay revealed that the down-regulation of miR-196b-5p in hypoxic exosomes 0.99±0.06 attenuated the proliferation of chondrocytes compared to control group 1.20±0.07, the differences were statistically significant ( P<0.05); the expression of Col2 0.56±0.04, Aggrecan 0.74±0.09, and SOX9 0.45±0.05 in chondrocytes was reduced in the miR-196b-5p knockdown group compared to the control group (1.00±0.09, 1.00±0.12, 1.00±0.07), the differences were statistically significant ( P<0.05). Co-transfection of pmirGLO-BACH1-WT reporter vector with miR-196b-5p mimics decreased the luciferase activity 0.73±0.06, the differences were statistically significant ( P<0.05). Co-transfection of pmirGLO-BACH1-MUT reporter vector with miR-196b-5p mimics showed no change in luciferase activity. BACH1 is the target of miR-196b-5p. Subcutaneous culture in nude mice showed that hypoxic exosomes significantly promoted the deposition of sGAG 383.2±21.54 and collagen 67.40±3.45, while reducing the expression of miR-196b-5p in hypoxic exosomes weakened the deposition of sGAG 258.4±19.50 and collagen 57.15±4.95, the differences were statistically significant ( P<0.05). Conclusion:Hypoxic exosomes promoted the functions of chondrocytes by inhibiting the expression of BACH1 through miR-196b-5p. Hypoxic exosomes can be applied in cartilage regeneration.