[Effects of exosomes from human adipose-derived mesenchymal stem cells on inflammatory response of mouse RAW264.7 cells and wound healing of full-thickness skin defects in mice].

Objective: To investigate the effects of exosomes from human adipose-derived mesenchymal stem cells (ADSCs) on inflammatory response of mouse RAW264.7 cells and wound healing of full-thickness skin defects in mice. Methods: The experimental research methods were adopted. The discarded adipose tissue was collected from 3 female patients (aged 10-25 years) who underwent abdominal surgery in the First Affiliated Hospital of Air Force Medical University. ADSCs were extracted from the adipose tissue by collagenase Ⅰ digestion and identified with flow cytometry. Exosomes were extracted from the human ADSCs by differential ultracentrifugation, the morphology of the exosomes was observed by transmission electron microscopy, the particle diameter of the exosomes was detected by nanoparticle tracking analyzer, and the protein expressions of CD9, CD63, tumor susceptibility gene 101 (TSG101), and ß-actin were detected by Western blotting. The human ADSCs exosomes (ADSCs-Exos) and RAW264.7 cells were co-cultured for 12 h, and the uptake of RAW264.7 cells for human ADSCs-Exos was observed. The RAW264.7 cells were divided into phosphate buffer solution (PBS) group stimulated with PBS for suitable time, endotoxin/lipopolysaccharide (LPS) stimulation 2 h group, LPS stimulation 4 h group, LPS stimulation 6 h group, LPS stimulation 12 h group, and LPS stimulation 24 h group stimulated with LPS for corresponding time, with 3 wells in each group, and the mRNA expressions of interleukin 1ß (IL-1ß), tumor necrosis factor α (TNF-α), IL-6, and IL-10 were detected by real-time fluorescence quantitative reverse transcription polymerase chain reaction (RT-PCR) method. The RAW264.7 cells were divided into PBS group, LPS alone group, and LPS+ADSCs-Exos group, with 3 wells in each group, which were dealt correspondingly for the time screened out in the previous experiment, the mRNA expressions of IL-1ß, TNF-α, IL-6, IL-10, trasforming growth factor ß (TGF-ß,) and vascular endothelial growth factor (VEGF) were detected by real time fluorescence quantitative RT-PCR method, and the protein expressions of inducible nitric oxide synthase (iNOS) and arginase 1 (Arg1) were detected by Western blotting. Twenty-four 8-week-old male BALB/c mice were divided into PBS group and ADSCs-Exos group according to the random number table, with 12 mice in each group, and a full-thickness skin defect wound with area of 1 cm×1 cm was inflicted on the back of each mouse. Immediately after injury, the wounds of mice in the two groups were dealt correspondingly. On post injury day (PID) 1, the concentration of IL-1ß and TNF-α in serum were detected by enzyme-linked immunosorbent assay, and the mRNA expressions of IL-1ß, TNF-α, and IL-6 were detected by real time fluorescence quantitative RT-PCR method. On PID 3, 6, 9, 12, and 15, the wound healing was observed and the wound non-healing rate was calculated. On PID 15, the defect length of skin accessory and collagen volume fraction (CVF) were detected by hematoxylin eosin staining and Masson staining, respectively, the CD31 expression and neovascularization were detected by immunohistochemistry, and the ratio of Ki67 positive cells, the ratio of iNOS and Arg1 double positive cells, and the ratio of iNOS positive cells to Arg1 positive cells and their fluorescence intensities were detected by immunofluorescence method. The number of samples in animal experiments was 6. Data were statistically analyzed with analysis of variance for repeated measurement, one-way analysis of variance, and independent sample t test. Results: At 12 h of culture, the cells exhibited a typical spindle shape, which were verified as ADSCs with flow cytometry. The exosomes with a vesicular structure and particle diameters of 29-178 nm, were positively expressed CD9, CD63, and TSG101 and negatively expressed ß-actin. After 12 h of co-culture, the human ADSCs-Exos were endocytosed into the cytoplasm by RAW264.7 cells. The mRNA expressions of IL-1ß, TNF-α, IL-6, and IL-10 of RAW264.7 cells in LPS stimulation 2 h group, LPS stimulation 4 h group, LPS stimulation 6 h group, LPS stimulation 12 h group, and LPS stimulation 24 h group were significantly higher than those in PBS group (with t) values of 39.10, 14.55, 28.80, 4.74, 48.80, 22.97, 13.25, 36.34, 23.12, 18.71, 29.19, 41.08, 11.68, 18.06, 8.54, 43.45, 62.31, 22.52, 21.51, and 37.13, respectively, P<0.01). The stimulation 12 h with significant expressions of all the inflammatory factors was selected as the time point in the following experiment. After stimulation of 12 h, the mRNA expressions of IL-1ß, TNF-α, IL-6, and IL-10 of RAW264.7 cells in LPS alone group were significantly higher than those in PBS group (with t values of 44.20, 51.26, 14.71, and 8.54, respectively, P<0.01); the mRNA expressions of IL-1ß, TNF-α, and IL-6 of RAW264.7 cells in LPS+ADSCs-Exos group were significantly lower than those in LPS alone group (with t values of 22.89, 25.51, and 8.03, respectively, P<0.01), while the mRNA expressions of IL-10, TGF-ß, and VEGF were significantly higher than those in LPS alone group (with t values of 9.89, 13.12, and 7.14, respectively, P<0.01). After stimulation of 12 h, the protein expression of iNOS of RAW264.7 cells in LPS alone group was significantly higher than that in PBS group and LPS+ADSCs-Exos group, respectively (with t values of 11.20 and 5.06, respectively, P<0.05 or P<0.01), and the protein expression of Arg1 was significantly lower than that in LPS+ADSCs-Exos group (t=15.01, P<0.01). On PID 1, the serum concentrations of IL-1ß and TNF-α and the mRNA expressions of IL-1ß, TNF-α, and IL-6 in wound tissue of mice in ADSCs-Exos group were significantly those in lower than PBS group (with t values of 15.44, 12.24, 9.24, 7.12, and 10.62, respectively, P<0.01). On PID 3, 6, 9, 12, and 15 d, the wound non-healing rates of mice in ADSCs-Exos group were (73.2±4.1)%, (53.8±3.8)%, (42.1±5.1)%, (24.1±2.8)%, and 0, which were significantly lower than (82.5±3.8)%, (71.2±4.6)%, (52.9±4.1)%, (41.5±3.6)%, and (14.8±2.5)% in PBS group, respectively (with t values of 4.77, 8.93, 5.54, 7.63, and 7.59, respectively, P<0.01). On PID 15, the defect length of skin accessory in wounds of mice in PBS group was significantly longer than that in ADSCs-Exos group (t=9.50, P<0.01), and the CVF was significantly lower than that in ADSCs-Exos group (t=9.15, P<0.01). On PID 15, the CD31 expression and the number of new blood vessels (t=12.99, P<0.01), in wound tissue of mice in ADSCs-Exos group were significantly more than those in PBS group, and the ratio of Ki67 positive cells was significantly higher than that in PBS group (t=7.52, P<0.01). On PID 15, the ratio of iNOS and Arg1 double positive cells in wound tissue of mice in PBS group was (12.33±1.97)%, which was significantly higher than (1.78±0.29)% in ADSCs-Exos group (t=13.04, P<0.01), the ratio of iNOS positive cells and the fluorescence intensity of iNOS were obviously higher than those of ADSCs-Exos group, and the ratio of Arg1 positive cells and the fluorescence intensity of Arg1 were obviously lower than those of ADSCs-Exos group. Conclusions: The human ADSCs-Exos can alleviate inflammatory response of mouse RAW264.7 cells, decrease macrophage infiltration and secretion of the pro-inflammatory cytokines, increase the secretion of anti-inflammatory cytokines to promote neovascularization and cell proliferation in full-thickness skin defect wounds of mice, hence accelerating wound healing.