Résumé
BACKGROUND:Conditioned medium from mesenchymal stem cels (MSC-CM) that contains abundant MSCs paracrine substances may represent a promising alternative to MSCs transplantation. However, normal MSC-CM with insufficient paracrine ability is not effective for tissue damage repair. OBJECTIVE:To investigate the effects of MSC-CM with (MSC-CMHyp) and without hypoxic activation (MSC-CMNor) on the proliferation and apoptosis of radiation-induced injured intestinal epithelial cels (IEC-6) and to further discuss the paracrine mechanisms. METHODS: IEC-6 cels were exposed to 10 Gy irradiation and cultured in MSC-CMHyp, MSC-CMNor, and DMEM-F12 medium, respectively. RESULTS AND CONCLUSION: Findings from trypan blue staining, flow cytometry and western blot assay showed that, compared with the DMEM-F12 medium group, treatment with MSC-CMHyp significantly enhanced IEC-6 viability proliferation after radiation-induced injury, as wel as significantly decreased cel apoptosis and expression of Caspases-3/8 (P 0.05). On the other hand, the increased levels of vascular endothelial growth factor, basic fibroblast growth factor, insulin-like growth factor-1, and interleukin-10 were detected in the MSC-CMHyp group compared to the MSC-CMNor group (P < 0.05). These results suggest that the MSC-CMHyp improves the viability and proliferative capacity of IEC-6 cels after radiation-induced injuryvia up-regulating secretion of cytokines and down-regulating apoptotic signaling.
Résumé
BACKGROUND:Conditioned medium from mesenchymal stem cels (MSC-CM) may represent a promising alternative to MSCs transplantation. Previous studies have shown that inflammatory activation can strengthen the multiple biological potencies of MSCs; however, normal MSCs with insufficiency of immunocompetence and migration ability are not effective for tissue damage repair. OBJECTIVE:To investigate differential effects of MSC-CM with and without inflammatory activation on radiation-induced intestinal injury.METHODS:MSCs from the bone marrow of SD rats were separated, cultured and identified, and then co-cultured with non-irradiated IEC-6 or irradiated IEC-6 in a transwel system for 24 hours. Then, MSCs with inflammatory activation were cultured alone for another 48 hours. After that, the supernatant was colected as non-activated MSC-CM (MSC-CMNOR) and MSC-CM under radiation-induced inflammatory condition (MSC-CMIR). Rats were exposed to 14 Gy whole abdominal irradiation and randomly divided into four groups: control group, radiation injury group (DMEM/F12), MSC-CMNOR group and MSC-CMIR group. Continuous administration was givenvia tail vein and intraperitoneal implantation of Alzet microosmotic pumps. Intestinal samples were colected at 1, 3, 7 days after radiation for analysis of short circuit variation, at 3 days after radiation for analysis of intestinal epithelium ultrastructure, and at 1, 3, 5, 7, 14 days after radiation for histological observation of the intestinal epithelium using hematoxylin-eosin staining. Blood samples were colected at 1, 3, 7 days after radiation for analysis of serum xylose levels. In addition, the survival state and survival time of rats were observed and recorded. RESULTS AND CONCLUSION: The short circuit variation responding to electrical field stimulation was significantly reduced at al frequencies, but it was significantly improved in the MSC-CMIR group. Similarly, the intestinal absorption (serum xylose levels) was also significantly impaired by irradiation, but improved by delivery of MSC-CMIR (P < 0.05). At 3 days after MSC-CMIR infusion, the intestinal epithelium exhibited an increase in crypt size and vilous length (P < 0.05). Under the electron microscope, a reduction in intestinal microvili and open tight junctions in irradiated intestinal epithelium was found, and the intestine from rats treated with MSC-CMIR had more obvious tight junctions. In addition, treatment with MSC-CMIR dramaticaly improved the survival rate and mean survival time of irradiated rats as compared to those treated with DMEM/F12 or MSC-CMNOR (P < 0.05). Taken together, the present study demonstrated that MSC-CMIR , but not non-activated MSC-CM, improves the structural and functional restoration of the smal intestine after radiation-induced intestinal injury.