Human umbilical cord mesenchymal stem cells transplantation promotes cutaneous wound healing of severe burned rats

Abstract

Background: Severe burns are a common and highly lethal trauma. The key step for severe burn therapy is to promote the wound healing as early as possible, and reports indicate that mesenchymal stem cell (MSC) therapy contributes to facilitate wound healing. In this study, we investigated effect of human umbilical cord MSCs (hUC-MSCs) could on wound healing in a rat model of severe burn and its potential mechanism.

Methods: Adult male Wistar rats were randomly divided into sham, burn, and burn transplanted hUC-MSCs. GFP labeled hUC-MSCs or PBS was intravenous injected into respective groups. The rate of wound closure was evaluated by Image Pro Plus. GFP-labeled hUC-MSCs were tracked by in vivo bioluminescence imaging (BLI), and human-specific DNA expression in wounds was detected by PCR. Inflammatory cells, neutrophils, macrophages, capillaries and collagen types I/III in wounds were evaluated by histochemical staining. Wound blood flow was evaluated by laser Doppler blood flow meter. The levels of proinflammatory and anti-inflammatory factors, VEGF, collagen types I/III in wounds were analyzed using an ELISA.

Results: We found that wound healing was significantly accelerated in the hUC-MSC therapy group. The hUC-MSCs migrated into wound and remarkably decreased the quantity of infiltrated inflammatory cells and levels of IL-1, IL-6, TNF-α and increased levels of IL-10 and TSG-6 in wounds. Additionally, the neovascularization and levels of VEGF in wounds in the hUC-MSC therapy group were markedly higher than those in other control groups. The ratio of collagen types I and III in the hUC-MSC therapy group were markedly higher than that in the burn group at indicated time after transplantation.

Conclusion: The study suggests that hUC-MSCs transplantation can effectively improve wound healing in severe burned rat model. Moreover, these data might provide the theoretical foundation for the further clinical application of hUC-MSC in burn areas.

Figure 1. hUC-MSCs injection promoted wounds recovery of severe burn.

(A) Representative images of cutaneous wounds at different time points after hUC-MSC transplantation. (B) Statistical analysis of healing time of the wounds was presented in the histogram. The healing time of wounds in the burn transplanted hUC-MSCs group was significantly shorter than that in the burn group. (C) Statistical analysis of healing rate of wounds at 2, 3, 6, and 8 weeks after transplantation was presented in the histogram. The healing rate of wounds in the burn transplanted hUC-MSC group was significantly higher than that in the burn group at same time. Values are represented as mean±SD (n = 6), asterisk (*) and double asterisk (**) stand for P<0.05 and p<0.01 compared with burn group, respectively.

Figure 2. hUC-MSCs were cultured, labeled, and tracked in vivo in rats with severe burns.

(A) P3 hUC-MSCs were observed by bright-field microscopy using an inverted microscope. GFP-labeled hUC-MSCs were observed by inverted fluorescence microscopy, and positive rates of GFP-labeled cells were evaluated by flow cytome try. The magnification was 100 times. (B) GFP-labeled hUC-MSCs migrated into cutaneous wounds of rats with severe burns at different time points after cell transplantation. (C) The human-specific DNA in cutaneous wounds of rats with severe burns was assayed using RT-PCR.

Figure 3. Anti-inflammatory effect of hUC-MSCs on cutaneous wounds of rats with severe burns was detected (A) The inflammatory cell infiltration in wounds was assessed by H&E staining.

Positive staining for neutrophils (c-ANCA) and macrophages (ED-1) was examined by immunohistochemistry. (B) A quantitative analysis of positive staining for neutrophils (c-ANCA) and macrophages (ED-1) is shown in the corresponding histogram. (C, D, E) The proinflammatory cytokines IL-1, IL-6, and TNF-α in wounds were assessed using an ELISA kit. IL-1, IL-6, and TNF-α levels in the burn transplanted hUC-MSC group were significantly lower than those in the burn group, and their levels in the burn group were significantly higher than those in the sham group. (F, G) The anti-inflammatory cytokines IL-10 and TSG-6 in wounds were assessed using an ELISA kit. IL-10 and TSG-6 levels in the burn transplanted hUC-MSC group were significantly higher than other control groups. Values are represented as mean±SD (n = 6), double asterisk (**) stands for p<0.01.

Figure 4. Effects of hUC-MSCs on wound neovascularization at week 3 after cell transplantation.

(A) The wound samples in sham, burn, and burn transplanted hUC-MSC groups were stained for the vascular endothelial cell markers CD31 and vWF using immunohistochemistry. (B) A quantitative analysis of microvessels is shown in the corresponding histogram. (C) The level of VEGF in wounds was evaluated by ELISA kit. The VEGF level in the burn transplanted hUC-MSC group was significantly higher than that in other control groups. (D) Cutaneous wound microcirculation was evaluated using a laser Doppler blood flow meter. The cutaneous wound microcirculation in the burn transplanted hUC-MSC group was markedly higher than that in the burn group at weeks 1, 2, 3, 6 and 8 after transplantation. Values are represented as mean±SD (n = 6), asterisk (*) and double asterisk (**) stand for P<0.05 and p<0.01 respectively.

Figure 5. Modification collagen types I and III accumulation in the wound.

(A) Treatment of severely burned wounds with hUC-MSCs modified accumulation of collagen types I and III at week 3 after transplantation. (B) A quantitative analysis of ratio of collagen types I and III is shown in the corresponding histogram. (C) The levels of collagen types I and III in wounds at different time points after transplantation were assessed using an ELISA kit. Compared with wounds in severely burned group, hUC-MSCs significantly upregulated the ratio of collagen types I and III in the wound at weeks 1, 2, 3, 6, 8 and 11 after transplantation. Values are represented as mean±SD (n = 6), asterisk (*) and double asterisk (**) stand for P<0.05 and p<0.01 respectively.