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  • We have confirmed that HO suppressed TLR MyD dependent signa


    We have confirmed that HO-2 suppressed TLR4/MyD88-dependent signaling by down-regulating the downstream factors (TNF-α and IL-6) in mouse cerebral vascular endothelial cells [13]. In this study, HO-2 overexpression mouse model was generated and to investigated the role of HO-2 in macrophage inflammatory responses in vitro and in vivo. These results will provide a novel method to improve the survival of skin allografts.
    Methods and materials
    Discussion Heme oxygenase (HO), which catalyzes the degradation of heme into carbon monoxide (CO), iron, and biliverdin/bilirubin, has been implicated in processes involved in the resolution of inflammation [17]. HO-2 plays an important role in the polarization and phagocytic activity of macrophages during inflammation [15]. HO-2−/− macrophages have been demonstrated to exhibit an altered M1 phenotype, while their M2 phenotype was unaltered [18]. Impaired corneal wound healing has been observed in HO-2 null mice [19]. In this study, macrophages were isolated from HO-2-overexpressing mice and observed to have decreased expression of TNF-α, IL1β and IL-6 upon stimulation with LPS compared with that in macrophages isolated from WT mice. The number of infiltrating macrophages was measured using histological staining and cytokine profiling, both of which indicated that the number was increased in the corneas of HO-2−/− mice compared with those of WT mice [18,19]. We also found that the number of infiltrating inflammatory cells was increased over time in skin grafts, with the number of inflammatory cells being greater in the WT graft skins than in the HO-2-overexpressing skin grafts. The transplantation of skin grafts typically results in the donor tissue being attacked by the recipient's immune system. CD4+ and CD8+ T cells play an important role in the recognition of donor alloantigens. CD4+ T cells secrete cytokines that activate CD8+ T cells and Dextran sulfate sodium salt mg [20]. CD4+ and CD8+ levels in the HO-2 skin grafts were significantly decreased at 4 and 8d compared with those in the WT (control) skin grafts. HO-2 regulates the LPS-TLR4 pathway via the TLR4 adaptor protein TRAM. The expression of HO-2 in the diaphragm and primary macrophages has been found to be increased by LPS treatment [21]. These findings are in agreement with our previous finding that the overexpression of HO-2 inhibits the activity of the LPS-TLR4 pathway in mouse cerebral vascular endothelial cells [13]. In this study, we detected significant differences in the mRNA and protein levels of TNF-α, IL1β and IL-6, in the skin grafts taken from HO-2-overexpressing mice. These findings suggest that HO-2 may attenuate pro-inflammatory signaling. The heme oxygenase (HO) system also plays a vital role in transplantation biology [22]. There are many factors that contribute to organ rejection, such as vascular dysfunction and immune cell influx. The release of denatured heme proteins may promote an increase in progression of inflammation during the process of graft rejection. HO-1 expression plays an important role in the long-term survival of skin grafts by Dextran sulfate sodium salt mg promoting the induction of graft tolerance [23]. HO-1 has been previously demonstrated to exhibit proangiogenic activity; it is well-known that angiogenesis is crucial for proper wound healing [24]. The role of HO-1 in angiogenesis was demonstrated by the observation of delayed wound closure and impaired vascularization in HO-1 deficient mice [25]. Additionally, low vessel densities were observed in wounds in HO-2 null mice, however, while higher vessel densities were observed in the wounds in HO-2-overexpressing mice [26]. HO-2 deficiency was shown to delay cutaneous wound closure when compared to that of WT controls. Skin transplantation is often regarded as a model for organ rejection, and skin allografts are easily destroyed because of rejection by the host [27]. In the current study, HO-2 enhanced the survival of skin grafts in comparison with grafts taken WT mice.