Previously we demonstrated that injured kidney tissues can i

Previously, we demonstrated that injured kidney tissues can induce bone marrow stromal buy NSC74859 to differentiate into renal tubular epithelial-like cells in vitro and in vivo (Qian et al., 2008). However, another work reported that the beneficial effects of BMSCs are primarily mediated by complex paracrine actions, but not by their differentiation into target cells (Tögel et al., 2005). Recently, there is increasing evidence to indicate that immunomodulation does play a critical role in the therapeutic effect of multipotential stromal cells, since tissue injury is generally inflammation-related (Semedo et al., 2009; Aronin and Tuan, 2010; Jang et al., 2009). In particular, many studies have focused on the modulatory effect of stromal cells on macrophages (Kim and Hematti, 2009; Chen et al., 2008; Maggini et al., 2010). One study demonstrated that BMSCs can beneficially modulate the response of the host immune system to sepsis and interact with both circulating and tissue macrophages (Németh et al., 2009). Another report indicated that human gingiva-derived stromal cells can induce M2 polarization of macrophages, which may contribute to a marked acceleration of cutaneous wound healing (Zhang et al., 2010). In the present study, macrophage recruitment occurred rapidly in the interstitial area of injured kidneys and peaked at 5days after reperfusion, which was reduced significantly following hUCSC treatment. Furthermore, we sought to find out the role of chemokine MCP-1 in macrophage recruitment effected by hUCSCs. Our results showed that the number of MCP-1-positive tubular epithelial cells was also markedly reduced by hUCSC administration. Thus, these findings provide the first evidence that hUCSCs are capable of reducing macrophage infiltration in the injured kidneys, at least in part by downregulating the expression of MCP-1 in tubular epithelial cells. In vivo, we performed macrophage depletion by lipo-Cl2MBP and chose to deplete macrophages at different stages of reperfusion, to find out whether they have distinct functions which would result in conflicting conclusions (Duffield et al., 2005). Our results show that macrophage abolishment during the early injury phase promotes the ameliorating effect of hUCSCs on renal IRI. This finding is in agreement with current evidence demonstrating the contribution of macrophages to the initiation of renal damage (Jo et al., 2006; Day et al., 2005). Conversely, macrophage depletion during the late repair phase led to a loss of the therapeutic effect of hUCSCs on kidney damage. One group reported that macrophages are involved in the repair phase and are beneficial for kidney repair after IRI (Vinuesa et al., 2008). Here, we provide the first evidence that macrophage infiltration during recovery may be essential for the protective role of hUCSCs in renal IRI. In a coculture experiment, we found that hUCSCs suppressed the transcription of IL-1β and IL-6 mRNA in macrophages, whereas aginase-1 and IL-10 were upregulated. These findings suggest that hUCSCs can switch the cytokine expression of macrophages into an anti-inflammatory phenotype, characteristic of M2 macrophages, in vitro. In vivo, hUCSC-treated kidneys also showed a significant suppression of the expression of IL-1β and IL-6, and an upregulation of IL-10. Thus, our observations indicate that hUCSCs are capable of modulating the cytokine expression of macrophages, which may contribute to the resolution of inflammation at injury sites in renal IRI. On the other hand, flow cytometric analysis showed increased CD206 expression on the surface of macrophages cocultured with hUCSCs, and that the proportion of CD206+ macrophages was upregulated during recovery following hUCSC treatment in the kidney tissues. Taken together, our findings suggest that hUCSCs elicit the M2 polarization of macrophages, which may result in an accelerated recovery of renal IRI.
Conclusions