Human mesenchymal stem/stromal cells (hMSCs) cultured as spheroids are self-activated to produce prostaglandin E2 (PGE2) that directs stimulated macrophages into an anti-inflammatory phenotype

摘要

Culturing cells in 3D provides an insight into their characteristics in vivo. We previously reported that human mesenchymal stem/stromal cells (hMSCs) cultured as 3D spheroids acquire enhanced anti-inflammatory properties. Here we explored the effects of hMSC spheroids on macrophages that are critical cells in the regulation of inflammation. Conditioned medium from hMSC spheroids inhibited LPS-stimulated macrophages from secreting pro-inflammatory cytokines TNFα, CXCL2, IL6, IL12p40, and IL23. Conditioned medium also increased the secretion of anti-inflammatory cytokines IL10 and IL1ra by the stimulated macrophages, and augmented expression of CD206, a marker of alternatively activated M2 macrophages. The principal anti-inflammatory activity in conditioned medium had a small molecular weight, and microarray data suggested that it was PGE2. This was confirmed by the observations that PGE2 levels were markedly elevated in hMSC spheroid-conditioned medium, and that the anti-inflammatory activity was abolished by an inhibitor of COX-2, a silencing RNA for COX-2, and an antibody to PGE2. The anti-inflammatory effects of the PGE2 on stimulated macrophages were mediated by the EP4 receptor. Spheroids formed by human adult dermal fibroblasts produced low levels of PGE2 and displayed negligible anti-inflammatory effects on stimulated macrophages, suggesting the features as unique to hMSCs. Moreover, production of PGE2 by hMSC spheroids was dependent on the activity of caspases and NFκB activation in the hMSCs. The results indicated that hMSCs in 3D-spheroid cultures are self-activated, in part by intracellular stress responses, to produce PGE2 that can change stimulated macrophages from a primarily pro-inflammatory M1 phenotype to a more anti-inflammatory M2 phenotype.