Background aimsThe Akt/mammalian target of rapamycin (mTOR) pathway in macrophages converges inflammatory and metabolic signals from multiple receptors to regulate a cell's survival, metabolism and activation. Although mesenchymal stromal cells (MSCs) are well known to modulate macrophage activation, the effects of MSCs on the Akt/mTOR pathway in macrophages have not been elucidated. MethodsWe herein investigated whether MSCs affect the Akt/mTOR complex 1 (mTORC1) pathway to regulate macrophage polarization. ResultsResults showed that human bone marrow–derived MSCs induced activation of Akt and its downstream mTORC1 signaling in THP-1–differentiated macrophages in a p62/sequestosome 1–independent manner. Inhibition of Akt or mTORC1 attenuated the effects of MSCs on the suppression of tumor necrosis factor-α and interleukin-12 production and the promotion of interleukin-10 and tumor growth factor-β1 in macrophages stimulated by lipopolysaccharide/ATP. Conversely, activation of Akt or mTORC1 reproduced and potentiated MSC effects on macrophage cytokine production. MSCs with cyclooxygenase-2 knockdown, however, failed to activate the Akt/mTORC1 signaling in macrophages and were less effective in the modulation of macrophage cytokine production than control MSCs. ConclusionsThese data demonstrate that MSCs control THP-1–differentiated macrophage activation at least partly through upregulation of the Akt/mTORC1 signaling in a cyclooxygenase-2–dependent manner.