Inhibition of mTOR blocks the anti-inflammatory effects of glucocorticoids in myeloid immune cells

Abstract

A central role for the mammalian target of rapamycin (mTOR) in innate immunity has been recently defined by its ability to limit proinflammatory mediators. Although glucocorticoids (GCs) exert potent anti-inflammatory effects in innate immune cells, it is currently unknown whether the mTOR pathway interferes with GC signaling. Here we show that inhibition of mTOR with rapamycin or Torin1 prevented the anti-inflammatory potency of GC both in human monocytes and myeloid dendritic cells. GCs could not suppress nuclear factor-B and JNK activation, the expression of proinflammatory cytokines, and the promotion of Th1 responses when mTOR was inhibited. Interestingly, long-term activation of monocytes with lipopolysaccharide enhanced the expression of TSC2, the principle negative regulator of mTOR, whereas dexamethasone blocked TSC2 expression and reestablished mTOR activation. IntroductionCurrent immunosuppressive regimens to avoid allogeneic rejection after organ or bone marrow transplantation largely rely on drugs with potent immunosuppressive effects predominantly affecting different steps during T-cell activation. There is, however, increasing evidence that also the innate immune system is critical for the fate of allografts and may as well exert detrimental effector functions. 1-9 For example, monocytes are the first cells to enter the allograft immediately after transplantation; and recently, monocyte influx, rather than T-cell influx, into the allograft has been proposed to correlate with graft rejection. 9 Monocytes, macrophages, and dendritic cells (DCs) initiate the inflammatory response after stimulation by Toll-like receptor (TLR) ligands and trigger the subsequent adaptive T-cell response. 10,11 However, the molecular pathways targeted by immunosuppressants in particular when they are used as combination therapy and the ensuing functional consequences are still incompletely defined.Among the currently used immunosuppressants calcineurin inhibitors (CNI), such as cyclosporine A (CsA) or FK506, and antimetabolites, such as mycophenolic acid (mycophenolate mofetil [MMF]) are thought to exert distinct but rather modest effects on innate immune cells. 12,13 On the contrary, glucocorticoids (GCs) have a high anti-inflammatory potential and, consequently, are crucial constituents of various immunosuppressive regimens applied in many inflammatory conditions. 14 GCs differentially affect cytokine production in monocytes/macrophages with a prominent shift toward an anti-inflammatory phenotype. 15 Furthermore, DC differentiation and maturation are profoundly suppressed by GCs, leading to DCs with a tolerizing capacity characterized by increased interleukin-10 (IL-10), but blocked IL-12 secretion. 16,17 At the molecular level, GCs profoundly inhibit nuclear factor-B (NF-B) signaling via the glucocorticoid receptor (GR) to prevent recruitment of active NF-B dimers to the B promoter. 18 Moreover, it has been demonstrated that the c-Jun N-terminal kinase (JNK) pathway that specifically leads to the activation of the tr...

Effects of dietary protein levels on the disease resistance, immune function and physical barrier function in the gill of grass carp ( Ctenopharyngodon idella ) after challenged with Flavobacterium columnare

“…As reported, S6K1 and 4E-BP are the downstream effectors of TOR in humans [72], and Guertin et al [73] found that TOR activates S6K1 and inhibits 4E-BP expression in Drosophila. In human monocytes, TOR increases production of the anti-inflammatory cytokines IL-10 [74]. In the present study, compared with low or high levels of protein, optimal levels of dietary protein led to the up-regulation of TOR and S6K1 mRNA levels and to the down-regulation of 4E-BP1 and 4E-BP2 mRNA levels in the gills of grass carp.…”

TSC1 controls macrophage polarization to prevent inflammatory disease

“…Rapa enhanced inflammatory cytokine production in macrophages via enhancing NF-kB and blocking STAT3 activity 27,28 . Rapa significantly blocked the anti-inflammatory effects of glucocorticoids in myeloid immune cells including monocytes and DCs 29 . Rapa treatment enriched NF-kB-related proinflammatory expression pathways and monocyte lineagespecific transcripts in kidney-transplanted recipients 30 .…”

TSC1 controls IL-1β expression in macrophages via mTORC1-dependent C/EBPβ pathway

“…The reason for this inconsistency is possibly due to the different cell types used. Previous study showed that long-term treatment with Rapa (1 h then followed by LPS stimulation for another 24 h) promotes peripheral blood mononuclear cells to produce more IL-1b in culture supernatants 25 . We also observed the inhibition of mTORC1 by Rapa (48 h) or deletion of mTOR almost completely rescued the pro-IL-1b expression at the mRNA and protein levels in TSC1 KO macrophages, inferring that mTORC1 inhibited pro-IL-1b production indirectly and blocking mTORC1 pathway facilitated its synthesis.…”

“…The involvement of mTOR pathway in the regulation of and IL-1b expression has been studied in mouse and human macrophages 22,25,26 . In the present study, using TSC1-deficient macrophages and macrophage cell lines, we studied the role of TSC1 on pro-inflammatory cytokine IL-1b expression and explored the associated molecular mechanism.…”