Toll-like receptors (TLRs) play an important role in shaping the host immune response to infection and inflammation. Tissue hypoxia is a common microenvironmental feature of infected and inflamed tissues. Furthermore, hypoxia significantly impacts the development of immune and inflammatory responses through the regulation of host innate and adaptive immunity. Here, we will discuss current knowledge in relation to the crosstalk that exists between toll-like receptor- and hypoxia-dependent signaling pathways in health and disease.
AkiraS, UematsuS, TakeuchiO. Pathogen recognition and innate immunity. Cell2006;124:783–801.
3.
BeutlerBA. TLRs and innate immunity. Blood2009;113:1399–407.
4.
AndersonKV, BoklaL, Nüsslein–VolhardC. Establishment of dorsal-ventral polarity in the Drosophila embryo: the induction of polarity by the Toll gene product. Cell1985;42:791–8.
5.
LemaitreB, NicolasE, MichautL, . The dorsoventral regulatory gene cassette spatzle/Toll/cactus controls the potent antifungal response in Drosophila adults. Cell1996;86:973–83.
6.
MedzhitovR, Preston-HurlburtPJanewayCAJr. A human homologue of the Drosophila Toll protein signals activation of adaptive immunity. Nature1997;388:394–7.
7.
PandeyS, KawaiT, AkiraS. Microbial sensing by toll-like receptors and intracellular nucleic acid sensors. Cold Spring Harb Perspect Med2015;5:a016246.
8.
PoltorakA, HeX, SmirnovaI, . Defective LPS signaling in C3H/HeJ and C57BL/10ScCr mice: mutations in Tlr4 gene. Science1998;282:2085–8.
9.
TakeuchiO, HoshinoK, KawaiT, . Differential roles of TLR2 and TLR4 in recognition of gram-negative and gram-positive bacterial cell wall components. Immunity1999;11:443–51.
10.
SchwandnerR, DziarskiR, WescheH, . Peptidoglycan- and lipoteichoic acid-induced cell activation is mediated by toll-like receptor 2. J Biol Chem1999;274:17406–9.
11.
MeansTK, LienE, YoshimuraA, . The CD14 ligands lipoarabinomannan and lipopolysaccharide differ in their requirement for Toll-like receptors. J Immunol1999;163:6748–55.
12.
CamposMA, AlmeidaIC, TakeuchiO, . Activation of Toll-like receptor-2 by glycosylphosphatidylinositol anchors from a protozoan parasite. J Immunol2001;167:416–23.
13.
UnderhillDM, OzinskyA, HajjarAM, . The Toll-like receptor 2 is recruited to macrophage phagosomes and discriminates between pathogens. Nature1999;401:811–5.
14.
BiebackK, LienE, KlaggeIM, . Hemagglutinin protein of wild-type measles virus activates toll-like receptor 2 signaling. J Virol2002;76:8729–36.
15.
OzinskyA, UnderhillDM, FontenotJD, . The repertoire for pattern recognition of pathogens by the innate immune system is defined by cooperation between toll-like receptors. Proc Natl Acad Sci USA2000;97:13766–71.
16.
TakeuchiO, KawaiT, MühlradtPF, . Discrimination of bacterial lipoproteins by Toll-like receptor 6. Int Immunol2001;13:933–40.
17.
HayashiF, SmithKD, OzinskyA, . The innate immune response to bacterial flagellin is mediated by Toll-like receptor 5. Nature2001;410:1099–103.
18.
KimD, KimYJ, KohHS, . Reactive oxygen species enhance TLR10 expression in the human monocytic cell line THP-1. Int J Mol Sci2010;11:3769–82.
19.
LeeSM, KokKH, JaumeM, . Toll-like receptor 10 is involved in induction of innate immune responses to influenza virus infection. Proc Natl Acad Sci USA2014;111:3793–8.
20.
GuanY, RanoaDR, JiangS, . Human TLRs 10 and 1 share common mechanisms of innate immune sensing but not signaling. J Immunol2010;184:5094–103.
TanjiH, OhtoU, ShibataT, . Structural reorganization of the Toll-like receptor 8 dimer induced by agonistic ligands. Science2013;339:1426–9.
24.
MuzioM, BosisioD, PolentaruttiN, . Differential expression and regulation of toll-like receptors (TLR) in human leukocytes: selective expression of TLR3 in dendritic cells. J Immunol2000;164:5998–6004.
25.
AlexopoulouL, HoltAC, MedzhitovR, . Recognition of double stranded RNA and activation of NF-κB by Toll-like receptor 3. Nature2001;413:732–8.
BiondoC, MalaraA, CostaA, . Recognition of fungal RNA by TLR7 has a nonredundant role in host defense against experimental candidiasis. Eur J Immunol2012;42:2632–43.
28.
MancusoG, GambuzzaM, MidiriA, . Bacterial recognition by TLR7 in the lysosomes of conventional dendritic cells. Nat Immunol2009;10:587–94.
29.
HornungV, Guenthner-BillerM, BourquinC, . Sequence-specific potent induction of IFN-alpha by short interfering RNA in plasmacytoid dendritic cells through TLR7. Nat Med2005;11:263–70.
KrugA, FrenchAR, BarchetW, . TLR9-dependent recognition of MCMV by IPC and DC generates coordinated cytokine responses that activate antiviral NK cell function. Immunity2004;21:107–19.
32.
BaficaA, SantiagoHC, GoldszmidR, . Cutting edge: TLR9 and TLR2 signaling together account for MyD88-dependent control of parasitemia in trypanosoma cruzi infection. J Immunol2006;177:3515–9.
33.
TakahashiK, ShibataT, Akashi-TakamuraS, . A protein associated with Toll-like receptor (TLR) 4 (PRAT4A) is required for TLR-dependent immune responses. J Exp Med2007;204:2963–76.
34.
BrinkmannMM, SpoonerE, HoebeK, . The interaction between the ER membrane protein UNC93B and TLR3, 7, and 9 is crucial for TLR signaling. J Cell Biol2007;177:265–75.
35.
TabetaK, HoebeK, JanssenEM, . The Unc93b1 mutation 3d disrupts exogenous antigen presentation and signaling via Toll-like receptors 3, 7 and 9. Nat Immunol2006;7:156–64.
36.
KobeB, DeisenhoferJ. Proteins with leucine-rich repeats. Curr Opin Struct Biol1995;5:409–16.
37.
RockFL, HardimanG, TimansJC, . A family of human receptors structurally related to Drosophila Toll. Proc Natl Acad Sci USA1998;95:588–93.
38.
DunneA, O'NeillLA. The interleukin-1 receptor/Toll-like receptor superfamily: signal transduction during inflammation and host defense. Sci STKE2003;2003:re3.
39.
WrightSD, RamosRA, TobiasPS, . CD14, a receptor for complexes of lipopolysaccharide (LPS) and LPS binding protein. Science1990;249:1431–3.
40.
ShimazuR, AkashiS, OgataH, . MD-2, a molecule that confers lipopolysaccharide responsiveness on Toll-like receptor 4. J Exp Med1999;189:1777–82.
41.
O'NeillLA, BowieAG. The family of five: TIR-domain-containing adaptors in Toll-like receptor signalling. Nat Rev Immunol2007;7:353–64.
42.
MedzhitovR, Preston-HurlburtP, KoppE, . MyD88 is an adaptor protein in the hToll/IL-1 receptor family signaling pathways. Mol Cell1998;2:253–8.
43.
KawaiT, AdachiO, OgawaT, . Unresponsiveness of MyD88-deficient mice to endotoxin. Immunity1999;11:115–22.
44.
HondaK, YanaiH, MizutaniT, . Role of a transductional-transcriptional processor complex involving MyD88 and IRF-7 in Toll-like receptor signaling. Proc Natl Acad Sci USA2004;101:15416–21.
45.
TakaokaA, YanaiH, KondoS, . Integral role of IRF-5 in the gene induction programme activated by Toll-like receptors. Nature2005;434:243–9.
46.
NegishiH, FujitaY, YanaiH, . Evidence for licensing of IFN-gamma-induced IFN regulatory factor 1 transcription factor by MyD88 in Toll-like receptor-dependent gene induction program. Proc Natl Acad Sci USA2006;103:15136–41.
47.
KawaiT, AkiraS. Toll-like receptors and their crosstalk with other innate receptors in infection and immunity. Immunity2011;34:637–50.
48.
PengJ, YuanQ, LinB, . SARM inhibits both TRIF- and MyD88-mediated AP-1 activation. Eur J Immunol2010;40:1738–47.
49.
GilmoreTD. The Rel/NF-kappaB signal transduction pathway: introduction. Oncogene1999;18:6842–4.
50.
WescheH, HenzelWJ, ShillinglawW, . MyD88: an adapter that recruits IRAK to the IL-1 receptor complex. Immunity1997;7:837–47.
51.
LinSC, LoYC, WuH. Helical assembly in the MyD88-IRAK4-IRAK2 complex in TLR/IL-1R signalling. Nature2010;465:885–90.
52.
ClarkK, NandaS, CohenP. Molecular control of the NEMO family of ubiquitin-binding proteins. Nat Rev Mol Cell Biol2013;14:673–85.
53.
NapetschnigJ, WuH. Molecular basis of NF-kappaB signaling. Annu Rev Biophys2013;42:443–68.
54.
TaylorCT, McElwainJC. Ancient atmospheres and the evolution of oxygen sensing via the hypoxia-inducible factor in metazoans. Physiology (Bethesda)2010;25:272–9.
55.
AlbertsB, BrayD, HopkinK, . Molecular Biology of the Cells4th ed. New York: Garland Science; 2014.
56.
RichPR. The molecular machinery of Keilin's respiratory chain. Biochem Soc Trans2003;31:1095–105.
57.
RolfeDF, BrownGC. Cellular energy utilization and molecular origin of standard metabolic rate in mammals. Physiol Rev1997;77:731–58.
58.
SemenzaGL, WangGL. A nuclear factor induced by hypoxia via de novo protein synthesis binds to the human erythropoietin gene enhancer at a site required for transcriptional activation. Mol Cell Biol1992;12:5447–54.
59.
SemenzaGL. Targeting HIF-1 for cancer therapy. Nat Rev Cancer2003;3:721–32.
60.
HanahanD, WeinbergRA. Hallmarks of cancer: the next generation. Cell2011;144:646–74.
61.
IyerNV, KotchLE, AganiF, . Cellular and developmental control of O2 homeostasis by hypoxia-inducible factor 1 alpha. Genes Dev1998;12:149–62.
62.
SemenzaGL, JiangBH, LeungSW, . Hypoxia response elements in the aldolase A, enolase 1, and lactate dehydrogenase A gene promoters contain essential binding sites for hypoxia-inducible factor 1. J Biol Chem1996;271:32529–37.
63.
KimJW, TchernyshyovI, SemenzaGL, . HIF-1-mediated expression of pyruvate dehydrogenase kinase: a metabolic switch required for cellular adaptation to hypoxia. Cell Metab2006;3:177–85.
64.
FukudaR, ZhangH, KimJW, . HIF-1 regulates cytochrome oxidase subunits to optimize efficiency of respiration in hypoxic cells. Cell2007;129:111–22.
65.
WangGL, SemenzaGL. Purification and characterization of hypoxia-inducible factor 1. J Biol Chem1995;270:1230–7.
66.
EmaM, TayaS, YokotaniN, . A novel bHLH-PAS factor with close sequence similarity to hypoxia-inducible factor 1alpha regulates the VEGF expression and is potentially involved in lung and vascular development. Proc Natl Acad Sci USA1997;94:4273–8.
67.
FlammeI, FröhlichT, von ReuternM, . HRF, a putative basic helix-loop-helix-PAS-domain transcription factor is closely related to hypoxia-inducible factor-1 alpha and developmentally expressed in blood vessels. Mech Dev1997;63:51–60.
EpsteinAC, GleadleJM, McNeillLA, . C. elegans EGL-9 and mammalian homologs define a family of dioxygenases that regulate HIF by prolyl hydroxylation. Cell2001;107:43–54.
70.
KaelinWGJrRatcliffePJ. Oxygen sensing by metazoans: the central role of the HIF hydroxylase pathway. Mol Cell2008;30:393–402.
71.
MahonPC, HirotaK, SemenzaGL. FIH-1: a novel protein that interacts with HIF-1alpha and VHL to mediate repression of HIF-1 transcriptional activity. Genes Dev2001;15 :2675–86.
72.
BruickRK, McKnightSL. A conserved family of prolyl-4-hydroxylases that modifies HIF. Science2001;294:1337–40.
73.
JaakkolaP, MoleDR, TianYM, . Targeting of HIF-alpha to the von Hippel-Lindau ubiquitylation complex by O2-regulated prolyl hydroxylation. Science2001;292:468–72.
74.
LandoD, PeetDJ, GormanJJ, . FIH-1 is an asparaginyl hydroxylase enzyme that regulates the transcriptional activity of hypoxia-inducible factor. Genes Dev2002;16:1466–71.
75.
HagenT, TaylorCT, LamF, . Redistribution of intracellular oxygen in hypoxia by nitric oxide: effect on HIF1alpha. Science2003;302:1975–8.
76.
TaylorCT. Mitochondria and cellular oxygen sensing in the HIF pathway. Biochem J2008;409:19–26.
77.
NizetV, JohnsonRS. Interdependence of hypoxic and innate immune responses. Nat Rev Immunol2009;9:609–17.
78.
ColganSP, TaylorCT. Hypoxia: an alarm signal during intestinal inflammation. Nat Rev Gastroenterol Hepatol2010;7:281–7.
79.
CramerT, YamanishiY, ClausenBE, . HIF-1alpha is essential for myeloid cell-mediated inflammation. Cell2003;112:645–57.
80.
PeyssonnauxC, Cejudo-Martin P DoedensA, . Cutting edge: Essential role of hypoxia inducible factor-1alpha in development of lipopolysaccharide-induced sepsis. J Immunol2007;178:7156–9.
81.
SpirigR, DjafarzadehS, RegueiraT, . Effects of TLR agonists on the hypoxia-regulated transcription factor HIF-1alpha and dendritic cell maturation under normoxic conditions. PLoS One2010;5(6):e0010983.
82.
KuhlickeJ, FrickJS, Morote-GarciaJC, . Hypoxia inducible factor (HIF)-1 coordinates induction of Toll-like receptors TLR2 and TLR6 during hypoxia. PLoSOne2007;2(12):e1364.
83.
FredeS, StockmannC, FreitagP, . Bacterial lipopolysaccharide induces HIF-1 activation in human monocytes via p44/42 MAPK and NF-kappaB. Biochem J2006;396:517–27.
84.
MiZ, RapisardaA, TaylorL, . Synergystic induction of HIF-1alpha transcriptional activity by hypoxia and lipopolysaccharide in macrophages. Cell Cycle2008;7:232–41.
85.
RamanathanM, Pinhal-EnfieldG, HaoI, . Synergistic up-regulation of vascular endothelial growth factor (VEGF) expression in macrophages by adenosine A2A receptor agonists and endotoxin involves transcriptional regulation via the hypoxia response element in the VEGF promoter. Mol Biol Cell2007;18:14–23.
86.
SumbayevVV. LPS-induced Toll-like receptor 4 signalling triggers cross-talk of apoptosis signal-regulating kinase 1 (ASK1) and HIF-1alpha protein. FEBS Lett2008;582:319–26.
RiusJ, GumaM, SchachtrupC, . NF-kappaB links innate immunity to the hypoxic response through transcriptional regulation of HIF-1alpha. Nature2008;453:807–11.
89.
NishiK, OdaT, TakabuchiS, . LPS induces hypoxia-inducible factor 1 activation in macrophage-differentiated cells in a reactive oxygen species-dependent manner. Antioxid Redox Signal2008;10:983–95.
90.
GeraldD, BerraE, FrapartYM, . JunD reduces tumor angiogenesis by protecting cells from oxidative stress. Cell2004;118:781–94.
91.
PchejetskiD, NunesJ, CoughlanK, . The involvement of sphingosine kinase 1 in LPS-induced Toll-like receptor 4-mediated accumulation of HIF-α protein, activation of ASK1 and production of the pro-inflammatory cytokine IL-6. Immunol Cell Biol2011;89:268–74.
92.
TannahillGM, CurtisAM, AdamikJ, . Succinate is an inflammatory signal that induces IL-1β through HIF-1α. Nature2013;496:238–42.
93.
HamsE, SaundersSP, CumminsEP, . The hydroxylase inhibitor dimethyloxallyl glycine attenuates endotoxic shock via alternative activation of macrophages and IL-10 production by B1 cells. Shock2011;36:295–302.
94.
ScholzCC, CavadasMA, TambuwalaMM, . Regulation of IL-1β-induced NF-κB by hydroxylases links key hypoxic and inflammatory signaling pathways. Proc Natl Acad Sci USA2013;110:18490–5.