Hypoxia inducible factor (HIF)-1 coordinates induction of Toll-like receptors TLR2 and TLR6 during hypoxia.
BACKGROUND
During acute infection and inflammation, dramatic shifts in tissue metabolism are typical, thereby resulting in profound tissue hypoxia. Therefore, we pursued the hypothesis, that tissue hypoxia may influence innate immune responses by transcriptional modulation of Toll-like receptor (TLRs) expression and function.


RESULTS
We gained first insight from transcriptional profiling of murine dendritic cells exposed to hypoxia (2% oxygen for 24 h). While transcript levels of other TLRs remained unchanged, we found a robust induction of TLR2 (2.36+/-0.7-fold; P<0.05) and TLR6 (3.46+/-1.56-fold; P<0.05). Additional studies in different cells types and cell-lines including human dendritic cells, monocytic cells (MM6), endothelia (HMEC-1) or intestinal epithelia (Caco-2) confirmed TLR2 and TLR6 induction of transcript, protein and function during hypoxia. Furthermore, analysis of the putative TLR2 and TLR6 promoters revealed previously unrecognized binding sites for HIF-1, which were shown by chromatin immunoprecipitation to bind the pivotal hypoxia-regulating transcription factor HIF-1alpha. Studies using loss and gain of function of HIF-1 confirmed a critical role of HIF-1alpha in coordinating TLR2 and TLR6 induction. Moreover, studies of murine hypoxia (8% oxygen over 6 h) showed TLR2 and TLR 6 induction in mucosal organs in vivo. In contrast, hypoxia induction of TLR2 and TLR6 was abolished in conditional HIF-1alpha mutant mice.


CONCLUSIONS
Taking together, these studies reveal coordinated induction of TLR2 and TLR6 during hypoxia and suggest tissue hypoxia in transcriptional adaptation of innate immune responses during acute infection or inflammation.
Kuhlicke
Johannes
J
Department of Anesthesiology and Intensive Care Medicine, Tübingen University Hospital, Tübingen, Germany.
Frick
Julia S
JS
Morote-Garcia
Julio C
JC
Rosenberger
Peter
P
Eltzschig
Holger K
HK
D015153:Blotting, Western; D002460:Cell Line; D047369:Chromatin Immunoprecipitation; D004797:Enzyme-Linked Immunosorbent Assay; D006801:Humans; D000860:Hypoxia / Q000378:metabolism*; D007150:Immunohistochemistry; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D009363:Neoplasm Proteins / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D015398:Signal Transduction; D051195:Toll-Like Receptor 2 / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism; D051216:Toll-Like Receptor 6 / Q000096:biosynthesis* / Q000235:genetics / Q000378:metabolism
C405619:HIGD1A protein, human; D047908:Intracellular Signaling Peptides and Proteins; D024101:Mitochondrial Proteins; D009363:Neoplasm Proteins; D012333:RNA, Messenger; C495342:TLR2 protein, human; C495368:TLR6 protein, human; D051195:Toll-Like Receptor 2; D051216:Toll-Like Receptor 6