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Hypoxia inducible factor (HIF)-1 coordinates induction of Toll-like receptors TLR2 and TLR6 during hypoxia.

Kuhlicke J, Frick JS, Morote-Garcia JC, Rosenberger P, Eltzschig HK - PLoS ONE (2007)

Bottom Line: During acute infection and inflammation, dramatic shifts in tissue metabolism are typical, thereby resulting in profound tissue hypoxia.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).Studies using loss and gain of function of HIF-1 confirmed a critical role of HIF-1alpha in coordinating TLR2 and TLR6 induction.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology and Intensive Care Medicine, Tübingen University Hospital, Tübingen, Germany.

ABSTRACT

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.

Methodology/principal findings: 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/significance: 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.

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Pulmonary immunohistochemistry for TLR2 and TLR6 during hypoxia.A and B, Lungs from mice exposed to normoxia or normobaric hypoxia (8% O2, 92% N2 for 4h) were harvested, formalin-fixed and paraffin-embedded. Sections were stained with antibodies for TLR2 and TLR6 or isotype controls. This figure is representative of three experiments in each condition.
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pone-0001364-g007: Pulmonary immunohistochemistry for TLR2 and TLR6 during hypoxia.A and B, Lungs from mice exposed to normoxia or normobaric hypoxia (8% O2, 92% N2 for 4h) were harvested, formalin-fixed and paraffin-embedded. Sections were stained with antibodies for TLR2 and TLR6 or isotype controls. This figure is representative of three experiments in each condition.

Mentions: To confirm hypoxia induction of TLR2 and TLR6 in vivo, we utilized a previously described murine model of ambient hypoxia [26]–[30]. For this purpose, we exposed C57BL/6 mice over 6h to ambient hypoxia (8% oxygen), and examined TLR2 and TLR6 transcript levels in mucosal organs including the colon, liver and lungs. As shown in Figure 6A (TLR2) and 6B (TLR6), real-time PCR analysis revealed a significant increase of TLR2 and TLR6 transcript in all three examined organs. In addition, immunohistochemical staining of sections of lung tissues confirmed TLR2 (Figure 7A) and TLR6 (Figure 7B) induction in vivo. Taken together, these findings indicate that induction of TLR2 and TLR6 also occurs during ambient hypoxia in vivo.


Hypoxia inducible factor (HIF)-1 coordinates induction of Toll-like receptors TLR2 and TLR6 during hypoxia.

Kuhlicke J, Frick JS, Morote-Garcia JC, Rosenberger P, Eltzschig HK - PLoS ONE (2007)

Pulmonary immunohistochemistry for TLR2 and TLR6 during hypoxia.A and B, Lungs from mice exposed to normoxia or normobaric hypoxia (8% O2, 92% N2 for 4h) were harvested, formalin-fixed and paraffin-embedded. Sections were stained with antibodies for TLR2 and TLR6 or isotype controls. This figure is representative of three experiments in each condition.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC2147045&req=5

pone-0001364-g007: Pulmonary immunohistochemistry for TLR2 and TLR6 during hypoxia.A and B, Lungs from mice exposed to normoxia or normobaric hypoxia (8% O2, 92% N2 for 4h) were harvested, formalin-fixed and paraffin-embedded. Sections were stained with antibodies for TLR2 and TLR6 or isotype controls. This figure is representative of three experiments in each condition.
Mentions: To confirm hypoxia induction of TLR2 and TLR6 in vivo, we utilized a previously described murine model of ambient hypoxia [26]–[30]. For this purpose, we exposed C57BL/6 mice over 6h to ambient hypoxia (8% oxygen), and examined TLR2 and TLR6 transcript levels in mucosal organs including the colon, liver and lungs. As shown in Figure 6A (TLR2) and 6B (TLR6), real-time PCR analysis revealed a significant increase of TLR2 and TLR6 transcript in all three examined organs. In addition, immunohistochemical staining of sections of lung tissues confirmed TLR2 (Figure 7A) and TLR6 (Figure 7B) induction in vivo. Taken together, these findings indicate that induction of TLR2 and TLR6 also occurs during ambient hypoxia in vivo.

Bottom Line: During acute infection and inflammation, dramatic shifts in tissue metabolism are typical, thereby resulting in profound tissue hypoxia.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).Studies using loss and gain of function of HIF-1 confirmed a critical role of HIF-1alpha in coordinating TLR2 and TLR6 induction.

View Article: PubMed Central - PubMed

Affiliation: Department of Anesthesiology and Intensive Care Medicine, Tübingen University Hospital, Tübingen, Germany.

ABSTRACT

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.

Methodology/principal findings: 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/significance: 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.

Show MeSH
Related in: MedlinePlus