Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2012;7(4):e36200.
doi: 10.1371/journal.pone.0036200. Epub 2012 Apr 27.

Lipopolysaccharides impair insulin gene expression in isolated islets of Langerhans via Toll-Like Receptor-4 and NF-κB signalling

Julie Amyot  1 , Meriem Semache, Mourad Ferdaoussi, Ghislaine Fontés, Vincent Poitout
Affiliations

Lipopolysaccharides impair insulin gene expression in isolated islets of Langerhans via Toll-Like Receptor-4 and NF-κB signalling

Julie Amyot et al. PLoS One. 2012.

Abstract

Background: Type 2 diabetes is characterized by pancreatic β-cell dysfunction and is associated with low-grade inflammation. Recent observations suggest that the signalling cascade activated by lipopolysaccharides (LPS) binding to Toll-Like Receptor 4 (TLR4) exerts deleterious effects on pancreatic β-cell function; however, the molecular mechanisms of these effects are incompletely understood. In this study, we tested the hypothesis that LPS alters insulin gene expression via TLR4 and nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) in islets.

Methodology/principal findings: A 24-h exposure of isolated human, rat and mouse islets of Langerhans to LPS dose-dependently reduced insulin gene expression. This was associated in mouse and rat islets with decreased mRNA expression of pancreas-duodenum homebox-1 (PDX-1) and mammalian homologue of avian MafA/l-Maf (MafA). Accordingly, LPS exposure also decreased glucose-induced insulin secretion. LPS repression of insulin, PDX-1 and MafA expression, as well as its inhibition of insulin secretion, were not observed in islets from TLR4-deficient mice. LPS inhibition of β-cell gene expression in rat islets was prevented by inhibition of the NF-κB pathway, but not the p38 mitogen-activated protein kinase (p38 MAPK) pathway.

Conclusions/significance: Our findings demonstrate that LPS inhibit β-cell gene expression in a TLR4-dependent manner and via NF-κB signaling in pancreatic islets, suggesting a novel mechanism by which the gut microbiota might affect pancreatic β-cell function.

PubMed Disclaimer

Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Exposure to LPS dose-dependently represses insulin pre-mRNA expression in isolated rat and human islets.
Insulin pre-mRNA levels in response to increasing doses of LPS in isolated rat (A) and human (B) islets. Pre-mRNA levels were measured by RT-PCR and normalized to β-actin mRNA levels. Data are mean ± S.E.M. of 2–6 independent experiments; *p<0.05 vs 0 pg/mL.
Figure 2
Figure 2. Exposure to LPS decreases insulin, PDX-1 and MafA gene expression in isolated islets via TLR4.
(A) Insulin pre-mRNA expression (B) PDX-1 mRNA expression and (C) MafA mRNA expression in islets isolated from WT and TLR4-deficient mice exposed for 24 h to 2.8 (2.8 G) and 16.7 mM (16.7 G) glucose in the presence or absence of 0.5 mM palmitate (PA), 0.5 ng/mL IL-1β or 5 µg/mL LPS. mRNA levels were measured by RT-PCR and normalized to β-actin mRNA levels. Data are mean ± S.E.M. of 6 independent experiments; *p<0.05.
Figure 3
Figure 3. PDX-1 cellular localization is not altered in response to LPS.
HIT-T15 cells were transfected with a construct encoding a PDX-1-GFP fusion protein. PDX-1 localization (green) (A–F) was visualized by GFP fluorescence using a laser-scanning confocal microscope in cells cultured in 0.1 and 5 mM glucose with or without 0.5 mM palmitate or increasing doses of LPS. 4′,6-diamidino-2-phenylindole (DAPI) (blue) was used for nuclear staining (G–L). Images are representative of 3 replicate experiments.
Figure 4
Figure 4. Insulin secretion is reduced in response to LPS in WT but not TLR4-deficient mouse islets.
Insulin secretion (A), insulin content (B) and insulin secretion normalized by insulin content (C) as assessed in 1-h static incubations of isolated WT and TLR4-deficient islets at basal (2.8 mM) and stimulatory (16.7 mM) glucose following a 24-h exposure to 16.7 mM glucose in the presence or absence of 5 µg/mL LPS. Data are mean ± S.E.M. of 5 independent experiments; *p<0.05.
Figure 5
Figure 5. Inhibition of NF-κB, but not p38 MAPK, restores insulin, PDX-1, and MafA gene expression in islets exposed to LPS.
(A) Insulin pre-mRNA, (B) PDX-1 mRNA and (C) MafA mRNA expression in isolated rat islets exposed for 24 h to 16.7 mM (16.7 G) glucose in the presence or absence of 10 ng/mL LPS or 0.5 ng/mL IL-1β with or without SB202190 (10 µM) and IKK-2 Inh IV (10 µM). Data are mean ± S.E.M. of 3–4 independent experiments; *p<0.05.
Figure 6
Figure 6. Potential mechanism by which LPS repress insulin gene expression in isolated islets.
Exposure to LPS activates the NF-κB pathway in isolated islets and inhibits the expression of insulin, PDX-1 and MafA. The decrease in insulin expression might indirectly results from LPS inhibition of PDX-1 and MafA. NF-κB could also inhibit insulin gene expression by interacting with other proteins such as C/EBPβ and/or CREB, as observed in other cell types.
See this image and copyright information in PMC

Similar articles

See all similar articles

Cited by

See all "Cited by" articles

References

    1. Hotamisligil GS. Inflammation and metabolic disorders. Nature. 2006;444:860–867. - PubMed
    1. Kolb H, Mandrup-Poulsen T. An immune origin of type 2 diabetes? Diabetologia. 2005;48:1038–1050. - PubMed
    1. Maedler K, Sergeev P, Ris F, Oberholzer J, Joller-Jemelka HI, et al. Glucose-induced beta cell production of IL-1beta contributes to glucotoxicity in human pancreatic islets. J Clin Invest. 2002;110:851–860. - PMC - PubMed
    1. Maedler K, Spinas GA, Lehmann R, Sergeev P, Weber M, et al. Glucose induces beta-cell apoptosis via upregulation of the Fas receptor in human islets. Diabetes. 2001;50:1683–1690. - PubMed
    1. Larsen CM, Faulenbach M, Vaag A, Volund A, Ehses JA, et al. Interleukin-1-receptor antagonist in type 2 diabetes mellitus. N Engl J Med. 2007;356:1517–1526. - PubMed

Publication types

MeSH terms