High glucose induces toll-like receptor expression in human monocytes: mechanism of activation.
OBJECTIVE
Hyperglycemia-induced inflammation is central in diabetes complications, and monocytes are important in orchestrating these effects. Toll-like receptors (TLRs) play a key role in innate immune responses and inflammation. However, there is a paucity of data examining the expression and activity of TLRs in hyperglycemic conditions. Thus, in the present study, we examined TLR2 and TLR4 mRNA and protein expression and mechanism of their induction in monocytic cells under high-glucose conditions.


METHODS
High glucose (15 mmol/l) significantly induced TLR2 and TLR4 expression in THP-1 cells in a time- and dose-dependent manner (P < 0.05). High glucose increased TLR expression, myeloid differentiation factor 88, interleukin-1 receptor-associated kinase-1, and nuclear factor-kappaB (NF-kappaB) p65-dependent activation in THP-1 cells. THP-1 cell data were further confirmed using freshly isolated monocytes from healthy human volunteers (n = 10).


RESULTS
Pharmacological inhibition of protein kinase C (PKC) activity and NADPH oxidase significantly decreased TLR2 and TLR4 mRNA and protein (P < 0.05). Knocking down both TLR2 and TLR4 in the cells resulted in a 76% (P < 0.05) decrease in high-glucose-induced NF-kappaB activity, suggesting an additive effect. Furthermore, PKC-alpha knockdown decreased TLR2 by 61% (P < 0.05), whereas inhibition of PKC-delta decreased TLR4 under high glucose by 63% (P < 0.05). Small inhibitory RNA to p47Phox in THP-1 cells abrogated high-glucose-induced TLR2 and TLR4 expression. Additional studies revealed that PKC-alpha, PKC-delta, and p47Phox knockdown significantly abrogated high-glucose-induced NF-kappaB activation and inflammatory cytokine secretion.


CONCLUSIONS
Collectively, these data suggest that high glucose induces TLR2 and -4 expression via PKC-alpha and PKC-delta, respectively, by stimulating NADPH oxidase in human monocytes.
Dasu
Mohan R
MR
Laboratory for Atherosclerosis and Metabolic Research, University of California Davis Medical Center, Sacramento, California, USA.
Devaraj
Sridevi
S
Zhao
Ling
L
Hwang
Daniel H
DH
Jialal
Ishwarlal
I
D015153:Blotting, Western; D002460:Cell Line; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D005947:Glucose / Q000494:pharmacology*; D006801:Humans; D047468:Immunoprecipitation; D009000:Monocytes / Q000187:drug effects* / Q000378:metabolism; D016328:NF-kappa B / Q000378:metabolism; D011493:Protein Kinase C / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D051195:Toll-Like Receptor 2 / Q000235:genetics / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism; D051193:Toll-Like Receptors / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
D016328:NF-kappa B; D034741:RNA, Small Interfering; C495342:TLR2 protein, human; C495345:TLR4 protein, human; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D051193:Toll-Like Receptors; D011493:Protein Kinase C; D005947:Glucose