High glucose induces Toll-like receptor expression in human monocytes: Mechanism of activation

  1. Mohan R. Dasu1,
  2. Sridevi Devaraj1,
  3. Zhao Ling2,
  4. Daniel H. Hwang2 and
  5. Ishwarlal Jialal (ishwarlal.jialal{at}ucdmc.ucdavis.edu)1
  1. 1Laboratory for Atherosclerosis and Metabolic Research, University of California Davis Medical Center, Sacramento, CA
  2. 2Western Human Nutrition Research Center (USDA/ARS) & University of California, Davis, CA

    Abstract

    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 as well as 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 & Results: High glucose (HG-[15mM]) significantly induced TLR2 and TLR4 expression in THP-1 cells in a time and dose dependent manner (P<0.05). HG increased TLR expression, MyD88, IRAK-1, and NF-κB p65 dependent activation in THP-1 cells. THP-1 cell data was further confirmed using freshly isolated monocytes from healthy human volunteers (n=10). Pharmacological inhibition of 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 76% (P<0.05) decrease in HG induced NF-κB activity, suggesting an additive effect. Furthermore, PKC-α knock down decreased TLR2 by 61% (P<0.05), while inhibition of PKC-δ decreased TLR4 under HG by 63% (P<0.05). Small inhibitory RNA to p47Phox in THP-1 cells abrogated HG induced TLR2 and TLR4 expression. Additional studies revealed that, PKC-α, PKC-δ, and p47Phox knock down significantly abrogated HG induced NF-κB activation and inflammatory cytokine secretion.

    Conclusions: Collectively, these data suggests that HG induces toll like receptor 2 and 4 expression via PKC-α and PKC-δ respectively by stimulating NADPH oxidase in human monocytes.

    Footnotes

      • Received April 25, 2008.
      • Accepted July 21, 2008.

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