C-reactive protein triggers inflammatory responses partly via TLR4/IRF3/NF-κB signaling pathway in rat vascular smooth muscle cells.
OBJECTIVE
C-reactive protein (CRP) plays an important role in the inflammatory process of atherosclerosis. Toll-like receptor 4 (TLR4) participates in atherogenesis by mediating the inflammatory responses. The aim of this experiment was to investigate the pro-inflammatory effects and mechanisms of CRP in rat vascular smooth muscle cells (VSMCs), especially focusing on the effects of CRP on IL-6 and peroxisome proliferator-activated receptor γ (PPARγ), and TLR4-dependent signal pathway.


METHODS
rat VSMCs were cultured, and CRP was used as a stimulant for IL-6 and peroxisome proliferator-activated receptor γ (PPARγ). IL-6 level in the culture supernatant was measured by ELISA, and mRNA and protein expressions were assayed by quantitative real-time PCR and western blot, respectively. RNA interference was used to assess the roles of TLR4 and interferon regulatory factor 3 (IRF3) in the pro-inflammatory signal pathway of CRP.


RESULTS
CRP stimulated IL-6 secretion, and inhibited mRNA and protein expression of PPARγ in VSMCs in a concentration-dependent manner. Additionally, CRP induced TLR4 expression, promoted nuclear translocation of NF-κB (p65), and augmented IκBα phosphorylation in VSMCs. Taken together, CRP induces the inflammatory responses through increasing IL-6 generation and reducing PPARγ expression in VSMCs, which is mediated by TLR4/IRF3/NF-κB signal pathway.


CONCLUSIONS
CRP is able to stimulate IL-6 production and to inhibit PPARγ expression in VSMCs via MyD88-independent TLR4 signaling pathway (TLR4/IRF3/NF-κB). These provide the novel evidence for the pro-inflammatory action of CRP involved in atherogenesis.
Liu
Na
N
Department of Pharmacology, Xi'an Jiaotong University School of Medicine, Xi'an 710061, China.
Liu
Jun-Tian
JT
Ji
Yuan-Yuan
YY
Lu
Pei-Pei
PP
D000818:Animals; D002097:C-Reactive Protein / Q000494:pharmacology* / Q000502:physiology; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects / Q000235:genetics; D006801:Humans; D020672:I-kappa B Proteins / Q000378:metabolism; D007249:Inflammation / Q000139:chemically induced / Q000378:metabolism; D050838:Interferon Regulatory Factor-3 / Q000235:genetics / Q000378:metabolism*; D015850:Interleukin-6 / Q000096:biosynthesis / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000166:cytology*; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000378:metabolism; D000072000:NF-KappaB Inhibitor alpha; D016328:NF-kappa B / Q000037:antagonists & inhibitors / Q000378:metabolism*; D047495:PPAR gamma / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D011112:Polymyxin B / Q000494:pharmacology; D011392:Proline / Q000031:analogs & derivatives / Q000494:pharmacology; D034741:RNA, Small Interfering / Q000235:genetics; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000187:drug effects* / Q000502:physiology; D013859:Thiocarbamates / Q000494:pharmacology; D051197:Toll-Like Receptor 4 / Q000235:genetics / Q000378:metabolism*
D020672:I-kappa B Proteins; D050838:Interferon Regulatory Factor-3; D015850:Interleukin-6; D008070:Lipopolysaccharides; D016328:NF-kappa B; C000606204:NFKBIA protein, human; C000606206:Nfkbia protein, rat; D047495:PPAR gamma; D034741:RNA, Small Interfering; D013859:Thiocarbamates; C495347:Tlr4 protein, rat; D051197:Toll-Like Receptor 4; C066229:prolinedithiocarbamate; D000072000:NF-KappaB Inhibitor alpha; D002097:C-Reactive Protein; D011392:Proline; D011112:Polymyxin B