Acid sphingomyelinase plays a key role in palmitic acid-amplified inflammatory signaling triggered by lipopolysaccharide at low concentrations in macrophages.
Periodontal disease is more prevalent and severe in patients with diabetes than in nondiabetic patients. In addition to diabetes, a large number of studies have demonstrated an association between obesity and chronic periodontal disease. However, the underlying mechanisms have not been well understood. Since plasma free fatty acids (FAs) are elevated in obese patients and saturated FAs such as palmitic acid (PA) have been shown to increase host inflammatory response, we sought to find out how PA interacts with lipopolysaccharide (LPS), an important pathological factor involved in periodontal disease, to enhance inflammation. We found that whereas low concentration of LPS (1 ng/ml) stimulated interleukin (IL)-6 expression in RAW 264.7 macrophages, PA further augmented it fourfold. Besides IL-6, PA amplified the stimulatory effect of LPS on a large amount of Toll-like receptor (TLR)4-mediated expression of proinflammatory signaling molecules such as IL-1 receptor-associated kinase-like 2 and proinflammatory molecules, including monocyte chemotactic protein-1 and colony-stimulating factor. We also observed that PA augmented TLR4 but not TLR2 signal, and the augmentation was mediated by nuclear factor-κB (NF-κB) pathways. To further elucidate the regulatory mechanism whereby PA amplifies LPS signal, our studies showed that PA and LPS synergistically increased hydrolysis of sphingomyelin by stimulating acid sphingomyelinase (ASMase) activity, which contributed to a marked increase in ceramide production and IL-6 upregulation. Taken together, this study has demonstrated that PA markedly augments TLR4-mediated proinflammatory signaling triggered by low concentration of LPS in macrophages, and ASMase plays a key role in the augmentation.
Ralph H. Johnson Veterans Affairs Medical Center, Charleston, South Carolina;
Junfei
J
Jin
Xiaoming
X
Zhang
Zhongyang
Z
Lu
David M
DM
Perry
Yanchun
Y
Li
Sarah Brice
SB
Russo
L Ashley
LA
Cowart
Yusuf A
YA
Hannun
Yan
Y
Huang
D000818:Animals; D002460:Cell Line; D007249:Inflammation / Q000378:metabolism*; D053592:Interleukin-1 Receptor-Associated Kinases / Q000378:metabolism; D015850:Interleukin-6 / Q000378:metabolism; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008264:Macrophages / Q000187:drug effects / Q000276:immunology / Q000378:metabolism*; D051379:Mice; D016328:NF-kappa B / Q000378:metabolism; D019308:Palmitic Acid / Q000494:pharmacology*; D015398:Signal Transduction / Q000187:drug effects / Q000276:immunology / Q000502:physiology*; D013108:Sphingomyelin Phosphodiesterase / Q000378:metabolism*; D051195:Toll-Like Receptor 2 / Q000378:metabolism; D051197:Toll-Like Receptor 4 / Q000378:metabolism
D015850:Interleukin-6; D008070:Lipopolysaccharides; D016328:NF-kappa B; D051195:Toll-Like Receptor 2; D051197:Toll-Like Receptor 4; D019308:Palmitic Acid; D053592:Interleukin-1 Receptor-Associated Kinases; C112980:acid sphingomyelinase-1; D013108:Sphingomyelin Phosphodiesterase
fatty acid; inflammation; lipopolysaccharide; sphingomyelinase; toll-like receptor