TLR-4 agonistic lipopolysaccharide upregulates interleukin-8 at the transcriptional and post-translational level in vascular smooth muscle cells

Sparstolonin B suppresses rat vascular smooth muscle cell proliferation, migration, inflammatory response and lipid accumulation

Vascular smooth muscle cells (VSMCs) play a crucial role in atherosclerotic lesion formation. Sparstolonin B (SsnB) is a TLR2/TLR4 antagonist that inhibits inflammatory responses in multiple cell types. Herein, we investigated if SsnB inhibited VSMC proliferation, migration, inflammatory response and lipid accumulation. We found that SsnB suppressed VSMC proliferation and migration induced by PDGF. SsnB significantly suppressed the expression of MCP-1, TNFα and IL-6 in VSMCs stimulated by either lipopolysaccharide (LPS) or PDGF. Erk1/2 and Akt signaling pathways, which are responsible for the VSMC inflammatory response, were activated by LPS or PDGF stimulation, and SsnB significantly inhibited their activation. SsnB also substantially suppressed the intracellular cholesterol accumulation in VSMCs loaded with acetylated LDL. Mechanistically, SsnB remarkably repressed LPS-induced up-regulation of CD36, which is responsible for lipid uptake, and dramatically reversed LPS-induced inhibition of ABCA1, which promotes the efflux of intracellular free cholesterol. In conclusion, our results indicate that SsnB significantly inhibits VSMC proliferation, migration, inflammatory responses and lipid accumulation. Along with the previously reported anti-inflammatory activities of SsnB on macrophages and vascular endothelial cells, our data strongly suggest that SsnB may be developed as a new anti-atherogenic therapy.

Resveratrol post-transcriptionally regulates pro-inflammatory gene expression via regulation of KSRP RNA binding activity

Resveratrol shows beneficial effects in inflammation-based diseases like cancer, cardiovascular and chronic inflammatory diseases. Therefore, the molecular mechanisms of the anti-inflammatory resveratrol effects deserve more attention. In human epithelial DLD-1 and monocytic Mono Mac 6 cells resveratrol decreased the expression of iNOS, IL-8 and TNF-α by reducing mRNA stability without inhibition of the promoter activity. Shown by pharmacological and siRNA-mediated inhibition, the observed effects are SIRT1-independent. Target-fishing and drug responsive target stability experiments showed selective binding of resveratrol to the RNA-binding protein KSRP, a central post-transcriptional regulator of pro-inflammatory gene expression. Knockdown of KSRP expression prevented resveratrol-induced mRNA destabilization in human and murine cells. Resveratrol did not change KSRP expression, but immunoprecipitation experiments indicated that resveratrol reduces the p38 MAPK-related inhibitory KSRP threonine phosphorylation, without blocking p38 MAPK activation or activity. Mutation of the p38 MAPK target site in KSRP blocked the resveratrol effect on pro-inflammatory gene expression. In addition, resveratrol incubation enhanced KSRP-exosome interaction, which is important for mRNA degradation. Finally, resveratrol incubation enhanced its intra-cellular binding to the IL-8, iNOS and TNF-α mRNA. Therefore, modulation of KSRP mRNA binding activity and, thereby, enhancement of mRNA degradation seems to be the common denominator of many anti-inflammatory effects of resveratrol.

Palmitate induces interleukin-8 expression in human aortic vascular smooth muscle cells via Toll-like receptor 4/nuclear factor-κB pathway (TLR4/NF-κB-8)

BACKGROUND

Recent evidence demonstrates that saturated free fatty acids (FFAs) induce the inflammatory response via the Toll-like receptor 4 (TLR4) pathway. Interleukin-8 (IL-8) is a proinflammatory cytokine that induces vascular smooth muscle cell proliferation and migration in vitro. However, the regulation of IL-8 expression by palmitate in human vascular smooth muscle cells (HVSMCs) has not been clarified. The aim of this study was to investigate the regulation of IL-8 expression by free fatty acids and determine the underlying mechanisms in HVSMCs.

METHODS

Human vascular smooth muscle cells were cultured and treated with palmitate, various signaling inhibitors or TLR4 shRNA adenovirus, and the mRNA and protein expression levels of IL-8, nuclear factor κB (NF-κB) luciferase activity and NF-κB p65 binding activity were studied.

RESULTS

Palmitate induced IL-8 mRNA expression and secretion in a dose-dependent manner. Palmitate significantly stimulated both nuclear factor κB (NF-κB) luciferase activity and NF-κB p65 binding activity, which were markedly diminished by pretreatment with the NF-κB inhibitor, parthenolide. Parthenolide pretreatment also abolished IL-8 mRNA and protein induction by palmitate. By contrast, disrupting the ceramide and phosphoinositide-3 kinase (PI3K) pathways with myriocin and wortmannin did not affect palmitate-induced IL-8 expression. Inhibition of protein kinase C (PKC) activation with calphostin C and chelerythrine partially suppressed palmitate-stimulated IL-8 expression, but it had no effect on palmitate-induced NF-κB activation. Finally, knockdown of TLR4 markedly abolished palmitate-induced NF-κB activation and IL-8 expression.

CONCLUSIONS

Palmitate induces IL-8 gene expression in HVSMCs through the TLR4/NF-κB pathway.

The expression and functions of toll-like receptors in atherosclerosis

Inflammation drives atherosclerosis. Both immune and resident vascular cell types are involved in the development of atherosclerotic lesions. The phenotype and function of these cells are key in determining the development of lesions. Toll-like receptors are the most characterised innate immune receptors and are responsible for the recognition of exogenous conserved motifs on pathogens, and, potentially, some endogenous molecules. Both endogenous and exogenous TLR agonists may be present in atherosclerotic plaques. Engagement of toll-like receptors on immune and resident vascular cells can affect atherogenesis as signalling downstream of these receptors can elicit proinflammatory cytokine release, lipid uptake, and foam cell formation and activate cells of the adaptive immune system. In this paper, we will describe the expression of TLRs on immune and resident vascular cells, highlight the TLR ligands that may act through TLRs on these cells, and discuss the consequences of TLR activation in atherosclerosis.

Cellular actors, Toll-like receptors, and local cytokine profile in acute coronary syndromes

AIMS

Inflammation plays a key role in acute coronary syndromes (ACS). Toll-like receptors (TLR) on leucocytes mediate inflammation and immune responses. We characterized leucocytes and TLR expression within coronary thrombi and compared cytokine levels from the site of coronary occlusion with aortic blood (AB) in ACS patients.

METHODS AND RESULTS

In 18 ACS patients, thrombi were collected by aspiration during primary percutaneous coronary intervention. Thrombi and AB from these patients as well as AB from 10 age-matched controls without coronary artery disease were assessed by FACS analysis for cellular distribution and TLR expression. For further discrimination of ACS specificity, seven non-coronary intravascular thrombi and eight thrombi generated in vitro were analysed. In 17 additional patients, cytokine levels were determined in blood samples from the site of coronary occlusion under distal occlusion and compared with AB. In coronary thrombi from ACS, the percentage of monocytes related to the total leucocyte count was greater than in AB (47 vs. 20%, P = 0.0002). In thrombi, TLR-4 and TLR-2 were overexpressed on CD14-labelled monocytes, and TLR-2 was increased on CD66b-labelled granulocytes, in comparison with leucocytes in AB. In contrast, in vitro and non-coronary thrombi exhibited no overexpression of TLR-4. Local blood samples taken under distal occlusion revealed elevated concentrations of chemokines (IL-8, MCP-1, eotaxin, MIP-1alpha, and IP-10) and cytokines (IL-1ra, IL-6, IL-7, IL-12, IL-17, IFN-alpha, and granulocyte-macrophage colony-stimulating factor) regulating both innate and adaptive immunity (all P < 0.05).

CONCLUSION

In ACS patients, monocytes accumulate within thrombi and specifically overexpress TLR-4. Together with the local expression patterns of chemokines and cytokines, the increase of TLR-4 reflects a concerted activation of this inflammatory pathway at the site of coronary occlusion in ACS.