PF4 Is Expressed In ApoE～(-/-) Mice Atherosclerotic Plaques And Regulates TLR2 Expression

Atherosclerosis, formerly considered a lipid storage disease,actually involves ongoing inflammatory responses. Inflammation in the arterial vessel wall is considered to play an important role in the pathogenesis of atherosclerosis. Indeed, recent advances have established a fundamental role for inflammation in mediating all stages of this disease, from initiation through progression. In particular, the members of the toll like receptor family play a critical role in the inflammatory components of atherosclerosis. Toll-like receptors are a group of receptors that play a key role in innate immune signaling and initiating inflammatory responses. Ligation of these receptors initiates the activation of nuclear foctor-κB(NF-κB) resulting in the expression of a wide array of inflammatory genes. Recent animal studies, except TLR4, TLR2 also plays an important role in atherosclerotic plaque accumulation. Both exogenous ligands involved in microbial recognition as well as endogenous ligands involved in sterile inflammation pathways are implicated in the pathology of atherosclerosis.Recent studies have provided insight into platelet functions in inflammation and atherosclerosis.A range of molecules, present on the cross-talk of platelets with other inflammatory cells during the vascular inflammation involved in the development and progression of atherosclerosis. Platelet factor 4(PF-4),a member of the C-X-C subfamily of chemokines, is derived by proteolysis from platelet basic protein. Recent studies provide more evidence for the involvement of PF-4 in the development of atherosclerosis. Yu G et al demonostrate that E- selectin surface protein expression is increased by endothelial cells exposed to PF4. PF4 may be as a link between platelets, endothelium and macrophages in inflammatory disease like atherosclerosis. We try to explore the expression of TLR2 and PF4 in apoE-/- mice, and investigate the effects of PF4 on expression of TLR2 by endothelial cells in cell experiments.Part I PF4 and TLR2 are expressed in ApoE-/- mice atherosclerotic plaquesAim To investigate a potential role of TLR2 and PF4 in atherosclerosis, We assessed their expression in murine atherosclerotic plaques.Methods and Results Aortic lesions of high-fat diet-fed apoE–deficient mice were examined for TLR2 and PF4 expression by immunohistochemistry. Aortic atherosclerotic lesions in all apoE-deficient mice expressed TLR2, whereas aortic tissue obtained from control C57BL/6J mice showed no TLR2 expression. Serial sections immunostaining showed TLR2 colocalizing with macrophages and endothelial cells in murine atherosclerotic lesions. Furthermore, PF4 expression in murine atherosclerotic plaques were also observed.Conclusions Our study demonstrates that TLR2 is expressed by macrophages and endothelial cells in murine atherosclerotic lesions, and we find that PF4 is also expressed in the plaques. They may play a role to enhance and sustain the innate immue and inflammatory responses.Part II Platelet factor 4 regulates TLR2 expression in human umbilical vein endothelial cellsAim To investigate the effects of platelet factor 4 on toll like receptor 2 and proinflammatory cytokine ICAM-1 expression in cultured human umbilical vein endothelial cellsMethods We determined by reverse-transcription polymerase chain reaction and Western blot analysis PF4 regulate TLR2 expression in cultured endothelial cells, and whether this regulation influences NF-κB activation and increases cytokine ICAM-2 mRNA expressionResults Our results demonstrate that PF4 induces endothelial TLR2 expression, induces ICAM-1 mRNA increasing, and initiates the activation of nuclear foctor-κB(NF-κB).Conclusion PF4 increases the expression of TLR2 mRNA and protein in hUVECs.