The Role Of Apolipoprotein C3in The Pathogenesis Of Atherosclerosis

BackgroundAt present, cardiovascular disease has become a heavy burden of the globalhealth care and health resources and contributs to the leading cause of death. As theinitial lesions of those serious cardiovascular disease however pathogenesis ofatherosclerosis (AS) has not been clearly elucidated yet. Immune inflammation playsan important role in the development of AS, it almost throughout the whole process ofthe disease. Therefore, occurrence of AS was not a simple lipid deposition, itsformation needed a long-term chronic process. Therefore we had reasons to believethat a prerequisite for the occurrence of AS was the body sustained some chronicstimulation.Apolipoprotein C3(APOC3) existed in each of the body and distributed in TRL(triglyceride-rich lipoprotein) and HDL (high density lipoprotein), meals and diseasestate made it exchange fast between them and then distribution changed. Highexpression of APOC3in plasma could not only cause lipid metabolism disorders, buthas been re-recognized as an independent pro-inflammatory role in recent years.APOC3not only was an independent risk factor for coronary heart disease (CHD), butalso associated with type2diabetes (T2DM), hypertension and obesity. Highexpression of the protein in mice could cause severe hypertriglyceridemia (HTG) andinduce hepatic steatosis and insulin resistance after high fat diet. A SNP naturallyoccurred in human APOC3gene resulted in decreased expression of the proteinsignificantly. Compared with wild-type, their coronary artery calcification(CAC)score and10-year CHD risk was reduced significantly. The relationship betweenAPOC3gene polymorphism and cardiovascular disease still was a hot pot in rencentyears. Many researchs were performing in many kinds of ethnics and groups. C3175Gof the fourth exon in the untranslated region has been studied mostly in foreigncountry. Followed was the two polymorphic loci in promoter: C-482T and T-455C,and they were studied less in our country too. About the association with CHD, therewas only one report by Bi-nan et al for C-482T polymorphism in domestic. Theassociation between T-455C and CHD has not been reported yet in our country. Wehave investigated those two polymorphisms (SNPs) in promoter and found that thevariant allele in healthy populations were positively correlated with HTG, however,the relationship did not appear in the population of patients with T2DM. View from the basic research, the stimulation of APOC3could increase theexpression of PKC-activate NF-and increase the expression of VCAM-1andICAM-1in endothelial cells. And the stimulation of APOC3also could increase theexpression of PKC-activate NF-and raise the expression of-integrin inmonocytes. As a result, promoting monocyte adhesion to endothelial cells. The studyalso found that APOC3could inhibit insulin signal transduction in endothelial cellsand cause insulin resistance. And suppress release of NO at the same time, as a result,vascular endothelial was in state of tension and was difficult to relax. Endothelial cellimpaired, activation, and recruiting white blood cells and then adhesion, those all wasnecessary step in AS. But if the subsequent events not followed, AS would not be inprogress. However, AS developed in quietly and gradually. The incidence of CHDwas still high. In addition to the role of APOC3in promoting adhesion betweenmonocytes and endothelial cells, there was no other role of APOC3in contributing toAS been reported.Objective:1To determine the the correlation of levels of APOC3in serum with CHD and the relationship between APOC3level and the extent of artery stenosis;2To study the relationship between APOC3promoter T-455C and C-482T gene polymorphisms and CHD;3To determine whether APOC3upregulates the expression of JAM-1and to investigate whether APOC3affected the adhesion rate of THP-1cells with mouse aorta.4To determine whether APOC3upregulated TNF-and whether TNF-upregulated JAM-1.Through exploring the relationship between APOC3level and the extent ofartery stenosis, relationship between APOC3promoter gene polymorphisms andcoronary heart disease, relationship between APOC3and inflammatory cytokines,platelet adhesion, tight junctions, cell extravasation during the development of AS,expected to provide new ideas for the prevention and treatment of cardiovasculardisease.Methods:120cases non-AS and187cases of AS, application of automatic biochemical analyzer to determine total APOC3TRL-APOC3HDL-APOC3and conventional lipid levels of plasma, analyze their relationships with coronary heart disease and arterial stenosis.2Application of TaqMan SNP allele assay to investigate APOC3T-455C and C-482T gene polymorphisms and analyse the correlation with CHD.3Vitro cultured human umbilical vein endothelial cells (HUVEC), provided various APOC3concentrations as stimulus, application of real time quantitative PCR(QRT-PCR), immunofluorescence and immunohistochemical methods to determine the expression of JAM-1in endothelial cell from gene to protein levels; Application of cell adhesion assay to investigate whether APOC3affected the adhesion rate of THP-1cells to the aortas of mice.4Vitro cultured HUVEC, provided various APOC3concentrations as stimulus, application of QRT-PCR to determine the expression of TNF-in endothelial cell; Provided TNF-as stimulus, application of QRT-PCR to determine the expression of JAM-1in endothelial cell.Results:(1) Compared with non-CHD group, the serum APOC3level significantly increased(9.46g/L vs7.43g/L), while APOA1and HDL-C concentration decreased (1.22g/L vs1.40g/L1.09g/L vs1.24g/L, respectively)in the CHD group. However, there was no significant difference of TRL-APOC3, HDL-APOC3, TG, Tch, LDL-C or APOB between CHD and control. Compared with non-AS group, the plasma APOC3level significantly increased(9.46g/L vs7.42g/L), while APOA1and HDL-C concentration decreased (1.23g/L vs1.40g/L1.09g/L vs1.24g/L, respectively)in the AS group. However, there was no significant difference of TRL-APOC3, HDL-APOC3, TG, Tch, LDL-C or APOB between AS and control. Coronary artery stenosis were divided into3groups according to the degree of stenosis:1%-50%,51%-75%,>75%. As a result total APOC3level significantly increased in all three AS group than in control, while there was no significant difference of total APOC3level in the three AS group.(2) There was no significant difference in distribution of genotype and allele frequencies of T-455C and C-482T polymorphisms between CHD and control group. Nor significant association between the two polymorphisms and lipids parameter levels studied, either(P>0.05). No relationship between CHD and the two polymorphisms was found. There also was no haplotype frequencies differences between CHD and control was found. While APOC3T-455C and C-482T polymorphisms were in strong linkage disequilibrium (D>0.7, P <0.0001).(3) JAM-1localized in the tight junctions of endothelial cells; APOC3stimulated HUVEC cells to up-regulate the expression of JAM-1, and in concentration-dependent manner; APOC3enhanced THP-1cell adhesion to the aortas of mice.(4) APOC3stimulated HUVEC cells to up-regulate the expression of TNF-and TNF-stimulated HUVEC cells to up-regulate the expression of JAM-1.Conclusions:1High expression of the total serum APOC3in AS group, regardless of the degree of stenosis or clinical symptoms.2No ralationship between APOC3promoter T-455C/C-482T polymorphisms and coronary heart disease was found.3APOC3stimulated HUVEC cells to up-regulate the expression of JAM-1and enhanced THP-1cell adhesion to aortas of mice.4APOC3stimulated HUVEC cells to up-regulate the expression of TNF-and TNF-stimulated HUVEC cells to up-regulate the expression of JAM-1.