The Regulation Of Serum Opacity Factor To The Function Of High Density Lipoprotein

Background:Traditionally,it has been believed that high density lipoprotein-cholesterol（HDL-C）concentration is negatively correlated with the incidence of cardiovascular events.However,subsequent studies have found that high HDL-C concentration is also associated with higher mortality,so people’s attention has shifted from HDL-C content to HDL function.HDL mediates cholesterol reverse transport（RCT）which transports free cholesterol（FC）accumulated in macrophages and surrounding cells to the liver and then excretes it out through bile acid.Therefore,the function of HDL FC is essential for RCT.Thus,the HDL FC bioavailability was introduced,which represents whether FC transfers to HDL or other receptors,and it is composed of HDL particle amount number and HDL mol%FC.Scavenger receptor class B type 1（SR-B1）promotes the RCT process by promoting cholesterol efflux and selective cholesterol uptake in hepatocytes,so FC is enriched in the plasma of SR-B1 knockout mice with higher HDL content.HDL FC bioavailability of the mice is higher,and it shows a variety of diseases,such as red blood cell platelet abnormalities,female infertility,increased susceptibility to atherosclerosis,etc.So it is the preferred model to explore the high bioavailability of HDL FC.Streptococcus pyogenes secretes a protein,serum opacity factor（SOF）,that catalyzes HDL into three products:cholesteryl ester rich microemulsion（CERM）,neo HDL,and lipid-free apolipoprotein AI（LF apo AI）,and the generated product can promote the RCT process.People found that SOF can reduce the cholesterol content in mouse plasma and restore fertility by reducing plasma HDL FC in female SR-B1^-/-mice.However,there are no related studies on the regulatory mechanism of SOF to HDL FC bioavailability and its impact on abnormal HDL FC-related pathological manifestations.Therefore,we hypothesize that SOF could reduce the bioavailability of HDL FC by changing the distribution of lipoproteins and lipids,to correct abnormal HDL function,and reverse abnormal pathology.In order to detect the hypothesis,this study focused on exploring the regulatory of SOF to HDL function,aiming to provide evidence for SOF treatment and prevention of related diseases in the population with high HDL in the future.Methods:（1）Protein expression in E.coli were used to prepare SOF.Asymmetric flow field-flow fractionation mass spectrometry（AF4 MS）,classical enzyme reagents and size exclusion chromatography were used to detect the changes in the distribution of human plasma lipoproteins and their lipids before and after SOF treatment in vitro;（2）Adeno-associated virus（AAV）was used to deliver SOF into SR-B1^-/-mice,and enzyme reagents were used to detect the lipid content of plasma and erythrocyte.Compared with SR-B1^-/-mice and WT mice,and analyzed the changes in the morphology and function of erythrocytes in blood smears,and explored the correlation between erythrocyte FC and HDL FC or abnormal erythrocyte number;（3）The lipids content in each tissue after AAV_SOFtreatment were detected,and analysis of the correlation between HDL and tissue mol%FC.Results:（1）In vitro,SOF changed the size of lipoproteins of plasma,transferred CE and FC to newly formed CERM particles,and decreased the content and bioavailability of HDL FC;（2）After injecting AAV_SOFto SR-B1^-/-mice,the content of cholesterol in plasma,HDL and erythrocytes tended to be normal,and the ratio of abnormal erythrocytes and reticulocytes in peripheral blood smears also returned to that of WT mice.The FC content and mol%of erythrocyte were also positively correlated with that of HDL and abnormal erythrocyte ratio in smears;（3）AAV_SOFcould restore the FC content of female liver,female lung,male kidney,and the mol%FC of ovary,male adrenal gland.And there was no correlation between the liver,spleen,brain,testis and genital adipose tissue and HDL mol%FC.Conclusion:SOF can reduce high bioavailability of HDL FC by changing the distribution of lipoprotein lipids,also restore the abnormal HDL function,and pathological manifestations it causes.Therefore,this study illustrates the effectiveness of SOF in restoring abnormal HDL function,and lays the foundation for subsequent experiments and even clinical applications of SOF therapy to prevent the complications in populations with high HDL.