Hypercholesterol Suppresses Tumor Incidence And Growth Through Potentiating The Antitumor Function Of NK Cells

BACKGROUNDS&AIMS Cholesterol plays an important role in maintaining the physiological function of cells.However,with the change of human lifestyle and dietary structure,patients with hypercholesterolemia have increased dramatically.A large number of studies have shown that hypercholesterolemia is a risk factor for many serious diseases,including atherosclerosis,coronary heart disease and stroke.However,the relationship between total serum cholesterol and cancer risk has long been controversial.Some epidemiological data revealed that total serum cholesterol level exhibit protective effect against kinds of cancer,but the mechanisms behind this phenomenon remain to be elucidated.Therefore,it is of great significance to study the effect of hypercholesterolemia on tumor and to clarify the molecular mechanism,which is important for the prevention and treatment of tumor.In this study,we reported the pivotal role of cholesterol in the anti-tumour effect of natural killer cells and CD8+ T cells.METHODS 1.Relationship between blood cholesterol level and the risk of multiple tumors was elucidated by using evidence-based medicine research methods.2.Hypercholesterolemia model in mice was established by high cholesterol diet(HCD)and Apo E depletion.3.Tumor development and progression model was established in hypercholesteremia mice.4.Revealing the methods through which cholesterol affects the tumor development and progression by RNA-seq and other experiments 5.Exploring the effect of high cholesterol on immune cells and finding the functional cell subgroup by flow-cytometric analysis and neutralizing antibodies.6.Testing the effect of high cholesterol on the anti-tumor activity of NK and CD8+T cellsby cholesterol modulating experiment.7.The effect of cholesterol accumulation on lipid rafts formation and activating receptors clustering of NK cells were measured,and downstream signaling pathways were tested by western blot.8.Methods of potentiating the anti-tumor activity of NK cells by modulating cholesterol metabolism were explored.RESULTS We firstly showed that the incidence of total cancer,liver cancer and lung cancer was negatively correlated with the level of blood total cholesterol.In hypocholesteremia mice,the occurrence,growth and metastasis of kinds of cancer were inhibited.By RNA-seq analysis of tumor tissues and tumor-bearing experiment in NSG mice we proved that the suppression effect was closely related to the immune system.Further,we found that NK cells were required for the inhibitory effect of HCD on tumor growth,and spleen NK cells from the HCD mice showed potentiated effector function and enhanced cytotoxicity in both vivo and vitro.Interestingly,the cytotoxicity of NK cells is closely related to cell cholesterol content,intracellular cholesterol accumulation increased the number of lipid rafts and facilitated the clustering of activating-receptors such as NCR1 and NKG2 D,thus activated the downstream signaling pathways.Finally,we proved that overexpression of Ldlr or inhibition of Ldlr degradation by PCSK9 antibody can increase the cholesterol content of NK and CD8+T cells,and further enhance their antitumor activity.CONCLUSIONS Cholesterol accumulation in NK or CD8+ T cells can promote the migration of activating receptors to lipid rafts by increasing the number of lipid rafts on membrane surface,then upregulate downstream signaling pathways and enhance the effector function of immune cells.We also proved that regulating the intracellular level of cholesterol can potentiate the cytotoxicity and antitumor effect of immune cells.Our research provides new strategies for tumor immunotherapy.