Wen-Hao Qin1, Zhi-Shi Yang2, Mian Li3, Yao Chen1, Xiao-Fang Zhao1, Ying-Yi Qin4, Jia-Qi Song4, Bi-Bo Wang1, Bo Yuan1, Xiu-Liang Cui1, Feng Shen5, Jia He4, Yu-Fang Bi3, Guang Ning6, Jing Fu7, Hong-Yang Wang8. 1. International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China; National Center for Liver Cancer, Shanghai, China. 2. International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China; Department of Hepatic Surgery, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China. 3. National Clinical Research Center for Metabolic Diseases, Key Laboratory for Endocrine and Metabolic Diseases of Ministry of Health, Department of Endocrine and Metabolic Diseases, Rui-Jin Hospital, Shanghai Jiao-Tong University School of Medicine, Shanghai, China. 4. Department of Health Statistics, Second Military Medical University, Shanghai, China. 5. Department of Hepatic Surgery, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China. 6. National Clinical Research Center for Metabolic Diseases, Key Laboratory for Endocrine and Metabolic Diseases of Ministry of Health, Department of Endocrine and Metabolic Diseases, Rui-Jin Hospital, Shanghai Jiao-Tong University School of Medicine, Shanghai, China. Electronic address: gning@sibs.ac.cn. 7. International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China; National Center for Liver Cancer, Shanghai, China; Mengchao Hepatobiliary Hospital, Fujian Medical University, Fuzhou, China. Electronic address: fujing-724@163.com. 8. International Cooperation Laboratory on Signal Transduction, Eastern Hepatobiliary Surgery Hospital, Second Military Medical University, Shanghai, China; National Center for Liver Cancer, Shanghai, China; Ministry of Education Key Laboratory on Signaling Regulation and Targeting Therapy of Liver Cancer, Shanghai Key Laboratory of Hepato-Biliary Tumor Biology, Shanghai, China. Electronic address: hywangk@vip.sina.com.
Abstract
BACKGROUND AND AIMS: The relationship between serum cholesterol level and development of hepatocellular carcinoma (HCC) remains unclear. We investigated the effects of serum cholesterol level on development of liver tumors in mice. METHODS: We performed studies with C57BL/6J mice, mice with disruption of the low-density lipoprotein receptor gene (Ldlr-/-mice), and mice with conditional deletion of nature killer (NK) cells (NKdele mice). Some C57BL/6J and NKdele mice were given injections of diethylinitrosamine to induce liver tumor formation. Mice were placed on a normal diet (ND) or high-cholesterol diet (HCD) to induce high serum levels of cholesterol. We also studied mice with homozygous disruption of ApoE (ApoE-/- mice), which spontaneously develop high serum cholesterol. C57BL/6J and NKdele mice on the ND or HCD were implanted with Hep1-6 (mouse hepatoma) cells and growth of xenograft tumors and lung metastases were monitored. Blood samples were collected from mice and analyzed by biochemistry and flow cytometry; liver and tumor tissues were collected and analyzed by histology, immunohistochemistry, and RNA-sequencing analysis. NK cells were isolated from mice and analyzed for cholesterol content, lipid raft formation, immune signaling, and changes in functions. We obtained matched tumor tissues and blood samples from 30 patients with HCC and blood samples from 40 healthy volunteers; levels of cholesterol and cytotoxicity of NK cells were measured. RESULTS: C57BL/6J mice on HCD and ApoE-/- mice with high serum levels of cholesterol developed fewer and smaller liver tumors and lung metastases after diethylinitrosamine injection or implantation of Hep1-6 cells than mice on ND. Liver tumors from HCD-fed mice and ApoE-/- mice had increased numbers of NK cells compared to tumors from ND-fed mice. NKdele mice or mice with antibody-based depletion for NK cells showed similar tumor number and size in ND and HCD groups after diethylinitrosamine injection or implantation of Hep1-6 cells. NK cells isolated from C57BL/6J mice fed with HCD had increased expression of NK cell-activating receptors (natural cytotoxicity triggering receptor 1 and natural killer group 2, member D), markers of effector function (granzyme B and perforin), and cytokines and chemokines compared with NK cells from mice on ND; these NK cells also had enhanced cytotoxic activity against mouse hepatoma cells, accumulated cholesterol, increased lipid raft formation, and immune signaling activation. NK cells isolated from HCD-fed Ldlr-/- mice did not have increased cholesterol content or cytotoxic activity against mouse hepatoma cells compared with ND-fed Ldlr-/- mice. Serum levels of cholesterol correlated with number and activity of NK cells isolated from human HCCs. CONCLUSIONS: Mice with increased serum levels of cholesterol due to an HCD or genetic disruption of ApoE develop fewer and smaller tumors after injection of hepatoma cells or a chemical carcinogen. We found cholesterol to accumulate in NK cells and activate their effector functions against hepatoma cells. Strategies to increase cholesterol uptake by NK cells can be developed for treatment of HCC.
BACKGROUND AND AIMS: The relationship between serum cholesterol level and development of hepatocellular carcinoma (HCC) remains unclear. We investigated the effects of serum cholesterol level on development of liver tumors in mice. METHODS: We performed studies with C57BL/6J mice, mice with disruption of the low-density lipoprotein receptor gene (Ldlr-/-mice), and mice with conditional deletion of nature killer (NK) cells (NKdele mice). Some C57BL/6J and NKdele mice were given injections of diethylinitrosamine to induce liver tumor formation. Mice were placed on a normal diet (ND) or high-cholesterol diet (HCD) to induce high serum levels of cholesterol. We also studied mice with homozygous disruption of ApoE (ApoE-/- mice), which spontaneously develop high serum cholesterol. C57BL/6J and NKdele mice on the ND or HCD were implanted with Hep1-6 (mousehepatoma) cells and growth of xenograft tumors and lung metastases were monitored. Blood samples were collected from mice and analyzed by biochemistry and flow cytometry; liver and tumor tissues were collected and analyzed by histology, immunohistochemistry, and RNA-sequencing analysis. NK cells were isolated from mice and analyzed for cholesterol content, lipid raft formation, immune signaling, and changes in functions. We obtained matched tumor tissues and blood samples from 30 patients with HCC and blood samples from 40 healthy volunteers; levels of cholesterol and cytotoxicity of NK cells were measured. RESULTS: C57BL/6J mice on HCD and ApoE-/- mice with high serum levels of cholesterol developed fewer and smaller liver tumors and lung metastases after diethylinitrosamine injection or implantation of Hep1-6 cells than mice on ND. Liver tumors from HCD-fed mice and ApoE-/- mice had increased numbers of NK cells compared to tumors from ND-fed mice. NKdele mice or mice with antibody-based depletion for NK cells showed similar tumor number and size in ND and HCD groups after diethylinitrosamine injection or implantation of Hep1-6 cells. NK cells isolated from C57BL/6J mice fed with HCD had increased expression of NK cell-activating receptors (natural cytotoxicity triggering receptor 1 and natural killer group 2, member D), markers of effector function (granzyme B and perforin), and cytokines and chemokines compared with NK cells from mice on ND; these NK cells also had enhanced cytotoxic activity against mousehepatoma cells, accumulated cholesterol, increased lipid raft formation, and immune signaling activation. NK cells isolated from HCD-fed Ldlr-/- mice did not have increased cholesterol content or cytotoxic activity against mousehepatoma cells compared with ND-fed Ldlr-/- mice. Serum levels of cholesterol correlated with number and activity of NK cells isolated from human HCCs. CONCLUSIONS:Mice with increased serum levels of cholesterol due to an HCD or genetic disruption of ApoE develop fewer and smaller tumors after injection of hepatoma cells or a chemical carcinogen. We found cholesterol to accumulate in NK cells and activate their effector functions against hepatoma cells. Strategies to increase cholesterol uptake by NK cells can be developed for treatment of HCC.
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