β-carotene conversion to vitamin A delays atherosclerosis progression by decreasing hepatic lipid secretion in mice

Atherosclerosis is characterized by the pathological accumulation of cholesterol-laden macrophages in the arterial wall. Atherosclerosis is also the main underlying cause of cardiovascular diseases (CVDs), and its development is largely driven by elevated plasma cholesterol. Strong epidemiological data find an inverse association between plasma β-carotene with atherosclerosis, and we recently showed that β-carotene oxygenase 1 (BCO1) activity, responsible for β-carotene cleavage to vitamin A, is associated with reduced plasma cholesterol in humans and mice. In this study, we explore whether intact β-carotene or vitamin A affect atherosclerosis progression in the atheroprone low-density lipoprotein receptor (LDLR) - deficient mice. In comparison to control-fed Ldlr-/- mice, β-carotene-supplemented mice showed reduced atherosclerotic lesion size at the level of the aortic root and plasma cholesterol levels (P = 0.0003). These changes were absent in Ldlr-/-/Bco1-/- mice, despite accumulating β-carotene in plasma and atherosclerotic lesions. We discarded the implication of myeloid BCO1 in the development of atherosclerosis by performing bone marrow transplant experiments. Lipid production assays found that retinoic acid, the active form of vitamin A, reduced the secretion of newly synthetized triglyceride and cholesteryl ester in cell culture and mice. Overall, our findings provide insights into the role of BCO1 activity and vitamin A in atherosclerosis progression through the regulation of hepatic lipid metabolism. CD68+ cells accumulated in atherosclerotic lesions at the level of the aortic root were isolated by laser capture microdisection. Briefly, Eight-week-old male and female Ldlr-/-/Bco1-/- mice were lethally irradiated with a double dose of 550 rads (5.5 GY) from a cesium source four hours apart. Ten hours later, mice were transplanted with freshly isolated bone marrow from donor wild-type or Bco1-/- (ko) mice.

动脉粥样硬化（Atherosclerosis）以动脉壁内载胆固醇巨噬细胞的病理性堆积为特征。动脉粥样硬化亦是心血管疾病（cardiovascular diseases, CVDs）的主要潜在病因，其发生发展在很大程度上由血浆胆固醇水平升高驱动。现有强有力的流行病学数据表明，血浆β-胡萝卜素与动脉粥样硬化呈负相关。我们近期的研究显示，负责将β-胡萝卜素裂解为维生素A的β-胡萝卜素加氧酶1（β-carotene oxygenase 1, BCO1）的活性，与人类及小鼠体内的血浆胆固醇水平降低相关。本研究旨在探究完整的β-胡萝卜素或维生素A是否会在易发生动脉粥样硬化的低密度脂蛋白受体（low-density lipoprotein receptor, LDLR）缺陷小鼠中影响动脉粥样硬化的进展。与喂食普通饲料的Ldlr-/-小鼠相比，补充β-胡萝卜素的小鼠的主动脉根部动脉粥样硬化斑块面积及血浆胆固醇水平均显著降低（P = 0.0003）。尽管Ldlr-/-/Bco1-/-小鼠的血浆及动脉粥样硬化病变中蓄积了β-胡萝卜素，但上述改善并未在该类小鼠中出现。我们通过骨髓移植（bone marrow transplant）实验排除了髓系BCO1在动脉粥样硬化发生发展中的作用。脂质生成实验发现，维生素A的活性形式视黄酸（retinoic acid）可在细胞培养体系及小鼠体内减少新合成的甘油三酯与胆固醇酯的分泌。综上，本研究结果揭示了BCO1活性与维生素A通过调控肝脏脂质代谢参与动脉粥样硬化进展的作用机制。研究人员通过激光捕获显微切割（laser capture microdisection）分离了主动脉根部动脉粥样硬化病变中蓄积的CD68阳性细胞。简言之，将8周龄的雄性和雌性Ldlr-/-/Bco1-/-小鼠以两次间隔4小时的剂量，每次550拉德（5.5 GY）经铯源进行致死性辐照。10小时后，向小鼠移植供体野生型或Bco1-/-（ko）小鼠的新鲜分离骨髓。