Henson D A, St Clair R W, Lewis J C
Department of Pathology, Wake Forest University, Winston-Salem, NC.
Atherosclerosis. 1989 Jul;78(1):47-60. doi: 10.1016/0021-9150(89)90158-5.
Blood-derived monocytes are an important source of foam cells in atherosclerotic lesions of White Carneau pigeons. Based upon studies with cultured blood monocytes (monocyte macrophages) and peritoneal macrophages from a variety of mammalian species, it has been proposed that these cells become loaded with cholesteryl esters through the uptake of lipoproteins including beta-migrating very low density lipoproteins (beta-VLDL) and low density lipoproteins that have been chemically modified in a manner analogous to experimental acetylation (Ac-LDL). The purpose of this study was to determine whether similar mechanisms functioned in pigeon monocyte macrophages. Radioiodinated pigeon beta-VLDL and Ac-LDL were incubated with White Carneau pigeon monocyte macrophages that had been maintained in culture for 7 days. Scatchard analysis of the specific binding data revealed the presence of specific and saturable receptors for both beta-VLDL and Ac-LDL. beta-VLDL receptors had both low and high affinity binding components, whereas Ac-LDL receptors displayed a single class of high affinity binding sites. beta-VLDL binding remained relatively constant from 3 to 10 days in culture while Ac-LDL binding increased with time in culture. Competition studies demonstrated a high degree of binding specificity for 125I-Ac-LDL, but less for 125I-beta-VLDL. Binding of 125I-beta-VLDL was not competed for by Ac-LDL, but was by beta-VLDL and by low density lipoproteins from both normal and hypercholesterolemic pigeons. Following binding of beta-VLDL and Ac-LDL, the lipoproteins were rapidly internalized and degraded. Although the majority of degradation was secondary to internalization by the monocyte macrophages, approx. 5% of the degradation resulted from enzymatic activity in the culture medium, presumably due to secretion of proteolytic enzymes by the cells. As measured by esterification of [14C]oleate to cholesterol, it was shown that the cholesterol liberated from the degradation of both beta-VLDL and Ac-LDL stimulated cholesteryl ester synthesis in pigeon monocyte macrophages. These studies confirm the existence of specific beta-VLDL and Ac-LDL receptors on the surface of pigeon monocyte macrophages which facilitate both internalization of the lipoproteins and subsequent stimulation of cholesteryl ester synthesis. This is the first demonstration of beta-VLDL and Ac-LDL receptors on monocyte macrophages from an avian species, and the findings support the potential role for the receptor-mediated uptake of a variety of abnormal lipoproteins in the formation of monocyte-derived foam cells in the arterial wall of White Carneau pigeons during the development of atherosclerosis.
血液来源的单核细胞是白卡诺鸽动脉粥样硬化病变中泡沫细胞的重要来源。基于对来自多种哺乳动物物种的培养血液单核细胞（单核巨噬细胞）和腹腔巨噬细胞的研究，有人提出这些细胞通过摄取脂蛋白而负载胆固醇酯，这些脂蛋白包括β-迁移极低密度脂蛋白（β-VLDL）和以类似于实验性乙酰化（Ac-LDL）的方式进行化学修饰的低密度脂蛋白。本研究的目的是确定类似的机制是否在鸽单核巨噬细胞中起作用。将放射性碘化的鸽β-VLDL和Ac-LDL与在培养中维持7天的白卡诺鸽单核巨噬细胞一起孵育。对特异性结合数据的Scatchard分析显示存在β-VLDL和Ac-LDL的特异性和可饱和受体。β-VLDL受体具有低亲和力和高亲和力结合成分，而Ac-LDL受体显示出单一类别的高亲和力结合位点。在培养3至10天期间，β-VLDL结合保持相对恒定，而Ac-LDL结合随培养时间增加。竞争研究表明，125I-Ac-LDL具有高度的结合特异性，但125I-β-VLDL的结合特异性较低。125I-β-VLDL的结合不被Ac-LDL竞争，但被β-VLDL以及来自正常和高胆固醇血症鸽的低密度脂蛋白竞争。在β-VLDL和Ac-LDL结合后，脂蛋白迅速内化并降解。虽然大部分降解是单核巨噬细胞内化的继发结果，但约5%的降解是由于培养基中的酶活性，可能是由于细胞分泌蛋白水解酶所致。通过将[14C]油酸酯酯化到胆固醇来测量，结果表明从β-VLDL和Ac-LDL降解中释放的胆固醇刺激了鸽单核巨噬细胞中胆固醇酯的合成。这些研究证实了鸽单核巨噬细胞表面存在特异性β-VLDL和Ac-LDL受体，它们促进脂蛋白的内化以及随后对胆固醇酯合成的刺激。这是首次在鸟类物种的单核巨噬细胞上证明β-VLDL和Ac-LDL受体，这些发现支持了受体介导摄取多种异常脂蛋白在白卡诺鸽动脉粥样硬化发展过程中动脉壁单核细胞衍生泡沫细胞形成中的潜在作用。
