New therapeutic targets for atherosclerotic plaques - The role of acyl CoA : cholesterol acyltransferase and neutral cholesterol ester hydrolase in foam cell formation

载胆固醇酯（CE）的泡沫细胞是动脉粥样硬化的标志。胆固醇处于游离态和酯化态之间的动态平衡。酯化和水解分别由酰基辅酶A：胆固醇酰基转移酶（ACAT）和中性胆固醇酯水解酶（NCEH）介导。在目前的研究中，我们研究了ACAT-1（ACAT亚型）和负责NCEH的脂肪酶敏感性脂肪酶（HSL）在泡沫细胞形成和动脉粥样硬化形成中的作用。我们已经产生了ACAT-1 null（ACAT-1-/-）小鼠，由于睑板腺萎缩而导致眼睛开口减少，睑板腺是一种修饰形式的皮脂腺，通常表达高ACAT活性。为了确定ACAT-1在动脉粥样硬化形成中的作用，我们将ACAT-1-/-小鼠与缺乏载脂蛋白（apo）E或低密度脂蛋白受体（LDLR）的小鼠（易患动脉粥样硬化的高血脂模型）杂交。在ACAT-1/-：apoE-/-和ACAT-1-/-：LDLR-/-小鼠中，高脂肪喂养导致广泛的皮肤黄瘤病伴毛发脱落。他们皮肤中的游离胆固醇含量显著增加。与各自的对照组相比，两种突变小鼠的主动脉脂肪条纹病变大小以及胆固醇酯含量均适度降低。这些结果表明，组织巨噬细胞中ACAT活性的局部抑制可防止胆固醇酯蓄积，但在缺乏载脂蛋白E或LDLR的小鼠中可引起皮肤黄瘤病。此外，我们产生了HSL-null（HSL-/-）小鼠，其巨噬细胞与野生型相比具有相当大的NCEH活性。因此，缺乏HSL并不加重CE在巨噬细胞中的积聚。因此，HSL不是巨噬细胞中NCEH的主要酶是合理的。然而，腺病毒介导的HSL过表达显着减少CE积累，通过加速CE的水解和减少修饰的脂蛋白的摄取。

Cholesterol-ester (CE)-laden foam cells are a hallmark of atherosclerosis. Cholesterol is in a dynamic equilibrium between free and esterified form. The esterification and hydrolysis are mediated by acyl CoA : cholesterol acyltransferase (ACAT) and neutral cholesterol ester hydrolase (NCEH), respectively. In the current study, we investigated the role of ACAT-1, an ACAT isoform, and hormone-sensitive lipase (HSL) responsible for NCEH in foam cell formation and atherogenesis.We have generated ACAT-1 null (ACAT-1-/-) mice, which had decreased openings of the eyes because of atrophy of the meibomian glands, a modified form of sebaceous glands normally expressing high ACAT activities. To determine the role of ACAT-1 in atherogenesis, we crossed the ACAT-1-/- mice with mice lacking apolipoprotein (apo) E or the low density lipoprotein receptor (LDLR), hyperlipidemic models susceptible to atherosclerosis. High fat feeding resulted in extensive cutaneous xanthomatosis with loss of hair in both ACAT-1/-:apoE-/- and ACAT-1-/-:LDLR-/- mice. Free cholesterol content was significantly increased in their skin. Aortic fatty streak lesion size as well as cholesterol ester content were moderately reduced in both mutant mice compared with their respective controls. These results indicate that the local inhibition of ACAT activity in tissue macrophages is protective against cholesteryl ester accumulation but causes cutaneous xanthomatosis in mice lacking apo E or LDLR. Furthermore, we generated HSL-null (HSL-/-) mice, whose macrophages had a substantial activity of NCEH compared with those of wild-type. Consistently, lack of HSL did not aggravate the accumulation of CE in macrophages. Thus, it is rational that HSL is not the primary enzyme for NCEH in macrophages. However, adenoviral mediated overexpression of HSL markedly reduced the CE accumulation through accelerated hydrolysis of CE and decreased uptake of modified lipoproteins.