Yu J, Zhu H, Guo J T, de Beer F C, Kindy M S
Department of Biochemistry, University of Kentucky, Lexington, USA.
Lab Invest. 2000 Dec;80(12):1797-806. doi: 10.1038/labinvest.3780191.
Amyloid A (AA) amyloid deposition in mice is dependent upon isoform-specific effects of the serum amyloid A (SAA) protein. In type A mice, SAA1.1 and SAA2.1 are the major apolipoprotein-SAA isoforms found on high-density lipoproteins. During inflammation, both isoforms are increased 1000-fold, but only SAA1.1 is selectively deposited into amyloid fibrils. Previous studies showed that the CE/J mouse strain is resistant to amyloid induction. This resistance is not due to a deficiency in SAA synthesis, but is probably related to the unusual SAA isoform present. The CE/J mouse has a single acute-phase SAA protein (SAA2.2), which is a composite of the SAA1.1 and SAA2.1, with an amino terminus similar to the nonamyloidogenic SAA2.1. Recently, genetic experiments suggested that the SAA2.2 isoform might provide protection from amyloid deposition. To determine the amyloidogenic potential of the CE/J mouse, we generated SAA adenoviral vectors to express the various isoforms in vitro and in vivo. Purified recombinant SAA proteins demonstrated that SAA1.1 was fibrillogenic in vitro, whereas SAA2.2 was unable to form fibrils. Incubation of increasing concentrations of the nonamyloidogenic SAA2.2 protein with the amyloidogenic SAA1.1 did not inhibit the fibrillogenic nature of SAA1.1, or alter its ability to form extensive fibrils. Injection of the mouse SAA1.1 or SAA2.2 adenoviral vectors into mice resulted in isoform-specific expression of the SAA proteins. Amyloid induction after viral expression of the SAA1.1 protein resulted in the deposition of amyloid fibrils in the CE/J mouse, whereas SAA2.2 expression had no effect. Similar expression of the SAA2.2 protein in C57BL/6 mice did not alter amyloid deposition. These data demonstrate that the failure of the CE/J mouse to deposit amyloid is due to the structural inability of the SAA2.2 to form amyloid fibrils. This mouse provides a unique system to test the amyloidogenic potential of altered SAA proteins and to determine the important structural features of the protein.
小鼠中的淀粉样蛋白A（AA）淀粉样沉积取决于血清淀粉样蛋白A（SAA）蛋白的亚型特异性效应。在A型小鼠中，SAA1.1和SAA2.1是在高密度脂蛋白上发现的主要载脂蛋白-SAA亚型。在炎症期间，这两种亚型均增加1000倍，但只有SAA1.1被选择性地沉积到淀粉样纤维中。先前的研究表明，CE/J小鼠品系对淀粉样诱导具有抗性。这种抗性不是由于SAA合成缺陷，而是可能与存在的异常SAA亚型有关。CE/J小鼠有一种单一的急性期SAA蛋白（SAA2.2），它是SAA1.1和SAA2.1的复合物，其氨基末端类似于非淀粉样生成性的SAA2.1。最近，基因实验表明SAA2.2亚型可能提供对淀粉样沉积的保护。为了确定CE/J小鼠的淀粉样生成潜力，我们构建了SAA腺病毒载体以在体外和体内表达各种亚型。纯化的重组SAA蛋白表明，SAA1.1在体外具有纤维形成能力，而SAA2.2无法形成纤维。用非淀粉样生成性的SAA2.2蛋白与淀粉样生成性的SAA1.1进行浓度递增孵育，既不抑制SAA1.1的纤维形成特性，也不改变其形成广泛纤维的能力。将小鼠SAA1.1或SAA2.2腺病毒载体注射到小鼠体内会导致SAA蛋白的亚型特异性表达。SAA1.1蛋白病毒表达后的淀粉样诱导导致CE/J小鼠中淀粉样纤维的沉积，而SAA2.2表达则没有影响。在C57BL/6小鼠中类似表达SAA2.2蛋白不会改变淀粉样沉积。这些数据表明，CE/J小鼠未能沉积淀粉样物质是由于SAA2.2在结构上无法形成淀粉样纤维。该小鼠提供了一个独特的系统来测试改变的SAA蛋白的淀粉样生成潜力，并确定该蛋白的重要结构特征。
