Hart B A, Gong Q, Eneman J D, Durieux-Lu C C
Department of Biochemistry, University of Vermont College of Medicine, Burlington 05405, USA.
Toxicol Appl Pharmacol. 1995 Jul;133(1):82-90. doi: 10.1006/taap.1995.1129.
This study examined the ability of alveolar macrophages and alveolar type II epithelial cells to accumulate cadmium (Cd) and to express metallothionein (MT). Lung cells were isolated from Lewis rats repeatedly exposed to a Cd aerosol (1.6 mg Cd/m3). Intracellular Cd concentration rose following Cd exposure and showed an increasing rend as a function of exposure number. Alveolar macrophages accrued approximately four times more Cd than type II epithelial cells similarly exposed. Macrophages and type II cells responded to the presence of intracellular Cd by increasing MT protein levels. MT concentration was highly correlated with intracellular Cd. Immunocytochemical studies revealed that not all macrophages and type II cells from Cd-exposed animals were immunopositive for MT and that the intensity of immunostaining varied within each cell population. Although a greater percentage of macrophages were immunopositive for MT than type II cells, a greater proportion of type II cells showed moderate and dark MT staining patterns. Oligonucleotide probes, shown to distinguish between MT-1 and MT-2 mRNA isoforms, were used to test for cell-specific differences in MT isoform gene expression. The basal level of MT-1 mRNA was greater in macrophages than in type II cells. Following Cd administration, the level of MT-1 mRNA and MT-2 mRNA increased in each cell class but the response to Cd was three times greater in alveolar macrophages. Neither macrophages nor type II cells expressed MT mRNA isoforms in equal proportions. Macrophages expressed more MT-1 mRNA when exposed to air and more MT-2 mRNA in response to Cd exposure. Type II cells, on the other hand, expressed more MT-2 mRNA than MT-1 mRNA regardless of whether the cells were exposed to air or Cd. In conclusion, the present study has demonstrated that (1) alveolar macrophages and type II cells respond to in vivo Cd exposure by increasing MT protein and mRNA levels; (2) MT expression is greater in macrophages than in type II cells and correlates well with intracellular Cd concentration; and (3) the MT-2 mRNA to MT-1 mRNA ratio is cell and treatment specific.
本研究检测了肺泡巨噬细胞和肺泡Ⅱ型上皮细胞蓄积镉（Cd）以及表达金属硫蛋白（MT）的能力。从反复暴露于Cd气溶胶（1.6mg Cd/m³）的Lewis大鼠中分离出肺细胞。Cd暴露后细胞内Cd浓度升高，并呈现出随暴露次数增加的趋势。同样暴露的情况下，肺泡巨噬细胞蓄积的Cd比Ⅱ型上皮细胞多约四倍。巨噬细胞和Ⅱ型细胞通过增加MT蛋白水平来响应细胞内Cd的存在。MT浓度与细胞内Cd高度相关。免疫细胞化学研究显示，来自Cd暴露动物的并非所有巨噬细胞和Ⅱ型细胞对MT均呈免疫阳性，且每个细胞群体内免疫染色强度各不相同。尽管对MT呈免疫阳性的巨噬细胞百分比高于Ⅱ型细胞，但更大比例的Ⅱ型细胞呈现中度和深色MT染色模式。已证明可区分MT-1和MT-2 mRNA亚型的寡核苷酸探针，用于检测MT亚型基因表达的细胞特异性差异。巨噬细胞中MT-1 mRNA的基础水平高于Ⅱ型细胞。给予Cd后，每个细胞类型中MT-1 mRNA和MT-2 mRNA水平均升高，但肺泡巨噬细胞对Cd的反应是Ⅱ型细胞的三倍。巨噬细胞和Ⅱ型细胞均未等量表达MT mRNA亚型。巨噬细胞在暴露于空气时表达更多的MT-1 mRNA，对Cd暴露的反应则表达更多的MT-2 mRNA。另一方面，无论细胞暴露于空气还是Cd，Ⅱ型细胞表达的MT-2 mRNA均多于MT-1 mRNA。总之，本研究表明：（1）肺泡巨噬细胞和Ⅱ型细胞通过增加MT蛋白和mRNA水平来响应体内Cd暴露；（2）巨噬细胞中的MT表达高于Ⅱ型细胞，且与细胞内Cd浓度密切相关；（3）MT-2 mRNA与MT-1 mRNA的比例具有细胞和处理特异性。
