Matsuura T, Nagamori S, Hasumura S, Sujino H, Shimizu K, Niiya M, Hirosawa K
Department of Internal Medicine (I), Jikei University School of Medicine, Tokyo, Japan.
Exp Cell Res. 1993 May;206(1):111-8. doi: 10.1006/excr.1993.1126.
The mechanisms of specific transport of retinoids into stellate cells (SC) of liver remain to be elucidated. In the present study, we have conducted experiments to observe the intracellular retinoid metabolism of cultured SC of rat liver using light and electron microscope autoradiography (LMARG and EMARG). After 72 h of culture, the cells were incubated in the medium containing 1.06 x 10(-6) or 6.36 x 10(-8) M of [3H]retinol for either 5 or 30 min. In some cases, incubation with the labeled retinol was followed by a medium containing nonlabeled 1 x 10(-6) M retinol for 90 min. First, the incorporation of labeled retinol (1.06 x 10(-6) M) into SC and hepatocytes was compared by LMARG. After 5 min, silver grains were already present on both cells. After 30 min, label was concentrated on the lipid droplets of SC. After the chase, the number of grains on hepatocytes decreased. On the other hand, grains on the lipid droplets of SC remained. Second, we studied the fine morphology and intracellular retinoid metabolism in SC using EMARG. The SC, which contained abundant multivesicular bodies (MVB) and lamellar bodies, were found to have a heavy accumulation of grains. Even in the medium containing a lower concentration of retinol (6.36 x 10(-8) M), SC also took up retinol. After 90 min of chase, many grains moved on the lipid droplets in SC. The labeled MVB were often accompanied by lamellar bodies and found near the lipid droplets. Sometimes we noticed small labeled lipid droplets bound by membranes in MVB. From the results of this study, we concluded that the MVB and lamellar bodies might be important organelles for retinyl ester formation and the initial storage of retinoid in the lipid droplets in SC.
类视黄醇特异性转运至肝脏星状细胞（SC）的机制仍有待阐明。在本研究中，我们进行了实验，运用光镜和电镜放射自显影术（LMARG和EMARG）观察大鼠肝脏培养星状细胞的细胞内类视黄醇代谢。培养72小时后，将细胞置于含有1.06×10⁻⁶或6.36×10⁻⁸M [³H]视黄醇的培养基中孵育5或30分钟。在某些情况下，用标记视黄醇孵育后，接着在含有1×10⁻⁶M未标记视黄醇的培养基中孵育90分钟。首先，通过LMARG比较标记视黄醇（1.06×10⁻⁶M）进入星状细胞和肝细胞的情况。5分钟后，两种细胞上均已出现银颗粒。30分钟后，标记物集中在星状细胞的脂滴上。追踪后，肝细胞上的颗粒数量减少。另一方面，星状细胞脂滴上的颗粒仍然存在。其次，我们运用EMARG研究星状细胞的精细形态和细胞内类视黄醇代谢。发现含有丰富多囊泡体（MVB）和板层小体的星状细胞有大量颗粒积累。即使在含有较低浓度视黄醇（6.36×10⁻⁸M）的培养基中，星状细胞也摄取视黄醇。追踪90分钟后，许多颗粒在星状细胞的脂滴上移动。标记的MVB常伴有板层小体，并在脂滴附近发现。有时我们注意到MVB中有被膜包裹的小的标记脂滴。根据本研究结果，我们得出结论，MVB和板层小体可能是星状细胞中视黄酯形成以及类视黄醇在脂滴中初始储存的重要细胞器。
