Schraermeyer U, Peters S, Thumann G, Kociok N, Heimann K
Department of Vitreoretinal Surgery, University of Cologne, Joseph Stelzmann Str. 9, Cologne, 50931, Germany.
Exp Eye Res. 1999 Feb;68(2):237-45. doi: 10.1006/exer.1998.0596.
Melanosomes are closely related to lysosomes and lipofuscin granules. This paper indicates the potential involvement of lysosomal degradation processes in retinal pigment epithelial (RPE) cells. RPE cells cultured on Bruch's membrane and choroid were fed with indigestible latex beads. The RPE cells from this preparation were treated with chloroquine to investigate whether membrane swelling, typical for lysosomes under this condition, can be induced in melanosomes. To investigate the fate of indigestible material associated with rod outer segments (ROS), gold-labeled ROS were injected transsclerally into the subretinal space of Long Evans rats using a 32 gauge Hamilton syringe. The degradation of labeled ROS was observed after 5 and 12 days by electron microscopy. The following results were observed. Latex particles fuse with the melanin granules of the RPE. Following chloroquine treatment, the membranes of melanin granules fused, and formed large clusters and vacuoles. Gold granules were detected inside both early stage melanosomes and mature melanin granules of the RPE cells 5 and 12 days following subretinal injection of the labeled ROS. Higher numbers of gold granules were predominantly found in immature melanosomes containing still melanofilaments and in small fused mature melanin granules. In conclusion the effect of chloroquine clearly demonstrates that the melanosomes possess active proton pumps which is typical for lysosomes. In RPE cells stressed by overload with rod outer segments or by ingestion of undegradable material (latex beads, gold particles), fusion of these phagosomes with melanosomes of different maturity is more a general rule than an exception. Therefore, melanosomes are connected to lysosomal pathways in RPE cells.
黑素小体与溶酶体和脂褐素颗粒密切相关。本文指出溶酶体降解过程可能参与视网膜色素上皮（RPE）细胞的活动。将培养在布鲁赫膜和脉络膜上的RPE细胞用难消化的乳胶珠喂养。对该制剂中的RPE细胞用氯喹进行处理，以研究在此条件下溶酶体典型的膜肿胀是否能在黑素小体中诱导产生。为了研究与视杆外段（ROS）相关的难消化物质的命运，使用32号汉密尔顿注射器经巩膜将金标记的ROS注射到Long Evans大鼠的视网膜下间隙。在5天和12天后通过电子显微镜观察标记的ROS的降解情况。观察到以下结果。乳胶颗粒与RPE的黑色素颗粒融合。氯喹处理后，黑色素颗粒的膜融合，并形成大的聚集体和液泡。在视网膜下注射标记的ROS后5天和12天，在RPE细胞的早期黑素小体和成熟黑色素颗粒内均检测到金颗粒。在含有黑素丝的未成熟黑素小体和小的融合成熟黑色素颗粒中主要发现了更多数量的金颗粒。总之，氯喹的作用清楚地表明黑素小体具有溶酶体典型的活性质子泵。在因视杆外段过载或摄入不可降解物质（乳胶珠、金颗粒）而受到应激的RPE细胞中，这些吞噬体与不同成熟度的黑素小体融合更像是一种普遍规律而非例外情况。因此，黑素小体与RPE细胞中的溶酶体途径相关。
