Hall Michael O, Abrams Toshka A, Burgess Barry L
Jules Stein Eye Institute, UCLA Medical Center, 100 Stein Plaza, Los Angeles, CA 90095-7008, USA.
Exp Eye Res. 2003 Sep;77(3):281-6. doi: 10.1016/s0014-4835(03)00158-1.
The phagocytosis of photoreceptor outer segments (OS) by the retinal pigment epithelium (RPE) is a receptor mediated process. A key component of this process is the receptor tyrosine kinase, Mer. RPE cells from the RCS rat, which lacks a functional mer gene, and do not express Mer protein, are able to bind OS, but are unable to ingest them, suggesting that both a binding receptor and an ingestion receptor (Mer) are required for phagocytosis to occur. These rats become blind shortly after birth. To date the binding receptor has not been identified. Recent studies, using an SV40 transformed rat RPE cell line, RPE-J, or cultured human RPE cells, have suggested that the receptor for OS binding is the integrin alphavbeta5. However, the results presented here clearly show that this integrin plays at most a minor role in the phagocytosis of OS by primary cultures of rat RPE cells. OS phagocytosis by normal RPE cells is not affected by a function-blocking antibody to alphavbeta5 integrin, nor by the integrin-specific blocking peptide GRGDSP. Additionally, RPE-J cells do not express the Mer receptor protein, which has been shown to be obligatory for OS phagocytosis, or RPE65, a specific marker for RPE cells. We suggest that the RPE-J cell line is not a valid model with which to study the complex process of OS phagocytosis.
视网膜色素上皮（RPE）对光感受器外段（OS）的吞噬作用是一个受体介导的过程。该过程的一个关键成分是受体酪氨酸激酶Mer。来自RCS大鼠的RPE细胞缺乏功能性的mer基因，不表达Mer蛋白，它们能够结合OS，但无法摄取OS，这表明吞噬作用的发生既需要结合受体也需要摄取受体（Mer）。这些大鼠在出生后不久就会失明。迄今为止，结合受体尚未被鉴定出来。最近的研究使用了SV40转化的大鼠RPE细胞系RPE-J或培养的人RPE细胞，提示OS结合受体是整合素αvβ5。然而，此处给出的结果清楚地表明，这种整合素在大鼠RPE细胞原代培养物对OS的吞噬作用中至多起次要作用。正常RPE细胞对OS的吞噬作用不受针对αvβ5整合素的功能阻断抗体或整合素特异性阻断肽GRGDSP的影响。此外，RPE-J细胞不表达已被证明对OS吞噬作用必不可少的Mer受体蛋白，也不表达RPE细胞的特异性标志物RPE65。我们认为RPE-J细胞系不是研究OS吞噬作用这一复杂过程的有效模型。
