Florey Institute of Neuroscience and Mental Health, University of Melbourne, Parkville, Victoria, Australia.
FASEB J. 2013 Apr;27(4):1479-87. doi: 10.1096/fj.12-215368. Epub 2013 Jan 9.
Age-related macular degeneration (AMD) is a leading cause of blindness in Western countries and is diagnosed by the clinical appearance of yellow subretinal deposits called drusen. Genetic changes in immune components are clearly implicated in the pathology of this disease. We have previously shown that the purinergic receptor P2X7 can act as a scavenger receptor, mediating phagocytosis of apoptotic cells and insoluble debris. We performed a genetic association study of functional polymorphisms in the P2RX7 and P2RX4 genes in a cohort of 744 patients with AMD and 557 age-matched Caucasian control subjects. The P2X4 Tyr315Cys variant was 2-fold more frequent in patients with AMD compared to control subjects, with the minor allele predicting susceptibility to disease. Pairwise linkage disequilibrium was observed between Tyr315Cys in the P2RX4 gene and Gly150Arg in the P2RX7 gene, and these two minor alleles formed a rare haplotype that was overrepresented in patients with AMD (n=17) compared with control subjects (n=3) (odds ratio 4.05, P=0.026). Expression of P2X7 (wild type or variant 150Arg) in HEK293 cells conferred robust phagocytosis toward latex beads, whereas coexpression of the P2X7 150Arg with P2X4 315Cys variants almost completely inhibited phagocytic capacity. Fresh human monocytes harboring this heterozygous 150Arg-315Cys haplotype showed 40% reduction in bead phagocytosis. In the primate eye, immunohistochemistry indicated that P2X7 and P2X4 receptors were coexpressed on microglia and macrophages, but neither receptor was seen on retinal pigment epithelial cells. These results demonstrate that a haplotype including two rare variants in P2RX7 and P2RX4 confers a functional interaction between these two variant receptors that impairs the normal scavenger function of macrophages and microglia. Failure of this P2X7-mediated phagocytic pathway may impair removal of subretinal deposits and predispose individuals toward AMD.
年龄相关性黄斑变性（AMD）是西方国家致盲的主要原因，其诊断依据是黄斑下出现黄色的称为玻璃膜疣的视网膜下沉积物。免疫成分的遗传变化显然与这种疾病的病理有关。我们之前已经表明，嘌呤能受体 P2X7 可以作为一种清道夫受体，介导对凋亡细胞和不溶性碎片的吞噬作用。我们在 744 名 AMD 患者和 557 名年龄匹配的白种人对照组中进行了 P2RX7 和 P2RX4 基因功能多态性的遗传关联研究。与对照组相比，P2X4 Tyr315Cys 变体在 AMD 患者中出现的频率增加了两倍，其次要等位基因预测疾病易感性。在 P2RX4 基因中的 Tyr315Cys 和 P2RX7 基因中的 Gly150Arg 之间观察到了成对的连锁不平衡，并且这两个次要等位基因形成了一种罕见的单倍型，在 AMD 患者（n=17）中比对照组（n=3）更为常见（比值比 4.05，P=0.026）。HEK293 细胞中 P2X7（野生型或变体 150Arg）的表达赋予了对乳胶珠的强大吞噬作用，而 P2X7 150Arg 与 P2X4 315Cys 变体的共表达几乎完全抑制了吞噬能力。携带这种杂合 150Arg-315Cys 单倍型的新鲜人类单核细胞的珠吞噬作用降低了 40%。在灵长类动物眼中，免疫组织化学表明 P2X7 和 P2X4 受体在小胶质细胞和巨噬细胞上共表达，但在视网膜色素上皮细胞上未见这两种受体。这些结果表明，包括 P2RX7 和 P2RX4 中的两个罕见变体的单倍型赋予了这两个变体受体之间的功能相互作用，从而损害了巨噬细胞和小胶质细胞的正常清道夫功能。这种 P2X7 介导的吞噬途径的失败可能会阻碍视网膜下沉积物的清除，并使个体易患 AMD。
