The role of receptor protein tyrosine kinase MERTK and intracellular Ca2+ playing in the phagocytosis of human retinal pigment epithelial cells

Abstract

Objective To investigate the role of intraeellular Ca2+ and MERTK in the phagocytosis of human retinal pigment epithelial (RPE) cells, and reveal the relationship between MERTK and intraeellular Ca2+. Methods The euhured RPE cells were incubated with rod outer segments (ROS) at 37℃, the phagoeytosis was terminated at different incubation time points. The concentration of intraeellular Ca2+ was assayed by Fluro-3/AM loading methods combined with fluorescence microscope and CCD system, and the mRNA level of MERTK gene was measured by reverse transcription polymerase chain reaction (RT-PCR). Treating the RPE cells with stimulator (A23187)or inhibitor(verapamile)of intraeellular Ca2+ to observe the changes of MERTK gene expression. Results ROS adhered to hRPE cells at the 15th minute, and the ingestion saturated at the 24th hour. The concentration of intracellular Ca2+ increased at the 15th minute, and kept the high level in 24 hours. The level of MERTK mRNA increased at the 5th minute, and kept the high level duration the whole incubation. When RPE cells were treated by A23187, the expression of MERTK increased in a dose-dependent manner. After RPE cells was pretreated by A23187, the expression level of MERTK was higher in the proceeding incubation groups than which in the control group except at the 3rd hour. When RPE cells were treated by verapamil, the expression level of MERTK decreased in a dose-dependent manner. After RPE cells were pretreated by verapamil , the expression level of MERTK was lower in all the proceeding incubation groups than which in the control group (P<0.05). Conclusion MERTK gene and Ca2+ play an important role in sustaining RPE cells phagoeytizing ROS. As an up-stream regulator, the receptor tyrosine kinase MERTK keeps RPE cells phagocytizing ROS by starting the intracellular Ca2+. Key words: Pigment epithelium of eye/pathophysiology; Phagoeytosis/physiology; Ca2+MERTK gene