Is the polarized secretion of complement factor H of importance in age-related macular degeneration?

Abstract

Purpose : In the present study we, investigated the expression as well as the secretion of factor H (FH) from cultured human RPE, co-cultures, and from porcine retinas. A low secretion and or degradation of FH from RPE cells may be a mechanism that could contribute to a reduced FH function in AMD.

Methods : Highly differentiated, polarized, RPE monolayer cultures were derived from human embryonic stem cells as previously described. To mimic AMD conditions in vitro differentiated RPE cells were co-cultured with porcine retinas through time (0h-96h) under cyclic illumination 8h/day. FH was assessed in conditioned medium by using Luminex technology. Gene expression of FH and the heparan sulfate degrading enzyme heparanse was investigated by real-time PCR. Immunohistochemistry was used to investigate the expression of FH and heparan sulfate, a major binding partner for FH, in cultured specimens.

Results : FH showed a significant polarized secretion from the human RPE cells, appearing more than ten times higher from the apical compared to the basal side. There were no significant changes in secretion of FH from the human RPE cells when co-cultured with the porcine retina. Porcine retinas did not secrete detectable FH over time in the culture. The gene expression of FH was slightly, though significantly decreased in human RPE cells when co-cultured with the porcine retina, compared to RPE cells cultured alone. Neither changes in gene expression of heparanase could be found, nor could any variation in expression of heparan sulfate be detected in the cultured specimens.

Conclusions : In conclusion, we found that RPE cells contribute to the levels of FH on the retinal side of the Bruch’s membrane which has been shown elsewhere to prevent passage of FH to the retinal side. A loss of RPE cells such as in AMD, would therefore lead to complement dysregulation and possible damage to the RPE cell layer/Bruch’s membrane. Co-culturing human RPE cells with porcine retina over time did not change the secretion of FH, although a decreased gene expression could be observed. Expression of heparanase did not change under similar conditions.

This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.