AMD (Age-related Macular Degenerescence) is the first cause of visual impairment. The main characteristic of the disease is the occurrence of drusen at an early stage (age-related maculopathy), followed years later by choroidal neovascularization (exudative AMD), or progressive retinal pigment epithelial (RPE) and loss of photoreceptor cells in the macular area (atrophic AMD).
This disease usually affects people sixty years old or more and its prevalence increases with age. There is currently no curative treatment for dry AMD, whereas exudative AMD benefits from anti-VEGF treatment (ranibizumab, aflibercept, and bevacizumab).
Notwithstanding many studies, the etiology of AMD remains unclear even if environmental (oxidative stress, smoking…) and genetic (CFH, ARMS2…) factors are known to be involved. According to the physiopathologic hypothesis, RPE cell dysfunction is likely to play a pivotal role in the cascade of events leading to AMD. These cells fulfill many roles: nutriment input to the photoreceptor, water input, vitamin A recycling, light absorption, and phagocytosis of the photoreceptors’ external segments.
The ARPE-19 cell line is currently used as an in vitro model for retinal diseases such as AMD. These cells have been derived from an immortalized RPE cell line in a 19- year-old male. For many years, several studies have highlighted a number of morphological and genetic differences between ARPE-19 cells and human fetal or adult RPE cells, suggesting that these cells cannot adequately model retinal disease in vitro.
To confirm this hypothesis, our study aims to compare ARPE-19 cells to the hRPE cells derived from human-induced pluripotent stem cells (hiPSCs) in both basal and oxidative stress conditions. Four somatic cell lines (erythroblasts and fibroblasts) from aged healthy people without retinal disease were reprogrammed and differentiated into hRPE cells by spontaneous protocol.
At basal condition, we observed that the hiPSC-RPE cells derived from aged healthy people expressed a senescent profile (beta-galactosidase activity) whereas ARPE-19 did not.
Iron is a natural element that accumulates with normal aging and it has been observed that it does so within the retina, especially within the macular area and RPE cells, in people affected by dry AMD. The intracellular level of iron was increased in the culture media to mimic in vitro an AMD oxidative environment.
In our study, we demonstrated that ARPE-19 and hiPSC-RPE cells responded differently to intracellular accumulation of iron. More precisely, hiPSC-RPE cells had higher ROS production and cell death under oxidative stress compared to ARPE-19 cells.
Conclusion:
- Even if ARPE-19 cells are a useful tool for preclinical studies in AMD, these cells may not be a reliable model for investigation of the pathogenic mechanisms of hRPE cells leading to AMD.
- Our results suggest that a hiPSC-RPE cell model could be more sensitive in detecting the toxicity of a potential therapeutic agent in preclinical studies, whereas ARPE-19 cells might not be able to detect a potential toxicity at the same concentration. This important parameter should be taken into consideration in therapeutic screening.
These findings are described in the article entitled hRPE cells derived from induced pluripotent stem cells are more sensitive to oxidative stress than ARPE-19 cells, recently published in the journal Experimental Eye Research by Voisin A. et al.