The Silk Protein Sericin Promotes Viability of ARPE-19 and Induced Pluripotent Stem Cell-Derived Retinal Pigment Epithelial Cells in vitro

ABSTRACT

Purpose

Maintaining mature and viable retinal pigment epithelial cells (RPE) in vitro has proven challenging. Investigating compounds that can promote RPE-viability and maturation is motivated by RPE transplantation research, the quest to understand RPE physiology, and a desire to modulate RPE in pathological states. We have previously reported that the silk protein sericin promotes viability, maturation, and pigmentation of human fetal RPE. In the present study, our aim was to uncover whether these effects can be seen in adult retinal pigment epithelial cell line-19 (ARPE-19) and induced pluripotent stem cell-derived RPE (iPSC-RPE).

Methods

ARPE-19 and iPSC-RPE were cultured with or without 10 mg/mL sericin. After 7 days, viability was assessed with calcein-acetoxymethyl ester (CAM) and ethidium homodimer-1 (EH-1) assays, flow cytometry, and morphometric analysis. Expression levels of RPE65, tyrosinase, and Pmel17 were quantified to compare maturation between the sericin-treated and control cultures. Light microscopy and staining of the tight junction protein zonula occludens protein 1 (ZO-1) were employed to study sericin’s effects on RPE morphology. We also measured culture medium pH, glucose, lactate, and extracellular ion content.

Results

Sericin-supplemented RPE cultures demonstrated significantly better viability compared to control cultures. Sericin appeared to improve ARPE-19 maturation and morphology in vitro. No effects were seen on RPE pigmentation with the concentration of sericin and duration of cell culture herein reported.

Conclusions

This is the first study to demonstrate that supplementing the culture media with sericin promotes the viability of iPSC-RPE and ARPE-19. Sericin’s viability-promoting effects may have important implications for retinal therapeutics and regenerative medicine research.

KEYWORDS:

• Sericin
• retinal pigment epithelium
• viability
• maturation
• induced pluripotent stem-cell-derived RPE
• ARPE-19

Acknowledgments

The authors thank Ms. Ingunn Rode Grorud, Senior Executive Officer at the Division of Laboratory Medicine, Faculty of Medicine, University of Oslo for her kind, flexible and timely logistical support.

Disclosure statement

A patent application has been filed by the research group on the use of sericin in culture media (European Patent Application No. 16733583.5).

Additional information

Funding

This work was supported by grants from Norwegian Research Council [Forskerlinje-grant to AZK, 2014-2019]; Futura Fond til vitenskapelig medisinsk forskning [grant to AZK, 2019-2020]; and Fylkesmann H.B. Guldahl og hustru Lucy Guldahls legat til bekjempelse av kreft og andre alvorlige sykdommer [grant to AZK, 2019-2020].